Carboxylate-intercalated layered double hydroxides for H2 sorption

Li-Al layered double hydroxides (LDHs) intercalated with two different arylate anions, terephthalate (TA) and p-toluate (pTA), and those mixed with acetate ions were prepared by a one-pot co-precipitation method. The hydrogen storage capacities of the resultant LDHs and those intercalated with carbonate were examined. The XRD patterns showed that all LDHs with different anion species had well-defined crystalline structures and the incorporation of organic anions was proved by IR spectroscopy and thermal analysis. The surface areas and pore volumes of the LDHs increased when a portion of the interlayer arylate anions was replaced by acetate ions (aa(-)). The adsorption enthalpies of LDHs toward H-2 varied with the interlayer anions and increased in the order of pTA(-) similar to aa(-) < CO32- < TA(2-). However, the adsorption enthalpies became directly proportional to the micropore surface areas and volumes for LDHs containing mixed arylate and acetate ions. The latter materials also showed higher hydrogen uptakes than those intercalated with pure organic anions. Higher hydrogen uptakes were observed on TA-intercalated LDHs than on pTA-intercalated LDHs. The maximal H-2 uptake per micropore surface area of the LDH materials was higher than that of MOFs reported in the literature.