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.