Submitted Successfully!
To reward your contribution, here is a gift for you: A free trial for our video production service.
Thank you for your contribution! You can also upload a video entry or images related to this topic.
Version Summary Created by Modification Content Size Created at Operation
1 -- 5170 2023-06-15 12:40:47 |
2 format -3 word(s) 5167 2023-06-16 03:54:23 |

Video Upload Options

Do you have a full video?

Confirm

Are you sure to Delete?
Cite
If you have any further questions, please contact Encyclopedia Editorial Office.
Khdary, N.H.; Almuarqab, B.T.; El Enany, G. Development and Production of Nano-Based Polymeric Membranes. Encyclopedia. Available online: https://encyclopedia.pub/entry/45646 (accessed on 18 June 2024).
Khdary NH, Almuarqab BT, El Enany G. Development and Production of Nano-Based Polymeric Membranes. Encyclopedia. Available at: https://encyclopedia.pub/entry/45646. Accessed June 18, 2024.
Khdary, Nezar H., Basha T. Almuarqab, Gaber El Enany. "Development and Production of Nano-Based Polymeric Membranes" Encyclopedia, https://encyclopedia.pub/entry/45646 (accessed June 18, 2024).
Khdary, N.H., Almuarqab, B.T., & El Enany, G. (2023, June 15). Development and Production of Nano-Based Polymeric Membranes. In Encyclopedia. https://encyclopedia.pub/entry/45646
Khdary, Nezar H., et al. "Development and Production of Nano-Based Polymeric Membranes." Encyclopedia. Web. 15 June, 2023.
Development and Production of Nano-Based Polymeric Membranes
Edit

There has been increasing interest in the study and development of nanoparticle-embedded polymeric materials and their applications to special membranes. Nanoparticle-embedded polymeric materials have been observed to have a desirable compatibility with commonly used membrane matrices, a wide range of functionalities, and tunable physicochemical properties. The development of nanoparticle-embedded polymeric materials has shown great potential to overcome the longstanding challenges faced by the membrane separation industry. One major challenge that has been a bottleneck to the progress and use of membranes is the balance between the selectivity and the permeability of the membranes. 

nanoparticules membrane composite membrane

1. Introduction

The development and production of nano-based polymeric membranes offer a promising approach to enhancing the performance of polymeric membranes in various applications. This technology has the potential to improve the efficiency, selectivity, and durability of membrane processes, leading to the development of more sustainable and cost-effective solutions. However, the performance of polymeric membranes is often limited by their relatively low selectivity and permeability. The development of nano-based polymeric membranes aims to overcome these limitations by incorporating nanomaterials into the polymer matrix to enhance the membrane properties.
As noted by Yang and Yang, the use of nanoparticle-embedded polymeric materials is in its early stages. Therefore, all the achievements and developments in this field ought to be compiled. In this section, the recent developments and the commonly used methods of fabricating nanoparticle-embedded polymeric materials will be discussed. The recent advancements in polymer science have contributed to the development of nanoparticle-embedded polymeric materials. These include protein nanoparticles, polyelectrolyte nanoparticles, hyperbranched polymers, and polymeric nanofibers among other separation materials [1].

2. Nanoparticle-Embedded Polymeric Membranes Manufacturing Processes and Applications

Nanoparticle-embedded polymeric membranes are composite materials that combine the properties of polymers with the unique characteristics of nanoparticles, such as high surface area, high reactivity, and unique optical and magnetic properties. These materials have potential applications in various fields such as biomedical, environmental, and energy-related technologies.
In the field of water treatment, these membranes can be used in desalination, water purification, wastewater treatment, and polluted air treatment. In gas separation, these membranes are used to separate gases such as hydrogen, helium, and methane. In addition to the above, they have uses in the medical and biomedical fields such as tissue engineering, drug delivery, and biosensors [2]. As a result, industries specializing in petrochemical, oil production, pharmaceutical products, and food processing are embracing emerging separation techniques to gain a competitive edge and protect consumers from substandard products [2].
One of the most common uses for hydrophobic hollow fiber membranes is in gas-liquid membrane contactors. The liquid and gas phases are separated by a hollow fiber membrane. This also serves as an interface and provides a vast contact surface. Hollow fiber membrane contactors have many advantages, including a high surface-area-to-volume ratio, linear scalability, design, and a wide range of possible applications [3]. However, the most significant difficulty faced by membrane contactors is the wetting of membranes due to the penetration of liquid adsorbent which results in a significant decrease in performance. Therefore, it is vital to improve the hydrophobicity and chemical stability of membranes in order to boost the efficiency of this equipment [4][5][6][7][8][9].

3. Nano-Based Polymeric Mixed-Matrix Membranes (MMMs)

Polymeric nanomaterial-based mixed-matrix membranes (MMMs) possess good performance stability and demonstrate effective membrane separation due to their perfect compatibility and the dispersibility of the nanomaterials involved [10]. However, the permeability of the infused membranes is still lower than the permeability of the pure nanomaterials due to the higher resistance exhibited by the polymeric matrices [11]. Mixed-matrix membranes are created through the fusion of monomer solutions with the nanoparticles [12][13][14]. In this process, the two join reactively to form mixed-matrix membranes, commonly known as MMMs [15]. Occasionally, mixed-matrix membranes are commonly known as hybrid membranes since they comprise nanoparticles linked to polymers. MMMs constitute classical porous fillers, nonporous fillers, and carbon molecular sieves. Notably, MMMs are effective for gas separation due to the presence of polymers with indispensable processing capabilities.

Sol-Gel Process

Sol-gel is the most essential of numerous methods that can be used to improve the hydrophobicity and chemical stability of polymeric membranes. A surface with high hydrophobicity can be fabricated by carefully controlling the various parameters that affect the synthesis of nanoparticles in the sol-gel process [16][17][18]. A hydrophobic polyetherimide hollow fiber membrane was created by Wang et al. by covering the surface of the membranes with fluorinated silica NPs using the sol-gel technique. The experimental findings demonstrated that the hydrophobicity and chemical stability of these membranes were significantly enhanced after the coating of the materials with fluorinated silica nanoparticles [3][8]. The CH3-grafted silica NPs were incorporated into a polypropylene hollow fiber membrane to create a superhydrophobic composite hollow fiber membrane. This was then used to absorb CO2 with a membrane contactor. The results showed that protecting the polymeric membrane from liquid absorbents was another benefit of incorporating the CH3-g silica NPs into the surface of the polypropylene membrane [3].
Challenges such as nanoparticle agglomeration, incompatibility with the polymer matrix, and potential environmental and health risks associated with some types of nanoparticles must be addressed. Further research is needed to optimize the manufacturing processes and explore the full potential applications of nanoparticle-embedded polymeric membranes in different applications.

Electrospinning

Electrospinning is a process in which a polymer solution is passed through a high-voltage field to produce nanofibers. Electrospinning is based on the principle of charge repulsion, whereby an electric field is applied to a polymer solution, causing the formation of charged droplets. These droplets are then spun into ultrafine fibers, which are collected on a grounded collector. The fibers are collected onto a collector and form a porous membrane. The electrospinning process is a versatile and cost-effective method for the production of polymeric nano-based membranes. The technology offers the potential to produce highly uniform porous membranes with tunable pore sizes and high surface areas, making it a promising solution for use in various applications, including water purification, gas separation, and biomedicine.
The process parameters, such as solution concentration, applied voltage, and spinning distance, have a significant impact on the morphology and properties of the resulting membrane. In recent years, various modifications have been made to the traditional electrospinning process to improve the quality of the membranes produced [19][20][21]. For example, the addition of surfactants and other additives to the polymer solution can improve the stability of the droplets and the uniformity of the fibers produced. Recent studies have reported the use of electrospinning to produce membranes with pore sizes which range from a few nanometers to several microns in size. These are ideal for use in a variety of applications, including molecular separation and filtration. Additionally, the technology has also been utilized to produce composite membranes by combining different polymers or incorporating inorganic materials into the fibers. Many of the recent studies in the field of electrospinning for the production of nanoparticle-embedded polymers cover areas such as the electrospinning of polyvinyl alcohol nanofiber membranes for water treatment applications [22] and the fabrication and characterization of electrospun polyvinylidene fluoride nanofiber membranes for water treatment [23].

Phase Inversion Process

Phase inversion is one of the most widely used methods for producing nanoparticle-embedded polymers [24]. During this process, a polymer solution is cast onto a substrate and then subjected to a phase change that transforms the solution into a solid, porous membrane. This process can be controlled to produce membranes with precise pore size, porosity, and selectivity [25]. The factors of pore size and distribution can be controlled by adjusting the process parameters. The phase inversion process is an efficient and widely used method for producing nanoscale polymeric films. It has the potential to play an essential role in the development of new nanoparticle-incorporated membranes. One of the key advantages of the phase inversion process is its versatility and scalability, making it suitable for the production of membranes on a large scale. Additionally, the phase inversion process allows for the precise control of the membrane’s pore size, porosity, and selectivity, making it a highly desirable method for producing nanoparticle-embedded polymers [26]. In recent years, new phase inversion techniques have been developed to enhance the performance and durability of nanoparticle-embedded polymers produced through the phase inversion process. For example, non-solvent-induced phase inversion [27][28] uses a different approach to produce a gel-like structure. Conversely, supercritical fluid phase inversion [29] and thermally induced phase inversion [28] employ alternative methods to induce the phase change from a solution to a solid, porous membrane. These new techniques have shown promising results and have the potential to provide high-quality, high-performance nanoparticle-embedded polymers for use in a variety of applications. In addition, the parameters that influence the phase inversion process, including the choice of solvent and polymer, are under continuous investigation to optimize membrane production [29]. This includes casting conditions such as temperature and pressure. By manipulating these parameters, researchers aim to manufacture nanoparticle-embedded polymers with accurate pore size, porosity, and selectivity.
Phase inversion is the regulated transition of a polymer from its liquid phase to its solid phase. Precipitation from vapor phase, precipitation by controlled evaporation, thermally induced phase separation, and immersion precipitation are the four fundamental methods utilized to make phase inversion membranes. In the process, there is an exchange of non-solvent and solvent molecules, leading to the formation of a film that contains both a matrix and polymeric nano-fillers [30]. The film produced in this stage is then washed and subjected to post-treatment in order to further refine the matrix–filler material produced [31].
Polyethersulfone is commonly used to prepare mixed-matrix membranes due to its mechanical, thermal, and chemical capabilities. The phase inversion process is used to manufacture MMMs due to their ability to form a thin coating on a membrane. The membrane comprises a thin coating and a porous sublayer as these components improve gas molecules’ permeability and selectivity properties. Notably, the polymer membrane size is affected by temperature and pressure changes [32]. Hence, industrial experts introduce nanomaterials with a high permeation rate and morphological properties in order to improve the mechanical strength of membranes. Additionally, graphene nanosheets (GNs) have been shown to have a high water content for reasons of hybrid matrix membrane fabrication. Graphene nanosheets (GNs) accelerate the movement of mole molecules within the membrane. Occasionally, the process involves fabricating graphene nanosheets (GNs) with a mixture of four mixed-matrix membranes and pristine PES membranes through the phase inversion method [32]. In a previous study, the graphene nanosheets (GNs) used had weights of 0.01, 0.02, 0.03, and 0.04 wt%, and the homogeneous solution was subjected to a temperature of 50 °C for 6 h. The membranes were later immersed in deionized water at a temperature of 70 °C for 10 min. The solution was removed from the glass material and dipped in fresh deionized water at room temperature for less than 24 h. Finally, the membrane was dried and used in biogas production and oil manufacturing. [33].
Phase inversion was used to create ultrafiltration membranes using polyacrylonitrile (PAN) and polyvinylidene fluoride (PVDF) blends. These were then modified by the addition of silicon dioxide nanoparticles (SiO2) and titanium dioxide nanoparticles (TiO2) [14].
The chemistry of the dope polymer solution is drastically altered by the interaction between nanoparticles, polymer chains, and solvent molecules [14].
NPs, possessing large surface areas and an affinity for water, not only improve flow, and chemical and mechanical characteristics, but they also give antibacterial and antifouling qualities to membranes made from an extensively dope polymer solution using the phase inversion approach. The progressive rise in nano silica concentration may cause a shift in the rate of solvent-to-non-solvent exchange during phase inversion, resulting in a gradual change in membrane shape [14]. This type of membrane has been successfully used to purify conventional solvents, such as ethanol and isopropanol [34].

Layer-by-Layer Assembly

Layer-by-layer (LbL) can be used to produce membranes with a range of pore sizes and pore distributions. The layer-by-layer assembly method has emerged as a promising manufacturing process for the production of polymeric nano-based membranes. In this approach, the polymer layers are deposited onto a substrate through alternate adsorption of cationic and anionic polymers, resulting in the formation of a dense, uniform, and well-defined membrane.
The LbL assembly method offers several advantages over traditional membrane fabrication methods such as dip-coating, spin-coating, and casting. The LbL assembly process allows for the creation of multilayer membranes of well-defined thickness and composition that can be precisely controlled by selecting polymers and the number of layers deposited. This results in improved performance and functionality compared to single-layer membranes [35].
One of the key benefits of using nanoparticle-embedded polymers fabricated using the LbL assembly method is their enhanced mechanical stability. By incorporating nanoparticles into polymers, the strength and durability of the membranes can be greatly improved for their use in advanced energy and environmental applications. This makes them suitable for use in a range of harsh environments, such as in high-pressure and high-temperature applications [36].
Recent advancements in the LbL assembly method have led to the development of new nanoparticle-embedded polymers with enhanced properties. For example, the use of nanoparticles and other nanoscale materials as building blocks has enabled the creation of membranes with improved mechanical strength, permeability, and selectivity. Furthermore, the incorporation of functional groups into the polymers has enabled the design of membranes with specific properties, such as pH sensitivity, biocompatibility, and catalytic activity [37][38][39]. The LbL assembly method also enables the creation of nanoparticle-embedded polymers with controlled drug delivery capabilities. By incorporating functional groups into the polymers, membranes can be designed to respond to specific stimuli, such as changes in pH or temperature, and to release drugs in a controlled manner. This information was reviewed by Park in a study on the layer-by-layer assembly of nanoparticle-embedded polymers for use in controlled drug delivery [40]. The utilization of renewable and biodegradable materials to produce nanoparticle-embedded polymers is also a growing area of research, as highlighted in many studies on the layer-by-layer assembly of green and sustainable polymeric nano-based membranes.

Template-Assisted Methods

Template-assisted methods involve the use of a template to produce a polymer membrane with a specific pore size and structure. The template can be a porous material such as a sieve, or a solid material. The polymer is then deposited onto the template; after the removal of the template, a porous membrane is produced.
One popular template-assisted method is the track-etched (or shadow-masked) method. This involves the use of a metal template with microscopic pores that define the shape and size of the membrane [41] and the use of a track-etched method to produce nanoparticle-embedded polymers with uniform and controlled pore sizes. Another template-assisted method is the nano-imprinting method, which involves pressing a polymer film onto a template and then removing the template to obtain the desired pattern. A third template-assisted method is a soft-lithography method, which uses a mold made from a soft, flexible material to create complex patterns and shapes. A study by Wang et al. (2021) explored the use of soft lithography for the production of nanoparticle-embedded polymers with enhanced mechanical stability and permeability [42].
In conclusion, template-assisted methods, including layer-by-layer assembly, electrospinning, chemical vapor deposition, solvent casting, and phase inversion, continue to offer promising avenues for the production of nanoparticle-embedded polymers with improved properties. Ongoing research efforts are focused on exploring new materials and techniques for the production of membranes with a superior performance in various applications.

Track-Etching Methods

Track-etching methods for membrane characterization have gained popularity in recent years due to their ability to create uniform and controlled pores in membranes for a variety of applications. These methods include two primary techniques: particle-induced track etching and nuclear track etching. Both techniques use ion beams to create tracks in polymer membranes. Particle-induced track etching involves the use of heavy ions, such as alpha particles or heavy ions, to create tracks in the membrane [43]. On the other hand, nuclear track etching involves the use of fast neutrons to create tracks in the membrane. Once the tracks are created, the membrane is chemically etched to remove the polymer around the tracks, leaving behind uniform and controlled pores in the membrane. The pore size and density can be controlled by adjusting the ion beam energy, the etching time, and the chemical etching conditions [44]. The primary advantage of this method is the ability to create uniform and controlled pores in the membrane [45]. This allows for precise control of pore size, shape, and density. This is critical for many applications, such as filtration, separation, and drug delivery. Additionally, track-etching methods are compatible with a wide range of polymer materials, making them versatile for different applications.
Although track-etching methods have several advantages, they also have some limitations. One limitation is the inability to create pores smaller than the ion track diameter. This limits the minimum pore size that can be achieved using these methods. Additionally, the ion beam used in these techniques can cause damage to the polymer membrane, leading to degradation or changes in the mechanical properties of the membrane. The chemical etching process can also cause damage to the membrane, leading to irregularities in pore size and shape [46].
Track-etched membranes (TeMs), manufactured from polycarbonate and poly(ethylene terephthalate) (PET), have a wide range of physical, chemical and mechanical properties and are perfect templates for developing composite materials. Varying the irradiation conditions makes it possible to obtain TeMs with pore density, while the modification of the conditions of the etching stage provides the production of membranes with different geometries (cylindrical, cone-shaped, bottle-shaped, etc.) and with pore diameters ranging in size from 50 nm to 5 μm [46].

3.1.2. Homogeneous Nanoparticle-Embedded Polymers (HPMs)

Based on nanomaterials, homogenous polymeric membranes possess better selectivity and higher permeability and are mostly fabricated using surface coating and self-assembly methods. Such applications have been made in the separation of organic molecules and inorganic salts in gas and liquid mixture systems by capitalizing on the better permeability, anti-fouling, stability, and accuracy of the nano-based polymeric membranes [47]. The advantages of HPMs include their high permeability, selectivity, and mechanical stability. Additionally, they are easy to process and can be produced in large quantities. HPMs also have the potential to be modified with functional groups to enhance their performance in specific applications [48][49][50][51].
Researchers are exploring various approaches with which to synthesize and modify these polymers, including the use of copolymers and block copolymers, and general surface modification. There has also been a growing interest in the use of HPMs for various applications, such as desalination, wastewater treatment, and gas separation. The development of polymeric nanoparticles in the last decade has been used as a steppingstone into the discovery, development, and fabrication of HPMs, which theoretically have been presumed to possess excellent performance attributes [52][53]. HPMs are theoretically expected to display performance advantages over conventional MMMs due to the continuous transfer channels formed between the various blocks of materials making up the polymeric membrane [54]. Furthermore, the surface structure and hierarchical nature of HPMs can be adjusted to suit the requirements of the project by adjusting the physicochemical properties of the nanoparticles making up the membrane. HPMs are also constructed using self-assembly and surface coating techniques, which are also used to manufacture mixed-matrix membranes [55].
Polydopamine (PDA) nanoparticles, hyper-branched polymers, and other nanoparticles are used to manufacture homogenous polymeric membranes through surface coating methods [56]. Surface coating in HPMs generation is used to produce elements such as zwitterionic colloid nanoparticles. These, when subjected to further processing, produce zwitterionic colloid nanoparticles membranes (ZCPMs) [57].
In terms of desalination, HPMs are effective at removing salt from water, and they have been shown to have a high salt rejection rate and high water permeability [58]. In the area of wastewater treatment, HPMs have been used to remove organic pollutants and heavy metals from water, and they have shown promising results in terms of their ability to effectively purify contaminated water [59]. For gas separation, HPMs have been used to separate a variety of gases, including nitrogen, oxygen, carbon dioxide, and hydrogen. The unique properties of these materials, such as their high permeability and selectivity, make their use practical in gas separation applications, and they have the potential to be used as alternatives to traditional gas separation methods. Furthermore, the versatility of HPMs has led to the exploration of their use in various other applications, such as biomedicine. HPMs are biocompatible and have been used to develop drug delivery systems and implantable medical devices. Their ability to control the release of drugs, as well as their biocompatibility, makes them suitable for use in these applications. In the field of energy production, HPMs have been used in the development of fuel cells to serve as proton exchange membranes. The high proton conductivity and stability of HPMs make them appropriate for this application, and they have the potential to be used as a more efficient alternatives to traditional fuel cell membranes [60].
Polymeric nanomaterials can also be fabricated using the filtration assembly method, which, in comparison to the surface coating method, can also produce the desired nano-based membranes [61]. In the filtration assembly method, a vacuum-driven or pressure-driven force is used. The polymeric nanoparticles, which are pre-dispersed before the process starts, are used to make the filtration solutions that are used later in the process, and the solution of dispersed nanoparticles is filtered through regulated pores to create the desired films [62].
The manufacturing process of HPMs is complex and multi-faceted, with a range of techniques being used to produce membranes with improved properties. Ongoing research efforts are focused on exploring new materials and techniques for the production of HPMs with superior performances in various applications.

Surface Coating

Surface coating is a method of depositing a thin layer of polymeric material onto a substrate surface to form a uniform and homogenous membrane. This technique has several advantages over other membrane manufacturing methods, including the ability to produce membranes with a high degree of control over pore size and distribution, and the ability to produce membranes with uniform and consistent properties [63].
The process of manufacturing HPMs using surface coating techniques typically involves substrate preparation, the deposition of polymeric material, cross-linking, characterization, and modification (if necessary). In the first step, the substrate material is cleaned and treated in order to ensure a high-quality and uniform surface. The polymeric material, such as polysulfone or polyvinylidene fluoride, is then deposited onto the substrate using techniques such as dip-coating, spin-coating, or spray-coating. The deposited polymeric material is cross-linked to form a stable and continuous membrane through chemical cross-linking, thermal cross-linking, or UV cross-linking. The final membrane is characterized to evaluate its performance and properties, such as pore size, surface area, and water flux.
Modifications to the membrane can be made by incorporating functional groups or nanoparticles in order to enhance its performance for specific applications [64]. For example, the incorporation of nanoparticles can increase the mechanical strength of the membrane and improve its resistance to fouling.
The use of surface coating techniques to manufacture HPMs has resulted in the production of high-quality and consistent membranes which possess excellent performance and durability. The ability to control pore size and distribution, as well as the ability to modify the membrane surface, has enabled the development of membranes with specific properties for use in various applications.
Surface coating was used to produce HPMs with high selectivity and flux. The authors used a combination of dip-coating and spin-coating techniques to deposit a thin layer of polyvinylidene fluoride (PVDF) onto a porous support, where the resulting HPMs showed excellent performance in the separation of small organic molecules [65].
The process involves the use of hyperbranched polymers, and zwitterionic and PDA nanoparticles. In order to improve the surface coating, recent developments are being integrated into existing techniques. These include combining the propylene imine dendrimers that are developed by 16 thiol groups (DAB-3-(SH)16) to produce polymeric modified membranes [66]. Alternatively, dopamine can be electrosprayed in its aqueous solution onto an ultrafiltration substrate membrane in order to produce a PDA membrane. Additionally, through surface coating, zwitterionic nanoparticles are being improved to promote the manufacturing of homogenous polymeric nano-based membranes.
The improved zwitterionic nanostructure can be separated by adjusting the monomer ratio of the zwitterionic colloid nanoparticles (ZCPs) and regulating the acid concentration. Additionally, the process involves the polyelectrolyte method that assists in classifying different ionic groups. In their study, Clarizia and Bernardo (2022) argue that the surface coating method utilized protection and de-protection methods to identify weak and strong nanoparticles. The homogenous polymeric PECN-based membrane that formed eased the separation of PV and NF elements. Notably, PAA–PDDA PECNs exhibited a strong perm selectivity membrane in the aqueous ethanol solution. The membrane separation ability has recently been improved by combining organic–inorganic hybrid PECNs. Recent developments in inorganic nanomaterials have integrated silica oxide (SiO2) into carbon nanotubes. Such an improvement results in the formation of an inorganic nanomaterial combined with a PECN matrix with high perm selectivity and stable thermal capability [66]. Moreover, the homogenous PECN developed is used for industrial and research purposes.

Self-Assembly Process

In self-assembly, the polymeric material is dissolved in a solvent and then cast onto a substrate. The solvent evaporates, leaving behind a thin film of polymeric material. The film can then be manipulated to form the desired structure and pore size, leading to the formation of a functional HPM.
This bottom-up methodology can only be used to fabricate single-sided coatings on planar substrates. This method can be easily applied to a wide range of materials without the need for complicated equipment [67]. Additionally, the filtration assembly process can prepare the homogenous polymeric nano-based membrane. The process involves polymeric nanomaterial that is used to prepare filtration elements. Firstly, the isolated solutions are filtered through porous sieves to develop nano-assembled films [68]. Recently, reversed filtration has been used to improve the deposition of PDA particles onto the internal pores of the polymeric membrane. Alternatively, improving polyethersulfone (PES) ultrafiltration membrane leads to the development of charged membranes, crucial in facilitating the assembly of oppositely charged membranes. Notably, the recent development of the assembly method has influenced the development of ferritin-based membranes and thick UF membranes that regulate the polymeric nanomaterials and self-assembled layers.
Despite the improved membranes, most of them are fabricated, hindering ionic separation. To improve the separation, self-assembled membranes are developed from PECN nanomaterials. Sodium vinyl sulfonate and PECN nanomaterials are combined in a vacuum filtration chamber to improve the structure of the membrane [66]. Hence, the thickness of the membrane and structure alignment of the membrane depend on the preparation condition and the size of the particles. The PECN membrane demonstrates a strong thermal and mechanical capability. Moreover, the process involves the use of an electrostatic layer-by-layer assembly method to fabricate the developed PECN membrane. Depending on the industrial use, the membrane thickness can be changed by regulating the number of nano layers used and several layers-to-layer structures.

Interfacial Polymerization (IP)

Interfacial polymerization refers to the chemical reaction that takes place at the interface between two immiscible polymer systems. The objective of interfacial polymerization of HPMs is to synthesize ultrathin polymer films by inducing polymerization reactions at the interface between a monomer solution and a continuous polymer matrix. This process has become increasingly popular in the development of advanced materials, particularly in the field of nano-based membranes. One of the most important steps in the interfacial polymerization process of HPMs is the selection of the monomer and the initiator. The monomer must be water-soluble and have a low viscosity, and the initiator must have a high degree of reactivity in order to ensure a fast polymerization reaction. A commonly used monomer for the synthesis of HPMs is acrylamide, and the initiator is usually a redox system composed of a reducing agent and an oxidizing agent [69].
This technique is mostly used to prepare the reverse osmosis and nanofiltration membranes that are commercially available in the market. In this process, appropriate polymeric nanomaterials are added into reactive solutions of either organic phase or aqueous monomer solutions and mixed through interfacial polymerization [70]. Interfacial polymerization is performed under the regulation of some specific nanomaterials. These include protein nanosheets, and nanocrystals of cellulose, among other additives, which vary according to the desired output. The protein nanosheets usually used in this process should be appropriately porous to enable better control over the process [71].
Hydrophilic nanomaterials, one of the most used nanomaterials in the interfacial polymerization process, are used to create the desired mixed-matrix membranes by adding to the aqueous phase solutions, and the structure and performance of resultant separation membranes can be adjusted by changing some elements of the interfacial polymerization process. Although these nanoparticles used in the interfacial polymerization process improve the performance of the resultant membranes, the process of acquiring and manufacturing these specific nanoparticles is time-consuming, delicate, requires greater attention, and is generally more costly than the tasks of other performing techniques [72]. There are many examples and applications of them:
Thin-film composite nanofiltration membranes are produced by performing an interfacial polymerization process of piperazine and trimesoylchloride on virgin- and nanoparticle (SiO2/TiO2)-modified substrates. Substrates of 70:30 polyacrylonitrile and 30:70 polyacrylonitrile, relevant for their use in ultrafiltration, are composed of a polyacrylonitrile polyvinylidenefluoride mix. NF membranes constructed on TiO2-modified substrates demonstrate greater flux than other membranes. Salts that are moving from divalent to monovalent salts are rejected at the greatest rate (4.63) by membranes produced on TiO2-modified 70:30 substrate blends. Th flux recovery ratio (FRR) and total fouling ratio (TFR) values of nanofiltration membranes fabricated on nanoparticle-modified substrates are much greater than those of NF membranes fabricated on unmodified ultrafiltration substrates [73].
In one study, the utilization of a PS/8PVP substrate in the interfacial polymerization process formed a thin, laminate-like polyamide skin layer of 40 nm thickness and a nanoporous, compressible, sponge-like substrate layer (middle layer). The substrate’s symmetric surface pore shape permitted the creation of an ultrathin polyamide rejection layer in the form of a laminate (of almost uniform thickness) with minimal pore penetration. The barrier layer (polyamide), a thin-film composite nanofiltration (TFCNF) membrane, required sufficient stiffness and functionality, something that was ensured by optimizing relative monomer concentrations, polymerization time, and curing conditions (Curing temperature and time). For the barrier layer of this (NF/PS/8PVP) membrane, the O/N ratio was 2.76, and the study indicated that this layer (polyamide layer) consisted of a well-balanced combination of crosslinked segments as well as many linear subunits containing carboxylic acid groups. These facts rendered the membrane surface hydrophilic with a lower contact angle and imparted a negative zeta potential that increased with an increase in the pH. This membrane with a narrow pore size distribution (median pore radius of 0.26 nm) had an outstanding water flow of 158 L M−2H−1 at 50 pressure and a strong rejection (>99%) of bivalent salt (Na2SO4) [74].
Additionally, through the incorporation of negatively charged hydrophilic PSS into the polyamide layer during the (IP) process over a PAN membrane substrate, polypiperazinetrimesamide–PSS semi-IPN-based TFC membranes were fabricated. NF membranes had a greater hydrophilicity and surface potential than virgin polypiperazinetrimesamide NF membranes. On a PAN substrate, semi-IPN membranes revealed a nodular surface architecture with a somewhat thinner polyamide layer. These modified membranes demonstrated a 2–2.5-fold increase in flow, salt rejection (%R of Na2SO4 and MgSO4), and rejection ratios of bivalent and monovalent salts compared to the ratios of the virgin polypiperazinetrimesamide membranes. Due to their hydrophilic nature, these membranes prevented protein molecules from adhering to their surface and exhibited superior antifouling capabilities compared to virgin polypiperazinetrimesamide membrane [75].

References

  1. Lu, X.; Elimelech, M. Fabrication of desalination membranes by interfacial polymerization: History, current efforts, and future directions. Chem. Soc. Rev. 2021, 50, 6290–6307.
  2. Vinti, G.; Vaccari, M. Solid Waste Management in Rural Communities of Developing Countries: An Overview of Challenges and Opportunities. Clean Technol. 2022, 4, 1138–1151.
  3. Zhai, X.; Wang, Y.-L.; Dai, R.; Li, X.; Wang, Z. Roles of Anion–Cation Coupling Transport and Dehydration-Induced Ion–Membrane Interaction in Precise Separation of Ions by Nanofiltration Membranes. Environ. Sci. Technol. 2022, 56, 14069–14079.
  4. Raveshiyan, S.; Amirabedi, P.; Yegani, R.; Pourabbas, B.; Tavakoli, A. CO2 absorption through PP/fSiO2 nanocomposite hollow fiber membrane contactor. Polyolefins J. 2022, 9, 61–71.
  5. Ramezani, M.; Vaezi, M.R.; Kazemzadeh, A. Preparation of silane-functionalized silica films via two-step dip coating sol–gel and evaluation of their superhydrophobic properties. Appl. Surf. Sci. 2014, 317, 147–153.
  6. Mansourizadeh, A.; Ismail, A.F. Hollow fiber gas–liquid membrane contactors for acid gas capture: A review. J. Hazard. Mater. 2009, 171, 38–53.
  7. Hamdi, A.; Chalon, J.; Laurent, P.; Dodin, B.; Dogheche, E.; Champagne, P. Facile synthesis of fluorine-free, hydrophobic, and highly transparent coatings for self-cleaning applications. J. Coatings Technol. Res. 2021, 18, 807–818.
  8. Zhang, Y.; Wang, R. Gas–liquid membrane contactors for acid gas removal: Recent advances and future challenges. Curr. Opin. Chem. Eng. 2013, 2, 255–262.
  9. Zhang, Y.; Wang, R. Fabrication of novel polyetherimide-fluorinated silica organic–inorganic composite hollow fiber membranes intended for membrane contactor application. J. Membr. Sci. 2013, 443, 170–180.
  10. Ganbavle, V.V.; Bangi, U.K.H.; Latthe, S.S.; Mahadik, S.A.; Rao, A.V. Self-cleaning silica coatings on glass by single step sol-gel route. Surf. Coat. Technol. 2011, 205, 5338–5344.
  11. Bakonyi, P.; Koók, L.; Kumar, G.; Tóth, G.; Rózsenberszki, T.; Nguyen, D.D.; Chang, S.W.; Zhen, G.; Bélafi-Bakó, K.; Nemestothy, N. Architectural engineering of bioelectrochemical systems from the perspective of polymeric membrane separators: A comprehensive update on recent progress and future prospects. J. Membr. Sci. 2018, 564, 508–522.
  12. Santosh, V.; Babu, P.V.; Gopinath, J.; Rao, N.N.M.; Sainath, A.V.S.; Reddy, A.V.R. Development of hydroxyl and carboxylic acid functionalized CNTs–polysulphone nanocomposite fouling-resistant ultrafiltration membranes for oil–water separation. Bull. Mater. Sci. 2020, 43, 1–12.
  13. Najim, A. A review of advances in freeze desalination and future prospects. npj Clean Water 2022, 5, 1–15.
  14. Polisetti, V.; Ray, P. Hydrophilic modification through incorporation of nanoparticles in ultrafiltration membranes. Mater. Today Proc. 2021, 54, 797–809.
  15. Chudasama, N.A.; Polisetti, V.; Maity, T.K.; Reddy, A.; Prasad, K. Preparation of seaweed polysaccharide based hydrophobic composite membranes for the separation of oil/water emulsion and protein. Int. J. Biol. Macromol. 2021, 199, 36–41.
  16. Xie, Y.-T.; Chen, J.-R.; Chen, Y.-T.; Jiang, B.-C.; Sie, Z.-H.; Hsu, H.-Y.; Chen, T.-L.; Chiang, Y.-Y.; Hsueh, H.-Y. Sol–gel-derived hierarchically wrinkled mesoporous ceramics for enhancement of cell alignment. Chem. Eng. J. 2020, 405, 126572.
  17. Arya, S.; Mahajan, P.; Mahajan, S.; Khosla, A.; Datt, R.; Gupta, V.; Young, S.-J.; Oruganti, S.K. Review—Influence of Processing Parameters to Control Morphology and Optical Properties of Sol-Gel Synthesized ZnO Nanoparticles. ECS J. Solid State Sci. Technol. 2021, 10, 023002.
  18. Yu, H.J.; Chiou, D.-S.; Hsu, C.-H.; Tsai, H.-Y.; Kan, M.-Y.; Lee, J.S.; Kang, D.-Y. Engineering CAU-10-H in the preparation of mixed matrix membranes for gas separation. J. Membr. Sci. 2022, 663, 121024.
  19. Ahmed, F.E.; Lalia, B.S.; Hashaikeh, R. A review on electrospinning for membrane fabrication: Challenges and applications. Desalination 2015, 356, 15–30.
  20. Chen, H.; Huang, M.; Liu, Y.; Meng, L.; Ma, M. Functionalized electrospun nanofiber membranes for water treatment: A review. Sci. Total. Environ. 2020, 739, 139944.
  21. Liao, Y.; Loh, C.-H.; Tian, M.; Wang, R.; Fane, A.G. Progress in electrospun polymeric nanofibrous membranes for water treatment: Fabrication, modification and applications. Prog. Polym. Sci. 2018, 77, 69–94.
  22. Kusumaatmaja, A.; Sukandaru, B.; Chotimah; Triyana, K. Application of polyvinyl alcohol nanofiber membrane for smoke filtration. AIP Conf. Proc. 2016, 1755, 150006.
  23. Lalia, B.S.; Guillen-Burrieza, E.; Arafat, H.A.; Hashaikeh, R. Fabrication and characterization of polyvinylidenefluoride-co-hexafluoropropylene (PVDF-HFP) electrospun membranes for direct contact membrane distillation. J. Membr. Sci. 2012, 428, 104–115.
  24. Chen, T.; Wei, X.; Chen, Z.; Morin, D.; Alvarez, S.V.; Yoon, Y.; Huang, Y. Designing energy-efficient separation membranes: Knowledge from nature for a sustainable future. Adv. Membr. 2022, 2, 100031.
  25. Al Harby, N.F.; El-Batouti, M.; Elewa, M.M. Prospects of Polymeric Nanocomposite Membranes for Water Purification and Scalability and their Health and Environmental Impacts: A Review. Nanomaterials 2022, 12, 3637.
  26. Geleta, T.A.; Maggay, I.V.; Chang, Y.; Venault, A. Recent Advances on the Fabrication of Antifouling Phase-Inversion Membranes by Physical Blending Modification Method. Membranes 2023, 13, 58.
  27. Lin, K.-Y.; Wang, D.-M.; Lai, J.-Y. Nonsolvent-Induced Gelation and Its Effect on Membrane Morphology. Macromolecules 2002, 35, 6697–6706.
  28. Duraikkannu, S.L.; Castro-Muñoz, R.; Figoli, A. A review on phase-inversion technique-based polymer microsphere fabrication. Colloid Interface Sci. Commun. 2021, 40, 100329.
  29. Baldino, L.; Cardea, S.; Reverchon, E. Supercritical Phase Inversion: A Powerful Tool for Generating Cellulose Acetate-AgNO3 Antimicrobial Membranes. Materials 2020, 13, 1560.
  30. Salahshoori, I.; Seyfaee, A.; Babapoor, A. Recent advances in synthesis and applications of mixed matrix membranes. Synth. Sinter. 2021, 1, 1–27.
  31. Escorihuela, J.; Olvera-Mancilla, J.; Alexandrova, L.; del Castillo, L.F.; Compañ, V. Recent Progress in the Development of Composite Membranes Based on Polybenzimidazole for High Temperature Proton Exchange Membrane (PEM) Fuel Cell Applications. Polymers 2020, 12, 1861.
  32. Subtil, E.L.; Ragio, R.A.; Lemos, H.G.; Scaratti, G.; García, J.; Le-Clech, P. Direct membrane filtration (DMF) of municipal wastewater by mixed matrix membranes (MMMs) filled with graphene oxide (GO): Towards a circular sanitation model. Chem. Eng. J. 2022, 441, 136004.
  33. Zhou, W.-L.; Wu, T.; Du, Y.; Zhang, X.-H.; Chen, X.-C.; Li, J.-B.; Xie, H.; Qu, J.-P. Efficient fabrication of desert beetle-inspired micro/nano-structures on polypropylene/graphene surface with hybrid wettability, chemical tolerance, and passive anti-icing for quantitative fog harvesting. Chem. Eng. J. 2023, 453.
  34. Ma, Y.; He, X.; Tang, S.; Xu, S.; Qian, Y.; Zeng, L.; Tang, K. Enhanced 2-D MOFs nanosheets/PIM-PMDA-OH mixed matrix membrane for efficient CO2 separation. J. Environ. Chem. Eng. 2022, 10, 107274.
  35. Azzaroni, O.; Lau, K.H.A. Layer-by-layer assemblies in nanoporous templates: Nano-organized design and applications of soft nanotechnology. Soft Matter 2011, 7, 8709–8724.
  36. Lengert, E.V.; Koltsov, S.I.; Li, J.; Ermakov, A.V.; Parakhonskiy, B.V.; Skorb, E.V.; Skirtach, A.G. Nanoparticles in Polyelectrolyte Multilayer Layer-by-Layer (LbL) Films and Capsules—Key Enabling Components of Hybrid Coatings. Coatings 2020, 10, 1131.
  37. Abdelhamid, H.N.; Mathew, A.P. Cellulose–metal organic frameworks (CelloMOFs) hybrid materials and their multifaceted Applications: A review. Co-Ord. Chem. Rev. 2021, 451, 214263.
  38. Yoon, H.; Chang, M.; Jang, J. Sensing Behaviors of Polypyrrole Nanotubes Prepared in Reverse Microemulsions: Effects of Transducer Size and Transduction Mechanism. J. Phys. Chem. B 2006, 110, 14074–14077.
  39. Lee, K.M.; Kim, K.H.; Yoon, H.; Kim, H. Chemical Design of Functional Polymer Structures for Biosensors: From Nanoscale to Macroscale. Polymers 2018, 10, 551.
  40. Park, S.; Han, U.; Choi, D.; Hong, J. Layer-by-layer assembled polymeric thin films as prospective drug delivery carriers: Design and applications. Biomater. Res. 2018, 22, 1–13.
  41. Stucki, M.; Loepfe, M.; Stark, W.J. Porous Polymer Membranes by Hard Templating—A Review. Adv. Eng. Mater. 2017, 20.
  42. Lee, J.-S.; Yu, J.-H.; Hwang, K.-H.; Nam, S.-H.; Boo, J.-H.; Yun, S.H. Patterning ITO by Template-Assisted Colloidal-Lithography for Enhancing Power Conversion Efficiency in Organic Photovoltaic. J. Nanosci. Nanotechnol. 2016, 16, 5024–5028.
  43. Apel, P.Y. TRACK-ETCHING. In Encyclopedia of Membrane Science and Technology; Hoek, E.M.V., Tarabara, V.V., Eds.; John Wiley & Sons, Inc.: Hoboken, NJ, USA, 2013.
  44. Yeszhanov, A.B.; Korolkov, I.V.; Dosmagambetova, S.S.; Zdorovets, M.V.; Güven, O. Recent Progress in the Membrane Distillation and Impact of Track-Etched Membranes. Polymers 2021, 13, 2520.
  45. Mashentseva, A.A.; Barsbay, M.; Zdorovets, M.V.; Zheltov, D.A.; Güven, O. Cu/CuO Composite Track-Etched Membranes for Catalytic Decomposition of Nitrophenols and Removal of As(III). Nanomaterials 2020, 10, 1552.
  46. Mashentseva, A.A.; Kozlovskiy, A.L.; Zdorovets, M.V. Influence of deposition temperature on the structure and catalytic properties of the copper nanotubes composite membranes. Mater. Res. Express 2018, 5, 065041.
  47. Korolkov, I.V.; Mashentseva, A.; Güven, O.; Gorin, Y.G.; Zdorovets, M.V. Protein fouling of modified microporous PET track-etched membranes. Radiat. Phys. Chem. 2018, 151, 141–148.
  48. Zhang, Y.; Almodovar-Arbelo, N.E.; Weidman, J.L.; Corti, D.S.; Boudouris, B.W.; Phillip, W.A. Fit-for-purpose block polymer membranes molecularly engineered for water treatment. npj Clean Water 2018, 1, 2.
  49. Algarra, M.; Vázquez, M.I.; Alonso, B.; Casado, C.M.; Casado, J.; Benavente, J. Characterization of an engineered cellulose based membrane by thiol dendrimer for heavy metals removal. Chem. Eng. J. 2014, 253, 472–477.
  50. Wang, L.; Ji, S.; Wang, N.; Zhang, R.; Zhang, G.; Li, J.-R. One-step self-assembly fabrication of amphiphilic hyperbranched polymer composite membrane from aqueous emulsion for dye desalination. J. Membr. Sci. 2013, 452, 143–151.
  51. Krishnan, J.N.; Venkatachalam, K.R.; Ghosh, O.; Jhaveri, K.; Palakodeti, A.; Nair, N. Review of Thin Film Nanocomposite Membranes and Their Applications in Desalination. Front. Chem. 2022, 10, 6.
  52. Roy, S.; Ragunath, S. Emerging Membrane Technologies for Water and Energy Sustainability: Future Prospects, Constrains and Challenges. Energies 2018, 11, 2997.
  53. Castro-Muñoz, R.; Msahel, A.; Galiano, F.; Serocki, M.; Ryl, J.; Ben Hamouda, S.; Hafiane, A.; Boczkaj, G.; Figoli, A. Towards azeotropic MeOH-MTBE separation using pervaporation chitosan-based deep eutectic solvent membranes. Sep. Purif. Technol. 2021, 281, 119979.
  54. Li, B.; Wang, C.-G.; Surat’Man, N.E.; Loh, X.J.; Li, Z. Microscopically tuning the graphene oxide framework for membrane separations: A review. Nanoscale Adv. 2021, 3, 5265–5276.
  55. Feng, F.; Liang, C.-Z.; Wu, J.; Weber, M.; Maletzko, C.; Zhang, S.; Chung, T.-S. Polyphenylsulfone (PPSU)-Based Copolymeric Membranes: Effects of Chemical Structure and Content on Gas Permeation and Separation. Polymers 2021, 13, 2745.
  56. Fernández-Castro, P.; Ortiz, A.; Gorri, D. Exploring the Potential Application of Matrimid® and ZIFs-Based Membranes for Hydrogen Recovery: A Review. Polymers 2021, 13, 1292.
  57. Ming, W.S.; Jawad, Z.A.; Qasim, M. Grand Challenges in Membrane Process for Gas Separation. J. Appl. Membr. Sci. Technol. 2022, 26, 43–48.
  58. Park, J.; Lee, S. Desalination Technology in South Korea: A Comprehensive Review of Technology Trends and Future Outlook. Membranes 2022, 12, 204.
  59. Ethaib, S.; Al-Qutaifia, S.; Al-Ansari, N.; Zubaidi, S.L. Function of Nanomaterials in Removing Heavy Metals for Water and Wastewater Remediation: A Review. Environments 2022, 9, 123.
  60. Zhao, Q.; An, Q.F.; Ji, Y.; Qian, J.; Gao, C. Polyelectrolyte complex membranes for pervaporation, nanofiltration and fuel cell applications. J. Membr. Sci. 2011, 379, 19–45.
  61. Flejszar, M.; Chmielarz, P. Surface Modifications of Poly(Ether Ether Ketone) via Polymerization Methods—Current Status and Future Prospects. Materials 2020, 13, 999.
  62. Ahmad, S. Engineered ‘Nanomaterials by design’ theoretical studies experimental validations current and future prospects. Exp. Theor. Nanotechnol. 2019, 301–364.
  63. Yazid, A.F.; Mukhtar, H.; Nasir, R.; Mohshim, D.F. Incorporating Carbon Nanotubes in Nanocomposite Mixed-Matrix Membranes for Gas Separation: A Review. Membranes 2022, 12, 589.
  64. Ji, Y.-L.; Zhao, Q.; An, Q.-F.; Shao, L.-L.; Lee, K.-R.; Xu, Z.-K.; Gao, C.-J. Novel separation membranes based on zwitterionic colloid particles: Tunable selectivity and enhanced antifouling property. J. Mater. Chem. A 2013, 1, 12213–12220.
  65. Butt, M.A. Thin-Film Coating Methods: A Successful Marriage of High-Quality and Cost-Effectiveness—A Brief Exploration. Coatings 2022, 12, 1115.
  66. Clarizia, G.; Bernardo, P. Polyether Block Amide as Host Matrix for Nanocomposite Membranes Applied to Different Sensitive Fields. Membranes 2022, 12, 1096.
  67. Koseoglu-Imer, D.Y.; Koyuncu, I. Fabrication and application areas of mixed matrix flat-sheet membranes. In Application of Nanotechnology in Membranes for Water Treatment; CRC Press: Boca Raton, FL, USA, 2018; pp. 49–66.
  68. Raheem, I.; Mubarak, N.M.; Karri, R.R.; Solangi, N.H.; Jatoi, A.S.; Mazari, S.A.; Khalid, M.; Tan, Y.H.; Koduru, J.R.; Malafaia, G. Rapid growth of MXene-based membranes for sustainable environmental pollution remediation. Chemosphere 2023, 311.
  69. Deshmukh, A.; Boo, C.; Karanikola, V.; Lin, S.; Straub, A.P.; Tong, T.; Warsinger, D.M.; Elimelech, M. Membrane distillation at the water-energy nexus: Limits, opportunities, and challenges. Energy Environ. Sci. 2018, 11, 1177–1196.
  70. Janczura, M.; Luliński, P.; Sobiech, M. Imprinting Technology for Effective Sorbent Fabrication: Current State-of-Art and Future Prospects. Materials 2021, 14, 1850.
  71. Li, Y.; Li, F.; Yang, Y.; Ge, B.; Meng, F. Research and application progress of lignin-based composite membrane. J. Polym. Eng. 2021, 41, 245–258.
  72. Meng, X.; Meng, S.; Liu, Y. The Limitations in Current Studies of Organic Fouling and Future Prospects. Membranes 2021, 11, 922.
  73. Polisetti, V.; Ray, P. Nanoparticles modified Polyacrylonitrile/Polyacrylonitrile—Polyvinylidenefluoride blends as substrate of high flux anti-fouling nanofiltration membranes. J. Appl. Polym. Sci. 2020, 138, 50228.
  74. Thummar, U.G.; Koradiya, A.; Saxena, M.; Polisetti, V.; Ray, P.; Singh, P.S. Scaling-up of robust nanofiltration membrane of ultrathin-film-composite structure. Desalination 2022, 530, 115650.
  75. Polisetti, V.; Ray, P. Thin film composite nanofiltration membranes with polystyrene sodium sulfonate–polypiperazinetrimesamide semi-interpenetrating polymer network active layer. J. Appl. Polym. Sci. 2020, 137, 49351.
More
Information
Subjects: Polymer Science
Contributors MDPI registered users' name will be linked to their SciProfiles pages. To register with us, please refer to https://encyclopedia.pub/register : , ,
View Times: 331
Revisions: 2 times (View History)
Update Date: 16 Jun 2023
1000/1000
Video Production Service