A mixture of hydroxypolychlorodibenzofurans was isolated from technical pentachlorophenol. The alkyl ethers were prepared, and analyzed by fused silica capillary column gas chromatography electron capture negative ion chemical ionization mass spectrometry. The appearance of intense molecular ion peaks for the alkyl ethers apparently depends on the ring position of alkoxy substitution. Loss of chlorine atoms from the ring, followed by protonation of the resultant anion as the alkyl group is eliminated, is postulated on the basis of deuterium labeling experiments. Evidence is also presented for the presence of a hydroxyheptachlorodibenzodioxin in technical penthchlorophenol.
A rigorous theory of wall effects in du Nouy ring tensiometry is developed which is no more difficult to compute than the infinite-wall theory of Huh and Mason. The predictions of the theory are compared with experimental measurements on wetting and non-wetting walls.
Colloides J PhotochemistryThe quantum yields for the photodissolution of colloidal CdS in Ludox stabilized aerated solutions, have been measured as a function of pH. It has been found that the quantum yield decreases with increasing pH. Electrophoresis measurements indicate that this decrease is due to the formation of Cd2+ hydrolysis products on the surface of the colloid as the pH is increased. Support for this conclusion is obtained from experiments in which hydrolysed Co", Nil' and Zn" species were deliberately deposited onto CdS colloids. The reactions involved in the photocorrosion of CdS are discussed in light of the present results and with respect to mechanims proposed in the literature.
IntroductionThe thermal-and photo-oxidation of metal sulphides have received considerable attention over many years because of their relevance to mineral flotation [l]. The products of oxidation are various: elemental sulphur, metal hydroxides, thiosulphates (SzOi-), polythionates (S,O;-, x = 2 -6), sulphate (SO: -) and volatile SO2. The amount and type of oxidation product depends on the conditions such as pH, oxygen pressure, temperature, presence of catalytic agents and duration of the oxidation reaction.In more recent years the photo-oxidation of metal sulphides has come under quite intense study because of the possibility of utilizing some colloidal metal sulphides as photocatalysts for the production of H2 from water [2]. CdS in particular has been extensively investigated because its catalytic activity can be initiated using visible light, an important advantage for the photochemical conversion of solar energy [3].Although a good deal of understanding of the photooxidation of CdS has been attained, there remain some aspects that are unclear. The purpose of the present study was to provide additional information on the photo-degradation of CdS as a function of pH and in the presence of hydrolysable metal ions in order to explain some of the observed photocatalytic behaviour of CdS colloids. To this end we have investigated CdS particles in 3 systems (i) CdS/Ludox solutions, (ii) CdS in water (iii) systems (i) and (ii) with added hydrolysable metal ions. The two metal ions Ni" and Co" were investigated in order to test their potential as scavengers for photoproduced holes in CdS. Both ions have been shown to catalyse H2Oz/OZ formation from H 2 0 [4,5].
029ChemInform Abstract have been investigated in Ludox stabilized and Ludox-free solution in the presence and absence of Co(II) and Ni(II) ions. The quantum yield for the photodissolution of colloidal CdS decreases with increasing pH. Electrophoresis measurements indicate that this decrease is caused by the formation of Cd2+ hydrolysis products on the surface of the colloid as the pH increases. The deposition of hydrolysed metal ions appears to enhance the recombination of the photo-separated electron-hole pair, leading to a reduction in the photo-degradation of the colloid. Attempts to scavenge the hole using deposited hydrolysed Ni(II) or Co(II) species failed, in contrast with other studies in which Rh2O3 and RuO2 deposited on CdS colloids succeeded in hole scavenging and subsequent O2 production.
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