New Insights into the Sorption and Detoxification of Chromium(VI) by Tetraethylenepentamine Functionalized Nanosized Magnetic Polymer Adsorbents: Mechanism and pH Effect

In this study, sorption and detoxification mechanisms of chromium­(VI) by tetraethylenepentamine (TEPA)-functionalized nanosized magnetic polymer adsorbents, named as TEPA-NMPs, have been studied. Mechanisms of adsorption and solid state in situ redox of Cr­(VI) at different pH were proposed based on batch tests, thermodynamic and kinetic studies, and XPS, XRD, and FTIR analyses of the adsorbents before and after Cr­(VI) adsorption/desorption. The results showed that the adsorption of Cr­(VI) on TEPA-NMPs could be related to electrostatic attraction, and partially formation of Cr­(III) through solid state in situ reduction of Cr­(VI) via charge transport on the surface of the TEPA-NMPs, and further coordination interactions between Cr­(III) and amine groups (NH₂). The Fe₃O₄ magnetic core, C–O–C and C–OH groups in the adsorbents might play important roles during the redox process. TEPA-NMPs were testified to be potential adsorbents for detoxification of Cr­(VI) with high efficiency

Iodine-Sensitized Degradation of 2,4,6-Trichlorophenol under Visible Light

Molecular iodine has been studied, for the first time, as a sensitizer for the degradation of 2,4,6-trichlorophenol (TCP) in aqueous solution under visible light (λ ≥ 450 nm). TCP was degraded in the presence of commercial I₂, but the reaction rate decreased significantly after 2 h. When a solution of NaI and H₂O₂ was used as an iodine source with phosphotungstic acid (PW) as a catalyst, TCP degradation was not only fast but also followed zero-order kinetics. Importantly, the I₂ concentration remained unchanged with time, indicative of I₂ recycling as a kind of photocatalyst. During TCP degradation, 2,6-dichloro-1,4-benzoquinone was produced as the main intermediate (76%), which slowly degraded in the irradiated solution. For every equivalent of TCP consumed at the 2 h time point, approximately 1.7 equivalents of chloride ions were produced. Further study of the effect of variables including the type of polyoxometalates (POM) and the initial concentration of each component revealed that the rate of TCP degradation under visible light was determined by the rate of I₂ production in the dark. The optimum pH and apparent activation energy for TCP disappearance were 4.5 and 42.8 kJ/mol, respectively. It is proposed that TCP degradation is initiated by iodine radicals produced from I₂ photolysis, followed by I₂ regeneration through a POM-catalyzed oxidation of I₃^– by H₂O₂