近年来，二氧化碳（CO₂）减排与资源化已成为研究热点。作为“碳排放行业”前十位的污水处理厂，如何减少CO₂外排并将其还原转化为有价物质，是对“碳中和”技术的深入探索与完善。同时，工业废水中常见的高浓度硝酸盐（NO₃⁻）亦可通过还原转化为有价物质。因此，本研究以污水厂碳减排与碳氮资源化为目标，筛选并优化CO₂和NO₃⁻电催化共还原阴极材料，构建阴极C-N共还原耦合阳极难降解有机物双酚A（BPA）氧化的穿透流电催化体系，从而利用电催化阳极氧化难降解有机污染物提升其可生化性，同时将有机物矿化产生的CO₂与污水中含有的NO₃⁻共还原，转化为含氮的高附加值化学品尿素（CO(NH₂)₂）和氨（NH₃），实现有机物去除及CO₂和NO₃⁻的资源化利用。主要研究内容如下：

(1)通过化学吸附法制备了g-C₃N₄负载的单金属催化剂阴极（Zr/CN、Fe/CN、Zn/CN、Ti/CN、Cu/CN），通过电化学测试和性能评价比较了不同阴极材料催化CO₂和NO₃⁻共还原的性能。结果表明，Zr/CN的尿素和氨产率具有显著优势：在-0.7 V vs. RHE的条件下，尿素和氨产量分别为5.94 和50.32 mmol h^-1 g_cat^-1，法拉第效率（FE）分别为10.66%和45.67%。Fe/CN和Ti/CN的尿素产率、尿素和氨总产率仅低于Zr/CN，其中Zr/CN和Fe/CN在催化过程中没有更高毒性产物亚硝酸盐（NO₂⁻）的生成，因此在本研究中g-C₃N₄分别负载单金属Zr和Fe具有较好的C-N共还原性能。此外，Zr/CN和Fe/CN的差分电荷密度计算结果表明，Zr和Fe原子与其周围N位的电荷得失方向相反，分别形成了亲核和亲电的化学活性中心，有利于CO₂和NO₃⁻分别吸附及电子转移。

(2)通过主客体策略制备了g-C₃N₄负载Zr和Fe双金属催化剂（Zr-Fe/CN），与Zr/CN相比，双金属负载电极的还原性能进一步提高，在-0.8 V vs. RHE的条件下，尿素和氨产量分别达到10.18和63.21 mmol h^-1 g_cat^-1，FE分别为19.55%和53.90%。阳极双酚A（BPA）氧化的耦合不仅同时实现了有机污染物降解和CO₂和NO₃⁻共还原，而且提高了电催化体系中电子的利用率，促使阴极尿素和氨产量分别提高了18.4%和8.3%。探究了阳极BPA氧化所产CO₂直接进入阴极还原的可行性，相比通过N₂吹脱CO₂进入阴极室，直接利用阳极氧化后电解液中溶解CO₂的方式产尿素效率更高。

(3)为了实现阳极污染物降解所产CO₂在阴极高效原位利用，设计了强化传质的穿透流式电催化反应器。在较优化的实验条件（外加直流电压为3 V，pH=6.3，初始BPA和NO₃⁻浓度分别为40 mg L^-1和0.1 M）下，阳极BPA主要通过•OH和直接电子转移被氧化，去除率为84.49%，TOC下降了约72%，其中约59%的CO₂转化为尿素，尿素和氨产量分别为19.6 mmol h^-1 g_cat^-1和106.1 mmol h^-1 g_cat^-1，C转化效率（从BPA到尿素）为42.4%，总产物FE为96.3%。与非穿透流的单室搅拌反应器相比，相同运行参数下穿透流式电催化反应器C转化效率提高12.2%，产尿素和氨的总FE提高24.8%。

In recent years, the reduction of carbon dioxide (CO₂) emissions and its resource utilization have become research hotspots. Wastewater plants, as one of the top ten "carbon emissions industry", are causing a significant amount of CO₂ emissions. Thus, how to reduce CO₂ emissions from wastewater plants and convert them back into valuable substances is an in-depth exploration and refinement of "carbon neutrality" technologies. At the same time, the common high-concentration nitrate (NO₃⁻) in industrial wastewater can also be reduced into valuable substances. Therefore, this study aims to reduce carbon emissions in the sewage treatment process, while resourcing carbon and nitrogen of wastewater. In this study, we selected and optimized cathode catalysts for the electrocatalytic co-reduction of CO₂ and NO₃⁻, and constructed a flow-through cell for cathodic C-N co-reduction coupled with anodic oxidation of refractory organics _ bisphenol A（BPA）. In the flow-through reactor, it can enhance the biodegradability by utilizing electrocatalytic anodic oxidation of refractory organic pollutants, while co-reducing the CO₂ produced in this process with the NO₃⁻ contained in wastewater into high-value nitrogen-containing chemicals, such as urea (CO(NH₂)₂) and ammonia (NH₃). It has achieved organic pollutants removal and the resource utilization of CO₂ and NO₃⁻. The main research contents are as follows:

(1) The g-C₃N₄-supported single metal catalysts (Zr/CN, Fe/CN, Zn/CN, Ti/CN, Cu/CN) were prepared using the chemical adsorption method. Through electrochemical testing and performance evaluation, the effectiveness of different cathode materials in the co-reduction of CO₂ and NO₃⁻ was compared. The results indicated that Zr/CN exhibited significant advantages in urea and NH₃ yield: under -0.7 V vs. RHE, the urea production rate was 5.94 mmol h^-1 g_cat^-1, and the NH₃ production rate was 50.32 mmol h^-1 g_cat^-1, with a Faraday efficiency (FE) of 10.66% and 45.67%, respectively. The urea yield and total yield of urea and NH₃ for Ti/CN and Fe/CN were only lower than Zr/CN. Among them, Zr/CN and Fe/CN didn’t produce higher toxic products, nitrite (NO₂⁻), during the catalytic process. Therefore, in this study, the g-C₃N₄-supported single metal Zr and Fe exhibited good C-N co-reduction performance. Furthermore, the density functional theory (DFT) results of charge density of Zr/CN and Fe/CN showed that the charge accumulation and depletion direction of Zr and Fe atoms was opposite to that of the surrounding N sites, which formed nucleophilic and electrophilic chemical active centers, respectively. It is beneficial for the adsorption of CO₂ and NO₃⁻ and electron transfer.

(2) The preparation of the g-C₃N₄ supported Zr and Fe bimetallic catalyst (Zr-Fe/CN) was achieved through a host-guest strategy. Compared to Zr/CN, the reduction efficiency of the Zr-Fe/CN was further enhanced. Under -0.8 V vs. RHE, the yield of urea reached 10.18 mmol h^-1 g_cat^-1, with an NH₃ yield of 63.21 mmol h^-1 g_cat^-1, and the respective FE were 19.55% and 53.90%. The coupling of anodic bisphenol A (BPA) oxidation not only achieved the degradation of organic pollutants and the co-reduction of CO₂ and NO₃⁻ simultaneously, but also improved the utilization rate of electrons in the electrocatalytic system, resulting in an increase of urea by 18.4% and NH₃ by 8.3% in the cathode production. The feasibility of direct reduction of CO₂ produced from anodic BPA oxidation into the cathode chamber was investigated. Compared to introducing CO₂ into the cathode chamber by N₂, the direct utilization of CO₂ dissolved in the electrolyte after anodic oxidation resulted in a higher efficiency in producing urea.

(3) To achieve the efficient in-situ utilization of CO₂ produced by the degradation of BPA, a flow-through reactor was designed. Under optimized experimental conditions (with an applied voltage of 3 V, pH = 6.3, an initial BPA concentration of 40 mg L^-1, and an initial NO₃⁻ concentration of 0.1 M), the anodic BPA was primarily oxidized via hydroxyl radicals (•OH) and direct electron transfer, achieving a removal rate of 84.49%. Most of the BPA was mineralized into CO₂, with a decrease of total organic carbon (TOC) by approximately 72%. Among this, approximately 59% of the CO₂ was converted into urea, with urea and NH₃ yields of 19.6 mmol h^-1 g_cat^-1 and 106.1 mmol h^-1 g_cat^-1, respectively. The conversion efficiency from BPA to urea (C conversion efficiency) was 42.4%, and the total product (urea and NH₃) FE was 96.3%. Compared to the single-chamber stirred reactor, under the same operating condition, the C conversion efficiency of the flow-through reactor increased by 12.2%, and the total FE of urea and NH₃ production increased by 24.8%.