E. Pelizzetti

Photodegradation of surfactants: Part vi complete photocatalytic degradation of anionic, cationic and nonionic surfactants in aqueous semiconductor dispersions

Abstract Various kinds of anionic ( e.g ., C 12 -DBS, C 12 -DS, C 12 -LES-3, C 14 -AOS, and C 12 -DG), cationic ( e.g ., C 16 -HTAB and C 12 -BDDAC) and nonionic ( e.g ., NPE n (n = 7, 9, 17, 50), C 18 -PEA-15, C 12–14 -BHA, C 12–14 -PAE-10, C 12–14 -NOE and C 14–16 -NOE) surfactants have been photodegraded in a heterogeneous dispersion of TiO 2 semiconductor particles under UV illumination. These surfactants are ultimately converted to CO 2 . A relationship between the structure of surfactants and the photodegradation rate is indicated in a comparison of the results with literature studies of biodegradation. CO 2 evolution from the photooxidation of anionic surfactants is faster than that observed from cationic surfactants in the initial stages of irradiation (2h). The nonionic surfactants photodegrade more slowly, evolving CO 2 at about 20% mineralization yield. UV-illuminated titanium dioxide affords strongly oxidizing catalytic sites, irrespective of the structure of surfactant.

Photocatalytic degradation of polychlorinated dioxins and polychlorinated biphenyls in aqueous suspensions of semiconductors irradiated with simulated solar light

Abstract The complete photocatalytic degradation of two polychlorinated dibenzo-p-dioxins and one polychlorinated biphenyl to CO 2 and HC1 has been investigated in aerated aqueous suspensions of several semiconductors (TiO 2 , ZnO, CdS, TiO 2 Pt 5% by weight, and Fe 2 O 3 ) irradiated by simulated solar light. The particular compounds were the 2-chlorodibenzo-p-dioxin (CDD), the 2,7-dichlorodibenzo-p-dioxin (DCDD), and the 3,3′-dichlorobiphenyl (DCB). TiO 2 shows the highest photo-activity for the degradation process studied; platinization seems to have little effect. The presence of conduction band electron scavengers such as Ag + and Fe 3+ ions increase the activity of TiO 2 .

Light-assisted 1,4-dioxane degradation

Abstract The oxidative degradation induced by light of 1,4dioxane been investigated in homogeneous solution in the presence of inorganic peroxides (either hydrogen peroxide or peroxydisulfate) and under heterogeneous photocatalytic conditions in the presence of titanium dioxide. The effect of photon energy spectral distribution, pH, O2 and scavengers has been examined. The degradation mechanism involves common intermediates. Ethylene glycol diformate was observed as the main intermediate. In the presence of UV light peroxydisulfate showed high degradation efficiency. A tentative chain radical oxidation mechanism is postulated. The distinctive features of heterogeneous photocatalytic treatment were the good efficiency under simulated solar spectrum and the absence of inhibition of the degradation rate by HCO3−. The presence of peroxydisulfate enhances the TiO2 photocatalytic degradation rate.

Photocatalytic degradation of bentazon by TiO2 particles

The degradation of 3-isopropy1–2,1,3-benzothiadiazin-4-one-2,2-dioxide, the herbicide bentazon, by AMI simulated sunlight has been investigated in the presence of aqueous suspensions of TiO2. The half-life of the degradation process is ca. 30 minutes at pH=2 and ca. 4 minutes at pH=7 in the presence of 0.5 g L−1 of TiO2. The near quantitative recovery of sulfate ions and CO2 as well as the variation with time of dissolved and adsorbed organic carbon suggest that the process leads to complete mineralization of the herbicide. The process is extremely efficient even at very low concentration: in fact irradiation of 20 ppb of bentazon in the presence of 50 ppm TiO2 allows to recover < 0.1 ppb after 10 minutes.

Identification of photocatalytic degradation pathways of 2-Cl-s-triazine herbicides and detection of their decomposition intermediates

Abstract the photocatalytic degradation of three 2-chloro-s-triazine herbicides (simazine, propazine, atrazine) over TiO 2 particles under simulated solar light has been investigated. In the early steps, the degradation progresses through competitive reactions such as oxidation of the side alkyl chain and substitution of chlorine with hydroxyl groups, the last process occurring for less than 10% of degradation. Further oxidative processes give rise to the formation of dealkylated products. Several intermediates have been detected by GC-MS and comprehensive degradation schemes are proposed. The three herbicides, bearing different alkyl groups, exhibit relevant differences in the relative role of the competitive degradation pathways.

Photodegradation of surfactants. V. Photocatalytic degradation of surfactants in the presence of semiconductor particles by solar exposure

Abstract Anionic sodium dodecylbenzenesulphonate (DBS), cationic benzyl-dodecyldimethyl ammonium chloride (BDDAC) and non-ionic p-nonyl-phenyl poly(oxyethylene). (NPE-n) surfactants can be photodegraded in aqueous suspensions of titanium dioxide powder by solar exposure. Vertical and horizontal type solar reactors were employed out of doors. The photodegradation of linear and iso-DBS were compared by surface tension, UV absorption and dye extraction measurements. The degradation processes of DBS and NPE-9 were examined by IR and nuclear magnetic resonance (NMR) spectroscopy. The aromatic moiety in the surfactants is decomposed more easily than the alkyl and/or ethoxylate groups. This photodegradation system may be practical for treatment of wastewater containing surfactants.

Micelles: a new dimension in analytical chemistry

Abstract A brief description of the properties of micelles is presented and the main applications of these organized systems in analytical chemistry are surveyed. The performances of some important micelle-based separation techniques are compared with those of classical methods and the utility of functionalized amphiphiles is stressed.

HOST-GUEST CHEMISTRY IN THE GAS PHASE AND AT THE GAS-SOLID INTERFACE : FUNDAMENTAL ASPECTS AND PRACTICAL APPLICATIONS

The study of host-guest interactions has recently expanded from solution chemistry to the gas phase, where solvent effects are not present, allowing better understanding of the intrinsic phenomena responsible for molecular recognition. Important aspects under investigation include the mechanism of interaction, the identification of binding groups, as well as the discovery of structural requirements for the host to undergo inclusion complexation. The information gained from these gas phase studies can be exploited to design new practical applications of host-guest chemistry, particularly when gas-solid interactions are involved. Analytical devices such as gas sensors and chromatographic adsorbing cartridges take advantage of the structural recognition capability of the host to achieve high levels of selectivity.

Molecular recognition in the gas phase

Several examples of molecular recognition taking place entirely in the gas-phase are demonstrated for the first time. Experiments involve highly selective host-guests complexations occuring between neutral counterparts inside the ion source of a mass spectrometer, where two cavitands are vaporized simultaneously in a gas-phase containing two candidate guests and an excess of methane. The relative gas-phase complexation constants are measured. The unique characteristic of this investigation method is that supramolecular interactions between specific functional groups of hosts and guests are made free from the solvation effects.

Partition equilibria of phenols between water and anionic micelles : Correlation with the Octanol/Water System

Abstract The partition equilibria of a series of thirty substituted phenols bearing different chemical groups between aqueous solutions and sodium dodecylsulfate micelles was investigated by using micellar high-performance liquid chromatography and by studying the variation of the acidity constant. The contribution of each substituent to the free energy of transfer from water to micelles was estimated. The group contribution approach is shown to be valid for polysubstituted compounds under well defined conditions. A comparison with partition coefficients obtained in classical two-phase system (1-octanol/water), frequently used as biochemical model systems, is discussed