Danyun Xu

Metallic 1T phase MoS2 nanosheets as a highly efficient co-catalyst for the photocatalytic hydrogen evolution of CdS nanorods

Conversion of solar energy to hydrogen requires efficient, low-cost and earth-abundant H-producing photocatalysts. Herein, a novel noble metal-free photocatalyst 1T–MoS2/CdS NRs was prepared via a simple method. The 1T–MoS2/CdS NRs hybrid showed the highest photocatalytic activity when the optimized weight ratio of metallic 1T–MoS2 to CdS NRs is 10 wt% in a lactic acid solution under visible light. A 794.93 μmol h−1 H2 evolution rate of the 1T–MoS2/CdS NRs hybrid reached not only 35 times improvement than pure CdS NRs but also 4.5 times enhancement than the 2H–MoS2/CdS NRs hybrid. The relative mechanism has been investigated. 1T–MoS2/CdS NRs interfaces could form ohmic contact with very low contact resistances to promote photoexcited electron transfer, which was different from the p/n junction on the 2H–MoS2/CdS NRs hybrid.

Microwave-assisted 1T to 2H phase reversion of MoS2 in solution: a fast route to processable dispersions of 2H-MoS2 nanosheets and nanocomposites.

Exfoliated molybdenum disulfide (MoS2) has unique 2H phase and semiconductor properties and potential applications across a wide range of fields. However, the chemically exfoliated MoS2 nanosheets from Li x MoS2 have a 1T phase, and searching for a fast route to get processable 2H-MoS2 nanosheets and its nanocomposites is still an urgent task. This study reports on a simple, fast and efficient microwave strategy to achieve the 1T to 2H phase conversion of MoS2 and the successful preparation of processable 2H-MoS2 nanosheets and their nanocomposites. The method here may be easily changed to achieve the phase change of other exfoliated TMDs.

High Yield Exfoliation of WS2 Crystals into 1–2 Layer Semiconducting Nanosheets and Efficient Photocatalytic Hydrogen Evolution from WS2/CdS Nanorod Composites

Monolayer WS2 has interesting properties as a direct bandgap semiconductor, photocatalyst, and electrocatalyst, but it is still a significant challenge to prepare this material in colloidal form by liquid-phase exfoliation (LPE). Here, we report the preparation of 1-2 layer semiconducting WS2 nanosheets in a yield of 18-22 wt % by a modified LPE method that involves preintercalation with substoichometric quantities of n-butyllithium. The exfoliated WS2 nanosheeets are n-type, have a bandgap of ∼1.78 eV, and act as a cocatalyst with CdS nanorods in photocatalytic hydrogen evolution using lactate as a sacrificial electron donor. Up to a 26-fold increase in H2 evolution rate was observed with WS2/CdS hybrids compared with their pure CdS counterpart, and an absorbed photon quantum yield (AQE) of >60% was measured with the optimized photocatalyst.

Reduction of RGO by BH3: a facile route to partially hydrogenated RGO preparation

We demonstrated a facile borane hydrogenation route to hydrogenate reduced graphene oxide (RGO). This strategy is simple and might be scaleable for mass production of partially hydrogenated RGO with a band gap of ∼1.8 eV.

Rational Design of Fe/N/S-Doped Nanoporous Carbon Catalysts from Covalent Triazine Frameworks for Efficient Oxygen Reduction

Porous organic polymers (POPs) are promising precursors for developing high performance transition metal-nitrogen-carbon (M/N/C) catalysts for the oxygen reduction reaction (ORR). The rational design of POP precursors remain a great challenge, because of the elusive structural association between the sacrificial POPs and the final M/N/C catalysts. Based on covalent triazine frameworks (CTFs), we developed a series of S-doped Fe/N/C catalysts by selecting six different aromatic nitriles as building blocks. A new mixed solvent of molten FeCl3 and S was used for CTF polymerization, which benefited the formation of Fe-Nx sites and made the subsequent pyrolysis process more convenient. Comprehensive study of these CTF-derived catalysts showed that their ORR activities are not directly dependent on the theoretical N/C ratio of the building block, but closely correlated to the ratio of the nitrile group to benzene ring (Nnitrile /Nbenzene ) and geometries of the building blocks. The high ratios of Nnitrile /Nbenzene are crucial for ORR activity of the final catalysts owing to the formation of more N-doped micropores and Fe-Nx sites in pyrolysis possess. The optimized catalyst shows high ORR performances in acid and superior ORR activity to the Pt/C catalysts under alkaline conditions.

Ti2C3Tx nanosheets as photothermal agents for near-infrared responsive hydrogels

Poly(N-isopropylacrylamide) (PNIPAM) is broadly applicable in many fields due to its temperature-induced phase transition property. Herein, a facile method to incorporate exfoliated Ti2C3Tx nanosheets in the PNIPAM network is reported. Due to compatibility, stability and photothermal properties of the incorporated Ti2C3Tx nanosheets, the obtained MXene/PNIPAM composite hydrogel shows excellent photothermal properties, expanding the pure thermal-responsive property of the PNIPAM hydrogel. Based on the smart composite hydrogel, remote light-control of the microfluidic pipeline is also demonstrated.

Controllable Preparation of Ultrathin Sandwich-Like Membrane with Porous Organic Framework and Graphene Oxide for Molecular Filtration.

Porous organic frameworks (POFs) based membranes have potential applications in molecular filtration, despite the lack of a corresponding study. This study reports an interesting strategy to get processable POFs dispersion and a novel ultrathin sandwich-like membrane design. It was accidentally found that the hydrophobic N-rich Schiff based POFs agglomerates could react with lithium-ethylamine and formed stable dispersion in water. By successively filtrating the obtained POFs dispersion and graphene oxide (GO), we successfully prepared ultrathin sandwich-like hybrid membranes with layered structure, which showed significantly improved separation efficiency in molecular filtration of organic dyes. This study may provide a universal way to the preparation of processable POFs and their hybrid membranes with GO.