Fabrication of TIO2 nanotube arrays by anodization and its applications in photoreduction of chromium(VI)

Abstract

This research focuses on preparation and characterization of TiO2 nanotube arrays prepared by anodic oxidation of Ti substrates using pulse voltage waveforms. Voltages were pulsed between 20 V and -4 V or between 20 V and 0 V with varying durations from 2 to 16 seconds at the lower limit of the pulse waveform. Ammonium fluoride were used as the electrolyte with or without added medium modifier (glycerol, ethylene glycol, or poly (ethylene glycol) (PEG 400)) in these experiments. The pulse waveform was optimized to electrochemically grow TiO2 nanotubes and chemically etch their walls during its cathodic current flow regime. The resultant TiO2 nanotube arrays showed a higher quality of nanotube array morphology and photoresponse than samples grown via the conventional continuous anodization method. Films grown with a 20 V/-4 V pulse sequence and pulse duration of 2 s at its negative voltage limit afforded superior photoresponse compared to other pulse durations. Specifically, the negative voltage limit of the pulse (-4 V) and its duration promote the adsorption of NH4+ species that in turn inhibits chemical attack of the growing oxide nanoarchitecture by the electrolyte Fˉ species. The co-doping effects by metal cations on photoelectrochemistry properties were also observed on photocatalysis reduction. Thus, it was found that transition metal doping into photocatalysts with wide band gaps was effective for the development of photoelectrochemical response and photocatalytic activity if a suitable combination of dopant–codopant is chosen. Finally, photocatalytic reduction of hexavalent chromium were studied under ultraviolet light using anodically growth Ti/TiO2 and metal modified TiO2 nanotube show quantum yield up to 3.2×10-2 obtain by film were prepared with NiF2 and used glycerol as dopant.