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The present study demonstrates lignin (L), fragments of lignin (FL), and oxidized fragmented lignin (OFL) as templates for the synthesis of zinc oxide nanoparticles (ZnO NPs) viz., lignin-ZnO (L-ZnO), hierarchical FL-ZnO, and OFL-ZnO NPs. The X-ray diffraction patterns confirmed the formation of phase pure ZnO NPs with a hexagonal wurtzite structure. Electron microscopy confirmed the hierarchical structures with one-dimensional arrays of ZnO NPs with an average particle diameter of 40 nm. The as-synthesized L-ZnO, FL-ZnO, and OFL-ZnO NPs were tested in-vitro for growth and virulence inhibition (morphogenesis and biofilm) in Candida albicans. L-ZnO, FL-ZnO, and OFL-ZnO NPs all inhibited growth and virulence. Growth and virulence inhibitions were highest (more than 90%, respectively at 125, 31.2, and 62.5 μg/mL) in presence of FL-ZnO NPs, indicating that the hierarchical FL-ZnO NPs were potent growth and virulence inhibiting agent than non-hierarchical ZnO NPs. Furthermore, the real-time polymerase chain (RT-PCR) was used to study the virulence inhibition molecular mechanisms of L-ZnO, FL-ZnO, and OFL-ZnO NPs. RT-PCR results showed that the downregulation of phr1, phr2, efg1, hwp1, ras1, als3 and als4, and the upregulation of bcy1, nrg1, and tup1 genes inhibited the virulence in C. albicans. Lastly, we also performed in-vitro test cell cytotoxicity on the cell line, mouse embryo 3T3L1, and in-vivo toxicity on Rats, which showed that FL-ZnO NPs were biocompatible and nontoxic.

Cu-doped zinc oxide (Cu–ZnO) nanostructure was prepared using Whatman filter paper as a template by combustion method. For the synthesis of porous Cu–ZnO nanostructures the stoichiometric amount of precursors were impregnated in the filter papers and processed, thermally. The formation of wurtzite phase having crystallite size in the range of 20–24 nm was confirmed by X-ray diffraction (XRD) analysis. The morphological study by field emission scanning electron microscopy (FESEM) and field emission transmission electron microscopy (FETEM) shows size of nanoparticles in the range of 25–50 nm. The optical study shows red shift i.e. extended absorbance in the visible region due to Cu doping. The photoluminescence study of Cu–ZnO results quenching in the photoluminescence peak as effect of Cu doping in ZnO lattice. Considering the extended band gap in the visible region of as synthesized Cu–ZnO, the photocatalytic dye degradation activity of methylene blue (MB) was executed in presence of sunlight irradiation. The effect of salt concentration and PH on dye degradation activity also studied. The highest photocatalytic activity was observed for Cu–ZnO with 4% doping as compared with other Cu–ZnO and ZnO nanostructure. The photocatalytic performance of Cu–ZnO shows complete degradation of MB dye within 30 min for 4% Cu–ZnO nanostructure. The photocatalytic activity obtained is much higher as compare to earlier reports. The synthesis of Cu doped ZnO by paper templated method and its photocatalytic activity is hitherto unattempted.

In the present study, we demonstrated the use of fragmented lignin in the synthesis of a hierarchical-type structure of ZnO nanorods. Lignin was isolated from bagasse by the microwave assisted method and its fragmentation was achieved in alkaline conditions along with hydrogen peroxide. Lignin and fragmented lignin were purified by crystallisation followed by column chromatography and characterized by UV-visible spectroscopy, Frontier infra-red spectroscopy (FTIR), 1H-NMR and high resolution mass spectroscopy (HRMS). Fragmented lignin was utilized as a template for the synthesis of ZnO nanorods, which were characterized by powder XRD, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and UV-DRS for the determination of crystal structure, particle morphology and band gap. XRD of the ZnO samples revealed a hexagonal wurtzite structure. The morphology of ZnO without fragmented lignin showed agglomerated nanoparticles and with fragmented lignin, a self-assembled hierarchical nanostructure due to nanorods of 30 nm diameter and 200–500 nm length was observed. The fragmented lignin showed a pronounced effect on the particle size and morphology of ZnO nanoparticles. We measured the response of the hierarchical ZnO nanostructure (50 ppm) for sensing NH3 in terms of change in voltage across known resistance. We observed the response and recovery upon introduction of the analyte ammonia gas at 175 °C.

Herein, we report visible light active mesoporous cadmium bismuth niobate (CBN) nanospheres as a photocatalyst for hydrogen (H 2 ) generation from copious hydrogen sulfide (H 2 S). CBN has been synthesized by solid state reaction (SSR) and also using combustion method (CM) at relatively lower temperatures. The as-synthesized materials were characterized using different techniques. X-ray diffraction analysis shows the formation of single phase orthorhombic CBN. Field emission scanning electron microscopy and high resolution-transmission electron microscopy showed the particle size in the range of ∼0.5–1 µm for CBN obtained by SSR and 50–70 nm size nanospheres using CM, respectively. Interestingly, nanospheres of size 50–70 nm self assembled with 5–7 nm nanoparticles were observed in case of CBN prepared by CM. The optical properties were studied using UV–visible diffuse reflectance spectroscopy and showed band gap around ∼3.0 eV for SSR and 3.1 eV for CM. The slight shift in band gap of CM is due to nanocrystalline nature of material. Considering the band gap in visible region, the photocatalytic activity of CBN for hydrogen production from H 2 S has been performed under visible light. CBN prepared by CM has shown utmost hydrogen evolution i.e. 6912 µmol/h/0.5 g which is much higher than CBN prepared using SSR. The enhanced photocatalytic property can be attributed to the smaller particle size, crystalline nature, high surface area and mesoporous structure of CBN prepared by combustion method. The catalyst was found to be stable, active and can be utilized for water splitting.

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.

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.

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.

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.

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.

The hierarchical nanostructures of CdIn2S4 were selectively prepared through hydrothermal process in the presence of different surfactants. Structural study demonstrated existence of cubic spinel structure and micro structural study shown a pretty marigold flower like morphology without any surfactant. The effect of surfactants on the morphology and microstructure of CdIn2S4 has been studied by using Polyvinyl pyrrolidone (PVP) and Cetyltrimethyl ammonium bromide (CTAB) as a surfactants. The CdIn2S4 bipyramids with length of 0.7–1 μm have been obtained using PVP. Interestingly, the nanopetals (thin and transparent) of CdIn2S4 are self assembled into hollow spheres in the presence of CTAB. Considering the importance of these unique nanostructures, the growth mechanism has also been proposed. The optical properties demonstrated the band gap in the range of 2.12–2.29 eV which is well within the visible region. In this contest, photocatalytic activity for hydrogen production using the above nanostructures under visible light was also demonstrated. The prima-fascia observations shows that the bipyramidal CdIn2S4 exhibit excellent photocatalytic activity for hydrogen production (3238 μmolh−1) than other nanostructures. Being a nanostructured semiconductor chalcogenide with a good stability will also have potential applications in solar cells and LED.

Hydrogen is a future fuel and hence production of cheap hydrogen is an important area of research. Recently, the photocatalysts were used to generate hydrogen from water and hydrogen sulfide splitting under solar light. Hence, we designed Zinc Indium Vanadate, a novel visible light active photocatalyst and used for the generation of hydrogen by using solar light. We have demonstrated the synthesis of ZnIn2V2O9 (ZIV) catalyst by sonochemical route using NH4VO3, In (NO3)3 and Zn(CH3COO)2 as a precursors and PVP as a capping agent. The obtained product was further characterized by XRD, UV-DRS and FESEM. The XRD pattern reveals the existence of monoclinic crystal structure and broader peaks indicating the nanocrystalline nature of the material. The particle size was observed in the range of 50-70 nm. The optical study showed the absorption edge cut off at 520 nm with estimated band gap about 2.3 eV. Considering the band gap in visible range, ZnIn2V2O9 was used as a photocatalyst for photodecomposition of H2S under visible light irradiation to produce hydrogen. We observed excellent photocatalytic activity for the hydrogen generation by using this photocatalyst.

In the present investigation, we have demonstrated the synthesis of novel photocatalyst, zinc indium vanadate (ZIV) by solid–solid state route using respective oxides of zinc, indium and vanadium. This novel photocatalyst was characterized using XRD, FESEM, UV-DRS and FTIR in order to investigate its structural, morphological and optical properties. XRD clearly shows the formation of phase pure ZIV of triclinic crystal structure with good crystallinity. FESEM micrographs showed the clustered morphology having particle size between 0.5 and 1 μm. Since, optical study showed the band gap around 2.8 eV, i.e. in visible region, we have performed the photocatalytic activity of phenol degradation under visible light irradiation. The photodecomposition of phenol by ZIV is studied for the first time and an excellent photocatalytic activity was obtained using this novel photocatalyst. Considering the band gap of zinc indium vanadate in visible region, it will also be the potential candidate for water splitting.

We report here a new ternary chalcogenide material, cadmium lanthanum sulfide (CdLa2S4) produced using a facile hydrothermal method at 433 K. The effect of the solvent on the morphology of the CdLa2S4 was demonstrated for the first time. The prima facie observations revealed the formation of highly crystalline hexagonal structures in the form of flowers in aqueous medium. The flowers comprise hexagonal columns ∼300 nm in diameter and 1–1.2 μm in length. All the hexagonal structures have a sharp tip with a cavity of 10 nm and are almost equal in size. The nanoprisms have an average base size of 35 nm with 35 nm edges, and the nanowires have a diameter of 10–15 nm; both were obtained in methanol. Crystal and electronic structure calculations were performed using the Vienna ab initio simulation package (VASP) based on density functional theory (DFT). Considering the band gap of pristine CdLa2S4 in the visible region (2.3 eV), we have demonstrated CdLa2S4 as a photocatalyst for the production of H2 under solar light. Nanostructured CdLa2S4 prisms gave the maximum hydrogen production, i.e. 2552 μmol h−1. Being a stable ternary nanostructured metal sulfide (with nanohexagons, nanoprisms, nanowires), CdLa2S4 may have other potential prospective applications in solar cells and optoelectronic devices.

We report the solvothermal synthesis of nanostructured ZnO hexagons by hydrothermal method via intermediate zinc adipate. The intermediate zinc adipate was obtained using precursors zinc acetate and adipic acid in aqueous and organic medium. Detailed XRD analysis of the zinc adipate was studied for the first time. Thermal study of intermediate showed the formation of ZnO at 400 °C. XRD study demonstrated the existence of wrutzite ZnO of high degree of crystallinity with crystallite size in the range of 20–25 nm. Scanning Electron Microscopy (SEM) showed distinguished morphology in different medium. Transmission Electron Microscopy (TEM) demonstrated nanostructured ZnO hexagons with average size 25–50 nm. The band gap for aqueous and organic mediated ZnO was found to be 3.24 and 3.26 eV, respectively. The band gap obtained is higher than the bulk ZnO, which implies nanocrystalline nature of the material.

In this study, we report the synthesis of well-aligned nanocrystalline hexagonal zinc oxide (ZnO) nanoparticles by facile solid-state and co-precipitation method. The co-precipitation reactions were performed using aqueous and ethylene glycol (EG) medium using zinc acetate and adipic acid to obtain zinc adipate and further decomposition at 450 °C to confer nanocrystalline ZnO hexagons. XRD shows the hexagonal wurtzite structure of the ZnO. Thermal study reveals complete formation of ZnO at 430 °C in case of solid-state method, whereas in case of co-precipitation method complete formation was observed at 400 °C. Field emission scanning electron microscope shows spherical morphology for ZnO synthesized by solid-state method. The aqueous-mediated ZnO by co-precipitation method shows rod-like morphology. These rods are formed via self assembling of spherical nanoparticles, however, uniformly dispersed spherical crystallites were seen in EG-mediated ZnO. Transmission electron microscope (TEM) investigations clearly show well aligned and highly crystalline transparent and thin hexagonal ZnO. The particle size was measured using TEM and was observed to be 50–60 nm in case of solid-state method and aqueous-mediated co-precipitation method, while 25–50 nm in case of EG-mediated co-precipitation method. UV absorption spectra showed sharp absorption peaks with a blue shift for EG-mediated ZnO, which demonstrate the mono-dispersed lower particle size. The band gap of the ZnO was observed to be 3.4 eV which is higher than the bulk, implies nanocrystalline nature of the ZnO. The photoluminescence studies clearly indicate the strong violet and weak blue emission in ZnO nanoparticles which is quite unique. The process investigated may be useful to synthesize other oxide semiconductors and transition metal oxides.

We have investigated an economical green route for the synthesis of a p-type N-doped ZnO photocatalyst by a wet chemical method. Significantly, hazardous H2S waste was converted into eco-friendly hydrogen energy using the p-type N-doped ZnO photocatalyst under solar light, which has previously been unattempted. The as-synthesized p-type N-doped ZnO shows a hexagonal wurtzite structure. The optical study shows a drastic shift in the band gap of the doped ZnO in the visible region (3.19–2.3 eV). The doping of nitrogen into the ZnO lattice is conclusively proved from X-ray photoelectron spectroscopy analysis and Raman scattering. The morphological features of the N-doped ZnO are studied from FESEM, TEM and reveal particle sizes to be in the range of ∼4–5 nm. The N-doped ZnO exhibits enhanced photocatalytic hydrogen generation (∼3957 μmol h−1) by photodecomposition of hydrogen sulfide under visible light irradiation, which is much higher as compared to semiconductor metal oxides reported so far. It is noteworthy that a green catalyst is investigated to curtail H2S pollution along with production of hydrogen (green fuel) using solar light, i.e., a renewable energy source. The green process investigated will have the potential to synthesize other N-doped metal oxides.

It is quite well-known that refineries are producing huge amount of H2S which has been used to produce sulphur and water using the well-known Claus process. This process is not an economically viable process, due to the high-cost chemical process and creates further acute environmental problems. Therefore, we have demonstrated the conversion of poisonous H2S into H2 using an ecofriendly phocatalysis process which is a green unconventional energy source. We have investigated ecofriendly nanostructured ZnIn2S4 photocatalyst to produce hydrogen from H2S using solar light. We also demonstrate the controlled synthesis of hierarchical nanostructured ZnIn2S4 using a facile hydrothermal method. The morphologies obtained have been greatly influenced by the presence of triethylamine (TEA) with various concentrations during the reaction. Surprisingly, a highly crystalline hexagonal layer structured ZnIn2S4 was obtained instead of cubic spinel. The hierarchical nanostructure, i.e. marigold flower-like morphology, was obtained without any surfactant. The thin and transparent petals self-assembled to form the unique nanostructured marigold flower. The highly crystalline puffy marigold flowers and nanoplates/nanostrips were obtained using TEA-assisted hydrothermal synthesis. Optical study shows the band gap in the range of 2.34–2.48 eV. Considering the band gap in the visible region, ZnIn2S4 is used as photocatalyst for hydrogen production from hydrogen sulphide under solar light which is hitherto unattempted. The constant photocatalytic activity of hydrogen evolution, i.e. 5287 μmol h−1, was obtained using such hierarchical nanostructured ZnIn2S4 under visible light irradiation. It is noteworthy that the H2 evolution rate obtained is much higher compared to earlier reported photocatalysts. Considering the significance of morphologies for photocatalytic application, the formation mechanism has also been furnished. The unique hierarchical nanostructured ZnIn2S4 ternary semiconductor having hexagonal layer will have potential applications in solar cells, LEDs, charge storage, electrochemical recording, thermoelectricity and other prospective electronic and optical devices.