The Mechanisation And Characteristics For The Photocatalytic Conversion Of Gaseous VOCS On Lanthanum-Doped Titanium Dioxide Nanotubes

In recent years, environmental pollution problems caused by have received more and more public attention. Single biological treatment technology showed low efficiencies for some hydrophobic and recalcitrant VOCs, because they were difficult to be degraded or even non-degraded. Consequetly, it was more concerned to find a technology which could transfer VOCs into easily degradable product for the complete removal by biopurification.The photocatalytic properties of titanium dioxide (TiO2) made it an attractive material for environmental remediation, In the present study, lanthanum (La3+)-doped TiO2 nanotubes with excellent photocatalytic activity were fabricated by a combination of sol-gel method and hydrothermal technique. Compared with pure TiO2 nanoparticles,1.2% -La3+- doped -titania nanotubes (1.2%-La3+-TNTs) exhibited higher activity under 254 nm UV for conversion of EB and Pinene.The influene of initial concentrations and relative humidity (RH) on the photocatalytic activity of 1.2%-La3+-TNTs were investigated. It could be found that the optimal humidity was 40-50% for the conversion of EB and a-pinene (93% and 94% respectively). When the initial concentration was from 50 to 250 mg/m3 and 50 to 400 mg/m3, the conversion of EB and a-pinene were from 94% to 58% and 94% to 78%, respectively. The photocatalytic behavior of EB and a-pinene matched the classical kinetic mode of Langmuir-Hinshelwood. GC/MS were used to analyze the intermediates generated in the conversion of EB and a-pinene. The mian intermediates were benzoic acid, benzaldehyde, phenol, verbenone, pinocamphone and other short-chain carboxylic acids. The conversion characteristics of waste mixtures of EB and a-pinene during the photocatalytic process were also investigated. The low concentration of EB would hardly influence the conversion of a-pinene and the high concetration of EB would restrain the conversion of a-pinene under the same humidity. However, no matter what the concetration of a-pinene was, the conversion of EB would be restrained.The study made rigorous analysis of biological water-solubilty and ecological toxicity of intermediate products. EB and a-pinene would transfer into a lot of water soluble product with the relative humidity of 40-50%. The LC50 for zebrafish was 111.13 ppm during the residence time and relative humidity were 60 s and 80% respectively, and much better than that of blank control.The above reslults have shown that the prepared photocatalyst 1.2%-La3+-TNTs exhibited good photocatalytic activity for the conversion of VOCs. Such purification technology based the prepared catalyzer could be used as the single technology or the pretreatment before the subsequent biopurification.