Nickel nanoparticles have wide-ranging applications in diverse fields, including electronics, catalysis, and biomedicine. The unique properties of these nanoparticles depend on their physical and chemical attributes. Consequently, there is a growing interest in understanding the performance relationships through a nuanced comprehension of their controlled synthesis. This review explores the advancements related to precisely defined nickel nanoparticles, with a specific focus on unraveling the connections between performance and their physical/chemical characteristics. The emphasis is on elucidating how manipulating synthetic parameters, such as precursor concentration, reductant agent properties, temperature, time, and the presence of stabilizing agents, can provide additional avenues for refining the performance in terms of size and morphology. Through the analysis of each variable, we illustrate the methodology for synthesizing well-controlled nickel nanoparticles, showcasing the ability to exert precision over their composition, size, and surface morphology.

The widespread utilization of plastic materials across various industrial sectors drives a continuous increase in global polymer demand. The exponential production growth generates severe environmental challenges regarding municipal solid waste management, as substantial fractions of post-consumer residuals enter landfills due to limited recycling infrastructure. Mitigating the global environmental burden requires the implementation of advanced recovery strategies to transition polymer waste into viable secondary feedstocks. Consequently, deploying efficient sorting techniques constitutes a fundamental requirement to integrate plastic materials into formal waste management protocols and optimize recycling yields. Technological innovations currently drive the transition from traditional manual segregation towards highly sophisticated automated sensor-based sorting architectures, maximizing separation efficiency. In this context, the present study comprehensively reviews pretreatment classification techniques engineered to fractionate heterogeneous waste streams into high-purity material flows. Rather than restricting the analysis to polyolefins, this review encompasses a broad spectrum of commodity polymers predominantly found in urban solid waste environments.

The sol–gel synthesis of titanium dioxide (TiO₂) nanostructures is investigated in the present work in order to optimize synthesis parameters and enhance the optical properties and cost-effectiveness of the obtained materials. TiO₂ is widely used in photocatalysis, photovoltaics, and environmental applications due to its high stability, tunable band gap, and strong light absorption. The sol–gel method offers a scalable, cost-effective route for producing nanostructured TiO₂, although the precise control over particle morphology remains challenging. For this reason, in the present work, a statistical design of experiments (DOE) approach is employed to systematically refine reaction conditions through the manipulation of precursor concentrations, solvent ratios, and reaction volume. The experimental results obtained indicate that acetic acid is a key catalyst and stabilizing agent, significantly improving nucleation control and particle formation. Moreover, it is also shown that solvent dilution, particularly with acetic acid, leads to the formation of TiO₂ nanorods with enhanced optical properties. Additionally, scanning electron micrographs revealed that controlled synthesis conditions can reduce the particle size distribution and improve structural uniformity. Moreover, X-ray diffraction analyses confirmed the formation of a pure anatase crystalline phase, while ultraviolet–visible spectroscopy analyses indicated the existence of an optimal band gap for photocatalytic applications. Finally, the cost analysis showed that acetic acid-assisted synthesis can reduce production costs and simultaneously maintain high optical properties. Therefore, the present study highlights that proper manipulation and control of reaction conditions during sol–gel syntheses can allow the manufacture of high-performance TiO₂ nanomaterials for advanced technological applications, also providing a foundation for the development of cost-effective materials.