Wancheng 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.

Zirconium–cyanuric acid coordination polymer: highly efficient catalyst for conversion of levulinic acid to γ-valerolactone

Transformation of levulinic acid (LA) to γ-valerolactone (GVL) is essential for biomass conversion into value-added chemicals. The development of an efficient and heterogeneous catalyst for the above reaction has become a hot topic. In this work, a porous zirconium–cyanuric acid coordination polymer (Zr–CA) with an average pore diameter of 3.5 nm was successfully synthesized. As expected, the as-synthesized Zr–CA has very high activity for the catalytic transformation of LA and its esters to GVL. Systematic examinations indicated that both the acidic sites and the basic sites contributed significantly to the excellent catalytic performance of Zr–CA, which verified our assumption. This work provides a new route for designing cyanuric acid-based solid acid catalysts.

Highly efficient I2 capture by simple and low-cost deep eutectic solvents

The efficient removal and storage of radioactive nuclear contaminants including an isotope of iodine (131I) has attracted great concern especially after the explosion of the Fukushima nuclear power plant. In this study, deep eutectic solvents (DESs) are proposed for the removal and storage of iodine (I2). These DESs can be obtained by simply mixing two simple components (also cheap and biodegradable), which form liquids with melting points far below that of the individual components. A series of hydrogen bond donors (HBDs) and hydrogen bond acceptors (HBAs) are selected for the preparation of DESs. The properties and I2 capture efficiency of the prepared DESs have been investigated. The results indicate that some DESs have higher efficiencies for I2 removal than the previously reported materials. Among them, ChI–methylurea shows the best I2 uptake efficiency of approximately 100% within 5 hours. Moreover, ChI–methylurea exhibits a good capability of I2 storage with only 4.6% of the iodine evaporated after 10 hours of strong N2 sweeping, which is also important since I2 is easy to sublimate. Additional calculations also suggest that the high efficiency for I2 capture by DESs mainly comes from the formation of halogen bonding (XB) between DESs and I2. This work opens a new way for the application of DESs.

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.

The dynamic process of radioactive iodine removal by ionic liquid 1-butyl-3-methyl-imidazolium acetate: discriminating and quantifying halogen bonds versus induced force

With the increasing demand for nuclear energy and the Fukushima Daiichi nuclear disaster in 2011, the removal of radioactive and hazardous iodine has attracted more and more attention. Here, we investigate the dynamic process of radioactive iodine sorption in a representative acetate-based ionic liquid (AcIL), 1-butyl-3-methyl-imidazolium acetate [BMIM][Ac], via in situ UV-Vis spectroscopy in combination with a two-dimensional correlation technique. More importantly, the halogen bonds (including interior and exterior types) and induced force (only possessing an exterior form) resulting in iodine sorption in [BMIM][Ac] at specific time points are discriminated and quantified. The results show that the iodine sorption in [BMIM][Ac] can be divided into three zones. In the first 140 min, only halogen bonds occur (Zone 1). From 140 to 240 min, (exterior) halogen bonds and induced force occur simultaneously (Zone 2). After 240 min, only induced force occurs (Zone 3). Specifically, Zone 1 consists of two subzones, i.e., Zone 1a (before 90 min) and Zone 1b (90–140 min), corresponding to interior and exterior halogen bonds, respectively. Zone 2 is composed of three subzones, i.e., Zone 2a (140–180 min), Zone 2b (180–200 min), and Zone 2c (200–240 min), with (exterior) halogen bonds taking up the majority, approximately one half, and a small part of the total iodine sorption, respectively. The proportion of halogen bonds and induced force resulting in iodine sorption by [BMIM][Ac] can be approximately derived as 100% and 0% within 140 min, 96% and 4% within 240 min, and 91% and 9% within 570 min, respectively. Furthermore, the proportion of interior and exterior halogen bonds resulting in iodine sorption by [BMIM][Ac] could be approximately derived as 85% and 15% within 140 min, 80% and 20% within 240 min, and 80% and 20% within 570 min, respectively. These processes and quantifications can provide insight into the radioactive iodine removal by ILs in addition to the [BMIM][Ac] that we investigated here, and may motivate further experimental or theoretical studies on the application of halogen bonds for removal of iodine by designing new types of ILs.

Heterogeneous Nb-containing catalyst/N,N-dimethylacetamide–salt mixtures: novel and efficient catalytic systems for the dehydration of fructose

The development of efficient catalytic systems for the dehydration of carbohydrates to produce 5-hydroxymethylfurfural (HMF) is a very attractive topic. In this work, we synthesized a novel Nb-containing catalyst by the reaction of niobium chloride and nitrilotris(methylenephosphonic acid) (NTMPA), denoted as Nb–NTMPA. The synthesized Nb–NTMPA was characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N2 adsorption–desorption, and Fourier transform infrared spectroscopy and used as the heterogeneous catalyst for the dehydration of fructose into HMF using the mixture of N,N-dimethylacetamide (DMA) and salts as the reaction solvent. It was found that Nb–NTMPA was very active for the reaction and a HMF yield of 85.6% could be achieved in a DMA–NaBr mixture under the optimal reaction conditions. Further study indicated that the salts could affect the activity of the reaction systems by the formation of DMA·M+ (M = Li, Na and K) macrocations and weakly ion-paired halide ions. Moreover, Nb–NTMPA/DMA–salt systems could also be used in the production of HMF from inulin and sucrose with satisfactory yields.

Niobium phytate prepared from phytic acid and NbCl5: a highly efficient and heterogeneous acid catalyst

The preparation of functional catalysts using naturally-occurring building blocks is of great importance. In this work, we designed a functional heterogeneous acid catalyst, niobium phytate, using phytic acid, which could be obtained from the seeds and grains of plants, as the building block to react with NbCl5. The prepared niobium phytate was characterized by XRD, FT-IR, XPS, SEM, TEM, NH3-TPD and N2 adsorption–desorption examinations. Niobium phytate showed very high activity for both cyanosilylation of carbonyl compounds and dehydration of carbohydrates. It was also found that niobium phytate had higher activity than commercial Nb2O5. In addition, niobium phytate could be easily recovered and reused without reducing the reaction activity considerably. Further study indicated that both higher acidity and lower crystallinity contributed significantly to the excellent catalytic performance of niobium phytate. The findings in this work provide insights into the design of new functional catalysts using naturally-occurring building blocks for various organic reactions.

Highly Efficient, Green, and Scalable β‐Cyclodextrin‐Assisted Aqueous Exfoliation of Transition‐Metal Dichalcogenides: MoS2 and ReS2 Nanoflakes

The β-cyclodextrin-assisted aqueous-exfoliation method was used to prepare transition-metal dichalcogenide (TMD) nanosheets, in a cheap, highly efficient, scalable and environmentally friendly manner. As study cases, MoS2 and ReS2 nanoflakes were prepared according to this method. Particularly, the effective exfoliation of ReS2 crystals in an aqueous environment was observed for the first time. Moreover, exfoliated nanomaterials can be readily utilized in hydrogen evolution reactions (HERs) as noble-metal-free catalysts. This work provides new opportunities for highly efficient exfoliation of TMDs and other 2D nanomaterials into few-layer nanosheets in aqueous media. Their production process showed high biocompatibility, broad applicability and excellent sustainability.

CO2-in-PEG emulsion-templating synthesis of poly(acrylamide) with controllable porosity and their use as efficient catalyst supports

CO2-in-PEG emulsions were made with Pluronic 104 at different CO2 pressure. In these emulsions, porous poly(acrylamide)s (PAM) nanoparticles around 250 nm were prepared. The nano-sized metal Ru particles were loaded on the porous PAM, which have much higher catalytic activity for benzene hydrogenation reaction compared to commercial Ru/C catalyst. More importantly, the drop size of internal phase CO2 and the pore diameter of as-prepared PAMs can be simply tuned by changing the pressure of CO2.