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Cellulose-based reduced graphene oxide materials (r-nGO) were fabricated and anchored onto polyvinyl alcohol stabilized gold nanoparticles. Their potential in applications in the electrocatalytic r ...

Bio-based resources are of high scientific importance these days due to their abundance, renewability, environment compatibility, recyclability, and many more aspects of sustainable material production and its consumption. Cellulose, the naturally occurring plant polymer has been a widely worked out substrate material for value addition as their supply from the forest products industry and agricultural wastes is huge and inexpensive. Cellulose is a fascinating polymer, with the repeating units of monosaccharide molecules containing secondary and tertiary –OH functional groups. These –OH groups are the primary target locations to modify cellulose chemically or physically. Topochemical engineering is a method of directed assembly or directed disassembly of functional materials. Directed assembly and disassembly are controlled via the design of intermolecular interactions in a topological space. This chapter covers recent advances in topochemical engineering of cellulose-based functional materials with the emphasis on valorization methods, chemistry, composition, and applications for the readers of sustainable biomaterials chemistry.

Topochemical engineering is a method of designing the fractionation (disassembly) and fabrication (assembly) of highly engineered functional materials using a combination of molecular and supramolecular techniques. Cellulose is one of the naturally occurring biopolymers, currently considered to be an important raw material for the design and development of sustainable products and processes. This feature article deals with new insights into how cellulose can be processed and functionalized using topochemical engineering in order to create functional fibers, enhance biopolymer dissolution in water-based solvents, and control the shaping of porous materials. Subsequently, topochemical engineering of cellulose offers a variety of morphological structures such as highly engineered fibers, functional cellulose beads, and reactive powders that find relevant applications in pulp bleaching, enzyme and antimicrobial drug carriers, ion exchange resins, photoluminescent materials, waterproof materials, fluorescent materials, flame retardants, and template materials for inorganic synthesis. The topochemical engineering of biopolymers and biohybrids is an exciting and emerging area of research that can boost the design of new bioproducts with novel functionalities and technological advancements for biobased industries. ispartof: LANGMUIR vol:34 issue:34 pages:9857-9878 ispartof: location:United States status: published

Technical composite materials derived from renewable sources are always of high importance due to cost-effectiveness and environmental concern. Cellulose, a renewable biopolymer stays constantly at the high realm in terms of valorization for functional materials, chemicals and other raw-materials. Cellulose based moisture-repellent materials have challenged the chemists in recent decade as the inherent hydrophilic nature of cellulose should be overcome by chemical modification or hydrophobic insulation. In the present study, cellulose is hydrophobized by eco-friendly stearic acid (SA) through inorganic linker/interface/sandwich material namely layered double hydroxides (LDH) for the first time as the layers have affinity to both cellulose and stearic acid at molecular level. The novel idea of utilizing the charge centres on LDH has been effectively materialized to make conjugation with hydrophobic SA and hydrophilic cellulose simultaneously. This produces an entirely new kind of hybrid material which offers not only hydrophobicity but super-hydrophobicity to cellulose network. This novel SA-LDH-CEL interfaced composite material surpasses all other materials that have been reported in the literature in terms of its water-repellency which is a mandatory requirement for water-proof packaging, thin films, paper, sorbent and sanitary materials.

Topochemical engineering of hybrid materials is an efficient way of synthesizing hydrophobic and highly tensile fiber composites by utilizing the intermolecular hydrogen bonds in natural materials. These materials include wood pulp fibers, abietic acid (resin acid) and inexpensive metal salts. In this work, a hybrid composite was created using bleached and unbleached kraft pulp fibers as cellulose platform. In situ co-precipitation of layered double hydroxide (LDH) was performed to grow LDH crystals on the surface of the cellulose fibers, followed by the immobilization of abietic acid (AA) on LDH-grafted cellulose. Here we aimed to benefit from the hydrogen bonding between -OH groups of cellulose and LDH, and the -COOH groups of AA to obtain charge-directed assembly of one material on the other material. Thus, composite hybrid fibers (C-HF) were produced and then characterized by optical (CAM), spectroscopic (XRD, IR) and microscopic techniques (SEM) to determine their average length and distribution, structure and purity, bonding, and morphology. These fibers further were tested for water contact angle (hydrophobicity), oil absorption (lipophilicity), tensile strength and ISO brightness measurements. The performance of C-HF was compared with unmodified reference fibers (REF), fibers composed with only AA (C-F) and LDH-hybridized fibers (HF). The results revealed a variety of correlations between materials and their properties due to characteristic surface morphology, functional groups, hydrogen bonding and natural co-materials such as lignin and hemicelluloses. Attractive and repulsive van der Waals forces between material entities play a crucial role in the resulting properties. ispartof: BEILSTEIN JOURNAL OF NANOTECHNOLOGY vol:10 pages:589-605 ispartof: location:Germany status: published

Size & shape controlled synthesis of metal nanoparticles are of high importance in catalysis. Colloidal techniques offer fine tunings in synthesis process as it involve multiple steps and reaction parameters. An efficient way of producing morphology controlled palladium nanostructures viz. palladium nanocubes (Pd-nc), palladium nanoicosahedrons (Pd-nico) supported on reduced graphene oxide (rGO) and its application in electro-catalysis is reported here. These Pd nano-shapes were achieved via sequential chemical reduction of Pd metal precursor and graphene oxide in the presence of reductant, ethylene glycol (EG) and stabilizer (capping agent), polyvinylpyrrolidone (PVP). Potassium bromide (KBr) and ascorbic acid (AA) were used as structure directing and secondary reducing agents respectively, to tune the geometry of Pd nanoparticles (Pd NPs). The preparation steps were optimized to yield cube shaped Pd nanoparticles (Pd-nc) with mean diameter of 4 nm in the presence of KBr/AA; while in their absence, icosahedron shaped Pd nanoparticles (Pd-nico) with mean diameter of 3.1 nm were formed and then homogeneously distributed over rGO sheets as evidenced by SEM-EDX and TEM. Further, Pd-nc/rGO and Pd-nico/rGO hybrid composite materials were used to investigate the electrochemical oxidation of oxalic acid (OA) in acidic medium. The results reveal that, these optimal size ranged nanostructures exhibit enhanced electro-catalytic activity when compared to bare glassy carbon electrode (GCE), towards OA oxidation. Among the two, Pd-nico/rGO showed enhanced activity than Pd-nc/rGO. The activity difference was justified based on the particle size distribution and no of surface exposed sites. The synthesis approach provides a versatile route for morphology (shape and size) controlled synthesis of metal nanostructures immobilized on support materials aiming towards fabrication of low cost composites in electro-catalysis and potential sensor applications.

The use of precious metals in heterogeneous catalysis relies on the preparation of small nanoparticles that are stable under reaction conditions. To date, most conventional routes used to prepare noble metal nanoparticles have drawbacks related to surface contamination, particle agglomeration, and reproducibility restraints. We have prepared titania-supported palladium (Pd) and platinum (Pt) catalysts using a simplified vapor deposition technique termed chemical vapor impregnation (CVI) that can be performed in any standard chemical laboratory. These materials, composed of nanoparticles typically below 3 nm in size, show remarkable activity under mild conditions for oxidation and hydrogenation reactions of industrial importance. We demonstrate the preparation of bimetallic Pd-Pt homogeneous alloy nanoparticles by this new CVI method, which show synergistic effects in toluene oxidation. The versatility of our CVI methodology to be able to tailor the composition and morphology of supported nanoparticles in an easily accessible and scalable manner is further demonstrated by the synthesis of Pdshell-Aucore nanoparticles using CVI deposition of Pd onto preformed Au nanoparticles supported on titania (prepared by sol immobilization) in addition to the presence of monometallic Au and Pd nanoparticles. © 2013 American Chemical Society.

The utilisation of gold-palladium nanoparticles either in the form of colloids or supported nanoparticles has received enormous attention in recent years. These materials are very effective for the transformation of organic compounds to highly useful chemical products. The catalytic materials are usually prepared using deposition-precipitation and impregnation techniques, but recently significant attention has been focused on the use of colloidal methods. Here we compare and contrast the preparation and catalytic reactivity of Au-Pd supported nanoparticles synthesised by deposition-precipitation and colloidal methods. The catalyst materials have been evaluated for three different reactions, namely, the oxidation of benzyl alcohol, the direct synthesis of hydrogen peroxide and the oxidation of carbon monoxide. In addition, we have focused our attention on the pre-treatment temperature and the improvement of the deposition-precipitation method by using urea and sodium borohydride for the preparation of highly active Au-Pd supported nanoparticles. © 2010 Elsevier B.V. All rights reserved.

We report the preparation of Au-Pd nanocrystalline catalysts supported on activated carbon prepared via a sol-immobilization technique and explore their use for the direct synthesis of hydrogen peroxide and the oxidation of benzyl alcohol. In particular, we examine the synthesis of a systematic set of Au-Pd colloidal nanoparticles having a range of Au/Pd ratios. The catalysts have been structurally characterized using a combination of UV-visible spectroscopy, transmission electron microscopy, STEM HAADF/XEDS, and X-ray photoelectron spectroscopy. The Au-Pd nanoparticles are found in the majority of cases to be homogeneous alloys, although some variation is observed in the AuPd composition at high Pd/Au ratios. The optimum performance for the synthesis of hydrogen peroxide is observed for a catalyst having a Au/Pd 1:2 molar ratio. However, the competing hydrogenation reaction of hydrogen peroxide increases with increasing Pd content, although Pd alone is less effective than when Au is also present. Investigation of the oxidation of benzyl alcohol using these materials also shows that the optimum selective oxidation to the aldehyde occurs for the Au/Pd 1:2 molar ratio catalyst. These measured activity trends are discussed in terms of the structure and composition of the supported Au-Pd nanoparticles. © 2010 American Chemical Society.

The selectivity of photocatalytic phenol production from the direct oxidation of benzene can be enhanced by fine adjustment of the morphology and composition of Au-Pd metal nanoparticles supported on titanium dioxide thereby suppressing the decomposition of benzene and evolution of phenolic compounds.

Photocatalytic hydrogen evolution may provide one of the solutions to the shift to a sustainable energy society, but the quantum efficiency of the process still needs to be improved. Precise control of the composition and structure of the metal nanoparticle cocatalysts is essential, and we show that fine-tuning the Au-Pd nanoparticle structure modifies the electronic properties of the cocatalyst significantly. Specifically, Pdshell-Aucore nanoparticles immobilized on TiO2 exhibit extremely high quantum efficiencies for H2 production using a wide range of alcohols, implying that chemical byproducts from the biorefinery industry can be used as feedstocks. In addition, the excellent recyclability of our photocatalyst material indicates a high potential in industrial applications. We demonstrate that this particular elemental segregation provides optimal positioning of the unoccupied d-orbital states, which results in an enhanced utilization of the photoexcited electrons in redox reactions. We consider that the enhanced activity observed on TiO2 is generic in nature and can be transferred to other narrow band gap semiconductor supports for visible light photocatalysis. © 2014 American Chemical Society.

Trimetallic Au-Pd-Pt nanoparticles have been supported on activated carbon by the sol-immobilisation method. They are found to be highly active and selective catalysts for the solvent-free aerobic oxidation of benzyl alcohol. The addition of Pt promotes the selectivity to the desired product benzaldehyde at the expense of toluene formation. Detailed aberration corrected STEM-XEDS analysis confirmed that the supported particles are indeed Au-Pd-Pt ternary alloys, but also identified composition fluctuations from particle-to-particle which vary systematically with nanoparticle size. © 2013 The Royal Society of Chemistry.

Selective oxidation of primary carbon-hydrogen bonds with oxygen is of crucial importance for the sustainable exploitation of available feedstocks. To date, heterogeneous catalysts have either shown low activity and/or selectivity or have required activated oxygen donors. We report here that supported gold-palladium (Au-Pd) nanoparticles on carbon or TiO(2) are active for the oxidation of the primary carbon-hydrogen bonds in toluene and related molecules, giving high selectivities to benzyl benzoate under mild solvent-free conditions. Differences between the catalytic activity of the Au-Pd nanoparticles on carbon and TiO(2) supports are rationalized in terms of the particle/support wetting behavior and the availability of exposed corner/edge sites.

Metal nanoparticles that comprise a few hundred to several thousand atoms have many applications in areas such as photonics, sensing, medicine and catalysis. Colloidal methods have proven particularly suitable for producing small nanoparticles with controlled morphologies and excellent catalytic properties. Ligands are necessary to stabilize nanoparticles during synthesis, but once the particles have been deposited on a substrate the presence of the ligands is detrimental for catalytic activity. Previous methods for ligand removal have typically involved thermal and oxidative treatments, which can affect the size or morphology of the particles, in turn altering their catalytic activity. Here, we report a procedure to effectively remove the ligands without affecting particle morphology, which enhances the surface exposure of the nanoparticles and their catalytic activity over a range of reactions. This may lead to developments of nanoparticles prepared by colloidal methods for applications in fields such as environmental protection and energy production. © 2011 Macmillan Publishers Limited. All rights reserved.

Akeydiscoveryinthelasttwodecadeshasbeentheidentifica-tion that gold, when prepared as supported nanoparticles, isexceptionallyeffectiveasanoxidationcatalyst.Followingthisdiscovery, there has been an explosion of interest in gold as acatalyst and several hundred papers and tens of patents arebeing published annually. Gold catalysis is now a major topicforbothheterogeneousandhomogeneouscatalysisworldwide.Previouslywehaveshownthatsupportedgoldandgoldpalla-dium catalysts are very active and selective for the oxidationof alcohols and hydrocarbons and also the direct synthesis ofhydrogen peroxide