The oxidation of ammonium (NH 4 + ) to dinitrogen (N 2 ) with high selectivity and high efficiency is still a challenge. Herein, a novel sunlight induced persulfate (PS)-based AOPs process (MgO/Na 2 SO 3 /PS/ hv ) was proposed by introducing solid base (MgO) and hydrated electron (e aq − ), to selectively oxidize NH 4 + to N 2 , with high selectivity and high efficiency at a wide range of pH value. The deprotonation of NH 4 + into NH 3 by MgO and the generation of •OH and SO 4 −• by PS activation were responsible for the high efficiency of NH 4 + oxidation. The buffering capacity provided by MgO to proton released from PS activation made the NH 4 + oxidation possible at a wide pH range. The e aq − from the Na 2 SO 3 / hv process was the main active specie to reduce NO 2 − and NO 3 − (NO x − ) into N 2 , responsible for high N 2 selectivity of NH 4 + oxidation. 100% NH 4 + could be oxidized within 30 min, and N 2 selectivity exceeded 96% at the initial pH range of 3–11 and the initial concentration of NH 4 + of 30 mg N/L. This work could offer an efficient AOPs process for selective NH 4 + oxidation, which is promising for the chemical denitrification of wastewater ….
The selective oxidation of ammonia to dinitrogen gas in some special wastewater is of paramount significance, but still a challenge. In this study, chlorine radical (Cl•)-mediated oxidation process was developed to realize the selective oxidation of NH 4 + -N to N 2 , in which Cl• was generated in Co 2+ /peroxymonosulfate (PMS)/chloridion (Cl − ) system. The effect of various operational parameters on the efficiency and selectivity of ammonia oxidation to N 2 was investigated, such as PMS concentration, Co 2+ concentration, Cl − concentration and pH value. The experiment results showed that Cl•-mediated NH 4 + -N oxidation reaction exhibited high NH 4 + -N removal efficiency and considerable selectivity to N 2 in the range of pH from 2.0 to 6.5. The removal efficiency of NH 4 + -N was 90.39%, and the selectivity of NH 4 + -N to N 2 achieved up to 97.16%. The possible mechanism for high efficient and selective oxidation of NH 4 + -N to N 2 was tentatively proposed. The process developed in this study could provide a novel technology for the treatment and selective oxidation of ammonium in some special types of ammonium-containing wastewater.
Selective electrocatalytic nitrate reduction reaction (NO 3 RR) to dinitrogen (N 2 ) is essential to nitrogen-cycle management and environmental sustainability. Palladium-based nanomaterials were extensively studied as NO 3 RR catalysts, but only delivered limited N 2 selectivity (<50%, NH 3 dominated the product). Here we report that, by tuning bimetallic composition of CuPd alloy nanowires, the Cu 28 Pd 72 nanowires deliver a near-unit conversion of NO 3 – -N and an unprecedented N 2 product selectivity of 75.9 ± 5.2% in treating 22.5 mg L −1 NO 3 – -N solution at −0.80 V vs. Ag/AgCl. Combining in-situ spectrometric measurements and theoretical calculations, we demonstrate that the contiguous Pd ensemble with a specific size at catalyst surface is essential to the N 2 formation via a kinetically-favored pathway of NO 2 * → NO* → N* → N 2 *. Alloying Pd with Cu is indispensable as Cu contributes to the N*-N* pairing by initiating the NO 3 – –NO 2 * conversion and lowering the H ads coverage on catalyst. This work discloses the key surface atomic structure for N 2 formation, and provides a guideline for the design of efficient NO 3 RR catalyst that enables selective NO 3 – –N 2 conversion.
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