Nanostructured bio-photocatalyst hydroxyapatite (HAp) was synthesized by a simple and productive wet chemical precipitation method to explore the photocatalytic performance of the material for degradation of Remazol Brilliant Blue R (RBBR) dye. Wet chemically synthesized nano-HAp was characterized through x-ray diffraction, Transmission electron microscope, scanning electron microscope, N₂-adsorption–desorption, thermo gravimetric analyzer, Fourier transform infrared and UV–vis absorption techniques. Photocatalytic degradation of RBBR under ultraviolet irradiation was examined and ∼80% degradation was achieved in 120 min by using nano-HAp. The photocatalytic degradation followed Parabolic Diffusion kinetics. Fast degradation kinetics and removal of RBBR dye was achieved by nano-HAp due to modification of surface entities leading to suppression of photo-generated electron-hole recombination. This makes nano-HAp a remarkable bio-photocatalyst material for removing dyes from water.

Pristine and dysprosium-doped ZnO thin films, highly c-axis oriented, were grown on a c-Al2O3 substrate using the pulsed laser deposition technique. During the deposition process, the growth was impacted by changes in the oxygen partial pressure. The structural, optical, and compositional properties of the pristine and dysprosium-doped ZnO thin films were systematically characterized using various state-of-the-art experimental techniques. The crystallinity associated with these films was observed to be highly dependent on the oxygen partial pressure maintained during the growth process. An average optical transparency of more than ∼90% in the visible spectral range (i.e., 400–800 nm) was observed for all specimens. For doped specimens, expected intra-4fn emissions of (dysprosium) Dy3+ ions that emanated from the 4F9/2 energy state were observed in room-temperature photoluminescence spectra under direct excitation. The Jacobian-transformed wavelength-to-energy plot for Dy-doped ZnO thin films in the UV-Visible region revealed intriguing findings. Specifically, it depicted a prominent peak at 2.82 eV, indicative of the energy state of Dy3+ ions, alongside intense band-edge emission and various defect-related emissions. The intensity of these transitions was observed to depend on the oxygen partial pressure kept during deposition. An x-ray photoelectron spectroscopy analysis of the doped specimen confirmed the +3 oxidation state of dysprosium into the ZnO matrix. These results provide a promising approach for controlling the doping and growth strategy of Dy-doped ZnO thin films, thereby opening up a wide range of applications and enhancement for next-generation optoelectronic devices.

High yield, low cost, environmentally friendly chemical bath synthesis process is used to produce submicron structures of ZnO and ZnO-carbon composites. Synthesis of ZnO rod structures (submicron sized) were confirmed using SEM images. To synthesis ZnO-carbon composites, well characterized carbon spheres produced using aerosol assisted CVD technique was used. Use of carbon spheres as a seed during synthesis of ZnO is observed to produce multipod structures of ZnO on to the surface of carbon spheres; the growth is explained by proposing suitable model. Room temperature photoluminescence spectra recorded for ZnO and ZnO-carbon composites synthesized show a systematic disappearance of a band-edge emission (sharp peak present at ∼380 nm observed for pure ZnO) with increased number of carbon spheres. Competent photo-catalytic activity of synthesized composite is confirmed by studying photo degradation investigation performed using a model dye molecule i.e. methyl orange. The work reveals possibility to use synthesized composites as a nontoxic and biocompatible catalyst for fragmentation of a methyl orange dye molecule. Photo-degradation mechanism of a methyl orange dye is proposed herewith considering the role of carbon spheres and ZnO in presence of UV photon.