Biogenic Carboxylation of Granular Activated Carbon via Citrus aurantiifolia Juice for Fluoride Removal
Year: 2026
Type: article
Abstract: Excess fluoride (F⁻) in potable water matrices poses a critical global public health threat, including endemic dental and skeletal fluorosis across vulnerable populations. Conventional defluoridation techniques like electrocoagulation and ion exchange are frequently constrained by prohibitive operational cost, complex synthesis protocols, and infrastructure limitations in decentralized settings. Herein, we demonstrate a surface functionalization approach for granular activated carbon (GAC) using raw Citrus aurantiifolia (lime) juice as a naturally derived, citric-acid-rich modifying agent. The procedure employs food-grade, non-hazardous materials as an alternative to conventional analytical-grade chemical reagents. Following modification, surface carboxyl-group concentrations increased from 1.26 mmol/g for GAC to 1.98 mmol/g for lime-modified GAC (LGAC) and 1.85 mmol/g for citric acid modified GAC (CAGAC). XPS showed a corresponding increase in surface oxygen content, from 5.92 at% (GAC) to 12.29 at% (CAGAC) and 21.28 at% (LGAC), with distinct C–O and O–C = O contributions on LGAC. Despite a 47% reduction in BET surface area, LGAC exhibited an empirical maximum monolayer adsorption capacity (q max ) of 1.63 mg/g, making its thermodynamic performance statistically identical ( p > 0.05) to CAGAC (1.65 mg/g) and yielding > 85% enhancement over unmodified GAC (0.88 mg/g). Geochemical speciation modeling (PHREEQC) further elucidated a possible immobilization pathway in LGAC via localized aqueous metal-F⁻ complexation dynamics, which were absent in synthetic CAGAC systems. Robust sorption kinetics were maintained across environmentally pertinent pH range (pH 4.0–8.0) and under competitive ionic strength conditions with co-existing groundwater anions. Fixed-bed continuous-flow experiments with multicomponent synthetic groundwater showed that LGAC’s column capacity was 26% higher than that of GAC and ~ 89% of that of CAGAC. These findings validate Citrus aurantiifolia juice as a food-grade, bio-derived modifier, thereby lowering synthesis barriers and offering a practical approach for point-of-use (POU) defluoridation in resource-constrained settings.
Language: English
Topic: Fluoride Effects and Removal
Subfield: Water Science and Technology
Field: Environmental Science
Domain: Physical Sciences
Open Access status: hybrid
Estimated APC paid: $3,290
OpenAlex ID: W7225789836