The Malaysian Journal of Analytical Sciences Vol 12 No 1 (2008): 77 - 87

 

 

DEGRADATION STUDIES ON PARAQUAT AND MALATHION USING TiO₂/ZnO BASED PHOTOCATALYST

 

Rusmidah Ali and Siti Habsah Hassan

 

Chemistry Department, Faculty of Science, Universiti Teknologi Malaysia,

81310 Skudai, Johor Bahru, Malaysia.

 

Abstract

Paraquat, a herbicide and malathion, an insecticide are pesticides that are always polluting our water system. Thus a lot of efforts has been conducted to treat the polluted water. The latest technology proposed is using photocatalyst.  In this study, ZnO  and  TiO₂    were  used  as  photocatalysts  to  degrade  the  pesticide  in  the  presence  of  UV  light  (λ=354 nm).  The photodegradation  rate  was  measured  using  UV-Visible  spectrophotometer  and  TOC  analyzer.  Malathion  showed  the absorption peak at λ=210 nm while for  paraquat at λ=258 nm. The best coupled photocatalyst for degrading malathion solution  is ZnO/TiO₂    with  % weight ratio 1:0.05 and the best coupled photocatalyst in degrading paraquat  solution is TiO₂/ZnO with % weight ratio 1:0.03. The result shows that Fe²⁺ ion present in the reaction mixture was better than   Fe³⁺  ion present as a dopant (which is added during the catalyst preparation). The optimum photocatalyst calcinations temperature for degrading paraquat and malathion were 550°C for TiO₂  and 500°C for ZnO. The physical properties of the best catalyst were characterized using SEM, XRD, UV-Vis-NIR spectrophotometer and elipsometer. By increasing the calcinations temperature up to 600°C, XRD data showed  the transformation of TiO₂  anatase to rutile phase    while for ZnO, the increment of the intensity of ZnO catalyst was observed, indicating that, the quality of ZnO wurtzite crystal was improved. The thicknesses for ZnO, ZnO/TiO₂   1:0.05 and ZnO/TiO₂   doping with Fe³⁺   thin film were 130.57 nm, 150.68 nm and 153.84 nm respectively. The band gap energy values measured using UV-Vis NIR were in the range of 2.95 – 3.09 eV.

 

Keywords: Paraquat, Malathion, Photodegradation, Mineralization, ZnO, TiO₂

 

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