图文摘要

成果简介

近日，张礼知教授课题组在Water Research上发表了题为“Renewable Energy Driven Electroreduction Nitrate to Ammonia and in-situ Ammonia Recovery via a Flow-Through Coupled Device”的研究论文(DIO: 10.1016/j.watres.2023.120256)，开发了用于连续电化学还原硝酸根产氨和原位回收氨的透过式耦合装置。作者通过将透过式流动电解池和中空疏水透气膜单元进行巧妙组合，实现了硝酸根到氨的快速转换和同步高效回收氨。这项工作为硝酸根废水资源化利用提供了一个可行方案。

全文速览

本研究设计了一种可再生能源驱动的新型透过式耦合装置，旨在实现NO₃⁻废水资源化利用。该装置的紧凑透过式流动电解池能够强化NO₃⁻传质，有利于促进NO₃⁻还原到NH₃。同时，无需调节废水pH和额外输入能量，疏水透气膜组件能够快速原位回收NH₃。通过耦合高性能的Cl-Cu整体电极，该透过式耦合装置能够在50 mg NO₃⁻-N L⁻¹废水中持续稳定运行100 h，并实现420 μg h⁻¹ cm⁻¹的氨回收速率。在太阳能驱动下，该装置也能将工业NO₃⁻废水达标处理并实现接近100%的NH₃回收效率，展现出巨大的工业应用潜力。

引言

电化学还原处理硝酸根废水并原位回收氨，有利于控制水体氮污染和实现氮循环利用。然而，该技术面临巨大挑战是缺乏连续还原NO₃⁻和原位回收NH₃的集成式装置。合理设计反应器是应对上述挑战的关键。针对低浓度NO₃⁻废水中电化学转换效率受限于传质的问题，优化电解池中流体流动模型被证实是有效措施。当溶液透过式穿过（Flow-through）多孔电极时，其扩散层距离将会从300 μm降低至1μm，这将显著促进NO₃⁻传质。此外，采用紧凑的两电极单池构型能够避免膜污染和降低内阻，进而降低能耗。

图文导读

Fig. 1. Scenario of renewable energy driven electrochemical nitrate reduction and in-situ NH₃ recovery. Copyright 2023, Elsevier Inc.

材料表征

Fig. 2. Structure characterizations. (a) Evolution of LSV curves during the electrochemical leaching process. (b) High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) image of Cl-Cu. (c) STEM-EELS elemental mapping images of Cl-Cu. (d) Cu LMM Auger spectra of Cl-Cu, CuCl and Cu. (e) The normalized XANES spectra of the Cl-Cu, referenced Cu foil, CuCl and CuCl₂. (f) FT k³-weighted χ(k)-function of the EXAFS spectra at Cu K-edge. Copyright 2023, Elsevier Inc.

Cl-Cu电化学还原NO₃⁻性能测试

Fig. 3. Electrocatalytic NITRR performance. (a) LSV curves of Cl-Cu and Cu with the presence or absence of NO₃^-. (b) The comparison of NH₃ yield and corresponding faradaic efficiency over Cl-Cu and Cu at different working potentials. (c) Comparisons of NH₃ yield, NO₃^- removal efficiency, selectivity and Faradaic efficiency between Cl-Cu and Cu. (d) The consecutive recycling tests at -0.65 V over Cl-Cu.  Copyright 2023, Elsevier Inc.

在三电极体系中初步评估Cl-Cu电化学还原NO₃⁻产氨的性能。Cl修饰能够显著提升Cu的还原硝酸根的转换率、选择性、法拉第效率和产氨速率。同时，Cl-Cu在20次循环中也具有优异的稳定性。

机理分析

Fig. 4. Mechanism analysis. (a) Time-resolved ATR-FTIR spectra of Cl-Cu and Cu. (b) Schematic diagram of NO₃^- distribution on the surface of Cl-Cu and Cu. (c) In situ ATR-FTIR spectra of Cl-Cu and Cu at -0.65 V. (d) DMPO spin-trapping ESR spectra of Cl-Cu and Cu under argon atmosphere at -0.65 V. (e) The ELF of Cu (top) and Cl-Cu (below). (f) The NO₃^– adsorption configuration and charge density difference on Cu (top) and Cl-Cu (below), respectively. The yellow and blue iso-surfaces represent charge accumulation and depletion in the space, respectively. The iso-value is 0.0015 a.u. (g) The free-energy diagrams and pathways of H₂O dissociation on Cu and Cl-Cu. Copyright 2023, Elsevier Inc.

时间分辨的原位红外光谱（ATR-FTIR）揭示Cl诱导产生的Cu^δ+能够增强吸附NO₃⁻，这将增加电极界面NO₃⁻浓度，有利于促进反应动力学。同时，原位电化学ATR-FTIR光谱，电子顺磁波谱（ESR）和理论计算结果表明Cl和电极表面吸附H₂O间存在的氢键作用(Cl···H−OH)，能够高效促进H₂O解离产生活性物种氢自由基(H^*)用于NO₃⁻还原。

基于Cl-Cu电极的透过式耦合装置电化学还原硝酸根和原位回收氨性能测试

Fig. 5. Electrochemical nitrate conversion and in-situ ammonia recovery by the flow-through coupled device.(a) Optical image of the flow-through coupled device for synchronous electrocatalytic nitrate conversion and in-situ ammonia recovery. (b) Time-dependent product distribution using the flow-through coupled device. (c) IC chromatograms after treatment. (d) Long-term operation at 800 mA with a sustained NH₃ recovery. (e) XRD pattern of the recovered NH₄Cl(s) product. The inset shows the mass of NH₄Cl(s). (f) Time-dependent distribution of nitrogen species during the treatment of real industrial wastewater. (g) TN_removal efficiency and the concentration of generated NO₂^--N in the effluent during the continuous-flow operation of two tandem units for industrial wastewater treatment. Copyright 2023, Elsevier Inc.

经济价值分析

Fig. 6. Economic feasibility analysis of flow-through coupled device. (a) The expenditure analysis with or without the consideration of ammonia profits under multiple NO₃⁻-N concentration from 50 to 300 mg L⁻¹. (b) Optical image of the solar-driven coupled device. (c) Time-dependent distribution of nitrogen species during the real wastewater treatment with the solar driven coupled device under real sunlight. (d) The evolution of current and recovered NH₄⁺concentration under real sunlight at different time. Copyright 2023 Elsevier Inc.

回收氨产生的收益能够降低电化学技术废水处理成本的21% ~ 33%。在太阳能驱动下，该耦合装置也能将工业NO₃^-废水达标处理和高效回收NH₃。

小结

课题组介绍

么艳彩 上海交通大学环境科学与工程学院副教授、博士生导师。研究方向为单原子催化、环境/能源电催化。以第一作者/通讯作者身份在Nature Catalysis、Journal of the American Chemical Society、Angewandte Chemie International Edition（2篇）、Water Research、Science Bulletin等期刊发表SCI论文12篇，部分研究成果被Chemical Review、Chemical Society Reviews、Technology Times、EurekAlert! 等国际科学媒体广泛报道, 并多次被新华社、人民日报、《人民日报（海外版）》、人民网、科学网等多家国内外主流媒体关注。申请发明专利6项，授权并成果转化1项。撰写英文专著1部。曾获中科院“百篇优博论文”和中科院院长优秀奖、第7届全国水处理与循环利用学术会议优秀报告奖。先后获得国家自然科学基金、上海市科委面上项目、科技部重点研发计划项目子课题、博士后站前特别资助、博士后面上资助等7项省部级项目资助。现任Colloid and Surface Science编委。

https://doi.org/10.1016/j.watres.2023.120256