Stefano Salvestrini

Kinetics of the chemical degradation of diuron.

The influence of pH and buffer concentration on the chemical degradation of diuron in water has been analysed over a wide temperature range. The process irreversibly gives 3,4-dichloroaniline as the only product containing the phenyl ring. H+, OH- and phosphate buffer are efficient catalysts of the reaction. The rate constant first increases rapidly at low buffer concentrations and then gradually levels off at higher ones. At 40 degrees C and high phosphate concentration (>0.01 M), or in the extreme pH regions, the half-life is approximately 4 months and the activation energy is 127 +/- 2 kJmol(-1).

Sorption of non-ionic organic pollutants onto a humic acids-zeolitic tuff adduct: Thermodynamic aspects

Sorption isotherms from water solutions for toluene, cyclohexane, o-xylene, benzyl alcohol, phenol and cyclohexanol onto a humic acid-zeolite adduct were determined at 4, 14, 24 and 34 °C and utilized to calculate the isosteric enthalpy (ΔadsHi) and isosteric entropy (ΔadsSi) of the process. For hydrocarbon compounds, toluene, cyclohexane and o-xylene, both ΔadsHi and ΔadsSi were negative, the process was exothermic. In contrast, for hydroxyl compounds, benzyl alcohol, phenol and cyclohexanol, ΔadsHi and ΔadsSi were positive, the increase in entropy possibly reflecting the release of water molecules during sorption. The results suggest that sorption/desorption of either class of compounds could be controlled by operating on the temperature.

A novel organo-zeolite adduct for environmental applications: Sorption of phenol

A novel organo-zeolite adduct has been synthesized by sorbing humic acids (HA) onto zeolitic tuff and then heating the resulting complex at 330°C for 1.5h. Desorption tests showed that this procedure effectively immobilized HA on the tuff. The crystal structure of the zeolitic tuff and the chemical structure of HA were not altered during the preparation. Phenol sorption analysis demonstrated that the HA-zeolite adduct had good sorbing properties; moreover, the sorbed amount markedly decreased with increased ionic strength. These results point to prospective application of the HA-zeolite adduct as a low-cost and environmentally friendly sorbent for water purification from phenol and possibly other neutral organic pollutants.

Comment on “Removal of anionic dye Congo red from aqueous solution by raw pine and acid-treated pine cone powder as adsorbent: Equilibrium, thermodynamic, kinetics, mechanism and process design”

* Corresponding author. Tel.: þ39 0 823 2746 E-mail address: sante.capasso@unina2.it 0043-1354/

Kinetics and mechanism of hydrolysis of phenylureas

e see front matter a 2012 Publi doi:10.1016/j.watres.2012.05.040 Recently, Dawood and Sen (2012) published a paper reporting a kinetic analysis of Congo red adsorption by natural material. In section 2.4.4. Thermodynamic study, they describe the determination of the thermodynamic parameters DH e DS by means of the van’t Hoff equation as follows:

Identification of stationary sources of air pollutants by concentration statistical analysis

The hydrolysis of phenylureas has been found to be affected by temperature, pH and buffer concentration. Kinetic evidence suggests that the formation of phenylisocyanate, the initial product in the title reaction, occurs via an intermediate zwitterion. Depending on pH and buffer concentrations, the zwitterion can be produced through three parallel routes: at low pH, specific acid–general base catalysis, followed by slow deprotonation of a nitrogen atom by a general base; at high pH, specific basic–general acid catalysis, followed by slow protonation of a N atom by a general acid; at intermediate pH the reaction proceeds through a proton switch promoted by buffers. Bifunctional acid–base buffers such as HCO3−/CO32−, H2PO4−/HPO42− and CH3COOH/CH3COO− are very efficient catalysts. At high buffer concentration, as well as at pH 12, the breakdown of the zwitterion is rate-determining. The results are discussed in relation to recently published papers reporting different pathways.

Modelling the biphasic sorption of simazine, imidacloprid, and boscalid in water/soil systems

The atmospheric concentrations of benzene, toluene, ethylbenzene and isomeric xylenes (BTEX) in a medium-sized town (S. Maria Capua Vetere, about 32000 inhabitants, Southern Italy) have been determined during working days and weekends in 2006. The procedure used was 24h passive adsorption by samplers distributed throughout the town followed by GC/MS analysis. On a yearly base, the arithmetic mean benzene concentrations were above the limit required by the 2000/69/CE European Directive. The Pearson correlation coefficients of the 24h geometric mean BTEX concentrations were indicative of stationary sources of toluene located in a well circumscribed area of the urban territory, active only during the working days and not officially recognized. The results highlight the effectiveness of the statistical approach used in this study for the identification of pollutant sources.

Use and Misuse of Sorption Kinetic Data: A Common Mistake that Should be Avoided

The sorption kinetics of simazine (6-chloro-N,N′-diethyl-1,3,5-triazine-2,4-diamine), imidacloprid (1-(6-chloro-3-pyridylmethyl)-N-nitroimidazolidin-2-ylideneamine), and boscalid (2-chloro-N-(4′-chlorobiphenyl-2-yl)nicotinamide), three pesticides of wide use in agriculture, was determined in five different water/soil systems over a time interval from the initial few seconds to about 1 month. In all the experiments, sorption kinetics showed a biphasic pattern characterized by an initial, relatively short phase with a high sorption rate and a later phase with much a lower sorption rate. Initial sorption capacity increased with soil organic carbon content and with sorbate hydrophobicity. We postulate that the first phase of the process involves a fast second-order sorption reaction on superficial sites of soil particles, whereas the second phase depends on diffusion-controlled migration to internal binding sites. A kinetic equation based on this hybrid model accurately fitted all data sets. Less satisfactory results were obtained employing the pseudo-first order, pseudo-second order, Elovich, two site non-equilibrium, or Weber-Morris equation. The superior performance of the hybrid model for describing boscalid sorption probably reflects the high hydrophobic character and consequent low diffusion rates of this compound. The accuracy of modelling was in any case strongly dependent on the time interval considered.

Sorption of non-ionic organic pollutants onto immobilized humic acid

Numerical simulation of sorption dynamics showed that the use of data recorded at (or very close to) equilibrium in the search for the kinetic equation that best describes the process frequently leads to incorrect conclusions. Notably, it has been demonstrated that the fit of the adsorption data at equilibrium (t/qt versus t) is a straight line irrespective of the sorption kinetics. In order to distinguish pseudo-first-order from pseudo-second-order sorption kinetics, the data near the equilibrium should be omitted from the least-squares fit and the result confirmed by a different method. A straightforward method based on Δ(qt/qe)/Δt versus 1 – qt/qe and versus (1 – qt/qe)2 plots is suggested. Some recent papers reporting incorrect sorption kinetic analyses are discussed.

Catalytic effect of dissolved humic acids on the chemical degradation of phenylurea herbicides.

AbstractSorption isotherms from water solution onto immobilized humic acid have been determined at 4, 14, 24, and 34°C for toluene, cyclohexane, o-xylene, benzyl alcohol, phenol, and cyclohexanol. The experimental data were well described by the Freundlich sorption equation. The higher values of K constant were obtained for the two aromatic hydrocarbon compounds, toluene (924 mmoln−1 Ln kg−1) and o-xylene (1,350 mmoln−1 Ln kg−1). The isosteric sorption enthalpy (ΔistH) and the standard enthalpy were negative for all compounds analyzed, and the absolute values of ΔistH decreased with increasing sorbate loading. Comparisons with data for a humic acid-zeolitic tuff adduct supports the conclusion that the sorption properties of combined materials may not be the sum of the components, thus strengthening the rationale for research of novel adducts.