No abstract

No abstract

Magnetic multi‐walled carbon nanotubes‐Fe3C nanocomposite was synthesized by chemical vapor deposition process and was used as an adsorbent for the removal of acid dye Acid Red 88 (AR88) from aqueous solution. The effects of various parameters such as initial AR88 concentration (10–58 mg L−1), pH (3.1–11.3) and temperature (20–60°C) were investigated. The properties of this adsorbent were characterized by X‐ray diffraction, high‐resolution transmission electron microscopy, energy dispersive X‐ray analysis, fourier transform IR, N2 adsorption/desorption isotherms, and particle size distribution by laser diffraction. The experimental data were analyzed by the Langmuir and Freundlich models of adsorption. Equilibrium data fitted well with the Freundlich model. Kinetic adsorption data were analyzed using the Lagergren pseudo‐first‐order kinetic model, the pseudo‐second‐order model and the intraparticle diffusion model. The regression results showed that the adsorption kinetics was more accurately represented by pseudo‐second‐order model. Thermodynamics parameters, Gibbs free energy (ΔG0), enthalpy (ΔH0), and entropy (ΔS0), were calculated. All ΔG0 values were negative. The values of ΔH0 and ΔS0 were −4.70 and −7.98 J mol−1 K−1, respectively, indicating that adsorption of AR88 onto magnetic multi‐walled carbon nanotubes nanocomposites was spontaneous and exothermic in nature.

No abstract

A system consisting of at least two components was considered. In this system, nanocrystalline material is formed at high temperature, at which diffusion does not limit the mass transport. The structure results from establishing an equilibrium between surface and volume of the crystallites and their surroundings in isothermal-adiabatic conditions. The surface of each crystallite is covered with another substance. On the basis of the performed energy-balance calculations it was concluded that the reduction in the surface area is associated with a decrease in the surface coverage degree and thus with the necessity to provide energy to the system in order to remove chemisorbed atoms. An increase in the temperature of a nanocrystalline substance to a temperature higher than the preparation temperature results in the formation of a new state of equilibrium. At temperatures below the maximum temperature only the equilibrium between the gas phase and the surface exists.