Fabrication of ZnO Scaffolded CdS Nanostructured Photoanodes with Enhanced Photoelectrochemical Water Splitting Activity under Visible Light.

CdS, characterized by its comparatively narrow energy band gap (∼2.4 eV), is an appropriate material for prospective use as a photoanode in photoelectrochemical water splitting. Regrettably, it encounters several obstacles for practical and large-scale applications, including issues such as bulk carrier recombination and diminished conductivity. Here, we have tried to address these challenges by fabricating a novel photoelectrode (ZnO/CdS) composed of one-dimensional ZnO nanorods (NRs) decorated with two-dimensional CdS nanosheets (NSs). A facile two-step chemical method comprising electrodeposition along with chemical bath deposition is employed to synthesize the ZnO NRs, CdS NSs, and ZnO/CdS nanostructures. The prepared nanostructures have been investigated by UV-visible absorption spectroscopy, X-ray diffraction, Raman spectroscopy, transmission electron microscopy (TEM), and scanning electron microscopy. The fabricated ZnO/CdS nanostructures have shown enhanced photoelectrochemical properties due to the improvement of the semiconductor junction surface area and thereby enhanced visible light absorption. The incorporation of CdS NSs has been further found to promote the rate of the charge separation and transfer process. Subsequently, the fabricated ZnO/CdS photoelectrodes achieved a photocurrent conversion efficiency 3 times higher than that of a planar ZnO NR photoanode and showed excellent performance under visible light irradiation. The highest applied bias photon-to-current conversion efficiency (% ABPE) of about ∼0.63% has been obtained for the sample with thicker CdS NSs on ZnO NRs with a photocurrent density of ∼1.87 mA/cm2 under AM 1.5 G illumination. The newly synthesized nanostructures further demonstrate that the full photovoltaic capacity of nanomaterials is yet to be exhausted.

Pioneering method for the synthesis of lead sulfide (PbS) nanoparticles using a surfactant-free microemulsion scheme.

In this study, we report the synthesis of PbS particles having dimensions in the quantum-dot regime (13.17 to 26.91 nm) using a cyclohexane:isopropanol:dimethyl-sulfoxide surfactant-free microemulsion (CID-SFME) scheme without a capping agent. We found that with an increase in the microemulsion concentration and particle size, there was a simultaneous reduction in band gap due to the quantum confinement effect. Furthermore, a microemulsion concentration of 0.0125 M was the optimum microemulsion concentration for the growth of uniformly distributed, small particle-sized, ordered PbS nanoparticles using CID-SFME at a constant temperature and other effective parameters. From the results obtained in the present study, we believe that during the reaction, it was not the low values of viscosity and dielectric constant that were responsible for keeping PbS stabilized inside the core of the micelle of the CID microemulsion, but rather the van der Waals forces that also controlled the growth of spherical PbS. We fabricated a highly stable FTO/TiO2/PbS/PANI/NiS/C photodetector at an optimized microemulsion solution concentration. The fabricated photodetector showed a rise time of ∼0.39 s and a decay time of ∼0.22 s, with a photoresponsivity of ∼5.466 µA W-1, external quantum efficiency of ∼0.116 × 10-4%, and detectivity of 6.83 × 107 Jones. Therefore, the CID-SFME scheme is an easy, low-cost route to fabricate efficient, precise, stable, and fast-switching photodetector devices.