Search Results (263)

The replacement of synthetic dyes with natural food colorants has become a priority for the food industry, as emerging evidence from in vitro and animal studies on the potential neurotoxic and pro-inflammatory effects of certified dyes converges with consumer pressure for clean-label formulations. Yet despite this, the industrial uptake of natural pigments remains uneven, held back by stability limitations that differ considerably from one pigment class to the next and from one food matrix to another. This review covers the chemistry, industrial applications, and stabilization approaches of the main natural colorant groups: carotenoids, anthocyanins, betalains, chlorophylls, curcuminoids, phycocyanin, and genipin-derived pigments, with particular attention to the physicochemical reasons behind their instability and the practical tools available to address it. Among stabilization strategies, spray-drying microencapsulation with composite protein–polysaccharide wall materials is often the most scalable and cost-effective option, whereas freeze drying may be preferable for high-value pigments or applications in which maximum pigment retention is the priority. Whether the encapsulating matrix remains in a glassy or rubbery state stands out as a key factor governing oxidative degradation across all pigment categories, which makes water activity management a non-negotiable element of any serious formulation effort. Anthocyanins require more than physical encapsulation alone: copigmentation and structural approaches such as acylation and pyranoanthocyanin formation hold degradation routes that no shell material can prevent on its own. For hydrophobic pigments like carotenoids and curcuminoids, lipid-based delivery systems consistently deliver higher bioaccessibility than aqueous or dried formats. pH control, antioxidant incorporation, and modified atmosphere packaging add a useful but ultimately incomplete third line of defense. One development worth attention is the use of pH-responsive pigments in biopolymer packaging films, where color instability, long treated as a drawback, becomes a real-time indicator of food freshness. Bridging the remaining performance gap with synthetic dyes will call for stabilization platforms that tackle the molecular, physical, and environmental dimensions of degradation together, built around the particular chemistry of each pigment and the demands of each application. Full article

An adsorptive stripping voltammetric method for the determination of ultra trace amounts of Mo(VI) using an electrode based on a mixture of carbon nanotubes and spherical glassy carbon (CNT/SGC) was developed. The electrode was modified by depositing a lead film in situ during each measurement cycle. In a supporting electrolyte containing 0.2 mol/L of acetic buffer pH = 5.3; 0.2 mmol/L of Pb(II); and 0.15 mmol/L of cupferron, the stripping response observed at −0.62 V was proportional to the Mo(VI) concentration within the range of 7 nmol/L to 0.6 µmol/L. The measurement protocol involved a 20 s electrode modification followed by a 30 s adsorption of Mo(VI)–cupferron complexes. The limit of detection was found to be 2.5 nmol/L with a correlation coefficient of 0.997. The method has been applied to the determination of Mo(VI) in mineral water samples. Full article

Carbon-based materials, including graphene, carbon nanotubes, laser-induced graphene, and pyrolyzed glassy carbon, are widely used in sensing applications due to their high conductivity, large surface area, and tunable surface chemistry. Meanwhile, microfluidic systems enable precise fluid handling, reduced sample consumption, and enhanced analytical performance through improved mass transport and device miniaturization. The integration of carbon-based materials with microfluidic platforms has enabled the development of compact, portable, and highly sensitive devices for water monitoring. This review summarizes recent advances in carbon-based microfluidic sensors for water monitoring applications. Key carbon materials and their sensing mechanisms, particularly electrochemical transduction, are discussed. Various microfluidic integration strategies, including paper-based devices, polymer-based devices, MEMS-based systems, and flexible platforms, are highlighted, with emphasis on mass transport enhancement and overall system performance. Representative recent advances in carbon-based microfluidic sensors for water monitoring, including the detection of heavy metal ions, nutrients, and emerging contaminants, are reviewed. Finally, challenges related to scalable manufacturing, long-term operational stability, biofouling/surface fouling, and reproducible system integration are discussed, together with future perspectives on intelligent carbon-based microfluidic platforms featuring AI-assisted analytics, sense-response functionality, and self-healing and dynamic antifouling capabilities for water monitoring. These advances are expected to enable real-time, low-cost, and field-deployable water monitoring systems for environmental protection and public health management. Overall, this review highlights the critical role of integrating carbon-based sensing materials with microfluidic engineering in advancing next-generation water monitoring technologies. Full article

Grape pomace (GP) is the main residue of the winemaking process; it is rich in phenolics with great bioactive potential. This study applied subcritical water extraction (SWE) to GP at 120, 140, and 160 °C to fractionate it into value-added products. The extraction performed at 120 °C and 1.3 bar (E-120) was the most efficient, resulting in the highest soluble fraction yield (61 g/100 g GP) with high phenolic content (4.1 g GAE (gallic acid equivalent)/100 g extract solids) and strong antioxidant capacity (EC₅₀: 0.79 mg extract/mg DPPH (2,2-Diphenyl-1-picrylhydrazyl)), while it inhibited the growth of Listeria innocua at 325 mg/mL. The insoluble extraction residue (38 g/100 g GP) also retained substantial phenolic content (10 g GAE/100 g), with high antioxidant activity (EC₅₀: 1.5 mg residue/mg DPPH) and a fibre-rich composition, supporting its value as a functional ingredient. To improve handling and stability, the E-120 extract was encapsulated in maltodextrin or pectin. For both polymers, a 40% polymer ratio with respect to the extract solids yielded a stable, single-phase, glassy powder (T_g ~50 °C), with thermal stability extending up to 200 °C. Therefore, SWE constitutes an efficient and sustainable technique for obtaining functional ingredients from GP, allowing for its valorisation. Full article

Electrochemical impedance spectroscopy (EIS) is a powerful, non-destructive tool for evaluating ion-selective electrode (ISE) membrane condition. This work investigated EIS for identifying degradation mechanisms in all-solid-state Pb²⁺-selective electrodes. Graphene-containing PVC membranes deposited on glassy carbon electrodes were exposed to synthetic urine, river water, and seawater (24 h and 1 week) and to mechanical damage (cutting, needle puncture, or both). Degradation was assessed using EIS, potentiometric measurements, contact-angle analysis, profilometry, and SEM. River water and urine exposure decreased hydrophobicity, increased roughness, and produced fouling deposits. Seawater caused only minor morphological and wettability changes, though impedance data showed increased membrane hydration due to high ionic strength. Mechanical damage substantially disrupted membrane integrity, causing pronounced impedance changes, increased potential drift, and reduced analytical performance. Fouling and mechanical damage produced distinct electrochemical signatures: fouling mainly affected surface properties, while mechanical damage altered the membrane–transducer interface, increasing capacitance and reducing resistance. Notably, needle-punctured electrodes retained a near-Nernstian response despite clear impedance changes and reduced long-term stability, showing that EIS detects defects invisible to conventional calibration. These results confirm EIS as a sensitive method for distinguishing fouling from physical damage, useful for early degradation detection and lifetime monitoring of all-solid-state ISEs. Full article

A new method is described for the determination of vanadium using adsorptive stripping voltammetry of V(V) complexed with cupferron at a CNTs/SGC electrode modified with a lead film. The CNTs/SGC electrode is based on carbon nanomaterials such as carbon nanotubes and spherical glassy carbon, which form the foundation of modern sensor technology. Optimal conditions of adsorptive voltammetric measurement were found to be modification/accumulation potential and time of −1.6 V and 60 s, respectively, and supporting electrolyte of 0.2 mol/L NaAc–HAc buffer (pH 5.3) containing 0.3 mmol/L cupferron and 0.15 mmol/L Pb(II). The response of the system was found to be linear in a range of V(V) concentrations from 0.25 nmol/L to 10 nmol/L. The detection limit was found to be 0.08 nmol/L. The selectivity of the procedure was determined by analysing the effect of other interfering ions on the vanadium analytical signal. The method was successfully validated by analysing natural environmental waters. Full article

A nitrogen/sulfur co-doped reduced graphene oxide (N,S-RGO) material was rationally prepared via a modified Hummers method followed by microwave-assisted reduction. The resulting material was uniformly deposited onto a glassy carbon electrode (GCE) to fabricate an electrochemical sensor for nitrobenzene (NB) detection. The prepared N,S-RGO material was characterized in detail using Fourier-transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy, confirming the successful incorporation of heteroatoms. Furthermore, electrochemical studies, including cyclic voltammetry (CV) and linear sweep voltammetry (LSV), revealed the enhanced electrical conductivity of the material. The fabricated N,S-RGO/GCE sensor exhibited remarkable electroanalytical performance, achieving a low detection limit (LOD) of 7 nM within a linear concentration range of 0.05 to 147 µM. The enhanced sensing performance is attributed to the synergistic effect of nitrogen and sulfur doping, which improves electron transfer kinetics and abundant active sites for NB reduction. Furthermore, the sensor demonstrated outstanding selectivity toward NB in the presence of common interfering substances. Its practical applicability was confirmed through the successful detection of NB in environmental water samples, yielding convincing recovery rates. These results highlight the potential of the N,S-RGO/GCE platform as an efficient and reliable electrochemical sensor for environmental monitoring of NB contamination. Full article

A pyranochromene-based ligand, 2-amino-4-(4-chlorophenyl)-5-oxo-4H,5H-pyrano[3,2-c]chromene-3-carbonitrile (ACLPh-PC-3-CN), was employed as a chelating modifier for the electrochemical determination of Cd(II) in water samples. ACLPh-PC-3-CN was co-immobilized with Nafion on a glassy carbon electrode to form a stable ACLPh-PC-3-CN/Nafion film that combines ligand-based coordination with cation-exchange-assisted preconcentration of Cd²⁺ at the electrode surface. The Cd(II) response at the modified electrode was characterized by cyclic voltammetry and differential pulse anodic stripping voltammetry, and the data support a predominantly 1:1 Cd(II)–ligand interaction at the interface under the selected conditions. At an optimized pH of 6.0, the sensor provided a linear calibration range from 16.21 to 56.72 μM, with a detection limit of 0.60 μM and a quantification limit of 2.0 μM, and showed good precision (repeatability 2.3% RSD, reproducibility 3.1% RSD) and short-term stability (94% of the initial response after 14 days). The ACLPh-PC-3-CN/Nafion-modified electrode tolerated common inorganic ions and surfactant species (≤5% signal change) and was successfully applied to the determination of Cd(II) in tap water and Red Sea water, affording recoveries between 98.7% and 101%. While the current detection limit is higher than typical guideline values for Cd in drinking water, the proposed sensor compares favorably with several reported electrochemical Cd(II) sensors in terms of simplicity, precision, and matrix tolerance, and represents a useful platform for coordination-based electrochemical sensing of cadmium in environmental water samples. Full article

Inorganic mercury ions (Hg²⁺) are highly toxic, posing a threat to aquatic ecosystems and human health. In this study, iron phthalocyanine (FePc) was anchored onto the surface of MXene via a self-assembly strategy to construct an FePc/MXene-x (F/M-x) heterostructure. Characterization by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and nitrogen adsorption–desorption (BET) confirmed that the high specific surface area and good conductivity of MXene effectively inhibited FePc aggregation and increased the exposure of active sites. The F/M-x composite was then modified onto a glassy carbon electrode (GCE) to fabricate an electrochemical sensor, and the detection performance for Hg²⁺ was evaluated using square-wave anodic stripping voltammetry (SWASV). Under optimized conditions (pH = 5.0, accumulation at −1.2 V for 180 s), the F/M-100/GCE exhibited a linear range of 0.1–1.0 μM, a sensitivity of 19.02 μA/μM, and a detection limit of 5.9 nM. The sensor showed good anti-interference ability against coexisting metal ions such as Cd²⁺, Cu²⁺, and Pb²⁺, with a batch-to-batch RSD of 2.03% and a long-term stability RSD of 2.49%. Spike recovery experiments in real water samples (lake water and groundwater) verified the accuracy of the method. This study provides a new electrochemical platform for the rapid detection of trace Hg²⁺ in water environments. Full article

Glaze flaking is widespread in Hongzhou kiln celadon dating from the Eastern Han to the Tang Dynasty, yet its underlying mechanism cannot be attributed to a single factor. In this study, 11 Hongzhou kiln celadon specimens from the Eastern Han, Southern Dynasties, and Sui–Tang periods were examined using microscopic observation, SEM–EDS, Raman spectroscopy, crack-width measurements, glaze-area analysis, water-absorption tests, and burial environment analysis to investigate the characteristics and causes of glaze flaking. The results show that crazing-crack width is significantly and positively correlated with the extent of glaze flaking. The body–glaze interlayer generally exhibited heterogeneous features, including anorthite crystallization, unmelted quartz grains, bubbles, and locally phase-separated droplets. Anorthite crystals and adjacent regions were frequently associated with crystal-shaped corrosion pits, irregular voids, and localized structural loosening; degraded areas showed depletion of Ca and Si and relative enrichment of Al and Fe. The burial soils were generally neutral to slightly alkaline and showed no evident salt accumulation, suggesting that high salinity was not the primary direct cause of glaze flaking in these samples. These findings suggest that glaze flaking in Hongzhou kiln celadon results from the interaction between firing-induced heterogeneity at the body–glaze interface and prolonged post-burial corrosion. Crazing and interconnected cracks acted as pathways for moisture and soluble ions to penetrate the body–glaze interlayer, triggering selective corrosion of Ca-rich crystalline phases and adjacent glassy phases and ultimately causing interfacial destabilization and glaze loss. Full article

The accelerated deployment of hydrogen technologies is widely discussed as a pathway to mitigate climate change and reduce environmental pollution associated with fossil fuel use. In this context, intermediate-temperature proton-exchange membranes that operate in the 120–200 °C window, similar to the one characterizing liquid-acid PAFC systems (much larger in their power range), are sought as a bridge between low-temperature PFSA-based PEMFCs and low-temperature PCFs, thus combining reduced sensitivity to external humidification with solid-electrolyte handling. This Part I review surveys phosphate- and silicate-based glassy proton conductors as single-anion baseline matrices and organizes the literature around a mechanistic screening framework that links processing fingerprints—particularly sol–gel hydrolysis/condensation conditions, aging, drying, and thermal treatment—to pore architecture, hydration state, and the dominant proton-transport regime. Across both families, conductivity is governed by coupled variables: network chemistry (acidic site density and connectivity), water activity (RH), and microstructure-controlled percolation and retention. Reported σ values can arise from fundamentally different regimes, ranging from hopping-dominated transport supported by dense hydrogen-bond networks and proton-bearing groups to carrier-assisted, water-mediated transport in connected porosity, with distinct humidity dependence and stability implications. Accordingly, the review treats σ(T,RH) and activation energy together with hydration/porosity indicators as primary screening metrics, and it records missing durability and device-level information—chemical stability (hydrolysis and leaching/acid migration), mechanical robustness and cycling response, and current/power density where available—as explicit knowledge gaps. While substantial progress has been achieved within single-anion phosphate and silicate glasses, particularly through engineered acidity and microstructural control, most systems remain limited by hydration drift under gradients, thermal/humidity cycling stability, and electrode/electrolyte interfacial constraints when evaluated against intermediate-temperature membrane requirements. These conclusions establish a quantitative baseline and comparison rules for Part II, which will assess mixed-network, composite, and hybrid strategies designed to decouple conductivity from water-retention and durability trade-offs. Full article

The extensive use of 2,4-dichlorophenoxyacetic acid (2,4-D) in agriculture has led to water contamination and associated health risks, highlighting the need for eco-friendly detection strategies. Herein, Fe₃O₄ nanoparticles were green-synthesized for the first time using an aqueous extract of Rumex nervosus (R. nervosus) as a natural reducing and stabilizing agent and successfully employed for the electrochemical sensing of 2,4-D, representing the first reported application of R. nervosus-mediated Fe₃O₄ nanoparticles for this purpose. The phytochemical composition of the extract and synthesized R-Fe₃O₄ nanoparticles were systematically characterized. The R-Fe₃O₄-modified glassy carbon electrode (GCE) was evaluated for charge transfer properties using electrochemical impedance spectroscopy (EIS). Cyclic voltammetry (CV) showed no redox peak for 2,4-D at the bare GCE, whereas R-Fe₃O₄/GCE exhibited a distinct reduction peak at ~−1.5 V in 0.1 M phosphate buffer (pH 7), attributed to reductive dechlorination. Square-wave voltammetry (SWV) exhibited a linear response over the concentration range of 50–325 µM with a detection limit of 3.35 µM for 2,4-D. Although this performance is slightly above the guideline limits recommended by the World Health Organization (~0.14 µM) and the United States Environmental Protection Agency (~0.32 µM), it is suitable for the routine monitoring of elevated 2,4-D levels in environmental samples. The sensor demonstrated high selectivity with negligible interference and satisfactory recoveries of 96.6–98.3% in real water samples. Full article

Graphene oxide (GO) was employed as an additive to improve the electrochemical activity of zinc oxide (ZnO) used as both a photoelectrocatalyst for water splitting and an electrochemical sensor for detection of diclofenac. To comprehend the influence of a small amount of GO on the electrochemical activity of ZnO, a series of ZnO/xGO (x = 0, 0.1, and 0.5) particles was synthesized by microwave processing of Zn(OH)₂ precipitate in the presence of 0.1 and 0.5 wt.% of previously prepared GO. The phase composition and crystal structure ordering of ZnO/xGO particles were investigated by XRD and Raman spectroscopy. The optical properties were studied by UV–Vis DRS and PL spectroscopy. The particle morphology was inspected by FE–SEM while the textural properties were analyzed by the low-temperature nitrogen adsorption–desorption method. The (photo)electrocatalytic and electrochemical sensing activities were examined on the ZnO/rxGO modified glassy carbon electrodes (GCEs) prepared by in situ reduction of the ZnO/xGO modified GCEs for 120 s. The electro- and photoelectrocatalytic activity of ZnO/rxGO modified GCEs for water splitting was tested in dark conditions and after 60 min under illumination, respectively, employing linear sweep voltammetry in 0.1 M NaOH and 0.1 M H₂SO₄ as electrolytes. The electrochemical sensing activity of ZnO/rxGO modified GCEs was tested for detection of diclofenac in aqueous solution. The improvement in the electrochemical activity of ZnO was correlated with the added amount of GO, structural defects, and particle morphology. Full article

The effect of water on the dynamics and ionic conductivity of the ionic liquids 1-ethyl-1-methylpyrrolidinium levulinate ([C₂C₁Pyr]Lev) and 1-butyl-1-methylpyrrolidinium levulinate ([C₄C₁Pyr]Lev) was investigated using differential scanning calorimetry (DSC) and broadband dielectric spectroscopy (BDS) over a wide temperature range. Although both ILs share the same levulinate anion, water induces markedly different dynamical responses depending on cation structure. In both systems, water acts as a plasticizer, lowering the glass transition temperature; however, the extent of plasticization and the resulting relaxation dynamics are cation-dependent. Stronger water–cation interactions are observed in [C₂C₁Pyr]Lev, whereas in [C₄C₁Pyr]Lev, water primarily disrupts alkyl-chain packing, enhancing ionic mobility. Increasing hydration shifts the main relaxation to higher frequencies and increases liquid fragility, while translational ionic motion remains decoupled from structural relaxation. These results demonstrate that water plays a cation-specific and mechanistically distinct role in levulinate-based ILs, providing new insights into hydration-controlled glassy dynamics and charge transport relevant to the design of IL-based electrolytes under non-anhydrous conditions. Full article

Coal gangue (CG) and iron tailings (ITs) are major industrial solid wastes, and their high-value reuse is crucial for sustainable construction materials. This study explores the feasibility of fabricating sintered porous bricks using CG and ITs as primary constituents, with shale as an auxiliary component. To evaluate durability in cold regions, laboratory freeze–thaw (F-T) cycling experiments were conducted. A degradation assessment framework based on the Wiener stochastic process was developed to predict frost-resistance service life by integrating experimental data with regional climatic conditions. Results show that the fabricated bricks exhibit satisfactory initial properties, with a compressive strength of 10.6 MPa and water absorption of 13.3%. With increasing F-T cycles, compressive strength decreases significantly, accompanied by increased mass loss and water absorption. Stress–strain analysis reveals progressive stiffness reduction and a transition from brittle to ductile failure. Microstructural observations confirm degradation of the glassy phase, pore expansion, and enhanced interconnectivity. The Wiener process-based model effectively describes the stochastic accumulation of F-T damage. By establishing equivalence between laboratory and natural F-T cycles, the long-term service life of coal gangue–iron tailing sintered porous bricks (CG-IT SPBs) in cold regions is theoretically evaluated. This work provides an integrated understanding of F-T damage behavior and establishes a scientific foundation for durability-oriented design and application of such bricks in extremely cold environments. Full article