Synthetic of functionalized magnetic titanium-based metal-organic frameworks to efficiently remove Hg(Ⅱ) from wastewater

Selective removal of Hg(II) by chitosan derivative covalently modified with double cross-linking agents abundant in N and S atoms

With rapid industrialization and urbanization, numerous wastewater contains elevated concentration of Hg(II), and its concentration must be reduced to the discharge limit, so as not to cause serious pollution to the environment. In this paper, a modified chitosan adsorbent material, AMT-DMTD-CS (CS = chitosan, AMT = 2-amino-5-mercapto-1,3,4-thiadiazole, DMTD = 1,3,4-thiadiazole-2,5-dithiol) was prepared. FT-IR, XPS, elemental analysis, and FE-SEM confirmed that AMT and DMTD were successfully grafted covalently onto CS, with BET analysis showing a specific surface area of 105.55 m2/g for AMT-DMTD-CS. Adsorption study suggests that the optimal pH environment for AMT-DMTD-CS to adsorb Hg(II) is 4.0, and the saturated uptake capacity reaches 687.17 mg/g at 318 K, even after eight regenerations, the removal is still maintained at 80.06 %. Moreover, the adsorption behavior is in perfect agreement with the pseudo-second order kinetic model and the Langmuir isotherm model. In addition, AMT-DMTD-CS shows quite favorable selectivity for Hg(II) in a variety of co-existing metal ions. According to the FT-IR and XPS analysis of AMT-DMTD-CS-Hg(II), the synergistic complexation of -OH, -NH2, -NH, CN, CS and -SH to Hg(II) is considered as the main reason that leading to the elevated adsorption capacity.

A novel magnetic Ti-MOF/chitosan composite for efficient adsorption of Pb(II) from aqueous solutions: Synthesis and investigation

In this investigation, a composite material comprising Ti-MOF and chitosan, denoted as BD-MOF(Ti)@CS/Fe3O4, was successfully designed for the efficient adsorption of Pb(II) from aqueous solutions. A comprehensive array of characterization techniques, including SEM, XRD, BET, FT-IR, and XPS, were meticulously employed to scrutinize the structural attributes and morphological features of the Pb(II) adsorbent. Notably, the material exhibits adaptability to a broad pH range, with adsorption efficiency reaching 99 % between pH 3 and 6. Kinetic studies reveal that the adsorption process of Pb(II) by BD-MOF(Ti)@CS/Fe3O4 adheres closely to a pseudo-second-order kinetic model. Impressively, within a short duration of 40 min, the adsorption efficiency can reach 85 %. Furthermore, the adsorption isotherm aligns with the Hill isotherm model, signifying cooperative adsorption. This observation underscores the synergistic interplay among the functional groups on the surface of BD-MOF(Ti)@CS/Fe3O4 in capturing Pb(II). As per the Hill model, the theoretical maximum capacity was an impressive 944.9 mg/g. Thermodynamic assessments suggested that the adsorption process was spontaneous, entropy increasing and exothermic. Even in the presence of various interfering ions, BD-MOF(Ti)@CS/Fe3O4 exhibited robust adsorption performance, thereby affirming its utility in complex environments. Moreover, the material demonstrates noteworthy reusability, sustaining effective Pb(II) removal across five consecutive cycles in aqueous solutions.