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The opposing effect of gamma irradiation on proton and sodium ion conduction in Na2Ti3O7 and its defective analog
(2026-10-01)
Maluangnont, Tosapol
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Chaithaweep, Kanokwan
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Sangtawesin, Tanagorn
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Vittayakorn, Naratip
It is known that γ-irradiation of Na<inf>2</inf>Ti<inf>3</inf>O<inf>7</inf> induces Na + ion deintercalation, oxygen-vacancy formation, and proton/water incorporation, yielding the defective phase Na<inf>2- x </inf>H<inf>0.5 x </inf>Ti<inf>3</inf>O<inf>7-0.5 x </inf>(OH)<inf>0.5 x </inf> with multiple charge carriers. Although Na<inf>2</inf>Ti<inf>3</inf>O<inf>7</inf> is a well-studied ion conductor, charge-transport details in its γ-irradiated analogs remain limited. Here, we report their AC conductivity and dielectric properties under a temperature cycle (RT→350 °C→RT). Proton conduction dominates at ambient temperature but diminishes upon heating. This produces a dehydration-driven increase of resistivity known as the apparent Positive Temperature Coefficient of Resistivity (PTCR) effect, consistent with the Heywang model recently applied to water-adsorbing ceramics. Proton conductivity increases with γ-irradiation dose up to 200 kGy, then decreases at 400 kGy due to excessive structural disorder. At high temperatures, Na+ ion conduction prevails and follows Arrhenius behavior, with activation energy decreasing with dose. This discrepancy might be understood considering that Na+ ion conduction is governed primarily by its concentration rather than mobility; excessive doses lower activation energy but deplete Na+ ions and decrease conductivity. Dielectric-loss fitting using Jonscher's universal dielectric response (UDR) indicates that proton-transport pathways are sensitive to thermal history, whereas Na+ ion conduction exhibits low-frequency dispersion (LFD) across all conditions.
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Kinetic analysis of liquid–solid contact electrification: Using adsorption models as mechanistic probes for hybrid EDL behavior
(2026-08-01)
Chaithaweep, Kanokwan
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Pharino, Utchawadee
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Pongampai, Satana
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Sriphan, Saichon
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Charoonsuk, Thitirat
Liquid–solid interfaces are central to technologies ranging from energy storage to triboelectric nanogenerators (TENGs). Whereas classical electric double layer (EDL) theory describes these interfaces mainly in terms of electrostatic ion adsorption, hybrid EDL concepts suggest that interfacial electron transfer may also contribute importantly to charge generation. However, the hybrid EDL model has so far been discussed primarily at a qualitative level or through complex theoretical and computational treatments, and a simple, experimentally accessible macroscopic kinetic handle that can discriminate, in operando, between adsorption‑dominated and ET‑influenced regimes remains lacking. By analyzing high-resolution charging dynamics over systematically varied H₂SO₄ and HNO₃ concentrations, a clear concentration-dependent kinetic transition is identified. At low ionic strengths, the charging process is described more effectively by pseudo-second-order (PSO) kinetics, consistent with a reaction-influenced interfacial step, whereas at higher concentrations the system becomes pseudo-first-order (PFO) dominated, consistent with transport- and ion-screening-controlled behavior. Although previous studies have provided compelling theoretical and spectroscopic evidence that interfacial electron transfer contributes to liquid–solid contact electrification in TENGs, these mechanisms have rarely been examined through such simple macroscopic kinetic formalisms. In this work, classical adsorption kinetic models are used as operational probes for distinguishing electron-transfer-influenced regimes from ion-transport-dominated regimes at PTFE/liquid interfaces. The PSO-to-PFO crossover reported here is interpreted within the hybrid EDL framework as a kinetic marker of a transition from an electron-transfer-influenced charging regime at low concentration to an ion-transport- and screening-dominated regime at high concentration, thereby demonstrating how adsorption kinetics can serve as a practical diagnostic language for liquid–solid triboelectric systems.
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A Radiation-Tolerant g-C3N4 Dielectric Insulator: Local Structure Redistribution under γ-Irradiation
(2026-06-05)
Maluangnont, Tosapol
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Chaithaweep, Kanokwan
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Worathat, Supakarn
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Sangtawesin, Tanagorn
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Wasapinyokul, Kamol
Graphitic carbon nitride (g-C<inf>3</inf>N<inf>4</inf>) is a defect-rich polymeric material whose local structure is difficult to resolve using techniques dominated by average structural motifs. Here, pristine and γ-irradiated g-C<inf>3</inf>N<inf>4</inf> samples are examined using solid-state nuclear magnetic resonance (NMR) spectroscopy. Combined 13C, 15N, and 1H NMR reveal decreased terminal −NH<inf>2</inf> species and redistribution of interheptazine −NH– linkages with dose, while the heptazine framework remains intact. X-ray diffraction shows a non-monotonic evolution of stacking coherence, accompanied by IR evidence of C–N linkage modification. Despite these changes, the electrical resistivity remains extremely high at ∼109 Ω·cm and nearly independent of irradiation dose (10–400 kGy), temperature (RT–350 °C), and frequency (104–106 Hz). The dielectric permittivity decreases slightly from ∼7.2 to ∼4.7–5.2, while the dielectric loss tangent remains low (∼0.02). The refractive index similarly decreases from ∼2.6 in pristine g-C<inf>3</inf>N<inf>4</inf> to ∼2.2–2.3 after γ-irradiation. Analysis of the frequency dependence follows the universal dielectric response, consistent with correlated barrier hopping conduction with predominantly three-dimensional charge transport. Together, these observations show that γ-irradiation primarily reorganizes linkage environments without significantly perturbing the π-conjugated heptazine framework that governs charge transport. These characteristics make γ-irradiated g-C<inf>3</inf>N<inf>4</inf> promising for radiation-resistant dielectric and insulating components in nuclear and high-radiation electronic environments.
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Complex Impedance Formalism for Probing Dehydration, Dehydroxylation, and Rehydroxylation Dynamics of UiO-66-Based Metal–Organic Frameworks
(2026-02-12)
Maluangnont, Tosapol
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Chaithaweep, Kanokwan
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Sriphan, Saichon
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Meejaiyen, Parinya
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Anutrasakda, Wipark
It is known that the UiO-66 metal–organic framework (MOF) undergoes dehydration of physisorbed water and dehydroxylation of the zirconium clusters from RT to ∼300 °C, while the porous structure remains intact. These two processes are typically studied by thermogravimetric analysis and its derivative method (TGA/DTG), as well as differential scanning calorimetry (DSC). Here, we probe the same phenomena using temperature-dependent complex impedance spectroscopy. Peaks observed in the AC conductivity and in the real and imaginary parts of the dielectric permittivity (σ<inf>AC</inf>, ε′, and ε″) are due to thermally accelerated proton (Grotthuss) hopping competing with the loss of proton carriers during guest removal and dehydroxylation up to 350 °C. Meanwhile, peaks in the loss tangent (tan δ) and phase shift (Θ) identify the temperature at which dielectric-to-heat conversion is maximized. Additionally, peaks in the imaginary part of the impedance (−Z″) and in the real part of the electric modulus (M′) mark the temperature at which the material exhibits its highest insulating character. The MOFs examined include UiO-66 with the 1,4-benzenedicarboxylate linker and UiO-66-Py with the 2,5-pyridinedicarboxylate linker, the latter further modified through trifluoroacetic acid modulation, 1-bromopropane functionalization, and optional intermediate heat treatment. Impedance measurements under cooling reveal composition-dependent rehydroxylation behavior, with the conductivity recovery as early as at 250 °C in some Py-based derivatives vs flat response in pristine UiO-66. Overall, our work provides a comprehensive analysis of several complex electrical quantities and their physical interpretation, offering complementary insights into the dehydration, dehydroxylation, and rehydroxylation dynamics of UiO-66-based MOFs.
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Gamma irradiation produces graphitic carbon nitride with decreased water affinity
(2026-01-15)
Maluangnont, Tosapol
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Worathat, Supakarn
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Chaithaweep, Kanokwan
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Sangtawesin, Tanagorn
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Khamman, Orawan
Absorption of water on surfaces of graphitic carbon nitride (g–C<inf>3</inf>N<inf>4</inf>) can be lessened by organic molecules functionalization or post-annealing treatment. In contrast to this knowledge, we show that γ-irradiation (10–400 kGy) of g–C<inf>3</inf>N<inf>4</inf> results in a defective material with decreased water affinity on surface and at bulk alike without those modifications. Irradiated g–C<inf>3</inf>N<inf>4</inf> samples show diminished water content (2.52 wt% to 1.91–0.96 wt%) and decreased crystallinity but slightly increased surface area, including slit-shape pores formation in platy particles. However, their IR spectra and optical bandgap do not change. Despite the radiation-induced increase of N/C, the diminished water content is consistently observed on surfaces by XPS, and at the depth ∼1 μm deeper by EDX. It is found that γ-irradiation generates a higher proportion of pyridinic N which disfavors water adsorption. This is correlated to a decreasing apparent activation energy of water evaporation in a γ-irradiated material compared to a pristine one (29 vs 47 kJ·mol−1). Also, γ-irradiation generates dangling bonds which facilitate bonding/agglomeration between particles such that the access of water to adsorption sites is prohibited. The demonstrated application of γ-irradiation to reduce water wettability, which is chemical-free and easily controllable, encourages further studies to other hydrophilic materials.
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Application of Heywang model to the apparent PTCR effect in water-adsorbing layered materials
(2026-01-01)
Pulphol, Phieraya
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Sriphan, Saichon
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Chaithaweep, Kanokwan
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Vittayakorn, Naratip
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Maluangnont, Tosapol
Surface proton/hydroxide conduction predominates at ambient conditions prior to levelling off at elevated temperatures due to water evaporation and subsequent loss of charge carriers. This water-induced charge transport results in the “apparent” positive temperature coefficient of resistivity (PTCR) effect. Herein, we show that Heywang model typical of classical ferroelectric PTCR ceramics is applicable to a wide range of water-adsorbing layered materials (0.17–4.76 wt% H<inf>2</inf>O). Several examples include layered alkali titanates with negatively-charge sheets; one van der Waals material (g‒C<inf>3</inf>N<inf>4</inf>) with neutral sheets; and a NiFe layered double hydroxide with positively-charge sheets. The linear log ρ<inf>DC</inf> vs (ε′<inf>DC</inf>T)-1 plots (ρ<inf>DC</inf> = static resistivity, ε′<inf>DC</inf> = static dielectric permittivity, and T temperature) are observed from 25 to 250 °C where resistivity and dielectric permittivity varied up to five orders of magnitude. Using Cs<inf>2</inf>Ti<inf>6</inf>O<inf>13</inf> as a representative sample, the density of acceptor states at the grain boundary N<inf>s</inf> (the exact nature to be elucidated) is ∼1010-1011 cm-2, slightly dependent on the heating/cooling rates (0.5, 2 and 5 °C·min-1). Complex plane analyses show that capacitances at grain/grain boundaries alike are constant regardless of temperatures, but resistances in both cases peak at 150–200 °C. While rigorous theoretical basis is yet to be constructed, the observed linearity suggests that there could be a common foundation between these two classes of PTCR materials which have been treated separately so far.
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A Kirigami-Engineered “Skeletal Framework” Composite for Ultralow Hysteresis and Highly Stable Strain Sensors
(2025-11-24)
Pongampai, Satana
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Chaithaweep, Kanokwan
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Pakawanit, Phakkhananan
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Charoonsuk, Thitirat
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Bongkarn, Theerachai
Wearable strain sensors are pivotal for next-generation human–machine interfaces, yet achieving high fidelity, robustness, and sustainability in a single platform remains a significant challenge. A primary obstacle is the inherent viscoelasticity of soft materials, which leads to signal drift and hysteresis. Here, we report a highly stretchable and ultrastable strain sensor fabricated through a synergistic integration of Kirigami-based structural engineering and nanocomposite material design. By introducing titanium dioxide nanotubes (TNTs) into a bacterial cellulose (BC) matrix, we create a composite with a unique internal “skeletal framework”. This framework substantially reduces viscoelastic losses, resulting in an exceptionally low hysteresis of 0.6% and ensuring robust performance with 99.4% signal stability over >10 000 cycles. Concurrently, the Kirigami-patterned structure enhances stretchability to ∼235% while the framework amplifies sensitivity 5.8-fold. The practical viability of this high-fidelity sensor is demonstrated through the precise and repeatable control of a robotic arm, where ultralow hysteresis proves more critical than raw sensitivity. The sensor’s eco-friendly, water-based fabrication aligns high-fidelity sensing with sustainable processing, presenting a clear design paradigm for engineering reliable and eco-conscious wearable electronic devices.
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AC Electrical Properties of a NiFe-Layered Double Hydroxide with an Exceptionally Low Charge Density
(2025-05-08)
Maluangnont, Tosapol
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Sriphan, Saichon
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Chaithaweep, Kanokwan
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Vittayakorn, Naratip
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Wijitwongwan, Rattanawadee Ploy
Single-phase NiFe-layered double hydroxides (LDHs) with low and high charge densities [CD, 0.85 vs 3.23 nm-2; FeIII/(NiII + FeIII) = 0.05 and 0.25] were successfully prepared via urea-assisted coprecipitation in aqueous glycerol under hydrothermal conditions. The low-CD NiFe-LDH showed decreased apparent activation energies of water evaporation and of glycerol thermal decomposition, suggesting diminished intercalate/layer interactions relative to the high-CD one. The alternating current properties of the two samples were investigated on frequency and temperature domains by several formalisms that highlight distinct electrical components. We found that the low-CD NiFe-LDH exhibited smaller static dielectric permittivity and slower relaxation time, and it was less conducting than the high-CD analog. Complex plane analyses revealed the temperature dependence of resistance and capacitance at grain and grain boundary, varying by 7-10 orders of magnitude due to water loss and glycerol loss (∼9.5 and 11.3 wt %, respectively). Our work provides insights into intercalate dynamics in a low charge density LDH, which is difficult to obtain so far, from ambient to elevated temperatures (RT-250 °C) prior to decarbonation and layer collapse.
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High-Performance Droplet-Based Triboelectric Nanogenerators: A Comparison of Device Configuration and Operating Parameters
(2025-05-06)
Chaithaweep, Kanokwan
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Pharino, Utchawadee
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Pongampai, Satana
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Hajra, Sugato
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Kim, Hoe Joon
Droplet-based electricity generators (DEGs) harness liquid-solid electrification to convert water droplets impacts into electrical energy. This study systematically examines how droplet height, droplet volume, flow rate, and substrate tilt angle influence DEG performance using polytetrafluoroethylene (PTFE) as a triboelectric layer and deionized water. Three electrode designs (double, top, bottom) are evaluated, revealing that the double-electrode configuration delivers the highest output. This enhanced performance arises from synergistic droplet motion, electrical double-layer formation, and charge discharge, as validated by an equivalent circuit model. By varying droplet heights from 1–20 cm, volumes of 7.7–50 µL, flow rates of 50–300 drops/min, and tilt angles of 0–90°, an optimized setup yields −70 V and 22 mA, translating to a power density of 0.28 µW cm−2. High-speed imaging correlates these outputs with droplet impact dynamics and the resulting charge transfer. Additionally, the optimized DEG can power small electronic devices, charge capacitors, and monitor artificial acid rain in real-time, displaying distinct electrical signals compared to typical rainwater. These findings underscore the potential of DEGs as renewable energy harvesters and smart environmental sensors, paving the way for advanced on-demand power generation in diverse settings.
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A highly sensitive disease pre-screening approach for glycosuria: Triboelectric sensing at the liquid-solid interface
(2025-03-15)
Pharino, Utchawadee
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Chaithaweep, Kanokwan
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Pongampai, Satana
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Chanlek, Narong
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Kothan, Suchart
Prescreening and disease detection offer significant benefits in the prevention of serious illnesses. Traditional screening methods for disease identification have been complex and expensive, often requiring invasive procedures, which can be both harmful and uncomfortable. To address these limitations, various non-invasive screening technologies have been developed. Among recent innovations, the liquid–solid interface concept has emerged as a promising avenue for nanogenerator applications, enabling the harvesting and sensing of liquid energy and substances. In this study, we introduce a liquid–solid interface triboelectric sensor (LS-TES) for non-invasive disease screening and sensing. The LS-TES, utilizing a double-electrode configuration, delivers an immediate electrical response upon droplet contact with the solid surface and top electrode. In the case of urine glucose monitoring, our findings demonstrate a significant reduction in electrical signals with increasing concentrations of glucose, as glucose molecules hinder electron transfer from water to the solid surface, thereby disrupting the formation of the electrical double layer at the liquid–solid interface. The sensor exhibits excellent glucose sensing performance within a concentration range of 0.2 mM to 14 mM, with a detection limit of 0.25 mM and a rapid response time of 5–10 s. The LS-TES is cost-effective, highly stable, and reusable, maintaining consistent electrical responses across ten cycles of alternating droplet measurements. This work presents a preclinical assessment approach, specifically for urine glucose monitoring, utilizing an innovative sensor based on the liquid–solid interface. The proposed concept has the potential to serve as an individual indicator for early medical symptom detection, offering relief to a large number of patients.

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