Sanjay K. Apte

A Facile Template-Free Approach for the Large-Scale Solid-Phase Synthesis of CdS Nanostructures and Their Excellent Photocatalytic Performance

The simple, template-free, low-temperature, large-scale synthesis of nanostructured CdS with the hexagonal wurtzite phase from bulk cadmium oxide under solid-phase conditions is demonstrated for the first time. The novel approach involves the homogenization of cadmium oxide (CdO) and thiourea in various stoichiometric ratios at moderate temperature. Among the different molar ratios of CdO and thiourea studied, the CdO/NH(2) CSNH(2) molar ratio of 1:2 is found to be the best to obtain highly pure CdS. The obtained CdS nanostructures exhibit excellent cubic morphology and high specific surface area with a particle size in the range of 5-7 nm. The bandgap of the nanostructured CdS is in the range of 2.42 to 2.46 eV due to its nanocrystalline nature. In photoluminescence studies, emission is observed at 520.34 and 536.42 nm, which is characteristic of the greenish-yellow region of the visible spectrum. Considering the bandgap of the CdS is within the visible region, the photocatalytic activity for H(2) generation and organic dye degradation are performed under visible-light irradiation. The maximum H(2) evolution of 2945 μmol h(-1) is obtained using nanostructured CdS prepared in the 1:2 ratio, which is three times higher than that of bulk CdS (1010 μmol h(-1) ). CdS synthesized using the 1:2 molar ratio shows maximum methylene blue degradation (87.5%) over a period of 60 min, which is approximately four times higher than that of bulk CdS (22%). This amazing performance of the material is due to its nanocrystalline nature and the high surface area of the CdS. The proposed simple methodology is believed to be a significant breakthrough in the field of nanotechnology, and the method can be further generalized as a rational preparation scheme for the large-scale synthesis of various other nanostructured metal sulfides.

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.

Confinement of nano CdS in designated glass: a novel functionality of quantum dot–glass nanosystems in solar hydrogen production

The present work is the investigation of our novel approach to designing quantum dot–glass nanosystems by confining nano CdS in designated glass and the first employment of such a quantum dot system in solar hydrogen production. The CdS quantum dots were grown in a special glass matrix, which involved a sequence of steps. The obtained glass was of uniformly bright yellow in color and the bulk glass was pulverized to a fine powder of micron size particles. The glass powder was characterized structurally and morphologically. X-Ray diffraction and electron diffraction patterns reveal a hexagonal crystallite system for the CdS quantum dots. Field emission scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray fluorescence spectroscopy and chemical leaching with HCl studies demonstrate that the 2.5 nm size CdS quantum dots distribute homogeneously in a monodispersed form in the glass domain and on the surface with a “partially embedded exposure” configuration. This disposition imparts an excellent photostability against photocorrosion and also a facile catalytic function. Therefore, even a very small amount of CdS quantum dots (0.005 g per gram of glass powder) is able to photodecompose H2S under visible light (λ ≥ 420 nm) both in alkaline and pure aqueous media and produce solar hydrogen with markedly high quantum yields of 17.5 and 11.4%, respectively at 470 nm. Salient features like reusability after simple washing, corrosionless-stability and remarkable catalytic activity of this quantum dot–glass nanosystem are brought forth by our novel catalyst design and are much acclaimed in large scale solar H2 production.

P1.8.3 Ink-Jet Printed Conducting Polyaniline based Flexible Humidity Sensor

Ink-Jet Printed, Intrinsically Conducting Polymer (ICP), polyaniline have been used for humidity sensing at room temperature. Polyaniline based, aqueous ink-jet printable ink has been synthesized by single step, chemical oxidative polymerization technique. Sulphonic acids were used as a dopant during the in-situ polymerization process. This is a single step polymerization process for the direct synthesis of conducting emeraldine salt phase of the polymer as an ink formulation. The synthesized polyaniline ink was further characterized by spectroscopic (UV-Vis. and FT-IR) analysis which confirmed the presence of conducting emeraldine salt phase of the polymer. The viscosity of the ink was measured by using Brook-field viscometer. The successive trials were performed for the printing of IDT pattern on the flexible, untreated polymer substrate using HP ink-jet- printer. The printed sensor was subjected for the humidity sensing measurements. The change in the resistance with change in the %RH was observed. It is suggested that the increase in conductivity at high humidity may be related to a vapour-induced change in the transfer of charge carriers between the polymer chains. The synthesized polyaniline based ink can also be considered as a good candidate for variety of ink-jet printed low cost electronics devices.

Eco-friendly solar light driven hydrogen production from copious waste H2S and organic dye degradation by stable and efficient orthorhombic CdS quantum dots–GeO2 glass photocatalyst

It is renowned that the oil refineries are venting off 15–20% H2S and hardly 5% has been utilized to produce sulphur and water ubiquitously by the Claus process. This process is un-economical, highly polluting and by-products create further acute environmental problems. Here, we have demonstrated the significant approach of the conversion of poisonous H2S into H2 by stable orthorhombic QD–CdS–glass nanosystems using a most abundant solar light energy source. This is an eco-friendly process that produces cheaper hydrogen as well as degrades organic dyes efficiently. We have investigated a novel, Q-CdS (highly mono-dispersed) germanate glass nanocomposite. Surprisingly, the CdS quantum dots (QDs) obtained in the glass matrix are orthorhombic in structure and highly thermally stable. Generally, the orthorhombic CdS powder is in a metastable state i.e. unstable at normal conditions. The quantum dots of 4–14 nm size of CdS were grown for the first time in the germanate glass. The confinement of orthorhombic CdS was studied using UV-Vis spectroscopy and photoluminescence. There is a drastic change in the band gap of glass without CdS nanocrystals (3.16 eV) as compared to the glass with orthorhombic CdS QDs (2.25 eV). Considering the suitable band gap of the CdS quantum dot–glass for the visible light absorption, the studies of the photocatalytic activity for H2 generation and dye degradation was performed under visible light irradiation for the first time. High H2 evolution, i.e. 3780 μmol h−1, was obtained, which is much higher than earlier reported for CdS nano-powder. More significantly, the catalyst is stable and easily regenerated as compared to other normal catalysts. The glass nanocomposite also showed excellent methylene blue degradation under visible light irradiation. Such orthorhombic QD–CdS–glass nanocomposites have great significance because they have potential applications in solar cell, LED and other optoelectronic devices.

A novel template free, one pot large scale synthesis of cubic zinc sulfide nanotriangles and its functionality as an efficient photocatalyst for hydrogen production and dye degradation

Herein, we have demonstrated a novel, facile, template free method for the synthesis of nanostructured zinc sulfide from bulk zinc oxide. This synthesis method may provide an easy, inexpensive and pollution free way to synthesize nanostructured zinc sulfide on a large scale. Zinc oxide and thiourea in various stoichiometric ratios were homogenized at moderate temperature to obtain zinc sulfide. The phase pure nanostructured cubic zinc sulfide was obtained using a 1 : 2 molar ratio of zinc oxide & thiourea and in excess of thiourea as well. Surprisingly, monodispersed nanotriangles of zinc sulfide were obtained using all molar ratios of zinc oxide and thiourea. The nanotriangles of size 5–6 nm were obtained for zinc sulfide of a 1 : 2 molar ratio. The band gap of nanostructured zinc sulfide was observed to be in the range of 3.86 to 3.75 eV, which is higher than that of the reported value. The blue shift was obtained due to the nanocrystalline nature of the zinc sulfide. Considering the significant morphology of zinc sulfide, it has been used as a photocatalyst for water splitting to produce hydrogen and for degradation of methylene blue as well. The hydrogen evolution rate was observed to be 2050 μmol h−1 g−1, which is much more than the bulk zinc sulfide (410 μmol h−1 g−1) as well as reported nanostructured ZnS. Three fold enhancements in the degradation of methylene blue as compared to bulk zinc sulfide have also been observed. The proposed simple methodology is believed to be a significant breakthrough in the field of nanotechnology and the method can be further generalized as a rational preparation scheme for the large-scale synthesis of various other nanostructured metal sulfides.

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 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.

Nano‑hydroxyapatite and its contemporary applications

Combination of nano‑sized hydroxyapatite (nHA) with restorative materials like glass ionomer cement and composite resins has been reported recently in 2011. The documented effects of these nano‑sized particles on the chemistry of these materials include increased biocompatibility and mechanical strength. nHA has been utilized for various applications like pulp capping agent, root canal sealer, filler for bleaching agents and toothpastes, osseo‑conductive bone graft etc., A nHA has been obtained using natural bovine bone, carbon template technique, hydroxyapatite‑chitosan template technique, wet precipitation technique, plasma spraying technique etc. This paper presents a review of the various aspects of nHA and summarizes the methods of fabrications and potential clinical applications of the same.