CdS decorated MnWO4 nanorod nanoheterostructures: a new 0D-1D hybrid system for enhanced photocatalytic hydrogen production under natural sunlight.

Constructing a heterostructure is an effective strategy to reduce the electron-hole recombination rate, which enhances photocatalytic activity. Here, we report a facile hydrothermal method to grow CdS nanoparticles on MnWO4 nanorods and their photocatalytic hydrogen generation under solar light. A structural study shows the decoration of hexagonal CdS nanoparticles on monoclinic MnWO4. Morphological studies based on FE-TEM analysis confirm the sensitization of CdS nanoparticles (10 nm) on MnWO4 nanorods of diameter-35 nm with mean length ∼100 nm. The lower PL intensity of MnWO4 was observed with an increasing amount of CdS nanoparticles, which shows inhibition of the charge carrier recombination rate. A CdS@MnWO4 narrow band gap semiconductor was employed for photocatalytic hydrogen generation from water under solar light and the highest amount of hydrogen, i.e. 3218 µmol h-1 g-1, is obtained which is 21 times higher than that with pristine MnWO4. The enhanced photocatalytic activity is ascribed to the formation of a CdS@MnWO4 nanoheterostructure resulting in efficient spatial separation of photogenerated electron-hole pairs due to vacancy defects. More significantly, direct Z-scheme electron transfer from MnWO4 to CdS is responsible for the enhanced hydrogen evolution. This work signifies that a CdS decorated MnWO4 nanoheterostructure has the potential to improve the solar to direct fuel conversion efficiency.

Plasmonic Ag decorated CdMoO4 as an efficient photocatalyst for solar hydrogen production.

The synthesis of Ag-nanoparticle-decorated CdMoO4 and its photocatalytic activity towards hydrogen generation under sunlight has been demonstrated. The CdMoO4 samples were synthesized by a simple hydrothermal approach in which Ag nanoparticles were in situ decorated on the surface of CdMoO4. A morphological study showed that 5 nm spherical Ag nanoparticles were homogeneously distributed on the surface of CdMoO4 particles. The UV/DRS spectra show that the band gap of CdMoO4 was narrowed by the incorporation of a small amount of Ag nanoparticles. The surface plasmonic effect of Ag shows broad absorption in the visible region. The enhanced photocatalytic hydrogen production activities of all the samples were evaluated by using methanol as a sacrificial reagent in water under natural sunlight conditions. The results suggest that the rate of photocatalytic hydrogen production using CdMoO4 can be significantly improved by loading 2% Ag nanoparticles: i.e. 2465 µmol h-1 g-1 for a 15 mg catalyst. The strong excitation of surface plasmon resonance (SPR) absorption by the Ag nanoparticles was found in the Ag-loaded samples. In this system, the role of Ag nanoparticles on the surface of CdMoO4 has been discussed. In particular, the SPR effect is responsible for higher hydrogen evolution under natural sunlight because of broad absorption in the visible region. The current study could provide new insights for designing metal/semiconductor interface systems to harvest solar light for solar fuel generation.

Hierarchical CdMoO4 nanowire-graphene composite for photocatalytic hydrogen generation under natural sunlight.

Herein, a facile in situ solvothermal technique for the synthesis of a CdMoO4/graphene composite photocatalyst is reported. Graphene oxide (GO) was synthesised by an improved Hummers' method and was further used for the in situ synthesis of graphene via GO reduction and the formation of a CdMoO4 nanowire/graphene composite. The structural phase formation of tetragonal CdMoO4 was confirmed from X-ray diffraction measurements. The small nanoparticle assembled nanowires, prismatic microsphere morphology and crystalline nature of the synthesized material were investigated using field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). Due to its unique morphology and stability, the CdMoO4/graphene composite was used as a photocatalyst for H2O splitting. In comparison to pristine CdMoO4, the CdMoO4/graphene composite showed the best hydrogen evolution rate, i.e. 3624 µmole h-1 g-1, with an apparent quantum yield of 30.5%. The CdMoO4/graphene composite has a higher photocatalytic activity due to the inhibition of charge carrier recombination. H2 production measurements showed that the ternary semiconductor/graphene composite has enhanced photocatalytic activity for H2 generation.

Photodegradation of spent wash, a sugar industry waste, using vanadium-doped TiO2 nanoparticles.

Waste from the sugar cane industry and alcohol distilleries is one of the sources of water pollution, and the degradation of this effluent is a very challenging task. Photocatalytic degradation can be an attractive alternative to conventional degradation processes. A vanadium-doped TiO2 (V-TiO2) photocatalyst for the degradation of spent wash and industrial dyes has been studied and reported here. V-doped TiO2 nanoparticles were prepared using a sol-gel method based on aqueous titanium peroxide with titanium isopropoxide as the Ti precursor and V2O5 as the V precursor. In order to observe the effect of the dopant on sol-gel behaviour, physicochemical and structural properties, the concentration of V was varied between 1.0% and 5% by weight. The crystallization temperature and time were optimized to obtain the required phase of V-TiO2. The physicochemical and structural characteristics of the V-doped TiO2 catalyst were determined using Brunauer-Emmett-Teller (BET), X-ray diffraction, FESEM, TEM, TG, FT-IR, Raman, PL and UV-visible spectroscopic techniques. UV-visible analysis showed a red shift in the absorption edge of TiO2 upon doping with V metal, which suggested an increase in the absorption of visible light due to a decrease in the effective band gap. The application potential of the V-TiO2 catalyst was studied via the degradation of sugar industry waste (spent wash) and Jakofix red dye (HE 8BN) under natural sunlight, as well as a standard artificial solar energy source (Xe lamp). The highest activity was observed for a 1% V-TiO2 photocatalyst for the degradation of spent wash and Jakofix red dye under natural sunlight. The degradation of coloured compounds in spent wash was monitored by gel permeation chromatography (GPC), which showed the degradation of high-molecular-weight compounds into low-molecular-weight fractions. The catalyst decomposed 90% of Jakofix red dye (HE 8BN) in 3.5 h and 65% of spent wash in 5 h under irradiation with natural sunlight, whereas Degussa P-25 TiO2 was only able to decompose 35% of the dye and 20% of spent wash under identical reaction conditions. A cycling stability test showed the high stability and reusability of the photocatalyst for degradation reactions, with a recovery of around 94-96%.