Water-soluble natural organic acid for highly efficient photoreduction of hexavalent chromium
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Ó Indian Academy of Sciences Sadhana (0123456789().,-volV)FT3](0123456 789().,-volV)
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Water-soluble natural organic acid for highly efficient photoreduction of hexavalent chromium HONGBO HEa,*, ZHUANGZHU LUOb,* and CHANGLIN YUc a School
of Materials Science and Engineering, Sun Yat-sen University, Guangzhou 510000, People’s Republic of China b School of Materials, Sun Yat-sen University, Shenzhen 518107, People’s Republic of China c Faculty of Environmental Science and Engineering, Guangdong University of Petrochemical Technology, Maoming 525000, People’s Republic of China E-mail: [email protected]; [email protected] MS received 5 April 2020; revised 26 May 2020; accepted 27 May 2020
Abstract. Successful studies have demonstrated that citric acid can significantly improve the photocatalytic reduction efficiency of Cr(VI) over semiconductor photocatalysts as a sacrificial donor. Here, we studied the Cr(VI) photoreduction performance of citric acid monohydrate (CAM) without any semiconductor photocatalysts. Water-soluble CAM displays extremely efficient photoreduction activity for Cr(VI), which is attributed to the synergism of H?, C5H7O5COO- and hv. Hence, the role of citric acid in photoreduction of Cr(VI) may be underestimated in the previous studies. This work may open a new perspective for the development of low-cost, high-efficient and green water-soluble materials applied in heavy metal ion wastewater treatment. Keywords. Citric acid; Cr(VI) reduction; photocatalyst; wastewater treatment.
1. Introduction Environmental pollution is a worldwide problem, which has come to the foreground in recent years.1 Water, as we all know, is the source of life and an indispensable substance in all living beings on this planet. The depressing thing is that water pollution, one of the most serious environmental problems, has constantly caused tremendous pressure on the ecological environment.2,3 Among them, heavy metal ion (HMIs) wastewater is widely concerns as it is harmful, persistent and difficult to treat. Chromium is a common pollutant in natural waters, primarily due to its widespread application in industries such as plating and pigment industries,4 leather tanning,5 wood preservation,6 steel manufacturing,7 etc. Chromium mainly exists in two forms, Cr(III) and Cr(VI), and have quite different perniciousness in nature.8 Cr(VI) is one of the most undesirable carcinogenic agents and has been classified under class 1 by the International Agency for Research on Cancer
(IARC) in 2006.9 However, Cr(III) is much less toxic than that of Cr(VI), and is an essential trace element for human and animals.10 Thus reduction of Cr(VI) to Cr(III) has great significance to reduce the harmful effects of chromium-containing wastewater. A number of approaches have been applied for the reduction of Cr(VI), including chemical precipitation,11 ion exchange,12 adsorption,13 membrane filtration14 and photocatalytic reduction.15 The Cr(VI) reduction over photocatalysis is considered as one of the most promising
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