L-Histidine Immobilized Montmorillonite for As(III) Adsorption and Statistical Verification of Data by PDF, AICcorrected and AADR Models

Abstract L-Histidine immobilized montmorillonite is prepared and used as an adsorbent for removal of As(III) from aqueous solutions. The L-Histidine immobilized montmorillonite is characterized by FTIR, XRD, TGA and PZC techniques that confirmed the successful insertion of Histidine into interlayer of montmorillonite structure. The various parameters such as pH, reaction time, temperature, concentration of As(III) and adsorbent dosage are optimized to obtain maximum As(III) adsorption. It is observed that usually the removal of As(III) is increased with increasing the amount of adsorbent, contact time, temperature and till pH 6. The results showed that all these adsorption parameters greatly influenced the adsorption process. The various adsorption isotherm models including Langmuir, Freundlich, Temkin and Dubinin-Radishkevich (DR) as well as kinetics models are applied to the adsorption data. The Langmuir isotherm and pseudo-second order kinetics model are well-fitted to the adsorption data. Further, the probability distribution function (PDF) is applied that verified the adsorption data well while the Akaike’s Information Criterion (AICcorrected) and Absolute Average Relative Deviation (AARD) statistical models supported the best fit adsorption isotherms. The PDF model have provided a good statistical identification of adsorption parameters, adsorption rates and maxima whereas AICcorrected and AARD models revealed the well-fitting of Langmuir adsorption isotherm model in correlating the equilibrium data. Thermodynamic parameters (ΔH, ΔS, ΔG) proved the endothermic and spontaneous nature of adsorption process along with entropical changes occurring at solid-solution interface. The results showed that L-Histidine immobilized montmorillonite is an excellent material for As(III) adsorption with maximum adsorption capacity of 87.7 mg g−1.