Plasma-catalytic remediation of pharmaceutical-contaminated wastewater: Catalyst design and mechanistic insights from...

Contaminants of emerging concern (CECs), characterized by persistence, poor biodegradability, and high toxicity, pose significant risks to aquatic ecosystems and human health. Plasma-catalytic processes may eliminate CECs, particularly micropollutants, from wastewater. However, discharge-zone thermalization and heavy-metal leaching from metal-based catalysts pose challenges for industrial adoption of cold plasma technology. This study presents a novel coaxial plasma electrode and a heteroatom-doped carbonaceous catalyst that overcome these limitations. Catalysts with varying boron and oxygen contents are synthesized through the pyrolysis of waste wood, boric acid, and zinc borate at 1000 °C. Boron-doped graphene-like carbon with 15-wt.% boric acid and 15-wt.% zinc borate exhibits superior ozone degradation and hydrogen-peroxide formation. The plasma-catalytic system demonstrates high-efficacy micropollutant degradation, achieving complete naproxen degradation in less than 30 min with a 0.1112 degradation rate and 75.67 % mineralization. Additionally, it effectively removed naproxen, rhodamine B, and Congo red from real wastewater spiked with 10 ppm of each pollutant. Density functional theory calculations elucidate the high affinity of armchair BC₂O for ozone adsorption. Moreover, the dual role of zinc borate as both an activator and dopant in the synthesis of boron-doped graphene-like carbon is revealed. As the synthesized metal-free catalyst exhibits high performance for treatment of real wastewater samples, and the plasma setup is simple and efficient, this system has scalability and practical applicability in wastewater treatment plants.