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This review article summarizes the last few decades of research on nickel hydroxide, an important material in physics and chemistry, that has many applications in engineering including, significantly, batteries. First, the structures of the two known polymorphs, denoted as α-Ni(OH)2 and β-Ni(OH)2, are described. The various types of disorder,which are frequently present in nickel hydroxide materials, are discussed including hydration, stacking fault disorder, mechanical stresses and the incorporation of ionic impurities. Several related materials are discussed, including intercalated α-derivatives and basic nickel salts. Next, a number of methods to prepare, or synthesize, nickel hydroxides are summarized, including chemical precipitation, electrochemical precipitation, sol - gel synthesis, chemical ageing, hydrothermal and solvothermal synthesis, electrochemical oxidation, microwaveassisted synthesis, and sonochemical methods. Finally, the known physical properties of the nickel hydroxides are reviewed, including their magnetic, vibrational, optical, electrical and mechanical properties. The last section in this paper is intended to serve as a summary of both the potentially useful properties of these materials and the methods for the identification and characterization of 'unknown' nickel hydroxide-based samples.

Microbially induced calcium carbonate precipitation (MICP) is a potential method for improvement of soil. A laboratory study was conducted to investigate the influence of temperatures for soil improvement by MICP. The ureolytic activity experiments, MICP experiments in aqueous solution and sand column using Sporosarcina pasteurii were conducted at different temperatures(10, 15, 20, 25 and 30°C). The results showed there were microbially induced CaCO3 precipitation at all the temperatures from 10 to 30°C. The results of ureolytic activity experiments showed that the bacterial had higher ureolytic activity at high temperatures within the early 20 hours, however, the ureolytic activity at higher temperatures decreased more quickly than at lower temperatures. The results of MICP experiments in aqueous solution and sand column were consistent with tests of ureolytic activity. Within 20 to 50 hours of the start of the test, more CaCO3 precipitation was precipitated at higher temperature, subsequently, the precipitation rate of all experiments decreased, and the higher the temperature, the faster the precipitation rate dropped. The final precipitation amount of CaCO3 in aqueous solution and sand column tests at 10 °C was 92% and 37% higher than that at 30 °C. The maximum unconfined compressive strength of MICP treated sand column at 10 °C was 135% higher than that at 30 °C. The final treatment effect of MICP at lower temperature was better than that at high temperature within the temperature range studied. The reason for better treatment effect at lower temperatures was due to the longer retention time of ureolytic activity of bacteria at lower temperatures.

Nowadays, antimicrobial agents are currently being employed using noble metal nanoparticles such as gold and silver. NiO nanoparticles are a good alternative in this case, since they are less expensive than gold and silver. Antimicrobial agents are very important in textiles, water disinfection, medicine and food packaging. Most of these applications employ nanoparticles of specific shape, size and chemical composition. For these reason, present work focuses on synthesis of Nickel oxide nanoparticles by Chemical precipitation method. Obtained particles by this method were characterizes for their structural, optical, and antimicrobial properties after calcination process at various temperature of 400 °C, 600 °C, and 800 °C at 2 h. The Rietveld refinement was carried out to obtain the crystal structure and purity of synthesis was achieved. The analysis of peak broadening was performed to estimate the discrepancy in crystallite size and microstrain components of the nanoparticles with the calcination temperatures and were compared with Transmission Electron Microscope results. The calculated band gap value varies from 3.37 to 3.3 eV by increasing the calcination temperature. The emission peak at 490 and 580 nm affirmed the presence of defects in the NiO lattice. The formation of NiO was confirmed using FTIR for all the calcination at different temperatures nanoparticles. Antimicrobial activities of prepared nanoparticles were tested against selected four distinct pathogenic bacterial and three non-identical fungi species by the disc diffusion method. Results of the zone of inhibition values (mm) indicate that the test samples were exhibited significant antimicrobial activity.

We reported on the synthesis of nanosized hydroxyapatite particles by wet chemical precipitation method and the consolidation of the nanoparticles by spark plasma sintering. We studied the effect of the synthesis temperature on the particle size and phase composition of the obtained HAp. During synthesis beyond HAp, another phase supposedly nonstoichiometric HAp was also formed as a by-product that can be detected by thermal analysis combined with XRD. Its amount gradually decreased with the increase in synthesis temperature and practically disappeared at 80 °C. Using this nanopowder for sintering, the spark plasma-sintered ceramics retained their nanostructure comprising only HAp phase in contrast to the powders synthesized at lower temperature when transformed products of the nonstoichiometric HAp could also be detected.

Studies on chemical precipitation of the calcium orthophosphates have shown that their phase compositions do not vary depending on molar ratio Ca/P but are sensitive to solutions acidity and temperature. These are two key factors that determine the phase transformation progress of metastable phases into less soluble precipitates of the phosphates. It was proposed to compare calcium orthophosphates solubility products with calcium cations quantities in their formulas. It was found that there was a linear correlation between calcium orthophosphates specific solubility products and their molar ratios Ca/P if hydroxyapatite and its Ca-deficient forms were excluded from consideration. It was concluded that the relatively large deviations of their solubility products from the found correlation should be thought of as erroneous data. That is why solubility products were changed in accordance with correlation dependence: pKS for hydroxyapatite was 155, pKS for Ca-deficient hydroxyapatites was 114–155. The solubility isotherms, which were calculated on the basis of the corrected pKS values, coincided with the experimental data on solid-phase titration by Pan and Darvell.

This research work reports the magnetic adsorption of fluoride from drinking water through silica-coated Fe3O4 nanoparticles. Chemical precipitation and wet impregnation methods were employed to synthesize the magnetic nanomaterials. Moreover, the synthesized nanomaterials were characterized for physicochemical properties through scanning electron microscopy, Fourier-transform infrared spectroscopy, and X-ray powder diffraction. Screening studies were conducted to select the best iron oxide loading (0.0–1.5 wt%) and calcination temperature (300–500 °C). The best selected nanomaterial (0.5Fe-Si-500) showed a homogenous FeO distribution with a 23.79 nm crystallite size. Moreover, the optimized reaction parameters were: 10 min of contact time, 0.03 g L−1 adsorbent dose, and 10 mg L−1 fluoride (F−) concentration. Adsorption data were fitted to the Langmuir and Freundlich isotherm models. The Qm and KF (the maximum adsorption capacities) values were 5.5991 mg g−1 and 1.869 L g−1 respectively. Furthermore, accelerated adsorption with shorter contact times and high adsorption capacity at working pH was among the outcomes of this research work.

In the current study, the combined anti-tumor efficacy of bioactive hydroxyapatite nano- particles (HA-NPs) loaded with altretamine (ALT) was evaluated. The well-known fact that HA has great biological compatibility was confirmed through the findings of the hemolytic experiments and a maximum IC50 value seen in the MTT testing. The preparation of HA-NPs was performed using the chemical precipitation process. An in vitro release investigation was conducted, and the results demonstrated the sustained drug release of the altretamine-loaded hydroxyapatite nanoparticles (ALT-HA-NPs). Studies using the JURKAT E6.1 cell lines MTT assay, and cell uptake, as well as in vivo pharmacokinetic tests using Wistar rats demonstrated that the ALT-HA-NPs were easily absorbed by the cells. A putative synergism between the action of the Ca2+ ions and the anticancer drug obtained from the carrier was indicated by the fact that the ALT-HA-NPs displayed cytotoxicity comparable to the free ALT at 1/10th of the ALT concentration. It has been suggested that a rise in intracellular Ca2+ ions causes cells to undergo apoptosis. Ehrlich’s ascites model in Balb/c mice showed comparable synergistic efficacy in a tumor regression trial. While the ALT-HA-NPs were able to shrink the tumor size by six times, the free ALT was only able to reduce the tumor volume by half.

This study presents a sustainable method for converting waste Charru mussel shells into high-value biomaterials: calcium oxide (CaO) and hydroxyapatite (HAp). The CaO extraction was optimized by investigating calcination temperatures (750 °C, 850 °C, and 950 °C) and durations (2, 3, and 4 h). Higher temperatures and longer durations increased calcium and decreased carbon content, confirming effective decomposition. Fourier Transform Infrared (FTIR) spectroscopy confirmed the absence of carbonate peaks at 950 °C, identifying 950 °C for 2 h as the optimal condition for complete decomposition without sintering. At this temperature, XRF analysis indicated the highest CaO conversion of approximately 63%. Subsequently, the extracted CaO was used to synthesize HAp via wet chemical precipitation. The researchers optimized the synthesis by varying phosphate precursor concentrations (0.30 M, 0.33 M, and 0.36 M) and aging times (0, 12h, and 24h). According to the two-way ANOVA, the gravimetric HAp yield (0.75–0.88 g HAp/g CaO) was not significantly impacted by variations in phosphate concentration (p = 0.097) or aging time (p = 0.109), indicating these parameters are more critical for controlling HAp quality than the quantity synthesized. Analysis using SEM-EDX revealed fine, spherical-shaped and small aggregates HAp particles. X-Ray Diffraction (XRD) confirmed the presence of characteristic peaks of HAp and its crystallite size. FTIR confirmed the characteristic HAp functional groups. Treatments with phosphate precursor concentrations of 0.33 M and 0.36 M aged for 24 h produced Ca/P molar ratios of 1.70 and 1.93, respectively, close to the ideal stoichiometric ratio (1.67). Moreover, these treatments produced crystallinities of 78.30% and 77.14%, respectively, which are considered suitable for drug delivery and bone scaffold applications. This research highlights the potential of Charru mussel shell waste for producing high-value biomaterials for biomedical applications, as well as addresses the ecological threat of invasive species in Philippine aquaculture, providing a method for population control and waste valorization that directly supports UN Sustainable Development Goal 14, Life Below Water.

In this paper, α-Fe2O3 was prepared by hydrothermal and chemical precipitation methods, respectively, and its gas sensing properties toward CH4 were systematically studied. The larger specific surface area of the materials provided them potential and considerable gas adsorption abilities. The results of gas-sensing measurements indicated the synthesized α-Fe2O3 materials presented a p-type conductive nature. The sensitivities of the devices based on the different material fabrication methods were measured to be 195% and 214%, respectively, at 370°C for the concentration of 2000 ppm CH4. In addition, the sensing mechanism was discussed and simulated by first-principles calculation. The results revealed the higher surface adsorption energy of α-Fe2O3, which verified the experimental conclusions of our work. Our research suggests that α-Fe2O3 is a promising candidate for CH4 gas sensing in many fields such as mining safety and environmental monitoring.

Electrode materials are important indicators for evaluating the performance of electrochemical capacitors, and designing nanostructured materials with high specific capacitance and excellent cycling stability performance is an important way to enhance the performance of supercapacitors. In this study, cetyltrimethylammonium bromide (CTAB) was used as a cationic surfactant, and flower cluster-like Mn 3 O 4 particles were prepared by the vesicle soft template method, and different concentrations of CTAB were set in order to investigate its effect on the formation and electrical properties of Mn 3 O 4 nanoparticles. Physical and electrochemical characterization was carried out using various means such as XRD, SEM, TEM, BET, CV, EIS, and GCD. The results show that the Mn 3 O 4 electrode material exhibits a higher specific capacitance of 261 F/g in 1 M Na 2 SO 4 electrolyte when the current density is 0.5 A/g and still maintains 253 F/g when the current density is increased to 10 A/g. Excellent capacitance retention is observed after 10,000 cycles at a current density of 5 A/g (up to 93%). In addition, a Mn 3 O 4 //AC asymmetric supercapacitor (ASC) was assembled using Mn 3 O 4 as the positive electrode and commercially available activated carbon (AC) as the negative electrode, and the device provided a maximum energy density of 30.56 Wh/kg at 452.74 W/kg.