Joule Heating Effect Of Carbon Aerogel And Its Application In The Degradation Of Sulfamethoxazole Through Persulfate Activation

Sulfamethoxazole（SMX）is a kind of antibiotics with high frequency of use and detection,which has high stability and poor biodegradability,so it is difficult to remove it by conventional sewage treatment technology,which poses a serious threat to human and ecosystem health.At present,the advanced oxidation process（SR-AOPs）based on sulfate radical(SO₄^·-)has been proved to have unique advantages in the removal of antibiotics.SR-AOPs is the free radical degradation of pollutants produced by the activation of persulfate（PS）.Among them,thermally activated PS is considered to be the most suitable SR-AOPs technology for engineering applications because of its advantages such as simple operation,no catalyst and not easy to cause secondary pollution.Carbon aerogel is a kind of light,porous and amorphous carbon material,which has high specific surface area,controllable pore size and good electrochemical performance.It can catalyze and activate PS and produce Joule heat when a certain external voltage is applied.Based on this,carbon aerogel with vertical pore structure was prepared by ice template method using chitosan as precursor.The solution containing SMX and PS was pumped into the vertical pore of carbon aerogel,and the reaction solution was heated by Joule heat produced by the pore wall to realize the rapid activation of PS and the degradation of SMX.The main research contents and conclusions are as follows:（1）Carbon aerogels with vertical pore structure were prepared by ice template method using chitosan as precursor.The internal morphology of carbon aerogel was observed by scanning electron microscope（SEM）.The cross section was composed of honeycomb pores and the longitudinal section showed parallel pores.Through the characterization of X-ray photoelectron spectroscopy（XPS）,it was found that the surface of carbon aerogel（CA-60）prepared with 60 g/L chitosan contained functional groups such as Coluo,Cmurc,Cmurn,pyridinic-N and graphite-N.The Joule heat effect of carbon aerogel is positively correlated with the concentration of chitosan in the preparation process.When the voltage is 5 V,the surface temperature of carbon aerogel（CA-50）prepared with 50 g/L chitosan is maintained at～256.5^oC,while the temperature of CA-60 soars to 344.6 ^oC when the power is turned on 2 min.（2）The activation effect of peroxymonosulfate（PMS）and peroxydisulfate（PDS）and the temperature change of outlet in CA-60 Joule heating system were investigated.At the same time,with the initial concentration of 10 mg/L as the main target pollutant,the effects of different applied voltage,flow rate and real water matrix on the degradation of SMX in CA-60Joule heating system were investigated.When the applied voltage increases from 1 V to 5 V,the equilibrium temperature of the outlet increases from 28.3 ^oC to 80.8 ^oC.The degradation rate of SMX increases from 87.5%to 100%within 120 min.When the flow rate is 4 m L/min,5 m L/min and 6 m L/min,the equilibrium temperature of the outlet is 89.4 ^oC,80.8 ^oC and 72.0^oC and the degradation rate of SMX is 98.8%,100%and 100%within 120 min,respectively.The decomposition rate of PMS in 120 min is 91.8%.The decomposition rate of PDS in 120min is 81.3%.In addition,the CA-60 Joule heating system has high stability.After 5 cycles,the degradation rate of SMX is still 91.7%,and the Joule heating effect and electrical conductivity of CA-60 are not significantly reduced.（3）Through free radical quenching experiment and electron paramagnetic resonance spectroscopy（EPR）analysis,it is inferred that PMS mainly produces SO₄^·-,hydroxyl radical（·OH）,superoxide radical(O₂^·-)and singlet oxygen（¹O₂）through catalytic activation,thermal activation and electron direct activation of CA-60.Among them,·OH made a great contribution to the degradation of SMX in CA-60 Joule heating system.In addition to the oxidative decomposition of SMX by the reactive oxygen species（ROS）,some SMX in the system is degraded through the electron transfer mechanism.Finally,11 kinds of SMX degradation intermediates were detected by liquid chromatography-mass spectrometry（LC-MS）.It is speculated that there may be three degradation pathways of SMX in this system.