Removal Of Short-chain Perfluorosulfonic Acid Compounds In Water By Absorption-VUV Photochemical Reduction

Perfluorohexane sulfonate?PFHxS?and perfluorobutane sulfonic?PFBS?are the typical short-side-chain perfluorochemicals in water,with the characteristics of low concentration,high chemical stability,toxic effects,and strong hydrophilicity.Due to the ineffective removal of these two kinds of compounds by the traditional biological and chemical oxidation method,the author herein explored a new protocol for their removal by using adsorption enrichment followed by enhanced photochemical degradation.Prior to the adsorption treatment,the aminated magnetic mesoporous materials?Fe₃O₄@nSiO₂@mSiO₂-NH₂?were first prepared by using solvothermal method and sol-gel method,and the optimization of the preparation conditions was then studied,thus obtaining the optimum conditions shown as follows:during the organic silane treatment of 100 mg Fe₃O₄ nanoparticles used as magnetism nucleus,the reactive solvent was consisted of 80 mL isopropanol and 20 mL deionized water,with the ammonia addition of 1 mL/100 mL.For the amination modification,a reactive solvent mixture of 100 mL ethanol and 40 mL deionized water was chosen,with the APTS addition of 120?L/140 mL.And 6 g/L ammonium nitrate-ethanol solution was employed as the extraction reagent for the removal of template agent CTAB.The adsorption properties of PFHxS and PFBS were studied with Fe₃O₄@nSiO₂@mSiO₂-NH₂ as adsorbent after optimization preparation.The results showed that the adsorption rate of PFHxS and PFBS decreased with the increase of pH,with the maximum value at pH 4.The presence of copper ions and humic acids reduced the adsorption rate of Fe₃O₄@nSiO₂@mSiO₂-NH₂ toward the target pollutants,while chloride ions and nitrate ions had no effect on the adsorption of PFHxS and PFBS.The electrostatic adsorption of single-layer adsorption plays a leading role in the adsorption process,and the equilibrium adsorption value of PFHxS and PFBS can reach 58.83 and17.54 mg/g respectively.The adsorption isotherm of the PFHxS and PFBS adsorption were well in agreement with both the Langmuir and Freundlich models.The desorption experiments showed that desorption efficiency increased with the increase of pH.When pH was above 10.5,desorption rate could reach above 95%.After four cycles,the adsorption rate decreased to 82%and 76%of the initial values for PFHxS and PFBS adsorption respectively.The degradation of PFHxS and PFBS in various photochemical reduction systems was further investigated after the adsorption enrichment,and VUV-SO₃^2-was found to be the optimum reaction system.In this case,after reacting 5 h,the degradation and defluorination efficiencies for PFHxS with the initial concentration of 20 mg/L could reach 99.5%and 60.3%under the operation conditions of pH of 11.0±0.1,SO₃^2-concentration of 20 mmol/L,temperature of 25?.Under the same conditions,the degradation and defluorination efficiencies for PFBS was only 67.2%and 47.1%.Reduction of PFHxS and PFBS initial concentration,increasing SO₃^2-concentration and initial pH value,as well as the nitrogen atmosphere were favorable for the degradation and defluorination of PFHxS and PFBS.In coexistence substances,the presence of Cl^-facilitates the removal of the target pollutant,while NO₃^-,HCO₃^-and humic acid all hinder the degradation.The main active specie was the reductive hydrous electron in the degradation system.