Facile synthesis of zinc-based organic framework for aqueous Hg (II) removal: Adsorption performance and mechanism

Mercury (Hg) ions can lead to a serious impact on the environment; therefore, it was necessary to find an effective method for absorbing these toxic Hg ions. Here, the adsorbent (Zn-AHMT) was synthesized from zinc nitrate and 4-amino-3-hydrazine-5-mercapto-1,2, 4-triazole (AHMT) by one-step method and, characterized the microstruc-ture and absorption performance by fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), Thermal Gravimetric Analyzer (TGA) and X-ray photoelectron spectroscopy (XPS). Through a plethora of measurements, we found that the maximum adsorption capacity was 802.8 mg/g when the optimal pH of Zn-AHMT was 3.0. The isothermal and kinetic experiments confirm that the reaction process of Zn-AHMT was chemisorption, while the adsorption process conforms to the Hill model and pseudo second order kinetic model. Thermodynamic experiments showed that the adsorption process was spontaneous and exothermic. Selective experiments were performed in the simulated wastewater containing Mn, Mg, Cr, Al, Co, Ni, Hg ions. Our results showed that the Zn-AHMT has a stronger affinity for Hg ions. The removal rate of Zn-AHMT remained above 98%, indicating that the Zn-AHMT had a good stability validated by three adsorption-desorption repeatable tests. According to the XPS results, the adsorption reaction of Zn-AHMT was mainly attributed to the chelation and ion exchange. This was further explained by both density functional theory (DFT) calculation and frontier molecular orbital theory. We therefore propose the adsorption mechanism of Zn-AHMT. The adsorption reaction facilitates via the synergistic action of S and N atoms. Moreover, the bonding between the adsorbent and the N atom has been proved to be more stable. Our study demonstrated that Zn-AHMT had a promising application prospect in mercury removal.

Automated summary

By synthesizing a novel adsorbent Zn-AHMT, a method with strong adsorption capacity for wastewater containing Hg ions was successfully discovered, demonstrating promising application prospects for this adsorbent.