Jerzy A. Mielczarski

Quantitative and qualitative evaluation of adsorption/desorption of bovine serum albumin on hydrophilic and hydrophobic surfaces.

We studied the adsorption of bovine serum albumin (BSA) from phosphate-buffered saline (pH 7.4) to hydrophilic and hydrophobic surfaces. Attenuated total reflection Fourier transform infrared spectroscopy, supported by spectral simulation, allowed us to determine with high precision the amount of BSA adsorbed (surface coverage) and its structural composition. The adsorbed BSA molecules had an alpha-helical structure on both hydrophobic and hydrophilic surfaces but had different molecular conformations and adsorption strengths on the two types of surface. Adsorption of BSA was saturated at around 50% surface coverage on the hydrophobic surface, whereas on the hydrophilic surface the adsorption reached 95%. The BSA molecules adsorbed to the hydrophilic surface with a higher interaction strength than to the hydrophobic surface. Very little adsorbed BSA could be desorbed from the hydrophilic surface, even using 0.1 M sodium dodecyl sulfate, a strong detergent solution. The formation of BSA-phosphate surface complexes was observed under different BSA adsorption conditions on hydrophobic and hydrophilic surfaces. The formation of these complexes correlated with the more efficient blocking of nonspecific interactions by the adsorbed BSA layer. Results from the molecular modeling of BSA interactions with hydrophobic and hydrophilic surfaces support the spectroscopic findings.

2. Sensitized degradation of chlorophenols on iron oxides induced by visible light: Comparison with titanium oxide

Abstract The sensitized photocatalytic degradation of mono-, di- and trichlorophenols on iron oxides aqueous suspensions of α-Fe 2 O 3 and α-FeOOH is reported in detail. The degradation of these compounds followed pseudo-first-order kinetics when α-Fe 2 O 3 was used as photocatalyst. α-FeOOH was found to be inactive for chlorophenols degradation with the exception of 2,4-dichlorophenol (2,4-DCP) where a modest effect was observed. The formation of a surface complex by the chlorophenols with the iron oxide and the solubility of the particular chlorophenol in aqueous solution were observed to be the controlling parameters during the photodegradation. The results obtained with the most active catalyst α-Fe 2 O 3 are compared with TiO 2 . Total mineralization of chlorophenols was observed on TiO 2 while on α-Fe 2 O 3 only partial mineralization was observed. In either case, the intermediates produced in solution during the photodegradation were found to be significantly more biodegradable than the initial compound. For mono-, di- and trichlorophenols the overall photocatalytic degradation was observed to increase in the order: 2,4,6-trichlorophenol (2,4,6-TCP) 3- DCP ) chlorophenol (2- CP) ,4-DCP. The former sequence shows that the recalcitrant 2,4-DCP degrades more rapidly than other chlorophenols tested during this study. The photodegradation of chlorophenols on α-Fe 2 O 3 and TiO 2 proceeds mechanistically through para -hydroxylation of the initial compound as suggested by the intermediates found by high-pressure liquid chromatography HPLC during the course of the degradation.

Polyoxometalate-based layered structures for charge transport control in molecular devices.

Hybrid organic-inorganic films consisted of molecular layers of a Keggin-structure polyoxometalate (POM: 12-tungstophosphoric acid, H(3)PW(12)O(40)) and 1,12-diaminododecane (DD) on 3-aminopropyl triethoxysilane (APTES)-modified silicon surface, fabricated via the layer-by-layer (LBL) self-assembly method are evaluated as molecular materials for electronic devices. The effect of the fabrication process parameters, including primarily compositions of deposition solutions, on the structural characteristics of the POM-based multilayers was studied extensively with a combination of spectroscopic methods (UV, FTIR, and XPS). Well-characterized POM-based films (both single-layers and multilayers) in a controlled and reproducible way were obtained. The conduction mechanisms in single-layered and multilayered structures were elucidated by the electrical characterization of the produced films supported by the appropriate theoretical analysis. Fowler-Nordheim (FN) tunneling and percolation mechanisms were encountered in good correlation with the structural characteristics of the films encouraging further investigation on the use of these materials in electronic and, in particular, in memory devices.

Magnetron-sputtered Ag surfaces. New evidence for the nature of the ag ions intervening in bacterial inactivation.

DC-magnetron sputtering with an Ag target on textile surfaces produced Ag particles with sizes approximately 4.7 nm (+/-15%). Sputtering for 15 s led to Ag layers of 15-20 nm. The threshold sputtering time precluding airborne bacterial growth was about 60 s. In this case, the coating was approximately 40-50 nm thick and the cotton Ag loading was 0.0026 wt %. The Ag particle size did not vary significantly with sputtering time between 15 and 600 s. Only coatings above this thickness lead to bacterial inactivation. Ag/Pt targets with sputtering times<60 s did not increase the bactericide performance of the Ag cotton samples with respect to sputtering from an Ag target alone, as expected from the position of Pt respect to Ag in the electrochemical series (Galvanic effect). The Ag cotton deposition led to very thin metallic semitransparent gray color coatings. X-ray of the Ag cotton suggested the presence of amorphous and crystalline Ag species. By X-ray photoelectron spectroscopy (XPS), it was found that the amount of oxidized silver species on the cotton was similar for sputtering times of 60 and 600 s, but the total amount of Ag deposited was almost two times higher after 600 s sputtering. This suggests that the positive silver-ions were located mainly at the silver interface. The type of silver ions produced using the Ag/Pt sputtering was determined to be very similar at 15, 60, and 600 s with the silver ions produced with the Ag target. This explains the lack of an increased inhibitory effect of Pt during the inactivation of airborne bacteria when present in the Pt/Ag target with respect to the Ag target, because in both cases similar silver ionic species were found.

The surface-segregated nanostructure of fluorinated copolymer-poly(dimethylsiloxane) blend films.

Two fluorinated/siloxane copolymers, O5/19 and D5/3, carrying 6 and 8 CF(2) groups in the fluoroalkyl tail, respectively, were used as the surface-active components of cured poly(dimethylsiloxane) (PDMS) blends at different loadings (0.3-5.0 wt % with respect to PDMS). The surface chemical composition was determined by angle-resolved X-ray photoelectron spectroscopy at the takeoff angles theta of 0 degrees, 60 degrees, and 75 degrees. It was found that the fluorinated copolymer was surface-segregated, and in-depth segregation (approximately 5 nm) depended upon the chemical structure of the copolymer. The surface fluorine atomic percentage of the blends with D5/3 was up to 3 orders of magnitude higher than the theoretical value expected for ideal homogeneous samples. Moreover, small amounts of the copolymer in the blends were sufficient to saturate the outermost surface in fluorine content. The chemical composition of the surface-segregated nanostructure of the films was also proven to be affected by external environment, namely, exposure to water.

XPS study of ethyl xanthate adsorption on oxidized surface of cuprous sulfide

Abstract The surface of cuprous sulfide (chalcocite) has been oxidized in aerated water at pH 9.5, and cupric hydroxide and carbonate are formed. No oxidized sulfur species are observed. Upon subsequent immersion in an ethyl xanthate solution the oxidation products are found to be gradually removed from the surface with the simultaneous adsorption of xanthate, and a randomly oriented layer of cuprous ethyl xanthate is also found. After removal of oxidation products and contamination, a well-oriented monolayer of ethyl xanthate molecules is formed directly on chalcocite surface. The multilayer coverage of cuprous ethyl xanthate is unevenly distributed on the chalcocite surface. These results show that the amount of oxidation products on the chalcocite surface prior to xanthate treatment has an important effect on the structure of the xanthate layer at different stages of the adsorption.

Influence of chain length on adsorption of xanthates on chalcopyrite

The direct characterization at a molecular level of the surface products formed by the interaction of aqueous solutions of ethyl and amyl xanthate with chalcopyrite polarized to different potentials were carried out by the infrared external reflection technique recently developed for detailed study of the adsorbed layer on mineral surfaces. The experimental spectroscopic data combined with the simulation of hypothetical adsorption layers have let us determine the type, structure and the surface distribution of the adsorbed species produced at different adsorption conditions, and to propose mechanisms of the interaction between the aqueous solutions of collectors and the surface of chalcopyrite. The spectroscopic results show striking differences in the composition of the outermost layer of chalcopyrite contacted with ethyl or amyl xanthate solutions, which obviously will produce differences in the flotation behavior of the mineral and in consequence will influence its separation from other ore components. These observations explain why different xanthate homologues should be used in flotation practice. A detailed discussion of flotation pulp solution conditions to produce different types of hydrophobic surface species for either collector and collectorless flotation of chalcopyrite is also presented.

Evidence for immobilized photo-Fenton degradation of organic compounds on structured silica surfaces involving Fe recycling

The present study reports on the use of novel structured inorganic silica fabrics loaded with Fe ions by exchange-impregnation as a heterogeneous photocatalyst. These Fe–silica fabrics are denoted EGF/Fe(0.4%). Experimental evidence shows that Fe ions are released from the silica fabrics and react with H2O2 to form oxidative radicals in solution; the Fe ions are reduced to Fe(II) during oxalic acid and oxalate oxidation. The Fe3+ is extracted from the support to the aqueous medium where it is re-oxidized by being re-adsorbed onto the silica fabric. The contributions of the homogeneous and heterogeneous photocatalysis processes during the degradation of oxalic acid and oxalates were quantified as a function of the solution pH and the results presented agree with the modeling of the iron oxide surface in the presence of oxalates at different pH values. By attenuated total reflection infrared spectroscopy (ATRIR), the asymmetric stretching vibration doublet band at 1740 cm−1 and the satellite peaks corresponding to surface carboxylates were followed during the photocatalytic destruction of the oxalates. The results obtained indicate that the oxalate decomposition channel involves a fast light-activated decarboxylation of the Fe complex: [RCO2Fe]2+ → [R˙] + CO2 + Fe2+. The structural features of the EGF/Fe(0.4%) surfaces were investigated before and after the oxalate photocatalysis by high resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS) and gas adsorption studies (BET).

Sorption of uranium (VI) species on zircon: structural investigation of the solid/solution interface

This work is an investigation of the mechanisms of interaction between uranium (VI) ions and zirconium silicate. The speciation of uranium (VI) sorbed on zircon was studied using four complementary techniques as probes of the local structure around the uranium atom: laser spectrofluorimetry, X-ray photoelectron spectroscopy (XPS), diffuse reflectance infrared Fourier-transformed (DRIFT) spectroscopy, and EXAFS spectroscopy. The sorption of uranyl on zirconium oxide was also studied to allow structural comparisons. Spectrofluorimetry and XPS results allowed an identification of the silicate sorption sites on the solid. These methods associated with spectrofluorimetry and DRIFT led to a characterization of the sorbed surface complexes, taking into account the influence of the nature of the background salt and of the pH on the structure of the U(VI) surface species. EXAFS measurements, either on air-dried samples or in situ, were then carried out on well-characterized samples and allowed identification of the sorption mechanism on zircon as the formation of an inner-sphere polydentate surface complex.

The role of impurities of sphalerite in the adsorption of ethyl xanthate and its flotation

Abstract The adsorption of ethyl xanthate on two samples of sphalerite was investigated with X-ray photoelectron spectroscopy and ‘in situ’ internal reflection spectroscopy in infrared. One of the samples showed good floatability in acidic (pH 4.8–5.7) and weakly basic (pH 7.6–8.2) solutions. It was found that the sphalerite was self-activated by the lead ions contained in the mineral (a dozen-fold increase of the lead concentration in the surface layer) and a monolayer form of lead ethyl xanthate was observed on the surface. The flotation depression observed in neutral solutions, despite a significant amount of xanthate adsorbed, is caused by clusters of a precipitated form of lead ethyl xanthate on the sphalerite surface. Above a pH of about 9 neither xanthate adsorption nor sphalerite flotation is observed. Ethyl xanthate adsorption at pH 9, hence flotation, is possible if the sphalerite sample is self-activated by treating with an acidic solution (even without xanthate) for several minutes. The second sample of sphalerite, which had a much lower lead content than the first one, was investigated within a pH range from 4 to 10. It adsorbed only a very small amount of ethyl xanthate (about 15% of the statistical monolayer) which did not provide sufficient hydrophobic properties required for flotation.