Massimo Barbeni

Chemical degradation of chlorophenols with Fenton's reagent (Fe2+ + H2O2)

Aqueous solutions of Fentons reagent (Fe2+ + H2O2) have been used to effect the total decomposition of the chlorophenols: 2-chlorophenol, 3-chlorophenol, 4-chlorophenol, 3,4-dichlorophenol and 2,4,5-trichlorophenol. The mineralization of these chlorinated aromatic substrates to CO2 and free Cl− has been studied as a function of [Fe2+] and [HClO4]. Increasing the concentration of Fe2+ enhances the decomposition process, while an increase in the concentration of HClO4, inhibits the reaction. The presence of Fe3+ alone (without any Fe2+) with H2O2 has no effect on the degradation of the chlorophenols. In all cases, the stoichiometric quantity of free Cl− was obtained at the completion of the decomposition reaction; but the rates of disappaearance of the chlorophenol and of the formation of the Cl− are not similar. This suggests that some chlorinated aliphatic species may be formed as possible intemediates.

Photodegradation of pentachlorophenol catalyzed by semiconductor particles

Abstract The heterogeneous photocatalytic degradation of pentachlorophenol (PCP) in aqueous solutions containing a suspension of TiO2 leads to the quantitative formation of CO2 and HC1. The photodegradation has also been studied in other semiconductor dispersions such as ZnO, CdS, WO3, and SnO2. TiO2 appears the most efficient. Oxygen and water are essential ingredients in the complete mineralization of this pollutant found near pulp and paper industries. Experiments with sunlight show a promising route for the water treatment processes; the half life of PCP (initial concentration 4.5 × 10−5M) is about 8 minutes, in the presence of 2 g/l of TiO2.

Sunlight Photodegradation of 2,4,5-Trichlorophenoxy-acetic Acid and 2,4,5-Trichlorophenol on TiO2. Identification of Intermediates and Degradation Pathway

The photocatalytic degradation of 2,4,5-trichlorophenoxyacetic acid and 2,4,5-trichlorophenol has been investigated in oxygenated aqueous suspensions of TiO2. Complete mineralization to CO2 and HC1 occurs with half-lives of 30–90 minutes. The effect of loading and thermal pre-treatment of the semi-conductor catalyst, as well as the influence of added chloride ions have been examined. In the degradation of the 2,4,5-trichlorophenoxyacetic acid, several intermediates were detected by gas-chromatographic/mass-spectrometric techniques. A scheme for the photodegradation is formulated.

Photochemical degradation of chlorinated dioxins, biphenyls phenols and benzene on semiconductor dispersion

Abstract The degradation of various aromatic pollutants present in aqueous media was performed using suspensions of semiconductor particles under illumination. The efficiency of the process has been shown to be dependent on the nature of the catalyst. The complete mineralization of halophenols has been observed after long term experiments.

Photochemical reduction of gold(III) on semiconductor dispersions of TiO2 in the presence of CN− ions: disposal of CN− by treatment with hydrogen peroxide

Abstract The reduction and recovery of gold from samples containing CN− ions have been investigated employing TiO2 semiconductor dispersions irradiated with either UV light (λ ⩾ 210 nm) or AM1 simulated sunlight (λ ⩾ 310 nm). The photoreduction is very efficient at low pH; disposal of cyanide, which acts as a buffer to a pH of about 9.3, was imperative. The degradation of CN− was investigated employing two peroxides, H2O2 and S2O82−, in the presence and absence of light. Treatment of cyanide solutions with H2O2 and UV light irradiation leads to efficient conversion of CN− to NH3 and CO2 (the main products detected). The H2O2 decomposition of CN− also occurs in the dark, but to a lesser extent. The kinetics of the conversion process(es) have been studied; under irradiation, kobs is about ten times the rate of the dark process. A mechanism involving OH· radicals is proposed for the cyanide decomposition by UV light. Cyanate ion, OCN−, is the intermediate in both the dark and the illuminated pathways. Recovery of gold on TiO2 powder, following cyanide oxidation and removal of unreacted H2O2, is favored in acidic aqueous media. The implications of our findings towards practical disposal of cyanide and recovery of gold from actual indusrial waste samples are discussed.

Hydrogen from hydrogen sulfide cleavage. Improved efficiencies via modification of semiconductor particulates

Reference LPI-ARTICLE-1985-027doi:10.1016/0360-3199(85)90095-3View record in Web of Science Record created on 2006-02-21, modified on 2017-05-12

Effect of CdS preparation on the photo-catalyzed decomposition of hydrogen sulfide in alkaline aqueous media

Band-gap irradiation of CdS dispersions in alkaline aqueous media (pH 14) containing 0.1 M Na2S produces hydrogen and sulfur. The reaction is photo-decomposition of hydrogen sulfide by two quanta of visible light (λ > 400 nm). Various batches of commercially available cadmium sulfide, as well as CdS precipitated from nitrate, sulfate, and chloride solutions at neutral pH, produce different amounts of hydrogen. Electronically pure CdS (puratronic grade) generates almost no hydrogen. By contrast, CdS precipitates prepared in the presence of excess cadmium yield forty times more hydrogen than CdS prepared in the presence of excess sodium sulfide. Differences are rationalized in terms of possible surface modification and/or changes in the active sites by anions present as ‘impurities’ which could affect separation and recombination of the charge carries, eCB− and hVB+, in CdS.

Efficient photochemical conversion of aqueous sulphides and sulphites to hydrogen using a rhodium-loaded CdS photocatalyst

Abstract An efficient photocatalytic dispersion has been developed from CdS and a 0.2 wt.% rhodium(III) salt via photodeposition. The catalyst is presumed to contain rhodium species on the surface of the CdS particles and has been exploited in the photocleavage of hydrogen sulphide in the absence and presence of SO2 in alkaline media (pH 14) to produce hydrogen and sulphur or hydrogen and S2O32− respectively. The thermodynamic energy conversion efficiency is 0.17% or more and the quantum efficiency measured at 436 nm (bandpass, about 22 nm) is 0.45 ± 0.05 or more for hydrogen atom formation; the engineering energy conversion efficiency (energy in compared with energy out) is 2.6% or more. The turnover number is 2200 for rhodium and 15 for the CdS particles. One interesting aspect of this photocatalyst is that oxygen seems not to affect the hydrogen evolution rate.

Putting Photocatalysis to Work

This paper emphasizes the practical aspects of photocatalysis as applied to practical problems of some concern and employs semiconductor dispersions of CdS and TiO2. It presents our recent contributions to (i) the photocleavage of hydrogen sulfide, (ii) the treatment of wastes, and (iii) the photoreduction of and recovery of metals on TiO2. It further stresses the point that our present knowledge of photocatalysis and photocatalytic processes can be and must be applied to resolving environmental problems caused by discharge of toxic materials into the aquatic and atmospheric ecosystems. The problems are many; they must be addressed.