Hexagonal Crystal Structure Research Articles

Effect of Tb3+ and Ce3+ Co-doping on the Structure and Photoluminescence Properties of Hexagonal Boron Nitride Phosphors.

In the paper, we have successfully prepared hexagonal boron nitride (h-BN:Tb3+, Ce3+) phosphors with melamine as the nitrogen source. The X-ray powder diffraction patterns confirm that the sample possesses a hexagonal crystal structure within the P m2 space group. It is interesting that the co-doping combination of Tb3+ and Ce3+ can markedly enhance the threshold concentration of doped activators within the limited solid solution of h-BN phosphors. Under 302nm excitation, the h-BN:Ce3+ phosphors exhibit broadband blue light emission at 406nm. In h-BN:Tb3+, Ce3+ phosphors, the co-doping of Ce3+ not only ensures high phase purity but also results in strong green light emission. The energy transfer efficiency from Ce3+ to Tb3+ is about 55%. The fluorescence lifetime increases with the increase of Ce3+ and Tb3+ concentration, and the fluorescence lifetime of h-BN:0.025Tb3+, 0.05Ce3+ phosphor reached 2.087ms. Additionally, the h-BN:0.025Tb3+, 0.05Ce3+ phosphor exhibits excellent thermal performance with an activation energy value of 0.2825eV. Moreover, the photoluminescence quantum yield of the sample exceeds 52%. Therefore, the h-BN:Tb3+, Ce3+ samples can be used as green phosphors for solid state lighting and fluorescent labeling.

Binary ZnS–ZnO films as an alternative buffer layer for solar cell applications

In this research, binary ZnS–ZnO films were fabricated by a two-step process, offering an alternative buffer layer solution for photovoltaic solar cell applications. ZnS films were attained through thermal evaporation, after which they were annealed in air at separate temperatures resulting in films containing both ZnS and ZnO phases. Structural, electrical, ellipsometric, optical, and surface properties were examined in detail to elucidate their applicability as a buffer layer in photovoltaic applications. X-ray diffraction patterns revealed that the films exhibit cubic ZnS and hexagonal ZnO crystal structures, wherein crystallite size is augmented with higher annealing temperatures. ZnS films exhibited a needle-shaped surface morphology, as confirmed through atomic force microscopy (AFM) and field emission scanning electron microscopy (FESEM) images. Annealing caused noteworthy modifications on the surfaces of the films. Additionally, absorption spectra denote two distinct absorption regions forming as a result of the annealing process, possibly indicating the emergence of ZnS and ZnO phases. Photoluminescence analyses demonstrate that binary ZnS–ZnO films exhibit greater emission intensities than single-phase ZnS films. Additionally, the annealing process caused the electrical resistivity of films to reduce from 1.28 × 105 to 3.84 × 101 Ω cm. These results suggest that binary ZnS–ZnO films produced via annealing can be considered as promising buffer layers in potential photovoltaic solar cell applications.

Microstructure and thermoelectric properties of as-cast Ag2Te/AgBiTe2 and Ag2Te/Bi2Te3 two-phase alloys

The microstructure and thermoelectric properties of Ag2Te/AgBiTe2/Bi2Te3 eutectic alloys in the Ag-Bi-Te system were investigated in the present study. A self-consistent, thermodynamically optimized database of the Ag-Bi-Te system was developed to explain the microstructural features in the investigated alloys. Samples namely B0 (Bi2Te3 – 0 at.% Ag), B1 (Bi2Te3 – 5 at.% Ag), B2 (Bi2Te3 – 18.35 at.% Ag), B3 (Bi2Te3 – 28.35 at.% Ag), and B4 (Bi2Te3 – 38.35 at.% Ag) were synthesized by flame melting. Scanning electron micrographs of alloys reveal lamellar eutectic structures in which alloys B1 and B2 exhibit two distinct phases, consisting of β-Bi2Te3 and AgBiTe2, whereas alloys B3 and B4 display phase compositions corresponding to Ag2Te and AgBiTe2 phases. The X-ray diffraction reveals that the solidified alloys have hexagonal (AgBiTe2, Bi2Te3) and cubic β-Ag2Te crystal structures. The Scheil cooling calculations of these alloys using the developed thermodynamic database explain the microstructural features of the alloys. Furthermore, the mechanical characteristics of eutectic alloys B1 and B3 demonstrated improved hardness values, measuring 1.1 GPa and 1.2 GPa, respectively. Moreover, the transport characteristics show favourable attributes for thermoelectrics in high-temperature applications. It is important to highlight that all these alloys showcase transport properties that are highly advantageous for thermoelectrics. Notably, alloy B2 distinguishes itself with a remarkable ZT value of 0.42 at 540 K.

Structural and magnetic properties of YNi4-xCoxSi alloys

The transition-metal based alloy system YNi4-xCoxSi shows a second-order ferromagnetic-to-paramagnetic transition near room temperature. Here, the magnetic structure, the magnetocaloric properties and the magnetic anisotropy of YNi4-xCoxSi (x = 0–4) are investigated. For x = 3.5, 3.75 and 4.0 a Curie temperature near room temperature is observed with TC = 250, 283 and 310 K, respectively. In orientated YNi4-xCoxSi powder samples the c axis of the hexagonal crystal structure is found to be the easy magnetic axis, with a large dominant K2 anisotropy constant (K2 >K1 > 0). The magnetic structure and the preferred atomic position for Ni are demonstrated by neutron diffraction measurements. We have found a dramatic decrease in the magnetic moment at the 3g site in the CaCu5-type structure (space group P6/mmm), the saturation magnetization and the Curie temperature with increasing Ni concentration.

Multiwalled carbon nanotubes decorated with molybdenum sulphide (MoS2@MWCNTs) for highly selective electrochemical picric acid (PA) determination

Nitrophenols are industrially versatile yet environmentally detrimental compounds. Herein, we have synthesised molybdenum sulphide based dichalcogenide supported multiwalled carbon nanotubes i.e. MoS2@MWCNTs electrocatalyst by simple wet chemical method for PA determination. The successful decoration of MoS2 over MWCNTs were confirmed by various characterizations techniques including scanning electron microscopy (SEM) shows MoS2 layers grown on MWCNTs and having average size is –80 nm. Energy dispersive X-ray analysis (EDAX) reveals elements are homogenously distributed in nanocomposite. High resolution-transmission electron microscopy (HR-TEM) shows increase in average diameter after decoration of MoS2 over MWCNTs from 30 nm to 70 nm. The Fourier transform infrared (FT-IR) analysis suggests the presence of Mo-S stretching frequency at 605 cm−1 in addition to hydroxyl, carbonyl, C–C, C–O stretching frequencies are also observed. In Raman spectrum from apart D and G bands, the characteristic intense bands E2g1 and A1g of MoS2 were pointed towards presence of molybdenum and sulphur. The X-ray diffraction (XRD) confirms synthesised electrocatalyst is in hexagonal crystal structure with P63/mmc space group. The X-ray photoelectron spectroscopy (XPS) reveals that for Mo 3d is found to be two characteristics peaks at 231.2 eV and 233.2 eV corresponds to Mo4+ 3d3/2 and 3d5/2 respectively. The peak at 229 eV corresponds to S 2s. Whereas, the signal appears at 162.7 eV, 165 eV, 169 eV and 170 eV shows sulphur is in 2S3/2 and 2S5/2 states. Electrochemical performance was examined by cyclic voltammetry (CV) tests. The Electrocatalyst is highly selective, having appreciable anti-interference property, lower limit of detection (LoD), i.e., 0.5 μM with wide linear range. The low Rct and high k⁰ pointed that MoS2@MWCNTs performed better towards electrochemical detection of PA.

Photocatalytic degradation of methyl orange using CuO/Al2O3 nanocomposite obtained by microwave-assisted thermal decomposition route

Aluminum oxide (Al2O3) and copper oxide (CuO) are known to exhibit very exceptional properties including high thermal and chemical properties that promise a wide area of applications. In this paper, we report the microwave-assisted thermal decomposition route to CuO/Al2O3 nanocomposite and its application as a photocatalyst for methyl orange (MO) degradation. Al2O3 was first prepared at different temperatures of 900, 1000, and 1100 °C, denoted as Al2O3(1), Al2O3(2), and Al2O3(3). Subsequently, the best temperature (1000 °C) was selected for the synthesis of CuO/Al2O3 nanocomposite. XRD analysis confirmed the hexagonal crystal structure for all the Al2O3 and the monoclinic phase for the CuO within the composite. The crystallite sizes of the alumina increased with temperature and a similar growth pattern occurred in the entire samples. Scanning electron microscopy and transmission electron microscopy (SEM and TEM) show clear spherical morphology for all the samples with obvious agglomeration as temperature increases. Optical characterization displayed decreasing band gap energies with increasing temperature, implying size increase due to particle interaction, boundary energy reduction, and grain boundary migration. The photocatalytic performance of the CuO/Al2O3 under visible light was evaluated on methyl orange (MO), and the degradation was studied with some process parameters such as the effect of catalysts dosage and initial concentration of MO. Results showed that the CuO/Al2O3 exhibited about 94.2 % efficiency within 3 h using an optimum dose of 2.0 g/L and an initial MO concentration of 20 mg/L. However, the use of CuO/Al2O3 nanocomposites to remove other organic pollutants could confirm the robustness of this catalyst.

Improving performance of cathode NMC-811 by CeO2-coating for Li-ion battery

The high energy density layered oxide LiNi0.8Mn0.1Co0.1O2 (NMC811) holds great promise as a cathode material for future Li-ion batteries. However, its application in electric vehicles is hindered by issues such as inadequate cycle performance and rate capability. Additionally, the corrosion caused by the electrolyte poses limitations on high voltage operation. In this study, Cerium Oxide (CeO2) was used to coat NMC811 using wet chemical method followed by heat treatment. Distilled water was used to dissolve Ce salt instead of ethanol so that it can reduce coating costs and is more environmentally friendly. XRD analysis showed no significant change in the hexagonal crystal structure of NMC811 material but the appearance of small CeO2 peaks in patterns. Electrochemical test of CeO2 coated NMC811 exhibited 18% and 9% higher cyclic and rate performance, respectively in comparison to pristine material.

Plasma-assisted pyrolysis for converting oil palm fronds into reduced graphite oxide

One of the oil palm tree’s solid waste is oil palm fronds. Due to its lignocellulosic composition, it has the potency to convert it into carbon. The common heat treatment method to convert oil palm fronds into carbon-based material is pyrolysis. However, this process has some disadvantages, such as being time-consuming and just producing amorphous carbon. Different from common pyrolysis temperatures, in this study we use a higher temperature (4000 °C) generated by DC current arc plasma. This process is faster than the common pyrolysis process (less than 10 minutes) and produces crystalline material. This product is then characterized by Raman spectroscopy, SAED-TEM, XRD, FT-IR, and SEM/EDX. Based on Raman spectroscopy, this crystalline material shows the characteristics of semiconductor carbon. Based on the SAED-TEM, there is a (002) plane of hexagonal crystal structure detected (graphite phase characteristics). An XRD analysis shows the characteristics of the trigonal crystal structure (P3) constructed by O and H atoms. An FT-IR characterization shows that there are C=C, C-H, and O-H bonds, while the EDX analysis result shows a carbon-to-oxygen ratio of about 4.23. Therefore, based on the whole interpretation, the plasma-assisted pyrolysis treatment is successfully used to convert oil palm fronds into reduced graphite oxide (rGO).

Highly Efficient CdSe Quantum Dot-Sensitized Solar Cells via a Facile SILAR Method: Dependence of the SILAR Cycles on Optical Properties and Photovoltaic Performance

This work emphasizes using CdSe as a sensitizer in quantum dot-sensitized solar cells (QDSSCs) due to its beneficial band alignment with TiO2, enhancing effective charge injection. This study presents highly efficient CdSe QDSSCs developed using the successive ionic layer adsorption and reaction (SILAR) method. The XRD analysis revealed a hexagonal crystal structure for the synthesized CdSe quantum dots (QDs) with an average particle size of 9.2 nm. Increasing the SILAR cycles from 3 to 5 showed a decrease in the energy bandgap, reducing it from 1.79 eV to 1.68 eV, as observed in the investigation of optical properties. The optimal photovoltaic performance of CdSe QDSSCs was achieved at 4 SILAR cycles, yielding a notable power conversion efficiency (PCE) of 6.77% (Jsc = 14.63 mA/cm2, Voc = 0.71 V, FF = 65.2%), which is higher than that of a previous report of SILAR-prepared CdSe QDSSCs.

Ultra-thin double-layered hexagonal CuI: strain tunable properties and robust semiconducting behavior.

In this study, the freestanding form of ultra-thin CuI crystals, which have recently been synthesized experimentally, and their strain-dependent properties are investigated by means of density functional theory calculations. Structural optimizations show that CuI crystallizes in a double-layered hexagonal crystal (DLHC) structure. While phonon calculations predict that DLHC CuI crystals are dynamically stable, subsequent vibrational spectrum analyzes reveal that this structure has four unique Raman-active modes, allowing it to be easily distinguished from similar ultra-thin two-dimensional materials. Electronically, DLHC CuI is found to be a semiconductor with a direct band gap of 3.24 eV which is larger than that of its wurtzite and zincblende phases. Furthermore, it is found that in both armchair (AC) and zigzag (ZZ) orientations the elastic instabilities occur over the high strain strengths indicating the soft nature of CuI layer. In addition, the stress-strain curve along the AC direction reveal that DLHC CuI undergoes a structural phase transition between the 4% and 5% tensile uniaxial strains as indicated by a sudden drop of the stress in the lattice. Moreover, the phonon band dispersions show that the phononic instability occurs at much smaller strain along the ZZ direction than that of along the AC direction. Furthermore, the external strain direction can be deduced from the predicted Raman spectra through the splitting rates of the doubly degenerate in-plane vibrations. The mobility of the hole carriers display highly anisotropic characteristic as the applied strain reaches 5% along the AC direction. Due to its anomalous strain-dependent electronic features and elastically soft nature, DLHC of CuI is a potential candidate for future electro-mechanical applications.

Mössbauer and magnetic studies of Fe-doped ZnO nanoparticles prepared by solution co-precipitation method

A series of Zn[Formula: see text]FexO ([Formula: see text], 0.015, 0.045, 0.075) nanoparticles were synthesized using the solution co-precipitation method, and their structural and property characteristics were investigated. X-ray diffraction (XRD) analysis revealed that all Zn[Formula: see text]FexO samples exhibited a hexagonal wurtzite crystal structure with the P63mc space group. The introduction of Fe doping led to a slight lattice distortion in the samples. The morphology of the nanoparticles, including polydispersion and agglomeration, as well as the presence of the second phase ZnFe2O4, was examined by scanning electron microscope (SEM) and transmission electron microscope (TEM). UV–Vis diffuse reflectance spectroscopy demonstrated that the band gap of Zn[Formula: see text]FexO lies between 3.152 and 3.163[Formula: see text]eV. With the increase in Fe ion doping, the band gap shows a slight decreasing trend. Mössbauer spectroscopy revealed that iron ions in the nanoparticles existed in a trivalent state and exhibited two different configurations: One involved iron replacing zinc without creating a vacancy, while the other involved iron substituting zinc with a vacancy. The ferromagnetic nature of the Fe-doped samples can be attributed to the exchange interaction between two Fe[Formula: see text] ions mediated by the F-center mechanism.

Facile bio-inspired synthesis of polysaccharide-mediated zinc oxide nanoparticles and their efficient antimicrobial and photocatalytic activity

BackgroundGreen synthesis for nanomaterials, an eco-friendly and sustainable technology, has gained prominence in recent decades, especially in dye removal. The widespread use of toxic organic dyes in various industries has become a significant concern for human health, mainly when these dyes contaminate wastewater. This current study focuses on the prevalent use of hazardous dyes, known for their ecotoxicity, and the challenge of effectively removing these pollutants from wastewater. AimThe primary goal is to achieve a bio-inspired synthesis of zinc oxide nanoparticles using polysaccharides as mediators. This synthesis is designed to enhance the antimicrobial attributes of the nanoparticles and facilitate the photocatalytic degradation of organic dyes. Notably, polysaccharides serve a dual purpose as both a reducing and stabilizing agent for synthesizing ZnO nanoparticles. Significant findingsThe XRD distinctive lattice pattern peaks, such as (1 0 0), (0 0 2), and (1 0 1), affirmed the pure formation of the ZnO structure with a hexagonal wurtzite crystal structure. The chemical composition and product purity of green-produced SB-ZnO NPs were assessed through SEM and XPS analysis. The study then utilized polymer-mediated green-synthesized ZnO NPs for the photocatalytic degradation of Congo red and crystal violet under visible light irradiation. The results demonstrated remarkable photocatalytic activity, with around 88.2% of Congo red dye degradation observed within 80 min of visible light exposure. Notably, Congo red exhibited higher catalytic efficiency compared to crystal violet dye. The antimicrobial activity of SB-ZnO NPs obtained through green synthesis was also investigated. The antimicrobial study revealed the formation of zones against both gram-positive and gram-negative bacterial pathogens. These bioassay metal oxides are recognized for their potential in environmental remediation due to their low cost, stability, efficiency, and minimal environmental impact. The enhanced photocatalytic efficiency of polymer-metal nanocomposites shows significant potential in propelling the utilization of photocatalysts for environmental applications, specifically in wastewater treatment and bactericidal processes.

Enhanced photocatalytic degradation of methylene blue and methyl orange using biogenic ZnO NPs synthesized via Vachellia nilotica (Babool) leaves extract

Biogenic zinc oxide (b-ZnO) NPs were synthesized via the leaf extract of Vachellia nilotica (Babool) due to their rich source of bioactive complexes, which have great potential as a reliable, sustainable, and eco-friendly system. Sharp peaks in the XRD pattern of b-ZnO NPs confirmed the hexagonal wurtzite crystal structure. The crystallite size, D, of b-ZnO, decreased from 22.22 nm to 10.13 nm, and the lattice strain (τ) increased from 5.22 × 10−3 to 11.47 × 10−3 as the material changed from synthetic to biogenic, respectively. The Eg of b-ZnO was observed to be 3.37 eV. The specific surface area, total pore volume and average pore diameter of ZnO and b-ZnO NPs were increased from 9.5 to 34 m2/g, 0.3536–0.3854 cm3/g, and 17.24–19.56 nm, respectively. The photocatalytic degradation of b-ZnO increased from 72% to 80% for MO dye, from 87% to 93% for MB dye and completely degraded MB within 2 h. This work presents an essential advancement towards achieving enhanced photocatalytic performance to reduce water pollutants using b-ZnO and will guide the use of biogenic nanomaterials for photocatalytic applications.

Fabrication, microstructure and upconversion luminescence properties of Er:Sr5(PO4)3F transparent nanostructured ceramics

Fluoride-upconversion transparent ceramic materials doped with Er ions have attracted extensive interest due to their higher stability, lower phonon energy, and higher upconversion efficiency. xEr:Sr5(PO4)3F (S-FAP) (x=0.5–5 at%) transparent ceramics have been synthesized by hot pressing sintering in this work, and the maximum optical transmittance of the sample reached 74.52 and 82.45% at 500 and 1000 nm, respectively. The XRD results of the powder and ceramic samples were consistent with the diffraction characteristics of the hexagonal S-FAP crystal structure. The SEM and TEM images of powder revealed that the morphology of the sample was composed of mostly rice grains with a diameter of around 20 nm. The XPS and EDS results confirmed the presence of Er3+ and the uniform distribution of Er elements. The thermally etched surface and cross section of ceramics revealed residual pores as the most important scattering source, and the SEM images of the ceramics show that Er doping can obviously promote the growth of the average grain size of S-FAP transparent ceramics. Furthermore, the upconversion luminescence characteristics and fluorescence lifespan of S-FAP transparent ceramics with varied Er doping concentrations were examined, as well as the upconversion luminescence process. The findings in this work indicate that Er:S-FAP transparent ceramics can be employed as a potential upconversion fluorescent material in display technology, biomedicine, temperature sensing, and other applications.

Enhanced Photoelectrochemical Activity Realized from WS2 Thin Films Prepared by RF‐Magnetron Sputtering for Water Splitting

AbstractWe report the synthesis of tungsten sulfide (WS2) films using RF‐magnetron sputtering at different RF powers. X‐ray diffraction (XRD) data confirm the hexagonal crystal structure of WS2 with an average crystallite size of ∼44.54 Å. With increased RF power, the preferred orientation of WS2 crystallites shifts from (002) to (100). Linear sweep voltammetry (LSV) was used to assess the Photoelectrochemical (PEC) activity of WS2 films. The film deposited at 150 W demonstrated the highest photocurrent density of 5.44 mA/cm2. The 150 W film also showed a lower Tafel slope of ∼0.374 V/decade, indicating superior PEC activity. Mott Schottky's (MS) analysis revealed a notable shift in the flat band potential towards the negative side, suggesting a shifting of the Fermi level towards the conduction band. WS2 film grown at 150 W demonstrated a majority charge carrier density of 6.2×1021 cm−3 and a depletion layer width of 1.54 nm. The observed low charge transfer resistance of 155 Ω contributed to the enhanced PEC activity with a relaxation time constant of 37 ms. These properties suggest that WS2 can be suitable for PEC water splitting.

The characterization of Ag-doped tin indium oxide/copper electrodes prepared by cold pressing method and their electrocatalytic efficiency in hydrogen production

In the present study, tin indium oxide (SnIn2O3) powder was synthesized by hydrothermal technique. In order to improve the structural property of SnIn2O3, a small amount of silver (Ag) nanoparticles was added into SnIn2O3 powder. Finally, the prepared Ag-doped SnIn2O3 (Ag@SnIn2O3) were embedded into copper (Cu) powder with different ratios. The electrocatalytically improved hetero-structured Ag@SnIn2O3/Cu materials were obtained by cold pressing method. The structural and morphological properties of different Ag@SnIn2O3/Cu materials were studied via X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). XRD pattern depicted In2O3 have both cubic and hexagonal crystal structures. FE-SEM images show that Ag@SnIn2O3 nanoparticles are homogeneously dispersed into Cu powder. The size of nanoparticles of Ag@SnIn2O3/Cu materials increases with increasing the ratio of Ag@SnIn2O3. Electrochemical impedance spectroscopy (EIS) and potentiodynamic (PD) polarization tests were carried out to investigate the electrocatalytic activities of the materials toward hydrogen evolution reaction (HER). Energy consumption and energy efficiency values for the HER on the materials were also calculated. Furthermore, the polarization resistances of the 1-Ag@SnIn2O3/Cu, 2.5-Ag@SnIn2O3/Cu, 5-Ag@SnIn2O3/Cu, and 10-Ag@SnIn2O3/Cu materials were determined as 127.4, 103.1, 552.4, and 558.7 Ω cm2, respectively after 5 days of electrolysis periods.

Influence of ZnO/MWCNTs based hybrid electrodes for boosting the performance of photovoltaic and supercapacitor devices

In this work, multi-wall carbon nanotubes (MWCNTs with 1, 3 and 5 wt.%) are mixed with zinc oxide (ZnO) to prepare nanocomposites for energy conversion and storage applications. Further, UV–Vis spectra of synthesized pure ZnO and ZnO/MWCNTs nanocomposite material shows enhanced light absorption in the visible region. Hexagonal wurtzite crystal structure of the nanocomposites is confirmed by X-ray diffraction (XRD) spectra. Field emission scanning electron microscopy (FE-SEM) and High resolution-transmission electron microscopy (HR-TEM) images explores the formation of nanocomposite with flake like ZnO and tube structured MWCNTs at nanoscale region. Dye sensitized solar cells (DSSC) are constructed with pure and nanocomposite material as photoanode and the effect of addition of MWCNTs on the performance of solar cells are studied. Further, the cyclic voltammetry (CV), galvanic charge-discharge (GCD) and electrochemical impedance spectroscopy (EIS) are employed to examine the electrochemical characteristics of the prepared electrode in a 1 M Na2SO4 electrolyte. In three electrode configuration, the CV and GDC curves exhibits good reversibility and attains a specific capacitance value of 115.7 F g−1 with the addition of MWCNTs onto the ZnO. Also, the asymmetric supercapacitor device exhibits the improved storage performance. The EIS spectra shows lowest Rs and Rct resistance, indicating the prepared electrode is favorable for DSSC and supercapacitor application.

Preparation of chromium barium oxide catalysts for hydrogen evolution from sodium borohydride methanolysis

This paper describes the synthesis of Cr2O3, Cr1.7Ba0.3O3, and Cr1.4Ba0.6O3 nanoparticles as catalysts to enhance hydrogen evolution in sodium borohydride methanolysis. Various characterization techniques, comprising X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and others were utilized to characterize the prepared nanoparticles. The XRD analysis showed that the formed Cr2O3 exhibits a hexagonal crystal structure, with an estimated mean crystallite size of 24 nm. SEM micrographs showed nanoparticles with homogeneous distributions, exhibiting spherical or distorted spherical shapes. XPS analysis showed that all synthetic Cr2-xBaxO3 materials consist of Cr, O, and the presence of Ba for doped samples. The energy gap for pure Cr2O3 nanoparticles was determined to be 3.28 eV. Inclusion of Ba into the Cr2O3 nanostructure modified the band gap, resulting in values of 2.8 and 1.5 eV at 15 % and 30 % barium content. The hydrogen production rate from NaBH4 methanolysis for Cr2O3, Cr1.7Ba0.3O3, and Cr1.4Ba0.6O3 catalysts were 5984, 31176 and 11913 mL/g.min, respectively.

Enhanced thermal conductivity of plasma generated ZnO–MgO based hybrid nanofluids: An experimental study

Hybrid nanofluids (HNFs) of metallic oxide-based nanoparticles (NPs) have been prepared in different basefluids (BFs) employing the thermal plasma technique. NPs of ZnO–MgO were directly dispersed into pristine coolant, engine oil, distilled water (DW), and coconut oil. Plasma was generated between two identical electrodes applying 8.0 kV at the ambient conditions and proved economically viable in preparing stable HNFs. X-ray Diffractometry (XRD) showed ZnO and MgO NPs possessed hexagonal and cubic crystal structures, respectively. The band gap is calculated through UV-visible spectroscopy. The thermal conductivity (TC) of the HNFs has been measured using a thermal conductivity analyzer based on the transient hot wire method. The band gaps of pristine coolant and its HNFs were obtained to be 3.35 eV and 3.33 eV, respectively. In engine oil and its HNFs, band gaps of 3.16 eV and 3.02 eV have been extracted. There appears to be a slight reduction in band gap for coolant and engine oil-based HNFs. The band gap value of coconut oil-based HNFs was 4.05 eV, which showed a higher value than the pristine coconut oil-based HNFs (3.95 eV). The band gap calculated in the case of DW-based HNFs was 3.79 eV. TC of HNFs with volume concentration of 0.019 % for DW, 0.020 % for coolant, 0.016 % for engine oil, and 0.017 % for coconut oil were tested between 20 and 60 °C. An increase in TC was observed with the rise in temperature of the HNFs. Maximum increment in TC was observed at 60 °C for coolant-based HNFs, which was 19 %, followed by DW (18%), coconut oil (18%), and engine oil (16%), respectively. DW-based HNFs can be used as a coolant and optical filter for optoelectronics devices like photovoltaic cells for better performance. The study underscores precise control of NPs size as pivotal for band gap influence. HNFs hold promise as the next-gen heat transfer fluids (HTFs), revolutionizing thermal conductivity across industries. This research lays a firm foundation for plasma-synthesized HNFs' application in enhanced heat transfer and optoelectronic devices. Coolant-based HNFs excel in thermal conductivity, addressing heat transfer challenges.

Morphological and Optical Characterization of Hydrothermally-Synthesized Two-Dimensional MoS2 Nanosheets

Transition metal dichalcogenides (TMDs) are extensively utilized in optoelectronics, sensors, and battery storage due to their versatile properties. Among the TMDs, Molybdenum disulfide (MoS2) nanosheets possess remarkable optical, electronic, and chemical properties. This study employed a cost-effective hydrothermal method to synthesize high-quality 2D MoS2 nanosheets. Different characterization techniques such as XRD, SEM, EDS, FTIR, Raman, UV–vis, and photoluminescence (PL) spectroscopy were utilized to evaluate the structural, morphological, chemical, and optical characteristics of the nanosheets. The XRD analysis revealed that the MoS2 nanosheets have a hexagonal crystal structure, with an average crystallite size of 27.76 nm. Furthermore, SEM images confirmed the formation of thin MoS2 nanosheets, with an estimated thickness ranging from 20–30 nm. The growth mechanism of the formation of MoS2 is discussed in detail. Different functional groups present in the material were analyzed using FTIR spectra. The difference in vibration modes analysed by Raman spectroscopy indicated the presence of layered nanosheets. The optical bandgap (2.20 eV) of the material was determined by analyzing its UV–vis spectroscopy data using the Tauc plot. PL analysis indicates a direct transition between the upper valence and lower conduction bands, suggesting that the nanosheets were synthesized with high quality. These findings have opened new possibilities for the use of MoS2 nanosheets in various applications such as optoelectronics and sensing devices.