engleski

HETEROGENEOUS PHOTOCATALYTIC DEGRADATION OF TERBUTHYAZINE

Modern industrial progress has generated a vast range of toxic, non-biodegradable compounds of synthetic nature, such as pharmaceuticals, personal care products, dyes as well as pest control compounds. These compounds can be present in the surrounding soil, leachate and wastewater, but their removal using conventional wastewater treatment (biological, physical and chemical) has proven to be expensive and ineffective. Photocatalytic oxidation proved to be suitable, especially when very toxic compounds present in small concentrations in wastewater need to be removed. TiO2 is the most investigated and used photocatalyst, with main features, such as availability, great catalytic activity and non- toxicity, especially if used in heterogeneous catalysis. The aim of this work is to develop a photocatalytic process for efficient removal of herbicides from different water sources. Two types of the photoreactors were used: the photocatalytic batch reactor of annular type and flow type of reactor, both with immobilized TiO2 layer and equipped with a commercial 8W UV lamp. A common herbicide in Croatia, was obtained from the producer Herbos d.d., RADAZIN EXTRA TZ. We received pure components (terbuthylazine and acetochlor) and terbutylazine was chosen as model component. The catalyst layer consisted of the P25 TiO2 catalyst mixed with chitosan for immobilisation. The physico-chemical properties of the photocatalyst were investigated using different techniques such as scanning electron microscopy, FTIR, TGA-DTA, nitrogen absorption/desorption, etc. The stability of the photocatalyst was determined using TOC analysis (chitosan stability) and AAS (Ti leaching). The influences of various operating conditions, such as temperature, initial reactant concentration, catalyst surface/mass ratio, pH values, flow rate (or flow rate recirculation), intensity and irradiation time of the UV lamp on photodegradation of the selected herbicides were investigated. The source of irradiation was placed in the center of reactor. The reaction temperature was kept at selected temperature using a thermostat. The reaction system was oxygenated continuously by the ambient air. Samples from the reactor were analyzed using HP 1090 HPLC using a 5 mm, 250x4, 6 mm Zorbax SB-C18 column and DAD. Measurements were confirmed on a GC-MS from an independent laboratory. Catalytic tests for heterogeneous degradation of the selected herbicides were carried out in two different types of reactors. Results showed considerable reductions of herbicides concentration, using the 254 nm UV lamp and the TiO2/chitosan photocatalyst. Prolonged exposure of the catalyst layer to the UV lamp provoked some catalyst leaching due to chitosan degradation. The influence of different parameters of TiO2/chitosan photocatalyst preparation on its physico-chemical and catalytic properties was examined. The efficiency of the process depended strongly on the experimental conditions. The kinetics of photocatalytic removal of herbicides followed the mechanistic Langmuir-Hinshelwood model. According to the correlation of the physico-chemical and catalytic properties, the proposed kinetic and reactor models and model validation the key parameters of the photocatalyst design and reactor performance were determined, crucial for the development of an efficient process of photocatalytic degradation. Results show that experimental photoreactors used in the present study appear to be a promising technology for removal of herbicides and similar environmentally persistent compounds from wastewaters.

herbicides ; heterogeneous catalysis ; photocatalytic oxidation ; terbutylazine

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