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

Abstract

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.

Coupling of kenaf Biochar and Magnetic BiFeO3 onto Cross-Linked Chitosan for Enhancing Separation Performance and Cr(VI) Ions Removal Efficiency

“…Analogous results of adsorption-coupled reduction were also reported [3,57]. The possible adsorption mechanism is as following: first, Cr(VI) ions are captured on the surface or inner pores of CKB through electrostatic attraction at acidic environment; second, some adsorbed Cr(VI) is reduced to Cr(III) under visible light, which is mainly because CKB contains a certain amount of BiFeO 3 that exhibit the photocatalytic capacity and -NH 3 , -COOH, and other functional groups may also provide the electrons [3]; finally, Cr(III) is also adsorbed onto CKB, coexisting with Cr(VI). It is noted that during the adsorption process, Cr(III) may be oxidized back to Cr(VI) by photogenerated holes produced on CKB, and simultaneously, Cr(VI) ions are reduced to Cr(III).…”

“…BiFeO 3 was prepared using the sol-gel method [21]. Firstly, 0.08 mol of Fe(NO 3 ) 3 and Bi(NO 3 ) 3 were dissolved in 200 mL of 2-Methoxyethanol and 0.2 mL of 0.1 mol/L nitric acid in a 500 mL beaker. Then 0.08 mol of citric acid was dissolved in 100 mL of ethylene glycol.…”

Biochar from Agricultural by-Products for the Removal of Lead and Cadmium from Drinking Water

“…The raw materials were washed with deionized water to remove impurities. After, raw materials were dried at 105 • C for 24 h [28,29].…”

“…10, respectively. The biochar particles were washed with deionized distilled water to remove impurities and ash [29,37], finally biochar were dried at 105 • C during 60 min [28,38].…”

Activated Carbon from Yam Peels Modified with Fe3O4 for Removal of 2,4-Dichlorophenoxyacetic Acid in Aqueous Solution

“…Activated carbon is an efficient adsorbent for the removal of organic pollutants in aqueous solutions due to its physicochemical properties, such as high surface area and microporosity [5]. Additionally, agroindustrial wastes are being used for the production of activated carbons, allowing us to solve two environmental problems in one approach through the transformation of these natural sources into adsorbent materials [15][16][17]. Adsorption of 2,4-D using activated carbon prepared from natural sources has been reported to show good adsorption capacity [5,6,18].…”