Highly efficient and selective Hg(II) removal from water by thiol-functionalized MOF-808: Kinetic and mechanism study

Mercury pollution poses a serious threat to the ecological environment and public health due to its high toxicity and persistence, but there is still a lack of rapid and effective Hg(II) removal technology, especially emergency response of Hg(II) leakage. Herein, an effective metal-organic framework adsorbent, MOF-808-SH, was fabricated by grafting thioglycollic acid on MOF-808 for Hg(II) removal. The MOF-808-SH demonstrated high adsorption capacity of 977.5 mg/g, impressively ultrafast adsorption kinetics (Co = 10 mg/L, removal > 99 % in 10 s) with a rate constant k of 36.89 g mg(-1) min(-1), which is dozens of times faster than that of ever reported Hg (II) adsorbents. Batch experiments show that MOF-808-SH exhibits high selectivity toward Hg(II) with a distribution coefficient K-d as high as 5.0x10(6) mL/g. Moreover, MOF-808-SH exhibits excellent recyclability with a negligible loss of capacity after 6 adsorption-regeneration cycles. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectrometry (XPS) unveil that the -SH groups in MOF-808-SH are the key adsorption sites, and specific inner-sphere coordination with Hg(II) is responsible for the high selectivity. In addition, large surface area, well-developed porous structures and high -SH loading of MOF-808-SH reasonably explains ultrafast kinetics and high adsorption capacity for Hg(II). This study indicates the potential of MOF-808-SH to remove Hg(II) from wastewater.