Al2O3-enhanced Macro/Mesoporous Fe/TiO2 for Breaking Down Nitric Oxide

Abstract

High air contaminant levels in the indoor environment come from either the ambient air or from indoor sources. (Cao, 2001) Nitrogen oxide is one of the most common gaseous pollutants found in the indoor environment with the concentration in the range of 70-500 parts-per-billion (ppb) levels. This has serious implications on the environment and health of the mankind. (Huang et al., 2009) Conventional techniques to treat nitric oxide in industrial emission mainly include physical adsorption, biofiltration, and thermal catalysis methods. However, these methods usually suffer from some disadvantages, such as the low efficiency for pollutants at the parts per billion level and the difficulty in solving the postdisposal and regeneration problems. (Huang et al., 2008) As a promising environmental remediation technology, semiconductor-mediated photocatalytic technology has been widely used to purify contaminated air and wastewater. (Fox & Dulay, 1993 ) Titanium dioxide is the most widely used photocatalyst because of its superior photoreactivity, nontoxicity, long-term stability and low price. Recently, great attention has been paid to macro/mesoporous TiO2 for its interconnected macroporous and mesoporous structures. Such hierarchical material may enhance properties compared with single-sized pore materials due to increased mass transport through the material and minimized pressure drop over the monolithic material.(Yuan et al. 2006) Meanwhile the macroporous channels could serve as light-transfer paths for the distribution of photon energy onto the large surface of inner photoactive mesoporous frameworks. Therefore, higher light utilization efficiency could be obtained for heterogeneous photocatalytic systems including photooxidation degradation and solar cells. In addition, the hierarchical structure-in-structure arrangement of mesopore and macropore is benefit for the molecule traffic control and for the resistance of the photocatalyst to poisoning by inert deposits.(Rolison 2003) Though such structure contributes great advantages to TiO2, such as a readily accessible pore-wall system and better transport of matter compared to the traditional TiO2 photocatalysts, the anatase TiO2 semiconductor has a relatively large band gap of 3.2 eV, corresponding to a wavelength of 388 nm.(Yu et al., 2006) The requirement of UV excitation impedes the development of solar-driven photocatalytic systems. As a promising way, doping method can effectively extend the light absorption of TiO2 to the visible region and reduce the recombination of photoinduced electrons and holes.(Zhu et al., 2007) Among