氮磷共掺杂活性炭负载Fe催化剂制备及湿式催化降解哌嗪性能

Wet catalytic degrading piperazine over Fe supported activated carbon by co-doped nitrogen and phosphorus

摘要:

铁基催化剂因低成本和良好催化性能广泛应用于湿式催化氧化领域，为探索杂原子掺杂对铁基催化剂湿式催化氧化性能的调控机制，以双氰胺、磷酸二氢钠和六水氯化铁为主要原料，通过两步浸渍蒸发法制备了氮磷双掺杂活性炭低负载铁催化剂Fe/AC-NP，将其用于湿式催化氧化降解哌嗪，采用XRD、SEM、XPS、BET对Fe/AC-NP微观形貌、结构组成和孔隙参数进行表征，考察原料比例、杂原子掺杂类型对Fe/AC-NP催化氧化降解哌嗪的化学需氧量（COD）和氨氮含量的影响，优化反应条件，通过自由基淬灭实验、水接触角测试和XPS表征，推测催化反应机理和历程。结果表明，n(双氰胺)∶n(NaH2PO4)＝2∶1是最佳原料配比，Fe/AC-NP比表面积为699.647 m2/g，晶面间距为0.0169 nm，Fe/AC-NP上Fe均匀分布且未形成大颗粒，成功负载并与N、P相互作用，主要以Fe(Ⅱ)和Fe(Ⅲ)形式存在。Fe/AC-NP湿式催化氧化降解哌嗪的最优条件为：反应温度230 ℃，反应压力1.2 MPa，Fe/AC-NP加入量（以哌嗪废水体积为基的催化剂质量，下同）1.25 g/L，转速500 r/min。此条件下，70 min将COD完全去除，150 min可以实现对88.7%以上的氨氮进行降解，循环使用五次后，COD和氨氮去除率可达95.3%和83.4%。石墨氮和吡咯氮协同作用可促进氧气吸附，通过羟基自由基主导的链式反应及碳载体与金属间电子转移机制，实现了污染物的降解。通过掺杂磷调节催化剂的酸碱性，增强了Fe—N键稳定性，同时氮磷掺杂碳载体通过电子调控来维持反应循环。

Abstract:

ron-based catalysts are widely used in the field of wet catalytic oxidation due to their low cost and excellent catalytic performance. To explore the regulatory mechanism of heteroatom doping on the wet catalytic oxidation performance of iron-based catalysts, an activated carbon with nitrogen and phosphorus dual-doping and low-load iron catalyst Fe/AC-NP was prepared using dicyandiamide, sodium dihydrogen phosphate, and ferric chloride as the main raw materials through a two-step impregnation and evaporation method. This catalyst was used for the wet catalytic oxidation of piperazine, and its microstructure, composition, and pore parameters were characterized by XRD, SEM, XPS, and BET. The effects of raw material ratios and heteroatom doping types on the catalytic oxidation degradation of piperazine by Fe/AC-NP were investigated, and the reaction conditions were optimized. Through free radical quenching experiments, water contact angle tests, and XPS characterization, the catalytic reaction mechanism and process were speculated. The results showed that the optimal raw material ratio was n(C2H4N4) : n(NaH2PO4) = 2 : 1. The specific surface area of Fe/AC-NP was 699.647 m2/g, the interplanar spacing was 0.0169 nm, and Fe was uniformly distributed on Fe/AC-NP without forming large particles. It was successfully loaded and interacted with N and P. It mainly existed in the form of Fe(Ⅱ) and Fe(Ⅲ). The optimal conditions for the wet catalytic oxidation of piperazine by Fe/AC-NP were: reaction temperature 230 ℃, reaction pressure 1.2 MPa, Fe/AC-NP loading (based on the volume of piperazine wastewater, the same below) 1.25 g/L, and rotation speed 500 r/min. Under these conditions, 70 minutes completely removed COD, and 150 minutes could achieve the degradation of more than 88.7% of ammonia nitrogen. After five cycles of reuse, the removal rates of COD and ammonia nitrogen could reach 95.3% and 83.4%, respectively. The synergistic effect of graphite nitrogen and pyrrole nitrogen can promote oxygen adsorption. Through the chain reaction dominated by hydroxyl radicals and the electron transfer mechanism between carbon carrier and metal, the degradation of pollutants was achieved. By doping phosphorus to regulate the acidity and basicity of the catalyst, the stability of Fe-N bond was enhanced, and at the same time, the nitrogen-phosphorus doped carbon carrier maintained the reaction cycle through electron regulation.