Rapid and effective nitrate reduction over wide pH range using CuxO-CNT with the presence of KBH4: The role of in situ produced hydrogen and zero-valent copper

CNTs-CuxO prepared by impregnation was used with KBH4 to reduce NO3–-N as the first step. CNTs-CuxO was characterized by SEM, EDS-mapping, TEM, XRD and XPS. The NO3–-N reduction batch experiment showed that 100% of NO3–-N removal efficiency was achieved in < 10 min with the initial pH of 3.0, 5.0 and 7.0, NO3–-N concentration of 30 mg(N)/L, CNTs- CuxO dosage of 3 g/L and KBH4 concentration of 3 mmol/L. At the initial pH of 9.0, NO3–-N was completely removed in 15 min. The main product of the first step reaction was NO2–-N, which was accumulated in the solution and rapidly reduced to N2 by NH2SO3H as the second step. The reusability of CNTs-CuxO was evaluated and the experiment result showed that 96% of NO3–-N removal efficiency was achieved in 10 min after CNTs-CuxO was reused for 5 cycles of reaction. Moreover, the Cu2+ dissolution was kept monitored for the reaction system, and the analysis result showed that there was no Cu2+ leaching for all cycles of reutilization.