Showing papers by "Alan L. Chaffee published in 2017"

Correlations between Oxygen Uptake and Vacancy Concentration in Pr-Doped CeO2.

Abstract: The oxygen uptake of a series of Pr–CeO2 materials was measured using thermogravimetric analysis at 420 and 600 °C, and at both temperatures, 20% Pr–CeO2 was found to have the highest uptake. The materials were characterized using X-ray diffraction and scanning transmission electron microscopy. Defects in the materials were identified using Raman spectroscopy, and ultraviolet–visible spectroscopy was used to show the presence of Pr cations in the +3 oxidation state. The existence of these species was attributed to be responsible for the ability of the materials to uptake oxygen. Electron energy loss spectroscopy was used to investigate the effect of Pr addition to CeO2; the Ce M5/M4 and O IB/IC ratios were calculated to indicate the relative changes in the Ce3+ and oxygen vacancy concentration, respectively. There was no observable increase in the Ce3+ concentration; however, the oxygen vacancy concentration increased with an increase in the Pr content. Thus, Pr increases the defect concentration and the ...

Utilization of raw and dried Victorian brown coal in the adsorption of model dyes from solution

Abstract: Being plentiful and readily available in many parts of the world, brown coal is probably one of the most potential substitutes for activated carbon. Many reports include the brown coal drying stage prior to adsorption despite the fact that it may lead to coal shrinkage and reduction of its pore volume, thus diminishing its adsorption capacity. In this study, various types of raw (wet) brown coal were investigated as adsorbents for anionic and cationic dyes in aqueous solution. The adsorption capacities of these raw brown coals were compared with those of oven dried brown coals and also with activated carbon. It was found that raw brown coals exhibit high adsorption capacities for cationic dye, but very low capacities for anionic dyes, suggesting the involvement of a cation-exchange mechanism. Additionally, the cation exchange capacities correlate positively with its cation adsorption capacity highlighting the major role of strongly acidic groups in the adsorption process. Drying the brown coal significantly reduces its adsorption capacity for cationic dye, supporting the hypothesis of coal shrinkage and the consequent reduced pore volume upon drying. These findings suggest that raw (wet) brown coal may perform as well as activated carbon for the removal of positively charged species in aqueous solution. Regeneration of the used adsorbent may also not be necessary, since the used brown coal can be simply burnt as fuel or composted.

Coordination polymers from a flexible alkyldiamine-derived ligand

Abstract: A traditionally good chelating motif has been incorporated into a ligand for the synthesis of coordination polymers with vacant amine sites. A novel tetracarboxylic acid diamine ligand, isolated as N,N,N′,N′-tetra(4-carboxybenzyl)-1,3-diaminopropane dihydrochloride trihydrate (H6L1)Cl2·3H2O, has been prepared, structurally characterised, and subsequently used in the formation of three new coordination polymers. Poly-[Cu2(L1)(OH2)2]·6DMF·3H2O 1 consists of (4,4) sheets formed by each L1 ligand coordinating to four copper(II) ‘paddlewheel’ dinuclear clusters. The amines of the ligand are non-coordinating. After solvent exchange and evacuation, 1 was found to adsorb approximately 23 cm3(STP) g−1 of CO2 at atmospheric pressure at 273 K. The isostructural compounds poly-[Zn(H2L1)(OH2)]·DMF·4H2O and poly-[Cd(H2L1)(OH2)]·DMF·3H2O 2Zn/2Cd are self-penetrating (10,3) coordination polymers containing square-shaped one-dimensional solvent channels. After solvent exchange it was found that 2Zn and 2Cd lost crystallinity, which accounts for the low N2 and CO2 uptakes observed.

Oxygen uptake, selectivity and reversibility of Tb–CeO2 mixed oxides for air separation

Abstract: A series of Tb–CeO2 mixed oxides were investigated as novel oxygen sorbents. The relationship between %Tb content-oxygen uptake, alongside the selectivity and reversibility of these materials, was determined via chemisorption (400, 500 and 600 °C) and supporting thermogravimetric studies at 500 and 600 °C. Oxygen chemisorption experiments conducted at 600 °C showed higher uptakes were achieved by incorporating more Tb into the CeO2 crystal lattice. The uptake of 40 mol% Tb–CeO2 was 121 μmol g−1 and for 10 mol% Tb–CeO2 the uptake was 34 μmol g−1. Increasing the analysis temperature for each material resulted in an increase in uptake as more oxygen was able to be removed. All materials exhibited good reversibility and cyclic stability during alternating N2 and air atmospheres at 600 °C. High O2/N2 selectivity was also demonstrated as no detectible uptake was observed at 600 °C using N2 as the adsorbate. The data suggests that these materials may have applications in air trace gas removal or as membranes for air separation applications.