By incorporating three organic carboxylic acids with different lengths

fumaric (FUM)

1

4-benzene- dicarboxylate (BDC) and 4

4'-biphenyl-dicarboxylate (BPDC) acids

three novel Hf-based metal-organic frameworks (MOFs)

Hf-FUM

Hf-BDC and Hf-BPDC

were synthesized using a solvothermal method combined with conventional electric heating. These MOFs were characterized by various experimental techniques including PXRD

N2 adsorption

TG and SEM. Moreover

the stabilities of these materials were examined by soaking the samples in water. The PXRD results reveal that all of these Hf-based MOFs have a topology similar to that of UiO-66(Zr)

and Hf-FUM is stable up to 400 ℃ while Hf-BDC and Hf-BPDC remain stable at 500 ℃. The structures of Hf-FUM and Hf-BDC are water-resistant

while that of Hf-BPDC will decompose after water treatment. On the basis of the adsorption isotherms of CO2

N2 and CH4 at 298 K

the effect of pore size on the separation of CO2/N2 and CO2/CH4 systems were also investigated. It is found that Hf-FUM with the smallest pore size possesses the highest adsorption selectivity for CO2 over N2 and CH4. This is the first study on the performance of Hf-based MOFs for gas separation

and the knowledge obtained in this work provides a foundation for the design of new nanoporous materials towards CO2 capture from various gas mixtures.