Functionalized locust bean pod (Parkia biglobosa) activated carbon for Rhodamine B dye removal

Abstract

Activated carbon prepared from locust bean husk was modified using ortho-phosphoric acid (ALBP) and used to scavenge Rhodamine B (RhB) dye from aqueous solutions. Characteristic features of the adsorbents were investigated using SEM, FTIR, pH pzc and Boehm Titration (BT) techniques respectively. Batch studies were used to determine the influences of contact time, temperature and initial Rh–B dye concentrations. Adsorption data were analysed using four different isotherm models. The maximum monolayer adsorption capacity of 1111.1 mgg -1 was obtained for RhB dye adsorption. The kinetics of the adsorption process was studied using pseudo-first-order, pseudo-second-order Elovich and intraparticle diffusion models respectively. The experimental data was best described by pseudo-second-order kinetic model. Favourability of the process of adsorption was also established by the separator factor (R L ) value ranging from 0 and 1, while the mean energy of adsorption (E a ) was 1.12 kJmol -1 suggesting that the removal of Rh–B dye from aqueous solution followed a physisorption process. For the thermodynamic investigations, the positive values of ΔS (280.956 Jmol −1 K −1 ) indicates the affinity of adsorbent for the Rh–B dye uptake and increase randomness at the solid–solution interface during adsorption of Rh–B dye onto the surface of the active sites of ALBP. The negative value of ΔG (-31.892 to -26.355 kJmol -1 ) depicts the spontaneity and feasibility of the adsorption process. The cost analysis provides a simple proof that ALBP (42.52 USD per kg) is approximately six times cheaper than Commercial Activated Carbon, CAC (259.5 USD per kg). The present study therefore established the suitability of ALBP for effective removal of Rh–B dye from aqueous solutions.

Rhodamine B dye sequestration using Gmelina aborea leaf powder

“…Since the value of E a obtained were less 80 kJ/mol, it suggests that the process of adsorption followed physio-sorption mechanism. These observations agreed with other findings reported in several studies [4,39,76,108,127,128].…”

“…To evaluate the surface acidity and basicity of GAL; two assumptions were made: (i) acidic groups would only be neutralized by NaOH, Na 2 CO 3 or NaHCO 3 and (ii) all basic groups are neutralized by HCl. The concentration of the acidic and basic groups are shown in Table 4, The basic group value was lower than the acidic group indicating that the adsorbent surface is predominantly acidic, Similar result was obtained in the adsorption of Ba 2þ and Fe 2þ ions [107] from aqueous solutions using activated carbon produced from mazot ash [108]. Acidic functional groups results in increased adsorption of RhB dye molecules [109,110].…”

“…These molecules are unable to enter the pores as a result of their size thereby resulting in lower percentage removal at high pH. Optimum adsorption at pH of 3 has been previously reported in one of our studies [53,108]. Figs.…”

“…The thermodynamic parameters (Table 8) indicate that the value ΔH was 11.51 kJ/mol; this positive value reveals an endothermic nature of the process of adsorption. The positive value of (ΔS, 0.388 kJ/mol K) revealed that the affinity of adsorbent for RhB dye uptake occurred with increasing randomness at the interface of GALAC-RhB dye system [108,126]. However, ΔG values were -22.71, -19.56, and -18.19 kJ/mol at 303K, 313K, 323K respectively, confirming that the process of adsorption was endothermic, with an increase in degree of disorderliness.…”

“…Thermodynamic parameters such as ΔG, ΔH and ΔS are significant features in adsorption systems [108]. The values of ΔG, ΔH and ΔS were calculated using Eqs.…”