Suzhou University Avenue Jianmei team: photocatalytic met emulsion separation, waste water purification change
Important: 1 was prepared using the visible light from the drive assembly processes of self-cleaning thin-dimensional heterostructures. 2. palygorskite enhance doping the graphene layer spacing and the heterojunction structure, increasing the flux of the membrane, to avoid the film pitch is reduced when compressed. 3. The heterojunction catalytic visible light can effectively prevent membrane fouling and decreased permeation flux. 4. Preparation of planar membranes having excellent separation performance and high throughput and high efficiency oil-water emulsions.
water shortage and water pollution a serious impact on human life and sustainable development, to solve the problem of water pollution is a major challenge facing the world today, and the organic solvent and oil pollution are domestic and industrial wastewater common sources of water pollution. Membrane separation techniques may be used to treat wastewater, but a large amount of oily wastewater need for more efficient high-throughput membrane. Graphene oxide (GO) readily dispersible in water, has excellent electrical and mechanical properties. However, separation at a high flux through the membrane is easily contaminated, the GO layer spacing decreases during use, thereby reducing the throughput. Meanwhile, the surface energy of the membrane, and flux balance is a key issue. Photocatalytic has many applications in environmental restoration. The photocatalyst film separation grease degradation, combined with the organic solvent contamination, can be greatly improved membrane separation technology in wastewater treatment. Graphene – carbon nitride (g-CN) having a two-dimensional layered structure, visible light, metal-free, good stability, the heterojunction structure can be prepared by binding the photocatalyst g-CN and Bi2O2CO3 (BOC), pole Great change of the light absorption range Bi2O2CO3 improved photocatalytic performance. Palygorskite (PG) has a unique acicular structure, with a soft, light weight, heat insulation, high temperature, adsorption properties, chemical stability, good pulping performance characteristics. Suzhou University road construction US team using self-assembly, self-cleaning one kind of GO, CN @ BOC heterojunction structure and composition of PG sunlight-driven Preparation a laminated film (Scheme 1). And with A Self-Cleaning Heterostructured Membrane for Efficient Oil-in-Water Emulsion Separation with Stable Flux for the title in the recently published \”Advanced Materials \”on.
1. Preparation of membrane structures
The CN as the carbon source, hydrothermal Preparation of CN @ BOC-D heterojunction catalyst. Bi2O2CO3 prepared plate is circular nano topography, thickness of 125nm (FIG. 1a, b). g-CN nanosheet layer structure, BOC g-CN grow after changing the surface topography (FIG. 1c, d). After the fixing piece is formed square nanometer BOC CN @ BOC heterojunction structure on the surface of the g-CN, BOC nanosheet thickness reduced to about 50 nm ((FIG. 1e, f) .HRTEM-EDX and SAED images demonstrated g-CN Bi2O2CO3 successful coating on the surface (FIG. 1 g)
2 by XRD and FT-IR analysis heterojunction CN @ BOC-D crystal structure and chemical composition.
In the XRD pattern (FIG. 2a), all peaks is consistent with the simulation of Bi2O2CO3 synthetic Bi2O2CO3. G-CN two peaks are derived from three aromatic sulfur-triazine units and sections. CN @ BOC Bi2O2CO3 both peaks and the g-CN. Wherein all FT-IR spectra of both samples Bi2O2CO3 CN @ BOC g-CN and absorption bands (FIG. 2b). XRD and FT-IR confirmed that the results for the g-CN CN @ BOC heterojunction carbon successfully prepared in-situ. Analysis of the chemical composition and coupling CN @ BOC heterojunction test further confirmed by XPS CN @ BOC heterojunction is formed (FIG. 2c-f). Meanwhile, UV-Vis spectra demonstrated and compared to pure Bi2O2CO3 pure g-CN, BOC @ CN visible light absorbent composite stronger. After the introduction of the g-CN in Bi2O2CO3, BOC @ CN red shift of the absorption band edge, fully described BOC @ CN may generate photoelectrons visible light and a hole for the photocatalytic process.
3. The surface morphology and properties of films
On a cellulose membrane having a layered structure of a self-assembled self-cleaning capability prepared using GO, PG and CN @ BOC heterojunction film (Scheme 1b). In order to study the surface morphology and properties of different films, a series of composite samples were prepared in the same manner. GO / PG film surface occurs many needle PGs, the two components poor binding capacity. GO / CN film surface wrinkles more, g-CN less (FIG. 3a, b). As more CN @ BOC heterojunction is formed, a composite film surface roughening, the number of two-dimensional projection conjunctival surface heterogeneity (Fig. 3c-f). The layers of the heterojunction increases the spacing between the GO and the heterostructure is further increased, the film forming hierarchical structure facilitates subsea superoleophobic interface.
4. Superoleophobicity underwater film and antifouling property
the wettability of the film surface is key to wastewater treatment. Test contact angle of water with an organic solvent and underwater contact angle of the organic solvent in the air is an important means to test the two-dimensional heterogeneity conjunctiva wettability. Prepared in heterogeneous conjunctiva air both hydrophilic and lipophilic, but the performance in the water surplus lipophilicity. Because the GO / PG more hydrophilic than the g-CN, GO water / PG film contact angle less than GO / PG / CN film. However, since the Bi2O2CO3 has good hydrophilicity, the contact angle of water with the content of the heterojunction increases CN @ BOCDecreases (FIG. 4a). GO / PG / CN @ BOC-3 and GO / PG / CN @ BOC-4 reduced the water contact angle of 10 ° in 2min, 15min within less than 10 °. When water contacts the membrane surface, and surface bound superhydrophilic surface roughness rapid diffusion of water to form a stable aqueous layer. When the oil in contact with the membrane surface, the contact area of the oil and the aqueous layer surface of the film is minimized. Thus, the underwater may be prepared by coordinating superoleophobic surface hydrophilicity and surface roughness. With the increased roughness and hydrophilicity, subsea oil contact angle GO / PG / CN @ BOC-3 and GO / PG / CN @ BOC-4 reaches 160 ° (Figure 4b). The results indicate that the heterogeneity conjunctiva prepared having superoleophobic and underwater antifouling property.
5. The self-cleaning and anti-fouling properties of the film
In practice, self-cleaning and anti-fouling capacity of the membrane separation membrane off to water emulsification important. CN @ BOC oil film after being contaminated, since the ultra-lipophilic decreased, underwater oil contact angle decreased, but the light 1h after simulated superoleophobic recovery (Figure 5a). After 1 hour GO film after light pollution, which has not been restored underwater superoleophobicity (FIG. 5B), described a heterojunction having high optical performance degradation. In addition, the adhesion after irradiation with the underwater surface of the film is very small oil droplets (FIG. 5c).
6. The emulsion membrane separation performance
Preparation of a series of film emulsion oil-water separation experiment, all film Oil is greater than 99.9 % (Figure 6a). Furthermore, as the content heterostructure (GO / PG / CNBOC-1 to GO / PG / CNBOC-3), flux through the membrane increases. The authors also tested different types of emulsions (gasoline – water, n-hexane – water, petroleum ether – water and chloroform – water) separation performance, efficiency of their separation of more than 99.9% . Self-cleaning properties of the films from different ordersSegment flux value is further evaluated water flux and oil in water emulsion have a heterojunction with increasing content increases (Figure 6c). GO / PG / CN @ flux BOC-3 film highest recovery rate was 99.8%. And GO / PG / CN @ BOC-3 film almost no change 10 cycles (FIG. 6d) separation performance within. Hetero conjunctiva prepared with good self-cleaning properties and separation of the emulsion, and After repeated cycles, the flow rate hardly changes.
On the GO / PG prepared by self-assembly method / CN @ BOC heterostructure film, a film having a high permeation flux and good self-cleaning ability, It can be used to separate oil and water emulsions. High throughput film prepared, a stable flow rate over many cycles, to stabilize the water in oil emulsion having a good self-cleaning properties (flux greater than 95% recovery). Because of PG and CN @ BOC heterojunction, pure water flux through the membrane than pure GO film greatly improved. The membrane having a heterojunction underwater superoleophobic properties, greatly improving the oil-water separation performance of the membrane. Photocatalytic self cleaning in combination with the emulsion separation provides a more efficient new way for waste water treatment.