Study On Degradation Of Typical Dyes By CuMnFe-LDHs/PMS Process Enhanced By HA And QSAR Model Prediction

Dye wastewater,as an important sources of water pollution,is causing increasingly serious environmental problems due to its substandard discharge.It is difficult to effectively purify dye wastewater by conventional water treatment processes,therefore,it is very meaningful to explore an efficient,economical and environmentally friendly water treatment process.In this work,the oxidation process of peroxymonosulfate activated by CuMnFe-LDHs with enhancement of hydroxylamine（HA/CuMnFe-LDHs/PMS）process was used to degrade rhodamine B（Rh B）,a typical dye present in water.The optimal CuMnFe-LDHs catalyst was obtained and characterized by optimizing the molar concentration ration conditions of Cu²⁺,Mn²⁺and Fe³⁺.The effects of different factors on the degradation efficiency of Rh B in the HA/CuMnFe-LDHs/PMS process were systematically investigated.The degradation capacity of the proposed process was also explored at the simulated printing and dyeing wastewater.According to the radicals analysis,interactions between substances and catalyst,surface metals valence change and Rh B degradation pathway,the degradation mechanism of Rh B was investigated in the process,and then the process enhancement mechanism,catalytic mechanism and toxicity change during Rh B degradation were analyzed by combining with computational simulation methods.Furthermore,quantitative structure-activity relationship（QSAR）models were constructed and the key factors of dye degradation were suggested based on the degradation rate constants and computational chemical parameters of 12 typical dyes in the HA/CuMnFe-LDHs/PMS process.The CuMnFe-LDHs catalysts exhibited the best catalytic properties when the molar ratio of Fe³⁺:Cu²⁺:Mn²⁺was 1:1:1.The catalyst layers showed three-dimensional flower-like aggregates stacked on top of each other and the crystalline structure and surface functional groups were consistent with the typical structure of LDHs.Compared with the CuMnFe-LDHs/PMS process,the HA/CuMnFe-LDHs/PMS peocess exhibited stronger degradation capacity and was able to degrade 94.6%of Rh B within 30 min.The results of influence factors showed that the degradation efficiency of Rh B in theHA/CuMnFe-LDHs/PMS process decreased with the increase of Rh B concentration,while the increase of catalyst dosage,PMS concentration,HA concentration and temperature promoted the release of radicals to improve the Rh B degradation.Low concentration of Cl^-（0～10 m M）and NO₃^-（0～25 m M）showed less effect on the degradation of Rh B.In addition,the CuMnFe-LDHs catalyst revealed excellent catalytic stability and the proposed oxidation process was still effective for Rh B removal from simulated water.Mechanism analysis indicated that the addition of HA enhanced the decomposition of PMSby CuMnFe-LDHs.The existing forms of Rh B,PMS and HA and the surface charge of CuMnFe-LDHs in the process were the key to influence the radical release and Rh B degradation.Hydroxyl radical（·OH）was the dominant radicals dedicating to the degradation of Rh B.In addition,based on the catalyst surface metal element valence change and simulation calculation analysis,it was concluded that Cu elements could act as electron acceptors to transfer electrons from HA to higher valence Fe and Mn elements,thus contributing to the rapid and sustained decomposition of PMS.The degradation intermediate products of the Rh B were analyzed and Rh B degradation pathways were speculated in the HA/CuMnFe-LDHs/PMS process.Deacetylation,dealkylation,deamination,and decarboxylation were the main ways involved in the degradation of Rh B.Furthermore,an overall decreasing trend was found for biotoxicity,bioconcentration factor,and developmental toxicity of Rh B degradation products,and no mutagenicity was observed.QSAR models were further constructed based on the calculated chemical parameters and degradation rate constants of 12 typical dyes in HA/CuMnFe-LDHs/PMS process.Under acidic condition,the model was obtained as:k=-0.298+0.201*q（C）_max+0.384*Bo_min,the key parameters for degradation of dyes were q（C）_max and Bo_min;Under about neutral condition,the model was:k=-1.125+0.597*q（H）_max+1.154*Bo_min-3.884*E_GAP²,the key parameters for degradation of dyes were q（H）_max,Bo_min and E_GAP².Therefore,the active site,the chemical activity and the adsorption on the catalyst of the target were the key factors for its efficient degradation in the HA/CuMnFe-LDHs/PMS process.