Journal Articles
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Item Recent advances in the preparation of levulinic esters from biomass-derived furanic and levulinic chemical platforms using heteropoly acid (HPA) catalysts(Elsevier B.V., 2021) Bhat, N.S.; Mal, S.S.; Dutta, S.The esters of biomass-derived levulinic acid (LA) have several potential applications, including cleaner-burning fuel additive, green solvent, fragrance ingredient, and a renewable chemical intermediate for downstream value addition. The levulinic esters (LEs) can be prepared by the acid-catalyzed alcoholysis of the biomass-derived furanic and levulinic chemical platforms such as LA, furfuryl alcohol (FAL), 5-(hydroxymethyl)furfural (HMF), and angelica lactone (AGL). The acid-catalyzed deconstruction of carbohydrates in an alcoholic medium affords the one-pot preparation of LEs. Choosing the right catalyst is of paramount importance for synthesizing LEs from both the economic and environmental perspectives. In this regard, heteropoly acids (HPAs), a class of polyoxometalates (POMs) bearing protons as the counter cation, have found widespread applications as acid catalysts in various organic transformations. HPAs are blessed with conducive properties such as controlled Brønsted and Lewis acidity, high thermal stability, robust structural features, non-toxic nature, tunable solubility, and less corrosiveness. Over the past several years, HPAs have found extensive applications as efficient and environment-friendly catalysts in biorefinery operations, including the synthesis of LEs. At this juncture, it is imperative to ascertain the achievements in this field to date and re-evaluate the challenges. This review attempts to provide up-to-date information about the preparation of LEs using HPA-based catalysts, critically analyze the literature cited, draw conclusions, and propose future prospects. © 2021 Elsevier B.V.Item An Insight into the Gelatinization Properties Influencing the Modified Starches Used in Food Industry: A review(Springer, 2022) Chakraborty, I.; N, P.; Mal, S.S.; Paul, U.C.; Rahman, M.H.; Mazumder, N.Native starch is subjected to various forms of modification to improve its structural, mechanical, and thermal properties for wider applications in the food industry. Physical, chemical, and dual modifications have a substantial effect on the gelatinization properties of starch. Consequently, this review explores and compares the different methods of starch modification applicable in the food industry and their effect on the gelatinization properties such as onset temperature (To), peak gelatinization temperature (Tp), end set temperature (Tc), and gelatinization enthalpy (ΔH), studied using differential scanning calorimetry (DSC). Chemical modifications including acetylation and acid hydrolysis decrease the gelatinization temperature of starch whereas cross-linking and oxidation result in increased gelatinization temperatures. Common physical modifications such as heat moisture treatment and annealing also increase the gelatinization temperature. The gelatinization properties of modified starch can be applied for the improvement of food products such as ready-to-eat, easily heated or frozen food, or food products with longer shelf life. © 2022, The Author(s).Item An insight into microscopy and analytical techniques for morphological, structural, chemical, and thermal characterization of cellulose(John Wiley and Sons Inc, 2022) Chakraborty, I.; Rongpipi, S.; Govindaraju, I.; Rakesh, B.; Mal, S.S.; Gomez, E.W.; Gomez, E.D.; Kalita, R.D.; Nath, Y.; Mazumder, N.Cellulose obtained from plants is a bio-polysaccharide and the most abundant organic polymer on earth that has immense household and industrial applications. Hence, the characterization of cellulose is important for determining its appropriate applications. In this article, we review the characterization of cellulose morphology, surface topography using microscopic techniques including optical microscopy, transmission electron microscopy, scanning electron microscopy, and atomic force microscopy. Other physicochemical characteristics like crystallinity, chemical composition, and thermal properties are studied using techniques including X-ray diffraction, Fourier transform infrared, Raman spectroscopy, nuclear magnetic resonance, differential scanning calorimetry, and thermogravimetric analysis. This review may contribute to the development of using cellulose as a low-cost raw material with anticipated physicochemical properties. Highlights: Morphology and surface topography of cellulose structure is characterized using microscopy techniques including optical microscopy, transmission electron microscopy, scanning electron microscopy, and atomic force microscopy. Analytical techniques used for physicochemical characterization of cellulose include X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, nuclear magnetic resonance spectroscopy, differential scanning calorimetry, and thermogravimetric analysis. © 2022 Wiley Periodicals LLC.Item Hervé- and Krebs-Type Magnetic Polyoxometalate Dimers(MDPI, 2022) Kondinski, A.; Banerjee, A.; Mal, S.S.Lacunary polyoxometalates (POMs) are negatively charged metal–oxo clusters, formally obtained from plenary topologies via fragment removal. Owing to the fragment removal, the lacunary POMs archetypes are rich in nucleophilic terminal oxo ligands, making them suitable for post-synthetic coordination with various heterometals. Trilacunary heteropolytungstates (hetero-POTs) based on bowl-shaped {W9O30} framework incorporating a central lone-pair containing {XO3} hetergroup (X = AsIII, SbIII, and BiIII) function as all-inorganic scaffolds that in the presence of d-block metal cations typically construct sandwich-like dimers of Hervé and/or Krebs. Herein we review the preparative approaches, as well as compositional and magnetic versatility of the constructed Hervé- and Krebs-type dimers and discuss prospective uses as POMtronics. © 2022 by the authors.Item Polyoxometalate-based materials for the effluent treatment of removing heavy metals in the water pollutants: mini review(Springer Science and Business Media Deutschland GmbH, 2023) Madhusree, J.E.; Mal, S.S.Water contamination is a big concern nowadays due to increased human activity and the quick expansion of modern industry and agriculture. In our current environment, heavy metal pollution has become a primary concern. Treatment of heavy metals is especially significant, because these metals absorb into biological cells and can lead to severe illness and disorders. Several studies have been conducted over the last several years to remove heavy metals from wastewater using various strategies and materials. Among those strategies, complexation's reaction and the electrochemical sensor are attractive because of their excellent metal selectivity, cost-effectiveness, short analytical time, and high removal efficiency. Polyoxometalates (POMs) are a group of metal–oxygen cluster compounds with extremely electronegative and oxo-enriched surfaces and variable structure and size. POMs have drawn much interest in removing toxins from wastewater due to their electrical and physical characteristics. The removal of heavy metals from wastewater is covered in this review using POM and POM-based MOF nanocomposites in various treatment methods like complexation and electrochemical sensor, which have the advantages of high removal efficiency, excellent metal selectivity, in-expansive, and rapid analytical times. © 2023, King Abdulaziz City for Science and Technology.Item The cyclic 48-tungsto-8-phosphate [H7P8W48O184]33− Contant-Tézé polyanion and its derivatives [H6P4W24O94]18− and [H2P2W12O48]12−: structural aspects and reactivity(Royal Society of Chemistry, 2025) Mal, S.S.; Banerjee, A.; Kortz, U.Polyoxometalates (POMs) are discrete, anionic metal-oxo clusters of early transition metals in high oxidation states (e.g., WVI, MoVI, VV) usually comprised of edge- and corner-shared MO6 octahedra. Lacunary POMs are defect heteropolyanions mainly of the Keggin or Dawson type, and they can be formed by the loss of one or more MO6 octahedra by controlled base hydrolysis. The largest subclass of POMs are tungstophosphates, and several lacunary derivatives are known, such as the Keggin-based [PW11O39]7− and [PW9O34]9−, and the Dawson-based [P2W17O61]10− and [P2W15O56]12−. This review is based on the cyclic 48-tungsto-8-phosphate [H7P8W48O184]33− (P8W48) as well as its smaller derivatives [H6P4W24O94]18− (P4W24), and [H2P2W12O48]12− (P2W12), with a focus on structural aspects, solution stability and reactivity. All three polyanions can be considered as inorganic multidentate O-donor ligands that coordinate with d, f or p-block metal ions. Here we provide a comprehensive overview of guest metal-containing derivatives of the P8W48 wheel, the P4W24 half-wheel and the P2W12 quarter wheel. The structures containing P2W12 as a building unit are presented in a sequence of increasing number of POM units in the resulting assembly. Transition metal-containing POMs have been of interest for decades due to their remarkable capability of forming novel and unexpected structures associated with interesting and relevant physicochemical properties (e.g., catalysis, magnetism, biomedicine, electrochemistry), and this also applies for derivatives containing P8W48, P4W24 and P2W12 © 2025 The Royal Society of Chemistry.Item Electrocatalysis by crown-type polyoxometalates multi-substituted by transition metal ions; Comparative study(Elsevier Ltd, 2015) Naseer, R.; Mal, S.S.; Kortz, U.; Armstrong, G.; Laffir, F.; Dickinson, C.; Vagin, M.; McCormac, T.Abstract The difference in electrochemical properties of three crown-type polyoxometalates multi-substituted by Fe3+, Ni2+ or Co2+ ions and their precursor has been rationalized with respect to their electrocatalytic performances studied in solution and in the immobilized state within the layer-by-layer film formed with a positively charged pentaerythritol-based Ru(II)-metallodendrimer. The film assembly was monitored with electrochemical methods and characterized by surface analysis techniques. An influence of the terminal layer on the electrode reaction and on film porosity has been observed. The electrocatalytic performance of the compounds on nitrite reduction was assessed in solution and in the immobilized state. © 2015 Elsevier Ltd.Item Characterization of PtIV-containing polyoxometalates by high-resolution solid-state 195Pt and 51V NMR spectroscopy(Royal Society of Chemistry, 2016) Dugar, S.; Izarova, N.V.; Mal, S.S.; Fu, R.; Joo, H.-C.; Lee, U.; Dalal, N.S.; Pope, M.T.; Jameson, G.B.; Kortz, U.We report on the feasibility of applying high-resolution solid-state 195Pt MAS NMR spectroscopy for several PtIV-containing polyoxotungstates, and of 195Pt as well as 51V for a PtIV-containing polyoxovanadate. This method is particularly useful for polyanions which are unstable in solution and/or poorly soluble, as well as for systems exhibiting crystallographic disorder of Pt and W sites. We also report solution 195Pt and 183W NMR spectra of hexatungstoplatinate(iv) [H3PtW6O24]5- for the first time. © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2016.Item Dependence of the 0.5 × (2e2/h) conductance plateau on the aspect ratio of InAs quantum point contacts with in-plane side gates(American Institute of Physics Inc. subs@aip.org, 2017) Das, P.P.; Jones, A.; Cahay, M.; Kalita, S.; Mal, S.S.; Sterin, N.S.; Yadunath, T.R.; Advaitha, M.; Herbert, S.T.The observation of a 0.5 × (2e2/h) conductance plateau in asymmetrically biased quantum point contacts (QPCs) with in-plane side gates (SGs) has been attributed to the onset of spin-polarized current through these structures. For InAs QPCs with the same width but a longer channel length, there is roughly a fourfold increase in the range of common sweep voltage applied to the SGs over which the 0.5 × (2e2/h) plateau is observed when the QPC aspect ratio (ratio of length over the width of the narrow portion of the structure) is increased by a factor 3. Non-equilibrium Green's function simulations indicate that the increase in the size of the 0.5 × (2e2/h) plateau is due to an increased importance, over a larger range of common sweep voltage, of the effects of electron-electron interactions in QPC devices with a larger aspect ratio. The use of asymmetrically biased QPCs with in-plane SGs and large aspect ratio could therefore pave the way to build robust spin injectors and detectors for the successful implementation of spin field effect transistors. © 2017 Author(s).Item A Liquid Derivative of Phosphotungstic Acid as Catalyst for Benzyl Alcohol Oxidation in Water: Facile Separation and Stability of Benzaldehyde at Room Temperature†(Wiley-Blackwell, 2017) Bhattacharjee, R.R.; Thangamani, S.; Mal, S.S.Polyetheramines belong to a class of green di-block copolymer with ethylene oxide and propylene oxide moieties along with terminal amine functionality. The polymers are biocompatible and show temperature dependant phase separation properties. Herein, we report the effect of a polyetheramine (Jeffamine®) on the catalytic properties of a well studied polyoxometalate catalysts, phosphotungstic acid (PTA). The catalytic reaction chosen for the test is the hydrogen peroxide-mediated oxidation of benzyl alcohol (BzOH). Modification of PTA with Jeffamine® (PTA-Jeffamine®) resulted in a solvent-less liquid-like material accessible to a wide range of solvents. The PTA-Jeffamine® catalyst was observed to enhance the conversion of BzOH compared to that of pristine PTA and facilitated easy separation of benzaldehyde (BzH) and catalyst from reaction mixture. Stability of synthesized BzH was studied with gas chromatography attached with mass spectrometry (GC-MS). Synthesis of the catalyst is cost-effective and scalable due to easy availability of the individual components and nature of the synthetic protocol. UV-visible spectroscopy, Fourier transform infrared spectroscopy (FT-IR) and field emission scanning electron microscopy (FE-SEM) were used to characterize the catalyst. Surface tension experiment, FE-SEM, ICP-MS and controlled experiments were performed to understand the effect of Jeffamine® in the catalytic process. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim