Probing capping mechanisms and polymer matrix loading of biogenic vaterite CaCO3-Ag hybrid through X-ray photoelectron spectroscopy (XPS)

Despite extensive research in the literature, the synthesis of silver nanoparticles (AgNPs) via capping mechanisms remains incompletely understood. This study employs a mechanistic approach to unravel the underlying molecular interactions driving the capping process of biogenic vaterite CaCO3-Ag and explores their interactions with different polymer matrices. X-ray photoelectron spectroscopy (XPS) was used to reveal the capping mechanisms, surface composition alterations, and vaterite polymorph transitions. The oxidation states of AgNPs exhibited distinct changes under different capping agents. The Ag3d spin-orbit splitting profiles revealed the coexistence of Ag+ and Ag0 within CaCO3-Ag, with a significant presence of Ag0 when poly(sodium 4-styrene sulfonate) was employed as the capping agent. Conversely, the use of carboxy methyl cellulose as the capping agent resulted in Ag+ dominance. XPS analysis illuminated the transformation of CaCO3 polymorphs from calcite to vaterite structure, which remained stable following embedding within polymer matrices. Integrating CaCO3-Ag microspheres into polymer matrices and investigating their surface characteristics represents a strategic step toward tailoring material properties for potential applications in active packaging and biomedicine.

Pioneering dielectric materials of Sn-doped Nb0.025Ti0.975O2 ceramics with excellent temperature and humidity stability for advanced ceramic capacitors

In this study, the rutile TiO2 system, widely acclaimed for its superior properties, was enhanced through co-doping with isovalent Sn4+ ions and 2.5% Nb5+ donor ions, diverging from traditional acceptor doping practices. This novel doping strategy was implemented by employing a conventional solid-state reaction method, resulting in the synthesis of Sn-doped Nb0.025Ti0.975O2 (Sn-NTO) ceramics. These ceramics demonstrated remarkable dielectric characteristics, with a high dielectric constant (ε') ranging from ∼27 000 to 34 000 and an exceptionally low loss tangent between 0.005 and 0.056 at ∼25 °C and 1 kHz. Notably, the temperature coefficient of ε', , aligned with the stringent specifications for X7/8/9R capacitors. Furthermore, the Sn-NTO ceramics exhibited a stable Cp response across various frequencies within a humidity range of 50 to 95% RH, with ΔCp (%) values within ±0.3%, and no hysteresis loop was detected, suggesting the absence of water molecule adsorption and desorption during humidity assessments. This behavior is primarily attributed to the effective suppression of oxygen vacancy formation by the Sn4+ ions, which also affects the grain growth diffusion process in the Sn-NTO ceramics. The observed heterogeneous electrical responses between semiconducting grains and insulating grain boundaries in these polycrystalline ceramics are attributed to the internal barrier layer capacitor effect.

Magnetic Graphene Oxide Nanocomposites for Selective miRNA Separation and Recovery

In this study, we developed magnetic graphene oxide composites by chemically attaching Fe3O4 nanoparticles to graphene oxide nanosheets. Characterization techniques, including Fourier transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD), Raman spectroscopy, thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and transmission electron microscopy (TEM), confirmed the successful synthesis of Fe3O4@GO composites with desirable properties. The resulting composites exhibited superparamagnetic behavior, solubility, and compatibility for efficient miRNA separation. Using miR-29a as a model, we demonstrated the effective binding of miR-29a to the magnetic graphene oxide (GO) composites at an optimal concentration of 1.5 mg/mL, followed by a simple separation using magnetic forces. Additionally, the addition of 5.0 M urea enhanced the miRNA recovery. These findings highlight the potential use of our magnetic graphene oxide composites for the efficient separation and recovery of miR-29a, suggesting their broad applicability in various miRNA-based studies. Further exploration can focus on investigating endogenous miRNAs with aberrant expression patterns, contributing to the advancements in precision medicine.

Hydroxy and surface oxygen effects on 5-hydroxymethylfurfural oxidation to 2,5-furandicarboxylic acid on β-MnO2: DFT, microkinetic and experiment studies

Manganese dioxide, β-MnO2, has shown potential in catalyzing the oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA), a monomer of bioplastic polyethylene furanoate (PEF). Herein, the insight into the hydroxy (OH) and surface oxygen effects on the HMF-to-FDCA reaction over β-MnO2 is clarified through a comprehensive investigation using density functional theory (DFT) calculations, microkinetic modeling, and experiment. Theoretical analyses revealed that both active surface oxygen and OH species (from either base or solvent) facilitate C-H bond breaking and OH insertion, promoting the catalytic activity of β-MnO2. Microkinetic modeling demonstrated that the FFCA-to-FDCA and DFF-to-FFCA steps are the rate-limiting steps of the hydroxylated and non-hydroxylated surfaces, respectively. These theoretical results agree well with the experiment when water and dimethyl sulfoxide (DMSO) were used as solvents. In addition, the synthesized β-MnO2 catalyst showed high stability and activity, maintaining stable HMF conversion (≥99 mol%) and high FDCA yield (85-92 mol%) during continuous flow oxidation for 72 hours at pO2 of 1 MPa, 393 K and LHSV of 1 h-1. Thus, considering both hydroxy and surface oxygen species is a new strategy for enhancing the catalytic activity of Mn oxides and other metal oxide catalysts for the HMF-to-FDCA reaction.

Fabrication and Characterization of a Polydopamine-Modified Bacterial Cellulose and Sugarcane Filter Cake-Derived Hydroxyapatite Composite Scaffold

The search for environmentally friendly and sustainable sources of raw materials has been ongoing for quite a while, and currently, the utilization and applications of agro-industrial biomass residues in biomedicine are being researched. In this study, a polydopamine (PDA)-modified bacterial cellulose (BC) and hydroxyapatite (HA) composite scaffold was fabricated using the freeze-drying method. The as-prepared hydroxyapatite was synthesized via the chemical precipitation method using sugarcane filter cake as a calcium source, as reported in a previous study. X-ray diffraction analysis revealed a carbonated phase of the prepared hydroxyapatite, similar to that of the natural bone mineral. Wide-angle X-ray scattering analysis revealed the successful fabrication of BC/HA composite scaffolds, while X-ray photoelectron spectroscopy suggested that PDA was deposited on the surface of the BC/HA composite scaffolds. In vitro cell viability assays indicated that BC/HA and PDA-modified composite scaffolds did not induce cytotoxicity and were biocompatible with MC3T3-E1 preosteoblasts. PDA-modified composite scaffolds showed enhanced protein adsorption capacity in vitro compared to the unmodified scaffolds. On a concluding note, these results demonstrate that agro-industrial biomass residues have the potential to be used in biomedical applications and that PDA-modified BC/HA composite scaffolds are a promising biomaterial for bone tissue engineering.

Unraveling Structural and Acidic Properties of Al-SBA-15-supported Metal Phosphates: Assessment for Glucose Dehydration

5-Hydroxymethylfurfural (5-HMF) synthesized through glucose conversion requires Lewis acid (L) site for isomerization and Brønsted acid (B) site for dehydration. The objective of this work is to investigate the influence of the metal type of Al-SBA-15-supported phosphates of Cr, Zr, Nb, Sr, and Sn on glucose conversion to 5-HMF in a NaCl-H2 O/n-butanol biphasic solvent system. The structural and acid property of all supported metal phosphate samples were fully verified by several spectroscopic methods. Among those catalysts, CrPO/Al-SBA-15 provided the best performance with the highest glucose conversion and 5-HMF yield, corresponding to the highest total acidity of 0.65 mmol/g and optimal L/B ratio of 1.88. For CrPO/Al-SBA-15, another critical parameter is the phosphate-to-chromium ratio. Moreover, DFT simulation of glucose conversion to 5-HMF on the surface of the optimized chromium phosphate structure reveals three steps of fructose dehydration on the Brønsted acid site. Finally, the optimum reaction condition, reusability, and leaching test of the best catalyst were determined. CrPO/Al-SBA-15 is a promising catalyst for glucose conversion to high-value-added chemicals in future biorefinery production.

Electrochemical and electrical characteristics of ball milled Cs2Ti6O13 modified by the surface-to-bulk migration of hydroxyl groups

Ball milling of solids under benign conditions leads to surface functionalization without altering the crystal structure and morphology. However, these additional surface functional groups are rarely fixed but instead mobilized across such ball milled solids. This phenomenon, including its effects on electrochemical and electrical properties, has received limited attention. We report herein that dry vibratory ball milling of lepidocrocite-type Cs2Ti6O13 generated hydroxyl groups which subsequently migrated from surfaces to bulk. The increased number of bulk hydroxyl groups is deduced from Raman, IR, and solid state 1H nuclear magnetic resonance spectroscopy, and thermogravimetric analysis. In contrast, the decrease in the relative proportion of surface hydroxyl groups/water and carbon-oxygen species was deduced from X-ray photoelectron spectroscopy. The inaccessible hydroxyl groups in ball milled Cs2Ti6O13 lead to a smaller amount of stored charge and increased charge transfer resistance, according to galvanostatic charge-discharge experiments and electrochemical impedance spectroscopy studies in 1 M Na2SO4. The alternating current electrical properties were also measured, revealing fundamental insights such as the one-dimensional conduction pathway and the relaxation time in microseconds. A model has been proposed for this surface-to-bulk migration of the hydroxyl groups, which competes with surface dangling bonds leading to particle agglomeration.

Correction: Effects of Ni precursors on the formation of Mg-Fe-Ni intermetallic hydrides, kinetics, and reversibility

[This corrects the article DOI: 10.1039/D3RA01914D.].

Synthesis and Characterization of Zeolite NaY Dispersed on Bamboo Wood

Zeolites in powder form have the potential to agglomerate, lowering access to active sites. Furthermore, a suspension of fine zeolite powder in liquid media is difficult to separate. Such drawbacks could be improved by dispersing zeolite crystals on support materials. This work demonstrates the dispersion of zeolite NaY crystals on bamboo wood by mixing the wood with zeolite gel before hydrothermal treatment. The syntheses were performed with acid-refluxed and non-refluxed wood. The phase of zeolites, particle distribution and morphology, zeolite content in the wood, and zeolite-wood interaction were investigated using X-ray diffraction, X-ray tomography, scanning electron microscopy, thermogravimetric analysis, nitrogen sorption analysis, and X-ray photoelectron spectroscopy. Higher zeolite content and better particle dispersion were obtained in the synthesis with the acid-refluxed wood. The composite of NaY on the acid-refluxed wood was demonstrated to be an effective adsorbent for Ni(II) ions in aqueous solutions, providing a higher adsorbed amount of Ni(II) per weight of NaY.

Effects of Ni precursors on the formation of Mg-Fe-Ni intermetallic hydrides, kinetics, and reversibility

This work focuses on the effects of Ni precursors (metallic Ni or Mg2NiH4) on the formation of Mg-Fe-Ni intermetallic hydrides as well as their de/rehydrogenation kinetics and reversibility. After ball milling and sintering, the formation of Mg2FeH6 and Mg2NiH4 are found in both samples, while MgH2 is observed only in the sample with metallic Ni. Both samples show comparable hydrogen capacities of 3.2-3.3 wt% H2 during the 1st dehydrogenation, but the sample with metallic Ni decomposes at a lower temperature (ΔT = 12 °C) and shows faster kinetics. Although phase compositions after dehydrogenation of both samples are comparable, their rehydrogenation mechanisms are different. This affects the kinetic properties upon cycling and reversibility. Reversible capacities of the samples with metallic Ni and Mg2NiH4 during the 2nd dehydrogenation are 3.2 and 2.8 wt% H2, respectively, while those during the 3rd-7th cycles reduce to ∼2.8 and 2.6 wt% H2, respectively. Chemical and microstructural characterizations are carried out to explain de/rehydrogenation pathways.

Significantly improved giant dielectric properties and enhanced nonlinear coefficient of Ni2+ doped CaCu3Ti4O12/CaTiO3 composites

CaCu_3-xNi_xTi₄O₁₂/CaTiO₃ ceramic composites were fabricated using initial Ca₂Cu_2-xNi_xTi₄O₁₂ compositions (x = 0, 0.05, 0.10, and 0.20) to improve the dielectric properties (DPs) of the CaCu₃Ti₄O₁₂ ceramics. CaCu₃Ti₄O₁₂ and CaTiO₃ phases were confirmed. Microstructural analysis and Rietveld refinement showed that the Ni²⁺ dopant might substitute the Cu²⁺ sites of the CaCu₃Ti₄O₁₂ structure. The average grain sizes of CaCu₃Ti₄O₁₂ (4.1-5.6 μm) and CaTiO₃ (1.2-1.4 μm) changed slightly with the Ni²⁺ doping concentration. The best DPs were obtained for the CaCu_3-xNi_xTi₄O₁₂/CaTiO₃ with x = 0.2. The loss tangent was significantly reduced by an order of magnitude compared to that of the undoped composite, from tanδ∼0.161 to ∼0.016 at 1 kHz, while the dielectric permittivity slightly decreased from ε'∼5.7 × 10³ to ∼4.0 × 10³. Furthermore, the temperature dependence of ε' could be improved by doping with Ni²⁺. The improved DPs were caused by the enhanced electrical responses of the internal interfaces, which resulted in enhanced non-Ohmic properties. The largest nonlinear coefficient (α∼7.6) was obtained for the CaCu_3-xNi_xTi₄O₁₂/CaTiO₃ with x = 0.05. Impedance spectroscopy showed that the CaCu_3-xNi_xTi₄O₁₂/CaTiO₃ composites consisted of semiconducting and insulating components. The DPs of CaCu_3-xNi_xTi₄O₁₂/CaTiO₃ were explained based on the space-charge polarization at the active-interfaces.

Bio-Electroanalysis Performance of Heme Redox-Center for π-π Interaction Bonding of a Methylene Blue-Graphene Modified Electrode

Hemeprotein detection has motivated extensive research on the direct reaction of a heme molecule and a redox dye. The present study used methylene blue as both donor and acceptor for a redox reaction. First, the solid phases of methylene blue (MB) and graphene (GP) formed a π-π interaction bond at the aromatic rings. The conductivity of GP was better than that of carbon in a carbon electrode (CE). Then, the working CE was modified using strong adsorption of MB/GP on the electrode surface. The surface of the electrode was investigated using a modified and an unmodified electrode. The electrode's properties were studied using voltammograms of redox couple K₃[Fe(CN)₆]^3-/4-. Its reaction was used to find the active area of the modified electrode, which was 1.76 times bigger than that of the unmodified electrode. The surface coverage values of the modified and unmodified electrodes were 8.17 × 10^-6 and 1.53 × 10^-5 mol/cm², respectively. This research also studied the application of hemeprotein detection. Hemoglobin (Hb), myoglobin (Mb), and cytochrome c (Cyt. C) were studied by the reaction of Fe (III/II) at the heme-redox center. The electrocatalytic reaction between MB/GP and hemeproteins produced an anodic peak at 0.35 V for Hb, Mb, and Cyt. C. This nanohybrid film enhanced electron transfer between protein molecules and the modified carbon electrode. The amperometric measurements show that the limit of detection was 0.2 µM, 0.3 µM, and 0.1 µM for Hb, Mb, and Cyt. C, respectively. The measurement spanned a linear range of 0.2 µM to 5 µM, 0.3 µM to 5 µM, and 0.1 µM to 0.7 µM for Hb, Mb, and Cyt. C, respectively. Hb showed the lowest sensitivity compared with Mb and Cyt. C due to the role of steric hindrance in the hemeprotein specificity structure. This study offers a simple and efficient fabrication platform for electrochemical sensors for hemeproteins. When compared to other complex immobilization processes, the fabrication method for this sensor has many benefits, including no need for special chemicals and easy preparation and electrode modification-both of which are crucial for the development of electrochemical sensing devices.

Extremely reduced loss tangent with retaining ultra high dielectric permittivity in Mg2+-doped La1.9Sr0.1NiO4 ceramics

An extremely reduced loss tangent while retaining ultrahigh dielectric permittivity can be successfully obtained in La_1.9Sr_0.1NiO₄ ceramics by doping with Mg²⁺ ions. A single phase of La_1.9Sr_0.1NiO₄ was detected in all the sintered ceramics, while the lattice parameters increased with increasing doping concentration, indicating that Mg²⁺ ions can enter the Ni²⁺ sites. A highly dense microstructure is achieved. Microstructural analysis revealed that Mg²⁺ ions disperse well in the microstructure of La_1.9Sr_0.1NiO₄ ceramics. Interestingly, ultra-high dielectric permittivity of approximately 8.11 × 10⁵ at 1 kHz is achieved in the La_1.9Sr_0.1Ni_0.6Mg_0.4O₄ ceramic, while the loss tangent is significantly reduced by two orders of magnitude compared to the undoped La_1.9Sr_0.1NiO₄ ceramic. The DC conductivity significantly decreased by three orders of magnitude. The giant dielectric responses are described by Maxwell-Wagner polarization and small polaron hopping mechanisms. Thus, the significant reduction in the loss tangent can be attributed to the significantly enhanced resistance of the grain boundaries.

Effects of sintering condition on giant dielectric and nonlinear current-voltage properties of Na1/2Y1/2Cu3Ti3.975Ta0.025O12 ceramics

The effects of sintering conditions on the microstructure, giant dielectric response, and electrical properties of Na_1/2Y_1/2Cu₃Ti_3.975Ta_0.025O₁₂ (NYCTTaO) were studied. A single phase of Na_1/2Y_1/2Cu₃Ti₄O₁₂ and a high density (>98.5%) were obtained in the sintered NYCTTaO ceramics. First-principles calculations were used to study the structure of the NYCTTaO. Insulating grain boundaries (i-GBs) and semiconducting grains (semi-Gs) were studied at different temperatures using impedance and admittance spectroscopies. The conduction activation energies of the semi-Gs and i-GBs were E_g ≈ 0.1 and E_gb ≈ 0.6 eV, respectively. A large dielectric constant (ε' ≈ 2.43-3.89 × 10⁴) and low loss tangent (tanδ ≈ 0.046-0.021) were achieved. When the sintering temperature was increased from 1070 to 1090 °C, the mean grain size slightly increased, while ε' showed the opposite tendency. Furthermore, the breakdown electric field (E_b) increases significantly. As the sintering time increased from 5 to 10 h, the mean grain size did not change, whereas ε' and E_b increased. Variations in the dielectric response and non-linear electrical properties were primarily described by the intrinsic (E_gb) and extrinsic (segregation of Na-, Cu-, Ta-, and O-rich phases) properties of the i-GBs based on the internal barrier layer capacitor effect.

Denitrification of nitrate in regeneration waste brine using hybrid cation exchanger supported nanoscale zero-valent iron with/without palladium nanoparticles

The Sustainable Development Goals require that reducing waste is a priority. This work described the application of an innovative zero-waste hybrid ion exchange nanotechnology that concurrently removed nitrate and induced denitrification to ammonia, with the ability to generate fertilizer for the agriculture sector from the recycled by-products. Herein, hybrid cation exchanger-supported zero-valent iron (Fe⁰), and bimetallic Fe⁰/Pd nanoparticles (HCIX-Fe⁰ and HCIX-Fe⁰/Pd) were synthesized and successfully validated for denitrification of nitrate in spent waste brine that contained nitrate. The kinetics of nitrate catalysis by both HCIX-Fe⁰ and HCIX-Fe⁰/Pd were compared and presented by six kinetic models, namely, zero-order, pseudo first- and second-order reaction, pseudo first- and second-order adsorption, and Elovich. HCIX-Fe⁰/Pd displayed a higher kinetic value than HCIX-Fe⁰, with k₁ of 0.0019 and 0.0026 min^-1, respectively. Nitrate was predominantly catalysed to NH₄⁺ at a ratio of ammonia to other nitrogen compounds of around 80:20. Although HCIX-Fe⁰/Pd showed slightly better (14%) kinetic results, it was determined as unfavourable for real-life application due to low selectivity toward N₂ gas and the need to use H₂ gas. Based on practicability, the HCIX-Fe⁰ was further validated. The effect of salt (using NaCl) and the role of initial pH conditions were optimized and discussed. The recovery of nitrate removal was also calculated, and a recovery range of 91.42-99.14% was obtained for three consecutive runs. The sustainable, novel, zero waste hybrid ion exchange nanotechnology using the combination of two fixed-bed columns containing nitrate-selective resin for nitrate removal and novel HCIX-Fe⁰ for nitrate reduction to NH₄⁺ may be a promising sustainable solution toward the goal of discharging zero nitrate waste to the environment.

Enhanced Electrochemical Performance of Sugarcane Bagasse-Derived Activated Carbon via a High-Energy Ball Milling Treatment

Activated carbon (AC) from sugarcane bagasse was prepared using dry chemical activation with KOH. It was then subjected to a high-energy ball milling (HEBM) treatment under various milling speeds (600, 1200 and 1800 rpm) to produce AC nanoparticles from micro-size particles. The AC samples after the HEBM treatment exhibited reduced particle sizes, increased mesopore volume and a rich surface oxygen content, which contribute to higher pseudocapacitance. Notably, different HEBM speeds were used to find a good electrochemical performance. As a result, the AC/BM12 material, subjected to HEBM at 1200 rpm for 30 min, exhibited the highest specific capacitance, 257 F g^-1, at a current density 0.5 A g^-1. This is about 2.4 times higher than that of the AC sample. Moreover, the excellence capacitance retention of this sample was 93.5% after a 3000-cycle test at a current density of 5 A g^-1. Remarkably, a coin cell electrode assembly was fabricated using the AC/BM12 material in a 1 M LiPF₆ electrolyte. It exhibited a specific capacitance of 110 F g^-1 with a high energy density of 27.9 W h kg^-1.

An Operando X-ray Absorption Spectroscopy Study on Sensing Characteristics of Vertically Aligned ZnO Thin Film for Methane Gas Sensors

In this work, a simple, facile growth approach for a vertically aligned ZnO thin film is fabricated and its application towards methane gas sensors is demonstrated. ZnO thin film was prepared by a combination of hydrothermal and sputtering methods. First, a ZnO seed layer was prepared on the substrate through a sputtering technique, then a ZnO nanorod was fabricated using a hydrothermal method. The surface morphology of the ZnO film was observed by scanning electron microscopy (SEM). A ZnO nanorod coated on the dense seed layer is clearly visible in the SEM image. The average size of the hexagonal-shaped ZnO rod was around 50 nm in diameter, with a thickness of about 1 mm. X-ray absorption near-edge structures (XANES) were recorded to characterize the structural properties of the prepared film. The obtained normalized Zn K-edge XANES of the film showed the characteristic features of ZnO, which agreed well with the standard ZnO sample. The measurement of Zn K-edge XANES was performed simultaneously with the sensing response. The results showed a good correlation between sensor response and ZnO structure under optimal conditions.

Comparative Properties of K/NaX and K/NaY from Ultrasound-Assisted Impregnation and Performance in Transesterification of Palm Oil

This work aims to compare physicochemical properties and catalytic performance of potassium supported on zeolite NaX and NaY (K/NaX and K/NaY, respectively) prepared by ultrasound-assisted impregnation from potassium acetate buffer precursor. Calcination converts the potassium precursor to carbonate, which occupies the zeolite cavities and disperses on the external surface. Both calcined samples show a decrease in zeolite phases, BET surface areas, and pore volumes. With the smaller changes, K/NaX is more stable than K/NaY. Moreover, K/NaX has higher basicity than K/NaY and is more active in the decomposition of 2-methylbut-3-yn-2-ol (MBOH), producing dominant products from basic sites. Both K/NaX and K/NaY are active in the transesterification of palm oil, producing more than 94% of the biodiesel yields in the first run. However, the yields drop in the second run because of the leaching of potassium species into glycerol and biodiesel products. The spent K/NaX has a similar phase to the fresh one, whereas the spent K/NaY shows more structure collapse. With better structural stability, less potassium leaching, and less decline in biodiesel yields in the second run, K/NaX is a better catalyst than K/NaY.

Mechanical and Dielectric Properties of Fly Ash Geopolymer/Sugarcane Bagasse Ash Composites

Fly ash (FA) and sugarcane bagasse ash (SCBA) are the wastes from lignite power plants and sugar industries, usually disposed of as landfills. In this research, these wastes were effectively utilized as a construction material, namely geopolymer. The effect of the SCBA (0–40 wt.%) addition to the FA geopolymers was investigated. The compressive strength of the FA geopolymers was reduced with the SCBA addition. The reduction was mainly due to the presence of the highly stable and non-reactive quartz (SiO₂) phase in SCBA. The SCBA was not dissolved in the alkaline activated solution and hence did not contribute to the geopolymerization process. The unreacted SCBA particles remained in the geopolymer matrix but did not provide strength. However, if the amount of SCBA was about 10 wt.% or less, the impact on the characteristics and properties of FA geopolymers was minimal. Furthermore, this research also studied the dielectric properties of the FA geopolymer/SCBA composites. The relatively large dielectric constant (ε′ = 3.6 × 10³) was found for the pristine geopolymer. The addition of SCBA decreased the ε′ slightly due to high carbon content in SCBA. Nevertheless, the variation in ε′ was mainly controlled by the geopolymerization process to form the aluminosilicate gel structure.

Improved microstructure and significantly enhanced dielectric properties of Al3+/Cr3+/Ta5+ triple-doped TiO2 ceramics by Re-balancing charge compensation

The charge compensation mechanism and dielectric properties of the (Al _x Cr_0.05-x )Ta_0.05Ti_0.9O₂ ceramics were studied. The mean grain size slightly changed with the increase in the Al³⁺/Cr³⁺ ratio, while the porosity was significantly reduced. The dielectric permittivity of the co-doped Cr_0.05Ta_0.05Ti_0.9O₂ ceramic was as low as ε'∼ 10³, which was described by self-charge compensation between Cr³⁺-Ta⁵⁺, suppressing the formation of Ti³⁺. Interestingly, ε' can be significantly increased (6.68 × 10⁴) by re-balancing the charge compensation via triple doping with Al³⁺ in the Al³⁺/Cr³⁺ ratio of 1.0, while a low loss tangent (∼0.07) was obtained. The insulating grains of [Cr_0.05 ³⁺Ta_0.05 ⁵⁺]Ti_0.9 ⁴⁺O₁₂ has become the semiconducting grains for the triple-doped Al _x ³⁺[Cr_0.05-x ³⁺Ta_0.05-x ⁵⁺][Ta _x ⁵⁺Ti _x ³⁺Ti_0.9+x ⁴⁺]O_12+3x/2. Considering an insulating grain with low ε' of the Cr_0.05Ta_0.05Ti_0.9O₂ ceramic, the electron-pinned defect-dipoles and interfacial polarization were unlikely to exist supported by the first principles calculations. The significantly enhanced ε' value of the triple-doped ceramic was primarily contributed by the interfacial polarization at the interface between the semiconducting and insulating parts, which was supported by impedance spectroscopy. This research gives an underlying mechanism on the charge compensation in the Al³⁺/Cr³⁺/Ta⁵⁺-doped TiO₂ system for further designing the dielectric and electrical properties of TiO₂-based ceramics for capacitor applications.

Enhancement of V2O5 Li-ion cathode stability by Ni/Co doped Li-borate-based glass

In this research, we investigate the stability of a Li-ion cathode created by mixing a borate based glass which has been doped with Ni/Co and vanadium pentoxide (V2O5).

Structural elucidation of hexavalent Cr adsorbed on surfaces and bulks of Fe3O4 and α-FeOOH

Magnetite (Fe3O4) and goethite (α-FeOOH) were synthesized via a hydrothermal approach and utilized as adsorbents for Cr6+ removal in an aqueous medium. Cr3+ could migrate into bulk Fe3O4 and stabilize in form of a solid solution.

Microstructural Evolution and High-Performance Giant Dielectric Properties of Lu3+/Nb5+ Co-Doped TiO2 Ceramics

Giant dielectric (GD) oxides exhibiting extremely large dielectric permittivities (ε' > 104) have been extensively studied because of their potential for use in passive electronic devices. However, the unacceptable loss tangents (tanδ) and temperature instability with respect to ε' continue to be a significant hindrance to their development. In this study, a novel GD oxide, exhibiting an extremely large ε' value of approximately 7.55 × 104 and an extremely low tanδ value of approximately 0.007 at 103 Hz, has been reported. These remarkable properties were attributed to the synthesis of a Lu3+/Nb5+ co-doped TiO2 (LuNTO) ceramic containing an appropriate co-dopant concentration. Furthermore, the variation in the ε' values between the temperatures of -60 °C and 210 °C did not exceed ±15% of the reference value obtained at 25 °C. The effects of the grains, grain boundaries, and second phase particles on the dielectric properties were evaluated to determine the dielectric properties exhibited by LuNTO ceramics. A highly dense microstructure was obtained in the as-sintered ceramics. The existence of a LuNbTiO6 microwave-dielectric phase was confirmed when the co-dopant concentration was increased to 1%, thereby affecting the dielectric behavior of the LuNTO ceramics. The excellent dielectric properties exhibited by the LuNTO ceramics were attributed to their inhomogeneous microstructure. The microstructure was composed of semiconducting grains, consisting of Ti3+ ions formed by Nb5+ dopant ions, alongside ultra-high-resistance grain boundaries. The effects of the semiconducting grains, insulating grain boundaries (GBs), and secondary microwave phase particles on the dielectric relaxations are explained based on their interfacial polarizations. The results suggest that a significant enhancement of the GB properties is the key toward improvement of the GD properties, while the presence of second phase particles may not always be effective.

Structural and Compositional Characteristics of Ball-Milled Lepidocrocite Alkali Titanate and the Correlation to Its Surface Acidic-Basic Properties

The studies on mechanical treatments of layered alkali metal oxides are limited despite their diverse compositions/structures and potential for property tuning. In this work, we vibratory mill Cs_0.7Zn_0.35Ti_1.65O₄, K_0.8Zn_0.4Ti_1.6O₄, and Cs₂Ti₆O₁₃ for up to 4 h, during which the lepidocrocite-type structure and the plate-like morphology are well preserved. X-ray diffraction (XRD) indicates a tiny (≤0.6 Å) interlayer expansion accompanied by the enhancement of the preferred orientation along the stacking direction. Chemical analyses across multiple length scales suggest Cs deintercalation, elemental redistributions, and bulk-to-surface (or crystal edge) Cs migration. This ball-milling-induced Cs-rich moiety partially blocks the surface acid sites, although the solids still show a dominating acidic character. The ball-milled samples Cs_0.7-pZn_0.35-qTi_1.65O_4-δ contain vacancies between the sheets (p) and at the sheets (q and δ). It is deduced from Sanderson's electronegativity equalization principle and experimentally verified by X-ray photoelectron spectroscopy (XPS) that ball milling increases (decreases) the partial charge at the surface acidic Ti⁴⁺/Zn²⁺ (basic O^2-) sites. These nonporous solids (≤20 m²·g^-1) contain water sorbed on the external surface as high as 1.1 mol·mol^-1, which is comparable to that in a water-intercalated sample. Our work expands the current understanding of the reactivity vs robustness in layered alkali titanates under physically demanding conditions, complementing knowledge gathered via the soft chemistry approach.

Significantly Improved Colossal Dielectric Properties and Maxwell-Wagner Relaxation of TiO2-Rich Na1/2Y1/2Cu3Ti4+xO12 Ceramics

In this work, the colossal dielectric properties and Maxwell-Wagner relaxation of TiO2-rich Na1/2Y1/2Cu3Ti4+xO12 (x = 0-0.2) ceramics prepared by a solid-state reaction method are investigated. A single phase of Na1/2Y1/2Cu3Ti4O12 is achieved without the detection of any impurity phase. The highly dense microstructure is obtained, and the mean grain size is significantly reduced by a factor of 10 by increasing Ti molar ratio, resulting in an increased grain boundary density and hence grain boundary resistance (Rgb). The colossal permittivities of ε' ~ 0.7-1.4 × 104 with slightly dependent on frequency in the frequency range of 102-106 Hz are obtained in the TiO2-rich Na1/2Y1/2Cu3Ti4+xO12 ceramics, while the dielectric loss tangent is reduced to tanδ ~ 0.016-0.020 at 1 kHz due to the increased Rgb. The semiconducting grain resistance (Rg) of the Na1/2Y1/2Cu3Ti4+xO12 ceramics increases with increasing x, corresponding to the decrease in Cu+/Cu2+ ratio. The nonlinear electrical properties of the TiO2-rich Na1/2Y1/2Cu3Ti4+xO12 ceramics can also be improved. The colossal dielectric and nonlinear electrical properties of the TiO2-rich Na1/2Y1/2Cu3Ti4+xO12 ceramics are explained by the Maxwell-Wagner relaxation model based on the formation of the Schottky barrier at the grain boundary.

Photoenhanced Water Electrolysis in Separate O2 and H2 Cells Using Pseudocapacitive Electrodes

Water electrolysis has received much attention in recent years as a means of sustainable H₂ production. However, many challenges remain in obtaining high-purity H₂ and making large-scale production cost-effective. This study provides a strategy for integrating a two-cell water electrolysis system with solar energy storage. In our proposed system, CuO-Cu(OH)₂/Cu₂O was used as a redox mediator between oxygen and hydrogen evolution components. The system not only overcame the gas-mixing issue but also showed high gas generation performance. The redox reaction (charge/discharge) of CuO-Cu(OH)₂/Cu₂O led to a significant increase (51%) in the initial rate of H₂ production from 111.7 μmol h^-1 cm^-2 in the dark to 168.9 μmol h^-1 cm^-2 under solar irradiation. The effects of light on the redox reaction of CuO-Cu(OH)₂/Cu₂O during water electrolysis were investigated by in situ X-ray absorption and photoemission spectroscopy. These results suggest that surface oxygen vacancies are created under irradiation and play an important role in increased capacitance and gas generation. These findings provide a new path to direct storage of abundant solar energy and low-cost sustainable hydrogen production.

Gold-Nanoparticle-Deposited TiO2 Nanorod/Poly(Vinylidene Fluoride) Composites with Enhanced Dielectric Performance

Flexible dielectric polymer composites have been of great interest as embedded capacitor materials in the electronic industry. However, a polymer composite has a low relative dielectric permittivity (ε' < 100), while its dielectric loss tangent is generally large (tanδ > 0.1). In this study, we fabricate a novel, high-permittivity polymer nanocomposite system with a low tanδ. The nanocomposite system comprises poly(vinylidene fluoride) (PVDF) co-filled with Au nanoparticles and semiconducting TiO2 nanorods (TNRs) that contain Ti3+ ions. To homogeneously disperse the conductive Au phase, the TNR surface was decorated with Au-NPs ~10-20 nm in size (Au-TNRs) using a modified Turkevich method. The polar β-PVDF phase was enhanced by the incorporation of the Au nanoparticles, partially contributing to the enhanced ε' value. The introduction of the Au-TNRs in the PVDF matrix provided three-phase Au-TNR/PVDF nanocomposites with excellent dielectric properties (i.e., high ε' ≈ 157 and low tanδ ≈ 0.05 at 1.8 vol% of Au and 47.4 vol% of TNRs). The ε' of the three-phase Au-TNR/PVDF composite is ~2.4-times higher than that of the two-phase TNR/PVDF composite, clearly highlighting the primary contribution of the Au nanoparticles at similar filler loadings. The volume fraction dependence of ε' is in close agreement with the effective medium percolation theory model. The significant enhancement in ε' was primarily caused by interfacial polarization at the PVDF-conducting Au nanoparticle and PVDF-semiconducting TNR interfaces, as well as by the induced β-PVDF phase. A low tanδ was achieved due to the inhibited conducting pathway formed by direct Au nanoparticle contact.

A Redox Cu(II)-Graphene Oxide Modified Screen Printed Carbon Electrode as a Cost-Effective and Versatile Sensing Platform for Electrochemical Label-Free Immunosensor and Non-enzymatic Glucose Sensor

A novel copper (II) ions [Cu(II)]-graphene oxide (GO) nanocomplex-modified screen-printed carbon electrode (SPCE) is successfully developed as a versatile electrochemical platform for construction of sensors without an additionally external redox probe. A simple strategy to prepare the redox GO-modified SPCE is described. Such redox GO based on adsorbed Cu(II) is prepared by incubation of GO-modified SPCE in the Cu(II) solution. This work demonstrates the fabrications of two kinds of electrochemical sensors, i.e., a new label-free electrochemical immunosensor and non-enzymatic sensor for detections of immunoglobulin G (IgG) and glucose, respectively. Our immunosensor based on square-wave voltammetry (SWV) of the redox GO-modified electrode shows the linearity in a dynamic range of 1.0-500 pg.mL-1 with a limit of detection (LOD) of 0.20 pg.mL-1 for the detection of IgG while non-enzymatic sensor reveals two dynamic ranges of 0.10-1.00 mM (sensitivity = 36.31 μA.mM-1.cm-2) and 1.00-12.50 mM (sensitivity = 3.85 μA.mM-1.cm-2) with a LOD value of 0.12 mM. The novel redox Cu(II)-GO composite electrode is a promising candidate for clinical research and diagnosis.