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The effect of hexadecyltrimethylammonium bromide (HTAB) on the photocatalytic degradation of phenol (Phe), 2,5-dichlorophenol (2,5-DCP) and 2,4,5-trichlorophenol (2,4,5-TCP) in the presence of aqueous TiO2 suspensions at pH ca. 5 was investigated using a laboratory photoreactor equipped with a medium-pressure mercury lamp. Inhibition of substrate decomposition was observed for phenol, both below and above the surfactant critical micellar concentration, whereas a more complex behaviour was exhibited by chlorophenols. It was found that adsorption of these compounds onto the surfactant-modified semiconductor particles facilitates their faster decomposition, but the competitive partition of substrates between adsorbed surfactant structures and micellar aggregates tends to limit the beneficial kinetic effects at higher amphiphile concentrations. The crucial influence of surfactant adsorption was clearly evidenced in some runs performed at pH 3. Relevant inhibition of chloride release from chlorophenols, observed in the presence of HTAB, indicates a higher persistence of reaction intermediates in the reaction media, suggesting the need for a careful investigation of surfactant effects on all the degradation steps of the process.

The effect of sodium dodecyl sulphate (SDS) on the photocatalytic degradation of 2,4,5-trichlorophenol (2,4,5-TCP) in aqueous TiO2 dispersions under irradiation with simulated AM1 solar light was investigated. A peculiar kinetic behaviour was observed, with increasing inhibition of the substrate degradation as a function of SDS concentration below the critical micellar concentration (cmc), followed by a subsequent faster degradation around this concentration range and a further degradation rate decrease above the cmc. The role of surfactant adsorption onto the suspended semiconductor and the disaggregation of TiO2 microparticles seems to be crucial. The complete degradation of the investigated substrate, still achievable in the presence of SDS without relevant changes in the reaction mechanism, was confirmed suggesting the possible application of photocatalysis for the treatment of surfactant-containing wastes.

The photocatalytic oxidation of methyl-orange (C14H14N3SO3Na) dye was carried out in aqueous suspensions of polycrystalline TiO2 irradiated with artificial light until its complete mineralization was achieved. The performances of two widely used semiconductor powders were studied for comparison purposes. The dependence of dye photo-oxidation rate on various experimental parameters, including substrate concentration, semiconductor amount, and pH was investigated by using both catalysts. The observed dye degradation rates followed pseudo-first order kinetics with respect to the substrate concentration under the experimental conditions used. The two investigated TiO2 powders (Degussa P25 and Merck) showed different photoactivities. TOC analyses confirmed the complete mineralization achievable using both photocatalysts. Three main transient products still maintaining the chromophoric azo group were identified prior to their transformation into other degradation products which are non-absorbing in the visible region.

A procedure to extract polycyclic aromatic hydrocarbons (PAHs) from a contaminated river sediment is discussed; this combines short extraction times obtained by microwave energy with the peculiar solvent capability of aqueous micellar solutions. The technique, named microwave-assisted micellar extraction (MAME), was tested for the extraction of 11 PAHs from a spiked river sediment using polyoxyethylene (23) dodecyl ether (Brij 35), polyoxyethylene (10) dodecyl ether (C 12 E 10 ) or cetyl trimethylammonium bromide (CTAB). Different temperatures and extraction times were explored to establish whether this method has merit. Comparative measurements were made using sonication and Soxhlet extraction with acetone-hexane. Generally, Soxhlet extraction was revealed to be the most effective method to extract the PAHs from the solid matrix, with percent of recovery ranging from 92% to 102%. Nevertheless, high recoveries were also achieved by MAME using C 12 E 10 ; in fact, with only the exception of indeno[1,2,3- c...

The photodegradation of two common and very stable azo-dyes, i.e. methyl-orange (C14H14N3SO3Na) and orange II (C16H11N2SO4Na), is reported. The photocatalytic oxidation was carried out in aqueous suspensions of polycrystalline TiO2 irradiated by sunlight. Compound parabolic collectors, installed at the “Plataforma Solar de Almeria” (PSA, Spain) were used as the photoreactors and two identical reacting systems allowed to perform photoreactivity runs for the two dyes at the same time and under the same irradiation conditions. The disappearance of colour and substrates together with the abatement of total organic carbon content was monitored. The main sulfonate-containing intermediates were found to be in lower number in respect to those obtained under artificial irradiation. In particular there were no more evidence of the presence of hydroxylated transients. The dependence of dye photooxidation rate on: (i) substrate concentration; (ii) catalyst amount; and (iii) initial pH was investigated. The influence of the presence of strong oxidant species (H2O2, S2O82−) and some ions (Cl−, SO42−) on the process was also studied.

The photocatalytic degradation of the anthraquinonic dye Acid Blue 80 in aqueous solutions containing TiO2 dispersions has been investigated. The process has been monitored by following either the disappearance of the dye (via HPLC) and the formation of its end-products (via IC, GC, and TOC analysis). Although a relatively fast decolorization of the solutions has been observed, the mineralization is slower, and the presence of residual organic compounds was evidenced even after long term irradiation, confirming the relevant stability of anthraquinone derivatives. The identification of various unstable intermedi ates formed after low irradiation times was performed by HPLC-MS, allowing us to give insight into the early steps of the degradation process which mainly involve C−N bonds breaking and substrate hydroxylation. Complete and relatively fast mineralization of the substrate was achieved by irradiating the semiconductor dispersions in the presence of added K2S2O8.

The possible use of flow injection (FI) to monitor the photocatalytic mineralization of dicamba (3,6-dichloro-2-methoxybenzoic acid) present at the trace level in aqueous solutions containing TiO2 suspensions has been evaluated. Experiments were performed in a stirred photochemical reactor equipped with a simple FI manifold, integrating an online filtration unit able to perform the monitoring of the UV absorbance of the irradiated solution every 4 min. The light source used was a medium pressure mercury lamp (125 W). During the initial steps of the reaction the formation of UV absorbing intermediates, which completely disappear in less than 80 min, was evidenced. Additional HPLC, DOC and chloride ion measurements carried out on manually taken samples confirmed the complete mineralization of dicamba within about 90 min. The proposed on-line monitoring looks particularly suitable for the control of degradation treatments where primary degradation and mineralization steps take place after a comparable irradiation time.

The photodegradation process of aniline, 4-ethylaniline, and 4-chloroaniline in aqueous suspension of irradiated TiO2 (anatase) powder has been investigated. A batch photoreactor with immersed lamp irradiating in the near-UV region has been used for carrying out the reactivity experiments. For each substrate the influence of the initial concentration of organic compound and of pH on the degradation rate has been investigated. The main intermediates and the end products have been identified and determined, the total mass balance being satisfied. The kinetic modelling of the series of reactions occurring in the system has been satisfactorily carried out with a Langmuir-Hinshelwood rate law. The values of the parameters involved in the model have been also determined.

The photocatalytic degradation of 2,3,6-trichlorobenzoic acid (2,3,6-TBA) in aqueous TiO2 dispersions irradiated with simulated solar light was investigated. Fast primary degradation of the herbicide, which obeys a pseudo-first order law, was observed. Complete mineralisation of the organic carbon to CO2 was obtained after long term irradiation, with corresponding stoichiometric transformation of organic chlorine into chloride ion. Various aromatic intermediates, originating from 2,3,6-TBA, were detected during the treatment and identified using GC-MS. From the analytical data, a possible multi-step degradation scheme was proposed. The photocatalytic treatment of the pesticide was also performed in the presence of Brij 35 micellar solutions, although strong inhibition of the process was observed. When surfactant aggregates are present the photocatalytic destruction of 2,3,6-TBA is still possible at reasonable rates only after a proper dilution of the waste and by increasing significantly the semiconductor/pollutant ratio.

The photocatalytic degradation of several aniline derivatives present in aqueous solutions containing TiO2 suspensions was investigated. The process leads to the complete and fast decomposition (within about 1 h) of the pollutant molecules, promoted by oxidizing radical species formed at the irradiated semiconductor/water interface. The stoichiometric formation of CO2 from the organic carbon was assessed, whereas other inorganic end-products were detected depending on the nature of the aniline substituents. Unstable hydroxyaromatic intermediates were also identified during the initial steps of the treatment. The primary degradation, which follows pseudo-first-order kinetics, changes with the aniline substituents and is strongly dependent on pH.

Chelating aggregates consisting of Triton X100 host micelles and hydrophobic derivatives of PAN have been examined as suitable candidates for preconcentration and selective separation of transition metal ions through micellar-enhanced ultrafiltration. The effective accumulation in the surfactant-rich retentate of nickel(II), copper(II), cobalt(II), manganese(II) and zinc(II), present at trace levels in aqueous samples, has been achieved by operating at pH ca. 6 with a ligand having a binding constant to the host micelles higher than 2000 l./mol. The efficient separation of micelle-bound metal chelates from unreactive ions has been assessed, together with the feasibility of selective enrichment and purification of the investigated metal ions present in mixtures through a multistage process.