Activation of peroxydisulfate by phosphoric acid-modified microwave biochar for tetracycline removal in water: Mechanistic insights

Abstract

Phosphoric acid activation and microwave pyrolysis have clear benefits in biochar production. This research investigated the effects of pyrolysis power and phosphoric acid concentration on the physicochemical properties of modified biochar. The biochar with optimal activity was selected as a catalyst and used to activate peroxodisulfate (PDS) for the efficient removal of tetracycline (TC). The results revealed that the most active sample was MHP500–1500. It was prepared at a microwave power of 1500 W with 10 mol/L phosphoric acid at 500 °C. This sample had abundant active sites and excellent electron transfer capability. The specific surface area was 1508 m²/g. The MHP500–1500/PDS system achieved a TC removal rate of 92 % within 1 h. The internal graphitic carbon structure of MHP500–1500 accelerated the electron transfer in the MHP500–1500/PDS system, successfully activating PDS. PDS was adsorbed on the surface of MHP500–1500, forming a complex. The complex attacked the electron-rich pollutant TC through electron transfer, and the singlet oxygen (¹O₂) generated during the activation process could also attack TC. The combined action of these two non-radical pathways achieved the removal of TC. Additionally, the MHP500–1500/PDS system exhibited stability in different water environments. After five repetitions of the experiments, the removal rate of TC still reached 77 %. Compared with other carbon-based catalysts, the catalyst prepared in this study not only has a higher specific surface area but also exhibits better TC removal efficiency at a lower dosage. This study provides new insights into the non-radical pathway for pollutant removal.