Silica rich MIL-101(Cr) for enhanced hydrogen uptake

Abstract

Hybrid composite of MIL-101 with silica rich rice husk ash (RHA) was fabricated to explore such materials for improved low pressure hydrogen storage applications, compared to the well explored carbon based composites of MIL-101. RHA–MIL-101 was prepared by in situ incorporation of RHA in MIL-101 during the synthesis, under hydrothermal conditions. The incorporation of RHA in MIL-101 was confirmed by P-XRD, FTIR, TGA, SEM, EDS, and N2 adsorption and desorption isotherms studies. The as-synthesized RHA–MIL-101 composite displayed enhanced BET surface area (8.6% compared to bare MIL-101), whereas AC–MIL-101 showed an enhancement of 12.7% in BET surface area compared to bare MIL-101. Hydrogen uptake properties of these materials were evaluated at 77 K and 1 bar. Despite that RHA–MIL-101 exhibited lower surface area as compared to AC–MIL-101, the hydrogen uptake capacities of RHA–MIL-101 reached an enhanced value of 1.54 wt%, which is obviously higher than the bare MIL-101 (1.40 wt%) and AC–MIL-101 (1.48 wt%) by 9.1% and 5.7%, respectively, as well as comparable to most of the reported carbon incorporated MOFs. It has been observed that improved hydrogen uptake properties was due to the bifunctional properties of the synthesized RHA–MIL-101, abundance of silanol bonds of RHA (which shows high affinity towards H2 molecules), and tuned porous properties of RHA–MIL-101. Moreover, hydrogen adsorption isotherms data of these materials were best fitted with three parameter non-linear adsorption equilibrium isotherm equations.