Physical and chemical properties of carbon nanotubes and silica nano-composites on the photo-catalytic activity of titania nanoparticles for selected organic pollutants.
High surface area materials were synthesized in order to support titanium dioxide (TiO2) photo-catalysts with the aim of enhancing the overall photo-catalytic properties of the catalyst. Mesoporous silica dioxide (SBA-15), multi-walled carbon nanotubes (CNTs), and silica dioxide coated multi-walled carbon nanotubes (SBA-CNTs) were prepared using a sol-gel method with structure directing agents (surfactants) to ensure mesoporosity and maximize the available surface area. A loading of 10 wt. % TiO2 was chosen to study the effects of the supports, SBA-15, CNTs and 30 wt. % SBA-CNT composite respectively. Physical and chemical properties of the materials were evaluated with Transmission electron microscope (TEM); high resolution electron microscope (HRTEM); scanning electron microscope (SEM); powder x-ray diffraction (XRD); thermo-gravimetric analysis (TGA); Nitrogen (N2) sorption; Raman spectroscopy; UV-Vis Diffuse reflectance spectroscopy; Fluorescence spectroscopy; and UV-Vis spectroscopy. Photo-catalytic properties of the materials were tested using a 10 mg L-1 methylene blue (MB) dye solution. The best photo-catalytically performing material (10 wt. % TiO2/SBA-CNT) was identified and regarded as an optimum catalyst composite for further studies to be conducted. The effect of TiO2 loading (5 and 20 wt. % TiO2 on SBA-CNT composite) was studied, and the physical-chemical properties of the catalyst were further evaluated and tested on MB de-colorization experiments. The activity of the most efficient catalyst in the MB test was further evaluated on the degradation of 2-chloro-4-methylphenoxyacetic acid (MCPA) herbicide, a known real-world refractory organic pollutant. High performance liquid chromatography (HPLC) with a DAD detector was employed for the quantitative analysis of the herbicide degradation. The study of different substrates showed that the efficiency of the photo-catalyst was highly influenced by the pollutant structure as opposed to the physical-chemical properties of the catalyst system. Additionally, these studies showed that composites of TiO2 with electron trapping species such as CNTs reduce one of the core problems associated with TiO2 semiconductor which is electron – hole recombination rate. Plus the composite offer the advantage of using the catalyst under visible light energy and the catalyst can be employed to degrade organic pollutants in solution medium.