Adsorption And Photocatalytic Degradation Properties Of Highly Hydrophobic Molecular Sieve Supported TiO₂for Phthalic Ester

Environmental endocrine disruptors have caused worldwide concern at present.Phthalate acid ester is a class of environment endocrine disruptors widespread. Most ofthem are lipophilic and difficult to degrade, and can accumulate in body through the foodchain and bioaccumulation, causing huge impact on the ecological balance and humanhealth. However, Phthalate acid ester cannot be effectively removed by conventional watertreatment methods. In this study,3,3,3-trifluoropropyltrimethoxysiane was used as amodifier for the surface hydrophobic modification of MCM-41molecular sieve adsorbent.With the adsorbent as support, a hydrophobic composite photocatalyst was synthesized toachieve effective in situ adsorption-degradation removal of phthalate esters.3,3,3-trifluropropyl grafted MCM-41i.e. TFP-MCM-41was synthesized by modifyinghydrothermal MCM-41with3,3,3-trifluoropropyltrimethoxysiane via post-grafting method.TFP-MCM-41adsorbents prepared under different modifier dose, temperature and reactiontime were compared through adsorption of dibutyl phthalate (DBP) and characterization ofXRD and FT-IR, so as to optimize the synthesis condition. The optimum temperature andreaction time were110℃and18hours, respectively. The optimum molar ratio of modifierand molecular sieve was o.4.The propyl-grafted MCM-41i.e. P-MCM-41was prepared under the same conditionswith n-propyltrimethoxysilane. By comparing TFP-MCM-41with P-MCM-41andunmodified MCM-41, it was found that P-MCM-41was more hydrophobic than MCM-41,and due to the existence of–CH3, the hydrophobicity of TFP-MCM-41was higher thanP-MCM-41, as well as the adsorption capacity of DBP. The water contact angles ofTFP-MCM-41, P-MCM-41and MCM-41were151.0°,86.1°and20.5°, respectively.Under the condition of25℃and adsorbent dose of0.05g/L, the adsorption amount ofDBP on TFP-MCM-41was65.18mg/g, which was2.5and8.7times of P-MCM-41andMCM-41, respectively. TFP-MCM-41had a high adsorption rate for DBP, and theadsorption process could be described by pseudo-second dynamic model. The adsorptionisotherms conformed to Linear adsorption model. Calculated thermodynamic parameterdemonstrated that the adsorption of DBP on TFP-MCM-41was exothermic, spontaneous process, and low temperature was more favorable. In the mixed system of DBP and phenol(Ph), TFP-MCM-41had a good selective adsorption for DBP. The selective adsorptioncoefficient was much greater than P-MCM-41, and it increased with the increase in theconcentration of coexisting Ph.Hydrophobic composite photocatalysts, i.e. TiO2/MCM-41, P-TiO2/MCM-41andTFP-TiO2/MCM-41were synthesized using sol-gel method. Composite photocatalystretained the good structure properties of the MCM-41support, and TiO2was highlydispersed on the surface of MCM-41support as fine particles. Compared withTiO2/MCM-41and P-TiO2/MCM-41, the degradation efficiency of DBP byTFP-TiO2/MCM-41was enhanced significantly due to the good hydrophobic adsorptionperformance. The effective degradation of DBP by composite photocalyst was the result ofsynergistic effect of adsorption and photodegradation. There exist a best ratio between thecontent of adsorbent support and active component of catalyst. In this study, the bestphotocatalytic degradation effect was received when the mass ratio of adsorbent support andTiO2was80:20.