Anandarup Goswami

Cu and Cu-Based Nanoparticles: Synthesis and Applications in Catalysis

The applications of copper (Cu) and Cu-based nanoparticles, which are based on the earth-abundant and inexpensive copper metal, have generated a great deal of interest in recent years, especially in the field of catalysis. The possible modification of the chemical and physical properties of these nanoparticles using different synthetic strategies and conditions and/or via postsynthetic chemical treatments has been largely responsible for the rapid growth of interest in these nanomaterials and their applications in catalysis. In addition, the design and development of novel support and/or multimetallic systems (e.g., alloys, etc.) has also made significant contributions to the field. In this comprehensive review, we report different synthetic approaches to Cu and Cu-based nanoparticles (metallic copper, copper oxides, and hybrid copper nanostructures) and copper nanoparticles immobilized into or supported on various support materials (SiO2, magnetic support materials, etc.), along with their applications in catalysis. The synthesis part discusses numerous preparative protocols for Cu and Cu-based nanoparticles, whereas the application sections describe their utility as catalysts, including electrocatalysis, photocatalysis, and gas-phase catalysis. We believe this critical appraisal will provide necessary background information to further advance the applications of Cu-based nanostructured materials in catalysis.

Core–shell nanoparticles: synthesis and applications in catalysis and electrocatalysis

Core-shell nanoparticles (CSNs) are a class of nanostructured materials that have recently received increased attention owing to their interesting properties and broad range of applications in catalysis, biology, materials chemistry and sensors. By rationally tuning the cores as well as the shells of such materials, a range of core-shell nanoparticles can be produced with tailorable properties that can play important roles in various catalytic processes and offer sustainable solutions to current energy problems. Various synthetic methods for preparing different classes of CSNs, including the Stöber method, solvothermal method, one-pot synthetic method involving surfactants, etc., are briefly mentioned here. The roles of various classes of CSNs are exemplified for both catalytic and electrocatalytic applications, including oxidation, reduction, coupling reactions, etc.

Covalent functionalization of monolayered transition metal dichalcogenides by phase engineering

Chemical functionalization of low-dimensional materials such as nanotubes, nanowires and graphene leads to profound changes in their properties and is essential for solubilizing them in common solvents. Covalent attachment of functional groups is generally achieved at defect sites, which facilitate electron transfer. Here, we describe a simple and general method for covalent functionalization of two-dimensional transition metal dichalcogenide nanosheets (MoS₂, WS₂ and MoSe₂), which does not rely on defect engineering. The functionalization reaction is instead facilitated by electron transfer between the electron-rich metallic 1T phase and an organohalide reactant, resulting in functional groups that are covalently attached to the chalcogen atoms of the transition metal dichalcogenide. The attachment of functional groups leads to dramatic changes in the optoelectronic properties of the material. For example, we show that it renders the metallic 1T phase semiconducting, and gives it strong and tunable photoluminescence and gate modulation in field-effect transistors.

Efficient noble metal-free (electro)catalysis of water and alcohol oxidations by zinc-cobalt layered double hydroxide.

Replacing rare and expensive noble metal catalysts with inexpensive and earth-abundant ones for various renewable energy-related chemical processes as well as for production of high value chemicals is one of the major goals of sustainable chemistry. Herein we show that a bimetallic Zn-Co layered double hydroxide (Zn-Co-LDH) can serve as an efficient electrocatalyst and catalyst for water and alcohol oxidation, respectively. In the electrochemical water oxidation, the material exhibits a lower overpotential, by ~100 mV, than monometallic Co-based solid-state materials (e.g., Co(OH)2 and Co3O4)-catalytic systems that were recently reported to be effective for this reaction. Moreover, the materials turnover frequency (TOF) per Co atoms is >10 times as high as those of the latter at the same applied potentials. The Zn-Co-LDH also catalyzes oxidation of alcohols to the corresponding aldehydes or ketones at relatively low temperature, with moderate to high conversion and excellent selectivity.

N-, O-, and S-Tridoped Nanoporous Carbons as Selective Catalysts for Oxygen Reduction and Alcohol Oxidation Reactions

Replacing rare and expensive metal catalysts with inexpensive and earth-abundant ones is currently among the major goals of sustainable chemistry. Herein we report the synthesis of N-, O-, and S-tridoped, polypyrrole-derived nanoporous carbons (NOSCs) that can serve as metal-free, selective electrocatalysts and catalysts for oxygen reduction reaction (ORR) and alcohol oxidation reaction (AOR), respectively. The NOSCs are synthesized via polymerization of pyrrole using (NH4)2S2O8 as oxidant and colloidal silica nanoparticles as templates, followed by carbonization of the resulting S-containing polypyrrole/silica composite materials and then removal of the silica templates. The NOSCs exhibit good catalytic activity toward ORR with low onset potential and low Tafel slope, along with different electron-transfer numbers, or in other words, different ratios H2O/H2O2 as products, depending on the relative amount of colloidal silica used as templates. The NOSCs also effectively catalyze AOR at relatively low temperature, giving good conversions and high selectivity.

Dielectric behaviour of dysprosium oxide films

Abstract The dielectric properties of vacuum-deposited dysprosium oxide films have been studied in the audio-frequency range (102–104 Hz) at various temperatures (78–373 K). The dielectric constant (6.7) was independent of film thickness for thicker films (d > 1000 A). The capacitance was dependent both on temperature and frequency, but became constant for all frequencies at low temperature. Tan δ showed a frequency minimum and its variation with frequency and temperature was in agreement with the model proposed earlier by Goswami and Goswami. The breakdown field (≌106 V cm-1) followed the Forlani-Minnaja relation. The activation energy and the refractive index of these films were also measured.

Ultrasmall palladium nanoparticles supported on amine-functionalized SBA-15 efficiently catalyze hydrogen evolution from formic acid

The success of the so-called “hydrogen economy” for large-scale applications will ultimately depend on efficient and sustainable production, storage and distribution of hydrogen. Owing to its low toxicity, high volumetric H2 storage capacity and availability both from renewable resources (e.g., biomass) and non-renewable resources (e.g., fossil fuel feedstocks), formic acid is one of the most favorable chemical hydrogen storage media for large-scale energy storage applications. However, for FA to become a viable hydrogen storage medium, efficient catalysts that enable it to release H2 at low cost are necessary. Herein we report a facile synthetic route to amine-functionalized nanoporous silica-supported ultrasmall Pd nanoparticles (SBA-15-Amine/Pd) that are highly active catalysts for formic acid dehydrogenation, producing hydrogen at ambient temperature with a high turn-over-frequency (TOF) of 293 h−1, which is among the highest TOFs ever reported for the reaction by a heterogeneous catalyst. We also show that the material is easily recyclable multiple times, without losing its catalytic activity. So, the catalyst we developed can be expected to be part of the solutions of our sustainability challenges.

Lithium Phenolates Solvated by Tetrahydrofuran and 1,2-Dimethoxyethane: Structure Determination Using the Method of Continuous Variation

The method of continuous variation in conjunction with (6)Li NMR spectroscopy was used to characterize lithium phenolates solvated by tetrahydrofuran and 1,2-dimethoxyethane. The strategy relies on the formation of ensembles of homo- and heteroaggregated phenolates. The symmetries and concentration dependencies of the heteroaggregates attest to the aggregation numbers of the homoaggregates. The structurally diverse phenols afford substrate- and solvent-dependent combinations of lithium phenolate monomers, dimers, trimers, tetramers, and pentamers. We discuss the refinement of protocols for characterizing O-lithiated species. Computational studies examine further the substituent and solvent dependencies of aggregation.

Reductive Deprotection of Monolayer Protected Nanoclusters: An Efficient Route to Supported Ultrasmall Au Nanocatalysts for Selective Oxidation

Bulk gold has long been considered too inert to be a catalyst until the discovery that Au nanoparticles (AuNPs) supported on metal oxides such as TiO 2 , CeO 2 and Fe 2 O 3 could be very active for CO oxidation. [ 1 ] Supported Au and other NPs have now been successfully shown to catalyze various chemical reactions. [ 2 ] AuNP-catalyzed oxidation reactions, in particular, have attracted special attention because the reactions can lead to a range of important value-added oxygenated chemical products and pharmaceuticals, and also because oxidation (or epoxidation) of various alkenes, arenes and alcohols are proven to be effectively catalyzed by AuNPs. [ 3 ]

Yeast Cells-Derived Hollow Core/Shell Heteroatom-Doped Carbon Microparticles for Sustainable Electrocatalysis

The use of renewable resources to make various synthetic materials is increasing in order to meet some of our sustainability challenges. Yeast is one of the most common household ingredients, which is cheap and easy to reproduce. Herein we report that yeast cells can be thermally transformed into hollow, core-shell heteroatom-doped carbon microparticles that can effectively electrocatalyze the oxygen reduction and hydrazine oxidation reactions, reactions that are highly pertinent to fuel cells or renewable energy applications. We also show that yeast cell walls, which can easily be separated from the cells, can produce carbon materials with electrocatalytic activity for both reactions, albeit with lower activity compared with the ones obtained from intact yeast cells. The results reveal that the intracellular components of the yeast cells such as proteins, phospholipids, DNAs and RNAs are indirectly responsible for the latters higher electrocatalytic activity, by providing it with more heteroatom dopants. The synthetic method we report here can serve as a general route for the synthesis of (electro)catalysts using microorganisms as raw materials.