Electrochemical removal of nitrate using a nanosheet structured Co3O4/Ti cathode: Effects of temperature, current and pH adjusting

Co3O4 nanosheet film is synthesized through electrodeposition and used as cathode in electrochemical NO3- removal. The electrodeposition conditions are optimized and the NO3- removal rate is enhanced by 1.7 times in comparison with Co3O4 solid particle cathode, which mainly results from its large surface area and high efficient electron transfer and utilization capacities. The effects of reaction temperature and current are then deeply investigated. NO3- removal rate is enhanced from 0.00667 min(-1) to 0.0156 min(-1) at 0.08 A with reaction temperature rising from 5 degrees C to 45 degrees C, and it can further be enhanced to 0.0220 min(-1) with current increasing to 0.16 A. Furthermore, the physical properties of Co3O4 nanosheet cathode are more stable during the reaction at high temperature. Low reaction temperature not only destroys nanosheet structure, but also changes the ratio of Co2+/Co3+ and the numbers of oxygen vacancy and lattice oxygen. Almost 60% TN removal is obtained under 0.16 A at 45 degrees C, however, most of which is obtained through NH3 escape instead of N-2 generation. Adjusting the pH around neutral condition during the reaction can effectively fix NH3 in solution. The NH3 can then be oxidized to N-2 in the presence of certain amount of Cl-.