Assessing phase discrimination via the segmentation of an elemental energy dispersive X-ray spectroscopy map: a case study of Bi2Te3 and Bi2Te2S

The present case study critically assesses the efficacy of a previously proposed segmentation methodology as a means to discriminate phases via post-processing the image of an elemental map. In the Bi₂Te_2.5S_0.5 multiphase compound, the reference spectra of the Bi₂Te₃ and Bi₂Te₂S phases are distinct enough to effectively distinguish two phases during map acquisition. Since the counts of the sulphur-K peak in the X-ray emission data are significantly higher for Bi₂Te₂S compared to Bi₂Te₃, the segmentation methodology exploits this variation and enables successful phase discrimination via post-processing the image of the elemental map.

The present case study critically assesses the efficacy of a previously proposed segmentation methodology as a means to discriminate phases via post-processing the image of an elemental map.     

The synthesis of a Bi2MoO6/Bi4V2O11 heterojunction photocatalyst with enhanced visible-light-driven photocatalytic activity

A novel Bi₂MoO₆/Bi₄V₂O₁₁ heterostructured photocatalyst was successfully fabricated using a facile one-pot solvothermal method. This heterojunction consists of homogeneous dispersed Bi₄V₂O₁₁ nanocrystals anchored on the surface of Bi₂MoO₆ nanoflakes, endowing the heterojunction with nanosized interfacial contact. Based on the favorable interfacial contact, the band alignment at the heterojunction effectively facilitated photo-generated carrier transfer, which was verified by photoelectrochemical and photoluminescence measurements. Thereby, in contrast with pristine Bi₂MoO₆ and Bi₄V₂O₁₁, the as-synthesized heterojunction with nanoscale contact exhibited significantly enhanced photocatalytic activity towards the degradation of MB and the reduction of Cr(vi). In addition, the as-fabricated Bi₂MoO₆/Bi₄V₂O₁₁ heterojunction exhibited good cycling stability for MB degradation after 4 cycles. Finally, a plausible photocatalytic mechanism for MB degradation over the Bi₂MoO₆/Bi₄V₂O₁₁ heterojunction was discussed in detail. This work not only reports a highly efficient photocatalyst but also sheds light on the design and optimization of a heterojunction.

A Bi₂MoO₆/Bi₄V₂O₁₁ heterojunction exhibits remarkably enhanced photocatalytic activity for MB degradation and Cr(vi) reduction under visible-light illumination compared to its pristine samples.     

Enhancing the thermoelectric power factor of nanostructured ZnCo2O4 by Bi substitution

Bi_xZnCo_2−xO₄ (0 ≤ x ≤ 0.2) nanoparticles with different x values have been prepared by the sol–gel method; the structural, morphological, thermal and thermoelectric properties of the prepared nanomaterials are investigated. XRD analysis confirms that Bi is completely dissolved in the ZnCo₂O₄ lattice till the x values of ≤0.1 and the secondary phase of Bi₂O₃ is formed at higher x value (x > 0.1). The synthesized nanomaterials are densified and the thermoelectric properties are studied as a function of temperature. The electrical resistivity of the Bi_xZnCo_2−xO₄ decreased with x value and it fell to 4 × 10⁻² Ω m for the sample with x value ≤ 0.1. The Seebeck coefficient value increased with the increase of Bi substitution till the x value of 0.1 and decreased for the sample with higher Bi content (x ≤ 0.2) as the resistivity of the sample increased due to secondary phase formation. With the optimum Seebeck coefficient and electrical resistivity, Bi_0.1ZnCo_1.9O₄ shows the high-power factor (α²σ_{550 K}) of 2.3 μW K⁻² m⁻¹ and figure of merit of 9.5 × 10⁻⁴ at 668 K respectively, compared with other samples. The experimental results reveal that Bi substitution at the Co site is a promising approach to improve the thermoelectric properties of ZnCo₂O₄.

Nanostructuring and Bi substitution have considerably increased the thermoelectric power factor and ZT of Bi_xZnCo_2−xO₄; Bi_1.9ZnCo_1.9O₄ shows a higher power factor than that of other Bi substituted samples.     

Bi2Te3 single crystals with high room-temperature thermoelectric performance enhanced by manipulating point defects based on first-principles calculation

Intrinsic Bi₂Te₃ is a representative thermoelectric (TE) material with high performance at low temperature, which enables applications for electronic cooling. However, antisite defects easily form in p-type Bi₂Te₃, resulting in the difficulty of further property enhancement. In this work, the formation energy of native point defects in Bi₂Te₃ supercells and the electronic structure of Bi₂Te₃ primitive unit cell were calculated using first-principles. The antisite defect Bi_Te₁ has a lower formation energy (0.68 eV) under the Te-lack condition for p-type Bi₂Te₃. The effects of point defects on TE properties were investigated via a series of p-type Bi₂Te_3−x (x = 0, 0.02, 0.04, 0.06, 0.08) single crystals prepared by the temperature gradient growth method (TGGM). Apart from the increased power factor (PF_∥) which originates from the increased carrier concentration (n_∥) and m*, the thermal conductivity (κ_∥) was also cut down by the increased point defects. Benefitting from the high PF_∥ of 4.09 mW m⁻¹ K⁻² and the low κ_∥ of 1.77 W m⁻¹ K⁻¹, the highest ZT_∥ of 0.70 was obtained for x = 0.06 composition at 300 K, which is 30% higher than that (0.54) of the intrinsic Bi₂Te₃.

This study prepared Bi₂Te₃ single crystals and investigated the thermoelectric properties of Bi₂Te₃ based on the electronic structure and formation energy of point defects which are calculated by density functional theory.     

Synthesis,structure, and electronic properties of the Li11RbGd4Te6O30 single crystal

Materials with spin dimers have attracted much attention in the last several decades because they could provide a playground to embody simple quantum spin models. For example, the Bose–Einstein condensation of magnons has been observed in TlCuCl₃ with anti-ferromagnetic Cu₂Cl₆ dimers. In this work, we have synthesized a new kind of single-crystal Li₁₁RbGd₄Te₆O₃₀ with Gd₂O₁₅ dimers. This material belongs to the rhombohedral system with the lattice parameters: a = b = c = 16.0948 Å and α = β = γ = 33.74°. First-principles calculations indicate that Li₁₁RbGd₄Te₆O₃₀ is a wide-bandgap (about 4.5 eV) semiconductor. But unlike many other well studied quantum dimer magnets with an anti-ferromagnetic ground state, the Gd₂O₁₄ dimers in Li₁₁RbGd₄Te₆O₃₀ show ferromagnetic intra-dimer exchange interactions according to our calculations. Our work provides a new material which could possibly extend the studies of the spin dimers.

The prime novelty of this research is the synthesis and theory analyses of a new kind of single crystal compound Li₁₁RbGd₄Te₆O₃₀ with Gd₂O₁₅ dimers.     

Infrared and Raman spectra of Bi2O2X and Bi2OX2 (X = S,Se, and Te) studied from first principles calculations

The bismuth oxychalcogenide compounds contain many different kinds of materials, such as Bi₂O₂X and Bi₂OX₂ (X = S, Se, and Te). These materials have different but similar layered crystal structures and exhibit various interesting physical properties. Here, we have theoretically investigated their Raman and infrared spectra by first principles calculations based on density functional theory. It is found that in Bi₂O₂Se the calculated frequency of the A_1g Raman active mode is in good agreement with the experimental measurements while the other three modes are ambiguous or not observed yet. The Raman and infrared spectra of other materials are also presented and need further confirmation. Our work provides the structural fingerprints of these materials, which could be helpful in identifying the crystal structures in future experiments.

Crystal structures of bismuth oxychalcogenide compounds Bi₂O₂X and Bi₂OX₂ (X = S, Se, and Te).     

Asymmetric faradaic assembly of Bi2O3 and MnO2 for a high-performance hybrid electrochemical energy storage device

In the current study, we have explored the coupling of Bi₂O₃ negative electrode and MnO₂ positive electrode materials as an asymmetric faradaic assembly for a high-performance hybrid electrochemical energy storage device (HEESD). Aiming at a low-cost device, both the electrodes have been synthesized by a simple, scalable, and cost-effective chemical synthesis method. After their requisite structure-morphological confirmation and correlation, these electrodes were separately examined for their electrochemical performance in a three-electrode configuration. The results obtained confirm that Bi₂O₃ and MnO₂ exhibit 910 C g⁻¹ and 424 C g⁻¹ specific capacity, respectively, at 2 A g⁻¹ current density. Notably, the performance of both electrodes has been analyzed using Dunn''s method to highlight the distinct nature of their faradaic properties. Afterwards, the asymmetric faradaic assembly of both electrodes, when assembled as a HEESD (MnO₂//Bi₂O₃), delivered 411 C g⁻¹ specific capacity at 1 A g⁻¹ current density due to the inclusive contribution from the capacitive as well as the non-capacitive faradaic quotient. Consequently, the assembly offers an excellent energy density of 79 W h kg⁻¹ at a power density of 702 W kg⁻¹, with a magnificent retention of energy density up to 21.1 W h kg⁻¹ at 14 339 W kg⁻¹ power density. Moreover, it demonstrates long-term cycling stability at 10 A g⁻¹, retaining 85.2% of its initial energy density after 5000 cycles, which is significant in comparison with the previously reported literature. Additionally, to check the performance of the device in real time, two HEESDs were connected in series to power a light-emitting diode. The results obtained provide significant insight into hybrid coupling, where two different faradaic electrodes can be combined in a synergistic combination for a high-performance HEESD.

A hybrid electrochemical energy storage device assembled with faradaic Bi₂O₃ and MnO₂ electrodes exhibits superior electrochemical performance with a high energy density of 79 W h kg⁻¹ at a power density of 702 W kg⁻¹.     

The effects of Bi2O3 on the selective catalytic reduction of NO by propylene over Co3O4 nanoplates

Bi₂O₃/Co₃O₄ catalysts prepared by the impregnation method were investigated for the selective catalytic reduction of NO by C₃H₆ (C₃H₆-SCR) in the presence of O₂. Their physicochemical properties were analyzed with SEM, XRD, H₂-TPR, XPS, PL and IR measurements. It was found that the deposition of Bi₂O₃ on Co₃O₄ nanoplates enhanced the catalytic activity, especially at low reaction temperature. The SO₂ tolerance of Co₃O₄ in C₃H₆-SCR activity was also improved with the addition of Bi₂O₃. Among all catalysts tested, 10.0 wt% Bi₂O₃/Co₃O₄ achieved a 90% NO conversion at 200 °C with the total flow rate of 200 mL min⁻¹ (GHSV 30 000 h⁻¹). No loss in its C₃H₆-SCR activity was observed at different temperatures after the addition of 100 ppm of SO₂ to the reaction mixture. These enhanced catalytic behaviors may be associated with the improved oxidizing characteristics of 10.0 wt% Bi₂O₃/Co₃O₂. XRD results showed that Bi₂O₃ entered the lattice of Co₃O₄, resulting in the formation of lattice distortion and structural defects. H₂-TPR results showed that the reduction of Co₃O₄ was promoted and the diffusion of oxygen was accelerated with the addition of Bi₂O₃. XPS measurements implied that more Co³⁺ formed on the 10.0% Bi₂O₃/Co₃O₂ catalysts. The improved oxidizing characteristics of the catalyst with the addition of Bi₂O₃ due to the synergistic effect of the nanostructure hybrid, thus enhanced the C₃H₆-SCR reaction and hindered the oxidization of SO₂. Therefore, the 10.0% Bi₂O₃/Co₃O₄ catalyst exhibited the highest NO conversion and strongest SO₂ tolerance ability.

Bi₂O₃/Co₃O₄ catalysts prepared by the impregnation method were investigated for the selective catalytic reduction of NO by C₃H₆ (C₃H₆-SCR) in the presence of O₂.     

Multifunctional property exploration: Bi4O5I2 with high visible light photocatalytic performance and a large nonlinear optical effect

Exploration of the versatility of materials is very important for increasing the utilization of materials. Herein, we successfully prepared Bi₄O₅I₂ powders via a facile solvothermal method. The Bi₄O₅I₂ photocatalyst exhibited significantly higher photocatalytic activity as compared to the common BiOI photocatalyst in the degradation of methyl orange, methylene blue and rhodamine B under visible light irradiation. Especially, for the degradation of methyl orange, the photocatalytic activity of Bi₄O₅I₂ is about 10 times that of BiOI. Moreover, Bi₄O₅I₂ exhibits an extremely high second harmonic generation response of about 20 × KDP (the benchmark) estimated by the unbiased ab initio calculations. The coexisting multifunction of Bi₄O₅I₂ is mainly because of the increased dipole moment due to the stereochemical activity of lone pairs that promotes separation and transfer of photogenerated carriers, then enhances the photocatalytic activity and results in a high second harmonic generation response. This indicates that Bi₄O₅I₂ may have good potential applications in photocatalytic and nonlinear optical fields.

Bi₄O₅I₂ exhibits an extremely high second harmonic generation response and enhanced photocatalytic activity. The multifunction of Bi₄O₅I₂ is mainly resulting from the dipole moment of the stereochemical activity of Bi 6s lone pairs.     

Insights into the photocatalytic performance of Bi2O2CO3/BiVO4 heterostructures prepared by one-step hydrothermal method

This paper describes the synthesis of Bi₂O₂CO₃/BiVO₄ heterostructures through a one-step method based on the difference in solubility between two semiconductors that possess a metal in common. The as-synthesized Bi₂O₂CO₃/BiVO₄ heterostructures were characterized by X-ray diffraction (XRD), thermogravimetric analysis (TGA), Raman spectroscopy, ultraviolet-visible diffuse reflectance spectroscopy (UV-vis DRS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N₂ physisorption, X-ray photoelectron spectroscopy (XPS) and time resolved photoluminescence spectroscopy (TRPL). The role of the heterojunction formed was evaluated by methylene blue (MB) dye and amiloride photodegradation. The formation of the heterostructure was observed indirectly by the great increase in the thermal stability of the Bi₂O₂CO₃ phase when compared to its pure phase. The amount of heterojunctions formed between the Bi₂O₂CO₃ and BiVO₄ was tuned by vanadium precursor concentration. The proposed strategy was efficient for obtaining Bi₂O₂CO₃/BiVO₄ heterostructures with enhanced photocatalytic performance when compared to their isolated phases, MB and amiloride photodegradation occurred mainly by the action of ˙OH radicals, i.e. by an indirect mechanism. Based on TRPL spectroscopy and VB-XPS results, an enhancement of photoactivity related to an increase in the spatial separation of photo-generated electron/hole pairs was observed due to the formation of a type-II heterostructure.

A novel visible-driven heterojunction of Bi₂O₂CO₃/BiVO₄ was prepared by an efficient hydrothermal self-sacrificial synthesis method based on the difference in solubility.     

Development of pristine and Au-decorated Bi2O3/Bi2WO6 nanocomposites for supercapacitor electrodes

Pristine and Au-decorated Bi₂O₃/Bi₂WO₆ nanocomposites were synthesized via a facile hydrothermal method. Characterization techniques such as XRD, FESEM, HRTEM and XPS were used to explore the structural, morphological and electronic properties. Furthermore, electrochemical characterizations including cyclic voltammetry (CV), the galvanostatic charge–discharge (GCD) method, and electrochemical impedance spectroscopy (EIS) were performed to investigate the supercapacitance behaviour of the synthesized materials. Interestingly, the Au-decorated Bi₂O₃/Bi₂WO₆ nanocomposite showed a higher capacitance of 495.05 F g⁻¹ (1 M aqueous KOH electrolyte) with improved cycling stability (99.26%) over 2000 cycles, measured at a current density of 1 A g⁻¹, when compared to the pristine Bi₂O₃/Bi₂WO₆ composite (capacitance of 148.81 F g⁻¹ and good cycling stability (95.99%) over 2000 cycles at a current density of 1 A g⁻¹). The results clearly reveal that the decoration of the Bi₂O₃/Bi₂WO₆ composite with Au nanoparticles enhances its supercapacitance behaviour, which can be attributed to an increase in electrical conductivity, good electrical contact between the electrode and electrolyte, and an increase in effective area. The Au-decorated Bi₂O₃/Bi₂WO₆ nanocomposite can be considered as an electrode material for supercapacitor application.

Pristine and Au-decorated Bi₂O₃/Bi₂WO₆ nanocomposites were synthesized via a facile hydrothermal method, and find its application in supercapacitor.     

Construction of 2D/2D layered g-C3N4/Bi12O17Cl2 hybrid material with matched energy band structure and its improved photocatalytic performance

A series of visible-light-induced 2D/2D layered g-C₃N₄/Bi₁₂O₁₇Cl₂ composite photocatalysts were successfully synthesized by a one step chemical precipitation method with g-C₃N₄, BiCl₃ and NaOH as the precursors at room temperature and characterized through XRD, FTIR, XPS, TEM, BET and UV-vis DRS measurements. The results of XRD, FTIR and XPS indicated that g-C₃N₄ has been introduced in the Bi₁₂O₁₇Cl₂ system. The TEM image demonstrated that there was strong surface-to-surface contact between 2D g-C₃N₄ layers and Bi₁₂O₁₇Cl₂ nanosheets, which contributed to a fast transfer of the interfacial electrons, leading to a high separation rate of photoinduced charge carriers in the g-C₃N₄/Bi₁₂O₁₇Cl₂ system. Rhodamine B was considered as the model pollutant to investigate the photocatalytic activity of the resultant samples. The g-C₃N₄/Bi₁₂O₁₇Cl₂ composite showed a clearly improved photocatalytic degradation capacity compared to bare g-C₃N₄ and Bi₁₂O₁₇Cl₂, which was ascribed to the interfacial contact between the 2D g-C₃N₄ layers and Bi₁₂O₁₇Cl₂ sheet with a matched energy band structure, promoting the photoinduced charges'' efficient separation. Finally, combined with the results of the trapping experiment, ESR measurements and the band energy analysis, a reasonable photocatalytic mechanism over the 2D/2D layered g-C₃N₄/Bi₁₂O₁₇Cl₂ composite was proposed.

Surface-to-surface contact g-C₃N₄/Bi₁₂O₁₇Cl₂ hybrid material with a matched energy band structure could efficiently transfer photoinduced charges, improving the photocatalytic activity.     

Promoting the photocatalytic activity of Bi4Ti3O12 microspheres by incorporating iron

Small amounts of Fe(NO₃)₃ were added to the synthesis mixture prior to the hydrothermal synthesis of Bi₄Ti₃O₁₂ microspheres. The physicochemical properties of the resulting materials were changed accordingly. The photocatalytic activities of several samples were studied through the photocatalytic degradation of organic pollutants. The samples with a theoretical Fe atomic percentage of 5.9% showed the highest photocatalytic activity among these samples. The main active species in photocatalytic degradation was demonstrated by radical capturing experiments as h⁺. The introduction of a suitable amount of Fe to the photocatalyst can facilitate the separation of electron–hole pairs generated upon light irradiation, inhibit their recombination efficiently, and prominently expand the light absorption region, thus leading to higher photocatalytic activity.

Small amounts of Fe(NO₃)₃ were added to the synthesis mixture prior to the hydrothermal synthesis of Bi₄Ti₃O₁₂ microspheres.     

Enhanced photocatalytic performance of rhodamine B and enrofloxacin by Pt loaded Bi4V2O11: boosted separation of charge carriers,additional superoxide radical production,and the photocatalytic mechanism

Photocatalytic performance is influenced by two contradictory factors, which are light absorption range and separation of charge carriers. Loading noble metals with nanosized interfacial contact is expected to improve the separation and transfer of photo-excited charge carriers while enlarging the light absorption range of the semiconductor photocatalyst. Therefore, it should be possible to improve the photocatalytic performance of pristine nontypical stoichiometric semiconductor photocatalysts by loading a specific noble metal. Herein, a series of novel Pt–Bi₄V₂O₁₁ photocatalysts have been successfully prepared via a surface reduction technique. The crystal structure, morphology, and photocatalytic performance, as well as photo-electron properties of the as-synthesized samples were fully characterized. Moreover, the series of Pt–Bi₄V₂O₁₁ samples were evaluated to remove typical organic pollutants, rhodamine B and enrofloxacin, from aqueous solutions. The photoluminescence, quenching experiments and the electron spin resonance technique were utilized to identify the effective radicals during the photocatalytic process and understand the photocatalytic mechanism. The photocatalytic performance of Pt–Bi₄V₂O₁₁ was tremendously enhanced compared with pristine Bi₄V₂O₁₁, and there was additional ˙O²⁻ produced during the photocatalytic process. This study deeply investigated the relation between the separation of charge carriers and the light harvesting, and revealed a promising strategy for fabricating efficient photocatalysts for both dyes and antibiotics.

The Effect of Pt for producing additional superoxide radicals, and the photocatalytic mechanism.     

Surface morphology smoothing of a 2 inch-diameter GaN homoepitaxial layer observed by X-ray diffraction topography

We investigated the surface morphology changes in a 2 inch-diameter, c-plane, free-standing GaN wafer using X-ray diffraction topography in a grazing-incidence geometry. We observed a decrease in the peak intensity and increase in the full width at half maximum of the GaN 11$\bar{2}$4 Bragg peak after the deposition of a homoepitaxial layer on the same GaN wafer. However, the lattice plane bending angles did not change after homoepitaxial layer deposition. Distorted-wave Born approximation calculations near the total external reflection condition revealed a decrease in the X-ray incidence angle of the 11$\bar{2}$4 Bragg peak after the homoepitaxial layer deposition. The decrease in both X-ray penetration and incidence angle induced broader and weaker diffraction peaks from the surface instead of the bulk GaN.

We investigated the surface morphology changes in a 2 inch-diameter, c-plane, free-standing GaN wafer using X-ray diffraction topography in a grazing-incidence geometry.     

Superconducting properties and non-isothermal crystallization kinetics of a Bi2Sr2CaCu2O8+δ (Bi2212) superconductor prepared by the Pechini sol–gel method

Bi2212 superconductors with crystallization treatments at different temperatures were prepared by the Pechini sol–gel method, and their structural, thermal and transport properties were investigated. The X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) results revealed the high purity and sheet crystal structures of the prepared samples. The non-isothermal crystallization kinetics and process of the Bi2212 superconductor were characterized and analyzed by differential scanning calorimetry (DSC) and Jeziorny and Mo methods, respectively. The results showed that both the Jeziorny and Mo methods were well suitable for describing the non-isothermal crystallization process of the Bi2212 superconductor prepared by the Pechini sol–gel method. The Avrami exponent (n = 2) confirmed the two-dimensional sheet growth mechanism of the Bi2212 superconductor. In addition, the non-isothermal crystallization kinetic parameter Z_c increased with the increase in cooling rate. The crystallization parameter F(T) also increased with the increase in crystallinity, and the F(T) values were calculated to be 4.79 and 42.66 when the crystallinity values were 20% and 90%, respectively, indicating that for the Bi2212 superconductor, it was harder to crystallize at relatively larger crystallinity. Furthermore, the transport properties of the samples were greatly improved after the cooling crystallization process. Sample J3 had the highest onset of the superconducting transition T_(c,onset) of 80.1 K, which was higher than the 73.1 K value determined for sample J0. Also, sample J2 had the best zero resistivity superconducting transition temperature T_(c,zero) value of 70.1 K, which was higher than the value of 63.2 K for sample J0. The maximum calculated J_c value was 7.62 × 10⁴ A cm⁻² at 2 K for sample J2, which was higher than the 4.70 × 10⁴ A cm⁻² value determined for J0.

Bi2212 superconductors with crystallization treatments at different temperatures were prepared by the Pechini sol–gel method, and their structural, thermal and transport properties were investigated.     

One-pot synthesis of CoFe2O4/rGO hybrid hydrogels with 3D networks for high capacity electrochemical energy storage devices

CoFe₂O₄/reduced graphene oxide (CoFe₂O₄/rGO) hydrogel was synthesized in situ via a facile one-pot solvothermal approach. The three-dimensional (3D) network structure consists of well-dispersed CoFe₂O₄ nanoparticles on the surfaces of graphene sheets. As a binder-free electrode material for supercapacitors, the electrochemical properties of the CoFe₂O₄/rGO hybrid hydrogel can be easily adjusted by changing the concentration of the graphene oxide (GO) precursor solution. The results indicate that the hybrid material made using 3.5 mg mL⁻¹ GO solution exhibits an outstanding specific capacitance of 356 F g⁻¹ at 0.5 A g⁻¹, 68% higher than the pure CoFe₂O₄ counterpart (111 F g⁻¹ at 0.5 A g⁻¹), owing to the large specific surface area and good electric conductivity. Additionally, an electrochemical energy storage device based on CoFe₂O₄/rGO and rGO was assembled, which exhibits a high energy density of 17.84 W h kg⁻¹ at a power density of 650 W kg⁻¹ and an excellent cycling stability with 87% capacitance retention at 5 A g⁻¹ after 4000 cycles. This work takes one step further towards the development of 3D hybrid hydrogel supercapacitors and highlights their potential application in energy storage devices.

CoFe₂O₄/reduced graphene oxide (CoFe₂O₄/rGO) hydrogel was synthesized in situ via a facile one-pot solvothermal approach.     

Luminescence properties of ZnGa2O4:Cr3+,Bi3+ nanophosphors for thermometry applications

Chromium(iii) and bismuth(iii) co-doped ZnGa₂O₄ nanoparticles are synthesized by a hydrothermal method assisted by microwave heating. The obtained nanoparticles, with a diameter smaller than 10 nm, present good luminescence emission in the deep red range centered at 695 nm after coating with a silica layer and calcination at 1000 °C during 2 h. Persistent luminescence and photoluminescence properties are investigated at several temperatures. Bandwidth and luminescence intensity ratio of persistent emission do not present enough change with temperature to obtain a competitive nanothermometer with high sensitivity. Nevertheless, persistent luminescence decay curves present a significant shape change since the trap levels involved in the deexcitation mechanism are unfilled with increase of temperature. Even if the sensitivity reaches 1.7% °C⁻¹ at 190 °C, the repeatability is not optimal. Furthermore, photoluminescent lifetime in the millisecond range extracted from the photoluminescence decay profiles drastically decreases with temperature increase. This variation is attributed to the thermal equilibrium between two thermally coupled chromium(iii) levels (²E and ⁴T₂) that have very different deexcitation lifetimes. For ZnGa₂O₄:Cr³⁺_0.5%,Bi³⁺_0.5%, the temperature sensitivity reaches 1.93% °C⁻¹ at 200 °C. Therefore, this kind of nanoparticle is a very promising thermal sensor for temperature determination at the nanoscale.

Luminescence properties of chromium(iii) and bismuth(iii) co-doped ZnGa₂O₄ nanoparticles are investigated for thermometry applications.     

Spinel LiMn2O4 nanoparticles fabricated by the flexible soft template/Pichini method as cathode materials for aqueous lithium-ion capacitors with high energy and power density

Spinel LiMn₂O₄ (LMO) with a three-dimensional structure has become one of the cathode materials that has gained the most interest due to its safety, low price and abundant resources. However, the lithium ion transmission is limited by large particle size and particle agglomeration of LMO. Thus, reducing the particle size and agglomeration of LMO can effectively improve its lithium ion transmission. Here, we synthesized a LMO cathode material with a nanoscale crystal size using the flexible expanded graphite (EG) soft template and Pichini method. EG-controlled particle size and particle agglomeration of LMO is conducive to charge transfer and diffusion of lithium ions between LMO and the electrolyte, meanwhile, there are more redox sites on the nanosized LMO particles, which makes the redox reaction of LMO more thorough during the charge and discharge process, resulting in high capacitance performance. In order to obtain the considerably required lithium-ion capacitors (LICs) with high energy density and power density, we assembled aqueous LMO//activated carbon (AC) LICs with 5 M LiNO₃ as the aqueous electrolytes, which are environmentally friendly, safe, low cost and have higher electrical conductivity than organic electrolytes. The optimal LIC has an energy density of 32.63 W h kg⁻¹ at a power density of 500 W kg⁻¹ and an energy density of 8.06 W h kg⁻¹ at a power density of 10 000 W kg⁻¹, which is higher than most of the LMO-based LICs in previous reports. After 2000 cycles, the specific capacitance retention rate was 75.9% at a current density of 3 A g⁻¹. Therefore, our aqueous LMO//AC LICs synthesized by the soft template/Pichini method have wide prospects and are suitable for low-cost, high-safety and high-power applications.

LiMn₂O₄ nanoparticles were synthesized by flexible Pichini method with expanded graphite as the soft template to effectively control particle size and agglomeration, contributing to high energy/power densities of its aqueous lithium-ion capacitor.     

Synthesis of Bi2O3/g-C3N4 for enhanced photocatalytic CO2 reduction with a Z-scheme mechanism

Bi₂O₃/g-C₃N₄ nanoscale composites with a Z-scheme mechanism were successfully synthesized by high temperature calcination combined with a hydrothermal method. These synthesized composites exhibited excellent photocatalytic performance, especially the 40 wt% Bi₂O₃/g-C₃N₄ composite, which produced about 1.8 times the CO yield of pure g-C₃N₄. The obtained products were characterized by X-ray diffraction (XRD) patterns, X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET), UV-vis diffuse reflectance spectroscopy (UV-vis DRS) and so on. Characterization results revealed that Bi ions had well covered the surface of g-C₃N₄, thus restraining the recombination of electron–hole pairs and resulting in a stronger visible-light response and higher CO yield. In addition, the electron transfer process through the Z-scheme mechanism also promoted the photocatalytic activity.

Bi₂O₃/g-C₃N₄ composites were synthesized and used in photocatalytic reduction of CO₂ with a Z-scheme mechanism.