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Open AccessArticle

Efficient Removal of Cr(VI) from Water by Biochar and Activated Carbon Prepared through Hydrothermal Carbonization and Pyrolysis: Adsorption-Coupled Reduction Mechanism

1
Faculty of Urban Infrastructure Engineering, University of Architecture Ho Chi Minh City, Ho Chi Minh City 700000, Vietnam
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Center of Excellence for Green Energy and Environmental Nanomaterials, Nguyen Tat Thanh University, Ho Chi Minh City 755414, Vietnam
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Hydraulic and Civil Engineering Department, University of El Oued, PO Box 789, El Oued 39000, Algeria
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Mapua University Muralla St. Intramuros, Manila 1002, Philippines
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Institute of Fundamental and Applied Sciences, Duy Tan University, Ho Chi Minh City 700000, Vietnam
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Department of Environmental Engineering, Chung Yuan Christian University, Taoyuan 32023, Taiwan
*
Authors to whom correspondence should be addressed.
Water 2019, 11(6), 1164; https://doi.org/10.3390/w11061164
Received: 21 May 2019 / Revised: 30 May 2019 / Accepted: 31 May 2019 / Published: 3 June 2019
Three carbonaceous porous materials (biochar and activated carbon) were developed from the Tectona grandis tree sawdust. The applied process of two-stage preparation included pre-treatment through hydrothermal carbonization at 190 °C and subsequent pyrolysis at 800 °C. Two chemical activating agents (K2CO3 and ZnCl2) were used to prepared activated carbons (K2CO3-AC and ZnCl2-AC), respectively. They were characterized by textural property, morphology, and surface element components and applied to remove Cr(VI) from solution at various solution pH values and initial Cr(VI) concentrations. Results showed that the textural parameters (SBET and VTotal) of the prepared material were 1757 m2/g and 1.027 cm3/g for Zn-Cl2-AC, 1013 m2/g and 0.418 cm3/g for K2CO3-AC, and 792 m2/g and 0.345 cm3/g for biochar. The adsorption process reached the highest efficiency at pH 3.0. The Langmuir maximum adsorption capacity indicated the decreasing order: ZnCl2-AC (127 mg/g) > K2CO3-AC (103 mg/g) > biochar (83.5 mg/g). The removal mechanism of Cr(V) from solution was regarded as an adsorption-coupled reduction, namely (1) partial reduction of Cr(VI) into Cr(III) during the adsorption process and (2) adsorption of the Cr(VI) anions through electrostatic attraction and pore filling and the reduced Cr(III) cations through complexation, Cπ–cation interaction, cation exchange, and pore filing. Therefore, the prepared biochar and activated carbon can server as promising adsorbents to efficiently remove both Cr(VI) and Cr(III) from water. View Full-Text
Keywords: hydrothermal carbonization; activated carbon; biochar; adsorption mechanism; hexavalent chromium; adsorption-coupled reduction hydrothermal carbonization; activated carbon; biochar; adsorption mechanism; hexavalent chromium; adsorption-coupled reduction
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Vo, A.T.; Nguyen, V.P.; Ouakouak, A.; Nieva, A.; Doma, B.T., Jr.; Tran, H.N.; Chao, H.-P. Efficient Removal of Cr(VI) from Water by Biochar and Activated Carbon Prepared through Hydrothermal Carbonization and Pyrolysis: Adsorption-Coupled Reduction Mechanism. Water 2019, 11, 1164.

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