A novel Chitosan-Barbituric acid hydrogel supersorbent for sequestration of chromium and cyanide ions: Equilibrium studies and optimization through RSM

The objective of this study is to transform chitosan biopolymer by crosslinking with barbituric acid into an amine-rich product that could be applied as a water treatment agent. Chitosan-barbituric acid (CBA) was syn-thesized by lyophilization process and characterized using FT-IR, XRD, TGA-DTA, SEM-EDX, BET surface area and BJH pore size distribution analysis. The pHpzc was found to be 7.7 indicating applicability towards both cations and anion adsorption. The CBA was used for seizure of CrVI and CN- from aqueous solutions in batch adsorption as well as fixed bed column experiments. Response surface methodology (RSM) was used as a sta-tistical tool to optimize the functioning parameters resulting in more than 90 % removal of these ions. As shown by isotherm and kinetics data, Langmuir isotherm and pseudo second order kinetics exhibited a good fit for the adsorption process. The maximum adsorption capacities of CBA towards CrVI and CN- evaluated using Langmuir isotherm fitment were 534.75 mg g-1 and 251.66 mg g-1 at pH 4.0 and 6.0 respectively. Thermodynamic studies indicated spontaneous and enthalpy driven course with large negative enthalpy changes of-56.39 and-31.81 kJ mol-1 respectively. Fixed bed column studies showed that the material could be used for larger sample volume treatment even at 200 mg/L CrVI and 100 mg/L CN-1 concentration. Regeneration studies of adsorbent was conducted over five adsorption-desorption cycles with removal efficiency more than 50 %indicating reusability of the adsorbent. Analysis of adsorbent sustainability revealed that the synthesis was eco-friendly as indicated by low value of E-factor of 0.32.