Realistic dielectric response of high temperature sintered ZnO ceramic: a microscopic and spectroscopic approach

High temperature sintering (1200–1400 °C) has been performed on ZnO ceramics. An X-ray Absorption Fine Structure (XAFS) study shows that high sintering temperature introduces a constant amount of V_O and V_Zn defects without any significant effect on the crystal or electronic structure of Wurtzite ZnO. The combined effects of grain boundaries and voids are considered responsible for the apparent colossal dielectric constant (ε′) > 10⁴ at low frequency (∼10² Hz) for all the sintered ZnO ceramics. The superior contact among grains of the ZnO-1200 sample enhances both the interfacial and orientational polarization of the Zn²⁺–V_O dipoles, which results in the increase of low and high frequency dielectric constants (ε′) and the corresponding dielectric loss (tan δ) also increases. On the other hand, high temperature sintering of ZnO at 1300 °C and 1400 °C introduces voids at the expense of reduced grain and grain boundary contact areas, thus affecting both the interfacial and orientational polarization with corresponding reduction of dielectric constant (ε′) and dielectric loss. Orientational polarizations due to Zn²⁺–V_O dipoles are suggested to remain fixed and it is the microstructure which controls the dielectric properties of high temperature sintered ZnO ceramics.

Superior grain contacts of ZnO-1200 samples enhance low and high frequency dielectric constants (ε′) and dielectric loss (tan δ).     

Suppressing loss tangent with significantly enhanced dielectric permittivity of poly(vinylidene fluoride) by filling with Au–Na1/2Y1/2Cu3Ti4O12 hybrid particles

Three-phase gold nanoparticle–Na_1/2Y_1/2Cu₃Ti₄O₁₂ (Au–NYCTO)/poly(vinylidene fluoride) (PVDF) composites with 0.095–0.487 hybrid particle volume fractions (f) were fabricated. Au nanoparticles with a diameter of ∼10 nm were decorated on the surfaces of high-permittivity NYCTO particles using a modified Turkevich''s method. The polar β-PVDF phase was confirmed to exist in the composites. Significantly enhanced dielectric permittivity of ∼98 (at 1 kHz) was obtained in the Au–NYCTO/PVDF composite with f_Au–NYCTO = 0.487, while the loss tangent was suppressed to 0.09. Abrupt changes in the dielectric and electrical properties, which signified percolation behavior, were not observed even when f_Au–NYCTO = 0.487. Using the effective medium percolation theory model, the percolation threshold (f_c) was predicted to be at f_Au–NYCTO = 0.69, at which f_Au was estimated to ∼0.19 and close to the theoretical f_c value for the conductor–insulator composites (f_c = 0.16). A largely enhanced dielectric response in the Au–NYCTO/PVDF composites was contributed by the interfacial polarization effect and a high permittivity of the NYCTO ceramic filler. Au nanoparticles can produce the local electric field in the composites, making the dipole moments in the β-PVDF phase and NYCTO particles align with the direction of the electric field.

Three-phase gold nanoparticle–Na_1/2Y_1/2Cu₃Ti₄O₁₂ (Au–NYCTO)/poly(vinylidene fluoride) (PVDF) composites with 0.095–0.487 hybrid particle volume fractions (f) were fabricated.     

Relationship between dynamic fatigue crack propagation properties and viscoelasticity of natural rubber/silicone rubber composites

In this paper, dynamic fatigue crack propagation properties of natural rubber/silicone rubber (NR/VMQ) composites are studied under constant tearing energy (G) input. Through dynamic fatigue crack growth testing, it is found that with the increase of VMQ fraction, NR/VMQ exhibits a lower crack growth rate (dc/dN). The viscoelastic parameters have been recorded in real-time during crack propagation, including the storage modulus E′, loss factor tan δ, and loss compliance modulus J′′, and their relationships with crack propagation behaviour have been established. The improved crack propagation resistance is attributed to the reduced J′′, resulting from the synergistic effect of increased E′ and decreased tan δ, and thus more energy dissipation occurred in the linear viscoelastic region in front of the crack tip, which consumed part of the energy for crack growth. Finally, good correlation between dc/dN and J′′ could be successfully established.

The successfully established relationship between dynamic fatigue crack propagation behaviour and viscoelasticity of NR/VMQ composites.     

Microwave absorption properties of steelmaking dusts: effects of temperature on the dielectric constant (ε′) and loss factor (ε′′) at 1064 MHz and 2423 MHz

The microwave absorption properties of a material depend largely on the dielectric properties of the material being heated. Therefore, the influences of temperature on the dielectric constant (ε′), loss factor (ε′′), loss tangent (tan δ_d) and penetration depth (D_P) of steelmaking dust at frequencies of 1064 MHz and 2423 MHz were measured. Three steelmaking dust samples were studied. The effects of temperature on the dielectric properties of the samples were insignificant at temperatures below 600 °C. However, above this temperature, a rapid rise in the values of the dielectric properties of the samples was observed. Comparing the thermogravimetric analysis and differential scanning calorimetry (TGA-DSC) results and mass spectra (MS) of the dusts with their dielectric properties revealed that the changes in the dielectric values of the dusts were associated with the thermal decomposition of calcium carbonate and the release of CO/CO₂ gases. Furthermore, the increase in the electrical conductivity of the samples at high temperature resulted in increased dielectric values. The behavior of the loss tangent of the samples with increasing temperature coincided with the behavior of the loss factor. The penetration depth decreased with an increase in temperature at both frequencies, while an increase in the dielectric properties caused a significant decrease in the penetration depth. The results indicated that steelmaking dusts have good microwave absorbing properties owing to their carbon and iron oxide contents.

The effect of temperature on the dielectric properties was found to be minor at temperatures below 600 °C. Above this temperature, sharp rises in the values of both the dielectric constant and the loss factor were observed.     

Significant enhancement of dielectric permittivity and percolation behaviour of La2−xSrxNiO4/poly(vinylidene fluoride) composites with different Sr doping concentrations

The percolation behaviour and dielectric properties of La_2−xSr_xNiO₄ (LSNO)/poly(vinylidene fluoride) (PVDF) composites with different Sr doping concentrations were investigated. The semiconducting LSNO filler particles with x = 0.2 (LSNO-1) and x = 0.4 (LSNO-2) were prepared using a chemical combustion method. The microstructures, thermal properties, and phase compositions of the polymer composites and filler particles were systematically investigated. The conductivity of the LSNO fillers increased with the Sr content and had an important impact on the dielectric properties of the LSNO/PVDF composites. The percolation threshold of the LSNO-2/PVDF composite was lower than that of the LSNO-1/PVDF composite. An ultra-high dielectric permittivity (ε′) of 3384.7 (at 1 kHz and room temperature), which was approximately 340 times higher than that of pure PVDF, was obtained for the LSNO-2/PVDF composite with a filler volume fraction of 25 vol%. The enhanced dielectric properties were attributed to interfacial polarisation at the semiconductor–insulator interface, a micro-capacitor model, and the intrinsically remarkable dielectric properties of the LSNO ceramic.

The percolation behaviour and dielectric properties of La_2−xSr_xNiO₄ (LSNO)/poly(vinylidene fluoride) (PVDF) composites with different Sr doping concentrations were investigated.     

Dielectric relaxation of the double perovskite oxide Ba2PrRuO6

Samples of Ba₂PrRuO₆ were prepared by the solid state reaction method and the structure was characterized by X-ray diffraction (XRD). Scanning electron microscopy (SEM) and dielectric measurements were performed in order to investigate the morphology and electric properties of the ceramics. X-ray diffraction data reveal that the Ba₂PrRuO₆ samples are of the cubic crystal structure with the space group Fm$\bar{3}$m at room temperature. The dielectric properties were studied in the range of 20 Hz to 1 MHz in the temperature range from 10 K to 300 K. Strong dispersion in frequency and a rapid increase in ε′ are observed when T > 150 K. The observed steps of the ε′(T) curves are correlated with the peaks of the tan δ(T) curves, with the peak temperature shifting to higher values as the frequency increases. Impedance spectroscopy studies indicate the presence of grain and grain boundary relaxations in the sample at high temperatures, while at low temperatures only grain relaxation can be observed. Both grain and grain boundary relaxation times follow the Arrhenius law with activation energies of 0.16 eV and 0.17 eV, respectively.

Complex plane impedance plots for Ba₂PrRuO₆ sample at different temperatures. The solid lines represent the fitting from the equivalent circuits.     

α-Glucosidase inhibitors from Chinese bayberry (Morella rubra Sieb. et Zucc.) fruit: molecular docking and interaction mechanism of flavonols with different B-ring hydroxylations

Inhibition of α-glucosidase alleviates postprandial high glycemic levels in diabetic or prediabetic population. In Chinese bayberry fruit, myricetin, quercetin and kaempferol are main flavonols, which differ only in their hydroxylation on the B-ring. Kaempferol (4′-OH) showed high IC₅₀ (65.36 ± 0.27 μmol L⁻¹) against α-glucosidase, while quercetin (3′,4′-OH) exhibited stronger inhibition (46.91 ± 0.54 μmol L⁻¹) and myricetin (3′,4′,5′-OH) possessed the strongest inhibitory activity (33.20 ± 0.43 μmol L⁻¹). Molecular docking analysis illustrated that these flavonols could insert to the active cavity of α-glucosidase. Adjacent hydroxyl groups at B-ring of myricetin and quercetin positively contributed to form hydrogen bonds that were important to the stability of flavonol–enzyme complex, while kaempferol had no adjacent hydroxyl groups. Such observation was further validated by molecular dynamics simulations, and in good consistency with in vitro kinetic analysis and fluorescence spectroscopy analysis. Among three flavonols tested, myricetin possessed the strongest inhibition effects on α-glucosidase with the lowest dissociation constant (K_i = 15.56 μmol L⁻¹) of myricetin-α-glucosidase, largest fluorescence quenching constant (K_sv) of (14.26 ± 0.03) × 10⁴ L mol⁻¹ and highest binding constant (K_a) of (1.38 ± 0.03) × 10⁵ L mol⁻¹ at 298 K with the enzyme. Bio-Layer Interferometry (BLI) and circular dichroism (CD) analysis further confirmed that myricetin had high affinity to α-glucosidase and induced conformational changes of enzyme. Therefore, myricetin, quercetin and kaempferol are all excellent dietary α-glucosidase inhibitors and their inhibitory activities are enhanced by increasing number of hydroxyl groups on B-ring.

Inhibition of α-glucosidase alleviates postprandial high glycemic levels in diabetic or prediabetic population.     

Peculiarities of the microwave properties of hard–soft functional composites SrTb0.01Tm0.01Fe11.98O19–AFe2O4 (A = Co,Ni, Zn,Cu, or Mn)

Herein, we investigated the correlation between the chemical composition, microstructure, and microwave properties of composites based on lightly Tb/Tm-doped Sr-hexaferrites (SrTb_0.01Tm_0.01Fe_11.98O₁₉) and spinel ferrites (AFe₂O₄, A = Co, Ni, Zn, Cu, or Mn), which were fabricated by a one-pot citrate sol–gel method. Powder XRD patterns of products confirmed the presence of pure hexaferrite and spinel phases. Microstructural analysis was performed based on SEM images. The average grain size for each phase in the prepared composites was calculated. Comprehensive investigations of dielectric properties (real (ε′) and imaginary parts (ε′′) of permittivity, dielectric loss tangent (tan(δ)), and AC conductivity) were performed in the 1–3 × 10⁶ Hz frequency range at 20–120 °C. Frequency dependency of microwave properties were investigated using the coaxial method in frequency range of 2–18 GHz. The non-linear behavior of the main microwave properties with a change in composition may be due to the influence of the soft magnetic phase. It was found that Mn- and Ni-spinel ferrites achieved the strongest electromagnetic absorption. This may be due to differences in the structures of the electron shell and the radii of the A-site ions in the spinel phase. It was discovered that the ionic polarization transformed into the dipole polarization.

Paper presents the correlation between the composition, microstructure, and microwave properties of composites based on Tb/Tm-doped Sr-hexaferrites and spinel ferrites (AFe₂O₄), which were fabricated by a one-pot citrate sol–gel method.     

Enhanced thermoelectric performance of CNT/P3HT composites with low CNT content

Carbon nanotubes (CNTs) have emerged as one of the leading additives for improving the thermoelectric properties of organic materials due to their unique structure and excellent electronic transport properties. However, since as-grown CNTs generally possess different diameters, it is of high interest to determine the influence of the diameter of carbon nanotubes on the thermoelectric properties of CNT/poly(3-hexylthiophene) (P3HT) composite films. Herein, we prepared CNT/P3HT composite films with diameters of <8 nm, 8–15 nm, 20–30 nm, 30–50 nm and >50 nm and studied their thermoelectric properties. It was found that the diameter of CNTs had an important influence on the TE performance of the composite films. The P3HT-d_CNT (<8 nm) and P3HT-d_CNT (8–15 nm) composite films exhibited almost the same thermoelectric performance and almost more than double that of the other three composite films with increased CNT diameter. The different mass fractions of CNT/P3HT composite films have also been investigated. The maximum TE power factor of CNT (d < 8 nm)/P3HT composite films reached 49.0 μW mK⁻² at the mass fraction of 95 wt% P3HT, that is, 5 wt% CNTs. This superior TE power factor of CNT (d < 8 nm)/P3HT composite films can be ascribed to the fully connected interlayer of the P3HT polymer and also the heterogeneous dispersion of short-length CNTs.

The maximum TE power factor of CNT (d < 8 nm)/P3HT composite films reached 49.0 μW mK⁻² at the mass fraction of 5 wt% CNTs.     

Improvements in piezoelectric and energy harvesting properties with a slight change in depolarization temperature in modified BNKT ceramics by a simple technique

For many BNT-based ceramics, an attempt to increase the piezoelectric properties usually results in a decrease in depolarization temperature (T_d). This trend limits the applications of the materials. Many previous experiments have used different methods to enhance the piezoelectric properties and improve the T_d characteristic. In this study, we demonstrated a simple technique (thermal annealing) to enhance the piezoelectric properties with a very slight decrease in T_d by ∼2 °C for a modified BNKT ceramic (BNKT doped with ZnO). Other phase transition characteristic temperatures of the studied ceramics were also slightly changed. The optimum dielectric (ε_r = 651, tan δ = 0.0503, T_F–R = 167.38 °C, T_m = 305.41 °C, ε_max = 5551, T_B = 367.15 °C, T_d = 155.98 °C, and γ = 1.43), ferroelectric (P_max = 41.28 μC cm⁻², P_r = 35.85 μC cm⁻², E_c = 42.60 kV cm⁻¹ and R_sq = 1.42), piezoelectric (d₃₃ = 198 pC N⁻¹, k_p = 0.598, and g₃₃ = 34.35 × 10⁻³ Vm N⁻¹), and energy harvesting (FoM = 6.80 pm² N⁻¹) were obtained for the 8 h annealed ceramic. Furthermore, higher energy harvesting properties (which were 32% higher than that of the unannealed ceramic) were obtained after employing this technique.

In this study, we demonstrated a simple technique (thermal annealing) to enhance the piezoelectricity with a very slight decrease in T_d by ∼2 °C for a modified BNKT ceramic (BNKT doped with ZnO).     

Fabrication of PVDF/graphene composites with enhanced β phase via conventional melt processing assisted by solid state shear milling technology

The β-phase crystal, which decides the final electric properties of poly(vinylidene fluoride) (PVDF), is extremely difficult to obtain via conventional melt processing due to its thermal instability. In this work, with the assistance of our independently developed solid state shear milling (S³M) technology, which could provide multiple stresses and form a micro-stretching field on PVDF to promote the transformation of more α phase to β phase, PVDF/graphene (PVDF/GP) composite with relatively higher β phase (42.2%), higher than that directly prepared by melt blending without S³M (33.0%), and dielectric properties was achieved through conventional melt extrusion and injection. When the GP content was 1.0 wt%, the dielectric constant of the composite was 465 at 1000 Hz, about 42 times that of pure PVDF. The special squeezing and shearing forces of S³M also realized the exfoliation of GP as well as the solid grafting of GP layers on PVDF molecules, improving the dispersion of GP layers in PVDF and making them effectively exert their heterogeneous nucleation as well as enhancement effects on PVDF, thus increasing the crystallinity, thermal stability and mechanical properties of the composites.

With the assistance of our independently developed solid state shear milling (S³M) technology, PVDF/GP composite with relatively high β phase (42.2%), higher than that directly gotten by melt blending (33.0%), were achieved via common melt process.     

The electrical modulus and other dielectric properties by the impedance spectroscopy of LaCrO3 and LaCr0.90Ir0.10O3 perovskites

We have prepared LaCrO₃ (LCO) and 10% Ir doped LCO samples by the solid state reaction method and studied the electrical modulus and the other dielectric properties of the samples by means of the impedance spectroscopy in the −100 °C to 100 °C range, with steps of 20 °C. It has been clearly observed that the dielectric properties change due to Ir doping. The absolute dielectric constant value of Ir doped LCO has decreased and this reduction was attributed to decreasing Cr⁶⁺ ions which may play a vital role in space charge polarization and charge hopping. A plateau region appeared in the temperature-dependent real electrical modulus M′ versus f curves of the pure LCO sample while almost no plateau region is visible in the Ir doped LCO sample. The temperature-dependent imaginary modulus M′′ versus f curves has two peaks at each temperature; one of the peaks is at low frequency and the other at the high frequency region, which shifts through higher frequency region with increasing temperature. This originates from free charge accumulation at the interface with the increase of the temperature. Furthermore, it has been seen that the Ir doped LCO sample has higher impedance and resistance values than the undoped LCO sample at the same frequency and temperature. This phenomenon was attributed to doped Ir ions behaving like a donor in LCO because LCO is a p-type compound. Moreover, the activation energy values of 0.224 eV and 0.208 eV for LCO and of 0.161 eV and 0.265 eV for the Ir doped LCO have been obtained from the slopes of the ρ_dcvs. (kT)⁻¹ curves, respectively. Also the activation energies were calculated from the slopes of the f_maxvs. (kT)⁻¹ curves and the obtained results from low frequency region were in good agreement with ρ_dcvs. (kT)⁻¹ ones.

In this work, LaCrO₃ and Ir doped LaCrO₃ compounds were synthesized and their frequency dependent electrical properties were studied.     

Inhibition of Aminoglycoside 6′-N-Acetyltransferase Type Ib by Zinc: Reversal of Amikacin Resistance in Acinetobacter baumannii and Escherichia coli by a Zinc Ionophore

In vitro activity of the aminoglycoside 6′-N-acetyltransferase type Ib [AAC(6′)-Ib] was inhibited by ZnCl₂ with a 50% inhibitory concentration (IC₅₀) of 15 μM. Growth of Acinetobacter baumannii or Escherichia coli harboring aac(6′)-Ib in cultures containing 8 μg/ml amikacin was significantly inhibited by the addition of 2 μM Zn²⁺ in complex with the ionophore pyrithione (ZnPT).     

Phase transition and dewetting of a 5CB liquid crystal thin film on a topographically patterned substrate

We report thermally induced nematic to isotropic (N–I) phase transition as well as dewetting of 5CB Liquid Crystal (LC) thin films coated on flat and topographically patterned substrates with grating geometry of different line width (l_P) and periodicity (λ_P). On a flat substrate, the nematic to isotropic (N–I) phase transition, which takes place within a temperature range between 31.1 °C and 34.4 °C is fully reversible, with re-appearance of identical Schlieren texture when the sample is cooled down during isotropic to nematic (I–N) transition. Upon further heating beyond N–I transition and annealing at T ≈ 65 °C, the film undergoes nucleated dewetting with formation and growth of holes, which eventually merge to form isolated droplets. The morphology of the dewetted structures remains unaltered when the film is cooled to room temperature from this stage, though the features undergo phase transition to the nematic state. In contrast on a topographically patterned substrate, the phase transition cycle is associated with a change of the texture of the film during cooling to the nematic stage. Interestingly the molecules exhibit homeotropic anchoring when λ_P ≈ 1.5 μm and planar anchoring when λ_P large (≈10 μm). When heated further to T ≈ 65 °C, the film dewets on topographically patterned substrates resulting in a collection of droplets, which are aligned to the substrate patterns when λ_P is large (≈10 μm). In contrast the dewetted droplets are random and not correlated to the patterns when λ_P is lower (≈1.5 μm).

Thermally induced nematic to isotropic (N–I) phase transition and dewetting of 5CB liquid crystal thin films on flat and topographically patterned substrates.     

A new mechanism for improving electromagnetic properties based on tunable crystallographic structures of FeCoNiSixAl0.4 high entropy alloy powders

Mechanical grinding method was employed to prepare FeCoNiSi_xAl_0.4 high entropy alloy powders, which present a simple solid solution structure (FCC and BCC). After annealing at 673 K, a large amount of BCC phase precipitate and a small amount of CoFe₂O₄ phase generate. The change of crystal structure may lead to an increase in M_s (from 100.3 emu g⁻¹ to 124.2 emu g⁻¹) and a decrease in H_c (from 107 Oe to 59.5 Oe for FeCoNiSi_0.3Al_0.4). The silica content has a significant effect on the electromagnetic parameters of the as-milled and as-annealed alloy powders, presenting the trend of first increase and then decrease. And the dielectric constant is obviously improved after annealing (e.g. from 8.48 to 11.21 and from 0.15 to 2.84 for the ε′ and ε′′ of FeCoNiSi_0.3Al_0.4 at 18 GHz, respectively), while the permeability is reduced. Compared with those of the as-milled samples, the μ′ of as-annealed FeCoNiSi_xAl_0.4 (x = 0.1, 0.3, 0.4) remain unchanged or even increase due to the formation of CoFe₂O₄. Meanwhile, the relative content of the precipitated BCC to FCC for FeCoNiSi_0.3Al_0.4 enhance with the annealing temperature increase from 573 K to 773 K, and then reduce. And the ε′ and μ′ at 2 GHz present the same trend as the content ratio (A_BCC/A_FCC), while the ε′′ improve obviously after annealing, corresponding to the elevation of conductivity.

Mechanical grinding method was employed to prepare FeCoNiSi_xAl_0.4 high entropy alloy powders, which present a simple solid solution structure (FCC and BCC).     

Microwave dielectric properties of low-temperature-fired MgNb2O6 ceramics for LTCC applications

MgNb₂O₆ ceramics doped with (Li₂O–MgO–ZnO–B₂O₃–SiO₂) glass were synthesized by the traditional solid phase reaction route. The effects of LMZBS addition on microwave dielectric properties, grain growth, phase composition and morphology of MgNb₂O₆ ceramics were studied. The SEM results show dense and homogeneous microstructure with grain size of 1.72 μm. Raman spectra and XRD patterns indicate the pure phase MgNb₂O₆ ceramic. The experimental results show that LMZBS glass can markedly decrease the sintering temperature from 1300 °C to 925 °C. Higher density and lower porosity make ceramics have better dielectric properties. The MgNb₂O₆ ceramic doped with 1 wt% LMZBS glass sintered at 925 °C for 5 h, possessed excellent dielectric properties: ε_r = 19.7, Q·f = 67 839 GHz, τ_f = −41.01 ppm °C⁻¹. Moreover, the favorable chemical compatibility of the MgNb₂O₆ ceramic with silver electrodes makes it as promising material for low temperature co-fired ceramic (LTCC) applications.

MgNb₂O₆ ceramics doped with (Li₂O–MgO–ZnO–B₂O₃–SiO₂) glass were synthesized by the traditional solid phase reaction route.     

Structural,optical and dielectric properties of tellurium-based double perovskite Sr2Ni1−xZnxTeO6

In this paper, Sr₂Ni_1−xZn_xTeO₆ (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) double perovskite compounds were synthesised by the conventional solid-state method, and the structural, optical and dielectric properties were investigated. The Rietveld refinement of X-ray diffraction data shows that all compounds were crystallised in monoclinic symmetry with the I2/m space group. Morphological scanning electron microscopy reported that the grain sizes decreased as the dopant increased. The UV-vis diffuse reflectance spectroscopy conducted for all samples found that the optical band gap energy, E_g, increased from 3.71 eV to 4.14 eV. The dielectric permittivity ε′ values increased for the highest Zn-doped composition, Sr₂Ni_0.2Zn_0.8TeO₆, being ∼1000 and ∼60 in the low- and high-frequency range, respectively. All samples exhibited low dielectric loss (tan δ ≤ 0.20) in the range of 10⁴–10⁵ Hz frequency. Impedance measurement revealed that grain resistance decreased with enhancement in Zn content in the Sr₂NiTeO₆ crystal lattice.

In this paper, Sr₂Ni_1−xZn_xTeO₆ (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) double perovskite compounds were synthesised by the conventional solid-state method, and the structural, optical and dielectric properties were investigated.     

Synthesis of a novel hexaazatriphenylene derivative for the selective detection of copper ions in aqueous solution

A hexaazatriphenylene (HAT) derivative, naphtho[2,3-h]naphtho[2′,3'':7,8]quinoxalino[2,3-a]naphtho[2′,3′:7,8]quinoxalino[2,3-c]phenazine-5,10,15,20,25,30-hexaone (NQH) was synthesized, characterized, and found to have novel properties in being selective toward the detection of copper (Cu²⁺) ions. The capability of NQH to be employed as a colorimetric, chemo-fluorescence and electrochemical sensor for the detection of Cu²⁺ was demonstrated by performing UV-Vis absorbance, fluorescence intensity, and cyclic voltammetry (CV) measurements. The interaction between NQH and Cu²⁺ was initially observed with an obvious color change from yellow to brown upon the addition of Cu²⁺ ions to NQH. The interaction was also confirmed by UV-Vis absorbance, fluorescence intensity, and mass spectroscopy (MS/MS) measurements. UV absorbance, fluorescence and CV of NQH toward Cu²⁺ showed good linearity with a detection limit of 3.32 μM, 2.20 μM and 0.78 μM, respectively, which are lower than the toxicity levels of copper in drinking water (20–30 μM) set by the U.S. Environmental Protection Agency (EPA) and World Health Organization (WHO). A 1 : 2 stoichiometry complexation between NQH and Cu²⁺ was confirmed by Job''s plot and MS/MS. In addition, the selectivity and sensitivity of the NQH compound towards Cu²⁺ ions were further confirmed by performing CV on a screen printed flexible and planar electrochemical sensor.

A hexaazatriphenylene (HAT) derivative, naphtho[2,3-h]naphtho[2′,3′:7,8]quinoxalino[2,3-a]naphtho[2′,3′:7,8]quinoxalino[2,3-c]phenazine-5,10,15,20,25,30-hexaone (NQH) was synthesized, characterized, and found to be selective to copper (Cu²⁺) ions.     

Rapid prototyping of a novel and flexible paper based oxygen sensing patch via additive inkjet printing process

A novel and flexible oxygen sensing patch was successfully developed for wearable, industrial, food packaging, pharmaceutical and biomedical applications using a cost-efficient and rapid prototypable additive inkjet print manufacturing process. An oxygen sensitive ink was formulated by dissolving ruthenium dye and ethyl cellulose polymer in ethanol in a 1 : 1 : 98 (w/w/w) ratio. The patch was fabricated by depositing the oxygen sensitive ink on a flexible parchment paper substrate using an inkjet printing process. A maximum absorbance from 430 nm to 480 nm and a fluorescence of 600 nm was observed for the oxygen sensitive ink. The capability of the oxygen sensitive patch was investigated by measuring the fluorescence quenching lifetime of the printed dye for varying oxygen concentration levels. A fluorescence lifetime decay (τ) from ≈4 μs to ≈1.9 μs was calculated for the printed oxygen sensor patch, for oxygen concentrations varying from ≈5 mg L⁻¹ to ≈25 mg L⁻¹. A sensitivity of 0.11 μs mg L⁻¹ and a correlation coefficient of 0.9315 was measured for the printed patches. The results demonstrated the feasibility of employing an inkjet printing process for the rapid prototyping of flexible and moisture resistant oxygen sensitive patches which facilitates a non-invasive method for monitoring oxygen and its concentration levels.

A paper-based low cost and rapid prototypable flexible oxygen sensing patch was developed for the first time using a cost-efficient additive inkjet print manufacturing process for wearable, food packaging, pharmaceutical and biomedical applications.     

TLC-smartphone in antibiotics determination and low-quality pharmaceuticals detection

Thin layer chromatography (TLC) is a powerful and simple technique for screening and quantifying low quality and counterfeit pharmaceutical products. The detection methods used to detect and quantify separate analytes in TLC ranges from the densitometric method to mass spectrometric or Raman spectroscopic methods. This work describes the development and optimization of a simple and sensitive TLC method utilizing a smartphone CCD camera for verification of both identity and quantity of antibiotics in dosage form, namely ofloxacin and ornidazole. Mixtures of ofloxacin and ornidazole were chromatographed on a silica gel 60 F₂₅₄ plate as a stationary phase. The optimized mobile phase is n-butanol : methanol : ammonia (8 : 1 : 1.5 by volume). Iodine vapor has been used as a “universal stain” to visualize the spots on the TLC plates in order to obtain a visual image using the smartphone camera and a desk lamp as an illumination source, thus eliminating the need for a UV illumination source. The recorded images were processed to calculate the R_f values (R_f values for ofloxacin and ornidazole were 0.12 and 0.76, respectively) which provide identity of the drugs while spot intensity was calculated using a commercially available smartphone app and employed for quantitative analysis of the antibiotics and “acetaminophen” as an example of a counterfeit substance. The smartphone TLC method yielded a linearity of ofloxacin and ornidazole in the range of 12.5–62.5 μg/band and 500–1000 μg/band, respectively. The limit of detection was found to be 1.6 μg/spot for ofloxacin and 97.8 μg/spot for ornidazole. The proposed method was compared with the bench top densitometric method for verification using a Camag TLC Scanner 3, the spot areas were scanned at 320 nm. The R_f value of ofloxacin and ornidazole was calculated to be 0.12 and 0.76, respectively. The densitometric method yielded a linearity of ofloxacin and ornidazole in the range of 5–40 μg/band and 5–50 μg/band, respectively. The limit of detection was found to be 0.8 μg/spot for ofloxacin and 1.1 μg/spot for ornidazole. The proposed method has been successfully applied for the determination of ofloxacin and ornidazole present in more than one pharmaceutical dosage form and was comparable to the densitometric method.

Low-quality and counterfeit pharmaceutical detection has been performed based on the processing of an iodine stained TLC plate image captured by a smartphone CCD camera.