Alessandra Bianco Prevot

Characterization of methyl orange and its photocatalytic degradation products by HPLC/UV–VIS diode array and atmospheric pressure ionization quadrupole ion trap mass spectrometry

Abstract HPLC/UV–VIS diode array and HPLC/MS techniques were successfully applied to the analysis of sulfonated molecules present in samples coming from the photocatalytic degradation of the azo dye indicator, methyl orange. The substrate was chosen as a simple model for the study of reactions involving the more complex commercial products used for the dyeing of textile fibers. Unexpected MS fragmentation path was observed, due to the very stable methyl orange molecular structure. The chromatographic information were combined with the obtained MS, MS/MS data and the UV–VIS diode array spectra and allowed to rationalize the molecular structures attributable to the various degradation products.

Photocatalytic degradation of naphthalene in aqueous TiO2 dispersions: Effect of nonionic surfactants

The decomposition of naphthalene in the presence of TiO2 dispersions irradiated with simulated solar light has been investigated in water and in aqueous Brij 35 solutions, used to wash soil samples containing the adsorbed pollutant. The monitoring of the reaction system performed during the treatment showed the formation of various aromatic intermediates, in turn degraded, which were identified using suitable analytical techniques. Fast and complete mineralization of naphthalene to CO2 was achieved when working in the absence of additives, whereas a neat inhibition of the degradation was observed in the presence of amphiphiles and other organic components coming from soil. Experimental conditions under which surfactant-containing washes can be treated were investigated and defined.

Intermediate distributions and primary yields of phenolic products in nitrobenzene degradation by Fenton’s reagent

Nitrobenzene thermal degradation was investigated using the Fenton reagent in different experimental conditions. Reaction products were analyzed by HPLC, GC-MS, LC-MS and IC. The products obtained at different nitrobenzene conversion degrees show that degradation mainly involves successive hydroxylation steps of the aromatic ring and its subsequent opening followed by oxidation of corresponding aliphatic compounds. Our results show as primary reaction products: 4-nitrophenol, 3-nitrophenol, 2-nitrophenol, phenol and 1,3-dinitrobenzene, indicating that both hydroxylation and nitration reactions are involved. The formation of phenolic products can be explained by postulating an initial step of HO() addition to nitrobenzene ring. The mechanisms of primary reaction pathways are discussed and a detailed kinetic analysis to obtain the true primary yields of phenolic products is proposed. The relative yields observed for nitrophenol isomers do not follow the expected orientation according to deactivating characteristics of the nitro group but significantly depend on Fe(+2), Fe(+3), H(2)O(2) and O(2) concentrations. The understanding of the effect of reaction conditions on the relative product distribution benefits the application of Fenton and Fenton-like systems to waste water treatment.

Photocatalytic treatment of laboratory wastes containing aromatic amines

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.

Paramagnetic Iron-Doped Hydroxyapatite Nanoparticles with Improved Metal Sorption Properties. A Bioorganic Substrates-Mediated Synthesis

This paper describes the synthesis of paramegnetic iron-containing hydroxyapatite nanoparticles and their increased Cu(2+) sorbent capacity when using Ca(2+) complexes of soluble bioorganic substrates from urban wastes as synthesis precursors. A thorough characterization of the particles by TEM, XRD, FTIR spectroscopy, specific surface area, TGA, XPS, and DLS indicates that loss of crystallinity, a higher specific area, an increased surface oxygen content, and formation of surface iron phases strongly enhance Cu(2+) adsorption capacity of hydroxyapatite-based materials. However, the major effect of the surface and morphologycal modifications is the size diminution of the aggregates formed in aqueous solutions leading to an increased effective surface available for Cu(2+) adsorption. Maximum sorption values of 550-850 mg Cu(2+) per gram of particles suspended in an aqueous solution at pH 7 were determined, almost 10 times the maximum values observed for hydroxyapatite nanoparticles suspensions under the same conditions.

Quantitative removal of uranyl ions from aqueous solutions using micellar-enhanced ultrafiltration

Abstract Quantitative removal of uranyl ions present in aqueous solutions at the μg ml −1 concentration level was achieved using the micellar-enhanced ultrafiltration technique. Suitable chelating micelles were formed by dissolving selective hydrophobic acyclic ligands in the usual amphiphilic aggregates. These ligand-doped miceles accumulate the uranyl ions through the formation of tightly bound chelates. The aggregates and their guest metal complexes were successively separated by ultrafiltration through hydrophilic membranes of suitable pore size. The efficiency of the process is related to the affinity of the ligands for the micelles. Non-ionic and cationic surfactants were investigated. Quantitative retention of the analyte in the surfactant-rich retente solution was achieved when working with cetyltrimethylammonium bromide micelles. The uranyl recovery was significantly increased by introducing trioctylphosphine oxide as an auxiliary ligand, which allowed for very efficient preconcentrations at lower pH.

Waste-derived bioorganic substances for light-induced generation of reactive oxygenated species.

Urban waste-derived bioorganic substances (UW-BOS) have shown promise as chemical auxiliaries for a number of technological applications in the chemical industry and in environmental remediation. In this study, the application of these substances in the photodegradation of organic pollutants is addressed. The experimental work is specifically focused on the photolysis mechanism promoted by AC8, a UW-BOS isolated from a 2:1 w/w mixture of food and green residues, composted for 110 days, using 4-chlorophenol (4-CP) as probe molecule. The production of (⋅)OH and the ¹O₂ is monitored by EPR spectroscopy. The correlation between radical species evolution and photodegradation of 4-CP is investigated. The effect of ¹O₂ and (⋅)OH scavengers on the 4-CP degradation process is also checked. The results suggest that the role of these species in the photodegradation of 4-CP depends on AC8 concentration. AC8 is thereby proven to be a photosensitizer for applications in environmental remediation. The results on AC8 further support the use of urban bio-waste as a versatile source of chemical auxiliaries of biological origin for use in diversified applications.

High-performance liquid chromatography coupled to ultraviolet diode array detection and electrospray ionization mass spectrometry for the analysis of intermediates produced in the initial steps of the photocatalytic degradation of sulfonated azo dyes

High-performance liquid chromatography coupled to ultraviolet diode array detection and electrospray ionization mass spectrometry was applied to monitor the photocatalytic degradation mediated by TiO2 of three sulfonated monoazo dyes (Orange I, Orange II, and Ethylorange) present in aqueous solution. Photobleaching, organic carbon, nitrogen and sulfur evolution were also followed during the process. Delayed carbon mineralization was observed with respect to both dyes disappearance and photobleaching, due to the formation of transient intermediate compounds which were in turn completely degraded. Among the intermediates produced during the initial degradation steps the formation of several hydroxylated derivatives, mostly coloured, was evidenced. The MS(2) spectra allowed one to formulate hypothesis about the OH attack positions; a peculiar reactivity of the azo moiety was shown by Orange I and Orange II.

Analytical monitoring of photocatalytic treatments. Degradation of 2,3,6-trichlorobenzoic acid in aqueous TiO2 dispersions

The photocatalytic degradation of 2,3,6-trichlorobenzoic acid (2,3,6-TBA) in aqueous TiO(2) 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 CO(2) 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.

Selective recovery of uranium(VI) from aqueous acid solutions using micellar ultrafiltration

Preconcentration and removal of uranyl ions from aqueous solutions were achieved by using micellar-enhanced ultrafiltration with complexing micellar aggregates composed of Triton X-100 and different hydrophobic ligands. Derivatives of 4-aminosalicylic acid (PAS) and of 1-(2-pyridylazo)-2-naphthol (PAN) having tuned alkyl chains were used as suitable chelating agents. The selective recovery of uranyl from acid samples containing also SrII and CdII is possible using the multi-step ultrafiltration approach with the PAN derivatives, whereas effective uranyl retention can be obtained with salicylates only in neutral to basic media.