Indigo Carmine Dye Adsorptive Removal by Polyethylene Glycol-Modified Hydroxyapatite Nanoparticles as an Efficient Adsorbent

Polyethylene glycol-modified hydroxyapatite nanoparticle was employed as a new and effective adsorbent for the removal of indigo carmine dye from an aqueous solution. The synthesized adsorbent was characterized by X-ray diffraction (XRD), Fourier transformation infrared spectroscopy (FTIR), energy-dispersive X-ray spectroscopy (EDX), and field-emission scanning electron microscopy (FESEM). In addition, the effects of factors such as pH, temperature, dye concentration, time, and amount of adsorbent on the removal efficiency or adsorbent capacity were investigated. The pH, temperature, and concentration (C) of dye solution positively affect q while the temperature and adsorbent dosage (m) negatively affects q. For R%, the m and C effects are inverse. With the increase of pH, the amount of electrostatic attraction between the adsorbent surface and dye increases. It will lead to an increase in dye adsorption. The optimum conditions were obtained as t = 60 min, pH = 7, T = 25C, m = 0.06 mg, and C = 700 mg.L-1. To study the equilibrium behavior of adsorbent-adsorbate interaction, Langmuir, Freundlich, Sips, Dubinin-Radushkevich, and Temkin isotherms were considered. Experimental data were well described by Sips with R-2 = 0.9927. The maximum adsorption capacity (q(max)) of the Sips model was 129.3 (mg.g(-1)). The kinetic experimental data obey the pseudo-second-order model (R-2 = 0.9989). Based on the negative value of thermodynamic parameters including increment H degrees, increment S degrees, and increment G degrees, the adsorption process is exothermic and spontaneous chemisorption at various temperatures (298, 308, 318, and 328 K). Based on the effect study of the presence of Mg2+, Ca2+, K+, and Na+ ions on the removal efficiency of indigo carmine dye, the adsorption capacity decreases with increasing salt concentration, especialy for the + 2 charged ions. Furthermore, the desorption of indigo carmine dye from the modified hydroxyapatite nanoparticles was evaluated with NaOH, HCl, HNO3, and CH3COOH. Also, indigo carmine removal by this adsorbent from tap water was investigated in comparison with laboratory conditions.

Automated summary

Polyethylene glycol-modified hydroxyapatite nanoparticle was used as an effective adsorbent for removing indigo carmine dye. Various factors such as pH, temperature, dye concentration, time, and adsorbent dosage were investigated for their effects on the removal efficiency. The results showed that pH, temperature, and dye concentration positively affected the adsorbent capacity, while temperature and adsorbent dosage had a negative effect. Langmuir, Freundlich, Sips, Dubinin-Radushkevich, and Temkin isotherms were considered to study the adsorbent-adsorbate interaction.