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18 pages, 6572 KiB

Open AccessArticle

Tuning Optical Excitations of Graphene Quantum Dots Through Selective Oxidation: Effect of Epoxy Groups

by Igor V. Ershov, Anatoly A. Lavrentyev, Dmitry L. Romanov and Olga M. Holodova

C 2025, 11(3), 51; https://doi.org/10.3390/c11030051 - 14 Jul 2025

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Graphene quantum dots (GQDs) have strong potential in optoelectronics, particularly in LEDs, photodetectors, solar cells, and nanophotonics. While challenges remain in efficiency and scalability, advances in functionalization and hybrid material integration could soon make them commercially viable for next-generation optoelectronic devices. In this [...] Read more.

Graphene quantum dots (GQDs) have strong potential in optoelectronics, particularly in LEDs, photodetectors, solar cells, and nanophotonics. While challenges remain in efficiency and scalability, advances in functionalization and hybrid material integration could soon make them commercially viable for next-generation optoelectronic devices. In this work, we assess the stability of various epoxy positions and their impact on the electronic and optical properties of GQDs. The oxygen binding energies and the potential barrier heights at different positions of epoxy groups at the edges and in the core of the GQD were estimated. The effect of possible transformations of epoxy groups into other edge configurations on the structural and optical properties of GQDs was evaluated. The results demonstrate that the functionalization of the GQD surface and edges with an epoxy groups at varying binding sites can result in substantial modification of the electronic structure and absorption properties of the GQDs. The prospects of low temperature annealing for controlling optical properties of epoxidized GQDs were discussed. The present computational work offers atomistic insights that can facilitate the rational design of optoelectronic systems based on GQD materials. Full article

(This article belongs to the Special Issue Carbon-Based Polymer Composites: Synthesis, Processing, Characterization and Applications (2nd Edition))

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18 pages, 1777 KiB

Open AccessReview

Biochar in Agriculture: A Review on Sources, Production, and Composites Related to Soil Fertility, Crop Productivity, and Environmental Sustainability

by Md. Muzammal Hoque, Biplob Kumar Saha, Antonio Scopa and Marios Drosos

C 2025, 11(3), 50; https://doi.org/10.3390/c11030050 - 11 Jul 2025

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Abstract

Due to soil nutrient depletion and rising food demand from an increasing global population, it is essential to find sustainable ways to boost crop yields, improve soil health, and address the environmental issues induced by agriculture. The most appropriate approach is to consider [...] Read more.

Due to soil nutrient depletion and rising food demand from an increasing global population, it is essential to find sustainable ways to boost crop yields, improve soil health, and address the environmental issues induced by agriculture. The most appropriate approach is to consider sustainable amendments, such as biochar and its derivatives, which are vital constituents of soil health due to their affordability, low reactivity, large surface area, and reduced carbon footprint. In this context, biochar and its derivatives in farming systems focus on improving soil structure, nutrient holding capacity, microbial activities, and the perpetuation of soil fertility. Despite its benefits, biochar, if it is used in high concentration, can sometimes become highly toxic, causing soil erosion due to reducing surface area, increasing pH levels, and altering soil properties. This review highlights the production methods and sources of feedstocks, emphasizing their important contribution to the soil’s physicochemical and biological properties. Furthermore, it critically evaluates the environmental applications and their impacts, providing data built upon the literature on contaminant removal from soil, economic factors, heavy metal immobilization, carbon sequestration, and climate resilience. This review emphasizes the main challenges and future prospects for biochar use in comparison to modified biochar (MB) to propose the best practices for sustainable farming systems. Full article

(This article belongs to the Special Issue Carbons for Health and Environmental Protection (2nd Edition))

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11 pages, 2969 KiB

Open AccessArticle

First-Principles Study of CO, C₂H₂, and C₂H₄ Adsorption on Penta-Graphene for Transformer Oil Gas Sensing Applications

by Min-Qi Zhu and Xue-Feng Wang

C 2025, 11(3), 49; https://doi.org/10.3390/c11030049 - 9 Jul 2025

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Abstract

Penta-graphene, a novel two-dimensional carbon allotrope entirely composed of pentagonal carbon rings, has attracted increasing attention due to its unique geometric structure, mechanical robustness, and intrinsic semiconducting nature. In this study, we systematically investigate the adsorption behavior of three typical dissolved gases in [...] Read more.

Penta-graphene, a novel two-dimensional carbon allotrope entirely composed of pentagonal carbon rings, has attracted increasing attention due to its unique geometric structure, mechanical robustness, and intrinsic semiconducting nature. In this study, we systematically investigate the adsorption behavior of three typical dissolved gases in transformer oil (CO, C₂H₂, and C₂H₄) on penta-graphene using first-principles calculations based on density functional theory. The optimized adsorption configuration, adsorption energy, charge transfer, adsorption distance, band structure, density of states, charge density difference, and desorption time are analyzed to evaluate the sensing capability of penta-graphene. Results reveal that penta-graphene exhibits moderate chemical interactions with CO and C₂H₂, accompanied by noticeable charge transfer and band structure changes, whereas C₂H₄ shows weaker physisorption characteristics. The projected density of states analysis further confirms the orbital hybridization between gas molecules and the substrate. Additionally, the desorption time calculations suggest that penta-graphene possesses good sensing and recovery potential, especially under elevated temperatures. These findings indicate that penta-graphene is a promising candidate for use in gas sensing applications related to the monitoring of dissolved gases in transformer oils. Full article

(This article belongs to the Special Issue Carbon and Related Composites for Sensors and Energy Storage: Synthesis, Properties, and Application (2nd Edition))

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19 pages, 2749 KiB

Open AccessArticle

Mechanism of Fluorescence Characteristics and Application of Zinc-Doped Carbon Dots Synthesized by Using Zinc Citrate Complexes as Precursors

by Yun Zhang, Yiwen Guo, Kaibo Sun, Xiaojing Li, Xiuhua Liu, Jinhua Zhu and Md. Zaved Hossain Khan

C 2025, 11(3), 48; https://doi.org/10.3390/c11030048 - 7 Jul 2025

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Abstract

Zn-doped carbon dots (Zn@C-210 calcination temperature at 210 °C and Zn@C-260 calcination temperature at 260 °C) were synthesized via an in situ calcination method using zinc citrate complexes as precursors, aiming to investigate the mechanisms of their distinctive fluorescence properties. A range of [...] Read more.

Zn-doped carbon dots (Zn@C-210 calcination temperature at 210 °C and Zn@C-260 calcination temperature at 260 °C) were synthesized via an in situ calcination method using zinc citrate complexes as precursors, aiming to investigate the mechanisms of their distinctive fluorescence properties. A range of analytical methods were employed to characterize these nanomaterials. The mechanism study revealed that the coordination structure of Zn-O, formed through zinc doping, can induce a metal–ligand charge-transfer effect, which significantly increases the probability of radiative transitions between the excited and ground states, thereby enhancing the fluorescence intensity. The Zn@C-210 in a solid state and Zn@C-260 in water exhibited approximately 71.50% and 21.1% quantum yields, respectively. Both Zn@C-210 and Zn@C-260 exhibited excitation-independent luminescence, featuring a long fluorescence lifetime of 6.5 μs for Zn@C-210 and 6.2 μs for Zn@C-260. Impressively, zinc-doped CDs displayed exceptional biosafety, showing no acute toxicity even at 1000 mg/kg doses. Zn@C-210 has excellent fluorescence in a solid state, showing promise in anti-photobleaching applications; meanwhile, the dual functionality of Zn@C-260 makes it useful as a folate sensor and cellular imaging probe. These findings not only advance the fundamental understanding of metal-doped carbon dot photophysics but also provide practical guidelines for developing targeted biomedical nanomaterials through rational surface engineering and doping strategies. Full article

(This article belongs to the Special Issue Carbon Nanohybrids for Biomedical Applications (2nd Edition))

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14 pages, 4383 KiB

Open AccessArticle

Optimized Adsorptive Desulfurization Using Waste Tire-Derived Carbon

by Ming-Liao Tsai, An-Ya Lo, Jun-Hao Liu and Yong-Ming Dai

C 2025, 11(3), 47; https://doi.org/10.3390/c11030047 - 7 Jul 2025

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Abstract

The inclusion of adsorption thermodynamic analysis and performance benchmarking with existing adsorbents reinforces both the theoretical significance and practical applicability of this study. The modified rubber-derived carbon demonstrated a remarkably high DBT adsorption capacity of 254.45 mg/g. These results establish it as a [...] Read more.

The inclusion of adsorption thermodynamic analysis and performance benchmarking with existing adsorbents reinforces both the theoretical significance and practical applicability of this study. The modified rubber-derived carbon demonstrated a remarkably high DBT adsorption capacity of 254.45 mg/g. These results establish it as a promising alternative to conventional materials such as commercial activated carbon, zeolites, and even metal–organic framework materials. In addition to confirming the superior performance of the adsorbent, the findings provide a deeper understanding of the DBT adsorption mechanism and offer a solid scientific basis for large-scale fuel desulfurization applications. This research highlights the potential of transforming end-of-life tire waste into value-added functional materials and contributes to the advancement of sustainable and efficient desulfurization technologies. Future work should focus on optimizing surface functionalization and regeneration strategies to further improve long-term adsorption stability and practical deployment. Full article

(This article belongs to the Special Issue Carbon Functionalization: From Synthesis to Applications)

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13 pages, 1309 KiB

Open AccessArticle

Thermal Conductivity of Graphene Moiré Superlattices at Small Twist Angles: An Approach-to-Equilibrium Molecular Dynamics and Boltzmann Transport Study

by Lorenzo Manunza, Riccardo Dettori, Antonio Cappai and Claudio Melis

C 2025, 11(3), 46; https://doi.org/10.3390/c11030046 - 30 Jun 2025

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Abstract

We investigate the thermal conductivity of graphene Moiré superlattices formed by twisting bilayer graphene (TBG) at small angles, employing approach-to-equilibrium molecular dynamics and lattice dynamics calculations based on the Boltzmann Transport Equation. Our simulations reveal a non-monotonic dependence of the thermal conductivity on [...] Read more.

We investigate the thermal conductivity of graphene Moiré superlattices formed by twisting bilayer graphene (TBG) at small angles, employing approach-to-equilibrium molecular dynamics and lattice dynamics calculations based on the Boltzmann Transport Equation. Our simulations reveal a non-monotonic dependence of the thermal conductivity on the twisting angle, with a local minimum near the first magic angle (

θ \sim

1.1°). This behavior is attributed to the evolution of local stacking configurations—AA, AB, and saddle-point (SP)—across the Moiré superlattice, which strongly affect phonon transport. A detailed analysis of phonon mean free paths (MFP) and mode-resolved thermal conductivity shows that AA stacking suppresses thermal transport, while AB and SP stackings exhibit enhanced conductivity owing to more efficient low-frequency phonon transport. Furthermore, we establish a direct correlation between the thermal conductivity of twisted structures and the relative abundance of stacking domains within the Moiré supercell. Our results demonstrate that even very small changes in twisting angle (<2°) can lead to thermal conductivity variations of over 30%, emphasizing the high tunability of thermal transport in TBG. Full article

(This article belongs to the Special Issue 10th Anniversary of C — Journal of Carbon Research)

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14 pages, 18495 KiB

Open AccessArticle

Analysis of Biochar–Cement Composites by SEM/EDS: Interfacial Interactions and Effects on Mechanical Strength

by Rafaela Paula, Jaqueline Carvalho, Antônio Júnior, Filipe Fagundes, Robson de Lima, Evaneide Lima, Carlos Oliveira, Magno de Oliveira, Augusto Bezerra, Osania Ferreira and Alan Machado

C 2025, 11(3), 45; https://doi.org/10.3390/c11030045 - 29 Jun 2025

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Abstract

Portland cement production is one of the main global sources of CO₂ emissions, driving the search for sustainable solutions to reduce its environmental footprint. This study evaluated the use of biochar derived from sugarcane bagasse as a partial cement replacement in cementitious [...] Read more.

Portland cement production is one of the main global sources of CO₂ emissions, driving the search for sustainable solutions to reduce its environmental footprint. This study evaluated the use of biochar derived from sugarcane bagasse as a partial cement replacement in cementitious composites, aiming to investigate its effects on mechanical and microstructural properties. Composites were prepared with 0, 2, and 5 (% w w⁻¹) biochar at two water-to-cement (w/c) ratios: 0.28 and 0.35. It was hypothesized that the porous structure and carbon-rich composition of biochar could enhance the microstructure of the cementitious matrix and contribute to strength development. Characterization of the biochar indicated compliance with the European Biochar Certificate (EBC) standard, high thermal stability, and notable water retention capacity. Mechanical testing revealed that incorporating 5% w w⁻¹ biochar increased compressive strength by up to 48% in the 0.35 w/c formulation compared to the control. Microstructural analyses (SEM/EDS) showed good interaction between the biochar and the cementitious matrix, with the formation of hydration products at the interfaces. The results confirm the potential of sugarcane bagasse biochar as a supplementary cementitious material, promoting more sustainable composites with improved mechanical performance and reduced environmental impact. Full article

(This article belongs to the Section Carbon Materials and Carbon Allotropes)

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18 pages, 1917 KiB

Open AccessArticle

Bimetallic Copper–Indium Co-Doped Titanium Dioxide Towards Electrosynthesis of Urea from Carbon Dioxide and Nitrate

by Youcai Meng, Tianran Wei, Zhiwei Wang, Caiyun Wang, Junyang Ding, Yang Luo and Xijun Liu

C 2025, 11(3), 44; https://doi.org/10.3390/c11030044 - 27 Jun 2025

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Abstract

Electrocatalytic urea synthesis offers great potential for sustainable strategies through CO₂ and NO₃⁻ reduction reactions. However, the development of high-performance catalysts is often hampered by the complexity of synthetic methodologies and the unresolved nature of C-N coupling pathways. In this [...] Read more.

Electrocatalytic urea synthesis offers great potential for sustainable strategies through CO₂ and NO₃⁻ reduction reactions. However, the development of high-performance catalysts is often hampered by the complexity of synthetic methodologies and the unresolved nature of C-N coupling pathways. In this study, we present a copper–indium co-doped titanium dioxide (CuIn-TiO₂) catalyst that exhibits remarkable efficacy in enhancing the synergistic reduction of CO₂ and NO₃⁻ to produce urea. The bimetallic CuIn site functions as the primary active site for the C-N coupling reaction, achieving a urea yield rate of 411.8 μg h⁻¹ mg_cat⁻¹ with a Faradaic efficiency of 6.7% at −0.8 V versus reversible hydrogen electrode (vs. RHE). A body of experimental and theoretical research has demonstrated that the nanoscale particles enhance the density of active sites and improve the feasibility of reactions on the surface of TiO₂. The co-doping of Cu and In has been shown to significantly enhance electronic conductivity, increase the adsorption affinity for *CO₂ and *NO₃⁻, and promote the C-N coupling process. The CuIn-TiO₂ catalyst has been demonstrated to effectively promote the reduction of NO₃⁻ and CO₂, as well as accelerate the C-N coupling reaction. This effect is a result of a synergistic interaction among the catalyst’s components. Full article

(This article belongs to the Special Issue 10th Anniversary of C — Journal of Carbon Research)

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10 pages, 1436 KiB

Open AccessArticle

Theoretical Investigation of O₂ and CO₂ Adsorption on Small PdNi Clusters Supported on N-Doped Graphene Quantum Dots

by Brenda García-Hilerio, Lidia Santiago-Silva, Pastor T. Matadamas-Ortiz, Alejandro Gomez-Sanchez, Víctor A. Franco-Luján and Heriberto Cruz-Martínez

C 2025, 11(3), 43; https://doi.org/10.3390/c11030043 - 27 Jun 2025

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Abstract

A density functional theory (DFT) investigation was conducted to study the O₂ and CO₂ adsorption on very small Pd_3−nNi_n (n = 0–2) clusters supported on N-doped graphene quantum dots (N-GQDs). The study was carried out in two stages. [...] Read more.

A density functional theory (DFT) investigation was conducted to study the O₂ and CO₂ adsorption on very small Pd_3−nNi_n (n = 0–2) clusters supported on N-doped graphene quantum dots (N-GQDs). The study was carried out in two stages. First, the interaction between Pd_3−nNi_n (n = 0–2) clusters and N-GQDs was analyzed. Subsequently, the adsorption behavior of O₂ and CO₂ molecules on the supported clusters was examined. The calculated interaction energies (E_int) of Pd_3−nNi_n (n = 0–2) clusters on N-GQDs were found to be higher than those on pristine graphene, indicating enhanced cluster stability on N-GQDs. Furthermore, the adsorption energies (E_ads) of the O₂ molecule on the Pd₃ and Pd₂Ni clusters deposited on N-GQDs were similar. Meanwhile, the PdNi₂ cluster deposited on N-GQDs exhibited the highest E_ads (−1.740). The E_ads of CO₂ on Pd_3−nNi_n (n = 0–2) clusters embedded in N-GQDs were observed to be close to or exceed 1 eV. Upon adsorption of O₂ and CO₂ on the Pd_3−nNi_n (n = 0–2) clusters supported on N-GQDs, an elongation of the O–O and C–O bond lengths was observed, respectively. This structural change may facilitate the dissociation of these molecules on the supported clusters. Full article

(This article belongs to the Section Carbon Materials and Carbon Allotropes)

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14 pages, 61510 KiB

Open AccessArticle

Enhancing High-Temperature Oxidation Stability of Recycled Carbon Fibers Through Ceramic Coating

by Carmela Borriello, Sabrina Portofino, Loredana Tammaro, Pierpaolo Iovane, Gabriella Rametta and Sergio Galvagno

C 2025, 11(3), 42; https://doi.org/10.3390/c11030042 - 26 Jun 2025

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Abstract

Carbon fiber-reinforced composites (CFRCs) have attracted considerable attention in recent years due to their excellent properties, enabling their use across various sectors. However, their application at high temperatures is limited by the fibers’ lack of oxidation resistance. This study demonstrates a significant advancement [...] Read more.

Carbon fiber-reinforced composites (CFRCs) have attracted considerable attention in recent years due to their excellent properties, enabling their use across various sectors. However, their application at high temperatures is limited by the fibers’ lack of oxidation resistance. This study demonstrates a significant advancement in enhancing the oxidation stability performance of carbon fiber-reinforced composites (CFRCs) by developing a silicon carbide (SiC) coating through the ceramization of carbon fibers using silicon (Si) powder. For the first time, this method was applied to recycled carbon fibers from CF thermoplastic composites. The key findings include the successful formation of a uniform SiC coating, with coating thickness increasing with process duration and decreasing at higher temperatures. The treated fibers exhibited substantially improved oxidation resistance, maintaining structural stability above 700 °C—markedly better than that of their uncoated counterparts. Thermogravimetric analysis confirmed that oxidation resistance varied depending on the CF/Si ratio, highlighting this parameter’s critical role. Overall, this study offers a viable pathway to enhance the thermal durability of recycled carbon fibers for high-temperature applications. Full article

(This article belongs to the Special Issue High-Performance Carbon Materials and Their Composites (2nd Edition))

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13 pages, 6606 KiB

Open AccessArticle

Preparation and Properties of C/C-(TiZrHfNbTa)C Composites via Inorganic Salt Precursor Method

by Haibo Ouyang, Jiyong Liu, Cuiyan Li, Tianzhan Shen, Jiaqi Liu, Mengyao He, Yanlei Li and Leer Bao

C 2025, 11(3), 41; https://doi.org/10.3390/c11030041 - 25 Jun 2025

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Abstract

Using low-cost transition-metal chlorides and furfuryl alcohol as raw materials, the (TiZrHfNbTa)C precursor was prepared, and a three-dimensional braided carbon fiber preform (C/C) coated with pyrolytic carbon (PyC) was used as the reinforcing material. A C/C-(TiZrHfNbTa)C composite was successfully fabricated through the precursor [...] Read more.

Using low-cost transition-metal chlorides and furfuryl alcohol as raw materials, the (TiZrHfNbTa)C precursor was prepared, and a three-dimensional braided carbon fiber preform (C/C) coated with pyrolytic carbon (PyC) was used as the reinforcing material. A C/C-(TiZrHfNbTa)C composite was successfully fabricated through the precursor impregnation pyrolysis (PIP) process. Under extreme oxyacetylene ablation conditions (2311 °C/60 s), this composite material demonstrated outstanding ablation resistance, with a mass ablation rate as low as 0.67 mg/s and a linear ablation rate of only 20 μm/s. This excellent performance can be attributed to the dense (HfZr)₆(TaNb)₂O₁₇ oxide layer formed during ablation. This oxide layer not only has an excellent anti-erosion capability but also effectively acts as an oxygen diffusion barrier, thereby significantly suppressing further ablation and oxidation within the matrix. This study provides an innovative strategy for the development of low-cost ultra-high-temperature ceramic precursors and opens up a feasible path for the efficient preparation of C/C-(TiZrHfNbTa)C composites. Full article

(This article belongs to the Special Issue High-Performance Carbon Materials and Their Composites (2nd Edition))

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17 pages, 5479 KiB

Open AccessArticle

Fracture Mechanics of Tetragraphene: Effects of Structural Variations and Loading Conditions

by Elnaz Haddadi and Alireza Tabarraei

C 2025, 11(3), 40; https://doi.org/10.3390/c11030040 - 24 Jun 2025

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Abstract

Despite the promising electronic properties of graphene, its lack of an intrinsic bandgap limits its applicability in semiconductor technologies. This has catalyzed the investigation of newly developed two-dimensional carbon materials, including tetragraphene (TG), a quasi-2D semiconducting material featuring a combination of hexagonal and [...] Read more.

Despite the promising electronic properties of graphene, its lack of an intrinsic bandgap limits its applicability in semiconductor technologies. This has catalyzed the investigation of newly developed two-dimensional carbon materials, including tetragraphene (TG), a quasi-2D semiconducting material featuring a combination of hexagonal and tetragonal rings. This study aims to investigate the mechanical and fracture behaviors of TG using density functional theory (DFT) and molecular dynamics (MD) simulations, studying two distinct atomic configurations of tetragraphene. DFT simulations assess the mechanical properties, while MD simulations explore the fracture dynamics subjected to mixed mode I (opening mode) and mode II (in-plane shear mode) loading. Our analysis focuses on the influence of loading phase angle, crack edge chirality, crack tip configuration, and temperature on crack propagation paths and critical stress intensity factors (SIFs) in TG structures. Our results show that the critical SIF varies by 12.5–21% depending on the crack chirality. Across all loading conditions, increasing the temperature ranging from 300 K to 2000 K reduces the critical SIF by 10–45%, with the largest reductions observed under pure mode I loading. These outcomes offer important insights into the structural integrity of TG and inform its potential integration into flexible nanoelectronic devices, where mechanical reliability is essential. Full article

(This article belongs to the Special Issue 10th Anniversary of C — Journal of Carbon Research)

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