The Boron Doping And CdS Quantum Dots Coating On TiO₂ Nanotube Arrays And Their Photoelectrocatalytic Activity

In this paper, the element doping and semiconductor coating are adopted as modification methods for TiO₂ nanotube arrays to get increased photoelectrochemical property or photoelectrocatalysis activity. Electrodeposition method for the first time is applied to fabricate boron-doped TiO₂ nanotube arrays. X-ray photoelectron spectroscopy (XPS) analysis reveal incorporated B atoms in the lattice of a TiO₂ nanotube array and combined with atoms Ti and O. The X-ray diffraction (XRD) spectrums indicate improved crystallinity of boron-doped TiO₂ nanotube arrays, relative to undoped TiO₂ nanotube arrays. Red shift and new absorption shoulder (380-510 nm) of boron-doped TiO₂ nanotube arrays are observed, and the degree of red shift or the intensity of second shoulder is boron content depended via diffuse reflectance spectroscopy (DRS). In photoelectrochemical measurements, under either ultraviolet (UV) or visible light irradiation, the photocurrent conversion efficiency was enhanced because of boron doping. The photoelectrocatalysis of phenol under simulated solar irradiation was performed using boron-doped or undoped TiO₂ nanotube arrays, and the kinetic constants of boron-doped TiO₂ nanotube arrays photoelectrodes are increased with doped-boron content, compared to that of an undoped TiO₂ nanotube array photoelectrode.Quantum-sized CdS coating is the second modification method in this paper. The SILAR method for fabricating CdS coated TiO₂ nanotube arrays was improved for accelerating crystal growth rate of CdS and shortening the fabrication time, by addition of drying with nitrogen after immerse in CdS precursor solution. The images of the scanning electron microscopy and transmission electron microscopy demonstrated that quantum-sized CdS crystals grown on TiO₂ nanotube arrays via the improved-SILAR method. The X-ray Fluorescence spectrometer and UV-Vis diffuse reflectance spectra illustrated that the amount of CdS was increased and the size distribution of CdS quantum dots was widened because of the improvement on SILAR method, which could lead to increased photoelectrochemical properties. The effects of fabrication conditions, included immerse cycle and calcinations temperature, were determined and the mechanism was discussed in details.