Controlled growth and composition of multivariate metal-organic frameworks-199 via a reaction-diffusion process

In this paper,we exploit our prior successful synthesis of MOF-199 single crystals using the reaction-diffusion framework(RDF),to synthesize multivariate metal-organic frameworks(MTV-MOFs)version with enhanced properties.The MTV-MOFs are synthesized by creating defects within the MOF-199 crystal structure by integrating organic linkers entailing different functional groups.Accordingly,5-aminoisophthalic acid(NH_(2)-BDC)and 5-hydroxyisophthalic acid(OH-BDC)are separately mixed with 1,3,5-benzenetricarboxylic acid(BTC)in three different starting ratios of X-BDC:BTC(1:3,1:1)and(3:1).The effects of this linker on the morphology of the synthesized MTV-MOFs,their thermal stability,and their surface area are investigated.The extent of the incorporation of the linkers in the framework is elucidated via^(1)H-NMR spectroscopy and it is shown that the incorporation varies as a function of the location along the tubular reactor,a characteristic of RDF.The enhanced properties of the synthesized MTV-MOFs are further demonstrated by measuring its adsorptive capability for methylene blue(MB)and rhodamine B(Rh B)in aqueous solution,and compared with that of the as-synthesized MOF-199.The kinetic and thermodynamic studies reveal that MTV-MOFs with the ratio of X-BDC:BTC(1:1)exhibit the best uptakes of MB(263 mg/g)for X=OH and Rh B(156 mg/g)for X=NH_(2).The adsorbents are also easily regenerated for three consecutive cycles without losing their efficiency.We finally demonstrate that MTV-MOFs can be designed to tune the dye removal selectivity and enhance the removal capacity of both MB and RhB in a binary aqueous solution of these dyes.