New silica based adsorbent material from rice straw and its in-flow application to nitrate reduction in waters: Process sustainability and scale-up possibilities.

This paper shows a particular example to move to a sustainable circular economical process from valorization of rice straw ashes by developing a green synthesis for obtaining a useful sub-product. This strategy can palliate negative effects of the agriculture waste practices on the environment and also the obtained silica reduced nitrate content in waters. It is demonstrated that the silica synthesis developed at lab was scalable more than a hundred times with good results. Adsorption studies of nitrate in standards and real well waters at lab scale and scaling-up provided similar results. Adsorption values near to 15 mg/g for nitrate standards and 8.5 mg/g for well water were obtained until achieving the initial nitrate concentration. Experimental breakthrough curves fitted to Thomas model, which gave similar results for adsorption capacities. The adsorption capacity was checked with that obtained by a commercial resin, providing improved results. The method at large scale was compared with industrial traditional methods and green adsorbents.

In-tube solid phase microextraction coupled to miniaturized liquid chromatography for both, noble metal nanoparticle assessment and sensitive plasmonic assay development.

Colorimetric localized surface plasmon resonance (LSPR) as analytical response is applied for a wide number of chemical sensors and biosensors. However, the dependence of different factors, such as size distribution of nanoparticles (NPs), shape, dielectric environment, inter-particle distance and matrix, among others, can provide non-reliable results by UV-vis spectrometry in complex matrices if NP assessment is not carried out, particularly at low levels of analyte concentrations. Miniaturized liquid chromatography, capillary (CapLC) and nano (NanoLC), coupled on line with in-tube solid phase microextraction (IT-SPME) is proposed for the first time for both, controlling suitability of used noble metal NP dispersions and developing plasmonic assays. Several capped noble NPs and target analytes were tested from variations in the chromatographic profiles obtained by using diode array detection. The IT-SPME step, which influenced the chromatographic fingerprint provided by noble NP dispersions, was studied by asymmetrical flow field flow fractionation (AF4) too. We monitored NP aggregation induced by interaction with several analytes like acids and spermine (SPN). Assessment of NPs was achieved in less than 10 min and it permitted to develop suitable plasmonic tests. Here, it was also demonstrated that these assays can be followed by IT-SPME-miniaturized LC-DAD and more sensitivity and selectivity than those provided by UV-Vis spectrometry were achieved. Analysing urine samples to determine SPN as a cancer biomarker as a proof of concept is presented.

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

The capacity of different soils to capture silver nanoparticles (AgNPs) by measuring changes of an AgNP intrinsic property such as the plasmon for the first time, was studied. In-tube solid-phase microextraction (IT-SPME) coupled on-line to capillary liquid chromatography (CapLC) with diode array detection (DAD) was employed for 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 (4.6-8.3%) 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.