Sunlight-Sensitive Anti-Fouling Nanostructured TiO2 coated Cu Meshes for Ultrafast Oily Water Treatment

Nanostructured materials with desired wettability and optical property can play an important role in reducing the energy consumption of oily water treatment technologies. For effective oily water treatment, membrane materials with high strength, sunlight-sensitive anti-fouling, relative low fabrication cost, and controllable wettability are being explored. In the proposed oily water treatment approach, nanostructured TiO2-coated copper (TNS-Cu) meshes are used. These TNS-Cu meshes exhibit robust superhydrophilicity and underwater oleophobicity (high oil intrusion pressure) as well as excellent chemical and thermal stability (≈250 °C). They have demonstrated high separation efficiency (oil residue in the filtrate ≤21.3 ppm), remarkable filtration flux (≥400 kL h−1 m−2), and sunlight-sensitive anti-fouling properties. Both our theoretical analysis and experimental characterization have confirmed the enhanced light absorption property of TNS-Cu meshes in the visible region (40% of the solar spectrum) and consequently strong anti-fouling capability upon direct solar light illumination. With these features, the proposed approach promises great potential in treating produced oily wastewater from industry and daily life.

In order to test the temperature stability, the as prepared etched copper mesh sample (NaOH/Na3PO4/NaClO2 =5:10:3.75) were heat treated at temperature of 50, 100, 150, 200, 250°C for 24 hours. The result SEM images were shown in Figure S1.

Sputtering-hydrothermal Coating Method (TNS-Cu-II)
Depositions were done by using DC Magnetron sputtering (as shown in Figure S5).
Titanium target of 99.999% purity was used. In order to get enough thick titanium layer, the condition was set at 100 W power and 60 minutes operation time. At 100 W, the sputtering speed is 0.32 angstrom per second. Therefore, the calculated thickness of titanium is 115.2 nm. Before sputtering target samples were ultrasonic washed with deionized water, acetone, isopropanol alcohol, and deionized water each 6 minutes in order.
After sputtering, samples were ultrasonic washed with acetone, isopropanol alcohol and deionized water each 3 minutes in order. After that, all the samples were immersed in DI water to avoid contamination. Then, samples were taken out one by one, rinsed it in highpressure water and then dried by using high-pressure nitrogen.

LBL Assembly Method (TNS-Cu-III)
500M copper meshes and nanostructured copper meshes were cleaned in an ultrasonic bath with acetone for 15 minutes and then rinsed with methanol, isopropyl alcohol, and DI water.
A clear solution of 0.6 mL TiOBu4 and 20 mL ethanol was prepared. Then, the LBL assembly approach was used to coat titanium dioxide by using the following procedure.
1) The as cleaned copper meshes were immersed into the clear solution for 10 minutes.
2) Samples were taken out, and the water contact angle was measured.
3) The samples were immersed into deionized water for 3 minutes. 4) Samples were taken out, and the water contact angle was measured again, and difference of contact angles was noted.
5) The procedure was repeated from step 1.
6) After several cycles, the prepared samples were annealed at 450°C.
As the Figure S6 described, TiOBu4 will first react with the hydroxyl groups on the surface of the copper mesh. After the reaction, the surface becomes more hydrophobic. Then, hydrolysis reaction makes the surface more hydrophilic. Figure S7. The mechanism of layer by layer coating. Reprinted with permission from [3]. Figure S7 showed the EDS result of samples prepared by LBL. The content of titanium element is 6.4% (on weight) while on the right is 0.06% (w%). Figure S9b and Figure S9c demonstrated the EDS mapping results. As it shown in the Figure S9c, the distribution of oxygen is uniform but titanium is not, which indicates that titanium dioxide did not fully cover the copper mesh.

Oil/water separation experiments
In the separation experiment, a 150 mL filtration flask was used. The copper mesh was fixed on the top of a 10 mm wide tube. Before the experiment, copper mesh was wetted by DI water. Then, the oil/water mixture was poured into the copper mesh fitted flask from the top and the separation was solely driven by gravity. To mimic the continuous oil/water separation experiments, the mesh was adjusted on to the glass cylinder in a way that the lower part of the mesh was in continuous contact with water and upper part was in contact with oil/water mixture for continuous seven days of experiments. During each day at different time intervals, filtration flux was measured and filtered samples were collected to measure the COD values.