Evaluating Gelatin-Based Films with Graphene Nanoparticles for Wound Healing Applications.

In this study, gelatin-based films containing graphene nanoparticles were obtained. Nanoparticles were taken from four chosen commercial graphene nanoplatelets with different surface areas, such as 150 m2/g, 300 m2/g, 500 m2/g, and 750 m2/g, obtained in different conditions. Their morphology was observed using SEM with STEM mode; porosity, Raman spectra and elemental analysis were checked; and biological properties, such as hemolysis and cytotoxicity, were evaluated. Then, the selected biocompatible nanoparticles were used as the gelatin film modification with 10% concentration. As a result of solvent evaporation, homogeneous thin films were obtained. The surface's properties, mechanical strength, antioxidant activity, and water vapor permeation rate were examined to select the appropriate film for biomedical applications. We found that the addition of graphene nanoplatelets had a significant effect on the properties of materials, improving surface roughness, surface free energy, antioxidant activity, tensile strength, and Young's modulus. For the most favorable candidate for wound dressing applications, we chose a gelatin film containing nanoparticles with a surface area of 500 m2/g.

Enhanced supercapacitor materials from pyrolyzed algae and graphene composites.

This study focuses on the synthesis and characterization of supercapacitor materials derived from pyrolyzed natural compounds. Four compounds were investigated: methylcellulose with lysine (ML), methylcellulose with lysine-graphene composite (MLG), algae (A), and algae-graphene composite (AG). The pyrolysis process was utilized to convert these natural compounds into carbon-based materials suitable for supercapacitor applications. The properties of the resulting materials were analyzed extensively to evaluate their potential as supercapacitor electrodes. The electrochemical performance, including specific capacitance, cyclic stability, and rate capability was measured using various characterization techniques. The effects of incorporating graphene into the lysine-methylcellulose and algae matrices were also studied to explore the enhancements in supercapacitor performance. In both cases, the addition of graphene resulted in a positive effect. Among all the materials investigated, the algae-graphene composite exhibited the most favorable properties, demonstrating a specific capacitance of 192 F g-1 after 10,000 galvanostatic charge-discharge cycles at a current of 5 A g-1 in K2SO4 electrolyte. This exceptional performance underscores the potential of the algae-graphene composite as a highly efficient and durable electrode material for supercapacitor applications.

Synergistic effects of nitrogen-doped carbon and praseodymium oxide in electrochemical water splitting.

Hybrid materials featuring perovskite-type metal oxide in conjunction with heteroatom-doped graphene hold immense promise as alternatives to costly noble metal catalysts for electrochemical water splitting, facilitating the generation of environmentally friendly hydrogen. In this study, perovskite-type oxide containing praseodymium, barium, strontium, cobalt, and iron atoms dispersed in a carbon matrix as a catalyst is synthesized via annealing of the carbon material with substrates for the preparation of perovskite oxide. The mass ratio of reagents regulates the porous structure and elemental composition. The result of the hydrogen evolution reaction (HER), suggests that the hybrid catalysts exhibit intermediate HER kinetics compared to the commercial Pt/C and the catalyst without carbon. The Tafel slope for HER is lower for materials containing carbon, because of the improved reaction kinetics, facilitated proton transfer, and enhanced electrochemical surface area. Therefore, the study provides an effective strategy for the preparation of catalyst and their use as the active catalyst of water splitting.

Modified graphene foam as a high-performance catalyst for oxygen reduction reaction.

Gelatine and chitosan were used as natural precursors for nitrogen-doping of the graphene foam structure, creating specific types of active sites. The quantitative and qualitative content of nitrogen groups in the carbon structure was determined, which, under the influence of high temperature, were incorporated and transformed into forms of functional groups favorable for electrochemical application. Electrochemical studies proved that the form of pyridine-N, pyrrole-N, and quaternary-N groups have favorable electrochemical properties in the oxygen reduction reaction comparable to commercial platinum-based electrode materials. Using these materials as electrodes in metal-air batteries or fuel cells may eliminate the use of noble metal-based electrodes.

Exfoliated graphite with spinel oxide as an effective hybrid electrocatalyst for water splitting.

The aim of the conducted research was to develop hybrid nanostructures formed from MnCo2O4 and exfoliated graphite. Carbon added during the synthesis allowed for obtaining a well-distributed MnCo2O4 particle size with exposed active sites contributing to the increased electric conductivity. The influence of the weight ratios of carbon to a catalyst for hydrogen and oxygen evolution reactions was investigated. The new bifunctional catalysts for water splitting were tested in an alkaline medium with excellent electrochemical performance and very good working stability. The results for hybrid samples show better electrochemical performance compared to the pure MnCo2O4. The highest electrocatalytic activity was for sample MnCo2O4/EG (2/1), where the value of the overpotential was 1.66 V at 10 mA cm-2, and also for this sample a low value of Tafel slope (63 mV dec-1) was denoted.

3D-Structured and Blood-Contact-Safe Graphene Materials.

Graphene is a promising material that may be potentially used in biomedical applications, mainly for drug delivery applications. In our study, we propose an inexpensive 3D graphene preparation method by wet chemical exfoliation. The morphology of the graphene was studied by SEM and HRTEM. Moreover, the volumetric elemental composition (C, N, and H) of the materials was analyzed, and Raman spectra of prepared graphene samples were obtained. X-ray photoelectron spectroscopy, relevant isotherms, and specific surface area were measured. Survey spectra and micropore volume calculations were made. In addition, the antioxidant activity and hemolysis rate in contact with blood were determined. Activity against free radicals of graphene samples before and after thermal modification was tested using the DPPH method. The RSA of the material increased after graphene modification, which suggests that antioxidant properties were improved. All tested graphene samples caused hemolysis in the range of 0.28-0.64%. The results showed that all tested 3D graphene samples might be classified as nonhemolytic.

Modification of TiO2 nanotubes by graphene-strontium and cobalt molybdate perovskite for efficient hydrogen evolution reaction in acidic medium.

Herein, we demonstrate that modification of TiO2 nanotubes with graphene-strontium and cobalt molybdate perovskite can turn them into active electrocatalysts for hydrogen evolution reaction (HER). For this purpose, a simple method of hydrothermal synthesis of perovskites was developed directly on the TiO2 nanotubes substrate. Moreover, the obtained hybrids were also decorated with graphene oxide (GO) during one-step hydrothermal synthesis. The obtained materials were characterized by scanning electron microscopy with energy dispersive X-ray analysis, Raman spectroscopy, and X-ray diffraction analysis. Catalytic properties were verified by electrochemical methods (linear voltammetry, chronopotentiometry). The obtained hybrids were characterized by much better catalytic properties towards hydrogen evolution reaction compared to TiO2 and slightly worse than platinum. The optimized hybrid catalyst (decorated by GO) can drive a cathodic current density of 10 mA cm-2 at an overpotential of 121 mV for HER with a small Tafel slope of 90 mV dec-1 in 0.2 M H2SO4.

Obtaining N-Enriched Mesoporous Carbon-Based by Means of Gamma Radiation.

In this paper, we present the results of the gamma irradiation method to obtain N-doped mesoporous activated carbons. Nitrogen-enriched mesoporous carbons were prepared from three chosen commercial activated carbons such as Carbon Black OMCARB C-140, KETJENBLACK EC-600JD and PK 1-3 Norit. HRTEM, SEM, Raman spectra, elemental analysis, XPS studies and widely approved N2 adsorption-desorption measurements allowed us to evaluate the effectiveness of N atom insertion and its influence on the BET surface area and the pore structure of modified carbons. The obtained materials have an exceptionally high N content of up to 3.2 wt.%. Additionally, selected N-doped activated carbons were fully characterized to evaluate their applicability as carbon electrode materials with particular emphasis on Oxygen Reduction Reaction (ORR). The proposed method is a relatively facile, efficient and universal option that can be added to the already known methods of introducing heteroatoms to different carbons.

The effect of nitrogen species on the catalytic properties of N-doped graphene.

The production of effective catalysts in the oxygen reduction reaction (ORR) continues to be a great challenge for scientists. A constant increase in demand for energy storage materials is followed by a proportionate increase in the number of reports on electrocatalyst synthesis. The scientific world focuses on environmentally friendly materials synthesized in accordance with the safest possible. In this work, we developed a facile method of obtaining heavy-metal-free electrode materials that are effective in ORR. Graphene-based catalysts were doped using azodicarbonamide (ADC) as the source of nitrogen, then carbonized at high temperatures in the range of 700-900 °C under inert gas flow. The produced materials were tested as catalysts for ORR, which is the most important reaction for Zn-air batteries and fuel cells. All obtained nitrogen-doped graphene foams showed increased catalytic activity in ORR owing to active sites created by nitrogen functional groups on the graphene surface. This paper shows that carbonization temperature has a significant impact on nitrogen content and that a small percentage of nitrogen may have a positive effect on the catalytic activity of the obtained materials. The number of transferred electrons in ORR was found to range from three to the maximal theoretical value, i.e., four.

High surface area micro-mesoporous graphene for electrochemical applications.

The manuscript presents results on the influence of external pressure on graphene exfoliation and subsequent 3D structuring by means of liquid-phase exfoliation. In contrast to known and applied exfoliation methods, the current study exploits the enhancement of splitting forces caused by the application of high pressure. The manufacturing pathway allowed to increase the surface area from 750 m2/g (nanoplatelets) to ca. 1100 m2/g (after 3D structuring). Electrochemical studies revealed that the 3D graphene materials were active in the oxygen reduction reaction (ORR). The outstanding ORR activity of 3D structured graphene materials should not be ascribed to heteroatom catalytic centers since such heteroatoms were successively removed upon increasing the carbonization temperature. XPS data showed that the presence of transition metals and nitrogen (usually regarded as catalytic centers) in G-materials was marginal. The results highlight the importance of structural factors of electrodes in the case of graphene-based materials for Zn-air batteries and ORR.

Combined effect of nitrogen-doped functional groups and porosity of porous carbons on electrochemical performance of supercapacitors.

In this work, nitrogen-doped porous carbons obtained from chitosan, gelatine, and green algae were investigated in their role as supercapacitor electrodes. The effects of three factors on electrochemical performance have been studied-of the specific surface area, functional groups, and a porous structure. Varying nitrogen contents (from 5.46 to 10.08 wt.%) and specific surface areas (from 532 to 1095 m2 g-1) were obtained by modifying the carbon precursor and the carbonization temperature. Doping nitrogen into carbon at a level of 5.74-7.09 wt.% appears to be the optimum for obtaining high electrochemical capacitance. The obtained carbons exhibited high capacitance (231 F g-1 at 0.1 A g-1) and cycle durability in a 0.2 mol L-1 K2SO4 electrolyte. Capacitance retention was equal to 91% at 5 A g-1 after 10,000 chronopotentiometry cycles. An analysis of electrochemical behaviour reveals the influence that nitrogen functional groups have on pseudocapacitance. While quaternary-N and pyrrolic-N nitrogen groups have an enhancing effect, due to the presence of a positive charge and thus improved electron transfer at high current loads, the most important functional group affecting energy storage performance is graphite-N/quaternary-N. The study points out that the search for the most favourable organic precursors is as important as the process of converting precursors to carbon-based electrode materials.

Adsorption of Hexavalent Chromium and Divalent Lead Ions on the Nitrogen-Enriched Chitosan-Based Activated Carbon.

Optimizing the physicochemical properties of the chitosan-based activated carbon (Ch-ACs) can greatly enhance its performance toward heavy metal removal from contaminated water. Herein, Ch was converted into a high surface area (1556 m2/g) and porous (0.69 cm3/g) ACs with large content of nitrogen (~16 wt%) using K2CO3 activator and urea as nitrogen-enrichment agents. The prepared Ch-ACs were tested for the removal of Cr(VI) and Pb(II) at different pH, initial metal ions concentration, time, activated carbon dosage, and temperature. For Cr(VI), the best removal was at pH = 2, while for Pb(II) the best pH for its removal was in the range of 4-6. At 25 °C, the Temkin model gives the best fit for the adsorption of Cr(VI), while the Langmuir model was found to be better for Pb(II) ions. The kinetics of adsorption of both heavy metal ions were found to be well-fitted by a pseudo-second-order model. The findings show that the efficiency and the green properties (availability, recyclability, and cost effectiveness) of the developed adsorbent made it a good candidate for wastewaters treatment. As preliminary work, the prepared sorbent was also tested regarding the removal of heavy metals and other contaminations from real wastewater and the obtained results were found to be promising.

The Importance of Structural Factors for the Electrochemical Performance of Graphene/Carbon Nanotube/Melamine Powders towards the Catalytic Activity of Oxygen Reduction Reaction.

In this paper, we show the carbonization of binary composites consisting of graphene nanoplatelets and melamine (GNP/MM), multi-walled carbon nanotubes and melamine (CNT/MM) and trinary composites containing GNP, CNT, and MM. Additionally, the manuscript presents results on the influence of structural factors for the electrochemical performance of carbon composites on their catalytic activity. This study contributes to the wide search and design of novel hybrid carbon composites for electrochemical applications. We demonstrate that intensive nitrogen atom insertion is not the governing factor since hybrid system modifications and porous structure sometimes play a more crucial role in the tailoring of electrochemical properties of the carbon hybrids seen as a noble metal-free alternative to traditional electrode materials. Additionally, HRTEM and Raman spectra study allowed for the evaluation of the quality of the obtained hybrid materials.

The Improvement of Energy Storage Performance by Sucrose-Derived Carbon Foams via Incorporating Nitrogen Atoms.

This paper addresses the problem of improving electrochemical energy storage with electrode materials obtained from common raw ingredients in a facile synthesis. In this study, we present a simple, one-pot route of synthesizing microporous carbon via a very fast reaction of sucrose and graphene (carbon source), chitosan (carbon and nitrogen source), and H3PO4. Porous carbons were successfully produced during high temperature carbonization, using nitrogen as a shielding gas. Samples were characterized using X-ray powder diffractometry, elemental analysis, N2 adsorption-desorption measurements, scanning electron microscopy, and Raman spectroscopy. The developed carbon material possessed a high surface area, up to 1313 m2 g-1, with no chemical or physical activators used in the process. The structural parameters of the microporous carbons varied depending on the ratio of reagents and mass composition. Samples were prepared both with and without chitosan. The present synthesis route has the advantages of being a single-step approach and only involving low-cost and environmentally friendly sources of carbon. More importantly, microporous carbon was prepared without any activators and potentially offers great application in supercapacitors. Cyclic voltammetry and constant current charge-discharge tests show that sucrose-based porous carbons show excellent electrochemical performance with a specific capacitance of up to 143 F g-1 at a current density of 1 A g-1 in a 6 M KOH electrolyte.

Green algae and gelatine derived nitrogen rich carbon as an outstanding competitor to Pt loaded carbon catalysts.

The development of effective catalysts for the oxygen reduction reaction (ORR) is a significant challenge in energy conversion systems, e.g., Zn-air batteries. Herein, green-algae- and gelatine-derived porous, nitrogen-rich carbons were extensively investigated as electrode materials for electrochemical catalytic reactions. These carbon-based catalysts were designed and optimized to create a metal-free catalyst via templating, carbonization, and subsequent removal of the template. The additional incorporation of graphene improved electronic conductivity and enhanced the electrochemical catalytic reaction. Porous carbons with heteroatoms were used as effective platinum-free ORR electrocatalysts for energy conversion; the presence of nitrogen in the carbon provided more active sites for ORR. Our catalyst also displayed notable durability in a rechargeable Zn-air battery energy system. More importantly, the nitrogen-containing porous carbons were found to have comparable ORR performance in alkaline media to commercially available electrocatalysts. The manuscript demonstrates that nitrogen atom insertion is an appropriate approach when aiming to eliminate noble metals from the synthesis route. N-doped carbons are competitive materials compared to reference platinum-based catalysts.

N-doped graphene foam obtained by microwave-assisted exfoliation of graphite.

The synthesis of metal-free but electrochemically active electrode materials, which could be an important contributor to environmental protection, is the key motivation for this research approach. The progress of graphene material science in recent decades has contributed to the further development of nanotechnology and material engineering. Due to the unique properties of graphene materials, they have found many practical applications: among others, as catalysts in metal-air batteries, supercapacitors, or fuel cells. In order to create an economical and efficient material for energy production and storage applications, researchers focused on the introduction of additional heteroatoms to the graphene structure. As solutions for functionalizing pristine graphene structures are very difficult to implement, this article presents a facile method of preparing nitrogen-doped graphene foam in a microwave reactor. The influence of solvent type and microwave reactor holding time was investigated. To characterize the elemental content and structural properties of the obtained N-doped graphene materials, methods such as elemental analysis, high-resolution transmission electron microscopy, scanning electron microscopy, and Raman spectroscopy were used. Electrochemical activity in ORR of the obtained materials was tested using cyclic voltamperometry (CV) and linear sweep voltamperometry (LSV). The tests proved the materials' high activity towards ORR, with the number of electrons reaching 3.46 for tested non-Pt materials, while the analogous value for the C-Pt (20 wt% loading) reference was 4.

Highly Effective Methods of Obtaining N-Doped Graphene by Gamma Irradiation.

The design and fabrication of a new effective manufacturing method of heteroatom-doped carbon materials is still ongoing. In this paper, we present alternative and facile methods to obtain N-rich graphene with the use of low energy gamma radiation. This method was used as a pure and facile method for altering the physical and chemical properties of graphene. The obtained materials have an exceptionally high N content-up to 4 wt %. (dry method) and up to 2 wt %. (wet method). High-resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectra and X-ray photoelectron spectroscopy (XPS) studies allowed us to evaluate the quality of the obtained materials. The presented results will provide new insights in designing and optimizing N-doped carbon materials potentially for the development of anode or cathode materials for electrochemical device applications, especially supercapacitors, metal-air batteries and fuel cells. Nitrogen atoms are exclusively bonded as quaternary groups. The method is expandable to the chemical insertion of other heteroatoms to graphene, especially such as sulfur, boron or phosphorus.

3D hierarchical porous hybrid nanostructure of carbon nanotubes and N-doped activated carbon.

In this work, carbon nanotubes (CNTs)/nitrogen-doped activated carbon (AC) hybrids were designed and fabricated using a facile and one-step synthesis. The synthesis of CNTs is based on the recently discovered phenomenon of thermally-induced polyfurfuryl alcohol (PFA) conversion. Hybrid materials are fabricated through the in-situ free growth of closed carbon nanotubes on low-cost activated carbon substrates which were obtained from green algae or amino acids. Herein, three types of carbon nanotubes were observed to freely grow on an activated carbon background from Chlorella vulgaris or L-lysine, types such as multiwalled carbon and bamboo-like nanotubes, whose structure depends on the background used and conditions of the synthesis. Structure type is identified by analyzing transmission electron microscopy images. HRTEM images reveal the tubes' outer diameter to be in the range of 20-120 nm. Because the carbon surface for the growth of carbon tubes contains nitrogen, the final hybrid materials also possess pyridinic-N and quaternary-N groups, as indicated by X-ray photoelectron spectra.

Synthesis of Hybrid Carbon Materials Consisting of N-Doped Microporous Carbon and Amorphous Carbon Nanotubes.

The N-doped hybrid carbon materials containing amorphous carbon nanotubes (ACNTs) were obtained by free growth of a polymer at 200 °C. The improvement of electrical conductivity was achieved by a final carbonization at 600-800 °C under the flow of nitrogen. The microstructure of ACNT/N-doped hybrids was characterized using a transmission electron microscope and X-ray diffusion. Furthermore, their elemental composition was measured using energy-dispersive X-ray spectroscopy and an elemental analyzer. The experimental results indicated that the ACNTs had a diameter in the range of 40-60 nm and the N-doped carbon background contained nitrogen atoms in most bonded pyrrolic-N and quaternary-N groups. The results revealed that the microstructure of the as-grown nanotubes, prepared by the proposed method, is mainly amorphous. This technique introduces the advantages of low cost and process simplicity, which may redeem some drawbacks of the methods commonly used in ACNT synthesis.

Improving the Performance of Zn-Air Batteries with N-Doped Electroexfoliated Graphene.

The constantly growing demand for active, durable, and low-cost electrocatalysts usable in energy storage devices, such as supercapacitors or electrodes in metal-air batteries, has triggered the rapid development of heteroatom-doped carbon materials, which would, among other things, exhibit high catalytic activity in the oxygen reduction reaction (ORR). In this article, a method of synthesizing nitrogen-doped graphene is proposed. Few-layered graphene sheets (FL-graphene) were prepared by electrochemical exfoliation of commercial graphite in a Na2SO4 electrolyte with added calcium carbonate as a separator of newly-exfoliated FL-graphene sheets. Exfoliated FL-graphene was impregnated with a suspension of green algae used as a nitrogen carrier. Impregnated FL-graphene was carbonized at a high temperature under the flow of nitrogen. The N-doped FL-graphene was characterized through instrumental methods: high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy. Electrochemical performance was determined using cyclic voltamperometry and linear sweep voltamperometry to check catalytic activity in ORR. The N-doped electroexfoliated FL-graphene obeyed the four-electron transfer pathways, leading us to further test these materials as electrode components in rechargeable zinc-air batteries. The obtained results for Zn-air batteries are very important for future development of industry, because the proposed graphene electrode materials do not contain any heavy and noble metals in their composition.