Light-Activated Hydroxyapatite Photocatalysts: New Environmentally-Friendly Materials to Mitigate Pollutants

Polysaccharide Hydroxyapatite (Nano)composites and Their Biomedical Applications: An Overview of Recent Years

Hydroxyapatite can combine with polysaccharide originating biomaterials with special applications in the biomedical field. In this review, the synthesis of (nano)composites is discussed, focusing on natural polysaccharides such as alginate, chitosan, and pectin. In this way, advances in recent years in the development of preparing materials are revised and discussed. Therefore, an overview of the recent synthesis and applications of polyssacharides@hydroxyapatites is presented. Several studies based on chitosan@hydroxyapatite combined with other inorganic matrices are highlighted, while pectin@hydroxyapatite is present in a smaller number of reports. Biomedical applications as drug carriers, adsorbents, and bone implants are discussed, combining their dependence with the nature of interactions on the molecular scale and the type of polysaccharides used, which is a relevant aspect to be explored.

Facile Synthesis of Ni-Doped ZnO Nanoparticles Using Cashew Gum: Investigation of the Structural, Optical, and Photocatalytic Properties

This work adopted a green synthesis route using cashew tree gum as a mediating agent to obtain Ni-doped ZnO nanoparticles through the sol-gel method. Structural analysis confirmed the formation of the hexagonal wurtzite phase and distortions in the crystal lattice due to the inclusion of Ni cations, which increased the average crystallite size from 61.9 nm to 81.6 nm. These distortions resulted in the growth of point defects in the structure, which influenced the samples' optical properties, causing slight reductions in the band gaps and significant increases in the Urbach energy. The fitting of the photoluminescence spectra confirmed an increase in the concentration of zinc vacancy defects (VZn) and monovacancies (Vo) as Zn cations were replaced by Ni cations in the ZnO structure. The percentage of VZn defects for the pure compound was 11%, increasing to 40% and 47% for the samples doped with 1% and 3% of Ni cations, respectively. In contrast, the highest percentage of VO defects is recorded for the material with the lowest Ni ions concentration, comprising about 60%. The influence of dopant concentration was also reflected in the photocatalytic performance. Among the samples tested, the Zn0.99Ni0.01O compound presented the best result in MB degradation, reaching an efficiency of 98.4%. Thus, the recovered material underwent reuse tests, revealing an efficiency of 98.2% in dye degradation, confirming the stability of the photocatalyst. Furthermore, the use of different inhibitors indicated that •OH radicals are the main ones involved in removing the pollutant. This work is valuable because it presents an ecological synthesis using cashew gum, a natural polysaccharide that has been little explored in the literature.