Photocatalytic Degradation Of Chlorinated Phosphate Flame Retardants In TiO₂ Aqueous Solution

In recent years, organic phosphate ester flame retardants were widely added into many kinds of industrial chemical products, and are now frequently detected in various environmental media, which has aroused people’s wide concern. As chlorinated organic phosphate flame retardants are difficult to remove in wastewater treatment plants, and their natural degradation is also slow, we need to deal with it with other methods. Due to the wide application, highly catalytic activity, clean and secondary-pollution-free property as well as low price, TiO2 has been broadly used in the removal of many kinds of organic and inorganic pollutants. The catalytic effect of TiO2 depends largely on its exposed exterior surface, thus the synthesis of anatase TiO2 with highly active (001) crystal plane, and study on the degradation of chlorinated organophosphate is of great significance.In this article, commercialised P25 was adopted to decompose typical chlorinated organophosphate TCPP, and then nanosized TiO2 with (001) crystal plane exposition was synthesised. Using the synthesized material, the study of photocatalytic degradation of TCEP、TCPP and TDCP has been carried out, and TCPP was chosen to investigate the influence of different factors on the degradation and to speculate its possible degradation pathway as a case study. Main results were summarized as follows:(1) Under the condition of both P25 and UV, the degradation efficiency of TCPP reached 80% in 12 hours, and pH value of solution decreased from 6.36 to 5.53, and the reaction conformed to pseudo-first-order kinetics. The degradation efficiency of TCPP increased with the enhancement of light intensity. The degradation efficiency decreased with the increasing initial concentration of TCPP from 1.0 to 6.0 mg/L. And the degradation efficiency of TCPP increased with the increase of the P25 dosage from 0.5 to 2.0 g/L. When the initial pH of solution changed from 2.0 to 11.0, the degradation efficiency of TCPP showed a downward trend.(2) TiO2 synthesized by high-temperature solvothermal method was characterized by XRD, SEM, TEM, laser Raman spectrometer as well as ultraviolet absorption spectrometer, to confirm the exposed face of anatase TiO2; The prepared material combined with UV light-365 nm could effectively degrade TCPP, degradation rate could reach 50% within 90 minutes, nearly 100% within 360 minutes, and the degradation also conformed to pseudo-first-order kinetics. The degradation rate of TiO2-001 on TCPP was higher in acidic condition than that in alkaline condition, but not significantly. When the initial concentration of TCPP augmented from 1.0 to 6.0 mg/L, the degradation efficiency decreased; the degradation rate of TCPP increased with the increase of TiO2-001 dosage; the degradation rate of TCPP under TiO2-001 system also increased with enhancement of light intensity. By adding inhibitors of free radicals and holes, it was proved that · OH was the main active factor in TiO2-001-UV system.(3) The degradation of TCEP、TCPP and TDCP could all occur in TiO2-001-UV system, and pH value decreased in the process, and during the equivalent time and with same molar concentration, the order of degradation efficiency is TCPP>TDCP> TCEP; Ion chromatography results showed that degradation of three kinds of chlorinated organophosphate can all generate Cl- and CH3COO-; The data collected from MS spectrometer indicated that degradation products of TCPP include phosphorate,2-hydroxyl phosphate ester, aldehyde, oxalic acid and other small organic molecules, from which we could infer its possible degradation process: dechlorination, dealkylation and further oxidation of alkyl, which engendered phosphorate, carbon dioxide and water, which rendered the pollutants thorough innocuousness.