Hong-Hui Wang

Activating Cobalt Nanoparticles via the Mott–Schottky Effect in Nitrogen-Rich Carbon Shells for Base-Free Aerobic Oxidation of Alcohols to Esters

Heterogeneous catalysts of inexpensive and reusable transition-metal are attractive alternatives to homogeneous catalysts; the relatively low activity of transition-metal nanoparticles has become the main hurdle for their practical applications. Here, the de novo design of a Mott-Schottky-type heterogeneous catalyst is reported to boost the activity of a transition-metal nanocatalyst through electron transfer at the metal/nitrogen-doped carbon interface. The Mott-Schottky catalyst of nitrogen-rich carbon-coated cobalt nanoparticles (Co@NC) was prepared through direct polycondensation of simple organic molecules and inorganic metal salts in the presence of g-C3N4 powder. The Co@NC with controllable nitrogen content and thus tunable Fermi energy and catalytic activity exhibited a high turnover frequency (TOF) value (8.12 mol methyl benzoate mol-1 Co h-1) for the direct, base-free, aerobic oxidation of benzyl alcohols to methyl benzoate; this TOF is 30-fold higher than those of the state-of-the-art transition-metal-based nanocatalysts reported in the literature. The presented efficient Mott-Schottky catalyst can trigger the synthesis of a series of alkyl esters and even diesters in high yields.

Encapsulating Palladium Nanoparticles Inside Mesoporous MFI Zeolite Nanocrystals for Shape‐Selective Catalysis

Pd nanoparticles were successfully encapsulated inside mesoporous silicalite-1 nanocrystals (Pd@mnc-S1) by a one-pot method. The as-synthesized Pd@mnc-S1 with excellent stability functioned as an active and reusable heterogeneous catalyst. The unique porosity and nanostructure of silicalite-1 crystals endowed the Pd@mnc-S1 material general shape-selectivity for various catalytic reactions, including selective hydrogenation, oxidation, and carbon-carbon coupling reactions.

Nitrogen-doped graphene microtubes with opened inner voids: Highly efficient metal-free electrocatalysts for alkaline hydrogen evolution reaction

A facile method was developed to fabricate nitrogen-doped graphene microtubes (N-GMT) with ultra-thin walls of 1–4 nm and large inner voids of 1–2 μm. The successful introduction of nitrogen dopants afforded N-GMT more active sites for significantly enhanced hydrogen evolution reaction (HER) activity, achieving a current density of 10 mA·cm–2 at overpotentials of 0.464 and 0.426 V vs. RHE in 0.1 and 6 M KOH solution, respectively. This HER performance surpassed that of the best metal-free catalyst reported in basic solution, further illustrating the great potential of N-GMT as an efficient HER catalyst for real applications in water splitting and chlor-alkali processes.

Wrinkled Graphene Monoliths as Superabsorbing Building Blocks for Superhydrophobic and Superhydrophilic Surfaces

Superhydrophobic and superhydrophilic surfaces are of great interest because of a large range of applications, for example, as antifogging and self-cleaning coatings, as antibiofouling paints for boats, in metal refining, and for water-oil separation. An aqueous ink based on three-dimensional graphene monoliths (Gr) can be used for constructing both superhydrophobic and superhydrophilic surfaces on arbitrary substrates with different surficial structures from the meso- to the macroscale. The surface wettability of a Gr-coated surface mainly depends on which additional layers (air for a superhydrophobic surface and water for a superhydrophilic surface) are adsorbed on the surface of the graphene sheets. Switching a Gr-coated surface between being superhydrophobic and superhydrophilic can thus be easily achieved by drying and prewetting with ethanol. The Gr-based superhydrophobic membranes or films should have great potential as efficient separators for fast and gravity-driven oil-water separation.

Activating Pd nanoparticles on sol–gel prepared porous g-C3N4/SiO2via enlarging the Schottky barrier for efficient dehydrogenation of formic acid

A highly active heterogeneous catalyst, Pd nanoparticles@g-C3N4/SiO2 with tunable band structure, was successfully fabricated by a sol–gel method. The nanocomposite catalyst exhibits an extraordinary hydrogen production rate from formic acid which leads to a high turnover frequency (TOF) of around 306 mol H2 per mole Pd per h after 10 min. The characterization analysis shows that the bandgap of the g-C3N4/SiO2 support widens with decreasing synthesis temperature, which in turn allows tuning of the band structure by simply controlling the synthesis temperature. After Pd nanoparticles were embedded, the nanocomposite Pd@g-C3N4/SiO2 showed excellent catalytic performance in the dehydrogenation of formic acid at 303.15 K, and the lower the synthesis temperature of the catalyst, the higher its performance. Introduction to the international collaboration Since 2009, cooperative researches have been conducted between Prof. Chen from Shanghai Jiao Tong University (SJTU) and Prof. Antonietti and Dr Li from Max Planck Institute (MPI), who together developed sustainable methods for fabricating graphene aqueous dispersion and graphene–carbon nitride dyads. The cooperation between MPI and SJTU was further strengthened after Dr Li joined SJTU in 2013. In 2016, a Max Planck Partner Group was co-founded by MPI and SJTU based on the former cooperative achievements. The MPI-SJTU Partner Group for Sustainable Carbon Materials Chemistry strengthens the personal collaborative ties between the Partner Group Leader (Dr Li), the host of the partner group in China, represented by Prof. Chen of SJTU, and MPI, represented by Prof. Antonietti of MPI for Colloids and Interfaces. They also intend to foster interest-oriented research collaborations, safeguarding the continuity of scientific collaboration and research activities for their mutual benefit and progress.

Oxygen Vacancy Engineering of Co3O4 Nanocrystals through Coupling with Metal Support for Water Oxidation

Oxygen vacancies can help to capture oxygen-containing species and act as active centers for oxygen evolution reaction (OER). Unfortunately, effective methods for generating a high amount of oxygen vacancies on the surface of various nanocatalysts are rather limited. Here, we described an effective way to generate oxygen-vacancy-rich surface of transition metal oxides, exemplified with Co3 O4 , simply by constructing highly coupled interface of ultrafine Co3 O4 nanocrystals and metallic Ti. Impressively, the amounts of oxygen vacancy on the surface of Co3 O4 /Ti surpassed the reported values of the Co3 O4 modified even under highly critical conditions. The Co3 O4 /Ti electrode could provide a current density of 23 mA cm-2 at an OER overpotential of 570 mV, low Tafel slope, and excellent durability in neutral medium. Because of the formation of a large amount of oxygen vacancies as the active centers for OER on the surface, the TOF value of the Co3 O4 @Ti electrode was optimized to be 3238 h-1 at an OER overpotential of 570 mV, which is 380 times that of the state-of-the-art non-noble nanocatalysts in the literature.

Polarized few-layer g-C3N4 as metal-free electrocatalyst for highly efficient reduction of CO2

The greenhouse effect and global warming are serious problems because the increasing global demand for fossil fuels has led to a rapid rise in greenhouse gas exhaust emissions in the atmosphere and disruptive changes in climate. As a major contributor, CO2 has attracted much attention from scientists, who have attempted to convert it into useful products by electrochemical or photoelectrochemical reduction methods. Facile design of efficient but inexpensive and abundant catalysts to convert CO2 into fuels or valuable chemical products is essential for materials chemistry and catalysis in addressing global climate change as well as the energy crisis. Herein, we show that two-dimensional fewlayer graphitic carbon nitride (g-C3N4) can function as an efficient metal-free electrocatalyst for selective reduction of CO2 to CO at low overpotentials with a high Faradaic efficiency of ~ 80%. The polarized surface of ultrathin g-C3N4 layers (thickness: ~ 1 nm), with a more reductive conduction band, yields excellent electrochemical activity for CO2 reduction.

Activating Oxygen Molecules over Carbonyl-Modified Graphitic Carbon Nitride: Merging Supramolecular Oxidation with Photocatalysis in a Metal-Free Catalyst for Oxidative Coupling of Amines into Imines

Carbonyl‐modified carbon nitride (m‐O=C3N4) can act as a highly efficient metal‐free photocatalyst for selective oxidation reactions, as exemplified herein by the oxidative coupling of amines to imines by using dioxygen molecules and visible light. The C=O groups built‐in on the surface of the material significantly boosted the activity by following the principle of supramolecular oxidation, that is, they largely promoted the oxidation reaction at room temperature by binding in situ formed H2O2 photogenerated on the surface from the dioxygen molecules and accelerated the reaction between H2O2 and the amines.

Atomic-scale Mott-Schottky heterojunctions of boron nitride monolayer and graphene as metal-free photocatalysts for artificial photosynthesis

Abstract Heterojunction photocatalysts at present are still suffering from the low charge separation/transfer efficiency due to the poor charge mobility of semiconductor‐based photocatalysts. Atomic‐scale heterojunction‐type photocatalysts are regarded as a promising and effective strategy to overcome the drawbacks of traditional photocatalysts for higher photoenergy conversion efficiencies. Herein, an atomic‐scale heterojunction composed of a boron nitride monolayer and graphene (h‐BN‐C/G) is constructed to significantly shorten the charge transfer path to promote the activation of molecular oxygen for artificial photosynthesis (exemplified with oxidative coupling of amines to imines). As the thinnest heterojunction, h‐BN‐C/G gives the highest conversion, which is eightfold higher than that of the mechanical mixture of graphene and boron nitride monolayers. h‐BN‐C/G exhibits a high turnover frequency value (4.0 mmol benzylamine g−1 h−1), which is 2.5‐fold higher than that of the benchmark metal‐free photocatalyst in the literature under even critical conditions.

Mesoporous H-ZSM-5 nanocrystals with programmable number of acid sites as “solid ligands” to activate Pd nanoparticles for C–C coupling reactions

In this work, we described a proof-of-concept method to promote the activity and selectivity of Pd nanoparticles for heterogeneous catalysis (exemplified by C–C coupling reactions) by using acid sites within a zeolite framework. The Pd nanoparticles were encapsulated inside the crystalline walls of mesoporous H-ZSM-5 leading to hybrid samples (denoted as Pd@mZ-x-H) with controlled number of acid sites. A linear relationship between the number of acid sites of the zeolite nanocrystals and the catalytic activities of the Pd nanoparticles in organic reactions was established. Moreover, the shape-dependent selectivity of Pd@mZ-x-H was not sacrificed when the final activity was enhanced.