Adsorption Characteristics of Allura Red AC onto Sawdust and Hexadecylpyridinium Bromide-Treated Sawdust in Aqueous Solution

• Published in: ACS omega 2020-06, Vol.5 (22), p.13358-13374
• Main Authors: Saha, Tapan Kumar, Bishwas, Raton Kumar, Karmaker, Subarna, Islam, Zinia
• Format: Article
• Language: English
• ISSN: 2470-1343; 2470-1343
• DOI: 10.1021/acsomega.0c01493

The Allura red AC (ARAC) dye adsorption onto natural sawdust (NSD) and hexadecylpyridinium bromide-treated sawdust (MSD) was investigated in aqueous solution as a function of contact time, solution pH, particle size, adsorbent dosage, dye concentration, temperature, and ionic strength. The adsorbents were characterized by Fourier transform infrared spectroscopy and X-ray diffraction crystallography. The dye adsorption onto both adsorbents was confirmed by field emission scanning electron microscopy and energy-dispersive X-ray spectroscopy. The maximum dye adsorption was found within 120 min at pH 2.0 for NSD and pH 3.0 for MSD, respectively, with a particle size of 0–75 μm and an adsorbent dosage of 0.07 g/50 mL ARAC dye solution (50 μmol/L). The batch adsorption kinetic data were followed by the pseudo-second-order kinetic model rather than the pseudo-first-order and Elovich kinetic models. Equilibrium adsorption isotherms were explained by the Langmuir isotherm model, and the maximum extent of adsorption was found to be 52.14 μmol/g for NSD and 151.88 μmol/g for MSD at 55 °C. The values of activation energy ( E a ) and thermodynamic parameters (Δ G ⧧ , Δ H ⧧ , Δ S ⧧ , Δ G °, Δ H ° and Δ S °) proved that the ARAC dye adsorption onto both adsorbents NSD and MSD is a spontaneous-endothermic physisorption process. ARAC (98–99%) was released from dye-loaded adsorbents in aqueous solution (pH ≥ 12) within 120 min. The adsorbents NSD and MSD were reused for a second time without significant loss of their adsorption efficiency.