Synthesis and Characterization of Monodispersed β‑Ga₂O₃ Nanospheres via Morphology Controlled Ga₄(OH)₁₀SO₄ Precursors

To our best knowledge, monodispersed β-Ga₂O₃ nanospheres were successfully synthesized for first time via morphology-controlled gallium precursors using the forced hydrolysis method, followed by thermal calcination processes. The morphology and particle sizes of the gallium precursors were strongly dependent on the varying (<i>R</i> = SO₄^2–/NO₃^–) concentration ratios. As <i>R</i> decreased, the size of the prepared gallium precursors decreased and morphology was altered from sphere to rod. The synthesized S2 (<i>R</i> = 0.33) consists of uniform and monodispersed amorphous nanospheres with diameters of about 200 nm. The monodispersed β-Ga₂O₃ nanospheres were synthesized using thermal calcination processes at various temperatures ranging from 500 to 1000 °C. Monodispersed β-Ga₂O₃ nanospheres (200 nm) consist of small particles of approximately 10–20 nm with rough surface at 1000 °C for 1 h. The UV (375 nm) and broad blue (400–450 nm) emission indicate recombination via a self-trapped exciton and the defect band emission. Our approach described here is to show the exploration of β-Ga₂O₃ nanospheres as an automatic dispersion, three-dimensional support for fabrication of hierarchical materials, which is potentially important for a broad range of optoelectronic applications

Effect of Cooling Condition on Chemical Vapor Deposition Synthesis of Graphene on Copper Catalyst

Here, we show that chemical vapor deposition growth of graphene on copper foil is strongly affected by the cooling conditions. Variation of cooling conditions such as cooling rate and hydrocarbon concentration in the cooling step has yielded graphene islands with different sizes, density of nuclei, and growth rates. The nucleation site density on Cu substrate is greatly reduced when the fast cooling condition was applied, while continuing methane flow during the cooling step also influences the nucleation and growth rate. Raman spectra indicate that the graphene synthesized under fast cooling condition and methane flow on cool-down exhibit superior quality of graphene. Further studies suggest that careful control of the cooling rate and CH₄ gas flow on the cooling step yield a high quality of graphene

Flexible Thermochromic Window Based on Hybridized VO₂/Graphene

Large-scale integration of vanadium dioxide (VO₂) on mechanically flexible substrates is critical to the realization of flexible smart window films that can respond to environmental temperatures to modulate light transmittance. Until now, the formation of highly crystalline and stoichiometric VO₂ on flexible substrate has not been demonstrated due to the high-temperature condition for VO₂ growth. Here, we demonstrate a VO₂-based thermochromic film with unprecedented mechanical flexibility by employing graphene as a versatile platform for VO₂. The graphene effectively functions as an atomically thin, flexible, yet robust support which enables the formation of stoichiometric VO₂ crystals with temperature-driven phase transition characteristics. The graphene-supported VO₂ was capable of being transferred to a plastic substrate, forming a new type of flexible thermochromic film. The flexible VO₂ films were then integrated into the mock-up house, exhibiting its efficient operation to reduce the in-house temperature under infrared irradiation. These results provide important progress for the fabrication of flexible thermochromic films for energy-saving windows

Facile Synthesis of Hierarchically Structured Bi₂S₃/Bi₂WO₆ Photocatalysts for Highly Efficient Reduction of Cr(VI)

Varied morphologies and compositions of bismuth tungstate nanocomposites have been investigated as promising materials for photocatalytic applications. Among these nanocomposites, hierarchically structured bismuth sulfide (Bi₂S₃)/bismuth tungstate (Bi₂WO₆) hybrids have significant photocatalytic efficiency toward heavy metal ions. To simplify the synthetic procedure for this desirable composite, we developed a robust single-step hydrothermal synthesis for the formation of hierarchically structured heterocatalysts of Bi₂S₃/Bi₂WO₆ with a high yield (>95%). The synthesized heterostructures were characterized by various spectroscopic, microscopic, and surface area analysis techniques, which confirmed the successful incorporation of Bi₂S₃ into the Bi₂WO₆ matrix and were used to optimize pore size for enhanced catalytic activity. The resulting Bi₂S₃/Bi₂WO₆ heterocatalysts were used to remove toxic Cr­(VI) ions via reduction to water insoluble Cr­(III) utilizing visible-light irradiation. We also investigated the role of citric acid as a hole scavenger in the reduction of Cr­(VI) with minimizing the rate of electron–hole recombination during photocatalysis. Likewise, the observed catalytic activity was significantly enhanced under a condition of an appropriate balance between hierarchical structure of catalysts and the amount of hole scavenger

Large-Scale Graphene Micropatterns via Self-Assembly-Mediated Process for Flexible Device Application

We report on a method for the large-scale production of graphene micropatterns by a self-assembly mediated process. The evaporation-induced self-assembly technique was engineered to produce highly ordered graphene patterns on flexible substrates in a simplified and scalable manner. The crossed stripe graphene patterns have been produced over a large area with regions consisting of single- and two-layer graphene. Based on these graphene patterns, flexible graphene-based field effect transistors have been fabricated with an ion-gel gate dielectric, which operates at low voltages of < 2 V with a hole and electron mobility of 214 and 106 cm²/V·s, respectively. The self-assembly approach described here may pave the way for the nonlithographic production of graphene patterns, which is scalable to large areas and compatible with roll-to-roll system

Reduced Graphene Oxide/Mesoporous TiO₂ Nanocomposite Based Perovskite Solar Cells

We report on reduced graphene oxide (rGO)/mesoporous (mp)-TiO₂ nanocomposite based mesostructured perovskite solar cells that show an improved electron transport property owing to the reduced interfacial resistance. The amount of rGO added to the TiO₂ nanoparticles electron transport layer was optimized, and their impacts on film resistivity, electron diffusion, recombination time, and photovoltaic performance were investigated. The rGO/mp-TiO₂ nanocomposite film reduces interfacial resistance when compared to the mp-TiO₂ film, and hence, it improves charge collection efficiency. This effect significantly increases the short circuit current density and open circuit voltage. The rGO/mp-TiO₂ nanocomposite film with an optimal rGO content of 0.4 vol % shows 18% higher photon conversion efficiency compared with the TiO₂ nanoparticles based perovskite solar cells