Yuanzhi Zhu

Combining palladium complex and organic amine on graphene oxide for promoted Tsuji–Trost allylation

In this study, we develop a facile strategy to combine an organic amine with a palladium complex on graphene oxide (GO) as a cooperative catalyst for Tsuji–Trost allylation. A tertiary amine and palladium–diamine complex are simultaneously immobilized on a GO support through silylation and further in situ coordination processes. PdCl2 is employed as the palladium precursor, with no necessity for extra coordination ligands. Various characterizations confirm the successful preparation of the cooperative supported catalyst (GO–NEt2–2N–Pd). Systematic investigation reveals the immobilized palladium–diamine complex (GO–2N–Pd) with very low Pd loading is effective for Tsuji–Trost allylation, and incorporation of the tertiary amine shows a significant promoting effect towards the catalytic activity. GO–NEt2–2N–Pd can be readily recovered and recycled several times without reduction of its efficiency. Its excellent performance should be ascribed to synergistic catalysis effect, excellent support properties, and robust immobilization interaction.

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.

General acid and base bifunctional graphene oxide for cooperative catalysis

In this study, a bifunctional graphene oxide material (GO–AEP–UDP) with a general acid, the ureidopropyl (UDP) group, and a general base, the 3-[2-(2-aminoethylamino)ethylamino]-propyl (AEP) group, was synthesized by silylanization of graphene oxide (GO) with organoalkoxysilane precursors. Characterization of the obtained GO–AEP–UDP was carried out by Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS) and zeta potential measurements. Systematic studies demonstrated that GO–AEP–UDP has superior catalytic performance in the classic Henry reaction of 4-nitrobenzaldehyde with nitromethane. It was found that the relative concentration and spatial arrangement of cooperative functional groups were very important factors in the synergistic catalysis.

Rapid exfoliation of layered covalent triazine-based frameworks into N-doped quantum dots for the selective detection of Hg2+ ions

Metal-free carbon quantum dots (CQDs) have attracted great interest, but the rapid preparation of doped CQDs with tunable optical properties is still an urgent task. Herein, we report that covalent organic frameworks (covalent triazine-based frameworks, CTF-1) with layered structures can be rapidly exfoliated and cut into N-doped CQDs. The cutting mechanism involves triazine hydrolysis and breaking the bonds between the triazines and benzene rings. Experiments and density functional theory (DFT) calculations confirm that the fluorescence of the obtained CQDs mainly originates from the intrinsic state emission induced by localized π–π* transitions, despite the contribution of the defect state emission. Due to their unique chemical structure, the CQDs could be further utilized as an efficient PL probe for detecting Hg2+. This study may open up new avenues for developing new kinds of CQDs using covalent organic frameworks as the starting materials.

Direct exfoliation of the anode graphite of used Li-ion batteries into few-layer graphene sheets: a green and high yield route to high-quality graphene preparation

Recycling anode graphite remains a significant barrier to the recovery of used Li-ion batteries. In this study, we show that anode graphite in used lithium-ion batteries is a cheap and ideal candidate for the high yield production of high-quality graphene. Attributed to the reduced interlayer force after repeated charge–discharge cycles, the sonication assisted exfoliation efficiency of the used anode graphite can be 3 to 11 times that of natural graphite, with a highest mass yield of the dispersed graphene sheets of ∼40 wt%. Importantly, the layer numbers of most of the exfoliated graphene sheets are 1–4 , and their lateral sizes are over 1 μm. Their conductivity after annealing at moderate temperature (500 °C) is up to 9100 S m−1, and their potential application in conductive ink was also demonstrated.

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.

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.

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.