Design of a Sustainable Polysaccharide‐Lignocellulosic‐Mineral Granular Biocomposite Sorbent for Methylene Blue Removal

ABSTRACT Four granular biocomposite adsorbents containing spent coffee grounds (SCG), eggshells (ES), and chitosan (Chi) for remediation of waterborne methylene blue (MB) were prepared. The role of epichlorohydrin (ECL) crosslinking and variable NaOH concentration (a = 0.5 M, b = 1.8 M) during the adsorbent synthesis was investigated for its role on the MB adsorption capacity ( Q m ). Materials characterization employed complementary methods ( 13 C solids NMR spectroscopy; thermogravimetry; BET analysis). The Sips isotherm model yielded equilibrium Q m values for non‐crosslinked (SCG80‐a (82 mg/g) and SCG80‐b (119 mg/g)), and crosslinked (SCG80‐ECL‐a (94 mg/g) and SCG80‐ECL‐b (139 mg/g)) at pH 6.5–7 and an adsorbent dosage of ca. 3 mg/mL of solution. Environmental conditions (< 20 mg/L MB) revealed dye removal (RE; %) from 90% to 95% with increased NaOH adsorbent treatment. Spiked river water with both 5 mg/L and 20 mg/L MB led to a decreased RE of 63% (0.5 M NaOH) and 76%–77% (1.8 M NaOH) versus lab water. Decreased RE values of 41%–47% and 49%–55% were observed in saline well water. Methanol regeneration yielded a slight drop in RE (%) after the initial cycle and remained stable after the second cycle up to 6 cycles. Increasing the NaOH concentration during adsorbent synthesis increases the MB adsorption capacity of SCG‐based adsorbents.