Transition metal nanoparticle / graphene oxide self-assembled catalytic membrane for removing oxysalt as well as preparation method and application of transition metal nanoparticle / graphene oxide self-assembled catalytic membrane

Abstract

The invention discloses a transition metal nanoparticle graphene oxide self-assembled catalytic membrane for effectively removing oxysalt in a water body, and belongs to the technical field of water treatment functional membranes. A transition metal nanoparticle (such as iron, manganese and the like) dispersion liquid and a graphene oxide dispersion liquid are directly mixed, and the composite catalytic membrane is formed through self-assembly by utilizing the interaction between nanoparticles and graphene oxide lamellas. Metal ion adsorption and in-situ reduction steps are not needed, the process is simple and efficient, and large-scale preparation is easy. The obtained composite membrane has a remarkable nano confinement effect, can efficiently activate sulfite to generate reducing free radicals and rapidly degrade oxysalt pollutants such as bromate in a water body, the removal rate of 80 micrograms / L bromate in 3 minutes exceeds 96%, and the composite membrane has good stability and reusability.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of water treatment advanced reduction technology and nanocomposite membrane materials, and particularly relates to a transition metal nanoparticle graphene oxide self-assembled catalytic membrane for effectively removing oxygen-containing acid salts in water bodies as well as a preparation method and application thereof. BACKGROUND

[0002] Oxygen-containing acid salts (such as bromate, chlorate, nitrate, etc.) are common toxic pollutants in water bodies, which pose a serious threat to human health and water ecological safety. The advanced reduction process (ARPs) based on transition metal (such as iron, manganese, etc.) activation of sulfite is widely studied due to its high efficiency and low cost, and can be used for rapid reduction and removal of oxygen-containing acid salts. However, traditional powder catalysts are prone to agglomeration and difficult to recover, and metal ion dissolution can easily cause secondary pollution.

[0003] Graphene oxide (GO) as an ideal two-dimensional carrier material can effectively load metal nanoparticles through its rich oxygen-containing functional groups and ultra-large specific surface area, forming a composite catalytic membrane with a confinement effect. The mainstream technology in this field is the "in-situ reduction method", that is, first adsorb metal ions on the GO layer, and then reduce the metal ions to zero-valent nanoparticles on the GO surface by using a chemical reducing agent. For example, the inventors developed a Fe / GO catalytic membrane, and the preparation process also involved in-situ reduction of NaBH4 on the Fe 3+ adsorbed on GO, which proved the high efficiency of the material in catalytic reduction dehalogenation. However, the above existing "in-situ reduction" preparation method has the following obvious shortcomings: 1. Complex preparation process and poor controllability: the "adsorption-reduction" two-step process is relatively cumbersome. The reduction reaction process (such as using strong reducing agent NaBH4) is violent and fast, which is difficult to accurately control the nucleation and growth of nanoparticles, and may lead to uneven particle size distribution, and some nanoparticles may agglomerate due to excessive growth, thereby affecting the number and accessibility of active sites; 2. Potential risk of structural damage: the strong chemical reducing agent not only reduces the metal ions, but also strongly reduces the graphene oxide, resulting in a large reduction of oxygen-containing functional groups (such as carboxyl, epoxy) on the GO layer. Although this improves the conductivity of graphene, it weakens the hydrophilicity between GO layers and the stability of the formed membrane, which may make the prepared catalytic membrane brittle and prone to cracking, and the mechanical properties decrease; 3. Single metal-carrier interface bonding mechanism: the metal nanoparticles formed by in-situ reduction are mainly combined with the GO carrier through chemical bonding. Under harsh reduction conditions, this bonding method may not be optimal, and the interface may not be stable during long-term use, leading to the detachment of nanoparticles from the carrier, i.e. the problem of metal dissolution has not been fundamentally solved.

[0004] Therefore, developing a preparation method of transition metal nanoparticle / graphene oxide composite film with simple process, no need for in-situ reduction, maximum retention of the structural integrity of the carrier, and excellent stability and selectivity has important research value and application prospect for promoting the practical application of advanced reduction technology in water treatment. SUMMARY

[0005] The application aims to provide a transition metal nanoparticle graphene oxide self-assembled catalytic film for effectively removing oxygen-containing acid salts in water bodies and a preparation method and application thereof.

[0006] The application provides a transition metal nanoparticle graphene oxide self-assembled catalytic film for effectively removing oxygen-containing acid salts in water bodies, which is composed of graphene oxide sheets and pre-synthesized transition metal nanoparticles by physical adsorption and hydrogen bonding.

[0007] In the application, the transition metal nanoparticles are one or more of iron, manganese, cobalt, and nickel.

[0008] The application provides a preparation method of a transition metal nanoparticle graphene oxide self-assembled catalytic film for effectively removing oxygen-containing acid salts in water bodies, and the specific steps are as follows: (1) preparing a graphene oxide dispersion liquid, and controlling the concentration of the graphene oxide dispersion liquid to be 0.5-2 mg / mL; (2) preparing a transition metal nanoparticle dispersion liquid, and controlling the concentration of the transition metal nanoparticle dispersion liquid to be 1-5 mg / mL, wherein the nanoparticles are pre-synthesized by a chemical reduction method; (3) mixing the products obtained in steps (1) and (2) according to the mass ratio of graphene oxide to nanoparticles (0.1-2):1, and performing ultrasonic treatment for 0.5-3 h to make the products fully dispersed; (4) vacuum suction filtering the mixture obtained in step (3) on a base film to form a self-supporting composite catalytic film; (5) drying the product obtained in step (4) at room temperature or low temperature (≤80℃) to obtain the final product.

[0009] In the application, the base film in step (4) is a PVDF, nylon, or ceramic membrane, and the pore size is 0.22-0.45 µm.

[0010] This invention relates to the application of a transition metal nanoparticle graphene oxide self-assembled catalytic membrane for effectively removing oxyacids from water in the construction of a high-efficiency membrane catalytic-reduction system. This self-assembled composite membrane is used in conjunction with sulfite to construct a high-efficiency membrane catalytic-reduction system for the efficient removal of bromate, chlorate, or nitrate from water. It can achieve a removal rate of over 96% for 80 μg / L bromate within 3 minutes, and its performance does not significantly decrease after being reused 20 times. The beneficial effects of this invention are as follows:

[0011] 1. This invention adopts a strategy of direct self-assembly of pre-synthesized nanoparticles and GO, which avoids the damage to the GO structure caused by in-situ reduction and simplifies the preparation process; 2. In this invention, transition metal nanoparticles are uniformly distributed between GO layers, forming a highly open confined reaction space, which promotes reaction mass transfer and free radical generation. 3. The composite membrane described in this invention has good mechanical strength, catalytic activity and stability, and extremely low metal leaching. 4. The preparation process of this invention is simple and the conditions are mild, making it easy to prepare on a large scale. It has significant practical value and prospects for widespread application. Attached Figure Description

[0012] Figure 1 Schematic diagram of the self-assembled composite membrane preparation process.

[0013] Figure 2 Photographs of GO and FeNPs / GO composite membranes.

[0014] Figure 3 The composite membrane degrades bromate in water.

[0015] Figure 4 TEM image of the composite membrane.

[0016] Figure 5 SEM-EDS image of the composite membrane.

[0017] Figure 6 Figure a shows the efficiency of the composite membrane in removing bromate in deionized water and tap water, while figure b shows the effect of the composite membrane in removing chlorate and nitrate from water.

[0018] Figure 7 pH and DO concentration of the composite membrane system before and after the reaction.

[0019] Figure 8 Results of recycling composite membranes. Detailed Implementation

[0020] The present invention will be further described below with reference to the embodiments and accompanying drawings. Example 1: Preparation and application of iron nanoparticle / graphene oxide self-assembled catalytic membranes

[0021] (1) 100 mg of graphene oxide (GO) was dispersed in 100 mL of deionized water and sonicated for 2 h to obtain a 1 mg / mL GO dispersion; (2) Commercially available iron nanoparticles (FeNPs, with a particle size of about 30 nm) were dispersed in ethanol to form a dispersion of 2 mg / mL; (3) Mix 50 mL of GO dispersion with 10 mL of iron nanoparticle dispersion and sonicate for 1 h to complete self-assembly through physical adsorption and hydrogen bonding. (4) The mixture was vacuum filtered onto a hydrophilic PVDF base membrane (0.22 μm) to form a composite membrane. The membrane was dried at 40 °C for 12 h to obtain the self-assembled catalytic membrane (see preparation process). Figure 1 The resulting composite membrane photograph can be found in [the image]. Figure 2 ); (5) The self-assembled catalytic membrane obtained in step (4) was loaded into a continuous flow membrane reactor. The influent was initially bromate with a concentration of 80 μg / L, and 1 mM sodium sulfite (Na2SO3) was added as a reducing agent. The operating results showed that the hydraulic retention time was about 3 minutes, and the bromate removal rate was stable at over 98%. Figure 3 ). Through TEM (e.g. Figure 4 ) and SEM-EDS characterization (e.g. Figure 5 As can be seen, iron nanoparticles are uniformly distributed in the GO sheets, forming a stable porous layered structure. Example 2: Preparation and application of self-assembled catalytic membranes of manganese nanoparticles / graphene oxide

[0022] (1) 100 mg of graphene oxide was dispersed in 100 mL of deionized water and sonicated for 2 h to obtain a 1 mg / mL GO dispersion; (2) Commercially available manganese nanoparticles (with a particle size of about 50 nm) were dispersed in ethanol to form a dispersion of 2 mg / mL. (3) Mix 50 mL of GO dispersion with 10 mL of manganese nanoparticle dispersion and sonicate for 1 h; (4) The mixture was vacuum filtered onto a hydrophilic PVDF base membrane (0.22 μm) to form a composite membrane, and dried at 40℃ for 12 h; (5) The self-assembled catalytic membrane obtained in step (4) is applied to a continuous flow membrane reaction system, with 80 μg / L bromate wastewater as the influent and 1 mM Na2SO3 added. Furthermore, as... Figure 6 As shown in b, this catalytic membrane is effective against chlorate (ClO3). - ) and nitrates (NO3) -It also showed excellent removal effect, with removal rates of 95% and 93% respectively. Figure 6 The results show that the composite membrane is not only effective in deionized water, but also maintains a bromate removal rate of over 93% in actual water bodies (such as tap water), demonstrating strong anti-interference ability and practical application potential. The pH of the system changes only slightly during the reaction, and the dissolved oxygen (DO) concentration remains stable. Figure 7 This indicates that the reaction conditions were mild. Example 3:

[0023] (1) 150 mg of graphene oxide was dispersed in 100 mL of deionized water and sonicated for 3 h to obtain a 1.5 mg / mL GO dispersion. (2) Commercially available cobalt nanoparticles (Co NPs, with a particle size of about 40 nm) were dispersed in ethanol to form a dispersion of 1.5 mg / mL; (3) Mix 50 mL of GO dispersion with 15 mL of cobalt nanoparticle dispersion and sonicate for 1.5 h to allow Co NPs and GO to fully self-assemble; (4) The mixture was vacuum filtered onto a hydrophilic PVDF substrate membrane and dried at 40°C for 24 h to obtain a Co / GO self-assembled catalytic membrane; (5) The catalytic membrane was applied to the test system. Under the conditions of 100 μg / L bromate in the influent and the addition of 1.5 mM Na2SO3, the bromate removal rate was greater than 97%. The results showed that the bromate removal rate reached 96% within 3 minutes. Figure 8 As shown, the composite membrane maintained a bromate removal rate of over 93% after 20 consecutive cycles, demonstrating excellent reusability. Fe / GO catalytic membrane prepared by conventional reduction method

[0024] The traditional "adsorption-reduction" method involves first immersing the GO membrane in a Fe²⁺ solution for adsorption, followed by reduction with NaBH₄. While this method produces a catalytic membrane with a bromate removal rate of 95%, the preparation process is complex and requires stringent conditions (a strong reducing agent is necessary), making large-scale production difficult.

Claims

1. A transition metal nanoparticle graphene oxide self-assembled catalytic membrane for effectively removing oxyacids from water, characterized in that... The self-assembled catalytic membrane is composed of graphene oxide sheets and pre-synthesized transition metal nanoparticles through physical adsorption and hydrogen bonding. The loading of the transition metal nanoparticles is 1~20 wt%, the particle size is 10~100 nm, the composite membrane thickness is 50~500 nm, and the water flux is 5~50 L / (m²·h·bar).

2. The transition metal nanoparticle graphene oxide self-assembled catalytic membrane for effectively removing oxyacids from water, as described in claim 1, is characterized in that... The transition metal nanoparticles are one or more of iron, manganese, cobalt, or nickel.

3. A method for preparing a transition metal nanoparticle graphene oxide self-assembled catalytic membrane for effectively removing oxyacids from water, as described in claim 1, characterized in that... The specific steps are as follows: (1) Prepare a graphene oxide dispersion and control the concentration of the graphene oxide dispersion to be 0.5~2 mg / mL; (2) Prepare a dispersion of transition metal nanoparticles, and control the concentration of the dispersion of transition metal nanoparticles to be 1~5 mg / mL. The nanoparticles are pre-synthesized by chemical reduction method. (3) Mix the products obtained in steps (1) and (2) at a mass ratio of graphene oxide to nanoparticles of (0.1~2):1, and sonicate for 0.5~3 h to ensure full dispersion; (4) Vacuum filter the mixture obtained in step (3) onto the base membrane to form a self-supporting composite catalytic membrane; (5) After drying the product obtained in step (4) at room temperature or low temperature (≤80℃), the final product is obtained.

4. The method according to claim 3, characterized in that... The base film mentioned in step (4) is any one of PVDF, nylon or ceramic film, with a pore size of 0.22~0.45 μm.

5. The application of a transition metal nanoparticle graphene oxide self-assembled catalytic membrane for effectively removing oxyacids from water in the construction of a high-efficiency membrane catalysis-reduction system, characterized in that... The self-assembled composite membrane was used in conjunction with sulfite to construct a highly efficient membrane catalytic-reduction system for the efficient removal of bromate, chlorate or nitrate in water. It can achieve a removal rate of over 96% for 80 μg / L bromate within 3 minutes, and its performance does not significantly decrease after being reused 20 times.

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