Bio-Templating: An Emerging Synthetic Technique for Catalysts. A Review

In the last few years, researchers have focused their attention on the synthesis of new catalyst structures based on or inspired by nature. Biotemplating involves the transfer of biological structures to inorganic materials through artificial mineralization processes. This approach offers the main advantage of allowing morphological control of the product, as a template with the desired morphology can be pre-determined, as long as it is found in nature. This way, natural evolution through millions of years can provide us with new synthetic pathways to develop some novel functional materials with advantageous properties, such as sophistication, miniaturization, hybridization, hierarchical organization, resistance, and adaptability to the required need. The field of application of these materials is very wide, covering nanomedicine, energy capture and storage, sensors, biocompatible materials, adsorbents, and catalysis. In the latter case, bio-inspired materials can be applied as catalysts requiring different types of active sites (i.e., redox, acidic, basic sites, or a combination of them) to a wide range of processes, including conventional thermal catalysis, photocatalysis, or electrocatalysis, among others. This review aims to cover current experimental studies in the field of biotemplating materials synthesis and their characterization, focusing on their application in heterogeneous catalysis.

Mild Oxidation of Organosulfur Compounds with H2O2 over Metal-Containing Microporous and Mesoporous Catalysts

Mild catalytic oxidation of thioethers and thiophenes is an important reaction for the synthesis of molecules with pharmaceutical interest, as well as for the development of efficient processes able to remove sulfur-containing pollutants from fuels and wastewater. With respect to the green chemistry principles, hydrogen peroxide (H2O2) is the ideal oxidant and the Me-containing porous materials (Me = Ti, V, Mo, W, Zr) are among the best heterogeneous catalysts for these applications. The main classes of catalysts, including Me-microporous and mesoporous silicates, Me-layered double hydroxides, Me-metal–organic frameworks, are described in this review. The catalytic active species generated in the presence of H2O2, as well as the probable oxidation mechanisms, are also addressed. The reactivity of molecules in the sulfoxidation process and the role played by the solvents are explored.

ZnO–TiO2 composites and ternary ZnTiO3 electrospun nanofibers: the influence of annealing on the photocatalytic response and reusable functionality

By using understanding from the construction of composites to ternary-phased 1D NFs, we design a layout for ZnO–TiO₂ composite and ZnTiO₃ electrospun NFs with different band structures as a function of the annealing temperature with the possibility of defect states.

Chitin Liquid-Crystal-Templated Oxide Semiconductor Aerogels

Chitin nanocrystals have been used as a liquid crystalline template to fabricate layered oxide semiconductor aerogels. Anisotropic chitin liquid crystals are transformed to sponge-like aerogels by hydrothermally cross-linked gelation and lyophilization-induced solidification. The hydrothermal gelation of chitin aqueous suspensions then proceeds with peroxotitanate to form hydrogel composites that recover to form aerogels after freeze-drying. The homogeneous peroxotitanate/chitin composites are calcined to generate freestanding titania aerogels that exhibit the nanostructural integrity of layered chitin template. Our extended investigations show that coassembling chitin nanocrystals with other metal-based precursors also yielded semiconductor aerogels of perovskite BaTiO₃ and CuO_x nanocrystals. The potential of these materials is great to investigate these chitin sponges for biomedicine and these semiconductor aerogels for photocatalysis, gas sensing, and other applications. Our results present a new aerogel templating method of highly porous, ultralight materials with chitin liquid crystals.

Synthesis of textured polysaccharide–silica nanocomposites: a comparison between cellulose and chitin nanorod precursors

Through a straightforward sol–gel procedure, two polysaccharide (cellulose and chitin) nanorods can be used to elaborate textured hybrid nanocomposites and mesoporous silica-based materials whose textural properties are defined by the nanorod dimensions and concentrations.

TiO2 microspheres supported polyoxometalate-based ionic liquids induced catalytic oxidative deep-desulfurization

A series of TiO₂ microspheres supported [SiW₁₂O₄₀]⁴⁻-based ionic liquids were successfully prepared and used as catalysts in oxidative desulfurization system. DBT was oxidized to DBT sulfone (DBTO₂) efficiently with the help of the catalyst and H₂O₂.

Mesoporous alumina from colloidal biotemplating of Al clusters

A simple and green synthesis route was disclosed for the achievement of mesoporous alumina microparticles employing polysaccharide nanoparticles (α-chitin nanorods) as templates. Pore textures can be tuned by the cationic alumina precursor. Compared to small cations, the use of Al13 and Al30 oxo-hydroxo clusters leads to better defined and elongated mesopores. Electron microscopy and spectroscopic ((13) C, (27) Al NMR, XPS) measurements demonstrated that this is related to the effective coating of α-chitin nanorods by these pre-condensed colloids.