A. Bianco Prevot

Photocatalytic and photolytic transformation of chloramben in aqueous solutions

The photocatalytic degradation of chloramben (3-amino-2,5-dichlorobenzoic acid) was investigated in aqueous solutions containing TiO2 suspensions under irradiation with simulated solar light. The primary degradation of the herbicide, the mineralisation of the organic carbon to CO2 and the formation of chloride ion from organic chlorine proved to be relatively fast, whereas the conversion of organic nitrogen into ammonium and nitrate ions took place only at delayed irradiation times. Photolytic degradation processes proved also to be active in the examined time interval, but they were far from producing complete mineralisation, leaving considerable amounts of residual organic products. Various aromatic intermediates that originated from chloramben during the photocatalytic treatment were detected and identified using GC-MS. Similarly, the main aromatic products arising from photolytic decomposition were also identified, and, in turn, they proved to undergo complete mineralisation upon addition of TiO2.

Vacuum-ultraviolet (VUV) photolysis of water; mineralization of atrazine

The versatility and efficiency of the VUV photolysis of water as an “Advanced Oxidation Procedure” for the light-induced oxidative degradation of atrazine as a pollutant of surface and ground waters is evaluated. The oxidation of atrazine using TiO2 as a photocatalyst has been reported to produce almost stoichiometric amounts of cyanuric acid. Mineralization to CO2, water and inorganic nitrogen containing ions occurred to a very low extent implying that cyanuric acid is resistant to further degradation under the chosen experimental conditions. Our present results show that in oxygen saturated solutions 50% of the initial atrazine is converted to cyanuric acid, whereas only 10% of the initial atrazine is isolated as cyanuric acid in argon saturated solutions. The results indicate that mineralization is more efficient in not strictly oxidative reaction media.

Photocatalytic degradation of carbaryl in aqueous TiO2 suspensions containing surfactants

The effect of ionic and non-ionic aliphatic surfactants on the photocatalytic degradation of Carbaryl (1-naphtyl-N-methylcarbamate) in aqueous solutions containing suspended TiO2 (anatase) particles, under irradiation with simulated AM1 solar light, was investigated. A neat inhibitory effect on the degradation rate was observed, depending on the nature of the surfactant and on the initial pH of the solution. The decay profiles of the primary process corresponded to the usual pseudo-first order kinetics for surfactant concentrations below the critical micellar concentration range, whereas a more complicate behaviour was observed in the presence of micellar aggregates. Mineralization of the pesticide to CO2, NO3− and NH4+ was evidenced also in the presence of added amphiphiles, suggesting the feasibility of photocatalytic treatment of surfactant-containing aqueous wastes.

Photocatalytic oxidation of acetonitrile in aqueous suspension of titanium dioxide irradiated by sunlight

The photocatalytic oxidation of acetonitrile (CH3CN) was carried out in aqueous suspensions of polycrystalline TiO2 P25 Degussa irradiated by sunlight. A plug flow photoreactor in a total recycle loop was used for carrying out reactivity experiments in which the concentrations of acetonitrile, of its intermediate oxidation products and of not-purgeable organic carbon (NPOC) were monitored. The influence of the presence of strong oxidant species (H2O2, S2O82−, ClO−) on the process rate was studied. The dependence of acetonitrile photo-oxidation rate on the substrate concentration and on the catalyst amount was also investigated. The photodegradation rate of substrate and NPOC followed first order kinetics with respect to acetonitrile and NPOC concentrations, respectively. The presence of S2O82− and solar irradiation determined the occurrence of homogeneous degradation of acetonitrile and NPOC. In the presence of irradiated catalyst, a significant synergetic effect was observed for NPOC degradation while for the acetonitrile oxidation this effect was not evident. H2O2 did not affect the process while ClO− affected negatively the acetonitrile oxidation rate and it inhibited the NPOC degradation.

Photocatalytic degradation of bentazone in soil washing wastes containing alkylpolyoxyethylene surfactants.

Three alkylpolyoxyethylene surfactants bearing the same hydrophobic chain and a different number of oxyethylene groups were investigated as suitable candidates for the soil washing treatment of contaminated soil samples containing bentazone. Comparable good recoveries of the pesticide were obtained working with these surfactants. The photocatalytic treatment of the collected washing wastes, performed in the presence of suspended TiO(2) particles under irradiation with simulated sunlight, leads to the effective degradation of bentazone residues after a time depending on the nature and concentration of the chosen amphiphile. Brij 35 was found to be the best surfactant candidate, giving the faster abatement of the pesticide in the collected wastes. The overall treatment time depends on the bentazone mineralization kinetics, markedly slow in the presence of surfactants. Useful information about the photocatalytic degradation route was obtained from the HPLC-MS analysis of transient intermediates formed in water.

Photodegradation kinetics of aniline, 4-ethylaniline, and 4-chloroaniline in aqueous suspension of polycrystalline titanium dioxide

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.

Photocatalytic degradation of chlorophenols in soil washing wastes containing Brij 35. Correlation between the degradation kinetics and the pollutants–micelle binding

The photocatalytic degradations of 4-chlorophenol (CP), 4-chloro-2-methylphenol (CMP), 4-chloro-3,5-dimethylphenol (CDMP) and 4-chloro-2-isopropyl-5-methylphenol (CIMP) were investigated in water and in simulated soil washing wastes containing Brij 35 (polyoxyethylene(23)dodecyl ether) in the presence of TiO2 dispersions. A neat inhibition of substrate decomposition proportional to their growing hydrophobicity was observed in the washing wastes for CP, CMP and CDMP, whereas CIMP showed a different behaviour. The mineralization of the organic chlorine of CP and CIMP was relatively fast and complete, whereas it was much slower for CMP and CDMP. Micellar solubilization and substrate adsorption onto the semiconductor play opposite roles on the degradation kinetics, and a breakpoint between the corresponding induced effects was evidenced when the pollutants become completely bound to the micellar aggregates.

Analytical monitoring of the photo-induced degradation of 3,6-dichloro-2-methoxybenzoic acid in homogeneous and heterogeneous systems

The photo-induced degradation of 3,6-dichloro-2-methoxybenzoic acid present at the trace level in aqueous solutions has been studied by comparing the UV photolytic treatment with the processes operating in the presence of either irradiated TiO2 aqueous suspensions and irradiated hydrogen peroxide. The efficiency of the treatments was evaluated by monitoring the kinetics of the primary degradation process, the chloride release and the DOC evolution. The identification of aromatic intermediates by means of GC-MS and LC-MS analysis evidenced a common degradation path for TiO2- and H2O2-mediated degradation, whereas the photolytic mechanism resulted quite different. The mixed TiO2-t-H2O2−UV treatment was found to exhibit the best performances.

Soluble Bio-based Substances Obtained from Urban Wastes: Isolation and Characterization

The organic fraction of urban wastes can be considered a cost effective source of added value products for a wide number of uses. The present chapter describes different possible strategies for the treatment of organic wastes, used at the present time in many waste treatment plants. Subsequently the chapter deals with the isolation process of soluble bio-based substances (SBO) from urban biowastes at both laboratory and pilot plant scale. A detailed description of SBO composition and physical-chemical characterization is given.

Ecofriendly in-line process monitoring: a case study. Anthracene photodegradation in the presence of refuse-derived soluble bio-organics.

Photodegradation of anthracene has been studied in aqueous solutions containing soluble bio-organic substances isolated from urban refuse. To perform a preliminary rapid feasibility study of this process while reducing the amount of analytical effort and reagents, an experimental set-up was developed comprising a Teflon coil surrounding a UV-lamp and coupled with an in-line spectrofluorimeter. In this fashion only few millilitres of solution are needed to study the degradation process. Furthermore, the in-line spectroscopic approach enables monitoring of the process without consumption of reagents. Additional studies by liquid chromatography and use of toxicity tests clearly indicated that the apparent inhibition effect of bio-organic compounds on anthracene degradation is not relevant. The results imply that urban refuse may be used as an auxiliary in the recovery of polycyclic aromatic hydrocarbons from contaminated soil by washing, without deleterious effects on the photodegradation of anthracene and other aromatic pollutants.