RESUMEN
Metallothermic, especially magnesiothermic, solid-state reactions have been widely applied to synthesize various materials. However, further investigations regarding the use of this method for composite syntheses are needed because of the high reactivity of magnesium. Herein, we report an in situ magnesiothermic reduction to synthesize a composite of Ge@C as an anode material for lithium-ion batteries. The obtained electrode delivered a specific capacity of 454.2 mAh·g-1 after 200 cycles at a specific current of 1000 mA·g-1. The stable electrochemical performance and good rate performance of the electrode (432.3 mAh·g-1 at a specific current of 5000 mA·g-1) are attributed to the enhancement in distribution and chemical contact between Ge nanoparticles and the biomass-based carbon matrix. A comparison with other synthesis routes has been conducted to demonstrate the effectiveness of contact formation during in situ synthesis.
RESUMEN
Within moderate band gap, g-C3N4 and CdS are both promising visible light driven photocatalysts. However, their intrinsic high recombination rate of photo-induced electron-hole pairs along with the poor susceptibility in photocorrosion of CdS is main limitations hindering their practical application. In this study, the CdS/g-C3N4 composites with various weight ratios of CdS to g-C3N4 were solvothermal prepared from the dispersion of components, g-C3N4 and CdS, in ethanol. The physicochemical characterizations demonstrate the success in the fabrication of well-dispersed CdS nanoparticles in the g-C3N4 matrix. The enhanced photocatalytic activity of the g-C3N4/CdS composite over the degradation of methylene blue under visible light was ascribed to the effective photo-induced electron-hole separation via the step scheme (S-scheme) pathway in which the main contribution of high oxidative hydroxyl radicals (â¢OH) was demonstrated. Furthermore, via S-scheme model, we also clarify the depletion of photo-induced holes on CdS which is ascribed as the reason for improvement in resistance to photocorrosion of composites.
RESUMEN
The SnO2/g-C3N4 composites were fabricated via an annealing mixture of g-C3N4 and SnO2, which were obtained from calcinating melamine and hydrothermal treatment of SnCl4 solution, respectively. The photocatalytic properties of g-C3N4/SnO2 were studied over the degradation of Rhodamine B (RhB) under visible light, which exhibits a significantly improved photocatalytic activity compared to the single components, g-C3N4 and SnO2. The enhancement in photocatalytic activity of SnO2/g-C3N4 could be described by the S-scheme pathway, in which the effective charge transfer between components is demonstrated toward the suppression in recombination of the photogenerated electron-hole pairs within redox potential conservation. Besides, a new criterion, photochemical space-time yield, was applied to evaluate the photocatalytic performance of our samples.
Asunto(s)
Electrones , Luz , CatálisisRESUMEN
Despite pioneering as the holy grail in photocatalysts, abundant reports have demonstrated that g-C3N4 performs poor photocatalytic activity due to its high recombination rate of photo-induced charge carriers. Many efforts have been conducted to overcome this limitation in which the semiconductor-semiconductor coupling strategies toward heterojunction formation were considered as the easiest but the most effective method. Herein, a one-pot solid-state reaction of thiourea and sodium molybdate as precursors at different temperatures under N2 gas was applied for preparing composites of MoS2/g-C3N4. The physicochemical characterization of the final products determines the variation in contents of components (MoS2 and g-C3N4) via the increase of synthesis temperature. The enhanced photocatalytic activity of the MoS2/g-C3N4 composites was evaluated by the degradation of Rhodamine B in an aqueous solution under visible light. Therein, composites synthesized at 500 °C showed the best photocatalytic performance with a degradation efficiency of 90%, much higher than that of single g-C3N4. The significant improvement in photocatalytic performance is attributed to the enhancement in light-harvesting and extension in photo-induced charge carriers' lifetime of composites which are originated from the synergic effect between the components. Besides, the photocatalytic mechanism is demonstrated to well-fit into the S-scheme pathway with apparent evidences.
RESUMEN
The demand for well-designed nanostructured composites with enhanced electrochemical performance for lithium-ion batteries electrode materials has been emerging. In order to improve the electrochemical performance of MoS2-based anode materials, MoS2 nanosheets integrated with g-C3N4 (MoS2/g-C3N4 composite) was synthesized by a facile heating treatment from the precursors of thiourea and sodium molybdate at 550 °C under N2 gas flow. The structure and composition of MoS2/g-C3N4 were confirmed by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, infrared spectroscopy, X-ray photoelectron spectroscopy, thermogravimetric analysis and elemental analysis. The lithium storage capability of the MoS2/g-C3N4 composite was evaluated, indicating high capacity and stable cycling performance at 1 C (A·g-1) with a reversible capacity of 1204 mA·h·g-1 for 200 cycles. This result is believed the role of g-C3N4 as a supporting material to accommodate the volume change and improve charge transport for nanostructured MoS2. Additionally, the contribution of the pseudocapacitive effect was also calculated to further clarify the enhancement in Li-ion storage performance of the composite.
RESUMEN
Lamellar phases of the general formula [CnH(2n+1)N(CH3)3]VO3 (n = 14, 16, 18) have been prepared by an ion-exchange/precipitation reaction of alkyltrimethylammonium surfactants and NaVO3 in an aqueous medium at room temperature. The phases were characterized by powder X-ray diffraction, transmission electron microscopy, infrared spectroscopy, thermogravimetric analysis and differential scanning calorimetry. The data support a proposed crystal structure model in which single arrays of the one-dimensional chains of oligomers {(VO3)n}(n-) that may be generated from the starting material NaVO3 fragmented by the hydration during the dissolution into water and the surfactants layers alternate. The alkyl chains of the surfactants in these materials are arranged as monolayers or deeply penetrate into the interlayer region with a tilt angle of 37 degrees. The phenol adsorption in aqueous solution on a representative lamellar phase was investigated. The data being fitted to Langmuir Isotherms and a maximum adsorption capacity calculated from the Langmuir equation to be 178.6 mg of phenol/g for [C16H33N(CH3)3]VO3 have been obtained. The effect of pH on the adsorption and desorption of phenol has also been studied. Acetone solution of 20% is the best eluent for desorption of phenol from the loaded adsorbent with a desorption efficiency of 90.8%.