Xiaoyong Yang

Photocatalytic methods are extensively used in the treatment of uranium-containing wastewater. However, the reduction of uranium in natural sunlight remains a central challenge. This work proposed a MoS₂ nanoflower-coupled Ti₃C₂ MXene reduction cocatalyst for bifunctional catalytic systems to remove U(VI) and degrade organic pollutants under natural sunlight. Advanced spectral characterization showed that MoS₂/Ti₃C₂ had excellent photogenerated carrier transfer and light absorption capabilities. The experimental results show that when uranium and organic pollutants coexist, the removal rate of uranium is as high as 99%, and no sacrificial agents or inert gases are involved in this process. Further, theoretical calculations demonstrate that the bond behavior in the MoS₂/Ti₃C₂ composites combines covalent bonds and ionic bonds, and about 0.497 electrons are transferred from Ti₃C₂ to the MoS₂ monolayer. Two possible random adsorption interaction scenarios of [UO₂·(H₂O)₅]²⁺ on MoS₂/Ti₃C₂ composites are revealed meaningfully. The efficient removal of uranium and organic pollutants under real sunlight confirms the significant potential of the bifunctional photocatalyst for practical applications in radioactive wastewater.

Given the rapid recombination of photogenerated charge carriers and photocorrosion, transition metal sulfide photocatalysts usually suffer from modest photocatalytic performance. Herein, S-vacancy-rich ZnIn₂S₄ (V_S-ZIS) nanosheets are integrated on 3D bicontinuous nitrogen-doped nanoporous graphene (N-npG), forming 3D heterostructures with well-fitted geometric configuration (V_S-ZIS/N-npG) for highly efficient photocatalytic hydrogen production. The V_S-ZIS/N-npG presents ultrafast interfacial photogenerated electrons captured by the S vacancies in V_S-ZIS and holes neutralization behaviors by the extra free electrons in N-npG during photocatalysis, which are demonstrated by in situ XPS, femtosecond transient absorption (fs-TA) spectroscopy, and transient-state surface photovoltage (TS-SPV) spectra. The simulated interfacial charge rearrangement behaviors from DFT calculations also verify the separation tendency of photogenerated charge carriers. Thus, the optimized V_S-ZIS/N-npG 3D hierarchical heterojunction with 1.0 wt % N-npG exhibits a comparably high hydrogen generation rate of 4222.4 μmol g^-1 h^-1, which is 5.6-fold higher than the bare V_S-ZIS and 12.7-fold higher than the ZIS without S vacancies. This work sheds light on the rational design of photogenerated carrier transfer paths to facilitate charge separation and provides further hints for the design of hierarchical heterostructure photocatalysts.

Compared with the Haber Bosch process, the electrochemical nitrogen reduction reaction (NRR) under mild conditions provides an alternative and promising route for ammonia synthesis due to its green and sustainable features. However, the great energy barrier to break the stable N≡N bond hinders the practical application of NRR. Though Fe is the only common metal element in all biological nitrogenases in nature, there is still a lack of study on developing highly efficient and low-cost Fe-based catalysts for N₂ fixation. Herein, Co-doped Fe₃S₄ nanoflowers were fabricated as the intended catalyst for NRR. The results indicate that 4% Co-doped Fe₃S₄ nanoflowers achieve a high Faradaic efficiency of 17% and a NH₃ yield rate of 37.5 μg·h^-1·mg^-1_cat. at -0.55 V versus RHE potential in 0.1 M HCl, which is superior to most Fe-based catalysts. The introduction of Co atoms can not only shift the partial density states of Fe₃S₄ toward the Fermi level but also serve as new active centers to promote N₂ absorption, lowering the energy barrier of the potential determination step to accelerate the catalytic process. This work paves a pathway of the morphology and doping engineering for Fe-based electrocatalysts to enhance ammonia synthesis.

Material-enhanced heterogonous peroxymonosulfate (PMS) activation on emerging organic pollutant degradation has attracted intensive attention, and a challenge is the electron transfer efficiency from material to PMS for radical production. Herein, an interface architecture of Co(OH)₂ nanosheets growing on the KNbO₃ perovskite [Co(OH)₂/KNbO₃] was developed, which showed high catalytic activity in PMS activation. A high reaction rate constant (k₁) of 0.631 min^–1 and complete removal of pazufloxacin within 5 min were achieved. X-ray photoelectron spectroscopy, X-ray absorption near edge structure spectra, and density functional theory (DFT) calculations revealed the successful construction of the material interface and modulated electronic structure for Co(OH)₂/KNbO₃, resulting in the hole accumulation on Co(OH)₂ and electron accumulation on KNbO₃. Bader topological analysis on charge density distribution further indicates that the occupations of Co-3d and O-2p orbitals in Co(OH)₂/KNbO₃ are pushed above the Fermi level to form antibonding states (σ*), leading to high chemisorption affinity to PMS. In addition, more reactive Co(II) with the closer d-band center to the Fermi level results in higher electron transfer efficiency and lower decomposition energy of PMS to SO₄^•–. Moreover, the reactive sites of pazufloxacin for SO₄^•– attack were precisely identified based on DFT calculation on the Fukui index. The pazufloxacin pathways proceeded as decarboxylation, nitroheterocyclic ring opening reaction, defluorination, and hydroxylation. This work can provide a potential route in developing advanced catalysts based on manipulation of the interface and electronic structure for enhanced Fenton-like reaction such as PMS activation.