Search

Abstract: We report here a simple and modified solvothermal synthesis of NiO nanoparticles by using nickel nitrate hexahydrate [Ni(NO3)2⋅6H2O], hexamethylenetetramine [C6H12N4], sodium hydroxide [NaOH] and ethanol [C2H5OH] as refluxing solvent. Nickel hydroxide [β-Ni(OH)2] nanostructures were first formed which were then calcined at 400°C to obtain nickel oxide (NiO) nanoparticles. The nano-powder was investigated by means of X-ray diffraction, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, Fourier transform infrared spectroscopy, ultraviolet–visible spectroscopy and Brunauer–Emmett–Teller surface area studies. The size of the NiO nanoparticles was estimated by X-ray powder diffraction pattern, which was in close agreement with the particle size obtained by transmission electron microscopy analysis. Scanning electron microscopy studies revealed that the synthesized nickel oxide nanostructures showed various morphologies and the morphologies can be easily tailored by adjusting the pH value. The chemical structure information of the products was studied by Fourier transform infrared spectroscopy. Electronic spectra were used to clarify qualitatively the change in absorption band positions on changing the particle size of NiO. The values of the optical band gap of the NiO nanoparticles increases from 2.9 to 3.5eV as the particle size decreases and indicated a direct transition. The specific surface area of NiO nanoparticles was found to increase from 58.3 to 131.4m2/g with decrease in the particle size from 20nm to 5nm. It also exhibited excellent adsorption of Co(II) and Pb(II), demonstrating a promising application in waste water treatment. [Copyright &y& Elsevier]

CO 2 sequestration into coalbed seams is one of the practical routes for mitigating CO 2 emissions. The adsorption mechanisms of CO 2 onto Malaysian coals, however, are not yet investigated. In this research CO 2 adsorption isotherms were first performed on dry and wet Mukah-Balingian coal samples at temperatures ranging from 300 to 348 K and pressures up to 6 MPa using volumetric technique. The dry S1 coal showed the highest CO 2 adsorption capacity of 1.3 mmol g−1, at 300 K and 6 MPa among the other coal samples. The experimental results of CO 2 adsorption were investigated using adsorption isotherms, thermodynamics, and kinetic models. Nonlinear analysis has been employed to investigate the data of CO 2 adsorption onto coal samples via three parameter isotherm equilibrium models, namely Redlich Peterson, Koble Corrigan, Toth, Sips, and Hill, and four parameter equilibrium model, namely Jensen Seaton. The results of adsorption isotherm suggested that the Jensen Seaton model described the experimental data well. Gibb's free energy change values are negative, suggesting that CO 2 adsorption onto the coal occurred randomly. Enthalpy change values in the negative range established that CO 2 adsorption onto coal is an exothermic mechanism. Webber's pore-diffusion model, in particular, demonstrated that pore-diffusion was the main controlling stage in CO 2 adsorption onto coal matrix. The activation energy of the coals was calculated to be below −13 kJ mol−1, indicating that adsorption of CO 2 onto coals occurred through physisorption. The results demonstrate that CO 2 adsorption onto coal matrix is favorable, spontaneous, and the adsorbed CO 2 molecules accumulate more onto coal matrix. The observations of this investigation have significant implications for a more accurate measurement of CO 2 injection into Malaysian coalbed seams. • CO 2 adsorption was investigated onto dry and wet coals at 300–348 K and 6 MPa • CO 2 interacts with the coal surface at high pressure in presence of water molecules. • Enthalpy value change confirmed that CO 2 adsorption with coal is an exothermic process. • Jensen Seaton model showed CO 2 adsorption best compliance with the experimental data. • Webber's pore-diffusion model showed the pore-diffusion was the major controlling step. [ABSTRACT FROM AUTHOR]