In situ modification of ZIF-67 with multi-sulfonated dyes for great enhanced methylene blue adsorption via synergistic effect

It is essential mean to adsorptive remove organic pollutants such dyestuff for water remediation. Herein in situ modification of the classic metal-organic framework ZIF-67 with –SO₃⁻ groups was easily achieved by the efficient adsorption of multi-sulfonated dyes due to the coordinative interaction between the unoccupied Co(II) of ZIF-67 and –SO₃⁻ of the dyes. Interestingly, highly efficient synergistic absorption of multi-sulfonated dyes towards methylene blue (MB⁺) upon ZIF-67 was discovered for the first time. The improved adsorption capacity of ZIF-67 for MB⁺ in presence of cotton blue (CB⁻) was measured with a record-high value of 5,857.9 mg/g. The underlying mechanism of the synergistic adsorption was probed, showing that, after the initial coordination between the –SO₃⁻ of the dyes and the unoccupied Co(II) of ZIF-67, the available –SO₃⁻ groups of multi-sulfonated dyes can interact with –N⁺(CH₃)₂ in MB⁺ and hence greatly improving the adsorption capacity of MB⁺.