ABSTRACT
The extensive use of biocide surfactant benzalkonium chloride (BAC) during the SARS-CoV-2 pandemic has led to the buildup of this hazardous chemical in waste, surface and groundwater. e The study aims to elucidate whether various low-cost household materials are suitable, in their unmodified and untreated form, to effectively adsorb BAC from its aqueous solutions.. Additionally, if a proper adsorbent is identified, a description of the kinetics and thermodynamics of the process is also targeted. From among the five tested materials, a commercially available white household paper towel was chosen to best satisfy the criteria of low price, large availability, and standardization degree, as well as high adsorption capacity within a fairly short time window needed until equilibrium. Batch experiments were carried out with a commercial mixture of BAC-12 and BAC-14 within a temperature range of 18-45 degrees Celsius, and a 25-100 mg/g BAC/adsorbent initial mass ratio range, respectively. The overall process follows a pseudo-second-order kinetic law, with an apparent activation energy of 73.35 KJ/mole. Both the Langmuir and the Redlich-Peterson isotherms describe the equilibrium data at 298 K well, with a Gibbs free energy of -20.64 KJ/mole. These findings are in agreement with previous reports and suggest a hybrid but chemisorption-dominated process.
ABSTRACT
Kinetic and mechanistic related approaches for mostly titania were intensively studied in the literature. However, combined modelling and kinetic studies are few. Therefore, the present work focuses on modelling the dependence of the degradation kinetics of two model compounds (salicylic acid-SA and methyl orange-MO) on Evonik Aeroxide P25, hydrothermally prepared hierarchical TiO2 and P25/WO3 nanostars, obtained also by hydrothermal crystallization. The obtained individual semiconductors and the composites were characterized using XRD, DRS, SEM, while the photocatalytic degradation of the model pollutants were carried out varying the catalyst load, the initial pollutant concentration and incident light intensity. It was found that the degradation kinetics were independent from the hierarchical nature of the material, while significant dependencies of the degradation efficiency was found from the previously mentioned investigation parameters. All these parametric interdependences were successfully studied and a kinetic model was proposed for both bare TiO2 and TiO2/WO3 composite systems.
ABSTRACT
While various reactions in the inorganic subset of the oscillatory Briggs-Rauscher (BR) reaction were clarified in the recent years, the organic subset of the present mechanisms contains only one process: the iodination of malonic acid. Further organic reactions can play a role, however, if malonic (MA) and iodomalonic (IMA) acids can be oxidized in the BR reaction. As CO2 and CO should be products if such oxidations can take place, the main aim of this work was to learn whether these gases are produced in a significant amount in a BR system. In our BR experiments, a rather intense evolution of both gases was observed with an oscillatory and a nonoscillatory component. With the initial conditions applied here, one from every 6 carbon atoms was oxidized either to CO2 or to CO in the course of the BR reaction. The amount of CO2 was about 4 times higher than that of CO. Experiments are in progress to disclose the reactions which generate the measured gases and their role in the mechanism of the BR reaction.
ABSTRACT
The analytical potential of the redox reactions between N, N-dimethyl- or N, N, N', N'-tetramethyl- p-phenylenediamine (DMPPD or TMPPD, respectively) and peroxodisulfate in acidic media for kinetic spectrophotometric determination of trace amounts of ascorbic acid (AA) has been investigated. The goal was to explore reaction conditions ensuring an excess or a deficit of S(2)O(8)(2-), and to identify some kinetic features of the global process for the purpose of calibration. Because the induction period of the overall reaction increases significantly in the presence of micromolar amounts of AA, the most suitable calibration graphs are generated by plots of induction period against the analyte concentration. The best sensitivity was achieved for oxidation of DMPPD with a deficit of S(2)O(8)(2-). The calibration line obtained has an RSD of 2.6% for 4 x 10(-6) mol L(-1) AA (n=3) and the detection limit is 4 x 10(-8) mol L(-1) (7 micro g L(-1)), a value comparable with the best mentioned by the literature. No systematic study of interferents was performed. Instead, the effect of buffer reagents (phosphate, phthalate, citrate) and dissolved oxygen on the results is discussed. Experiments were performed under closely controlled conditions. This is the first report of ascorbic acid analysis in which "contamination" by environmental oxygen was prevented by rinsing all vessels and saturating all solutions with argon, an approach which enables determination of the actual ascorbic acid content. Because of the effort involved, however, the method might not be suitable for routine analysis. Analysis of a commercially available vitamin C pellet gave good results when a "special" calibration graph, obtained in the presence of all other constituents of the sample except AA, was employed. The AA was "removed" from the pellet by oxidation with environmental air. Although it seems rather elaborate, this procedure did not require prior preparation of the sample nor extraction and/or concentration of ascorbic acid from it.
