A rational design of layered metal-organic framework towards high-performance adsorption of hazardous organic dye.

Water pollution originated from organic dyes is endangering the survival and development of human society, however, the adsorbents with high capacity (>5000 mg·g-1) and fast removal (≤30 min) of Congo Red (CR) in aqueous solution have been not reported. In present work, an acid-base stably layered MOF, [Cd(H2L)(BS)2]n·2nH2O (L-MOF-1, H2L = N1,N2-bis(pyridin-3-ylmethyl) ethane-1,2-diamine, BS = benzenesulfonate), has been hydrothermally prepared. L-MOF-1 exhibits high-performance adsorption of CR in aqueous solution at room temperature. The experimental adsorption capacity of L-MOF-1 adsorbent towards CR can reach up to about 12000 mg·g-1 in 20 min under the range of pH = 2.2~4.7, which has been the excellent adsorbent bearing larger capacity and faster adsorption to CR till now. The spontaneous adsorption process can be described by pseudo second-order kinetic and Langmuir isotherm model. Meanwhile, the L-MOF-1 absorbent has highly positive Zeta potential in acid condition (even pH = 2.2, Zeta potential = 36.2 mV). The good adsorption performance mainly originates from the strong electrostatic attraction between L-MOF-1 and CR in acidic condition, as well as accompanying diverse hydrogen bonds and π···π stacking interactions. Furthermore, L-MOF-1 absorbent has good selectivity, and can be reused for five times through simply washing and its adsorption efficiency is hardly reduced, therefore, it would be a potential absorbent for effectively removing the CR from dye waste-water.