Europium (II)-Doped CaF₂ Nanocrystals in Sol-Gel Derived Glass-Ceramic: Luminescence and EPR Spectroscopy Investigations

The remarkable properties of Eu2+-activated phosphors, related to the broad and intense luminescence of Eu2+ ions, showed a high potential for a wide range of optical-related applications. Oxy-fluoride glass-ceramic containing Europium (II)-doped CaF2 nanocrystals embedded in silica matrix were produced in two steps: glass-ceramization in air at 800° with Eu3+-doped CaF2 nanocrystals embedded followed by Eu3+ to Eu2+ reduction during annealing in reducing atmosphere. The broad, blue luminescence band at 425 nm and with the long, weak tail in the visible range is assigned to the d → f type transition of the Eu2+ located inside the CaF2 nanocrystals in substitutional and perturbed sites, respectively; the photoluminescence quantum yield was about 0.76. The X-ray photoelectron spectroscopy and Electron paramagnetic spectroscopy confirmed the presence of Eu2+ inside the CaF2 nanocrystals. Thermoluminescence curves recorded after X-ray irradiation of un-doped and Eu2+-doped glass-ceramics showed a single dominant glow peak at 85 °C related to the recombination between F centers and Eu2+ related hole within the CaF2 nanocrystals. The applicability of the procedure can be tested to obtain an oxy-fluoride glass-ceramic doped with other divalent ions such as Sm2+, Yb2+, as nanophosphors for radiation detector or photonics-related applications

Origins of the photocatalytic NOx oxidation and storage selectivity of mixed metal oxide photocatalysts: prevalence of electron-mediated routes, surface area, and basicity

MgO, CaO, SrO, or BaO-promoted TiO2/Al2O3 was utilized in the photocatalytic NOx oxidation and storage reaction. Photocatalytic performance was investigated as a function of catalyst formulation, calcination temperature, and relative humidity. Onset of the photocatalytic activity in TiO2/Al2O3 coincides with the transition from the anatase to rutile phase and increasing number of paramagnetic active centers and oxygen vacancies. Disordered AlOx domains enable the formation of oxygen vacancies and paramagnetic centers on titania domains, hindering the nucleation and growth of titania particles, as well as increasing specific surface area (SSA) to store oxidized NOx species away from titania active sites. Both e-- and h+-mediated pathways contribute to photocatalytic NO conversion. Experiments performed using an e- scavenger (i.e., H2O2), suppressing the e--mediated route, attenuated the photocatalytic selectivity by triggering NO2(g) release. Superior NOx storage selectivity of 7.0Ti/Al-700 as compared to other TiO2/Al2O3 systems in the literature was attributed to an interplay between the presence of electrons trapped at oxygen vacancies and superoxide species allowing a direct pathway for the complete NO oxidation to HNO3/NO3- species, and the relatively large SSA of the photocatalyst prevents the rapid saturation of the photocatalyst with oxidation products. Longevity of the 7.0Ti/Al-700 was improved by the incorporation of CaO, emphasizing the importance of the surface basicity of the NOx storage site

Vanadium-doped magnesium oxide nanoparticles as electrodes in supercapacitor devices

Vanadium (V)-doped MgO nanoparticles were used as electrode materials in all-in-one solid-state supercapacitor applications. The prepared samples’ structural and morphological properties were thoroughly analyzed using XRD, Raman spectroscopy, TEM, PL, and BET. EPR spectroscopy was employed to analyze the paramagnetic centers induced in the host material and showed that all V-doped samples displayed a V4+ characteristic EPR signal. The electrochemical analysis of the assembled symmetric supercapacitors was done using cyclic voltammetry, galvanostatic cycling with potential limitation technique, and potentiostatic electrochemical impedance spectroscopy. The results reveal that the novel V-doped MgO material displayed excellent capacitance performance between 0 and 1 V, delivering a specific capacitance of 50 F/g at a 10 mV/s scan rate. It also exhibits a maximum energy density of 4.17 Wh/kg, comparable to values obtained from other symmetric supercapacitor configurations. When a booster material like carbon black was added, the specific capacitance value increased dramatically to 1200 F/g, values that were never reported before in the literature for MgO-based materials

Origins of the Photocatalytic NO_<i>x</i> Oxidation and Storage Selectivity of Mixed Metal Oxide Photocatalysts: Prevalence of Electron-Mediated Routes, Surface Area, and Basicity

MgO, CaO, SrO, or BaO-promoted TiO2/Al2O3 was utilized in the photocatalytic NOx oxidation and storage reaction. Photocatalytic performance was investigated as a function of catalyst formulation, calcination temperature, and relative humidity. Onset of the photocatalytic activity in TiO2/Al2O3 coincides with the transition from the anatase to rutile phase and increasing number of paramagnetic active centers and oxygen vacancies. Disordered AlOx domains enable the formation of oxygen vacancies and paramagnetic centers on titania domains, hindering the nucleation and growth of titania particles, as well as increasing specific surface area (SSA) to store oxidized NOx species away from titania active sites. Both e–- and h+-mediated pathways contribute to photocatalytic NO conversion. Experiments performed using an e– scavenger (i.e., H2O2), suppressing the e–-mediated route, attenuated the photocatalytic selectivity by triggering NO2(g) release. Superior NOx storage selectivity of 7.0Ti/Al-700 as compared to other TiO2/Al2O3 systems in the literature was attributed to an interplay between the presence of electrons trapped at oxygen vacancies and superoxide species allowing a direct pathway for the complete NO oxidation to HNO3/NO3– species, and the relatively large SSA of the photocatalyst prevents the rapid saturation of the photocatalyst with oxidation products. Longevity of the 7.0Ti/Al-700 was improved by the incorporation of CaO, emphasizing the importance of the surface basicity of the NOx storage site

All-in-one supercapacitor devices based on nanosized Mn4+-doped WO3

In this study, nanosized Mn-doped WO3-based materials were used as electrode materials for high-performance supercapacitor devices. Various Mn concentrations (0.5, 1, and 1.5%) were used to change the defect structure of WO3, which improved the material's electrical properties. A thorough morpho-structural and defect structure analysis of the undoped and doped WO3 was performed through various characterization techniques, among which EPR and PL spectroscopy gave insight into the effect that Mn-doping caused on the defect structure and optical properties of WO3. The presence of Mn4+ ions and a high concentration of oxygen vacancies was observed, strongly influencing the electrode material when used in symmetric supercapacitors, where the electrochemical performance was tested. The symmetric supercapacitors were designed without booster materials (like carbon black) and showed increased specific capacitance (115 F/g) and energy density (16 Wh/Kg) values

Copper (II) Species with Improved Anti-Melanoma and Antibacterial Activity by Inclusion in β-Cyclodextrin

To improve their biological activity, complexes [Cu(bipy)(dmtp)2(OH2)](ClO4)2·dmtp (1) and [Cu(phen)(dmtp)2(OH2)](ClO4)2·dmtp (2) (bipy 2,2′-bipyridine, phen: 1,10-phenantroline, and dmtp: 5,7-dimethyl-1,2,4-triazolo [1,5-a]pyrimidine) were included in β-cyclodextrins (β-CD). During the inclusion, the co-crystalized dmtp molecule was lost, and UV-Vis spectra together with the docking studies indicated the synthesis of new materials with 1:1 and 1:2 molar ratios between complexes and β-CD. The association between Cu(II) compounds and β-CD has been proven by the identification of the components’ patterns in the IR spectra and powder XRD diffractograms, while solid-state UV-Vis and EPR spectra analysis highlighted a slight modification of the square-pyramidal stereochemistry around Cu(II) in comparison with precursors. The inclusion species are stable in solution and exhibit the ability to scavenge or trap ROS species (O2·− and HO·) as indicated by the EPR experiments. Moreover, the two inclusion species exhibit anti-proliferative activity against murine melanoma B16 cells, which has been more significant for (2)@β-CD in comparison with (2). This behavior is associated with a cell cycle arrest in the G0/G1 phase. Compared with precursors, (1a)@β-CD and (2a)@β-CD exhibit 17 and 26 times more intense activity against planktonic Escherichia coli, respectively, while (2a)@β-CD is 3 times more active against the Staphylococcus aureus strain

Copper (II) Species with Improved Anti-Melanoma and Antibacterial Activity by Inclusion in &beta;-Cyclodextrin

To improve their biological activity, complexes [Cu(bipy)(dmtp)2(OH2)](ClO4)2&middot;dmtp (1) and [Cu(phen)(dmtp)2(OH2)](ClO4)2&middot;dmtp (2) (bipy 2,2&prime;-bipyridine, phen: 1,10-phenantroline, and dmtp: 5,7-dimethyl-1,2,4-triazolo [1,5-a]pyrimidine) were included in &beta;-cyclodextrins (&beta;-CD). During the inclusion, the co-crystalized dmtp molecule was lost, and UV-Vis spectra together with the docking studies indicated the synthesis of new materials with 1:1 and 1:2 molar ratios between complexes and &beta;-CD. The association between Cu(II) compounds and &beta;-CD has been proven by the identification of the components&rsquo; patterns in the IR spectra and powder XRD diffractograms, while solid-state UV-Vis and EPR spectra analysis highlighted a slight modification of the square-pyramidal stereochemistry around Cu(II) in comparison with precursors. The inclusion species are stable in solution and exhibit the ability to scavenge or trap ROS species (O2&middot;&minus; and HO&middot;) as indicated by the EPR experiments. Moreover, the two inclusion species exhibit anti-proliferative activity against murine melanoma B16 cells, which has been more significant for (2)@&beta;-CD in comparison with (2). This behavior is associated with a cell cycle arrest in the G0/G1 phase. Compared with precursors, (1a)@&beta;-CD and (2a)@&beta;-CD exhibit 17 and 26 times more intense activity against planktonic Escherichia coli, respectively, while (2a)@&beta;-CD is 3 times more active against the Staphylococcus aureus strain

Photo-supercapacitors based on nanoscaled ZnO

Abstract In this study, zinc oxide (ZnO) powders in two different morphologies, nanowire (NW) and nanoflower (NF), have been synthesized by the hydrothermal method. The eligibility of the pristine ZnO nanopowders as a photo-active material has been revealed by designing P-SC devices via the facile drop-casting method on both glass and plastic substrates in large-area applications. The impact of physical properties and especially defect structures on photo-supercapacitor (P-SC) performance have been explored. Although the dark Coulombic efficiency (CE%) of both NW and NF-based P-SC were very close to each other, the CE% of NW P-SC increased 3 times, while the CE% of NF P-SC increased 1.7 times under the UV-light. This is because the charge carriers produced under light excitation, extend the discharge time, and as confirmed by electron paramagnetic resonance, photoluminescence, and transmission electron microscopy analyses, the performance of P-SCs made from NF powders was relatively low compared to those produced from NW due to the high core defects in NF powders. The energy density of 78.1 mWh kg−1 obtained for NF-based P-SCs is very promising, and the capacitance retention value of almost 100% for 3000 cycles showed that the P-SCs produced from these materials were entirely stable. Compared to the literature, the P-SCs we propose in this study are essential for new generation energy storage systems, thanks to their ease of design, adaptability to mass production for large-area applications, and their ability to store more energy under illumination

Hybrid supercapacitors based on X-site Ba(II) ions substituted by Sr(II) in Langbeinite-type phosphates

The compounds KBa1-xSrxCr2(PO4)3 (with x = 0.00; 0.25; 0.50; 0.75; 1.00) were synthesized by a solid-state reaction, and they were thoroughly characterized by different spectroscopic and microscopic techniques. Their structures were indexed in a cubic system with a P213 space group forming a 3D framework built on CrO6 octahedra and PO4 tetrahedra sharing vertices leading to identical Cr2P3O18 (U) units. The interconnection between the tetrahedral and octahedral groups leads to the formation of two large closed cavities (K, MII)(1) and (K, MII)(2), statistically occupied by K+ and M2+ (M = Ba, Sr) atoms. Electron paramagnetic resonance spectroscopy confirmed the presence of paramagnetic Cr3+ ions, showing the effects of substituting the Ba2+ ions with smaller Sr2+ ions on the dipolar coupling between the Cr3+ centers. The obtained materials and active carbon were used as electrode materials in hybrid SC devices. At the same time, their electrochemical properties were assessed by potentiostatic electrochemical impedance spectroscopy, cyclic voltammetry, and galvanostatic charge–discharge measurements, showing promising results with a maximal specific capacitance (3.86 F/g), energy density (343 mWh/kg), and power density (30.9 kW/kg) in the case of KBa0.5Sr0.5Cr2(PO4)3, proving them as good candidates for positive and/or negative electrode materials for energy storage applications

Author Correction: Photo-supercapacitors based on nanoscaled ZnO (Scientific Reports, (2022), 12, 1, (11487), 10.1038/s41598-022-15180-z)

Correction to: Scientific Reports, published online 07 July 2022 The original version of this Article contained an error in the Acknowledgements section. “I.I. acknowledges the partial financial support from the SONATA BIS project 2020/38/E/ST5/00176.” now reads: “I.I. was partly funded by the NCN SONATA-BIS Program (UMO-2020/38/E/ST5/00176).” The original Article has been corrected