Strontium (II) Biosorption Studies on Starch-Functionalized Magnetic Nanobiocomposites Using Full Factorial Design Method

Abstract

The purpose of this research was to fabricate starch based magnetic nanobiocomposites using two different starch types (corn and wheat) and to examine the effects of some experimental parameters (such as starch concentration, NaOH concentration and aging time of nanoparticles) that play a role in the synthesis products. The characterization of the starch-based magnetic-nanobiocomposite materials were realized with several techniques. In the previous study, MW_S3 and MC_S3 from starch stabilized magnetite nanobiocomposites were selected for further studies with smaller particle size and large surface areas, as a result of calculations based on XRD results and BET surface area. The usability of starch-based magnetic-nanobiocomposite materials, which can provide rapid separation with their magnetic properties and are not toxic, in removing Sr(II) ions from aqueous solutions has been investigated. The parameters affecting the biosorption were investigated using a full factorial experimental design. In the biosorption study, pH, temperature, initial Sr(II) concentration and contact time were determined as four independent variables. The regression coefficients were found using the least squares method and the response surface graphs were created according to the polynomial equation obtained from the full factorial experimental design. ANOVA (analysis of variance) analysis within the 95% confidence interval of the model applied for the full factorial experimental design was examined and the compatibility of the model with the experimental findings was examine. It is seen that the biosorption of Sr(II) on MW_S3 and MC_S3 nanobiocomposites increases with increasing concentration in the range of 25–75 ppm. As a result of the regression analysis, it was observed that pH was statistically significant (p < 0.05) and had an increasing effect for MW_S3. Evaluating the results obtained, it was found that the combined effects of the parameters on the biosorption of Sr(II) on MW_S3 adsorbent were not significant, but the combined effects of concentration and time were only significant on the adsorption of Sr(II) on MC_S3 adsorbent. From the solution of the equation obtained in the full factorial experimental design, it has been determined that the optimum biosorption conditions for MW_S3 adsorbent are; pH is 7, temperature is 34.87 °C, initial Sr(II) concentration is 75 mg/L and contact time is 30 min. Optimum adsorption conditions for MC_S3 adsorbent were determined to be pH is 8, temperature is 34.46 °C, initial Sr(II) concentration is 74.83 mg/L and contact time is 59.54 min. The composition and chemical state of the magnetic nanobiocomposites were investigated by XPS analysis after Sr(II) biosorption. For the purpose of determine the adsorption model, the relevant parameters were calculated using Langmuir, Freundlich and Dubinin–Radushkevich isotherms. Gibbs free energy change, enthalpy and entropy values, which are the values of adsorption thermodynamics, were calculated.