M. Qamar

Highly efficient and selective oxidation of aromatic alcohols photocatalyzed by nanoporous hierarchical Pt/Bi2WO6 in organic solvent-free environment.

Selective conversion of aromatic alcohols into corresponding aldehydes is important from energy and environmental stance. Here, we describe highly selective (>99%) and efficient conversion (>99%) of aromatic alcohols (e.g., 4-methoxybenzyl alcohol and 4-nitrobenzyl alcohol) into their corresponding aldehydes in the presence of Pt-modified nanoporous hierarchical Bi2WO6 spheres in water under simulated sunlight at ambient conditions. Overoxidation of p-anisaldehyde, formed during photooxidation process, was not observed until comprehensive alcohol oxidation was attained. Furthermore, the catalyst showed substantial oxidation under dark and course of conversion was different than that of under light. Dependency of alcohol oxidation on substrate concentration, photocatalyst amount, and Pt loading was studied. The effect of various radical scavengers was investigated, and the rate-determining step was elucidated. It has been envisaged that the reduction site of semiconductor photocatalysts plays more decisive role in determining the selectivity as alcohol preferably get oxidized over that of water. Furthermore, the chemical stability and recyclability of the photocatalyst were investigated.

Metal–organic framework-guided growth of Mo2C embedded in mesoporous carbon as a high-performance and stable electrocatalyst for the hydrogen evolution reaction

Large-scale production of H2 by electrochemical water splitting is discerned as one of the most economical and viable approaches and designing Pt-less electrocatalysts remains at the forefront of this technology development. Herein, in situ transformation of metal–organic frameworks (MOF), impregnated with a molybdenum precursor, into a porous and rigid carbon support and molybdenum carbide (Mo2C) was demonstrated to fabricate highly active and stable β-Mo2C/C heterostructure for electrocatalytic H2 evolution. The two-step synthesis approach involved the impregnation of molybdenum source into frameworks of MOF (namely MIL-53(Al)) followed by nucleation and growth of Mo2C nanocrystals into confined porous texture through carburization. Characterization revealed the formation of mesoporous carbon embodied with crystalline nanoparticles of β-Mo2C (between 5 and 10 nm). A probable mechanism for the formation of Mo2C/C nanocomposite is proposed. The propensity of the catalyst was tested towards the electrocatalytic H2 evolution reaction (HER) under alkaline aqueous media (1 M KOH). The electrocatalyst showed a remarkable HER activity as compared to the benchmark electrocatalyst Pt/C and Mo2C/XC72 black catalysts at 10 mA cm−2 and stability for 20 h at the same current density. Electrochemical impedance spectroscopy results of Mo2C/C were construed by two time constants, porosity and charge transfer, and the HER reaction followed the Volmer–Heyrovsky mechanism.

Mesoporous hierarchical bismuth tungstate as a highly efficient visible-light-driven photocatalyst

The synthesis of flower-like hierarchical bismuth tungstate (Bi2WO6) consisting of a mesoporous surface was carried out by a hydrothermal method using the non-ionic surfactant Pluronic F127. The mesoporous and hierarchical surface of the bismuth tungstate was further modified with platinum nanoparticles and the photocatalytic activity was evaluated by studying the removal of rhodamine B under visible light (>420 nm). The effect of synthesis temperature and platinum amount on the photocatalytic activity was investigated and resulting photocatalytic activity of Pt/Bi2WO6 was compared with other visible-light-responsive photocatalysts, namely Pt/WO3, N-doped TiO2 and Pt/N-doped TiO2. Photoelectrochemical studies were performed to shed light on the involvement of excited charged carriers in the photooxidation of rhodamine B and a plausible mechanism was proposed based on the photocatalytic and photoelectrochemical behaviour of the catalysts.

Single-Pot Synthesis of ⟨001⟩-Faceted N-Doped Nb2O5/Reduced Graphene Oxide Nanocomposite for Efficient Photoelectrochemical Water Splitting.

Due to exciting catalytic activity and selectivity, tailoring of nanocatalysts consisting of preferred crystal facets and desired structural properties remains at the forefront of materials engineering. A facile one-step nonhydrolytic solvothermal synthesis of a nanocomposite of reduced graphene oxide and one-dimensional nitrogen-doped Nb2O5 (N-NbOx) with exposed ⟨001⟩ facet is described. Triethylamine performed the dual role as nitrogen source and capping agent to control the size and unidirectional growth of Nb2O5 nanocrystallites. The nanocomposite showed efficient visible-light-mediated (λ > 420 nm) water splitting in a photoelectrochemical cell. A plausible mechanism for the formation of N-NbOx nanorods and improved photoelectrochemical efficacy in terms of their oriented growth is proposed.

Selective photocatalytic oxidation of aromatic alcohols into aldehydes by tungsten blue oxide (TBO) anchored with Pt nanoparticles

Achieving selective transformation of organic functional groups in an energy efficient and environmentally benign way is an important yet challenging endeavour in the field of chemical science. Utilization of heterogeneous photocatalysis for selective conversion holds great potential from cost, energy, and environment viewpoints. In this work, we report the fabrication of nanocomposites comprising hypostoichiometric tungsten oxide (WO3−x) modified with platinum nanoparticles and/or reduced graphene oxide (RGO) and their deployment in highly selective (>99%) and efficient (>80%) conversion of aromatic alcohols into corresponding aldehydes under simulated sunlight and ambient conditions. Efficacy of the nanocomposites was investigated by studying the oxidation of benzyl alcohol (BA), 4-methoxybenzyl alcohol (4-MBA) and cinnamyl alcohol (CA) into corresponding aldehyde, in terms of alcohol concentration, RGO and/or Pt loading, and the amount of photocatalyst employed. Systematic investigations on the chemical stability, recyclability, photocatalytic and photoelectrocatalytic aspects helped to shed light on the role of excitons towards the observed selectivity. A plausible mechanism to explain the observed attributes of the photocatalyst is proposed that provides impetus to design future photocatalysts with anticipated attributes for selective oxidation reactions.

Metal Carbides in Fuel Cell Cathode

Moderate-temperature fuel cells are clean power generators for both stationary and mobile applications. In particular, polymer electrolyte membrane fuel cells (PEMCs) have attracted much attention due to their high gravimetric and volumetric power densities. However, due to their acidic environment, platinum-based nanocatalysts are the only feasible electrocatalyts for such systems. High cost and limited resources of this precious metal hinder the commercialization of PEMFCs. As a result, tremendous efforts are being exerted to either reduce Pt loading or substitute Pt metal with other non-noble metals. In this context, metal carbides have been extensively investigated due to their bifunctional mechanism as a catalyst as well as a catalyst support. Hence, the aim of using metal carbides is to replace carbon support since carbon suffers from corrosion problem and at the same time to reduce a substantial amount of Pt in fuel cell cathode. In this chapter, we have given an overview on metal carbides and their benefits as catalyst support for fuel cell cathode reactions.

A Mesopore-Dependent Catalytic Cracking of n-Hexane Over Mesoporous Nanostructured ZSM-5

Herein, pore size, crystalinity, and Si/Al ratio of mesoporous ZSM-5 (MFI) nanocrystals was controlled by synthesis parameters, such as surfactant concentration ([3-(trimethoxysilyl)propyl] hexa-decyl dimethyl ammonium chloride), sodium hydroxide concentrations, synthesis temperature and time. The morphology, surface structure and composition of the MFI particles was systematically investigated. More notably, the mesopore-dependent catalytic activity of ZSM-5 was evaluated by studying the cracking of n-hexane. The findings suggest the porosity has pronounced impact on the catalytic activity, selectivity and stability of ZSM-5 nanocrystals. Critical surface attributes such as nature of acid sites (Brønsted and Lewis), concentration, and strength are obtained by the infrared study of adsorbed probe molecules (pyridine) and the temperature programmed desorption. In spite of being weaker in Si/Al ratio or acidic strength, mesoporous catalysts showed more stable and efficient cracking of n-hexane suggesting that acidity seems not the predominant factor operative in the activity, selectivity and stability.

Emissive lead(II) benzenedicarboxylate metal-organic frameworks

Two known Pb(II) metal-organic frameworks (MOFs), pseudo-supramolecular isomeric pairs synthesized namely, [Pb

Semiconductor-Mediated Photocatalysed Degradation of Various Pesticide Derivatives and Other Priority Organic Pollutants in Aqueous Suspensions

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