Photocatalytic Decomposition Of Perfluorooctanoic Acid （PFOA） By TiO₂and Pt Doped TiO₂

Perfluorooctanoic acid (PFOA) has gained wordwide concerncs because of their widespread usage, persistence, bioaccumulation and it is recognized as a new persistent organic pollutant (POPs) in the "Stockholm Convention". Thus, decomposition of PFOA is of prime importance. Heterogeneous photocatalytic decomposition of PFOA by TiO2under UV light was investigated. Major mechanisms including the primary oxidants in the photocatalysis and the rate-determining step were discussed in details. Further more, the photocatalytic using Ag, Pd, or Pt doped TiO2prepared by chemical impregnation-reduction were investigated. The catalysts were characterized and the data were correlated to the photocatalytic activity in order to understand the mechanistic detail of the metal dosage on the activities enhancement, as well as the different intermediates and decomposition pathway. This is important for the application of the photocatalyitic decomposition of PFOA by TiO2.1. Heterogeneous photocatalytic decomposition of PFOA by TiO2(P25) under UV light was investigated. Experimental conditions were varied to demonstrate their effects on the decomposition of PFOA. It was observed that photocatalytic degradation kinetics of PFOA fit to the quasi-first-order equation. The pH played a determining role in the decomposition of PFOA and the presence of O2increased the degradation rate. Optimal conditions for completely removal were obtained using1.5g·L-1TiO2at pH3in O2atmosphere, the rate constant is0.588h-1.2. A possible mechanism for photocatalytic degradation of PFOA was proposed. It was found that photogenerated holes (hvb+) were the major reactive species which responsible for66.1%of the degradation rate, and the·OH involved in PFOA degradation as well. In addition, the photocatalytic experiment with the addition of NaF indicated that the adsorption of PFOA is of primary importance for the photocatalytic decomposition. Perfluorocarboxylic acids (PFCAs) with shorter carbon chain length as intermediates and products were identified with UPLC-QTOF/MS and a possible mechanism for PFOA decomposition was proposed.3. The photocatalytic decomposition of perfluorooctanoic acid (PFOA) in aqueous solution using Ag, Pd, or Pt doped TiO2prepared by chemical impregnation-reduction was investigated. The deposition of noble metallic particles on TiO2-P25led to an enhancement of the activity of the bare semiconductor. Photocatalytic activity for PFOA TOC removed and defluoridation with Ag, Pd or Pt doped TiO2were2.1,1.5,1.1and8.7,5.4,2.6times higher than that by TiO2.I is shown that the ability of the catalyst to mineralize PFOA depends on the ability of UV light (365nm) absorption and electron affinity of the deposited metal. 4. Heterogeneous photocatalytic decomposition of PFOA by Pt-TiO2under UV light was investigated. Optimal conditions for completely removal were obtained using1at%Pt doped,0.5g-L-1Pt-TiO2at pH3in air atmosphere.5. A possible mechanism for noble metal doped TiO2photocatalytic degradation of PFOA was proposed by using Pt-TiO2as a representative. The intermediates and products were identified with UPLC-QTOF/MS and the product can be classified into two Categories:CnF2n+1, CnF2n+1O, CnF2n+1COO and CnF2n-1, CnF2n-1O, CnF2n-iCOO. The-OH simultaneous with the Pt (e-) were responsible for the efficient removed rate of PFOA.