Xinhui Zhao

Large-Scale, Highly Efficient, and Green Liquid-Exfoliation of Black Phosphorus in Ionic Liquids

We developed a facile, large-scale, and environmentally friendly liquid-exfoliation method to produce stable and high-concentration dispersions of mono- to few-layer black phosphorus (BP) nanosheets from bulk BP using nine ionic liquids. The prepared suspensions can stabilize without any obvious sedimentation and aggregation in ambient air for one month. In particular, the concentration (up to 0.95 mg mL(-1)) of BP nanoflakes obtained in 1-hydroxyethyl-3-methylimidazolium trifluoromethansulfonate ([HOEMIM][TfO]) is the highest reported for BP nanosheets dispersions. This work provides new opportunities for preparing atomically thin BP nanosheets in green, large-scale, and highly concentrated processes and achieving its in situ application.

A PEGylated deep eutectic solvent for controllable solvothermal synthesis of porous NiCo2S4 for efficient oxygen evolution reaction

As ionic liquid analogues or quasi-ionic liquids, deep eutectic solvents (DESs) have been applied in many fields in the past few years. Herein, a novel PEGylated DES composed of PEG 200 and thiourea was formed for the first time and used for solvothermal synthesis of nickel cobalt sulfides. The structure and composition of the as-synthesized sulfides can be tuned by adjustment of the ratio of the reactants. The PEGylated DES plays multiple roles as a solvent, a shape-control agent, and a sulfur source in the synthesis of sulfides. Compared with traditional sulfuration routes, this proposed route is cost-effective and energy-efficient by combining solvothermal synthesis and the sulfuration process. The prepared sulfides were used as catalysts for electrochemical water oxidation and they exhibited excellent oxygen evolution reaction (OER) performance, especially for NiCo2S4 with hierarchical pores. The overpotential (η) demand was 337 mV for the current density reaching 10 mA cm−2 and the Tafel slope was 64 mV dec−1 in an alkaline medium (1 M KOH) for NiCo2S4. In addition, NiCo2S4 demonstrated long-term stability with little deactivation after either thirty hours of continuous operation or two thousand cycles and a high faradaic efficiency of 95.8%. Synergistic effects including a relatively high Brunauer–Emmett–Teller area, abundant active sites, easy diffusion of electrolytes and oxygen gas, and strong structural integrity contribute to the high activity and long-term stability of the catalyst for OER. This study provides a new method for the synthesis of hierarchically structured metal sulfides for energy conversion and storage applications.

The electrochemical stability of ionic liquids and deep eutectic solvents

Room temperature ionic liquids (ILs) composed of cations and anions, as well as deep eutectic solvents (DESs) composed of hydrogen bond donors (HBDs) and hydrogen bond acceptors (HBAs), are regarded as green solvents due to their low volatility. They have been used widely for electrochemically driven reactions because they exhibit high conductivity and excellent electrochemical stability. However, no systematic investigations on the electrochemical potential windows (EPWs), which could be used to characterize the electrochemical stability, have been reported. In this regard, the EPWs of 33 ILs and 23 DESs have been studied utilizing cyclic voltammetry (CV) method and the effects of structural factors (cations and anions of ILs, and HBDs and HBAs of DESs) and external factors (electrode, water content) on the EPWs have been comprehensively investigated. The electrochemical stability of selected ILs comprising five traditional cations, namely imidazolium, pyridinium, pyrrolidinium, piperidinium and ammonium and 13 kinds of versatile anions was studied. The results show that for ILs, both cation and anion play an important role on the reductive and oxidative potential limit. For a same IL at different working electrode, for example, glassy carbon (GC), gold (Au) and platinum (Pt) electrode, the largest potential window is almost observed on the GC working electrode. The investigations on the EPWs of choline chloride (ChCl), choline bromide (ChBr), choline iodide (ChI), and methyl urea based DESs show that the DES composed of ChCl and methyl urea has the largest potential window. This work may aid the selection of ILs or DESs for use as a direct electrolyte or a solvent in electrochemical applications.

Controlled deposition of Pt nanoparticles on Fe3O4@carbon microspheres for efficient oxidation of 5-hydroxymethylfurfural

2,5-Furandicarboxylic acid (FDCA) is an important environmentally benign and sustainable chemical which can be derived from biomass and produced by the oxidization of 5-hydroxymethylfurfural (HMF). However, the oxidation of HMF relies highly on catalysts to improve the yield of FDCA. In this study, a series of novel superparamagnetic Pt nanoparticle-containing catalysts with a core–shell structure (Fe3O4@C@Pt) were synthesized and applied for HMF oxidation. These novel spherical catalysts possess a Fe3O4 core and a protective amorphous carbon shell with a surface decorated by Pt nanoparticle clusters. By changing the synthesis temperature, the morphology of the active Pt species on the carbon shell of the microspheres can be transformed from highly dispersed nanoparticles to nanoparticle clusters. The catalytic HMF oxidation results reveal that microspheres decorated with larger nanoparticle clusters (110-Fe3O4@C@Pt) have the best catalytic activity for HMF oxidation, owing to a unique islet morphology coupled with the high-degree crystallization of Pt nanoparticles. The yield of FDCA could reach 100% after 4 h of reaction at 90 °C in water which is superior to previous reports. Furthermore, this catalyst can be reused at least three times without significant performance loss.

Bifunctional Boron Phosphate as an Efficient Catalyst for Epoxide Activation to Synthesize Cyclic Carbonates with CO2

Development of inexpensive, easily prepared, non-toxic, and efficient catalysts for the cycloaddition of CO2 with epoxides to synthesize five-membered cyclic carbonates is a very attractive topic in the field of CO2 transformation. In this work, we conducted the first work on the cycloaddition of CO2 with epoxides to produce cyclic carbonates catalyzed by a binary catalyst system consisting of KI and boron phosphate (BPO4 ), which are both inexpensive and non-toxic, and various corresponding cyclic carbonates could be produced with high yields (93-99 %) at 110 °C with a CO2 pressure of 4 MPa under solvent-free conditions. In the BPO4 /KI catalyst system, BPO4 , a Brønsted and Lewis acid hybrid, played the role of activating the epoxy ring through the formation of hydrogen bonds with Brønsted acidic sites and the interaction with Lewis acidic sites simultaneously, and thus enhanced the activity of KI for the cycloaddition of CO2 with epoxides significantly. Additionally, the activity of the BPO4 /KI catalyst system showed no noticeable decrease after being reused five times, indicating that the BPO4 was stable under the reaction conditions.

Transfer hydrodehalogenation of aryl halides accelerated by a saturated sodium acetate aqueous solution

Development of catalytic hydrodehalogenation of halogenated organic compounds is an important topic from the viewpoint of environment protection. Herein, we conducted the first work on the utilization of a saturated aqueous solution of sodium acetate (CH3COONa) as an efficient and environmentally-friendly reaction medium for transfer hydrodehalogenation of various aryl halides using Pd/C as the catalyst. It was found that the transfer hydrodehalogenation could be accelerated significantly by the saturated CH3COONa aqueous solution due to the surfactant-similar effect of CH3COONa and the activation of the C–Cl bond by the dissolved solvated ions.

Green synthesis of porous β-cyclodextrin polymers for rapid and efficient removal of organic pollutants and heavy metal ions from water

Metal ions and organic pollutants pose a serious threat to public health and are often found to coexist in industrial wastewaters. Herein, we developed a general route for the synthesis of porous polymers by joining β-cyclodextrin (β-CD), EDTA-modified chitosan (CS-EDTA) (the chitosan could be substituted by other biomass polymers) and pentafluoropyridine together, and using biomass-derived 2-methyltetrahydrofuran as an environmentally benign solvent. Some of these as-prepared porous polymers could be used as very attractive and effective adsorbents for the removal of organic pollutants and heavy metal ions such as Pb(II), Ni(II), Cu(II), Co(II), Hg(II), and Cr(II) from wastewater simultaneously with very fast uptake kinetics compared to other adsorbents. The as-prepared porous polymers from β-CD and CS-EDTA, cellulose, sodium alginate, or alkali lignin were named P-CDEC, P-CDMCC, P-CDSA, and P-CDAL, respectively. Taking P-CDEC as an example, k2 (18.6 g mg−1 min−1 for Pb(II) and 4.9 g mg−1 min−1 for trichlorophenol) is one to three orders of magnitude higher than that of other common adsorbents. More importantly, the polymers can be recycled and after five cycles, more than 91% adsorption capacity still remained. Therefore, these polymers are potential materials for integrative and efficient treatment of coexisting toxic pollutants. The as-developed green route for the synthesis of porous polymers from biomass could be extended for the preparation of other functional materials.