Emy Marlina, Samsudin (2016) Improved titanium dioxide promoted photocatalyst for degradation of pollutant in water / Emy Marlina Samsudin. PhD thesis, University of Malaya.
Abstract
The quality of drinking water is testified to be satisfactory in most developed countries. However, the United Nations has reported that 783 million people do not have access to safe drinking water. Furthermore, only 1% of available water resources can be used as drinking water. One of the most common pollutants found in drinking water is atrazine herbicide. Malaysia, being an active player in agriculture consumes large quantity of atrazine and other pesticides. Atrazine is classified as low toxic herbicides but prolong consumption leads to cardiovascular and mutagenic effects. The current technology is via granulated activated carbon (GAC) however it leads to leaching, non-selective and waste disposal costs. An alternative effective method is by photocatalytic degradation using semiconductor photocatalyst. The key factor for a successful photocatalytic activity is to sustain large concentrations of surface active radicals to oxidize pollutants into simpler and less hazardous substance. In photocatalysis, TiO2 is a preferred semiconductor as it is cheap, photo-active, stable and is non-toxic. However, the photocatalytic ability of TiO2 is limited to only a small fraction of solar light (4%) and hence hampers its activity. Numerous efforts are initiated to improve TiO2 properties which include anion doping and most recent hydrogenation of TiO2. Nevertheless, the photocatalytic activity of anion-doped TiO2 was only accessible under UV and visible light. In addition, hydrogenated TiO2 was reported to possessed rapid electrons and holes recombination although the optical response was extended towards the infra-red region. In this work, hydrogenated F-doped TiO2 showed remarkable enhancement for the photocatalytic degradation of atrazine by a factor of ~8.5 relative to as prepared TiO2. Within 180 min of photocatalytic activity, more than 95 % of 0.5 mg/l atrazine was removed. Atrazine removal was shown to exceed those of N,F co-doped TiO2 (85 %), hydrogenated TiO2 (70 %), N-doped TiO2 (70 %), F-doped TiO2 (40 %) and F127- TiO2 (35 %). F-doped TiO2 was prepared using pluronic F127 as surfactant and iv trifluoroacetic acid as the fluorine precursor, followed by hydrogenation at 500 °C and 1 atm to obtain hydrogenated F-doped TiO2. Acid catalyzed sol-gel method was used to prepare F-doped TiO2 and other photocatalysts as it allows efficient control of purity, homogeneity, crystal phase and particle size. In addition, sol-gel method does not require needs of special equipment and can be conducted at low temperature. Hydrogenated F-doped TiO2 showed enhanced solar light absorption with ability to absorb light in the UV, visible and infra-red region. The sustainability of photogenerated electrons and holes on the photocatalyst surface enables larger formation of active surface radicals. Furthermore, the synergy between hydrogenation and F-doping modifies the morphology, crystal structure, surface charge, hydrophilicity, defects and surface area which were shown to favor the photocatalytic activity. High photocatalyst reusability up to 10th cycles was achieved. Hydrogenated F-doped TiO2 could serve as a new potential photocatalyst and thus supports the water industry for the abatement of recalcitrant organic pollutants. Furtherance, this leads to the possibility in providing safe drinking water by adapting a more sustainable and feasible approach.
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