Rajendra P. Panmand

A green process for efficient lignin (biomass) degradation and hydrogen production via water splitting using nanostructured C, N, S-doped ZnO under solar light

Herein, we have reported the simultaneous water splitting and lignin (biomass) degradation using C, N and S-doped ZnO nanostructured materials. The synthesis of C, N and S-doped ZnO was achieved via calcination of bis-thiourea zinc acetate (BTZA) complex. Calcination of the complex at 500 °C results in the formation of C, N, and S doping in a mixed phase of ZnO/ZnS, whereas calcination at 600 °C gives a single phase of ZnO with N and S-doping, which is confirmed by XRD, XPS and Raman spectroscopy. The band gap of the calcined samples was observed to be in the range of 2.83–3.08 eV. Simultaneous lignin (waste of paper and pulp mills) degradation and hydrogen (H2) production via water splitting under solar light has been investigated, which is hitherto unattempted. The highest degradation of lignin was observed with the sample calcined at 500 °C, i.e., C, N, S-doped ZnO/ZnS when compared to the sample calcined at 600 °C, i.e., N and S doped ZnO. The degradation of lignin confers the formation of a useful fine chemical as a by-product, i.e., 1-phenyl-3-buten-1-ol. However, excellent H2 production, i.e., 580, 584 and 643 μmol h−1 per 0.1 g, was obtained for the sample calcined at 500, 550 and 600 °C, respectively. The photocatalytic activity obtained is considerably higher as compared to earlier reported visible light active oxide and sulfide photocatalysts. The reusability study shows a good stability of the photocatalyst. The prima facie observations show that lignin degradation and water splitting is possible with the same multifunctional photocatalyst without any scarifying agent.

Self-assembled hierarchical nanostructures of Bi2WO6 for hydrogen production and dye degradation under solar light

Three dimensional (3D) hierarchical nanostructures of orthorhombic Bi2WO6 with unique morphologies were successfully synthesized by a solvothermal method. The precursor concentration plays a key role in the architecture of the hierarchical nanostructures. A peony flower-like morphology was obtained at higher precursor concentrations, and a red blood cell (RBC)-like morphology with average diameter of 1.5 μm was obtained at lower concentrations. These hierarchical nanostructures were assembled by self-alignment of 20 nm nanoplates. As their band gap is in the visible region, the photocatalytic activity of the Bi2WO6 hierarchical nanostructures for the production of hydrogen from glycerol, and the degradation of rhodamine B (RhB) and methylene blue (MB) under ambient conditions in the presence of solar light was investigated. The Bi2WO6 with peony flower morphology was observed to be the most efficient photocatalyst (H2: 7.40 mmol h−1 g−1, kRhB: 0.240 and kMB: 0.100) of the reported nanostructures. The higher activity of the peony flowers was due to their porous nature, high surface area and lower band gap. Such unique 3D nanostructures of Bi2WO6 have been fabricated for the first time, and their use as photocatalysts in the production of hydrogen from glycerol has hitherto not been attempted. These nanostructures may have potential in ferroelectric, piezoelectric, pyroelectric and nonlinear dielectric applications.

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.

A stable Bi2S3 quantum dot–glass nanosystem: size tuneable photocatalytic hydrogen production under solar light

The present work comprises a novel approach to design a bismuth sulfide (Bi2S3) quantum dot (QD) glass nanocomposite system by confining nano-Bi2S3 in a designated glass composition for solar light driven hydrogen (H2) production. Numerous methods have been reported for the synthesis of Bi2S3, however, we have demonstrated the synthesis of Bi2S3 QDs (0.5–0.7%) in silicate glass using the melt and quench method. X-ray diffraction and electron diffraction patterns of the glass nanosystem exhibit an orthorhombic crystallite system of the Bi2S3 QDs. Transmission electron microscopy demonstrates that 3–5 and 7–10 nm size Bi2S3 QDs are distributed homogeneously in a monodispersed form in the glass domain and on the surface with a “partially embedded exposure” configuration. The role of glass on the control of the size and shape of Bi2S3 QDs and their effect on the photocatalytic hydrogen generation has been discussed. The maximum H2 production i.e. 6418.8 μmol h−1 g−1 was achieved for the Bi2S3–glass nanosystem under solar light irradiation. This glass nanosystem shows an excellent photostability against photocorrosion and also has a facile catalytic function. Therefore, even a very small amount of Bi2S3 QDs is able to photodecompose H2S and produce hydrogen under visible light. The salient features of this QD glass nanosystem are reusability after simple washing, enhanced stability and remarkable catalytic activity.

Enhanced hydrogen production under a visible light source and dye degradation under natural sunlight using nanostructured doped zinc orthotitanates

The nanostructured Ag and Co doped zinc orthotitanates (ZOT) were synthesized using a combustion method. The structural and optical analysis shows the existence of cubic and tetragonal phases. Morphological study by FESEM reveals the formation of a web like structure along with pot holes by the self-assembly of spherical nanoparticles of ∼50 nm size. Further, TEM investigations reveal diffused and uneven shaped nanoparticles in the range of 10–25 nm. BET surface area measurements show a decrease in surface area due to doping. These ZOTs were employed for photocatalytic dye degradation (Acid Orange-8 and Rhodamine-B) under natural sunlight. The prima facie observations showed Ag@Zn2TiO4 to be an excellent photocatalyst for dye degradation. The kinetics study shows the order of the reaction to be in the range of 1.1–1.41. The ZOTs synthesized have also been used for photocatalytic hydrogen production from H2S under visible light irradiation. It is noteworthy that utmost H2 production (2784 μmol h−1/100 mg) was observed for Ag@Zn2TiO4 which is much higher than that achieved with visible light active photocatalysts reported so far. The dye degradation and hydrogen production from H2S using ZOT are hitherto unattempted. The nanostructured Zn2TiO4 will be a potential visible light active photocatalyst for waste degradation and water splitting.

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.

In situ fabrication of highly crystalline CdS decorated Bi2S3 nanowires (nano-heterostructure) for visible light photocatalyst application

In situ synthesis of the orthorhombic Bi2S3 nanowires decorated with hexagonal CdS nanoparticles (nano-heterostructure) has been demonstrated by a facile solvothermal method. The tiny 5–7 nm CdS spherical nanoparticles are decorated on the surfaces of 30–40 nm Bi2S3 nanowires, successfully. Structural, morphological and optical studies clearly show the existence of CdS on the nanowires. A possible sequential deposition growth mechanism is proposed on the basis of experimental results to reveal the formation of the nano heterostructure. The heterostructures have been used as a photocatalyst for hydrogen production as well as degradation of methylene blue under solar light. The maximum hydrogen evolution i.e. 4560 and 2340 μmol h−1 0.5 g was obtained from H2S splitting and glycerol degradation for Bi2S3 NWs decorated with CdS nanoparticles (nano-heterostructure) which is higher than that of the Bi2S3 NWs (3000 and 1170 μmol h−1 0.5 g, respectively). The enhanced photocatalytical hydrogen evolution efficiency of the heterostructures is mainly attributed to its nanostructure. In the nano heterostructure, the CdS nanoparticles control the charge carrier transition, recombination, and separation, while the Bi2S3 nanowire serves as a support for the CdS nanoparticles. The photogenerated electrons migration is faster than the holes from the inside of a CdS nanoparticle to its surface or to the phase interface, resulting in a relatively higher hole density inside the CdS nanoparticle leaving electron density at surface of the Bi2S3 NWs. This influences the photocatalytic activity under solar light. Such nano-heterostructures may have potential in other photocatalytic reactions.