Color-mixing effects of photosensitive organic dyes initiated by superoxide anion radicals under visible-light irradiati

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ORIGINAL PAPER

Color‑mixing effects of photosensitive organic dyes initiated by superoxide anion radicals under visible‑light irradiation Jin Yang1 · Yan Cao1 · Naidong Zhang1,2  Received: 13 March 2020 / Accepted: 23 June 2020 © Springer Nature Switzerland AG 2020

Abstract Water pollution by dyes is a major health and environmental issue. Photosensitive organic dyes produce hydrated electrons, eaq−, singlet oxygen, 1O2, and superoxide anion radicals, O ­ 2·−. ­O2·− catalyzes H ­ 2O2 transformation into hydroxyl radicals ·OH, which can be used to degrade wastewater under sunlight. Here, we measured eaq−, 1O2, ­O2·− and ·OH generated under visible light irradiation of photosensitive organic dyes in the presence of the auxiliary F ­ e3+, the 1,5-diphenylcarbazide molecular probe, the N ­ H2OH molecular probe and the dimethyl sulphoxide probe. Results show that single photosensitive organic dyes are not degraded in the visible light/H2O2 system. However, they were degraded when mixed in a certain proportion to produce a brown coloration, a phenomenon named the ‘color-mixing effect.’ Likewise, the average yields of ­O2·− in single photosensitive organic dye solutions were lower, of 0.015 (ΔA510), than that in mixed brown solutions, of 0.113. The colormixing effect is explained mainly by higher ·OH generation from increased ­O2·− production. Findings imply that sunlight irradiation is a promising way to clean colorful and dye-containing wastewater. Keywords  Photosensitive organic dyes · Visible light · Hydrated electron · Singlet oxygen · Superoxide anion radical · Hydroxyl radical

Introduction Water pollution is a major environmental issue of worldwide concern (Ali et al. 2005, 2013; Basheer 2018a, b). Many countries and governmental organizations have formulated policies and measures regarding water pollution (Alharbi et al. 2018; Basheer 2018a, b). In addition, many chemical, physical and biological water treatment methods Electronic supplementary material  The online version of this article (https​://doi.org/10.1007/s1031​1-020-01043​-4) contains supplementary material, which is available to authorized users. * Naidong Zhang [email protected] Jin Yang [email protected] Yan Cao [email protected] 1



College of Environmental Science and Engineering, Dalian Maritime University, Dalian 116026, China



State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology, Harbin 150090, China

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have been studied for wastewater treatment (Ali et al. 2016, 2017, 2018; Burakova et al. 2018). Organic dye pollutants in wastewater have always been one of the most serious water pollution problems (Shanker et al. 2017; Mashkoor et al. 2020). Chromophoric dissolved organic matters are an important light-absorbing substance in water and include photosensitive organic dyes as an important component of colored and dye-containing wastewater (Nie and Xiao 2020). Chromophoric dissolved organic matters are the major factor dominating ultraviolet light and visible light penetration in