Effect Of Surface Oxygen Vacancy Over BiOCl On The Oxygen Activation And The Photodegradation Of Organic Pollutants

The rapid development of economy in modern society has brought many conveniences to our lives,but also caused problems such as energy shortage and environmental pollution.Among them,water pollution is particularly prominent.A large amount of wastewater rich in organic pollutants is randomly discharged into natural water bodies without treatment,causing great harm to both human health and the ecological environment.Because of the advantages,such as environment-friendly,mild reaction condition and low energy consumption,semiconductor photocatalysis technology has attracted world wide attention recently.Bismuth oxychloride（BiOCl）is an ideal semiconductor photocatalyst due to its low toxicity,unique layered structure,and easy control of surface structure.However,the preparation of efficient BiOCl photocatalysts is still an urgent problem to be solved.In this paper,phosphate was surface modified on BiOCl exposed with（001）or（010）facets,respectively by impregnation method,and the purpose of this work was to study the effect of surface anion modification on BiOCl molecular oxygen activation,electron-hole separation and degradation of organic pollutants.The details are as follows:1.BiOCl exposed with（001）facets（BOC-001）was synthesized by a simple hydrothermal method,and BOC-001 was treated by phosphoric acid solution via impregnation method to obtain the phosphate-modified BiOCl（P-BOC-001）.Characterizations show that the surface modification of phosphate would construct a surface hydrogen bond network between the BiOCl surface and the phosphoric acid,thus selectively weaken the Bi-O bonds in a short range,which facilitate the formation and regeneration of surface oxygen vacancy（OVs）,thereby improving its O₂ activation capacity.In addition,fluorescence spectroscopy and electrochemical analysis indicated that P-BOC-001 had higher electron-hole separation efficiency and charge transfer rate.P-BOC-001 showed higher photocatalytic activity in the photocatalytic degradation of p-chlorophenol（4-CP）,the reaction rate was about 7.2 times higher than that of BOC-001,and the mineralization rate could reach 65.6%.The reactive species capture experiments showed that the main active species were h⁺and ¹O₂ during the 4-CP photodegradation over P-BOC-001.Meanwhile,it is interesting to find that there was?Cl in the reaction process,which could convert into HCl O and participate in the conversion of active species（HCl O+H₂O₂→¹O₂+H₂O+H⁺+Cl^-）.The 4-CP photodegradation pathway was further schemed based on the intermediated detected by GC-MS and HPLC,and the role of ¹O₂ on the photodegradation was specifically analyzed.2.BiOCl exposed with（010）facets（BOC-010）was synthesized by hydrothermal method,and then modified with phosphoric acid by the similar method to prepare P-BOC-010.The（010）crystal facet is composed of coordinatively unsaturated Bi,O and Cl atoms with an open channel structure,characterizations revealed that phosphate ions were adsorbed on the surface of BiOCl through hydrogen bonds,neither change in the crystal structure of BiOCl nor new substances formed.P-BOC-010 exhibited higher molecular oxygen activation ability,carrier separation efficiency and charge transport rate than that of BOC-010.In the photocatalytic degradation of sulfamethazine（SM2）,P-BOC-010 showed better catalytic activity,the photodegradation rate was 2.2 times higher than that of BOC-010,and the mineralization efficiency was 1.5 times higher for P-BOC-010 in compare with BOC-010.Mechanism studies show that ¹O₂ and h⁺are the main active species during the SM2photodegradation.