A comparison of adsorption capacity of several synthesis methods of cellulose-based absorbent towards Pb(II) removal: Optimization with response surface methodology

The effects of various synthesis methods of a novel biodegradable magnetically recyclable cellulose-based adsorbent (a magnetized modified silica aerogel) on Pb(II) removal efficiency were studied. QSM (quince seed mucilage) was modified via hydrothermal and ultrasonic modes. Oven-drying and freeze-drying procedures were then used to obtain the final adsorbents. The adsorbents were named A1 to A4 and B1 to B4, depending on the synthesis and drying techniques. XRD, FTIR, BET, and SEM are characterization techniques for identifying the adsorbents. Average crystallite sizes of 15.5, 8.3, 10.9, and 2.7 nm were obtained for A1, A2, A3, and A4 samples (Scherrer formula). SEM image confirmed a Sticky bullets-like morphology. The pHpzc values of 3.4, 6.0, and 4.1 were also determined for Fe-silica aerogel, Fe-QSM, and Fe-silica aerogel-QSM samples. The highest adsorption efficiency of the A2 adsorbent towards Pb(II) cations was followed via the experimental design by the RSM (response surface methodology) approach. ANOVA results showed model F value 185 (>F-0.05,F- 14,F- 15 = 2.42) and LOF F-value of 0.3831 (<F-0.05,F- 10,F- 5 = 4.74) at a 95 % confidence interval. The center point run conditions were catalyst dose: 7 g/L, pH: 3.2; C-Pb: 11 mg/L, and contact time: 55 min, while the optimal run conditions were adsorbent dose: 1.0 g/L; pH: 2.6; C-Pb: 7 mg/L; and contact time: 80 min with about 94 % Pb(II) removal efficiency. The adsorption mechanism was studied, and correlation coefficient (R-2) values of Langmuir (0.9814), Freundlich (0.9328), Temkin (0.8898), and Redlich-Peterson (0.9977). They have recommended that the adsorption process fit best with the Langmuir and Redlich-Peterson models. A kinetic study revealed that adsorption was well described by pseudo-second-order kinetics. The thermodynamic studies showed a spontaneous and endothermic adsorption process.