Jaya Pal

Morphology Controlled Synthesis of SnS2 Nanomaterial for Promoting Photocatalytic Reduction of Aqueous Cr(VI) under Visible Light

A mild, template free protocol has been demonstrated for SnS2 nanoflake formation at the gram level from SnCl2 and thioacetamide (TAA). The SnS2 nanoflakes congregate to nanoflowers and nanoyarns with variable TAA concentrations. BET measurements reveal that the synthesized nanomaterials are highly porous having very high surface area, and the nanoflower has higher surface area than the nanoyarn. The synthesized nanomaterial finds application for promoting photoreduction of extremely toxic and lethal Cr(VI) under visible light irradiation due to their porous nature. The nanoflowers photocatalyst is proved to be superior to nanoyarn due to the increased surface area and higher pore volume. It was also inferred that increased pH decreased the reaction rate. The present result suggests that the morphology-dependent photoreduction of Cr(VI) by SnS2 nanomaterial under visible light exposure will endorse a new technique for harvesting energy and purification of wastewater.

Fabrication of superhydrophobic copper surface on various substrates for roll-off, self-cleaning, and water/oil separation.

Superhydrophobic surfaces prevent percolation of water droplets and thus render roll-off, self-cleaning, corrosion protection, etc., which find day-to-day and industrial applications. In this work, we developed a facile, cost-effective, and free-standing method for direct fabrication of copper nanoparticles to engender superhydrophobicity for various flat and irregular surfaces such as glass, transparency sheet (plastic), cotton wool, textile, and silicon substrates. The fabrication of as-prepared superhydrophobic surfaces was accomplished using a simple chemical reduction of copper acetate by hydrazine hydrate at room temperature. The surface morphological studies demonstrate that the as-prepared surfaces are rough and display superhydrophobic character on wetting due to generation of air pockets (The Cassie-Baxter state). Because of the low adhesion of water droplets on the as-prepared surfaces, the surfaces exhibited not only high water contact angle (164 ± 2°, 5 μL droplets) but also superb roll-off and self-cleaning properties. Superhydrophobic copper nanoparticle coated glass surface uniquely withstands water (10 min), mild alkali (5 min in saturated aqueous NaHCO3 of pH ≈ 9), acids (10 s in dilute HNO3, H2SO4 of pH ≈ 5) and thiol (10 s in neat 1-octanethiol) at room temperature (25-35 °C). Again as-prepared surface (cotton wool) was also found to be very effective for water-kerosene separation due to its superhydrophobic and oleophilic character. Additionally, the superhydrophobic copper nanoparticle (deposited on glass surface) was found to exhibit antibacterial activity against both Gram-negative and Gram-positive bacteria.

A one pot synthesis of Au–ZnO nanocomposites for plasmon-enhanced sunlight driven photocatalytic activity

To enhance the photocatalytic efficiency of ZnO nanomaterials, plasmonic Au nanoparticles (NPs) have deliberately been introduced into ZnO through a facile, inexpensive one pot hydrothermal approach. The enhanced photocatalytic efficiency was ascribed to surface plasmon resonance induced local electric field enhancement of Au. Thus the photoproduced e−–h+ pair in ZnO under sunlight irradiation is reluctant to recombine. The as-synthesized photocatalyst with an excellent sunlight driven photocatalytic activity can effectively decompose various kinds of organic dyes and maintain a high level of photoactivity even after four cycles. The photocatalytic activity of the Au–ZnO nanocomposites was examined by the photodegradation of a series of cationic and anionic dye molecules such as rhodamine B, Congo red, methyl orange, methylene blue, and Rose Bengal. It is interesting to note that with a reasonable increase in the Au concentration the shape of the nanocomposites remains unaltered but the visible light driven photocatalytic activity is enhanced. This observation and the result are promising for plasmonic photocatalysis. The presence of Au nanoparticles makes the Au–ZnO nanocomposite a superior photocatalyst over the ZnO nanomaterial and the nanocomposite presents altogether a different scenario. In a nut-shell the present study reports not only a new insight into the gram level synthesis of a plasmonic photocatalyst from one pot but also its application in waste water treatment through the degradation of toxic dye molecules upon direct sunlight exposure.

Account of Nitroarene Reduction with Size- and Facet-Controlled CuO–MnO2 Nanocomposites

In this work, we propose a systematic and delicate size- and shape-controlled synthesis of CuO-MnO2 composite nanostructures from time-dependent redox transformation reactions between Cu2O and KMnO4. The parental size and shape of Cu2O nanostructures are retained, even after the redox transformation, but the morphology becomes porous in nature. After prolonged reaction times (>24 h), the product shapes are ruptured, and as a result, tiny spherical porous nanocomposites of ∼100 nm in size are obtained. This method is highly advantageous due to its low cost, its easy operation, and a surfactant or stabilizing agent-free approach with high reproducibility, and it provides a facile but new way to fabricate porous CuO-MnO2 nanocomposites of varied shape and size. The composite nanomaterials act as efficient recyclable catalysts for nitroarene reduction in water at room temperature. The time-dependent reduction kinetics can be easily monitored by using UV-vis spectrophotometer. The catalytic system is found to be very useful toward the reduction of nitro compounds, regardless of the type and position of the substituent(s). Furthermore, it is revealed that CuO-MnO2 composite nanomaterials exhibit facet-dependent catalytic activity toward nitroarene reduction, where the (111) facet of the composite stands to be more active than that of the (100) facet. The results are also corroborated from the BET surface area measurements. It is worthwhile to mention that porous tiny spheres (product of 48 h reaction) exhibit the highest catalytic activity due to pronounced surface area and smaller size.

Hierarchical Au–CuO nanocomposite from redox transformation reaction for surface enhanced Raman scattering and clock reaction

Electrochemical processing has already manifested its prominence for obtaining well structured composite materials. The method is highly precise and is reduction potential driven. This methodology has resulted in a hierarchical Au–CuO nanocomposite from a chosen redox transformation reaction between the newly synthesized spherical and roughened Cu2O nanoparticles and HAuCl4. Thus the attractive shape as well as reducing capability of Cu2O made it promising as a starting material. The proposed redox transformation reaction does not need any additional reducing or stabilizing agents. The reduction potential value of CuO/Cu2O (+0.66 V vs. SHE) supports the quantitative reduction of Au(III) ions because of its higher reduction potential (+1.69 V vs. SHE) i.e., for the AuCl4−/Au half cell. The prescribed conditions, spontaneous redox reaction and the morphology of Cu2O nanoparticles help to produce the unique Au–CuO nanoflowers. The formation of Au–CuO nanocomposites from Cu2O nanospheres is characterised by several physical techniques such as XRD, XPS and FTIR. Finally the flower like Au–CuO nanocomposite shows higher SERS activity with 4-aminothiophenol (4-ATP) as a probe molecule than what is evident from the individual components (Au or Cu2O or CuO). Additionally the derived Au–CuO nanocomposite has also been found to be an effective catalyst for the clock reaction employing methylene blue and ascorbic acid in solution.

Fabrication of a ZnO nanocolumnar thin film on a glass slide and its reversible switching from a superhydrophobic to a superhydrophilic state

A simple, cost effective way to deposit ZnO thin films on glass slides has been observed under modified hydrothermal (MHT) conditions. The nanocolumnar growth of ZnO on glass surfaces takes place as a result of the hydrolysis of zinc sulfate by ethanolamine at 100 °C without employing any templates or surfactants. The evolved superhydrophobic thin film becomes hydrophilic upon UV light exposure and the film reverts back to its original superhydrophobic character upon storage in the dark. The water contact angle switches back and forth from 154° ± 1° to 15°. Characterization of the ZnO thin films and the nanocolumnar growth mechanism have been discussed.

Robust cubooctahedron Zn3V2O8 in gram quantity: a material for photocatalytic dye degradation in water

A simplistic, elegant approach has been invoked for the gram level synthesis of cubooctahedral Zn3V2O8 without the assistance of any template or growth directing agent. By heating on a water bath, ZnSO4 and ammonium vanadate produce unique cubooctahedral Zn3V2O7(OH)2(H2O)2. Then, cubooctahedral Zn3V2O8 is generated upon heating Zn3V2O7(OH)2(H2O)2 at a temperature of 500 °C in air. Interestingly, the morphology of Zn3V2O7(OH)2(H2O)2 remains unaltered even after complete dehydration by heat treatment. The unusual robust morphology of Zn3V2O8 exhibits enhanced photocatalytic dye mineralization activity, leaving behind Zn3V2O7(OH)2(H2O)2 and also NH4VO3. Cationic, nonionic and anionic dye degradation has become effective with a high turn over number (TON). The synthesized nanomaterial, being robust and highly photoactive, finds valuable application in environmental remediation under UV irradiation. In a nutshell, the present work provides some new insights for a low-cost and high-yielding greener synthetic protocol to produce a well defined photocatalytic material bearing a unique structure to benefit potential applications in wastewater treatment.

Green synthesis and reversible dispersion of a giant fluorescent cluster in solid and liquid phase.

A water-soluble highly fluorescent silver cluster on Au(I) surface has been synthesized with green chemistry under sunlight. The evolution of the silver cluster is synergistic, demanding gold and glutathione. The fluorescent Au(I)core-Ag(0)shell particles are huge in size and at the same time they are robust. That is why they become a deliverable fluorescing solid upon drying. Again, the giant particles run into common water miscible solvents. As a result, the fluorescence intensity increases to a great extent without any alteration of emission maxima. In this respect, acetone has been found to be the best-suited solvent. To have a universal applicability of the fluorescent clusters, the particles in the water pool of a reverse micelle have been prepared to transfer the particles into different water immiscible solvents. The comparatively lower fluorescence intensity of the particles has been ascribed to a space confinement effect. Finally, giant-cluster-impregnated yellow-orange fluorescent polymer film and fluorescent cotton wool, as well as paper substrate, have been prepared. The antibacterial activity of the fluorescent particle has also been tested involving modified cotton wool and paper substrate for Gram-negative and -positive Escherichia coli and Staphylococcus aureus, respectively.

Modified hydrothermal reaction (MHT) for CoV2O6·4H2O nanowire formation and the transformation to CoV2O6·2H2O single-crystals for antiferromagnetic ordering and spin-flop

A modified hydrothermal protocol (MHT) has been adopted for the synthesis of a single-crystal of CoV2O6·2H2O. The crystals grew as a result of prolonged hydrothermal reaction between precursor salts of CoCl2 and ammonium vanadate. At first, the adopted reaction conditions resulted in nanowires of CoV2O6·4H2O. Then with increased reaction time, nanowires changed to single crystals of molecular formula CoV2O6·2H2O. The nanowires have lengths of several tens of micrometers and average diameter of 100 nm. The well defined structure crystallizes in the orthorhombic crystal system having space group Pnma and it displays a = 5.5647(2) A, b = 10.6870(5) A, c = 11.8501(5) A, α = β = γ = 90.00°. Here, each vanadium atom is tetrahedrally connected to four oxygens where two oxygens are connected to vanadium atoms and another two connected to cobalt atoms. Magnetic moment measurement of the nanowires indicates that antiferromagnetic ordering is observed at around 14.9 K and 6.8 K and field induced antiferromagnetic to ferromagnetic (spin-flop-type) transitions have been observed at a low temperature (5–8.8 K) range while these are absent in the as-synthesized single crystals.

Intriguing Manipulation of Metal‐Enhanced Fluorescence for the Detection of CuII and Cysteine

Commercially available salicylaldehyde, in alkaline medium, exhibits strong fluorescence after one hour of UV exposure in the presence of Ag(I) . The phenolic group of salicylaldehyde is converted into the quinone form under alkaline conditions in the presence of AgNO3 , resulting in aggregated Ag(0), which causes approximately 250 times fluorescence enhancement of the in situ produced quinone. Such high silver-enhanced-fluorescence (SEF) is selectively quenched by cysteine, arginine, histidine, methionine, and tryptophan. In contrast to the other amino acids, ageing brings selectivity of the cysteine-induced quenching effect. Interestingly, Cu(II) is found to be the only metal ion that exclusively regenerates the lost fluorescence. Thus, quenching and recovery of fluorescence (Turn Off/On) can be used for the selective and sensitive detection of cysteine as well as Cu(II) ions in one pot. Alteration of the electric field density around the fluorophore (lightening rod effect) and scattering/absorption cross-section have been proposed to account for the Off/On fluorescence.