Enhancement of photocatalytic efficacy by exploiting copper doping in nano-hydroxyapatite for degradation of Congo red dye

This research deals with the photocatalytic activity of hydroxyapatite and the improvement of efficiency by doping various percentages of copper; the catalysts were synthesized by the wet-chemical method. Pure and copper-doped photocatalysts were characterized by several techniques including X-ray diffraction (XRD), Fourier Transform Infrared (FTIR) spectroscopy, Raman spectroscopy, scanning electron microscopy (SEM), thermogravimetric analysis (TGA), dynamic scanning calorimetry (DSC), and UV-Vis spectroscopy. The competency of pure and copper-doped hydroxyapatite as photocatalysts was assessed by their interaction with Congo red dye. The crystallographic parameters of the catalysts were also estimated by employing the XRD technique, and a relationship was established between the calculated parameters and photocatalytic performance. Crystallite size was calculated from various model equations, which revealed an acceptable crystallite size of 42-68 nm. Copper doping in hydroxyapatite impressively augmented the photocatalytic efficacy, for example 99% dye was degraded upon 0.63% Cu-doping compared to 75% for the pure HAp, which was exemplified not only by the reaction rate but also by the quantum yield. The degradation percentages changed with time but became fixed at 200 min. The molar extinction coefficient was estimated by employing the Beer-Lambert law and further utilized to compute the photonic efficiency of the catalysts. In the study of the photochemical reaction, a simplified reaction process was proposed, and the potentials of the conduction band and valence band were assessed, which influenced the activity. The doping of Cu in crystalline hydroxyapatite will enhance the photocatalytic activity towards Congo red dye under all experimental conditions.

Marine-Derived Biowaste Conversion into Bioceramic Membrane Materials: Contrasting of Hydroxyapatite Synthesis Methods

Marine-derived biowaste increment is enormous, yet could be converted into valuable biomaterial, e.g., hydroxyapatite-based bioceramic. Bioceramic material possesses superiority in terms of thermal, chemical, and mechanical properties. Bioceramic material also has a high level of biocompatibility when projected into biological tissues. Tuning the porosity of bioceramic material could also provide benefits for bioseparation application, i.e., ultrafiltration ceramic membrane filtration for food and dairy separation processes. This work presents the investigation of hydroxyapatite conversion from crab-shells marine-based biowaste, by comparing three different methods, i.e., microwave, coprecipitation, and sol-gel. The dried crab-shells were milled and calcinated as calcium precursor, then synthesized into hydroxyapatite with the addition of phosphates precursors via microwave, coprecipitation, or sol-gel. The compound and elemental analysis, degree of crystallinity, and particle shape were compared. The chemical compounds and elements from three different methods were similar, yet the degree of crystallinity was different. Higher Ca/P ratio offer benefit in producing a bioceramic ultrafiltration membrane, due to low sintering temperature. The hydroxyapatite from coprecipitation and sol-gel methods showed a significant degree of crystallinity compared with that of the microwave route. However, due to the presence of Fe and Sr impurities, the secondary phase of Ca9FeH(PO4)7 was found in the sol-gel method. The secondary phase compound has high absorbance capacity, an advantage for bioceramic ultrafiltration membranes. Furthermore, the sol-gel method could produce a snake-like shape, compared to the oval shape of the coprecipitation route, another benefit to fabricate porous bioceramic for a membrane filter.