Photolysis Of Tricresyl Phosphate (TCP) In Water

Organophosphorus flame retardants?OPFRs?are a class of emerging pollutants widely exist in various environmental media due to their large use.They have caused great concern because of their toxicity to organisms.Photochemical reaction has been a vital topic for a long time because it is one of the most important pathways for degradations of organic pollutants in the environment.However,most of the studies on the photochemistry of OPFRs were made under UV irradiation and in the presence of catalysts,little research has been done on the photochemical process of OPFRs in water under natural light irradiation.In the present study,the photodegradation of the most widely detected OPFRs-ticresyl phosphate?TCP?by UV irradiation in aqueous solution was investigated.The photochemical kinetics,reactive species generated during the process and photolysis products were investigated.The main research contents and results are as follows:?1?The direct photodegradation of TCP under different UV light intensities?4.67,12.89,61.6 mW/cm²?and different wavelengths?UV-A,UV-B and UV-C?were investigated.The results showed that TCP had no degradation under dark control.Direct photolysis?290 nm cut-off filters?of TCP could occur at different light intensities and wavebands,which followed the pseudo-first-order kinetics.TCP showed higher degradation rate with higher light intensity,the half-lives were 130.78 h,67.96 h and 8.75 h for light intensities of 4.67,12.89 and 61.6 mW/cm²,respectively.TCP could hardly degrade under UV-A irradiation,which indicated that the UV-B band played a crucial role for the photodegradation of TCP in natural light.Under the irradiation of UV-B light,TCP could degrade obviously and the half-life was 8.75 h while under the irradiation of UV-C light,TCP degraded rapidly with the half-life of 7.78 min.?2?The effects of initial concentration and typical natural water factors(including Fe³⁺,NO₂^-and HA)on the photodegradation of TCP under simulated solar light were studied.It was found that TCP showed higher degradation rate with the higher initial concentration.The presence of NO₂^-and Fe³⁺was observed to promote the photochemical loss of TCP,while humic acid played a negative role in TCP transformation.To further investigate the mechanisms of their effects,the reactive species generated during the reaction process were characterized by electron spin resonance EPR results showed that TCP solutions containing Fe³⁺,NO₂^-and HA could generate hydroxyl radical?·OH?,the hyperfine splitting constants were:?^N=?^H=15.07 G.Fe³⁺and NO₂^-mainly promoted the photodegradation of TCP by the formation of hydroxyl radical after irradiation.Although·OH was produced after irradiation for HA,the photodegradation rate of TCP decreased,it is speculated that HA mainly competed for a light source with TCP and thus inhibited the degradation of TCP.?3?The photolysis products of TCP were identified by high resolution liquid chromatography-mass spectrometry?LTQ-Orbitrap?.According to the previous studies on the degradation products of OPFRs and extraction of the precise molecular weight,three photodegradation products were tentatively identified.The possible degradation pathways were proposed according to the structure of the products,involving the cleavage of a phenoxy bond,C-H bond homogenization from the benzene ring structure of TCP and photoinduced hydrolysis.