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In this research work, we reported the synthesis of a spherical-shaped bismuth vanadate (BiVO4) photocatalyst using a cost-effective, simple, chemical hydrothermal method and studied the effect of deposition temperatures on the structural, morphological, optical properties, etc. The XRD result confirmed the monoclinic scheelite phase of BiVO4. An XPS study confirmed the occurrence of Bi, V, and O elements and also found that Bi and V exist in +3 and +5 oxidation states, respectively. SEM micrographs revealed the spherical-shaped morphology of the BiVO4 photocatalyst. Optical investigation showed that the bandgap of the BiVO4 photocatalyst varied between 2.25 and 2.32 eV. The as-synthesized BiVO4 photocatalyst was used to study the photocatalytic degradation of crystal violet (CV) dye under visible light illumination. The photocatalytic degradation experiment showed that the degradation percentage of crystal violet dye using BiVO4 reached 98.21% after 120 min. Mineralization of crystal violet dye was studied using a chemical oxygen demand analysis.

Dirac and Weyl nodal materials can host low-energy relativistic quasiparticles. Under strong magnetic fields, the topological properties of Dirac/Weyl materials can directly be observed through quantum Hall states. However, most Dirac/Weyl nodes generically exist in semimetals without exploitable band gaps due to their accidental band-crossing origin. Here, we report the first experimental observation of Weyl fermions in a semiconductor. Tellurene, the two-dimensional form of tellurium, possesses a chiral crystal structure which induces unconventional Weyl nodes with a hedgehog-like radial spin texture near the conduction band edge. We synthesize high-quality n-type tellurene by a hydrothermal method with subsequent dielectric doping and detect a topologically non-trivial π Berry phase in quantum Hall sequences. Our work expands the spectrum of Weyl matter into semiconductors and offers a new platform to design novel quantum devices by marrying the advantages of topological materials to versatile semiconductors.The accidental band-crossing origin of Weyl nodes paired with the absence of sizeable band gaps hampers the exploitation of low-energy relativistic quasiparticles in Weyl semimetals. In a gate-tunable high-quality tellurene film, quantum Hall measurements unveil a topologically non-trivial π Berry phase caused by unconventional Weyl nodes in these tellurium two-dimensional sheets.

Most chemical experiments are planned by human scientists and therefore are subject to a variety of human cognitive biases 1 , heuristics 2 and social influences 3 . These anthropogenic chemical reaction data are widely used to train machine-learning models 4 that are used to predict organic 5 and inorganic 6 , 7 syntheses. However, it is known that societal biases are encoded in datasets and are perpetuated in machine-learning models 8 . Here we identify as-yet-unacknowledged anthropogenic biases in both the reagent choices and reaction conditions of chemical reaction datasets using a combination of data mining and experiments. We find that the amine choices in the reported crystal structures of hydrothermal synthesis of amine-templated metal oxides 9 follow a power-law distribution in which 17% of amine reactants occur in 79% of reported compounds, consistent with distributions in social influence models 10 – 12 . An analysis of unpublished historical laboratory notebook records shows similarly biased distributions of reaction condition choices. By performing 548 randomly generated experiments, we demonstrate that the popularity of reactants or the choices of reaction conditions are uncorrelated to the success of the reaction. We show that randomly generated experiments better illustrate the range of parameter choices that are compatible with crystal formation. Machine-learning models that we train on a smaller randomized reaction dataset outperform models trained on larger human-selected reaction datasets, demonstrating the importance of identifying and addressing anthropogenic biases in scientific data. Human scientists make unrepresentative chemical reagent and reaction condition choices, and machine-learning algorithms trained on human-selected experiments are less capable of successfully predicting reaction outcomes than those trained on randomly generated experiments.

Hydrogen (H2) sensors are of great significance in hydrogen energy development and hydrogen safety monitoring. However, achieving fast and effective detection of low concentrations of hydrogen is a key problem to be solved in hydrogen sensing. In this work, we combined the excellent gas sensing properties of tin(IV) oxide (SnO2) and zinc oxide (ZnO) with the outstanding electrical properties of reduced graphene oxide (rGO) and prepared palladium (Pd)-doped rGO/ZnO-SnO2 nanocomposites by a hydrothermal method. The crystal structure, structural morphology, and elemental composition of the material were characterized by FE-SEM, TEM, XRD, XPS, Raman spectroscopy, and N2 adsorption–desorption. The results showed that the Pd-doped ZnO-SnO2 composites were successfully synthesized and uniformly coated on the surface of the rGO. The hydrogen gas sensing performance of the sensor prepared in this work was investigated, and the results showed that, compared with the pure Pd-doped ZnO-SnO2 sensor, the Pd-doped rGO/ZnO-SnO2 sensor modified with 3 wt% rGO had better hydrogen (H2)-sensing response of 9.4–100 ppm H2 at 380 °C. In addition, this sensor had extremely low time parameters (the response time and recovery time for 100 ppm H2 at 380 °C were 4 s and 8 s, respectively) and an extremely low detection limit (50 ppb). Moreover, the sensor exhibited outstanding repeatability and restoration. According to the analysis of the sensing mechanism of this nanocomposite, the enhanced sensing performance of the Pd-doped rGO/ZnO-SnO2 sensor is mainly due to the heterostructure of rGO, ZnO, and SnO2, the excellent electrical and physical properties of rGO and the synergy between rGO and Pd.

Graphene oxide (GO) was obtained through modified hummers method, and reduced graphene oxide (rGO) was acquired by employing heat treatment. Various concentrations (2.5, 5, 7.5, and 10 wt. %) of silver (Ag) were incorporated in GO nanosheets by adopting hydrothermal approach. Synthesized Ag decorated rGO photocatalyst Ag/rGO was characterized using X-ray diffraction (XRD) to determine phase purity and crystal structure. XRD patterns showed the formation of GO to Ag/rGO. Molecular vibration and functional groups were determined through Fourier Transform Infrared spectroscopy (FTIR). Optical properties and a decrease in bandgap with insertion of Ag were confirmed with UV-Visible (Uv-Vis) spectrophotometer and photoluminescence (PL). Electronic properties and disorders in carbon structures were investigated through Raman spectroscopy that revealed the existence of characteristic bands (D and G). Surface morphology of prepared samples was examined with field emission scanning electron microscope (FESEM). Homogeneous distribution, size, and spherical shape of Ag NPs over rGO sheets were further confirmed with the help of high-resolution transmission electron microscope (HR-TEM). Dye degradation of doped and undoped samples was examined through Uv-Vis spectra. Experimental results indicated that photocatalytic activity of Ag@rGO enhanced with increased doping ratio owing to diminished electron-hole pair recombination. Therefore, it is suggested that Ag@rGO can be used as a beneficial and superior photocatalyst to clean environment and wastewater.

Ethane oxidative dehydrogenation (ODH) is an alternative route for ethene production. Crystalline M1 phase of Mo-V mixed metal oxide is an excellent catalyst for this reaction. Here we show a hydrothermal synthesis method that generates M1 phases with high surface areas starting from poorly soluble metal oxides. Use of organic additives allows control of the concentration of metals in aqueous suspension. Reactions leading to crystalline M1 take place at 190 °C, i.e., approximately 400 °C lower than under current synthesis conditions. The evolution of solvated polyoxometalate ions and crystalline phases in the solid is monitored by spectroscopies. Catalysts prepared by this route show higher ODH activity compared to conventionally prepared catalysts. The higher activity is due not only to the high specific surface area but also to the corrugated lateral termination of the M1 crystals, as seen by atomic resolution electron microscopy, exposing a high concentration of catalytically active sites. Crystalline M1 phase of Mo-V-Te-Nb mixed oxide is an excellent catalyst for ethane oxidative dehydrogenation to ethene. Here, the authors show a method that synthesizes highly active materials by generating M1 crystals with corrugated terminations, thus exposing a large concentration of active sites.

Room temperature ferromagnetic ZnO thin magnetic semiconductor material can solve the problems of large electronic component volume and low integration density in traditional semiconductors. In this paper, direct and precipitation methods were used for the hydrothermal synthesis of Zn 1-x Mn x O (x = 0.05) crystals. The hydrothermal reaction conditions were 1 mol/L KOH or NaOH as mineralizers, and the reaction time was 24 hours at 180 °C. XRD measured the phase in the crystal and confirmed that Mn ions can be doped in ZnO, but the doping amount is limited. SEM displays the morphology of crystals, and the morphology of doped crystals synthesized under different processes varies. NaOH is more suitable as a mineralizer for Mn-doped ZnO than KOH. The powder distribution obtained by the direct precipitation method is more uniform and the dispersion is better than that obtained by a direct method, indicating that the direct precipitation method is more suitable as a precursor preparation method for Mn-doped ZnO.

Octahedral nickel ferrite oxide (NiFe 2 O 4 ) nanocrystals with average sizes of 81, 69, 63 and 46 nm were fabricated using hexamethylenetetramine as adscititious alkali via a facile hydrothermal route at various temperatures. The formation mechanism of octahedral nickel ferrite oxide nanocrystals was discussed in detail. Interestingly, the nanocrystalline size decreased with the increase in the hydrothermal reaction temperature. We studied the influence of hydrothermal temperatures on the evolution of the nanocrystalline and analyzed the relationship between the sizes of the nanocrystalline and their capacitive properties. Compared to the large-sized counterpart (81, 69 and 63 nm), the small-sized nanocrystals (46 nm) presented a maximum specific capacitance (562.1 F g −1 ) and remarkable cycling stability (80.3% capacity retention after 1500 cycles) at 4 A g −1 . The excellent performance of the NiFe 2 O 4 nanocrystals (46 nm) was mainly attributed to the unique octahedral nanostructures with a small size (fully exposing more electroactive sites and providing more sufficient expressways for rapid charge transfer) and their compositional advantages of nickel and cobalt (multiple oxidation states for redox reactions and relatively desirable electroconductivity). More remarkably, an asymmetric supercapacitor composed of NiFe 2 O 4 (as the positive electrode) and activated carbon (as the negative electrode) displayed an ultrahigh energy density (34.91 Wh kg −1 at 1100 W kg −1 ) and an advanced cycling stability (84.5% capacity retention after 1000 cycles), which suggested that the decreased crystal size played a pivotal role in size-dependent capacitive performance enhancement.

Molybdenum disulfide has been one of the most studied hydrogen evolution catalyst materials in recent years, but its disadvantages, such as poor conductivity, hinder its further development. Here, we employ the common hydrothermal method, followed by an additional solvothermal method to construct an uncommon molybdenum disulfide with two crystal forms of 1T and 2H to improve catalytic properties. The low overpotential (180 mV) and small Tafel slope (88 mV/dec) all indicated that molybdenum disulfide had favorable catalytic performance for hydrogen evolution. Further conjunctions revealed that the improvement of performance was probably related to the structural changes brought about by the 1T phase and the resulting sulfur vacancies, which could be used as a reference for the further application of MoS2.

The hydrothermal method was used to make the anatase phase of TiO 2 nanoparticles, TiO 2 /La 2 O 3 and TiO 2 /Al 2 O 3 composites. FTIR spectroscopy, X-ray diffraction (XRD), UV–Vis absorption spectroscopy and scanning electron microscopy (SEM) were used to investigate the crystal structure, shape, and optical characteristics of TiO 2 , TiO 2 /La 2 O 3 and TiO 2 /Al 2 O 3 nanomaterials. The photocatalytic studies were comparatively analyzed by degrading the textile dyes methylene blue (MB) and crystal violet (CV). The degradation process was carried out in both UV light and visible light irradiation. The efficiency achieved by TiO 2 , TiO 2 /La 2 O 3 and TiO 2 /Al 2 O 3 was 87, 95, 45% and 80, 92, 29%, respectively, for MB and CV dye under UV light while under visible light it is 34, 27, 84%, and 29, 24, 81%, respectively, for MB and CV dye.