STAGE 1. Establishing the conditions for the synthesis of composite membranes based on terpolymers and functionalized carbon nanotubes (MWCNTs) and their complex characterization

PERIOD: 13.05.2022-31.12.2022

OBJECTIVES

Act 1.1. – Studies on the synthesis and characterization of simple membranes based on terpolymer formulations.

Act 1.2. – Functionalization of carbon nanotubes (MWCNTs) using non-covalent methods.

Act 1.3. – Synthesis and characterization of composite membranes based on recipes of terpolymers and functionalized carbon nanotubes (MWCNTs).

Act 1.4. – Communication activities and writing of scientific papers in compliance with Open Access conditions.

SUMMARY

The I-ON-MEM project aims is to identify suitable solutions for treating metal-contaminated diluted water streams with removal efficiencies above 90%, relying only membrane technologies. The research study’s main objective will be synthesizing original composite membranes for the advanced retention of heavy metals in electrodialysis wastewater. In this sense, the following secondary objectives were established:

OS1. Studies regarding the synthesis and characterization of simple membranes based on terpolymer formulations.

OS2. Carbon nanotubes functionalization (MWCNT) using non-covalent methods.

OS3. Synthesis and complex characterization of composite membranes based on terpolymers and functionalized carbon nanotubes (MWCNT).

OS1. In order to obtain simple synthetic membranes, several polymer solutions of different concentrations were prepared. Moreover, it was also investigated the effect of changing the ratio between terpolymers. The membranes were prepared by the wet phase inversion method. The synthetic membranes were analyzed in terms of their rheological behavior and also the permeability point of view in order to choose the optimal composition. Synthetic membrane with the composition of 70% Acrylonitrile-acrylic acid copolymer (AN-AA), 7.5% polyvinyl alcohol (PVA) and 22.5% polysulfone (PSf) and biomembrane with the composition 0.2% sodium alginate (SA), 0.65% polyvinyl alcohol (PVA) and 0.05% biocellulose (BC) were chosen to be used in subsequent experiments in order to get composite membranes.

OS2. In order to functionalize MWCNTs with surfactants, two surfactants, i.e. cetrimonium bromide (CTAB) and behentrimonium chloride (BTAC), were tested. MWCNTs thus functionalized were characterized by Dynamic Light Scattering (DLS) and Raman Spectroscopy, which indicated that in the case of samples functionalized with surfactant the I_D/I_G ratio increased significantly due to good functionalization process and the attachment of surfactant molecules to CNTs by electrostatic forces or Van der Waals, but also due to the increase in the degree of disorder of the structure. In order to functionalize carbon nanotubes by covering them with organosilanes, silanes bearing different functional groups (amino, carboxy, sulfur) were used such as 3-Aminopropyltriethoxysilane (APTES), 3-(Trimethoxy silyl)propyl methacrylate (MAPTES) and (3-Mercaptopropyl)trimethoxy silane (MPTMS). This type of functionalization was achieved by 2 methods, which were differentiated by the presence and absence of the reaction medium. The functionalized MWCNT products obtained were intensively characterized by FTIR, XPS, XRD, Raman, TGA/DTG and SEM. All analyzes demonstrated that the functionalization process led to a less disordered network, leading to the attachment or interpenetration of surfactant/silane molecules with CNTs.

OS3. In order to obtain composite membranes, a percentage of 0.5% non-modified CNT or functionalized by both methods was chosen as optimal. Thus, the composite membranes were characterized in terms of chemical composition (FTIR), hydrophilicity (contact angle), permeability (water flow), thermal stability (TGA/DTG), morphology (SEM) and showed improved characteristics compared to the reference membranes and a significant improvement in final properties by introducing some functionalized MWCNTs.

Experimental models were developed for obtaining simple synthetic membranes and based on biopolymers, for functionalizing MWCNTs by non-covalent methods and for obtaining composite membranes based on synthetic polymers and from bio sources and functionalized nanotubes. The original results were disseminated by attending 2 conferences (1 national and 1 international), but also by publishing 2 ISI articles (published in journals indexed in Web of Science from the red zone (Q1), classified as article and review). The website of the I-ON-MEM project was also created.

The degree of achievement of the objectives was 100%.

DISSEMINATION

In the framework of stage I/2022, for the fulfillment of the deliverables from the implementation plan and for the presentation of the obtained results, the following dissemination actions were carried out, 2 published articles, which present the research that was the basis of the project’s activities and 2

participations in the form of poster-type communications or oral communications in international and national conferences, with exceptional visibility:

Published articles

1. Miron, A.; Sarbu, A.; Zaharia, A. Sandu, T.; Iovu, H.; Fierascu, R.C.; Neagu, A.-L.; Chiriac, A.-L.*; Iordache, T.-V. A Top-Down Procedure for Synthesizing Calcium Carbonate-Enriched Chitosan from Shrimp Shell Wastes. Gels 2022, 8(11), 742. https://doi.org/10.3390/gels8110742

2. Teodor Sandu, Andrei Sârbu, Simona Căprărescu, Elena-Bianca Stoica Tanța-Verona Iordache, Anita-Laura Chiriac*, Polymer Membranes as Innovative Means of Quality Restoring for Wastewater Bearing Heavy Metals. Membranes 2022, 12(12), 1179. https://doi.org/10.3390/membranes12121179

Scientific communications at national/international conferences

1. Verona Iordache, Anamaria Zaharia, Ana-Mihaela Gavrila, Bianca Elena Stoica, Ana Lorena Ciurlica, Marinela Dumitru, Andreea Olaru, Andrei Sarbu, Laura Anita Chiriac, Quaternary Ammonium Functionalized-Clay Microparticles with Bactericidal Activity Applied for Wastewater Treatment, 22nd Romanian International Conference on Chemistry and Chemical Engineering, Sinaia, ROMANIA – 7th-9thSeptember, 2022. Poster

2. Andreea Miron, Ana-Lorena Neagu, Sorin Dolana, Anamaria Zaharia, Ana-Mihaela Gavrila, Andrei Sarbu, Tanta-Verona Iordache, Anita-Laura Chiriac, Beads based on sodium alginate and titania composites for heavy metals removal from simulated waste waters, NATIONAL CHEMISTRY CONFERENCE, XXXVI EDITION, Călimănești-Căciulata, 4th-7th October 2022. Oral presentation

For better visibility, the idea of the I-ON-MEM Project was exposed to radio listeners in the show “Stiinta 360” on Radio Romania Cultural https://www.radioromaniacultural.ro/stiinta-360-30-noiembrie-2022-proiecte-complexe-derulate-la-icechim/

STAGE II Demonstration of reproducibility and optimization of the synthesis of composite membranes based on terpolymers and functionalized carbon nanotubes

PERIOD: 01.01.2023-31.12.2023

OBJECTIVES

Act 2.1. – Optimizing recipes for synthesizing unmodified membranes based on biopolymers and synthetic polymers, and non-covalent methods used for carbon nanotube functionalization.

Act 2.2. – Demonstration of the reproducibility of the results regarding both the physical/chemical/mechanical and thermal characteristics of the composite membranes, as well as from the point of view of their capacity to retain heavy metals from simulated wastewater.

Act 2.3. – Protocol configuration for assessing electrolysis membranes using synthetic wastewater bearing heavy metals.

Act 2.4. –  Dissemination activities and communication of original results.

Act 2.5. – Innovation activity and protection of intellectual property rights by registering a patent application.

SUMMARY

The purpose of the I-ON-MEM project bases its research on implementing an innovative solution for water protection and heavy metal pollution. Therefore, the project aims to develop innovative composite membranes for the advanced retention of metal ions in wastewater through the electrodialysis (ED) process.

In Stage 2/2023, the experiments aimed at demonstrating the reproducibility and optimizing the synthesis of composite membranes based on terpolymers and functionalized carbon nanotubes (CNTs) to obtain materials with superior characteristics and a high adsorption efficiency towards heavy metals.

In this sense, several optimized formulations were prepared using the phase inversion method and tested by ED regarding their capacity to capture Cd²⁺ ions. Improved physical, chemical and thermal properties (composition, morphology, and thermal stability), porosity, and hydrophilicity were the targeted characteristics of the unmodified polymer membrane. Membranes based on biopolymers were synthesized using the same three-component polymer mixture consisting of polyvinyl alcohol, sodium alginate, and cellulose. Unlike Stage 1, to obtain materials with improved properties, microcrystalline cellulose was used instead of biocellulose, also as a reinforcing agent. Another difference was using a crosslinker in the biomembrane synthesis process to develop more stable materials. In the case of unmodified membranes based on synthetic polymers, the ratio between the three constituents was kept the same as that which, in the previous stage, led to the best properties of the final materials and presented outstanding characteristics for the retention of heavy metals. Thus, the synthetic membranes were prepared using acrylonitrile-acrylic acid copolymer, polyvinyl alcohol, and polysulfone by the wet phase inversion approach.

The appropriate non-covalent functionalization methodology was identified and finally optimized for CNT to allow homogeneous dispersion in the formulation of bio or synthetic polymer mixtures. Two functionalization methods were considered: surfactants and coating with organic compounds having different functional groups (amino, carboxy, and mercapto). The surfactant CTAB from a selected series of unreported compounds and the organosilanes APTES, MAPTES, and MPTMS were tested. The organosilanes were immobilized on the MWCNT surface by silylation, without the reaction medium and in excess of silane. To achieve this objective, special attention was paid to the composition of the surface and its Zeta potential in aqueous dispersion, in the case of functionalization with surfactants and the demonstration of functionalization with organosilane by a significant percentage in the case of functionalization by coating with organic compounds. The CNT functionalization was proven by modern FTIR, XPS, Raman, XRD, TGA/DTG, and SEM techniques. The Raman analysis indicated a higher ratio of ID/IG compared to the material synthesized in Stage 1 and the Zeta potential of the sample went towards positive values due to a good functionalization and attachment of surfactant molecules on the CNT surface. The XPS analysis confirmed the presence of specific elements on the material’s surface, and the XRD curves highlighted a more amorphous structure of the functionalized nanotubes compared to the neat reference nanotubes. All the results obtained demonstrated that the functionalization process had an effect and aimed at reducing disorder of the CNT network.

The reproducibility of the characteristics of the composite membranes was demonstrated, as well as their capacity to retain heavy metals from simulated wastewater by incorporating functionalized CNTs into the polymer matrix, aiming to increase the specific surface area of the composite membranes and, thus, the retention yield for heavy metal ions. Using the methodologies previously developed for the two types of unmodified polymer matrix (bio and synthetic), composite membranes doped with functionalized MWCNTs (with surfactant or organosilane) were either prepared in the optimal three-component polymer system/CNT ration (1%). The properties of the composite membranes were evaluated using permeability, FTIR, TGA/DTG, contact angle, and SEM, proving the successful incorporation of functionalized CNTs into the polymer network.

Each viable composite membrane, based on biopolymers or synthetic polymers, was tested by ED for the retention of Cd²⁺ ions, establishing specific initial operational parameters and an experimental protocol configuration for evaluating composite membranes compared to references through this innovative test procedure. The removal ratio of Cd from the aqueous medium under different operating conditions of the ED was determined, and the initial concentration, conductivity and pH of the solutions, power consumption, and current efficiency were reported. Cd²⁺ ion removal tests demonstrated that factors such as pH, conductivity, and removal efficiency underwent changes after the ED process of the simulated wastewater. All the synthesized membranes, regardless of the polymer used or the type of functionalized CNT, showed very high values of heavy metal removal, over 87%, which proves a perfect optimization of both the recipes for the synthesis of simple and composite membranes as well as the method functionalization of the carbonaceous material. The best values were recorded in the case of composite synthetic membranes, over 94%.

The results showed the synthesized membranes can successfully retain heavy metals from wastewater

using the new ED system. Cadmium is among the most toxic ions dangerous to living organisms, and its permissible limit in drinking water is 0.005 mg/L. Thus, through the idea of the present project, the metal ion can be removed with an efficiency of over 90% from the contaminated, diluted water flows with the help of the originally developed composite membranes.

            A functional model for synthesizing synthetic and biopolymer-based composite membranes was developed, as well as an experimental protocol for membrane testing by ED using synthetic wastewater contaminated with metals.

The original results were disseminated by submitting a national patent application as well as by participating in 4 international conferences. The degree of achievement of the objectives was 100%.

DISSEMINATION

In Stage 2, in addition to the achieved scientific results, the project has an impressive component of disseminating the results. Part of the obtained results was disseminated by submitting 1 national patent application and participating in 4 national and international scientific events.

National patent application

      1. Chiriac A.-L., Miron A., Sârbu A., Iordache T.-V., Damian C.-M., Caprarescu S., Sandu T., Zaharia A., Gavrila A.-M., Dumitru M.V., “Membrane polimerice de electrodializă, multicomponente, conținând nanotuburi de carbon cu pereți multipli, funcționalizate și procedeu de producere a acestora”, A2023-00656/02.11.2023

Scientific communications at national/international conferences

1. A. Miron, S. Dolana, A.-M. Gavrila, A. Zaharia, T. Sandu, A. Sârbu, A. JM Valente, E. Bernardino, T.-V. Iordache, A.-L. Chiriac, Efficient copper removal from simulated wastewaters using alginate-based polymeric beads, Exploratory Workshop NeXT-Chem: “Innovative Cross-Sectoral Technologies “NeXT-Chem, 5th edition, 22-23 mai 2023. Oral presentation;

2. S. Căprărescu, A.-L. Chiriac, Polymeric membranes containing nanoparticles for water and wastewater treatment, Applications of Chemistry in Nanosciences and Biomaterials Engineering- NanoBioMat-2023, 28-30 June 2023. Poster;

3. A.-L. Chiriac, A. Zaharia, A. Miron, A.-M. Gavrila, T. Sandu, M. Dumitru, S.V. Dolana, A. Sarbu, C.M. Damian, T.-V. Iordache, An original approach of non-covalent surfacefunctionalization of multiwalled carbon nanotubes for polymer membranes obtaining, 5th Euro-Mediterranean Conference for Environmental Integration (EMCEI-2023), 2-5 octombrie 2023. Oral presentation;

4. A. Miron, I. Neblea, S. Dolana, A. Zaharia, A.-M. Gavrila, A. JM Valente, T.-V. Iordache, A.-L. Chiriac, Advanced adsorbent materials for remediation of contaminated waters with heavy metals by enhanced adsorption mechanisms, International symposium “PRIORITIES OF CHEMISTRY FOR A SUSTAINABLE DEVELOPMENT” PRIOCHEM – XIXth Edition, 11-13 octombrie 2023. Poster

SUMMARY

In Stage 3/2024, the experiments referred to the optimization and demonstration of the reproducibility of the synthesis methods of composite membranes and of the methods of obtaining functionalized carbon nanotubes, as well as the development of the laboratory technology of composite membranes based on terpolymers and functionalized carbon nanotubes to obtain materials with superior characteristics and high removal efficiency of heavy metals, over 90%.

 In this sense, the optimized formulations, made in Stage 2/2023, were tested to determine the reproducibility of the synthesis methods. Membranes based on biopolymers were synthesized based on the same mixture of terpolymers consisting of polyvinyl alcohol, sodium alginate, and cellulose, the membranes being cross-linked to ensure high stability. In synthesizing membranes based on synthetic polymers, a mixture consisting of acrylonitrile-acrylic acid copolymer, polyvinyl alcohol, and polysulfone was used, and a wet phase inversion process approached. Also, the appropriate non-covalent

functionalization methodology was tested and optimized for MWCNT synthesis to obtain a more homogeneous dispersion in the formulation of bio or synthetic membranes. In parallel, two distinct functionalization methods were followed, with surfactants and by coating with organic compounds with amino functional groups. The surfactant used was CTAB, and the organosilane used was APTES. APTES was immobilized on the surface of the nanotubes through a silylation process in the absence of the reaction medium and with an excess of silane. Modern techniques, such as FTIR, XPS, Raman, XRD, and TGA/DTG, proved the functionalization. Also, the success of functionalization with surfactant was followed with the help of DLS analysis to determine the sizes and the Zeta potential, which are critical parameters in the functionalization process with surfactants. The functionalization was proven by Raman Spectroscopy, which indicated a higher ratio of I_D/I_G compared to the synthesized material, and the Zeta potential of the sample went to higher values compared to unmodified nanotubes due to a good functionalization and the attachment of surfactant molecules on MWCNT surface. The XPS analysis confirmed the presence of specific elements on the surface of the material, and the XRD diffractogram highlighted a structure similar to that of the simple reference nanotubes, which confirmed that the process does not have a negative impact on the structure of the nanotubes. All the obtained results demonstrated that the functionalization process had the expected effect.

The reproducibility of the characteristics of the composite membranes was highlighted with the help of FTIR spectroscopy, thermal analysis (TGA/DTG), and from the point of view of the rheological behavior. The FTIR spectra showed the characteristic bands of the synthesized compounds. In contrast, the TGA shows an increase in the thermal stability of the composite membranes compared to the unmodified membranes, the characterizations performed proving the successful incorporation of the nanotubes into the polymer network. Also, the rheological behavior of the composite membranes is one of non-Newtonian pseudoplastic type, the shear stress increasing with the increase of the shear speed. At the same time, the viscosity decreased significantly at high shear speeds. Each composite membrane, based on biopolymers or synthetic polymers, was tested by electrodialysis for the retention of cadmium ions, establishing the initial specific operational parameters and a configuration of the experimental protocol for the evaluation of the composite membranes compared to the references through this innovative test procedure. The removal ratio of Cd ion from the aqueous medium under different operating conditions of the electrodialysis system was determined, and the initial concentration, conductivity, pH of the solutions, power consumption, and current efficiency were reported. Finally, the level of cadmium metal ions deposited on the cathode was evaluated. Cd²⁺ ion removal tests demonstrated that factors such as pH, conductivity, and removal efficiency changed after the simulated wastewater electrodialysis process occurred. All the synthesized membranes, regardless of the polymer used or the type of functionalized carbon nanotube, showed very high values of heavy metal removal, over 87%, which proves a perfect optimization of both the recipes for the synthesis of unmodified and composite membranes as well as of the carbon material functionalization method. The best values were recorded in the case of composite synthetic membranes, over 95%. The results showed that the modified composite membranes could represent a perfect choice for better separating cadmium ions from wastewater by electrodialysis.

The laboratory technology was developed t synthesize synthetic and biopolymer-based composite membranes by incorporating carbon nanotubes functionalized with APTES/CTAB. The original results were disseminated by publishing an ISI article plus 1 ISI article published in Stage (which was not planned in the Work Plan for the respective stage but was achieved) and participating in an international conference.

The degree of achievement of the objectives in this stage was 100%.

DISSEMINATION

In Stage 3, in addition to the achieved scientific results, the project has an impressive component of disseminating the results. Thus, part of the obtained results were disseminated by publishing an ISI article in a journal in the red zone (Q1) and attending one international scientific event as an oral presentation.

Publishes papers

1. Andreea Miron, Tanta-Verona Iordache, Artur J. M. Valente, Luisa Maria Rocha Durães, Andrei Sarbu, Georgeta Ramona Ivan, Anamaria Zaharia, Teodor Sandu, Horia Iovu, Anita-Laura Chiriac*, Chitosan-Based Beads Incorporating Inorganic–Organic Composites for Copper Ion Retention in Aqueous Solutions, Int. J. Mol. Sci. 2024, 25, 2411. https://doi.org/10.3390/ijms25042411

Scientific Communications within national/international conferences:

1. Andreea MIRON, Roxana Ioana MATEI, Marinela-Victoria DUMITRU, Iulia-Elena NEBLEA, Sorin DOLANA, Andrei SARBU, Anamaria ZAHARIA, Tanta-Verona IORDACHE, Anita-Laura CHIRIAC, New adsorbents based on chitosan and inorganic-organic composite for efficient remediation of heavy metals in wastewater, NeXT-Chem, 6^th edition, 21-22 March 2023. Oral presentation