Cu2O nanoparticles sensitize TiO2/CdS nanowire arrays to prolong charge carrier lifetime and highly enhance unassisted photoelectrochemical hydrogen generation with 4.3% efficiency.

Effective separation of charge carriers and substantial prolongation of charge carrier lifetime are two vital issues for a photoanode to achieve highly efficient photoelectrochemical (PEC) hydrogen generation. Herein, a Cu2O-nanoparticle-sensitized TiO2/CdS (TiO2/CdS/Cu2O) nanowire array photoanode is fabricated via subtly combining successive ionic layer adsorption and reaction with a chemical bath deposition method. Both the type-II band alignment with a stair-like structure and a p-n junction are integrated into this ternary photoanode. The fabricated photoanode shows a significant enhancement in the PEC H2 production with 4.3% efficiency. The measurements of light absorption, photoluminescence and electrochemical spectra undoubtedly demonstrate that the enhanced PEC H2 generation is ascribed to the remarkable enhancement of visible-light absorbing ability, efficient space charge separation and substantial prolongation of charge carrier lifetime, which are achieved by the synergetic effects of the type-II band alignment with a stair-like structure and the p-n junction. The enhanced PEC H2 generation demonstrates the potential of the TiO2/CdS/Cu2O nanowire arrays as a photoanode to efficiently convert solar energy into chemical fuels.

Methyl orange adsorption from aqueous solutions on 3D hierarchical PbS/ZnO microspheres.

In this study, three-dimensional (3D) hierarchical PbS/ZnO heterojunction microspheres were successfully fabricated by combining a facile hydrothermal method and an improved successive ionic-layer adsorption and reaction (SILAR). As an adsorbent for the first time, the adsorption activities for the methyl orange (MO) of the prepared 3D hierarchical PbS/ZnO heterojunction microspheres were investigated. By optimizing the loading of PbS nanoparticles (NPs), the 3D hierarchical PbS/ZnO heterojunction microspheres show enhanced adsorption ability for MO with a high removal rate of more than 91% and a maximum adsorption capacity of 159 mg g-1 at equilibrium time within less than 40 min. The kinetics, thermodynamics, and isotherm investigations for the adsorption process of MO over the 3D hierarchical PbS/ZnO heterojunction microspheres experimentally demonstrate that the adsorption process follows a pseudo-second-order model with the nature of spontaneous and endothermic and is well fitted with the normal Langmuir isotherm model. Based on the comparative investigations and the experimental results of kinetics, thermodynamics, and isotherm studies, a reasonable adsorption mechanism of MO over the 3D hierarchical PbS/ZnO heterojunction microspheres was proposed. This work not only describes a new semiconductor heterojunction adsorbent but also offers a new idea for the fabrication of other semiconductor heterojunction adsorbents.

Heterogeneous p-n Junction CdS/Cu2O Nanorod Arrays: Synthesis and Superior Visible-Light-Driven Photoelectrochemical Performance for Hydrogen Evolution.

Heterogeneous p-n junction CdS/Cu2O nanorod arrays have been fabricated by using a facile successive ionic-layer adsorption and reaction process to grow Cu2O nanoparticles on the surface of ordered CdS nanorod arrays. The heterogeneous p-n junction nanorod arrays exhibit superior photoelectrochemical performance for hydrogen (H2) generation and high stability under visible-light irradiation. The highest photocurrent density achieved by heterogeneous nanorod array photoelectrode is 4.2 mA cm-2 in a sacrificial Na2S and Na2SO3 mixture electrolyte solution at 0 V versus Ag/AgCl, which is 4 times higher than that of a pure CdS nanorod array photoelectrode. In addition, the heterogeneous nanorod array photoelectrode achieves an incident photon conversion efficiency value of 40.5% at 470 nm. The photocatalytic hydrogen generation rate of the heterogeneous nanorod array photoelectrode reaches up to 161.2 µmol h-1, around 3-fold increase compared to that of a bare CdS photoelectrode. Furthermore, the heterogeneous p-n junction CdS/Cu2O nanorod arrays show an excellent stability under long light illumination of 7200 s. The improved photoelectrochemical performance, photocatalytic activity, and excellent stability of the heterogeneous nanorod array photoelectrode resulted from the efficient separation of photoinduced electron-hole pairs, which is achieved by the synergistic effects of CdS, Cu2O, p-n junction, and an inner electric field in the photoelectrode. The present work provides a new strategy to fabricate a heterogeneous photoelectrode. This facile strategy is expected to be utilized to fabricate electrodes of other materials for highly efficient solar-driven water splitting application.