Abstract
The photodegradation of stearic acid has been studied through evaluation of changes in the contact angles of water and from absorbance measurements. The photodegradation of 0.02 M stearic acid coatings and solutions were initiated by TiO2 nanoparticles of average size of 9.80 ± 2.92 nm embedded in cements in 1.66 wt.%, 3.33 wt.%, 5.0 wt.% and 6.67 wt.% to generate modified cement composites with photocatalytic capability. It was noted that the photodegradation efficiencies increased with the increase in the weight-percent of TiO2 present in the modified cement samples. A modified Cassie-Baxter and the Langmuir-Hinselwood models were used to compute the rate constants, based on changes in the contact angles of water and in the concentration of the stearic acid respectively, on exposure to the UV light source. The modified Cassie-Baxter model successfully provided a route to relate the changes in water contact angle to the rate of photodegradation of a hydrophobic, long-chain stearic acid. The values of the rate constant estimated from both models increased with increase in the amount of TiO2 present in the modified cement samples. However, the rate constant values obtained from the modified Cassie-Baxter model were lower than those obtained from the Langmuir-Hinselwood model. The values of these rate contants were in the range of 0.11-0.50 hr-1 and 0.78-1.33 hr-1 as btained from the modified Cassie-Baxter and Langmuir-Hinselwood models respectively. This disparity in the values was attributed to a higher mobility of the charge carriers and free-radicals that induced the photodegradation in liquid medium as compared to the solid medium.
Highlights
Photodegradation and advanced oxidation processes have received a lot of interest from researchers [1]
The various results obtained from these experiments based on the absorption studies and water contact angle studies, whose procedures have earlier been stated are as presented below: 3.1
The reduction in the water contact angles and in the values of CT are due to the degradation of the stearic acid which is both hydrophobic and shows marked absorbance values
Summary
Photodegradation and advanced oxidation processes have received a lot of interest from researchers [1]. This is because photodegradation provides a spectacular route for the resolution of environmental problems through the detoxification and mineralization of organic pollutants and organic wastes [2,3]. Methods for remediation of waste generally involved thermal procedures, which resulted in the generation of carbon monoxide and other residues that aredeleterious to the environment. It is in this regards that the decomposition of organic molecules, with TiO2 serving as a photocatalyst, has become well-defined [5,6]. TiO2 as a photocatalyst, has been explored for application in anti-fogging and self-cleaning behaviour on the basis of photo-induced hydrophillicity [7,8,9]
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