Lei Jin

Heterogeneous acidic TiO2 nanoparticles for efficient conversion of biomass derived carbohydrates

Selective conversion of biomass derived carbohydrates into fine chemicals is of great significance for the replacement of petroleum feedstocks and the reduction of environmental impacts. Levulinic acid, 5-hydroxymethyl furfural (HMF) and their derivatives are recognized as important precursor candidates in a variety of different areas. In this study, the synthesis, characterization, and catalytic activity of acidic TiO2 nanoparticles in the conversion of biomass derived carbohydrates were explored. This catalyst was found to be highly effective for selective conversion to value-added products. The nanoparticles exhibited superior activity and selectivity towards methyl levulinate from fructose in comparison to current commercial catalysts. The conversion of fructose to methyl levulinate was achieved with 80% yield and high selectivity (up to 80%). Additionally, conversions of disaccharides and polysaccharides were studied. Further, the production of versatile valuable products such as levulinic esters, HMF, and HMF-derived ethers was demonstrated using the TiO2 nano-sized catalysts in different solvent systems.

Studies on Dehydrogenation of Ethane in the Presence of CO2 over Octahedral Molecular Sieve (OMS‐2) Catalysts

Carbon dioxide, a major greenhouse gas, can be used as a source of carbon. Conversion of CO2 into organic compounds has been studied intensively. For example, ethane catalytic dehydrogenation [Equation (1)] offers an attractive route for converting CO2. Firstly, the coke-formation problem, particularly troublesome in the steam-cracking industry, can be solved by treating the coke with CO2 to generate CO over the catalyst. In addition, CO2 can act as a medium for supplying heat to the endothermic dehydrogenation reaction. 4] Furthermore, the products from Equation (1), C2H4 and CO, are precursors for olefin/CO copolymerization reactions. By varying the feedstock ratio (C2H6/CO2) in the reaction, different ratios of the products (C2H4/CO) can easily be obtained for the specific copolymerization process. Hence, the dehydrogenation of ethane in the presence of CO2 is an ideal feedstock for any process involving ethylene carbonylation with an additional benefit of recycling the greenhouse gas.

A facile synthesis of Fe3C@mesoporous carbon nitride nanospheres with superior electrocatalytic activity

We report a colloidal amphiphile-templating approach to preparing nanosized Fe3C encapsulated within mesoporous nitrogen-doped carbon nanospheres (Fe3C@mCN). The obtained Fe3C@mCN hybrids having a high surface area and ultrafine Fe3C nanocrystals exhibited superior activity and durability for oxygen reduction.

Potassium modified layered Ln2O2CO3 (Ln: La, Nd, Sm, Eu) materials: efficient and stable heterogeneous catalysts for biofuel production.

Potassium modified layered Ln2O2CO3 (Ln: La, Nd, Sm, Eu) biodiesel catalysts were prepared by a coprecipitation method followed by an overnight reflux. A high fatty acid methyl ester (FAME) yield (>95%) was achieved under mild reaction conditions (<100 °C). The FAME yields were investigated as a function of temperature and catalyst weight percentage. Nd2O2CO3 shows a better catalytic performance with a higher reaction rate than the industrial homogeneous KOH catalyst using both microwave irradiation and conventional heating methods. Approximately 100% FAME yield can be reached at 95 °C (microwave radiation) by 1.0 wt% Nd2O2CO3 within 10 min, while the same yield can be reached by 3.0 wt% Nd2O2CO3 at 95 °C (conventional heating method). In addition, leaching tests of the catalysts were performed; no leached rare earth metal ions were detected and the amounts of leached potassium were all under 5 ppm (ASTM standard). The synthesized layered Ln2O2CO3 materials offer a group of ideal alternative catalysts for industrial biodiesel production.

Synthesis of Mesoporous CoS2 and NixCo1–xS2 with Superior Supercapacitive Performance Using a Facile Solid-Phase Sulfurization

Synthesis of nanostructured transition metal sulfides is of particular interest in providing new methods to control their porosity and improve their surface area because those sulfides hold promising applications in high-energy density devices. Significant challenges remain currently to prepare metal sulfides having three-dimensional (3-D) continuous mesoporous structures, known to be critical for increasing their active surface sites and enhancing ion transport. We herein present a facile solid-phase sulfurization method to synthesize 3-D continuous mesoporous CoS2, NiS2, and their binary sulfides in a two-step nanocasting using bicontinuous KIT-6 as hard templates. The solid-phase sulfurization taking place at 400 °C yields mesoporous sulfides with highly crystalline frameworks and a stoichiometric ratio of metal-to-sulfur, 1:2 (mol), within 30 min. Elemental sulfur as an inexpensive sulfur source can be directly used for the solid-phase sulfurization of mesoporous oxides of Co3O4, NiO, and their binary oxides. This facile synthetic method is highly efficient to prepare mesoporous sulfides in the gram-scale production at a very low cost. Mesoporous sulfides are demonstrated to be superior electrode materials for pseudo-supercapacitors, given their high surface area and accessible bicontinuous mesopores, the suitable crystalline sizes, and the enhanced ion transport capability. The use of binary mesoporous sulfides presents interesting synergetic effect where the doping of metal ions can significantly enhance the capacitive performance of single-component sulfides. The binary sulfides of mNi0.32Co0.68S2 show a specific capacitance up to 1698 F g-1 at a current density of 2 A g-1. The supercapacitor device of mNi0.32Co0.68S2 has a high energy density of 37 Wh kg-1 at a power density of 800 W kg-1. We believe that the reported solid-phase synthesis offers a universal method toward the conversion of mesoporous oxides materials into various useful and functional forms for energy conversion and storage applications.

Multiblock thermoplastic elastomers via one-pot thiol–ene reaction

We report a facile approach to designing multiblock thermoplastic elastomers using a two-step thiol–ene polyaddition reaction. It is based on the utilization of intermolecular hydrogen bonding of widely available and cost-effective monomer of N,N′-methylenebis(acrylamide) (MBAm) as physical cross-links. Thiol-terminated “soft” prepolymers were first prepared using ethylene glycol dimethacrylate (EGDMA) and an excess of 1,6-hexanedithiol (HDT); subsequently, the thiol-terminated prepolymers were further reacted with MBAm as a chain-extension reaction to yield the multiblock thermoplastic elastomers. The prepolymers with oligo(ethylene glycol) segments had a low glass-transition temperature, acting as elastic “soft” blocks; while MBAm units could form up to 4 hydrogen bonds that serve as physical networks to endow the elasticity to multiblock polymers. Proton nuclear magnetic resonance spectroscopy and gel permeation chromatography indicated the occurrence of the two-step thiol–ene reactions. The reaction kinetics of thiol–ene reactions was found to be highly dependent on the molecular weights of monomers. The first thiol–ene reaction of EGDMA and HDT could reach >90% conversion of both monomers within 5 min; while the kinetics of the second chain extension reaction was relatively slow and it took approximately 7 h to reach 90% conversion. The formation of the intermolecular hydrogen bonding between amide groups of MBAm units was confirmed by variable-temperature Fourier transform infrared spectroscopy and differential scanning calorimetry. The viscoelasticity and elasticity of the thermoplastic elastomers were found to be largely determined by the content of MBAm. With a molar ratio of 15% MBAm relative to EGDMA, the maximum elongation at break of elastomers reached >400%. Our synthetic method has the advantages of mild reaction conditions, high conversion and adjustable mechanical properties of elastomers; additionally, it does not involve heavy syntheses and expensive monomers/catalysts. Our findings conceivably stand out as a new tool to synthesize and engineer thermoplastic elastomers using the combination of thiol–ene chemistry and supramolecular interaction.

Ultrafine and Ligand‐Free Precious Metal (Ru, Ag, Au, Rh and Pd) Nanoclusters Supported on Phosphorus‐Doped Carbon

We report the use of phosphorus-doped carbon (P-C) as support to grow ultrasmall (1-3 nm) and ligand-free precious metal nanocrystals (PMNCs) via chemical reduction. We show that the valence states of surface phosphorus species are critical in tuning the affinity between the carbon support and metal precursors, which rationally controls the loading size and uniformity of resultant PMNCs. Five kinds of PMNCs, including Ru, Ag, Au, Rh, and Pd, were grown in situ to demonstrate the key role of surface phosphorus sites on the P-C support. As a proof-of-concept application, Ru nanocatalysts with an average diameter of 1.0±0.2 nm supported on P-C were examined for the electrocatalytic hydrogen evolution reaction (HER). Ultrasmall and ligand-free Ru nanocatalysts exhibited superior HER activity and stability compared to its counterparts with surface agents or larger sizes. An overpotential of 27.6 mV (vs. reversible hydrogen electrode) for Ru nanocatalysts was achieved at a current density of 10 mA cm-2 . This novel method opens a new avenue to immobilize ligand-free and well-dispersed PMNCs on carbon; and, more importantly, it provides a new library of supported PMNCs with high catalytic activity.

“Enzymatic” Photoreduction of Carbon Dioxide using Polymeric Metallofoldamers Containing Nickel-Thiolate Cofactors

The photoreduction of CO2 by using enzyme‐mimicking polymeric metallofoldamers containing Ni–thiolate cofactors was explored. Metallofoldamers consisting of folded polymers incorporated with Ni–thiolate complexes were prepared by intramolecular Ni–thiolate coordination with thiol‐functionalized linear copolymers. The folded polymer backbone may resemble the protein framework to provide a second coordination environment to the active sites. We showed that Ni–metallofoldamers were superiorly active and selective for CO2 photoreduction. At 80 °C, the turnover frequency of the Ni–metallofoldamers could reach 0.69 s−1, which corresponds to 2500 turnovers per hour per Ni site. Our findings are expected to provide useful guidelines to investigate artificial enzymes and to understand the role of protein frameworks in photosynthesis.

Co-Template Directed Synthesis of Gold Nanoparticles in Mesoporous Titanium Dioxide

A bottom-up synthetic methodology to encapsulate pre-synthesized, well-defined gold nanoparticles (AuNPs) into mesoporous titanium dioxide framework (Au@mTiO2 ) is reported. This method employs two structurally and chemically similar templates of amphiphilic block copolymers as well as poly(ethylene oxide)-tethered AuNPs, which showed excellent stability during sol-gel transition and thermal annealing at elevated temperatures. Such synthesis enabled precise control of sizes and loading of AuNPs within the mesoporous TiO2 framework. In light-driven methanol dehydrogenation, the presence of AuNPs significantly enhanced the photocatalytic activity of mTiO2 . This co-template-directed synthesis presents new opportunities to understand the effect of AuNP size in photocatalysis using Au@mTiO2 materials.

Surface Engineering of Spherical Metal Nanoparticles with Polymers toward Selective Asymmetric Synthesis of Nanobowls and Janus-Type Dimers

New synthetic methods capable of controlling structural and compositional complexities of asymmetric nanoparticles (NPs) are very challenging but highly desired. A simple and general synthetic approach to designing sophisticated asymmetric NPs by anisotropically patterning the surface of isotropic metallic NPs with amphiphilic block copolymers (BCPs) is reported. The selective galvanic replacement and seed-mediated growth of a second metal can be achieved on the exposed surface of metal NPs, resulting in the formation of nanobowls and Janus-type metal-metal dimers, respectively. Using Ag and Au NPs tethered with amphiphilic block copolymers of poly(ethylene oxide)-block-polystyrene (PEO-b-PS), anisotropic surface patterning of metallic NPs (e.g., Ag and Au) is shown to be driven by thermodynamical phase segregation of BCP ligands on isotropic metal NPs. Two proof-of-concept experiments are given on, i) synthesis of Au nanobowls by a selective galvanic replacement reaction on Janus-type patched Ag/polymer NPs; and ii) preparation of Au-Pd heterodimers and Au-Au homodimers by a seed-mediated growth on Janus-type patched Au/polymer NPs. The method shows remarkable versatility; and it can be easily handled in aqueous solution. This synthetic strategy stands out as the new methodology to design and synthesis asymmetric metal NPs with sophisticated topologies.