Preparation of pt-tio2-nts-psf membrane material and application in recovery of protein in potato wastewater

Abstract

The application discloses a kind of preparation of PT-TiO2-NTs-PSF membrane material and application in recycling potato wastewater protein, in the preparation process, TiO2-NTs, polyvinylpyrrolidone is added to N-methyl-2-pyrrolidone, then heated under water bath condition, after adding polysulfone, it is fully stirred, to obtain the uniform casting membrane suspension, after degassing, casting membrane liquid is coated on transparent glass plate, to form composite membrane, then the suspension on glass is immersed in the mixed solution of ethanol and water, to obtain TiO2-NTs-PSF;TiO2-NTs-PSF is respectively after interface polymerization by piperazine solution and 1,3,5-benzene triformyl chloride solution, heating obtains PT-TiO2-NTs-PSF.The application of the above structure is used in the application of PT-TiO2-NTs-PSF membrane material preparation and recycling potato wastewater protein, TiO2-NTs-PSF composite membrane material has good hydrophilicity, mechanical property and thermal stability simultaneously, and the retention rate of potato wastewater protein is higher, and it has important application prospect in the field of potato wastewater resource recovery.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of film materials, in particular to preparation of a PT-TiO2-NTs-PSF film material and application of the PT-TiO2-NTs-PSF film material in recovery of protein in potato wastewater. BACKGROUND

[0002] The potato starch wastewater contains residual potato starch, cellulose, protein, amino acid, organic acid, polysaccharide and other nutrients, the content of the protein is about 2000-8000 mg / L, the solid suspended substance (SS) is about 8500-10000 mg / L, the chemical (COD) pollutant index can reach 6000-30000 mg / L, and the potato starch wastewater belongs to high-intensity organic wastewater. If the wastewater is directly discharged into a river or a sewer, environmental pollution and resource waste will be caused.

[0003] The membrane separation method is a method for separating, grading, purifying and enriching chemical components in a mixed solution by using natural or synthetic polymer membranes and taking extra pressure or chemical potential difference as driving force. The membrane separation method mainly includes microfiltration, ultrafiltration, nanofiltration and reverse osmosis. Compared with traditional separation methods, the membrane separation method has the characteristics of low temperature, energy saving, high efficiency, green environmental protection, simple operation and large treatment capacity. The concentration of pollutants in wastewater can be greatly reduced by recycling organic matters in high-concentration wastewater, and the utilization rate of potato raw materials can be improved.

[0004] The polymer material polysulfone (PSF) is widely used in ultrafiltration membranes due to good mechanical properties, strong chemical stability and wide pH operation range. It is worth noting that most of the membranes made of the above-mentioned materials are faced with the problem of pollution. At present, the simplest and most effective method to reduce membrane pollution is to enhance the surface hydrophilicity by blending with hydrophilic polymers such as polyvinylpyrrolidone (PVP) or grafting hydrophilic on the surface. The addition of inorganic nanoparticles is another method to overcome the defects of the membranes. TiO2 attracts more and more attention in the application of composite materials due to its abundance, non-toxicity, chemical and mechanical stability and easy surface modification. The incorporation of TiO2 nanotubes into the membrane matrix will form strong interaction with the host polymer, thereby improving the mechanical properties and thermal stability, and also changing the pore size and pore size distribution of the membrane. It can also improve the hydrophilicity, permeability and solute resistance of the membrane. However, the synthesized composite membrane cannot balance the anti-pollution property and the retention performance of the protein in the potato starch wastewater. SUMMARY

[0005] The application aims to provide a preparation method of a PT-TiO2-NTs-PSF film material and application of the PT-TiO2-NTs-PSF film material in recovery of protein in potato wastewater, so as to solve the problem that the above-mentioned composite membrane cannot balance the anti-pollution property and the retention performance.

[0006] To achieve the above object, the application provides a preparation method of PT-TiO2-NTs-PSF membrane material, which comprises the following steps:

[0007] (1) Preparation of TiO2-NTs nanomaterial

[0008] (2) Preparation of TiO2-NTs-PSF composite ultrafiltration membrane

[0009] TiO2-NTs and polyvinylpyrrolidone are added into N-methyl-2-pyrrolidone, then the temperature is increased under water bath condition, poly sulfone is added and fully stirred to obtain a uniform casting solution, after degassing, the casting solution is coated on a transparent glass plate to form a composite membrane, then the suspension on the glass is immersed into a mixed solution of ethanol and water to obtain TiO2-NTs-PSF;

[0010] (3) Preparation of PT-TiO2-NTs-PSF composite nanofiltration membrane

[0011] TiO2-NTs-PSF is heated after interfacial polymerization of piperazine solution and 1,3,5-benzene tricarboxylic acid chloride solution.

[0012] Preferably, the preparation process of TiO2-NTs nanomaterial in step (1) is as follows:

[0013] Cetyltrimethylammonium bromide and NaOH are dissolved in aqueous solution, a mixed solution of tetrabutyl titanate and anhydrous ethanol is slowly added dropwise under water bath stirring condition, stirring is continued until the reaction is completed, after separation, washing, drying, calcination and grinding, polytetrafluoroethylene is added into a reaction kettle for reaction, after washing and drying, TiO2-NTs is obtained.

[0014] Preferably, the molar ratio of cetyltrimethylammonium bromide and NaOH in step (1) is 16:1, and the volume of water solution is 50 mL;

[0015] The temperature of water bath reaction is 30℃, the stirring speed is 300 r / min, and the stirring time is 30 min;

[0016] The addition amount of the mixed solution of tetrabutyl titanate and anhydrous ethanol is 20 mL, and the volume ratio of tetrabutyl titanate and anhydrous ethanol in the mixed solution is 1:1;

[0017] After the reaction is completed, the precipitate is filtered, washed and dried with pure water and ethanol, and then calcined in a muffle furnace at 600℃ for 4 h;

[0018] The calcined and ground sample is added into 80 mL of 1 mol / L NaOH and reacted in a 100 mL polytetrafluoroethylene reactor at 150 DEG C for 10 h, the obtained precipitate is washed with 0.1 mol / L hydrochloric acid and then washed with pure water for multiple times until the filtrate is neutral, and then the precipitate is dried at 80 DEG C under vacuum for 10 h to obtain TiO2-NTs.

[0019] Preferably, the mass ratio of TiO2-NTs: polyvinylpyrrolidone: polysulfone in step (2) is 0.05-0.25:0.5:0.8, and the casting solution is always kept at 10 g.

[0020] Preferably, the water bath temperature in step (2) is 50 DEG C, and the time is 6-8 h.

[0021] Preferably, in step (2), the casting solution is placed at room temperature for 24 hours to remove bubbles, after degassing, the automatic film coater is used to coat the casting solution on a transparent glass plate with a thickness of 1 mm to form a composite film with a thickness of 0.2 mm, after being exposed to air for 10 seconds, the glass suspension is immediately immersed in a mixed solution of ethanol and water with a volume ratio of 2:8, and after complete solidification, the film is transferred to a room temperature water bath for 12 hours.

[0022] Preferably, in step (3), the concentration of the piperazine aqueous solution is 2.0 wt%, and the concentration of the 1,3,5-benzene tricarbonyl chloride organic phase solution in n-hexane is 0.15 wt%.

[0023] The TiO2-NTs-PSF is immersed in the piperazine aqueous solution for 30 min, and after air drying, it is immersed in the 1,3,5-benzene tricarbonyl chloride solution for 3 min.

[0024] Preferably, in step (3), after the immersion is completed, the temperature for further polymerization in the oven is 70 DEG C, and the time is 10 min.

[0025] The second aspect of the present application provides a PT-TiO2-NTs-PSF membrane material prepared by the above preparation method.

[0026] The third aspect of the present application provides an application of the PT-TiO2-NTs-PSF membrane material, and the application of the PT-TiO2-NTs-PSF membrane material in recovering proteins in potato starch wastewater.

[0027] Therefore, the present application adopts the above-mentioned preparation of a PT-TiO2-NTs-PSF membrane material and the application of the PT-TiO2-NTs-PSF membrane material in recovering proteins in potato wastewater, and has the following beneficial effects:

[0028] (1) The PT-TiO2-NTs-PSF composite membrane material prepared by the application has TiO2-NTs successfully doped in PT-TiO2-NTs-PSF, and the interfacial polymerization of piperazine and triformyl chloride on the membrane is successfully completed, and the doped TiO2-NTs make the membrane have higher porosity, pure water flux, average pore size and BSA retention rate.

[0029] (2) The PT-TiO2-NTs-PSF membrane material prepared by the application also has good mechanical properties, thermal stability and hydrophilicity.

[0030] (3) The PT-TiO2-NTs-PSF membrane material is applied to potato wastewater, which can recover proteins in wastewater, and has broad application prospects in resource recovery in wastewater.

[0031] The technical solutions of the application will be further described in detail below with the help of the drawings and examples. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 The rheological diagram of TiO2-NTs-PSF casting solution;

[0033] Figure 2 The viscosity diagram of TiO2-NTs-PSF casting solution;

[0034] Figure 3 The FT-IR diagram of TiO2-NTs, PSF and TiO2-NTs-PSF;

[0035] Figure 4 The XRD characterization diagram of TiO2-NTs, PSF and TiO2-NTs-PSF;

[0036] Figure 5 The TEM image of TiO2-NTs nanomaterial;

[0037] Figure 6 The SEM diagram of TiO2-NTs-PSF composite membrane material;

[0038] Figure 7 The thermogravimetric diagram of TiO2-NTs-PSF composite membrane material;

[0039] Figure 8 The mechanical property diagram of TiO2-NTs-PSF composite membrane material;

[0040] Figure 9 The water contact angle diagram of TiO2-NTs-PSF composite membrane material;

[0041] Figure 10Figure for porosity, average pore size, pure water flux and BSA rejection of TiO2-NTs-PSF composite membrane material;

[0042] Figure 11 Figure for BSA rejection of TiO2-NPs-PSF and TiO2-NTs-PSF composite membrane material composite membrane material;

[0043] Figure 12 Figure for FT-IR and XRD of PT-TiO2-NTs-PSF composite membrane material;

[0044] Figure 13 Figure for SEM of PT-TiO2-NTs-PSF composite membrane material;

[0045] Figure 14 Figure for BSA rejection of PT-TiO2-NTs-PSF composite membrane material;

[0046] Figure 15 Figure for anti-fouling performance of PT-TiO2-NTs-PSF composite membrane material;

[0047] Figure 16 Figure for BSA rejection of PT-TiO2-NTs-PSF composite membrane material; DETAILED DESCRIPTION

[0048] The present application will be further described below, it should be noted that the present embodiment is based on the technical solution, and detailed implementation and specific operation process are given, but the present application is not limited to the present embodiment.

[0049] Example 1

[0050] A preparation method of PT-TiO2-NTs-PSF membrane material, comprising the following steps:

[0051] (1) Preparation of TiO2-NTs material

[0052] Firstly, 50 mL of cetyltrimethylammonium bromide (CTAB) and NaOH with a molar ratio of 16:1 were dissolved in a solution, and the reaction was carried out at a water bath temperature of 30°C and a mechanical stirring speed of 300 r / min. After 30 min, 20 mL of a mixture of tetrabutyl titanate and anhydrous ethanol with a volume ratio of 1:1 was slowly added to the reaction system, and the obtained precipitate was collected after 12 h of continuous stirring. After being washed and dried with pure water and ethanol, the sample was calcined in a muffle furnace at 600°C for 4 h. The above-mentioned sample was added to 80 mL of 1 mol / L NaOH, and the reaction was carried out in a 100 mL polytetrafluoroethylene reactor at 150°C for 10 h. Subsequently, the material was washed with pure water for multiple times until the filtrate was neutral. Finally, the material was vacuum dried at 80°C for 10 h, and was recorded as TiO2-NTs.

[0053] (2) Preparation of TiO2-NTs-PSF composite membrane

[0054] 0.05 g of TiO2-NTs was added to N-methyl-2-pyrrolidone (NMP), and 0.4 g of polyvinylpyrrolidone (PVP) was added as a precipitant. Subsequently, 1.8 g of polysulfone (PSF) was dissolved in the above-mentioned suspension at a water bath temperature of 50°C, and was fully stirred for 6-8 h to obtain a uniform casting suspension, and the casting solution was always kept at 10 g. The casting solution was placed at room temperature for 24 h at room temperature to remove air bubbles. After degassing, the casting solution was coated on a transparent glass plate with a thickness of 1 mm using an automatic film coater to form a composite membrane (thickness about 0.2 mm). After being exposed to air for 10 s, the suspension on the glass was immediately immersed in a mixed solution of ethanol and water with a volume ratio of 2:8, and the obtained membrane was recorded as TiO2-NTs-PSF-0.05. After complete solidification, the membrane was transferred to a room temperature water bath for 12 h to remove the residual solvent in the membrane structure.

[0055] (3) Preparation of PT-TiO2-NTs-PSF composite membrane

[0056] An interface polymerization method was used to form a layer of skin on the TiO2-NTs-PSF-0.05 membrane to prepare a composite nanofiltration membrane. Firstly, a 2.0 wt% PIP aqueous solution and a 0.15 wt% triformyl chloride TWC organic phase solution in n-hexane were prepared. The prepared TiO2-NTs-PSF was first immersed in the PIP solution for 30 min, air-dried, and then immersed in the TWC solution for 3 min. After removing the excess solution, the membrane was heated in an oven at 70°C for 10 min for further polymerization. Finally, the membrane was washed with deionized water to obtain a nanofiltration composite membrane, which was recorded as PT-TiO2-NTs-PSF-0.05.

[0057] Example 2

[0058] The difference from Example 1 is that the amount of TiO2-NTs added in step (2) is 0.1 g, and the prepared nanofiltration composite membrane is denoted as PT-TiO2-NTs-PSF-0.1.

[0059] Example 3

[0060] The difference from Example 1 is that the amount of TiO2-NTs added in step (2) is 0.15 g, and the prepared nanofiltration composite membrane is denoted as PT-TiO2-NTs-PSF-0.15.

[0061] Example 4

[0062] The difference from Example 1 is that the amount of TiO2-NTs added in step (2) is 0.2 g, and the prepared nanofiltration composite membrane is denoted as PT-TiO2-NTs-PSF-0.2.

[0063] Example 5

[0064] The difference from Example 1 is that the amount of TiO2-NTs added in step (2) is 0.25 g, and the prepared nanofiltration composite membrane is denoted as PT-TiO2-NTs-PSF-0.25.

[0065] Comparative Example 1

[0066] The difference from Example 3 is that the polysulfone material is directly prepared into a polysulfone membrane, denoted as PSF original membrane.

[0067] Comparative Example 2

[0068] The difference from Example 3 is that steps (1) and (2) are omitted, and a layer of skin is directly formed on the surface of the polysulfone membrane by interfacial polymerization, and the prepared composite membrane is denoted as PT-PSF.

[0069] Comparative Example 3

[0070] The difference from Examples 1-5 is that step (3) is omitted, and the TiO2-NTs-PSF membrane is directly used as a nanofiltration composite membrane, and is denoted as TiO2-NTs-PSF-0.05, TiO2-NTs-PSF-0.1, TiO2-NTs-PSF-0.15, TiO2-NTs-PSF-0.2, and TiO2-NTs-PSF-0.25, respectively.

[0071] Comparative Example 4

[0072] The difference from Comparative Example 3 is that no cetyltrimethylammonium bromide is added in step (1), and TiO2-NPs are prepared, and TiO2-NPs are used to replace TiO2-NTs in step (2).

[0073] Test Example 1

[0074] The composite membranes prepared in Example 3, Comparative Example 1 and Comparative Example 3 were structurally characterized.

[0075] (1) Rheological analysis of casting solution

[0076] Figure 1 The shear stress of the casting solution with different TiO2-NTs doping amounts varies with shear rate. Figure 1 As shown in the figure, the shear stress of PSF and TiO2-NTs-PSF casting solution increases with the increase of shear rate. The rheological curve equations of PSF and TiO2-NTs-PSF casting solution can be obtained through linear fitting. The fitting results show that the intercept of the linear regression equation is too small and the correlation coefficient R 2 Both tend to 1, and the shear stress T is positively correlated with the shear rate D, indicating that the viscosity of the PSF and TiO2-NTs-PSF casting solutions conforms to Newton's viscosity law and belongs to Newtonian fluids. The slope of the regression line is the viscosity η (Pa·s) of the casting solution.

[0077] (2) Casting liquid viscosity analysis

[0078] from Figure 2 As can be seen in Figure 3, the addition of TiO2-NTs to the PSF casting solution increases the viscosity of the suspension. When a small amount of filler (0.05-0.15 g) is added, only a slight increase in viscosity is observed. A further increase in the filler doping amount to 0.2 g leads to a sharp increase in viscosity. This is likely due to the addition of a high concentration of dopant with a high specific surface area, which increases the free surface available for adsorption of PSF and PVP, which are captured during the membrane preparation process. This adsorption of the polymer at the partially exposed hydroxyl groups of the TiO2-NTs leads to the formation of a suspension with a mechanically stable structure, which in turn leads to a very high viscosity.

[0079] (3) Infrared spectroscopy analysis

[0080] The formation and existence of TiO2-NTs in TiO2-NTs-PSF composite film were studied by FT-IR analysis. The infrared spectra of PSF film, TiO2-NTs and TiO2-NTs-PSF film are shown in Figure 2. Figure 3 As shown, both the PSF film and the TiO2-NTs-PSF film have the highest wavelengths at wave numbers of 1150, 1300, 1250, 1490, and 1580 cm -1 Characteristic absorption peak appears at 1150cm -1 The symmetrical O=S=O stretching vibration in the PSF is at 1300 cm -1 The asymmetric O=S=O stretching vibration is at 1250cm -1at 1490 cm -1 and 1580 cm -1 are stretching vibration peaks of C=C aromatic ring. 690 cm -1 and 2960 cm -1 absorption peaks correspond to amine stretching and asymmetric CH2ring stretching peaks in PVP. 3300 cm -1 - 3500 cm -1 are stretching vibration peaks of O-H. 400 cm -1 - 700 cm -1 peaks at 1635 -1 cm-1 are related to the stretching vibration of Ti-O-Ti in TiO2-NTs. However, the Fourier transform infrared spectra of TiO2-NTs-PSF remain similar compared to PSF films, and this similarity can be related to the low concentration of nanoparticles added to these samples. Only using EDS can confirm the presence of TiO2-NTs in the PSF films. However, the O-H bending vibration peak located at 1635 -1 cm-1 shifts with the increase of TiO2-NTs doping amount, which can be due to the increase of O-H concentration with the increase of TiO2-NTs concentration, the increase of infrared active vibration, thus leading to the shift of spectral peak position.

[0081] Figure 12 (a) is the FT-IR graph of PT-TiO2-NTs-PSF film, 1614 cm -1 The peak at 1635

[0082] (4) X-ray diffraction (XRD) analysis

[0083] Figure 4The XRD patterns of the PSF film, TiO2-NTs, and TiO2-NTs-PSF film are shown in Figure 1. Comparison with the standard spectrum of anatase TiO2 (JCPDS 84-1286) reveals that the 2θ peaks of TiO2-NTs appear at 25.5°, 37.9°, 48.1°, 54.2°, 62.8°, and 69.1°, corresponding to the crystal planes (101), (004), (200), (211), (204), and (116), which are consistent with the positions of the standard spectrum, indicating the successful synthesis of anatase TiO2-NTs. A new peak appears at 2θ = 25.5° in the TiO2-NTs-PSF film, indicating that titanium dioxide is successfully incorporated into the film matrix. Furthermore, the anatase TiO2 peak increases with increasing TiO2-NTs doping levels. This is because the peak height or intensity is determined by the number of crystallites that diffract X-rays or the amount of phase that exhibits reflection. When incorporated into the PSF film, the intensity of the prominent TiO2 peak has been reduced due to fewer crystallites diffracting X-rays.

[0084] Figure 12 (b) is the XRD pattern of the PT-TiO2-NTs-PSF film. It can be seen that the composite film PT-TiO2-NTs-PSF has a similar spectrum to the TiO2-NTs-PSF film. Similarly, due to the small number of TiO2-NTs grains, they cannot be displayed in the figure. It can also be seen that the crystal form of the film has not been changed after interfacial polymerization.

[0085] (5)HRTEM

[0086] Figure 5 (a) It can be observed that the diameter of the TiO2-NTs is approximately 15-20nm and the length is 100-200nm. In addition, the lattice fringes of the TiO2-NTs can be clearly observed in 5(b), which are 0.35nm, very close to the (101) plane of the TiO2 anatase phase in the XRD results. This shows that the TiO2-NTs prepared under the current experimental conditions did not significantly change the lattice structure of the sample. It is confirmed that anatase titanium dioxide and titanium dioxide nanotubes were successfully synthesized.

[0087] (6) SEM images

[0088] Figure 6 The SEM images of PSF, TiO2-NPs-PSF, and TiO2-NTs-PSF show that all composite membranes exhibit an asymmetric structure consisting of a thin dense top layer and a porous sublayer with fully developed finger-like pores. This is because the addition of hydrophilic PVP improves the interconnectivity of the pores, resulting in finger-like pores. Figure 6(a) PSF and 6(d) TiO2-NTs-PSF planar view. It was found that the PSF surface was smooth and the pores were uniform, the TiO2-NTs-PSF surface had a titanium dioxide embedded film surface, and a macroporous structure was formed, which was due to the increase in the viscosity of the casting solution by the increase in the amount of TiO2-NTs doping, resulting in the interaction between the polymer matrix and TiO2-NTs, which slowed down or hindered the penetration of TiO2-NTs into the sublayer, prevented the polymer from shrinking during the phase inversion process, and TiO2-NTs were more embedded or adsorbed on the skin layer. By Figure 6 (b), (c) and (e), (f) contrast the cross-sectional pore diagram of PSF and TiO2-NTs-PSF, it can be seen that the addition of TiO2-NTs leads to an increase in finger-like protrusions and pores in the sublayer, and a decrease in pore size. Therefore, a small amount of TiO2 can greatly change the internal structure of the membrane and improve the flux.

[0089] Figure 13 (a) is the SEM diagram of the surface of the PT-TiO2-NTs-PSF membrane, it can be seen that the pore size of the membrane is significantly reduced, Figure 13 (b) is the cross-sectional diagram of the PT-TiO2-NTs-PSF membrane, it can be seen that a thin layer is covered on the base membrane. The results show that a skin layer is formed on the microporous base membrane, and the membrane successfully completes the interfacial polymerization.

[0090] Test Example 2

[0091] The performance of the composite membrane of Comparative Example 3 was characterized.

[0092] (1) Mechanical properties

[0093] Figure 7 is the relationship curve between the breaking strength of TiO2-NTs-PSF membrane and the amount of TiO2-NTs doping. From Figure 7It can be concluded that the breaking strength of TiO2-NTs-PSF membrane with TiO2-NTs doping amount of 0.05-0.2 g is significantly higher than that of PSF, and with the increase of TiO2-NTs doping amount, the breaking strength of TiO2-NTs-PSF increases sharply at first and then decreases, and when the TiO2-NTs doping amount is 0.05 g, the breaking strength reaches the maximum value (28.2 N). This is because the addition of TiO2 sol makes the pore size of the surface skin layer of the composite membrane smaller, and the formation of an organic-inorganic network structure with nanotube particles as crosslinking points increases the strength of the TiO2-NTs-PSF membrane. However, when the sol concentration is greater than 0.05 g, the agglomeration of nanoparticles causes large voids around the agglomeration points, resulting in a decrease in membrane strength. When the doping amount increases to 0.25 g, the breaking strength of the TiO2-NTs-PSF membrane is significantly lower than that of PSF, which may be due to the fact that when the nanoparticle content is relatively large, the agglomeration of particles in the membrane is more pronounced, and the increase in agglomerated particles not only weakens the reinforcing effect of nanoparticles, but also makes the agglomerated particles a stress defect when the composite membrane is subjected to external forces, to some extent, reducing the mechanical properties of the membrane.

[0094] (2) Thermogravimetry

[0095] Figure 8 The TGA curves of the prepared composite membranes with different TiO2-NTs doping amounts are shown. From Figure 8 It can be seen from the above that the pure PSF membrane is thermally unstable without TiO2-NTs particles. With the increase of TiO2-NTs doping amount, the thermal stability of TiO2-NTs-PSF membrane is significantly improved. After heating, the composite membrane degrades rapidly, and the first stage at 25-100°C is due to the elimination of water, while PSF at 100-200°C is mainly polyvinylpyrrolidone and TiO2-NTs Ti-OH, and the third stage decomposition at 350-510°C is considered to be the main polymer chain decomposition. Compared with PSF membrane, TiO2-NTs-PSF membrane does not show significant weight loss in the temperature range, which indicates that the thermal stability of the membrane increases with the increase of TiO2-NTs amount, and the reason for the increase of stability may be that TiO2-NTs has good thermal performance, which limits the decomposition of PSF membrane matrix and increases the thermal decomposition temperature of the composite membrane. The stronger the thermal stability of the membrane, the less likely the physical properties of the membrane will change, which means it is more durable and can be expected to have stable separation performance.

[0096] (3) Hydrophilic property

[0097] The contact angle can be explained as a measure of the hydrophilicity of the composite membrane, that is, the composite membrane with lower water contact angle shows better hydrophilicity. Figure 9The water contact angle of PSF composite film doped with different amounts of TiO2-NTs was tested. It can be seen that the contact angle of PSF film is the highest, reaching 75°, and the hydrophilicity is continuously enhanced with the increase of the amount of TiO2-NTs, and when the amount of TiO2-NTs is 0.25 g, the hydrophilicity reaches 50.7°. This is probably because TiO2-NTs itself has good hydrophilicity, and hydroxyl groups are provided by Ti-OH, so the TiO2-NTs-PSF composite film shows higher hydrophilicity.

[0098] (4) Determination of porosity, average pore size and pure water flux

[0099] Figure 10 (a) The porosity of TiO2-NTs-PSF film with different amounts of TiO2-NTs. Compared with PSF film, the porosity increases with the increase of the amount of TiO2-NTs. This is mainly because when the casting solution is cured to form a film, the interface stress relaxation between the organic and inorganic phases increases the number of micropores in the film, thereby increasing the porosity of the film. And when the amount of addition is greater than 0.15 g, the effect of increasing the porosity of the film slows down, and the high concentration of fillers increases the viscosity of the system and the solute concentration, increasing the compactness of the film, thereby slowing down the increase of the film porosity. Figure 10 (b) The average pore size of TiO2-NTs-PSF film with different amounts of TiO2-NTs. It can be seen that the addition of TiO2-NTs significantly reduces the average pore size of PSF film. This is probably because the hydrophilicity of TiO2-NTs makes the polymerization effect better during the phase inversion process of the film, and the titanium dioxide nanoparticles can be embedded in the film to block the pores. However, when the amount of addition is greater than 0.15 g, the hydrophilic TiO2-NTs are prone to agglomeration, and the viscosity of the suspension increases sharply, which makes it difficult for the nanoparticles to move and embed in the surface layer, preventing the polymer from shrinking during the precipitation process, and a large number of large surface pores are formed near the TiO2-NTs aggregates. Therefore, an appropriate amount of TiO2-NTs can increase the porosity and average pore size of the film. Figure 10 (c) The pure water flux of TiO2-PSF film with different amounts of TiO2-NTs can be seen. With the increase of the amount of TiO2-NTs, the pure water flux also gradually increases, which is consistent with the change trend of the porosity of TiO2-PSF.

[0100] Test Example 3

[0101] (1) Test the rejection rate of bovine serum protein of PSF original film of Comparative Example 1, TiO2-NTs-PSF film prepared in Comparative Example 3 and TiO2-NPs-PSF film prepared in Comparative Example 4.

[0102] The test process is as follows: the protein content is determined by using the Coomassie brilliant blue method (Bradford method), and a BSA (bovine serum albumin) solution with a concentration of 0.1 mg·mL -1 is used as a standard solution to draw a protein content standard curve. After the prepared bovine serum albumin is ultrafiltered, the absorbance of a certain volume of the permeate at 595 nm is determined, and the protein content of the permeate is calculated.

[0103] Figure 11 is the rejection rate of the composite membrane to bovine serum albumin, and Figure 11 (a) It can be seen that the rejection rate of the PSF original membrane without TiO2-NPs to BSA reaches 21.0%, and when the doping amount of TiO2-NPs is 0.15 g, the rejection rate to BSA reaches the maximum, which is 54.3%, which is 33.3% higher than that of PSF. Figure 11 (b) It can also be seen that when the doping amount of TiO2-NTs is 0.15 g, the rejection rate of TiO2-NTs-PSF to BSA reaches the maximum, which is 65.1%, which is consistent with the change trend of the average pore size of the TiO2-NTs-PSF membrane, and is 10.8% higher than that of the TiO2-NPs-PSF membrane. This may be due to the fact that the TiO2-NTs modified by cetyltrimethylammonium bromide are more dispersed, so that the membrane is not easy to produce more large pore structures due to the agglomeration of nanoparticles, and the porous structure of TiO2-NTs itself also has a certain rejection effect on BSA, so that the rejection rate of TiO2-NTs-PSF to BSA is higher.

[0104] (2) The rejection rate of the PT-PSF membrane prepared in Test Comparative Example 2 and the PT-TiO2-NTs-PSF membrane prepared in Example 3 to bovine serum albumin is tested.

[0105] It can be seen from Figure 14 that the rejection rate of the PT-PSF membrane to BSA is the lowest, which is 35.6%, and when the doping amount of TiO2-NTs reaches 0.15 g, the rejection rate of the composite membrane to BSA reaches the maximum, which is 76.7%. This is because the PT-TiO2-NTs-PSF composite membrane itself has the smallest pore size when 0.15 g of PT-TiO2-NTs is doped, and has the highest rejection rate to BSA. After the interface polymerization of piperazine and triformyl chloride, the rejection rate of the membrane to BSA is improved by 11.6%.

[0106] Test Example 4

[0107] The anti-pollution performance of the PSF original membrane of Test Comparative Example 1 and the PT-TiO2-NTs-PSF membrane material prepared in Examples 1-5 is tested.

[0108] The test process is as follows: firstly, the membrane is pre-pressed at 0.2 MPa for 60 min with pure water, and the pure water flux at 0.1 MPa for 60 min is calculated; then, the pure water is replaced by 1 g / L BSA solution (pH = 7.4), and the permeation flux for 60 min is calculated; subsequently, the contaminated membrane is washed with pure water for 30 min, and the recovery flux of the cleaned membrane is continuously measured, and the permeation rate reduction rate is calculated to evaluate the anti-pollution performance of the membrane.

[0109] Figure 15 (a) is the anti-pollution performance of the PSF original membrane and the PT-TiO2-NTs-PSF membrane material. As can be seen from the figure, after three cycles of filtering BSA, the pure water flux recovery rates of PSF and PT-TiO2-NTs-PSF doped with 0.05 g-0.25 g TiO2-NTs are 49.5%, 65.0%, 68.5%, 75.5%, 79.6%, 81.3% respectively, which is due to the increase in hydrophilicity of the composite membrane caused by the doping of hydrophilic TiO2-NTs, so that the anti-pollution ability of the membrane is enhanced.

[0110] Figure 15 (b) is the BSA retention rate of the PT-TiO2-NTs-PSF-0.15 composite membrane after three cycles of use. As can be seen, the BSA retention rate decreases from 76.7% to 65.3%, a decrease of 11.5%, which shows that PT-TiO2-NTs-PSF has good anti-pollution ability.

[0111] Test Example 5

[0112] The retention rates of the TiO2-NTs-PSF-0.15 membrane material prepared in Test Comparative Example 3 and the PT-TiO2-NTs-PSF-0.15 membrane material prepared in Example 3 for potato wastewater protein are tested.

[0113] Figure 16 The retention rates of TiO2-NTs-PSF and PT-TiO2-NTs-PSF for potato wastewater protein are as follows: it can be seen that the retention rate of TiO2-NTs-PSF for potato protein can reach 63%, and the retention rate for protein after interfacial polymerization of piperazine and trimethyloyl chloride can be increased to 81.2%. It shows that the method can be used for the pore shrinkage treatment of TiO2-NTs-PSF, and the protein retention rate is increased.

[0114] Therefore, the application adopts the above structure, and the preparation of a PT-TiO2-NTs-PSF membrane material and the application thereof in recovering protein in potato wastewater, the TiO2-NTs-PSF composite membrane material has good hydrophilicity, mechanical properties and thermal stability, and has a high retention rate for potato wastewater protein, and has an important application prospect in the field of potato wastewater resource recovery.

[0115] It should be pointed out finally that the above examples are only used to illustrate the technical solutions of the present application but not to limit it, and although the present application has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that the technical solutions of the present application can still be modified or replaced equivalently, and these modifications or equivalent replacements should not make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present application.

Claims

1. A method for preparing a PT-TiO2-NTs-PSF film material, characterized by: The method comprises the following steps: (1) Preparation of TiO2-NTs nanomaterials (2) Preparation of TiO2-NTs-PSF composite ultrafiltration membrane TiO2-NTs and polyvinylpyrrolidone are added into N-methyl-2-pyrrolidone, then heated under water bath condition, and stirred fully after adding polysulfone to obtain a uniform casting solution, after degassing, the casting solution is coated on a transparent glass plate to form a composite membrane, then the suspension on the glass is immersed into a mixed solution of ethanol and water to obtain TiO2-NTs-PSF; (3) Preparation of PT-TiO2-NTs-PSF composite nanofiltration membrane After interfacial polymerization of TiO2-NTs-PSF with piperazine solution and 1,3,5-benzene tricarbonyl chloride solution respectively, heating is performed to obtain PT-TiO2-NTs-PSF.

2. The method for preparing a PT-TiO2-NTs-PSF film material according to claim 1, characterized in that: The preparation process of TiO2-NTs nanomaterials in step (1) is as follows: Cetyltrimethylammonium bromide and NaOH are dissolved in an aqueous solution, a mixed solution of tetrabutyl titanate and anhydrous ethanol is slowly added dropwise under water bath stirring condition, and stirring is continuously performed until the reaction is completed, then after separation, washing, drying, calcination and grinding, the sample is added into a polytetrafluoroethylene reaction kettle for reaction, and after washing and drying, TiO2-NTs is obtained.

3. The method for preparing a PT-TiO2-NTs-PSF film material according to claim 2, characterized in that: The molar ratio of cetyltrimethylammonium bromide and NaOH in step (1) is 16:1, and the volume of water solution is 50 mL; The water bath reaction temperature is 30℃, the stirring speed is 300 r / min, and the stirring time is 30 min; The addition amount of the mixed solution of tetrabutyl titanate and anhydrous ethanol is 20 mL, and the volume ratio of tetrabutyl titanate and anhydrous ethanol in the mixed solution is 1:1; After the reaction is completed, the precipitate is filtered, and after washing and drying with pure water and ethanol, the sample is calcined at 600℃ in a muffle furnace for 4 h; The calcined and ground sample needs to be added into 80 mL of 1 mol / L NaOH, and reacted at 150℃ for 10 h in a 100 mL polytetrafluoroethylene reaction kettle, the obtained precipitate is washed with 0.1 mol / L hydrochloric acid, and then washed with pure water for multiple times until the filtrate is neutral, and then vacuum dried at 80℃ for 10 h to obtain TiO2-NTs.

4. The method for preparing a PT-TiO2-NTs-PSF film material according to claim 1, characterized in that: In step (2), the mass ratio of TiO2-NTs: polyvinylpyrrolidone: polysulfone is 0.05-0.25:0.5:0.8, and the casting solution always maintains 10 g.

5. The method for preparing a PT-TiO2-NTs-PSF film material according to claim 1, characterized in that: In step (2), the water bath temperature is 50℃, and the time is 6-8 h.

6. The method for preparing a PT-TiO2-NTs-PSF film material according to claim 1, characterized in that: In step (2), the casting solution is placed at room temperature for 24 hours to remove bubbles, after degassing, the automatic film coater is used to coat the casting solution on a transparent glass plate with a thickness of 1 mm to form a composite membrane with a thickness of 0.2 mm, after being exposed to air for 10 seconds, the suspension on the glass is immediately immersed into a mixed solution of ethanol and water with a volume ratio of 2:8, and after complete solidification, the membrane is transferred into a room temperature water bath for 12 hours.

7. The method for preparing a PT-TiO2-NTs-PSF film material according to claim 1, characterized in that: In step (3), the concentration of piperazine aqueous solution is 2.0 wt%, and the concentration of 1,3,5-benzene tricarbonyl chloride organic phase solution in n-hexane is 0.15 wt%. The TiO2-NTs-PSF was immersed in the aqueous piperazine solution for 30 min, air-dried, and then immersed in the 1,3,5-benzene tricarbonyl chloride solution for 3 min.

8. The method for preparing a PT-TiO2-NTs-PSF film material according to claim 1, characterized in that: The temperature for further polymerization in the oven after the completion of the immersion in step (3) was 70℃, and the time was 10 min.

9. A PT-TiO2-NTs-PSF membrane material, characterized in that: The preparation method according to any one of claims 1-8.

10. Use of a PT-TiO2-NTs-PSF membrane material according to claim 9, characterized in that: Application of the PT-TiO2-NTs-PSF membrane material in the recovery of proteins in potato starch wastewater.

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