Study On The Efficiency And Mechanism Of Degradation Of Rhodamine B By Heterogeneous Cobalt-activated Peroxymonosulfate Under Ultraviolet Ligh

With the rapid development of industry and the improvement of people’s demand for quality of life,the production of synthetic dyes commonly used for coloring in textile,paper,plastic,leather,food and cosmetic industries has proliferated,but their discharge into water bodies will cause serious water pollution.In recent years,Advanced Oxidation Processes（AOPs）based on sulfate radicals(SO₄^·-)have been effective in treating printing and dyeing wastewater,among which Peroxysulphate（PMS）is easily activated due to its highly asymmetric molecular structure.However,little research has been reported on the activation of PMS by introducing non-homogeneous cobalt-based catalysts under ultraviolet（UV）radiation conditions.Therefore,in this study,we firstly established the UV/Co₃O₄/PMS system and selected Rhodamine B（RhB）as the target pollutant to investigate the catalytic degradation performance of the system;secondly,we loaded Co₃O₄ on rice husk biochar（BC）to prepare Co₃O₄@BC composites and established the UV/Co₃O₄@BC/PMS system to degrade RhB.In addition,the effects of PMS concentration,catalyst dosage,UV intensity,initial concentration of RhB,and background components on the degradation efficiency were investigated in this study,and the safety and reusability of the catalyst were also analyzed,and the possible degradation mechanism of RhB was explored and proposed.The following results were obtained:（1）Under the conditions of PMS concentration of 0.4 g/L,Co₃O₄ dosing of 100 mg/L,UV radiation intensity of 40 W·m^-2 and initial RhB concentration of 30 mg/L,the degradation rate of RhB by UV/Co₃O₄/PMS system could reach 90%within 30 min,and the reaction rate constant reached 0.07309 min^-1,which was 4.4 times and 3.4 times higher than that of UV/PMS and Co₃O₄/PMS systems respectively.（2）BC was used as a carrier to load Co₃O₄ nanoparticles.The SEM and TEM characterization showed that Co₃O₄ was successfully loaded on BC and the Co₃O₄ particles in the composite were of nanoscale size;the Raman characterization showed that the resulting material had a high degree of defects and graphitization;the FT-IR spectra showed that the Co₃O₄@BC composite had a spinel structure.the absorption peaks of the full range XPS spectrum prove the presence of C 1s,Co 2p and O 1s,and the presence of Co³⁺and Co²⁺in the Co 2p spectrum is determined in the Co₃O₄@BC,which also indicates that Co₃O₄ is successfully loaded on BC.（3）Under the same conditions and the catalyst dosage of 20 mg/L,the degradation rate of RhB by UV/Co₃O₄@BC/PMS system reached 99.8%in 25 min with a reaction rate constant of0.25007 min^-1,which was about 11.23 times higher than that of UV/Co₃O₄/PMS system under the same reaction conditions.（4）The degradation rate of RhB in both systems increased and then decreased with the concentration of PMS,increased with the amount of catalyst added and the intensity of UV radiation,and decreased with the initial concentration of RhB.The degradation rate was greatly inhibited in a strong acidic environment（pH=3）,remained at a high level as the pH increased,and was best in a weak alkaline environment（pH=8.4）.（5）In the UV/Co3O4/PMS system,Cl^-and NO₃^-played a dual role in the degradation of RhB,inhibiting it at low concentrations and promoting it at high concentrations;SO₄^2-inhibited the degradation of RhB and humic acid promoted it to some extent;while in the UV/Co₃O₄@BC/PMS system,Cl^-had an inhibitory effect,NO₃^-had no significant effect on the degradation rate of RhB,the presence of SO₄^2-also inhibited the degradation of RhB,and humic acid promoted the degradation of RhB.Overall,the UV/Co₃O₄@BC/PMS system had a broader range of natural water background components than the UV/Co₃O₄/PMS system.（6）The catalyst safety and reusability studies were carried out for UV/Co₃O₄/PMS and UV/Co₃O₄@BC/PMS.The dissolved cobalt ion concentrations were 86.3μg/L and 121.1μg/L,respectively,which were within the limit of 1 mg/L specified in the Emission Standards for Industrial Sources of Copper,Cobalt and Nickel（GB25467-2010）.The degradation rates of the two systems were maintained at over 80%and 90%respectively after four replicate experiments.（7）The radical burst experiments revealed that the active species in the two systems were ¹O₂,SO₄^·-and·OH,and the contribution of active species:¹O₂>SO₄^·->·OH.Based on UV-Vis spectroscopy and liquid quality analysis,it was shown that the degradation process of RhB includes four processes:N-de-ethylation,chromogenic group cleavage,ring opening and mineralization,but the UV/Co₃O₄@BC/PMS system produced more intermediates and more ring-opening small molecules compared to the UV/Co₃O₄/PMS system.Therefore,this study speculates that RhB undergoes degradation processes based on different pathways in these two systems.