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► Review on ‘green’ methods for synthesis of nanoparticles using natural products. ► Polyphenols in plant extracts can act as chelating/reducing and capping agents. ► One-step processes without surfactants and capping agents. ► Techniques for a given metal nanoparticle can also be applied to other metals. ► Discussion of experimental setup for biosynthesis of silver nanoparticles. In this review, we examine ‘greener’ routes to nanoparticles of zerovalent metals, metal oxides, and salts with an emphasis on recent developments. Products from nature or those derived from natural products, such as extracts of various plants or parts of plants, tea, coffee, banana, simple amino acids, as well as wine, table sugar and glucose, have been used as reductants and as capping agents during synthesis. Polyphenols found in plant material often play a key role in these processes. The techniques involved are simple, environmentally friendly, and generally one-pot processes. Tea extracts with high polyphenol content act as both chelating/reducing and capping agents for nanoparticles. We discuss the key materials used in the field: silver, gold, iron, metal alloys, oxides, and salts.

Compared to conventional metal oxide nanoparticles, metal oxide nanocomposites have demonstrated significantly enhanced efficiency in various applications. In this study, we aimed to synthesize zinc oxide–copper oxide nanocomposites (ZnO-CuO NCs) using a green synthesis approach. The synthesis involved mixing 4 g of Zn(NO3)2·6H2O with different concentrations of mangosteen (G. mangostana) leaf extract (0.02, 0.03, 0.04 and 0.05 g/mL) and 2 or 4 g of Cu(NO3)2·3H2O, followed by calcination at temperatures of 300, 400 and 500 °C. The synthesized ZnO-CuO NCs were characterized using various techniques, including a UV-Visible spectrometer (UV-Vis), photoluminescence (PL) spectroscopy, Fourier Transform Infrared (FTIR) spectroscopy, X-ray powder diffraction (XRD) analysis and Field Emission Scanning Electron Microscope (FE-SEM) with an Energy Dispersive X-ray (EDX) analyzer. Based on the results of this study, the optical, structural and morphological properties of ZnO-CuO NCs were found to be influenced by the concentration of the mangosteen leaf extract, the calcination temperature and the amount of Cu(NO3)2·3H2O used. Among the tested conditions, ZnO-CuO NCs derived from 0.05 g/mL of mangosteen leaf extract, 4 g of Zn(NO3)2·6H2O and 2 g of Cu(NO3)2·3H2O, calcinated at 500 °C exhibited the following characteristics: the lowest energy bandgap (2.57 eV), well-defined Zn-O and Cu-O bands, the smallest particle size of 39.10 nm with highest surface area-to-volume ratio and crystalline size of 18.17 nm. In conclusion, we successfully synthesized ZnO-CuO NCs using a green synthesis approach with mangosteen leaf extract. The properties of the nanocomposites were significantly influenced by the concentration of the plant extract, the calcination temperature and the amount of precursor used. These findings provide valuable insights for researchers seeking innovative methods for the production and utilization of nanocomposite materials.

Herein, we report the green synthesis of flower-like carrageenan-silver nanoparticles (c-AgNPs) through a facile hydrothermal reaction at 90 °C for 2 h. The reduction of silver nitrate (AgNO3) to c-AgNPs was evident by the colour change of the solution from colourless to dark brown and further confirmed by a UV-Vis surface plasmon resonance (SPR) peak at ~420 nm. The FTIR spectra showed that the abundance of functional groups present in the carrageenan were responsible for the reduction and stabilisation of the c-AgNPs. The XRD pattern confirmed the crystalline nature and face-centred cubic structure of the c-AgNPs, while the EDX analysis showed the presence of a high composition of elemental silver (85.87 wt%). Interestingly, the morphological characterisations by SEM and FE-SEM revealed the formation of flower-like c-AgNPs composed of intercrossed and random lamellar petals of approximately 50 nm in thickness. The growth mechanism of flower-like c-AgNPs were elucidated based on the TEM and AFM analyses. The c-AgNPs displayed promising antibacterial properties against E. coli and S. aureus, with zones of inhibition ranging from 8.0 ± 0.0 to 11.7 ± 0.6 mm and 7.3 ± 0.6 to 9.7 ± 0.6 mm, respectively, as the concentration of c-AgNPs increased from 0.1 to 4 mg/mL.

Sustainable synthesis of reduced graphene oxide (rGO) is of crucial significance within the development of carbon nanomaterials. In this study, a green and eco-friendly strategy for the synthesis of rGO using lemon juice as the reducing agent for graphene oxide (GO) without using toxic and harmful chemicals was demonstrated. The reduction with lemon juice effectively eliminated the oxygen-containing functionalities of GO and regenerated the conjugated systems as confirmed by the UV-vis and FTIR spectroscopic and X-ray diffraction analyses. Microscopic evaluation showed the successful manufacturing of exfoliated and separated few layers of nano-sheets of rGO. The application of the resultant rGO as an adsorbent for organic pollutants was investigated using methylene blue (MB) as a model. The adsorption kinetics of MB on rGO is best matched with the pseudo-second-ordered kinetic model and the Langmuir model with a high adsorption capacity of 132.2 mg/g. The rGO exhibited good reusability with a removal efficiency of 80.4% in the fourth cycle. This green method provides a new prospect for the large-scale production of rGO in a cost-effective and safe manner.

Nanotechnology has become a promising and emerging field of research in creating and modifying nanomaterials for different applications. Nanoparticles are considered to be the basic element of nanotechnology as they are the primary source of several nanostructured materials. During the last few decades, several metal oxide nanoparticles (NPs) were synthesized and their applications were investigated in various fields of science and technology, including biomedical, environmental, energy and agricultural practices. Moreover, metal oxide NPs have been synthesized by physical and chemical methods, while the chemical method used different chemicals as reducing and stabilizing agents. However, the wet chemical synthesis strategy become responsible for various biological and environmental risks due to the toxicity of used chemicals. Recently, biological synthesis of metal oxide nanoparticles using plants, algae, and microbes as a source of precursor material has emerged as a green and safe method. Additionally, the green synthesized metal oxide nanoparticles have shown a pivotal role in several applications such as nano-adsorbents, nano-membranes, photocatalysts and disinfection of wastewater from microbes. In this review, we present an overview of the biosynthesis of metal oxide nanoparticles such as; ZnO, CeO 2 , TiO 2 , CdO, CuO, Fe 3 O 4 , SnO 2 , NiO etc. Their method of characterization and properties is also discussed. Finally, their applications towards environmental protection is presented with particular attention to water treatment and remediation.

The quest to synthesize nanomaterials with improved properties, but less undesirable effects on the environment necessitated this research. Zinc Oxide (ZnO) nanoparticles and zinc oxide–silver (ZnO–Ag), zinc oxide–copper (ZnO–Cu) nanocomposites were synthesized with pure eco-friendly dye extracted from Bridelia ferruginea , zinc acetate (Zn(CH 3 COO) 2 ) as host, copper acetate (Cu (CH 3 COO) 2 ), and silver nitrate (AgNO 3 ) as dopant precursors. Phytochemical screening of dyes showed high, presence of phenols and terpenoids. The nanomaterials were characterized by Fourier-transform infrared, X-ray diffraction, scanning electron microscopy with energy dispersive X-ray analysis, transmission electron microscopy and ultraviolet–visible spectroscopy. The results showed the capping agents in the dyes were responsible for reducing the bulk materials. The crystallinity of the nanomaterials were found to be 19.02, 18.98 and 18.90 nm for the ZnO, ZnO–Ag and ZnO–Cu nanoparticles respectively. The ZnO nanoparticles were flakelike in shape, whereas the Cu and Ag doped particles were spherical. An optical bandgap of 4.73 eV was recorded for the dye and 3.24 eV for the ZnO nanoparticles. This was narrowed to 3.18 and 3.13 eV by silver and copper dopant respectively. These results showed the nanoparticles as a potential agent for photovoltaics and other optical applications.

Green synthesis method for nanoparticle synthesis offers many advantages over physical and chemical methods as it does not involve any hazardous chemicals and also it is a one-pot, and economically cheap process. In this regard, the present research describes the green synthesis of Zinc oxide nanoparticles (ZnO-NPs) using Punica granatum leaf extract. The various properties such as morphological, structural, and optical properties of green zinc oxide nanoparticles were characterized by Transmission Electron Microscopy (TEM), Fourier Transform Infrared Spectroscopy, UV–Visible spectroscopy, Field Emission Scanning Electron Microscopy (FESEM), Energy Dispersive X-ray Spectroscopy and X-Ray diffraction (XRD). The XRD pattern revealed the crystalline nature of ZnO-NPs and the average diameter of particles is 20 nm.TEM and FESEM analysis show the spherical shape of ZnO-NPs with size ranging from 10 to 30 nm. The synthesized ZnO-NPs shows the commendable potential towards the photocatalytic degradation of Coomassie brilliant blue R-250 dye under direct sunlight irradiations. Thus, this work provides a positive step in the area of a green photocatalyst to alleviate the noxious dyes from water. Graphical abstract

In the present work, copper oxide nanoparticles have been fabricated by using a biological method. Copper oxide nanoparticles (CuO NPs) have received more attention than other metal oxides due to their distinctive properties and applications. Plant-mediated synthesis of nanoparticles has gained the attention of researchers because of its simple and ecologically sustainable approach. The biosynthesis of CuO NPs included the use of Passiflora edulis leaf extract that acts as a stabilizing and reducing agent. A non-toxic, cost-effective, and ecologically acceptable method was the use of plant leaf extract in the biogenesis of nanoscale materials. UV-vis, SEM, FTIR, and XRD techniques were used to examine the biologically produced copper oxide nanoparticles. The findings of the SEM examination, which gives morphological information, demonstrate that the synthesized NPs have a spherical shape and have an average particle size of between 60 and 65 nm. CuO has been further investigated in the current study as a photo-catalyst in the methylene blue (MB) dye degradation and as an antioxidant in free radical scavenging activities. The decolorization efficiency was approximately 93% after 160 min. Furthermore, CuO nanoparticles were tested for antioxidant performance by scavenging 2, 2-diphenyl-1-picrylhydrazyl hydrate free radicals (DPPH) and evaluated by UV-Vis spectroscopy. The result showed that biologically synthesized CuO NPs can be used as an effective antioxidant. The half maximal inhibitory concentration IC50 of copper oxide nanoparticles was found to be in the range of 0.13–0.20.

Abundant lignocellulosic biomass components have been a source of inspiration for designing complex materials with high surface area and potent applications in a wide variety of commercial products, including water purification, biosensors, catalysis, and others. Billion tons of lignocellulosic biomass waste are produced in a year. This lignocellulosic biomass waste could be a good source of precursor for activated carbon and other carbonbased nanomaterials. Activated carbon was prepared from Seed pods of lignocellulosic biomass of Jacaranda mimosifolia, which was treated as waste using a single-step green method of synthesis. Synthesized activated carbon was characterized using high-resolution scanning electron microscopy (HRSEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), N2 adsorption/desorption, and Zeta potential. It was evident that the synthesis method was free from chemical use and thus eco-friendly. We have reported maximum removal of heavy metal, lead ion (Pb+2), and dye Eriochrome Black T (EBT) using prepared activated carbon was 58.77 and 286.56 mg·g-1, respectively. The adsorption was rapid, with 97% of Pb+2 and 90% of EBT adsorption accomplished within 60 min. The synthesized material could be used in the design of a filter for sustainable water purification.

The application of plant extracts or plant-derived compounds in the green synthesis of metal nanoparticles (NPs) was researched. Determining the exact metabolite implicated in the formation of NPs would necessitate comprehensive investigations. Copper nanoparticles (CuNPs) are gaining a lot of attention because of their unique properties and effectiveness against a wide range of bacteria and fungi, as well as their potential for usage in catalytic, optical, electrical, and microelectronics applications. In the course of this study, we aimed to formulate CuNPs utilizing pure tamarixinin A (TA) ellagitannin isolated from Tamarix aphylla galls. The main particle size of the formed CuNPs was 44 ± 1.7 nm with zeta potential equal to −23.7 mV, which emphasize the stability of the CuNPs. The X-ray diffraction spectroscopy showed a typical centered cubic crystalline structure phase of copper. Scanning electron microscopy images were found to be relatively spherical and homogeneous in shape. The antimicrobial properties of TA, as well as its mediated CuNPs, have been evaluated through well diffusion assays against four bacterial, Bacillus subtilis NCTC 10400, Staphylococcus aureus ATCC 25923, Escherichia coli ATCC 25922, and Pseudomonas aeruginosa ATCC 27853, and two fungal, Candida albicans and Aspergillus flavus, strains. The distinctive antimicrobial activities were noted against the fungal strains and the Gram-negative bacterial strains P. aeruginosa ATCC 27853, and E. coli ATCC 25922. In conclusion, CuNPs mediated by TA can be applied for combating a wide range of bacterial and fungal species especially C. albicans, Asp. flavus, and P. aeruginosa in a variety of fields.