Large-Scale Synthesis of Graphene-Like MoSe₂ Nanosheets for Efficient Hydrogen Evolution Reaction

Two-dimensional (2D) materials have attracted great attention by researchers due to their fascinating properties and promising applications. However, the synthesis methods for few layers are usually difficult to expand to large area applications because of their low yield. In this paper, graphene-like MoSe₂ nanosheets are successfully and scaleable synthesized by a facile and low-cost hydrothermal method under the synergy of PVP and graphene. The ultrathin MoSe₂ nanosheets are typically 1–3 layers, which are confirmed by HRTEM. This unique structure makes this MoSe₂ electrode material show superior activity toward the electrocatalytic hydrogen production with a low Tafel slope about 70 mV·dec^–1. Furthermore, the synthesized graphene-like MoSe₂ nanosheets had a high stability during the electrocatalytic process and we nearly cannot find the degradation after 1000 cyclic voltammetric sweeps

Oxygen Vacancy Promoted Heterogeneous Fenton-like Degradation of Ofloxacin at pH 3.2–9.0 by Cu Substituted Magnetic Fe₃O₄@FeOOH Nanocomposite

To develop an ultraefficient and reusable heterogeneous Fenton-like catalyst at a wide working pH range is a great challenge for its application in practical water treatment. We report an oxygen vacancy promoted heterogeneous Fenton-like reaction mechanism and an unprecedented ofloxacin (OFX) degradation efficiency of Cu doped Fe₃O₄@FeOOH magnetic nanocomposite. Without the aid of external energy, OFX was always completely removed within 30 min at pH 3.2–9.0. Compared with Fe₃O₄@FeOOH, the pseudo-first-order reaction constant was enhanced by 10 times due to Cu substitution (9.04/h vs 0.94/h). Based on the X-ray photoelectron spectroscopy (XPS), Raman analysis, and the investigation of H₂O₂ decomposition, ^•OH generation, pH effect on OFX removal and H₂O₂ utilization efficiency, the new formed oxygen vacancy from in situ Fe substitution by Cu rather than promoted Fe³⁺/Fe²⁺ cycle was responsible for the ultraefficiency of Cu doped Fe₃O₄@FeOOH at neutral and even alkaline pHs. Moreover, the catalyst had an excellent long-term stability and could be easily recovered by magnetic separation, which would not cause secondary pollution to treated water

Surface Facet of CuFeO₂ Nanocatalyst: A Key Parameter for H₂O₂ Activation in Fenton-Like Reaction and Organic Pollutant Degradation

The development of efficient heterogeneous Fenton catalysts is mainly by “trial-and-error” concept and the factor determining H₂O₂ activation remains elusive. In this work, we demonstrate that suitable facet exposure to elongate O–O bond in H₂O₂ is the key parameter determining the Fenton catalyst’s activity. CuFeO₂ nanocubes and nanoplates with different surface facets of {110} and {012} are used to compare the effect of exposed facets on Fenton activity. The results indicate that ofloxacin (OFX) degradation rate by CuFeO₂ {012} is four times faster than that of CuFeO₂ {110} (0.0408 vs 0.0101 min^–1). In CuFeO₂ {012}-H₂O₂ system, OFX is completely removed at a pH range 3.2–10.1. The experimental results and theoretical simulations show that ^•OH is preferentially formed from the reduction of absorbed H₂O₂ by electron from CuFeO₂ {012} due to suitable elongation of O–O (1.472 Å) bond length in H₂O₂. By contrast, the O–O bond length is elongated from 1.468 to 3.290 Å by CuFeO₂ {110} facet, H₂O₂ tends to be dissociated into −OH group and passivates {110} facet. Besides, the new formed ≡Fe²⁺* on CuFeO₂ {012} facet can accelerate the redox cycle of Cu and Fe species, leading to excellent long-term stability of CuFeO₂ nanoplates