WO2023092809A1 - 改性Nb2CTx纳米片膜及其制备方法 - Google Patents

改性Nb2CTx纳米片膜及其制备方法 Download PDF

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WO2023092809A1
WO2023092809A1 PCT/CN2021/142822 CN2021142822W WO2023092809A1 WO 2023092809 A1 WO2023092809 A1 WO 2023092809A1 CN 2021142822 W CN2021142822 W CN 2021142822W WO 2023092809 A1 WO2023092809 A1 WO 2023092809A1
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modified
nanosheet
preparation
membrane
mxene
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PCT/CN2021/142822
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French (fr)
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胡文吉豪
黄俊楠
付奕铭
赵飞平
柯勇
沈锋华
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中南大学
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
    • B01D71/02—Inorganic material
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
    • B01D67/0039—Inorganic membrane manufacture
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
    • B01D69/02—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor characterised by their properties
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
    • B01D69/06—Flat membranes
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/44—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2325/00—Details relating to properties of membranes
    • B01D2325/42—Ion-exchange membranes

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  • the invention belongs to the technical field of functional membrane separation, and more specifically relates to a modified Nb 2 CT x nano sheet membrane and a preparation method thereof.
  • seawater desalination, purification, and ion transport through functional membranes with well-controlled nanoconfined channels formed by 2D nanosheets have attracted extensive attention.
  • seawater besides water, there are many other components, such as lithium salts and magnesium salts, and lithium salts and magnesium salts are valuable resources in energy-related applications.
  • the purpose of the present invention is to provide a design method for functionalized layered two-dimensional nanosheet membrane structures in a confined space, and on this basis to demonstrate the synergistic effect between ion-water clusters and dynamic ion-water exchange processes,
  • a modified Nb 2 CT x nanosheet membrane and its preparation method and application are specifically provided.
  • a method for preparing a modified Nb 2 CT x nanosheet film specifically comprising:
  • the modifier was added to the Nb 2 CT x MXene suspension and mixed ultrasonically, and then it was uniformly distributed on the surface of the polyvinylidene fluoride film by vacuum filtration to form a thin layer of modified Nb 2 CT x , and after drying, it was combined with polyvinylidene difluoride Vinyl fluoride film separation, you can.
  • the modifying agent is a functional organic substance that can provide hydroxyl and/or carboxyl.
  • the ratio of the modifier to Nb 2 CT x MXene is 1:1, that is, the modifier is added in an amount of 1 mg/ml.
  • the concentration of the Nb 2 CT x MXene suspension is 0.5-12 mg/mL.
  • the pore diameter of the polyvinylidene fluoride film is 0.22 ⁇ m.
  • the pressure of the vacuum filtration is 0.5-1.0 bar.
  • the modifying agent is one of polyacrylic acid, polyvinyl alcohol and gallic acid.
  • the ultrasonic time of the ultrasonic mixing is 60-84h.
  • the Nb 2 CT x MXene suspension is prepared by the following method:
  • the rotation speed of the stirring is controlled to be 175-250 rpm.
  • the rotation speed and time of the centrifugal separation are respectively 4500-6000 rpm and 8-15 min.
  • the times of adding ethanol and rinsing are 3-6 times.
  • the amount of dimethyl sulfoxide added is 1.5 times that of Nb 2 CT x MXene nanosheets.
  • the time for the layered reaction is 15-30min.
  • the drying temperature and time are respectively 50-75° C. and 250-360 min.
  • Another aspect of the present invention also provides the modified Nb 2 CT x nanosheet film prepared by the above preparation method.
  • Another aspect of the present invention also provides the application of the above-mentioned preparation method or the above-mentioned modified Nb 2 CT x nanosheet membrane in the selective separation of Li + , Mg 2+ and water.
  • the modifier when it is a functional organic substance that can provide carboxyl groups, it is used to promote the penetration of water and increase the retention rate of Li + and Mg2 + .
  • the modifying agent is a functional organic substance that can provide hydroxyl groups, it is applied to reduce the penetration of water and enhance the permeability of Li + and Mg 2+ .
  • the present invention has the following advantages:
  • the present invention discusses the basic concept of ion transport behavior (synergistic effect between ion-water clusters and exchange rate) and two-dimensional nanosheet surface modification strategy for ion-selective separation, mixed carboxyl and hydroxyl modification Surfaces bring new concepts to the design of ion-selective membranes, advance the understanding of the transport of solvated ions in nano-confined two-dimensional channels, and explore their applications in ion screening, energy storage, and desalination on this basis. potential applications of
  • the present invention is different from the traditional size exclusion mechanism and the low selectivity cognition of 2D material base membrane.
  • the concept of ion water cluster formation and dynamic ion water exchange process reveals that under relatively high ion concentration, the membrane
  • the interconnected ionic water network in the matrix has greater guiding significance for the application prospects of the two-dimensional material base membrane in the fields of seawater desalination, wastewater treatment, lithium ion and magnesium ion separation.
  • Figure 1 is the characterization result of the nanosheets prepared in the embodiment of the present invention (wherein: 1a is the cross-sectional field emission scanning electron microscope photo of Nb 2 CT x MXene nanosheets, 1b, 1c and 1d are the Nb prepared in Example 1 respectively Scanning electron micrographs of 2 CT x -PAA nanosheet film, Nb 2 CT x -PVA nanosheet film prepared in Example 2 and Nb 2 CT x -GA nanosheet film prepared in Example 3, 1e is the obtained The surface microscopic TEM morphology of the multilayer Nb 2 CT x MXene nanosheets, the left and right images of 1f are respectively the Nb 2 CT x -PAA nanosheet film prepared in Example 1 and the Nb 2 prepared in Example 2 Surface microscopic TEM morphology of CT x -PVA nanosheet film, 1g, 1h and 1i are the Nb 2 CT x -PAA nanosheet film prepared in Example 1, the Nb 2 CT x -PVA nano
  • Figure 2 shows commercially available Nb 2 AlC powder, multilayer Nb 2 CT x MXene nanosheets, Nb 2 CT x -PAA nanosheet film prepared in Example 1, and Nb 2 CT x -PVA nanosheet prepared in Example 2
  • Fig. 3 is the ion selective separation figure of the embodiment of the present invention.
  • Fig. 4 is the hydroxyl ratio water flux figure of the embodiment of the present invention.
  • Fig. 5 is a spatially limited domain ion selectivity diagram of an embodiment of the present invention.
  • compositions As used herein, the terms “comprises,” “includes,” or any other variation thereof, are intended to cover a non-exclusive inclusion.
  • a composition, step, method, article, or device comprising listed elements is not necessarily limited to those elements, but may include other elements not explicitly listed or inherent to such composition, step, method, article, or device. element.
  • the raw materials used in the examples of the present invention are all commercially available products.
  • the preparation process of the Nb 2 CT x MXene suspension used includes the following steps:
  • step S2 Add the Nb 2 CT x MXene nanosheets obtained in step S1 into dimethyl sulfoxide, and a layering reaction occurs at room temperature. After the reaction is completed, centrifuge, and the obtained multilayer Nb 2 CT x MXene nanosheets are separated from Dimethyl sulfoxide was separated, dried and uniformly dispersed in deionized water to obtain Nb 2 CT x MXene suspension.
  • the embodiment of the present invention provides a method for preparing polyacrylic acid modified Nb 2 CT x nanosheet film, the specific process is as follows:
  • Nb 2 CT x MXene suspension with 1 mg/ml polyacrylic acid aqueous solution at a ratio of 1:1 by weight, and ultrasonically mix for 24 hours to obtain Nb 2 CTx-PAA suspension; then suspend Nb 2 CTx-PAA
  • the liquid was evenly distributed on the surface of polyvinylidene fluoride film (pore size 0.22 ⁇ m, diameter 47 mm) by vacuum filtration ( ⁇ 0.7 bar) to form a thin layer of Nb 2 CT x -PAA, and after drying for 3 days, it was combined with polyvinylidene fluoride film Separation to obtain Nb 2 CT x -PAA nanosheet film.
  • the embodiment of the present invention provides a preparation method of polyvinyl alcohol modified Nb 2 CT x nanosheet film, the specific process is as follows:
  • Nb 2 CT x MXene suspension 2 mg/ml Nb 2 CT x MXene suspension with 1 mg/ml polyvinyl alcohol aqueous solution at a weight ratio of 1:1, and ultrasonically mix for 24 hours to obtain Nb 2 CTx-PVA suspension; then Nb 2 CTx-PVA
  • the suspension was evenly distributed on the surface of polyvinylidene fluoride film (pore size 0.22 ⁇ m, diameter 47 mm) by vacuum filtration ( ⁇ 0.7 bar) to form a thin layer of Nb 2 CT x -PVA, dried for 3 days and mixed with polyvinylidene fluoride Thin films are separated to obtain Nb 2 CT x -PVA nanosheet films.
  • the embodiment of the present invention provides a preparation method of gallic acid-modified Nb 2 CT x nanosheet film, the specific process is as follows:
  • Nb 2 CT x MXene suspension with 1 mg/ml gallic acid aqueous solution at a ratio of 1:1 by weight, and ultrasonically mix for 24 hours to obtain Nb 2 CTx-GA suspension; then suspend Nb 2 CTx-GA
  • the liquid was evenly distributed on the surface of polyvinylidene fluoride film (pore size 0.22 ⁇ m, diameter 47 mm) by vacuum filtration ( ⁇ 0.7 bar) to form a thin layer of Nb 2 CT x -GA, dried for 3 days, and polyvinylidene fluoride film After separation, the Nb 2 CT x -GA nanosheet film is obtained.
  • Fig. 1 is the characterization result of the nanosheets prepared in the embodiment of the present invention.
  • Figure 1a is a cross-sectional field emission scanning electron microscope photo of Nb 2 CT x MXene nanosheets
  • Figure 1b, Figure 1c and Figure 1d are Nb 2 CT x -PAA nanosheet films prepared in Example 1, Example 2
  • Figure 1e is the prepared multilayer Nb 2 CT x MXene nanosheet Surface microscopic TEM morphology
  • Figure 1f is the surface microscopic images of the Nb 2 CT x -PAA nanosheet film prepared in Example 1 and the Nb 2 CT x -PVA nanosheet film prepared in Example 2 TEM morphology
  • Figure 1g, Figure 1h and Figure 1i are the Nb 2 CT x -PAA nanosheet film prepared in Example 1, the Nb 2 CT x -PVA nanosheet film prepared in Example 2 and the example 3 Transmission electron micrographs of the
  • Figure 2 shows commercially available Nb 2 AlC powder, multilayer Nb 2 CT x MXene nanosheets, Nb 2 CT x -PAA nanosheet film prepared in Example 1, and Nb 2 CT x -PVA prepared in Example 2 XRD diffraction patterns of the nanosheet film and the Nb 2 CT x -GA nanosheet film prepared in Example 3.
  • Fig. 3 is an ion selective separation diagram of an embodiment of the present invention.
  • the -COOH model membrane (200nm thick) exhibited ultrahigh rejection of Li + or Mg2 + ( ⁇ 99%) and enhanced water permeability ( ⁇ 50L ⁇ m2 ⁇ h -1 , while the bare membrane is 31L ⁇ m 2 ⁇ h -1 , Fig. 3a-b); -OH model membrane (200nm thick) enhances the permeation of Li + and Mg 2+ (only about 50-60% rejection ), while reducing the water transport performance (compared with the bare membrane, about 20L ⁇ m 2 ⁇ h -1 , Fig.
  • Fig. 4 is a graph of hydroxyl ratio water flux in an embodiment of the present invention.
  • Figure 4a-b 5 mg loaded thick Nb 2 CT x -GA nanosheet membrane for the selective separation of Li + and Mg 2+ varies with the volume ratio; in Figure 4c, lattice
  • the output water velocity (velocity intensity representing the value of a random position within the membrane, compared to the initial state) of the Boltzmann method varies from 20% to 100% with model-OH content/nanosheet.
  • Fig. 5 is a spatially limited domain ion selectivity diagram of an embodiment of the present invention.
  • the tip-ion-water-cluster surface interaction may lead to a significant increase in adhesion beyond the critical concentration point.
  • the ion concentration after the critical point increases the adhesion; when the concentration ratio of Li + and Mg2 + increases, it can be observed
  • the contact angle on the Nb 2 CT x -GA model film was significantly reduced (from ⁇ 40 ⁇ 2° to ⁇ 26.6 ⁇ 2°) to a clear macroscopic percolation effect (Fig. 5g).

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Engineering & Computer Science (AREA)
  • Inorganic Chemistry (AREA)
  • Water Supply & Treatment (AREA)
  • Manufacturing & Machinery (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Hydrology & Water Resources (AREA)
  • Environmental & Geological Engineering (AREA)
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  • Separation Using Semi-Permeable Membranes (AREA)

Abstract

一种改性Nb 2CT x纳米片膜及其制备方法，制备方法包括，将改性剂加入到Nb 2CT xMXene悬浮液中超声混合，随后通过真空抽滤将其均匀分布在聚偏二氟乙烯薄膜表面形成改性Nb 2CT x薄层，干燥后与聚偏二氟乙烯分离即可，改性剂为可提供羟基和/或羧基的功能性有机物。讨论了离子输运行为的基本概念和用于离子选择性分离的二维纳米片表面修饰的方法，混合羧基、羟基修饰表面为离子选择膜的设计带来新思路，对溶剂化离子在纳米受限二维通道中传输的认知更进一步，并探索了其潜在应用；与传统的尺寸排阻机制和2D材料基膜的低选择性认知不同，揭示了高离子浓度下膜基质内相互连接的离子水网络。

Description

改性Nb 2CT x纳米片膜及其制备方法 技术领域
本发明属于功能性膜分离技术领域，更具体地，涉及一种改性Nb 2CT x纳米片膜及其制备方法。
背景技术
由于对淡水需求的不断增加，海水淡化、净化和通过功能膜的离子传输引起了广泛关注，该功能膜具有由2D纳米片形成的控制良好的纳米受限通道。海水(盐水)中除了水之外，还存在许多其他成分，如锂盐和镁盐，且锂盐和镁盐是能源相关应用中的宝贵资源。
然而，从海水中提取的锂盐和镁盐由于其化学和物理性质的相似性而难以分离，因此限制了它们的综合利用。由2D纳米片形成的层状膜已被证明对多种独立盐溶液具有高截留率或水渗透率，但由于在水中溶胀而导致选择性差。
因此，为了有效且环保地利用海水(盐水)来源的锂盐和镁盐，开发具有高离子选择性的低成本膜，了解表面改性2D纳米片形成的纳米受限膜通道内可能的分离机理是非常必要的。
为了在不影响良好分离性能的情况下开发2D膜，了解受限纳米通道内的离子传输现象具有重要意义，这一点很少有报道。此外，已有大量研究报告揭示了受限毛细管纳米通道内的水渗透活性，但表面修饰2D纳米片形成的互连纳米通道与纳米通道内渗透物之间的关系仍不清楚。最新研究表明，膜分离性能的可能机制主要是尺寸排斥。因此，设计高离子选择性2D基膜的一个关键科学挑战是了解离子传输现象和水渗透活性与功能化2D纳米片构建的膜的可控孔结构和功能性的关系。
鉴于此，特提出本发明。
发明内容
本发明的目的是提供一种在受限空间下功能化层状二维纳米片膜结构的设计方法，并在此基础上证实离子-水簇和动态离子-水交换过程之间的协同效应，从而实现选择性渗透，具体提供了一种改性Nb 2CT x纳米片膜及其制备方法和应用。
为实现上述目的，本发明的技术方案如下：
一种改性Nb 2CT x纳米片膜的制备方法，具体包括：
将改性剂加入到Nb 2CT x MXene悬浮液中超声混合，随后通过真空抽滤将其均匀分布在聚偏二氟乙烯薄膜表面形成改性Nb 2CT x薄层，干燥后与聚偏二氟乙烯薄膜分离，即可。
详细地，在上述技术方案中，所述改性剂为可提供羟基和/或羧基的功能性有机物。
在上述技术方案中，所述改性剂与Nb 2CT x MXene的加入量之比为1∶1，即所述改性剂的加入量为1mg/ml。
在上述技术方案中，所述Nb 2CT x MXene悬浮液的浓度为0.5-12mg/mL。
在上述技术方案中，所述聚偏二氟乙烯薄膜的孔径为0.22μm。
在上述技术方案中，所述真空抽滤的压力为0.5-1.0bar。
进一步地，在上述技术方案中，所述改性剂为聚丙烯酸、聚乙烯醇和没食子酸中的一种。
优选地，在上述技术方案中，所述超声混合的超声时间为60-84h。
进一步地，在上述技术方案中，所述Nb 2CT x MXene悬浮液采用如下方法制备：
将粉末状Nb 2AlC加入到氢氟酸中，室温下搅拌反应68-75h，反应结束后离心分离，加入乙醇将氢氟酸漂洗干净；随后往得到的Nb 2CT xMXene纳米片中加入二甲基亚砜，分层反应后离心将多层MXene纳米 片从二甲基亚砜分离，干燥后均匀分散在去离子水中，即得。
在上述技术方案中，在室温下搅拌反应的过程中，控制所述搅拌的转数为175-250rpm。
在上述技术方案中，所述离心分离的转数和时间分别为4500-6000rpm和8-15min。
在上述技术方案中，所述加入乙醇并漂洗的次数为3-6次。
在上述技术方案中，所述二甲基亚砜的加入量为Nb 2CT x MXene纳米片的1.5倍。
在上述技术方案中，所述分层反应的时间为15-30min。
在上述技术方案中，所述干燥的温度和时间分别为50-75℃和250-360min。
本发明另一方面还提供了上述制备方法制备得到的改性Nb 2CT x纳米片膜。
本发明再一方面还提供了上述制备方法或上述改性Nb 2CT x纳米片膜在选择性分离Li +、Mg 2+和水中的应用。
具体地，所述改性剂为可提供羧基的功能性有机物时，应用于促进水的渗透并提高对Li +和Mg 2+的截留率。
具体地，所述改性剂为可提供羟基的功能性有机物时，应用于降低水的渗透并增强对Li +和Mg 2+的渗透率。
本发明与现有技术相比，具有以下优点：
(1)本发明讨论了离子输运行为的基本概念(离子-水团簇和交换率之间的协同效应)和用于离子选择性分离的二维纳米片表面修饰策略，混合羧基和羟基修饰表面为离子选择膜的设计带来了新的概念，对溶剂化离子在纳米受限二维通道中传输的理解更进一步，并在此基础上探索了其在离子筛选、储能和脱盐等方面的潜在应用；
(2)本发明与传统的尺寸排阻机制和2D材料基膜的低选择性认 知不同，离子水团簇的形成和动态离子水交换过程的概念揭示了在相对高的离子浓度下，膜基质内相互连接的离子水网络，对二维材料基膜在海水淡化、废水处理、锂离子和镁离子分离等领域的应用前景具有更大的指导意义。
附图说明
图1为本发明实施例所制得纳米片的表征结果(其中：1a为Nb 2CT xMXene纳米片的横截面场发射扫描电镜照片，1b、1c和1d分别为实施例1所制备的Nb 2CT x-PAA纳米片膜、实施例2所制备的Nb 2CT x-PVA纳米片膜和实施例3所制备的Nb 2CT x-GA纳米片膜的扫描电镜照片，1e为所制得的多层Nb 2CT x MXene纳米片的表面微观TEM形貌，1f的左图和右图分别为实施例1所制备的Nb 2CT x-PAA纳米片膜和实施例2所制备的Nb 2CT x-PVA纳米片膜的表面微观TEM形貌，1g、1h和1i分别为实施例1所制备的Nb 2CT x-PAA纳米片膜、实施例2所制备的Nb 2CT x-PVA纳米片膜和实施例3所制备的Nb 2CT x-GA纳米片膜的透射电镜照片)；
图2为市售Nb 2AlC粉末、多层Nb 2CT x MXene纳米片、实施例1所制备的Nb 2CT x-PAA纳米片膜、实施例2所制备的Nb 2CT x-PVA纳米片膜和实施例3所制备的Nb 2CT x-GA纳米片膜的的XRD衍射谱图；
图3为本发明实施例的离子选择性分离图；
图4为本发明实施例的羟基比例水通量图；
图5为本发明实施例的空间有限域离子选择性图。
具体实施方式
为了使本发明的目的、技术方案及优点更加清楚明白，以下结合实施例，对本发明进行进一步详细说明。
应当理解，此处所描述的具体实施例仅仅用以解释本发明，并不用于限定本发明。
实施例中，如无特别说明，所用手段均为本领域常规的手段。
本文中所用的术语“包含”、“包括”或其任何其它变形，意在覆盖非排它性的包括。例如，包含所列要素的组合物、步骤、方法、制品或装置不必仅限于那些要素，而是可以包括未明确列出的其它要素或此种组合物、步骤、方法、制品或装置所固有的要素。
此外，下面所描述的本发明各个实施方式中所涉及到的技术特征只要彼此之间未构成冲突就可以相互组合。
本发明实施例中所用的原料均为市售产品。
在本发明实施例中，所用Nb 2CT x MXene悬浮液的制备过程包括如下步骤：
S1、将1.032g市售Nb 2AlC粉末(纯度98％，粒径为过400目)加入到装有50mL氢氟酸(49wt％)的聚四氟反应罐中，在室温下以200rpm转速搅拌72h，反应结束后离心分离(5000rpm，10min)，并用乙醇洗涤沉淀物多次(至少4次)直至氢氟酸完全漂洗干净，取洗涤后的Nb 2CT x MXene纳米片备用；
S2、将步骤S1中得到的Nb 2CT x MXene纳米片加入到二甲基亚砜中，在室温下发生分层反应，反应结束后离心，将得到的多层Nb 2CT xMXene纳米片从二甲基亚砜分离，干燥后均匀分散在去离子水中，即得Nb 2CT x MXene悬浮液。
实施例1
本发明实施例提供了一种聚丙烯酸改性Nb 2CT x纳米片膜的制备方法，具体过程如下：
将2mg/ml的Nb 2CT x MXene悬浮液与1mg/ml的聚丙烯酸水溶液按重量比1∶1的比例混合，超声混合24h得到Nb 2CTx-PAA悬浮液；随后将Nb 2CTx-PAA悬浮液通过真空抽滤(～0.7bar)将其均匀分布在聚偏二氟乙烯薄膜(孔径0.22μm，直径47mm)表面形成Nb 2CT x-PAA 薄层，干燥3d后与聚偏二氟乙烯薄膜分离，即得Nb 2CT x-PAA纳米片膜。
实施例2
本发明实施例提供了一种聚乙烯醇改性Nb 2CT x纳米片膜的制备方法，具体过程如下：
将2mg/ml的Nb 2CT x MXene悬浮液与1mg/ml的聚乙烯醇水溶液按重量比1∶1的比例混合，超声混合24h得到Nb 2CTx-PVA悬浮液；随后将Nb 2CTx-PVA悬浮液通过真空抽滤(～0.7bar)将其均匀分布在聚偏二氟乙烯薄膜(孔径0.22μm，直径47mm)表面形成Nb 2CT x-PVA薄层，干燥3d后与聚偏二氟乙烯薄膜分离，即得Nb 2CT x-PVA纳米片膜。
实施例3
本发明实施例提供了一种没食子酸改性Nb 2CT x纳米片膜的制备方法，具体过程如下：
将2mg/ml的Nb 2CT x MXene悬浮液与1mg/ml的没食子酸水溶液按重量比1∶1的比例混合，超声混合24h得到Nb 2CTx-GA悬浮液；随后将Nb 2CTx-GA悬浮液通过真空抽滤(～0.7bar)将其均匀分布在聚偏二氟乙烯薄膜(孔径0.22μm，直径47mm)表面形成Nb 2CT x-GA薄层，干燥3d后与聚偏二氟乙烯薄膜分离，即得Nb 2CT x-GA纳米片膜。
图1为本发明实施例所制得纳米片的表征结果。
其中，图1a为Nb 2CT x MXene纳米片的横截面场发射扫描电镜照片，图1b、图1c和图1d分别为实施例1所制备的Nb 2CT x-PAA纳米片膜、实施例2所制备的Nb 2CT x-PVA纳米片膜和实施例3所制备的Nb 2CT x-GA纳米片膜的扫描电镜照片，图1e为所制得的多层Nb 2CT xMXene纳米片的表面微观TEM形貌，图1f的左侧和右侧分别为实施 例1所制备的Nb 2CT x-PAA纳米片膜和实施例2所制备的Nb 2CT x-PVA纳米片膜的表面微观TEM形貌，图1g、图1h和图1i分别为实施例1所制备的Nb 2CT x-PAA纳米片膜、实施例2所制备的Nb 2CT x-PVA纳米片膜和实施例3所制备的Nb 2CT x-GA纳米片膜的透射电镜照片。
图2所示为市售Nb 2AlC粉末、多层Nb 2CT x MXene纳米片、实施例1所制备的Nb 2CT x-PAA纳米片膜、实施例2所制备的Nb 2CT x-PVA纳米片膜和实施例3所制备的Nb 2CT x-GA纳米片膜的的XRD衍射谱图。
图3为本发明实施例的离子选择性分离图。
从图3中可以看出，-COOH模型膜(200nm厚)显示出对Li +或Mg 2+的超高截留率(～99％)，并提高了水渗透率(～50L·m 2·h -1，而裸膜为31L·m 2·h -1，图3a-b)；-OH模型膜(200nm厚)增强了Li +和Mg 2+的渗透(仅约50-60％的截留率)，同时降低了水传输性能(与裸膜相比，约20L·m 2·h -1，图3c-d)；使用晶格玻尔兹曼方法模拟上述现象，发现输出水通过原始膜的渗透速率保持不变(图3e)，相对速度(膜内随机局部空间的速度与初始空间的速度相比)与增加的膜层间距呈指数关系(图3f-g)；输出水渗透速率随-OH含量/纳米片含量比的增加呈二阶指数衰减关系，膜内随机局部空间的相对速度随层间距的增加呈二阶指数关系增加(图3g-h)。
图4为本发明实施例的羟基比例水通量图。
从图4中可以看出，图4a-b，5mg负载厚的Nb 2CT x-GA纳米片膜用于选择性分离Li +和Mg 2+随体积比的不同而变化；图4c中，lattice Boltzmann方法的输出水速度(速度强度表示膜内随机位置的值，与初始状态相比)随模型-OH含量/纳米片从20％到100％变化。
图5为本发明实施例的空间有限域离子选择性图。
从图5中可以看出，在初始状态下，粘附力随离子浓度的增加而减小；然而，在离子浓度达到临界点后，粘附力将显著增加(图5a-c)；发现在Li +和Mg 2+溶液中，COOH-COOH相互作用模型(COOH-PAA)和OH-OH相互作用模型(OH-PVA)具有相同的临界浓度点，而混合模型(OH-PAA)的临界浓度不同；这一动态过程可以用离子水团簇的形成与离子水交换速率差之间的协同效应来解释，这种协同效应发生在二维纳米片膜的纳米通道内。此外，尖端-离子-水-团簇表面的相互作用可能导致临界浓度点以外的粘附力显著增加。在没有离子水团簇或水团簇的情况下，随着离子水团簇的增长，临界点后的离子浓度会增加粘附力；当Li +和Mg 2+的浓度比增加时，可以观察到明显的宏观渗透效应，Nb 2CT x-GA模型膜上的接触角显著降低(从～40±2°到～26.6±2°)(图5g)。
以上所述实施例仅表达了本发明的几种实施方式，其描述较为具体和详细，但并不能因此而理解为对发明专利范围的限制。
应当指出的是，对于本领域的普通技术人员来说，在不脱离本发明构思的前提下，还可以做出若干变形和改进，这些都属于本发明的保护范围。因此，本发明专利的保护范围应以所附权利要求为准。

Claims (10)

  1. 一种改性Nb 2CT x纳米片膜的制备方法，其特征在于，
    包括，将改性剂加入到Nb 2CT x MXene悬浮液中超声混合，随后通过真空抽滤将其均匀分布在聚偏二氟乙烯薄膜表面形成改性Nb 2CT x薄层，干燥后与聚偏二氟乙烯薄膜分离，即可；
    所述改性剂为可提供羟基和/或羧基的功能性有机物。
  2. 根据权利要求1所述的改性Nb 2CT x纳米片膜的制备方法，其特征在于，
    所述改性剂与Nb 2CT x MXene的加入量之比为1∶1；
    和/或，所述Nb 2CT x MXene悬浮液的浓度为0.5-12mg/mL。
  3. 根据权利要求1所述的改性Nb 2CT x纳米片膜的制备方法，其特征在于，
    所述聚偏二氟乙烯薄膜的孔径为0.22μm；
    优选地，所述真空抽滤的压力为0.5-1.0bar。
  4. 根据权利要求1-3任一项所述的改性Nb 2CT x纳米片膜的制备方法，其特征在于，
    所述改性剂为聚丙烯酸、聚乙烯醇和没食子酸中的一种；
    优选地，所述超声混合的超声时间为60-84h。
  5. 根据权利要求1-4任一项所述的改性Nb 2CT x纳米片膜的制备方法，其特征在于，
    所述Nb 2CT x MXene悬浮液采用如下方法制备：
    将粉末状Nb 2AlC加入到氢氟酸中，室温下搅拌反应68-75h，反应结束后离心分离，加入乙醇将氢氟酸漂洗干净；随后往得到的Nb 2CT x MXene纳米片中加入二甲基亚砜，分层反应后离心将多层MXene纳米片从二甲基亚砜分离，干燥后均匀分散在去离子水中，即得。
  6. 根据权利要求5所述的改性Nb 2CT x纳米片膜的制备方法，其 特征在于，
    在室温下搅拌反应的过程中，控制所述搅拌的转数为175-250rpm；
    和/或，所述离心分离的转数和时间分别为4500-6000rpm和8-15min；
    和/或，所述加入乙醇并漂洗的次数为3-6次。
  7. 根据权利要求5所述的改性Nb 2CT x纳米片膜的制备方法，其特征在于，
    所述二甲基亚砜的加入量为Nb 2CT x MXene纳米片的1.5倍；
    和/或，所述分层反应的时间为15-30min；
    和/或，所述干燥的温度和时间分别为50-75℃和250-360min。
  8. 权利要求1-7任一项所述的制备方法制备得到的改性Nb 2CT x纳米片膜。
  9. 权利要求1-7任一项所述的制备方法或权利要求8所述的改性Nb 2CT x纳米片膜在选择性分离Li +、Mg 2+和水中的应用。
  10. 根据权利要求9所述的应用，其特征在于，
    所述改性剂为可提供羧基的功能性有机物时，应用于促进水的渗透并提高对Li +和Mg 2+的截留率；
    所述改性剂为可提供羟基的功能性有机物时，应用于降低水的渗透并增强对Li +和Mg 2+的渗透率。
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