64 research outputs found
Sulfonated graphene oxide as innovative self-assembling electrolyte for PEM fuel cells
No full textSulfonated graphene oxide (SGO) membranes have been developed and evaluated as a viable alternative to Nafion® in polymer electrolyte membrane fuel cells (PEMFCs). Even though Nafion® is currently the most widely used electrolyte in PEMFC systems, some crippling drawbacks induce the need of finding feasible replacements. In particular, Nafion® suffers a severe conductivity drop upon dehydration, which limits the possibility of operation in conditions of high temperature and low relative humidity [1]. As shown in previous works, graphene oxide (GO) appears to be an excellent candidate for making both freestanding [2] and polymer-based hybrid membranes [3], thanks to its good mechanical properties and to the presence of oxygen-containing functionalities that are likely to improve water retention. However, we verified in a preliminary study [4] that, at high temperatures, GO suffers a partial loss of the chemical groups which foster protons transport and a lowering of the structural integrity of the carbon network. Hence, its properties may be enhanced by functionalization with some acid groups more tightly bound to its skeleton, e.g. sulfonic acid groups (–SO3H) analogous to those of Nafion®.
In this work, we present an effective method for the sulfonation of graphene oxide, based on the reaction between sulfuric acid and a commercial aqueous dispersion of GO. Different samples have been prepared by varying the quantity of sulfuric acid employed in the sulfonation reaction, and an optimal acid-to-GO molar ratio has been identified, taking into account an empirical formula of GO. Such formula has been derived, as a first approximation, from the elemental analysis of the commercial solution and confirmed by the results of SEM and EDX analysis. The sulfonated membranes have been widely characterized by ATR-FTIR, XRD, SEM and EDX spectroscopies, thermogravimetric (TG-DTG) analysis, optical microscopy and static contact angle (OCA) measurements. These techniques confirmed the effective functionalization of GO and the stability of sulfonic acid groups even after water uptake (WU) experiments, which have been carried out at different temperatures and relative humidity. The ion exchange capacity (IEC) of the different samples has been evaluated as well, and a correlation among WU, IEC and degree of sulfonation (DS) can be established. Test results showed that sulfonated membranes have an improved WU behaviour with respect to both Nafion and unfunctionalized GO, especially at low temperature and humidity (Fig. 1); they also show an IEC value higher than 1 meq/g, which is even better than IEC determinations reported for Nafion® [5]. The increase of the amount of sulfuric acid seems to be beneficial for both properties. Then, one sulfonated membrane has been selected and subjected to a preliminary test in a lab-scale hydrogen-fed fuel cell. Promising results have been found from the point of view of mechanical resistance, even though a low open circuit voltage (OCV) has been measured (0.63 V) at 40 °C, which might be ascribed to hydrogen crossover issues. These issues should be addressed in future developments of such components. However, after testing, the active area showed absence of carbon residues left by the gas diffusion electrode (GDE), which are a typical problem in the case of Nafion®.
[1] Q. Li, R. He, J. O. Jensen, N. J. Bjerrum. Chem. Mater., 2003, 15, 4896.
[2] T. Bayer, S. R. Nishihara, K. Sasaki, S. M. Lyth. J. Power Sources, 2014, 272, 239.
[3] M. Vinothkannan, A. R. Kim, G. G. Kumar, D. J. Yoo. Rsc Adv., 2018, 8, 7494.
[4] S. Latorrata, A. Basso Peressut, P. Gallo Stampino, C. Cristiani, G. Dotelli. ECS Trans., 2018, 86, 347.
[5] H. Dai, H. Zhang, Q. Luo, Y. Zhang, C. Bi. J. Power Sources, 2008, 185, 19
Self-assembling reduced graphene oxide and TiO2-based materials for solar photocatalytic wastewater treatment
No full textIn this study, we employed a simple and eco-friendly method to prepare self-assembling self-standing membranes of: i) graphene oxide (GO), ii) reduced GO (rGO), iii) rGO and TiO2 (rGO-TiO2). We tested the three membranes for adsorption and solar photodegradation of Imidacloprid in water, obtaining evidence of a remarkable solar photocatalytic activity of rGO. To the best of our knowledge, no other photocatalytic rGO self-standing membranes have been reported yet
Development and characterization of novel PBI/SGO composites as possible proton exchange membranes filling the “conductivity gap”
No full textThe research for non-fluorinated polymeric electrolytes able to operate at temperatures of 80–120 °C, the so-called “conductivity gap”, is becoming central. Within this frame, the present work discusses the investigation of innovative self-assembling polybenzimidazole/sulfonated graphene oxide (PBI/SGO) composite membranes. A set of five samples, characterized by never-explored PBI-to-SGO mass ratios between 3:1 and 1:3, is studied through surface and cross-sectional SEM, XRD, ATR-FTIR spectroscopy, and TGA. The experimental outcomes reveal the reciprocal compatibility between PBI and SGO, whose main features appear to be evenly distributed within the composites. Water immersion tests demonstrate the excellent interplay between the membranes and the aqueous environment. EIS experiments, performed with the in-plane and through-plane configurations, disclose the improvement of the proton transfer ability (σ) in both directions. At 120 °C, PBI/SGO 1:2 achieves the highest in-plane σ of 0.113 S cm−1, while PBI/SGO 1:3 shows the best through-plane σ of 0.025 S cm−1. The preference toward planar proton migration is confirmed by the computation of the anisotropy factor, which is attenuated to ≈0.5 with the aid of temperature. Based on these findings, the composites with large SGO content seem to possess great potential as alternative non-fluorinated proton exchange membranes
Self-standing membranes of reduced graphene oxide, TiO2 and waste-derived TiO2 for water treatment through adsorption and photocatalysis
No full textAs stated in United Nations SDG 6, improvement of wastewater treatment and reuse
is an urgent necessity. In this context, titanium dioxide (TiO2) and reduced graphene
oxide (rGO) deserve a particular attention. The former is a well-known photocatalytic
material, the latter shows a significant capture ability toward metal ions and organic
molecules. Compared to pure TiO2, rGO-TiO2 composites are proved to have a
reduced bandgap, which allows to exploit lower-energy photons for photocatalysis.
In this work, we developed composite self-assembling membranes of rGO and TiO2.
Our purpose is to obtain a self-standing material having the double functionality of
adsorbent and photocatalyst, able to decontaminate wastewater from both inorganic
and organic pollutants. To the best of our knowledge, no other self-standing
membranes of rGO and TiO2 have been reported in literature yet. Fulfilling a circular
economy approach, we also investigated the replacement of TiO2 with tionite (TIO),
a waste-derived TiO2-containing material.
Composite rGO-TiO2 and rGO-TIO membranes, with 2:1, 1:1 or 1:2 mass ratio, were
simply prepared by mixing of an rGO aqueous suspension with commercial TiO2
nanopowder or tionite, followed by vacuum filtration and mild drying. The resulting
self-assembling membranes were extensively characterized through XRD, SEMEDX, thermogravimetry, Raman and UV-Vis spectroscopy.
Their water remediation properties were evaluated toward contaminants of different
nature. Membranes were employed as filters for aqueous solutions of Fe3+ and
Cu2+, representative of heavy metals contaminated wastewater. Then, membranes
were tested for adsorption and photodegradation of organic molecules, namely the
pesticide Imidacloprid, the dye methylene blue and the analgesic drug paracetamol.
Experiments were carried out in dynamic and static conditions for 5 h, irradiating the
membranes with UV-A, visible and simulated solar light. All the membranes exhibited
a significant adsorption capacity (75%) toward the three molecules. In addition,
composite membranes were responsible for pollutants photodegradation. Despite
being limited (between 10% and 20%), the photocatalytic activity of these
membranes is notable, considering the small amount of TiO2 and TIO contained.
Moreover, the anatase content of tionite is as low as 1/6 of the one of commercial
TiO2
Facile coating of reduced graphene oxide and TiO2 on floating polyurethane foams for photocatalytic water decontamination
No full textReduced graphene oxide and TiO2 coated floating foams for photocatalytic wastewater treatment
No full textWater pollution is one of the most concerning issues of our times, requiring the development of effective decontamination technologies, as remarked in UN Sustainable Development Goal 6. Photocatalysis represents a promising and sustainable strategy for water decontamination. Photocatalytic materials are able to mineralize organic pollutants and, compared to sorbent materials, offer the advantages of being reusable multiple times and being effective toward a broad range of contaminants. Titanium dioxide (TiO2) is the most studied and used photocatalyst. However, its practical application is still restricted for two main reasons: i) TiO2 large energy gap of 3.2 eV requires UV light for photocatalysis, implying a significant energy consumption, ii) TiO2 is mostly used in the form of nanoparticles, which are hardly recoverable from water and tend to agglomerate, reducing their photocatalytic activity. Coupling TiO2 with reduced graphene oxide (rGO) has already been proved as an effective strategy to obtain photoactive materials with lower bandgap. Nevertheless, as TiO2, rGO/TiO2 composites are mainly studied as slurries.
In this research, we developed a green and facile methodology to immobilize TiO2 in rGO/ TiO2 membranes and coatings, exploiting the self-assembling properties of rGO. Briefly, we obtained a rGO/ TiO2 aqueous dispersion by mixing TiO2 nanopowder with a GO commercial dispersion, after controlled reduction with L-Ascorbic Acid at ambient temperature and pressure. Membranes were produced by vacuum filtration of the dispersion onto a PVDF filter, obtaining, to the best of our knowledge, the first self-standing rGO/TiO2 membrane reported in the literature [1]. The same dispersion was also employed as coating for 3D porous structures. The deposition method consisted in dip-coating followed by mild drying. Polyurethane flexible foams of 10 PPI, 20 PPI and 30 PPI were used as supports. For both membranes and coatings, rGO: TiO2 mass ratios of 1:1, 1:2 and 1:3 were considered. A higher content of TiO2 was found to compromise rGO self-assembling properties and, consequently, membranes integrity.
Membranes and coated foams were also tested for photodegradation of organic molecules in water. The pesticide Imidacloprid and the drug paracetamol were selected as representative organic pollutants. Degradation tests were performed in dynamic conditions, under UV-A and simulated solar light. Adsorption experiments in dark were also carried out. Preliminary results indicated a pollutants degradation of approximately 20%, obtained with the rGO/TiO2 1:1 membrane after 5 h under UV-A light. Despite being limited, this photocatalytic activity is notable, considering the low amount of TiO2 contained in the sample. We may reach a higher photodegradation level with membranes containing a double or triple quantity of TiO2. Coated foams appear particularly promising for their geometry, as it allows to maximize the interaction surface between water, light and photocatalyst, and to minimize shaded areas
Titanium Dioxide and Reduced Graphene Oxide-Based Materials for Photocatalytic Water Decontamination
No full textWater pollution is one of the most concerning issues of our times, requiring the development of effective decontamination technologies, as remarked in UN Sustainable Development Goal 6. Photocatalysis represents a promising and sustainable strategy for water decontamination. Photocatalytic materials are able to mineralize organic pollutants and, compared to sorbent materials, offer the advantages of being reusable multiple times and being effective toward a broad range of contaminants. Titanium dioxide (TiO2) is the most studied and used photocatalyst. However, its practical application is still restricted for two main reasons: i) TiO2 large energy gap of ∼3.2 eV requires UV light for photocatalysis, implying a significant energy consumption, ii) TiO2 is mostly used in the form of nanoparticles, which are hardly recoverable from water and tend to agglomerate, reducing their photocatalytic activity. Coupling TiO2 with reduced graphene oxide (rGO) has already been proved as an effective strategy to obtain photoactive materials with lower bandgap. Nevertheless, as TiO2, rGO/TiO2 composites are mainly studied as slurries.
In this research, we developed a green and facile methodology to immobilize TiO2 in rGO/TiO2 membranes and coatings, exploiting the self-assembling properties of rGO. Briefly, we obtained a rGO/TiO2 aqueous dispersion by mixing TiO2 nanopowder with a GO commercial dispersion, after controlled reduction with L-Ascorbic Acid at ambient temperature and pressure. Membranes were produced by vacuum filtration of the dispersion onto a PVDF filter, obtaining, to the best of our knowledge, the first self-standing rGO/TiO2 membrane reported in the literature [1]. The same dispersion was also employed as coating for 3D porous structures. The deposition method consisted in dip-coating followed by mild drying. Polyurethane flexible foams of 10 PPI, 20 PPI and 30 PPI were used as supports. For both membranes and coatings, rGO:TiO2 mass ratios of 1:1, 1:2 and 1:3 were considered. A higher content of TiO2 was found to compromise rGO self-assembling properties and, consequently, membranes integrity.
Membranes and coated foams were also tested for photodegradation of organic molecules in water. The pesticide Imidacloprid and the drug paracetamol were selected as representative organic pollutants. Degradation tests were performed in dynamic conditions, under UV-A and simulated solar light. Adsorption experiments in dark were also carried out. Preliminary results indicated a pollutants degradation of approximately 20%, obtained with the rGO/TiO2 1:1 membrane after 5 h under UV-A light. Despite being limited, this photocatalytic activity is notable, considering the low amount of TiO2 contained in the sample. We may reach a higher photodegradation level with membranes containing a double or triple quantity of TiO2. Coated foams appear particularly promising for their geometry, as it allows to maximize the interaction surface between water, light and photocatalyst, and to minimize shaded areas
Self-assembling reduced graphene oxide and TiO2-based materials for photocatalytic wastewater treatment
No full textImprovement of wastewater treatment is an urgent necessity of our times, as stated in the United
Nations SDG 6. For this purpose, photocatalysis presents multiple advantages over traditional
treatment methods (e.g. adsorption), such as mineralization of organic contaminants and
reusability of the catalyst. However, its application is limited by the 3.2 eV bandgap of TiO2, the
most common photocatalyst, which requires high-energy photons. Moreover, TiO2 used in slurry
form tends to agglomerate, reducing the specific surface area available for photocatalysis [1].
Coupling TiO2 with graphene oxide (GO), particularly in its reduced form (rGO), represents a valid
strategy to enhance applicability of photocatalysis. Having a smaller bandgap, rGO/TiO2
nanocomposites result particularly promising for visible and solar light-driven photocatalysis [2].
However, their investigation is currently limited mainly to slurry or supported systems.
To the best of our knowledge, the self-assembling rGO-TiO2 membrane recently developed by
our research group is the first and only self-standing membrane of rGO and TiO2 reported in the
literature [3]. The preparation method is simple and environmental-friendly. Briefly, being reduced
with L-ascorbic acid, rGO is mechanically mixed with TiO2 nanopowder in 1:1 mass ratio. Upon
vacuum filtration and mild drying, a self-standing composite membrane (rGO-TiO2) is obtained.
Following a circular economy approach, we also investigated the replacement of TiO2 with
tionite (TIO), a waste-derived TiO2-containing material, obtaining a rGO-TIO
membrane.
In this research, we tested rGO-TiO2, rGO-TIO, rGO and GO membranes for photodegradation
of organic molecules in water, namely the pesticide Imidacloprid and the drug paracetamol.
Experiments were carried out under UV-A, visible and simulated solar light irradiation, in static
and dynamic conditions. Adsorption tests in dark were also performed. Irradiated for 5 h with UVA light, both composite membranes showed a pollutants photodegradation between 10% and
20%. Despite limited, the photocatalytic activity of these membranes is notable, considering the
small amount of TiO2 and TIO contained. Moreover, the anatase content of tionite is as low as
1/6 of the one of commercial TiO2. Under simulated solar light, instead, an Imidacloprid
photodegradation of 25% after 5 h in static conditions was achieved with rGO-TiO2 and with the
membrane consisting of only rGO.
In order to maximize the surface interaction between photocatalyst and wastewater, we also
developed rGO/TiO2-coated open cell flexible foams. In particular, we dip-coated polyurethane
foams with coatings having the same composition of the above-mentioned membranes (GO, rGO,
rGO-TiO2 and rGO-TIO). Having blown away the excess coating inside pores, they were dried at
just 40 °C. Such coated foams are going to be tested as floating photocatalysts and related results
will be shown during the conference
Study of functionalized graphene oxide as an alternative self-assembling proton conductor for PEM fuel cells
No full textPFASs-free PBI-PGO composites as promising polymer electrolyte membranes for bridging the “conductivity gap”
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