Adsorption mechanism of hexavalent chromium onto layered double hydroxides-based adsorbents : a systematic in-depth review

Tran, H. N. and Nguyen, D. T. and Le, G. T. and Tomul, F. and Lima, Ader c. and Woo, S. H. and Sarmah, A. K. and Nguyen, H. Q. and Nguyen, P. T. and Nguyen, D. D. and Nguyen, T. V. and Vigneswaran, S. and Vo, Dai-Viet N. and Chao, H. -P. (2019) Adsorption mechanism of hexavalent chromium onto layered double hydroxides-based adsorbents : a systematic in-depth review. Journal of Hazardous Materials, 373. pp. 258-270. ISSN 0304-3894. (Published)

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An attempt has been made in this review to provide some insights into the possible adsorption mechanisms of hexavalent chromium onto layered double hydroxides-based adsorbents by critically examining the past and present literature. Layered double hydroxides (LDH) nanomaterials are typical dual-electronic adsorbents because they exhibit positively charged external surfaces and abundant interlayer anions. A high positive zeta potential value indicates that LDH has a high affinity to Cr(VI) anions in solution through electrostatic attraction. The host interlayer anions (i.e., Cl−, NO3−, SO42−, and CO32−) provide a high anion exchange capacity (53–520 meq/100 g) which is expected to have an excellent exchangeable capacity to Cr(VI) oxyanions in water. Regarding the adsorption-coupled reduction mechanism, when Cr(VI) anions make contact with the electron-donor groups in the LDH, they are partly reduced to Cr(III) cations. The reduced Cr(III) cations are then adsorbed by LDH via numerous interactions, such as isomorphic substitution and complexation. Nonetheless, the adsorption-coupled reduction mechanism is greatly dependent on: (1) the nature of divalent and trivalent salts utilized in LDH preparation, and the types of interlayer anions (i.e., guest intercalated organic anions), and (3) the adsorption experiment conditions. The low Brunauer–Emmett–Teller specific surface area of LDH (1.80–179 m2/g) suggests that pore filling played an insignificant role in Cr(VI) adsorption. The Langmuir maximum adsorption capacity of LDH (Qomax) toward Cr(VI) was significantly affected by the natures of used inorganic salts and synthetic methods of LDH. The Qomax values range from 16.3 mg/g to 726 mg/g. Almost all adsorption processes of Cr(VI) by LDH-based adsorbent occur spontaneously (ΔG° <0) and endothermically (ΔH° >0) and increase the randomness (ΔS° >0) in the system. Thus, LDH has much potential as a promising material that can effectively remove anion pollutants, especially Cr(VI) anions in industrial wastewater.

Item Type: Article
Additional Information: Hai Nguyen Tran, Dong Thanh Nguyen, Giang Truong Le, Fatma Tomul, Eder C. Lima, Seung Han Woo, Ajit K. Sarmah, Hung Quang Nguyen, Phuong Tri Nguyen, Dinh Duc Nguyen, Tien Vinh Nguyen, SaravanamuthVigneswaran, Dai-Viet N. Vo, Huan-Ping Chao; Indexed by Scopus
Uncontrolled Keywords: Hexavalent chromium; Layered double hydroxides; Adsorption-coupled reduction; Anion exchange; Isomorphic substitution; Critical review
Subjects: Q Science > QD Chemistry
T Technology > TD Environmental technology. Sanitary engineering
T Technology > TP Chemical technology
Faculty/Division: Faculty of Chemical & Natural Resources Engineering
Depositing User: Mrs Norsaini Abdul Samat
Date Deposited: 24 Oct 2019 07:12
Last Modified: 24 Oct 2019 07:12
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