Dimosthenis L. Giokas

Sample preparation typically involves multiple steps to create conditions for separating analytes from the sample matrix. These steps involve the preparation of reagents and materials, their addition into the sample, mixing by external energy input, and timing of each step. All these steps increase analysis time, reduce sample throughput, and require benchtop laboratory equipment and trained personnel. In this work, we report layered effervescent tablets to simplify multistep sample preparation. The tablets consist of layers that dissolve sequentially at a controlled rate, releasing stored, pre-quantified reagents at specific time intervals. As a proof-of-concept demonstration, we designed tablets for the extraction of copper ions, as model analyte, from aqueous solutions. The tablets autonomously perform a series of steps that involve adjustment of pH, dissolution and dispersion of a chelating agent, incubation, mixing and extraction of the metal chelates in a magnetic sorbent by the action of effervescence. The preliminary analytical application of the method to the determination of copper in environmental samples revealed analytical features, which are comparable to standard laboratory practices (recoveries > 80%, RSD < 8%). In this manner it is demonstrated that layered effervescent tablets can be a promising tool for simplifying multistep sample preparation by reducing reliance on human and technical resources and allowing extractions to be performed with minimal intervention and basic infrastructure. AbstractSection Graphical abstract

The steadily increasing use of gold and the limited gold reserves have instigated a significant research effort to develop materials with efficient gold recovery. However, most works focus only on the uptake of Au ions, ignoring Au nanoparticles, which are increasingly used in various applications and represent a critical source of Au. Furthermore, the reported gold recovery studies involve powder-form materials that cannot be easily retrieved after the sorption process, thus making them unattractive for real, large-scale applications. The present work reports a Zr-(IV) metal-organic framework (MOF) with a defective microporous structure and amino-thiophene functional groups, which exhibit strong interactions with Au species. The MOF was immobilized on cotton fabric via an in situ method to create an easily retrievable bulk sorbent composite, which was investigated in detail for its sorption properties toward Au ions and Au nanoparticles (AuNPs). The immobilized sorbent showed relatively fast sorption kinetics (85%) of gold either as ions or AuNPs from genuine water samples. The latter property allowed the use of the MOF-fabric sorbent for the development of the first passive sampling sorbent phase for the long-term monitoring or recovery of AuNPs from natural waters. Notably, the sorbent was highly effective for the selective recovery of Au (∼97%) from an electronic waste simulant under flow conditions. The reusability of the MOF, in a composite form with calcium alginate, as Au sorbent was demonstrated under flow conditions for several cycles, indicating the potential of the material for Au separation applications. Overall, the reported sorbent offers a practical and cost-effective means for efficiently recovering ionic and nanoparticle Au species from complex water and wastewater media.

A paper-based UV dosimeter/indicator based on the solid-state photochemical reduction of gold-cationic surfactant complexes is described. Upon exposure to UV light, the photoreductive elimination of chloride ions from the CTA-AuCl₄ ⁻ complex leads to the reduction of Au ions and the formation of small Au nuclei. After hydration, the Au nuclei are washed away by capillary flow and produce gold nanoparticles by coalescence and aggregation, resulting in a blue-purple coloration on the paper surface. The reaction is initiated by UV light of variable wavelength (from UVA at 254 nm tο UVC at 365 nm) and over a wide range of UV doses (up to 3000 mJ/cm² for UVB at 312 nm and UVC at 365 nm). This versatility allows for its application in monitoring light exposure in germicidal sterilization, UV phototherapy, and as a personal solar UV indicator. The user-friendly paper facilitates both the fabrication and use of the devices, which can be activated on demand by simply wetting the paper surface. Graphical abstract

In this work, we revisited the method of effervescence-assisted microextraction, aiming to assess the effects of the process of effervescence on the extraction efficiency of organic compounds. We used a magnetic nano-sorbent material composed of stearic acid-coated cobalt-ferrite magnetic nanoparticles as an adsorbent and dispersed it in water using 12 combinations of acid and base mixtures at two different mass ratios. The solution pH, the ionic strength, and the duration of effervescence were calculated and correlated to the extraction efficiency of nonpolar UV filters from aqueous samples as model organic compounds. Our findings provide a general perspective into the influence of the process of effervescence on extraction efficiency. Based on these findings, we developed and optimized a new analytical method for extracting UV filters from water samples using HPLC-UV as a detector. Under the optimum experimental conditions (0.2 g fumaric acid/0.1 g Na₂CO₃, 50 mg of magnetic nanoparticles and methanol as an elution solvent assisted by vortex agitation for 5 min) the method was found to afford good linearity in the calibration curves expanding by two orders of magnitude, satisfactory reproducibility and repeatability (1.8–11.1%), and high recoveries (78.4–127.1%). This research provides a new perspective on the influence of the process of effervescence on the extraction efficiency of nonpolar organic compounds and introduces a new method for extracting UV filters from aqueous media.

One of the driving forces behind the significant advancements in environmental separation science is the need for creative solutions to the evolving environmental challenges.

In this work, the total content of seven metallic elements (Fe, Cu, Zn, Mg, Pb, Ni, and Co) in common edible herbs was determined and related to their bioaccessibility by an in vitro human digestion model. Specifically, the unified bioaccessibility protocol developed by the BioAccessibility Research Group of Europe (BARGE) was used to determine the release of each element during gastric and gastrointestinal digestion. The results show that Fe, Zn, and Mg are released during gastric digestion (34–57% Fe, 28–80% Zn, 79–95% Mg), but their overall bioaccessibility is reduced in the gastrointestinal tract (<30%). On the contrary, Cu is more bioaccessible during gastrointestinal digestion (38–60%). Pb, Ni, and Co exhibited similar bioaccessibility in both gastric and gastrointestinal fluids. Principle component analysis of the data shows that the classification of the nutritional value of herbs differs between the total and the gastrointestinal concentration, suggesting that the total concentration alone is not an adequate indicator for drawing secure conclusions concerning the nutritional benefits of edible plant species.

The direct use of nanosorbents for water purification is limited due to their aggregation and the lack of techniques for their recovery from natural waters. To overcome these problems, the affixation of nanomaterials onto bulk, non-mobile supports has been proposed. However, a method to simulate the efficiency of these sorbents under realistic conditions is still not available. To address this need, this work describes a method for evaluating the sorption efficiency of nanosorbent materials incorporated on bulk supports under non-equilibrium conditions. The method combines the principles of passive sampling, an environmental monitoring technique that is based on passive diffusion of dissolved contaminants from water to a sorbent, with batch sorption experiments that measure sorption under equilibrium conditions, to determine the parameters associated with water purification. These parameters are the maximum sorption capacity of the sorbent and the sampling rate, which is the volume of contaminated water treated per unit of time. From these variables, the deployment time of the sorbent until reaching saturation is proposed as an alternative indicator of sorbent efficiency. As proof-of-principle, the removal of oxyanions from a Zr-metal-organic framework (MOR−1) immobilized on cotton textiles was investigated. The results show that the sorption capacity under passive diffusion uptake conditions, is approximately 20 mg/g for As(VI) and 36 mg/g Se(IV), which is 10 to 30 times lower compared to that determined in batch sorption studies, indicating that conventional equilibrium sorption overestimates the efficiency of the sorbents under realistic conditions. The application of the method to a worst-case scenario, involving the severe contamination of freshwaters with arsenate species, is also demonstrated.

The cornerstone of nanomaterial-based sensing systems is the synthesis of nanoparticles with appropriate surface functionalization that ensures their stability and determines their reactivity with organic or inorganic analytes. To accomplish these requirements, various compounds are used as additives or growth factors to regulate the properties of the synthesized nanoparticles and their reactivity with the target analytes. A different rationale is to use the target analytes as additives or growth agents to control the formation and properties of nanoparticles. The main difference is that the analyte recognition event occurs before or during the formation of nanoparticles and it is based on the reactivity of the analytes with the precursor materials of the nanoparticles (e.g., metal ions, reducing agents, and coatings). The transition from the ionic (or molecular) state of the precursor materials to ordered nanostructured assemblies is used for sensing and signal transduction for the qualitative detection and the quantitative determination of the target analytes, respectively. This review focuses on assays that are based on analyte-mediated regulation of nanoparticles’ formation and differentiate them from standard nanoparticle-based assays which rely on pre-synthesized nanoparticles. Firstly, the principles of analyte-mediated nanomaterial sensors are described and then they are discussed with emphasis on the sensing strategies, the signal transduction mechanisms, and their applications. Finally, the main advantages, as well as the limitations of this approach, are discussed and compared with assays that rely on pre-synthesized nanoparticles in order to highlight the major advances accomplished with this type of nano-sensors and elucidate challenges and opportunities for further evolving new nano-sensing strategies. Graphical abstract