Two-dimensional
(2D) metal–organic frameworks (MOFs), as
a newly emerged member of 2D materials, have gained extensive attention
due to their great potential in gas separation, sensing, and catalysis.
However, it is still challenging to synthesize 2D MOFs with controllable
size and functionalities using direct and scalable approaches at mild
conditions (e.g., room temperature). Herein, we demonstrated one-step,
room-temperature synthesis of a series of 2D MOFs based on Cu(II)
paddle-wheel units, where the intrinsically anisotropic building blocks
led to the anisotropic growth of 2D MOF nanoparticles, and the pillared
structure led to high surface areas. The size of 2D MOFs can be adjusted
by using a DMF/H2O mixed solvent. The thinnest particles
were around 3 nm, and the highest aspect ratio was up to 200. The
functionalization of 2D MOFs was also achieved by selecting ligands
with desired functional groups. The gas sorption results revealed
that amino and nitro-functionalized 2D MOFs showed higher CO2 sorption selectivity over CH4 and N2, suggesting
these materials can be further applied in natural gas sweetening (CO2/CH4 separation) and carbon capture from flue gas
(CO2/N2 separation).
Rhodamine
B-doped poly(3-mercaptopropylsilsesquioxane) (RB-PMPSQ)
fluorescent microspheres with thiol groups were prepared by a facile
sol–gel method. Initially, 3-mercaptopropyltrimethoxysilane
(MPTMS) monomer was hydrolyzed in an aqueous acid solution with rhodamine
B (RB) as the hydrolysis catalyst and the fluorescent dye at the same
time, and then an ammonia solution was added into the reaction solution
to catalyze the condensation reactions of silanol. Through this method,
a high yield of RB-PMPSQ fluorescent microspheres with narrow distribution
of particle sizes was obtained, and the size of the particles could
be effectively controlled depending upon the concentration of the
monomer. The morphology and the fluorescent property of RB-PMPSQ microspheres
were characterized by scanning electron microscopy (SEM) and fluorescence
spectrophotometer, respectively. The fluorescent microspheres showed
excellent photostability. The formation mechanism of the fluorescent
microspheres was also proposed.
A two-step acid−base catalyzed sol−gel method has been used to prepare monodispersed poly(3mercaptopropylsilsesquioxane) (PMPSQ) microspheres. Initially, the hydrolysis of 3-mercaptopropyltrimethoxysilane was catalyzed by hydrochloric acid in an aqueous medium, and then the addition of ammonium hydroxide initiated the condensation of hydrolysate. The formation process of PMPSQ microspheres was characterized by field emission scanning electron microscopy and 29 Si NMR. The formation mechanism of the monodispersed microspheres was also discussed. Through this method, monodispersed PMPSQ microspheres with a high yield were achieved and the particle size could be adjusted by changing the precursor concentration.
Metal–organic
frameworks (MOFs) are a class of customizable
porous material, which have shown good performance in separation processes,
because of their large surface area and molecular recognition property.
Although the effects of chemical structure of MOFs on their separation
performance were extensively studied, the exploration of their surface
properties was still limited. This work demonstrated a MOF nanosheet
with large amount of coordinatively unsaturated metal sites, Cu(BDC)
(copper(II) benzenedicarboxylate), where the unsaturated Cu sites
were utilized to selectively adsorb organic molecules with Lewis basicity.
This work also investigated the direct growth of Cu(BDC) on the cellulose
substrate, where the MOF nanosheets were immobilized on the cellulose
substrate, enabling the composite material for practical applications.
The heterogeneous nucleation and growth of MOF nanosheets on the cellulose
were achieved by tuning the basicity of solution and reaction temperature.
We believe this direct growth approach can be applied to other MOF
composite materials for separation and purification purposes, as well
as other applications involving molecular recognition properties of
MOFs, such as sensing, catalysis, and enzyme immobilization.
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