Point-of-use
(POU) devices with satisfying mercury (Hg) removal
performance are urgently needed for public health and yet are scarcely
reported. In this study, a thiol-laced metal–organic framework
(MOF)-based sponge monolith (TLMSM) has been investigated for Hg(II)
removal as the POU device for its benchmark application. The resulting
TLMSM was characterized by remarkable chemical resistance, mechanical
stability, and hydroscopicity (>2100 wt %). Importantly, the TLMSM
has exhibited high adsorption capacity (∼954.7 mg g–1), fast kinetics (k
f ∼ 1.76 ×
10–5 ms–1), broad working pH range
(1–10), high selectivity (K
d >
5.0 × 107 mL g–1), and excellent
regeneration capability (removal efficiency >90% after 25 cycles).
The high applicability of TLMSM in real-world scenarios was verified
by its excellent Hg(II) removal performance in various real water
matrices (e.g., surface waters and industrial effluents).
Moreover, a fixed-bed column test demonstrated that ∼1485 bed
volumes of the feeding streams (∼500 μg L–1) can be effectively treated with an enrichment factor of 12.6, suggesting
the great potential of TLMSM as POU devices. Furthermore, the principal
adsorption complexes (e.g., single-layer -S-Hg-Cl
and double-layer -S-Hg-O-Hg-Cl and -S-Hg-O-Hg-OH) formed during the
adsorption process under a wide range of pH were synergistically and
systematically unveiled using advanced tools. Overall, this work presents
an applicable approach by tailoring MOF into a sponge substrate to
achieve its real application in heavy metal removal from water, especially
for Hg(II).
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.
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