Montmorillonite-Hydrochar Nanocomposites as Examples of Clay–Organic Interactions Delivering Ecosystem Services

Abstract

Clay-organic interaction is an important natural process that underpins soil ecosystem services. This process can also be tailored to produce clay-organic nanocomposites for industrial and environmental applications. The organic moiety of the nanocomposites, typically represented by a toxic surfactant, could be replaced by hydrochar formed from biomolecules (e.g. glucose) via hydrothermal carbonization. The effect of montmorillonite (Mnt) and glucose dosage on hydrochar formation, however, has not been clarified. In addition, the mechanisms by which Mnt-hydrochar nanocomposites (CMnt) can detoxify and remove carcinogenic Cr(VI) from aqueous solution are not well understood. In the current study, research milestones in terms of clay-organic interactions are summarized, following which the synthesis and characterization of CMnt for Cr(VI) adsorption are outlined. Briefly, 1 g of Mnt was reacted with 75 mL of glucose solution (0.1, 0.2, 0.3, 0.4, 0.5, and 0.6 mol L −1 ) by hydrothermal carbonization at 200°C for 16 h. The resultant CMnt samples were analyzed for chemical composition, functional groups, morphological features, and Cr(VI) adsorptive properties. Mnt promoted the conversion of glucose to hydrochars, the particle size of which (~80 nm) was appreciably smaller than that formed in the absence of Mnt (control). Furthermore, the hydrochars in CMnt had an aromatic structure with low hydrogen substitution and high stability (C/H atomic ratio 0.34-0.99). The weakened OH (from hydrochar) and Si-O-Si stretching peaks in the Fouriertransform infrared (FTIR) spectra of CMnt are indicative of chemical bonding between Mnt and hydrochar. The CMnt samples were effective at removing toxic Cr(VI) from acidic aqueous solutions. Several processes were involved, including direct reduction of Cr(VI) to Cr(III), complexation of Cr(III) with carboxyl and phenolic groups of hydrochar, electrostatic attraction between Cr(VI) and positively charged CMnt at pH 2 followed by indirect reduction of Cr(VI) to Cr(III), and Cr(III) precipitation.

Engineering clay minerals to manage the functions of soils

“…Adding montmorillonite minerals is a promising alternative for improving specific properties, such as increased adsorption capacity for water and compounds. The synthesis of hydrochar–montmorillonite nanocomposites through hydrothermal carbonization of glucose in the presence of montmorillonite is an example of obtaining fit-for-purpose materials using biomass from photosynthesis (Yuan et al , 2021). The use of montmorillonite minerals is justified because they are low-cost, readily available and environmentally friendly, making them suitable for extensive agriculture applications.…”

Tectonic controls on the ecosystem of the Mara River Basin, East Africa, from geomorphological and spectral indices analysis

“…They have higher cation exchange capacities (CECs) and 2:1 clay minerals provide plant available 420 potassium, which often is a limiting macronutrient for plants (Barre et al, 2007). Also, clay-organic interaction stabilizes organic matter against rapid microbial decomposition (Yuan et al, 2021).…”