Study On Degradation Of Reactive Black 5 And Tetracycline In Water By Zero-Valent Aluminum/Oxidant System

Advanced Oxidation Processes（AOPs）are high-efficiency,low-pollution,and are a hot research topic in pollutant treatment.The zero-valent aluminum/oxygen/acid（Al⁰/O₂/H⁺）system is a green and clean advanced oxidation technology,but The reaction rate is slightly slow.In this paper,a certain amount of oxidant such as Permonosulfuric（PMS）,Peroxydisulfate（PDS）,Hydrogen Peroxide（HP）is added to the original Al⁰/O₂/H⁺system.to promote the degradation of pollutants.The degradation rate and its influencing factors of Al⁰/PDS,Al⁰/PMS and Al⁰/HP were investigated by Reactive Black 5（RBK5）and Tetracycline（TC）.The mechanism of substance production,the intermediate product of TC degradation was determined by HPLC-MS,and the degradation pathway of TC to the three systems was presumed.The main contents are as follows:（1）The optimal conditions for determining the degradation of RBK5 in Al⁰/PDS system are pH=3,PDS=50 mmol L^-1,Al⁰=0.4 g,RBK5=50 mg L^-1.Under the optimal conditions,the degradation rate is 98.06%which is the best in 120 min.The increase of temperature is beneficial to the degradation of RBK5.The anion Cl^-,NO₃^-,HCO₃^-react with SO₄·^-and·OH to form less oxidative free radicals and are not conducive to the degradation of RBK5.The quenching experiment showed that the most effective free radicals in the system was SO₄·^-.The ultraviolet-visible absorption spectrum of TC process and the change of aniline concentration in the system by Al⁰/PDS system indicate that the free radicals can easily attack the molecular structure of RBK5bisazo bond,and the degradation effect of Al⁰/PDS system on small molecule benzene ring intermediates better than Al⁰/O₂/H⁺system,but RBK5 is not completely mineralized,and the TOC degradation rate is 34.09%.（2）The optimal conditions for degradation of TC in Al⁰/PDS,Al⁰/PMS and Al⁰/HP systems were determined:pH=3,PDS=30 mmol L^-1,Al⁰=0.6 g,TC=20 mg L^-1（Al⁰/PDS system）;pH=3,PMS=20 mmol L^-1,Al⁰=0.6 g,TC=20 mg L^-1（Al⁰/PMS system）;pH=2,HP=3 mmol L^-1,Al⁰=0.6 g,TC=20 mg L^-1（Al⁰/HP system）.The degradation rate of TC under optimal conditions was:Al⁰/PMS（98.86%）>Al⁰/PDS（95.76%）>Al⁰/HP（76.47%）.（3）By examining the annihilation experiments of free radicals,the changes of H₂O₂ and·OH content in Al⁰/PDS,Al⁰/PMS and Al₀/HP systems with time indicating that the main effect of TC degradation in Al⁰/PDS system is SO₄·^-,in the Al⁰/PMS system SO₄·^-and·OH play a major role in degradation,and the total amount of free radicals in the Al⁰/PMS system is higher than that in the Al⁰/PDS system;the Al⁰/HP system only produces·OH,so that The degradation rate of TC is low.Oxygen promotes the degradation of TC.（4）Through the calculation of quantum chemistry theory,it is concluded that the E_HOMO–E_LUMO is the smallest,O-O bond is the most unstable,and it is easy to accept electrons to generate free radical to degradation TC,followed by PDS,and finally HP.It is proposed that the degradation rate and reaction rate constant of TC with three oxidant systems increase with the E_HOMO–E_LUMO decrease,which further explains the reason of Al⁰/PDS and Al⁰/PMS and Al⁰/HP systems have different reasons for the degradation rate of TC theoretically.（5）In the degradation of TC,13 kinds of intermediates in Al⁰/PDS,Al⁰/PMS and Al⁰/HP systems were detected by HPLC-MS.Most of them were four-membered ring and three-membered ring organic compounds which were opened by free radical oxidation.The degradation pathways of four TCs were inferred.Among them,the Al⁰/PDS system only contains the paths I,II,and III in which SO₄·^-acts.The Al⁰/HP system only contains the paths I,IV,in which·OH acts.Al⁰/PMS systems contains all four paths.