Experimental and Computational Evaluation of Heavy Metal Cation Adsorption for Molecular Design of Hydrothermal Char

Abstract

A model hydrochar was synthesized from glucose at 180 °C and its Cu(II) sorption capacity was studied experimentally and computationally as an example of molecular-level adsorbent design. The sorption capacity of the glucose hydrochar was less than detection limits (3 mg g−1) and increased significantly with simple alkali treatments with hydroxide and carbonate salts of K and Na. Sorption capacity depended on the salt used for alkali treatment, with hydroxides leading to greater improvement than carbonates and K+ more than Na+. Subsequent zeta potential and infrared spectroscopy analysis implicated the importance of electrostatic interactions in Cu(II) sorption to the hydrochar surface. Computational modeling using Density Functional Theory (DFT) rationalized the binding as electrostatic interactions with carboxylate groups; similarly, DFT calculations were consistent with the finding that K+ was more effective than Na+ at activating the hydrochar. Based on this finding, custom-synthesized hydrochars were synthesized from glucose-acrylic acid and glucose-vinyl sulfonic acid precursors, with subsequent improvements in Cu(II) adsorption capacity. The performance of these hydrochars was compared with ion exchange resins, with the finding that Cu(II)-binding site stoichiometry is superior in the hydrochars compared with the resins, offering potential for future improvements in hydrochar design.

Evaluation of characteristics of raw tea waste-derived adsorbents for removal of metals from aqueous medium

“…These results showed a complexation reaction between Cu 2+ and functional groups of -OH, -CH, and -COOH. Similar results were reported for various biochar samples such as peanut straw char, soybean straw char, canola straw char, glucose hydrochar [92], black carbon derived from wheat residues [93], biochar derived from pistachio green hull [94], halophyte biochar [95], and woodchipderived biochar [96].…”

Charcoal as an Alternative Reductant in Ferroalloy Production: A Review

“…Specifically, HTC removes a significant fraction of undesired inorganic elements such as Na and K that would otherwise contribute to slag [135]. Previous studies showed that the alkali content can be further reduced by increasing the heat treatment temperature or by washing the hydrochar with the deionized water after the pre-treatment [136]. In addition, hydrochar has superior mechanical properties and pelletability compared with torrefaction or pyrolysis biochar [129,137].…”

Biomass carbon mining to develop nature-inspired materials for a circular economy

“…On the modeling side, very few DFT studies involving hydrochar have been reported, although the few models that have been developed for biochar should be easily transferable. Hydrochar synthesized from glucose and treated with hydroxide and carbonate salts of potassium and sodium was studied using DFT 197 on a previously developed hydrochar model with furan rings. 198 A second study developed a model of graphitized hydrochar to study the sorption of methyl orange and methylene blue on a Fe-doped porous graphite hydrochar derived from the HTC of dry cotton straw.…”