| Magnéli titanium suboxide is a series of non-stoichiometric titanium oxides,and its general formula is TinO2n-1(4?n?10).These compounds are highly conductive and have high chemical stability in corrosive media.Magnéli phase Ti4O7,which has high conductivity(1500 S cm-1),high oxygen evolution potential and corrosion resistance,has attracted widespread attention in the field of electrocatalysis.Ti4O7 reactive electrochemical membrane(REM)has both high electrochemically active surface area and convection-enhanced mass transport of pollutants.Meanwhile,the active substances(·OH)generated on its surface can oxidize pollutants in the electrochemical process,making its unique advantages in the field of water treatment.The conventional methods for Ti4O7 membrane preparation is thermal H2 reduction method,which is seriously limited by the risk of explosion,long thermal reaction time and low purity production.Therefore,much more convenient and efficient strategy is in urgent to be developed to obtain Ti4O7 membrane,which is of great significance for the application and development of Ti4O7 membrane in wastewater treatment.To address these limitations,this work used rutile Ti O2 as raw material and carbon black as reducing agent to prepare magnéli phase Ti4O7 reactive electrochemical membrane under high temperature in vacuum.The highest purity nanostructured Ti4O7was obtained at temperature of 1473 K for 5 h.The Brunauer–Emmett–Teller results showed that the most pores of Ti4O7 were micropores and mesopores due to high temperature in sintering progress,with the Barrett–Joyner–Halenda adsorbed surface area of 1.264 m2 g-1 and the average pore size is about 1.5 nm.Cyclic voltammetry was used to calculate the electrochemically active surface area of Ti4O7 membrane,the results showed that the roughness of the electrochemically active surface area was 1075 and the calculated active area is about 0.36 m2,which is 1100 times the geometric area of the electrode.The linear sweep voltammetry results show that the oxygen evolution potential of Ti4O7 is 2.5 V(vs.SCE),which has reached the highest value reported in the literature.To adjust the pore size of the Ti4O7 membrane and further improve the active area and purity of the membrane electrode,Ti O2 precursor with abundant pores was fabricated using different proportions of carbon black.Titanium powder was used as solid reducing agent and separated from Ti O2 precursor in the whole sintering progress.The highest purity nanostructured Ti4O7 with a purity of 97%was obtained at temperature of 1333 K for 4 h.Scanning electron microscopy shows that these membranes has interconnected pore structure.The results of mercury intrusion porosimetry showed that the pore size and porosity of the membrane increase with the increase of carbon black content,and The average pore size is 0.4?0.6?m.Though the maximum porosity is 60%,sufficient membrane strength can still be maintained.The pure water flux test shows that the permeation flux of Ti4O7 membrane can reach 1379±8 LMH bar-1,which lays the foundation for its use as a flow-through membrane electrode in wastewater treatment.The highest electrochemical active area roughness of the four samples measured by cyclic voltammetry is the membrane with a carbon content of 5 wt%.The measurements reached to 3250,equaling to 1.1 m2,which is 3?4 orders of magnitude higher than the geometric area of the electrode(3.38 cm2)and three times higher than that of the membrane prepared by carbothermal reduction method,.EIS analysis shows that the resistance of the prepared Ti4O7 film increases with the increase of pore size and porosity,reaching a minimum value of about 17?cm-2 which may be due to the existence of voids in the sample reducing the effective area of current conduction.The mass transfer resistance value of the sample is about 4?cm-2,which is 3 to 4 orders of magnitude lower than that of the graphite electrode.The oxidative degradation experiment of p-benzoquinone shows that high flux is beneficial to the removal of COD in water,and the removal rate of COD after2.5 hours is 97%.In general,to solve the high cost,time-consuming,and low product purity problems of traditional methods for preparing Ti4O7,this study proposed a strategy for the efficient preparation of Ti4O7 electrochemically active membranes and precisely controlled the pore size and porosity of Ti4O7 membrane.The prepared Ti4O7 membrane has larger electrochemically active area,lower mass transfer resistance and lower membrane inherent resistance,which lays an important theoretical and technical foundation for the application of Ti4O7electrochemically active membranes in water pollution remediation. |
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