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Doping β-tricalcium phosphate (β-TCP) with copper (Cu²⁺) has great potential in various applications due to its rich chemistry. However, the doping characteristics are rarely studied in detail and are yet to be fully understood, creating a gap in the existing knowledge of these multifunctional materials. In this work, a series of Cu²⁺ doped β-TCP (Cu_x-TCPs) were prepared and comprehensively characterized to investigate the correlation between Cu²⁺ doping and the material properties. Also, the synthesis of Cu_x-TCPs was modeled using thermodynamic equilibrium calculations to investigate their formation pathways. The calculations predicted a possible inclusion of Cu²⁺ in intermediate phosphate phases during the material synthesis, depending on the temperature. The structural analyses revealed lattice shrinkage due to the Cu²⁺ doping and that Cu²⁺ occupied Ca4 and Ca5 sites in the β-TCP crystal. The vibrational spectroscopy of the Cu_x-TCPs showed noticeable deformation of ν₁ band of PO₄³⁻ ligand. The ultraviolet-visible absorption analysis revealed a reduction in the band gap energy induced by Cu²⁺ doping. Photoluminescence spectroscopy demonstrated an enhanced emission tunability of Cu_x-TCPs in the blue and orange–red regions depending on Cu²⁺ concentration. These findings are a step toward a deeper understanding of the structure–property relationships of Cu²⁺ doped β-TCPs and can play a significant role in their multidisciplinary applications.

In this study, the impact of Zn2+ doping on β-Ca3(PO4)2 characteristics was investigated with particular focus on its influence on the surface, structure, and photocatalytic properties. Zn2+ doped β-Ca3(PO4)2 (Znx-TCPs) were synthesized using a solid-state method and were thoroughly studied to evaluate the modification induced by cationic substitution. The structural analysis revealed a noticeable shrinkage in the lattice parameters a and c and the unit cell volume induced by Zn2+ doping. Minor spectral changes in the vibrational modes of PO43− were also observed in the infrared and Raman spectra of Znx-TCPs. The influence of doping on the materials’ morphology was insignificant; however, molten grain boundaries were noticeable at high Zn concentration, x ≥ 1. X-ray photoelectron spectroscopy (XPS) revealed that the surface of the doped materials was rich in Zn. Optical absorption measurements indicated that Zn2+ doping slightly affects the optical bandgap of β-Ca3(PO4)2. The photocatalytic activities of the materials were investigated for the degradation of Rhodamine B (RB) and Methylene blue (MB). The photocatalytic experiments were carried out in the presence of hydrogen peroxide and under simulated solar light. The samples exhibited enhanced catalytic activity compared to β-Ca3(PO4)2, and the Zn0.5-TCP sample demonstrated the highest degradation efficiency. This sample showed excellent stability during the reusability tests, which suggests the suitability of Zn0.5-TCP for use as an efficient photocatalyst. Surface defects are believed to play an important role in the production of active species during the photocatalytic reaction.

A three-stage solid state synthesis assisted by thermodynamic modelling was developed to prepare highly pure (>99 %) beta tricalcium phosphate (β-TCP) powder. The optimal synthesis temperature was experimentally determined to be 1000 °C in good agreement with the theoretical calculations. The synthesis design described here has substantially improved the product quality and eliminated the presence of secondary phosphate phases compared to one- and two-stage methods investigated in this work. A comprehensive characterization of the material's structural, vibrational, and morphological characteristics was conducted. Rietveld refinement of the X-ray diffraction data confirmed the high purity of the samples. The crystal structure of the prepared β-TCP was determined and the refined unit cell parameters agreed well with the reference values. From infrared and Raman spectral analyses, the characteristics of β-TCP were observed and discussed in details. Furthermore, the morphology and elemental composition of the products were examined and found to be homogenous and impurity free. The reproducibility of the material was scrutinized and showed no significant data variations. Using our three-stage synthesis method, it is possible to produce β-TCP powder of high purity with consistent repeatability.

Nutrient recovery is an integral part of sustainable clean energy production where one of the most important nutrients is phosphorus (P). Phosphorus recovery from biomass and waste ashes has been a hot topic for research and development activities for decades. However, the chemical speciation of heavy metals (HM) that may be included in recovered phosphates is yet to be resolved. Numerous trial and error approachs have been applied to lower the amount of HM content by fuel design and/or additives. Nevertheless, the connection between P and HM is theses complex phosphate systems on the atomic level is not fully understood. Therefore, exploring if HM are associated with phosphates is paramount for creating a naturallink between sustainable energy production and primary production of biomass.

This study aims to examine the formation of different phosphates found in ashes and the potential inclusion of HM in their structures. The inclusion of Zn and Cu in whitlockite phosphates is investigated by powder X-ray diffraction and FTIR/RAMAN spectroscopy to identify possibilities and challenges with direct application of P-rich ash fractions as a nutrient source for plants. These measurements will be complemented by synchrotron-based X-rayabsorption spectroscopy analysis in future work.