VUV Photocatalytic Degradation Of Formaldehyde And Ozone Decomposition By Modified TiO₂ Film

VUV (vacuum ultraviolet) photocatalysis is a pollutant removal technology under mild conditions, which has wide perspective and practicability on the purification treatment of wastewater and air. Meanwhile, TiO₂ modified with noble metal nanopartilces as a new and efficient photocatalyst has become a hot research topic at home and abroad in recent years. But such catalysts used in the VUV system have not been reported. Therefore, Au, Pd, Pt/TiO₂ and different types of Mn-contained TiO₂ catalysts were prepaired in this study. Performances of different catalysts on the simultaneous removal of formaldehyde and ozone were investigated, and the reaction mechanism was also explored. This study is of great significance to accelerate the application of photocatalytic technology for indoor air purification.First, noble metal nanopartilces (Au, Pt, Pd) were supported on TiO₂ nanocomposite film with low-temperature adsorption method. Nanoparticles with an average diameter <5 nm were homogeneously dispersed on the TiO₂ films. Au and Pt are 0 valence, and Pd was in the form of PdO. The removal rate of formaldehyde can be improved by noble metal nanopartilces loaded on TiO₂ surface, while the ozone concentration was significantly reduced in the VUV system. The catalysts performance in the tests remained stable within 35h. Reactions in the dark condition were also carried out, which suggested the reaction mechanisms between different nano-particles and ozone were different.The influence of relative humidity and Pd loading on formaldehyde degradation and ozone decomposition by Pd/TiO₂/VUV was investigated. The removal rate of formaldehyde and ozone both increased with increasing relative humidity. The removal rate of ozone finally reached a maximum and remained stable. Pd excessive load was not conducive to the removal of formaldehyde; Ozone removal rate first increased and then decreased with increasing Pd loading.The performances of formaldehyde degradation and ozone decomposition by different Mn-containing TiO₂ catalysts under VUV were studied. Mn ion doping method was not conducive to the simultaneous removal of formaldehyde and ozone. MnO_x/TiO₂,MnO_x/Pd/TiO₂ and nano-MnO₂/Pd/TiO₂ maintained a high removel rate of formaldehyde and significantly enhanced the decomposition of ozone at the same time. Nano-MnO₂/Pd/TiO₂ performance on ozone removal was the most stable. MnO_x/TiO₂ and MnO_x/Pd/TiO₂ gradually stabilized after 20h reaction. It was found that ozone was significant decomposed by MnO_x/TiO₂ and MnO_x/Pd/TiO₂ in the dark condition, but the catalysts gradually lost activity. VUV could inhibit the deactivation of MnO_x catalysts.