S-scheme SrTiO₃/porous ZnO derived by pyrolysis of ZIF-8 composite with efficient photocatalytic activity for pollutant degradation

Semiconductor catalyst with high photocatalytic activity can be exploited via heterojunction. In this study, a new S-scheme SrTiO₃/porous ZnO composite was rationally devised, successfully prepared by utilizing a two-step pyrolysis of SrTiO₃/ZIF-8, and analyzed by various characterization technologies including XRD, SEM, TEM, BET, XPS, PL, UV–vis DRS, and photoelectrochemical and DFT theoretical calculations. A porous structure, tight contact, and a heterojunction formed between SrTiO₃ and porous ZnO (ZnOT) can be observed by SEM and TEM images. BET testing indicates that the SrTiO₃/porous ZnO composite (S3ZT) shows the highest specific surface area (30.37 m²/g). The band gap values (E_g) of SrTiO₃ and ZnOT are around 3.17 and 2.95 eV, which agree with those obtained from DFT calculations. Compared to other samples, the SrTiO₃/porous ZnO composite (S3ZT) shows higher light absorption and lower transfer resistance as demonstrated by UV–vis DRS and EIS results. S3ZT presents a superior photocatalytic efficiency of 48.8% in degrading 5 mg/L methyl orange (MO) irradiated by 1 h UV–vis light, which are 7- and 1.5-fold higher than pristine SrTiO₃ and ZnOT, respectively. Moreover, based on Mott-Schottky theory, active species trapping experiments, XPS determination, and DFT calculations (energy band gap and work function), it was shown to be reasonable to utilize the S-scheme charge migration process for an explanation regarding the better photocatalytic activity of SrTiO₃/porous ZnO composite. Overall, this work will provide an effective protocol for devising and preparing semiconductor photocatalysts with S-scheme heterojunction by utilizing the superior characteristics of MOFs.