Development of nonmetal-doped TiO2 nanotube photocatalyst for decolorization of methyl orange
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Date
2015-10-01
Authors
Khairul Arifah Saharudin
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Abstract
Well aligned TiO2nanotubes (NT) arrays have attracted substantial attention in the area of photocatalysis (PC). Although TiO2 is a widely used catalyst support, its poor visible light absorption and high recombination of charge carriers remains a major challenge for its application. Hence, this work aims to develop carbon (C) incorporated TiO2 NT and carbon phosphorus (CP)incorporated TiO2 NT for photocatalytic decolorization of methyl orange (MO) dye. The formation of C-TiO2 NT by anodization was successful in fluorinated organic electrolyte. Glycerol and ethylene glycol (EG) were the organic electrolyte with their neutral pH. The properties including morphology and structural of the nanotubular oxide formed were investigated. During anodization, the main factors effecting nanotubular structures are types of electrolyte, its composition, anodization voltage applied to anode and anodization time.C-TiO2 NT arrays were rapidly grown in EG containing 0.89 wt% of water (H2O) and 0.66 wt% of ammonium fluoride (NH4F). The optimized rate of formation was 308 nm/min. The incorporation of C into TiO2 NT induced the formation of a new state above valence band (VB), which is attributed to the C 2p state of the interstitial carbon, as well as new state below the conduction band (CB), corresponding to antibonding C–O state produced due to the formation of oxygen vacancies.C-TiO2 NT arrays annealed at 500 °C with average pore size of 95 nm, wall thickness of 18 nm and length of 18.5 m, with high aspect ratio (141.2) and surface area (1025.6 m2g-1) exhibited decolorization of about 39% under visible light illumination with rate constant of k = 5.9 x 10-3 min-1as compared to TiO2
nanoparticle of 25 nm which possessed 11% decolorization. In order to improve further the photocatalytic activity of C-TiO2 NT, incorporation of P into C-TiO2 NT was done via anodization of Ti in EG containing 1 M phosphoric acid (H3PO4) and wet impregnation in H3PO4. It was found that C-TiO2 NT impregnated in 0.02 M H3PO4 for 90 min at 40 °C and annealed at 500 °C exhibited 45% decolorization with rate constant of k = 8.1 x 10-3 min-1. It was found that the doped phosphorus existed in a pentavalent oxidation state, replacing part of Ti4+ in the anatase lattice in the form of Ti-O-P bonds, thus extended the spectral response of TiO2 NT to the visible region.