Macro kinetic studies for photocatalytic degradation of benzoic acid in immobilized systems (original) (raw)

Conversion of benzoic acid during TiO2-mediated photocatalytic degradation in water

Chemical Engineering Journal, 2008

The photocatalytic degradation of benzoic acid in water over Degussa P-25 TiO 2 suspensions was studied. UVA irradiation at 365 nm was supplied by a medium pressure mercury lamp providing 25 mW cm −2 light intensity. Experiments were conducted at benzoic acid initial concentrations between 25 and 150 mg L −1 , catalyst loadings between 0.2 and 1 g L −1 and initial solution pH values between 2 and 10.6. Conversion increased with increasing catalyst loading up to about 0.6 g L −1 and it was favored at alkaline or neutral conditions but impeded at extremely acidic conditions. Increasing initial substrate concentration led to decreased benzoic acid conversion, which was found to follow a Langmuir-Hinshelwood kinetic expression. High performance liquid chromatography (HPLC) was employed to follow benzoic acid concentration profiles as well as to identify reaction by-products, while chemical oxygen demand (COD) and total organic carbon (TOC) analyses were carried out to assess the extent of mineralization. Benzoic acid hydroxylation by-products, namely 2-, 3-and 4-hydroxybenzoic acids as well as phenol were identified as reaction intermediates, although these contributed only a small fraction of the residual organic content. Although benzoic acid at 50 mg L −1 was not ecotoxic to marine photobacteria Vibrio fischeri, its photodegraded solution exhibited substantial toxicity, which, however, proved not to be due to the identified intermediates.

Removal of an Organic Refractory Compound by Photocatalysis in Batch Reactor - Kinetic Studies

Environmental Engineering and Management Journal, 2015

The present work systematically investigates the photocatalytic degradation of carbamazepine (CBZ), an organic compound, known as refractory to the conventional wastewater treatment by the titanium dioxide PC 500 catalyst. The effects of some fundamental operating parameters in heterogeneous photocatalysis were investigated in this work in order to determine the main ones affecting the degradation kinetics. The obtained results clearly showed that the removal rate of the target compound is strongly influenced by the initial concentration of the pollutant. The degradation reaction rate increases when the concentration of CBZ decreases due to a lower OH • /CBZ ratio. On the other hand, it was shown that during the first 30 minutes the reaction of photocatalytic degradation follows a first order kinetic and also that when the incident light flux increases, the photocatalytic degradation process is accelerated due to the increases of the catalyst excitation probability with sufficient photon energy. A relatively high CBZ removal yield (of about 87%) was obtained for an initial pollutant concentration of 2 mg/L and an irradiation time of 150 min. A total organic carbon (TOC) reduction of about 74% was observed confirming the mineralization of the parent compound under UV light conditions. As expected, it was observed that the effect of TiO 2 concentration on the degradation kinetics was significant confirming the positive influence of the increased number of TiO 2 active sites on the process. Finally, the Langmuir-Hinshelwood (L-H) model was successfully used to fit the experimental results and the L-H model constants were also calculated.