Brief introduction of results
Graphene oxide (GO) membranes are unstable due to water-inducing effects (e.g., swelling) and poor interfacial adhesion to the substrate, which largely limits its separation performance and long-term application (e.g., potential risk of GO leakage). To address this issue, in this paper, researchers such as Yi Jiang/Yiliang Lu of the Hong Kong Polytechnic University published a paper titled "Magnetically Ultrastabilized Graphene Oxide-Based Membrane Filter for Point-of-Use Water Treatment" in the journal ACS EST Engg. The study proposes a magnetic ultra-stable GO membrane filter, which is different from traditional methods such as chemical crosslinking. GO nanosheets modified with in situ formed Fe 3O4 nanoparticles are first assembled into a membrane filter by vacuum filtration. The filter is then placed in a magnetic field (≤0.50 T) generated by the permanent magnet and tuned by a custom porous carrier embedded with magnetizable particles.
The GO–Fe3O4 (GOF) membrane filter remains intact under harsh ultrasonic instabilities (≥ duration of 20 minutes, power of 144 W, frequency of 45 kHz) and turbulent hydrodynamic conditions (e.g., cross-flow velocity of 30 cm/s for at least 7 days) without any deteriorated permeation or repulsion properties. Our experimental and theoretical studies highlight the indispensable role of magnetizable carriers in achieving this super-stabilization, which increases the magnetic flux density gradient and magnetic force by nearly 1 order of magnitude. GOF membrane filters not only have separation performance comparable to commercial ultrafiltration membranes, but are also effective in inactivating waterborne pathogens (e.g., E. coli). This simple strategy of magnetically stabilizing functional engineered nanomaterials on the surface of the substrate opens up new opportunities for the development of nanofilters that minimize leaks and health risks for water purification at the point of use.
Illustrated reading
Figure 1. (a) Schematic diagram of a home-made filter unit for ultrafiltration processes in magnetic fields (illustration showing a photograph of the filtering unit). (b) Schematic diagram of the assembly of parts for homemade filters. (c) Assembly drawings of parts and (d) home-made filter units.
Figure 2. (a) FTIR spectra of GO and GOF composites; (b) XRD maps of GO membranes and GOF membrane filters; (c) TEM images of GOF composites (illustration showing the size distribution of Fe 3 O4 nanoparticles estimated from TEM images) ;(d) Raman spectra of GO and GOF composites; (e) hysteresis curves of GOF composites (illustration showing an enlarged plot of hysteresis curves) ;(f) photographs of GOF membrane filters (inset: GOF membrane filters are covered). NdFeB ring magnet suction) ;(g) top view of the GOF membrane filter and (h) cross-section SEM image (mass load 0.22 mg cm –2) (illustration: enlarged SEM image) ;(i) Hysteresis curve of the GOF composite (illustration: magnification of the hysteresis curve) ;(j) Photo of the magnetizable carrier (inset shows the magnetizable carrier attracted by the NdFeB magnet) ;(k) Top view of the magnetizable carrier and (l) cross-section SEM Image (yellow dotted circle marks NdFeB particles embedded in the carrier).
Figure 3. (a) Stability comparison of GOF membrane filters in NMF/(N)S, MF/NS and MF/S systems (two magnetizable brackets, four NdFeB ring magnets). (b) Changes in water permeability and PEG (300 kDa) rejection after 20 minutes of sonication in NMF/(N)S, MF/NS, and MF/S systems (two magnetizable carriers, four NdFeB magnets). J 0 and J x represent the water permeability of the GOF membrane filter before and after ultrasound treatment, while R0 and R x refer to the PEG rejection rate before and after treatment, respectively. (c) The effect of the number of magnetizable carriers (i.e. 0, 2 and 4) on the stability of the GOF membrane filter in the MF/S system (power input of 171 W, four NdFeB magnets). (d) Effect of the number of NdFeB magnets (i.e., 1, 2 and 4) on the stability of the GOF membrane filter in the MF/S system (four magnetizable supports). The mass load of the GOF membrane filter is 0.22 (b) or 0.44 mg cm –2 (a, c, d). As noted, the ultrasonic power input is 144 W and the frequency is 45 kHz; the ultrasound time is 10 minutes.
Figure 4. (a,b) local magnetic flux density distribution, (c,d) magnetic flux density gradient distribution, and (e,f) 3O4 nanoparticles in MF/NS (a,c,e) and MF/S (b,d,f) systems in a multiplying integral cloth (in a rectangular region of 30 × 30 nm2) and MF/S (b, d, f). In calculations for the MF/S system and the 1.79 × 10 -8 N m-1, their products around the Fe 3O4 nanoparticles are integrald to 1.12 × 10 -7 N m-1 and the MF/NS system.
literature:
https://doi.org/10.1021/acsestengg.1c00364