Enhanced tetracycline degradation by a confinement structure rGO/Fe1/C3N4 photocathode during the sequential oxygen reduction process

Photoelectrocatalytic (PEC) process based on hydroxyl radicals (•OH) can effectively remove refractory pollutants, however, reducing molecular oxygen to •OH by a PEC process remains a challenge. In this work, an atomically dispersed Fe catalyst (rGO/Fe1/C3N4) was proposed. The rGO/Fe1/C3N4 photocathode showed high efficiency (88.3%, 60 min) and low energy consumption (0.072 kWh/g) in removing tetracycline (TC), and •OH was the main active species for TC degradation. The results of experimental and theoretical calculations revealed that the efficient TC degradation is due to the coupling effect of rGO and Fe atoms. The rGO enhances light absorption and effective electron transfer, thus facilitating the reduction of O2 to H2O2. Subsequently benefiting from the low H2O2 adsorption energy on Fe single atoms, enhanced electron and mass transfer between Fe single atoms and the coordination environment, H2O2 is further reduced to •OH in the confinement structure. Stability test and toxicity analysis in TC degradation demonstrate that the PEC process is an environmentally friendly technology that is stable in the long term. This work provides a new idea for designing photoelectrocatalysts with excellent •OH generation and TC degradation capacity.