Adsorption Of Hydrophobic Compounds Research Articles

Dispersion of ceria nanoparticles on γ-alumina surface functionalized using long chain carboxylic acids

Dispersion and stability of nanoparticles on a support is determined by the interaction between these phases. In case of hydrophobic nanoparticles (e.g. synthesized by reverse microemulsion method) the interaction with hydrophilic support (e.g. γ-Al2O3) is weak and agglomeration as well as poor resistance to sintering may cause problems. The bonding of the particles to the support may be effectively strengthened by proper modification of the support, e.g. by adsorption of hydrophobic compounds on its surface. In this work decanoic, myristic, stearic and oleic acid were used for the first time to cover γ-Al2O3 surface in order to enhance the dispersion of ceria nanoparticles deposited afterward by impregnation on such support. TGA and FTIR methods revealed that at monolayer coverage (1.1–2.5 molecules per nm2) the acid molecules are firmly bounded to the alumina surface. Morphology, textural properties, phase composition and reducibility of the CeO2/γ-Al2O3 samples were investigated using TEM, SEM, BET, XRD and H2-TPR methods. It has been shown that deposition of CeO2 nanoparticles on γ-Al2O3 surface covered with all studied acids enhances its dispersion, stability and reducibility. The most effective modification of the γ-Al2O3 surface was obtained at loading of 2.3 molecules of decanoic acid per nm2 of the support.

Adsorption of hydrophobic compounds onto NF/RO membranes: an artifact leading to overestimation of rejection

This study addresses the adsorption of hydrophobic compounds at low concentration (∼100 ppb) onto NF/RO membranes. In this study, three surrogate compounds and three NF/RO membranes were tested under cross-flow conditions. Experimental results showed that the adsorption of hydrophobic compounds was significant for neutral compounds and ionizable compounds when electrostatically neutral. Also, operating conditions such as the permeate flow rate (flux) had a significant effect on the degree of compound adsorption. A comparison of the adsorption observed in dynamic filtration tests with that in static batch adsorption tests suggests that more adsorption sites are accessible for molecules during membrane filtration due to the pressurized advective flow. It was observed that the concentration of the tested compounds changed during filtration tests due to adsorption. Therefore, an accurate evaluation of a given membrane in terms of the rejection of a hydrophobic compound is not possible until saturation of the membrane with the compound of interest is accomplished. The experimental results demonstrated that a relatively large amount of the feed water needed to be filtered to reach saturation conditions.

On the enrichment of hydrophobic organic compounds in fog droplets

The unusual degree of enrichment of hydrophobic organics in fogwater droplets reported by several investigators can be interpreted as a result of (a) the effects of temperature correction on the reported enrichment factors, (b) the effects of colloidal organic matter (both filterable and non-filterable) in fog water and (c) the effects of the large air-water interfacial adsorption of neutral hydrophobic organics on the tiny fog droplets. The enrichment factor was directly correlated to the hydrophobicity (or the activity coefficient in water) of the compounds, as indicated by their octanol-water partition constants. Compounds with large octanol-water partition coefficients (high activity coefficients in water) showed the largest enrichment. Available experimental data on the adsorption of hydrophobic compounds at the air-water interface and on colloidal organic carbon were used to show that the large specific air-water interfacial areas of fog droplets contribute significantly to the enrichment factor.