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In this work, we successfully synthesized Cr 3+ doped ZnO nanoparticles using a sol-gel method, and elucidated how Cr 3+ dopant is critical for enhancing photocatalytic activity. The nature of the point defect analyzed by electron spin resonance (ESR), and photoluminescence (PL) emission revealed the role of the Cr 3+ dopant. When introducing Cr 3+ ions in ZnO, the PL emission intensity decreased, indicating a reduction of the radiative recombination rate due to the heterojunction formation between the dopant and the host. The Cr 3+ doped ZnO nanostructures showed that the typical ESR signal with g-factor value ∼1.96 was completely passivated, indicating the diffusion of electrons near the conduction band into the dopant ions. The doped Cr 3+ ion acts as an electron trap in the ZnO crystal described as3 2The mechanism for enhancing the photocatalytic activity of heterogeneous ZnO:Cr 3+ was proposed in respect of point defect evolution through the manner of Cr 3+ doping. As a result, the photocatalytic efficiency investigated by measuring methylene blue degradation under 210 min of direct sunlight irradiation reached 93.5% for 1 at % Cr 3+ doped ZnO, which was significantly improved compared to 59.8% of the pure ZnO.

The application of first-order derivative and wavelet transforms to UV spectra and ratio spectra was proposed for the simultaneous determination of ibuprofen and paracetamol in their combined tablets. A new hybrid approach on the combined use of first-order derivative and wavelet transforms to spectra was also discussed. In this application, DWT (sym6 and haar), CWT (mexh), and FWT were optimized to give the highest spectral recoveries. Calibration graphs in the linear concentration ranges of ibuprofen (12–32 mg/L) and paracetamol (20–40 mg/L) were obtained by measuring the amplitudes of the transformed signals. Our proposed spectrophotometric methods were statistically compared to HPLC in terms of precision and accuracy.

Herein we studied the structure deformation and photoluminescence properties of titanium dioxide nanotube (TNT) hydrothermally grown on pristine graphene (Gr) surfaces. This Gr/TNT composite shows photocatalytic enhancement in terms of methylene blue degradation efficiency and short saturation time, as a result of heterogeneous junction formation through the interfacial connection of graphene by a facile one-step hydrothermal method. The Gr content within the composites was varied between 0.5 wt.%–8 wt.%, and the sample containing 5 wt% Gr (0.01 g) displayed the highest photocatalytic activity with methylene blue (20 ppm) degradation efficiency of 99.63%. In addition, all the composites exhibited a very short saturation time of ~5 min under sunlight irradiation. The morphological, crystal structural, optical and photocatalytic properties of the composite material were investigated using transmission electron microscopy, scanning electron microscopy, x-ray diffraction, Raman scattering spectroscopy and photoluminescence spectroscopy. The TNTs grown in situ with graphene showed that it enhanced their photocatalytic activity via the reduced carrier recombination rate of TNTs, which was studied by photoluminescence emission measurement. Furthermore, the mechanism by which the combined material properties affect the photocatalytic performance were characterized and clarified.