Building Mesoporous Catalytic Nanoarchitectures: From Organometallic To Nanocrystal To Enzyme

Climate change is a growing concern around the world.Numerous research endeavors are being conducted in order to determine a variety of energy sources and technologies that can be implemented in order to mitigate the impacts of global warming.The design and application of new catalysts and catalytic systems is vital to achieving the dual goals of environmental protection and renewable energy generation. By examining activities in Nature,a beautiful world can be sustained depending on the ability to create specific and high efficiency system,and the ability to develop various mutual assemblies with different components in multi-level dimensions. Inspired by biological systems in Nature,the objective of this current research is to develop novel mesoporous catalytic systems based on the self-assembly of various functional building blocks composed of organometallic complexes,nanocrystals and enzymes.Several important catalytic reactions used in the environmental and energy fields have been adopted to characterize their superior catalytic efficiency over conventional supported catalyst.An effective method for the preparation of mesoporous organometallic catalyst (MOC) with pore structure and adjustable chemical compositions has been developed. A surfactant is used as the mesoporous-channel-building molecules,organosilanes are utilized as the scaffold-building molecules,and organornetallic silanesas provide the catalytic-functionality-building molecules.Hydrolysis and condensation reactions of the silanes generated silicate clusters that were subsequently assembled with the surfactant through hydrogen bonding.Hydrophobic interactions preferably locate the active sites(hydrophobic ligands) near the hydrophobic moieties of the surfactant assemblies.Silicate condensation reactions crosslink the building clusters,resulting in nanocomposites containing lytropic surfactant liquid crystalline phases.Subsequent surfactant removal creates mesoporous silica with surface-anchored active sites.This self-directing process spontaneously anchors the active sites on the scaffold while retaining the catalytic molecular configuration and activity.Judicious selection of the surfactant and the scaffold-building silanes allows for precise control of the pore structure(substrate diffusion pathways) and scaffold composition.Meanwhile,MOC materials with multiple catalytic active sites(MMOC) can easily be prepared by simply employing several functional organometallic silanes in the assembly process. The MMOC material has superior activity in water medium cascade reactions due to the synergic effect arisen from selective distribution in the mesopores.Mesoporous coupled semiconductor or noble metal alloy catalysts have been synthesized.The catalyst were formed via evaporate induced self-assmbly or microemulsion method by taking the use of CdS,TiO₂ or FePt nanocrystal as building blocks,The CdS/TiO₂ catalysts exhibit strong visible light absorption at about 550 nm. Meanwhile,it has high surface area and mesoporous character based on the average pore diameter.As expected,the CdS nanocrystal sensitized the TiO₂ nanocrystal materials resulting in enhanced activity in the oxidation of methylene blue in water. This is due to the effective transfer of photo-generated electrons from the conduction band of CdS to that of TiO₂.Also the as-synthesized mesoporous FePt alloy is approximately 100 nm in size and has a spherical shape.The results demonstrated that the assembled FePt catalyst exhibited similar catalytic activity and higher toxic tolerability in comparison to that of polycrystal Pt catalyst from the formic acid oxidation reaction.A novel approach towards the synthesis of bioactive inorganic composites with better-retained bioactivity has been developed.In comparison to current experimental approaches in which naked biomolecules are directly exposed to non-physiological environment,in this work we pre-wrapped each biomolecule with an enzyeme that functions as an artificial skin.The artificial skin is a thin layer of a soft hydrogel that helps to retain the structure and functionality of the biomolecules in the non-physiological environment.Using the above single enzyme nanogel as building blocks,bioactive mesoporous silica can be obtained by this assembly approach.This organic-inorganic hybrid nanomaterial has soft and hard properties.The soft polymer could retain the enzyme 3D structure;while the hard mesoporous silica can decrease enzyme leaching.Meanwhile,the mesopore channel allows effective transport of the substrates to contact the enzyme active sites.Single enzyme(liapse) or multiple enzymes(Glucose oxidase and Horseradish peroxidase) systems are also investigated. The results show that the assembled bioactive catalyst can retain the enzyme activity and increase stability.