Study On The Degradation Of Sulfamethazine By Sodium Percarbonate Activated By Iron Ion

Sulfonamides are widely and extensively used as antibacterial drugs and growth promoters.They have been detected in surface water,underground water,and the effluent of wastewater treatment plants.Although their concentration levels are generally in the range of nanograms to micrograms per liter,they could damage ecological environment and public health.Therefore,the research on the degradation of SAs has become a hot spot in environmental protection.The Fenton process is widely used domestically and abroad for its advantages of safety,easy operation and cleanliness.However,the traditional Fenton process has some disadvantages when treating the organic waste water,such as high cost of treatment,low degradation rate and secondary pollution.In order to avoid these drawbacks,studies have done to improve it.It is simple and feasible to find a new type of oxidant to replace H2O2 in traditional Fenton process,and then combining it with photocatalyst can greatly improve the mineralization efficiency of organic pollutants in wastewater.Thus,it will play an important role in treating organic pollutants as a new composite oxidation process.The performance of Fe(?)-catalyzed sodium percarbonate stimulating the oxidation of Sulfamethazine(SMT)was investigated in the present study.The effects of initial concentration of Fe(?)and SPC and the initial solution pH were evaluated.Results showed that the degradation rate was enhanced with the increase of the initial concentration.When the concentration reached a certain value,however,it became an inhibition instead.Therefore,the best ratio of Fe(?)/SPC/SMT was 15:10:1 where the degradation rate reached84%.The increase of initial pH had a little inhibiting effect on the SMT degradation rate,but the degradation rate was still higher than expected even in the alkaline condition(the degradation rate reached 74% under pH 8.0).The main active species in Fe(?)/SPC system were also discussed by adding scavenger,and HO· was found to be the main active specie in the system.And then the main product were identified by using LC-MS technique and possible degradation pathway was proposed,indicating that hydroxylation,[S-N] bond cleavage and SO2 extrusion were three possible degradation pathway.It can be predicted that Fe(?)/SPC system has a certain application prospect in the degradation of refractory organic wastewater.On this basis,we combine it with photocatalytic technology to improve the degradation.Metal–organic framework MIL-53(Fe)was prepared by a mild solvothermal process.The morphology,structure,composition and photochemical properties of MIL-53(Fe)were characterized,and the results were consistent with those of previous studies.suggesting that our synthesis method is feasible.Then,we investigated the degradation effect of SMT by MIL-53(Fe)cooperating with Fe(?)/SPC under the illuminating by a 9-watt wavelength range 450-455 nm LED light source.Result showed that the system has a stronger catalytic effect compared with MIL-53(Fe)/SPC and Fe(?)/SPC.The degradation rate of SMT is as high as 91% and the removal rate of TOC can reach 55% in 60 min,indicating that the adding Fe(?)can significantly improve the synergism.It can be seen that the MIL-53(Fe)/Fe(?)/SPC system can exert a strong oxidation effect even adding a low amount of reactants.In all the experiment,the concentration of MIL-53(Fe),Fe(?)and SPC are 0.2g/L,0.3mmol/L and 0.1mmol/L,respectively;and it is noted that the system is suitable for a wide range of pH condition.There is no significant difference between the SMT degradation rate in the range of pH 4-10 and the degradation rate is still remarkable even in the alkaline condition.The mechanism study indicated that the electron holes h+ and HO· played an important role in the degradation of SMT in MIL-53(Fe)/Fe(?)/SPC system.The Fe(?)ions in the system was considered as the electron carrier.Photoinduced Electrons and holes generated on the surface of MIL-53(Fe)under light irradiation,and then the holes could react with OH-in the solution to produce HO· participating in the degradation of SMT,while photoinduced electrons transferred through Fe(?)ions to react with H2O2 and produced HO· involved in the degradation of SMT.It can be seen that the introduction of Fe(?)at a low stoichiometric concentration can significantly accelerate the photocatalytic degradation of SMT in the MIL-53(Fe)/Fe(?)/SPC process.It may provide a new opportunity to develop more highly efficient visible-light-driven photocatalysts for water disinfection.