The NRF SARChI Chair in Energy Materials

This research area involves the synthesis of various types of inorganic nanomaterials ranging from II-VI, metal oxide, phosphide, and nitride nanocrystals, metal nanoparticles, 2D layered nanostructures, ternary and quaternary nanocrystals, carbon nanomaterials, and most recently perovskite nanoparticles. Hybrid nanostructures such as quantum dots decorated carbon nanotubes are also undertaken. Various methods have been employed in our group to synthesize these materials, ranging from colloidal synthesis, CVD, as well as microwave-assisted methods.

Robust nanomaterials research has demonstrated that semiconductors can be used as photocatalysts in treating water. Intrinsic properties of nanophotocatalysts such as; surface area, active sites, charge separation efficiency, light absorption range, redox potential and stability are key contributors in the photodegradation processes. Our research group has actively synthesized and employed various nanomaterials in the photodegradation of azo dyes. The semiconductors absorb solar radiation, resulting in the formation of active species such as electrons (), holes (), superoxide () and hydroxyl () radicals that attack the dye molecules.

Reverse osmosis (RO) membrane technology has emerged as one of the major solutions to produce potable water from seawater and other saline water sources. RO is a high pressure-driven membrane-based desalination technique in which an applied pressure greater than the natural osmotic pressure is required to push water through a semipermeable membrane (usually polymeric thin film composite membrane (TFC)), leaving behind salt and other impurities. Although the RO membranes have been continually improved over the past three decades, they are still confronted with challenges such as severe biofouling and chlorine degradation, which results in lower performance efficiency, higher energy demand, and shorter membrane life-span. Recent advances in nanotechnology have opened-up new alternatives to develop nano-enhanced RO membranes with superior properties. Surface modification or functionalization of RO membranes with different nanomaterials has led to new membranes that exceed the performance of conventional membranes, with high permeability, chemical stability, and low-biofouling properties. In our group, we explore the use of chemically modified 2D carbon nanomaterials and silver oxide nanoparticles to produce energy-efficient membranes with enhanced permeability, selectivity, mechanical, chemical, and biological stability.

Semiconductor materials are attractive materials for use in solar cells mainly as a result of their tuneable absorption and photoluminescence spectra, large surface area (because of their small size), their adaptability, their ability to generate multiple excitons as well as their capability of hot carrier injection from excited state i.e. by minimizing energy loss during thermalization of excited state. Semiconductor nanocrystals in solar cells are very versatile and can be used in various types of photovoltaic cells and as various components in solar cells. Currently we are focused on three types of solar cells, namely, the metal junction solar cells, dye sensitized solar cells and perovskite solar cells. In the metal junction solar cells, we vary the materials used, from visible emitting QDs to infrared emitting. The sunlight at zenith provides an irradiance of just over 1 kilowatt per square meter at sea level. Of this energy, 527 watts is infrared radiation, 445 watts is visible light, and 32 watts is ultraviolet, therefore varying the band gap of the active material is crucial. For the DSCCs we seek to replace either the tradition ruthenium dyes in conventional dye sensitized solar cells with quantum dots as they have better properties than dyes such as high quantum yields, photo-stability and tuneable absorbance or the Pt counter electrode with metal chalcogenides. Finally, we look at using perovskite nanoparticles as the absorber layer in perovskite solar cells.

Hydrogen is the ideal fuel for the future because it is clean, energy efficient, and abundant in nature. While various technologies can be used to generate hydrogen, only some of them can be considered environmentally friendly. Recently, hydrogen generated via catalytic water splitting has attracted tremendous attention and has been extensively studied because of its great potential for clean hydrogen production. Hydrogen is an ideal energy storage medium or carrier because of the following reasons; firstly, it is the most abundant element and exists in both water and biomass; secondly, it has a high energy yield (122 kJ/g) compared to other fuels such as gasoline (40 kJ/g) and thirdly, it is environmentally friendly as it does not produce pollutants, greenhouse gases, nor any harmful effect on the environment. Last, but not least, hydrogen can be stored in gaseous, liquid or metal hydride form and can be distributed over large distances through pipelines or via tankers. There are number of ways of generating hydrogen. The most common method of generating hydrogen is through a process called steam reforming. Another process involves fossil fuels and is called coal gasification. Both these process suffer from using very high temperatures, high pressures as well as the production of high amounts of CO₂. Water splitting through electrolysis can therefore be an alternative greener process in producing hydrogen. Water splitting through electrolysis is however expensive due to the use of Pt as an electrocatalyst. In our group, we make use of highly catalytic 2D metal dichalcogenides and metal phosphides for hydrogen evolution reaction (HER). By using the colloidal synthetic method, we can engineer the resultant properties of the nanomaterials.

Gold and silver nanocrystals functionalized with Raman active molecules serve as good substrates to be used as SERS sensors. Raman spectroscopy has emerged as a promising spectroscopic technique for the early diagnosis of diseases, such as malaria and cancer. This technique measures the optical fingerprints of molecules present in chemicals and biomaterials, which gives rise to its high chemical specificity. However, its detection sensitivity is limited due to the weak Raman scattering cross-section (10^-29 to 10^-32 cm²). In contrast, SERS effect can augment the Raman scattering cross-section by the order of 10⁶ to10¹⁵ for metal nanoparticles and target molecules in close proximity. SERS enables trace level detection of key chemical biomarkers and changes in the chemical makeup of bodily fluids, which in turn can provide early indications of disease. As these measurements can be taken in aqueous bodily fluids, with measurement times of seconds to minutes, it opens the possibility of a real-time point of care diagnosis and treatment.

Ag and Cu nanoparticles have proven to display outstanding antimicrobial activity as a result of their ability to deactivate respiratory enzymes of bacteria by interfering with DNA replication and disrupting the cell membrane. Herein, Ag and Cu nanoparticles are incorporated with antimicrobial peptides to further improve their antimicrobial activities and improve the stability of the nanoparticles. In addition, the nanoparticles are encapsulated with biomimetic polymer coating to prevent oxidation. The resultant nanoparticles are then used in wound healing as wound dressings. 

Nanomaterials based gas sensors potentially offer many advantages over the traditional macro-counterparts such as faster operation time, lower power consumption, lower limit of detection, operation at lower temperatures, they may prevent the need for expensive catalysts and may even come at a lower cost as less material is needed due to the high surface to volume ratio. In our research group, we look at using various nanomaterials spanning metal oxides, metal chalcogenides and hybrid polymeric structures in room temperature FET based gas sensors.