Photocatalytic potential of ZnO/TiO2: a bionanocomposite from Ocimum basilicum

Decolorization of textile dyes by photocatalysis is an area that has gained considerable interest due to the need to minimize pollution. Nanocomposites possess prominence owing to their small size, good catalytic activity, high surface area and selectivity. Although nanocomposites have been synthesized by conventional techniques, green synthesis remains an unexplored area. Thus, the present study is the first one on ‘green’ synthesis of a zinc oxide (ZnO)/titanium dioxide (TiO2) nanocomposite using leaf extract of Ocimum basilicum L. var. purpurascens Benth. Lamiaceae as a novel source, along with an insight into its photocatalytic potential for decolorization of the textile dye Blue RGB under sunlight and ultraviolet (UV) irradiation. Hexagonal-shaped zinc oxide/titanium dioxide nanocomposites with a size of 50 nm have been synthesized and characterized using X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy and energy-dispersive X-ray spectroscopy. Maximum photodecolorization was observed for sunlight-mediated photocatalytic decolorization (99·8%) compared to UV (95·8%) within 8 h. The study adds value to the applications of nanoparticles in various fields such as photocatalysis for degradation of pollutants and in wastewater treatment.

Enhanced Photoelectrochemical Activity of ZnO-Coated TiO2 Nanotubes and Its Dependence on ZnO Coating Thickness

One-dimensional heterogeneous nanostructures in the form of ZnO-coated TiO2 nanotubes (ZnO/TiO2 NTs) were fabricated by atomic layer deposition of an ultrathin ZnO coating on electrochemical anodization-formed TiO2 nanotubes (NTs) with the thickness of ZnO coating being precisely controlled at atomic scale, and the photoelectrochemical activity of the fabricated ZnO/TiO2 NTs and the influence of ZnO coating and its thickness were studied. The structures of TiO2 NTs and ZnO coatings were characterized by X-ray diffraction, Raman backscattering spectroscopy, and transmission electron microscopy. The photoelectrochemical activity was studied through the measurements of electrochemical impendence, flat-band potential, and transient photocurrent density. The TiO2 NTs exhibit anatase structure, and the ZnO coatings are structured with hexagonal wurtzite. The photoelectrochemical activity of the ZnO/TiO2 NTs is strongly dependent on the thickness of ZnO coating. ZnO/TiO2 NTs with a thinner rather than a thicker ZnO coating exhibit better photoelectrochemical activity with reduced charge transfer resistance, increased negative flat-band potentials, and enhanced photocurrent densities. Under visible illumination, an increase of about 60 % in the photoelectrochemical activity is obtained for ZnO/TiO2 NTs with an about 2-nm-thick ZnO coating.

A Heterojunction Design of Single Layer Hole Tunneling ZnO Passivation Wrapping around TiO2Nanowires for Superior Photocatalytic Performance

Nanostructured hybrid heterojunctions have been studied widely for photocatalytic applications due to their superior optical and structural properties. In this work, the impact of angstrom thick atomic layer deposited (ALD) ZnO shell layer on photocatalytic activity (PCA) of hydrothermal grown single crystalline TiO2 nanowires (NWs) is systematically explored. We showed that a single cycle of ALD ZnO layer wrapped around TiO2 NWs, considerably boosts the PCA of the heterostructure. Subsequent cycles, however, gradually hinder the photocatalytic activity (PCA) of the TiO2 NWs. Various structural, optical, and transient characterizations are employed to scrutinize this unprecedented change. We show that a single atomic layer of ZnO shell not only increases light harvesting capability of the heterostructure via extension of the absorption toward visible wavelengths, but also mitigates recombination probability of carriers through reduction of surface defects density and introduction of proper charge separation along the core-shell interface. Furthermore, the ultrathin ZnO shell layer allows a strong contribution of the core (TiO2) valence band holes through tunneling across the ultrathin interface. All mechanisms responsible for this enhanced PCA of heterostructure are elucidated and corresponding models are proposed.

Enhanced performance of PbS-sensitized solar cells via controlled successive ionic-layer adsorption and reaction

The performance of PbS-sensitized solar cells is significantly improved by controlling successive ionic layer adsorption and reaction.