Abstract—In this study, a composite photocatalyst of TiO2/silica was prepared, analyzed and used in a batch reactor for the photocatalytic degradation of synthetic textile (methyl orange) wastewater. The successive photocatalyst was characterized by Scanning Electron Microscopy and Energy Dispersive Spectroscopy (SEM- EDS) and zeta potential (ZP) analyses. Operating parameters such as loading, initial pollutant concentration and pH were optimized. The performance of the photocatalyst reactor was evaluated on the basis of color removal and degradation kinetics. The equilibrium data was analyzed using the Langmuir and Freundlich isotherm models. Experimental data was best represented by the Langmuir isotherm model. The maximum adsorption capacity of dye onto composite photocatalyst was found to be 20.24 mg/g. The pseudo second order kinetic model adequately described the kinetic data. Keywords—Composite photocatalyst, kinetics, methyl orange, photocatalysis I. INTRODUCTION HE accelerated growth of textile industry and the increasing worldwide concern for environmental conservation have revealed the great problem of environmental pollution by azo dyes. Due to the stability and toxicity of azo dyes and the presence of residual surfactants, azo dye textile wastewaters are resistant to the conventional biological treatment [1]. With this growing demand, heterogeneous photocatalysis employing TiO 2 semiconductor catalyst is one of the few attractive alternatives to resolve this problem. A number of important features for the heterogeneous photocatalysis have extended their feasible applications in water treatment, such as operating at ambient temperature and pressure, low operative costs and complete mineralization of parents and Kwena Pete was with the Faculty of Technology, Lappeenranta University of Technology, Sammonkatu 12, FI-50130 Mikkeli, Finland. She is now with the Centre for Renewable and Water, Vaal University of Technology, Private Bag X021 Vandebijlpark 1900, South Africa (*Corresponding author. Email address: [email protected]; Tel. +27-73-446-2988; Fax: +27-16-950-9796). Mika M Sillanpää is with the Faculty of Technology, Lappeenranta University of Technology, Sammonkatu 12, FI-50130 Mikkeli, Finland Maurice S. Onyango is with the Department of Chemical and Metallurgical Engineering, Tshwane University of Technology, Pretorai,0001 Ochieng Aoyi is with the Centre for Renewable and Water, Vaal University of Technology, Private Bag X021 Vandebijlpark 1900, South Africa their intermediate compounds without secondary pollution [2]. The post-separation of the semiconductor TiO 2 catalyst after water treatment remains as the major problem towards the practicality at an industrial process. The fine particle size of the TiO 2 , together with their large surface area-to-volume ratio and surface energy creates a strong tendency for catalyst agglomeration during the process. Such particles agglomeration is highly disadvantageous in views of surface- area reduction and its reusable lifespan. To solve this problem, TiO 2 catalyst powder is loaded onto supporting silica material in such a way as to provide high surface area and accessibility of the catalyst. The main aim of this work was to investigate the heterogeneous photocatalytic degradation of methyl orange dye using TiO 2 /silica composite photocatalyst. The effect of operating parameters such as the composition of the composite particle size, catalyst loading, initial pollutant concentration and solution pH were determined. II. MATERIALS AND METHODS A. Materials Chemicals used were of analytical reagent grade, used as received and purchased from Sigma Aldrich. Methyl orange (MO, 99 %,), an azo dye pollutant in wastewater. The TiO 2 was used as photocatalyst with Ludox HS-30 colloidal silica, as the supporting material. B. Synthesis of Composite photocatalyst The TiO 2 supported-silica samples were prepared by adding Ludox HS-30 colloidal silica solution to TiO 2 with proper mixing to ensure a homogeneous TiO 2 supporting onto silica. After mixing, the mixture was dried at 110 °C and screened to different particle sizes (particle sizes 0-38 75-150, 150-250 μm). The coated particles were then dispersed in Mill Q-plus water, till the pH of the suspension was close to 6.5. By this procedure, a sample of 3-20 wt% of TiO 2 onto silica particles was prepared. C. Photocatalytic experiment Photocatalytic degradation experiments were carried out in 100 ml semi batch reactor at 25 ± 3°C. Milli Q-plus water (resistance = 18.2 M.Ω) was used for all experimental work. Analysis of Kinetic Models in Heterogeneous Catalysis of Methyl Orange Using TiO 2 /Silica Composite Photocatalyst Kwena Y. Pete, Mika M Sillanpää, Maurice S. Onyango, and Ochieng Aoyi T Intl' Conf. on Chemical, Integrated Waste Management & Environmental Engineering (ICCIWEE'2014) April 15-16, 2014 Johannesburg 169
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Abstract—In this study, a composite photocatalyst of TiO2/silica
was prepared, analyzed and used in a batch reactor for the
photocatalytic degradation of synthetic textile (methyl orange)
wastewater. The successive photocatalyst was characterized by
Scanning Electron Microscopy and Energy Dispersive Spectroscopy
(SEM- EDS) and zeta potential (ZP) analyses. Operating parameters
such as loading, initial pollutant concentration and pH were
optimized. The performance of the photocatalyst reactor was
evaluated on the basis of color removal and degradation kinetics. The equilibrium data was analyzed using the Langmuir and
Freundlich isotherm models. Experimental data was best
represented by the Langmuir isotherm model. The maximum
adsorption capacity of dye onto composite photocatalyst was found
to be 20.24 mg/g. The pseudo second order kinetic model adequately