China
Africa
Explore chapters and articles related to this topic
“Soft” Chemical Synthesis and Manipulation of Semiconductor Nanocrystals
Published in Victor I. Klimov, Nanocrystal Quantum Dots, 2017
Jennifer A. Hollingsworth, Victor I. Klimov
Owing to the ease with which high-quality samples can be prepared, the II-VI compound, CdSe, has comprised the “model” NQD system and been the subject of much basic research into the electronic and optical properties of NQDs. CdSe NQDs can be reliably prepared from pyrolysis of a variety of cadmium precursors, including alkyl cadmium compounds (e.g., dimethylcadmium)20 and various cadmium salts (e.g., cadmium oxide, cadmium acetate, and cadmium carbonate),21 combined with a selenium precursor prepared simply from Se powder dissolved in trioctylphosphine (TOP) or tributylphosphine (TBP). Initially, the surfactant–solvent combination, technical-grade trioctylphosphine oxide (TOPO) and TOP, was used, where tech-TOPO performance was batch specific due to the relatively random presence of adventitious impurities.20 More recently, tech-TOPO has been replaced with “pure” TOPO to which phosphonic acids have been added to controllably mimic the presence of the tech-grade impurities.22 In addition, TOPO has been replaced with various fatty acids, such as stearic and lauric acid, where shorter alkyl chain lengths yield relatively faster particle growth. The fatty-acid systems are compatible with the full range of cadmium precursors, but are most suited for the growth of larger NQDs (>6 nm in diameter), compared to the TOPO/TOP system, as growth proceeds quickly.21 For example, the cadmium precursor is typically dissolved in the fatty acid at moderate temperatures, converting the Cd compound into cadmium stearate. Alkyl amines were also successfully employed as CdSe growth media.21 Incompatible systems are those that contain the anion of a strong acid (present as the surfactant ligand or as the cadmium precursor) and thiol-based systems.23 Perhaps the most successful system, in terms of producing high quantum yields (QYs) in emission and monodisperse samples, uses a more complex mixture of surfactants: stearic acid, TOPO, hexadecylamine (HDA), TBP, and dioctylamine.24
A comparative study of the solvent extraction of lanthanum(III) from different acid solutions
Published in Mineral Processing and Extractive Metallurgy, 2021
V. Agarwal, M.S. Safarzadeh, J. Galvin
Organophosphorus-type extractants are commonly used for the solvent extraction of REEs. Among the many possible extractants, di-(2-ethylhexyl)phosphoric acid (DEHPA), PC88A, and di-2,4,4-trimethylpentylphosphinic acid (Cyanex 272) are perhaps the most popular extractants for REEs. Peppard et al. (1958) investigated the extraction behaviour of lanthanides with several acidic esters of organophosphorus extractants and found that the distribution coefficients followed an inverse third power dependency on the concentration of H+ and a direct third power dependency on the concentration of the extractant. Saleh et al. (2002) investigated the solvent extraction of La(III) with Cyanex 272 diluted in toluene with and without trioctylphosphine oxide (TOPO) in nitrate-acetate medium. They observed that, at a high concentration of La(III), a white precipitate (LaA3) formed, affecting the distribution ratio (D) significantly. It was concluded that the complexes extracted into the organic phase were La(Ac)2A.3HA and La(Ac)2A2.B, respectively, in the absence and presence of TOPO. Morais and Ciminelli (2004) investigated the recovery of La(III) using DEHPA and PC88A in Exxsol™ (purified kerosene) from HCl solutions. They suggested that DEHPA performed better than PC88A in terms of extraction of La(III) but the selectivity of La(III) over Pr(III) and Nd(III) was better with PC88A than DEHPA.
Dimerization of 2-Ethylhexylphosphonic Acid Mono-2-ethylhexyl Ester (HEH[EHP]) as Determined by NMR Spectrometry
Published in Solvent Extraction and Ion Exchange, 2021
Ashleigh Kimberlin, Kenneth L. Nash
The HEH[EHP] (Carbosynth and eNovation Chemicals) was purified using the third-phase method, as described previously.[21] HDEHP was purified using the copper purification method.[22] The purity of HEH[EHP]and HDEHP was verified using 1H and 31P NMR and each was determined to be at least 98% pure. Trioctylphosphine oxide (TOPO, Sigma Aldrich) was also purified of acidic impurities by contacting a 0.5 M solution of TOPO in toluene with a 0.5 M solution of sodium bicarbonate. The organic solution was contacted with 18 MΩ cm−1 DI water to remove excess sodium bicarbonate and the solution was dried with magnesium sulfate. Triphenylphosphine oxide (Alfa Aesar. 98%), 18-crown-6 (Fluka, 99.5%), anthracene (Eastman Organic Chemicals), 1,3-diisopropylbenzene (Alfa Aesar, 96%), decalin (Sigma Aldrich, 98% cis and trans), toluene (Fisher 99.9%), tributyl phosphate (Fisher), and n-dodecane (Sigma Aldrich, 99%) were used as received. Structures of chemicals used are reported in Figure 1. Concentrated nitric acid (EMD) was used as received. Lu(NO3)3 solutions were made by dissolving Lu2O3(s) with nitric acid and Lu(NO3)3 solutions were standardized via cation exchange/acid titration. Stock solutions of Lu3+ were then diluted as needed without further standardization.
Extraction equilibrium conditions of beryllium and aluminium from a beryl ore for optimal industrial beryllium compound production
Published in Canadian Metallurgical Quarterly, 2019
Alafara A. Baba, Daud T. Olaoluwa, Ayo F. Balogun, Abdullah S. Ibrahim, Fausat T. Olasinde, Folahan A. Adekola, Malay K. Ghosh
Solvent extraction; one of the most important, economical and practical process in the hydrometallurgical industry for separation and purification of several metals, has also been reported to purify beryllium from aluminium using di-2-ethylhexylphosphoric acid (HDEHP)as investigated by several authors [8–11]. From sulphate medium, Be(II) can be extracted by HDEHP and separated from Al(III), but the extraction rate is slow and the extraction is very sensitive to pH changes. Mishra and Dhadke [12], used CYANEX 921 in cyclohexane for extraction and separation of Be(II) from Al(III) for analytical purposes. CYANEX 921 was also used for extraction chromatographic separation of Be(II) from Al(III) from hydrochloric acid solution [13]. Zaki et al. [14] reported the extraction of Be(II) and Al(III) from aqueous sulphate solution by CYANEX 921 (commercial trioctylphosphine oxide) in kerosene and explained that Be(II) was highly extracted from an aqueous medium of 0.001 M sulphate at pH 9.0, while Al(III) was highly extracted from a similar solution at pH 5.0. Be(II) extraction was found to decrease with temperature (exothermic), while Al(III) extraction increased with temperature (endothermic). Extraction of Be(II) and Al(III) by purified TOPO under similar experimental conditions showed that purified TOPO gives relatively less extraction, especially for Al(III) in the pH range 4.0–6.0.