CN111375316A

CN111375316A - Preparation method of multi-walled carbon nanotube low-pressure film for strengthening removal of humic acid in water and relieving pollution

Info

Publication number: CN111375316A
Application number: CN202010203323.6A
Authority: CN
Inventors: 郭瑾; 栾桂荣; 马燕林; 薛小雷
Original assignee: Beijing University of Technology
Current assignee: Beijing University of Technology
Priority date: 2020-03-20
Filing date: 2020-03-20
Publication date: 2020-07-07
Anticipated expiration: 2040-03-20
Also published as: CN111375316B

Abstract

A preparation method of a multi-walled carbon nanotube low-pressure membrane for strengthening removal of humic acid in water and relieving pollution belongs to the crossing field of nano materials and water treatment technology. According to the invention, the multi-walled carbon nanotube is subjected to non-covalent modification by the blending ultrasound of PEG and the multi-walled carbon nanotube, and then the multi-walled carbon nanotube low-pressure membrane is prepared by a vacuum filtration method. The low-pressure membrane prepared from the PEG non-covalently modified multi-walled carbon nano-tube can effectively improve the removal of humic acid in water and can obviously improve the pollution resistance of the membrane. Compared with the common PVDF ultrafiltration membrane with the diameter of 0.01 mu m, the invention improves the removal of humic acid by nearly 50 percent, effectively relieves the membrane pollution problem caused by humic organic substances represented by humic acid and biological macromolecular substances represented by bovine serum albumin, improves the effluent quality and prolongs the service life of the membrane. The method is simple and feasible to operate and easy to realize.

Description

Preparation method of multi-walled carbon nanotube low-pressure film for strengthening removal of humic acid in water and relieving pollution

Technical Field

The invention relates to a technology for preparing a multi-walled carbon nanotube low-pressure membrane and removing organic pollutants in a water body, belonging to the crossing field of nano materials and water treatment technology.

Background

Low Pressure Membrane filtration (LPM) is a Membrane separation technique that operates at a relatively Low operating Pressure (below 1-2 bar), commonly referred to as ultrafiltration and microfiltration. Since the beginning of the application of the technology in the field of water treatment, the technology has become one of the most promising technologies in the field of water treatment because of its ability to effectively trap pollutants, bacteria and pathogenic bacteria. However, in practical applications, membrane fouling reduces the filtration performance of the membrane, and increases the cost of membrane technology due to membrane cleaning and replacement, which greatly limits the application of membrane separation technology in the field of water treatment.

Low pressure membrane fouling mainly includes inorganic, organic and biological contamination. Among them, organic pollution and biological pollution are more serious pollution phenomena in the low-pressure membrane pollution process. In addition, the occurrence of low pressure membrane organic contamination can further exacerbate biological contamination. Therefore, developing a low pressure membrane that can effectively remove organic contaminants and mitigate fouling is a key to controlling membrane fouling.

Organic pollutants in water can be divided into two main categories of natural organic pollutants and artificially synthesized organic pollutants, wherein humus organic matters are generally considered to be one of the most serious pollutants causing membrane pollution in the water treatment process. Humic Acid (HA), which is a main component of humus organic substances, widely exists in polluted water bodies, and not only can generate unpleasant color and smell, but also can form carcinogenic trihalomethane in a chlorine disinfection process. In addition, HA can also have a certain adsorption and complexation effect on toxic organic matters and heavy metal ions in the water body, so that composite pollutants are formed.

In order to relieve the pollution of humus organic matters in water to membranes, common technologies mainly comprise pretreatment (coagulation, filtration and ozone adsorption preoxidation) and membrane modification technologies. Although the reduction of the humic substances content of water by pretreatment is the main means of ameliorating membrane fouling, the ability to control membrane fouling is still quite limited.

Membrane modification techniques include blend modification and membrane surface modification. The blending modification is mostly carried out by a phase conversion method. The membrane surface modification method comprises the following steps: surface coating modification, interfacial polymerization modification, plasma grafting modification, nano material addition and the like. The addition of Multi-walled carbon nanotubes (MWCNTs) to modify the surface of the membrane to improve the anti-fouling performance and the ability to remove contaminants of the membrane is one of the hot spots studied in recent years. Some scholars coat MWCNTs on the membrane surface by using a pressurized, filter coating method. The method is simple to operate, and the MWCNT modified membrane prepared by the method has excellent anti-pollution performance and pollutant interception effect.

As a nano material with a hydrophobic surface, the multi-wall carbon nano tube is usually promoted to agglomerate in an aqueous solution, so that the application of the multi-wall carbon nano tube in the field of membrane treatment is limited. Therefore, many scholars improve the dispersibility and hydrophilicity of the multi-wall carbon nano-tubes in a solvent by modifying the multi-wall carbon nano-tubes so as to achieve better application effects. The modification of the multi-wall carbon nano tube is mainly divided into covalent modification and non-covalent modification. The covalent modification of the multi-walled carbon nanotube is to graft some functional groups or polymer chains onto the surface of the multi-walled carbon nanotube through covalent bonds, however, the covalent modification destroys the inherent properties of the multi-walled carbon nanotube, such as electrical conductivity, mechanical property and the like. The non-covalent modification of the multi-wall carbon nano-tube is mainly realized by intermolecular interaction force (such as Van der Waals force, pi-pi bond and hydrogen bond) or by utilizing the hydrophobic effect between the dispersant and the multi-wall carbon nano-tube, and the dispersant is adsorbed or wound on the multi-wall carbon nano-tube to improve the dispersibility and the hydrophilicity of the multi-wall carbon nano-tube. In addition, the non-covalent modification method of the multi-wall carbon nano tube is simple and cannot damage the inherent properties of the carbon nano tube.

At present, the scholars successfully prepare the multi-wall carbon nano-tube by non-covalent modification and vacuum filtrationMulti-walled carbon nanotube films are provided. Sweetman et al, utilize antibiotic cyprohexate to non-covalently modify multi-walled carbon nanotubes, and prepare multi-walled carbon nanotube membranes by vacuum filtration, which can effectively remove Escherichia coli from water at a removal rate>99 percent. (Jenny et al, Bacterial Filtration Using Carbon nanotubes/antibacterial Buckypaper membranes. journal of nanomaterials.2013,2013: 1-11.). Rashid et al, prepared a multi-walled carbon nanotube membrane by non-covalent modification of multi-walled carbon nanotubes with surfactant Triton X-100 or various macrocyclic ligands (derivatized porphyrins, phthalocyanines or calixarenes) by vacuum filtration. The removal capability of the non-covalent modified multi-wall carbon nanotube film on Trace organic compounds (Trocs) is researched. The result shows that most of the non-covalent modified multi-wall carbon nanotube films have good removal effect on the Trocs. Wherein, the removing rate of 11 of 12 kinds of Trocs by the multi-wall carbon nanotube membrane prepared by the non-covalent modification of Triton X-100 exceeds 80%. However, the multi-walled carbon nano-film prepared by utilizing the phthalocyanine non-covalent modification has low removal rate of the Trocs. (sweet animal, Synthesis, Properties, Water and solvent Performance of MWNTBuckypapers. journal of Membrane science.2014,456: 175-. Furthermore, Rashid et al non-covalently modified multi-walled carbon nanotubes with different biopolymers (bovine serum albumin, lysozyme, gellan gum and chitosan) as dispersants prepared multi-walled carbon nanotube membranes with pore diameters of 21 + -5 nm, and pure water flux of the membranes was only 23 + -6 L.m^-2·h^-1·bar^-1Belongs to the field of nano-filtration membranes, and the membrane has a good removal effect on trace organic matters. (rashed et al, nanofiltraction Applications of Tough MWNT Buckypaper Membranes containment biopolymers. journal of Membrane science.2017,529: 23-34.).

Polyethylene glycol (PEG) as an amphiphilic polymer has the characteristics of neutrality, no toxicity, no antigen, no immunogenicity and the like, and also has good biocompatibility. Is widely applied to the field of biological medicine. Research shows that the PEG modified multi-walled carbon nano-tube can effectively relieve the adhesion of protein and reduce the biotoxicity of the multi-walled carbon nano-tube. Please see "Adsorption of Plasma Proteins on to PEGylated Single-Walled carbon nanotubes: The Effects of Protein Shape, PEG Size and gradient Density", (H.Lee.journal of Molecular Graphics and modeling.2017, 75(75): 1-8); "CarbonNanotubes in Cancer Therapy: A More Precise hook at the Role of CarbonNanotube-Polymer Interactions" (M.Adeli, R.Soleuman, Z.Beiranvand and F.Madani.chemical Society reviews.2013,42(12): 5231-. At present, the method for modifying the multi-wall carbon nano-tube by PEG is mostly a covalent modification method. No systematic study on the aspects of enhancing the removal of humic acid in water and relieving pollution by directly preparing a multi-walled carbon nano tube low-pressure membrane by using PEG to carry out non-covalent modification on the multi-walled carbon nano tube is available. The PEG non-covalent modification method for preparing the carbon nanotube low-pressure film is simple to operate and easy to realize, and cannot damage the space structure and other properties of the carbon nanotube, such as conductivity, mechanical properties and the like.

Disclosure of Invention

In view of the above, the invention provides a preparation method of a multi-walled carbon nanotube low-pressure membrane capable of enhancing removal of HA in water and relieving pollution, the membrane effectively improves removal of HA in water, relieves membrane pollution problems caused by humus organic matters represented by humic acid and biomacromolecules represented by bovine serum albumin, and prolongs service life of the membrane while improving effluent quality.

The membrane-passing water is 5mg/L HA solution and 200mg/L Bovine Serum Albumin (BSA) solution which are prepared in a laboratory and are respectively used for testing the HA removal effect and the anti-fouling capacity of the multi-walled carbon nanotube low-pressure membrane prepared by PEG non-covalent modification; the BSA solution was used only to examine the anti-fouling ability of the membrane.

The ultrasonic method for preparing the multi-walled carbon nanotube dispersion liquid is to add the multi-walled carbon nanotube into a PEG solution and carry out ultrasonic treatment for a period of time by using an ultrasonic cell crusher, wherein the concentration of the multi-walled carbon nanotube dispersion liquid is 0.5-2 mg/mL.

The invention prepares the multi-wall carbon nanotube membrane by PEG non-covalent modification, which comprises the following steps:

(1) preparing a multi-wall carbon nano tube dispersion liquid: weighing a certain amount of multi-walled carbon nanotubes, adding the multi-walled carbon nanotubes into a polyethylene glycol solution, and carrying out ultrasonic treatment for a period of time to uniformly disperse the multi-walled carbon nanotubes.

(2) Preparing a multi-wall carbon nano tube low-pressure film: because the polyethylene glycol solution has viscosity, the viscosity of the polyethylene glycol solution is higher along with the increase of the molecular weight of the polyethylene glycol and the increase of the concentration of the solution, in order to ensure that the MWCNT after the non-covalent modification of the polyethylene glycol is_-COOHThe dispersion solution can more easily pass through a microfiltration porous membrane, the non-covalent modified multi-wall carbon nano tube dispersion solution is diluted to 0.2-0.25mg/mL by Milli-Q water, and the ultrasonic treatment is carried out for 5-10min again. And (3) passing the multi-walled carbon nanotube dispersion liquid through a microfiltration porous membrane by a vacuum filtration method, then cleaning a multi-walled carbon nanotube low-pressure membrane by Milli-Q water and ethanol, and drying for later use.

The multi-walled carbon nanotube is preferably a multi-walled carbon nanotube with an outer diameter of more than 30-50nm in order to ensure that the prepared multi-walled carbon nanotube film is more stable.

The multi-walled carbon nanotube has the carbon nanotube loading capacity of 30-50g/m for ensuring the more stable and pollution-resistant performance of the prepared multi-walled carbon nanotube film²The load amount used in the present invention is 45g/m²。

In the step (1), the ultrasonic power and the ultrasonic time of the multiwall carbon nanotube dispersion liquid are comprehensively considered, the ultrasonic power is 100-300W, and the ultrasonic time is at least 15min, preferably about 20 min.

In the step (2), the economic benefit, the dispersion effect of the multi-walled carbon nano-tube and the performance of the modified membrane are comprehensively considered, the concentration of the PEG solution is 2-50mg/mL, the molecular weight of the PEG is 3350-.

In the step (2), the microfiltration porous membrane used for suction filtration is a polyether sulfone (PES) membrane which is a commercial flat membrane, and the effective filtration area of the membrane used in the invention is 13.4cm²。

And (3) the vacuum degree in the step (2) is 50-300mbar during vacuum filtration.

According to the invention, the method for preparing the multi-walled carbon nanotube low-pressure membrane by PEG non-covalent modification is simple, no special equipment is needed, the prepared multi-walled carbon nanotube membrane is stable and uniform, the removal of natural organic matters HA by the multi-walled carbon nanotube membrane is effectively improved, the problem of membrane pollution caused by humus organic matters represented by HA and biomacromolecule substances represented by BSA is solved, the effluent quality is improved, and the service life of the membrane is prolonged.

In the invention, a multi-walled carbon nanotube low-pressure membrane prepared by PEG non-covalent modification is subjected to a membrane dynamic pollution experiment in a constant-current filtering device, and the flow rate of the passing membrane is 75L/(m)²H). The result proves that compared with the traditional commercial PVDF membrane with the diameter of 0.01 mu m, the PEG non-covalent modified multi-walled carbon nanotube low-pressure membrane HAs better HA removal capability and effectively improves the effluent quality. In addition, the change of transmembrane pressure difference is monitored, and the multi-walled carbon nanotube low-pressure membrane subjected to non-covalent modification can effectively relieve the membrane pollution problem caused by humus organic matters represented by HA and biomacromolecule substances represented by BSA, so that the service life of the membrane is prolonged.

Drawings

FIG. 1 is a 0.01 μm PVDF membrane (left side of FIG. 1) non-covalently modified MWCNT with PEG_-COOHMembrane (fig. 1 right);

FIG. 2 is a 0.01 μm PVDF membrane and PEG non-covalently modified MWCNT_-COOHPure water flux comparison plots for membranes;

FIG. 3 is a 0.01 μm PVDF membrane and PEG non-covalently modified MWCNT_-COOHContact angle contrast plot for film;

FIG. 4 is a 0.01 μm PVDF membrane, PES-based membrane and PEG non-covalently modified MWCNT_-COOHA comparison of membrane to HA removal;

FIG. 5 is a 0.01 μm PVDF membrane, PES-based membrane and PEG non-covalently modified MWCNT_-COOHA comparison of the transmembrane pressure difference when the membrane is depleted of HA;

FIG. 6 is a 0.01 μm PVDF membrane, PES-based membrane and PEG non-covalently modified MWCNT_-COOHA comparison of the transmembrane pressure difference of the membrane when BSA was removed;

FIG. 7 is a graph comparing HA removal rates for 0.01 μm PVDF membrane, PES-based membrane, and PEG non-covalently modified MWCNT membrane;

FIG. 8 is a graph comparing the transmembrane pressure difference when HA was removed for 0.01 μm PVDF membrane, PES-based membrane and PEG non-covalently modified MWCNT membrane;

FIG. 9 is a graph comparing the transmembrane pressure difference between a 0.01 μm PVDF membrane, a PES-based membrane and a PEG non-covalently modified MWCNT membrane when BSA was removed;

Detailed Description

The present invention is illustrated by the following examples, but is not limited thereto.

Example 1:

this example provides a MWCNT using PEG-6000 pair_-COOH(outer diameter of 30-50nm, length>10um) to prepare the multi-wall carbon nano-tube low-pressure film. The membrane effectively improves the removal of HA in water, relieves the membrane pollution problem caused by humus organic matters represented by HA and biomacromolecule substances represented by BSA, and prolongs the service life of the membrane while improving the water quality of effluent. The method comprises the following specific steps:

before the experiment, PES-based membranes (effective filtration area 13.4 cm) were first filtered²) Cleaning, soaking a new PES membrane in 50% ethanol for 2h to remove a membrane surface protective agent glycerol, then cleaning with ultrapure water, and soaking in the ultrapure water for later use after cleaning.

Weighing 60mg MWCNT with outer diameter of 30-50nm_-COOHAdding the mixture into a polyethylene glycol solution with the concentration of 5mg/mL and the volume of 60mL, and carrying out ultrasonic treatment on the mixture by an ultrasonic crusher, wherein the ultrasonic treatment time is 20min and the ultrasonic power is 150W.

Because the polyethylene glycol solution has viscosity, the viscosity of the polyethylene glycol solution is higher along with the increase of the molecular weight of the polyethylene glycol and the increase of the concentration of the solution, in order to ensure that the MWCNT after the non-covalent modification of the polyethylene glycol is_-COOHThe MWCNT prepared by the method is easier to pass through PES-based membrane_-COOHThe dispersion was diluted with 130mL of Milli-Q water and MWCNT was obtained after dilution_-COOHThe concentration of the dispersion is 0.24mg/mL, and then ultrasonic cleaning is carried out for 10min by an ultrasonic cleaning instrument.

Diluting MWCNT at 230mbar vacuum_-COOHPassing the dispersion through a polyethersulfone-based membrane by vacuum filtration, and then cleaning with 250mL of LLIII-Q water and 10mL of ethanolWashing MWCNT low-pressure membrane, drying for use. MWCNT based on effective area of PES-based membrane_-COOHThe calculated amount of the modified MWCNT is 45g/m²。

As can be seen from FIG. 1, MWCNT is aligned using PEG_-COOHThe MWCNT is successfully prepared by non-covalent modification and vacuum filtration_-COOH-PEG-6000 membrane.

As can be seen from FIG. 2, MWCNT was compared with 0.01 μm PVDF film_-COOHThe pure water flux of the-PEG-6000 membrane is lower.

As can be seen from FIG. 3, the MWCNT was compared with the 0.01 μm PVDF film_-COOHThe contact angle of the-PEG-6000 film is lower, and is reduced by about 40 degrees. The reduction of the contact angle shows that the PEG-6000 introduced into the multi-wall carbon nanotube low-pressure membrane further improves the hydrophilicity of the modified membrane.

Using MWCNTs_-COOHThe PEG-6000 membrane is used for carrying out membrane filtration pollution experiments on HA and BSA solutions;

for comparison, a membrane filtration contamination experiment was performed using a 0.01 μm PVDF membrane under the same conditions;

the constant-current filtering device is adopted to carry out membrane filtration pollution experiments, and the flow rate of the filtered membrane is 75L/(m)²·h)；

UV measurement with a spectrophotometer₂₅₄Absorbance of (b) represents MWCNT_-COOHThe HA removal effect of PEG-6000 and commercial 0.01 μmVDF membranes;

and the transmembrane pressure difference of the membrane is monitored in real time in the experimental process by adopting a pressure sensor, and data is acquired and recorded. The anti-contamination performance of the membrane and the recoverability of the membrane contamination were evaluated by observing the change in transmembrane pressure difference.

As can be seen from FIG. 4, MWCNT is_-COOHCompared with a 0.01 mu m PVDF membrane, the PEG-6000 membrane HAs higher HA removal efficiency, and the removal rate can reach 78 percent at most; although the removal rate of the PES basement membrane to HA can reach 47% at the initial point, the removal rate is rapidly reduced to below 10% along with the extension of the filtration time and is finally stabilized to about 2%, so that the MWCNT is treated by the PES basement membrane_-COOHThe effect of the HA removal efficiency of the PEG-6000 membrane is substantially negligible.

As can be seen from FIG. 5, MWCNT is_-COOHPEG-6000 membrane compared to 0.01 μm PVDF membrane, the transmembrane pressure difference increased slowly during HA removal, cross-flow washing towards MWCNT_-COOHThe pollution of the PEG-6000 membrane is better recovered, and the recovery rate is about 55 percent. Can effectively relieve membrane pollution and prolong the service life of the membrane. While 0.01 μm PVDF membrane in HA removal, TMP growth rate is not only higher than that of MWCNT_-COOHThe PEG-6000 membrane is quick, and the recovery condition after cross-flow washing is poor, and the recovery rate is only about 14.7%. PES-based Membrane transmembrane pressure Difference growth (P-P)₀) The PES-based membrane is always stabilized at about 0.5Kpa, so that the MWCNT is composed of the PES-based membrane_-COOHThe effect of the change in transmembrane pressure difference of the PEG-6000 membrane is likewise substantially negligible.

As can be seen from FIG. 6, the 0.01 μm PVDF membrane is most contaminated with BSA, TMP (P-P)₀) The growth is fast. Although TMP has good recovery after cross-flow washing, membrane fouling becomes more severe as the number of cycles increases. MWCNTs compared to commercial 0.01. mu. mVDF membranes_-COOHThe PEG-6000 membrane can effectively relieve the pollution of BSA to the membrane, and the transmembrane pressure difference recovery rate of the membrane after cross-flow washing is about 70 percent. PES-based Membrane transmembrane pressure Difference growth (P-P)₀) The PES-based membrane is always stabilized at about 0.5Kpa, so that the MWCNT is composed of the PES-based membrane_-COOHThe effect of the change in transmembrane pressure difference of the PEG-6000 membrane is likewise substantially negligible.

Example 2:

MWCNT-COOH of 30-50nm in example 1 was replaced with MWCNT of the same size, and the other operations were the same as in example 1;

as can be seen from fig. 7, 8 and 9, compared with the 0.01 μm PVDF film, the MWCNT-PEG-6000 film prepared by PEG non-covalent modification of MWCNTs effectively improves the removal of humic acid, alleviates the problem of film pollution caused by humic organic substances represented by HA and biomacromolecule substances represented by BSA, improves the quality of effluent, and prolongs the service life of the film, which is basically the same as that of example 1.

While the preferred embodiments of the present invention have been illustrated and described in detail, such disclosure should not be considered as limiting the scope of the invention. All equivalent changes and modifications made within the scope of the present invention are within the scope defined by the claims.

Claims

1. A preparation method of a multi-walled carbon nanotube low-pressure film for strengthening removal of humic acid in water and relieving pollution is characterized by comprising the following steps:

(1) preparing a non-covalent modified multi-walled carbon nanotube dispersion liquid: adding the multi-walled carbon nanotube into a polyethylene glycol solution with the concentration of 2-50mg/mL, and performing ultrasonic treatment by using an ultrasonic crusher to uniformly disperse the multi-walled carbon nanotube, wherein the concentration of the prepared non-covalent modified multi-walled carbon nanotube dispersion liquid is 0.5-2 mg/mL;

(2) preparing a multi-wall carbon nano tube low-pressure film: diluting the non-covalent modified multi-walled carbon nanotube dispersion liquid with Milli-Q water to the concentration of 0.2-0.25mg/mL, and performing ultrasonic treatment for 5-10 min; and (3) enabling the diluted multiwalled carbon nanotube dispersion liquid to pass through a microfiltration porous membrane by a vacuum filtration method, then cleaning the multiwalled carbon nanotube low-pressure membrane by Milli-Q water and ethanol, and drying for later use.

2. The method as claimed in claim 1, wherein the ultrasonic power of the MWCNT dispersion in step (1) is 100- & 300W.

3. The method according to claim 1, wherein the polyethylene glycol is sonicated for a period of 15 to 30min in step (1).

4. The method as set forth in claim 1, wherein the polyethylene glycol of step (2) has a molecular weight of 3350-10000 Da.

5. The method as set forth in claim 1, wherein the polyethylene glycol of step (2) has a molecular weight of 5000-.

6. The method according to claim 1, wherein the vacuum degree in the vacuum filtration in the step (2) is 50 to 300 mbar.

7. The method of claim 1, wherein the loading of the multi-walled carbon nanotubes in step (2) is in the range of 30 to 50g/m²。