| Developing novel and efficient wastewater treatment technologies is of great significance to solve the increasingly serious water pollution.As a novel water treatment technology,the electric-field enhanced filtration process which combines membrane separation and electrochemical oxidation has attracted extensive attention from researchers owing to the advantages of both membrane separation and electrochemical oxidation.However,the relatively high production costs and complicated preparation processes of the currently reported reactive conductive membranes may limit their further popularization and application.To solve these problems,a low-cost coal-based conductive carbon membrane(CCM)derived from different caking coal via self-bonding was design and prepared in this work.A series of research work was carried out to optimize its structure and performance,as well as wastewater treatment applications.The main conclusions are as follows:(1)The effects of raw coal blending ratio,carbonization temperature(CT)and the addition of pore former on the performance of CCM were systematically studied.The high caking property of the raw coal resulted in high mechanical strength CCMs but also led to low porosity and small pore size,which may cause high hydraulic resistance.The comprehensive performance of the CCM could be improved by blending two raw coal samples.With increasing CT,the pore structure of the CCM changed little,but the electrical conductivity of CCM increased obviously.The pore structure of the CCM could be effectively improved by adding the organic pore former PVB,however,the mechanical strength decreased with increasing pore former percentage.On the basis of these research,the preparation process and technology of CCM were developed.The CCM obtained at the optimal conditions exhibited electrochemical oxidation activity for all three organic pollutants tested.Under the applied voltage of 2.0 V,the CCM-60 exhibited the outstanding removal efficiencies of 97.59%,99.98%and 100%for phenol,tetracycline and rhodamine B,respectively.(2)During the carbonization,the precursor membrane was transformed into an CCM with condensed and compacted aromatic structure by the violent thermal decomposition and condensation.As CT increased from 500? to 1100? the amorphous carbon in CCM decreased violently and was conversed into defected graphitic carbon,promoting the growth of lateral size of ordered carbon crystallites.The graphitization occurred in CCM when CT was higher than 1100?,and some of the defected graphitic carbon gradually converted into the ideal graphitic lattices.The electric conductivity of CCM mainly dependent on the proportion of ordered carbon crystallites.As CT rised from 500? to 1100?,the electrical conductivity of ECM was enhanced owing to the growth of the ordered carbon crystallites in the lateral dimension,which facilitated to form more effective "channels" to transport electrons.Then the electrical conductivity kept almost constant with further increased CT from 1100? to 1500? due to the well established pathway for electron transfer.The electrochemical performance of CCM mainly depend on the proportion of defected graphitic carbon(active sites),which first increased and reached the highest value at 950 ??1100 ?,then slightly decreased as CT further increased.The water treatment performance of CCM was strongly correlated to its electrochemical properties.The CCM carbonized at 950? exhibited the optimal water treatment performance during electric-filed enhanced filtration process.(3)The electrochemical oxidation activity of CCM was explored by using organic probe and electron spin resonance spectroscopy.The minerals in CCM was removed by acid treatment,and the influence of minerals on its electrochemical oxidation performance was investigated to reveal the electrochemical oxidation mechanism of CCM.The removal of main minerals in CCM has little effects on its carbon structure and electrochemical properties.The mechanism of electrochemical oxidation showed for the ECM involved the direct oxidation and indirect oxidation,and the direct oxidation played the dominant role during the electric-filed enhanced filtration process.The indirect oxidation activity was attributed to the electro-catalytic activity of minerals existed in CCM.(4)The wastewater treatment performance of CCM uder the applied of voltage was systematically investigated by using bisphenol A(BPA)as the target pollutant.The separation rate of CCM on BPA was low,while an outstanding removal rate was obtained by CCM under applied of electric field.The residence time(RT),initial BPA concentration and electrical conductivity of aqueous solution will affact the BPA removal rate and energy consumption of CCM during the treatment.The water treatment performance of CCM can be improved by optimizing the operation conditions.Under the optimal conditions of applied voltage of 2.0 V,initial BPA concentration of 50 ppm,0.1 mol·L-1 Na2SO4 and RT of 0.88 min,the BPA and COD removal rate obtained by CCM was nearly 97%and 90%,respectively,and the energy consumption achieved a lowest value of 0.51 kWh·kgCOD-1,There were synergistic effects between membrane filtration and electrochemical oxidation during the water treamtnet process.The membrane separation performance was enhanced by the electrochemical oxidation.In the meantime,electrochemical oxidation rate of BPA was effectively improved owing to the enhancement of mass transfer efficiency during the filtration.During the treatment,the BPA molecules were first decomposed into 4-Isopropylphenol and hydroquinone,which were further degraded into organic acids and even H2O and CO2 eventually.In summary,the novel CCM shows great potential on the large-scale production and application owing to the advantages of low cost,simple preparation process and excellent water treatment performance.This work not only provides the technical support for the controllable preparation and large-scale production of high-performance CCMs,but also promotes its application on water purification. |
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