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Given their unique characteristics and properties, Hydroxyapatite (HAp) nanomaterials and nanocomposites have been used in diverse advanced catalytic technologies and in the field of biomedicine, such as drug and protein carriers. This paper examines the structure and properties of the manufactured HAp as well as a variety of synthesis methods, including hydrothermal, microwave-assisted, co-precipitation, sol-gel, and solid-state approaches. Additionally, the benefits and drawbacks of various synthesis techniques and ways to get around them to spur more research are also covered. This literature discusses the various applications, including photocatalytic degradation, adsorptions, and protein and drug carriers. The photocatalytic activity is mainly focused on single-phase, doped-phase, and multi-phase HAp, while the adsorption of dyes, heavy metals, and emerging pollutants by HAp are discussed in the manuscript. Furthermore, the use of HAp in treating bone disorders, drug carriers, and protein carriers is also conferred. In light of this, the development of HAp-based nanocomposites will inspire the next generation of chemists to improve upon and create stable nanoparticles and nanocomposites capable of successfully addressing major environmental concerns. This overview's conclusion offers potential directions for future study into HAp synthesis and its numerous applications., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Herein, a novel nanocomposite, namely, Zn-modified CeO 2 @biochar (Zn/CeO 2 @BC), is synthesized via facile one-step sol-precipitation to study its photocatalytic activity towards the removal of methylene blue dye. Firstly, Zn/Ce(OH) 4 @biochar was precipitated by adding sodium hydroxide to cerium salt precursor; then, the composite was calcined in a muffle furnace to convert Ce(OH) 4 into CeO 2 . The crystallite structure, topographical and morphological properties, chemical compositions, and specific surface area of the synthesized nanocomposite are characterized by XRD, SEM, TEM, XPS, EDS, and BET analysis. The nearly spherical Zn/CeO 2 @BC nanocomposite has an average particle size of 27.05 nm and a specific surface area of 141.59 m 2 /g. All the tests showed the agglomeration of Zn nanoparticles over the CeO 2 @biochar matrix. The synthesized nanocomposite showed remarkable photocatalytic activity towards removing methylene blue, an organic dye commonly found in industrial effluents. The kinetics and mechanism of Fenton-activated dye degradation were studied. The nanocomposite exhibited the highest degradation efficiency of 98.24% under direct solar irradiation of 90 min, at an optimum dosage of 0.2 g l -1 catalyst and 10 ppm dye concentration, in the presence of 25% (V/V) 0.2 ml (4 µl/ml) hydrogen peroxide. The hydroxyl radical generated from H 2 O 2 during the photo-Fenton reaction process was attributed to the nanocomposite's improved photodegradation performance. The degradation process followed pseudo-first-order kinetics having a rate constant (k) value of 0.0274 min -1 ., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Concerns over the availability of clean water and the quality of treated wastewater are significant problems that call for an appropriate solution to improve the water quality. The present work emphasized the synthesis of novel SnS 2 quantum dots (QDs) deposited on chitosan via a facile green precipitation method involving neem (Azadirachta indica) leaf extract and investigating its photocatalytic performance for the degradation of Crystal violet (CV) dye under varying reaction parameters, other organic and inorganic salts and water matrices. The crystal structure, surface morphology, and elemental composition of the prepared SnS 2 (QDs)/Ch composite were evaluated by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL) and energy dispersive X-ray analysis (EDAX) techniques. The average size of SnS 2 /Chitosan nanoparticles was calculated to be 8.8 nm using XRD, with the average diameter of SnS 2 QDs to be 3.3 nm from TEM. UV-visible spectroscopy was used to investigate its optical properties. The direct band gap of SnS 2 /Chitosan estimated from Tauc's plot came to be 2.5 eV. The prepared novel SnS 2 /Ch composite showed outstanding photocatalytic activity for the degradation of CV through the Advanced Oxidation Process (AOP). The fabricated photocatalyst caused 98.60 ± 1.34 % degradation of CV within a short period of 70 min under optimum conditions. The photodegradation reaction followed pseudo-first-order rate kinetics with a rate constant of 0.0815 min -1 . Furthermore, the photocatalyst showed high stability and was reusable for up to four cycles. The present work fulfils the aim of designing a novel, green, and efficient visible light-active nano-photocatalyst., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

The n-n-type ZnO-SnO 2 nanocomposite was fabricated using malic acid following a simple one-pot co-precipitation method. The fabricated ZnO-SnO 2 nanocomposite was employed as a photocatalyst in the degradation of Biebrich scarlet dye under UV 254 light. TEM, SAED, XRD, XPS, EDX, FTIR, and UV spectra have been recorded to characterize the synthesized ZnO-SnO 2 nanostructures. TEM studies found that the average particle size was 10-12 nm, and the SAED confirmed the polycrystalline nature of the synthesized nanocomposite. It was found that 97% of 10 mg/L Biebrich scarlet dye was degraded by 25 mg/L of photocatalyst within 40-min irradiation of UV 254 light at an optimum pH of 6. Further studies showed that the degradation followed pseudo-first-order kinetics with a rate constant of 5.48 × 10 -2  min -1 . The fabricated ZnO-SnO 2 nanocomposite was reusable up to 8 times; hence, it proved to be an efficient catalyst for the photodegradation of Biebrich scarlet dye., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)