Photothermal-catalytic activation periodate over MnO2/g-C3N4 S-scheme heterojunction for rapidly tetracycline removal: intermediates, toxicity evaluation and mechanism

The MnO₂/CN S-scheme heterojunctions were prepared using the hydrothermal method, which significantly promoted periodate (PI) activation for the TC removal. Notably, the MnO₂/CN-0.1 achieved a TC removal rate of 79.7 % within 25 min in the PI/Vis system, which was 1.39 and 3.68 times that of MnO₂ and g-C₃N₄, respectively. The improved TC degradation performance could be attributed to the synergetic effect of photothermal effect of MnO₂ and the S-scheme heterojunction. On the basis of the infrared thermography images, the photothermal properties of MnO₂ could increase temperatures of the reaction system, leading to the promotion of the PI activation. The formation of the MnO₂/CN S-scheme not only effectively suppressed charge recombination, but also facilitated the Mn(IV)/Mn(III) redox cycle within the reaction. Under different pH and anion conditions, the MnO₂/CN-0.1/PI system exhibited excellent capability in TC removal. Additionally, the toxicity of the degraded solution was evaluated based on the LC-MS test results and the growth experiment of Mung bean seeds. This work put forward an efficient approach on S-scheme photothermal catalysts to achieve efficient utilization of PI on TC degradation, which demonstrates a promising method for photothermal assistance PI activation to remediate the water environment efficiently.