Degradation Of Typical Pharmaceuticals By Nickel-cobalt Layered Double Hydroxide Activated Peroxymonosulfate

Pharmaceuticals,as a class of emerging pollutants,had been detected in a variety of environmental medias.The refractory characteristics made them persistent in the environment.Conventional water treatment techniques were difficult to completely remove such chemicals.Therefore,it was urgent to develop an effective strategy to achieve their effective degradation.Sulfate radical(SO4·-)based advanced oxidation processes(SR-AOPs)had been considered as a promising environmental remediation technology,and SO4·-could be produced through homogeneous or heterogeneous activation of peroxymonosulfate(PMS).As efficient heterogeneous catalysts,layered double hydroxides(LDHs)have been attracted wide scientific interests in the application of SR-AOPs.Multiple studies had revealed that nickel and cobalt systems had high redox activity and well coordination.However,up to date,researches on the activation of PMS by NiCo-LDH to remove pharmaceuticals were still quite limited.In the present study,NiCo-LDH was synthesized through a simple co-precipitation method.To explore the performance and mechanism of NiCo-LDH activation of PMS,carbamazepine(CBZ)was selected as a representative pollutant of pharmaceuticals to carry out degradation experiments.The results obtained from this work could provide abundant theoretical information for the understanding on LDHs induced heterogeneous SR-AOPs for the decomposition of pharmaceuticals.In addition,the degradation pathway of CBZ and the toxicity of its degradation products were also evaluated in this study,which provided a reference for water pollution remediation.Finally,NiCo-LDH was further synthesized through recovering Ni and Co in spent lithium batteries.Moreover,its effectiveness in pollutant degradation had also been investigated.This would lay a foundation for further exploration of the application of heavy metals in spent lithium batteries in advanced oxidation after recovery.The specific conclusions were as follows:(1)NiCo-LDH was successfully synthesized through simple co-precipitation method in this work.A variety of characterization results,including X-ray diffraction(XRD),field emission scanning electron microscopy(FESEM),transmission electron microscopy(TEM),X-ray photoelectron spectroscopy(XPS)and X-ray energy dispersive spectroscopy(EDS)characterization,revealed that NiCo-LDH had a typical layered double hydroxide structure,and Ni and Co were uniformly distributed on the catalyst surface with a ratio of 1:1.The results of N2 adsorption-desorption experiments displayed that NiCo-LDH was type Ⅳ isotherm with a hysteresis loop,suggesting the presence of mesoporous structure.Besides,the specific surface area and pore volume of the prepared NiCo-LDH were 72.99 m2/g and 0.26 cm3/g,respectively.CBZ degradation experiments showed that NiCo-LDH could effectively activate PMS to degrade target pollutant.In the range of 1～5 mg/L catalyst dosage and 0.05～0.3 mmol/L PMS concentration,the degradation efficiency of CBZ increased with the rising of NiCo-LDH dosage and PMS concentration.Specifically,94%CBZ removal could be achieved within 180 s under weakly acidic and neutral conditions with 5 mg/L NiCo-LDH and 0.3 mmol/L PMS.In addition,the presence of HCO3-and Cl-in the water had a significant inhibitory effect on the degradation of CBZ,while NO3-exhibited no effect on the degradation.Meanwhile,as a result of quenching of the existence of anions,cations and other organic substances in the actual water body,the degradation efficiency of CBZ in the actual water body(Zixia Lake)was significantly lower than that of ultrapure water.Three recycling tests and XRD results of NiCo-LDH before and after the reaction indicated that NiCo-LDH had good reusability and stability.Different five pollutants,namely,the anti epileptic drug carbamazepine(CBZ),the brominated flame retardant tetrabromobisphenol S(TBBPS),the herbicide picloram(PCLO),the resinous precursor bisphenol A(BPA)and the antibiotic sulfamethoxazole(SMX),showed efficient degradation in the NiCo-LDH/PMS system,demonstrating the wide applicability of the catalyst.(2)The presence of SO4·-and HO·in the NiCo-LDH/PMS system was identified by electron paramagnetic resonance(EPR)and radical quenching experiments.The kinetic modeling suggested that SO4·-played a dominant role in the degradation of CBZ.The results of XPS analysis of Ni and Co demonstrated that some Ni2+ and Co2+ in NiCo-LDH were converted to Ni3+ and Co3+ during the degradation of CBZ by activated PMS.By the Combination of such results with ERP and radical quenching tests,it can be proposed that the cycle of Ni2+/Ni3+ and Co2+/Co3-on Ni/Co-LDH surface were responsible for efficient HO·/SO4·-generation from PMS.A total amount of 25 oxidation products was identified in NiCo-LDH/PMS system through high resolution mass spectrometry(HR-MS).Based on the detected intermediates,three main pathways were proposed for the initial attack on CBZ molecular,namely,deamidation,hydroxylation of benzene ring and electron transfer to generate heterocyclic central cation radicals.Moreover,Ecological Structure-Activity Relationship Model(ECOSAR)analysis found some degradation products were still very toxic compared with the parent product.Therefore,when dealing with organic pollutants in sewage,more attention should be paid to the toxicity of degradation products to avoid greater harm to the environment in the process of removing pollutants(3)NiCo-LDH was successfully prepared through hydrometallurgical recovery of Ni and Co from spent lithium batteries.Various characterization methods,including XRD,FESEM and TEM,indicated that NiCo-LDH had a typical structure of layered double hydroxides,and Ni and Co were uniformly distributed on the catalyst surface with a 1:1 ratio.Furthermore,trace impurities generated from the above recovery process had no significant effect on structure of NiCo-LDH.The results of CBZ degradation experiments and recycling test of catalyst indicated that NiCo-LDH had good performance and stability in SR-AOPs.Moreover,CBZ still had the best degradation efficiency at a catalyst addition of 5 mg/L,PMS concentration of 0.3 mmol/L,and solution pH of weak acidity and neutrality.Radical quenching experiments manifested that the main radicals involved in this system were still SO4·-and HO·.Similarly,the impact of trace impurities on the distribution of free radicals was also slight.The research results of this paper would develop a novel strategy for the recycling of spent lithium batteries,as well as a new idea for the acquisition of activated PMS catalyst raw materials.