Four different kinds of metal-organic framework (MOF) materials Zn-BTC, Cu-BTC, Cr-BTC, and Fe-BTC are incorporated into alginate, forming various hydrogels for n-hexane vapor adsorption. The cross-link networks between center cations of MOFs and alginate are verified by comparing the Fourier transform infrared characteristic peaks of the MOF/alginates with that of bare alginate. Interestingly, the MOF/alginate composites cross-linked by trivalent cations (Cr3+ and Fe3+) contain micropores while those cross-linked by divalent cations (Zn2+ and Cu2+) do not. The specific surface parameters of the as-prepared hydrogels are affected by the concentration of the alginate. In addition, the Fe-BTC/alginate performs the best n-hexane vapor adsorption capacity among the four kinds of composites. This study would be helpful for a better understanding of the effect of ionic cross-linking on the alginate hydrogel surface area parameters and provide basic knowledge and reference for expanding the applications of the MOF/alginate hydrogels.