Usually, the metastable vaterite phase transforms to the thermodynamically most stable calcite phase. We report here the phase transformation of vaterite to aragonite, which is seldom observed in the synthetic processes of calcium carbonate. The vaterite, upon equilibration with distilled water at room temperature, gradually transforms to aragonite. This transformation process is further accelerated when the vaterite sample is refluxed in distilled water. Under a different set of conditions, when equilibrated in the mother liquor, the same vaterite sample transforms to calcite without going through aragonite as an intermediate phase. The formation of all three crystalline polymorphs of calcium carbonate is achieved without the use of any additive. These polymorph transformations have been monitored using powder X-ray diffraction and FTIR spectroscopy. The morphological changes of the calcium carbonate samples isolated during the course of phase transformation processes are captured using scanning electron microscopy. The transformation either to aragonite or to calcite has been explained based on the dissolution-recrystallization mechanism.

In the present work, we describe a facile, green, and template-free solvothermal fabrication of vanadium sulfide (VS2) nanoparticles (NPs) and their application for the electrochemical detection of hydrogen peroxide (H2O2) and glucose. The morphology and composition of as-prepared samples were well-characterized by powder X-ray diffraction, energy-dispersive spectroscopy, transmission electron microscopy, scanning electron microscopy, UV–vis spectroscopy, and Brunauer–Emmett–Teller surface area measurement. Because of their interesting electrochemical responses toward H2O2, a novel nonenzymatic electrochemical sensor for H2O2 and glucose detection has been proposed based on a VS2 NP-modified glassy carbon electrode. The modified electrode showed an excellent electrochemical performance for the selective and sensitive nonenzymatic detection of H2O2 in a broad concentration range of 0.5 μM to 3.0 mM, with a wide linear range of 0.5 μM to 2.5 mM and a lower detection limit of 0.224 μM. The newly developed sensor also displayed high sensitivity (41.96 μA mM–1) toward the detection of glucose with a broad linear range of 0.5 μM to 3 mM. The as-fabricated sensor also showed very high sensitivity, excellent reusability, long-term stability, and negligible interference ability. Moreover, the synthesized NPs were applied for H2O2 and glucose detection in real samples, signifying their potential application in routine H2O2 and glucose analysis. The present study reveals that as-prepared VS2 NPs are promising for electrochemical H2O2 and glucose sensing and other biological applications.

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Herein, we developed a facile method to prepare an amorphous spherical MoS 2 21 via a simple solvothermal decomposition of a precursor complex MoO 2 (acda) 2 (Hacda = 2-22 33 Keywords: Amorphous MoS 2 , rose bengal, visible light photocatalyst, nitro compounds, 34 hydrogenation, heterogeneous catalyst 35 36 37 38 39 40 41 42 45different natural products, the reduction of p-nitrophenol 1-9 has drawn extensive attention in 46 recent years. Silver, gold, platinum and palladium metal NPs or metal nanocomposites [10][11][12] 47 are known to be typical catalysts applied in the catalytic hydrogenation of p-nitrophenol. 48Although the catalytic performances of these catalysts are relatively satisfactory, there is a 49 need to limit the use of such very expensive catalysts. It is thus desirable to move away from 50 rare elements and catalyze the reaction through cheap, earth-abundant materials. This 51 challenge has led to the exploration of molybdenum sulfides as catalysts for the 52 hydrogenation of p-nitrophenol. Moreover, preparation of MoS 2 are of considerable attention 53 for its potential applications in many areas as catalysis, 13 potential hydrogen storage media, 14 54 electrode materials for Mg 2+ ion and Li + ion batteries, 15,16 solid super lubricants, 17,18 55 superconductors, 19,20 and photo-electrochemical solar cells, 21,22 hydrogen evolution reaction. 56In contrast no such reports are concerned on the catalytic behaviour of amorphous MoS 2 for 57 the decomposition of organic pollutants like dyes 23-29 and for the catalytic reduction of nitro 58 groups to amino groups. Now a days, the synthesis of amorphous MoS 2 is a great challenge 59 due to its high performances mainly due to high surface area and large concentration of 60 lattice defects in the amorphous structures. Therefore a simple, cost-effective method for the 61 synthesis of amorphous MoS 2 is essential to explore the different catalytic activities. Despite 62 all other various solution-phase synthetic strategies, the thermo decomposition of a single-63 source precursor (SSP) method may be useful, since it has been proven facile and valid in 64 obtaining a variety of metal chalcogenide NPs with the characteristics of single crystallites, 65 pure phases, definite stoichiometries and monodispersities. O'Brien pioneered this facile 66 synthetic process and first obtained different chalcogenides 30-33 viz. sulphides and selinides 67 The ligand, 2-aminocyclopentene-1-dithiocarboxylic acid (Hacda) has already been 88 synthesized according to the previously reported method. 38 The precursor complex, 89 MoO 2 (acda) 2 was prepared according to the prescribed method. 39 90 91 The synthesis of amorphous MoS 2 was carried out through a solvothermal 93 decomposition of synthesized precursor complex using nucleophilic solvent TETA. The 94 precursor complex MoO 2 (acda) 2 (200mg) was dissolved in 4 mL TETA and transferred into a 95 10 mL round bottom flask. The reaction mixture was then heated for 1.5 hr at 200˚C in an 96 inert atmosphere. The black particles...