Correlation among the structural,electric and magnetic properties of Al3+ substituted Ni–Zn–Co ferrites

This study explored the structural, electrical, and magnetic properties of diamagnetic aluminium (Al³⁺) substituted nickel-zinc-cobalt (Ni–Zn–Co) mixed spinel ferrites, though the research on this area is in the infancy stage. Single-phase cubic spinel structures with the Fd$\bar{3}$m space group of the synthesized Ni_0.4Zn_0.35Co_0.25Fe_(2−x)Al_xO₄ (0 ≤ x ≤ 0.12) ferrite samples were confirmed by X-ray diffraction (XRD) analysis. The average particle size ranged from 0.67 to 0.39 μm. Selected area electron diffraction (SAED) patterns were indexed according to the space group Fd3m, representing the particle''s crystallinity. The optical band gaps ranged from 4.784 eV to 4.766 eV. Frequency-dependent dielectric constants and ac conductivity measurement suggested that the prepared ferrites were highly resistive. Relaxation times were reduced to a low value from 45.45 μs to 1.54 μs with the composition x. The Curie temperatures (T_c) were 615–623 K for all samples. Real part permeabilities (μ^/) were relatively stable up to an extended frequency range of 10⁶ Hz with relative quality factors (RQF) of around 10³. Tuning of the properties indicates that the fabricated ferrites may be promising for high-frequency electronic devices.

This study explored the structural, electrical, and magnetic properties of diamagnetic aluminium (Al³⁺) substituted nickel–zinc–cobalt (Ni–Zn–Co) mixed spinel ferrites, though the research on this area is in the infancy stage.     

Microstructural analysis,magnetic properties,magnetocaloric effect,and critical behaviors of Ni0.6Cd0.2Cu0.2Fe2O4 ferrites prepared using the sol–gel method under different sintering temperatures

This work focuses on the microstructural analysis, magnetic properties, magnetocaloric effect, and critical exponents of Ni_0.6Cd_0.2Cu_0.2Fe₂O₄ ferrites. These samples, denoted as S1000 and S1200, were prepared using the sol–gel method and sintered separately at 1000 °C and 1200 °C, respectively. XRD patterns confirmed the formation of cubic spinel structures and the Rietveld method was used to estimate the different structural parameters. The higher sintering temperature led to an increased lattice constant (a), crystallite size (D), magnetization (M), Curie temperature (T_C), and magnetic entropy change (−ΔS_M) for samples that exhibited second-order ferromagnetic–paramagnetic (FM–PM) phase transitions. The magnetic entropy changed at an applied magnetic field (μ₀H) of 5 T, reaching maximum values of about 1.57–2.12 J kg⁻¹ K⁻¹, corresponding to relative cooling powers (RCPs) of 115 and 125 J kg⁻¹ for S1000 and S1200, respectively. Critical exponents (β, γ, and δ) for samples around their T_C values were studied by analyzing the M(μ₀H, T) isothermal magnetizations using different techniques and checked by analyzing the −ΔS_Mvs. μ₀H curves. The estimated values of β and γ exponents (using the Kouvel–Fisher method) and δ exponent (from M(T_C, μ₀H) critical isotherms) were β = 0.443 ± 0.003, γ = 1.032 ± 0.001, and δ = 3.311 ± 0.006 for S1000, and β = 0.403 ± 0.008, γ = 1.073 ± 0.016, and δ = 3.650 ± 0.005 for S1200. Obviously, these critical exponents were affected by an increased sintering temperature and their values were different to those predicted by standard theoretical models.

This work focuses on the microstructural analysis, magnetic properties, magnetocaloric effect, and critical exponents of Ni_0.6Cd_0.2Cu_0.2Fe₂O₄ ferrites.     

Theoretical study of D–A′–π–A/D–π–A′–π–A triphenylamine and quinoline derivatives as sensitizers for dye-sensitized solar cells

We have designed four dyes based on D–A′–π–A/D–π–A′–π–A triphenylamine and quinoline derivatives for dye-sensitized solar cells (DSSCs) and studied their optoelectronic properties as well as the effects of the introduction of alkoxy groups and thiophene group on these properties. The geometries, single point energy, charge population, electrostatic potential (ESP) distribution, dipole moments, frontier molecular orbitals (FMOs) and HOMO–LUMO energy gaps of the dyes were discussed to study the electronic properties of dyes based on density functional theory (DFT). And the absorption spectra, light harvesting efficiency (LHE), hole–electron distribution, charge transfer amount from HOMO to LUMO (Q_CT), D index, H_CT index, S_m index and exciton binding energy (E_coul) were discussed to investigate the optical and charge-transfer properties of dyes by time-dependent density functional theory (TD-DFT). The calculated results show that all the dyes follow the energy level matching principle and have broadened absorption bands at visible region. Besides, the introduction of alkoxy groups into triarylamine donors and thiophene groups into conjugated bridges can obviously improve the stability and optoelectronic properties of dyes. It is shown that the dye D4, which has had alkoxy groups as well as thiophene groups introduced and possesses a D–π–A′–π–A configuration, has the optimal optoelectronic properties and can be used as an ideal dye sensitizer.

We have designed four dyes based on D–A′–π–A/D–π–A′–π–A triphenylamine and quinoline derivatives for DSSCs and studied their optoelectronic properties as well as the effects of the introduction of alkoxy groups and thiophene group on the properties.     

Hot exciton transition for organic light-emitting diodes: tailoring excited-state properties and electroluminescence performances of donor–spacer–acceptor molecules

The photophysical, electrochemical and electroluminescent properties of newly synthesized blue emitters with donor–π–acceptor geometry, namely, 4′-(1-(naphthalen-1-yl)-1H-phenanthro[9,10-d]imidazol-2-yl)-N,N-diphenyl-(2-[1,1′-biphenyl]vinyl)-4-amine (NSPI-TPA), 4′-(1-(2-methylnaphthalen-1-yl)-1H-phenanthro[9,10-d]imidazol-2-yl)-N,N-diphenyl-(2-[1,1′-biphenyl]vinyl)-4-amine (MNSPI-TPA), 4-(2-(4′-(diphenylamino)-(2-[1,1′-biphenyl]vinyl)-4-yl)-1H-phenanthro[9,10-d]imidazol-1-yl)-1-naphthalene-1-carbonitrile (SPNCN-TPA) and 4-(2-(4-(9H-carbazol-9-yl)styryl)-1H-phenanthro[9,10-d]imidazol-1-yl)naphthalene-1-carbonitrile (SPNCN-Cz) were analyzed. The conjugation length in the emitters is not conducive to pure emission and hence, a molecular twisting strategy was adopted in NSPI-TPA, MNSPI-TPA, SPNCN-TPA and SPNCN-Cz to enhance pure emission. The emissive state (HLCT) of twisted D–π–A molecules containing both LE and CT (HLCT) states was tuned for high PL (η_PL) (LE) and high exciton utilization (η_s) (CT) efficiencies by replacing triphenylamine (strong donor) with carbazole (weak donor). Among strong donor compounds, namely, NSPI-TPA, MNSPI-TPA and SPNCN-TPA, the SPNCN-TPA-based device exhibited blue emission (451 nm) with CIE coordinates (0.15, 0.08), maximum current efficiency (η_c) of 2.32 cd A⁻¹, power efficiency (η_p) of 2.01 lm W⁻¹ and external quantum efficiency (η_ex) of 3.02%. The device with SPNCN-Cz emitter exhibited higher electroluminescence efficiencies than the SPNCN-TPA-based device, with pure blue emission (443 nm, CIE: 0.15,0.07), η_ex of 3.15%, η_c of 2.56 cd A⁻¹ and η_p of 2.45 lm W⁻¹.

SPNCN-Cz device exhibits η_ex (3.15%), η_c (2.56 cd A⁻¹), η_p (2.45 lm W⁻¹) with CIE (0.15, 0.07).     

Nonstoichiometric oxygen in Mn–Ga–O spinels: reduction features of the oxides and their catalytic activity

The subject of this study was the content of oxygen in mixed oxides with the spinel structure Mn_1.7Ga_1.3O₄ that were synthesized by coprecipitation and thermal treatment in argon at 600–1200 °C. The study revealed the presence of excess oxygen in “low-temperature” oxides synthesized at 600–800 °C. The occurrence of superstoichiometric oxygen in the structure of Mn_1.7Ga_1.3O_4+δ oxide indicates the formation of cationic vacancies, which shows up as a decreased lattice parameter in comparison with “high-temperature” oxides synthesized at 1000–1200 °C; the additional negative charge is compensated by an increased content of Mn³⁺ cations according to XPS. The low-temperature oxides containing excess oxygen show a higher catalytic activity in CO oxidation as compared to the high-temperature oxides, the reaction temperature was 275 °C. For oxides prepared at 600 and 800 °C, catalytic activity was 0.0278 and 0.0048 cm³ (CO) per g per s, and further increase in synthesis temperature leads to a drop in activity to zero. The process of oxygen loss by Mn_1.7Ga_1.3O_4+δ was studied in detail by TPR, in situ XRD and XPS. It was found that the hydrogen reduction of Mn_1.7Ga_1.3O_4+δ proceeds in two steps. In the first step, excess oxygen is removed, Mn_1.7Ga_1.3O_4+δ → Mn_1.7Ga_1.3O₄. In the second step, Mn³⁺ cations are reduced to Mn²⁺ in the spinel structure with a release of manganese oxide as a single crystal phase, Mn_1.7Ga_1.3O₄ → Mn₂Ga₁O₄ + MnO.

The hydrogen reduction of Mn_1.7Ga_1.3O_4+δ proceeds in two steps. In the first step, excess oxygen is removed, Mn_1.7Ga_1.3O_4+δ → Mn_1.7Ga_1.3O₄. In the second step, Mn³⁺ cations are reduced to Mn²⁺ in the spinel structure and formation of MnO, Mn_1.7Ga_1.3O₄ → Mn₂Ga₁O₄ + MnO.     

A novel MnO–CrN nanocomposite based non-enzymatic hydrogen peroxide sensor

A MnO–CrN composite was obtained via the ammonolysis of the low-cost nitride precursors Cr(NO₃)₃·9H₂O and Mn(NO₃)₂·4H₂O at 800 °C for 8 h using a sol–gel method. The specific surface area of the synthesized powder was measured via BET analysis and it was found to be 262 m² g⁻¹. Regarding its application, the electrochemical sensing performance toward hydrogen peroxide (H₂O₂) was studied via applying cyclic voltammetry (CV) and amperometry (i–t) analysis. The linear response range was 0.33–15 000 μM with a correlation coefficient (R²) value of 0.995. Excellent performance toward H₂O₂ was observed with a limit of detection of 0.059 μM, a limit of quantification of 0.199 μM, and sensitivity of 2156.25 μA mM⁻¹ cm⁻². A short response time of within 2 s was achieved. Hence, we develop and offer an efficient approach for synthesizing a new cost-efficient material for H₂O₂ sensing.

A MnO–CrN composite was obtained via the ammonolysis of the low-cost nitride precursors Cr(NO₃)₃·9H₂O and Mn(NO₃)₂·4H₂O at 800 °C for 8 h using a sol–gel method.     

Synthesis of magnetic core–shell Fe3O4@PDA@Cu-MOFs composites for enrichment of microcystin-LR by MALDI-TOF MS analysis

Microcystin-LR (MC-LR) is a toxin released from cyanobacteria in eutrophicated water. MC-LR is the most abundant and the most toxic among microcystins. In this work, core–shell structured copper-based magnetic metal–organic framework (Fe₃O₄@PDA@Cu-MOFs) composites were synthesized via a solvothermal reaction and a sol–gel method. The Fe₃O₄@PDA@Cu-MOFs composites showed ultra-high surface area, strong magnetic response and outstanding hydrophilicity. The Fe₃O₄@PDA@Cu-MOFs composites combined with matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF-MS) were used to analyse the content of MC-LR in real water samples. Under the optimised conditions, our proposed method exhibited good linearity within a concentration range of 0.05–4 μg L⁻¹ and good detection even at low limits (0.015 μg L⁻¹). The method was also successfully applied to analyse traces of MC-LR with quantitative recoveries for the real water samples in the range from 98.67% to 106.15%. Furthermore, it was characterized by high sensitivity, short operation time, being environmental friendly and having the ability to analyse other pollutants in the environment.

The synthetic route of the Fe₃O₄@PDA@Cu-MOFs microspheres and enrichment process of MC-LR.     

Nano ferrites (AFe2O4, A = Zn,Co, Mn,Cu) as efficient catalysts for catalytic ozonation of toluene

Nano ferrites (AFe₂O₄, A = Zn, Co, Mn, Cu) were supported on the surface of γ-Al₂O₃ support by hydrothermal synthesis to prepare a series of novel composite catalysts (AFe₂O₄/γ-Al₂O₃) for catalytic ozonation for elimination of high concentration toluene at ambient temperature. The characterization results showed that the high-purity nano-AFe₂O₄ particles were uniformly loaded on mesoporous γ-Al₂O₃. Further, it was confirmed that among the several catalysts prepared, the amount of oxygen vacancies (O_vs), Lewis acid sites (LAS), and Brønsted acid sites (BAS) of the ZnFe₂O₄/γ-Al₂O₃ catalyst were the highest. This meant that the ZnFe₂O₄/γ-Al₂O₃ catalyst had a strong adsorption capacity for toluene and ozone (O₃), and had a strong catalytic activity. When the temperature was 293 K and the space velocity was 1500 h⁻¹, the mol ratio of O₃ to toluene was 6, the degradation rate of toluene (600 mg m⁻³) can reach an optimum of 99.8%. The results of electron paramagnetic resonance (EPR) and Fourier infrared (FT-IR) proved superoxide radicals and hydroxyl radicals by catalytic ozonation. Moreover, the GC-MS analysis results indicated that the toluene degradation began with the oxidation of methyl groups on the benzene ring, eventually producing CO₂ and H₂O. After repeated experiments, the toluene degradation rate remained stable, and the residual content of O₃ in each litre of produced gas was less than 1 mg L⁻¹, thereby indicating that the ZnFe₂O₄/γ-Al₂O₃ catalyst had excellent reusability and showed great potential for the treatment of toluene waste gas.

Nano ferrites (AFe₂O₄, A = Zn, Co, Mn, Cu) were supported on the surface of γ-Al₂O₃ by hydrothermal synthesis to prepare a series of novel catalysts (AFe₂O₄/γ-Al₂O₃) for catalytic ozonation of high concentration toluene at ambient temperature.     

Goethite–titania composite: disinfection mechanism under UV and visible light

Goethite–titania (α-FeOOH–TiO₂) composites were prepared by co-precipitation and mechanical milling. The structural, morphological and optical properties of as-synthesized composites were characterized by X-ray powder diffraction, scanning electron microscopy and UV-Vis diffuse reflectance spectroscopy, respectively. α-FeOOH–TiO₂ composites and TiO₂-P25, as reference, were evaluated as photocatalysts for the disinfection of Escherichia coli under UV or visible light in a stirred tank reactor. α-FeOOH–TiO₂ exhibited better photocatalytic activity in the visible region than TiO₂-P25. The mechanical activation increased the absorption in the visible range of TiO₂-P25 and the photocatalytic activity of α-FeOOH–TiO₂. In the experiments with UV light and α-FeOOH–TiO₂, mechanically activated, a 5.4 log-reduction of bacteria was achieved after 240 min of treatment. Using visible light the α-FeOOH–TiO₂ and the TiO₂-P25 showed a 3.1 and a 0.7 log-reductions at 240 min, respectively. The disinfection mechanism was studied by ROS detection and scavenger experiments, demonstrating that the main ROS produced in the disinfection process were superoxide radical anion, singlet oxygen and hydroxyl radical.

A photocatalytic mechanism for FeOOH–TiO₂ composite is proposed under UV-Vis light, the FeOOH–TiO₂ composite showed higher photocatalytic activity than TiO₂-P25.     

Influence of neodymium substitution on structural,magnetic and spectroscopic properties of Ni–Zn–Al nano-ferrites

Ni_0.6Zn_0.4Al_0.5Fe_1.5−xNd_xO₄ ferrite samples, with x = 0.00, 0.05, 0.075 and 0.1, were synthesized using the sol–gel method. The effects of Nd³⁺ doping on the structural, magnetic and spectroscopic properties were investigated. XRD Rietveld refinement carried out using the FULLPROF program shows that the Ni–Zn ferrite retains its pure single phase cubic structure with Fd$\bar{3}$m space group. An increase in lattice constant and porosity happens with increasing Nd³⁺ concentration. FTIR spectra present the two prominent absorption bands in the range of 400 to 600 cm⁻¹ which are the fingerprint region of all ferrites. The change in Raman modes in the synthesized ferrite system were observed with Nd³⁺ substitution. The magnetization curves show a typical transition, at the Curie temperature T_C, from a low temperature ferrimagnetic state to a high temperature paramagnetic state. The saturation magnetization, coercivity and remanence magnetization are found to be decreasing with increasing the Nd³⁺ concentration.

The incorporation of Nd³⁺ in the Ni–Zn–Al ferrite spinel causes an improvement in magnetic parameters. Spectroscopic properties were discussed based on FTIR and Raman measurements and proved the purity and good crystallization of the samples.     

Environment-friendly magnetic Fe–Ce–W catalyst for the selective catalytic reduction of NOx with NH3: influence of citric acid content on its activity-structure relationship

The influence of the citric acid content on the structural and redox properties of a magnetic iron–cerium–tungsten mixed oxide catalyst prepared through a microwave-assisted citric acid sol–gel method is investigated via TG–DTG–DSC, XRD, N₂ adsorption–desorption, XPS, H₂-TPR and NH₃-TPD. Additionally, the NH₃-SCR activity of the magnetic FeCeW-m (m = 0.25, 0.5 and 1.0) catalysts are also studied. The results indicate that an increase in citric acid content strengthens the sol–gel reaction between citric acid and metal ions and promotes the formation of the γ-Fe₂O₃ crystallite not α-Fe₂O₃. Meanwhile, it decreases the BET surface area and pore volume of the catalyst. Furthermore, the surface concentration of iron species on the catalyst is enhanced when the molar ratio of citric acid/(Fe + Ce + W) increases from 0.25 to 1.0, but its surface absorbed oxygen and total oxygen concentration decrease. The magnetic FeCeW-0.5 catalyst shows the best reducibility at temperatures below 790 °C. The increase in the citric acid content inhibits the formation of acid sites in the catalyst, thus the magnetic FeCeW-0.25 catalyst possesses the most Lewis acid sites and Brønsted acid sites among the catalysts. The enhancement in citric acid content is beneficial to improve the SCR reaction rates normalized by the surface area of the catalyst. This catalyst exhibits high anti-SO₂ and H₂O poisoning, and the molar ratio of citric acid/(Fe + Ce + W) affects the adsorption of NO_x species on its surface.

The enhancement of critic acid amount strengthened the sol–gel reaction between critic acid and metal ions, showed an important role on the structure properties of magnetic Fe–Ce–W mixed oxide catalyst, thereby affected its NH₃-SCR activity.     

Significantly improved dielectric properties of multiwall carbon nanotube-BaTiO3/PVDF polymer composites by tuning the particle size of the ceramic filler

The effects of different BaTiO₃ sizes (≈100 nm (nBT) and 0.5–1.0 μm (μBT)) on the dielectric and electrical properties of multiwall carbon nanotube (CNT)-BT/poly(vinylidene fluoride) (PVDF) composites are investigated. The fabricated three-phase composites using 20 vol% BT with various CNT volume fractions (f_CNT) are systematically characterized. The dielectric permittivity (ε′) of the CNT-nBT/PVDF and CNT-μBT/PVDF composites rapidly increases when f_CNT > 0.015 and f_CNT > 0.017, respectively. The former is accompanied by the dramatic increase in the loss tangent (tan δ) and conductivity (σ), but surprisingly, not for the latter. At 10³ Hz, the low tan δ and σ values of the CNT-μBT/PVDF composite are about 0.06 and 6.82 × 10⁻⁹ S cm⁻¹, while its ε′ value is greatly enhanced (≈154.6). The variation of the dielectric permittivity with f_CNT for both composite systems follows the percolation model with percolation thresholds of f_c = 0.018 and f_c = 0.02, respectively. With further increasing f_CNT to 0.02, ε′ is greatly increased to 253.8, while tan δ ≤ 0.1. Without μBT particles, the ε′ and tan δ values of the CNT/PVDF composite with f_CNT = 0.02 are as high as ≈240 and >10³, respectively. Greatly enhanced dielectric properties are described in detail.

The effects of different BaTiO₃ sizes (≈100 nm (nBT) and 0.5–1.0 μm (μBT)) on the dielectric and electrical properties of multiwall carbon nanotube (CNT)-BT/poly(vinylidene fluoride) (PVDF) composites are investigated.     

Effect of heat treatment on the microstructure and ablation performance of C/C–SiC composites containing ZrSi2–Si

Low-temperature reactive melt infiltration (LRMI) is advantageous for the fabrication of ceramic matrix composites (CMCs). However, residual metal in CMCs prepared by LRMI deteriorates the high-temperature properties. In this study, C/C–SiC composites containing ZrSi₂–Si were prepared using LRMI at 1400 °C, and the effect of heat treatment at 1400 °C for 10, 20, or 30 h on the microstructure and ablation properties of the composites fabricated using three different ternary alloys (e.g., Zr_0.047B_0.0378Si_0.9152, Zr_0.0724B_0.0366Si_0.891, and Zr_0.1B_0.05Si_0.85) was investigated. The results show that the residual Si in the composites can be decreased by volatilisation and the reaction between Si and C during heat treatment, resulting in a decrease in the density and an increase in the SiC content. The ablation rates of the composites after heat treatment for 20 h were lower than those of the samples after heat treatment for 30 and 10 h. Among the three alloys, the composites prepared using Zr_0.0724B_0.0366Si_0.891 demonstrated the best ablation performance. Their linear and mass ablation rates at 1911 °C were −0.11 μm s⁻¹ and 1.82 μg s⁻¹, respectively.

C/C–SiC composites containing ZrSi₂–Si were prepared using low-temperature reactive melt infiltration (LRMI) at 1400 °C, and the thermal chemical ablation of the composites was examined.     

A H2O2/HBr system – several directions but one choice: oxidation–bromination of secondary alcohols into mono- or dibromo ketones

In this work we found that a H₂O₂–HBr(aq) system allows synthesis of α-monobromo ketones and α,α′-dibromo ketones from aliphatic and secondary benzylic alcohols with yields up to 91%. It is possible to selectively direct the process toward the formation of mono- or dibromo ketones by varying the amount of hydrogen peroxide and hydrobromic acid. The convenience of application, simple equipment, multifaceted reactivity, and compliance with green chemistry principles make the application of the H₂O₂–HBr(aq) system very attractive in laboratories and industry. The proposed oxidation–bromination process is selective in spite of known properties of ketones to be oxidized by the Baeyer–Villiger reaction or peroxidated with the formation of compounds with the O–O moiety in the presence of hydrogen peroxide and Bronsted acids.

Convenience of application, multifaceted reactivity, and compliance with green chemistry principles: H₂O₂–HBr(aq) system for preparation of bromo ketones with yields up to 91%.     

Regio-regular alternating diketopyrrolopyrrole-based D1–A–D2–A terpolymers for the enhanced performance of polymer solar cells

We designed and synthesized regio-regular alternating diketopyrrolopyrrole (DPP)-based D₁–A–D₂–A terpolymers (PDPPF2T2DPP-T2, PDPPF2T2DPP-TVT, and PDPPF2T2DPP-DTT) using a primary donor (D₁) [3,3′-difluoro-2,2′-bithiophene (F2T2)] and a secondary donor (D₂) [2,2′-bithiophene (T2), (E)-1,2-di(thiophen-2-yl)ethene (TVT), or dithieno[3,2-b:2′,3′-d]thiophene (DTT)]. A PDPP2DT-F2T2 D–A polymer was synthesized as well to compare optical, electronic, and photovoltaic properties. The absorption peaks of the terpolymers (PDPPF2T2DPP-T2, PDPPF2T2DPP-TVT, and PDPPF2T2DPP-DTT) were longer (λ_max = 801–810 nm) than the peak of the PDPP2DT-F2T2 polymer (λ_max = 799 nm), which is associated with the high-lying HOMO levels of the terpolymers (−5.08 to −5.13 eV) compared with the level of the PDPP2DT-F2T2 polymer (−5.38 eV). The photovoltaic properties of these DPP-based polymers were investigated under simulated AM 1.5G sunlight (100 mW cm⁻²) with a conventional structure (ITO/PEDOT:PSS/polymer:PC₇₁BM/Al). The open-circuit voltages (V_oc) of photovoltaic devices containing the terpolymers were slightly lower (0.68–0.70 V) than the V_oc of the device containing the PDPP2DT-F2T2 polymer (0.79 V). The short-circuit current (J_sc) of the PDPPF2T2DPP-DTT device was significantly improved (14.14 mA cm⁻²) compared with that of the PDPP2DT-F2T2 device (8.29 mA cm⁻²). As a result, the power conversion efficiency (PCE) of the PDPPF2T2DPP-DTT device (6.35%) was increased by 33% compared with that of the simple D–A-type PDPP2DT-F2T2 device (4.78%). The highest J_sc and PCE values (the PDPPF2T2DPP-DTT device) were attributed to an optimal nanoscopically mixed morphology and strong interchain packing with a high face-on orientation in the blend film state. The study demonstrated that our strategy of using multiple donors in a regio-regular alternating fashion could fine-tune the optical, electronic, and morphological properties of D–A-type polymers, enhancing the performance of polymer solar cells.

We designed and synthesized regio-regular alternating diketopyrrolopyrrole (DPP)-based D₁–A–D₂–A terpolymers (PDPPF2T2DPP-T2, PDPPF2T2DPP-TVT, and PDPPF2T2DPP-DTT) for use in polymer solar cells.     

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.     

First principles study of electronic and nonlinear optical properties of A–D–π–A and D–A–D–π–A configured compounds containing novel quinoline–carbazole derivatives

Materials with nonlinear optical (NLO) properties have significant applications in different fields, including nuclear science, biophysics, medicine, chemical dynamics, solid physics, materials science and surface interface applications. Quinoline and carbazole, owing to their electron-deficient and electron-rich character respectively, play a role in charge transfer applications in optoelectronics. Therefore, an attempt has been made herein to explore quinoline–carbazole based novel materials with highly nonlinear optical properties. Structural tailoring has been made at the donor and acceptor units of two recently synthesized quinoline–carbazole molecules (Q1, Q2) and acceptor–donor–π–acceptor (A–D–π–A) and donor–acceptor–donor–π–acceptor (D–A–D–π–A) type novel molecules Q1D1–Q1D3 and Q2D2–Q2D3 have been quantum chemically designed, respectively. Density functional theory (DFT) and time-dependent density functional theory (TDDFT) computations are performed to process the impact of acceptor and donor units on photophysical, electronic and NLO properties of selected molecules. The λ_max values (321 and 319 nm) for Q1 and Q2 in DSMO were in good agreement with the experimental values (326 and 323 nm). The largest shift in absorption maximum is displayed by Q1D2 (436 nm). The designed compounds (Q1D3–Q2D3) express absorption spectra with an increased border and with a reduced band gap compared to the parent compounds (Q1 and Q2). Natural bond orbital (NBO) investigations showed that the extended hyper conjugation and strong intramolecular interaction play significant roles in stabilising these systems. All molecules expressed significant NLO responses. A large value of β_tot was elevated in Q1D2 (23 885.90 a.u.). This theoretical framework reveals the NLO response properties of novel quinoline–carbazole derivatives that can be significant for their use in advanced applications.

Materials with nonlinear optical properties have significant applications in nuclear science, biophysics, medicine, chemical dynamics, solid physics & materials science. We show how π bridges, donors & acceptors can be reconfigured to improve optical properties.     

Organic–inorganic hybrid sol–gel materials doped with a fluorescent triarylimidazole derivative

The development of sensors for pH monitoring is of extreme importance in the monitoring of concrete and reinforced concrete structures. Imidazole derivatives are promising probes for pH sensing due to the amphoteric nature of their heterocyclic ring, which can be protonated/deprotonated upon pH changes. In this work, a triarylimidazole was synthesised and used as a dopant in an organic–inorganic hybrid (OIH) sol–gel matrix to obtain a pH-sensitive membrane for further application in optical fibre sensors (OFS). The triarylimidazole probe shows fluorimetric response in pH between 9 and 13, which is the desired range for monitoring carbonation of concrete. This degradation process lowers the highly alkaline pH of concrete (12.5–13) to values below 9, which creates favourable conditions for corrosion of concrete reinforcement. The OIH membranes used were based on Jeffamine THF170 and 3-glycidoxypropytrimethoxysilane precursors, which had already been shown to be suitable and resistant in contact with cement-based materials. The OIHs were doped with three different contents of the triarylimidazole and the structural, dielectric, thermal and optical properties of the pure and doped OIH materials were evaluated. The structural analysis showed that the presence of the triarylimidazole did not change the structural properties of the OIH material. Electrochemical impedance spectroscopy showed that in the doped samples the conductivity increased with the imidazole concentration. The ε_r obtained for the doped samples ranged approximately from 11 to 19 and for the pure matrices was 8. Thermal analysis showed that these materials are stable up to 350 °C and that the presence of the probe did not change that feature. The optical properties showed that the prepared OIH materials have promising properties to be used as pH sensitive fluorimetric probes.

OIH sol–gel materials based on Jeffamine THF-170 and GPTMS, doped with triarylimidazole, were synthesized. The ε_r obtained for the OIH doped samples ranged between 11 and 19. The OIHs are thermally stable for fresh concrete purposes.     

Metal–organic framework bearing new viologen ligand for ammonia and Cr2O72− sensing

Three anionic metal–organic frameworks (MOFs) {[Zn₃(BTEC)₂(H₂O)(4-BCBPY)]·(H₂O)}_n (1–3) (BTEC⁴⁻ = 1,2,4,5-benzenetetracarboxylic acid anion, 4-BCBPY²⁺ = 1,1′-bis(4-cyanobenzyl)-4,4′-bipyridinium dication) were synthesized in the reaction of 1,2,4,5-benzenetetracarboxylic acid with different metal salts such as ZnNO₃, ZnCl₂, and ZnSO₄, under solvothermal conditions in the presence of 1,1′-bis(4-cyanobenzyl)-4,4′-bipyridinium chloride. Single crystal X-ray diffraction analysis shows that compounds 1, 2 and 3 have MOF structures based on binuclear metal building units, which are connected by two protonated BTEC⁴⁻ ligands and three zinc ions, and the viologen cation 4-BCBPY²⁺ is located in the channel to achieve charge balance. Compounds 1, 2 and 3 have good photosensitivity, respond to sunlight, UV light and blue ray, and turn blue. The D–A distance and π–π stacking distance of the discolored samples (1P, 2P and 3P) changed. In addition, the three compounds showed visible color changes to ammonia vapor, rapidly changing from white to blue. At the same time, the three compounds exhibited fluorescence quenching to ammonia vapor and Cr₂O₇²⁻. It is further proved that compounds 1, 2 and 3 are fluorescent sensors with a low detection limit (for Cr₂O₇²⁻: 10⁻⁵ M) and high sensitivity for ammonia vapor and Cr₂O₇²⁻. It was found that photochromic behavior, ammonia sensing properties can be tuned by the nature of metal salts.

Three MOFs based on different metal salts were synthesized, and metal salts were found to play a key role in regulating the performance of MOFs.     

Investigation on structure,thermodynamic and multifunctional properties of Ni–Zn–Co ferrite for Gd3+ substitution

This study presents a modification of structure-dependent elastic, thermodynamic, magnetic, transport and magneto-dielectric properties of a Ni–Zn–Co ferrite tailored by Gd³⁺ substitution at the B-site replacing Fe³⁺ ions. The synthesized composition of Ni_0.7Zn_0.2Co_0.1Fe_2−xGd_xO₄ (0 ≤ x ≤ 0.12) crystallized with a single-phase cubic spinel structure that belongs to the Fd$\bar{3}$m space group. The average particle size decreases due to Gd³⁺ substitution at Fe³⁺. Raman and IR spectroscopy studies illustrate phase purity, lattice dynamics with cation disorders and thermodynamic conditions inside the studied samples at room temperature (RT = 300 K). Ferromagnetic to paramagnetic phase transition was observed in all samples where Curie temperature (T_C) decreases from 731 to 711 K for Gd³⁺ substitution in Ni–Zn–Co ferrite. In addition, Gd³⁺ substitution reinforces to decrease the A-B exchange interaction. Temperature-dependent DC electrical resistivity (ρ_DC) and temperature coefficient of resistance (TCR) have been surveyed with the variation of the grain size. The frequency-dependent dielectric properties and electric modulus at RT for all samples were observed from 20 Hz to 100 MHz and the conduction relaxation processes were found to spread over an extensive range of frequencies with the increase in the amount of Gd³⁺ in the Ni–Zn–Co ferrite. The RLC behavior separates the zone of frequencies ranging from resistive to capacitive regions in all the studied samples. Finally, the matching impedance (Z/η₀) for all samples was evaluated over an extensive range of frequencies for the possible miniaturizing application.

This study presents a modification of structure-dependent elastic, thermodynamic, magnetic, transport and magneto-dielectric properties of a Ni–Zn–Co ferrite tailored by Gd³⁺ substitution at the B-site replacing Fe³⁺ ions.