Mphilisi M. Mahlambi

Synthesis and characterization of carbon-covered alumina (CCA) supported TiO2 nanocatalysts with enhanced visible light photodegradation of Rhodamine B

The anatase phase of titania (TiO2) nano-photocatalysts was prepared using a modified sol gel process and thereafter embedded on carbon-covered alumina supports. The carbon-covered alumina (CCA) supports were prepared via the adsorption of toluene 2,4-diisocyanate (TDI) on the surface of the alumina. TDI was used as the carbon source for the first time for the carbon-covered alumina support system. The adsorption of TDI on alumina is irreversible; hence, the resulting organic moiety can undergo pyrolysis at high temperatures resulting in the formation of a carbon coating on the surface of the alumina. The TiO2 catalysts were impregnated on the CCA supports. X-ray diffraction analysis indicated that the carbon deposited on the alumina was not crystalline and also showed the successful impregnation of TiO2 on the CCA supports. In the Raman spectra, it could be deduced that the carbon was rather a conjugated olefinic or polycyclic hydrocarbons which can be considered as molecular units of a graphitic plane. The Raman analysis of the catalysed CCAs showed the presence of both the anatase titania and D and G band associated with the carbon of the CCAs. The scanning electron microscope micrographs indicated that the alumina was coated by a carbon layer and the energy dispersive X-ray spectra showed the presence of Al, O and C in the CCA samples, with the addition of Ti for the catalyst impregnated supports. The Brunauer Emmet and Teller surface area analysis showed that the incorporating of carbon on the alumina surface resulted in an increase in surface area, while the impregnation with TiO2 resulted in a further increase in surface area. However, a decrease in the pore volume and diameter was observed. The photocatalytic activity of the nanocatalysts was studied for the degradation of Rhodamine B dye. The CCA-TiO2 nanocatalysts were found to be more photocatalytically active under both visible and UV light irradiation compared to the free TIO2 nanocatalysts.

Polymerization of Cyclodextrin-Ionic Liquid Complexes for the Removal of Organic and Inorganic Contaminants from Water

The removal of toxic contaminants from water still remains a huge challenge for water supplying companies and municipalities. Both organic and inorganic (mostly heavy metal) pollutants are often present in water distribution networks as a result of agricultural, domestic and industrial operations. To remove these pollutants from water distribution networks, effective techniques need to be developed. In our laboratories, research that involves the use of polymers of cone-shaped cyclodextrins (CDs) interconnected by linkers has been successfully demonstrated in the removal of organic pollutants from water. We have now undertaken a programme whereby polymers possessing moieties capable of removing both organic and inorganic contaminants from water, the so-called multifunctional complexes will be synthesised. To access these multifunctional complexes, CDs were attached to salts of organic cations (i.e. imidazolium and pyridinium) in a manner similar to the formation of ionic liquids (ILs). These cyclodextrin-ionic liquid (CD-IL) derivatives were then polymerised with bifunctional linkers with the expectation that the resulting polymers will be able to perform the dual role of removing a wide range of both organic and inorganic pollutants from water. Pollutants from many industries often end up in water systems; other pollutants emanate from domestic and agricultural run-offs. Organic pollutants such as organic solvents, pesticides, fungicides and inorganic pollutants such as nitrates, cyanides and dissolved gases are present in many water systems (Schwarzenbach et al, 2003). When these pollutants are introduced into the environment, they are subjected to physical, chemical and biological processes, leading in the generation of derivatives possessing different environmental behaviour and effects (Schwarzenbach et al, 2003). These contaminants may leach into the soil and contaminate ground water. They also tend to bioaccumulate in the bodies of organisms. The small size and chemical inertness (or unreactiveness) of these pollutants make their removal from water using the current water treatment methods difficult (Li and Ma, 1999). Also, they have health effects such as kidney and liver damage, the destruction of nerve and circulatory systems and other psychological effects detrimental to human health. Since communities need ultra pure water, there is a need to remove pollutants even at very low concentrations to ensure the health and safety of water users.

TiO2 Nanocatalysts Supported on a Hybrid Carbon-Covered Alumina Support: Comparison between Visible Light and UV Light Degradation of Rhodamine B

Titania nanoparticles were successfully supported on carbon-covered alumina (CCA) supports via the impregnation method to form carbon-covered alumna titania (CCA/TiO2). The CCA supports were synthesised through an equilibrium adsorption of toluene 2,4-diisocyante where the N=C=O irreversibly adsorbs on the alumina and pyrolysis at 700°C affords CCA supports. These CCA/TiO2 nanocatalysts were tested for their photocatalytic activity both under UV and visible light using Rhodamine B as a model pollutant. The reaction rate constant of the CCA/TiO2 was found to be higher than that of unsupported titania and the reaction kinetics were found to follow an apparent first-order rate law. The CCA/TiO2 nanocatalysts had a much larger surface area than the unsupported titania and they exhibited overall higher photodegradation efficiency under both UV and visible light than unsupported TiO2.

Synthesis, Characterization, and Visible Light Degradation of Rhodamine B Dye by Carbon-Covered Alumina Supported Pd-TiO2/Polysulfone Membranes

Palladium doped titania nanoparticles supported on carbon-covered alumina (CCA/Pd-TiO2) impregnated polysulfone (PS) membranes were prepared by the phase inversion technique. The nano-sized CCA/Pd-TiO2 nanoparticles were uniformly dispersed in 18 wt% PS casting solution to synthesize CCA/Pd-TiO2 polysulfone membranes (PS/CCA/Pd-TiO2). The amount of the CCA/Pd-TiO2 was varied between 0.25% and 0.5% to form two types of membranes. These were casted on a non-woven fabric. The nanoparticles were added in order to enhance the photodegradation potential of the PS membranes under visible light. Raman, XRD, SEM, TGA, TGA-FTIR was used to characterize the membranes. The mechanical strength of the membranes was determined with an Instron tensile tester. The SEM results suggested that these membranes had a high degree of porosity and the nanoparticles were distributed on and within the PS membrane. The Raman analysis revealed the presence of the nanoparticles within the membrane matrix while the XRD results exposed the probability of interactions between the polymer and the nanoparticles. The two membranes were then tested for their capability to photodegrade Rhodamine B under visible light illumination. The 0.5% PS/CCA/Pd-TiO2 membrane photodegraded 80.4% of the dye while the 0.25% PS/CCA/Pd-TiO2 membrane degraded 70.8% of Rhodamine B over a 270 min period. The photodegradation followed a pseudo first-order reaction rate and the apparent rates were 0.00597 and 0.00448 min−1 for 0.5% PS/CCA/Pd-TiO2 membrane and 0.25% PS/CCA/Pd-TiO2, respectively.