Low-temperature degradation of humic acid via titanium zirconium oxide@copper single-atom activating oxygen: Mechanism and pathways

Humic acid (HA), a refractory organic pollutant, has always been a key obstackle in wastewater treatment (such as biochemical landfill leachate). And catalytic air oxidation is one of the most promising methods to degrade HA efficiently and economically. In this study, a novel high-loading Cu single-atom catalyst (TiZrO4@Cu-SA) was facilely synthesized using isovolume vacuum impregnation and co-calcination method, and then used to accel-erate the oxidation of HA at low temperatures. The TiZrO4@5%Cu-SA catalytic system showed a superior per-formance, and 91 % of HA was degraded and 90 % of organic carbon was removed from HA solution within 10 min at 90 degrees C. Aberration-corrected electron microscopy, electron paramagnetic resonance spectroscopy, and density functional theory calculations were applied to reveal the catalytic mechanism of TiZrO (4)@5%Cu-SA. The active center of Cu single-atom co-catalyst with Cu - O coordination sites can quickly transfer electrons to O-2 in the water to form O-2(.-), exhibiting high activation efficiency. Gas chromatography (GC), liquid chromatograph-mass spectrometer (LC-MS), liquid chromatography-organic carbon detection (LC-OCD), and Fourier-transform infrared spectroscopy (FT-IR) spectroscopy provided the results of intermediate products, including 3-phe-noxy-benzaldehy, phenylglyoxal, ethanol, acetic acid, butyric acid, and valeric acid, and thus a catalytic degradation pathway of HA was speculated. Based on the new catalyst, a new process can be conceived for efficient and economic removal of HA from HA-containing wastewater.

腐植酸（HA）作为一种难降解的有机污染物，一直是废水处理（如生化垃圾渗滤液处理）中的关键障碍。催化空气氧化是一种高效且经济地降解腐植酸最有前景的方法之一。在本研究中，采用等体积真空浸渍和共煅烧法简便地合成了一种新型高负载铜单原子催化剂（TiZrO₄@Cu - SA），并将其用于低温下加速腐植酸的氧化。TiZrO₄@5%Cu - SA催化体系表现出优异的性能，在90℃下10分钟内，91%的腐植酸被降解，腐植酸溶液中90%的有机碳被去除。应用像差校正电子显微镜、电子顺磁共振波谱和密度泛函理论计算揭示了TiZrO₄@5%Cu - SA的催化机制。具有Cu - O配位位点的铜单原子助催化剂的活性中心能够快速将电子转移给水中的O₂形成O₂⁻·，表现出高活化效率。气相色谱（GC）、液相色谱 - 质谱联用仪（LC - MS）、液相色谱 - 有机碳检测（LC - OCD）和傅里叶变换红外光谱（FT - IR）提供了中间产物的结果，包括3 - 苯氧基苯甲醛、苯乙二醛、乙醇、乙酸、丁酸和戊酸，由此推测出腐植酸的一条催化降解途径。基于这种新型催化剂，可以构思一种从含腐植酸废水中高效且经济地去除腐植酸的新工艺。