BACKGROUND

Natural and synthetic porous materials and media are widely used as substrates in various articles and processes. Porous materials may include macroporous, mesoporous, microporous, or nanoporous materials, or combinations thereof. Porous materials may include metals, oxides, polymers, or other materials. Porous materials may be manufactured using casting, infiltration, foaming, deposition, drying, or supercritical drying. Depending on the application, porous materials may be pre-treated or further treated using thermal, chemical, acoustic, electrical, or other treatments.

Functionalized porous materials may be used in a wide variety of applications, For example, functionalized porous material, such as functionalized porous silica, may be used in applications including sensors, catalysts, heavy metal recovery, and drug delivery. Materials such as aminomethyl-anthracene functionalized, templated porous silica may be used for sensing ATP by fluorescence quenching. Materials such as thiol-functionalized, templated porous silica may be used for heavy metal ion recovery. Porous materials may be used for catalysis, for instance, silica based catalyst supports including W-peroxo compounds for epoxidation, Grubb's catalyst for metathesis (double replacement reaction) and allylic amination. Controlled release by chemical reduction of disulfide linkage between CdS and porous silica may be used for drug delivery via CdS nanoparticles.

Known techniques for such functionalization are performed using a synthetic grafting approach of porous oxides with pore sizes tailored for the particular target application. Some porous oxide surfaces may not be amenable to direct functionalization, and therefore some techniques for functionalization of porous substrates may include an intermediate hydroxylation step to introduce hydroxyl groups on surfaces, which can subsequently be functionalized with functional groups. However, in known techniques that employ hydroxylation as an intermediate step, the functionalization step functionalizes all available hydroxyl groups. Therefore, all hydroxylated surfaces may get functionalized.

Conventional techniques of functionalizing may result in nonselective functionalization of pores, where pores are randomly functionalized with functional groups irrespective of their pore size.FIG. 1is a conceptual diagram presenting a lateral cross-sectional view of a structure including a porous material exhibiting a broad pore size distribution, functionalized by existing nonselective techniques. Porous substrate120includes a plurality of pores140. The plurality of pores140includes a first plurality of pores140ahaving a first average pore size, a second plurality of pores140bhaving a second average pore size, and a third plurality of pores140chaving a third average pore size. In examples, the first average pore size is smaller than the second average pore size, and the second average pore size is smaller than the third average pore size. Nonselective techniques of functionalizing porous substrate120with different functional groups, for instance, a first functional group A, a second functional group B, and a third functional group C, typically result in nonuniform and nonselective functionalization of pores that is not correlated with the average pore size. This may result from a failure of conventional techniques to selectively hydroxylate pores depending on their pore sizes, whereby a subsequent functionalization of the hydroxylated pores results in nonselective functionalization. For example, each of the first plurality of pores140a, the second plurality of pores140b, and the third plurality of pores140c, may be hydroxylated and functionalized, or directly functionalized by either of functional groups A, B, or C, regardless of the average pore size of the respective plurality of pores, ultimately resulting in a nonselectively functionalized substrate, as shown inFIG. 1.

SUMMARY

In conventional techniques, functionalization occurs via available hydroxyl groups in all pores. The hydroxyl group content is primarily controlled by the synthesis method and calcination temperature of the corresponding oxide. However, certain applications may require selective functionalization of pores of a first average pore size with a first functional group, and pores of a second average pore size with a second functional group, and so on. Other applications may require that only pores of a first average pore size, or only pores having an average pore size less than a first threshold be functionalized with a first functional group, and that no other pores be functionalized.

In general, the present disclosure describes techniques for controlled functionalization of porous materials over a wide range of pore sizes. In contrast with nonselective techniques, methods of the present disclosure allow for selective hydroxylation of pores depending on their pore size, which can be used to target a specific band of pore sizes or diameters for functionalization, using an inexpensive base material.

An example technique includes exposing a porous substrate susceptible to one or both of hydroxylation and alkoxylation by a first protic solvent to a first relative pressure of the first protic solvent. The porous substrate includes a first plurality of pores having a first average pore diameter and a second plurality of pores having a second average pore diameter that is greater than the first average pore diameter. The first relative pressure is effective to one or both of hydroxylate or alkoxylate substantially only pores of the first average pore diameter to form a first modified porous substrate. The example technique may include reacting the first modified porous substrate with a first functionalizing reagent that is effective to functionalize one or both of hydroxylated or alkoxylated surfaces, thereby functionalizing substantially only the first plurality of the pores, to form a first functionalized porous substrate.

An example article includes a functionalized porous substrate including a first plurality of pores having a first average pore diameter and a second plurality of pores having a second average pore diameter that is greater than the first average pore diameter. The first plurality of pores is functionalized with a first predetermined functional group, and the second plurality of pores is substantially free of the first predetermined functional group.

Another example article includes a porous substrate including a first plurality of pores having a first average pore diameter and a second plurality of pores having a second average pore diameter that is greater than the first average pore diameter. Substantially only the first plurality of pores is hydroxylated, and the second plurality of pores is substantially non-hydroxylated.

In various examples, the techniques can be used to prepare articles that include pores of different average pore sizes functionalized with different functional groups, by using sequential functionalization depending on pore size, targeting specific pore size regimes with respective functionalizing agents. Thus example articles may exhibit different functions associated with particular pore sizes within the same material. The example techniques may also be used to functionalize relatively inexpensive porous materials that present a wide range of pore sizes.

The details of one or more aspects of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.

