Papers by Keyword: Chemisorption

Abstract: The article presents the results of studies on recovery of lithium from reservoir brines using both commercial and synthesized aluminum hydroxide and hydrated manganese oxide as sorbents. The research results showed that, when using commercial aluminum hydroxide and synthesized hydrated manganese oxide as sorbents, lithium recovery from brine was 21.8 and 20.1%, respectively. Studies were conducted on lithium chemisorption on freshly precipitated aluminum hydroxide, which was obtained by adding aluminum chloride solution and tri-calcium hydro-aluminate to the brine. Chemisorption of lithium was carried out under the following conditions: T = 50 °C; AlCl₃ solution concentration - 120 g/dm³; molar ratio Li/Al = 7; pH equal = 8.0-8.8; holding time with stirring 1 h. The degree of lithium extraction from brine was 71%; lithium capacity of freshly precipitated Al (OH)₃ was 5.9 mg/g. During calcareous leaching of lithium-aluminum precipitate, lithium was extracted into a solution by 74.7%.

Abstract: The use of cheap and eco-friendly adsorbents studied as an alternative to activated carbon for removal of dyes from wastewater is the focus of this paper. Chitosan, which was produced from food industry waste (crab shells), was synthesized, characterized and utilized as adsorbent to remove cationic dye, basic blue, from wastewater by adsorption. Characteristics of the synthesized chitosan biosorbents was established using scanning electron microscope (SEM), and Fourier Transform Infra-Red (FTIR) spectroscopy. Experiments were conducted in batch forms to investigate the effects of contact time, initial dye concentration and adsorbent dosage. Kinetic and isotherm analysis of the adsorption process were also carried out. The results obtained revealed that removal efficiency of the chitosan was increased as the contact time and chitosan biosorbent dose were increased, but a decrease with increasing initial concentration of basic dye was observed. The pseudo-second order reaction model was found to describe the biosorption process best, with chemisorption as the rate limiting step. The maximum colour removal efficiencies of chitosan at dosage of 4 g for time duration of 90 min was found to be 91.88% of the dye from a solution of 80 ppm. The pseudo-second order kinetic model was also seen to agree very well with the dynamic behaviour of the adsorption of basic blue on chitosan under different contact time, initial dye concentrations and adsorbent dosages. The dynamic behaviour of adsorption of basic blue onto chitosan has the model fitness in the following order: pseudo-second order > Elovich model > pseudo-first order. The Elovich equation was found to be the best fit equilibrium isotherm for the sorption of basic blue onto chitosan based on linearized correlation coefficient. Moreover, the equilibrium isotherm has its model fitness to be in the order of Elovich model > Langmuir model > Freundlich model.

Abstract: This is a preliminary study for hardness removal via modified starch combined with an ultrafiltration process that provides on high effluence quality and low cost, footprint and environmental impact treatment. This studied on potential of chemisorption process using modified starch as absorbents for hardness removal. Four modified tapioca starches were selected for evaluation that includes of oxidize starch, di-starch phosphate, hydroxyphophyl starch and phosphate monoester as well as non-modified tapioca starch too. Phosphate monoester starch achieved the highest efficiency about 98.2% of hardness removal within the adsorption capacity about 18 mg-hardness removed/g-starch. The modified starch had capable to reduced total hardness from 350.5 mg/L as CaCO₃ to 6.3 mg/L as CaCO₃ from water. However, the modified starch is an organic matter its can be contaminates in water. Then, a coagulation-flocculation processes were applied for starch colloidal destabilization and flocs by aluminum chloride (PAC) and cationic polymer for starch separation. After that process, turbidity was less than 1 NTU in the effluents. However, the total dissolved solids were increased that may be cause of some starch was solutes. These should be having a future treatment for particulate removal and cutoff the soluble starch in water likes an ultrafiltration process.

Abstract: We have developed a mathematical model of electrophysical and gas sensitive properties of nanosized ZnO film during chemisorption of gas molecules of CO, CO₂, CH₄, and NO₂ on its surface and figured out regularities of influence of thickness of depletion layer of nanosized ZnO films on their electric and gas sensitivity properties. We have determined optimal range of working temperatures and thicknesses of nanosized ZnO films for detecting CO, CO₂ CH₄, and NO₂ with maximum gas sensitivity and selectivity and theoretical investigated gas-sensitivity properties of nanosized ZnO films.

Abstract: The adsorption of Remazol by CEMPCRP was studied as a function of pH, contact time and concentration. All experiments were carried out using the batch method. The initial and final RBBR concentration were determinated using UV-Vis spectrometer at λ = 592.3 nm. The result showed that the optimum condition of RBBR adsorption were at pH 10, contact time 360 min, and concentration of 300 mg/L. This adsorption followed the Lagergren (first pseudo order) and Langmuir isotherm adsorption model. The adsorption capacity was obtained 6.51 x 10^-5 mol/L and the mechanism is a chemisorption (ΔG = 28.92 kJ/mol) that occurs in the monolayer.

Abstract: The thermal conductivity at 300K of (6, 6) carbon nanotubes and chemi-adsorbed carbon nanotubes with methyl groups at random positions through covalent bonding (chemisorption) has been calculated as a function of adsorption density using molecular dynamics. The results exhibit a rapid drop in thermal conductivity with chemisorptions, even chemisorption as little as 1.0% of the nanotube carbon atoms reduces the thermal conductivity significantly. Investigate its reason, defects caused by chemisorption blocking the transmission of phonons which plays a leading role in the heat conduction of nanotubes, affecting the temperature distribution and energy transmission, leading to the thermal conductivity decline.

Abstract: Chemisorption of CO molecule on the (001) surface of δ-Pu using the generalized gradient approximation of the density functional theory with the Perdew-Burke-Ernzerhof exchange-correlation functional has been investigated without spin-orbit coupling at the non-spin-polarized level to better understand the interaction and chemical reaction of CO with Pu surface. Band structure and density of states before and after CO molecule chemisorption on the bridge position of the (001) surface have been compared and analyzed. The result shows that s and p states of CO molecule hybrid with Pu 6d states. Chemisorption energy for this adsorption site and repulsion energy between CO molecules are 0.615046eV and 0.96768eV, respectively.Key words: density functional;chemisorption;energy band;density of states;repulsion energy

Abstract: TiO2 aggregates-based dye solar cells (DSCs) have gained an increasing interest due to their better light harvesting efficiency as a result of enhanced light scattering effect from the submicron spherical aggregates that can generate more electrons and the high internal surface area for dye chemisorption provided by nanocrystallites which made up the aggregates. Optimized TiO2 aggregates (0.45 µm) composing of nanocrystallites (10-40 nm) with desired physicochemical properties for enhanced overall light conversion efficiency of DSC were synthesized by varying the calcination temperature and water content in the hydrolysis of titanium alkoxide in ethanol. TiO2 aggregates obtained were characterized using FESEM, XRD and UV-Vis spectroscopy. The assembled DSCs were then evaluated using solar simulator under AM 1.5 (100 mW/cm2) simulated sunlight. Nanocrystallites were found to have an increasing size of 12 nm to 36 nm with increasing calcination temperature of 400C to 600C. Sample of aggregates calcined at 500C recorded the highest efficiency (4.456%) as the 20-nm nanocrystallites produced is considered to be the optimum size for dye absorption. With higher water content in the hydrolysis process, the aggregates lose their spherical shapes resulting in lower absorption intensity indicating the occurrence of low light scattering in the TiO2 film. Highest conversion efficiency was observed for DSC that used well-defined spherical TiO2 aggregates composing of 20-nm nanocrystallites which were synthesized using ethanol with low water content (0.9 vol%) followed by calcination at 500C. Thus, optimized TiO2 nanocrystallites which form spherical aggregate is critical in order to improve light harvesting efficiency of DSCs.

Abstract: In this work the total energy calculations on the atomic geometry and chemisorption properties of Co(0001)/H surface are performed by using the density-functional theory in the approach of the projector-augmented wave (PAW) method. For a clean Co(0001) surface the atomic relaxations of the top three Co(0001) layers are obtained. The adsorptions of atomic Hydrogen have been investigated in the surface periodicities of p(1×1), p(1×2), p(2×2), and (  )R30º combined with hcp hollow and fcc hollow sites. For the cases studied in this work, the atomic hydrogen occupies fcc hollow site preferably drawn from the total energies. In these surface structures the perpendicular distances between the adsorbate and the first layer of substrate (DH-Co) range from 0.93 Å to 0.99 Å. The calculations on the surface vibrational modes proved the frequencies of atomic hydrogen along substrate surface displayed strong dependence on the adsorption geometries.

Abstract: Atomic/molecular adsorption on a microcantilever surface can cause the cantilever to deflect as a result of the adsorption-induced surface stress. In this paper, based on atomic/molecular interactions, an energy-based model is proposed to calculate the chemisorption-induced surface stress. The connection between the chemisorption-induced surface stress and the covalent bond interactions is established. The results are consistent with relevant experimental observations. This study is helpful for characterizing and optimizing the mechanical response of cantilever-based sensors.