Research Interests

Nanomaterials Design
  • Ordered mesoporous silicas (soft-templating/self-assembly)

     Self-assembly of surfactant (Pluronic F127, P123, etc.) molecules in a solvent leads to the formation of micelles, which are manipulated to interact with selected inorganic molecules/salts (TEOS, sodium metasilicate, etc.). Next, the inorganic species condense resulting in polymer-inorganic mesostructures. Finally, mesoporous silicas can be obtained by removing the polymer through thermal treatment or solvent extraction.
     This part of research has been focused on exploration of silica sources, such as sodium metasilicate and water glass, which are cheaper than tetraethyl orthosilicate (TEOS) for synthesis of ordered mesoporous silicas (SBA-15 & KIT-6). The research aims to provide additional knowledge for selecting a suitable silica source to prepare SBA-15 with a given mesopore size, pore wall thickness, and complementary porosity. 

  • Mesoporous bismuth oxides (hard-templating)

     To begin with, SBA-15 (or KIT-6, mesoporous alumina) needs to be synthesized as the hard template by soft-templating. Next, the pore channels of SBA-15 are filled by a selected inorganic precursor, such as bismuth nitrate for the synthesis of bismuth oxides. Next, thermal treatment is carried out firstly at low temperatures to evaporate the solvent and subsequently at high temperatures to form crystals. Finally, the hard template can be removed by chemical etching.
     We have improved the hard-templating strategy to create porosity in bismuth oxides, the precursor of which undergoes very fast hydrolysis in water. NaOH used to remove SBA-15 was additionally found capable of converting bismuth vanadate (BiVO4) to bismuth oxide (Bi2O3). Further, the mesoporous structures were composed of Bi2O3 nanoparticles.

  • Bismuth/bismuth oxide heterojunction on porous carbon (soft-templating/self-assembly/one-pot synthesis)


     The synthesis of mesoporous carbon is relatively easy by soft-templating. F127 can be utilized as the soft template and resorcinol and formaldehyde as the carbon precursors. Different from the synthesis of mesoporous silicas, the synthesis of mesoporous carbon ends up with thermal treatment in nitrogen instead of air, which is crucial for the carbonization process. The bismuth oxide/carbon composite can be prepared by adding bismuth nitrate to the carbon precursors during the self-assembly process.
     Mesoporous carbon was designed to act as the support for bismuth oxide nanoparticles. However, one extra function of carbon that it is able to reduce bismuth oxide to metallic bismuth was discovered. In contrast to silver oxide and gold species, which have positive redox potentials and can easily be reduced by hydrogen gas, bismuth oxide possesses negative redox potentials; therefore, it was expected that bismuth oxide would not be reduced. The amount of resultant metallic bismuth in the composite can be tuned by adjusting the ratio of bismuth to carbon precursor in the reaction pot.

  • Mesoporous carbon nitride (soft-templating/self-assembly)

  • Bismuth oxyiodide/bismuth oxide heterojunction

Photocatalysis
  • Dye degradation
 
     Bismuth is a plasmonic metal and bismuth oxides are semiconductors with small band gaps. Therefore, the bismuth/bismuth oxide heterojunction has potential application in photocatalysis. In addition, carbon can act as an electron reservoir and possesses great electron transfer properties, and it is able to absorb visible light over a wide spectrum, which may facilitate the generation of charge carriers within the Bi0/Bi2O3 heterojunction.
     It turned out that the bismuth/bismuth oxide/carbon composites showed much higher efficiency in degrading methylene blue (MB), which is a dye, under simulated daylight irradiation as compared to bare Bi2O3. The adsorption of MB was much faster than the degradation reaction, which was likely a result of the porous structures. In other words, reaction-desorption process was the rate-determining step during the removal of MB by Bi/Bi2O3@C composites.

  • Hexavalent chromium (Cr(VI)) reduction

     Hexavalent chromium is a genotoxic carcinogen. Bismuth oxide, bismuth vanadate, and bismut oxyiodide have been demonstrated to be able to reduce Cr(VI) under visible light irradiation. Kinetics study showed that the reaction is first-order. The apparent quantum yield measured at 254 nm is among the highest without the use of a hole scavenger.

  • Hydrogen evolution/water splitting
     Graphitic carbon nitride (g-C3N4) is a metal-free semiconductor with a band gap around 2.5 eV. Both experimental and computational studies have shown that the potential of the conduction band minium for g-C3N4 is more negative than that of H+/H2, making g-C3N4 a promising photocatalyst for hydrogen production by splitting water.


Iodide capture


     As a result of the scarcity of iodine, as well as its threat to the environment if it is present in excess, iodine as a waste needs to be captured. Two Bi‐containing compounds, BiVO4 and Bi2O3, have been investigated comprehensively for iodide immobilization. The mechanism of the capture of iodide by BiVO4 and Bi2O3 has been studied and results showed that the capture is a chemisorption process with the formation of bismuth oxyiodide (BixOyIz). Iodide ions are able to penetrate into the bulk of BiVO4 and Bi2O3, which is believed to be responsible for their high capture capacity.


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