Removal Of Typical Perfluorinated Compounds(PFCs)by Adsorption And Photocatalysis

Perfluorinated compounds,represented by perfluorooctane sulfonate(PFOS)and perfluorooctanoic acid(PFOA),has became a serious environmental problem.The effective treatments for PFOS and PFOA in aqueous environment are highly desired due to their high biological toxicity.It is reported that adsorption is an effective strategy to remove PFOS from water at this stage.Taking economy and energy into consideration,photocatalysis is one of the commonly used techniques to degrade PFOA.Most of the reported adsorbents show limited adsorption amount.Besides,bulk photocatalysts have several drawbacks,such as high recombination rate of photogenerated electron-hole pairs.Thus,the research of highly active adsorbents and photocatalysts is the key point to remove PFOS and PFOA from water.In this paper,polyaniline nanotubes,platinum-modified indium oxide nanorods,and indium oxide nanosheets with cubic/hexagonal phase junction were prepared for the adsorption and photocatalytic degradation of PFOS and PFOA respectively.Polyaniline emeraldine salt nanotubes(PASNTs)were synthesized by one-step chemical polymerization with aniline as the precursor and camphorsulfonic acid as the soft template.Polyaniline emeraldine base nanotubes(PABNTs)were obtained through the deprotonation of PASNTs with ammonia.Both of PASNTs and PABNTs showed obvious hollow nanotube structures.Adsorption of PFOS and PFOA on PASNTs and PABNTs followed the pseudo-second-order kinetic model,and the adsorption process reached equilbrium after 30 hours.In addition,the adsorption isotherm data could be well fitted by the Langmuir model.The maximum adsorption capacity of PFOS and PFOA on PASNTs reached 1651 mg/g and 1100 mg/g respectively.Electrostatic attraction and hydrophobic interaction played important roles in the adsorption.The adsorption capacity of PFOS on PASNTs was higher at lower pH(<4.8)due to electrostatic attraction.Cycling experiments showed that PASNTs and PABNTs had high photocatalytic stability.The In2O3 nanorods were prepared with ordered mesoporous silicon SBA-15 as the template.In2O3 nanorods had a regular rod-like structure with a diameter of aprx.10 nm.Pt-modified In2O3 nanorods was synthesized by photodeposition.The Pt particles on In2O3 nanorods broadened the light absorption range and promoted the separation rate of photogenerated electron-hole pairs.The Pt-modified In2O3 nanorods prepared with 3 wt%of Pt under 700℃ showed the best photocatalytic activity(the degradation rate of PFOA with initial concentration of 200 mg/L reached 98%within 1 hour).Superoxide radicals(O2·-)and holes(h+)played leading roles in the photocatalytic degradation of PFOA.The cycling experiment results showed that Pt-modified In2O3 nanorods had high photocatalytic stability.The InOx(OH)y two-dimensional nanosheets were successfully prepared with graphitic carbon nitride nanosheets(CNS)as the template.InOx(OH)y could be converted into In2O3 nanosheets(IONS)with different crystal phases through the fast-heating treatment.IONS showed distinct two-dimensional nanosheet structure with thickness of aprx.12-15nm.Both of IONS-15 and IONS-20 showed hexagonal/cubic phase junction.IONS-15 showed the highest PFOA degradation rate,which reached 94%within 60 min.Besides,the mineralization rate of PFOA on IONS-15 reached 91%in 180 min.The degradation route of PFOA on IONS-15 was mainly the cyclic cleavage of-CF2-.In addition,the cycling experiments showed high photocatalytic stability of In2O3 nanosheets with hexagonal/cubic phase junction.