title: Removal of caffeine from aqueous solution by indirect electrochemical oxidation using a graphite-PVC composite electrode: A role of hypochlorite ion as an oxidising agent.
abstract: The electrochemical oxidation of caffeine, a widely over-the-counter stimulant drug, has been investigated in effluent wastewater and deionized water (DIW) using graphite-poly vinyl chloride (PVC) composite electrode as anode. Effects of initial concentration of caffeine, chloride ion (Cl(-)) loading, presence of hydrogen peroxide (H2O2), sample volume, type of sample and applied voltage were determined to test and to validate a kinetic model for the oxidation of caffeine by the electrochemical oxidation process. The results revealed that the electrochemical oxidation rates of caffeine followed pseudo first-order kinetics, with rate constant values ranged from 0.006 to 0.23 min(-1) depending on the operating parameters. The removal efficiency of caffeine increases with applied voltage very significantly, suggesting a very important role of mediated oxidation process. However, the consumption energy was considered during electrochemical oxidation process. In chloride media, removal of caffeine is faster and more efficiently, although occurrence of more intermediates takes place. The study found that the adding H2O2 to the NaCl solution will inhibit slightly the electrochemical oxidation rate in comparison with only NaCl in solution. Liquid chromatography-time of flight-mass spectrometry (LC-TOF-MS) technique was applied to the identification of the by-products generated during electrochemical oxidation, which allowed to construct the proposed structure of by-products.
authors.affiliation: School of Chemical Sciences and Food Technology, Faculty of Science and Technology, Universiti Kebangsaan Malaysia (UKM), 43600 Bangi, Selangor, Malaysia; Department of Chemistry, Faculty of Sciences for Women, Babylon University, P.O. Box 4, Hilla, Iraq.
authors.forename: Fouad F
authors.initials: FF
authors.lastname: Al-Qaim
authors.affiliation: School of Chemical Sciences and Food Technology, Faculty of Science and Technology, Universiti Kebangsaan Malaysia (UKM), 43600 Bangi, Selangor, Malaysia.
authors.forename: Zainab H
authors.initials: ZH
authors.lastname: Mussa
authors.affiliation: School of Chemical Sciences and Food Technology, Faculty of Science and Technology, Universiti Kebangsaan Malaysia (UKM), 43600 Bangi, Selangor, Malaysia; Centre for Water Research and Analysis (ALIR), Faculty of Science and Technology, Universiti Kebangsaan Malaysia (UKM), 43600 Bangi, Selangor, Malaysia.
authors.forename: Mohamed R
authors.initials: MR
authors.lastname: Othman
authors.affiliation: School of Chemical Sciences and Food Technology, Faculty of Science and Technology, Universiti Kebangsaan Malaysia (UKM), 43600 Bangi, Selangor, Malaysia; Centre for Water Research and Analysis (ALIR), Faculty of Science and Technology, Universiti Kebangsaan Malaysia (UKM), 43600 Bangi, Selangor, Malaysia. Electronic address: mpauzi@ukm.my.
authors.forename: Md P
authors.initials: MP
authors.lastname: Abdullah
mesh_terms: D002110:Caffeine / Q000302:isolation & purification* / Q000633:toxicity; D000697:Central Nervous System Stimulants / Q000302:isolation & purification* / Q000633:toxicity; D002712:Chlorides / Q000737:chemistry; D055664:Electrochemical Techniques; D004566:Electrodes; D004926:Escherichia coli / Q000187:drug effects; D006108:Graphite / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D006997:Hypochlorous Acid / Q000737:chemistry*; D007202:Indicators and Reagents; D007700:Kinetics; D016877:Oxidants / Q000737:chemistry*; D010084:Oxidation-Reduction; D011143:Polyvinyl Chloride / Q000737:chemistry*; D012996:Solutions
chemical_list: D000697:Central Nervous System Stimulants; D002712:Chlorides; D007202:Indicators and Reagents; D016877:Oxidants; D012996:Solutions; D002110:Caffeine; D006997:Hypochlorous Acid; D006108:Graphite; D011143:Polyvinyl Chloride
keywords: Caffeine removal; Combined NaCl/H(2)O(2) effect; Elecrochemical oxidation process; Graphite-PVC composite electrode; Identification of chlorinated by-products; Pseudo-first order kinetic; Toxicity