State Key Laboratory of Environmental Aquatic Chemistry, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China.
University of Chinese Academy of Sciences, Beijing 100049, China.
Environ Sci Technol. 2021 Sep 21;55(18):12596-12606. doi: 10.1021/acs.est.1c02825. Epub 2021 Sep 8.
Regulation of fast three-electron-transfer processes for electrocatalytic oxidation of ammonia to nitrogen by achieving efficient generation and utilization of active sites is the optimal strategy in ammonia-containing wastewater treatment. However, the limited number of accessible active sites and sluggish interfacial mass transfer are two main bottlenecks restricting conventional ammonia oxidation configurations. Herein, we develop a macroporous Ni foam electrode integrated with vertically aligned two-dimensional mesoporous NiP nanosheets to create sufficient exposure of active centers. A novel ammonia oxidation reactor with the developed hierarchical porous-structured electrodes was assembled to construct an intensified microfluidic process with flow-through operation to mitigate macroscopic mass transport limitations. The confined microreaction space in the hierarchical porous reactor further promotes spontaneous nanoscale diffusion/convection of the target contaminant to high-valence Ni sites and enhances the microscopic mass transfer. The combined results of electrochemical measurements and Raman spectra showed that the ammonia degradation mechanism results from direct oxidation by the high-valence Ni, significantly different from the conventional indirect active-chlorine-species-mediated oxidation. The optimized reactor achieves high-efficiency three-electron-transfer ammonia conversion with an ammonia removal efficiency of ∼70% from an initial concentration of ∼1400 mg/L and byproduct production of ∼4%, significantly superior to a conversion unit comprising a featureless Ni-based electrode in the immersed configuration, which had >50% byproduct yield. 20 days of continuous operation under variable conditions achieved >90% ammonia degradation performance and an energy consumption of 25.42 kW h kg N (1 order of magnitude lower than the active-chlorine-mediated process), showing the potential of the reactor in medium-concentration ammonia-containing wastewater treatment.
调控快速三电子转移过程以实现电催化氨氧化为氮气，从而高效产生和利用活性位点，是处理含氨废水的最佳策略。然而，可利用的活性位点数量有限和界面质量传输缓慢是限制传统氨氧化结构的两个主要瓶颈。在此，我们开发了一种具有垂直排列二维介孔 NiP 纳米片的大孔泡沫镍电极，以充分暴露活性中心。组装了具有开发的分级多孔结构电极的新型氨氧化反应器，构建了具有流通操作的强化微流处理，以减轻宏观质量传输限制。分级多孔反应器中的受限微反应空间进一步促进目标污染物在纳米尺度上自发扩散/对流至高价 Ni 位，并增强微观质量传递。电化学测量和拉曼光谱的综合结果表明，氨降解机制源自高价 Ni 的直接氧化，与传统的间接活性氯物种介导的氧化明显不同。优化后的反应器实现了高效的三电子转移氨转化，初始浓度约为 1400 mg/L 的氨去除效率约为 70%，副产物生成率约为 4%，明显优于在浸入式配置中包含无特征 Ni 基电极的转化单元，其副产物产率>50%。在可变条件下连续运行 20 天，氨的降解性能>90%，能耗为 25.42 kW h kg N（比活性氯介导的过程低 1 个数量级），表明该反应器在中浓度含氨废水中处理的潜力。
