Chanchal Mondal

Fabrication of porous β-Co(OH)2 architecture at room temperature: a high performance supercapacitor.

A facile, cost-effective, surfactant-free chemical route has been demonstrated for the fabrication of porous β-Co(OH)2 hierarchical nanostructure in gram level simply by adopting cobalt acetate as a precursor salt and ethanolamine as a hydrolyzing agent at room temperature. A couple of different morphologies of β-Co(OH)2 have been distinctly identified by varying the mole ratio of the precursor and hydrolyzing agent. The cyclic voltammetry measurements on β-Co(OH)2 displayed significantly high capacitance. The specific capacitance obtained from charge-discharge measurements made at a discharge current of 1 A/g is 416 F/g for the Co(OH)2 sample obtained at room temperature. The charge-discharge stability measurements indicate retention of specific capacitance about 93% after 500 continuous charge-discharge cycles at a current density of 1 A g(-1). The capacitive behavior of the other synthesized morphology was also accounted. The nanoflower-shaped porous β-Co(OH)2 with a characteristic three-dimensional architecture accompanied highest pore volume which made it promising electrode material for supercapacitor application. The porous nanostructures accompanied by high surface area facilitates the contact and transport of electrolyte, providing longer electron pathways and therefore giving rise to highest capacitance in nanoflower morphology. From a broad view, this study reveals a low-temperature synthetic route of β-Co(OH)2 of various morphologies, qualifying it as supercapacitor electrode material.

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.

Preformed ZnS nanoflower prompted evolution of CuS/ZnS p–n heterojunctions for exceptional visible-light driven photocatalytic activity

In this report, CuS/ZnS heterojunctions were obtained through ion-exchange between as-prepared ZnS nanoflowers (synthesized using a modified hydrothermal route) and copper(II) sulfate in an aqueous solution. Then, the as-prepared CuS/ZnS heterojunctions prompted exceptional visible-light driven (λ ≥ 400 nm) photocatalytic activity, which surpasses almost all the reported ones. The photocatalyst performs best when a particular ratio of CuS and ZnS is maintained during the synthesis. This is observed at the ratio where CuS anchors onto the pre-formed ZnS, and gives rise to an effective heterojunction, which is found to be capable of degrading cationic dyes (such as methylene blue, crystal violet, and malachite green) within 120 s under visible-light exposure. Furthermore, the efficiency of the photocatalyst is preserved up to the 4th cycle of operation without any photo-corrosion. The dramatic enhancement in the visible-light photocatalytic performance of the CuS/ZnS heterojunctions over pure ZnS and CuS can be attributed to the effective electron–hole separation at the interfaces of the two semiconductors due to the formation of a superior heterojunction between the n-type semiconductor, ZnS, and p-type semiconductor, CuS, which facilitates the interfacial transfer of photoinduced carriers. The CuS loading onto ZnS is crucial to make the composite exceptionally photoactive for fast kinetics, which leads to prompt waste water treatment. The present study provides a new avenue to gain in-depth insight to the design of a highly efficient photocatalyst with heterojunctions.

Tin oxide with a p–n heterojunction ensures both UV and visible light photocatalytic activity

Tuning of the tin oxide (SnO/SnO2) heterojunction (TOHJ) has been made possible by heating the as-prepared p-type SnO semiconductor in air in a controlled fashion. Thus a better photocatalytic activity for dye degradation under UV, visible as well as solar light irradiation was achieved. Multiple reflection of light and the TOHJ of SnO plates facilitate the photocatalysis reactions.

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.