Application Of Membrane Technology Research Articles

2D Membranes Interlayered with Bimetallic Metal-Organic Frameworks for Lithium Separation from Brines.

Efficient lithium extraction from salt lakes is essential for a sustainable resource supply. This study tackles the challenge of separating Li+ from Mg2+ in complex brines by innovatively integrating two-dimensional (2D) graphene oxide (GO) with bimetallic metal-organic frameworks (MOFs). Zn2+ and Co2+ ions are confined within GO interlayers through an in situ synthesis, forming a 2D Zn-Co MOFs/GO membrane (Zn-Co-GOM). This design exploits the unique advantages of bimetallic MOFs, including enhanced structural stability and superior ion separation capabilities due to the synergistic effects of Zn and Co. The Zn-Co-GOM demonstrates an impressive separation factor of 191 for Li+ over Mg2+, significantly surpassing traditional membranes. This exceptional selectivity is achieved through a combination of size exclusion effects and ion transport energy barriers. Our approach not only enhances the practical application of membrane technology for lithium extraction from salt lakes but also provides valuable insights into the underlying separation mechanisms.

Ultra-hydrophilic MOF-303 on electrospun nanofibers with Burr Puzzles structure for the purification of oily wastewater containing heavy metal ions

The current oil-water separation field is extremely complex and the material system is variable. Therefore, the full process applicability of membrane technology is extremely demanding, both in terms of high oil-water separation efficiency and the treatment of soluble substances in wastewater, such as heavy metal ions. The high demand for membrane performance is accompanied by the complexity of the membrane manufacturing process, resulting in the development of membrane technology being hindered. If we can purify heavy metal ions from wastewater while meeting the conditions of oil-water treatment, and simplify the process flow, it is an innovation that we are happy to see. Herein, the use of a seed pre-embedded growth strategy is taking polyacrylamide (PEI) as a breakthrough point, we take advantage of blending to introduce embedding sites in polyacrylonitrile (PAN) membranes. Uniform growth of MOF-303 with Burr Puzzle structure on membrane surface using in situ hydrothermal growth method. The Burr Puzzles structure on the membrane surface is not only able to effectively deal with nanoscale stabilized oil-water mixture and effectively adsorb heavy metal ions, but also enables the MOF-303 crystals to grow more firmly on the membrane surface, so that the modified membrane still maintains good performance in harsh environments. The separation fluxes of the oil-in-water emulsions were all higher than 6987 L m−2 h−1 for oil-in-water emulsion with a separation efficiency of 98.4 %, and the adsorption efficiency of heavy metal ions was also as high as 98.3 %. After 20 cycles, the membrane maintains its promising performance. Due to its simple preparation process and excellent efficiency of emulsions separation and heavy metal ions separation, simplifies complex membrane processes while meeting the rigors of wastewater treatment. it has great prospects for development in the current complex wastewater treatment process.

Mn-Fe bimetallic oxide catalytic oxidation combined with ultrafiltration for treating secondary effluent: EfOM molecular transformation and membrane fouling control mechanism

Despite extensive application and research of membrane technology in secondary effluent treatment, fouling induced by effluent organic matter (EfOM) remains a challenge. Herein, a pretreatment strategy involving Mn-Fe bimetallic oxide-activated peroxymonosulfate (MnFeO/PMS) was used before ultrafiltration to decompose EfOM and tackle membrane fouling. Results showed that membrane fouling was effectively alleviated, with reductions in reversible and irreversible fouling resistances of 88.3 % and 58.9 %, respectively. Theoretical analyses illustrated a more pronounced adsorption energy and decomposition tendency of PMS on the MnFeO surface. The generated OH and SO4− played a key role in the degradation of EfOM. The parallel factor analysis along with self-organizing maps revealed the preferential oxidative degradation of humic acids and fulvic acids over tryptophan-like substances, which contributed to the reversible fouling mitigation. In addition, MnFeO/PMS transformed high and middle molecular weight organics into low molecular weight compounds. The primary molecular reactions involved in the degradation of EfOM included oxygen addition, dealkylation and deamination, which changed the properties of EfOM and contributed to the mitigation of membrane fouling. Morphology analysis further indicated that the fouling layer on the membrane surface was inhibited when filtering the MnFeO/PMS-pretreated sample. This study offers revelations for integrating oxidation with ultrafiltration in secondary effluent treatment to alleviate EfOM-induced membrane fouling.

Structurally stable copolymer ultrafiltration membranes prepared via vinyl chloride suspension copolymerization and tannic acid in-situ modification integration

Polyvinyl chloride ultrafiltration membranes, widely used in various industries, are hindered by their high susceptibility to contamination. To address this concern, researchers have investigated diverse modification methods, encompassing surface modification and physical blending. Although surface modification provides stability, but it is intricate, expensive, and may result in pore clogging. Physical blending is a simpler approach but lacks durability and stability. Tannic acid (TA), a natural compound, has attracted attention for its potential in membrane modification due to its diverse benefits. However, the existing methods, such as TA-metal networks, encounter challenges of weakened stability and reduced permeability of membrane. To solve these issues, this research presents a novel approach that integrates suspension copolymerization, polyaddition, and a sol–gel process to fabricate structurally stable copolymer ultrafiltration membranes. Active sites for sol–gel reactions were embedded into the copolymer through copolymerization. Subsequently, TA was added to the copolymer casting solution, and isocyanate propyltriethoxysilane was decorated onto TA through a polyaddition reaction. Following this, a non-solvent induced phase separation method was used for membrane fabrication. During the formation of the membrane, a sol–gel reaction occurred between the copolymer and the modified TA, ensuring both stable chemical cross-linking. The membrane demonstrates excellent permeability, fouling resistance, and long-term operational stability. This innovative approach not only addresses compatibility and leakage issues associated with traditional methods but also ensures the stable integration of hydrophilic functional monomers within the copolymer matrix. The proposed method holds promise for advancing applications of ultrafiltration membrane technology in various complex environments.

Selective separation of structurally similar alkaloids by graphene oxide membranes

Matrine (MT) and oxymatrine (OMT) are alkaloids coexisting in Sophora flavescens, and they have similar structure but different clinical applications. Graphene oxide (GO) membranes with different oxidation degrees were used to explore the separation mechanism of MT and OMT. When the ratios of O-C=O and C=O groups remained basically unchanged, the higher C-OH content and the lower C-O-C content on the GO nanosheets provided higher O/C ratios, more negative Zeta potentials, stronger hydrophilicity, rougher surface, and larger interlayer spacing of the GO membranes. With the increases in the O/C ratio, the rejection rates for MT and OMT exhibited opposite trends, and it was considered that a competitive relationship between MT and OMT on the membrane converted from hydrophilic interaction to electrostatic interaction. Within the separation channels limited by the GO nanosheets, the tertiary amine in the alkaloid catalyzed C-O-C group ring opening and formed C-OH or O-C=O groups. As the C-OH content of the original GO membranes increased, the stability during alkaloid separation was improved. The GO-5 membrane showed stable separation ability within 72 h, and the separation factor of MT and OMT almost doubled during the secondary membrane process. This study provides new insight into the application of membrane technology for the separation of similar molecules of pharmacodynamic substances in traditional Chinese medicine.

Innovative membrane technology for water treatment solutions: Current status and future prospects of carbon nanotube membranes

Carbon nanotube (CNT)-based membranes are gaining attention for their unique properties and applications in membrane technology. This review comprehensively explores major types of CNT-based membranes—buckypaper, CNT mixed, and vertically aligned CNT membranes—along with their fabrication methods, pore size control strategies, unique properties, and potential applications. Understanding these aspects will help fully harness the potential of CNT-based membranes in addressing challenges in water treatment and other fields. CNTs offer promise as water treatment membranes due to their ability to enhance performance of existing membranes, overcome trade-offs, exhibit antibacterial properties, and facilitate fast water transport.

Ta-Fe in-situ coating PES membrane and its application in oily wastewater treatment: Insight into modification and anti-fouling mechanisms

Membrane fouling is a serious problem that limits the widespread application of membrane technology. Herein, we propose an effective modification method by in-situ modifying polyethersulfone (PES) ultrafiltration membrane with tannic acid (TA) and Fe3+ chelates to improve its pollution resistance. The TA-Fe3+ complexes could deposit on the PES membrane surface and form a hydration layer by Van Der Waals force, hydrogen bonding force, and hydrophobic association. The modified membrane (PES\\TA\\Fe3+) had enhanced fouling resistance and membrane flux due to its dual advantages of abundant OH groups and favorable spatial structure. After modification, the roughness of membrane surface increased from 219 nm to 257 nm, and its water contact angle decreased from 58.9° to 26.5°, endowing the PES\\TA\\Fe3+ membrane with a strong resistance to oil droplets through electrostatic repulsion, steric hindrance effect, and hydrogen bonding force. Polyaluminum chloride-polydimethyldiallylammonium chloride (PAC-PDMDAAC) could alleviate 85 % membrane fouling resistance. PAC-PDMDAAC mainly mitigated irreversible membrane fouling by removing oil droplets and forming large and loose flocs. While the use of PES\\TA\\Fe3+ membrane mainly reduced the adsorption resistance and the resistance of membrane itself. The anti-fouling performance of PES\\TA\\Fe3+ membrane changed with pH owing to the changes in the properties of TA-Fe3+ complexes. The hydrophilic layer would be decomposed under alkaline conditions due to the deprotonation of TA and excessive hydrolysis of Fe3+. This study provides an efficient anti-fouling strategy and reveals the modification and anti-fouling mechanisms of the hydrophilic membrane, providing theoretical guidance for the further development of membrane technology.

Membrane technologies for the separation and purification of functional oligosaccharides: A review

Functional oligosaccharides have numerous health benefits. They hold considerable promise in the food processing and healthcare sectors. However, oligosaccharides derived from microbial fermentation, chemical decomposition, and enzymatic hydrolysis often contain impurities, necessitating further purification to enhance the quality and economic value of the final product. Among various purification techniques, membrane separation stands out owing to its operational simplicity, low energy requirements, and scalability, making it ideal for industrial applications. Recently, this method has increasingly been used to separate and purify functional oligosaccharides. Microfiltration and ultrafiltration membranes are typically used in the early stages of filtration to remove proteins, bacterial contaminants, and particulates. In contrast, nanofiltration membranes offer higher separation precision, making them preferable for the detailed purification, concentration, and classification of functional oligosaccharides. This review article mainly focuses on the applications of nanofiltration membrane technologies in the processing of typical functional oligosaccharides, such as fructooligosaccharides, galactooligosaccharides, and xylooligosaccharides. Recent advancements in nanofiltration are discussed, and the properties of the feed liquid, operational parameters, and challenges related to membrane fouling are analyzed. This review aims to serve as a comprehensive guide for the efficient separation and purification of functional oligosaccharide membranes, and advocates for the broader implementation of membrane technologies in the food and medical industries.

Deciphering the behavior and potential mechanism of biochar at different pyrolysis temperatures to alleviate membrane biofouling

Biofouling limits applications of membrane technology in wastewater treatment, but dosing additives to membrane tanks is an effective method to alleviate biofouling. In this study, biochar derived from corncob and pyrolyzed at 300, 500, and 700°C was dosed to determine the underlying anti-biofouling mechanism. The effects of the biochar on the membrane properties and foulant behavior were systematically investigated. The results showed that biochar delayed the occurrence of the fouling transition (0.5–3.0 h), and decreased the flux decline rate, thus achieving a higher water flux (3.1–3.7 times of the control group). Biochar altered membrane surface properties, and increased the membrane surface charge, roughness, and hydrophilicity, which all contributed to higher membrane permeability. Moreover, adding biochar reduced the number of foulants in the fouling layer, particularly protein substances. The flux model fit and the XDLVO theory further revealed the mitigating effect of biochar on membrane biofouling. At the initial intermediate-blocking stage, the effect of biochar on membrane fouling was determined by its properties, and adsorption capacity to the foulants, BC500 presented the best mitigation performance. At the later cake-filtration stage, the role of biochar in membrane fouling was strongly associated with protein content in the fouling layer, and the minimum rate of flux decline occurred in BC300. This study promotes the understanding and development of biochar to alleviate membrane biofouling.

Nanocomposite ceramic membranes as novel tools for remediation of textile dye waste water – A review of current applications, machine learning based modeling and future perspectives

Textile effluent treatment has gained significant attention due to the carcinogenic effects of the dye pollutants present and their enhanced resistance to degradation. Porous ceramic membranes have gained growing interest for dye remediation due to various unique characteristics, including resistance to fungal invasion, adverse chemical conditions, and high temperature. The current study explores applications of ceramic membrane technology, including membranes like MF, UF, and NF, for dye remediation from textile effluent. The best-performing nanocomposite membranes for eliminating azo dyes from textile effluent and efficiencies achieved are reported as Clay-alumina (99%), yttria-stabilized-zirconia (99%), nano TiO2-bentonite UF (95%), and tight TiO2 UF (100%). Ceramic nanocomposites with TiO2 and Al2O3 active layer NF (99%), Ceramic Hybrid hollow fiber LNF (99.3%). Loose nanofiltration (LNF) ceramic membranes have demonstrated outstanding targeted separation performance for the separation of dyes, making them affirm the effective recoveries and recurrent use of high-value-added constituents amongst all the membrane approaches examined. The potential of ceramic membranes for future research and development, including membrane production and mechanism, are discussed. In addition, the implementation of AI-based methods and Machine learning (ML) algorithms are discussed in relation to predicting membrane filtration performance and fouling tendencies and dye removal processes, maximizing opportunities in this field.

Suppression of Coffee-ring Effect (CRE) in the Development of Low-cost Diagnostic Kit

One of the applications of membrane technology is using the polymeric membrane as an adsorber or assay-capturing matrix in the diagnostic kits' assembly. This study explores the addition of NaCl into a protein solution to suppress the coffee-ring effect (CRE) in developing a low-cost diagnostic kit. The highest concentration of NaCl addition shows the optimum results with no formation of CRE and high color intensity (low grey scale value). Adding NaCl into the protein solution is a safe and cheap alternative for lowering the cost of assembly, benefiting people in low-resource places.

Comprehensive Study of Physicochemical Properties in Poly‐(Vinylidene Fluoride) Membranes Loaded with OPEFB's Lignin/ Lignosulfonate via Phase Inversion

AbstractThe development of membrane technology is rapidly advancing, such as hydrophilic PVDF membranes, which provide anti‐fouling properties to the membrane. Therefore, this research innovates the development of hydrophilic PVDF membranes by incorporating lignin‐lignosulfonate fillers from OPEFBs in situ. This study successfully prepared hybrid PVDF membranes using the phase inversion method. ATR‐FTIR, XRD, and TGA/DSC analyses confirmed that the addition of 2 % filler promoted the formation of the β‐phase in PVDF, which was more dominant than with the addition of 4 % filler, especially in the PLs2 % membrane. SEM images of the membranes showed an asymmetric structure with finger‐like and sponge‐like pores. Interactive 3D surface imaging demonstrated increased pore potential peaks when lignosulfonate was added compared to lignin. The addition of 4 % filler had a hydrophilic‐hydrophobic repelling effect, increasing the porosity and water absorption of the PL4 % and PLs4 % membranes. Phase inversion membranes were relatively hydrophilic with a water contact angle of 61°, and adding filler reduced the membrane‘s contact angle by 8°. Based on the obtained results, it can be concluded that PVDF hybrid membranes with lignin and lignosulfonate fillers have significant potential for development in membrane technology applications that require hydrophilic membranes, such as wastewater treatment and seawater desalination.

Membrane-based microfluidic systems for medical and biological applications.

Microfluidic devices with integrated membranes that enable control of mass transport in constrained environments have shown considerable growth over the last decade. Membranes are a key component in several industrial processes such as chemical, pharmaceutical, biotechnological, food, and metallurgy separation processes as well as waste management applications, allowing for modular and compact systems. Moreover, the miniaturization of a process through microfluidic devices leads to process intensification together with reagents, waste and cost reduction, and energy and space savings. The combination of membrane technology and microfluidic devices allows therefore magnification of their respective advantages, providing more valuable solutions not only for industrial processes but also for reproducing biological processes. This review focuses on membrane-based microfluidic devices for biomedical science with an emphasis on microfluidic artificial organs and organs-on-chip. We provide the basic concepts of membrane technology and the laws governing mass transport. The role of the membrane in biomedical microfluidic devices, along with the required properties, available materials, and current challenges are summarized. We believe that the present review may be a starting point and a resource for researchers who aim to replicate a biological phenomenon on-chip by applying membrane technology, for moving forward the biomedical applications.

Membrane fouling and control in algae-rich water treatment

Microfiltration and ultrafiltration membrane technology has now become one of the important methods for algae-rich water treatment due to its better solid-liquid separation effect and microbial retention capacity, while the existence of membrane fouling has been restricting the full-scale promotion and application of low-pressure membrane technology. The main foulants causing membrane fouling in algal-rich water include algal cells, algal debris and algal organic matter AOM (EOM and IOM). In this paper, the mechanism of membrane fouling caused by algal foulants in MF/UF for high algal water treatment is analysed in terms of both individual and composite fouling. Both individual and composite effects of algal foulants can lead to severe membrane fouling, in which algal cells and algal debris mainly dominate the accumulation of filter cake, while AOM mainly leads to membrane pore blockage membrane fouling is exacerbated by compounding effects, with severe reversible and irreversible fouling caused by filter cake formation and membrane pore shrinkage. This paper also discusses several common membrane fouling control methods, including pretreatment (oxidation, coagulation, combined oxidation-coagulation and adsorption) and membrane modification, and it is found that these several membrane fouling control methods can achieve good results.

A novel approach to chiral separation: thermo-sensitive hydrogel membranes.

The application of membrane technology for separating chiral compounds is hindered due to the restricted availability of chiral recognition sites on the membrane surface. In this study, we propose a novel approach for chiral separation through a selector (bovine serum albumin, BSA) mediated thermo-sensitive membrane system. A thermo-sensitive hydrogel-coated membrane (termed PDTAN) was developed by anchoring poly(N-isopropylacrylamide) (PNIPAm) onto a polyethersulfone (PES) membrane through an adhesive and hydrophilic dopamine hydrochloride (PDA)/tannic acid (TA)/chitosan (Chi) intermediate layer. The results demonstrate outstanding chiral separation efficiency, achieving αL/D = 3.30 for D-phenylalanine (D-Phe) rejection at 40 °C on a BSA-mediated PDTAN membrane system, with significant stability and minimal fouling, surpassing previous findings. Moreover, the PDTAN membrane altered the selective properties of recognition sites in BSA, transitioning from rejecting L-Phe to rejecting D-Phe. Analysis using fourth-order derivative UV-vis, circular dichroism (CD), and in situ Fourier transform infrared spectroscopy (FTIR) techniques revealed a transition in the secondary structure of BSA from α-helix to β-sheet as the temperature increased. This transition, facilitated by hydrogen bonding between BSA and PNIPAm, enabled selective recognition of D-Phe, demonstrating a distinct shift in chiral recognition properties. Importantly, with D-Phe adsorbed onto β-sheet structures of BSA, hydrogen-bond interactions between BSA and the PDTAN membrane were significantly reduced, thereby minimizing membrane fouling and achieving the durability of membrane-based chiral separation.

Fabrication of high permeability and antifouling composite membrane loaded with Fe3O4 nanoparticles via a magnetic field induced phase separation

Membrane fouling increases operational expenses and limits the application of ultrafiltration technology in water treatment. To mitigate the membrane fouling, this study incorporated Fe3O4 nanoparticles (NPs) into the polyethersulfone (PES) membrane casting solution, and developed a non-solvent induced phase separation (NIPS) method assisted by a magnetic field (MGF) to fabricate the Fe3O4 NPs composite ultrafiltration membrane. The combination of MGF and Fe3O4 NPs synergistically enhanced the permeability and separation performance of the composite membrane. The performance of the membrane was determined by its structure. With the involvement of MGF, Fe3O4 NPs were enriched on the surface layer of the membrane, resulting in enhanced hydrophilicity of the composite membrane. The membrane permeability increased to 913.39 LMH·bar−1, and the rejection performance rose to 93 % due to the formation of tiny pores on the membrane surface that facilitated solvent diffusion during phase separation, thereby counteracting the adverse effects of heightened viscosity in the casting solution. Moreover, the Fe3O4 NPs composite membrane fabricated with MGF induction exhibited significantly enhanced antifouling capability in multi-cycle fouling tests, resulting in a 27.5 % increase in specific flux compared to the pure PES membrane. Additionally, the preparation procedures for the matrix membrane were optimized to include 15 wt% PES, 3 wt% PVP, and a pre-treatment time of 30 s. These findings have significant implications for advancing the widespread application of membrane technology.

A novel approach for sterilization and concentration of traditional functional drinks: Membrane‐based nonthermal processes

AbstractThe applicability of microfiltration (MF) and osmotic membrane distillation (OMD) for sterilization and concentration of traditional functional drink constituents, such as Curcuma xanthorrhiza, ginger, lime, Java tea, and sappan wood extracts, was evaluated in this study. MF showed excellent performance in microorganisms elimination, turbidity reduction, and maintaining antihyperglycemic activity performance. However, a reduction of total phenol and antioxidant activity were observed due to the retention by MF. Fouling in MF was challenging and resulted in rapid flux decline. The concentration of sterilized extracts by OMD operation resulted in a concentration factor of 1.15, 1.13, 1.10, 1.24, and 1.24 for ginger, lime, C. xanthorrhiza, Java tea, and sappan wood, respectively. The active compounds were well preserved, with a maximum of 20% reduction compared to sterilized extracts. Despite insignificant foulant deposition, the OMD flux in tests using C. xanthorrhiza, ginger, and lime as the feed decreased over time, indicating reduced driving force.Practical applicationsThe application of membrane technology for juices and liquid foods sterilization and concentration has been widely researched. In this research, we evaluated the performance of MF and OMD for the sterilization and concentration of traditional functional drinks. The results indicated that the functional drink can be sterilized by MF with excellent preservation of the active compounds, such as those responsible for the antihyperglycemic and antioxidant activities. The OMD could also concentrate the traditional functional drink, even though concentration polarization posed a challenge to flux stability. The degradation of phenolic compounds and antioxidant activity of the concentrated traditional functional drink was at a minimal value, indicating the promising application of MF and OMD. We believe this article provides new and exciting insights to push forward the sterilization and concentration process in industrial scale.

Application of membrane technology in the treatment of waste liquid containing radioactive materials

Application of membrane technology in the treatment of waste liquid containing radioactive materials

Application of Ultrafiltration for Recovery of Polyphenols from Rose Petal Byproduct.

One main objective of this study was to increase the utilization of raw material in the rose (Rosa damascena Mill.) essential oil industry by the application of membrane technologies. In this research, distilled (dearomatized) rose petals, the primary byproduct in essential oil production, were subjected to an enzyme-assisted extraction and subsequent membrane separation for partial concentration at different levels using UF1-PAN and UF10-PAN membranes. The results show that the permeate flux decreased with a rise in volume reduction ratio and increased with a rise in transmembrane pressure and feed flow rate. At the beginning of the process, the highest flux was with the UF1-PAN membrane, but at the end of the process, it was with the UF10-PAN membrane. Total polyphenols of the retentates increased by 27-39% and 26-67% during ultrafiltration with the UF1-PAN and UF10-PAN membranes, respectively, with the highest value obtained for the UF10-PAN membrane at VRR 6. The highest concentration factor and rejection of total solids, total polyphenols, redox-active antioxidants, and radical scavenging antioxidants were obtained at VRR 6 with the UF10-PAN membrane. The use of green technology based on enzyme-assisted extraction and ultrafiltration for recovery and concentration of polyphenols from rose petal byproduct solves practical environmental problems for the treatment and utilization of byproducts from the rose oil industry. The retentate obtained could be used in the food production, cosmetic, and pharmaceutical industries.

New insights into the interactions between two‐dimensional ice and two‐dimensional materials

AbstractWater is one of the most essential substances for life on Earth and plays a vital role in both natural and technological processes. Recently, there has been growing interest in studying the behavior of water molecules in confined spaces, particularly in low‐dimensional materials and structures. Regardless of whether it is in the form of gas, liquid, or solid, water can interact and form interfaces with many low‐dimensional structures. Given the current controversial understanding of two‐dimensional (2D) ice and the increasing interplay between water/ice and 2D materials such as graphene and transition‐metal dichalcogenides, we provide a brief overview of recent progresses on the interfaces of 2D ice and 2D van der Waals layered materials. This review highlights their potential contributions to the breakthroughs in tribology, membrane technology, nanofluidic, and nanodevice applications. Of particular interest is the recent discovery of ultrahigh lubricity between 2D ice and 2D layered materials, as well as the ability to modulate the surface adhesion between layers. These findings have the potential to enable new technological advances in both electronics and various industries. Meanwhile, this rapidly evolving field presents its own challenges, and we also discuss future directions for exploiting the interactions between 2D ice and 2D layered materials.