Synthesis Of B-O Based Photocatalytic Materials And Research Of Dechlorination Activity Of Chlorophenols

How to effectively separate photogenerated carriers in photocatalytic systems and efficiently use of solar energy is still a crucial scientific issue.The built-in electric field in non-centrosymmetric(NCS)material with spontaneous polarization properties can serve as an inherent driving force for efficient separation of photogenerated electrons and holes.In this paper,polarized material is constructed by incorporating alkali metal cations and halogen anions into the borate system,then defective photocatalyst material is formed,and the photocatalytic activity is enhanced in the synergy of built-in electric field and surface oxygen vacancy.In addition,the influence of different factors on the degradation activity for polar photocatalytic materials was also investigated.The specific research contents are as follows:(1)B-O based photocatalytic materials K3B6O10Br(KBB)and K3B6O10Cl(KBC)were successfully prepared by solid state reaction.The dechlorination activity was evaluated by photocatalytic degradation of CPs using K3B6O10X(X=Cl,Br)photocatalyst.The results show that the dechlorination efficiency of o-chlorophenol(2-CP)can reach more than 90%in 16 minutes under UV light irradiation,which is 6 times that of commercial P25 TiO2 catalyst.By studying the effects of different halogen anions on the structure and properties of materials,we found that the distortion of XK6 octahedrons is greatly affected by X atoms.The magnitude of the out-of-center distortion of KBC is 0.137,which is higher than KBB(0.027),indicating that the spontaneous polarization is higher,and it is more feasible to promote charge separation,thus showing better photocatalytic activity.The KPFM experiment was used to study the surface potential change of the polar photocatalyst,and it was found that KBC has a larger surface potential change.In addition,electron spin resonance(ESR)test and active species capture experiments show that·O2-plays a major role in photocatalytic degradation of 2-CP,followed by e-,h+ and ·OH.(2)Different halogen atom-substituted oxyhalide borate crystal materials RbNa2B6O10Cl and RbNa2B6O10Br were successfully synthesized by high temperature solid phase method.The photocatalytic activity of 2-CP over RbNa2B6O10X(X=Cl,Br)under UV light irradiation showed that the degradation efficiency of RNBB was lower than that of RNBC,and the reaction rate constants of RNBC and RNBB were 0.1577 and 0.1257 min-1 respectively.The solid powder sample was tested by ESR and the results showed that different halogen atom substitutions can affect the oxygen vacancy concentration on the surface of the material,and the oxygen vacancy signal intensity of RNBC is greater than that of RNBB.Active radical experiments by ESR experiments in solution system and acive species capture experiment confirmed that in the photocatalytic degradation of 2-CP,the order of active species was·O2->e->h+>·OH.(3)Polar photocatalyst Na3VO2B6O11 was prepared by a simple high temperature solid phase method.The effects of different factors on the photocatalytic activity of Na3VO2B6O11 polar photocatalyst for the degradation of 2,4-dichlorophenol(2,4-DCP)under UV-vis irradiation were investigated.The results showed that when H2O was used as solvent,the photocatalytic degradation efficiency of 2,4-DCP reached a maximum of 90%after 30 min reaction,followed by C2H5OH,and finally C3H6O.The degradation efficiency of low concentration 2,4-DCP is better than that of high concentration.Under low luminescence intensity,the photocatalytic degradation efficiency is proportional to the light intensity.The appropriate amount of photocatalyst can promote the photocatalytic activity;when the amount of the catalyst was 0.20 g,the photocatalytic degradation activity was the best,reaching 94%.Inorganic anions(Cl-,CO32-and PO43-)contribute to the photocatalytic degradation of 2,4-DCP,and CO32-has the strongest promoting effect.