Fluorescent composite beads: An advanced tool for environmental monitoring and harmful pollutants removal from water.

The quality and safety of water sources have been significantly impacted by various pollutants, including trace elements. To address this concern, this study utilized composite beads made of alginate and carbon quantum dots (CDs) for detecting and removing As(III) and Se(IV) ions in tap water. Fluorescent CDs were hydrothermally synthesized and incorporated into an alginate-Ca2+ matrix through a straightforward procedure. Characterization analyses revealed distinct properties of the composite beads, containing varying amounts of CDs, compared to the pristine beads. Optimal adsorption parameters (30 mg of adsorbent, 10 mg/L of initial pollutant concentration, 35 °C, and 180 min of contact time) for the beads containing 30 w/w-% of CDs (Alg@CDs30) were determined through a fractional factorial design. These composite beads exhibited the highest adsorption capacity for both metals, achieving a removal rate of 94.5% for As(III) and 98.0% for Se(IV) in tap water. Kinetic and isothermal analyses indicated that the adsorption of both metals on Alg@CDs30 involves a combination of chemisorption and diffusion processes. Recycling experiments demonstrated that the composite beads could be reused up to 20 times without a noticeable loss of adsorption efficiency. Regarding the sensing property, our experiments revealed a significant reduction in the fluorescence emission intensity of Alg@CDs30 upon interaction with As(III) and Se(IV), confirming its ability to detect both ions in tap water, with limits of detection (LOD) of 2.6 ± 0.5 µg/L for As(III) and 1.1 ± 0.2 µg/L for Se(IV). The alginate-Ca2+ matrix s contributed to the stability of the CDs' fluorescence. These results confirm the potential of Alg@CDs beads as effective tools for the simultaneous monitoring and removal of hazardous metal ions from real water samples.

Monitoring settling of anaerobic digestates using low-field MRI profiling and NMR relaxometry measurements.

Dewatering of anaerobic digestate from red meat processing was assessed using low field MRI profiling and NMR relaxometry. Samples were flocculated using a cationic flocculant (EM640CT) at dosing range (0 to 1.6% v/v) and monitored during the initial 30 min of settling via MRI profiling to assess changes in water fraction, settling time and initial settling velocity. The profiles showed decreasing settling time and increasing initial settling velocity with increased dosing, while sample porosity was observed to increase up to the optimal dosing point (0.8% v/v). Significant increases in sample variability were observed past this point due to flocculant overdosing. The samples were then analysed in terms of turbidity and NMR relaxometry. Increasing flocculant concentration caused turbidity to decrease from 210 to 13 NTU. The relaxation rate of free water showed a strong positive correlation with turbidity. T2 peaks observed before overdosing could be assigned to different water structures (free, interstitial, vicinal and hydration). An additional T2 population emerged in the T2 distributions at the optimal dosing point. Multivariate exploratory data analysis (MEDA) showed that this T2 population from the solids layer was strongly correlated with the total solids layer height and turbidity of the watery layer. This T2 peak formation may therefore be used to study opaque flocculated solids to monitor for water structures associated with flocculant overdosing. Further studies using this technique will aim to assess the potential of low field T2 relaxometry monitoring inline before mechanical dewatering, to monitor optimal flocculant dosing during continuous operations on systems with high solids concentration.

Composite hydrogel based on alginate-g-poly(acrylamide)/carbon nanotubes for solid phase extraction of metals from corn cereal samples.

Composite hydrogels containing nanofillers are extensively applied in the sorption of different compounds from aqueous solutions; however, this ability is poorly exploited in the extraction and pre-concentration of analytes from complex matrices. As a contribution to this field, this study reports the synthesis of a composite hydrogel of alginate-g-poly(acrylamide) matrix filled with functionalized multi-walled carbon nanotubes (ALG-g-PAAM/MWCNT-f). This composite served as a solid-phase extractor (SPE) for the separation of Pb2+ and Cd2+ ions from a digested corn cereal sample before their analytical determination. After composite characterization, a series of experiments using low dosages of ALG-g-PAAM/MWCNT-f demonstrated that the composite has a higher sorption capacity for Pb2+ (5.1 mg/g) and Cd2+ (3.9 mg/g) under favorable experimental conditions. As demonstrated, the presence of the MWCNT-f benefited the SPE performance of the composite. The sorption of both cations followed the pseudo-first order kinetics, while the experimental data were well-fitted by the Freundlich isotherm. Also, ALG-g-PAAM/MWCNT-f showed selectivity for Pb2+, and it is reusable up to 10 times without losing sorption performance. After sorption and extraction, both metals were completely recovered, facilitating their quantification by the MIP OES technique. In short, ALG-g-PAAM/MWCNT-f was an effective SPE for the separation and extraction of Pb2+ and Cd2+, which can be beneficial for food control and safety.