Adsorption and mechanistic study for phosphate removal by rice husk-derived biochar functionalized with Mg/Al-calcined layered double hydroxides via co-pyrolysis. (1st November 2019)

• Record Type: Journal Article
• Authors: Lee, Seon Yong; Choi, Jae-Woo; Song, Kyung Guen; Choi, Keunsu; Lee, Young Jae; Jung, Kyung-Won
• Is Part Of: Composites. Number 176(2019)
• Publication Date: 2019-11-01
• Subjects: Biochar -- Mg/Al calcined layered double hydroxides -- One-step functionalization -- Phosphate -- Adsorption; Composite materials -- Periodicals; Materials science -- Periodicals; Composite materials; Periodicals; Electronic journals; 620.118
• DOI: 10.1016/j.compositesb.2019.107209
• Languages: English
• ISSNs: 1359-8368

Abstract

Abstract: Direct or indirect emissions of phosphate from point or non-point sources into aquatic ecosystem may pose serious adverse risks to human life and environmental sustainability. Owing to their environmental and economic benefits, biochar-based adsorption processes have recently emerged as an ideal approach. However, the surface of biochar is normally negatively charged, thus limiting its binding affinity toward anionic contaminants. Herein, in order to address this weakness and further improve adsorption performance, we developed rice husk (RH)-derived biochar functionalized with Mg/Al-calcined layered double hydroxides (RHB/MgAl-CLDHs) via the co-pyrolysis of MgAl-LDH preloaded RH, and we examined its phosphate adsorption properties in aqueous environments. Multiple analyses and phosphate adsorption experiments revealed that the Mg:Al molar ratio (2:1–5:1) and co-pyrolysis temperature (300–700 °C) control the physicochemical properties of synthesized samples and their phosphate adsorption affinities. The molar ratio affects the charge density, whereas the co-pyrolysis temperature determines the surface functionality and porosity. Specifically, RHB/MgAl-CLDHs(2:1/500) (molar ratio = 2:1, co-pyrolysis temperature = 500 °C) exhibited the highest phosphate removal of 97.6% due to the conversion of RH into biochar, decomposition of interlayer water/nitrate, transformation of LDH structures to mixed metal oxides (layered double oxides), and improved porosity, favoring stronger adsorption and intercalation of phosphate. Spectroscopic solid-phase analyses demonstrated that the adsorption mechanism involves the "memory effect" and the formation of both outer- and inner-sphere surface complexes via attractive electrostatic interactions and monodentate/bidentate complexations. In conclusion, considering its high selectivity and excellent recyclability, RHB/MgAl-CLDHs(2:1/500) is a promising material for mitigating eutrophication. Graphical abstract: Image 1 Highlights: Rice husk-derived biochar functionalized with MgAl-calcined LDHs were synthesized. Lower Mg:Al molar ratio increased charge density and phosphate adsorption. Phosphate adsorption affinity was highly dependent on the co-pyrolysis temperature. The selectivity was followed the partial negative charge on oxygen atoms of anions. Mechanism involves memory effect and both outer-sphere and inner-sphere complexes.