Results

Results 2020

Polyaniline (PANI) and polypyrrole (PPY) nanostructures with different morphologies were synthesized, based on the existing protocols in the laboratory, being fulfilled all the activities and objectives proposed in this stage.

Two types of PANI samples were synthesized: PANI-A and PANI-B, using two different methods that favor the formation of nanostructures with tubular morphology (PANI-A) and of round-shape morphology (PANI-B). Polyaniline nanostructures (PANI) with tubular morphology, PANI-A, were obtained by the "free template" synthesis method, which involves the oxidation of aniline with ammonium persulfate (APS) in a mixed solution of ethanol and acetic acid. Polyaniline nanostructures with round-shape morphology, PANI-B, were obtained by a polymerization reaction involving the oxidation of aniline with ammonium persulfate (APS) in an acid medium. In addition, two types of PANI / Fe₃O₄ and PANI / Ferrocene composites were made by a similar method with as for PANI-B, Fe₃O₄ and ferrocene being added to the polymerization solution before the oxidation process of aniline.

Polypyrrole (PPY) nanostructures with tubular morphology were obtained using FeCl₃-MO complex as reactive templates, which self-degrades and allows directing the growth of PPY on its surface and their evolution to PPY nanotubular structures. PPY nanostructures with round-shape morphology were obtained by oxidative polymerization reaction of pyrrole with ferric chloride as oxidant and p-toluene sulfonic acid (PTA) as an anionic dopant.

In addition to the synthesis methods presented, X-ray diffraction was used to analyze the obtained samples.

Results 2021

In the first stage of the project, the synthesis and characterization of polyaniline (PANI) and polypyrrole (PPY) with different morphology (round shape or nanotubular particles) and as nitrogen containing precursors, based the existing protocol from our laboratory were done. The four type of nitrogen containing carbon nanostructures (NCNs) were obtained after thermal treatment of the nitrogen containing polymer, under nitrogen atmosphere at 900 ° C. The resulted samples were characterized using FT-IR spectroscopy and X-ray diffractions. Both characterization methods prove the conversion of polymer precursors into NCNs after the thermal treatment.

NCNs materials were used to modify both carbon cloths for the development planar electrodes of commercial sponge for the development of 3D electrodes. For the microbial fuel cell tests we used double chamber MFC (D-MFC) under fed-batch mode. Thus, we have tested 8 MFCs (2 for each NCN materials). The anode chambers was inoculated with municipal wastewater and e maintained under anaerobic conditions, while the catholyte consisted of phosphate buffer (pH 7, 0.05M) that was be purged with bubbling air during the operation. The microbial community and biofilm formation on the electrode surface significantly influence a system's performance. Studies of anode biofilms suggest there is no unique combination of bacteria that constitute an optimum electrogenic community. The characterization of the microbial communities of biofilms (based on alpha-diversity indices) showed that the wastewater samples have a higher number of observed species compared to the samples taken from MFC1-MFC8, the lower values ​​in the case of MFC samples are due to a process of selection that takes place at the level of the community of microorganisms deposited on the anode materials. The bacterial communities in the water samples show Proteobacteria and Firmicutes as the dominant phyla, and in the MFC samples Proteobacteria acquire a higher relative abundance, the abundance of Firmicutes decreases, and the members of the Bacteroidota and Campilobacterota phylums proliferated in different proportions.

In term of bioenergy production, the maximum power density has close values between ~30 and 40 has/m², with the best value obtained for MFC using NCN form polyaniline with round shape morphology as anode modifier, which are in agreement with the results obtained from the characterization of the biofilm grown at the anode, where the biofilms showed an increased abundance of the genus Geobacter (30.64%) recognized as having an electrogenic character.

And in term of wastewater treatment, the results showed that the most advanced mineralization of organic matter of around 80%, is obtained in the case of MFC which use NCN from polypyrrole with round-shape morphology.

Results 2022

In this stage of the projects, we achieved the following scientific goals:

• validation of nitrogen-containing carbon nanostructures as anode modifier in MFC with planar of 3D configuration (TRL4);

• validation of a functional model of MFC operating in fed-batch mode (TRL4);

• development of continuous mode operation MFCs working in the laboratory environment (TRL3);

• characterization of microbial communities of biofilms;

• evaluation fed-batch and continuous mode operation MFCs for wastewater treatment and bioenergy production taking in correlation with the microbial community of biofilm

Carbon nanostructures with nitrogen content (NCN) were validated for the modification of MFC anodes, at the laboratory level, using two materials obtained from the carbonization of PANI-polyaniline (different morphology, PANI-R-900 and PANI-T-900 ) (see Figure 1). For validation, 8 MFC with bicameral configuration were tested under the similar conditions, using the same water source, and 4 anodes modified with PANI-R-900 and 4 modified with PANI-T-900. The results obtained allowed the validation of the two materials for the modification of the MFC anodes and showed the superior performances given by the two types of anode modifications compared to the unmodified anode, with the best results obtained in the case of the anode modified with NCN with tubular/fibrillar morphology.

In order to validate MFC working in "fed-batch" conditions (at the laboratory level), the reproducibility and stability data of the MFC systems in laboratory conditions were supplemented by the results related to the treatment of municipal water using MFC technology and characterization of microbial communities of initial municipal waters and biofilms. Figure 2 shows an experimental assembly used for MFC testing in fed batch mode, that can accommodate planar and tridimensional electrodes. The second one was used for the validation of MFC working in fed batch conditions.

The results obtained in term of wastewater treatment using MFC with anode modified with PANI-R-900 and PANI-T-900 showed significant reductions of the main characteristics analyzed (CBO, CCO and TOC). The analysis of the communities of microorganisms from the initial municipal wastewaters as well as the biofilm grown on the anode allowed us to determine the relative abundance of the different taxa involved in electrogenic processes at the level of biofilms and complement the previous analyzes regarding bioenergy production and water treatment.

Based on our experience related to the design of two-chamber MFC, the design of the MFC reactors was modified for continuous operation mode. The modification of hydraulic retention times (HRT) to evaluate the performance of MFCs under continuous operating mode showed that HRT exerts an important impact on the maximum power density of MFC but also influences the degradation of COD and BOD parameters used for analysis of wastewater influent/effluent. The data obtained allowed the elaboration of an experimental MFC model with continuous operating mode at the laboratory scale.

Dissemination:

Papers:

1. Angel Vasile Nica, Elena Alina Olaru, Bradu Corina, Anca Dumitru, Sorin Marius Avramescu, Catalytic ozonation of ibuprofen in aqueous media over polyaniline derived nitrogen containing carbon nanostructures, Nanomaterials (FI 5.719) –accepted Manuscript ID: nanomaterials-1943184

2. Irina Lascu, Claudiu Locovei, Corina Bradu, Cristina Gheorghiu, Ana-Maria Tanase and Anca Dumitru, Polyaniline derived nitrogen containing carbon nanostructures with different morphology as anode modifier in Microbial Fuel Cells, International Journal of Molecular Science 2022, 23, 11230. https://doi.org/ 10.3390/ijms231911230 (FI 6.208)

3. C. Locovei, A.L.Chiriac, A. Miron, S. Iftimie, V. Antohe, A. Sarbu, A.Dumitru, Synthesis of titanium nitride via hybrid nanocomposites based on mesoporous TiO2/acrylonitrile, Scientific Report, 11(1) 2021, Art. No. 5055, doi: 10.1038/s41598-021-84484-3 (FI 4.996)

Conferences:

1. A. Dumitru, T. Suteu, S. Toader, S. Iftimie, R. Adrian and C. Locovei , Stability of microbial biofilm grown on the surface of polyaniline derived carbon nanostructures used as anode modifier in microbial fuel cell, 24^th International Conference - Materials, Methods & Technologies, 19-22 August 2022, Burgas, Bulgaria

2. Irina Lascu^, Iulia Chiciudean, Maria Preda, Anca Dumitru, Ana Maria Tanase, Effect of morphology of carbonized polypyrrole-modified anodes on the bacterial diversity of microbial fuel cells, FEMS Conference on Microbiology, 30June-2 July 2022, Beograd, Serbia

3. Tudor Suteu and Anca Dumitru, The influence of different polypyrrole polymer and carbon material morphologies on electrical properties, Annual session of scientific communications of Physics Faculty, 24 July 2022, Bucharest, Romania

4. A. Dumitru, T. Suteu, S. Galin, S. Iftimie and C. Locovei, Polypyrrole-based nitrogen containing carbons as microbial fuel cells anode, 23^rd International Conference - Materials, Methods & Technologies, 19-22 August 2021, Burgas, Bulgaria