Activation Of Peroxymonosulfate By Perovskite For Degradation Of Organic Pollutants

Sulfate radical(SO₄^·-)-based advanced oxidation processes have a promising application in the field of water treatment due to their potential ability to remove refractory organic pollutants.Recently,cobalt-based heterogeneous catalysts have been widely investigated for peroxymonosulfate（HSO₅^-/PMS）activation in SO₄^·--based advanced oxidation processes.However,the improvement of the catalytic performance for PMS activation remains to be a challenge.As the limiting step,the rapid transformation of Co²⁺/Co³⁺redox pairs is crucial for PMS activation.The A-and/or B-site cations of perovskites can be appropriately substituted by a foreign cation without destroying the structure,which can control the oxidation state of B-site cation and introduce the oxygen vacancies,thus accelerates the redox cycle of Co²⁺/Co³⁺.LaCo_1-xM_xO₃（M=Cu,Fe and Mn）perovskites as heterogeneous catalysts were synthesized for PMS activation.In this paper,the relationship between the type of substituted elements,amount of substituted Cu and the catalytic performance was investigated.In addition,the mechanism of degradation organic pollutants by PMS activation on perovskites was speculated.This provides the scientific support and theoretical basis for the exploitation of efficient cobalt-based heterogeneous catalysts.The following are the main research contents and results:（1）The perovskite catalysts with different substituted elements and Cu substituted amounts were prepared by changing the type and ratio of precursors（transition metal hydrate nitrates）using the sol-gel method,and the morphologies and structures of perovskite catalysts were observed via a series of characterization methods.The results demonstated that perovskites showd a rhombic hexahedral structure and consisted of a porous foam-like structure with spheroidal particles besides LaCuO₃.Furthermore,the presence of micropore and mesopore was in favour of mass transfer and diffusion.（2）Phenol,rhodamine B（RhB）,atrazine and sulfamethoxazole（SMX）were chose as the targeted pollutants to study the catalytic degradation performance of perovskite catalysts from substituted elements,Cu substituted amounts,influence factors and stability.The results showed that LaCo_0.4Cu_0.6O₃ exhibited the highest catalytic activity,and its kinetic constant of phenol degradation is about 5.0 and 53.6 times as high as Co²⁺and Co₃O₄,respectively.Apart from phenol,several other types of organic pollutants such as RhB,SMX and atrazine can also be almost completely removed within 12 min.The catalytic performance of LaCo_0.4Cu_0.6O₃/PMS system increased with the increase of reaction temperature,catalyst dosage and PMS concentration,meanwhile,LaCo_0.4Cu_0.6O₃/PMS system has the wide pH range of application（4.6-9.0）and low activation energy,which was beneficial to PMS activation.In addition,perovskite LaCo_0.4Cu_0.6O₃ has good reusability and stability.（3）The radicals involved in LaCo_0.4Cu_0.6O₃/PMS system were identified by quenching test and electron spin resonance spectroscopy.Besides,the transformation of transition metal valence state and oxygen species in perovskites before and after reactions was analyzed by X-ray photoelectron spectroscopy.The results indicated that SO₄^·-,·OH and ¹O₂ were generated in LaCo_0.4Cu_0.6O₃/PMS system,and SO₄^·-was the primary active radical.For LaCo_0.4Cu_0.6O₃/PMS system,the rapid Co²⁺/Co³⁺redox cycle played a dominant role in the catalytic property.The substitution of Cu accelerated the reduction of Co³⁺to Co²⁺,thus facilitated the PMS activation to generate more SO₄^·-.In addition,the oxygen vacancies also gave some contribution.