Immobilization of Bacillus subtilis bacteria into Biohybrid Crosslinked Chitosan-glutaraldehyde for acid red 88 Dye Removal: Box-Behnken Design Optimization and Mechanism Study

Herein, a novel biomaterial of crosslinked chitosan-glutaraldehyde combined with Bacillus subtilis biomass (CHS-GLU/BCL) was synthesized via hydrothermal synthesis to effectively remove the anionic dye (Acid red 88; AR88) from synthetic wastewater solution. The physicochemical properties of the CHS-GLU/BCL biomaterial were characterized using XRD, SEM-EDX, FTIR and pH(pzc) studies. To optimize the adsorption efficiency of CHS-GLU/BCL for AR88 dye removal, a Box-Behnken design (BBD) was utilized. The experiment utilized three independent variables including, the dosage of CHS-GLU/BCL (A: 0.02-0.1 g/100 mL), the contact time (B: 5-30 min), and the pH of the AR88 solution (C: 4-10). The investigation of adsorption kinetics confirms that the AR88 dye adsorption onto the CHS-GLU/BCL biomaterial mainly follows the pseudo first order (PFO) versus the pseudo second order (PSO) kinetic model. Moreover, the isotherm data fits the Langmuir isotherm model with R-2 of 0.98. The maximum monolayer adsorption capacity (q(max)) of AR88 dye onto CHS-GLU/BCL biomaterial was determined to be 148 mg/g at acidic pH conditions (pH = 4.2). The adsorption mechanism of AR88 and dye onto the biomaterial surface can be related to many contributions, such as hydrogen bonding, n-pi interactions, and electrostatic attraction. A reusability study indicated that the CHS-GLU/BCL adsorbent successfully adsorbed AR88, where the reduced adsorption across five cycles is related to structural changes of the biocomposite. Hence, the biomaterial CHS-GLU/BCL has a good affinity for adsorbing anionic dye species from aqueous media.