Green Synthesis and Applications of ZnO and TiO2 Nanostructures

Abstract

Over the last two decades, oxide nanostructures have been continuously evaluated and used in many technological applications. The advancement of the controlled synthesis approach to design desired morphology is a fundamental key to the discipline of material science and nanotechnology. These nanostructures can be prepared via different physical and chemical methods; however, a green and ecofriendly synthesis approach is a promising way to produce these nanostructures with desired properties with less risk of hazardous chemicals. In this regard, ZnO and TiO2 nanostructures are prominent candidates for various applications. Moreover, they are more efficient, non-toxic, and cost-effective. This review mainly focuses on the recent state-of-the-art advancements in the green synthesis approach for ZnO and TiO2 nanostructures and their applications. The first section summarizes the green synthesis approach to synthesize ZnO and TiO2 nanostructures via different routes such as solvothermal, hydrothermal, co-precipitation, and sol-gel using biological systems that are based on the principles of green chemistry. The second section demonstrates the application of ZnO and TiO2 nanostructures. The review also discusses the problems and future perspectives of green synthesis methods and the related issues posed and overlooked by the scientific community on the green approach to nanostructure oxides.

Green Fabrication of Zinc Oxide Nanoparticles Using Phlomis Leaf Extract: Characterization and In Vitro Evaluation of Cytotoxicity and Antibacterial Properties

“…Flavonoids, iridoids, diterpenoids, phenylpropanoids, triterpenoids, and other phenolic compounds detected in phlomis leaf extract may have played a role in nanoparticle formation, according to prior research [30]. Furthermore, as indicated by the foregoing results, the functional groups -OH (hydroxyl), -C=O (Carbonyl), and C-N (amine) found in the leaf extract were definitely implicated in the formation of ZnO NPs [31].…”

Breast Cancer Inhibition by Biosynthesized Titanium Dioxide Nanoparticles Is Comparable to Free Doxorubicin but Appeared Safer in BALB/c Mice

“…In the hunt for new anticancer drugs, there is a significant progress in the fabrication and characterization of tailored metal oxide NPs for the treatment of cancers. Over the last two decades, oxide metallic nanostructures have been continuously designed, evaluated, and used in many applications [12,15,16]. Thereby, various metals (e.g., titanium, silver, zinc) were used to design metallic NPs via synthetic or natural methods, and strengthen the pharmaceutical and medical potential [12,16,17].…”

“…Eventually, most of the published studies reported that TiO 2 nanostructures prepared via different physical and chemical routes through bottom-up or top-down approaches (e.g., sol-gel, hydrothermal, solvothermal, hydrolysis, thermolysis, flame, and co-precipitation) [28,29]. These methods were sometimes combined with the principles of 'green chemistry' [15]. However, these synthesis approaches required relatively high temperature pressure, optimization of other parameters (e.g., pH, reaction time) or entail expensive and noxious chemicals, which make such TiO 2 NPs unsuitable for their use as a safe theranostic modality [16,30].…”

“…However, these synthesis approaches required relatively high temperature pressure, optimization of other parameters (e.g., pH, reaction time) or entail expensive and noxious chemicals, which make such TiO 2 NPs unsuitable for their use as a safe theranostic modality [16,30]. Hence, the focus has shifted to the use of an eco-friendly, green, and cost-effective approach to synthesize, by combining principles of 'green chemistry' [15], or by metal bioreduction [16], various nanostructures with desired properties and less or no risk of hazardous chemicals [31]. Thereby, chemically 'green' syntheses of TiO 2 nanostructures have been recently reported as valuable options to reduce eco-toxicity and lower the energy waste associated with chemicals.…”

Green Synthesis of Flower-Shaped Copper Oxide and Nickel Oxide Nanoparticles via Capparis decidua Leaf Extract for Synergic Adsorption-Photocatalytic Degradation of Pesticides

“…Sustainable treatment approaches must consider the approach holistically, beyond the system level. Photocatalyst synthesis has to consider green and sustainable approaches to minimize environmental impact when considering the overall lifecycle of a treatment technology [26][27][28]. In recent decades, conventional metal oxide nanoparticle synthesis methods have relied on the use of hazardous chemicals and solvents plus energy-intensive approaches [29][30][31][32].…”