Editorial

3 pages, 552 KiB

Open AccessEditorial

Graphene-Based Materials, Their Composites, and Potential Applications

by Maria Cristina Ramirez and Maria Isabel Osendi

Materials 2022, 15(20), 7184; https://doi.org/10.3390/ma15207184 - 15 Oct 2022

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Since its isolation in 2004, monolayer graphene has attracted enormous attention within the scientific community, the industry, and the general public owing to its exceptional properties (electrical, optical, thermal, and mechanical) and prospects [...] Full article

(This article belongs to the Special Issue Graphene-Based Materials, Their Composites and Potential Applications )

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Research

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16 pages, 6406 KiB

Open AccessArticle

Tribochemical Interactions between Graphene and ZDDP in Friction Tests for Uncoated and W-DLC-Coated HS6-5-2C Steel

by Joanna Kowalczyk, Monika Madej, Wojciech Dzięgielewski, Andrzej Kulczycki, Magdalena Żółty and Dariusz Ozimina

Materials 2021, 14(13), 3529; https://doi.org/10.3390/ma14133529 - 24 Jun 2021

Cited by 9 | Viewed by 1643

Abstract

If a lubricant contains structures capable of conducting energy, reactions involving zinc dialkyldithiophosphate (ZDDP) may take place both very close to and away from the solid surfaces, with this indicating that ZDDP can be a highly effective anti-wear (AW) additive. The central thesis [...] Read more.

If a lubricant contains structures capable of conducting energy, reactions involving zinc dialkyldithiophosphate (ZDDP) may take place both very close to and away from the solid surfaces, with this indicating that ZDDP can be a highly effective anti-wear (AW) additive. The central thesis of this article is that the tribocatalytic effect is observed only when the energy emitted by the solids is transmitted by ordered molecular structures present in the lubricant, e.g., graphene. The friction tests were carried out for 100Cr6 steel balls in a sliding contact with uncoated or W-DLC-coated HS6-5-2C steel discs in the presence of polyalphaolefin 8 (PAO 8) as the lubricant, which was enhanced with graphene and/or ZDDP. There is sufficient evidence of the interactions occurring between ZDDP and graphene and their effects on the tribological performance of the system. It was also found that the higher the concentration of zinc in the wear area, the lower the wear. This was probably due to the energy transfer resulting from the catalytic decomposition of ZDDP molecules. Graphene, playing the role of the catalyst, contributed to that energy transfer. Full article

(This article belongs to the Special Issue Graphene-Based Materials, Their Composites and Potential Applications )

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13 pages, 23791 KiB

Open AccessArticle

Thermal Transport and Thermoelectric Effect in Composites of Alumina and Graphene-Augmented Alumina Nanofibers

by Ali Saffar Shamshirgar, Manuel Belmonte, Girish C. Tewari, Rocío E. Rojas Hernández, Jani Seitsonen, Roman Ivanov, Maarit Karppinen, Pilar Miranzo and Irina Hussainova

Materials 2021, 14(9), 2242; https://doi.org/10.3390/ma14092242 - 27 Apr 2021

Cited by 6 | Viewed by 2709

Abstract

The remarkable tunability of 2D carbon structures combined with their non-toxicity renders them interesting candidates for thermoelectric applications. Despite some limitations related to their high thermal conductivity and low Seebeck coefficients, several other unique properties of the graphene-like structures could out-weight these weaknesses [...] Read more.

The remarkable tunability of 2D carbon structures combined with their non-toxicity renders them interesting candidates for thermoelectric applications. Despite some limitations related to their high thermal conductivity and low Seebeck coefficients, several other unique properties of the graphene-like structures could out-weight these weaknesses in some applications. In this study, hybrid structures of alumina ceramics and graphene encapsulated alumina nanofibers are processed by spark plasma sintering to exploit advantages of thermoelectric properties of graphene and high stiffness of alumina. The paper focuses on thermal and electronic transport properties of the systems with varying content of nanofillers (1–25 wt.%) and demonstrates an increase of the Seebeck coefficient and a reduction of the thermal conductivity with an increase in filler content. As a result, the highest thermoelectric figure of merit is achieved in a sample with 25 wt.% of the fillers corresponding to ~3 wt.% of graphene content. The graphene encapsulated nanofibrous fillers, thus, show promising potential for thermoelectric material designs by tuning their properties via carrier density modification and Fermi engineering through doping. Full article

(This article belongs to the Special Issue Graphene-Based Materials, Their Composites and Potential Applications )

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13 pages, 5999 KiB

Open AccessArticle

Reinforced 3D Composite Structures of γ-, α-Al₂O₃ with Carbon Nanotubes and Reduced GO Ribbons Printed from Boehmite Gels

by Cristina Ramírez, Manuel Belmonte, Pilar Miranzo and Maria Isabel Osendi

Materials 2021, 14(9), 2111; https://doi.org/10.3390/ma14092111 - 22 Apr 2021

Cited by 11 | Viewed by 2082

Abstract

The ability of boehmite to form printable inks has sparked interest in the manufacturing of 3D alumina (Al₂O₃) and composite structures by enabling direct ink writing methods while avoiding the use of printing additives. These materials may exhibit high [...] Read more.

The ability of boehmite to form printable inks has sparked interest in the manufacturing of 3D alumina (Al₂O₃) and composite structures by enabling direct ink writing methods while avoiding the use of printing additives. These materials may exhibit high porosity due to the printing and sintering procedures, depending on the intended application. The 3D-printed porous composite structures of γ-Al₂O₃ and α-Al₂O₃ containing 2 wt.% of carbon nanotubes or reduced graphene oxide ribbons were fabricated from boehmite gels, followed by different heat treatments. The reinforcing effect of these carbon nanostructures was evidenced by compression tests carried out on the different alumina structures. A maximum relative increase of 50% in compressive strength was achieved for the γ-Al₂O₃ composite structure reinforced with reduced graphene oxide ribbons, which was also accompanied by an increase in the specific surface area. Full article

(This article belongs to the Special Issue Graphene-Based Materials, Their Composites and Potential Applications )

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17 pages, 6538 KiB

Open AccessArticle

Tribological Performance of Graphite Nanoplatelets Reinforced Al and Al/Al₂O₃ Self-Lubricating Composites

by Emad Omrani, Afsaneh Dorri Moghadam, Ashish K. Kasar, Pradeep Rohatgi and Pradeep L. Menezes

Materials 2021, 14(5), 1183; https://doi.org/10.3390/ma14051183 - 03 Mar 2021

Cited by 22 | Viewed by 3368

Abstract

In the present work, the effect of graphite nanoplatelets (GNPs) on tribological properties of the aluminum (Al), and Al/alumina (Al₂O₃) composite are studied. GNPs are multilayer graphene sheets which were used as a solid lubricant material. Two sets of [...] Read more.

In the present work, the effect of graphite nanoplatelets (GNPs) on tribological properties of the aluminum (Al), and Al/alumina (Al₂O₃) composite are studied. GNPs are multilayer graphene sheets which were used as a solid lubricant material. Two sets of composites, Al/GNPs and Al/GNPs/Al₂O₃ with varying amounts of reinforcements, were synthesized by powder metallurgy that involves cold compaction followed by hot compaction. The hardness of the composites increased with the addition of GNPs and Al₂O₃. The Al/GNPs composite with 1 wt.% of GNPs (Al/1GNPs) showed a 20% increase in hardness whereas Al/GNPs/ Al₂O₃ composite with 1 wt.% GNPs and 2 wt.% Al₂O₃ (Al/1GNPs/2Al₂O₃) showed 27% increases in hardness compared to the pure Al. The coefficient of friction measured at 20 N was observed to be 22% and 53% lesser for Al/1GNPs and Al/1GNPs/2Al₂O₃, respectively, compared to corresponding alloys without graphene Al. The X-ray diffraction and scanning electron microscopy analysis revealed the presence of GNPs at the worn surface after the tribology tests. The wear rate was also reduced significantly. In comparison with pure Al, the Al/1GNPs and Al/1GNPs/2Al₂O₃ composites resulted in 5- and 20-times lesser wear rate, respectively. The addition of Al₂O₃ caused reduction in wear rate due to higher hardness and load carrying ability, whereas composites with more than 1 wt.% GNPs showed higher wear rate due to lower hardness and higher porosity. The Al/1GNPs/2Al₂O₃ composite exhibited the least coefficient of friction (0.2–0.25) and wear rate (1 × 10⁻⁶–4 × 10⁻⁶ mm³/N.m) compared to other GNPs and Al₂O₃ reinforced Al composites. The worn surfaces were further analyzed to understand the wear mechanism by Raman spectroscopy, transmission electron microscopy, and x-ray diffraction to detect the Al₄C₃ phase formation, chemical bonding, and defect formation in graphene. Full article

(This article belongs to the Special Issue Graphene-Based Materials, Their Composites and Potential Applications )

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11 pages, 3910 KiB

Open AccessArticle

Highly Selective Fluorescence Sensor Based on Graphene Quantum Dots for Sulfamethoxazole Determination

by Thi Hoa Le, Hyun Jong Lee, Ji Hyeon Kim and Sang Joon Park

Materials 2020, 13(11), 2521; https://doi.org/10.3390/ma13112521 - 01 Jun 2020

Cited by 12 | Viewed by 3175

Abstract

In our research, a reliable fluorescence sensor for the detection of sulfamethoxazole (SMZ) was developed. This method relies on graphene quantum dots (GQDs) entrapped in a silica molecularly imprinted polymer (GQDs@SMIP), which was synthesized by the polymerization using GQDs, SMZ, tetraethoxysilane (TEOS) and [...] Read more.

In our research, a reliable fluorescence sensor for the detection of sulfamethoxazole (SMZ) was developed. This method relies on graphene quantum dots (GQDs) entrapped in a silica molecularly imprinted polymer (GQDs@SMIP), which was synthesized by the polymerization using GQDs, SMZ, tetraethoxysilane (TEOS) and 3-aminopropyltriethoxysilane (APTES) as fluorescence material, template, cross-linker, and functional monomers, respectively. The GQDs@SMIP was characterized by fluorometry, Fourier-transform infrared spectroscopy, transmission and scanning electron microscopies, X-ray photoelectron spectroscopy, and powder X-ray diffraction. The GQDs@SMIP exhibited a good capacity to absorb SMZ from solution, which resulted in the quenching of the GQD fluorescence intensity. The intensity of GQDs@SMIP decreased linearly with the SMZ concentration in the range of 1 to 100 µM with a correlation coefficient of 0.99537. In addition, the fluorescence responses of GQDs@SMIP to interfering substances were investigated. The results indicated that there was no effect of interfering substances on SMZ detection. Thus, the highly selective GQDs@SMIP fluorescence sensor is an effective and promising device for SMZ detection and analysis. Full article

(This article belongs to the Special Issue Graphene-Based Materials, Their Composites and Potential Applications )

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Review

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62 pages, 12239 KiB

Open AccessReview

Applications of Ceramic/Graphene Composites and Hybrids

by Cristina Ramírez, Manuel Belmonte, Pilar Miranzo and Maria Isabel Osendi

Materials 2021, 14(8), 2071; https://doi.org/10.3390/ma14082071 - 20 Apr 2021

Cited by 29 | Viewed by 5667

Abstract

Research activity on ceramic/graphene composites and hybrids has increased dramatically in the last decade. In this review, we provide an overview of recent contributions involving ceramics, graphene, and graphene-related materials (GRM, i.e., graphene oxide, reduced graphene oxide, and graphene nanoplatelets) with a primary [...] Read more.

Research activity on ceramic/graphene composites and hybrids has increased dramatically in the last decade. In this review, we provide an overview of recent contributions involving ceramics, graphene, and graphene-related materials (GRM, i.e., graphene oxide, reduced graphene oxide, and graphene nanoplatelets) with a primary focus on applications. We have adopted a broad scope of the term ceramics, therefore including some applications of GRM with certain metal oxides and cement-based matrices in the review. Applications of ceramic/graphene hybrids and composites cover many different areas, in particular, energy production and storage (batteries, supercapacitors, solar and fuel cells), energy harvesting, sensors and biosensors, electromagnetic interference shielding, biomaterials, thermal management (heat dissipation and heat conduction functions), engineering components, catalysts, etc. A section on ceramic/GRM composites processed by additive manufacturing methods is included due to their industrial potential and waste reduction capability. All these applications of ceramic/graphene composites and hybrids are listed and mentioned in the present review, ending with the authors’ outlook of those that seem most promising, based on the research efforts carried out in this field. Full article

(This article belongs to the Special Issue Graphene-Based Materials, Their Composites and Potential Applications )

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26 pages, 5417 KiB

Open AccessReview

Recent Trends and Developments in Graphene/Conducting Polymer Nanocomposites Chemiresistive Sensors

by Golnoush Zamiri and A. S. M. A. Haseeb

Materials 2020, 13(15), 3311; https://doi.org/10.3390/ma13153311 - 24 Jul 2020

Cited by 44 | Viewed by 5241

Abstract

The use of graphene and its derivatives with excellent characteristics such as good electrical and mechanical properties and large specific surface area has gained the attention of researchers. Recently, novel nanocomposite materials based on graphene and conducting polymers including polyaniline (PANi), polypyrrole (PPy), [...] Read more.

The use of graphene and its derivatives with excellent characteristics such as good electrical and mechanical properties and large specific surface area has gained the attention of researchers. Recently, novel nanocomposite materials based on graphene and conducting polymers including polyaniline (PANi), polypyrrole (PPy), poly (3,4 ethyldioxythiophene) (PEDOT), polythiophene (PTh), and their derivatives have been widely used as active materials in gas sensing due to their unique electrical conductivity, redox property, and good operation at room temperature. Mixing these two materials exhibited better sensing performance compared to pure graphene and conductive polymers. This may be attributed to the large specific surface area of the nanocomposites, and also the synergistic effect between graphene and conducting polymers. A variety of graphene and conducting polymer nanocomposite preparation methods such as in situ polymerization, electropolymerization, solution mixing, self-assembly approach, etc. have been reported and utilization of these nanocomposites as sensing materials has been proven effective in improving the performance of gas sensors. Review of the recent research efforts and developments in the fabrication and application of graphene and conducting polymer nanocomposites for gas sensing is the aim of this review paper. Full article

(This article belongs to the Special Issue Graphene-Based Materials, Their Composites and Potential Applications )

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