Search Results (29)

Materials with high carrier mobility, represented by graphene, have garnered significant interest. However, the zero band gap arising from linear dispersion cannot achieve an ideal on–off ratio in field-effect transistors (FETs), limiting practical applications in certain fields. In contrast, parabolic dispersion usually exhibits extremely high carrier mobility and an appropriate band gap. In this work, we predicted a planar pentagonal lattice composed entirely of pentagons (namely penta-MX₂ monolayer), where M = Ni, Pd and Pt, X = group V elements. Using first-principles calculations, we demonstrated a parabolic dispersion within this framework, which results in intriguing phenomena, such as a direct band gap (0.551–1.105 eV) and extraordinary high carrier mobility. For penta-MX₂ monolayer, the carrier mobility can attain ~1 × 10⁸ cm² V⁻¹ s⁻¹ (PBE), surpassing those of black phosphorene, graphene and 2D hexagonal materials. This monolayer also displays anisotropic mechanical properties and significant absorption peaks in the ultraviolet spectrum. Remarkably, 2D penta-MX₂ monolayers are promising for successful experimental exfoliation, particularly when X is a nitrogen element, opening up new possibilities for designing two-dimensional semiconductor materials characterized by high carrier mobility. Full article

The global challenge of oil spill treatment has been addressed using nanocomposite-based natural fibers. These materials offer great potential in oil spill cleanup and are considered due to their environmental friendliness, high efficiency, and low cost. Thus, the current study reports a novel composite fabricated from date palm fiber (DPF) and recycled polyethylene terephthalate (rPET) with a proper combination of a mixture of carbon nanotubes (CNTs) and graphene nanosheets (GNSs) for oil removal. The established nanocomposite (DPF-rPET/CNT/GNS) was fabricated via physical mixing of various quantities (0.9, 0.8, and 0.7 g) of PET, along with varying loads of DPF at different proportions of CNT:GNS. The prepared nanocomposite (DPF-rPET/CNT/GNS) was fully characterized using scanning electron microscopy–energy dispersive X-ray (SEM-EDX) analysis, transmission electron microscopy (TEM), thermogravimetric analysis (TGA), Fourier-transform infrared spectroscopy (FTIR), and Brunauer–Emmett–Teller (BET) analysis. In static experiments and under the optimal parameters of pH, sorbent doze, shaking time, and quantity of diesel oil), the established sorbent (DPF-rPET/CNT-GNS nanocomposite) displayed excellent adsorption capacity (98 mg/g). This study also expands the utility of the sorbent for the reusability of the oil adsorption, maintaining performance after five cycles. The adsorption data fitted well with the Langmuir isotherm model with a correlation coefficient (R²) of 0.99 and maximum adsorption capacity of 99.7 mg/g, indicating monolayer adsorption. Additionally, the adsorption kinetics followed a pseudo-second-order model, with an R² near unity and an adsorption capacity of 99.09 mg/g. This study highlights the promising potential of the DPF-rPET/CNT-GNS composite as an effective adsorbent for treating oily water. Full article

A novel graphene-based composite, 5-methyl-1,3,4-thiadiazol-2-amine (MTA) covalently functionalized graphene oxide (GO-MTA), was rationally developed and used for the selective sorption of Ga³⁺ from aqueous solutions, showing a higher adsorption capacity (48.20 mg g⁻¹) toward Ga³⁺ than In³⁺ (15.41 mg g⁻¹) and Sc³⁺ (~0 mg g⁻¹). The adsorption experiment’s parameters, such as the contact time, temperature, initial Ga³⁺ concentration, solution pH, and desorption solvent, were investigated. Under optimized conditions, the GO-MTA composite displayed the highest adsorption capacity of 55.6 mg g⁻¹ toward Ga³⁺. Moreover, a possible adsorption mechanism was proposed using various characterization methods, including scanning electron microscopy (SEM) equipped with X-ray energy-dispersive spectroscopy (EDS), elemental mapping analysis, Fourier transform infrared (FT-IR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). Ga³⁺ adsorption with the GO-MTA composite could be better described by the linear pseudo-second-order kinetic model (R² = 0.962), suggesting that the rate-limiting step may be chemical sorption or chemisorption through the sharing or exchange of electrons between the adsorbent and the adsorbate. Importantly, the calculated q_e value (55.066 mg g⁻¹) is closer to the experimental result (55.60 mg g⁻¹). The well-fitted linear Langmuir isothermal model (R² = 0.972~0.997) confirmed that an interfacial monolayer and cooperative adsorption occur on a heterogeneous surface. The results showed that the GO-MTA composite might be a potential adsorbent for the enrichment and/or separation of Ga³⁺ at low or ultra-low concentrations in aqueous solutions. Full article

Graphene oxide is a two-dimensional material that has been extensively studied in various fields due to its good mechanical properties, water dispersibility, and a large number of oxygen-containing functionalities on its surface. In this study, graphene oxide powder was prepared using graphite powder to take advantage of its large specific surface area and abundance of oxygen-containing functional groups. The graphene oxide powder was cross-linked with acrylic acid and acrylamide and polymerized to produce graphene oxide hydrogels, which were used to adsorb four metal ions including Cu(II), Pb(II), Zn(II), and Cd(II) from aqueous solutions. The adsorption performance of the graphene oxide hydrogels was investigated at different pHs, temperatures, initial metal ion concentrations, and competition principles, as well as their adsorption and desorption after three repeated adsorption–desorption experiments. It was found that the graphene oxide hydrogels exhibited good adsorption performance for all four metal ions under different conditions. The graphene oxide hydrogels for the adsorption of Cu(II), Pb(II), Zn(II), and Cd(II) ions were best fitted using the Langmuir monolayer adsorption model and the quasi-secondary reaction kinetic model. Good adsorption was achieved for all four metal ions under different competing adsorption principles. After three adsorption–desorption cycles, the adsorption capacity of the graphene oxide hydrogels for all four metal ions remained at 88% and above. These results indicate that graphene oxide hydrogels are a stable, efficient, low-cost, and reusable adsorbent material for the treatment of metal ions in solution. Full article

In this work, we present ultrashort pulse generation from passively mode-locked Cr:ZnS laser with a monolayer graphene-coated ZnSe substrate exhibiting high nonlinearity. The femtosecond Cr:ZnS laser produces output power up to 330 mW at a 233 MHz repetition rate. Even in the presence of an uneven negative dispersion profile, the enhanced self-phase modulation by the ZnSe substrate of the graphene saturable absorber enables the polycrystalline Cr:ZnS laser to produce slightly chirped 99 fs pulses at 2373 nm. With extracavity dispersion compensation using a mixture of 3 mm and 2 mm thick ZnSe plates, the pulse width was compressed from 99 fs to 73 fs, resulting in an improved time–bandwidth product from 0.431 to 0.318. Assuming a sech² pulse shape (0.315), the pulses were almost transform-limited. These results indicate that utilizing a graphene saturable absorber on a substrate with high nonlinearity presents an effective method for developing sub-100 fs solid-state lasers within the mid-IR spectral range. Full article

In this experimental investigation, a procreation approach was used to produce a catalyst based on SnO₂@rGO nanocomposite for use in a selective catalytic reduction (SCR) system. Plastic waste oil is one such alternative that helps to ensure the survival of fossil fuels and also lessens the negative impacts of improper waste disposal. The SnO₂@rGO nanocomposite was prepared by fine dispersion of SnO₂ nanoparticles on monolayer-dispersed reduced graphene oxide (rGO) and carefully investigated for its potential in adsorbing CO, CO₂, NO_X, and hydrocarbon (HC). The as-synthesized SnO₂@rGO nanocomposite was characterized by Fourier transform infrared spectroscopy, high-resolution transmission electron microscopy, scanning electron microscopy, X-ray diffraction spectroscopy, thermogravimetry, and surface area analyses. Then, the impact of catalysts inside the exhaust engine system was evaluated in a realistic setting with a single-cylinder, direct-injection diesel engine. As a result, the catalysts reduced harmful pollution emissions while marginally increasing brake-specific fuel consumption. The nanocomposite was shown to exhibit higher NO_X adsorption efficiencies when working with different toxic gases. Maximum reductions in the emission of NO_X, hydrocarbons, and CO were achieved at a rate of 78%, 62%, and 15%, respectively. These harmful pollutants were adsorbed on the active sites of catalyst and are converted to useful fuel gases through catalytic reduction thereby hindering the trajectory of global warming. Full article

Using exfoliating agents is one of the most promising ways for large-scale production of liquid dispersed graphenic materials from graphite. Therefore, it is crucial to know the reason why some molecules have a larger exfoliating power than others. The highest reported experimental yield for the liquid phase single-surfactant spontaneous exfoliation of graphite, i.e., without sonication, has been obtained using chlorosulfonic acid. The ability of this acid to disperse graphite is studied within the framework of Density Functional Theory (DFT). Equilibrium configurations, electron transfers, binding energies, and densities of states are presented for two acid concentrations and for two situations: adsorption (on monolayer and bilayer graphene) and intercalation (in between simple hexagonal and Bernal-stacked bilayer graphene). Experimental exfoliation power and dispersion stability are explained in terms of charge transfer—the largest found among several studied exfoliating and surfactant agents—facilitated by the good geometrical matching of chlorosulfonic acid molecules to constituent carbon rings of graphene. This matching is in the origin of the tendency toward adsorption of chlorosulfonic acid molecules on graphene monolayers when they separate, originating the charging of the monolayers that precludes their reaggregation. Full article

With the growing scarcity of water, the remediation of water polluted with heavy metals is the need of hour. The present research work is aimed to address this problem by adsorbing heavy metals ions (Pb (II) and Cr (VI)) on modified graphene oxide having an excess of carboxylic acid groups. For this, graphene oxide (GO) was modified with chloroacetic acid to produce carboxylated graphene oxide (GO-COOH). The successful synthesis of graphene oxide and its modification has been confirmed using Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, X-ray Diffraction (XRD), Scanning electron microscopy (SEM), Energy Dispersive X-ray Analysis (EDX) and Transmission electron microscopy (TEM). The increase in surface area of graphene oxide after treatment with chloroacetic acid characterized by BET indicated its successful modification. A batch experiment was conducted to optimize the different factors affecting adsorption of both heavy metals on GO-COOH. After functionalization, we achieved maximum adsorption capacities of 588.23 mg g⁻¹ and 370.37 mg g⁻¹ for Pb and Cr, respectively, by GO-COOH which were high compared to the previously reported adsorbents of this kind. The Langmuir model (R² = 0.998) and Pseudo-second-order kinetic model (R² = 0.999) confirmed the monolayer adsorption of Pb and Cr on GO-COOH and the chemisorption as the dominant process governing adsorption mechanism. The present work shows that the carboxylation of GO can enhance its adsorption capacity efficiently and may be applicable for the treatment of wastewater. Full article

In the latest ground-breaking experimental advancement (Nature (2022), 606, 507), zero-dimensional fullerenes (C₆₀) have been covalently bonded to form single-layer two-dimensional (2D) fullerene network, namely quasi-hexagonal-phase fullerene (qHPC₆₀). Motivated by the aforementioned accomplishment, in this communication, for the first time, we explore the phononic and mechanical properties of the qHPC₆₀ monolayer, employing state-of-the-art machine-learning interatomic potentials. By employing an efficient passive-training methodology, the thermal and mechanical properties were examined with an ab-initio level of accuracy using the classical molecular dynamics simulations. Predicted phonon dispersion confirmed the desirable dynamical stability of the qHPC₆₀ monolayer. Room temperature lattice thermal conductivity is predicted to be ultralow and around 2.9 (5.7) W/m·K along the x(y) directions, which are by three orders of magnitude lower than that of the graphene. Close to the ground state and at room temperature, the ultimate tensile strength of the qHPC₆₀ monolayer along the x(y) directions is predicted to be 7.0 (8.8) and 3.3 (4.2) GPa, respectively, occurring at corresponding strains of around 0.07 and 0.029, respectively. The presented computationally accelerated first-principles results confirm highly anisotropic and remarkably low tensile strength and phononic thermal conductivity of the qHPC₆₀ fullerene network nanosheets. Full article

In a recent advance, zirconium triselenide (ZrSe₃) nanosheets with anisotropic and strain-tunable excitonic response were experimentally fabricated. Motivated by the aforementioned progress, we conduct first-principle calculations to explore the structural, dynamic, Raman response, electronic, single-layer exfoliation energies, and mechanical features of the ZrX₃ (X = S, Se, Te) monolayers. Acquired phonon dispersion relations reveal the dynamical stability of the ZrX₃ (X = S, Se, Te) monolayers. In order to isolate single-layer crystals from bulk counterparts, exfoliation energies of 0.32, 0.37, and 0.4 J/m² are predicted for the isolation of ZrS₃, ZrSe₃, and ZrTe₃ monolayers, which are comparable to those of graphene. ZrS₃ and ZrSe₃ monolayers are found to be indirect gap semiconductors, with HSE06 band gaps of 1.93 and 1.01 eV, whereas the ZrTe₃ monolayer yields a metallic character. It is shown that the ZrX₃ nanosheets are relatively strong, but with highly anisotropic mechanical responses. This work provides a useful vision concerning the critical physical properties of ZrX₃ (X = S, Se, Te) nanosheets. Full article

When producing stable electrodes, polymeric binders are highly functional materials that are effective in dispersing lithium-based oxides such as Li₄Ti₅O₁₂ (LTO) and carbon-based materials and establishing the conductivity of the multiphase composites. Nowadays, binders such as polyvinylidene fluoride (PVDF) are used, requiring dedicated recycling strategies due to their low biodegradability and use of toxic solvents to dissolve it. Better structuring of the carbon layers and a low amount of binder could reduce the number of inactive materials in the electrode. In this study, we use computational and experimental methods to explore the use of the poly amino acid poly-L-lysine (PLL) as a novel biodegradable binder that is placed directly between nanostructured LTO and reduced graphene oxide. Density functional theory (DFT) calculations allowed us to determine that the (111) surface is the most stable LTO surface exposed to lysine. We performed Kubo–Greenwood electrical conductivity (KGEC) calculations to determine the electrical conductivity values for the hybrid LTO–lysine–rGO system. We found that the presence of the lysine-based binder at the interface increased the conductivity of the interface by four-fold relative to LTO–rGO in a lysine monolayer configuration, while two-stack lysine molecules resulted in 0.3-fold (in the plane orientation) and 0.26-fold (out of plane orientation) increases. These outcomes suggest that monolayers of lysine would specifically favor the conductivity. Experimentally, the assembly of graphene oxide on poly-L-lysine-TiO₂ with sputter-deposited titania as a smooth and hydrophilic model substrate was investigated using a layer-by-layer (LBL) approach to realize the required composite morphology. Characterization techniques such as X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), Kelvin probe force microscopy (KPFM), scanning electron microscopy (SEM) were used to characterize the formed layers. Our experimental results show that thin layers of rGO were assembled on the TiO₂ using PLL. Furthermore, the PLL adsorbates decrease the work function difference between the rGO- and the non-rGO-coated surface and increased the specific discharge capacity of the LTO–rGO composite material. Further experimental studies are necessary to determine the influence of the PLL for aspects such as the solid electrolyte interface, dendrite formation, and crack formation. Full article

Graphene is a type of two-dimensional material with special properties and complex mechanical behavior. In the process of growth or processing, graphene inevitably has various defects, which greatly influence the mechanical properties of graphene. In this paper, the mechanical properties of ideal monolayer graphene nanoribbons and monolayer graphene nanoribbons with vacancy defects were simulated using the molecular dynamics method. The effect of different defect concentrations and defect positions on the vibration frequency of nanoribbons was investigated, respectively. The results show that the vacancy defect decreases the vibration frequency of the graphene nanoribbon. The vacancy concentration and vacancy position have a certain effect on the vibration frequency of graphene nanoribbons. The vibration frequency not only decreases significantly with the increase of nanoribbon length but also with the increase of vacancy concentration. As the vacancy concentration is constant, the vacancy position has a certain effect on the vibration frequency of graphene nanoribbons. For nanoribbons with similar dispersed vacancy, the trend of vibration frequency variation is similar. Full article

Employing first-principles calculations based on density functional theory (DFT), we designed a novel two-dimensional (2D) elemental monolayer allotrope of carbon called hexatetra-carbon. In the hexatetra-carbon structure, each carbon atom bonds with its four neighboring atoms in a 2D double layer crystal structure, which is formed by a network of carbon hexagonal prisms. Based on our calculations, it is found that hexatetra-carbon exhibits a good structural stability as confirmed by its rather high calculated cohesive energy −6.86 eV/atom, and the absence of imaginary phonon modes in its phonon dispersion spectra. Moreover, compared with its hexagonal counterpart, i.e., graphene, which is a gapless material, our designed hexatetra-carbon is a semiconductor with an indirect band gap of 2.20 eV. Furthermore, with a deeper look at the hexatetra-carbon, one finds that this novel monolayer may be obtained from bilayer graphene under external mechanical strain conditions. As a semiconductor with a moderate band gap in the visible light range, once synthesized, hexatetra-carbon would show promising applications in new opto-electronics technologies. Full article

The strain in hybrid van der Waals heterostructures, made of two distinct two-dimensional van der Waals materials, offers an interesting handle on their corresponding electronic band structure. Such strain can be engineered by changing the relative crystallographic orientation between the constitutive monolayers, notably, the angular misorientation, also known as the “twist angle”. By combining angle-resolved photoemission spectroscopy with density functional theory calculations, we investigate here the band structure of the WS₂/graphene heterobilayer for various twist angles. Despite the relatively weak coupling between WS₂ and graphene, we demonstrate that the resulting strain quantitatively affects many electronic features of the WS₂ monolayers, including the spin-orbit coupling strength. In particular, we show that the WS₂ spin-orbit splitting of the valence band maximum at K can be tuned from 430 to 460 meV. Our findings open perspectives in controlling the band dispersion of van der Waals materials. Full article

Systematic investigations are performed to understand the temperature-dependent optical properties of graphene on Si and SiO₂/Si substrates by using a variable angle spectroscopic ellipsometry. The optical constants of graphene have revealed changes with the substrate and temperature. While the optical refractive index (n) of monolayer graphene on Si exhibited clear anomalous dispersions in the visible and near-infrared region (400–1200 nm), the modification is moderate for graphene on SiO₂/Si substrate. Two graphene sheets have shown a pronounced absorption in the ultraviolet region with peak position related to the Van Hove singularity in the density of states. By increasing the temperature from 300 K to 500 K, for monolayer graphene on Si, the n value is gradually increased while k decreased. However, the optical constants [n, k] of monolayer graphene on SiO₂/Si exhibited unpredictable wave variations. In the wavelength range of 400–1200 nm, an experiential formula of a like-Sellmeier equation is found well suited for describing the dispersions of graphene on Si and SiO₂/Si substrates. Full article