Kinetic Studies of Methyl Orange and Congo Red Adsorption and Photocatalytic Degradation onto PVP-Functionalized ZnO
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inetic Studies of Methyl Orange and Congo Red Adsorption and Photocatalytic Degradation onto PVP-Functionalized ZnO A. Khana, *, A. Naeema, and T. Mahmooda aNational
Centre of Excellence in Physical Chemistry, University of Peshawar, Peshawar, 25120 Pakistan *e-mail: [email protected] Received January 20, 2020; revised February 14, 2020; accepted March 2, 2020
Abstract—This study has focused on the applications of newly prepared zinc oxide (ZnO) composite with polyvinyl pyrrolidone (PVP) for adsorption and photocatalytic removal of methyl orange and congo red. Both the surface area and pore size of ZnO–PVP composite are relatively higher than the simple of unmodified ZnO. This finding signifies the role of PVP in the composites of metal oxide–PVP. The FT-IR analysis showed the chemical interactions of zinc oxide and different functional groups of polyvinyl pyrrolidone, which contribute significantly in removing the azo dyes from the aqueous system. A detailed kinetic study of the sorption used to remove methyl orange and congo red from aqueous solutions by ZnO–PVP composite was undertaken. Pseudo second order kinetic model was found to be best applicable for both the dyes. The mechanism governing the adsorption kinetics was examined by employing the Boyd and intraparticle diffusion models. The results confirmed that the adsorption of dyes by ZnO–PVP composite is mainly controlled by film diffusion (external diffusion) and internal transport of dye is inferior to the external transport. The obtained adsorption capacity for methyl orange is higher than that for congo red due to the presence of an additional functional group and size of the dye. The photocatalytic degradation of dyes with UV light was found to increase significantly with the addition of H2O2. Keywords: zinc oxide, polyvinyl pyrrolidone, methyl orange, congo red, photocatalytic degradation DOI: 10.1134/S0023158420050055
INTRODUCTION Methyl orange is one of the common water-soluble anionic azo dye widely used in paper, textile and chemical industries [1]. The IUPAC name of methyl orange is sodium 4-[[4-(dimethyl amino) phenyl] diazenyl] benzene sulfonate with a molecular formula (C14H14N3NaO3S). Likewise, congo red is also a secondary azo dye readily soluble in water. It is the sodium salt of benzidinediazo-bis-1-naphthylamine4-sulphonic acid with a molecular formula (C32H22N6Na2O6S2). Congo red is considered as a metabolizer to the carcinogenic product [2]. Because these dyes have great affinity for cellulose fibers, they are widely used in textile industries [3]. Some dyes are carcinogenic and mutagenic and can bring a serious health problem, for example kidney failure, brain, liver, respiratory, excretory system, central nervous system and reproductive system and hence should be processed before entering into the receiving water body [4]. Dyes have a complex structure that makes them stable to oxidation and light and difficult to biodegrade. The non-degradable nature and stability to Abbreviations: PVP, polyvinyl pyrrolidone; PZC, the point of
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