Artificial chloroplast-like phosphotungstic acid — iron oxide microbox heterojunctions penetrated by carbon nanotubes for solar photocatalytic degradation of tetracycline antibiotics in wastewater

Doping-inducted heterojunction is an effective strategy to boost the semiconductor photocatalysis. In this work, an artificial chloroplast-like HPWx@Fe2O3-CNTs photocatalyst was developed by a continuous hydrothermal process and microwave irradiation. This catalyst showed an excellent performance in degradation of biotoxic tetracycline (under mild conditions, tetracycline can be degraded by 100% in 100 min), the apparent rate constant of degradation was 5.5 times higher than that of pure Fe2O3. This is attributed to the synergistic photocatalysis of the Keggin unit of phosphotungstic acid to Fe2O3, which makes the photogenerated electrons trapped in the W5d vacancy state of the Keggin unit, thus delaying the recombination of electron–hole pairs. Moreover, the low-cost HPWx@Fe2O3-CNTs photocatalyst displayed a strong magnetism, leading to a facile separation of the photocatalyst. A relatively stable efficiency of degradation can be maintained. In the light radiation of “Baoxiang river” (Yunnan, China) water sample, the total organic carbon content decreased to 10.58%, which revealed a strong ability of organic carbon mineralization. In addition, E. coli as bacteria indicator was selected to quantitatively monitor the comprehensive toxicity changes in wastewater upon this photocatalytic technology. Both experimental and theoretical investigations demonstrated that the unique nano-scale biomimetic structures with high active sites, improvement of visible-light response, and separation and transfer of electrons and holes in heterojunction were responsible for the superior catalytic results.Graphical abstractArtificial Chloroplast-like H3PW12O40@Fe2O3-CNTs photocatalyst has remarkable photocatalytic activity, which is attributed to the synergistic photocatalytic effect of Keggin unit of phosphotungstic acid on Fe2O3, and the hybridization of Fe3d, O2p and W5d (forming Fe–O-W) leads to the improvement of visible light response and the rapid separation and transfer of electrons and holes.