Macro-structuring Uniform Metal–Organic Framework-Based Beads for Superselective Removal of Hg(II) from Water: Performance and Modeling

Abstract

Engineering nanocrystalline metal–organic frameworks (MOFs) into macroscopic granules is of vital significance to fulfill their real application in water treatment by resolving the operation difficulty (e.g., separation) and hydrolabil properties. In this study, a facile, environmentally benign, and cost-effective method was proposed to construct uniformly sized granular MOF-based beads (GMBs) (diameter ∼ 1.76 mm) for effective and selective mercury (Hg­(II)) removal. Specifically, the as-prepared GMBs demonstrated excellent Hg­(II) adsorption capacity (431.1 mg g–1 (2.15 mmol g–1) at 30 °C), fast kinetics (surface diffusion coefficient (D s) ∼ 5.58 × 10–11 m2 s–1), universal pH (1.0–11.0), high selectivity (K d > 2.5 × 107 mL g–1), and satisfactory anti-interfering ability of dissolved organic matters (DOMs). Benefiting from the mechanical strength and water resistance, the GMBs maintained great mechanical integrity and 99.0% removal efficiency after 20 cycles. Moreover, combined characterizations and experiments suggested that the proton exchange accompanied by Hg–S coordination mechanisms should account for high adsorption capacity and exceptional selectivity toward Hg­(II). Furthermore, the full-scale performance of GMBs under different operation conditions was systematically predicted and evaluated using the validated pore diffusion model (PDM). Overall, the proposed approach regarding GMB construction offers novel insight for promoting the practical applications of MOFs in water treatments.

Evaluating the Performance of Novel Cyclodextrin Polymer Granules to Remove Perfluoroalkyl Acids (PFAAs) from Water

“…More research is required to elucidate the rate-determining mechanisms for different PFAAs on CDP granules of different sizes and in the presence of more complex matrix constituents. The challenges encountered and described in this research are broadly relevant as more types of novel adsorbents are being discovered to address PFASs − and other emerging contaminants, , and more techniques to develop defined morphology of novel adsorbents are being explored. − …”

Preparation of Macroporous Double-Network MoS2-Based Beads for Efficient and Selective Removal of Hg(II) from Water

“…To identify the surface functionality of the material, Fourier transform infrared (FTIR) and Raman spectra were employed. As the FTIR spectra of DMBs illustrated in Figure g, intense doublets at 1406 and 1585 cm –1 were attributed to the asymmetric and symmetric stretching vibrations of the carboxylate groups (O–C–O) . These shifts to lower wavenumbers compared with the O–C–O in CA/PVA beads (1414 and 1592 cm –1 ) were indicative of the interaction between MoS 2 and polymers.…”

“…In detail, the positive enthalpy (Δ H °, 25.28 kJ mol –1 ) and negative standard Gibbs free energies (Δ G °, from −12.46 kJ mol –1 (15 °C) to −15.07 kJ mol –1 (35 °C)) demonstrate that the adsorption process is thermodynamically favorable and endothermic. Additionally, the positive entropy (Δ S °) of 131.36 J mol –1 K –1 suggests that the adsorption process of Hg­(II) on DMBs increased the disorderliness within the solid–liquid system, possibly due to the loss of hydration water from Hg­(II) …”

“…As the FTIR spectra of DMBs illustrated in Figure 1g, intense doublets at 1406 and 1585 cm −1 were attributed to the asymmetric and symmetric stretching vibrations of the carboxylate groups (O− C−O). 34 These shifts to lower wavenumbers compared with the O−C−O in CA/PVA beads (1414 and 1592 cm −1 ) were indicative of the interaction between MoS 2 and polymers. The broad peak around 3271 cm −1 in the DMBs and CA/PVA beads was assigned to the O−H stretching vibration that can provide the hydrogen-bonding interactions.…”

“…Additionally, the positive entropy (ΔS°) of 131.36 J mol −1 K −1 suggests that the adsorption process of Hg(II) on DMBs increased the disorderliness within the solid−liquid system, possibly due to the loss of hydration water from Hg(II). 34…”