Construction of crystal defect sites in N-coordinated UiO-66 via mechanochemical in-situ N-doping strategy for highly selective adsorption of cationic dyes

Alkaline N-compounds (pyrrole, dopamine and 2-methylimidazole) were applied to induce crystal defects on UiO-66 via mechanochemical in-situ N-doping strategy and their role on its selective adsorption for cationic dyes i.e. rhodamine B (RhB) and safranine T (ST) were investigated systematically. Alkaline N-compounds coordination were proved to simultaneously modulate pore sizes and intensify surface alkalinity of the original UiO-66. The crystal defects constructed 3-D multi-point adsorption structure, which dramatically enhanced specific adsorption for RhB and ST in binary system. Results showed that pyrrole coordinated UiO-66 possessed 30% enhancement in surface area (1549.1 m2/g) with micropores at 9 and 12 Å (larger defects in UiO-66). Furthermore, temperature programmed desorption (H2O and NH3) and corrosion resistance test concluded that N-doped UiO-66 possessed improved alkali-resistance and higher alkaline surface compared to pristine UiO-66. Separation performance revealed that pyrrole-doped UiO-66 showed two times enhanced adsorption capacity for RhB (384.1 mg/g), and 223 times higher selectivity for equimolar RhB/ST than that of parent UiO-66. Textural characterization, DFT simulation and electronic factors concluded that proper defect size and alkaline surface endow the novel defective UiO-66 excellent selectivity, adsorption and recycling performances. Thus, our in-situ N-doping strategy has guiding significance to design MOFs with special and useful defects for unique selective adsorption system beyond the circle of organic dyes on industrial level.