The poor mechanical strength of graphene oxide (GO) membranes, caused by the weak interlamellar interactions, poses a critical challenge for any practical application. In addition, intrinsic but large-sized 2D channels of stacked GO membranes lead to low selectivity for small molecules. To address the mechanical strength and 2D channel size control, thiourea covalent-linked graphene oxide framework (TU-GOF) membranes on porous ceramics are developed through a facile hydrothermal self-assembly synthesis. With this strategy, thiourea-bridged GO laminates periodically through the dehydration condensation reactions via NH and/or SH with OCOH as well as the nucleophilic addition reactions of NH to COC, leading to narrowed and structurally well-defined 2D channels due to the small dimension of the covalent TU-link and the deoxygenated processes. The resultant TU-GOF/ceramic composite membranes feature excellent sieving capabilities for small species, leading to high hydrogen permselectivities and nearly complete rejections for methanol and small ions in gas, solvent, and saline water separations. Moreover, the covalent bonding formed at the GO/support and GO/GO interfaces endows the composite membrane with significantly enhanced stability.
The layered graphene membrane has high potential for efficient desalination owing to its frictionless surface and hydrophobic nature. However, it has not been demonstrated so far due to the challenges related to controlling membrane microstructure. Herein, we develop a facile and simple thiol−ene click method to prepare a perfluoro-alkyl grafted graphene (fGraphene) membrane on porous ceramic, which features an ultrahigh antiwetting surface, oriented mesoporous surface entrances, and a well-defined interlamellar spacing of ∼1.1 nm. With vacuum membrane distillation, the fGraphene membranes post ∼100% rejections to the small ions of seawater, at least 1 order of magnitude higher water fluxes than those of commercial membranes and graphene-oxidebased membranes, as well as robust stability in the desalination. Fast NaCl desalinations on the fGraphene membrane were also confirmed by the reverse/forward osmosis tests. The complete rejection of ions and high flux are attributed to the interfacial sieving effect over the 2D nanochannels as well as the vapor-phase transport in the mesoscale channels, which is fundamentally different from the solution−diffusion mechanism of dense polymeric membranes and the size-sieving mechanism of microporous membranes. This work not only demonstrates a special separation effect for complete desalination over the layered graphene-based membrane but also offers a reliable method to functionalize and structure graphene membranes for other potential applications.
Graphene oxide (GO) membranes have shown great potential in ionic sieving from aqueous solutions. However, it remains challenging for GO membranes to exclude small ions with a large water flux. Herein, organic ions are confined onto the GO interlaminations to form a precisely restricted 2D channel size of 0.71 nm, which presents >99.9% NaCl rejections and high freshwater fluxes via the pervaporation method, both being orders of magnitude higher than that of common GO membranes. Theoretical calculations reveal that, apart from controlling the 2D channel size of GO by strong cation–/anion–π and π–π interactions, the organic ions act as vapor traps to remarkably shorten vapor diffusion distance and then as water pumps to significantly enlarge water permeability. It not only theoretically explains the low permeability over the common GO membranes with large 2D channels, but also experimentally demonstrates fast and complete desalination on the organic ions-GO membrane.
Urea methanolysis
is a green alternative to synthesize dimethyl
carbonate (UM-to-DMC). However, it is strongly challenged by the generated
NH3 induced thermodynamic equilibrium limitation and the
azeotropic products’ separation. Herein, these predicaments
are well-relieved by introducing membranes in both reaction and product
separation. An NH3 permselective membrane reactor (MR)
based on modified SAPO-34 membrane is successfully realized for UM-to-DMC.
The permselectivity and acidity of the SAPO-34 membrane are significantly
adjusted to cater the strict molecular sieving of NH3/methanol
and chemical inertness upon the reaction. The MR exhibits excellent
reactant conversion and DMC selectivity, resulting in >139% higher
DMC yield than that of the nonmembrane reactor, due to in
situ removal of NH3 by the membrane. The MR also
demonstrates reliable chemical, thermal, and mechanical stability
during >2000 h. Moreover, the regular SAPO-34 membrane with controlled
thickness presents remarkable separation performance for the methanol–DMC
azeotrope, in which the methanol–DMC separation factors and
the methanol permeance are 1–2 orders of magnitude higher than
those of the polymeric membranes. This study suggests the great potential
that integration of such membranes offers for process intensification,
energy savings, and efficiency improvement in a series of urea alcoholysis
and even other NH3 releasing reactions.
Transition metal oxides are the potential catalysts to replace noble-metal based catalyst for the catalytic combustion of methane due to the tolerable reactivity and low cost. However, these catalysts are challenged by the low temperature reactivity. Herein, the surface defective Co3O4 nanoplates are realized through a facile co-precipitation and thermal reduction method with the association of GO. The resultant catalysts (CoGO50) demonstrate a superior low-temperature reactivity for the methane oxidation to CO2 and H2O in comparison with the common Co3O4 catalyst. The reliable stability of CoGO50 catalyst was proved by 80 h testing with intermittent feeding of water vapor. The experimental analysis demonstrates that the presence of a small amount of GO significantly affects the catalysts in surface valence state, active oxygen species and surface oxygen vacancies through reacting with the cobalt oxide as a reductant. Moreover, GO plays as 2D confine template to form smaller and thinner nanoplates. This work provides a facile method to control the surface properties of catalyst not only for Co3O4 based catalysts but also for wider solid catalysts.
Supported graphene oxide membrane is endowed with selective function for olefins by a cation intercalation method. The metal-cation fixed GO membrane exhibits a high propane to propylene ideal selectivity of...
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