Single layer graphite, known as graphene, is an important material because of its unique two-dimensional structure, high conductivity, excellent electron mobility and high surface area. To explore the more prospective properties of graphene, graphene hybrids have been synthesised, where graphene has been integrated with other important nanoparticles (NPs). These graphene–NP hybrid structures are particularly interesting because after hybridisation they not only display the individual properties of graphene and the NPs, but also they exhibit further synergistic properties. Reduced graphene oxide (rGO), a graphene-like material, can be easily prepared by reduction of graphene oxide (GO) and therefore offers the possibility to fabricate a large variety of graphene–transition metal oxide (TMO) NP hybrids. These hybrid materials are promising alternatives to reduce the drawbacks of using only TMO NPs in various applications, such as anode materials in lithium ion batteries (LIBs), sensors, photocatalysts, removal of organic pollutants, etc. Recent studies have shown that a single graphene sheet (GS) has extraordinary electronic transport properties. One possible route to connecting those properties for application in electronics would be to prepare graphene-wrapped TMO NPs. In this critical review, we discuss the development of graphene–TMO hybrids with the detailed account of their synthesis. In addition, attention is given to the wide range of applications. This review covers the details of graphene–TMO hybrid materials and ends with a summary where an outlook on future perspectives to improve the properties of the hybrid materials in view of applications are outlined. Since the first report in 2004 [−1·K−1) [−1) [2·g−1) [Graphene consists of a single layer of carbon in a two-dimensional 2D) lattice. It is a densely packed, atomically thin layer of sp in 2004 , graphenD lattice in 2004 . Graphen in 2004 . It also[−1·K−1)  and elec−1) [−1)  and high [2·g−1) . Graphen [2·g−1)  and negl [2·g−1) . Due to  [2·g−1) , hydroge [2·g−1)  and sens [2·g−1) . DespiteIn the last few decades, the synthesis of transition metal oxide (TMO) NPs has attracted much attention, providing the advantages of controlled shape, size, crystallinity and functionality, as well as being ecologically benign, corrosion resistance, easily scalable and relatively cost effective –16. In pThe interest in preparing graphene–TMO NPs hybrids is increasing enormously due to the peculiarities in combining the required properties of building blocks for a specified application. In the recent review by Khan et al., the synthesis, properties and applications of graphene–metal oxide composite NPs are discussed in detail . The rev−1. However, this is not sufficient for applications requiring high energy capacity. Single layer graphene has a high theoretical lithium storage capacity of 744 mAh·g−1, but graphene has a tendency to stack due to van der Waals interactions between graphene layers [−1 with 100% capacity retention for up to 100 cycles [Graphite is commercially used as an anode material for LIBs due to its large lithium storage capacity of 372 mAh·ge layers . The ince layers . Poizot 0 cycles . For met0 cycles . These dGraphene is used as a supercapacitor because of its unique properties, such as high surface area, excellent flexibility, chemical inertness and good electrical conductivity . The praIn a photovoltaic cell, sunlight energy is directly converted to electricity. Graphene and graphene–NP hybrids have been investigated extensively in the field of solar cells because of their unique properties, such as high optical transparency, electrical conductivity, and mechanical flexibility. As mentioned before, graphene is an excellent electron-accepting and electron-transporting material. When graphene is integrated with semiconductor materials, it promotes photogenerated electrons through π–π bond interactions and suppresses the charge recombination in the semiconductor materials . As a co2/Si or glass [The first free-standing single-layer graphene was obtained in 2004 by the isolation of graphene from graphite by micromechanical cleavage . Later, or glass . For the2 which form amines, hydrazones or other similar functional groups covalently attached on the sheet of graphene [4 has been demonstrated as being more effective than hydrazine as a reducing agent of GO. NaBH4 is more effective at reducing the C=O group, while it has moderate efficiency in the reduction of epoxide and carboxylic acid [2 [The most common top-down approach for the synthesis of graphene is the reduction of GO and of graphite fluoride by thermal or chemical methods. The reduction of GO is a low cost, facile technique and yields bulk quantities of GSs. GO was first reported 150 years ago . It is ngraphene . NaBH4 hlic acid . Other rlic acid , gaseous acid [2 , alkalin acid [2 –59, and  acid [2 . Despite acid [2 –62, elec acid [2 –64, ther acid [2 ,65, phot acid [2 , solvoth acid [2 –68, ther acid [2 , or chem acid [2 . In termFor the preparation of graphene–NP hybrids, bulk quantities of GSs are required. So, for the synthesis of graphene–NP hybrid systems, in most cases, top-down approaches have been used. Different architectures of graphene–NP hybrids can be prepared by this one-pot synthesis method . In anot2 is an interesting material because of its unique optical and electrical properties. It has been used as a heterogeneous photocatalyst and it has outstanding advantages because of its low cost, scalability, nontoxicity, strong photo-oxidising power and stability in oxidative and acidic environments [2 nanomaterials has shown that the energy conversion efficiency of the photovoltaic devices that use TiO2 NPs critically depends on the morphology and size of the NPs [2–graphene hybrid systems, the morphology of TiO2 plays an important role in various applications.Nanocrystalline TiOronments . Extensi the NPs –80. Addi2 anode materials have outstanding cycling stability and almost no volume expansion occurs when TiO2 is fully lithiated. As the electrical conductivity of TiO2 is low, it has a weak rate capability in electrical devices. The modification of TiO2 with conductive materials like graphene improves its electrical performance significantly. The introduction of graphene into TiO2 results in increased conductivity of the hybrid material, higher transparency and efficient charge separation of the system which causes enhanced photocatalytic activity and other novel properties [2 anodes and is responsible for the improved photocurrent response of the hybrid materials [TiOoperties . Also, daterials .2–graphene hybrids, TiO2 is prepared by hydrolysis of Ti-containing precursors [2 NPs. The fabrication of TiO2–graphene hybrid systems results in a strong coupling between the components therefore resulting in superior activity as compared to the individual materials. The resultant hybrid material displays a synergistic effect of accumulated graphene and TiO2 NPs, exhibited by the extraordinary physical and chemical properties in comparison with pristine graphene and bare TiO2 NPs [In most cases, for the formation of TiOecursors –85 as thTiO2 NPs –87.2–graphene hybrid systems. Liang et al. prepared TiO2 NCs on the GO sheet by hydrolysis methods and then converted GO to graphene by hydrothermal treatment [2–graphene nanocomposite hydrogel (TGH) was prepared by Zhang et al. by a facile one-pot hydrothermal approach where the spherical nanostructured TiO2 NPs were densely decorated onto the GS [Different synthesis routes have been introduced; among them, hydrothermal methods are used extensively for the preparation of TiOreatment . A TiO2–o the GS .2 sandwich structure was prepared by using ethylenediamine/H2O solvent in a reduction–hydrolysis technique. The photocatalytic activity of the hybrid has been confirmed by the conversion of CO2 to valuable hydrocarbons (CH4 and C2H6) in water vapour  and GO nanosheets. The layer materials are spatially phase segregated to maintain unique 2D characteristics due to the functional separation of the layers at the nanoscale [An anionic surfactant-mediated growth of the self-assembled TiOge rates . When ananoscale . This hy2–Pt–graphene hybrid has been prepared by Xia et al. where the graphene was synthesised by the arc discharge method and the Pt–graphene hybrid electrocatalysts were prepared using a polyol process. This structure exhibits enhanced electrochemical performance due to the strong metal–support interaction and proposed synergetic effect [2 nanoparticle films for application in dye-sensitised solar cells. The conductivity of the film increases with the incorporation of the GSs, which in turn results in an enhancement of the power conversion efficiency [A highly efficient, stable, sandwich-structured TiOc effect . A molecficiency .2 intercalated between graphene layers as pillars which provide a 3D open space with distinct advantages when used as LIB anode materials [2 NPs, and then the TiO2 NPs were wrapped by graphene. These hybrids have high potential for photocatalytic application [2 nanospheres as efficient photocatalysts for the decomposition of rhodamine B with an efficiency up to 91% in 90 min, which is much higher than the efficiency of TiO2 nanospheres (65%) [2 nanospindles [2 nanorods [2 mesoporous [A unique three dimensional (3D) nanostructure was fabricated by Hu et al. with nanometre-sized TiOaterials . (3-Aminlication . Zhang ees (65%) . The graspindles , TiO2 nananorods  and TiO2soporous  shows im2 make use of its photocatalytic activity, there are also some applications of shape-controlled TiO2–graphene hybrids used in pollutant abatement [Although most of the applications of graphene–TiObatement , high-pebatement , and selbatement .2 has two crystalline phases, monoclinic and rutile. The monoclinic form of vanadium(IV) oxide can be transferred to the rutile form by a thermally induced, reversible treatment at 68 °C [2 (M) behaves as a semiconductor whereas VO2(R) behaves as a semimetal. Vanadium pentoxide (V2O5) has very low electronic conductivity due to its low d-band mobility. It also shows a thermochromic transition at 257 °C and this material is used as a catalyst for industrial processes, gas sensors and in LIBs [2O5 such as nanotubes, nanowires, nanofibers, nanobelts, and nanorods have been prepared by sol–gel processes, hydrothermal processes [2 is quite stable during lithium intercalation–deintercalation cycles and has been regarded as a promising electrode material for both organic and aqueous LIB owing to high capacity, unique structure and suitable electrode potential. However, its cyclic performance is limited by its high charge-transfer resistance. The incorporation of graphene solves its electrical resistance problem with the VO2 electrodes and it acts as a high-performance electrochemical capacitor [Vanadium has oxidation states ranging from −1 to +5. Binary vanadium oxides have already been proven as a potential material for studying superconductivity at high pressures and low-dimensional quantum-spin transitions . VO2 hasat 68 °C . VO2 (M) in LIBs . Variousrocesses , electrorocesses . Other vapacitor , shows eapacitor , and repapacitor .2–graphene architectures by using graphene as a substrate for the in situ growth of VO2 ribbons (2O5 by GO simultaneously in a Teflon lined autoclave [2 (M) nanotube–graphene hybrids cathode material is used in LIB, where the VO2 nanotubes are wrapped by and trapped between the GS [Yang et al. have prepared VO ribbons  via hydrutoclave . When thn the GS . Althoug2 nanosheet-built 3D flower hybrids [2O5 nanoribbons [2O5 which facilitates the Li+ diffusion, significantly improving the electrochemical performance. V2O5 quantum dot/graphene is a promising cathode material for use in long-life rechargeable Li batteries [2–graphene hybrid materials for the fabrication of thermochromic films for energy saving windows. VO2 crystals have been prepared on graphene and the graphene-supported VO2 is easily transferred to a plastic substrate which enables formation of a new type of flexible thermochromic film [To improve the rate capability, Nethravathi et al. use a hydrothermal method to prepare N-doped graphene–VO hybrids , where toribbons . These satteries –116. Kimmic film . This hy2O3, a trivalent chromium(III) oxide, is an important industrial material that has been used in abrading agents and pigments. Unlike other TMOs, Cr2O3 exhibits poor dispersion. It is insoluble in both acidic and alkaline media. The low electrical conductivity of Cr2O3 inhibits its application for practical use and electrical research fields. The poor dispersion results in a low surface area and a nonuniform porous structure which restricts its supercapacitive performance. Severe volume change happens for Cr2O3 during the charge–discharge cycles which results in a rapid capacity fading and the end of the cycle life.Cr2O3 to improve the properties of the materials and the other strategy is to develop Cr2O3 materials on the nanoscale. Graphene–Cr2O3 hybrids have been explored with respect to the oxygen reduction reaction (ORR) [2O3–rGO hybrid makes it a promising catalyst for fuel cells.Several strategies have been designed to increase the conductivity of the materials and also to improve the volume change. In that context, graphene has been hybridised with Cron (ORR)  and applon (ORR) . ORR is 2), hausmanite (Mn3O4) and bixbyite (Mn2O3) are important minerals of manganese. These oxides have attracted great attention because of their environmental benignity and the high abundance of Mn in nature. Among all the oxides of manganese, Mn3O4 has been studied widely as an anode material for LIB to achieve higher specific capacities than graphite [3O4 has a spinal structure and is a potentially interesting electrode material as an electrolytic supercapacitor because of its low cost, environmental compatibility and intrinsically high capacity [3O4 and Fe3O4, Mn3O4 is a much less conductive material, so it is a great challenge to explore the Mn3O4 graphene hybrids in LIB applications. As a bulk material, Mn3O4 has low electrical conductivity that limits its ability in terms of both capacitance and capacitance retention at high current density. The most and widely used strategy is to combine Mn3O4 to lightweight and electronically conducting graphene. Graphene–Mn3O4 hybrids have also been employed as active, stable and low cost cathode electrocatalysts used for high capacity anode materials for LIBs [2O4 is used for the vanadium redox flow batteries [3O4 is electrochemically oxidised to the more conductive MnO2. This explains the interesting phenomenon of increasing capacitance with cycling [Pyrolusite  [3O4 and N-doped rGO which shows pronounced electrocatalytic activity towards ORR in alkaline solutions [3O4 NPs on the GO sheets. The Mn3O4–graphene hybrid is being explored for high capacity, low cost, nontoxic anode materials for battery applications . The application of MnO in LIB is a great challenge because the low electric conductivity of MnO results in poor cycling stability and inferior rate capability. A long-term stable, nano-architecture of graphene-supported MnO NPs for LIB applications has been prepared by cycling where the oxidation of Mn(II) to Mn(III) and interfacial lithium storage upon cycling contribute to an enhanced specific capacity [The Mnlue (MB) , for thelue (MB) , for carlue (MB) , for ORRlue (MB) , for enhlue (MB) –133, andlue (MB) . Bag et olutions . This hyolutions , liquid olutions  or hydroolutions  for growications . MnO2 haeactions . Yu et afor LIBs . Dong et acidity . Ultrathpacitors . Graphenications . MnO hascapacity . N-dopedcapacity .2O3 has the advantages that it can be produced in high abundance, with low cost, and the nontoxicity of Fe results in a reduced environmental concern. Therefore, it is expected to meet the requirements of future energy storage systems. It is an attractive anode material for LIBs as it has a high theoretical capacity (1007 mAh·g−1) [2O3 electrode pulverisation and rapid capacity decay happens due to the large specific volume change and particle aggregation. These obstacles can be removed by creating hybrids of Fe2O3 and graphene which have superior performance regarding flexibility and electrical conductivity [2O3–graphene hybrids are prepared by hydrothermal methods without any reducing agent. Tian et al. have prepared α-Fe2O3 NP anchored graphene hybrid materials by hydrothermal methods which have good cycling performance and enhanced rate capability [2O3–graphene has been fabricated by vacuum filtration and a thermal reduction process. This network shows superior electrical performance because the porous nature of the hybrid accommodates the volume change [3O4 NPs (Fe3O4/N-GA) as efficient cathode catalysts for ORR [3O4/N-GA material shows excellent electrocatalytic activity for the ORR in alkaline electrodes. It is even larger than N-doped carbon black or N-doped GSs (N-GSs) due to its 3D macroporous structure and high surface area, in addition to exhibiting a higher current density, lower ring current, lower H2O2 yield, higher electron transfer, and better durability   which isuctivity . Most ofpability . A 3D nee change . Wu et a for ORR . This Ferability . Chen etormation . Fe2O3 smaterial . Fe2O3 g in LIBs –153. Li material . α-Fe2O3 of H2O2 . Graphennd Fe3O4 . Yang etnd Fe3O4 . Liang ene paper . In anotformance . One int storage . Anotherfor LIBs . The impe2O3 NPs ,162. Therocesses . Su et arocesses .2O3 NPs showed volume expansion and morphological changes upon lithiation, and the surface of the electrode was covered by a Li2O layer. They also found that the single crystalline Fe2O3 NPs were converted to polycrystalline NPs and the delithiated product is no longer Fe2O3 but FeO. A solvothermal process is introduced to construct 3D macroscopic Fe2O3 nanocube/N-doped graphene aerogels as an anode material for LIB applications [2O3 and GS hybrids, which have excellent prolonged cycling stability [3O4–rGO hybrids by one-pot solution chemistry which have good adsorption capability of various dyes , malachite green, and new coccine) [2O3 NPs. In addition, the materials could be regenerated and utilised via a simple annealing treatment.Feications . This aetability . Geng etcoccine) . These m3O4)–graphene hybrids can be synthesised by solution methods. Like other hybrid TMO–graphene materials, this hybrid is also used as an anode for LIBs [3O4–N-doped graphene exhibits similar catalytic activity like Co3O4–graphene hybrids but superior stability to Pt in alkaline solution [3O4 (Co3O4/N-rmGO than in Co3O4/rmGO) due to favourable nucleation and anchor sites for Co3O4 nanocrystals as N-groups help on rGO. In the ORR, the electronic effect of N-doping of graphene also plays a role. Mao et al. have prepared 3D crumbled cobalt–GO nanostructure hybrids which show both ORR and oxygen evolution reaction (OER) [3O4/flocculent graphene hybrids on Ni foam for supercapacitor applications as their nanocluster morphology synergistically results in an improved electrochemical performance [3O4 NPs on vertically aligned graphene. This hybrid has also been used for nonenzymatic glucose detection in microdroplets [Cobaltosic oxide  . Wu et aformance . Symmetrdroplets .3O4 hybrid electrodes constructed on a micropipette tip which can detect nonenzymatic glucose [3O4 has been used for selective oxidation of olefins and alcohols [3O4 NPs were anchored on conducting graphene and used as an anode for high-performance LIBs. This hybrid material exhibited large reversible capacity, excellent cyclic performance and good rate capability [3O4 NPs on N-doped graphene by using a hydrothermal method [3O4–graphene hybrid possesses catalytic performance for heterogeneous activation of peroxymonosulfate for the decomposition of phenol [3O4, homogeneous dispersion of the NPs, increased surface area of the catalyst, and most importantly, the synergetic interaction between the N-doped graphene and Co3O4 NPs. In another work, Singh et al. have prepared three different morphologies of Co3O4 nanocubes, blunt edge nanocubes and spherical particles supported on N-doped graphene by a hydrothermal method [3O4 NPs and their synergistic interaction between N-doped because graphene helps to tune the properties of the OER electrocatalyst. Yang et al. fabricated graphene encapsulated Co3O4 NPs which have a high reversible capacity of 1000 mAh·g−1 over 130 cycles and is superior to Co3O4 NPs with respect to capacitor applications [3O4-intercalated hybrid nanostructures using microwave irradiation [Wang et al. fabricated graphene–Co glucose . N-dopedalcohols , LIBs [1alcohols , and oxyalcohols , and as alcohols . Co3O4 Npability –179. Magpability . The Co–pability . Singh el method . Here, tf phenol . Moreovel method . Among tications . Kumar eadiation  and this2 for phenol degradation and it takes only 10 min for 100% phenol removal.CoO attracts extensive interest because of its high lithium storage capacity. CoO–NP-supported GSs effectively circumvent particle cracking, pulverisation, and aggregation upon cycling, thus serving as a high-performance anode material with long cycle life, high reversible specific capacity and excellent rate capability for LIB applications . Self-asII and NiIII. The NiO–graphene hybrids show good sensing capability for the reducing gases such as H2, NH3, H2S, NO2 [NiO, a p-type wide band gap semiconductor is extensively used as catalyst, battery cathode, electrochemical capacitor and magnetic material . NiO is H2S, NO2 . In anotH2S, NO2 . RecentlH2S, NO2 . This hyH2S, NO2 –208.Cu nanowire (NW) films and indium tin oxide (ITO) films have comparable sheet resistances and optical transmittance. A few drawbacks of Cu NW films, such as low oxidation resistance or weak adhesion to the substrate, can be compensated for by the addition of graphene. The resulting hybrid films have improved electrical conductivity as they provide 2D pathways for charge transfer . The gra2O) is a p-type semiconductor and is used for solar energy conversion, as sensors and for photocatalytic degradation. The controlled synthesis of Cu2O results in a vast palette of architectures including nanocubes, nanocages, nanowires, solid and hollow spheres. Graphene-wrapped Cu2O nanocubes exhibit higher electrocatalytic performance towards electro-oxidation of glucose with lower detection time, and this hybrid has improved electrochemical stability [2O microspheres on rGO by a one-step synthesis which have potential application for nonenzymatic electrochemical glucose and H2O2 sensors [2O and Cu NPs on copper foil by annealing at 200–1000 °C under an Ar atmosphere where the particle phase and particle size and shape strongly depend on the process temperature [2O NW mesocrystals by nonclassical crystallisation under hydrothermal conditions [2O NW–graphene hybrids, was used as a high-performance NO2 gas sensor  and partially encircle the ZnO NPs. The quasi-core–shell structure of the hybrid was prepared by a one-step chemical method [Most of the reports of graphene hybrid systems are related to ZnO NPs, as it is very easy to control the size and morphology of ZnO NPs as well as the properties of the material. ZnO is an important II–VI semiconductor with large direct band gap of 3.37 eV and large exciton binding energy of 60 meV. It has been extensively studied because of its potential application in solar cells, sensors, diode lasers, piezoelectric devices, as surface acoustic wave propagators, antibacterial agents and ultraviolet light emitters. Graphene-based ZnO hybrids proved to be promising materials having a much wider range of applications in the field of energy conversion and storage, such as catalysts and in optoelectronics. Comprehensive work has been done to prepare graphene-wrapped ZnO NPs for better performance in optoelectronics applications. Single-layer graphene-wrapped ZnO NPs  have beel method .For the formation of graphene-wrapped ZnO NPs, some other routes have been used, like chemical functionalisation of the ZnO surface. In this process there are three steps: surface modification of NPs mainly by amine groups, coating the NPs with a GO shell, and finally, conversion of GO to graphene by a reduction process. For the amine functionalisation of metal oxide NPs, poly (PAH) –227 and 3, NO [2 [2 [The optical properties of ZnO NPs change when they form hybrids with graphene. Pure ZnO exhibits a photoluminescence (PL) band at 373 nm, which is due to the exciton recombination corresponding to the band edge emission, and a green emission peak is most commonly observed that arises from the defect of ZnO NPs such as oxygen vacancies, zinc vacancies, oxygen interstitials, and zinc interstitials . Graphen3, NO , methane3, NO , NO2 [263, NO [2 , formald3, NO [2 –266, H2 NO [2 [2 , and alsNO [2 [2 . FurtherNO [2 [2 –270. TheNO [2 [2 .−1) but it has attracted less attention compared to the other metal oxides due to its poor cyclability resulting from huge volume change during charge–discharge cycles. Kushima et al. show that when ZnO NWs are partially lithiated, multiple cracks are induced and divided the NWs into multiple segments. This results in a lithium embrittlement effect in ZnO [ZnO can be used as an inexpensive anode material and has high theoretical capacity (978 mAh·gt in ZnO . Such stt in ZnO . ZnO–grat in ZnO .Excellent performance in lithium storage capability is observed by incorporation of a conductive nitrogen-doped graphene matrix with ZnO due to a synergistic effect . Boruah 4), has attracted increasing attention because it is a promising candidate for cathode materials [4 is a promising cathode material for LIBs because of its high stability, high power, environmental safety, and low cost. However, the main drawback for LiFePO4 battery commercialisation is their poor rate performance (at current >5 C) due to the low electrical conductivity and Li-ion diffusion rate which limits its usage for electrical applications. Those drawbacks are compensated for by hybridising LiFePO4 with graphene. Graphene-hybridised LiFePO4 has been largely used for LIBs [4 are mainly that the operating voltage and theoretical capacity can be increased by hybridisation with graphene. Shi et al. have prepared graphene-wrapped Li3VO4 microboxes by a one-step in situ hydrothermal method. This hollow structure could relax the stress and strain of Li+ insertion/extraction and provides extra space for the storage of Li ion. It also increases the surface area of the material, resulting in improved capacity, rate capability and cycling performance [Two TMOs can be hybridised with graphene for improved performance which increases the range of potential applications of the hybrid materials. Since the report of Padhi et al., the iron-based nanomaterial, olivine lithium iron phosphate Co(III)Mn(III)O4. Hybridisation of this material with graphene results in further optimisation of catalytic properties. Wang et al. prepared a MnCo2O4–graphene hybrid by a two-step solution method by using Co(OAc)2 and Mn(OAc)2 precursors [2O4–graphene has been used as a LiO2 battery cathode [2+ replacement in the Co3O4 matrix by M2+  for increasing the catalytic performance [2O4 hybrids have been used for the ORR [2O4 hybrids as a methanol-tolerant electrocatalyst for the ORR with improved performance [2O4–graphene has also been used in electrochemical pseudo-capacitor applications [2O4 was anchored on the N-doped graphene prepared by a hydrothermal method, used for LIB applications, where the N-doping further improved the ORR performance in the LiO2 batteries [2O4 nanostructures on a 3D graphene foam with in situ deposition by a facile hydrothermal method which is used as an enzyme mimic for glucose and calcium detection [2O4 nanoplatelets and graphene hybrids have been used for ORR and OER [Much effort has been attributed to the development of Co-based anodes for LIB applications by partially replacing Coecursors . The hyb cathode , an oxyg cathode , and in  cathode . Mohamedformance . For the the ORR . Zhang eformance . NiCo2O4ications . NiCo2O4atteries . Wu et aetection . NiCo2O4 and OER –304.2O4 outperformed Co3O4–graphene hybrids in terms of the onset potential and current densities. This property is attributed to the fact that the incorporation of Ni cations into the octahedral sites of the spinel crystal structure enhances the electrical conductivity as well as to the creation of new active sites with much lower activation energy [2O4, but can also offer effective buffering to accommodate the lithiation-induced stress which is beneficial to lithium storage and cycling stability [2O4–graphene is an attractive electrode material for supercapacitors [2S4–graphene hybrids synthesised by a one-pot solvothermal strategy are used for ORR and ORE [2O4 NPs on N-doped rGO. This was revealed to be an efficient electrocatalyst, produced by a two-step solvothermal method which exhibits ORR catalytic activity [2O4/N–rGO hybrid, GO was reacted with Co(OAc)2 and Cu(OAc)2 in a 2:1 molar ratio at 80 °C in ethanol/water/ammonia, which led to the selective formation of the hybrid  of CuCo2O4/N-rGO, Co3O4/N-rGO, CuCo2O4 + N-rGO, CuCo2O4, and N-rGO suggest that CuCo2O4/N-rGO outperforms the other catalysts in terms of disk current density and half-wave potential in an O2-saturated 1 M KOH solution at a rotational rate of 1,600 rpm  has attracted increased attention because of its large application as a catalyst. Spinal ferrites have interesting magnetic, magneto-resistive and magneto-optical properties. The high density magnetic storage is derived from the large surface area-to-volume ratio on the nanometre scale, and these materials have super-paramagnetic behaviour. These spinal ferrites are considered to be promising anode materials for LIBs given their high specific capacity which is typically 2–3 times higher than that of the graphite anode used in the commercial LIBs. Bai et al. have used a one-pot solvothermal method for the synthesis of MFe2O4  through the simultaneous reduction of GO and growth of MFe2O4 [2O4 microsphere can be controlled by adjusting the metal ion concentration. This hybrid displays a large adsorption capacity and photocatalytic activity towards RhB and MB and can be easily separated by a magnet. Among all the ferrites of the form MFe2O4 , manganese ferrite (MnFe2O4) has been found to exhibit usually large capacitance. A MnFe2O4–rGO hybrid which shows higher catalytic performance than pure MnFe2O4 to activate peroxymonosulfate (PMS) to various oxidatively degraded organic pollutants in water, has been prepared by a facile approach [Over the past years another spinal-type ferrite having the general formula MFef MFe2O4 . In thisapproach .2O4–graphene hybrids by immobilising the MnFe2O4 microspheres on the graphene nanosheets by a solvothermal route for supercapacitance application [2O4 nanohybrids are used for removal of lead and arsenic from water [Cai et al. have synthesised MnFelication . This hylication  and effilication . GO–MnFeom water .2O4) which was proposed for biomedical applications. The hybrid material shows good magnetism and could be separated from the solution by using a magnet. This hybrid has been prepared by a solvothermal method, a facial vapour diffusion method [2O4–graphene hybrids show improved electrochemical properties and are used as binder-free anode materials for LIBs [2O4–graphene hybrids by chemical precipitation of Fe and Co precursors and reduction of GO in a hydrazine hydrate solution; this hybrid has been used for the degradation of phenol [Another material in the family of spinal-type ferrites is magnetic cobalt ferrite  of phenol [Li et al. prepared graphene-functionalised CoFeom water . Yao et f phenol  (Figure 2Fe2O4–graphene hybrid shows that the hybrid shows better catalytic activity than pure CoFe2O4 (2Fe2O4–graphene hybrids can be easily removed from the reaction solution by applying an external magnetic field (2O4–graphene hybrids are used for photodegradation of MB [2O4 hybridised with N-doped graphene provides a simple and efficient way to configure hybridised electrode materials with high lithium storage capacity [2O4. Furthermore, this hybrid has been used for microwave absorption applications and as electromagnetic wave absorbers [2O4 superparamagnetic NCs [2O4 by the introduction of graphene is due to the synergistic effect between the remarkable magnetic loss from the superparamagnetic CoFe2O4 nanocrystals and high electric loss from the lightweight graphene. For LIB applications, graphene-hybridised CoFe2O4 [3Sn2@Co [A nitrogen absorption isotherm was used to estimate the pore size of the hybrid to be about 1.7–5.9 nm. The catalytic study of the Co CoFe2O4 . The Co2ic field . CoFe2O4on of MB –323, degon of MB  and the on of MB ,325. Thion of MB . The biccapacity . The autbsorbers . Li et aetic NCs . The enh CoFe2O4  and Co3S[3Sn2@Co  have bee2O4 is an important, promising anode candidate for LIB applications due to its low discharge potential and high theoretical specific capacity of 1072 mAh·g−1 [2O4-graphene hybrid films are directly usable anodes for rechargeable lithium half-cells without adding any polymer or conductive additives [2O4 is a magnetic semiconductor material, thus ZnFe2O4-based catalysts can be magnetically separated in the suspension system. ZnFe2O4–graphene hybrids prepared by the hydrothermal method show higher catalytic performance [2O4–graphene hybrid by a self-assembly method for application in LIBs [ZnFe mAh·g−1 . The ZnFdditives . ZnFe2O4formance –332. The in LIBs . The hyb in LIBs .In summary, graphene–TMO NPs hybrids have received particular attention because of their unique properties. Due to the advantageous properties of these graphene–TMO hybrids, they have wide-spread application potential as photocatalysts, anode materials in LIBs, solar cells, sensors, diodes and also for the removal of organic pollutants from water .A multitude of synthesis methods have been introduced by different research groups for the synthesis of the hybrids, among those, hydrothermal methods, sol–gel processes, chemical synthesis, and microwave-assisted growth have drawn the most attention in top-down approaches, while in bottom-up approaches, CVD and arc discharge methods have been mostly used. Depending on the application need, hybrids with different structures have been prepared by selecting the appropriate synthesis process .Since the first experimental demonstration of single sheet graphene in 2004, the field of graphene-related research has grown at an outstanding speed. Graphene has a unique morphology, large surface area, and extraordinary electronic properties. Graphene has been synthesised by various methods and its chemical structure can be modified by changing the fabrication methods and also by combining with various NPs. Such materials are produced to meet the increasing demands of high-performance materials in electronic devices.Enhanced knowledge on the surface chemistry and functionalisation of the graphene surface, and also on the improvement in the colloidal synthesis of NPs, will lead to a wide range of potential applications related to the preparation of graphene–NPs hybrid materials by the incorporation of various NPs. The synthesis of graphene-based composites also requires a large amount of graphene, preferably with surface modification. By tuning the surface chemistry of graphene, the fluorescent properties can be changed accordingly which enables its potential application in photovoltaics, sensors and also in bio-imaging. The number of publications related to graphene and graphene-based materials has increased exponentially in recent years. However, there is still need for the scientific community to develop graphene-based models, hybrid materials and devices, and their possible applications in various fields. By improving the quality of the synthesised graphene, better quality hybrids can be prepared for different applications.Knowledge of GO chemistry will provide valuable input about its reactive properties and the properties of the graphene derived from it. Controlled methods of graphene synthesis are particularly important for the controlled growth of layers, which still remains to be established. Regarding the fabrication of graphene NP hybrids, the key obstacle lies in the reproducibility of the structure. For the synthesis of graphene-encapsulated NPs, the difficulty is that the thin graphene layer is not ideally formed as a uniform layer on all the NPs. Thus, the design and synthesis of new graphene-based nanostructures and architectures with uniform structure will be an important task for the future. It is important to mention that no such unique analysis technique has been introduced which can confirm that all the NPs are uniformly coated. In most reports directed at graphene-encapsulated structures, a quasi-core–shell structure was obtained instead of the desired core–shell structure.By achieving a high level of uniformity and reproducibility of graphene–NP hybrids, the electrical properties of the devices can be optimised which will lead to higher sensitivity and selectivity. Inexpensive and large-scale fabrication of defect-free graphene is still a challenge due to the existence of defects or oxidation sites in graphene, which is partially restored in graphene derived from GO. However, there is no doubt that more efficient synthetic strategies for graphene and graphene-based hybrids will be developed in an economically feasible quantity, leading to the commercialisation of graphene in the near future. Some research shows that the surfactants and the reductants used for the synthesis of the hybrid materials have a detrimental effect. In this sense, the biocompatibility and toxicity of the chemicals should be investigated to enable application of the hybrid materials in biomedical applications. Most of the applications of TMO–graphene hybrid materials are in LIBs, although further study is required to gain control over the phase and morphology of the NPs for this application. A prerequisite is a well-mastered growth synthesis to obtain a well-defined uniform structure of graphene. Control over the interface and interaction between NPs and graphene is necessary to enhance the performance of LIBs. Much attention is devoted to the application of graphene–NP hybrids in supercapacitor applications but more research is necessary. During the charge–discharge process, the graphene layers become aggregated, which degrades the electrode material. In some cases, the electrode materials are contaminated by impurities introduced from the incomplete reduction of GO. When using graphene–TMO hybrids as a photocatalyst, the improved performance in the catalytic properties is generally ascribed to the extended absorption and faster charge transfer in graphene as compared to TMOs. Therefore, research on the interfacial status of the hybrid is important to obtain a detailed understanding of the origin of the improvement.Further challenges exist in the application of graphene–TMO NP hybrids on the industrial scale. Some advanced applications of the graphene-based hybrids require particular understanding of the contact between the surface of the graphene and the NPs, which will have a direct impact on the properties of the hybrid. Despite the enormous efforts and huge attention, a significant breakthrough application of graphene and graphene-based materials in energy harvesting systems has not been achieved to date, but solutions to the key challenges appear within reach. In view of the manifold of potential applications, each having different requirements regarding material properties, it can be anticipated that the research on graphene–TMO NP hybrid materials will have a very bright future.


A methyltransferase enzyme termed ‘MddA’, which catalyses the methylation of MeSH, generating DMS, in a wide range of bacteria and some cyanobacteria, may mediate this process, as the mddA gene is abundant in terrestrial metagenomes. This is the first study investigating the functionality of MeSH-dependent DMS production (Mdd) in a wide range of aerobic environments. All soils and marine sediment samples tested produced DMS when incubated with MeSH. Cultivation-dependent and cultivation-independent methods were used to assess microbial community changes in response to MeSH addition in a grassland soil where 35.9% of the bacteria were predicted to contain mddA. Bacteria of the genus Methylotenera were enriched in the presence of MeSH. Furthermore, many novel Mdd+ bacterial strains were isolated. Despite the abundance of mddA in the grassland soil, the Mdd pathway may not be a significant source of DMS in this environment as MeSH addition was required to detect DMS at only very low conversion rates.Dimethylsulfide (DMS) is an environmentally important trace gas with roles in sulfur cycling, signalling to higher organisms and in atmospheric chemistry. DMS is believed to be predominantly produced in marine environments via microbial degradation of the osmolyte dimethylsulfoniopropionate (DMSP). However, significant amounts of DMS are also generated from terrestrial environments, for example, peat bogs can emit ~6 μmol DMS m Microbes, particularly marine bacteria, drive the production of DMS, generating ~300 million tonnes er annum  through er annum . DMS oxier annum . Howeverer annum . When DMer annum .S-methyl-methionine, dimethylsulfoxide or methoxyaromatic compounds  in marine environments via DMSP lyase enzymes , nitrogen-fixing cyanobacteria and sediment-dwelling pseudomonads. The mddA gene is present in marine metagenomes such as the Global Ocean Sampling and the Monterey Bay microbial study, but, it is much more abundant in terrestrial environments and particularly in soils, where it is predicted to be present in up to 76% of bacteria , a forest soil and two agricultural soils  and MeSH added as sodium methanethiolate  as described in To study DMS production from MeSH by different environments, 1 g or 20 ml of sample was placed in a 125 ml serum vial containing distilled water supplemented with Y minimal medium 5% , succinat=0 and t=19 h by GC.Air-tight field chambers of 2 l volume were placed in the grassland soil studied and supplemented with MeSH (200 μmol) as described in −1 (Sigma-Aldrich) or with 100 μg ml−1 ampicillin, 50 μg ml−1 chloramphenicol, 5 μg ml−1 tetracycline and 400 μg ml−1 streptomycin (Sigma-Aldrich), incubated and assayed for Mdd by GC as described in Microcosm experiments were supplemented with cycloheximide 200 μg mlM). The second set of enrichments was supplemented with MeSH (20 μmol). The third set of microcosms was supplemented with succinate (5 mM) and MeSH (20 μmol). Vials were incubated at 22 °C for 14 days and supplemented daily with fresh MeSH to the corresponding samples as this gas disappeared after 24 h. MeSH and DMS in headspaces were monitored by GC as indicated on To study the effects of MeSH addition on the processes of DMS production and consumption, and on bacterial diversity, three different enrichments were each set up in triplicate. One set of enrichments was supplemented with succinate (5 mM) and MeSH (20 μmol) were set up in triplicate to estimate MeSH consumption and DMS production and consumption rates as detailed in Two sets of microcosms supplemented with succinate  and DMS (272 nmol) for 24 h at 30 °C before measuring MeSH and DMS concentrations in the headspace by GC, as detailed in GC was performed as described by t=0 and those enriched with succinate plus MeSH for 14 days were plated onto Y minimal medium supplemented with succinate (5 mM) and MeSH (1 mM) as carbon sources. Colonies with different morphologies were purified and selected for further characterisation. Isolates were taxonomically identified by sequencing the 16S rRNA gene and characterised for their MeSH and DMS production as detailed in Samples from For nucleic acids extraction from environmental samples, 16S rRNA gene amplicon sequencing, metagenomics and statistical analysis, see −1, which represents 0.1±0.01% of the added substrate. In control incubations with sterile soil supplemented with MeSH, MeSH disappeared but there was no DMS production. Chemical oxidation of MeSH to dimethyldisulfide (DMDS) was also studied, but there was no variation in DMDS in the soil samples  or sterile controls  over the incubation period. No other sulfurous compounds were detected in any of the samples. From these results, we conclude that the Mdd pathway is active in microorganisms in this grassland soil when MeSH is available.To study the significance of the Mdd pathway in the environment, we initially analysed the ability of a local grassland soil with neutral pH (6.7) to produce DMS from MeSH. Soil samples incubated in the absence of MeSH produced no MeSH or DMS above our detection limits (0.2 nmol for DMS and 4 nmol for MeSH), likely indicating that MeSH is not abundant in this environment or that these gases are quickly consumed by the microbial population. However, samples incubated with MeSH (20 μmol) consumed it all in 24 h and produced 15.2±1.5 nmol DMS·g soilHaving demonstrated that the Mdd pathway was active in the grassland soil samples in microcosm experiments, the sampling site was re-examined by placing two sets of 2 l air-tight field chambers over the soil. After 19 h, the results were congruent with those observed with serum vials, with the soil alone not making MeSH or DMS, but when it was supplemented with MeSH (200 μmol) the soil liberated 239.3±18.9 nmol of DMS (0.1±0.01% of MeSH added). Therefore, field measurements confirmed that microbes in the grassland soil had a functional Mdd pathway when MeSH is available.−1, 0.5±0.1% of the MeSH added) compared with the controls with no inhibitors added . In contrast, the eukaryotic inhibitor cycloheximide had no effect on DMS production , indicating that prokaryotes are probably the main contributors to DMS production from MeSH in this particular grassland soil.Grassland soil samples were supplemented with antibiotics effective against either prokaryotes or eukaryotes and incubated for 24 h. The vials with prokaryotic inhibitors added showed a ~50% reduction in DMS . Subsequently, DMS production steadily declined (−1), and then stabilising before DMS was more rapidly consumed after 11 days  to 7 days  and reached maxima of 3.3±0.1 μmol MeSH·h−1·g soil−1 and 6.1±1.8 nmol DMS·h−1·g soil−1 at 14 days, confirming that extended exposure to MeSH enhances the activity of the Mdd pathway and may enrich for microbes producing DMS from MeSH. As DMS production rates increased over the course of the MeSH enrichment, it was not surprising to see that net DMS consumption rates also increased. The DMS consumption rate at t=0 was 0.2±0.01 nmol DMS·h−1·g soil−1, but after 7 days it was 3.9±1.0 nmol DMS·h−1·g soil−1, reaching a maximum of 10.1±1.9 nmol DMS·h−1·g soil−1 after 14 days. The fact that at 14 days DMS consumption was greater than DMS production indicates that there has probably been an enrichment of DMS-degrading microorganisms.To study in greater detail how the addition of MeSH affected the processes of DMS production and consumption, we measured both rates at 0, 7 and 14 days. For this, we used samples enriched with succinate plus MeSH as they showed the highest DMS production levels (see above). We also measured MeSH consumption rates at the same time points. Both MeSH consumption and DMS production net rates increased from t=0 and from enrichments with MeSH alone, succinate alone and succinate plus MeSH after 7 and 14 days of incubation. Extracted DNA was used as template in 16S rRNA gene amplicon sequencing (see t=0 samples) was dominated by bacteria from the classes Actinobacteria (18.5±0.9%) and Deltaproteobacteria , and marginally non-significant increases in Betaproteobacteria to 12.4±0.9%  and Sphingobacteria to 12.8±0.5% , after 14 days. Deltaproteobacteria were still one of the most predominant classes (15.4±1.7%), but Actinobacteria were substantially reduced to 4.2±0.04%  in the 14-day succinate enrichments compared with t=0 samples (The addition of diluted Y medium with succinate as a carbon source (succinate-only enrichments) changed the profile of the natural microbial community with a significant increase in relative abundance of Gammaproteobacteria to 14.8±1.5% (Tukey honest significant difference (HSD),  samples .P=0.293) in the 14-day MeSH enrichments and to 5.2±0.6%  in the succinate plus MeSH enrichments compared with the 14-day succinate samples. MeSH increased the relative abundance of Betaproteobacteria to 17.9±0.1%  in the 14-day MeSH enrichments and to 23.6±1.2%  in the succinate plus MeSH enrichments. The relative abundance of Gammaproteobacteria also increased to 22.8±3.8% in the 14-day MeSH enrichments  and to 23.6±2.1%  in the enrichments with succinate and MeSH compared with the 14-day enrichments with succinate  was still one of the most abundant genera in the bacterial community of the 14-day enrichments with MeSH. However, it was notable that the presence of MeSH significantly increased the relative abundance of Methylotenera and Massilia in the 14-day enrichments with MeSH  and 14-day samples enriched with succinate plus MeSH , compared with the 14-day enrichments with succinate. Arthrobacter also increased in relative abundance, although not significantly, in the 14-day enrichments with succinate plus MeSH  compared with the 14-day succinate samples , but their relative abundance did not increase either in the MeSH alone or the MeSH plus succinate enrichments.Soil bacteria that are known to oxidise MeSH and DMS such as t=0 and from enrichments with succinate plus MeSH after 7 and 14 days of incubation was also used to perform metagenomics (see t=0 was dominated by members of the class Actinobacteria (51.4%), confirming the results of the 16S rRNA gene analysis. The most abundant bacteria in the t=0 community that MetaPhlAn could classify at a genus level belonged to Agromyces (13.7%), Thiomonas (8%), Rhodopseudomonas (6.7%) and Pedobacter (6.2%) genera (DNA extracted from samples at mics see . Phyloge) genera .Pseudomonas  and Betaproteobacteria (37.4%). The most abundant genus at this time point was s 41.6%, . MetagenM. mobilis JLW8T, which is >97% identical at the 16S rRNA gene level to the Methylotenera in our MeSH enrichments, was tested for its ability to degrade MeSH and DMS. Cultures of M. mobilis JLW8T were supplemented with MeSH or DMS and the amount of these gases in the headspace was quantified by GC at t=0 and 24 h. After 24 h of incubation, M. mobilis consumed 543.6±11.2 nmol MeSH  in the first 24 h .rst 24 h . These rt=0 and from enrichments supplemented with succinate plus MeSH after 14 days of incubation. These enrichments were chosen because the presence of both succinate and MeSH led to the greatest levels of DMS production and also the samples at 14 days had the highest rates of Mdd and consumption.To complement cultivation-independent work, we isolated bacteria from grassland soil samples at t=0 samples were Gammaproteobacteria (Pseudomonas spp.), Actinobacteria (Streptomyces spp.) and Bacilli .Strains isolated from the t=14 days were mainly Alphaproteobacteria , but also Gammaproteobacteria (Pseudomonas spp. and Acinetobacter spp.), with Pseudomonas being the most abundant genus isolated  or MeSH. Only ~5% of the isolates from  or MeSH . These rWhen isolates from the succinate plus MeSH enrichments (14 days) were analysed, ~42% were able to produce DMS from Y medium alone. This percentage increased to ~96% and 100% of the isolates generating DMS when Y medium was supplemented with Met or MeSH, respectively . These rt=0 and from enrichments with succinate plus MeSH after 7 and 14 days of incubation was subjected to metagenomic analysis  and, although increased up to 25.3% at 14 days, was still lower than t=0  and Thioalkalivibrio (12.9%) forms were still the most abundant mddA-like genes together with Nodosilinea mddA homologues , followed by Cyanothece (12.5%) and Bradyrhizobium (11.5%) mddA-like genes  and 25.8±4.7 nmol DMS·ml−1 , respectively, indicating that DMSP is probably a more effective precursor for DMS than MeSH in these environments.To determine whether the Mdd pathway was functional in a wider range of environments, we analysed different terrestrial, freshwater and marine samples . After 22S in the anaerobic layers of the soil and sediments  of the MeSH added to our microcosm experiments was captured as DMS despite all the MeSH disappearing within 24 h. Some of the MeSH added may have been enzymatically degraded to HdmoA, ddhA and tmm) was relatively abundant in the natural grassland soil bacterial population. However, the relative abundance of dmoA, ddhA and tmm did not increase over the succinate plus MeSH enrichments despite a 50-fold increase in DMS consumption rate, perhaps suggesting that there are as yet unidentified microbial genes for DMS degradation. In any case, it is clear that the DMS production levels reported here are an underestimation of the activity of the Mdd pathway in the grassland soil studied.The biotic and abiotic degradation of MeSH greatly affects the amount of this compound available for microorganisms that use the Mdd pathway to produce DMS. A further contributing factor to the low levels of DMS achieved in our microcosm experiments is the biotic and abiotic degradation of DMS. The rates of DMS consumption increased over the course of the succinate plus MeSH enrichments to levels above those for Mdd after 14 days. DMS can be photochemically  and enzymatically (in situ measurements of MeSH and none of them from soils (Although we have shown that the ability to generate DMS from MeSH is inherent in all of the different soils and marine sediments tested, it is still very difficult to estimate the exact contribution of the Mdd pathway to global DMS emissions, since there are very few om soils .Methylotenera significantly increased in 14-day enrichments supplemented with MeSH, when DMS consumption rates were maximal. This indicates that Methylotenera likely has a role in DMS degradation, as suggested by Methylotenera to remove DMS was confirmed when test cultures of M. mobilis JLW8T consumed both DMS and MeSH. To our knowledge, this represents the first proof that members of the Methylophilaceae family, which includes obligate and facultative methylotrophs, are able to degrade these volatile compounds. Increases in the relative abundance of Arthrobacter genera in the 14-day succinate plus MeSH enrichments, suggests that they may also be involved in DMS consumption. Indeed, some Arthrobacter strains are able to metabolise DMS to generate MeSH (Hyphomicrobium or Thiobacillus can oxidise MeSH and DMS (t=0 samples, and did not increase over the course of the MeSH enrichments, suggesting that they may not have a significant role in the removal of MeSH and DMS in our microcosms experiments. Finally, 16S rRNA gene amplicon sequencing data and metagenomics analysis also showed that the presence of MeSH increased the relative abundance of Massilia, some of which contain mddA-like genes (Massilia in DMS production.The addition of MeSH to the grassland soil samples not only increased DMS production and consumption rates, but also changed the diversity of the bacterial population. According to cultivation-independent methods, relative abundance of Pseudomonas, which is not surprising, given that many contain mddA (Acinetobacter, Gemmobacter, Phyllobacterium, Rhizobium, Ensifer and Sinorhizobium that converted MeSH into DMS. These bacteria were not previously suspected to have mddA or produce DMS from MeSH, since close relatives with sequenced genomes lack this gene. Thus, the Mdd pathway is more widespread among different bacterial taxa than previously thought. It is probable that other Mdd enzymes drive DMS production from MeSH in these bacteria. However, detailed molecular characterisation of these microorganisms is required to identify their Mdd enzymes and ultimately prove this. The presence of other Mdd enzymes in the bacterial population of the grassland soil could explain the observed discrepancies between metagenomics analysis and process rates, where the relative abundance of mddA did not increase throughout the enrichments despite the increase in DMS production rates. Such differences could also be due to the expression levels of the genes encoding the diverse Mdd proteins and/or their respective enzyme activity. Future studies will need to consider these factors to ascertain at a molecular level how and why Mdd levels change.Cultivation-dependent methods showed that the addition of MeSH to grassland soil samples selected for microorganisms containing the Mdd pathway. Most of the isolates that generated DMS from MeSH belonged to the genus In conclusion, we show that the Mdd pathway is present and active when MeSH is available in a wide range of terrestrial and marine environments, especially in soils. However, as only ~0.1% of MeSH added is transformed into DMS via this pathway, it is not likely a significant process in the tested environments under natural conditions. More microbiological studies and process-based measurements are required on environments where MeSH is likely abundant to make an accurate estimation of the contribution of the Mdd pathway to the global DMS cycle.


In this work we present a novel route to produce a graphene-based film on a polymer substrate. A transparent graphite colloidal suspension was applied to a slat of poly(methyl methacrylate) (PMMA). The good adhesion to the PMMA surface, combined with the shear stress, allows a uniform and continuous spreading of the graphite nanocrystals, resulting in a very uniform graphene multilayer coating on the substrate surface. The fabrication process is simple and yields thin coatings characterized by high optical transparency and large electrical piezoresitivity. Such properties envisage potential applications of this polymer-supported coating for use in strain sensing. The electrical and mechanical properties of these PMMA/graphene coatings were characterized by bending tests. The electrical transport was investigated as a function of the applied stress. The structural and strain properties of the polymer composite material were studied under stress by infrared thermography and micro-Raman spectroscopy. Many materials have been proposed for strain sensing applications including metals, silicon, carbon nanotubes and graphene. The unique thermal, mechanical and electrical properties of graphene  have insIn this work we describe a simple and direct fabrication process based on a new micrographite colloidal suspension to produce thin coatings with large electrical piezoresitivity. When applied to a slat of poly(methyl methacrylate) (PMMA), the adhesion to the PMMA surface, combined with the shear stress, allowed for the uniform and continuous spreading of the graphite nanocrystals on the substrate surface with formation of a very uniform graphene multilayer coating.R, to the mechanical strain, ε, namely the GF is given as ΔR/(εR0), where R0 is the unstrained resistance. The values of GF for graphene range from 1.9–2.4 [The electrical response to the mechanical deformation of a strain sensor is generally quantified by the gauge factor (GF), that is, the ratio of the relative change in electrical resistance,  1.9–2.4 . The GF  1.9–2.4  or graph 1.9–2.4 –8. The vI–V) measurements and micro-Raman spectroscopy (μ-RS) during bending tests. Moreover, infrared thermographic technique (IRT) was used to assess the sensitivity of the PMMA/graphene slats to bending deformation.The electrical resistance and mechanical properties of the graphene-coated PMMA slat were investigated by current–voltage (3), which was dried in air at room temperature to give the nanostructured graphite powder. Then a concentrated nanostructured graphite colloid was prepared by accurately dispersing the graphite in ethanol  under sonication. The nanostructured graphite colloid was gently rubbed on the surface of a slat of PMMA, by hand, using a low-density polyethylene (LDPE) film to achieve a very uniform coating of the substrate surface. The adhesion to the PMMA surface, combined with the applied shear stress, allowed a uniform and continuous spreading of the graphite nanocrystals on the substrate surface with formation of a very uniform graphene multilayer coating. The obtained PMMA slats coated by this very thin and optically transparent layer of graphene were rinsed in acetone and dried in air at room temperature.The graphite used for this strain sensor was prepared according to –10 as foThe graphene compound layer on the top of the PMMA surface is clearly visible in the images of The bending stress was applied to the sample by tuning a screw located on one side of the specimen as reported in An estimate of the applied load during the bending test can been obtained by using the follow relation :f is the displacement induced by the applied force F. E is the Young modulus and Ics the moment of inertia of the cross section. The lengths l and b are defined in where N is enough to induce a slat deflection f = 10 mm, that corresponds to the maximum bending of the slat during the experiment. The force F was estimated by assuming E = 3.8 GPa for the Young’s modulus value of PMMA [Ics = wh3/12, where w = 0.02 m and h = 3 × 10 −3 m are the width and thickness of PMMA/graphene sample, respectively, and l = b = 75 mm.In our case a force of 6  of PMMA , and a mThe upside surface of the PMMA/graphene material was monitored with an infrared camera , equipped with a quantum well infrared photon detector working in the 8–9 μm infrared band cooled at 70 K by a Stirling cooler, a noise equivalent differential temperature <35 mK, spatial resolution of 640 × 512 pixels (full frame) with pixel size 25 × 25 μm. In the present application, thermal images in time sequence at 60 Hz were collected and after were subjected to postprocessing procedures .t = 0) of the sequence  was subtracted from each subsequent image in order to determine a map of temperature variations:Firstly, to account for thermal changes with respect to the ambient temperature, the first image . Therefore, a time sequence of ΔT images are created. These images are further analyzed to bring out information on the temperature variations along the specimen surface and to provide structural analysis of the material under investigation. Infrared thermographic tests (IRT) were carried out on the PMMA/graphene coatings and compared to the IRT measurements performed on the various composite polymer-based systems. A sketch of the setup for the thermographic measurements is shown in where I−V) curves between the electrodes located on A1 and A2 areas, as shown in The composites under test include: glass-reinforced plastic (GRP), nanocomposites, and PMMA. The nanocomposite sample is made using an epoxy resin EC01 and filled with multiwalled carbon nanotubes (MWCNT) provided by Nanocyl with a purity grade >95% with an average diameter ≈10 nm and an average length of 1.5 μm. Further details on the nanocomposite fabrication are reported elsewhere –15. The F = 0 and F = 6.9 N. Structural deformation of graphene induced by bending the PMMA slat has been investigated by means of micro-Raman Spectroscopy (μ-RS). The μ-RS measurements were performed by using a Jobin-Yvon system from Horiba ISA, with a TriAx 180 monochromater, equipped with a liquid nitrogen-cooled charge-coupled detector. The grating with 1800 grooves/mm allows for a final spectral resolution of 4 cm−1. The spectra were recorded in air at room temperature using a 17 mW He–Ne (λ = 632.8 nm) laser source. The laser light was focused to a 10 μm spot size on the samples through an Olympus confocal microscope with a 50× optical objective.The same setup was used to monitor time changes of the current for T depends on the sign of strain.During the bending stress cycles between unload and maximum load conditions, the temperature variation on the sample surface is measured by the IRT technique over a surface area of (10 × 10 mm) as illustrated by A1 and A2 in T to the amplitude variation of mean applied stress Δσ (pressure) by the simple relation ΔT = −ΓTασ where T is the absolute temperature of the sample, Γ is the material thermoelastic constant, given by Γ = α/ρcp where α is the thermal expansion coefficient, ρ the density and cp the specific heat at constant pressure. For graphene we obtain ΓTα = 0.19 GPa−1 at room temperature (Tα = 300 K) using the thermal expansion coefficient α = −3 × 10−6 K−1 [3 Kg m−3 and cp = 2.125 × 103 J·kg−1·K−1 [T ≈ 0.1 °C) corresponds to a maximum value of applied stress Δσ of about 0.53 GPa. Accordingly, we obtain Δε/Δσ ≈ 0.28% GPa−1 which turns out to be about 0.1% higher than the value reported in [Indeed, using the thermoelastic effect –17 under10−6 K−1 , ρ = 2.2orted in , probablT for several composites is reported. Here, the different thermal behavior of the new material measured by the IRT technique is shown. The carbon nanotubes (CNTs) can be used as a filler in the polymer composite system to obtain ultralight structural materials (nanocomposites) with enhanced electrical, thermal and optical characteristics. Glass-reinforced plastic (GRP) is used for the realization of the components for use in the automotive and aerospace industry.In the Thermographic measurements were carried out across the area A1 see  in the sI–V) using the electrical connection shown The effect of the bending on the electrical properties of the PMMA/graphene compound were investigated by measuring the current–voltage  and maximum load (F = 6.9 N) conditions. Even after several cycles between the unload and loaded state, the electrical resistance value show no hysteretic effect, i.e., the PMMA/graphene does not store stress and the maximum load implemented can be considered as a reversible stress condition.Noteworthy, the graphene/PMMA sample exhibits a good Ohmic behavior with a linear increase in electrical resistance to value of about 0.3 MΩ upon application of load up to In order to evaluate the microscopic effect of applied stress on sample micro-Raman spectroscopy (μ-RS) has been performed in the region A2 see  during tR/R0 is plotted as a function of the applied strain ε  embedded in an insulating matrix and its electrical conduction properties were analyzed within the framework of a simple electron hopping mechanism. The high sensitivity in addition to high stability of the graphene/PMMA structure and the high thermal sensitivity in the infrared wavelength region are interesting aspects that enable us to propose this polymer/graphene supported coating as a new kind of stress sensor useful for applications in different fields from civil, to automotive and aerospace engineering.


High-harmonic generation in condensed-matter systems is both a source of fundamental insight into quantum electron motion and a promising candidate to realize compact ultraviolet and ultrafast light sources. While graphene is anticipated to efficiently generate high-order harmonics due to its anharmonic charge-carrier dispersion, experiments performed on extended samples using THz illumination have revealed only a weak effect. The situation is further complicated by the enormous electromagnetic field intensities required by this highly nonperturbative nonlinear optical phenomenon. Here we argue that the large light intensity required for high-harmonic generation to occur can be reached by exploiting localized plasmons in doped graphene nanostructures. We demonstrate through rigorous time-domain simulations that the synergistic combination of strong plasmonic near-field enhancement and a pronounced intrinsic nonlinearity result in efficient broadband high-harmonic generation within a single material. Our results support the strong potential of nanostructured graphene as a robust, electrically tunable platform for high-harmonic generation. High-harmonic generation is a nonlinear optical phenomenon that may be harnessed towards realisation of ultrafast light sources. Here, the authors theoretically show that localized plasmons in graphene nanodisks result in broadband and electrically tunable high-harmonic generation. High-harmonic generation (HHG) is an extreme nonlinear optical phenomenon first observed by driving atomic gases with intense ultrashort light pulses124578Recent observations of HHG from condensed-matter systems12131415171213151920The linear, gapless dispersion relation of graphene electrons22242526272830When resonantly driven by optical fields, plasmons, the collective oscillations of electrons in conducting media, concentrate the incident electromagnetic energy into extremely subwavelength volumes, generating intense local electric fields that are essential to trigger nonlinear optical phenomena. In graphene, plasmons offer an efficient way to couple the atomically thin carbon layer with impinging light34353637383931414344454634353639Here we predict that highly efficient HHG takes place in doped graphene nanostructures when the incident light is tuned to their localized plasmons. Specifically, we obtain harmonic intensities that are orders of magnitude higher than in other materials. In addition, no sharp cutoff is observed with harmonic order. Our results are based on nonperturbative time-domain numerical simulations of the nonlinear optical response of graphene using two complementary approaches: a random-phase approximation (RPA) description of the single-particle density matrix within a tight-binding (TB) model for the electrons of ribbons and finite islandsin situ electric field enhancers for HHG in gaseous media484950k at low energies, ɛk=ħvF|k|, where vF≈c/300 is the Fermi velocity. In the single-particle MDF description of doped monolayer graphene, neglecting interband electronic transitions, this linear dispersion relation leads to a maximum achievable surface current density Jmax=−envF sign{sin(ωt)} when illuminated by a monochromatic field E(t)=E0 cos(ωt) in the E0→∞ limit30n. This square-wave profile of the induced current density under intense illumination translates into efficient generation of odd-ordered harmonics  shows a prominent dipolar plasmon . In 12 W m−2 peak intensity as those considered in the upper panel of The marked increase in HHG from localized plasmons in graphene nanoribbons is clearly shown in EF=0.4 eV and illuminated with pulses resonant with the dominant, low-energy plasmon mode (λF∼10 nm (ref. λF) are then absent. In the undoped nanotriangle, a relative increase in harmonic generation appears at low energies, which we attribute to an overlap of the generated harmonic frequency with higher-energy electron-hole transitions in the discrete electronic spectrum of the nanotriangle , φ is the self-consistent electric potential including both the impinging light and the Hartree interaction, and a phenomenological relaxation is assumed to bring the system to the relaxed state ρ0 at a rate ħHTB, where ρjj′ are the sought-after time-dependent expansion coefficients. In particular, we have fj are Fermi-Dirac occupation numbers at the initial temperature T=300 K. For ribbons, the states are treated as Bloch waves, arranged in bands as a function of their momentum along the direction of translational invariance, and the calculation is simplified by the orthogonality of different bandsRl is then constructed as ajl represent the change of basis set between state j and site l representations. Finally, the time-dependent induced dipole and surface current are given by where π=p+(e/c)A, where p is the unperturbed electron momentum, E is the classically calculated in-plane electric field . Electron dynamics is governed by the Dirac equation for massless fermions, which can be recast in the form of Bloch equations as303157In a complementary approach, we model electron dynamics in graphene within the MDF picture by adopting a nonperturbative semi-analytical modelnp and Γp represent the population inversion and the interband coherence, respectivelyħ−1=50 meV is the same as in the TB-RPA approach. These equations describe both inter- and intraband transitions. We solve N=15. The current is then parallel to the local electric field where ω<J>|2, where J is the time-Fourier transform of J, and <…> denotes the space average over the graphene structure under examination.Finally, the far-field power spectrum of the emitted light is proportional to |s=0.5 nm) of permittivity σ(ω) is the local-RPA conductivity4059E of the MDF-CEM approach, with the carrier component classically calculated as explained above.The classical response of graphene nanostructures is simulated by numerically solving Maxwell's equations using the boundary-element methodThe data that support the findings of this study are available from the corresponding authors upon request.How to cite this article: Cox, J. D. et al. Plasmon-assisted high-harmonic generation in graphene. Nat. Commun.8, 14380 doi: 10.1038/ncomms14380 (2017).Publisher's note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.Supplementary Figures


R), absorption (A), and transmission (T) of electromagnetic waves is a key objective in quantum optics. To this end, one often utilizes hybrid structures comprised of elements with different optical properties in order to achieve features such as high R or high A for incident light. A desirable goal would be the possibility to tune between all three regimes of nearly perfect reflection, absorption, and transmission within the same device, thus swapping between the cases R → 1, A → 1, and T → 1 dynamically. We here show that a dielectric interfaced with a graphene layer on each side allows for precisely this: by tuning only the Fermi level of graphene, all three regimes can be reached in the THz regime and below. Moreover, we show that the inclusion of cylindrical defects in the system offers a different type of control of the scattering of electromagnetic waves by means of the graphene layers.Exerting well-defined control over the reflection ( EF, which allows the graphene layer to act as an effective sluice for the incident waves which depends on factors such as the electromagnetic frequency and polarization. In particular, several studies have been dedicated to how the radiation transmittance through graphene for normal incidence can be altered2324252830There has recently been a surge of interest in the use of graphene as an active component in structures where the aim is to control the propagation and energy flow of electromagnetic waves123456789101112131415161718192021Parallel with this development, there has also been a strong advancement in experimental techniques used to tailor metamaterial structures where either the permittivity tensor ε1 and permeability μ1) flanked by graphene layers on each surface, we show that one can operate the device in the THz regime and lower in three distinct regimes of high-reflectance, high-transmittance, and high-absorptance by tuning the Fermi levels in graphene. Dynamically swapping between these three regimes within a single device is highly unusual and could find use in a number of optics-related applications. We also comment in particular on limiting cases of special interest such as ENZ (ε1 → 0), and MNZ (μ1 → 0) metamaterials. Moreover, we include the role of cylindrical rods, or “defects” embedded in a matched impedance zero-index material (MIZIM) (μ1 → 0 and ε1 → 0), and show that defects interestingly allow for a different type of control of electromagnetic waves due to the presence of the graphene layers. The main novelty of our results compared to previous literature is that our proposed device, including only graphene and a dielectric layer, can be used to tune between the three distinct regimes of nearly perfect reflection, absorption, and transmission of electromagnetic waves, as opposed to operating in merely one of these regimes. Due to the simplicity of the structure, our results should be feasible to check experimentally and may find use in applications requiring a strong element of control of the reflection, absorption, and transmission of electromagnetic waves.One of the most fundamental challenges in quantum optics is the task of designing hybrid structures that offer tunable reflection, absorption, and transmission dynamically. Our work aims at delivering a progression toward this ambitious and important goal by combining graphene with a dielectric metamaterial. By considering such a material (characterized by a permittivity H) and electric (E) fields in each of the regions 0–3. The graphene layers are taken into account through the boundary condition n × (Hi+1 − Hi) = σjE⊥ where n is a unit vector pointing from region i to (i + 1), and E⊥ is the component of the electric field perpendicular to the interface. The correctness of modeling graphene as a surface conductivity sheet as opposed to using a slab model to treat the optical properties of graphene has recently been discussed and confirmed in ref. σj  can vary depending on their respective gate voltages. Additional details of the calculations are given in the Methods section. We present here the final result for the reflection and transmission coefficients:We consider first the system shown in R), transmission (T), and absorption (A) probabilities according to R = |r|2, T = |t|2, and A = 1 − |r|2 − |t|2 ≡ |a|2. Above, l = k1d where d is the length of the dielectric region, qi = σi/(cε0) is proportional to the conductivities at the interfaces, ω is the frequency.From t is invariant when interchanging the graphene layers, q1 ↔ q2, whereas the reflection coefficient is not, except in certain limiting cases, such as the limit of electrically small layers d/λ ≪ 1, leading to qi) ≪ Re(qi), allowing us to consider limits such as ωtrel ≪ 1 in the plots (see below for definition of trel), which provides precisely Im(qi) ≪ Re(qi).Before turning to our main results, some observations can be made regarding s → 0 and s → ∞, respectively. In the MNZ (s → ∞) case, we find d/λ ≫ 1, or when q1,2 ≫ 1, there is no transmission and perfect reflection. For the ENZ (s → 0) scenario, we findThe ENZ and MNZ cases are of particular interest, which correspond to andμ1 = μ0. Therefore if the conductivity in the first graphene sheet is large, q1 ≫ 1, we get total reflection. Increasing q2 to large values, again results in no transmission, however the reflection is tunable via q1: d/λ ≫ 1, we get t = 0. Here, the relevant variations in R or A are due to σ1. Indeed complete absorption can occur when q1 = 1, or equivalently when σ1 = cε0. This result is consistent with an incident beam normally incident on a graphene-based ENZ structureqi to tune between strong reflection, transmission, or absorption.where R, A, and T, as we now proceed to show. For a given structure, the value of d and s are locked and likely to be very difficult to tune dynamically. We thus fix the values of these quantities in what follows. To illustrate the versatility offered by the graphene layers in an analytically clear way, we first consider the case where l = k1d = π/2 + 2nπ, n = 0, ±1, ±2, …. Note that this means that we are not limiting the consideration to only one frequency ω: the transition between the R, A, and T regimes can be obtained for a range of frequencies due to the periodic nature of l. We provide results for the more general case where l is unrestricted in the Methods section, where the system can also transit between nearly perfect R, A, and T. We obtain with l = k1d = π/2 + 2nπ that:Arguably the most interesting regime somewhat surprisingly turns out to be the most “conventional” one, where the dielectric has a relative permittivity and permeability close to 1, or impedance matched with EFi is the Fermi energy of a given graphene sheet , ω is the frequency of the EM wave, EF ≫ kB ħω, we can write simply,The choice Perfect transmission: |t| → 1 when q1 ≪ 1 and q2 ≪ 1.Perfect reflection: |r| → 1 when q1 ≫ 1.Perfect absorption:t → 0, r → 0 when q2 ≫ 1 and From l, in which case the analytical expressions are more comprehensive (see Methods section). It is remarkable that one can dynamically tune between all three regimes in a single structure and for a range of frequencies. This is shown graphically in r, t, a) is shown. The two paths on the sphere depict how to acheive the desired admixtures of R, T, and A, by simply tuning the relative Fermi levels in the graphene sheets in the graphene/dielectric/graphene system. The first path (green curve) begins with the system in a highly reflective state as both graphene layers are gate tuned to equal levels of 800 meV. As the Fermi level in each graphene sheet is reduced by equal amounts, the structure then permits substantial transmission of the incident beam. Finally, by tuning EF1 and EF2 to be considerably different, we end up with a system that is a near perfect absorber. In panel (a) the reflectance is shown while the Fermi energies in the graphene layers are each varied. A wide range of energies are considered, from 0 meV, up to 800 meV. In this plot, it is evident that R can evolve from a state of no reflection to one of nearly perfect reflection when just increasing EF1 and keeping EF2 fixed. The conductivity of the first graphene layer nearest the incident beam clearly plays the bigger role here, as increases in EF1 cause σ1 to become large . The corresponding impedance mismatch between the two regions results in the observed enhanced reflectivity. Next, in σ1, σ2 → 0, or equivalently when q1 ≪ 1 and q2 ≪ 1. Next, for the structure to be a perfect absorber, it is of course necessary for there to not be any reflection or transmission of the incident wave. EF2 (so that q2 ≫ 1), the transmission of waves can then be restricted from entering the vacuum region 3 by the second graphene layer.One may also write down the conditions for the same three scenarios without limiting iωSx/∂x = 0. The quantity uE and uH, respectively: uE − uH, and the x-component of the time averaged complex Poynting vector Sx is given by Sx represents the energy flow within that segment, and the time averaged energy densities uE and uH correspond to the respective electric and magnetic field contributions, with uE = 1/4ε1|Ey|2, and uH = 1/4μ1|Hz|2. The net energy density is due to the energies of the forward and backward waves, whereas x direction (towards the second graphene sheet), with no net flow across the graphene sheets. This is consistent with the expression for The distribution of energy can be accounted for by using Poynting’s theorem for time harmonic fieldsSx/∂x.demonstrating from the conservation equation, the vanishing of the real part of ∂ε1 → 0 and μ1 → 0, the E and H fields become spatially uniform: If the region 1 is a MIZIM, whereby r and t are each independent of the material thickness, and equivalent to an electrically small region discussed above. We consider here a frequency dispersive permittivity and permeability in region 1, with ω → ωp, where ωp is a characteristic frequency of the Drude responses: q1,2 = 0, the system has complete transmission. By increasing the gate voltage so that the conductivities increase to levels corresponding to q1,2 ≫ 1, we get t → 0 and r → 1.Therefore We now consider the insertion of dielectric rods, or “defects” into the central metamaterial MIZIM region, where a different type of control over the transmission properties of the TEM mode can be achieved. Considering the system shown in The physical effect of the cylindrical defects is captured in the quantity Σ, which is purely real and can take any sign, defined as ref. w is the width of the sample, and the summation is taken over the number of defects. A given defect m has radius Rm, and wavenumber J0 and J1 are Bessel functions of the first kind of order 0 and 1, respectively.Here, km2Rm corresponds to a zero of the J0 or J1, then q1 ↔ q2. The reflection coefficient is, on the other hand, not invariant under the exchange q1 ↔ q2 except when Σ = 0 corresponding to an absence of defects, or if defects are present, each one satisfies J1(km2Rm) = 0. This is consistent with For a given frequency, the value of Σ is assumed fixed in what follows. If the quantity t as long as q1,2 ≠ 0. Interestingly, we can swap between perfect reflection and perfect absorption for a given Σ. To see this, consider the case Σ ≫ 1, which occurs when any defect has a radius and material parameters that satisfy J0(km2Rm) = 0. In that case, t → 0, q1 is tuned such that q1 = 1.From R, T, and A are shown in the left column of t = 0 and r = 1 in the limit q1 ≫ 1. It follows then that when the defects are designed so that Σ ≫ 1, the first graphene sheet described by q1 completely controls the reflection and absorption of EM waves.The relevant parameters r and t coefficients revert to the expressions shown in r and t are directly tunable via manipulating only q1 and q2. In the right column of q1,2 = 0, there is total transmission. Increasing the Fermi levels in one or both graphene sheets then increases the reflections of waves until q1,2 ≫ 1, at which point nearly complete reflection occurs. As the right column of q1 or q2 is small, we find qi is small). This quantity has a maximum when qi = 2, which gives A = 0.5.If the cylinders are now chosen so that Σ = 0, then the q1 and q2 that results in no reflections from the first graphene sheet. For example we get r = 0 if q2 = 0, and We can moreover control the reflectivity of the system in situations when the rods are not excited at resonance. In particular, if we relax the restriction that Σ ≫ 1, setting the numerator of e.g. three graphene layers separated by a dielectric spacer and an ENZ metamaterial4647492O3 and polytetrafluoroethylenet| → 0.8 instead of |t| → 1 in the transmission regime.Other works have shown high-absorption of normal incidence light by using δEF in the local Fermi level which typically are a few tens of meV. However, recent work using both single-layerEF considered in our work, the temperature needs to be less than 10 K in order to satisfy the requirement EF ≫ kB  Regarding the tunable Fermi level of graphene, one should acknowledge the experimental difficulty in minimizing fluctuations ε → 0 and μ → 0 in the microwave and infrared regimes5356If the central region is a MIZIM , there aWe here provide details for the solution of the Maxwell equations and the scattering coefficients.Dielectric case: we here provide some technical details regarding the calculation of the reflectance, transmittance, and absorptance of an air/graphene/dielectric/graphene/air region. For an incident TEM mode, we use the following fields where l is arbitrary, we find ∇ × Hj reveals that for the MIZIM region where ε1 → 0, we must have ∇ × H1 vanish so that the electric field remains finite. Therefore in region 1, we write simply H1 = h1, where h1 is a constant ∇ × Ej shows that ∇ × E1 must also vanish, for physical reasons that are similar to those requiring the vanishing of the curl of H1 above. If we apply Stoke’s theorem to the outer boundary ∂C of the MIZIM structure, which includes the PEC layers and graphene sheets, as well as the circular boundaries ∂Cm2 of each of the defects, the contributing paths in the line integral lead to the following expression involving the corresponding E field:Since within the MIZIM region we have a vanishing permeability E fields for the ∂C segments has been given above in Em2 involves a sum of Bessel functions of the first kindThe rm is the radial coordinate relative to the center of each defect of radius Rm, and mth cylinder. Inserting the electric fields into the line integral in where r or t, yielding the results found in where we have used EF ≫ kBT, i.e. the role of temperature. This is shown in Finally, we also provide plots that show the effect of relaxing the criterion How to cite this article: Linder, J. and Halterman, K. Dynamical tuning between nearly perfect reflection, absorption, and transmission of light via graphene/dielectric structures. Sci. Rep.6, 38141; doi: 10.1038/srep38141 (2016).Publisher's note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.