Abstract
Photocatalytic nanofiltration (NF) membranes with enhanced flux and anti-fouling properties were prepared from a layered in situ nanocomposite of metal organic framework (i.e., UiO-66) and graphene oxide (UiO-66_GO) on a polyamide NF membrane using a pressure-assisted self-assembly method. For filtering pure water and humic acid, the composite membrane with a 10% UiO-66_GO loading (UiO-66_GO/NF-10%) showed a higher water flux (up to 63 kg/m2 h bar), flux recovery (80%), and total fouling resistance (33%) than the pristine NF membrane. Physical and chemical characterization revealed that this performance was attributed to improvements in hydrophilicity, porosity, surface smoothness, and charge repulsion. The UiO-66_GO/NF-10% composite membrane exhibited better physical stability with a relatively low mass loss (8.64%) after five washes than the membranes with mass loadings of 5 and 15 wt%. Furthermore, the UiO-66_GO/NF-10% composite membrane exhibited considerable photocatalytic activity under ultraviolet (UV) irradiation (bandgap: 3.45 eV), which reduced irreversible fouling from 20.7% to 2.4% and increased flux recovery to 98%. This study demonstrated that surface modification with the UiO-66_GO nanocomposite produced a high-flux anti-fouling photocatalytic NF membrane, which is promising for water purification.
Highlights
Nanofiltration (NF), which was introduced in the late 1980s, has a high removal efficiency for hardness, multivalent ions, heavy metal, and organic molecules [1,2]
Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images confirmed that the dispersion of UiO-66 particles on the graphene oxide (GO) sheet was uniform (Figure 1)
The structure of the UiO-66_GO nanocomposite may prevent GO layer stacking, which is advantageous for membrane presence of oxygen hydrophilic functional groups (i.e., O−C−O, C=O, O−H) indicated that the
Summary
Nanofiltration (NF), which was introduced in the late 1980s, has a high removal efficiency for hardness, multivalent ions, heavy metal, and organic molecules (e.g., micropollutants and dyes) [1,2]. The material called UiO-66 can be integrated into a membrane, and the integrated membrane shows good membrane stability, high resilience to mechanical stress, and wide applicability [11] This is because the organic linker in UiO-66 provides a platform for chemical modifications of its surface, which allows better adhesion to polymeric membranes than other inorganic materials [12]. A membrane integrated with an in situ UiO-66 and GO (UiO-66_GO) nanocomposite showed higher flux and anti-fouling properties compared with the pristine polyethersulfone membrane because of its high hydrophilicity and the smoothness of the membrane surface [10]. The use of in situ UiO-66_GO nanocomposites on an NF membrane has not been reported, and the membrane synthesis method, water flux, anti-fouling properties, and rejection of organic micropollutants (OMPs) of these composite membranes need to be investigated. We demonstrated a synthesis method for the composite NF membranes, and for the membrane with 10% UiO-66_GO loading, we examined the stability, OMP rejection, and the recovery of the fouled membrane by ultraviolet (UV) photocatalysis
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