Biomass-based cellulose hydroxyapatite nanocomposites for the efficient sequestration of dyes: Kinetics, response surface methodology optimization, and reusability

In this study, cellulose hydroxyapatite nanocomposite (CBG@HAP) is used effectively to adsorb dyes such as methylene blue (MB), crystal violet (CV), brilliant green (BG), and Congo red (CR). The X-ray diffraction investigation of CBG@HAP confirms the crystalline structure of CBG@HAP. The surface area investigated by Brunauer–Emmett–Teller (BET) for CBG@HAP is 16.1995 m 2 /g, indicating a mesoporous structure. The adsorption efficiency of CBG@HAP was based on factors such as pH (2–10), contact time (5–240 min.), concentration (10–100 mg/L) of adsorbate, and temperature (298–308 K). The CBG@HAP exhibits a monolayer sorption capacity of 99.009 mg/g for MB at pH 7, 69.44 mg/g for CV at pH 6, 192.32 mg/g for BG at pH 6, and 120.48 mg/g for CR at pH 6. The CBG@HAP was accurately fitted by the Langmuir isotherm and exhibited kinetics of McKay and Ho order at an equivalence point of 120 min for all the dyes. The CBG@HAP exhibits endothermic, spontaneous, and physisorption toward all the dyes. Using central composite design response surface methodology, the experimental data were statistically optimized. The analysis revealed that the concentrated sodium hydroxide solution effectively desorbs MB (93.67%), CV (97.65%), and BG (91.21%), whereas the 0.1 M HCl solution effectively desorbs CR (98.43%).