Effects of surface crosslinking on sieving characteristics of chitosan/poly(acrylonitrile) composite nanofiltration membranes

doi:10.1016/S1383-5866(00)00188-X

Separation and Purification Technology

Volume 21, Issues 1–2, 1 November 2000, Pages 27-37

https://doi.org/10.1016/S1383-5866(00)00188-X Get rights and content

Abstract

Effects of surface crosslinking of chitosan/poly(acrylonitrile) (PAN) composite nanofiltration membranes at different crosslinker (glutaraldehyde) concentrations and crosslinking times on their surface chemical composition and sieving properties such as pure water permeation, molecular weight cut-off and the rejection of mono/divalent salts and mono/oligosaccharides were investigated. Fourier transform infrared-attenuated total reflectance spectroscopy (FTIR-ATRS) and X-ray photoelectron spectroscopy (XPS) studies revealed the crosslinking of chitosan with glutaraldehyde as well as variations in chemical composition with glutaraldehyde concentration and crosslinking time. Pure water permeation/swelling in water decreased and rejection of salts and sugars increased with increasing glutaraldehyde concentration, indicating pore contraction and increase in hydrophobicity as well as pore tortuosity due to crosslinking. Molecular weight cut-offs of surface crosslinked membranes were in the range of 550–700 Da, a characteristic of nanofiltration membranes, whereas uncrosslinked membrane had cut-off of >1500 Da. The crosslinked membranes were found to be stable over 10-h operation for pure water permeation and the stability increased with increasing glutaraldehyde concentration.

Introduction

Nanofiltration (NF) is relatively a new membrane process and is increasingly being used in a range of applications that involve removal of salts from small molecular weight organics or separation of small molecular weight solutes from macromolecules. Most of the NF membranes developed so far are composite in nature, with a selective layer on top of the microporous substrate. Various membrane materials have been used for a selective layer on polymeric or inorganic microporous substrates. The choice of materials depends on both chemical and physical compatibility of selective layer with the substrate, which in turn determines the stability and performance of the resulting composite membranes. Poly(acrylonitrile) (PAN), one of the versatile polymeric materials, in addition to its well established use for asymmetric ultrafiltration (UF) membranes has been used as a microporous substrate for making composite membranes [1], [2], [3]. Chitosan, a natural hydrophilic biopolymer, has been used as a membrane material for reverse osmosis [4], pervaporation (PV) [1], [5], and gas separation membranes [6], and recently we have demonstrated its use in composite UF membranes [7].

Since PAN is more hydrophilic compared to the commonly used polysulfone (PSF) substrate, the composite NF membranes of PAN with hydrophilic chitosan may be relatively more stable than chitosan/PSF composite membranes, during long-term operation. Although work on chitosan/PAN composite PV [1], [2], [8] and UF [7] membranes has been reported, to the best of our knowledge there is no literature on chitosan/PAN composite NF membranes. The hydrophilic chitosan/PAN composite NF membranes would be of interest in applications such as demineralization of whey, where hydrophilicity of the membranes would help to minimize fouling caused by protein adsorption. Most of the commercial NF membranes are charged, which is beneficial for removal of divalent salts by Donnan exclusion. However, charged membrane surface may cause significant fouling due to electrostatic interactions, particularly in processing protein containing feeds. Krajewska and Olech [9] have reported that crosslinking of chitosan gel membranes results in reduction in pore size and water absorption with increasing crosslinker (glutaraldehyde) concentration. Therefore it is of interest to study the formation of composite NF membranes with a hydrophilic and neutral (at pH ≥7.0) selective layer of chitosan on PAN substrate and subsequent surface crosslinking.

The present study reports the effect of surface crosslinking at different crosslinker (glutaraldehyde) concentrations and crosslinking times on surface chemical composition and sieving characteristics such as pure water permeation, molecular weight cut-off and rejection of model solutes, of chitosan/PAN composite NF membranes.

Section snippets

Materials

PAN (MW≈150 kDa) and chitosan (MW≈116 kDa and degree of deacetylation (d.d.) ≈86%) were obtained from Polysciences, USA. Polyethylene glycols of different molecular weights and glutaraldehyde were obtained from Fluka, USA, and Aldrich, USA, respectively while all other solutes and reagents were obtained from Anachemia, Canada and used as received. Reverse osmosis treated water with a conductivity of ≈5×10⁻⁴ S m⁻¹ was used for membrane preparation, swelling and permeation studies.

Preparation of chitosan/PAN composite NF membranes (PANCHINF)

The details of

Results and discussion

The average pore size of the composite membranes calculated using the PEG rejection data (Fig. 5) and Ferry's modified equation [12] was found to be of the order of ≈10⁻⁹ m. Therefore, after crosslinking the exterior surface, the diffusivity of glutaraldehyde molecules inside the top crosslinked chitosan layer may be reduced and hence we believe that crosslinking might have taken place only on the exterior surface of chitosan layer.

The reaction scheme for the crosslinking of chitosan with

Conclusions

This study concluded that crosslinking of top surface of chitosan/PAN composite NF membrane with glutaraldehyde could improve the membrane stability and lower molecular weight cut-offs.

The increase in C/N ratio on the membrane surface with increasing glutaraldehyde concentration as well as CT, observed by XPS spectroscopy, indicated an increase in crosslinking. FTIR-ATR spectra showed peaks characteristic of chitosan in the control membrane, whereas in case of crosslinked membranes, a distinct

Acknowledgements

The authors would like to thank G. Pleizier for SEM and XPS analysis, S. Argue for atomic absorption spectroscopic analysis and M.M. Dal-Cin for operation of automated casting machine for base membrane preparation.

References (16)

X.P Wang et al.
J. Membr. Sci.
(1996)
X Feng et al.
J. Membr. Sci.
(1996)
Y Mizushima
J. Non-Cryst. Solids
(1992)
B Krajewska et al.
Polymer Gels Networks
(1996)
G Capannelli et al.
Ultrafiltration membranes: characterization methods
J. Membr. Sci.
(1983)
T Uragami et al.
J. Membr. Sci.
(1994)
S.Y Nam et al.
J. Membr. Sci.
(1997)
J Schaep et al.
Sep. Purif. Tech.
(1998)

There are more references available in the full text version of this article.

Cited by (88)

Bio-sourced and biodegradable materials for membrane fabrication
2023, Green Membrane Technologies towards Environmental Sustainability
As the world aims to achieve sustainable development goals by 2030, the appeal for green materials and energy is burgeoning. Membrane technology is the most efficient for clean water production, where the membranes are the heart of the process. The membrane materials developed till now are successfully used for various separation processes in food, beverage, medical, pharmaceutical, laboratory, and industrial applications. However, conventional polymers’ nonbiodegradability and environmental toxicity have urged researchers to explore biopolymeric counterparts with comparable separation efficiency and robustness. Several biopolymers demonstrated excellent performance in terms of permeability and selectivity. Nevertheless, there is an ongoing debate about mechanical strength and long-term applicability. These issues can be partly addressed with the use of nanomaterials or surface modification methods. This chapter enlists the different genres of bio-based polymers with their development history and application. It also details the current research efforts to develop and deploy biopolymer-based membranes for a green economy and sustainability.
High-performance and robust polysulfone nanocomposite membrane containing 2D functionalized MXene nanosheets for the nanofiltration of salt and dye solutions
2022, Desalination
Polysulfone (PSF) is widely applied in the fabrication of nanofiltration membranes. However, its low hydrophilicity is a major problem that lowers the permeate flux and intensifies membrane fouling. MXene, as a promising nanomaterial in the hydrophilicity improvement of polymeric membranes, has not been incorporated into the PSF nanofiltration membranes yet. In the current research, hydrophilic MXene nanosheets were synthesized using Ti₃AlC₂ as the precursor. Energy dispersive X-ray (EDX) spectroscopy, X-ray diffraction spectroscopy (XRD), transmission electron microscopy, and scanning electron microscopy (SEM) were applied to assess the functionalization of MXene with the OH functional group and its layered structure, respectively. Then, PSF/MXene nanofiltration membranes were prepared for the first time. The membranes were characterized, and their performance was compared in the filtration of salt and dye solutions and a model foulant. Incorporating MXene nanosheets into the PSF matrix boosted the membrane porosity, hydrophilicity, and tensile properties. With loading 1 to 4 wt% MXene into the PSF membrane, nanofiltration membranes with rejection values higher than 90% for MgSO₄, MgCl₂, and methyl orange were obtained. PWF of the membrane loaded with 4 wt% MXene was almost four times as high as the neat PSF membrane, and its flux recovery was approximately 73% higher.
Nanofiltration membrane technologies
2022, Advancement in Polymer-Based Membranes for Water Remediation
With the increasing world population, the shortage of fresh water resources has become a serious issue. Thus the demand of new water treatment technologies increases. The development of nanofiltration (NF) membrane technology led to water treatment at lower operating pressures than that of reverse osmosis (RO). Due to its versatility as separation tool and with the properties between those of UF and RO, NF membrane is showing continuous interest since past two decades. Typically, NF membranes have pore size of the order of 1 nm, sodium chloride rejection between 20% and 80% and molecular weight cut-offs for dissolved organic solute of 200–1000 Da. Although some NF membranes are cellulose acetate based, some are also found as composite, especially, polyamide ones are used in water treatment. NF typically have high rejections of multivalent inorganic salts and small organic molecules at low applied pressure. Thus NF separation process is highly competitive in terms of selectivity and cost benefit. For efficient NF in water purification application, it should have a thin and porous selective layer with a narrow pore size distribution to ensure high selectivity. Salt rejection phenomena via NF membranes is due to effect of Gibbs–Donnan and dielectric effects. Therefore in this technology, salt rejection and water permeability depend on various factors, such as the pore distribution, size and interactions of the ions, and hydration at the nanopores and the membrane surface. NF has some advantages over RO, such as (1) high water fluxes, (2) low operating pressures, and (3) high rejection of divalent ions. NF plays an important role in different industrial applications, such as water treatment and resource recovery. Therefore many efforts have been dedicated to work on fouling reduction. This review summarizes the recent developments in this field and epitomizes the direction for potential future approaches to improve the separation efficiency of NF.
Separation mechanism, selectivity enhancement strategies and advanced materials for mono-/multivalent ion-selective nanofiltration membrane
2022, Advanced Membranes
Mono-/multivalent ion-selective separation has become a common requirement at the water-energy nexus, including energy storage and conversion, water purification, and sustainable industrial processes. In this review, we summarize the theory of ion transport through membrane and mechanisms of selective ion separation in nanofiltration (NF) briefly. Recent advancing in improving the mono-/multivalent ion selectivity of thin-film composite (TFC) NF membrane via size sieving enhancement, electric charge property regulation and co-enhancement of size sieving and electric charge properties are concluded. What's more, three material classes—surface assembly materials, nanomaterials and biomimetic ion channels are highlighted as candidates for the preparation of ion-selective NF membranes. Lastly, design directions and critical challenges for developing high-selectivity nanofiltration membranes based on the ion-selective mechanisms are provided.
Carboxymethyl cellulose/polyethersulfone thin-film composite membranes for low-pressure desalination
2021, Separation and Purification Technology
Citation Excerpt :
Indeed, by increasing the degree of crosslinking, more hydroxyl groups of the CMC react with aldehyde groups of GA, resulting in a decreasing number of free hydroxyl groups. In addition, more hydrophobic GA moieties were inserted into the selective layer of the NF membrane by enhancing the crosslinking degree, leading to a decrease in hydrophilicity of the membranes [47,48]. The stable permeate flux of the membranes after 75 min was observed, as shown in Fig. 5 ((a)-(f)).
Herein, we report the fabrication of carboxymethyl cellulose (CMC)/polyethersulfone (PES) thin-film composite nanofiltration membranes using a dip-coating method with glutaraldehyde (GA) as the crosslinking agent. The effects of crosslinking degree and the dip-coating parameters, including CMC concentration and dipping time, on the performance and morphology of the fabricated membranes were investigated. The properties of the prepared membranes were analyzed by ATR-FTIR, AFM, FE-SEM, and water contact angle analysis. The optimized membrane containing 0.2 wt% CMC, crosslinking degree of 20% by the dipping time of 10 min represented a rejection efficiency of 91.90%, 68.63%, and 45.90% towards the Na₂SO₄, MgSO₄, and NaCl solutions (100 mg/L), respectively. The pure water flux of the optimal membrane was 47.90 ± 1.77 L/m² h under a low transmembrane pressure of 0.4 MPa. The flux recovery ratio of the nanofiltration membrane was 63% higher than the PES support membrane, indicating an improvement in fouling resistance.
Membranes based on non-synthetic (natural) polymers for wastewater treatment
2020, Polymer Testing
During the last decades, rising environmental concerns about the widespread usage of petroleum-based synthetic polymers has caused naturally occurring polymers to gain momentous. As a biocompatible and environmentally friendly alternative, bio-based polymers are continuously gaining new domains of application in drug delivery systems, tissue engineering, membrane technology, bio-sensor devices, etc. There is an increasing number of scientists who have applied various kinds of biopolymers, such as cellulose, chitin, starch, and alginate to fabricate fully or semi-biodegradable membranes for wastewater treatment. Beside biocompatibility, biopolymers combine many attractive features such as hydrophilicity and functionalizability that makes them great candidates to enhance the performance of composite membranes to effectively purify water from hazardous pollutants. On the other hand, elevating thermo-mechanical and chemical stability of these bio-based materials by introducing new organic and inorganic additives is another main focus area. This review is concerned with 1) introducing the promising feature of biopolymers that can be used as a raw material to synthesize membranes for water treatment, 2) proposing a comprehensive categorization of these membranes based on their structure, and 3) discussing the performance of these membranes in eliminating various kinds of contaminants from effluents and their strength and weakness points.

View all citing articles on Scopus

^☆: Issued as NRCC No: 42009

View full text

Effects of surface crosslinking on sieving characteristics of chitosan/poly(acrylonitrile) composite nanofiltration membranes☆

Abstract

Introduction

Section snippets

Materials

Preparation of chitosan/PAN composite NF membranes (PANCHINF)

Results and discussion

Conclusions

Acknowledgements

J. Membr. Sci.

J. Membr. Sci.

J. Non-Cryst. Solids

Polymer Gels Networks

J. Membr. Sci.

J. Membr. Sci.

J. Membr. Sci.

Sep. Purif. Tech.