Comparative analysis of ZnO-catalyzed photo-oxidation of p-chlorophenols

Abstract

KEYWORDSThe present study compares for the first time the photocatalytic oxidation of three p-chlorophenols (4-chlorophenol, 2,4-dichlorophenol and 2,4,6-trichlorophenol) in irradiated ZnO suspensions. The effect of operating parameters such as catalyst and concentration doses on the decomposition rate of these p-chlorinated compounds has been studied and optimized. The optimal feed concentration for each of the chlorinated phenolic compounds is 50 mg/L whereas the ZnO doses decreased as the number of chlorine substituent is increased. Kinetic profiles on the decomposition of chlorophenols over ZnO agreed with the pseudo-zeroeth order rate scheme with rate constants following the order 2,4,6-trichlorophenol > 2,4dichlorophenol > 4-chlorophenol. The validity of the pseudo zero order model could be linked to the initial doses of the chlorophenols used vis-à-vis the catalyst. The study revealed stable intermediates of photocatalytic chlorophenol transformation by high performance liquid chromatography (HPLC) and gas chromatography-mass spectrometry (GC-MS) technique. A combined mechanism is given to account for the photocatalytic destruction of the chlorophenols. OxidationMechanism Chlorophenol ZnO Photodegradation Intermediates

Investigation of ZnTiO3/TiO2 composites and their application in photocatalysis

“…Over the past decades, titanium dioxide (TiO2) has attracted considerable scientific interest in the field of photocatalysis, due to the outstanding properties such as low cost, photochemical stability and security [1,2]. However, due to its large band gap (TiO2 ~3.2 eV) [3], TiO2 can only work under UV irradiation, which greatly restricts the use of sunlight as an energy source for photoreactions since only about 3-4% of the solar spectrum falls within the UV range [4][5][6].…”

Kinetic Concepts of Heterogeneous Photocatalysis

“…Similar explanation can be made on the photocatalytic degradation of other phenolics irrespective of semiconductor photocatalyst used. For instance, it has been observed that mono-chlorinated phenol regardless of substituent position degrades slower than dior tri-chlorinated congeners (Huqul et al 2002;Gaya 2011). …”

The Effect of Light Exposure on the Degradation of Latent Fingerprints on Brass Surfaces: The Use of Silver Electroless Deposition as a Visualization Technique

“…The metal squares to which a print had been applied were suspended at the top of the beaker which was covered with a large watch glass and heated to 65°C (the boiling point of cyanoacrylate). The potassium chloride was present to add humidity – at 65°C; it is known to give a relative humidity of 79.9 ± 0.5% . For some CFM‐enhanced prints, staining with a 0.004‐M solution of Basic Yellow (BY40) dye (supplied by Crime Scene Investigation Products.…”

“…Zinc oxide‐coated surfaces in particular have been shown to facilitate photooxidation of a wide range of organic compounds. Examples include alkenes , alcohols , chlorophenols , dyes such as methyl orange and amino acids . As such, we concluded that a study of fingerprints on brass surfaces where zinc oxide is known to be a component would be of interest, especially to compare this with our previously reported work of prints on black PVC surfaces .…”