Freshwater scarcity driven by climate variability, population growth, and uneven infrastructure is accelerating the need for decentralized water capturing technologies (WCT). Hydrogel-based materials have emerged as versatile platforms for three complementary pathways: solar steam generation (SSG) for desalination, sorption-driven atmospheric water harvesting (AWH), and surface-engineered fog capture (FC). Although numerous hydrogel formulations have been reported, performance metrics vary widely due to inconsistent testing conditions and limited long-term validation, complicating meaningful comparison and practical assessment. This review adopts a unified, mechanism-oriented framework to analyze hydrogel-enabled water capture. We examine how water-state regulation, hierarchical transport architecture, and surface interactions collectively govern heat and mass transfer across SSG, AWH, and FC systems. Rather than focusing only on laboratory performance, we extract frequent functional strategies, identify design trade-offs between sorption strength and regeneration, thermal localization and salt stability, and adhesion versus drainage control, and clarify ongoing discussions regarding evaporation thermodynamics. In addition, we discuss manufacturing scalability, cost-reporting limitations, and system-level integration required for real-world implementation. Finally, we synthesize durability mechanisms, including salt crystallization, microbial growth, UV exposure, mechanical fatigue, and additive migration, and propose standardized laboratory and field reporting parameters to improve reproducibility. By linking polymer design principles to application-specific constraints, this review provides a comparative and application-oriented roadmap for advancing hydrogel-based WCT.

Interfacial solar steam generation is a sustainable and emerging technique to collect water from seawater desalination. Herein, motivated by the porous structure and hydrophilicity of melamine foam (MF), a hydrophobic/hydrophilic (cup-cone shaped) graphene nanoplatelets/chitosan (GnPs/CS) coated melamine foam (GCM) is developed. However, the Janus structure of GCM, with its advantage of a hydrophobic top surface and a hydrophilic bottom surface, not only reduces heat losses to bulk water but also ensures water transport, enhances light absorption (96%), and stabilizes the evaporator, mitigating salt accumulation. Due to this fabrication strategy, the evaporation rate (ER) of water and the photothermal conversion efficiency of GCM are 1.42 kgm- 2 h- 1 and 95.7%, respectively, under 1 sun (1 kWm- 2) irradiation. The real seawater ER of 1.39 kgm- 2 h- 1 under 1 sun irradiation has been achieved. Furthermore, the removal of 99% of methylene blue and Rhodamine-B dyes highlights its potential for various applications in wastewater purification, desalination, and sustainable water production. These findings underscore the significance of this composite device as a pivotal advancement in sustainable solar-driven technologies and its potential to address critical global challenges related to access to clean water.

Lipophilic pentacyclic triterpenes (triterpenoids) such as betulin, betulinic acid and oleanolic acid are found in plants, where they serve as natural protectants. Birch trees, which are particularly rich in triterpenoids, are commonly used in pulping and papermaking. The presence of pentacyclic triterpenes disrupts pulping and papermaking processes because of their tendency to form aggregates, therefore a continuous detection of these compounds should be performed at the mills producing cellulose fibers from birch wood. Until now, no quick analytical method applicable to online analysis of triterpenoids has been established. This study was conducted to evaluate if voltammetric techniques can be applied for quantification of pentacyclic triterpenes extracted from bleached kraft pulps. We observed that during square wave voltammetry (SWV) in alkaline media, the oxidation signals are caused mainly by the solvent used to prepare the working solutions, rather than by the analytes. We discovered that SWV in neutral media could be successfully applied if bleached conifer and birch kraft pulp extracts are concentrated before the analysis. In situ deposition of a lead film on the working electrode was performed during differential pulse voltammetry in non-aqueous environment to facilitate the detection of triterpenes. It was possible to estimate the total triterpenoid content in pulp extracts. However, the electrode was not selective, so separation techniques need to be used if a particular compound is to be quantified.

Solid-contact ion-selective electrodes (SC-ISEs) are important analytical tools for ion detection due to their robustness, low cost, and miniaturization potential. However, recent findings suggest that the electrode body material may influence the potentiometric response of SC-ISEs. This work investigates the effect of electrode body material on the behavior of several potentiometric anion- and cation-selective electrodes, both SC-ISEs and conventional ones. Different anionic (bicarbonate, carbonate, chloride, nitrate, and benzoate) and cationic (potassium and calcium) SC-ISEs were prepared using either polyvinyl chloride (PVC), or polytetrafluoroethylene (PTFE) as the electrode body material. Two types of PVC rods, different in their apparent color (dark- and light-colored PVC), were used for making the sensors. Potentiometric measurements were performed to assess the influence of the body materials. The results showed clear difference in the selectivity of bicarbonate-, carbonate- and benzoate-selective sensors depending on the electrode body material, whereas the effect was negligible for the chloride-, nitrate- and cation-selective electrodes. These findings suggest that additives present in the PVC rods may, to some extent, migrate into the membrane and slightly influence its chemical composition. Such additives could potentially interact with analytes through hydrogen bonding or acid-base equilibrium of weak acid derivatives. Therefore, considering the composition of the electrode body material is essential for designing reproducible SC-ISEs.

Enzymatic electrochemical biosensors are a cornerstone technology in enabling further advancements in the field of Continuous Glucose Monitoring (CGM). Pulsed amperometric methods improve the sensitivity and accuracy of electrochemical biosensors. The literature shows that pulsed amperometry increases the sensitivity of enzymatic glucose biosensors based on Prussian Blue (PB). However, the underlying mechanism responsible for this improvement is poorly understood, which impedes further development of this promising measurement method. The present work elucidates the role of the spontaneous reaction between hydrogen peroxide (H2O2) and Prussian White (PW) in the sensitivity improvement observed with pulsed amperometry. A charged working electrode (WE) containing PW can catalyze the H2O2 reduction in the open-circuit regime (OCP). The consumption of H2O2 over a 30-min contact at OCP was 65 % at a PW WE, compared to 13 % at a PB WE. This spontaneous process is associated with a partial discharge of the WE (PW → PB) between the amperometric pulses. The subsequent re-charging (PB → PW) yields the current amplification observed with pulsed amperometry. Based on this consideration, we developed and validated a model for glucose quantification using pulsed amperometry that considers the spontaneous reaction of H2O2 with PW. The model achieves 0.998 determination coefficient between glucose concentration and four analytical signals. The insights presented in this work support the optimization and development of the pulsed amperometric detection method in enzymatic glucose biosensors. Additionally, this work advances the understanding of H2O2 detection at PB-based sensors, and contributes to the development of precise and accurate enzymatic glucose biosensors.

The nanoscale electrical double layer (EDL) governs macroscopic phenomena such as ion adsorption and reaction kinetics, serving as a fundamental determinant in diverse applications ranging from sensing, and catalysis, to energy storage. While classical EDL models primarily describe conductive interfaces, most naturally occurring EDLs form at non-conductive surfaces in liquid environment, where characterization remains fundamentally challenging due to the constraints of conventional techniques. Here, we present a triboelectric nanogenerator (TENG)-based triboelectric charge transfer probe that utilizes the intrinsic solid-liquid contact electrification (CE) process to operando monitor the formation and evolution of the EDL at non-conductive interfaces. This bias-free and electrode-independent approach enables direct probing of interfacial charge dynamics fundamentally inaccessible to conventional electrochemical approaches constrained by conductive substrate dependencies and external potential requirements. This method also reveals distinct EDL behaviors, particularly in electrolytes with asymmetric ion sizes at concentrations exceeding 10-1 M and at non-conductive interfaces. Its fundamental mechanism and measurement precision were rigorously validated via atomic force microscopy, Kelvin probe force microscopy, surface-enhanced Raman spectroscopy, and molecular dynamics simulations, establishing a robust analytical platform and theoretical basis for EDL studies. This work introduces a CE-based methodology for direct triboelectric charge characterization on dielectric surfaces, overcoming conventional conductive substrate limitations. By integrating classical EDL theory with triboelectric frameworks, we establish models resolving interfacial charge dynamics across diverse solid-liquid interfaces, including high ionic strength regimes. It confirms material-agnostic applicability. This paradigm simultaneously advances fundamental EDL mechanisms and enables programmable charge manipulation for next-generation iontronic power, sensing, and neuromorphic devices. A triboelectric nanogenerator-based probe monitors the formation and evolution of the electrical double layer at nonconductive interfaces via solid-liquid contact electrification.

Printed potentiometric sensors require reliable solid contacts to provide stable and reproducible ion-selective electrodes. However, hampering fabrications and unfavorable maintenance often hinder their breakthrough on a commercial scale. Herein, we develop a solid-contact calcium-selective screen-printed electrode harnessing straightforward manufacturing based on the combination of carbon black (CB) and poly(3,4-ethylene dioxythiophene) doped with poly(sodium 4-styrenesulfonate) (PEDOT:PSS) as an ion-to-electron transducer. Drop-casting was used to simply deposit the CB layer, while PEDOT:PSS was rapidly electropolymerized (71 s) onto the working electrode to deliver affordable manufacturing of the printed electrode while ensuring valid potentiometric performance. Subsequently, the ion-selective membrane (ISM) and the polyvinyl butyral (PVB)-based reference membrane were, respectively, drop-cast onto the working electrode and reference electrode (RE). Upon the optimization of solid-contact layers, the solid-contact Ca2+-ISEs were investigated by evaluating their potentiometric performance versus a conventional RE. CB/PEDOT:PSS-modified screen-printed electrodes demonstrated a low-frequency capacitance of 55 μF, and an outstanding standard potential interelectrode reproducibility (±1 mV). The combination of both types of ion-to-electron transducers provided calcium detection in the linear range 10-1-10-7 M with a Nernstian sensitivity (28.3 ± 0.3 mV/decade), ensured over 28 days under dry storage. Furthermore, the absence of the water layer effect was also demonstrated. Lastly, the fully printed platform was assembled to achieve a miniaturized and easily field-deployable potentiometric device, consisting of CB/PEDOT:PSS/ISM configuration and PVB-based reference membrane on the working electrode and the RE, respectively. The resulted all-solid-state sensor revealed a Nernstian sensitivity with a 29.0 ± 0.5 mV/decade slope and a stable signal up to 72 h (drift = -0.2 mV/h). Analysis carried out using commercially available bottled water also demonstrated the sensor successful performance in the determination of calcium ion in real samples.

Batteries, as one of the research directions for high-value utilization of biomass, often employ biomass-derived carbon as an active electrode material. However, the complex non-linear relationship between different biomass types, carbonization conditions, battery assembly conditions and testing conditions during the preparation process leads to the extensive experiments required to continuously explore the electrochemical performance of the electrodes, which impedes the rapid development of high-performance biomass-based electrodes. Therefore, in this study, based on nine machine learning models, nine types of input features were selected to predict the first cycle discharge capacity (Capacity-1), initial Coulombic efficiency (ICE), and discharge capacity after certain cycles (Capacity-x) of lithium/sodium ion batteries. The correlation of different input features was analyzed using the Spearman correlation coefficient. The feature importance and Shapley additive explanation analysis were utilized to elaborate the contribution of input features to the model prediction results. The results show that the gradient boosting regression model after hyper-parameter optimization is suitable for predicting Capacity-1 and Capacity-x, with R2 values of 0.93 and 0.90, respectively. The extreme gradient boosting model is suitable for predicting ICE, with an R2 value of 0.90. Carbonization temperature, doping conditions, and electrode components became the main influencing parameters for the three output features. Finally, the accuracy of the three models was verified by experiments. This study breaks through the traditional material research model and establishes a prediction model for the whole chain of chemical composition-microstructure-material properties of biomass electrodes, serving as a reference for the development of biomass-derived carbon electrodes.

The heterogeneity of lignin presents challenges in fabricating lignin-derived carbon materials with well-defined structures. This study investigated the use of magnesium as a fractionating agent via precipitation to modify the heterogeneity of lignin, which was then integrated with the MgO templating technique to produce functionalized porous carbon with tailored porosity. First, alkaline-dissolved spruce kraft lignin was precipitated under varied pH conditions, resulting in magnesium-lignin (MgL) complexes with different degrees of higher molecular weight lignin fractions. These complexes underwent a pre-heating treatment at 700 degrees C, facilitating the formation of nano-sized MgO domains within the carbon matrix. Acid leaching was subsequently carried out, followed by a high-temperature post-heating treatment at 1400 degrees C to remove the magnesium oxide (MgO), leaving behind nano-sized porous structures. The variation in fractionation pH affected the form of magnesium in the MgL complex, influencing MgO crystal formation during pyrolysis and allowing for tunable pore sizes in the resulting carbon during templating. Additionally, the presence of magnesium enhanced carbon yields after heat treatment at 1400 degrees C, with stoichiometric optimizations involving magnesium and pH increasing yields from 35% to 49%. These findings establish the groundwork for precise and more sustainable design of lignin-derived porous carbon materials.

Extractives in wood, despite being vital in plant survival in adverse environmental conditions, can cause issues in pulping and papermaking, leading to significant financial losses within the forest industry. Conventional analysis is time consuming due to the challenging sample preparation, data interpretation and complex nature of extractives. There is a clear need for the development of a quick, non-destructive method for on-line pulp extractives monitoring. In this work, a machine learning-supported procedure for classification and prediction of extractives based on near infrared (NIR) and Raman spectroscopies was proposed. To avoid the influence of many variables, the method was developed and validated using a model compound approach, where cellulose was spiked with model extractives compounds. The accuracy of sample classification depending on the extractive added was 92.4 % based on NIR. The accuracy of classification of six samples containing different concentrations of the model compound using NIR data was 89.5 %. Partial least squares calibration model applied to pretreated NIR spectra yielded R 2 and root standard error of 0.78 and 0.35, respectively This means that the method could be used for non-selective quick estimation of extractive content with potential application to forest industry in process and fiber quality control in pulp and paper.

Different materials such as PVC, PTFE, or PEEK are commonly used as the external body of solid-contact ion-selective electrodes (SC-ISEs). So far, the possible effect of these electrode body materials on the analytical behaviour of SC-ISEs has not been considered. In this study, we demonstrate that the selectivity of SC-ISEs can be strongly influenced by the type of the material used as the electrode body. To investigate this effect, different characterization techniques such as potentiometry, optical microscopy, NMR, and FTIR were used. Interestingly, the electrode body material significantly influences the selectivity in the case of bicarbonate SC-ISEs (anionic ISE), while the effect is negligible in the case of potassium SC-ISEs (cationic ISE). Results from NMR and FTIR indicate that some additives or compounds may migrate into the plasticised PVC membrane thereby influencing the selectivity of SC-ISEs. However, one cannot exclude the opposite process where membrane components will diffuse into the PVC electrode body. This can be quite a complex process as not only the chemical composition of the PVC rod would play a role but also its physical properties such as porosity or tortuosity.

Here, we propose a method for chemical sensing of Ag+ ions in pure water by utilizing single-use and unconditioned Nafion-coated Au electrodes together with capacitive and mass transduction principles. Ag+ ions were accumulated and simultaneously Ag was deposited in the Nafion membrane at an applied potential of -0.6 V vs. Ag/AgCl, followed by electrochemical impedance spectroscopy (EIS) to obtain the low-frequency capacitance. After Ag deposition, the resulting change in the low-frequency capacitance at 10 mHz of the Nafion-coated Au was determined with respect to the activity of Ag+ ion (aAg+) in solution in the range of logaAg+ = -11 to -2. The precision of the low-frequency capacitance was improved by utilizing spin-coated thin-layer Nafion membrane with applied single frequency at 1 Hz. Under identical experimental conditions, the capacitive response of the Nafion/Au electrode was larger than that of a Nafion-coated glassy carbon (Nafion/GC) electrode, indicating better electrocatalytic activity of Au than GC towards Ag+. Based on quartz crystal microbalance (QCM) measurements, the mass change due to Ag deposition at Nafion/Au was linearly proportional to logaAg+ in the range of -5 to -2. Both EIS and QCM methods show a response that correlates with the concentration or activity of Ag+ ions in pure water, which might give a possibility for calibration-free determination of Ag+ without any electrode conditioning needed.

Methods for automating the selection of key parameters for linear Kramers-Kronig tests are described. These methods include not only new methods and improvements to existing methods for suggesting the optimum number of time constants, but also methods for estimating the limits of the solution space. Methods for optimizing the range of time constants and a method for suggesting the representation of the immittance spectrum are also described. These methods are evaluated using both valid and invalid synthetic immittance spectra that present various challenges. Practical considerations regarding the implementation of the linear Kramers-Kronig tests and the various methods, the choice of linear Kramers-Kronig test and data representation to use, and the visualization and interpretation of results are also discussed.

Benzoic acid is used as a preservative in processed food, and occasionally in cosmetics and pharmaceuticals, while benzoic acid occurs naturally in, e.g., cranberry and lingonberry. Therefore, the determination of benzoate is of interest for product quality assurance, food safety, and personal health. In this work, a solid-contact benzoate-selective electrode (benzoate-ISE) was developed by utilising poly(3,4-ethylenedioxythiophene) (PEDOT) as solid contact and a solvent polymeric membrane containing a 1,3-bis(carbazolyl)urea derivative as ionophore. The benzoate-ISE was characterised in parallel with an ionophore-free control-ISE by electrochemical impedance spectroscopy and potentiometry. The presence of the ionophore in the membrane improved the selectivity to benzoate. Benzoate-ISEs and control-ISEs were used further to determine the benzoate concentration in cranberry and lingonberry by standard addition. The results obtained with both types of ISEs were compared with those obtained by ion chromatography. The results obtained with benzoate-ISEs were consistent with those obtained with ion chromatography. On the contrary, the control-ISE (without ionophore) gave significantly higher benzoate concentrations, especially in the case of cranberry where the benzoate concentration was low (ca 0.2 g kg-1) compared to lingonberry (ca 1 g kg-1). Hence, the benzoate-selectivity of the ionophore was crucial to obtain a benzoate-ISE that was practically applicable for determination of benzoate concentrations in cranberry and lingonberry.

Recent advances in non-invasive on-body chemical sensing over the last five years (2018–2022) are summarized in this review. The review illustrates major achievements enabled by chemical sensors and biosensors based on electrochemical and optical transduction that were tested on human subjects. The review is limited to purely non-invasive analysis of body fluids and therefore sampling methods using e.g. microneedles and implantable sensors are excluded. Based on the recent literature, major research efforts are currently directed towards epidermal chemical sensors, in particular electrochemical and optical sensors and biosensors for determination of electrolytes, pH and metabolites in sweat. Other types of samples, such as tears, saliva and dermal interstitial fluid, receive less attention. However, glucose monitoring often relies on interstitial fluid as a representative sample. Recent approaches utilize innovative design of chemical sensor and biosensor platforms as well as microfluidic sampling for non-invasive on-body chemical sensing.

This work demonstrates the innovative utilisation of sheer exfoliated few-layer graphene and graphene–CNC films as eco-friendly electrodes for efficient current extraction from cyanobacteria, promising advancements in biophotovoltaic applications.

A new type of coulometric transduction method for solid-contact ion-selective electrodes was introduced in 2015. The coulometric method utilized the capacitance of the solid contact to convert a potential change into a current transient that was integrated to obtain the corresponding charge. For a given potential change, the charge was increased by increasing the capacitance of the solid contact, which improved the sensitivity of solid-contact ion-selective electrodes. By introducing an electronic capacitor in series with the ion-selective electrode (ISE), the coulometric method became faster and feasible also for conventional ISEs with an internal filling solution. Alternative electrode configurations, where the ISE was connected as the reference electrode in the electrochemical cell, was used to avoid polarization of the ISE during the coulometric readout. Results published so far indicate that the coulometric readout method can significantly improve the analytical performance of ISEs, especially for detection of very small changes in ion activity. In this perspective article, the coulometric transduction method is revisited and critically evaluated.

Here, we propose a stripping voltammetric method for Ag+ ion determination in distilled water utilizing screen-printed Au electrodes coated with Nafion (Nafion/Au screen-printed electrodes). The concentration of Ag+ in pure water was determined by linear sweep voltammetry (LSV) after silver deposition on the Nafion/Au electrode. The anodic stripping peak current increased linearly with the concentration of Ag+ ion in the range from 1 ppm to 22 ppm. The LSV oxidative peak current was increased by extending the silver deposition time from 300 s to 500 s. Repetitive LSV measurements revealed satisfactory reproducibility of the Nafion/Au screen-printed electrodes. The detection mechanism was elucidated by recording mass changes of the Nafion/Au electrode with a quartz crystal microbalance (QCM), and by determining changes in the low-frequency capacitance of the Nafion/Au electrode by electrochemical impedance spectroscopy (EIS). The observed changes in mass and capacitance confirmed Ag+ accumulation and release processes at the Nafion/Au electrodes, in good agreement with stripping voltammetry. The combination of stripping voltammetry, QCM and EIS allowed a detailed characterization of the ion transfer, deposition and stripping processes at the Nafion/Au electrodes in presence of Ag+ ions. The Nafion/Au screen-printed electrode enabled voltammetric determination of low Ag+ concentrations in distilled water, without any sample pretreatment nor addition of supporting electrolyte.