Tuning the morphology, stability and optical properties of CsSnBr3 nanocrystals through bismuth doping for visible-light-driven applications.

In this investigation, we have demonstrated the synthesis of lead-free CsSnBr3 (CSB) and 5 mol% bismuth (Bi) doped CSB (CSB'B) nanocrystals, with a stable cubic perovskite structure following a facile hot injection technique. The Bi substitution in CSB was found to play a vital role in reducing the size of the nanocrystals significantly, from 316 ± 93 to 87 ± 22 nm. Additionally, Bi doping has inhibited the oxidation of Sn2+ of CSB perovskite. A reduction in the optical band gap from 1.89 to 1.73 eV was observed for CSB'B and the PL intensity was quenched due to the introduction of the Bi3+ dopant. To demonstrate one of the visible-light-driven applications of the nanocrystals, photodegradation experiments were carried out as a test case. Interestingly, under UV-vis irradiation, the degradation efficiency of CSB'B was roughly one order lower than that of P25 titania nanoparticles; however, it was almost five times higher when driven by visible light under identical conditions. The water stability of CSB'B perovskite and suppression of the oxidative degradation of Sn were confirmed through XRD and XPS analyses after photocatalysis. Moreover, by employing experimental parameters, DFT-based first-principles calculations were performed, which demonstrated an excellent qualitative agreement between experimental and theoretical outcomes. The as-synthesized Bi-doped CSB might be a stable halide perovskite with potential in visible-light-driven applications.

Structural, magnetic and optical properties of disordered double perovskite Gd2CoCrO6 nanoparticles.

We have synthesized disordered double perovskite Gd2CoCrO6 (GCCO) nanoparticles with an average particle size of 71 ± 3 nm by adopting a citrate sol-gel method to investigate their structural, magnetic, and optical properties. Rietveld refinement of the X-ray diffraction pattern showed that GCCO is crystallized in a monoclinic structure with space group P21/n, which is further confirmed by Raman spectroscopic analysis. The absence of perfect long-range ordering between Co and Cr ions is confirmed by the mixed valence states of Co and Cr. A Néel transition was observed at a higher temperature of TN = 105 K compared to that of an analogous double perovskite Gd2FeCrO6 due to a greater degree of magnetocrystalline anisotropy of Co than Fe. Magnetization reversal (MR) behavior with a compensation temperature of Tcomp = 30 K was also observed. The hysteresis loop obtained at 5 K exhibited the presence of both ferromagnetic (FM) and antiferromagnetic (AFM) domains. Super-exchange and Dzyaloshinskii-Moriya (DM) interactions between various cations via oxygen ligands are responsible for the observed FM or AFM ordering in the system. Furthermore, UV-visible and photoluminescence spectroscopy demonstrated the semiconducting nature of GCCO with a direct optical bandgap of 2.25 eV. The Mulliken electronegativity approach revealed the potential applicability of GCCO nanoparticles in photocatalytic H2 and O2 evolution from water. Due to a favorable bandgap and potentiality as a photocatalyst, GCCO can be a promising new member of double perovskite materials for photocatalytic and related solar energy applications.

Simple Low Temperature Technique to Synthesize Sillenite Bismuth Ferrite with Promising Photocatalytic Performance.

Sillenite-type members of the bismuth ferrite family have demonstrated outstanding potential as novel photocatalysts in environmental remediation such as organic pollutant degradation. This investigation has developed a low temperature one-step hydrothermal technique to fabricate sillenite bismuth ferrite Bi25FeO40 (S-BFO) via co-substitution of 10% Gd and 10% Cr in Bi and Fe sites of BiFeO3, respectively, by tuning hydrothermal reaction temperatures. Rietveld refined X-ray diffraction patterns of the as-synthesized powder materials revealed the formation of S-BFO at a reaction temperature of 120-160 °C. A further increase in the reaction temperature destroyed the desired sillenite structure. With the increase in the reaction temperature from 120 to 160 °C, the morphology of S-BFO gradually changed from irregular shape to spherical powder nanomaterials. The high-resolution TEM imaging demonstrated the polycrystalline nature of the S-BFO(160) nanopowders synthesized at 160 °C. The as-synthesized samples exhibited considerably high absorbance in the visible region of the solar spectrum, with the lowest band gap of 1.76 eV for the sample S-BFO(160). Interestingly, S-BFO(160) exhibited the highest photocatalytic performance under solar irradiation, toward the degradation of rhodamine B and methylene blue dyes owing to homogeneous phase distribution, regular powder-like morphology, lowest band gap, and quenching of electron-hole pair recombination. The photodegradation of a colorless organic pollutant (ciprofloxacin) was also examined to ensure that the degradation is photocatalytic and not dye-sensitized. In summary, Gd and Cr co-doping have proven to be a compelling energy-saving and low-cost approach for the formulation of sillenite-phase bismuth ferrite with promising photocatalytic activity.

A first-principles study on the phase stability and physical properties of a B-site ordered Nd2CrFeO6 double perovskite.

Here, the first-principles predictions on the structural stability, magnetic behavior and electronic structure of B-site ordered double perovskite Nd2CrFeO6 have been reported. Initially, the ground state of the parent single perovskites NdCrO3 and NdFeO3 has been studied to determine the relevant Hubbard U parameter to investigate the properties of Nd2CrFeO6. The thermodynamic, mechanical, and dynamic stability analyses suggest the possibility of the synthesis of the Nd2CrFeO6 double perovskite at ambient pressure. The compound shows a ferrimagnetic nature with 2 µB net magnetic moment and the magnetic ordering temperature has been estimated to be ∼265 K. The electronic structure indicates a higher probability of direct photon transition over the indirect transition with a band gap of ∼1.85 eV. Additional effects of Nd (4f) spin and spin-orbit coupling on the band edges have been found to be negligible for this 4f-3d-3d spin system. This first-principles investigation predicts that due to the ferrimagnetic nature and a significantly lower band gap compared to those of its antiferromagnetic parent single perovskites, the B-site ordered Nd2CrFeO6 double perovskite could be a promising material for spintronic and visible-light driven energy applications.

Lead-free CsSnCl3 perovskite nanocrystals: rapid synthesis, experimental characterization and DFT simulations.

Lead-free metal halide perovskites have attracted great attention as light harvesters due to their promising optoelectronic and photovoltaic properties. In this investigation, we have successfully synthesized thermally stable cubic phase cesium tin chloride (CsSnCl3) perovskite nanocrystals with improved surface morphology by adopting a rapid hot-injection technique. The excellent crystalline quality of these cubic shaped nanocrystals was confirmed by high-resolution transmission electron microscopy imaging. The binding of organic ligands on the surface of the sample was identified and characterized using nuclear magnetic resonance spectroscopy. UV-visible spectroscopy confirmed that the CsSnCl3 nanocrystals have a direct band gap of ∼2.98 eV, which was further confirmed using steady-state photoluminescence spectroscopy. The band edge positions calculated using the Mulliken electronegativity approach predicted the potential photocatalytic capability of the as-prepared nanocrystals, which was then experimentally corroborated through the photodegradation of rhodamine-B dye under both visible and UV-visible irradiation. Our theoretical calculations employing experimentally obtained structural parameters within the generalized gradient approximation (GGA) and GGA+U methods demonstrated a 90% accurate estimation of the experimentally observed optical band gap when Ueff = 6 eV was considered. The ratio of the effective mass of the hole and electron expressed as was also calculated for Ueff = 6 eV. Based on this theoretical calculation and experimental observation of the photocatalytic performance of CsSnCl3 nanocrystals, we have proposed a rational interpretation of the "D" value. We think that a "D" value of either much smaller or much larger than 1 is an indication of the low recombination rate of the photogenerated electron-hole pairs and the high photocatalytic efficiency of the photocatalyst. We believe that this comprehensive investigation might be helpful for the large-scale synthesis of thermally stable cubic CsSnCl3 nanocrystals and also for a greater understanding of their potential in photocatalytic, photovoltaic and other prominent optoelectronic applications.

MoS2 nanosheet incorporated α-Fe2O3/ZnO nanocomposite with enhanced photocatalytic dye degradation and hydrogen production ability.

We have synthesized MoS2 incorporated α-Fe2O3/ZnO nanocomposites by adapting a facile hydrothermal synthesis process. The effect of incorporating ultrasonically exfoliated few-layer MoS2 nanosheets on the solar-light driven photocatalytic performance of α-Fe2O3/ZnO photocatalyst nanocomposites has been demonstrated. Structural, morphological and optical characteristics of the as-synthesized nanomaterials are comprehensively investigated and analyzed by performing Rietveld refinement of powder X-ray diffraction patterns, field emission scanning electron microscopy and UV-visible spectroscopy, respectively. The photoluminescence spectra of the as-prepared nanocomposites elucidate that the recombination of photogenerated electron-hole pairs is highly suppressed due to incorporation of MoS2 nanosheets. Notably, the ultrasonicated MoS2 incorporated α-Fe2O3/ZnO nanocomposite manifests 91% and 83% efficiency in degradation of rhodamine B dye and antibiotic ciprofloxacin respectively under solar illumination. Active species trapping experiments reveal that the hydroxyl (˙OH) radicals play a significant role in RhB degradation. Likewise the dye degradation efficiency, the amount of hydrogen produced by this nanocomposite via photocatalytic water splitting is also considerably higher as compared to both non-ultrasonicated MoS2 incorporated α-Fe2O3/ZnO and α-Fe2O3/ZnO nanocomposites as well as Degussa P25 titania nanoparticles. This indicates the promising potential of the incorporation of ultrasonicated MoS2 with α-Fe2O3/ZnO nanocomposites for the generation of carbon-free hydrogen by water splitting. The substantial increase in the photocatalytic efficiency of α-Fe2O3/ZnO after incorporation of ultrasonicated MoS2 can be attributed to its favorable band structure, large surface to volume ratio, effective segregation and migration of photogenerated electron-hole pairs at the interface of heterojunctions and the plethora of exposed active edge sites provided by the few-layer MoS2 nanosheets.

Enhanced photocatalytic dye degradation and hydrogen production ability of Bi25FeO40-rGO nanocomposite and mechanism insight.

A comprehensive comparison between BiFeO3-reduced graphene oxide (rGO) nanocomposite and Bi25FeO40-rGO nanocomposite has been performed to investigate their photocatalytic abilities in degradation of Rhodamine B dye and generation of hydrogen by water-splitting. The hydrothermal technique adapted for synthesis of the nanocomposites provides a versatile temperature-controlled phase selection between perovskite BiFeO3 and sillenite Bi25FeO40. Both perovskite and sillenite structured nanocomposites are stable and exhibit considerably higher photocatalytic ability over pure BiFeO3 nanoparticles and commercially available Degussa P25 titania. Notably, Bi25FeO40-rGO nanocomposite has demonstrated superior photocatalytic ability and stability under visible light irradiation than that of BiFeO3-rGO nanocomposite. The possible mechanism behind the superior photocatalytic performance of Bi25FeO40-rGO nanocomposite has been critically discussed.

Sol-gel synthesis of DyCrO3 and 10% Fe-doped DyCrO3 nanoparticles with enhanced photocatalytic hydrogen production abilities.

DyCrO3 and 10% Fe-doped DyCrO3 nanoparticles have been synthesized using a sol-gel method to investigate their performance in photocatalytic hydrogen production from water. The synthesized nanoparticles have been characterized by performing X-ray diffraction, energy dispersive X-ray spectroscopy and UV-visible spectrophotometric measurements. In addition, field emission scanning electron microscopy has been performed to observe their size and shape. The Fe-doped DyCrO3 nanoparticles show a significantly smaller band gap of 2.45 eV compared to the band gap of 2.82 eV shown by the DyCrO3 nanoparticles. The Fe-doped DyCrO3 nanoparticles show better photocatalytic activity in the degradation of rhodamine B (RhB) compared to the photocatalytic activity shown by both the DyCrO3 and Degussa P25 titania nanoparticles. The recycling and reuse of Fe-doped DyCrO3 four times for the photo-degradation of RhB shows that Fe-doped DyCrO3 is a stable and reusable photocatalyst. To evaluate the extent of the photocatalytic hydrogen production ability of the synthesized nanoparticles, a theoretical model has been developed to determine their "absorptance", a measure of the ability to absorb photons. Finally, 10% Fe-doped DyCrO3 proves itself to be an efficient photocatalyst as it demonstrated three times greater hydrogen production than Degussa P25.

Low temperature synthesis of BiFeO3 nanoparticles with enhanced magnetization and promising photocatalytic performance in dye degradation and hydrogen evolution.

In this investigation, we have synthesized BiFeO3 nanoparticles by varying hydrothermal reaction temperatures from 200 °C to 120 °C to assess their visible-light driven photocatalytic activity along with their applicability for hydrogen production via water splitting. The rhombohedral perovskite structure of BiFeO3 is formed for hydrothermal reaction temperature up to 160 °C. However, for a further decrement of hydrothermal reaction temperature a mixed sillenite phase is observed. The XRD Rietveld analysis, XPS analysis and FESEM imaging ensure the formation of single-phase and well crystalline nanoparticles at 160 °C reaction temperature with 20 nm of average size. The nanoparticles fabricated at this particular reaction temperature also exhibit improved magnetization, reduced leakage current density and excellent ferroelectric behavior. These nanoparticles demonstrate considerably high absorbance in the visible range with a low band gap (2.1 eV). The experimentally observed band gap is in excellent agreement with the calculated band gap using first-principles calculations. The favorable photocatalytic performance of these nanoparticles has been able to generate more than two times of solar hydrogen compared to that produced by bulk BiFeO3 as well as commercially available Degussa P25 titania. Notably, the experimentally observed band gap is almost equal for both bulk material and nanoparticles prepared at different reaction temperatures. Therefore, in solar energy applications, the superiority of BiFeO3 nanoparticles prepared at 160 °C reaction temperature may be attributed not only to their band gap but also to other factors, such as reduced particle size, excellent morphology, good crystallinity, large surface to volume ratio, ferroelectricity and so on.

Magneto-structural coupling in [Formula: see text].

[Formula: see text] compound is well Known to show the frustration of the spin structure. At 12 K, [Formula: see text] distorts to break symmetry of the degenerated frustrated spin states by the spin-Peierls-like phase transition, accompanying with the antiferromagnetic ordering. On the other hand, [Formula: see text] undergoes a Jahn-Teller phase transition at a temperature of 310 K, differing from the low temperature ferrimagnetic transition temperature [Formula: see text] of about 60 K. It is also reported that [Formula: see text] shows another magnetic phase transition at about 30 K. These two phase transitions accompanying with the lattice change can be understood by the magneto-elastic interactions. Two interactions, the Jahn-Teller interaction and the spin-Peierls-like interaction are co-exist in [Formula: see text] system. In this report the [Formula: see text] compounds with x = 0.8, 0.6 and 1 are investigated by the X-ray diffraction measurements. From these measurements the crystal structures are determined. The full width at half maximum and integrated intensity give the fruitful information for magnetic elastic interactions.

Simple top-down preparation of magnetic Bi0.9Gd0.1Fe1-xTixO3 nanoparticles by ultrasonication of multiferroic bulk material.

We present a simple technique to synthesize ultrafine nanoparticles directly from bulk multiferroic perovskite powder. The starting materials, which were ceramic pellets of the nominal compositions Bi0.9Gd0.1Fe1-xTixO3 (x = 0.00-0.20), were prepared initially by a solid state reaction technique, then ground into micrometer-sized powders and mixed with isopropanol or water in an ultrasonic bath. The particle size was studied as a function of sonication time with transmission electron microscopic imaging and electron diffraction that confirmed the formation of a large fraction of single-crystalline nanoparticles with a mean size of 11-13 nm. A significant improvement in the magnetic behavior of Bi0.9Gd0.1Fe1-xTixO3 nanoparticles compared to their bulk counterparts was observed at room temperature. This sonication technique may be considered as a simple and promising route to prepare ultrafine nanoparticles for functional applications.