Indeed,nanomaterials hidden under the common “graphene” signboardare very rich in morphological and physicochemical variants. In thiswork, inspired by the adhesion chemistry of mussel biomaterials, wehave synthesized novel, water-processable graphene–polylevodopa(PDOPA) hybrids. Graphene and PDOPA were covalently amalgamated viathe “growth-from” polymerization of l-DOPA monomer in air, yielding homogeneouslyPDOPA-coated (23 wt %) (of thickness 10–20 nm) hydrophilicflakes. The hybrids formed >1 year stable and water-processableaqueousdispersions and further conveniently processable paints of viscosity0.4 Pa·s at 20 s–1 and a low yield stress τ0 up to 0.12 Pa, hence exhibiting long shelf-life stabilityand lacking sagging after application. Demonstrating their applicability,we have found them as surfactant-like nanoparticles stabilizing thelarger, pristine graphene agglomerates in water in the optimized graphene/graphene–PDOPAweight ratio of 9:1. These characteristics enabled the manufactureof conveniently paintable coatings of low surface resistivity of 1.9kΩ sq–1 (0.21 Ω·m) which, in turn,emerge as potentially applicable in textronics, radar-absorbing materials,or electromagnetic interference shielding.Water-based processingof graphene—typically consideredas physicochemically incompatible with water in the macroscale—emergesas the key challenge among the central postulates of green nanotechnology.These problematic concerns are derived from the complex nature ofgraphene in the family of sp Water-based processing of graphene bymeans of a naturalpolymer polylevodopa toward stable and functional electroconductivecoatings for textronics was elaborated and cross-verified. Unfortunately, dispersion of graphene is challengingdue to the strong intersheet van der Waals attractions (via π–πstacking) causing aggregation and/or precipitation.15Water-basedprocessing of graphene—the most studied 2D spN-methyl-2-pyrrolidone, and dimethyl sulfoxide could beapplied as graphite exfoliating agents and graphene dispersants, respectively.16 However, the most pressing technological requirementsfor the dispersing media are volatility and zero/minimal toxicity,as for water or ethanol.17 The latter greendispersants, as the key components in the more complex systems suchas elastomers, could lead to more convenient and safer processabilitytoward flexible electroconductive coatings18 for textronics,20 radar-absorbing materials (RAMs),22 or electromagnetic interference (EMI) shielding.23A variety of organic solvents inducing repulsiveforces after interflakepenetration and on-flake adsorption such as benzyl benzoate, 26 or physicaladsorption of stabilizers such as surfactants,29 polymers,32 or small molecules.35 Consequently, rather than using high crystallographicquality and pristine graphene—the availability of which islimited to small quantities due to the troublesome large-scale production—GOor rGO emerged thus far as the materials of choice.39 However, GO flakes which have no clearly defined chemical structureare not only difficult to process40 butalso exhibit the yet unraveled and complex cyto- and ecotoxicity profiles42 and undergo fragmentation in the aqueous environments.43 However, predominantly, GO does not retain thefundamental properties of graphene, with mechanical and electricalas the key ones.45 In turn, scalable water-baseddispersions, inks, or paints/pastes can be prepared under a ratherintense mechanical assistance from (bath to probe) ultrasonicationto microfluidization and have led so far to the functional solutionsmainly in the area of textronics. Nevertheless, they still requirea pretreatment with ethylcellulose,46 amixture of sodium deoxycholate and carboxymethylcellulose sodium salt,47 sodium silicate,48 sodium salt of flavin mononucleotide,49 or poly(N-vinyl pyrrolidone)50 (ultrasonication). Proteins can also serve as biofriendlysurfactants, while adhesion is the key prerequisite for the stabilizationof nanoparticles in water. It is well known that mussels stronglyadhere to wood/stones under high shear stress conditions from thewater flows. This behavior stems from the mussel foot functional proteinscontaining high contents of two amino acids: l-3,4-dihydroxyphenylalanine  and lysine.51 Such characteristics have instantly paved the way for themimicking of sustainable adhesives and stabilizers toward the newapplications in materials science , biology, and biomedicine.53To enhance the water dispersibility of graphene (understoodinthe broadest sense according to the ISO standardization ISO/TS 80004-13:2017)and to improve the performance of the graphene-based nanocomposites,several physicochemical modifications have been applied. These structuraladaptations involve, inter alia, treatment of carboxylic acid groupsretained on the chemically reduced graphene oxide (rGO), graftingof hydrophilic groups  ongraphene oxide (GO) through chemical reactions,l-DOPA (precursor ofdopamine) as the particularly promising one. l-DOPA, beingan in vivo instantly available catecholamine, oxidizes to polylevodopa(PDOPA). This reaction, proceeding under only the mechanical stirringregime, at the solid–liquid interface might form a controllablelayer of excellent adhesiveness/affinity to numerous materials.57 Such a biologically inspired functionalization, essential in theformation of mussels, could be “translated” into thesurface modification of graphene with l-DOPA and the subsequentinterface polymerization via the “grafting-from” mechanism.This route could be effective in preventing graphene from the excessiveagglomeration in the polar solvents.In the pursuit of developing novel physicochemicallymodified grapheneof enhanced hydrophilicity and simple but green processing, we hypothesizedits covalent functionalization with Taking all the above intoaccount, we have successfully performedthe functionalization of graphene toward its individualized, hydrophilic,and thus water-processable nanoparticles. The resulting material displaysthe enhanced stability of dispersions among variously functionalizedgraphene flakes. The optimized hybridization with the pristine grapheneflakes, serving as the active components of acrylic paints, led tothe flexible, on-textile electroconductive coatings of excellent electricalcharacteristics yet not achieved by the other available green approaches.l-DOPA (≥98%) and Tris-base(tris(hydroxymethyl)aminomethane, 2-amino-2-(hydroxymethyl)-propane-1,3-diol)(≥99.8%) were purchased from Sigma-Aldrich. All of the solutionsand dispersions were prepared using distilled water (0.5 μScm–1). Transparent aqueous base SX 150 acrylic (dedicatedto screen printing), used for the preparation of electroconductivepaints, was purchased from Sico Screen Inks NV .GrapheneCamGraph G3 was supplied by CambridgeNanosystems Ltd., UK. l-DOPA (2.00 g) were dispersed/dissolvedin the solution of Tris-base in water (10 mM) . Thereaction mixture was placed in a round-bottom flask (2 L) equippedwith a reflux condenser and a mechanical stirrer and sealed.53 After that, the polymerization reaction wasinitiated thermally and continued for 48 h at 60 °C using a heatingmantle. Upon processing, the dispersion changed color from yellowto brown. The postreaction mixture was centrifuged , and the resulting black powder (1.20 g),58 that is, poly(l-DOPA)-functionalized graphene(G3@PDOPA), was washed with water (1.0 L) and dried at 80 °Cfor 48 h. Exactly the same procedure was applied for the blank experiments,that is, the samples composed only from l-DOPA or only fromgraphene G3 flakes.Graphene  and –1) were prepared. After weighing out theappropriate amounts of graphene and water, the mixtures were ultrasonicated for 10 min.Additionally, in order to evaluate the dispersion effect of l-DOPA operating via the optional noncovalent modifications, we alsohave prepared the graphene dispersion but disabling polymerizationof l-DOPA.To evaluate the hydrophilic/hydrophobicbehavior of graphene and G3@PDOPA, the corresponding aqueous dispersions. The coating thickness wasmonitored during the painting and determined using an ElectronicaUniversal Micrometer LINEAR 0–25 mm/0.001 mm thickness gauge. Similarly, paints containing G3@PDOPA and the mixtureof pristine graphene G3 and G3@PDOPA in various ratios  were prepared.Pristine graphene G3 and G3@PDOPA were used forthe preparation ofelectroconductive paints. Deionized water (70 mL) and graphene (1.00g) were ultrasonicated for 15 min. Next, the dispersions were homogenized for 15 min in SX-150  to obtain the final graphene nanoparticle concentrationof 10 wt % per base.1H nuclearmagnetic resonance (1H NMR), electrospray ionization massspectrometry (ESI-MS), and thermogravimetric analysis (TGA) were performedto characterize the changes in morphology and (surface) physicochemistryof G3 flakes, PDOPA, and G3@PDOPA. The SEM images were taken on aSIX HITACHI S-3400 N SEM system . Nanomorphology ofthe graphene nanofillers was observed using HR-TEM with a TEM F20X-TWINsystem (FEI-Tecnai)  operated at 200 kV. One dropof a sample dispersion in ethanol  was placed on a coppergrid coated with an ultrathin amorphous carbon film and then driedunder ambient conditions. Raman spectra were obtained using  a green laser (532 nm) focused on a sample using 20×optical zoom, with the laser power of 5% and the exposure time of10 s. For each material, three accumulations were collected in threelocations of the sample. A Thermo Scientific FTIR Nicolet 6700 spectrometerwas used for the IR spectroscopic studies of the samples. ESI-MS spectrawere acquired on an ESI/MS spectrometer 4000 QTRAP LC/MS/MS system(AB SCIEX) in the positive and negative modes of ionization from thesamples dissolved/dispersed in methanol. Combustion elemental analyseswere obtained using a PerkinElmer 240C apparatus. TGA curves wererecorded using a PerkinElmer TGA 8000 thermobalance in a heating rateof 10 °C min–1 under an argon atmosphere. Additionally,particle size distribution  and zeta potential analyses were performed. The microstructureof dispersions was characterized using an optical microscope Levenhuk870t. The electric resistance (Ω) of the paths was measuredusing the voltage method in a custom-designed voltage measurementsystem.59 Due to the possibly heterogeneousnature of the electroconductive coatings, the system was customizedto textiles with the extended contact surface of the path/electrode.This approach enabled us to reduce the heterogeneity of the electricfield and the distribution of the current density.59 The measurements were done by placing multimeter aluminumelectrode block probes, with the distance between them of 10 cm, ontothe surface of coating. We have measured the resistance for each ofthe coatings in triplicate.Scanning electronmicroscopy (SEM),high-resolution transmission electron microscopy (HR-TEM), Raman spectroscopy,Fourier transform infrared spectroscopy (FTIR), 60 and the procedure was as follows: functionalized  graphene (60 mg) was dispersed for 48 h undercontinuous magnetic stirring in the specified aqueous reaction basesolutions: (1) 0.01 M NaOH, 60 mL; (2) 0.01 M Na2CO3, 30 mL; and (3) 0.01 M NaHCO3, 60 mL. The mixturewas filtered using a 0.2 mm PTFE filter and then 10 mL (or 5 mL inthe case of Na2CO3) of the appropriate filtrateswas titrated with 0.01 M HClaq (20 mL). The pH of the finalsolutions was measured using an EcoTestr2 pH meter. Each titrationwas performed in triplicate. As blank samples, 10 mL of each reactionbase (5 mL in the case of Na2CO3) was used.In turn, to determine the content of amine group,61 20 mg of each sample was added to 10 mL of HClaq (0.05 M). The mixture was shaken for 30 min in a sealed containerunder a N2 atmosphere and then filtered to remove graphenefrom the solution. Immediately after the filtration, the solutionwas titrated with NaOH (0.05 M). The pH of the final solutions wasmeasured using the abovementioned pH meter.The content of surface oxygen groupsin all samples was determined by Boehm titration,62 The samples of G3, G3@PDOPA, and PDOPA were sprayed on the surfaceof polished silicone  using airunder a pressure of 2.5 bar airbrush . The dispersions/solutions were sprayed up to a coverageof 0.1 mg cm–2. For G3 and G3@PDOPA, the suspensions(1.0 mg mL–1) in isopropanol  were used after sonication . For the PDOPA sample, 20% MeOHaq  addition wasrequired to stabilize the suspension (but still 10 mL of 1 mg mL–1 suspension was prepared). Spray-coated silicone sampleswere air-dried at room temperature for 24 h to evaporate the remainingsolvents.The water contactangle (WCA)  was measured at 25 °C  usingthe goniometric system used by us previously.–1) and ramp-down  tests with 30 s intervals.Also, we experimentally determined the yield stress of the samplesby subjecting them to very low shear  and then stopping the rheometer drive. The deformed spring causedthe rotating cylinder to move back, reducing the torque and shearstress on the surface until the cylinder stopped. When it happened,the value of the shear stress indicated by the viscometer was preciselythe yield stress of paints.63 The uncertaintyof rheological measurements was ±5.4%.The rheological properties of paints were characterizedat 40 °Cusing a Brookfield LVDVII+Pro spring-type rotational viscosimeterwith DIN-87 spindles. We conducted shear rate ramp-up .11 Thesynthesis of G3@PDOPA was performed via the complex “growth-from”polymerization mode . Thein-plane dimension of the G3 graphene flakes (the flake diameter)was in the range of 400 ± 150 nm, as determined by SEM, and theBrunauer–Emmett–Teller (BET) surface area equaled to130 ± 5 mion mode 1.642-and sp3-carbon as wellas oxygen atoms from hydroxyl groups —shownin x in the G3@PDOPA structure, where x = 0 and 1—could serve as the reactive hot spots.65 These centers could capture the l-DOPAradicals generated from the oxidation of monomer molecules by dissolvedair. This behavior was confirmed in the polymerization of catechol moieties in the presence of metallic surfaces suchas silver66 or surface hydroxyl groupsfrom iron oxides.67 This reaction wouldyield covalently modified graphene, excessively coated with PDOPAnegatively charged in water by carboxylates and phenolates. Overall,these prerequisites would correspond to the covalent nature of theherein graphene functionalization. Particularly, C-sp3 defects,also confirmed by complementary analyses, would be the reactive centersin the free-radical initiation of air-induced polymerization of l-DOPA as, in fact, they would exhibit benzylic-type (Ph3CH → Ph3C•) reactivity.69Both aromatic spThe morphology of the functionalized graphene flakes has beenevaluatedusing SEM and TEM 2. The imH-indole rings as well as the π–cation interactionsbetween the protonated amine group (−NH3+) from the PDOPA zwitterionic blocks and π–graphenelayer—could benefit from the steric stability in the aqueousenvironments. On the other hand, van der Waals and π–πstacking interactions between the graphene flakes—particularlyat the highly developed surface area of intrinsically hydrophobicflakes—might yield a substantial agglomeration over time. Thisphenomenon makes graphene a hard-to-process material to such an extentthat it is practically impossible to disperse graphene sheets in waterwithout the assistance of dispersing agents. However, when placedin an oil/water mixture, graphene becomes wettable and actually exhibitsamphiphilic properties driven by the hydrophilic edge domains.11Such a molecular hybridization—associatedwith the π–πstacking between the few-layer graphene flakes and PDOPA benzene/1l-DOPA monomer  behavior in water, with the support of opticalmicroscopy and (b) wettability 3. Pristi monomer 3B. The n monomer 3C. After monomer 3D.70 Indeed, G3 does notcontain a significant amount of oxygen functionalities, but one couldalso expect a perpendicular orientation of some flakes, causing astrong Cassie–Baxter effect, further increasing the WCA value.On the other hand, the abundance of oxygen-containing groups makesthe PDOPA surface hydrophilic—the WCA was found equal to 83°.The surface of the target G3@PDOPA hybrid showed almost the averageWCA value between G3 and PDOPA, that is, 123°. Overall, the hydrophilicityof graphene was increased due to, from one side, strong π–πinteractions of the aromatic PDOPA rings (tail-like) and the grapheneflakes,73 while from the otherside, the high content of the −COOH, −OH, and −NH2 serving as polar heads oriented outward water. Such a superstructurewould hence promote dispersibility and wettability of graphene in/bywater.Supporting Information, Figure S1). The z-average particle diameter corresponds to the intensity-weightedmean hydrodynamic size of the investigated particles. The z-average values in As a technique complementary to optical microscopy, dynamiclightscattering (DLS) was performed to obtain the lateral size distributionof the water-dispersed flakes, which actually confirmed the above-observedtendencies. 74 However, measuring the hydrodynamic diameterof graphene flake agglomerates can be done by DLS,75 though one must consider that DLS rather shows only thesize distribution of different particles. Accordingly, the hydrodynamicdiameter of G3@PDOPA particles was reduced up to 342 nm as comparedto the immeasurably large pristine graphene flakes in the suspension.In turn, zeta-potential measurement is one of the useful techniquesto determine the stability of the carbon nanomaterials in the solvents,as the optical observation could not determine the absolute stabilityof dispersions. Again, the zeta-potential of pristine graphene G3could not be recorded due to the strong hydrophobic character andits immiscibility/nonwettability with/by water. The stability of G3@PDOPAdispersion could be directly correlated to high negative ζ-values(−25.4 ± 1.52 mV). For PDOPA solution, the ζ-valuesare even more negative (−31.9 ± 0.79 mV) that correspondsto even better stability of the PDOPA dispersion  analysis(EA) 4, left4, right 46H2O) was composedof 97 wt % of carbon and only a small number of oxygen groups accompaniedby adsorbed water. In the case of G3@PDOPA, the oxygen and nitrogencontent increased to ca. 9 and 1%, respectively, clearly revealingthe presence of PDOPA. The more qualitative approach, that is, Boehmtitration, has further verified these results (Pristine graphene (ca. C results 2.–1) and phenol-like groups (1.14 mmolg–1)––which correspond to the minimumof 3.6 wt % of oxygen. After functionalization with PDOPA, the contentof carboxylic groups in G3@PDOPA increased to 1.10 mmol g–1, phenol-like groups to 1.75 mmol g–1, and lactoneto 0.49 mmol g–1. These characteristics emerge withthe grafting of graphene with the complex and cross-linked poly(l-DOPA). Additionally, during the l-DOPA polymerization,a fraction of carboxylic groups could undergo decarboxylation, whilesome hydroxyl groups oxidize to quinone-like moieties  and 1100 cm–1 (νC–O),absent in pristine graphene, resulted from the −OH stretchingvibration from PDOPA. In addition, the intense peak at 1630 cm–1 could be ascribed to the stretching vibration ofthe carbonyl group (νC=O). Further, weakersignals at ca. 3000 cm–1 correspond to the stretchingvibrations of CAr–H (νC–H). The N–H bending as well as the C–N stretching vibrationsresulting from the presence of amine groups can be observed at 1520(δN–H) and 1270 cm–1 (νC–N), respectively. Additionally, the 1HNMR spectra of PDOPA and G3@PDOPA confirmed: (1) a more pronouncedoxidation level of phenolic hydroxyl to 1,2-keto groups as signalsat 8.10 and 8.25 ppm were significantly reduced in G3@PDOPA and (2)a higher level of cross-linking as all of the 1H NMR signalswere significantly broadened . The presence of l-DOPA units in the oligo-and polymers (linear and cross-linked) in PDOPA and G3@PDOPA was furtherconfirmed via ESI-MS with an exemplary identification of the partiallyoxidized l-DOPA pentamer and dimer .Pristine graphene had a small amountof oxygen groups on the surface—carboxylic in TGA could be connected with the desorption of water. Above220 °C, PDOPA started to decompose, which was connected withthe degradation of the catechol moiety and decompositional volatilizationof the amine groups and decarboxylation.80 Thermal degradation of G3@PDOPA has been found to be qualitativelysimilar to that of pure PDOPA, although the degradation of the adsorbedpolydopamine occurred at a higher temperature around 300–400°C , G-band (∼1570–1590 cm–1), and the second-order band 2D at ∼2670 cm–1. According to Sadezky et al.’s deconvolution method, thespectra in the range of 1000–2000 cm–1 canbe separated into the following bands: G, D, A, and D4.81 The G-band (∼1591 cm–1) corresponds to the ideal graphitic lattice, the D-band (∼1332cm–1) to the disordered graphitic lattice , A-band (∼1497 cm–1)—amorphous carbon, and D4-band (∼1308 cm–1)—disordered graphitic lattice (A1g symmetry).The 2D-band (∼2656 cm–1) displays the highestintensity which is connected with the crystal size in the interlayerdimension.82 The other band is overtoneD + D′ at 2913 cm–1. It should be noted thatthe D-band is typically qualitatively and quantitatively related tothe non-sp2-C defects, that is, a number of sp3-C atoms. The G-band in the spectra of graphene samples revealedsignals at 1586 cm–1 (pristine graphene) and at1591 cm–1 (G3@PDOPA). The ID/IG ratio could be taken as ameasure of the sp3-carbon defect concentration. The crystallographicdefects here can be assigned to the C atoms which underwent additionand subsequent polymerization. The ID/IG ratio increased from ca. 0.54 (pristine graphene)to 0.88 (G3@PDOPA), indicating the conversion of sp2- to sp3-C atoms in the basal plane of thefunctionalized graphene, confirming the earlier observations. Theother Raman parameter of diagnostic relevance used for the characterizationof graphene is the ID/I2G ratio. The small ID/I2G ratio is the evidence of high crystallographicorder in the initial graphene structure. Therefore, after functionalizationwith PDOPA, the ID/I2G ratio increased from ca. 0.80 (pristine graphene) to ca.0.87 (G3@PDOPA). Nevertheless, not only intensity but also shiftsof the D- and G-bands provide information on the functionalizationof graphene. Therefore, while the positions of the D-band remainedpractically unchanged for all of graphene samples, the G-bands forG3@PDOPA were shifted to higher frequencies. To track the changesin the G-band positions, we have carried out a line-shape analysisto minimize the number of independent fitting parameters. After functionalization,the signals were shifted ca. 5 cm–1 to higher wavenumbers,indicating the consequence of electron transfer from the π-statesof graphene upon trapping radicals generated at the stage of initiationof polymerization. Subsequently, the growth of the polymer chain proceededfrom the graphene flake being an active sp2-carbon radicalscavenger.83 Importantly, chemisorptionof this first radical opens up the cascade of covalent bond formation,84 which eventually drives the process to the effectivecoating of graphene with PDOPA. This behavior has found clearly areflection in the results we obtained from the physiochemical studieson G3@PDOPA.The Stokes phonon energy shiftsin graphene correspond to the threemain peaks in the Raman spectrum: D-band  helps maintain product consistency and prevents phaseseparation and running or streaking after application to a verticalsurface, while low viscosity at medium/high shear rates during theprocessing and application of paints makes them easy to mix, pump,transport, and spread with brushes, rollers, and so forth.86 Furthermore, we observed very little differencebetween the shear rate ramp-up and ramp-down curves (no hysteresisloops); thus, the paints practically do not have time-dependent thixotropicproperties. Such an almost immediate rebuilding of the fluid structureupon the application of stress/strain indicates that the paints willbe devoid of sagging and droplet formation after application.87 In addition, the samples of G3 10 wt % and G39 wt % + G3@PDOPA 1 wt %, unlike the neat base SX-150, show the existenceof a low yield stress τ0 of 0.10 and 0.12 Pa, respectively.The yielding behavior of paints is important in many areas, includingthe evaluation of shelf-life stability and sagging after applicationto the surface. 880 is the yield stress , K is the consistency index, and n is the flow behavior index.The investigatedpaints at 40 °C are highly viscous, non-newtonian shear-thinningfluids, the viscosity of which declines with an increasing shear rateup to 83.7% for G3 9 wt % + G3@PDOPA 1 wt % 7. It is Having obtained the prospective characteristics,that is, the PDOPAcapability of individualizing graphene flakes, we attempted to preparea paint and consequently the functional, electroconductive textilecoating. Sheet resistance measurement is the first-of-choice parameter describingthe electrical properties of the coatings. It is also a method whichimmediately informs whether further deposition of new layers of paintwould bring any significant changes in the electrical conductivity.As presented in –1, which is slightly lower89 or an orderof magnitude lower90 than that reportedpreviously for the green solvent-based inks. Importantly, from themechanical properties point of view , the resistance for the most conductiveand graphene-only coating upon 100 bending cycles from 180 to 0°(a sharp edge) increased to 8 and 10 Ω sq–1, respectively. At the same time, the most perspective cotton coatingG3 9 wt % + G3@PDOPA 1 wt % emerged as more resistant to washing andstrain than G3 10 wt %, with an increase in ΔR/R0 as low as 7% after five cycles ofwashing/drying and a 90% increase upon 10% elongation, respectively.Deterioration of the electrical properties of G3@PDOPA wascausedby a high content of PDOPA ∼23 wt %. However, after the depositionof the paints containing a mixture of pristine graphene and G3@PDOPA,the electrical properties were synergistically augmented. We studiedlower (1–5 wt %) weight fractions of G3@PDOPA and found thatthe lowest resistance could be achieved for the composite containing1 wt % of G3@PDOPA . The electricalresistance after the deposition of 15 layers l-DOPA. Our method allows for a promptand simple production of excellent and time-stable aqueous graphenedispersions—at the same time opening up opportunities for thesustainable use of the green surface compatibilizers like PDOPA. Thecross-verified method emerges as an attractive alternative to themost frequently used ones, that is, those exploring structurally deeplyaltered graphene relatives—GO and rGO. It should be emphasizedthat it is also an effective way to modify the hydrophilicity andbiocompatibility of graphene toward the awaiting biomedical applications.Importantly, the uniform coating of graphene with PDOPA was achievedvia thermally driven polymerization of LDOPA. The PDOPA content inthe hybrid graphene/PDOPA solid reached 23 wt %, while the coatingrich in hydroxyl, carboxyl, and amine moieties guaranteed excellentwettability with water. Taking the results toward upscaling, we havedemonstrated that the graphene@PDOPA nanohybrid acts as a dispersingagent for the pristine graphene flakes, allowing to form long-lastingacrylic dispersions. As a consequence, flexible and printable/paintablecoatings of significantly lowered electrical resistance up to 1.9kΩ sq–1 could be straightforwardly manufactured,minimizing the need for graphene functionalization which, in turn,lowers the cost and the environmental impact. These value-added characteristicsmake graphene@PDOPA hybrids suitable for textronic sensors, chargedissipation, or EMI shielding. Importantly, the modification appearsas directly extendable to other sp2-carbon allotropes suchas CNTs, fullerenes, nano-onions, nanohorns, or quantum dots.Wedemonstrated the water-based hence green approach to the covalentlyfunctionalized graphene via the bioinspired “growth-from”polymerization of


Respiration monitoring is a promising alternative to medical diagnosis of several diseases. However, current techniques of respiration monitoring often require expensive and cumbersome devices which greatly limit their medical applications. Here, we present a fully integrated wearable device consisting of a flexible LCP-copper interdigital electrode, a sensing layer and a wireless electrochemical analysis system. The developed humidity sensor exhibits a high sensitivity, a good repeatability and a rapid response/recover time. The long-term stability is over 30 days at different relative humidity. By integrating the flexible humidity sensor with miniaturized electrochemical analysis system (0.8 cm × 1.8 cm), response current concerning respiration can be wirelessly transmitted to App-assisted smartphone in real time. Furthermore, the fabricated humidity sensor can realize skin moisture monitoring in a touch-less way. The large-scale production of miniaturized flexible sensor (4 mm × 6 mm) has significantly contributed to commercial deployment. Advancements in wearable flexible sensors and smartphone healthcare systems have contributed to the commercial market for wearable technology . At pres2) (2) (2)  board into a wearable sensor for respiration monitoring.Recently, transition metal dichalcogenides (TMDs) such as molybdenum disulfide (MoS2) , rhenium2) (2) , and tun (2) (2)  have gai sensing . Otherwi sensing . Here we sensing . Using i2, absolute ethanol (99.7 wt%) were purchased from Aladdin Ltd. . Poly (N-vinylpyrrolidone)  was purchased from Sigma-Aldrich Co., Ltd. . LCP substrate of 50 μm was provided from Taiflex Scientific Co., Ltd. All chemicals were of reagent grade.MoSAll electrochemical experiments were conducted on a CHI660E electrochemical workstation. Electrode appearance scanning microscopy was handled using VHX-5000 Ultra-depth three-dimensional microscope . Scanning electron microscopy (SEM) images were collected on a Sigma HV . Fourier transform infrared spectroscopy (FT-IR) spectra were collected on a Nicolet iN10 FT-IR spectrometer .2 was suspended in a mixed solution of absolute ethanol and deionized water  and subjected to ultrasonication with 380 W power. After exfoliating at room temperature for 1 h, 0.2 g PVP was added as surfactants and stabilizer for another 48 h under the same conditions. Then the suspension was centrifuged for 15 min at 7,500 rpm, and the resulting supernatant was preserved as the MoS2/PVP ink for inkjet printing .The humidity sensor was fabricated on a 50 μm thick LCP substrate with copper cladding on one side. The copper interdigital electrodes were fabricated on the initial flexible substrate by FPC technology, which involves two main steps as followed: First, optical dry film photoresist lithography (DFPL) was performed by roller lamination of the dry film photoresist  on LCP copper clad plate at 100°C and a speed of 1.4 m/min, followed by UV-exposure with the energy density of 130 mJ/cm2/PVP ink was inkjet-printed on LCP-copper interdigital electrodes which were pre-treated by oxygen plasma treatment  to fabricate humidity sensors. Inkjet printing was conducted using a commercial drop-on-demand Epson L310 printer. The printer cartridge was designed to dispense droplets with a volume of 3 pL based on the orifice of 63.5 μm in diameter 2 for 54% RH, NaCl for 75% RH, KCl for 84% RH and KNO3 for 94% RH, respectively 3O+) transfer is difficult to occur under the electrostatic field. With relative humidity increasing to high level, more water molecules are physiosorbed above the chemisorbed layer by hydrogen bonding to form continuous water multilayer. According to the Grotthuss chain reaction, the protons hopping-transfer is generated and used to ionic conductivity, leading to a rapid decrease in electrical resistance and increase in response current.At low relative humidity, chemisorption of water molecules occurs on the surface of the sensing layer. These chemisorbed water molecules act as electron donors for the sensing materials, allowing for decreased electrical resistance. However, due to the discontinuous of the water layer at this process, the hydronium ion . The consistent baseline (current response of device under 45% RH) and the current changes of the device under 30 cycles of exposure to the high relative humidity (above 90% RH) indicate good repeatability of the proposed humidity sensor . Long-teThe normal respiration of an adult lasts 3–5 s and exhaled air humidity is above 90% RH. In consideration of the high performance of the humidity sensors fabricated in this study, we further integrated the flexible copper interdigital electrode components, sensing layer, and miniaturized PCB board into a wearable patch sensor for respiration monitoring.The PCB board of electrochemical workstation with miniaturized format (0.8 cm × 1.8 cm) consists of a signal conditioning part, a Bluetooth transceiver and a programmable electrochemical chip. The signal is wireless communication between wearable humidity sensor and smartphone-based platforms. The system is powered by a 150 mAh rechargeable lithium battery. The applied potential was set as 200 mV during operation. Due to a low soldering temperature of LCP , conductive silver paste was used for the connection between wire and LCP-copper interdigital electrode.In order to evaluate the real-time breath monitoring application of the fabricated humidity sensor, the device was attached under a volunteer’s nose about 5 mm. As shown in 2 to nanoscale, increased the surface volume ratio and the edge active sites. Meanwhile, the lactam units of PVP are active binding sites for water molecules which enhance the mobility of charge carriers during polarization. Compared with other humidity sensors for respiration monitoring in literatures (In this study, we have developed a fully integrated flexible humidity sensor that enables wearable respiration monitoring. LCP proved to be one of the most desirable flexible materials for humidity sensing applications as its excellent chemical properties, electrical insulator and ultra-low water absorption. The humidity sensing material was prepared by simple liquid-phase ultrasonic exfoliation method. PVP-assisted exfoliation has considerably reduced the dimension of MoSeratures , the dev


Those novel organic–inorganic hybrid composites can be efficiently prepared via both covalent and noncovalent bonds by classic organic reactions and supramolecular interactions, respectively. Pillararene-functionalised graphene materials have been used in various applications, such as electrochemical sensing guest molecules, performing as the platform for fluorescent probes, carrying out fluorescence quenching as the sensor, biosensing toxic molecules in cells, Raman and fluorescence bioimaging of cancer cells, photoacoustic and ultrasound imaging, as well as storage materials and reactors in energy fields.Pillararene-modified graphene materials integrate the advantages of both graphene and pillararenes;  The current research progress on diverse pillararene derivative functionalised graphene materials, including different synthesis strategies and various applications, is reviewed. Similarly, the rim-differentiated functionalised pillar[5]arene X6  and fluorescence spectroscopy.The classic organic synthesis methods were popular in the preparation of hybrid materials. For example, by using the EDC–NHS coupling reaction between carboxylate groups on X5  and hydrarene X6 24 was gr25Alternatively, per-hydroxylated pillar[5]arene X7,  could co2 and RGO were prepared by a hydrothermal reduction between Na2MoO4 and l-cysteine (l-Cys) in the presence of graphene oxide sheets.22 The positively charged trimethylammonium perfunctionalised pillar[5]arene , MoS2/RGO has the morphology of wrinkled thin flakes. In another example, by using a similar hydrothermal synthetic route and driving forces for the fabrication of hybrid materials, water-soluble N-methylimidazole perfunctionalised pillar[5]arene X8  electrochemical and fluorescence sensing, (2) biomedicines and biosensing, Raman and fluorescent bioimaging, as well as photoacoustic and ultrasound imaging, (3) lithium storage and catalysis.In their application to electrochemical sensing, the electrical properties of graphene materials allow them to generate significant electrical signals towards guest molecules introduced by the supramolecular recognitions of pillararene cavities. In their application in fluorescence sensing, the two-dimensional morphologies of graphene materials perform as the platform to load pillararenes on the surface, which further serve as the active recognition sites for fluorescent guests or probes.19 Particularly, ternary hybrid materials RGO–AP5–AuNPs exhibited the best sensing abilities towards dopamine with a broad linear range from 1.5 × 10−8 to 1.9 × 10−5 mol L−1, as well as a low detection limit of 1.2 × 10−8 mol L−1 at a signal-to-noise ratio of 3, due to the synergetic action of multifunctional properties such as the capacity for supramolecular recognition by pillararenes, catalytic properties of gold nanoparticles as well as the electrochemical properties of graphene  by cyclic voltammetry. For example, the hybrid nanocomposites RGO–AP5 and RGO–AP5–AuNPs have selective supramolecular recognition and the capacity for enrichment towards guest molecules, as analysed among electroactive candidates such as dopamine, 4-acetamidophenol, uric acid, methylene blue, tryptophan and imidacloprid.graphene .25 have a good capacity for recognising guest molecules such as dopamine, ascorbic acid and uric acid, and exhibit selective electrochemical response towards dopamine, due to the molecular recognition by the cavities of pillararenes. Pillararenes also perform as promotors for enhancing the electrochemical response. In comparison with cyclodextrin-modified RGO, CP5-RGO32 exhibit better electrochemical catalytic activity as a sensor, e.g., the trace detection of methyl parathion with the low detection limit of 3.0 × 10−10 mol L−1 (S/N = 3) and the linear response range of 1.0 × 10−9 to 1.5 × 10−4 mol L−1.In another example, the hybrid composites RGO-P5A23 due to the π–π stacking interactions between aromatic dyes and RGO, as well as possible host–guest interactions between dyes and the cavity of pillar[5]arenes.Pillararene-functionalised graphene materials could also be applied in fluorescent dye sensing. For example, due to the carboxylate perfunctionalised pillar[5]arenes (X5), the composite RGO-CP5 nanosheets exhibit enhanced fluorescence-quenching properties towards rhodamine 6G and neutral red in comparison to unmodified RGO,via hydrophobic interactions by the cavity of pillar[5]arene, the AmPA5-RGO composite can act as a fluorescent sensing platform for the detection of acetaminophen, in which the acridine orange performed as the signal probe.27 It has been proved that this fluorescence sensing system has a low detection limit of 5.0 × 10−8 mol L−1 with a S/N ratio of 3, as well as a linear response range of 1.0 × 10−7 to 4.0 × 10−6 and 4.0 × 10−6 to 3.2 × 10−5 mol L−1.Due to the difference in supramolecular recognition towards guest molecules such as acridine orange and acetaminophen 30 PCP6-RGO also performs as a selective and sensitive fluorescence platform for detecting trinitrophenol with acridine orange as the probe, exhibiting a low detection limit of 3.5 × 10−9 mol L−1 (S/N = 3) and a wider linear response of 1.0 × 10−8 to 5.0 × 10−6 and 5.0 × 10−6 to 1.25 × 10−3 mol L−1.By using a similar fabrication strategy,e.g., Raman imaging or irradiating under near-infrared (NIR) light.The introduction of modified pillararene derivatives can not only improve the aqueous solubility of graphene materials, but can also enhance the biocompatibility of hybrid materials. Furthermore, pillararenes donate their electron-rich cavities for the supramolecular recognition of electron-deficient guests, which provides the possibility of including and delivering particular guest molecules for biomedicines. The unique physiochemical properties of graphene materials have been primarily explored, such as thermal structural properties, via supramolecular recognition. For example, after integrating with water-soluble pillararenes, hybrid materials X2-GO and X3-GO @RGO33 @RGO33  performs+˙X9)Y7  nanobubbles under the irradiation of a NIR laser Y7 performed significant roles in increasing the NIR absorption as monitored by the changes in temperature shown by an IR camera.The water-soluble tertiary amine perfunctionalised pillar[6]arene X9, -modified+˙X9)Y7 29via hosIR laser . Due to 2 and RGO together. During the preparation, the positively charged pillar[5]arene X8 could mitigate the charge incompatibility between MoO42− and the graphene oxide sheets in the fabrication of the hybrid composites MoS2/RGO-NP, in which the MoS2 sheets were well dispersed on the surface of RGO containing exposed active edge sites 28 could deliver a reversible specific capacity as high as 1289 mA h g−1 at the same current density of 1000 mA g−1. Particularly, the reversible capacity of 996 mA h g−1 can be retained after 1100 cycles at unchanged current density. Furthermore, the hydrogen evolution reaction is the key step in producing hydrogen via electrochemical water splitting using solar energy or electricity. The MoS2/RGO-NP composites  Regarding organic components, 36 should be borrowed to expand the current categorization and morphology of 2D layered inorganic structures, which could provide the possibility for applying the obtained hybrid materials to, e.g., the hydrogen evolution reaction.37,38 Furthermore, the special physiochemical functions of graphene, including but not limited to nanoscale morphologies, as well as inert, thermal structural, optical and electrical properties should be deeply explored in these hybrid materials.39(2) Regarding the inorganic components, new synthesis strategies such as the strategy of covalent cross-linking(3) Regarding the study of the binding mechanism, the driving forces during the fabrication of pillararene-functionalised graphene materials need further investigations such as computational calculations, high-resolution electron microscopic observations as well as crystallographic studies. The different synthesis strategies regarding covalent and noncovalent interactions should be re-evaluated to ascertain their advantages and disadvantages.via either the modification of pillararene derivatives or the decoration of the outer surface of graphene materials. The introduction of various functional moieties40,41 could allow pillararene-functionalised graphene materials to, for example, have better water dispersity and solubility, which promote the materials to have better biocompatibility and lower cytotoxicity, leading to the expansion of application to more aspects of biomedicines such as diagnosis and combined therapy.42(4) Concerning the expansion of the application fields, more functional groups could be introduced into the hybrid composites 2DTwo-dimensionalAFMAtomic force microscopyCLSMConfocal laser scanning microscopyGCEGlassy carbon electrodeGOGraphene oxidel-Cysl-CysteineMTT3--2,5-diphenyltetrazolium bromideNIRNear-infraredRGOReduced graphene oxideSEMScanning electronic microscopyTEMTransmission electron microscopyTGAThermal gravimetric analysisXPSX-ray photo-electron spectroscopyThe authors declare no conflict of interest.


Despite their importance, accurate prediction of MSA andH2SO4 from DMS oxidation remains challenging.With comprehensive experiments carried out in the Cosmics LeavingOutdoor Droplets (CLOUD) chamber at CERN, we show that decreasingthe temperature from +25 to −10 °C enhances the gas-phaseMSA production by an order of magnitude from OH-initiated DMS oxidation,while H2SO4 production is modestly affected.This leads to a gas-phase H2SO4-to-MSA ratio(H2SO4/MSA) smaller than one at low temperatures,consistent with field observations in polar regions. With an updatedDMS oxidation mechanism, we find that methanesulfinic acid, CH3S(O)OH, MSIA, forms large amounts of MSA. Overall, our resultsreveal that MSA yields are a factor of 2–10 higher than thosepredicted by the widely used Master Chemical Mechanism (MCMv3.3.1),and the NOx effect is less significantthan that of temperature. Our updated mechanism explains the highMSA production rates observed in field observations, especially atlow temperatures, thus, substantiating the greater importance of MSAin the natural sulfur cycle and natural CCN formation. Our mechanismwill improve the interpretation of present-day and historical gas-phaseH2SO4/MSA measurements.Dimethyl sulfide (DMS) influences climate via cloud condensationnuclei (CCN) formation resulting from its oxidation products (mainlymethanesulfonic acid, MSA, and sulfuric acid, H Understanding the OH-initiated DMS oxidationprocess inthe atmosphere is essential to properly describe the process chainfrom phytoplankton DMS emissions to climate effects. Theythus affect the formation, optical properties, and lifetime of marineclouds,8 influencing cloud radiative propertiesand therefore climate.16Dimethyl sulfide (DMS) is emitted intothe atmosphere by marinebacteria and as a result of the degradation of dimethylsulfoniopropionate(DMSP) produced from phytoplankton.18 Understanding how gaseousMSA contributes to this ratio is important in understanding the impactof DMS oceanic emissions leading to the formation of low-volatilityspecies via oxidation. The multiphase chemical mechanism is complex,and the yields of H2SO4 and MSA depend on temperature19 as well as atmospheric composition. Moreover,field measurements of gas-phase MSA and H2SO4 show a wide range of concentrations.23The ratioof particulate MSA to non-sea-salt sulfate varies between0.05 and 0.75 and is usually below 0.5.12 Atmospheric H2SO4 is formed from sulfur dioxide(SO2) oxidation, which comes from anthropogenic and volcanicemissions as well as DMS oxidation. It follows that the ratio of H2SO4 to MSA (H2SO4/MSA) isan important indicator of both regional variations and anthropogenicperturbation in both current and historical samples. Furthermore,both species may participate in new particle formation13 and CCN formation processes together with iodine oxoacids and ammoniain polar regions.25 Consequently, a quantitative,mechanistic understanding of the DMS oxidation mechanism(s), especiallythe resulting H2SO4/MSA, is essential to furtherour understanding of their roles in climate change.Atmospheric MSA is formed primarily from DMS oxidation, withhighconcentrations observed in polar regions.28 Recent experimental work and in situ field observations have shownthat autoxidation plays an important role in the oxidation of DMSat higher temperatures (>0 °C), proceeding through the formationof hydroperoxymethyl thioformate  viaisomerization of the methylthiomethylperoxy radical , which is the primary product of DMS hydrogenabstraction.32 However, subzero conditions (<0 °C) are challenging to investigateexperimentally and so have received less attention. Hydrogen abstraction,both by OH and via isomerization (autoxidation), is suppressed ata lower temperature, and the OH addition pathway is known to dominate,as shown in previous studies.35 Finally, wall reactions can beproblematic in the laboratory, and their effects on the DMS oxidationexperiments have been unclear so far.27DMS oxidationhas been studied extensively with a wide array ofinstrumentation. However, chamber and flow-tube experiments have haddifficulties reproducing DMS oxidation under atmospherically representativeconditions, leaving us with significant gaps in our chemical understanding.39 and aqueous-phase processes40 to close the gaps between themodeled and measured oxidation products, suggesting reduced importancefor OH-initiated DMS oxidation. However, even with recent revisionsbased on experimental findings, models with current state-of-the-artgas-phase mechanisms underestimate ambient MSA.40 Here, we show that those mechanisms overestimate H2SO4/MSA by a factor of 2–10 throughout the ambient temperaturerange. The mechanism adopted in this study is similar to the gas-phasemechanism in the study of Wollesen de Jonge et al.,41 which revised the gas-phase chemistry (MCM) to explaintheir high particulate MSA.Model studies have addressed the importance of halogen chemistry13 under conditionsthat closely match the marineboundary layer (MBL) with an extensive suite of instruments. We investigatedthe gas-phase OH-initiated DMS oxidation over a wide temperature range(−10 to +25 °C) and present a revised mechanism describinggas-phase DMS oxidation. In addition to H2SO4 and MSA, we quantified numerous intermediate products, includingthe key intermediate methanesulfinic acid (CH3S(O)OH, MSIA),and used them to evaluate and constrain the mechanism. In additionto the gas-phase chemistry, we quantified semiempirical rate coefficientsfor the heterogeneous formation of the important products dimethylsulfoxide (CH3S(O)CH3, DMSO) and dimethyl sulfone(CH3S(O)2CH3, DMSO2).We designed our experiments such that the particle condensation sink(CS) is negligible. In CLOUD and most experiments, these multiphaseprocesses occur on the chamber walls,41 but they canalso occur on or within aerosols and cloud droplets in the atmosphere.We investigated the effects of temperature and NOx on gas-phase OH-initiated DMS oxidation. Both our experimentsand our revised oxidation mechanism closely match ambient gas-phaseH2SO4/MSA, and together they provide a quantitativeunderstanding of this critical natural biogeochemical process.We performed experiments in theCLOUD chamber at CERN3. The chamber is surrounded by an insulated thermal housing,which maintains high-temperature uniformity and stability, and itcan be operated over a wide range of temperatures (from −70to +100 °C) and relative humidity (from below 1% to above 90%).Ultrapure synthetic, humidified air (cryogenic 79% N2 and21% O2) and a slight overpressure minimize contaminantsin the chamber. All trace gases  haveindependent gas lines connected to the chamber to avoid reactionscaused by mixing in the gas lines before injecting into the chamber.Dry nitrogen was used to dilute DMS, NO2, and O3 from standard high-concentration gas bottles before reaching thechamber to obtain close to atmospheric concentrations.The CLOUD chamber isan electropolished stainless steel cylinder with a volume of 26.1m3). The distributionof UV lamps and laser in the chamber make the gas-phase oxidationproducts  form uniformly in a few minutes. An LED sabre(LS3) at 385 nm was used to photolyze NO2 producing NO.Sulfur dioxide (SO2) was measured with a high-sensitivitypulse fluorescence analyser ,ozone with a UV photometric ozone analyser , carbon monoxide using a nondispersion cross-modulationinfrared analysis method , and nitrogen oxidesNO with an ECO Physics CLD 780TR and NO2 with a CavityEnhanced Differential Optical Absorption Spectroscopy (CE-DOAS). TheSO2 monitor employed at CLOUD was unfortunately not ableto measure the formed SO2 from DMS oxidation because ofits high detection limit (0.5 ppb). A chilled dew-point mirror (EdgeTechInstruments) and a direct tunable diode laser absorption spectrometer were usedto continuously monitor the water vapor concentration.Four200 W Hg–Xe UV lamps at wavelengths between 250 and 450 nm with adjustable power and axenon fluoride excimer laser (UVX) at 248 nm were used to generateOH radicals via photolysis of ozone  and to reduce wall loss ratesof DMS oxidation products to establish a new steady-state condition.Temperature-ramping experiments were conducted at two temperatureranges (+25 to +10 and +10 to −10 °C) with different initialconcentrations of DMS, OH, and CO. The temperature ramps took a fewhours each, which is only slightly longer than the residence timein the chamber. Therefore, unlike in a typical oxidation experiment,steady states were not reached for each temperature in the temperature-rampingexperiments. As such, H2SO4-to-MSA ratios inthese experiments should not be used directly in other contexts becausethey are not measured in steady state. They can, however, be usedfor investigating the temperature dependence by simulating the fullconcentration profile at each point in time and then comparing themodel results with the experimental results.The OH-initiatedDMS oxidation experiment was conducted as follows:Before the oxidation experiments, the mixing fan speed was set to100% to enhance turbulent mixing in the chamber, thus reducing theconcentrations of oxidation products due to faster wall loss. Theinjection rates of ozone, DMS, and NO3–-CIMS), a bromide chemical ionization mass spectrometer coupled witha multischeme chemical ionization inlet (Br–-MION-CIMS),the gas-phase channel of a bromide chemical ionization mass spectrometerequipped with a Filter Inlet for Gases and AEROsols inlet (Br–-FIGAERO-CIMS), selective reagent ionization mass spectrometers(SRI-TOF-MS), and proton-transfer reaction time-of-flight mass spectrometer.The experiments were grouped into three sets depending on the availabilityof instruments and temperature. We conducted experiment set 1 at −10°C, experiment set 2 at +10 and −10 °C, and experimentset 3 at +25 and +10 °C, with relative humidity ranging from20 to 70%. NO3–-CIMS and PTR3 workedduring all of the experiments. However, the mode of PTR3 was changedfrom a regular H3O+ mode to NH4+ mode in experiment set 3. Br–-MION-CIMSmeasurements were only available in experiment set 1 and Br–-FIGAERO-CIMS measurements were only in experiment set 2. The conditionsof the experiments and relevant instruments are listed in Table S1.State-of-the-artinstruments were operated simultaneously to measure the gas-phaseconcentrations of DMS and its oxidation products. They were measuredby a suite of advanced mass spectrometers including a nitrate-ion-basedchemical ionization mass spectrometer (NO3O+-CIMS) provided the DMS concentration.The instrument is based on the design of the proton-transfer reactiontime-of-flight mass spectrometer (PTR3) described in Breitenlechneret al.43 DMS concentrations were calibratedwith a gas standard at specific conditions between experiments. Theconcentrations of DMS for the second experiment set were providedby the selective reagent ionization mass spectrometer (SRI-TOF-MS)described in detail by Canaval et al.44 We calibrated both instruments regularly between experiments witha standard gas mixture containing multiple volatile organic compoundsto account for any possible drifts in transmission efficiency or absolutehumidity dependency.A proton-transfer reaction time-of-flight massspectrometer 2OOH were measured with anitrate-ion-based chemical ionization mass spectrometer . The specially designed inletfor chemical ionization at the ambient pressure system and its calibrationand quantification procedures are well described by previous studies.47 We applied the same calibration coefficient C2SO4H = 4.13 × 1010 cm–3 per normalized signal  for the experiments carried outat +10 and −10 °C since charging efficiency does not varysignificantly in this temperature range. The uncertainty for NO3–-CIMS is mainly caused by H2SO4 calibration, below ∼50%; this uncertainty includesthe systematic error from calibration setup and statistic error. Alluncertainties for each species from the different instruments arelisted in Table S2. We estimate that MSAhas a collision-limited charging efficiency and strong binding energywith less fragmentation than H2SO4 based onthe cluster binding enthalpy calculated by quantum chemical methods(see Text S1.3 and Tables S3 and S4 fordetails). The measurement sensitivity of methanesulfonic peroxide(CH3S(O)2OOH) is lower than the maximum sensitivity,and the given concentrations represent its lower limits. The detailedestimation for MSA and CH3S(O)2OOH can be foundin Text S1.3.The concentrations of H2, methylthioformate (CH3SCHO), and methanesulfenic acid (CH3SOH) were measured either by an H3O+- or NH4+-CIMS.48 Different ionization schemes  were used in different experimentsas shown in Table S1. We determined theinstrument’s collision limit calibration factor by ionizing1 ppbv of hexanone from a gas standard diluted in air. Applying thecollision limit calibration factor to all compounds ensures lower-limitestimates for their concentrations. As shown in Figure S2, the independence of the concentration ratios determinedby both ionization methods  with the collision limitcalibration factor on sample gas humidity and temperature suggeststhat both DMSO and DMSO2 are very likely ionized at thecollision limit in both ionization modes. The lower-limit estimatesare therefore most likely their true concentrations. The comparisonbetween the two ionization methods at the same time can be realizedwith additional experiments performed with high ammonia concentrationin the chamber. These additional experiments have much higher DMS,O3, and NH3 concentrations than the OH-initiatedDMS oxidation experiments to investigate the formed particles at largersizes of around 100 nm. In contrast to the OH oxidation experimentswhose goal is to investigate the chemical mechanism, the goal of theadditional experiments with high NH3 is to investigatethe CCN potential of the formed particles. That is, the much higherconcentrations of DMS, O3, and NH3 facilitatesustained condensation that leads to larger particles. Additionally,the conducted voltage scan experiment in Figure S3 shows that the DMSO and DMSO2 hydronium-waterand ammonium clusters are stable against fragmentation at the chosensettings and that their proton affinity is high enough to even keepthe charge upon collision-induced fragmentation at higher voltages.Their uncertainties are estimated at around 20% in H3O+-CIMS and 50–80% in NH4+-CIMSwith the larger uncertainty of the collision limit sensitivity inthe latter. The reported concentrations of CH3SCHO andCH3SOH are lower-limit estimates also based on the resultsof the voltage scans. See Text S1.4 forthe detailed description.The concentrations of DMSO, DMSO–-MION-CIMS) and the gas-phase measurement of bromide chemical ionizationmass spectrometer equipped with a Filter Inlet for Gases and AEROsols(Br–-FIGAERO-CIMS)49 werethe primary instruments to detect MSIA and HPMTF. The peaks of MSIAand HPMTF measured by Br–-MION-CIMS can be foundin Figure S4. If neither instrument wasavailable due to instrument malfunction or absence in some experiments,NO3–-CIMS was used to measure MSIA andHPMTF. The instrument setup and operation of Br–-MION-CIMS and FIGAERO are described in Rissanen et al.50 and Lopez-Hilfiker et al.,49 respectively. In addition to ionization with Br–, we also detected both MSIA and HPMTF with NH4+ and H3O+-CIMS. While direct calibrations ofMSIA and HPMTF were not available, the intercomparison between thethree ionization modes and the use of quantum chemical calculationsprovide reasonable constraints on the ionization efficiency of thetwo species and hence their concentrations.A bromide chemical ionization mass spectrometercoupled with a multischeme chemical ionization inlet (Br–-MION-CIMS andBr–-FIGAERO(g)-CIMS using the MSA concentrationmeasured by NO3–-CIMS. Afterward, MSAcalibration factors in both instruments are used to estimate the lowerlimits of HPMTF and MSIA concentrations with high uncertainty. Thetraces shown in Figure S7 for MSIA fromNH4+- and H3O+-CIMS arecalibrated using the collision limit assumption. It is very likelythat if ionization does not occur at the collision limit with allprimary ion clusters with water, a strong water dependence would beobserved between the different modes. The apparent humidity independenceof the ratio of the MSIA concentration derived from the three differentionization schemes  suggests that the compound isdetected at the collision limit in these ionization schemes. However,the fragmentation caused by the electric field in the vacuum chamberalso affects the detection efficiency. The signals of MSIA and HPMTFin Br–-MION-CIMS might underly some fragmentationor other unaccounted losses in the instrument or inlet. Yet, the voltagescan results in Figure S8 show that MSIAis detected at maximum sensitivity in both H3O+ and NH4+-CIMS. Therefore, we use the MSIAconcentration from H3O+-CIMS with around 28%uncertainty due to the calibration and inlet and instrumental losscorrection. The signal of HPMTF is influenced by neighboring peaksand is divided into many water clusters in H3O+-CIMS, while this is not the case in NH4+-CIMS.Unfortunately, NH4+-CIMS was not available formany of the experiments, and the limit of detection in H3O+-CIMS was too high to use the data during the hereinanalyzed experiments with low concentrations. As such, we use thelower-limit estimation for HPMTF concentrations from Br–-FIGAERO(g)-CIMS. See Section S1.5 for the detailed description and estimations.We first derivedMSA calibration coefficients for BrThe average residence time in the CLOUD chamber was ∼1.3 hfor experiment sets 1 and 2. The reaction rates of oxidation productswere derived from steady-state measurements, which means that theinflow of all gases, the concentration of oxidants, and oxidationproducts were kept constant. Under steady-state conditions, the rateof change of oxidation products equals zero, and we can writepX is the oxidationproduct, Y typically is OH or O3, kYi are the reactionrate coefficients for the reaction of X and Y, and kloss is either the ventilationloss (2.1 × 10–4 s–1 in experimentsets 1 and 2) or wall loss that is listed in Table S2. All of the oxidation product concentrations were measuredat the steady-state condition. The OH concentration used in this studyis estimated from our box model, and its reactions involved in formingOH radicals are listed in Table S7.Therefore, we can get the productionrate Table S1). We combine the simulation and experimental results to evaluateand constrain the role of different DMS gas-phase oxidation pathwaysin MSA and H2SO4 formation. The chemistry mechanismwas generated with the Kinetic PreProcessor (KPP)51 and solved with the ordinary differential equation solverRODAS3 (Rosenbrock method of order 3).52 The concentrations of oxidation products are determined by the chemicalproduction and loss from gaseous chemistry, wall reactions, ventilationloss, wall loss, and the condensation sink (CS) to generate particlesin the CLOUD chamber. The measured temperature, relative humidity,DMS, O3, CO, NOx concentrations(Table S1), and O3 photolysisrate with high time resolution were used as input to the model. Thephotolysis rate of O3 for UVH at full intensity or 5 Wof UVX is around 6 × 10–5 s–1. The OH concentrations are adjusted by changing the UV light intensity,O3, and H2O concentrations. The CLOUD chamberventilation loss is mainly determined by the flush-out flow . Specieslike H2SO4, MSA, and hydrogen oxide radicalsare readily lost to the wall surface. We measured the lifetime ofall species (Table S2) in the dark decay and cleaning stage  toestimate the losses and applied them to our box model. With the increaseof fan speed from 12 to 100%, the wall losses increased by a factorof 1.5–4.6 for different species. The measured loss of specieslike methyl thioformate (CH3SCHO) in the cleaning stageis slightly larger than the ventilation loss caused by the flush-outflow. It suggests that the loss of CH3SCHO is dominatedby ventilation whose loss increases mildly with the increased fanspeed. Therefore, we added extra loss terms for dimethyl sulfoxide(CH3S(O)CH3, DMSO), dimethyl sulfone (CH3S(O)2CH3, DMSO2), and CH3SCHO to fit their time evolutions in the cleaning stage. Theparticle condensation sink measured in this study is smaller than1 × 10–5 s–1, which is negligiblecompared to other loss processes. The detailed description of chemistrymechanisms used in the box model can be found in Text S2.In this study, a numerical model with zerodimension was set up and used to simulate DMS oxidation processesat different initial conditions 2OOH, CH3SCHO, and CH3SOH, as shown in the figures. Some speciesare quantified with proper calibration factors, while species likeCH3S(O)2OOH, HPMTF, CH3SOH, and CH3SCHO (by NH4+-CIMS) are lower-limitestimates due to the lack of authentic standards or generation methods.A more detailed description is given in the Text S1.3) concentrationsstabilized. The time sequences of different DMS oxidation productsshow different behaviors. The evolution of H2SO4, MSA, MSIA, HPMTF, CH3S(O)2OOH, and CH3SOH is consistent with the expected time response of gas-phaseproduction through OH oxidation (with lights on) and wall loss. Themeasured concentration reaches their maxima in the order of a fewminutes rather than a few hours like aqueous-phase reactions. TheCH3SCHO evolution is consistent with gas-phase productionand loss to ventilation rather than the walls, which has a timescaleof ∼1.3 h (26.1 m3/330 lpm). DMSO shows a smallfractional, but large absolute, increase with photochemistry, yetonly a modest fractional wall loss. DMSO rapidly reaches a steadystate, while DMSO2 decreases slowly and continuously fromthe onset of the run, associated with the slowly decreasing productof the DMS and O3 concentrations.The time traces in Figure S11 reveals that DMSO and DMSO2 have a sourcefrom the wall, which has also been shown in a previous study.27 As described in the 2 when the UV lights are on. Inturn, DMSO2 is long-lived in the gas phase and so has minimalinfluence on the chemistry. DMSO is also produced on the walls, butonce OH is present, both gas-phase production and loss of DMSO viaOH far exceed the wall production rate .2SO4 are far less abundantthan the first-generation oxidation product CH3SCHO, butMSA and H2SO4 have rapid wall loss, as do theirprecursors, such as MSIA, CH3SOH, and HPMTF. Consideringthe wall loss rate, we find that the production rates for MSA (3.2× 104 s–1) and CH3SCHO(4.5 × 104 s–1) are similar, withuncertainties at around 50 and 20%, mainly caused by their measuredconcentrations. We seek these production rates along with molar yieldsand branching ratios. To constrain the production rates, we need aphotochemical model of the chamber and the DMS oxidation sequence,including the walls.As shownin Table S2 show that MSA and H2SO4 have the same values,allowing a direct comparison of the two species’ concentrations.As shown in 2SO4, which cannot be explained when assuming that MSAis exclusively formed from the hydrogen abstraction channel  and CH3,55 but mayalso react with O2 to produce MSA. This pathway and itsreaction rate coefficients are not yet well understood. Therefore,in the box model, we add the pathway proposed by Yin et al.,57 Lucas et al.,58 andHoffmann et al.40 that MSIA reacts withOH or NO3 radicals forming methyl sulfonyl radicals (CH3S(O)2) as an intermediate, which then either decomposesto SO2 or reacts with O3 to form MSA (via CH3SO3 reaction with HO2) and SO3, instead of producing SO2 only. A recent study also appliedthis pathway to a multiphase model41 toexplain the observed high particulate MSA/sulfate at 0 and 20 °C.The measured wall losses in 55 suggested that the reactionof MSIA and O3 is unlikely to be competitive with MSIAand OH because of the large discrepancy between these two reactionrate coefficients. Even at high O3 concentrations (ca.100 ppbv), the first-order reaction rate coefficient of MSIA by O3 is 4.4 × 10–10 s–1, which is much smaller than the first-order reaction rate coefficientof MSIA by OH at 2.8 × 10–4 s–1 . Therefore, the critical conclusion is that we wouldsuggest that MSIA reacts with OH, producing both MSA and H2SO4. Thus, both the addition and abstraction pathwaysof DMS oxidation form MSA in the gas phase, explaining the higherMSA concentrations observed in field observations and CLOUD experiments.Lv et al.k3wallDMS + O and k3wallDMSO + O. Using anumerical model  toour DMS oxidation mechanism 1 by dire2SO4, CH3S(O)2OOH, and DMSO concentrations in –-FIGAERO-CIMS to HPMTF due to a stronger declusteringprocess compared to the maximum sensitivity compounds (see Text S1.5 for details). The discrepancy betweenthe modeled and measured HPMTF can be varied from 6 to 14 by applyingdifferent reaction rate coefficients of the isomerization of MSP.As shown in The modeled MSA, H2 concentrationsand their qualitative behaviors 2OOH are high, their influences on our mainconclusion—that MSA likely forms substantially via gas-phaseoxidation of MSIA by OH—are negligible since they are not thedetermining species in this argument.When we exclude the wall reaction from themodel, the resultingvast difference between the modeled and measured DMSOehaviors 3 indicat2, MSIA, MSA, and H2SO4), we conclude that the mechanism presented here can representDMS oxidation by OH radicals in the marine atmosphere.Overall, the underestimatedcalibration factor can explain thediscrepancy between the modeled and simulated HPMTF. Based on theclose agreement between the model and measurements for major oxidationproducts , degradation of MSIA (which is not fullyunderstood), and (4) peroxy radical isomerization of MSP in abstractionpathway 1b. All of these, especially the thermal decomposition, influenceH2SO4/MSA. We plot H2SO4/MSA versus temperature in x, respectively. Thepurple symbols are ambient data, and the black lines are box-modelsimulations with various mechanisms. The CLOUD data come from twoseparate temperature-ramping experiments, one cooling from +25 to+10 °C and the other from +10 to −10 °C, both withoutNOx. In 2SO4/MSA rangesfrom 0.3 to 1.3 (−10 to +10 °C) and 1.4 to ∼11(+10 to +25 °C), decreasing exponentially with decreasing temperature.Ambient observations of gas-phase H2SO4/MSAvary from 1 to 17 at Mace Head, Ireland (during Summer)21 and from 0.3 to 3 in polar regions (from Februaryto August).12 These observations can bereproduced by the inferred experimental temperature dependence. Theambient concentrations of DMS, O3, OH, and NOx during the measurements of H2SO4/MSA from Beck et al., presented in 2SO4 concentrationsreported in Beck et al.’s observation and our experiments.However, we find that the ratio of H2SO4/MSAis mainly determined by temperature  the branching ratio of addition/abstractionat the first step of DMS oxidation by OH radicals, (2) thermal decompositionof CHperature 4 instead2SO4/MSA with the OH-initiated DMS oxidation mechanismdeveloped here(solid line) and compare it to the gas-phase mechanism from MCMv3.3.159 (dashed line) and Hoffmann et al.40 (dotted line) in 3S(O)2 and CH3SO3 in abstraction pathway 1a, whichcontains an exponential temperature dependence that largely determinesH2SO4/MSA. However, our mechanism shows muchbetter agreement with the observed H2SO4/MSAcompared to the other two mechanisms. This is because the reactionof MSIA with OH radicals contributes more to MSA production and consequentlyreduces H2SO4/MSA rather than only contributingto SO2 formation, as e.g., in MCMv3.3.1. Overall, the observedtemperature effect suggests a potentially greater role for MSA incolder regions in important processes such as new particle formationand growth, as our mechanism and observations show that the H2SO4/MSA ratio is smaller than 0.5 when the temperatureis below roughly +2 °C.We modeled the temperature dependence of Hx  influences OH-initiated DMSoxidation, for example, through bimolecular reactions between peroxyradicals (RO2) and NO. As shown in 2SO4/MSA from twoexperiments with NOx (red circles) agreeswith the temperature-ramping experimental results (green circles),indicating that NOx has a negligible effectcompared to the temperature sensitivity over this same range. TheNOx-ramping experiments in Figure S15 confirm that NO2 and NOonly slightly enhance H2SO4/MSA in contrastto the strong effect from temperature change. The measured H2SO4/MSA at +10 °C  and −10 °C increase by 54 and 100% as NO2 increases from 0 to 400pptv. The effect of NOx on HPMTF formationis not clear . We observe aslight drop of HPMTF (17%) and almost constant DMS in Figure S15A. However, Figure S15B shows a 100% increase in HPMTF and a 20% drop in DMS becauseDMS reacts with NO3 radicals. We cannot quantify the effectof NOx on HPMTF formation because of theinterference from N2O5 formed from the reactionof O3 and NO2, which has a close molecular weightto HPMTF.In addition to temperature, NO2SO4/MSA  is very sensitive toNO2 concentration varies dramatically as NO2 increases from 0 to 160 pptv. However, the modeled H2SO4/MSA from the other two mechanisms 2, because it excludesthe isomerization reaction of CH3SO2 producingCH3S(O)2 . The isomerization reaction is estimated with a constantvalue of ∼1 s–1 in previous studies,61 which is higher than the bimolecular reaction rate of CH3SO with NO2 (∼1.2 × 10–1 s–1 with a maximum 400 pptv NO2), althoughit lacks the temperature dependence.In MCMv3.3.1, the modeled H2SO4/MSA S16 is vex on product distribution is greatly diminished comparedto the MCMv3.3.1. Second, the key ratio H2SO4/MSA is substantially reduced (MSA is increased), with the absoluteratio and temperature dependence in the mechanism agreeing with boththe experimental data and ambient observations.Overall, the suite of simultaneouslymeasured key intermediateshelped us to adjust the previous DMS oxidation schemes. Our mechanismhas two major improvements. First, the influence of NOx, the distribution of oxidants including OH,NO3, halogen compounds,62 and available water for multiphase oxidation in aerosolsand droplets.63 In this study, we followed thekinetics of a suite of gas-phase reaction intermediates and finalproducts in DMS oxidation experiments by OH to investigate the effectsof temperature and NOx. Our results showa strong temperature dependence for DMS oxidation, especially theyields of oxidation products such as MSA.DMS oxidationin the atmosphere is affected by temperature, NO2SO4/MSA from OH-initiated DMS oxidation, especiallyat low temperatures (<0 °C). From the box-model results, itis clear that the inclusion of the gas-phase MSA formation mechanismvia oxidation of MSIA by OH improves the agreement between modeledand experimental results at low temperatures. When MSIA reacts withOH, it may produce CH3S(O)2 or another adductintermediate; regardless, both CH3S(O)2 andthe adduct intermediate decompose to SO2 or SO3 to form H2SO4 or react with O3 orO2 to form MSA. For both pathways, we can expect a similartemperature dependence.Our experimental resultsshow high MSA concentrations and reducedH29 leads to the HPMTF formation, which increasesH2SO4 production substantially through oxidationof HPMTF.30At low temperatures, the oxidation ofDMS with OH proceeds morevia the OH addition channel, forming abundant DMSO and MSIA, and consequently,a large amount of MSA. At high temperatures, the reaction rate ofthe OH addition channel decreases, which lowers MSIA and MSA formation,while the hydrogen abstraction channel becomes more important. Also,the predominance of MSP isomerization 41 and field observations17 since both MSA andH2SO4 participate in particle growth. Interestingly,NOx is far less influential than previouslythought. At −10 °C, H2SO4/MSA increasesby 100% after ramping up NO2 (from 0 to 400 pptv) and NO(from 0 to 8 pptv). But the observed change (red circles) is small(less than 50%) compared to the effect of changing temperature (aboutan order of magnitude when the temperature decreases from +10 to −10°C).Therefore, we propose that MSIA isimportant in MSA formation atlow temperatures, which can also be connected to the observed highparticulate MSA/sulfate in laboratoryTable S5, ourexperimentalMSA (0.2 to 1.5 × 107 cm–3) andH2SO4 (0.3 to 3 × 106 cm–3) concentrations formed from OH-initiated DMS oxidationexperiments conducted at −10 °C are in the range of fieldmeasurements. For example, the concentrations of MSA and H2SO4 measured in Ny-Ålesund station  range from 0.1 to 4 × 107 cm–3 and 0.2 to 7 × 106 cm–3, respectively.Aerosol concentrations also affect gas-phase MSA and H2SO4 concentrations because of their different aerosolpartitioning. However, the particle condensation sink in this studyis smaller than 1 × 10–5 s–1, which is only slightly larger than the values at Ny-Ålesund(∼4 × 10–4 s–1) andVillum (∼3 × 10–4 s–1).As shown in 2 and DMSO are important sulfur reservoirsin ourstudy. They can also be formed from wall reactions without OH radicals.Our simulations show that wall reactions are the major source of DMSO2 but have a limited role for other oxidation products comparedto the gas-phase reactions (even DMSO). In the atmosphere, analogousto the wall of the chamber, cloud droplets and aerosol water couldplay a similar role. Therefore, the observed high concentrations ofDMSO2 (40–120 pptv) and DMSO (3–18 pptv)at night over the Arabian Sea64 and PacificOcean65 may be associated with multiphaseDMS oxidation.DMSOFigure S18, terminal products MSA andH2SO4 accumulate in parallel over time, ultimatelyconstituting the dominant reaction products. DMSO, MSIA, CH3SCHO, and CH3SOH are the precursors for MSA and H2SO4, reaching a steady state during the first dayof simulation. HPMTF is a precursor for SO2, and after1 week, both reach high concentrations and slowly approach steadystate. Field measurements indicate high concentrations of HPMTF (upto 50 pptv in the marine atmosphere32)and its possible participation in particle formation. Accounting HPMTFchemistry in a global chemistry transport model66 results in a significant decrease in boundary layer levelsof SO2 and H2SO4. Novak et al.67 demonstrate that the rapid loss of HPMTF toclouds terminates DMS oxidation to SO2. This is importantat high temperatures. On the other hand, at low temperatures, HPMTFproduction is strongly reduced, and the main product becomes MSA viaMSIA, so the fraction of oxidized DMS leading to SO2 issignificantly lowered. The concentration of DMSO2, a terminalproduct of OH-initiated oxidation of DMS, remains low in the absenceof heterogeneous reactions. These simulations suggest that MSA maybe the dominant oxidation product of DMS oxidation for conditionsfound in the high-latitude marine atmosphere with low temperatures.The DMS oxidation lasts only a few hours in theCLOUD chamber,while it can be for a few days in the atmosphere depending on theconditions. To gauge possible atmospheric evolution (a few days),we simulated OH-initiated DMS oxidation over a long timescale (∼1week) at −10 °C, excluding walls and ventilation. As shownin 2SO4 in the remote atmosphere. Our observationof many intermediate products closes gaps between the measured andmodeled MSA. Specifically, MSIA and HPMTF are useful intermediatesthat serve as markers for OH addition and hydrogen abstraction channels,respectively. Therefore, measurement and proper calibration of thesetwo species become important in future laboratory experiments andfield observations for studying DMS. These findings improve our understandingof the atmospheric DMS oxidation process and its contribution to thenatural sulfur cycle and potentially the formation of biogenic aerosoland thus CCN.The agreement between the present chamber study, our model, andambient observations over a wide temperature range is consistent withOH-initiated DMS oxidation governing the formation of gas-phase MSAand H


Marine mammals are facing many threats that impact their ability to obtain energy to survive and reproduce. Much remains unknown about marine mammal bioenergetics, which hinders real-world applications to conservation and management. We surveyed the bioenergetic community to identify ‘key’ unanswered questions to help guide future marine mammal research efforts. Bioenergetic approaches are increasingly used to understand how marine mammal populations could be affected by a changing and disturbed aquatic environment. There remain considerable gaps in our knowledge of marine mammal bioenergetics, which hinder the application of bioenergetic studies to inform policy decisions. We conducted a priority-setting exercise to identify high-priority unanswered questions in marine mammal bioenergetics, with an emphasis on questions relevant to conservation and management. Electronic communication and a virtual workshop were used to solicit and collate potential research questions from the marine mammal bioenergetic community. From a final list of 39 questions, 11 were identified as ‘key’ questions because they received votes from at least 50% of survey participants. Key questions included those related to energy intake  and expenditure , energy allocation priorities, metrics of body condition and relationships with survival and reproductive success and extrapolation of data from one species to another. Existing tools to address key questions include labelled water, animal-borne sensors, mark-resight data from long-term research programs, environmental DNA and unmanned vehicles. Further validation of existing approaches and development of new methodologies are needed to comprehensively address some key questions, particularly for cetaceans. The identification of these key questions can provide a guiding framework to set research priorities, which ultimately may yield more accurate information to inform policies and better conserve marine mammal populations. Published by Oxford University Press and the Society for Experimental Biology.

Received April 12, 2022; Revised June 28, 2022; Accepted July 15, 2022
 Bioenergetics is the study of the acquisition and allocation of energy by individuals to support maintenance, activity, growth and reproduction  or thermThe first comprehensive review of marine mammal bioenergetics occurred at the Mammals in the Seas conference organized by the United Nations Food and Agriculture Organization in 1976 , feedingDespite recent advances, the field is still hindered by many of the same uncertainties and data deficiencies that existed nearly four decades ago, especially for cetaceans. As it is not feasible to address these deficiencies for all 127 extant marine mammal species, research priorities must be identified based on the perceived needs of the bioenergetics community. To achieve this, increased communication within the bioenergetic community is needed to align data needs and data generation. Our aim was to identify ‘key’ outstanding questions in the field of marine mammal bioenergetics. The intent is to stimulate and focus research that will most effectively lead to an increased understanding of the ecology and population biology of marine mammals, ultimately facilitating conservation and management efforts. This effort was conducted in tandem with a bioenergetics workshop to discuss and review the current state of knowledge on marine mammal bioenergetics.We invited 62 scientists with experience in marine mammal physiology, bioenergetics, trophic ecology and population dynamics, to identify unanswered questions in marine mammal bioenergetics. The participant list was generated by the workshop organizers with additional suggestions from invited participants. Identification of participants by workshop organizers was based on personal knowledge of participants’ research and queries of the relevant bioenergetic and marine mammal literature. Participants were asked to submit no more than 10 questions each with the following guidelines. Questions (i) could not be answered with a simple ‘yes’, ‘no’ or ‘depends’; (ii) could be related to any aspect of bioenergetics but should be applicable to methods used in marine mammal management and conservation; (iii) could be unanswerable or infeasible given current methods; and (iv) could be either species-specific or broadly relevant to a taxonomic group . Questions were collated and revised over email discussions and during the bioenergetic workshop . QuestioThe final list of questions was circulated for voting to the original 62 survey invitees and 20 additional individuals identified by the co-authors of this paper during the process. Participants voted for no more than 15 questions each, with the guidance that a question need not be applicable to all marine mammals . Voting occurred virtually via a Google Forms survey (25 August–27 September 2021). Survey participants were also asked to provide information on their expertise in marine mammal physiology and whether they had experience developing bioenergetic models . This was to help inform whether any key questions were deemed important by individuals with greater expertise in one discipline over the other (physiologists vs. bioenergetic modellers).A total of 284 initial questions were submitted by 37 of the 62 original invited participants. They ranged from detailed physiological questions to broad overarching questions about the impacts of climate change, anthropogenic disturbance and fisheries on marine mammal populations. Questions were revised by co-authors and other bioenergetic workshop participants  such thaForty-two of the 82  invited participants voted in the final survey. Most of the voting participants had current jobs in academia (78%), followed by non-profits (7.1%), government agencies (4.8%), a combination of academia and consulting (2.4%), the private sector (2.4%) or were self-employed 2.4%; . One parThe following sections briefly describe how each question is relevant to bioenergetics and conservation efforts and highlight important data gaps. Additional information on topics covered here, such as bioenergetic models, metabolic rates, body condition and growth and reproductive energetics can be found elsewhere in this special issue  in the right place, at the right time to support individual and population energy needs? How do factors such as interannual variability, climate change, fisheries and habitat loss affect prey availability? Climate change, which is rapid in some regions, is predicted to have considerable impacts on the distribution, biomass, energy density and body size of prey species , leading to reduced weaning mass of pups  or cause direct (e.g. injuries from vessels or nets) or indirect  physical impacts that have implications for energy balance. For example, marine mammals may spend less time foraging when disturbed . Traumat of pups . Our abiTursiops truncatus) and harbour porpoise (Phocoena phocoena) indicate that FMRs of small odontocetes may align more closely with the high-energy lifestyle of otariids (Ziiphidae) and sperm whales  and baleen whales. These gaps often result in the use of general allometric equations to estimate metabolic rates in bioenergetic models (e.g. Field metabolic rates (FMRs) represent an individual’s daily energy expenditure at a given time, which underpins many of the other key questions we identified in this exercise. The costs contained within FMR comprise the majority of an individual’s energy budget , and limels e.g. . ExistinMirounga angustirostris; The amount of time an animal spends engaged in certain activities  influences its energy budget through changes in intake, expenditure or both. Climate change and habitat loss alter environmental conditions, forcing (or facilitating) species to either move into new environments or adapt to their existing ones that may be undergoing rapid changes . In addiEubalaena glacialis; Once ingested, energy is directed to a variety of processes, such as digestion, the maintenance of cellular function, production of waste products, thermoregulation, mechanical work/activity, structural growth, reproduction and storage . Energy Body condition, defined as the amount of energy reserves relative to structural size, is a physiological unit of considerable interest in conservation-focused bioenergetic studies. As the physical manifestation of energy balance, body condition provides essential information about the health of individuals and populations Williams . A univeBehavioural changes are one of the first observable responses of individuals to disturbances or environmental perturbations. The resulting impact of that behavioural change on survival and reproductive success is what drives population dynamics  by measuring changes in body size and condition of lactating females relative to the growth of their dependent calves  compare with methods that provide a more direct measure of FMR (e.g. DLW) and the level of uncertainty around estimates given the assumptions of such approaches  availability to aid in killer whale population recovery . The Office of Naval Research funded the bioenergetic workshop (N000142012392) that provided support for this work.The original submitted questions and final collated questions are included in supplemental material. There are no other data associated with this article.suppl_coac055Click here for additional data file.