Research

1. Electrochemically Switchable Catalysts for Polymerization Reactions.

Organometallic chemistry is an interplay between “inorganic” metals and “organic” ligands. In an effort to develop catalytic processes using external switches, organometallic complexes capable of reversible processes have been increasingly researched. Epoxides, otherwise known as oxiranes, are widely used monomers in ring-opening polymerization reactions (ROP) due to the significant ring-strain in their three-membered rings. They can be polymerized in a number of ways but a metal initiator or catalyst is often used in order to obtain polymers or copolymers with narrow dispersities via controlled or living polymerization reactions. Epoxides can also be copolymerized with carbon dioxide to yield polycarbonates and with cyclic anhydrides to yield polyesters. 

The most commonly used epoxides in this field are propylene oxide (PO) and cyclohexene oxide (CHO). The ring-opening copolymerization (ROCOP) of CHO and CO2 to give polycyclohexene carbonate (PCHC) has been thoroughly investigated for many years, through the use of metal-based catalysts including chromium, cobalt, zinc, iron and aluminum complexes. ROCOP of PO and CO2 on the other hand is more susceptible to backbiting leading to the formation of propylene carbonate. Systems capable of catalyzing the copolymerization to yield polypropylene carbonate (PPC) have been reported, but careful ligand design, along with choice of reaction conditions remain important to suppress backbiting reactions. Several other epoxides, including functionalized monomers such as vinylcyclohexene oxide (VCHO), have been screened by researchers in this area, but have been less explored in comparison. 

One method to modulate reactivity and selectivity is through the redox control of the supporting ligand in a metal complex. The goal of this research is to design a compound that exhibits orthogonal reactivity for different substrates by switching between the oxidized and reduced forms of a catalyst. In order to achieve redox-switchable catalysis, the catalyst must be able to change reversibly between the oxidized and reduced forms.

2. Noble Metal and Non-noble Metal Enhanced for Fuel Cell and Water Splitting (HOR, ORR, HER, OER).

Electrolytic water splitting holds the promise for global scale storage of renewable energy e.g. solar and wind in the form of hydrogen fuel, enabling the continuous usage of these intermittent energy sources when used together with fuel cells. However, the sluggish kinetics of oxygen evolution reaction (OER) on the anode often requires catalyst materials such as oxides of iridium (IrO2) and ruthenium (RuO2) to lower the energy barriers of OER so that hydrogen can be generated at the cathode with appreciable rate at relatively low applied voltages. However, the noble metal-based catalysts are costly, and their supply is not sustainable, which has severely restricted the large-scale implementation of this technology. 

Recently, significant research efforts have gone to the development of efficient OER catalysts based on oxides of first-row transition metals, such as Ni, Fe, Co and Mn. Transition metal oxides generally have intrinsically low conductivity, and the issue aggravates when nanoparticles of the metal oxides are used to enhance the catalytic sites. To circumvent this issue, nanoparticles of transition metal oxides are normally anchored onto conductive substrates such as carbon nanomaterials e.g. graphene and multiwall carbon nanotubes (MWCNTs). Such a design introduces large amounts of available catalytic sites and efficient charge transport, and the obtained composite catalysts exhibit enhanced catalytic activity towards OER, with some comparable to the benchmark Ir/C catalyst.

3. Carbon-based Materials Obtained By Electrochemically Methods.

As one of the essential elements of the organism, industry and society, carbon always occupies an important position in the development of modern science and technology. Carbon nanostructures, such as graphene, carbon nanotubes, and carbon quantum dots, have attracted considerable attention in the scientific and technological fields due to their unique chemical, physical, and electronic properties, possibilities of mass production, and controllable structural properties. 

Graphene, which is composed of sp2 bonded carbon atoms arranged in a one atom thick 2D honeycomb-like lattice, has been shown to be suitable for a wide spectrum of applications in the fields of energy, electronics, medical and biotechnology. From graphite to carbon nanotube and fullerene, the carbon family ushered in two new members, graphene and luminescent carbon materials. Because of its excellent electrical, mechanical, and optical properties, graphene has aroused much attention in the past decade and even won the Nobel Prize in 2010. However, luminescent carbon materials, carbon dots (CDs), were not synthesized in large quantities. This work caused a boom in research throughout the whole world because of their merits, such as high luminesce and upconversion luminescence, chemical stability, dispersibility in water, low photobleaching, biocompatibility, low cost, and low toxicity.

4. Polymeric Material for Water Absorption.

Hydrogel and composite sponges are porous, water-absorbent materials made from hydrophilic polymers. They can absorb and retain a huge amount of water. Therefore, this property makes them valueable in various applications such as environmental cleanup, personal care products or biomedicine. Recently, chitosan and gelatin have been widely utilized because of their biocompatibility, biodegradability and non-toxicity. However, these natural polymers alone are not effective enough, thus they should be combined or structurally modified in order to improve its physical properties.

In our research, we have published articles focusing on the synthesis of new materials based on chitosan, gelatin with hydroxyapatite and different polyols. Through these projects, we successfully synthesized the hydrogel and composite sponges with improved mechanical and thermal properties. Moreover, their water absorption ability was enhanced significantly in a wide range of pH and salt concentrations.