Experimental Study On Photocatalytic Degradation Of Mico-environment VOCs By The TiO₂ Nanotube Arrays

In recent years, with the increase of a big amount of indoor decoration and the popularity of closed transportation, the problem of VOCs pollution in mico-environment, which become hazardous to human health, was increasingly serious. The semiconductor photocatalysis had attracted extensive attention due to its energy saving and high efficiency. The photocatalytic performance was the key of the photocatalytic technology and TiO₂ was generally used to photocatalysis because of its low price and non-toxicity. However, the absorption of TiO₂ nanotube arrays for light was limited to UV light region due to the wide band gap, which was also limited to the utilization rate of solar energy. To enhance the visible light response, it was an effective method to the composite of narrow band gap semiconductor and TiO₂ nanotube arrays. In addition, as a photocatalysis, TiO₂ nanotube arrays was convenient to be placed and separated, and controlling the morphology and size of TiO₂ nanotube better was beneficial to combine the narrow band gap semiconductors with them.（1） TiO₂ nanotube arrays were fabricated by anodic oxidation, the influences of the conductivity, viscosity and he loop current were studied by changing water content. The main results showed that the viscosity decreases with the increases of water content, the cubics function relationship existes between initial viscosity decreases with the increases of water content, the cubic function relationship existed between initial viscosity and water content, the correlation coefficients were 0.9925. The conductivity increases gradually with the water content in the organic electrolyte, the cubics function relationship existes between initial conductivity and water content, the correlation coefficients were 0.9778. The I-t curves can be divided into 3 stages, that is decline stage, recoverable stage and stationary stage. At the decline stages, the current recovered with the increases of water content when it is less than 50%, and when the water content is 50%, the current had a slow recovery velocity. When the initial value of viscosity is between 7.0-8.0 Pa?S, the conductivity is between 900-1060μs/cm, the nanotubes’ morphology is highly in order and there is little debris on the surface of the TiO₂ nanotube arrays, the nanotubes’ diameter was between 50 nm and 72 nm, and the length was ranged from 850 nm to 1.9μm. The volume of TiO₂ films dissolved increases positively with the increasing of quantity of electric charge consumption during the oxidation process, the best quantity of electric charge consumption is 28.41C-36.44 C, which provide a theoretical basis for preparation of morphology and dimension controllable nanotube arrays.（2）Fe₂O₃/TiO₂ composite nanotubes were fabricated by cathodic deposition-anodic oxidation method, it had studied the reaction temperature, Fe2（NO3）3 concentration, stirring speed and oxidation voltage effects on the morphology, the results showed that Fe2O3 nanoparticles were even-doping on the surface of TiO₂ nanotubes and exhibites a better light absorption properties at the anodic voltage of 8V in 0.05mol/L Fe（NO3）3 electrolyte solutions with a rotational speed of 300 rpm and the temperature is 50℃; With Fe2O3 load area of indicators, stirring speed is the key regarding to the impact on Fe2O3 load area, secondly was the anodic oxidation voltage and temperature, the concentration of Fe（NO3）3 is the minimal factor.（3）The influence of the TiO₂ nanotubes and Fe2O3/TiO₂ composite nanomaterial on degradation properties to the VOCs in micro-environmental was studied by the static and dynamic photocatalytic experiment. The result indicated that the photocatalytic reactivity of Fe2O3/TiO₂ composite nanomaterial loading 1.46wt% was the best one, the degradation efficiency would reach 97.2% after 2h, and its degradation reaction was consistent with first order kinetics, the degradation coefficient is 0.0125min-1. This experiment also studied the effects of retention time, temperature, humidity, light intensity on the photocatalytic reaction efficiency in dynamic photocatalytic degradation process, the results showed that the optimal condition of degradation of VOCs in the experimental system is that retention time is 30 s, reaction temperature is 10℃, humidity is 0%, the light power density is 0.9w/cm2.