Designing photocatalysts with high light utilization and efficient photogenerated carrier separation for pollutant degradation is one of the important topics for sustainable development. In this study, hierarchical core–shell material α-Fe₂O₃@ZnIn₂S₄ with a step-scheme (S-scheme) heterojunction is synthesized by in situ growth technique, and MXene Ti₃C₂ quantum dots (QDs) are introduced to construct a double-heterojunction tandem mechanism. The photodegradation efficiency of α-Fe₂O₃@ZnIn₂S₄/Ti₃C₂ QDs to bisphenol A is 96.1% and its reaction rate constant attained 0.02595 min⁻¹, which is 12.3 times that of pure α-Fe₂O₃. Meanwhile, a series of characterizations analyze the reasons for the enhanced photocatalytic activity, and the charge transport path of the S-scheme heterojunction/Schottky junction tandem is investigated. The construction of the S-scheme heterojunction enables the photo-generated electrons of α-Fe₂O₃ and the holes of ZnIn₂S₄ to transfer and combine under the action of the reverse built-in electric field. Due to the metallic conductivity of Ti₃C₂ QDs, the photogenerated electrons of ZnIn₂S₄ are further transferred to Ti₃C₂ QDs to form a Schottky junction, which in turn forms a double-heterojunction tandem mechanism, showing a remarkable charge separation efficiency. This work provides a new opinion for the construction of tandem double heterojunctions to degrade harmful pollutants.

The formation of chemical bonds between metal ions and their supports is an effective strategy to achieve good catalytic activity. However, both the synthesis of active metal species on a support and control of their coordination environment are still challenging. Here, we show the use of an organic compound to produce tubular carbon nitride (TCN) as a support for Pd nanoparticles (NPs), creating a composite material (NP-Pd-TCN). It was found that Pd ions preferentially bind with the electron-rich N atoms of TCN, leading to strong metal–support interactions that benefit charge transfer from g-C₃N₄ to Pd. X-ray absorption spectroscopy further revealed that the metal–support interactions resulted in the formation of Pd–N bonds, which are responsible for the improvement in the charge dynamics as evidenced by the results from various techniques including photoluminescence (PL) spectroscopy, photocurrent measurements, and electrochemical impedance spectroscopy (EIS). Owing to the good dynamical properties, NP-Pd-TCN was used for photocatalytic hydrogen evolution under visible-light irradiation (λ > 420 nm) and an excellent evolution rate of ~ 381 μmol·h ⁻¹ (0.02 g of the photocatalyst) was attained. This work aims to promote a strategy to synthesize efficient photocatalysts for hydrogen production by controllably introducing metal nanoparticles on a support and in the meantime forming chemical bonds to achieve intimate metal-support contact.

Fenton or photocatalytic degradations of organic contaminants are recognized as promising approaches to address the increasing environmental pollution issues. Herein, we develop the effective synergistic catalysis reaction of Fenton and photocatalysis based on a loofah sponge-like Fe₂O_x/C nanocomposite, which exhibits excellent nitrobenzene photocatalytic degradation property. It is noted that Fe₂O₃ nanoparticles with surface Fe²⁺ species were encapsulated with an ultrathin carbon layer (denoted as Fe₂O_x/C) via a supramolecular self-sacrificing template and following thermal treatment process. The experimental results indicated that the thin layer carbon coating not only inhibited the Fe iron leaching from the Fe₂O_x but also prompted the separation and transferring of electrons–hole pairs. The introduction of Fe₂O_x/C enables the Fenton reaction to induce a rapid Fe²⁺/Fe³⁺ cycle, and meanwhile, together with the photocatalytic reaction to produce continuous active substances for the subsequent degradation catalytic reaction without successive H₂O₂, resulting in the inexpensive and the effective photocatalytic procedure. As a result, 100% nitrobenzene (100 mg/L) was degraded and 97% of the organic carbon was mineralized in 90 min using the Fe₂O_x/C (0.1 g/L) at a low H₂O₂ dosage (0.50 mM), under air mass (AM) 1.5 irradiation. Theoretical calculations confirmed that the Fe₂O_x/C-600 with thin carbon layer promoted the dissociation of H₂O₂ and the ·OH desorption. The synergistic catalysis of this work may provide new ideas for low-cost and more efficient treatment of pollutants.