One-pot synthesis of quaternized microcrystalline cellulose obtained from soybean hulls

A novel quaternized microcrystalline cellulose (Q-MCC) was obtained through a one-pot synthesis using agro-industrial waste, specifically soybean hulls (SBH), as the starting material. This work focuses on discussing the synthesis, physicochemical characterization, and application of Q-MCC, particularly its potential use in the removal of industrial textile dyes. The material underwent various characterization techniques, including Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction spectroscopy (XRD), scanning electron microscopy (SEM), optical microscopy, thermogravimetric analysis/differential thermal analysis (TGA/DTA), and differential scanning calorimetry (DSC). Additionally, Kjeldahl analysis, swelling measurements, and determination of the pH at the zero-point charge (pHzpc) were performed. FTIR spectroscopy confirmed the presence of attached quaternary ammonium groups. SEM and XRD analysis of Q-MCC revealed that the material consisted of short fibers with an average length of 30.93 µm and exhibited an increased crystallinity index of 76.4 %, respectively. Moreover, the pH at the point of zero charge (pHpzc) indicated that the adsorbent displayed a cationic nature across the tested pH range. The modification of SBH led to enhanced water absorption, and excellent dye removal results were achieved using two types of dyes: Direct Black 22 (DB 22) and Reactive Orange 122 (RO 122). To further investigate the behavior of Q-MCC in the adsorption of DB 22 dye, various studies were conducted, including kinetic, adsorption, thermodynamic analyses, and Weber-Morris intraparticle diffusion analysis. The kinetics results demonstrated that more than 90 % of the dye was adsorbed within just one minute of contact and were better represented by the pseudo-second order model, while the maximum adsorption capacity was approximately 470 mg/g. The experimental data fit very well with the Langmuir isotherm model. The adsorption process was determined to be exothermic, and the mechanism was proposed to be electrostatic interaction between the quaternary ammonium moiety and negatively charge anionic dyes. Finally, the Weber-Morris study suggested that both film diffusion and intraparticle diffusion contribute to the adsorption process.