A new approach on synergistic effect and chemical stability of graphene oxide-magnetic nanocomposite in the heterogeneous Fenton degradation of caffeine

Designing Sphere-like FeSe2-Carbon Composites with Rational Construction of Interfacial Traits towards Considerable Sodium-storage Capabilities

Due to their low cost and high stability, sodium-ion batteries have been increasingly studied. However, their further development is limited by the relative energy density, resulting in the search for high-capacity anodes. FeSe₂ displays high conductivity and capacity but still suffers from sluggish kinetics and serious volume expansion. Herein, through sacrificial template methods, a series of sphere-like FeSe₂-carbon composites are successfully prepared, displaying uniform carbon coatings and interfacial chemical FeOC bonds. Moreover, benefiting from the unique traits of precursor and acid treatment, rich structural voids are prepared, effectively alleviating volume expansion. Utilized as anodes of sodium-ion batteries, the optimized sample displays considerable capacity, achieving 462.9 mAh g^-1, with 88.75% coulombic efficiency at 1.0 A g^-1. Even at 5.0 A g^-1, their capacity can be kept at approximately 318.8 mAh g^-1, while the stable cycling can be prolonged to 200 cycles above. Supported by the detailed kinetic analysis, it can be noted that the existing chemical bonds facilitate the fast shuttling of ions at the interface, and the enhanced surface/near-surface properties are further vitrified. Given this, the work is expected to offer valuable insights for the rational design of metal-based samples toward advanced sodium-storage materials.

Adsorption of caffeine using steel wastes

Caffeine is the most widespread active pharmaceutical compound in the world, generally studied as a tracer of human pollution, since caffeine levels in surface water correlate with the anthropogenic load of domestic wastewater. This work investigated the use of different steel wastes named as SW-I, SW-II, SW-II, SW-IV, SW-V, and SW-VI in the adsorption of caffeine. These materials were pretreated and characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, and point of zero charge. The samples are mainly composed of iron (hematite and magnetite). The caffeine adsorption test indicated that SW-VI (steel slag dust) is the most efficient and promising (removal around 51.68%) in relation to the other residues, which it was selected for further studies. Equilibrium time was reached within 96 h of contact between the adsorbent and the adsorbate, with removal of 84.00%, 81.09%, and 73.19% for the initial concentrations of 10 mg L-1, 20 mg L-1, and 30 mg L-1 of caffeine. The pseudo-first-order, pseudo-second-order, and Elovich models presented a good fit to the experimental data. However, the pseudo-first order model described better the experimental behavior. Adsorption isotherms were performed at three temperatures (298, 308, and 318 K). The maximum adsorption capacity was 17.46 ± 2.27 mg g-1, and experimental data were better fitted by the Sips isotherm. Values of ΔG° and parameters equilibrium of the models of Langmuir, Sips, and Temkin were calculated from the standard enthalpies and standard entropies estimated. The values of ΔG° were negative for the temperatures studied indicating that the adsorption process is viable and spontaneous. Negative values for ΔH° were also found, indicating that the process of caffeine adsorption by SW-VI is an exothermic process (0 to -40 kJ mol-1). Thus, the adsorption of caffeine by SW-VI is a physical process. The SW-VI material showed economic viability and promising for the adsorption of caffeine in aqueous media.

Magnetic graphene oxide for methylene blue removal: adsorption performance and comparison of regeneration methods

A series of Fe₃O₄-graphene oxide (GO) composite materials (MGOs) with abundant surface area, rich oxygen-containing functional groups, and magnetic properties were prepared in a facile coprecipitation method and then employed for the adsorptive removal of methylene blue (MB) from water. The kinetic data were better fitted in the pseudo-second-order model than in the pseudo-first-order model, and the intraparticle diffusion model revealed the two-step diffusion process including diffusion in the boundary layer and in the porous structures. The maximum adsorption amounts of MB were calculated to be 37.5-108 mg/g at 25 °C and pH 9 using the Langmuir isotherm model. Thermodynamic study showed that the adsorption process was spontaneous, with ΔH° of 23.0-49.6 kJ/mol and ΔS° of 131-249 J∙mol^-1∙K^-1. The adsorption amount of MB increased with pH in the range of 4-10. Inorganic ions including Na⁺ and Ca²⁺ suppressed the adsorption of MB, and the more pronounced impact of Ca²⁺ was ascribed to its higher valence state. The cetyltrimethylammonium bromide (CTAB) surfactant showed a stronger inhibitory effect than Ca²⁺. The adsorption mechanism was proposed to be a combination of electrostatic interactions, hydrophobic adsorption, and electron donor-acceptor interactions. Two methods were used for the regeneration of spent MGO, and the results showed that the peroxomonosulfate (PMS) oxidation method was more favorable than the acid washing method, considering the better regeneration ability and lower amount of washing water used. Finally, the reaction mechanism of PMS oxidation was analyzed based on quenching tests and in situ open circuit potential measurements, which proved that OH and ¹O₂ played dominant roles and that the fine adsorption ability of MGO promoted the reaction between them and MB.