Sustainable and green persulfate-based chemiluminescent method for on-site estimation of chemical oxygen demand in waters

The standard method for estimating the chemical oxygen demand (COD) of water bodies uses dichromate as the main oxidant, a chemical agent whose use has been restricted in the European Union since 2017. This method is hazardous, time-consuming, and burdensome to adapt to on-site measurements. As an alternative and following the current trends of sustainable and green chemistry, a method using the less toxic reagent sodium persulfate as the oxidizing agent has been developed. In this method an excess of persulfate, activated through heating in an alkaline solution, oxidizes the chemically degradable organic fraction through a 2-step radical mechanism. The remaining persulfate is evaluated by chemiluminescence (CL) using luminol and a portable charge-coupled device (CCD) camera. The method provided quantitative recoveries and a sample throughput of >60 samples h. It was validated in river water samples by comparison of COD estimations with the standard dichromate method (R = 0.973, p < 0.05) and with a UV–Vis permanganate-based method (R = 0.9998, p < 0.05), the latter being also used for drinking waters. The proposed method is a sustainable and green alternative to the previous used methods. Overall, the method using activated persulfate is suitable for use as COD quantitation/screening tool in surface waters. Considering that its main components are portable, it can be ultimately adapted for in situ analysis at the point of need

Quantitative study of the capture of silver nanoparticles by several kinds of soils

The capacity of different soils lo capture silver nanoparticles (AgNPs) by measuring changes of an AgNP intrinsic property such as the plasmon for the first time, was studied. In-lube solid-phase microextraction (IT-SPME) coupled on-line to capillary liquid chromatography (CapLC) with diode an-ay detection (DAD) was employed fur measuring the interactions between soil and in-contact AgNP dispersions. Its achieved LOD 9 pM assures quantitative retention measurements and selectivity for soil lixiviation was suitable. Electronic microscopy was employed for corroborating the entrapped Ag into the soils. Capture % of AgNPs was calculated in compost (>99%), mountain (>99%), orchard (15 +/- 1%) and urban (48 +/- 1%) soils. Also, the relation between some soil characteristics: solid organic matter (SOM), composition, pH, redox potential (Eh), electrical conductivity (EC) and size, and the retention of these metallic nanoparticles was studied. The results have also been estimated after sieving and the capture % of AgNPs was similar in the resulting fractions. AgNP adsorption on a given soil is mainly affected by its organic matter content for studied soils with higher SOM amounts (23-62%). However, for the soils with lower SOM amounts (4.6-83%) the role of HAs could prevent AgNP deposition onto soils. The proposed methodology can be utilized for quickly assessing the potential of a given soil considering its properties for capturing these nanoparticles, which can come at handy for their administration, characterization or remediation