Doehlert design as optimization approach for the removal of Pb(II) from aqueous solution by Catalpa Speciosa tree leaves: adsorption characterization

Abstract

A B S T R A C TCatalpa speciosa tree leaves were used to remove Pb(II) from aqueous solutions. Removal process was optimized by applying experimental design strategy. Optimization was based on the application of a two-level full-factorial design for screening the significant variables followed by a Doehlert design to find out an appropriate model which leads to determine the optimum conditions. The empirical models were developed in terms of effective factors: pH, initial concentration of metal ion C m and sorbent mass(s) have been found statistically adequate to describe the process responses, that is, removal percent and the capacity uptake of Pb(II). The multiresponse optimization of Pb(II) removal process has been carried out using desirability function approach. To this end, Derringer's desirability function (D) has been applied for mathematical optimization of the simultaneous multiresponse problem. Thus, the optimum conditions of Pb(II) removal process have been found as: pH = 4.43, s = 0.07 g, and C m = 104 mg L −1 . Responses were confirmed by experiments 86 and 14.7 mg g −1 for R% and q, respectively. The morphology and structure of biosorbent during adsorption process was characterized by FT-IR spectroscopy, X-ray diffraction and scanning electron microscopy techniques. Experimental data were also fitted to various isotherm models. Potentiometric titration, pH PZC , and the competitive effect of alkaline and alkaline earth metal ions during the loading of Pb(II) indicate that ion exchange is the predominant mechanism for the adsorption of Pb(II) by C. speciosa tree leaves.

Hybrid central composite design optimization for removal of Methylene blue by Acer tree leaves: characterization of adsorption

“…If E = 8-16 kJ mol −1 , then chemical ionexchange dominates the reaction. If E < 8 kJ mol −1 , then physical biosorption takes place, while chemisorption processes have adsorption energy in the range of 20-40 kJ mol −1 [30,33,34,[46][47][48][49][50][51]. The mean free energy of biosorption (E) is found to be 31.6 kJ mol −1 .…”

“…3) [43][44][45][46][47][48][49][50][51]. The Langmuir model suggests that pollutant removal from the aqueous phase occurs on homogeneous surfaces by monolayer sorption without interactions between sorbate molecules, and the adsorption of each molecule onto the surface has equal adsorption activation energy.…”

“…According to the Morris and Weber theory, a plot of q t vs. t 1/2 should be linear if intraparticle diffusion is involved in the adsorption process, and if this line passes through the origin, then intra-particle diffusion is the rate-controlling step [45][46][47][48][49][50][51].…”

“…Such effective dye elimination in a short period of time would be privileged over other low-cost adsorbents when exploiting industrial wastewater. To understand the mechanism of the biosorption process and determine the rate of the dominating step, the biosorption data were analyzed using the three simplest kinetic models: pseudo-first-order, pseudo-second-order, and intra-particle diffusion [45][46][47][48][49][50][51]. The best-fitted model was chosen according to the linear regression coefficient of determination, R 2 values.…”

“…To quantitatively compare the applicability of each model, an error function is required. As a result, normalized standard deviation (Δq), the coefficient of determination (R 2 ), and Chi-square (χ 2 ) statistics are calculated as follows [44,46]:…”