Ajmal Shahzad

Fe-based heterogeneous catalytic advanced oxidation processes show great potential for treating wastewater. However, catalyst instability often hinders their practical use, mainly due to the slow regeneration of Fe²⁺ sites. Herein, we developed a Fe₃S₄/WO₃ catalyst, where the electron-rich Wx and Sx sites promoted efficient electron transfer, enabling continuous regeneration of Fe²⁺ active sites on the catalyst surface. The Fe₃S₄/WO₃ catalyst exhibited outstanding degradation efficiency for tetracycline (TC) in the peroxymonosulfate (PMS) system, achieving a 92.5% removal efficiency, significantly higher than its individual components of Fe₃S₄ (52.8%), WO₃ (43.1%), and WS₂ (53.2%). Moreover, the Fe₃S₄/WO₃/PMS system demonstrated a broad operational pH range (3.0–9.0), excellent degradation efficiency for various emerging pollutants, minimal interference from background electrolytes and organic matter, and strong stability in real water treatment. Chemical scavenger tests and electron paramagnetic resonance (EPR) analysis confirmed that the oxidative degradation of TC was driven by multiple reactive species, including SO₄^•−, ^•OH, ^•O₂⁻, and ¹O₂. This study provides a novel strategy for regulating active sites in Fe-based catalysts to ensure sustained performance, offering a pathway for the rational design of next-generation Fenton-like catalysts for efficient and sustainable micropollutant removal from wastewater.

Recently, carbonaceous materials have attracted increasing attention in advanced oxidation processes (AOPs) due to their capability, adaptability and efficiency in the degradation of organic wastewater contaminants with little or no leaching potential. Previous reviews have raised serious controversies regarding the occurrence and mechanism of the persulfate activation process but the detailed influence of the structural features on the persulfate activation performance is yet to be analyzed. This state-of-the-art review aims to discuss the recent structural adjustments, modifications and modulation of carbonaceous materials in relation to how they affect the persulfate activation performance. It was observed that tweaking the carbon structural features (such as the crystal structure and defects, the porous structure, surface area, pore size, and oxygen-containing groups) influences the reaction mechanism, further controlling the persulfate activation process. Hence, different reaction mechanisms involved in the carbon-based persulfate activation process were discussed. Also, the influence of the reaction pathway on the nature of the degradation or intermediate products was examined along with some real water investigations. Environmental application of carbon-based persulfate systems was discussed in relation to its influence on several background ions like Cl⁻, HCO₃ ⁻, CO₃ ²⁻, NO₃ ⁻, SO₄ ²⁻, H₂PO₄ ⁻, natural organic matter (NOM) and humic acid. Furthermore, future research directions for improving the design and properties of carbonaceous catalysts were proposed.