Surface fractal and structural properties of layered clay minerals monitored by small-angle X-ray scattering and low-temperature nitrogen adsorption experiments

Small-angle X-ray scattering of the clay minerals kaolinite, montmorillonite and illite was studied with a compact Kratky camera. From the scattering function, the correlation length, the Porod constant and the specific surface area were determined. The scattering functions also led to the surface fractal dimension. The pore volume distribution, the adsorption/desorption hysteresis, the specific surface area and the surface fractal dimension of the same samples were also determined by nitrogen adsorption at 77 K.     

Evaluation of an HPIC Method for Determination of Nitrates in Vegetables

The aim of the work was to verify the reliability of an HPIC method for determination of nitrates in vegetables using statistical analysis to evaluate validation parameters according the ISO/IEC 17025:2005. Standard solutions were used for the construction of a calibration curve, which was supported by Varian Star Workstation software. All calculated validation characteristics were summarized in an Excel table with final evaluation of the method. Repeatability was characterized by the selected variation coefficient s_R, calculated from the standard deviation s_d and arithmetic mean from a series of measurements under repeat conditions, accuracy by the variation coefficient s_R, and recovery. The repeatability of the method of 3.62% is under the set limit of 5%. The calculated uncertainty was 4.22% with a recovery of 99.2%. Determination of nitrate was linear over the whole range of the calibration graph. The LOQ was 0.60 mg L⁻¹, which is fully acceptable within the requirements for nitrate determination in plant materials. Standard uncertainty of these methods was calculated as an expanded uncertainty according to Eurachem documents in the PC program Metro2003, version 2.30.

     

Photocatalytic degradation of hydrocarbons by bentonite and TiO2 in aqueous suspensions containing surfactants

Organic substances (toluene, asphaltene dissolved in toluene) poorly soluble in water were solubilized by sodium dodecylsulfate (SDS) and the organic pollutants were mineralized together with the surfactants in diluted TiO₂ suspension by UV light. In concentrated aqueous suspension, crude oil was photodegraded on the surface of Na-bentonite and the photocatalyst TiO₂. Experiments have been carried out with Na-bentonite contaminated with crude oil mixed in a ratio of 1:1 with TiO₂ as well. The photooxidation processes were followed by total organic carbon content (TOC) and diffuse reflection infrared spectroscopy (DRIFT) measurements.