Carbon Letters最新文献

Considering the intrinsic activity of non-precious metal oxygen reduction reaction (ORR) catalysts is typically lower than that of precious metal catalysts, it is crucial to focus on the rational design of their micro-morphology and active site. This paper employed a simple molten salt-mediated template method to fabricate a Fe₃C composite N-doped C catalyst with a layered porous framework (Fe₃C@NC). Tannic acid was utilized to form a strong coordination with iron to limit the grain size of Fe₃C nanocrystals generated by high-temperature pyrolysis. Moreover, urea achieved nitrogen doping in tannic acid-derived porous carbon, while the graphite phase nitrogen-doped carbon (g-C₃N₄) formed by its pyrolysis, together with the molten salt-mediated environment, jointly controlled the two-dimensional sheet-like structure of the material. The optimized Fe₃C@NC-800 demonstrated efficient ORR performance, with an ORR half-wave potential of 0.883 V. Its application as a cathode catalyst in a liquid zinc-air battery (ZABs) exhibits a maximum power density of 211.5 mW cm⁻², surpassing that of a Pt/C-based ZAB and indicating the potential practical utility of this material.

Segregated composites, where fillers are selectively placed at the matrix interface to form a segregated filler network, are attracting attention because they can provide excellent conductive properties at low filler content. In this study, the anisotropic enhancement in thermal conductivity of composites was discovered due to the unique structure of the segregated network. The segregated composites were produced using a typical mechanical mixing of matrix pellets and the internal structure was precisely analyzed using three-dimensional non-destructive analysis. The segregated composites slightly improved in the through-plane thermal conductivity, but the in-plane thermal conductivity increased rapidly, showing the anisotropic thermal conductivity. The maximum improvement in the in-plane thermal conductivity of the segregated composites increased by 112.5 (at 7 wt% graphene nanoplatelet) and 71.4% (at 10 wt% multi-walled carbon nanotube), respectively, compared to that of the random composites filled with the same amount of filler. On the other hand, the electrical conductivity of the segregated composites was isotropic due to the difference in the transport mechanisms of electrons and phonons. The anisotropic thermal conductivity developed by the segregated network was helpful in inducing effective heat dissipation of commercial smartphone logic boards.

The structure and composition of coal tar pitch are critical in the production of superior needle coke. We used high-temperature refined coal tar pitch (HRCTP) to modify medium–low-temperature refined coal tar pitch (MLRCTP) for needle coke preparation. Various characterization techniques were applied to evaluate the effects of the HRCTP addition on the MLRCTP's structure and composition, and to investigate the microstructural and crystallographic differences in needle coke from different feedstocks. We identified the optimal HRCTP addition level and assessed how carbonization reaction conditions influenced needle coke quality. The findings indicated that HRCTP addition increased the aromatic hydrocarbons content while reducing the heterocyclic compounds and excess alkanes, leading to enhanced structure and composition, which supported the structured development of carbon-based structures during the thermal polycondensation process. Notably, higher HRCTP amounts did not equate to better outcomes. With a 25% HRCTP additive level, the needle coke’s microstructure showed a highly ordered fibrous texture with optimal orientation, the greatest degree of graphitization, and a mature graphite crystal content of 24.84%. Further optimization of the carbonization process demonstrated that very high temperatures might cause the formation of numerous mosaic structures due to disordered radical cross-linking. Properly reducing pressure at high temperatures could promote adequate directional airflow and apply shear force during orderly stacking of the mesophase, thus enhancing the carbon lamellae’s streamline and orientation. Following the carbonization process optimization, the mature graphite crystal content in the needle coke increased from 24.84% to 39.87%.

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We report the simple one-step hydrothermal green synthesis of carbon dots (CDs) without any chemical reagents using mangosteen pulp (CDs1), peel (CDs2), and leaf (CDs3) extract as a green carbon source. In the aqueous medium, these CDs had a size of 8–15 nm with an energy gap of about 4 eV. The CDs emitted a bright green color under ultraviolet (UV) irritation with an average fluorescence quantum yield of the CDs of 1.6%. Moreover, the CDs contained various functional groups, such as C = C, C–C, C–O–C, C–O, C = O, C–H, and O–H, which were beneficial for enhancing their fluorescence property. Furthermore, the CDs were applied in the stain fluorescent imaging of myosatellite chicken stem cells and Vero cells. The CDs2 and CDs3 induced a strong fluorescence emission intensity of the strain cells, whereas CDs1 acted as the highest potential enhancer in cell proliferation as confirmed by its cellular viability which was the around four times that of the control. Therefore, the CDs were highly biocompatible and acted as enhancers in cell proliferation in myosatellite chicken stem cells and Vero cells. Thus, simple, cost-effective, scalable, and green synthetic approach-based CDs show promise for the development of selective organelle labeling and optical sensing probes.

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Concentration-dependent multicolor emission is an unusual yet appealing photoluminescence property of various carbonaceous nanomaterials with interesting potential applications. While carbon dots (CDs) are no exception, the predictability and tuning of the microenvironment of CD to make it suitable for displaying concentration-dependent multicolor emission is far from adequately understood. Through the novel synthesis of bromine-doped CDs (Br-CDs) via controlled hydrothermal pyrolysis, we demonstrate the capacity of the same Br-CD to emit intense red (650 nm) as well as blue fluorescence (410 nm) including intermittent colors as a function of concentration and excitation wavelength. The concentration-dependent morphological transition of the Br-CDs was ascertained using electron microscopy shedding light on their optical evolution in response to concentration changes. The phenomenon is validated as being driven by unique rearrangement and surface functionality modulation, which is essentially linked to the concentration of CD in an ensemble. Notably, the synthesized Br-CDs displayed excellent enzyme-mimicking abilities where oxidase-like activity was assessed using a tetramethylbenzidine (TMB) substrate under visible light (LED, 23W), and peroxidase-like activity was evaluated with TMB and H₂O₂ over a wide range of pH and temperature. The visible-light-triggered generation of Reactive Oxygen Species (ROS) by Br-CDs proved to be an effective antibacterial agent demonstrating a significant eradication rate against both Gram-positive and Gram-negative bacteria. A captivating and unusual photophysical phenomenon is exhibited by Br-CD, showcasing their versatile applications in nanozymes and antibacterial interventions where emission color directly links to the activity eliminating the necessity of multiple titrations to determine concentration/units/dosage.

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Photocatalysis technology including hydrogen evolution from water splitting, CO₂ reduction and N₂ conversion to ammonia emerges as a significant approach for energy crisis and environmental pollution. For these conventional semiconductors such as TiO₂, ZnO, WO₃, CdS and g-C₃N₄, however, inefficient photoabsorption, rapid recombination of photogenerated carriers, and inadequate surface reactive sites hamper the photoinduced activity and stability. Defect engineering, especially oxygen vacancy, has recently drawn the attention of a number of investigators primarily in connection with its feasibility of regulatability, identifiability and effectiveness. A series of ferroelectric and piezoelectric semiconductors, with internal electric field generated by the polarization, are considered an excellent candidate for replacement of conventional semiconductors, because the observed charge separation ability of those is far from theoretical expectation. With the boost of oxygen vacancy, polarization behavior can be effectively regulated to further improve photocatalytic performance. Related studies based on the above background are the current hotspot of photocatalysis; this paper reviews the latest research progress of ferroelectric and piezoelectric photocatalysts with oxygen vacancy. Starting from the generation of oxygen vacancies, five preparation strategy including ion doping, thermal treatment, chemical reduction, ultraviolet irradiation, and plasma etching are introduced; advanced characterization are summarized in classification of spectroscopy, energy spectrum, electron microscopy, density function theory and in situ techniques. Secondly, the mechanism of oxygen vacancy regulated polarization and their synergistic photocatalytic reactions are reviewed and summarized. Finally, an overview on the prospect of advanced photocatalytic engineering concerned to oxygen vacancies involved ferroelectric and piezoelectric photocatalysts is proposed.

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Thermal decomposition of low-density polyethylene (LDPE) was monitored by thermogravimetry under N₂ atmosphere in the presence of solid acid catalysts such as alumina (α-Al₂O₃, γ-Al₂O₃), crystalline silica-alumina (SA, molar ratio of Si/Al = 0.19) and amorphous silica-alumina catalysts (ASA, molar ratio of Si/Al = 4.9). Crystal structure and surface area of solid acid catalysts were measured by XRD and BET, respectively. The strength and distribution of acid sites of solid acid catalysts were estimated by NH₃-TPD. It was observed that total acidity strength is in the order of ASA (1.77 μmmol NH₃/g) > AS (1.42 μmol NH₃/g) > γ-Al₂O₃ (1.06 μmol NH₃/g) > α-Al₂O₃ (0.06 μmol NH₃/g). Thermal degradation behavior of LDPE with and without solid acid catalyst was monitored by TGA, where heating rates (β) of 5, 10, and 20 °C/min were employed under an inert atmosphere, and their activation energies (E_a), onset temperatures (T_initial), decomposition temperatures (T_decomp) were calculated and compared. The activation energy (E_a) was evaluated using the Coats-Redfern method. Solid acid catalysts with stronger acidity and higher surface area showed a decrease in activation energy and onset temperature. Activation energy of LDPE over ASA catalyst is decreased to 97.3 kJ/mol from thermal decomposition of LDPE without catalyst of 117.2 kJ/mol under heating rate of 10 °C/min. The isothermal decomposition of LDPE was monitored at 300 °C for 3 h with a heating rate of 10 °C/min, where 13.1% and 24.2% wt. loss were observed over SA and ASA, respectively, while only 0.7% wt. loss was observed for LDPE without a solid acid catalyst.

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Single step decomposition of LDPE

Thermal degradation behavior of LDPE monitored by TGA, with different heating rates (β) of 5, 10, 20 °C/min.

The damage caused by water pollution has seriously affected human health, in which nitrate is difficult to remove effectively because of its stability and solubility in the water environment. Among the various technologies for nitrate removal, electrocatalytic conversion of nitrate to ammonia is one of the best choice because of its green and efficient nature as well as its ability to “turn waste into treasure”. In recent years, the development of high-performance electrocatalysts to promote the activity of electrocatalytic nitrate reduction (NO₃RR) has received extensive attention from researchers. Among various electrocatalytic materials for NO₃RR, carbon-based catalysts have become a promising electrocatalyst due to the advantages of affordable price, controllable structure, excellent stability and exceptional reactivity. Focusing on the carbon-based materials, this review summarizes the research progress of carbon-based catalysts for NO₃RR in recent years, including heteroatom-doped carbon-based catalysts as well as metal and metal oxide-loaded or modified carbon-based catalysts. Opinions on the current challenges and future research directions of carbon-based catalysts for NO₃RR are also presented. This review hopes to provide some references and principles for the design and preparation of carbon-based catalysts for high-performanceNO₃RR process.

Three-dimensional printed polycaprolactone/β-tricalcium phosphate (PCL/β-TCP) scaffolds reinforced with carbon nanotubes (CNTs) were fabricated and characterized for bone tissue engineering applications. The incorporation of CNTs significantly enhanced the mechanical properties, with the aligned PCL/β-TCP/CNT scaffold (1 wt% CNTs) exhibiting a 125% and 123% increase in compressive modulus (180.3 ± 10.1 MPa) and strength (7.8 ± 0.6 MPa), respectively, compared to the PCL/β-TCP scaffold. The β-glycerol phosphate (BGP)-modified PCL/β-TCP/CNT scaffold showed similar mechanical properties to the aligned scaffold. All scaffolds maintained high porosity (> 70%) and a wide pore size distribution (50–500 μm). The scaffolds demonstrated excellent biocompatibility, with hemolysis rates below 5% and high cell viability. The aligned PCL/β-TCP/CNT scaffold promoted the highest rat adipose-derived stem cell proliferation, while the BGP-modified scaffold enhanced human dental pulp stem cell proliferation and mineralization.