Mechanism And Application Of Electrolytic-Adsorption Degradation Of Toxic Pollutants In Dye Wastewater

Dye wastewater has the characteristics of high chroma,strong toxicity and difficult to degrade.Conventional advanced oxidation technology has very limited ability to degrade toxic pollutants in dye wastewater.Therefore,it is urgent to find a more efficient,inexpensive and widely used advanced oxidation combined treatment process to degrade toxic pollutants.Methylene blue?MB?is widely present in dye wastewater and is toxic and can be used as a representative of toxic pollutants in dye wastewater.So this study coupled biochar-titanium dioxide?TiO₂/BC?and electrocatalytic oxidation to synergistically degrade methylene blue?MB?.Firstly,the optimum preparation conditions for TiO₂/BC were determined.At the same time,its adsorption capacity,physical and chemical properties were investigated.Secondly,the response surface analysis method was used to optimize the optimal working conditions obtained by the single factor method.Finally,the reaction kinetics and degradation mechanism of MB degradation by electrolysis-adsorption were analyzed.The main research results obtained in this process are as follows:?1?Optimum preparation conditions of TiO₂/BC:solid-liquid ratio was 0.6 g:10mL,particle size range was 0.5 mm⁰.35 mm,immersion times was 2 times,secondary pyrolysis temperature was 500°C.The characterization results showed that TiO₂ covered the surface of TiO₂/BC in the form of thin film,which promoted the formation of free radicals.?2?The isothermal adsorption model showed that TiO₂/BC conformed to the Freundlich adsorption model and belonged to the surface non-uniform adsorption process.The maximum adsorption amount at the time of adsorption equilibrium was131.60 mg·g^-1.The adsorption kinetics results showed that the adsorption process of TiO₂/BC on MB was more in line with the quasi-secondary kinetic model,and its R²value exceeded 0.999,which indicated that chemisorption was the main factor controlling the adsorption rate.The adsorption process was divided into two stages:a rapid adsorption phase of the membrane diffusion mechanism?0 h⁶ h?and a slow adsorption phase of the intraparticle diffusion?6 h⁴8 h?.?3?The best condition of the reaction was obtained by single factor method:aeration volume was 50 L·h^-1,dosage ratio was 2:1,current density was 40 mA·cm^-2,initial solution pH was 9.The significant order of the four influencing factors on the degradation ratio of MB and TOC was respectively:dosing ratio>aeration volumet>current density>initial pH;aeration volume>current density>dosing ratio>initial pH.The interaction of the four factors was not significant.?4?The quadratic regression model obtained by response surface analysis was significant.The optimal reaction conditions for the model prediction electrolysis-adsorption method were:aeration volume was 64.448 L·h^-1,current density was 39.65 mA·cm^-2,dosage ratio was 2.42:1,initial solution pH was 8.964.The degradation ratios of MB and TOC under this condition were 85.16%and80.25%,respectively,which were close to the results of the confirmatory test,indicating that the model had higher reliability for the prediction of electrolysis-adsorption method.?5?Analysis of the variation of main parameters in the process of degradation of MB by electrolysis-adsorption method showed that the degradation process was divided into fluctuation period and stablele period.It was speculated that the degradation mechanism was divided into the direct oxidation of the anode plate and the catalytic oxidation of the TiO₂/BC microelectrode.The characterization results showed that the chemical adsorption mode of TiO₂/BC surface was hydrogen bond adsorption and electrostatic adsorption,which promoted the production of active substances such as·OH,·O₂^—.?6?The results of free radical inhibitor test proved that the main effect of degradation of MB was the direct oxidation of the anode plate and the catalytic oxidation of the TiO₂/BC microelectrode.The reaction kinetics results showed that the direct oxidation of the anode plate conformed to the quasi-first-order kinetic model.The electrocatalytic oxidation of TiO₂/BC surface microelectrodes was consistent with the Langmuir-Hinshelwood bimolecular model.It was inferred that there was a coupling between electrolysis and adsorption and followed the law of"adsorption-electrolysis-product desorption".