Milind V. Kulkarni

Nanowires of silver-polyaniline nanocomposite synthesized via in situ polymerization and its novel functionality as an antibacterial agent.

Silver-polyaniline (Ag-PANI) nanocomposite was synthesized by in situ polymerization method using ammonium persulfate (APS) as an oxidizing agent in the presence of dodecylbenzene sulfonic acid (DBSA) and silver nitrate (AgNO(3)). The as synthesized Ag-PANI nanocomposite was characterized by using different analytical techniques such as UV-visible (UV-vis) and Fourier transform Infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FE-SEM), thermo gravimetric analysis (TGA), X-ray diffraction (XRD), and transmission electron microscopy (TEM). UV-visible spectra of the synthesized nanocomposite showed a sharp peak at ~420 nm corresponding to the surface plasmon resonance (SPR) of the silver nanoparticles (AgNPs) embedded in the polymer matrix which is overlapped by the polaronic peak of polyaniline appearing at that wavelength. Nanowires of Ag-PANI nanocomposite with diameter 50-70 nm were observed in FE-SEM and TEM. TGA has indicated an enhanced thermal stability of nanocomposite as compared to that of pure polymer. The Ag-PANI nanocomposite has shown an antibacterial activity against model organisms, a gram positive Bacillus subtilis NCIM 6633 in Mueller-Hinton (MH) medium, which is hitherto unattempted. The Ag-PANI nanocomposite with monodispersed AgNPs is considered to have potential applications in sensors, catalysis, batteries and electronic devices.

Template-free synthesis of nanostructured CdxZn1-xS with tunable band structure for H2 production and organic dye degradation using solar light

We have demonstrated a template-free large-scale synthesis of nanostructured Cd(x)Zn(1-x)S by a simple and a low-temperature solid-state method. Cadmium oxide, zinc oxide, and thiourea in various concentration ratios are homogenized at moderate temperature to obtain nanostructured Cd(x)Zn(1-x)S. We have also demonstrated that phase purity of the sample can be controlled with a simple adjustment of the amount of Zn content and nanocrystalline Cd(x)Zn(1-x)S(x = 0.5 and 0.9) of the hexagonal phase with 6-8 nm sized and 4-5 nm sized Cd(0.1)Zn(0.9)S of cubic phase can be easily obtained using this simple approach. UV-vis and PL spectrum indicate that the optical properties of as synthesized nanostructures can also be modulated by tuning their compositions. Considering the band gap of the nanostructured Cd(x)Zn(1-x)S well within the visible region, the photocatalytic activity for H2 generation using H2S and methylene blue dye degradation is performed under visible-light irradiation. The maximum H2 evolution of 8320 μmol h(-1)g(-1) is obtained using nanostructured Cd(0.1)Zn(0.9)S, which is four times higher than that of bulk CdS (2020 μmol h(-1) g(-1)) and the reported nanostructured CdS (5890 μmol h(-1)g(-1)). As synthesized Cd(0.9)Zn(0.1)S shows 2-fold enhancement in degradation of methylene blue as compared to the bulk CdS. It is noteworthy that the synthesis method adapted provides an easy, inexpensive, and pollution-free way to synthesize very tiny nanoparticles of Cd(x)Zn(1-x)S with a tunnable band structure on a large scale, which is quite difficult to obtain by other methods. More significantly, environmental benign enhanced H2 production from hazardous H2S using Cd(x)Zn(1-x)S is demonstrated for the first time.

Hierarchical nanostructures of CdIn2S4via hydrothermal and microwave methods: efficient solar-light-driven photocatalysts

We have demonstrated the synthesis of nanostructured CdIn2S4 with a fascinating ‘marigold flower’ morphology using a hydrothermal method, and mixed morphologies (flowers, spheres and pyramids) using a microwave method. In the microwave synthesis, the product was formed within 15 min, whereas by the hydrothermal method more than 24 h was required. In the microwave method, various capping agents were used that result in different particle morphologies. Hydrothermal formation of crystalline CdIn2S4 nanotubes in methanol showed a significant effect of reaction medium on morphology. Synthesis of these crystalline CdIn2S4 nanopyramids and ‘marigold flowers’ has also been demonstrated using microwave synthesis for the first time. An XRD study showed a cubic spinel structure for CdIn2S4 prepared by both methods. The band gap for CdIn2S4 was 2.27 eV when synthesized using the microwave method, and 2.23 eV using the hydrothermal method, implying that the microwave method produces a lower particle size than the hydrothermal method. A noteworthy aspect of this work is that we obtained novel ternary chalcogenide hierarchical nanostructures by simple hydrothermal and microwave methods. Considering that the band gap of the hierarchical CdIn2S4 is within the visible region, we compared its ability to photocatalytically degrade methylene blue (MB) with that of CdS. The marigold flowers, nanoparticle spheres and nanopyramids of CdIn2S4 synthesised by microwave method gave almost 30% enhancement in the degradation of MB as compared to CdS under direct sunlight. This is of importance, considering that CdIn2S4 has potential for applications in solar energy conversion and opto-electronic devices.

Environmentally benign enhanced hydrogen production via lethal H2S under natural sunlight using hierarchical nanostructured bismuth sulfide

Nanorods and hierarchical nanostructures (dandelion flowers) of bismuth sulfide (Bi2S3) were synthesized using a solvothermal method. The effects of solvents such as water and ethylene glycol on the morphology and size of the Bi2S3 nanostructures were studied. A structural study showed an orthorhombic phase of Bi2S3. We observed nanorods 30–50 nm in diameter and dandelion flowers assembled with these nanorods. A formation mechanism for the hierarchical nanostructures of Bi2S3 is proposed. Based on the tuneable band gap of these nanostructures in the visible and near-IR regions, we demonstrated the photocatalytic production of hydrogen from H2S under normal sunlight. Abundantly available toxic H2S was used to produce hydrogen under normal sunlight conditions. We observed an excellent hydrogen production of 8.88 mmol g−1 h−1 under sunlight (on a sunny day between 11.30 am and 2.30 pm) for the Bi2S3 flowers and 7.08 mmol g−1 h−1 for the nanorods. The hierarchical nanostructures suppress charge carrier recombination as a result of defects, which is ultimately responsible for the higher activity. The evolution of the hydrogen obtained is fairly stable when the catalyst is used repeatedly. The evolution of hydrogen via water splitting was observed to be lower than that via H2S splitting. Bi2S3 was observed to be a good eco-friendly photocatalyst active under natural sunlight. The photo-response study showed that the Bi2S3 microstructures are good candidates for applications in highly sensitive photo-detectors and photo-electronic switches.

Nanostructured 2D MoS2 honeycomb and hierarchical 3D CdMoS4 marigold nanoflowers for hydrogen production under solar light

Unique two dimensional (2D) honeycomb layered MoS2 nanostructures and hierarchical 3D marigold nanoflowers of CdMoS4 were designed using a template free and facile solvothermal method. The MoS2 structure is depicted with a sheet like morphology with lateral dimensions of 5–10 μm and a thickness of ∼200 nm and a honeycomb nanostructure architecture produced via the self-assembling of vertically grown thin hexagonal nanosheets with a thickness of 2–3 nm. The 3D CdMoS4 marigold nanoflower architecture comprised thin nanopetals with lateral dimensions of 1–2 μm and a thickness of a few nm. The CdMoS4 and MoS2 structures displayed hydrogen (H2) production rates of 25 445 and 12 555 μmol h−1 g−1, respectively. The apparent quantum yields of hydrogen production were observed to be 35.34% and 17.18% for CdMoS4 and MoS2, respectively. The 3D nanostructured marigold flowers of CdMoS4 and honeycomb like 2D nanostructure of MoS2 were responsible for higher photocatalytic activity due to inhibition of the charge carrier recombination. The prima facie observation of H2 production showed that the ternary semiconductor confers enhanced photocatalytic activity for H2 generation due to its unique structure. Such structures can be designed and implemented in other transition metal dichalcogenide based ternary materials for enhanced photocatalytic and other applications.

Functionality of bismuth sulfide quantum dots/wires-glass nanocomposite as an optical current sensor with enhanced Verdet constant

We report optical studies with magneto-optic properties of Bi2S3 quantum dot/wires-glass nanocomposite. The size of the Q-dot was observed to be in the range 3–15 nm along with 11 nm Q-wires. Optical study clearly demonstrated the size quantization effect with drastic band gap variation with size. Faraday rotation tests on the glass nanocomposites show variation in Verdet constant with Q-dot size. Bi2S3 Q-dot/wires glass nanocomposite demonstrated 190 times enhanced Verdet constant compared to the host glass. Prima facie observations exemplify the significant enhancement in Verdet constant of Q-dot glass nanocomposites and will have potential application in magneto-optical devices.

Novel and stable Mn2+@Bi2S3 quantum dots–glass system with giant magneto optical Faraday rotations

Novel, highly stable Bi2S3 and Bi2−xMnxS3 quantum dots (QDs)–glass optical nanosystems were architectured successfully. These advanced nanosystems were characterized by High Resolution Transmission Electron Microscopy (HRTEM), UV-Vis-NIR spectroscopy and room temperature photoluminescence (PL) measurements. HRTEM of the Bi2S3 QD–glass nanosystem revealed the size of Bi2S3 QDs to be in the range of 5–7 nm. However, for the Bi2−xMnxS3 quantum dots (QDs)–glass nanosystem, the size of Bi2−xMnxS3 QDs were around 3–5 nm. The Bi2S3 quantum dots exhibit an orthorhombic structure with good crystallinity. Bi2−xMnxS3 QDs also exhibit the same structure with lower ‘d’ values due to Mn2+ incorporation. The optical study clearly reveals the growth of Bi2S3 and Bi2−xMnxS3 QDs in the glass matrix. Interestingly, a blue shift of the transmission edge was observed by incorporation of Mn2+ under the same thermodynamic conditions. Photoluminescence spectra show distinct Bi2S3 and Mn2+ related emissions, which are excited via the Bi2S3 host lattice. The Mn2+ emission intensity at 580 nm wavelength confirms the existence of Mn2+ in the Bi2S3 lattice in the glass matrix. The magneto optical Faraday rotation measurements were performed at room temperature with magnetic fields up to 5.6 mT for all the samples. Significantly, we observed a giant heightening in the Verdet constant i.e. from 159.34 to 507.30 deg T−1 cm−1 after incorporation of Mn2+ (0 to 0.4 moles), which is much higher than conventional single crystal systems like TGG, BFG (76.82 deg T−1 cm−1) as well as other materials reported so far. Our strategy provides a versatile route to controlled magneto optical properties of anisotropic semiconductor nanomaterials, which may create new opportunities for photonic devices, magnetic and current sensor applications.

Nanostructured CdS sensitized CdWO4 nanorods for hydrogen generation from hydrogen sulfide and dye degradation under sunlight.

In this report, CdS nanoparticles have been grown on the surface of CdWO4 nanorods via an in-situ approach and their high photocatalytic ability toward dye degradation and H2 evolution from H2S splitting under visible light has been demonstrated. The structural and optical properties as well as morphologies with varying amount of CdS to form CdS@CdWO4 have been investigated. Elemental mapping and high resolution transmission electron microscopy (HRTEM) analysis proved the sensitization of CdWO4 nanorods by CdS nanoparticles. A decrease in the PL emission of CdWO4 was observed with increasing amount of CdS nanoparticles loading possibly due to the formation of trap states. Considering the band gap in visible region, the photocatalytic study has been performed for H2 production from H2S and dye degradation under natural sunlight. The steady evolution of H2 was observed from an aqueous H2S solution even without noble metal. Moreover, the rate of photocatalytic H2 evolution over CdS modified CdWO4 is ca. 5.6 times higher than that of sole CdWO4 under visible light. CdS modified CdWO4 showed a good ability toward the photo-degradation of methylene Blue. The rate of dye degradation over CdS modified CdWO4 is ca. 7.4 times higher than that of pristine CdWO4 under natural sunlight. With increase in amount of CdS nanoparticle loading on CdWO4 nanorods the hydrogen generation was observed to be decreased where as dye degradation rate is increased. Such nano-heterostructures may have potential in other photocatalytic reactions.

Architecture of the CdIn2S4/graphene nano-heterostructure for solar hydrogen production and anode for lithium ion battery

The facile single step template free synthesis of hierarchical CdIn2S4/graphene nano-heterostructures with multi-functionality as a photocatalyst for solar hydrogen production and as an anode for lithium ion battery has been demonstrated. The nanopetals of CdIn2S4 are decorated on the graphene which shows extended visible light absorption. Hence, the photocatalytic hydrogen evolution study is performed under solar light. The nano-heterostructure showed excellent photocatalytic activity (4495 μmol h−1 per 0.2 g) for hydrogen production. The enhanced photocatalytic activity is attributed to the inhibition of charge carrier recombination due to graphene which acts as an excellent electron collector and transporter. Furthermore, the use of nano-heterostructures as an anode for Li-ion batteries demonstrated very high reversible capacity i.e. 678 mA h g−1 which on cycling, kept at 608 mA h g−1 at an applied current of 150 mA g−1 for 225 cycles and exhibited good rate capability. The excellent Li-storage properties of the nano-heterostructures is associated with the hierarchical flower like structure, high porosity of CdIn2S4 and the fast electron kinetics offered by the graphene support.

Self assembly of nanostructured hexagonal cobalt dendrites: an efficient anti-coliform agent

Highly crystalline self assemblies of three dimensional cobalt nanostructures are successfully synthesized by an electrochemical method without any template and surfactants. The cobalt nanostructures obtained by using two precursors, cobalt chloride (CoCl2) and cobalt acetate [(CH3–COO)2Co], shows similar dendritic structure, but with different hierarchical architecture. The architecture of cobalt dendrites (Co-DNDs) prepared by using CoCl2 consists of a long central trunk with hierarchical nanostructures of well aligned dendrites of length in the range 15–20 μm and sub branch is in the range 100–200 nm, while Co-DNDs prepared by using (CH3–COO)2Co additionally shows unique feature of hexagonal nanopoles orthogonal to main trunk. Well defined and highly crystalline Co-DNDs were obtained within thirty seconds at 15 V. Architecture of such well aligned and highly crystalline Co-DNDs with hexagonal fixtures within 30 seconds reaction is hitherto unattempted. The as-synthesized Co-DNDs showed an efficient antibacterial activity against model organisms, Bacillus subtilis NCIM 2063, Escherichia coli NCIM 2931, and fecal coliforms in a sewage waste. The inactivation of bacterial growth is due to the generation of reactive oxygen species (ROS) mediated rupture of cell membrane. An inactivation of fecal coliforms in the sewage wastewater is significant in eradicating water-borne diseases. This is an economical approach as compared to conventional and expensive metal nanoparticles like silver and gold.