No abstract

Vacuum ultraviolet (VUV, λ = 172 nm) irradiation of alkyl self-assembled monolayers (SAMs) in the presence of dry air alters their surface properties. In this work, UV photochemically prepared hexadecyl (HD)-SAMs on hydrogen-terminated silicon substrates were irradiated by VUV light in dry air, which generated active oxygen species upon excitation of the atmospheric oxygen molecules. These active oxygen species converted the terminal methyl groups of the SAMs to polar functional groups, which were examined quantitatively by X-ray photoelectron spectroscopy (XPS) and chemical labeling. At the first stage of VUV irradiation, the surface of SAMs was functionalized, and the ratios of the generated polar functional groups markedly increased. With the elongation of the irradiation period, the SAMs gradually degraded, and the total polar group percentages gradually decreased. The difference between the oxygenated carbon components derived by the deconvolution of the XPS carbon (C1s) spectrum and the chemical labeling of polar groups revealed enormous quantities of ethereal and ester groups that cannot react with the labeling reagents but are included in the C1s spectral envelope. These modifications were reflected on morphological structures of SAMs, which were gradually distorted until a complete amorphous structure was obtained after the complete elimination of HD-SAMs.

Through 172 nm vacuum ultraviolet light irradiation in a high vacuum condition (HV-VUV), well-defined micropatterns with a varied periodic friction were fabricated at the surface of self-assembled monolayers (SAMs) terminated with oxygenated groups. No apparent height contrast between the HV-VUV-irradiated and -masked areas was observed, which indicated the stability of the C-C skeleton of the assembled molecules. The trimming of oxygenated groups occurred through dissociating the C-O bonds and promoting the occurrence of α- and β-cleavages in the C═O-containing components. Hence, the HV-VUV treatment trimmed the oxygenated groups without degrading the C-C skeleton. The HV-VUV treatment influenced the order of the assembled molecules, and the step-terrace structure was distorted. The decrease in friction at the HV-VUV-irradiated domains was attributed to the dissociation of oxygenated groups. (3-Aminopropyl)trimethoxysilane (APTMS) aggregated at the masked areas of the HV-VUV-patterned SAM, where the oxygenated groups worked as anchors. APTMS aggregations did not exist at the irradiated areas, indicating the trimming of the oxygenated groups at these areas. The direct assembling of APTMS on the Si substrate at the irradiated areas was prevented by the remaining C-C skeleton.

Guava extract from Psidium guajaua L. fruit harvested in Egypt and purchased in a local market has been analysed using GC-MS and retention indices on polar and apolar columns, respectively. A total of 160 different mass spectra was recorded. Among them 132 were identified (or tentatively identified). They included 41 hydrocarbons (alkanes, cycloalkanes, alkenes), 9 aromatics, 3 monoterpenes, 15 sesquiterpene derivatives, 12 carbonyl compounds, 25 esters, 9 lactones, 13 alcohols and 5 miscellaneous compounds. Quantitatively, the major constituents were ( Z )-hex-3-en-1-yl acetate (11 %) and the corresponding alcohol (7.5%), pentan-2-one (9.1 %), cinnamyl alcohol (10.2%), 3-phenylpropyl acetate (5 %) and the corresponding alcohol (3.5 %). The composition is quite different from that of guava fruits from other countries (Japan, Venezuela, Brazil, Philippines). 3-Phenylpropyl acetate, cinnamyl alcohol, yand &lactones (especially jasmine lactone), and ethyl esters may play an important role in the characteristic sweet and very pleasant flavour of guava fruit from Egypt.Fresh guava fruits were macerated in ethanol for two months and the solution was extracted with trichlorofluoromethane to yield another aroma extract. The headspace above fresh guava fruit and fruit that had been stored for 2 months at -18°C and defrosted was also examined. Many compounds were identified in the fruit for the first time.

Removing organic contaminants such as dyes from water is essential to purify wastewater.