Comparative Adsorption Parameters Study of Hg(II) and As(III) Ions in Aqueous Solution and Wastewater Using Cellulose Nanocrystals (CNCs) and Cellulose Nanofibers (CNFs) Modified with Aminomethylphosphonic Acid (AMPA)

The synthesis of cellulose nanocrystals (CNC) and cellulose nanofibers (CNF) from palm empty bunches (PEB) is carried out by using two different methods: hydrolysis by 70% H₂SO₄ at 45°C and ultrasonication for 120 minutes. The features of CNC appear in our previous published works. Under optimal conditions, the yield, crystallinity index, and crystal size of CNF were measured to be 86.52%, 76.28%, and 1.51 nm, respectively. A 3% AMPA solution was used to modify CNC and CNF, resulting in an improvement of their optimal parameters. During examination, the spectra of CNCs/AMPA and CNFs/AMPA revealed the presence of new groups, namely amino and phosphite groups of AMPA. Furthermore, the diffractogram of CNFs/AMPA exhibited multiple diffraction peaks that corresponded to the characteristic peaks of AMPA. The crystallinity index and crystallite size of CNFs/AMPA were determined to be 74.41% and 3.63 nm, respectively. The morphological investigation of CNFs/AMPA reveals that their mean length measures 320.42 nm, while their mean diameter measures 15.27 nm. The elemental composition of CNFs/AMPA was determined to be C (30.30%), O (43.71%), N (11.70%), and P (13.10%). CNCs/AMPA and CNFs/AMPA have successfully removed Hg(II) and As(III) ions from aqueous solution and river water with optimum conditions at pH 5 for Hg(II) ions and pH 8 for As(III) in 60 minutes of contact time. Adsorption of Hg(II) and As(III) ions with CNCs/AMPA and CNFs/AMPA both involve pseudo-second-order kinetic models and Langmuir isotherm models.