Fabrication of easily separated biochar balls and their catalytic mechanism for PMS

In this work, N-doped biochar balls NBC 3 800 were prepared from waste biomass corn straw. The biochar balls supported by clay have an obvious spherical structure. Clay can enhance the adsorption capacity of the biochar balls to pollutants by its excellent adsorption property. Thus, the clay can speed up the catalytic reaction by strengthening the adsorption function. The biochar balls NBC 3 800 have the best catalytic performance and the removal rate of NC can reach 100% within 100 min. The electron transfer resistance of NBC 3 800 is only 36 Ω indicating a lower resistance value and higher conductivity to transfer electrons compared with carbon nanotube. Electron paramagnetic resonance (EPR) and electrochemical analysis show that sulfate radical (SO 4 •− ), hydroxyl radical (·OH), singlet oxygen ( 1 O 2 ), and electron transfer are all involved in the reaction. The removal rate of NC can still be maintained at 83.41% after being reused five times. Besides, it can be further improved to 100% by high temperature regeneration at 800 ℃. Most importantly, the biochar balls can be separated from the solution very easily which not only extremely improves the recyclability but also avoids secondary pollution to the water body.