Supercritical Carbon Dioxide Solutions Research Articles

Investigation of the supercritical deposition of platinum nanoparticles into carbon aerogels

The preparation of platinum/carbon aerogel (CA) nanocomposites by the supercritical deposition method was investigated. CAs were impregnated with dimethyl(cyclooctadiene)platinum, CODPtMe 2, from supercritical carbon dioxide (scCO 2) solutions and the resulting CODPtMe 2/CA composites were converted to Pt/CA composites. The adsorption isotherms of CODPtMe 2 on CAs were measured and could be represented by the Langmuir model. The results indicated a strong interaction between CODPtMe 2 molecules and the CA surface and that a substantial fraction of the surface of the CAs was covered with CODPtMe 2 molecules at relatively low concentrations. Four different reduction methods were used to convert the CODPtMe 2 impregnated CAs which were: (1) thermal reduction at atmospheric pressure in an inert atmosphere; (2) thermal reduction in scCO 2; (3) chemical reduction in scCO 2 with hydrogen; and (4) chemical reduction at atmospheric pressure with hydrogen. Method 1 gave highly dispersed Pt nanoparticles (1–3 nm) at loadings ranging from 10 to 40 wt.%. The use of hydrogen in Method 4 increased the average particle size by a factor of 2 over Method 1 at the same Pt loading, but the particles still had a narrow unimodal size distribution. When the thermal reduction was carried out in scCO 2, loadings as high as 73% could be obtained. Method 3 generated a composite having a disordered columnar Pt coating and equiaxed particles ≈1 μm in diameter on the external surface of the monolith and dispersed Pt nanoparticles in the interior. The analysis of the reaction products in scCO 2 indicated an autocatalytic reaction. Increasing the Pt loading was found to decrease the surface area of the CA, primarily through blockage of the micropores.

Modeling the Entrainer Effects on Solubility of Solutes in Supercritical Carbon Dioxide

Applicability of a previously published equation for calculating the solubility of solutes in supercritical carbon dioxide was extended to calculate the solubility in entrained supercritical carbon dioxide employing 42 experimental data sets collected from the literature. The accuracy of the proposed model was evaluated by calculating both the average absolute relative deviation and the individual absolute relative deviation. The proposed model showed superiority to a previously published similar model, from both correlation and prediction points of view.

Light Scattering Study of Polydimethyl Siloxane in Liquid and Supercritical Carbon Dioxide

In this paper, we report the results of static and dynamic light scattering investigations of polydimethyl siloxane (PDMS) solutions in both liquid and supercritical carbon dioxide (CO2). This study was performed below the theta point and provides quantitative information on the CO2 solvent quality over a large range of temperature (25−54 °C) and density (0.97−1.01 g/mL). The solvent quality of the CO2 can be adjusted by independently varying temperature or density, as demonstrated by the dependence of the second virial coefficient on these two parameters. The theta temperature was observed to be a strong function of CO2 density and may be a weak function of the PDMS molecular weight. The strength of the excluded volume interactions in the PDMS−CO2 solution was determined to be weaker than predicted, and no universal behavior was observed.

High-Pressure19F NMR Measurements of a Series of Fluorinated Benzenes in Supercritical Carbon Dioxide

The high-pressure and high-resolution NMR cell method has been developed for precise measurements of supercritical carbon dioxide solutions. 19F NMR chemical shifts of a series of fluorinated benzenes, C6H n F m (n = 6 − m and m = 1 ∼ 6) in CO2 at dilute concentrations were measured over a wide pressure range up to 35 MPa at 314.3 K. The density dependence of the corrected chemical shift, where the bulk magnetic susceptibility contribution was subtracted, was well represented by a cubic function of CO2 density for any fluorinated benzene. The linear coefficients, arising from pairwise intermolecular interactions, were found to be dependent on the numbers and positions of fluorine atoms in the fluorinated benzenes. The solute–solvent interaction between fluorine and CO2 was discussed.

Reactive Deposition of Cobalt and Nickel Films from Their Metallocenes in Supercritical Carbon Dioxide Solution

High-purity Co and Ni thin films were deposited directly onto the native oxide of Si wafers and onto TaN and TiN films supported on Si wafers by the hydrogen reduction of their respective metallocenes in supercritical CO2 solution using a batch, cold-wall chemical fluid deposition (CFD) reactor. For Co deposition from bis(cyclopentadienyl)cobalt, substrate temperatures ranged between 285 and 320 °C and reactor pressures were 220−260 bar. For Ni deposition from bis(cyclopentadienyl)nickel, substrate temperatures were 175−200 °C and reactor pressures were 190−230 bar. In all cases, the reactor wall temperatures were maintained between 90 and 120 °C, restricting the depositions to the heated substrates only. The deposited films were characterized by SEM, XRD, and XPS. The films were found to be essentially free from ligand-derived contamination.

HF Etchant Solutions in Supercritical Carbon Dioxide for “Dry” Etch Processing of Microelectronic Devices

A “dry” supercritical CO2-based etchant solution containing HF/pyridine as an anhydrous HF source effectively dissolves SiO2 thin films on silicon wafers. These dilute etchant solutions are active in removal of post-etch residues in back-end-of-line cleaning of microelectronic structures.

Thin fluoropolymer films and nanoparticle coatings from the rapid expansion of supercritical carbon dioxide solutions with electrostatic collection

Application of nanometer thick fluoropolymer films onto metal and semiconducting substrates is described. In the first step, nanometer-sized polymer particles are generated by a process of homogeneous nucleation during the rapid expansion of supercritical fluid solutions. These gas-phase particles are then charged as they are being formed by application of a high voltage to the expansion nozzle. In this way the charged nanoparticles can be collected on a solid surface forming uniform coatings with thicknesses from tens of nanometers to several micrometers thick. Supercritical carbon dioxide solutions of three different fluoropolymers were used to generate different types of coatings. This represents a ‘green’ process for film deposition. A further unique aspect of this process is that the small charged nanoparticles can be deposited to electrically conducting microscopic regions with a spatial resolution better than 50 nm.

Solubility of solid solutes in supercritical carbon dioxide with and without cosolvents

The solubility of 2-naphthol and anthracene in supercritical CO 2 was determined at 308.1, 318.1 and 328.1 K, with and without cosolvent. The influence of three polar or nonpolar cosolvents, acetone, ethanol and cyclohexane, was studied at concentrations of 3.6 and 4.0 mol%. The solubility enhancement with these cosolvents is considerable, and the cosolvent effect increases in the order ethanol, acetone, and cyclohexane for 2-naphthol and for anthracene, the order is cyclohexane, ethanol, and acetone. The influence of density and cosolvent on the solid solubility was studied and discussed.

Thermal and morphological characterization of micronized acetylsalicylic acid powders prepared by rapid expansion of a supercritical solution

Aim of this work was to investigate the solid-state characteristics of micronized acetylsalicylic acid (ASA), produced by rapid expansion of a supercritical carbon dioxide solution (RESS) and to assess whether a correlation could be found between process parameters and solid-state characteristics. Drug solubility in supercritical CO2 was first assessed under various pressure and temperature conditions. DSC, FT-IR, PXRD, SEM, laser light scattering and HPLC were used to characterise the solid phases produced by the RESS. The obtained particles were crystalline, with spectroscopical and diffractometrical pattern overlapping those of the starting available product. However, a strong reduction of particle size was obtained, linearly correlated to pressure imposed during the RESS process, while temperature did not seem to have a major effect. Similar influence of pressure was observed on the final melting temperature of the micronized ASA. The application of a mathematical model allowed to conclude that the melting temperature depression of RESS-prepared ASA powders can be attributed to the decrease of particle dimension rather than to the formation of different solid phases or impurities.

Polymorphic properties of micronized carbamazepine produced by RESS

Carbamazepine microparticles were produced by the rapid expansion of supercritical carbon dioxide solutions (RESS) method. The characteristics of the resulting particles were studied by X-ray powder diffraction (XRPD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and image analysis. X-ray diffractograms and SEM photomicrographs revealed that the crystalline nature of the produced carbamazepine microparticles depended on operating pressure and temperature conditions. Different polymorphs were obtained under various operating conditions. Under certain temperature (below 40 °C) and pressure (below 240 bar) conditions, it was possible to form primarily the carbamazepine polymorph stipulated by US Pharmacopeia. A significant reduction was observed in the particle size and size distribution range of carbamazepine produced by RESS. The processed particles had a mean diameter smaller than 3 μm and a size distribution range between 0.5 and 2.5 μm compared to unprocessed starting material with a mean diameter of approximately 85 μm and a size distribution range between 15 and 336 μm. Thus, this study demonstrates that the polymorphic characteristics of carbamazepine microparticles produced by the RESS method can be controlled by varying operating pressure and temperature parameters.

Electroplating of Nanostructured Nickel in Emulsion of Supercritical Carbon Dioxide in Electrolyte Solution

Abstract We report electroplating in emulsion of supercritical carbon dioxide and electrolyte solution for the first time. Compared to conventional electroplating, this technology has advantages in covering, leveling and throwing effects on plating. Moreover the particle sizes of plated nickel are sub-100 nm.

High-Quality Ultrathin Polymer Films Obtained by Deposition from Supercritical Carbon Dioxide As Imaged by Atomic Force Microscopy

Promising new technique of polymer deposition from solutions in supercritical carbon dioxide (sc CO2) has been applied to form ultrathin Teflon AF2400 copolymer films on substrates with different properties. Atomic force microscopy study of the coatings morphology has been performed for the first time and has revealed surprisingly high film uniformity, very low roughness, and good stability during the scanning procedure. Our findings have demonstrated the intriguing possibilities of the applied film-forming process allowing to deposit the thin-film coatings and also individual macromolecules in a controllable manner. This is because the variations of solution temperature and pressure influence significantly the dissolving power of sc CO2; therefore, the macromolecule precipitation depends strongly on the thermodynamic regime and can be easily controlled. The influence of substrate properties, exposure conditions, and deposition kinetics on the film morphology, thickness, and level of surface coverage has ...

Effect of polymer coatings from CO2, on water‐vapor transport in porous media

AbstractA variety of perfluorinated polyethers were coated onto surfaces of marble, sandstone and limestone samples from solutions in supercritical carbon dioxide. These polymers make ideal protectants for civil infrastructure by making stone surfaces hydrophobic and preventing penetration and deterioration of the stone by acid rain. The effective diffusivities of water vapor through coated and uncoated stones were measured as a function of polymer applied per unit area of sample. An analysis of the diffusive transport of water through the stones led to estimates of the penetration depths of the polymers and the percentages of blockage of the pores in the coated layers as a function of polymer surface coverage. Penetration depths were seen to strongly depend on the mean size and porosity of the stones. It is important for water‐vapor diffusion to occur through the samples to prevent water condensation inside polymer‐coated structural materials.

Deposition of conformal copper and nickel films from supercritical carbon dioxide.

Device-quality copper and nickel films were deposited onto planar and etched silicon substrates by the reduction of soluble organometallic compounds with hydrogen in a supercritical carbon dioxide solution. Exceptional step coverage on complex surfaces and complete filling of high-aspect-ratio features of less than 100 nanometers width were achieved. Nickel was deposited at 60 degrees C by the reduction of bis(cyclopentadienyl)nickel and copper was deposited from either copper(I) or copper(II) compounds onto the native oxide of silicon or metal nitrides with seed layers at temperatures up to 200 degrees C and directly on each surface at temperatures above 250 degrees C. The latter approach provides a single-step means for achieving high-aspect-ratio feature fill necessary for copper interconnect structures in future generations of integrated circuits.

Environmentally benign formation of polymeric microspheres by rapid expansion of supercritical carbon dioxide solution with a nonsolvent.

A novel method is reported for forming polymer microparticles, which reduce atmospheric emissions of environmentally harmful volatile organic compounds such as toluene and xylene used as paint solvent in paint industry. The polymer microparticles have formed through rapid expansion from supercritical solution with a nonsolvent (RESS-N). Solubilization of poly(styrene)-b-(poly(methyl methacrylate)-co-poly (glycidyl methacrylate)) copolymer(PS-b-(PMMA-co-PGMA), MW = 5000, PS/PMMA/PGMA = 2/5/3), poly(ethylene glycol) (PEG, M. W = 4000), bisphenol A type epoxy resin (EP, MW = 3000), poly(methyl methacrylate) (PMMA; MW = 15000, 75000, 120000), and poly(oxyalkylene) alkylphenyl ether (MW = 4000) in carbon dioxide (CO2) was achieved with the use of small alcohols as cosolvents. The solubility of the PS-b-(PMMA-co-PGMA) is extremely low in either CO2 or ethanol but becomes 20 wt % in a mixture of the two. Because ethanol is a nonsolvent for the polymer, it can be used as a cosolvent in rapid expansion from supercritical solution to produce 1-3 microm particles that do not agglomerate. Obtained polymer particles by RESS-N were applied as powder coatings. The resulting coatings have a smooth and coherent film. The particle size distribution of microspheres was controlled by changing the polymer concentration, preexpansion pressure, temperature, and injection distance. The feed compositions were more effective than the other factors in controlling the particle size. The polymeric microparticles formed by RESS-N method can be utilized to make the thin coating film without anytoxic organic solvents and/or surfactants.

Modeling of ternary solubilities of organics in supercritical carbon dioxide

A new thermodynamic model was developed for modeling the solubilities of solid solutes in supercritical carbon dioxide. The model combines the cubic Patel–Teja equation of state (EOS) with the Wong–Sandler (WS) mixing rules (MR). The model is applied to correlate the solubilities of different ternary systems and the corresponding binaries. The versatility of this model is indicated by the ability of the model to successfully predict the solubilities of both polar and non-polar mixtures. The model provides a better correlation than the conventional models that use Peng–Robinson-EOS (PR-EOS) with simple or WS MR.

Artificial aging of phenanthrene in porous silicas using supercritical carbon dioxide.

Expedited artificial aging is described and demonstrated using a novel system that circulates a solution of supercritical carbon dioxide and a hydrophobic organic sorbate (phenanthrene) through a closed loop containing a porous substrate. Unlike traditional methods used to simulate the natural aging process, our approach allows for real-time monitoring of sorption equilibria, and the process is highly accelerated due to the unique physical properties of supercritcal carbon dioxide. The effectiveness of the system to simulate aging was demonstrated with a series of experiments in which three silicas with varying particle and pore sizes were loaded with phenanthrene. Batch aqueous desorption experiments were used to evaluate the extent of the aging process. For the two types of particles containing the largest pores (i.e., mean diameters of 202 and 66 A), 95% and 86%, respectively, of the phenanthrene was released to the aqueous fraction within 3 h. In contrast, only 16% of the phenanthrene was released from particles having a mean pore diameter of 21 A after 24 h. These results were confirmed by the results from an aqueous column desorption experiment. Confounding factors that might contribute to slow aqueous desorption such as the hydration state of the particles' surfaces, the chemical form of the loaded phenanthrene, and the organic carbon content were investigated and/or normalized for all three particle types. Consequently, we were able to attribute the slow desorption behavior and the presence of the resistant fraction in the 21 A silica to pore effects. With properly designed experiments, the results of this study suggest that the supercritical fluid system could be extended to the study of contaminant aging and bioavailability in natural soils and sediments.

New Chelate Complexes of Copper and Iron: Synthesis and Impregnation into a Polymer Matrix from Solution in Supercritical Carbon Dioxide.

New Chelate Complexes of Copper and Iron: Synthesis and Impregnation into a Polymer Matrix from Solution in Supercritical Carbon Dioxide.

Spectroscopy, Solubility, and Modeling of Cosolvent Effects on Metal Chelate Complexes in Supercritical Carbon Dioxide Solutions

Extraction of metals from aqueous solutions and solid matrixes with supercritical CO2 is an attractive, environmentally benign alternative to organic solvent extraction to remove metal contaminants. Here, new measurements are presented for the solubility of iron tris(pentane-2,4-dionate) [Fe(acac)3], a representative metal chelate complex, in pure supercritical CO2 and in a mixture of supercritical CO2 and trichloromethane (chloroform), a typical organic co-contaminant, as a function of temperature and pressure. Solubilities ranged from 8.75 × 10-6 mole fraction to 1.34 × 10-3 mole fraction with an average uncertainty of just 12%. It is shown that the presence of 3 mol % chloroform increases the solubility of Fe(acac)3 by approximately a factor of 2. Thus, the co-extraction of organic contaminants with metals would be advantageous. In addition, spectroscopic measurements are presented of the local environment around the dissolved Fe(acac)3 in the CO2/chloroform mixture that show a cybotactic region that i...

New Chelate Complexes of Copper and Iron: Synthesis and Impregnation into a Polymer Matrix from Solution in Supercritical Carbon Dioxide

New chelate complexes of copper diiminate and iron diiminate were synthesized. Their physical characteristics have been studied. The diffusion of supercritical carbon dioxide (scCO2) into polyarylate (PAR) films and their impregnation with diiminates were investigated. The equilibrium degree of PAR swelling in scCO2 is about 10%. The conditions of impregnation (45 °C, 8 MPa, 1.5 h) were determined. The impregnation was confirmed by the FT-IR spectroscopic data. Thermal reduction of metal ions was investigated. Transformations of the chelate complexes on the polymer-film surface were studied by ESCA. The value of the Auger factor indicates that, after thermal reduction, the copper ion is in a nearly univalent state. The copper content in films is as large as 6.3 wt %; the iron content is 4.5 wt %. The FT-IR and ESCA spectroscopic studies showed that, in the course of impregnation, chelate complexes interact with functional groups of the polymer. Subsequent thermal reduction of metal in air results in diiminate evaporation and thermooxidative degradation with ligand decomposition and enrichment of the surface with metal atoms. According to the SAXS data, the size distribution of metal-containing particles ranges from 20 to 60 nm with a maximum at 34 nm.