pH Of Stock Solution Research Articles

Kinetics, Equilibrium and Thermodynamics Studies of Fe<sup>3+</sup> Ion Removal from Aqueous Solutions Using Periwinkle Shell Activated Carbon

Iron (III) adsorption from aqueous solutions unto periwinkle shell carbon (PSC) was studied using batch experiments. Activated periwinkle shell carbon was prepared (pyrolysed at 300°C and activated with nitric acid) and characterized to determine its physiochemical properties. Batch adsorption experiments were conducted to investigate the effects of process parameters (contact time, particle size, carbon dosage and pH of stock solution) on adsorption rate. Adsorption kinetics was tested using pseudo first and second order models. Adsorption Isotherms were analyzed using the Langmuir, Freundlich and Temkin isotherms while Thermodynamics parameters such as Enthalpy change (ΔH°), Entropy change (ΔS°) and Gibbs-free energy change (ΔG°) were determined. Results showed that adsorption rate increase with increase in contact time, adsorbent dose and pH and decreased with increase in particle size. Batch adsorption Kinetics experiments revealed that the mechanism of adsorption followed pseudo-second-order kinetic model. Isotherm data showed that the Langmuir isotherm accurately described the adsorption data indicating that adsorption process was mainly monolayer on a homogeneous adsorbent surface. Thermodynamic parameters results showed that adsorption process was endothermic with Enthalpy change (ΔH°): 222.91 kJ/mol; a positive Entropy change (ΔS°) of 19.19 kJ/mol, indicating an increase in the degree of freedom (or disorder) of the adsorbed species and a negative Gibb’s free energy (ΔG°) at all temperature indicating that the adsorption process was spontaneous and favorable at high temperature.

Synthesis and Luminescence Properties of La2W2O9:Eu3+ Micron-Crystals.

La2W2O9:2%Eu3+ phosphors were synthesized by a typical hydrothermal procedure. The samples were characterized by X-ray diffraction and scanning electron microscope (SEM). X-ray diffraction analysis showed that a stock solution pH value equal to 9 is the ideal value, while the crystallization of the hydroxyl sodium yttrium tungstate crystal is improved by increasing the PH values of stock solution within limits. Meanwhile, SEMs of different pH values were recorded. Additionally, photo-luminescence excitation (PLE) and emission (PL) spectra were measured. It was found that this phosphor can be effectively excited by C-T band (266 nm) and ultraviolet light 342 nm. The wave-lengths at 342 nm fit in nicely with the whole visible region, thus the La2W2O9:2%Eu3+ phosphors emit white light. Furthermore, the annealing temperature's impact on PLE and PL spectra was also studied. The Eu3+-doped La2W2O9 phosphor may be a better candidate than current method for solid-state lighting applications.