A Green, Economic Method for Bench-Scale Activation of a MIL-101(Cr) Nanoadsorbent

Research teams have been showing an increasing interest in using MIL-101(Cr) in a variety of applications, in recent years. Furthermore, the removal of unreacted terephthalic acid (ur-H2BDC) during post-synthesis purification is also among the greatest challenges in the synthesis of MIL-101(Cr), which if dealt with through simple, environmentally-friendly, and inexpensive methods can constitute a stride in the path to the commercial production and application of MIL-101(Cr). This research is focused on the development of a method based on the application of aqueous solutions of sodium bicarbonate (NaHCO3) with various concentrations, as well as applying various reaction times to remove ur-H2BDC to evaluate the efficiency of the method. The obtained results were compared to those of conventional activation methods, indicating the high efficiency of using a 0.06 M NaHCO3 solution for 24 h, which led to an acceptable BET surface area of 3271 m(2)center dot g(-1) without any damages to the framework as indicated by X-ray diffraction (XRD) analysis. The study also provides a novel approach to quantifying ur-H2BDC residuals (trapped inside of framework pores) using back-titration (1.67% residual ur-H2BDC in 1 g of the nanoadsorbent). CO2, CH4, and N-2 adsorption isotherms on the activated MILs were acquired using a volumetric laboratory facility at pressures ranging from 1 to 35 bar and 298 K. Data of the adsorption of CO2 on activated MIL-101(Cr)-NaHCO3 revealed great gas separation ability (23.1 mmol/g at 35 bar). According to the adsorbed ideal solution theory (IAST), the selectivity values of CO2/CH4 and CO2/N-2 were around 11.60 at 1 bar and 5.85 at 35 bar and 135.44 at 1 bar and 48.96 at 35 bar, respectively. Furthermore, the procedure was associated with bench-scale MIL-101(Cr) activation with satisfactory results.