ATR-IR spectroscopy has been used to probe the spectral changes resulting from UV irradiation of thin particulate films of anatase TiO2 under aqueous anoxic conditions. Irradiation under circumneutral solutions removed adsorbed impurities and produced a transient broad IR absorption peaking at ∼880 cm–1 that has been attributed to excitations associated with shallow electron traps. This shallow trap IR absorption (STIRA) was long-lived under acidic conditions with peak absorbance rising with decreasing pH. Formate was used as a hole scavenger to probe the impact of hole removal on the electron trapping processes. The adsorption of formate to anatase TiO2 was investigated in the absence of UV irradiation with the spectra showing a mixture of inner- and outer-sphere adsorbed species. UV irradiation of anatase films in the presence of formate at low concentrations enhanced STIRA intensity substantially. The STIRA scaled with TiO2 mass was more pronounced from larger crystallite anatase and was sensitive to [H+], suggesting that formation of the shallow trap state is accompanied by proton intercalation.

IR spectroscopic analysis of thin particle film anatase-containing TiO 2 systems during UV irradiation and when immersed in acidic anoxic aqueous solution reveals a striking broad asymmetric IR peak ∼880 cm -1 extending to over 2000 cm -1 , which has been previously attributed to electron excitations from a shallow trap level. The observations of this broad IR absorption in quasi-vacuum conditions or in aqueous solutions appear contradictory but are explained by the absence of electron scavengers or hole scavengers, respectively. The broad IR absorption associated with the shallow electron trap becomes more pronounced with a decrease in pH from 5 to 2 and is greatly enhanced in the presence of adsorbed oxalate. Oxalate ion adsorption/ desorption kinetics has been followed with IR spectroscopy during UV irradiation to show that the shallow trap IR absorption correlates with that of outer-sphere adsorbed oxalate acting as a hole scavenger. The IR spectra indicate the involvement of interfacial water in the electron trapping, probably via bridged hydroxyl groups which are more prevalent under acidic solution conditions.

Attenuated total reflection infrared spectroscopy has been used to study a broad mid-IR absorption attributed to electron polarons that was exhibited during ultraviolet (UV) irradiation of anatase TiO 2 particle films under aqueous photocatalytic conditions. The influence of formate hole scavenging and proton intercalation that accompanies electron trapping was investigated in anoxic solution conditions. The UV excitation and decay kinetics of the polaronic absorption (PA) varied with chemical conditions that influenced electron and hole scavenging and proton intercalation reactions. A striking near-linear decay of the PA under certain conditions indicated saturation of surface electron and oxygen sites, giving a constant reaction rate. The PA band shape varied with absorbance and between anatase samples. Water absorption losses concomitant with the PA have been ascribed to polaron-induced variation of sample refractive index. The PA likely arises from the photoionization of large polarons.

The influence on cell hydrophobicity of differential extension with ionic strength of lipopolysaccharide molecules (LPS), which exist as charged and uncharged polymers at the surface of the gram-negative bacterium Pseudomonas aeruginosa (PA01), has been investigated. Attenuated total reflection infrared (ATR-IR) spectral absorptions from a single layer of cells adsorbed to ZnSe increased in intensity with increasing NaCl concentration up to 0.1 mol L(-1). Dynamic contact angle measurements (Wilhelmy plate tensiometry) made with a ZnSe plate having an adsorbed cell layer and the adherence of the cells to hexadecane suggest that PA01 cells were most hydrophobic in contact with 0.1 mol L(-1) NaCl solutions. These data indicate a charge screening induced compression of the charged LPS polymers decreasing the cell-surface approach distance and increasing the cell hydrophobicity due to the greater surface predominance of the uncharged LPS polymers. Interestingly, adsorbed cell layers in 0.3 mol L(-1) NaCl had a lower IR absorption intensity, and PA01 cells suspended in 0.3 mol L(-1) were found to be more hydrophilic, indicating that other factors influence the cell-surface approach distance and hydrophobicity. The examination of cell electrophoretic mobility variation with NaCl concentration suggests that the compression of charged polysaccharides increases the polysaccharide charge density and may also reduce the flow of liquid through the polysaccharide layer affecting the effective potential at the interface, the cell hydrophobicity, and the cell-surface approach distance.

Adhesives from marine organisms are often the source of inspiration for the development of glues able to create durable bonds in wet environments. In this work, we investigated the adhesive secretions produced by germlings of two large seaweed species from the South Pacific, Durvillaea antarctica, also named 'the strongest kelp in the word', and its close relative Hormosira banksii. The comparative analysis was based on optical and scanning electron microscopy imaging as well as Fourier transform infrared (FTIR) spectroscopy and principal component analysis (PCA). For both species, the egg surface presents peripheral vesicles which are released soon after fertilization to discharge a primary adhesive. This is characterized by peaks representative of carbohydrate molecules. A secondary protein-based adhesive is then secreted in the early developmental stages of the germlings. Energy dispersive X-ray, FTIR and PCA indicate that D. antarctica secretions also contain sulfated moieties, and become cross-linked with time, both conferring strong adhesive and cohesive properties. On the other hand, H. banksii secretions are complemented by the putative adhesive phlorotannins, and are characterized by a simple mechanism in which all constituents are released with the same rate and with no apparent cross-linking. It is also noted that the release of adhesive materials appears to be faster and more copious in D. antarctica than in H. banksii. Overall, this study highlights that both quantity and quality of the adhesives matter in explaining the superior attachment ability of D. antarctica.