Photodegradation Of Propranolol Through The Synergistic Effect Of Visible Light-responsive Bismuth-based Composites And Persulfate

β-blockers are being used widely due to maximum patients of the cardiovascular diseases globally.They were discharged from the organism in the form of parent compounds into the municipal sewage treatment plant with sewage because they cannot be completely metabolized in the organism.Traditional sewage treatment technologies play a very weak role in their removal.Thus β-blockers were discharged into the natural water environment along with the effluent of the sewage plant.Many reports had confirmed that β-blockers were detected in various water bodies.Toxicological studies had shown that β-blockers residual in natural water bodies existed adverse effects on aquatic ecosystems and public health.Therefore,the elimination of β-blockers in the water environment is a problem that needs to be solved urgently.Recently,semiconductor photocatalysis technology is a potential method to deal with energy and environmental issues worldwide.It has aroused the interest of many researchers in recent years because of the advantages of green and low energy consumption.The development of high-efficiency photocatalysts for specific applications is one of the main challenges facing the field of photocatalysis.Bismuth-based materials are considered to be the promising photocatalysts for environmental remediation due to their high chemical stability,good catalytic performance,simple preparation and non-toxicity.Bismuth-based materials have a special layered structure,which can form an internal electric field which benefits to exhibit high photocatalytic activity.However,the bismuth-based materials exist the problems such as weak visible light response ability and low photogenerated carriers concentration in the actual application process.In response to these problems,the bismuth-based materials were modified to obtain high-efficiency visible light-responsive bismuth-based photocatalysts.Furthermore,persulfate,as an electron acceptor and oxidant,was introduced into the photocatalytic system in order to further improve the redox ability of the photocatalysts and achieve the efficient removal of the β-blocker in the environment.In this study,propranolol,the most toxic β-blockers,was selected as the target pollutant.The visible light-responsive bismuth-based materials were used as the photocatalysts and persulfate was used as the oxidant.The behaviors and mechanisms of propranolol photodegradation by visible light-responsive bismuth-based materials synergized with persulfate were studied.（1）The BiOCl_xI_1-x solid solution were synthesized by solvothermal method using bismuth nitrate pentahydrate as the bismuth source and ethylene glycol aqueous solution as the solvent.The microscopic morphology,crystal structure,optical properties,element analysis and element valence state of solid solution were characterized by SEM,XRD,UV-vis and XPS.The characterization results showed that BiOClxI1-x were successfully synthesized,and they were not the mechanical mixture of BiOCl and BiOI,but Cl and I lattices replaced each other to form a new solid solution.The performance of BiICl0.5I0.5 solid solution/persulfate system for photocatalytic degradation of propranolol was systematically studied.The photocatalytic activity of the solid solution was significantly higher than that of the single BiOCl and BiOI,which indicated that the formation of the solid solution effectively regulated the oxidation-reduction capacity and visible light response range of the photocatalyst.The photogenerated electrons generated by solid solution was captured by persulfate to reduce the carriers recombination rate and promote the degradation efficiency of the photocatalytic system.In the free radical capture experiments,the significant inhibitory effects of sodium oxalate and ascorbic acid on the degradation of propranolol indicated that h+and·O2-were the main active species for degradation,·OH was a secondary active species.（2）The Bi₂O₃/BiO₍1.4_I0.3 heterojunctions were prepared by solvothermal method.Similarly,the microscopic morphology,crystal structure,optical properties,element analysis and element valence of the catalyst were characterized by SEM,XRD,UV-vis and XPS.The microscopic morphology of the heterojunction was completely different from single Bi₂O₃ and BiO₍1.4_I0.3,indicating that the heterojunctions were not the simple mechanical mixture of them.When the molar ratio of bismuth oxide to defective bismuth oxyiodide in the heterojunction was 7:3,its photocatalytic performance was the best among them and was significantly better than that of single Bi₂O₃ and BiO₍1.4_I0.3.The activity of the photocatalytic system was further improved after further introduction of persulfate into the reaction system.The effects of different factors on the photodegradation of propranolol were systematically investigated.NO₃-had almost no effect on the photocatalytic system,but low concentration of Cl-promoted PRO degradation.It was beneficial to the catalytic degradation of propranolol when the solution pH was weakly alkaline.Humic acid inhibited the photocatalytic activity of the reaction system because it competed with the photocatalyst to absorb visible light.The free radical capture experiment proved that the key active species in the system were h+and·O₂-.And the possible photocatalytic oxidation mechanism was proposed based on all experimental results.