Jayasmita Jana

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.

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.

One pot synthesis of intriguing fluorescent carbon dots for sensing and live cell imaging.

We report a simple one-pot synthesis of highly fluorescent carbon dots (CDs) via modified hydrothermal (MHT) treatment of alkaline solution of dopamine and cysteine. These CDs (λex=320 nm, λem=390 nm, and quantum yield ∼ 5.1%) are of ∼ 2-3 nm in diameter. Further attempt of synthesizing CDs in some common water-miscible solvents ends up the fact that the MHT product from acetone medium is nonfluorescent. However, CDs, produced in aqueous medium, are so stable that they can be dried as a deliverable solid (WCD) without any alteration of fluorescing property if reversibly dispersed in water. Fluorescence of WCD is quenched selectively in acetone. Quenching occurs presumably due to the disruption of radiative recombination along with the hindrance in quantum confinement of the emissive energy traps to the particle surface. Successive quenching of fluorescence of WCD in different acetone concentration admixed in water paves the way to selective acetone sensing (LOD=8.75 × 10(-7) M). The synthesized CDs (in aqueous medium) are cytocompatible and are efficient fluorescent probe for cell imaging. Only living cells are recognized exclusively from fluorescence imaging leaving aside dead cells, while cells are treated with CDs.

Enlightening surface plasmon resonance effect of metal nanoparticles for practical spectroscopic application

Surface plasmon resonance (SPR) is the manifestation of a resonance effect due to the interaction of conduction electrons of metal nanoparticles with incident photons. The interaction relies on the size and shape of the metal nanoparticles and on the nature and composition of the dispersion medium. By understanding the mechanistic aspects of the interaction of altered nanoparticle morphologies together with the associated medium effect, a new technology has been developed for careful spectroscopic monitoring. Each change can be followed by various spectroscopic techniques, which lead to sensing applications and imaging events. From successful SPR band monitoring through spectroscopy, new optoelectronic technology and sensors, including color sensors and sensor devices, have been developed. In this review, we discuss the important role of SPR and its efficacy to heighten practical spectroscopic applications.

Photoproduced fluorescent Au(I)@(Ag2/Ag3)-thiolate giant cluster: an intriguing sensing platform for DMSO and Pb(II).

Synergistic evolution of fluorescent Au(I)@(Ag2/Ag3)-thiolate core-shell particles has been made possible under the Sun in presence of the respective precursor coinage metal compounds and glutathione (GSH). The green chemically synthesized fluorescent clusters are giant (∼600 nm) in size and robust. Among all the common water miscible solvents, exclusively DMSO exhibits selective fluorescence quenching (Turn Off) because of the removal of GSH from the giant cluster. Again, only Pb(II) ion brings back the lost fluorescence (Turn On) leaving aside all other metal ions. This happens owing to the strong affinity of the sulfur donor of DMSO for Pb(II). Thus, employing the aqueous solution containing the giant cluster, we can detect DMSO contamination in water bodies at trace level. Besides, a selective sensing platform has emerged out for Pb(II) ion with a detection limit of 14 × 10(-8) M. Pb(II) induced fluorescence recovery is again vanished by I(-) implying a promising route to sense I(-) ion.

Synergism of gold and silver invites enhanced fluorescence for practical applications

Synergism of gold and silver, causing enhanced fluorescence, has been reported in cluster science with higher photochemical stability and practical applications. The electronic factor, nuclearity, size effect etc., bring autofluorescence, doping/alloying, aggregation induced fluorescence, core–shell interaction, oxidation induced interaction and silver effect. The plausible interplaying mechanisms behind the synergism in the bimetallic clusters has been focused upon. Appropriate selection of the template is mandatory to achieving AuAg bimetallic clusters. Such templates are scarce and only a few are reported in the literature while templates to obtain individual Au and Ag clusters are numerous. Semi/complete reduced gold and non/complete reduced silver are one of the important features of such bimetallic clusters. Mingled Au and Ag has a profound effect on the stability, electronic structure and band energy of the bimetallic clusters. The arrangement of Au and Ag atoms in the bimetallic clusters is also a matter of interest. The bimetallic AuAg clusters are found to be superior to not only individual Au/Ag clusters but also carbon and semiconductor quantum dots, considering their emissive nature, toxicity, ease of synthesis, robustness etc. Water miscible as well as water immiscible solvents are equally efficient for the production of AuAg bimetallic clusters. Finally, such bimetallic clusters have proved to be unique candidates in the context of practical applications, namely sensing, catalysis, surface enhanced Raman spectroscopy (SERS), metal enhanced fluorescence (MEF), bio-imaging, synthesis of anti-bacterial cotton/papers etc. The ratio of Au and Ag not only tune the fluorescence behavior but also toxicity, as described.

Fluorescence enhancement via varied long-chain thiol stabilized gold nanoparticles: A study of far-field effect

Metal enhanced fluorescence of carbon dots has been reported in aqueous solution. Moderately fluorescing carbon dots (λex=360nm and λem=440nm) of 6-8nm diameters (CDA) have been synthesized from freshly prepared aqueous ascorbic acid solution under modified hydrothermal treatment. The CDA fluorescence is quenched at the close proximity with gold nanoparticles (AuNPs). Here, a substrate specific near-field electric field distribution is pronounced. Anticipating distance dependent fluorescence enhancement phenomenon, long-chain aliphatic thiol capped AuNPs are introduced to improve fluorescence of moderately fluorescing CDAs. The long-chain aliphatic thiols act as spacers between CDA and AuNP. Interestingly, the fluorescence of CDA is observed to be enhanced successively as the chain lengths of aliphatic thiols are increased. Fluorescing CDA, upon excitation, transfers energy to the nearby AuNP and a plasmon is induced. This plasmon radiates in the far-field resulting in fluorescence enhancement of CDAs. Such an interesting enhancement in emission with metallic gold is termed as gold enhanced fluorescence. This far-field effect for fluorescence enhancement of CDA particles becomes a general consensus in solution with varied long-chain aliphatic amine ligand capped silver nanoparticles (AgNPs). Finally, consequence of far-field effect of fluorescence enhancement has been observed while derivatized AuNP and AgNP are introduced into the CDA solution simultaneously which is described as reinforced fluorescence enhancement due to coupled plasmonic radiation.

Remarkable Facet Selective Reduction of 4-Nitrophenol by Morphologically Tailored (111) Faceted Cu2O Nanocatalyst

In this work, we have disclosed the facile syntheses of morphologically diverse Cu2O nanoparticles using our laboratory designed modified hydrothermal reactor employing low-cost copper (II) acetate precursor compounds. The reaction conditions dovetail the effect of ethylene glycol (EG) and glucose to exclusively evolve the morphology tuned Cu2O nanomaterial at different pHs. The morphology tuning produces octahedron (Oh), dwarf hexapod (DHP), and elongated hexapod (EHP) Cu2O structures only with the optimized reagent concentrations. Interestingly, all of them were bestowed with a (111) facet, a superlative facet for facile nitroarene reduction. Thus, the morphology reliant catalytic reaction becomes evident. However, when used individually, EG and glucose evolve ill-defined CuO/Cu2O and Cu2O structures, respectively. We have observed that a change in pH of the medium at the onset of the reaction is obligatory for the evolution of tailor-made morphologically diverse Cu2O nanoparticles. However, preformed Cu2O particles do not suffer further structure/morphology changes under deliberate pH (6.0–9.0) change. With the as-obtained Oh, DHP, and EHP Cu2O structures, we further delve into the realm of catalysis to understand the splendor of the nanocatalyst, morphology and surface area dependence, facet selective reactivity, and other factors affecting the catalytic efficiency. The remarkable rate of catalysis of 4-nitrophenol (4-NP), evident from the catalyst activity parameter (ka = 123.6 g–1 s–1), to produce 4-aminophenol in the presence of a reducing agent like sodium borohydride (NaBH4) of the as-prepared catalysts is evidence of the collaborative effects of the effective surface area, surface positive charge, and active (111) facet of the Cu2O nanocatalyst. We have also studied the effect of other common anions, namely, Cl–, NO2–, NO3–, CO32–, and SO42– on the reduction process. To obtain a general consensus about facets, we compared (100) and (111) faceted Cu2O nanocatalysts not only for 4-NP reduction but also for the reduction of toxic chromium Cr(VI) in the presence of formic acid to further emphasize the importance of facet selectivity in catalysis and the versatility of the morphology tuned as-prepared Cu2O.

An account of doping in carbon dots for varied applications

Abstract In recent times, carbon dots have emerged as new fluorescent probes. The unique electronic and physical properties of carbon dots find significant applications in different fields like sensing, cell-imaging, catalysis, medicine etc. The intriguing fluorescence, cytocompatibility and nontoxicity of carbon dots are considered for their use in biological science also. The inherent fluorescence of carbon dots is dependent on their structure, method of synthesis etc. However, the fluorescence of carbon dots is known to improve through different chemical manipulation techniques. Among them, doping of heteroatoms like nitrogen, boron, phosphorous, sulphur etc. has made a mark as an interesting protocol to improve the emissive property of carbon dots. In this review, the recent processes of doping have been discussed along with the application of doped carbon dots in different fields.

Solvent Polarity-Dependent Behavior of Aliphatic Thiols and Amines toward Intriguingly Fluorescent AuAgGSH Assembly

Highly stable fluorescent glutathione (GSH)-protected AuAg assembly has been synthesized in water under UV irradiation. The assembly is composed of small Ag2/Ag3 clusters. These clusters gain stability through synergistic interaction with Au(I) present within the assembly. This makes the overall assembly fluorescent. Here, GSH acts as a reducing as well as stabilizing agent. The assembly is so robust that it can be vacuum-dried to solid particles. The as-obtained solid is dispersible in nonaqueous solvents. The interaction between solvent and the assembly provides stability to the assembly, and the assembly shows fluorescence. It is interesting to see that the behavior of long-chain aliphatic thiols or amines toward the fluorescent assembly is altogether a different phenomenon in aqueous and nonaqueous mediums. The assembly gets ruptured in water due to direct interaction with long-chain thiols or amines, whereas in nonaqueous medium, solvation of added thiols or amines becomes pronounced, which hinders the interaction of solvent with the assembly. However, the fluorescence of the assembly is always quenched with thiols or amines no matter what the solvent medium is. In aqueous medium, the fluorescence quenching by aliphatic thiol or amine becomes pronounced with successive decrease in their chain length, whereas in nonaqueous medium, the trend is just reversed with chain length. The reasons behind such an interesting reversal of fluorescence quenching in aqueous and nonaqueous solvents have been discussed explicitly. Again, in organic solvents, thiol or amine-induced quenched fluorescence is selectively recovered by Pb(II) ion without any alteration of excitation and emission maxima. This phenomenon is not observed in water because of the ruptured fluorescent assembly. The fluorescence recovery by Pb(II) and unaltered emission peak only in nonaqueous solvent unequivocally prove the engagement of Pb(II) with thiols or amines, which in turn revert the original solvent-supported stabilization of the assembly.