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• rGO-NiO NC thin films were prepared on Al-substrates by solvothermal and dip-coating techniques. • XRD patterns of thin films confirmed the presence of NiO in the NC. • EDX spectrum showed presence of carbon in rGO-NiO NC thin film due to rGO. • XPS analysis disclosed presence of rGO in rGO-NiO NC thin film. • The 0.2% rGO-NiO NC thin film delivered a highest solar spectral selectivity of 19.56. Commercial solar selective absorbers prepared through several techniques have encountered drawbacks of necessitating complicated and expensive equipment, substantial materials requirement, and polluting environment. In this context, carbon incorporated metal oxide thin films have shown promise of low-cost, non-toxic, and efficient solar selective absorbers. In particular, association of reduced graphene oxide (rGO) and nickel oxide (NiO) could facilitate highly ascertained optical properties, environment friendliness, and low-cost. Present study focuses on preparing a novel, high performance, and low-cost rGO-NiO solar selective absorber thin films. Thin films comprised of reduced graphene oxide modified nickel oxide nanocomposites (rGO-NiO NCs) were prepared through solvothermal route and coated on aluminum (Al) substrates by dip-coating technique. The rGO-NiO NCs examined using X-ray diffractometer revealed formation of face centered cubic crystallite structure. The scanning electron microscope images disclosed spherical morphology of NiO decorated on the rGO sheets. The spectra derived from energy-dispersive X-ray spectroscopy ascertained absence of peaks corresponding to impurities. The Raman investigation exhibited high intensity ratio (0.97) of the rGO-NiO NCs that described higher disorder and binding sites. The optical property analysis of the rGO-NiO NC (0.2 wt% rGO) thin film performed in UV–vis-NIR reflectance spectroscopy showed high absorptance (α = 88.03 %) and low thermal emittance (ε = 4.5 %), which eventually delivered high solar selectivity (ξ) of 19.56. These findings suggest that the prepared 0.2 % rGO-NiO NC thin film can be utilized as an appropriate selective absorber for solar to thermal energy conversion. [ABSTRACT FROM AUTHOR]

Barium titanate nanoparticles were synthesized via a low temperature sol-gel technique using acetylacetone as a chelating agent. The X-ray diffraction pattern confirmed the formation of tetragonal perovskite structure of the material. The average crystallite size was found to be 49 nm using the Debye-Scherrer method. The Williamson–Hall plot was drawn for evaluating the micro-strain and crystallite size. Raman spectroscopic features typical for the tetragonal phase were identified for Barium titanate powder. In addition to these, an absorption band edge and an optical bandgap were found to be of 406 nm and 3.14 eV respectively. Barium titanate displays polychromatic luminescent peaks in UV -visible regions and it was attributed to the near-band-edge transition and defect states in the optical band gap of the perovskite structure. [ABSTRACT FROM AUTHOR]

Copper oxide films with diverse morphologies are prepared on copper (Cu) substrate by anodization method. The concentration of aqueous NaOH solution used as electrolyte during the anodization process is found as crucial towards formation of different nanostructured films. The reaction temperature impact on chemical composition and morphology of films is also determined. X-ray diffraction patterns disclose that CuO and Cu 2 O are presented in films and the share between both could be altered by changing the NaOH concentration and applied potential. Scanning electron microscopy images unveiled formation of films with diverse morphologies comprised of nanorods, nanoflakes, nanoparticles, and nanoleaves. Raman spectra confirmed the presence of CuO mode and its significant peak intensity has indicated high crystallinity. The prepared films have displayed high solar absorptance (63.5%–77.3%), low thermal emittance (4.5%–5.5%), and better solar selectivity (>14). These results suggest that the anodization method can be employed as a potential technique to prepare facile and affordable solar selective absorbers. [Display omitted] • CuO thin films with diverse morphology were prepared on Cu substrate by anodization technique. • Relative proportion of CuO and Cu 2 O in thin films could be altered by changing the concentration of NaOH and applied potential. • CuO nanorods, nanoflakes and nanoparticles thin films were formed through anodization technique. • High peak intensity modes in Raman spectra revealed high crystalline nature of CuO. • CuO thin films possessed low thermal emittance (4.5%–5.5%), high solar absorptance (63.5%–77.3%) and high solar selectivity (>14). [ABSTRACT FROM AUTHOR]

Mn doped SnO2 nanoparticles were synthesized in a sol-gel technique at various concentrations. A wide range of properties are analyzed by using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy with energy dispersive spectroscopy (SEM with EDAX), Transmission Electron Microscopy (TEM), UV-Visible spectroscopy, photoluminescence spectroscopy (PL), Vibrating Sample Magnetometer (VSM), and photocatalytic studies. Results from EDAX confirmed the presence of Sn and Mn ions in SnO2 nanoparticles doped with Mn. As a result of analyzing the luminescence of all synthesized samples, blue emission characteristic of lighting applications was observed. Furthermore, 0.2M Mn doped SnO2 sample shows the enhanced ferromagnetism at room temperature with elevated saturation magnetization value. The 0.2M Mn doped SnO2 nanoparticles show the significant increase in photocatalytic efficiency of SnO2 among the other doped samples. Thus, all experiment results demonstrated that the concentration of dopant influences the structure, optical properties, photocatalytic properties, and magnetic properties of SnO2. [ABSTRACT FROM AUTHOR]

A comparative investigation of the structural, optical, and magnetic properties of NiFe 2 O 4 (NFO) and ZnFe 2 O 4 (ZFO) spinel nanoparticles were synthesized by microwave combustion method. X-ray diffraction (XRD) showed that the ZFO spinel nanoparticles formed a cubic structure, but the NFO spinel nanoparticles formed with additional Fe 2 O 3 in them. The average crystallite size was observed to be in the range 16–20 nm. X-ray photoelectron spectroscopy (XPS) peak areas are often used to quantify the elemental compositions and oxidizing states of NFO and ZFO spinel surfaces. The appearance of FT-IR bands at around 548, 514 and 649 cm−1 were correlated to the Fe–O and Zn/Ni–O stretching modes of cubic NFO and ZFO structure. The direct band gap estimated using Kubelka–Munk (K–M) method to obtain by the NFO is 3.35 eV and ZFO is 2.13 eV respectively. The surface morphology revealed nanosized crystalline grains with agglomerate separated particles that are like spherical/non-spherical forms and fused grain boundaries. Magnetic measurements of NFO and ZFO spinel nanoparticles showed ferromagnetic behavior at room temperature. [ABSTRACT FROM AUTHOR]