a b s t r a c tAnion exchanger (Amberlite IRA-420; AMB) has been used in the removal of permanganate ions from potassium permanganate contaminated water. Operational conditions such as permanganate concentration, adsorption time, adsorption temperature, adsorption pH, agitation speed, and finally adsorbent dosage have been investigated, and its impact on the removal process efficiency has been presented. Moreover, the kinetic and equilibrium results obtained for permanganate ions sorption with different initial concentrations onto AMB were analyzed. Kinetic modeling analysis with three different types of kinetic sorption models (pseudo-first-order, pseudo-second-order, and simple Elovich models) was applied to simulate the permanganate ions sorption data. The analysis of the kinetic data indicated that the sorption was a second-order process. An ion-exchange mechanism may have existed in the permanganate ions-sorption process with AMB. The permanganate ions uptake by AMB was quantitatively evaluated with equilibrium sorption isotherms. To describe the isotherms mathematically, the experimental data of the removal equilibrium were correlated with the Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich (D-R) isotherm models, and the applicability of these isotherm equations to the sorption systems was compared by the correlation coefficients. The maximum sorption capacities, determined from the Langmuir isotherm was 20.54 mg/g at 25°C. Moreover, diffusion mechanism of permanganate ions was described by different adsorption diffusion models. The diffusion rate equations inside particulate of Dumwald-Wagner and intraparticle models were used to calculate the diffusion rate. The actual rate-controlling step involved in the permanganate ions sorption process was determined by further analysis of the sorption data applying the kinetic expression given by Boyd.

Gold, Au nanoparticles were deposited on ZnO, Al2O3, and Ga2O3 via colloidal method in order to investigate the role of support for CO2 hydrogenation to methanol. Au/ZnO was also produced using impregnation method to investigate the effect of colloidal method to improve methanol selectivity. Au/ZnO produced via sol immobilization showed high selectivity towards methanol meanwhile impregnation method produced Au/ZnO catalyst with high selectivity towards CO. The CO2 conversion was also influenced by the amount of Au weight loading. Au nanoparticles with average diameter of 3.5 nm exhibited 4% of CO2 conversion with 72% of methanol selectivity at 250 °C and 20 bar. The formation of AuZn alloy was identified as active sites for selective CO2 hydrogenation to methanol. Segregation of Zn from ZnO to form AuZn alloy increased the number of surface oxygen vacancy for CO2 adsorption to form formate intermediates. The formate was stabilized on AuZn alloy for further hydrogenation to form methanol.  The use of Al2O3 and Ga2O3 inhibited the formation of Au alloy, and therefore reduced methanol production. Au/Al2O3 showed 77% selectivity to methane, meanwhile Au/Ga2O3 produced 100% selectivity towards CO. Copyright © 2021 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).