Titanium dioxide / sulfonated graphene oxide / Ag nanoparticle composite membrane and preparation and application thereof

Abstract

Titanium dioxide/sulfonated graphene oxide/silver nanoparticle composite membrane and its preparation method and application are disclosed. Mixing graphene oxide, sodium chloroethanesulfonate, and sodium hydroxide uniformly in the water, and then adding concentrated nitric acid to obtain sulfonated graphene oxide; mixing the aqueous solution of said sulfonated graphene oxide with the aqueous solution of silver nitrate, stirring in the dark, then adding ascorbic acid, and continuing to stir to obtain a silver nanoparticle/sulfonated graphene oxide composite material; dispersing said silver nanoparticle/sulfonated graphene oxide composite material in water, and then deposited on said titanium dioxide nanorods arrays by vacuum deposition, and vacuum dried to obtain titanium dioxide/sulfonated graphene oxide/silver nanoparticle composite membrane. The membrane possessed photocatalytic effect under UV light and special wettability: super-hydrophobic oil under water/super-hydrophobic under oil, which could in situ separation and degradation of oil/water emulsion.

Claims

1. A preparation method of titanium dioxide/sulfonated graphene oxide/silver nanoparticle composite membrane, comprising the following steps: (1) mixing graphene oxide, sodium chloroethanesulfonate, and sodium hydroxide uniformly in the water, and then adding concentrated nitric acid to obtain sulfonated graphene oxide; (2) mixing the aqueous solution of said sulfonated graphene oxide with the aqueous solution of silver nitrate, stirring in the dark, then adding ascorbic acid, and continuing to stir to obtain a silver nanoparticle/sulfonated graphene oxide composite material; (3) preparing titanium dioxide nanoclusters on a metal mesh by using tetra-n-butyl titanate, glycerol, and ethanol as raw materials to obtain a metal mesh with titanium dioxide nanoclusters; then the metal mesh with titanium dioxide nanoclusters is put in a mixed solution of titanium trichloride, saturated aqueous solution of sodium chloride and urea, said metal mesh is removed after the reaction to obtain titanium dioxide nanorod arrays; (4) dispersing said silver nanoparticle/sulfonated graphene oxide composite material in water, and then deposited on said titanium dioxide nanorods arrays by vacuum deposition, and vacuum dried to obtain titanium dioxide/sulfonated graphene oxide/silver nanoparticle composite membrane.

2. The preparation method of titanium dioxide/sulfonated graphene oxide/silver nanoparticle composite membrane according to claim 1, wherein in step (1), the mass ratio of graphene oxide, sodium chloroethanesulfonate, and sodium hydroxide is 0.2:3:1.6; after mixing said graphene oxide, sodium chloroethanesulfonate, and sodium hydroxide uniformly in water, ultrasonic stirring for 3 hours at room temperature, and then adding concentrated nitric acid; after the reaction is completed, the product is centrifuged, washed and dried to obtain sulfonated graphene oxide.

3. The preparation method of titanium dioxide/sulfonated graphene oxide/silver nanoparticle composite membrane according to claim 1, wherein in step (2), the mass ratio of sulfonated graphene oxide, silver nitrate and ascorbic acid is 1:6.8:8.8; said stirring is carried out in the dark for 3 hours at 25 C.; the time of continued stirring is 1 hour.

4. The preparation method of titanium dioxide/sulfonated graphene oxide/silver nanoparticle composite membrane according to claim 1, wherein in step (3), the volume ratio of tetra-n-butyl titanate, glycerin, and ethanol is 1:5:15; the temperature of the preparation of titanium dioxide nanoclusters on the metal mesh is 180 C., the time is 24 hours; the mass ratio of urea, titanium trichloride, sodium chloride is 1:2:36.6; the temperature of the reaction is 160 C., and the time is 2 hours.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows scanning electron microscopy (SEM) picture of silver nanoparticles and sulfonated graphene oxide composites;

(2) FIG. 2 shows scanning electron microscopy (SEM) picture of titanium dioxide nanorods arrays;

(3) FIG. 3 shows the cross sectional SEM figure of the TSA membrane;

(4) FIG. 4 shows the wettability of TSA membrane;

(5) FIG. 5 shows the separation step of oil-water emulsion;

(6) FIG. 6 shows the separation efficiency of TSA membrane;

(7) FIG. 7 shows the degradation of the TSA membrane.

(8) FIG. 8 shows the measurement of the separation efficiency of the same TSA film after 10 cycles of separation.

DETAILED DESCRIPTION OF THE INVENTION

(9) Implementation 1: Synthesis of sulfonated graphene oxide, specific steps are as follows.

(10) 180 mL concentrated sulfuric acid and 20 mL concentrated phosphoric acid (180:20) are mixed well. Weighing 1.5 g of graphite flake accurately, and mixing for 15 minutes. Weighing 9 g potassium permanganate, which is added slowly with stirring. Then the mixture is stirred in oil bath at 50 C. for 12 hours. The products are poured in 200 mL water after cooling to room temperature. Then, adding suitable amount of hydrogen peroxide solution until the solution became yellow, the solution is washed with 5% hydrochloric acid for three times after centrifuging. Then, washing with deionized water for many times until PH is 5 to 6. The products are dialyzed for one week, and are changed the water every day. Lastly, the products are put in watch glass under 40 C., and vacuum drying until fluffy.

(11) 200 mg of GO, 3 g of sodium 2-chloroethanesulfonate hydrate (ClCH.sub.2CH.sub.2SO.sub.3Na) and 1.6 g of NaOH are carefully added into a beaker which is containing 500 mL of deionized (DI) water. The mixture is put into ultrasonic instrument for 3 h in room temperature and then 2 mL of HNO.sub.3 is added into the solution. After mixing well, the mixture is centrifuged and washed with ethanol for three times. Finally, the reaction products are dried in vacuum overnight.

(12) Implementation 2: Synthesis of SGO/Ag nanocomposites, specific steps are as follows.

(13) 20 mg of SGO is added into 20 mL DI water, and then dispersed uniformly under ultrasonic situation. 136 mg AgNO.sub.3 is dissolved into 4 mL DI water. The above prepared solution is put into 50 mL round bottom flask and stirred magnetically for 3 h at 25 C. in the dark. Then, 2 mL ascorbic acid (176 mg) is added into reaction solution quickly and the mixture is kept stirring magnetically for 1 h. The final products are separated by centrifugation and washed with DI water for several times until there is no impurity. The obtained product is stored in the DI water; FIG. 1 is scanning electron microscopy (SEM) picture of silver nanoparticles and sulfonated graphene oxide composites, indicating the distribution of the nanoparticles.

(14) Implementation 3: Preparation of TiO.sub.2 nanorod arrays mesh, specific steps are as follows.

(15) 2.5 mL tetra-n-butyl titanate (TBOT), 12.5 mL glycerol and 37.5 mL ethanol is mixed in the beaker and poured into a Teflon-lined autoclave. The cleaned copper mesh is placed in the solution standing against the wall of the autoclave. The autoclave is heated to 180 C. for 24 h, then cooling down to room temperature. Subsequently, the product is taken out, cleaned with DI water and dried in vacuum; 4.05 mL of TiCl.sub.3 solution, 37.5 mL supersaturated NaCl solution, 0.3 g of urea are mixed uniformly and poured into the autoclave which has been placed the TiO.sub.2 nanocluster-based Mesh. The autoclave is heated to 160 C. for 2 h in oven, then cooling down to room temperature. The mesh is cleaned in dilute sulfuric acid for 5 min, rinsed with DI water and ethanol successively. Finally, the mesh is dried in vacuum. FIG. 2 is scanning electron microscopy (SEM) of the titanium dioxide nanorod arrays, indicating the distribution of the nanorods.

(16) Implementation 4: Fabrication of TSA membrane, specific steps are as follows.

(17) 10 mg of SGO/Ag nanocomposites is dispersed uniformly in 200 mL DI water and filtered onto the surface of TiO.sub.2 nanorod arrays mesh in vacuum. Then the product is washed by DI water for several times until SGO/Ag nanocomposites are fully covered on the mesh. The final product is dried in vacuum drier at 60 C. for a night. FIG. 3 is cross sectional SEM diagram of the TSA membrane, indicating two distinct layers.

(18) Implementation 5: The Wettability of TSA Membrane

(19) FIG. 4 is wettability of the TSA membrane, we can see that the TSA membrane is easily wetted by water and organic solvents in air (contact Angle is 0), and when the TSA membrane is dipped in water, a drop of toluene (3 L) is dropped on the film, a spherical droplet is presented on the membrane (contact Angle is 152 C.), indicating the super-hydrophobic oil underwater. Likewise, when TSA membrane is put in the oil, the contact angle of the water droplet (3 L) on the membrane is 150 C., indicating that super-hydrophobic under oil. In conclusion, The TSA membrane has special wettability.

(20) Implementation 6: The emulsion separation, specific steps are as follows:

(21) 5 mL (45 mL toluene) water and 45 mL (5 mL water) toluene are mixed, then 5 mg cetyl trimethyl ammonium bromide is added in the mixture under ultrasonic for six hours, then making the emulsion separation. The as-fabricated TSA membrane is fixed into a glass tube, then 30 mL oil-in-water emulsion is poured into the glass tube. FIG. 5 shows the steps of oil-water emulsion separation, indicating that the oil-water emulsion containing methylene blue became clear after pouring in the glass tube with modified double layer stainless mesh. The result illustrates the good emulsion separation effect.

(22) Implementation 7: Separation efficiency and Flux, specific steps are as follows: Separation efficiency and permeate flux:

(23) The separation efficiency of the oil-in-water emulsions is calculated using the following equation (1):
R(%)=(1C.sub.p/C.sub.o)100%(1)

(24) Where R (%) is a water rejection coefficient, and C.sub.p and C.sub.o are the oil (or water) concentrations in the collected water (or oil) and the original oil/water emulsion, respectively. Purified water is measured by UV-Vis spectrophotometry. Determine moisture content before and after filtration using Karl Fischer moisture titration.

(25) The flux of the emulsion is determined by calculating the amount of permeation per unit time according to the following equation (2):
Flux=V/At(2)

(26) where A (cm.sup.2) is the effective filtration surface of the membrane, V (L/m.sup.2h) is the permeation volume, and t (h) is the separation time.

(27) For each test, a certain amount of oil-in-water emulsion is poured into the filter, and the system is tested with 6 samples to obtain average results.

(28) FIG. 6, 7 is the separation efficiency of different oil/water emulsion and degradation effect of TSA membrane, the TSA membrane (4 cm in diameter) is fixed on the sand core filtration device, 100 mL oil-in-water emulsion containing MB is slowly poured into it under the 250 W UV lamp. The whole separation process is driven by gravity. The figures illustrate a high separation efficiency (over 99.6%) and good degradation effect.

(29) FIG. 8 is the separation efficiency of TSA membrane after 10 times separation, indicating a good recycle ability.

(30) Throughout the above analysis, the TSA membrane fabricated by this invention via hydrothermal method and reduction method possessing the function of emulsion separation and dye degradation with one step. The membrane has advantages of high separation efficiency, good circulation, facile preparation methods and cheap raw materials. Therefore, the membrane has a good application prospect in the emulsion separation and sewage treatment.