Green synthesis of metal oxide nanostructures using naturally occurring compounds for energy, environmental, and bio-related applications

This review summarizes the synthesis and functional applications of metal oxide nanostructures synthesized using plant-derived phytochemicals for energy, environmental, and biomedical applications.

A Review on Green Synthesis and Applications of Cu and CuO Nanoparticles

Green routes of synthesis are simple, safe, nontoxic and eco-friendly methods to synthesize nanoparticles of various metals and their oxides by the application of bioactive compounds of plants, algae, fungi, yeast, etc. Green engineered copper and copper oxide nanoparticles (Cu and CuO NPs) synthesis has been reported to be more economical and best alternative method among available methods. Cu and CuO NPs have been applied as dietary additives, lubricant supplements, chemical sensors, coating materials in addition to large number of biotechnological and pharmaceuticals applications. The present review aims to bring awareness about various aspects of biogenic synthesis of Cu and its oxide NPs for multifunctional applications and discusses their characterization techniques and applications in antimicrobial activity evaluation, photocatalysis, organic dye degradation, biomedical, pharmaceutical, cosmetic, energy and catalysis.

Biosynthesis of copper nanoparticles using aqueous Tilia extract: antimicrobial and anticancer activities

A cost-effective method for the biosynthesis of copper nanoparticles (Cu-NPLs) using Tilia extract under optimum conditions has been presented. The use of Tilia extracts for the synthesis of Cu-NPLs has been investigated for the first time. The Cu-NPLs are stable due to in situ bio-capping by the Tilia extract residues. Formation of metallic Cu was revealed by UV-vis and XRD analyses. UV-vis of Cu-NPLs showed an SPR characteristic peak at 563 nm (energy bandgap = 2.1 eV). Morphology and size of the as-prepared Cu-NPLs were determined using SEM and TEM studies. TEM observations show that the produced Cu-NPLs are hemispherical in shape with different diameters in the range 4.7-17.4 nm. The electrical conductivity of the Cu-NPLs was determined as 1.04 × 10-6 S cm-1 (at T = 120 K). The antimicrobial studies exhibited relatively high activity against pathogenic bacteria like Gram-positive & Gram-negative bacteria. Anticancer studies demonstrated the in vitro cytotoxicity value of Cu-NPLs against tested human colon cancer Caco-2 cells, human hepatic cancer HepG2 cells and human breast cancer Mcf-7 cells. To conclude, Cu-NPLs are promising in electronic devices and they possess a potential anticancer application for some human cancer therapy as well.

From biotechnology principles to functional and low-cost metallic bionanocatalysts

Chemical, physical and mechanical methods of nanomaterial preparation are still regarded as mainstream methods, and the scientific community continues to search for new ways of nanomaterial preparation. The major objective of this review is to highlight the advantages of using green chemistry and bionanotechnology in the preparation of functional low-cost catalysts. Bionanotechnology employs biological principles and processes connected with bio-phase participation in both design and development of nano-structures and nano-materials, and the biosynthesis of metallic nanoparticles is becoming even more popular due to; (i) economic and ecologic effectiveness, (ii) simple one-step nanoparticle formation, stabilisation and biomass support and (iii) the possibility of bio-waste valorisation. Although it is quite difficult to determine the precise mechanisms in particular biosynthesis and research is performed with some risk in all trial and error experiments, there is also the incentive of understanding the exact mechanisms involved. This enables further optimisation of bionanoparticle preparation and increases their application potential. Moreover, it is very important in bionanotechnological procedures to ensure repeatability of the methods related to the recognised reaction mechanisms. This review, therefore, summarises the current state of nanoparticle biosynthesis. It then demonstrates the application of biosynthesised metallic nanoparticles in heterogeneous catalysis by identifying the many examples where bionanocatalysts have been successfully applied in model reactions. These describe the degradation of organic dyes, the reduction of aromatic nitro compounds, dehalogenation of chlorinated aromatic compounds, reduction of Cr(VI) and the synthesis of important commercial chemicals. To ensure sustainability, it is important to focus on nanomaterials that are capable of maintaining the important green chemistry principles directly from design inception to ultimate application.

Molecular insight to in vitro biocompatibility of phytofabricated copper oxide nanoparticles with human embryonic kidney cells

Aim: To investigate the biocompatibility of green synthesized copper oxide nanoparticles (CuO Np) using floral extract of Calotropis gigantea in room condition. Materials & methods: Green synthesized and characterized CuO Np was evaluated for their cellular and molecular biocompatibility by experimentally and computational molecular docking. Results: Synthesized CuO NP was found to have a size 32 ± 09 nm with ζ potential -35 ± 12 mV. LC50 value was found to be 190 μg/ml. In vitro and in silico cytotoxicity analysis with HEK293 cells revealed the cytotoxic effect of CuO Np as consequences of interaction with histidine and arginine amino acid residues of Sod3 and p53 proteins via hydrogen bond of length 3.09 and 3.32 Å leading to oxidative stress ensuing toward apoptosis and cell cycle arrest. Conclusion: The outcomes proved the synthesized material as an alternative to the conventional method of synthesizing copper nanoparticles for biomedical and clinical applications.

Plant-based metallic nanoparticles as potential theranostics agents: bioinspired tool for imaging and treatment

Theranostic approach provides us a platform where diagnosis and treatment can be carried out simultaneously. Biosynthesis of theranostic-capable nanoparticles (NPs) can be carried out by phytoconstituents present inside the plants that can act as capping as well as stabilising agents by offering several advantages over chemical and physical methods. This article highlights the theranostic role of NPs with emphasis on potential of plants to produce these NPs through ecofriendly approach that is called 'Green synthesis'. Biosynthesis, advantages, and disadvantages of plant-based theronostics have been discussed for better understanding. Moreover, this article has highlighted the approaches required to optimise the plant-mediated synthesis of NPs and to avoid the toxicity of these agents. Anticipating all of the challenges, the authors expect biogenic NPs can appear as potential diagnostic and therapeutic agents in near future.

Salt-Mediated Au-Cu Nanofoam and Au-Cu-Pd Porous Macrobeam Synthesis

Multi-metallic and alloy nanomaterials enable a broad range of catalytic applications with high surface area and tuning reaction specificity through the variation of metal composition. The ability to synthesize these materials as three-dimensional nanostructures enables control of surface area, pore size and mass transfer properties, electronic conductivity, and ultimately device integration. Au-Cu nanomaterials offer tunable optical and catalytic properties at reduced material cost. The synthesis methods for Au-Cu nanostructures, especially three-dimensional materials, has been limited. Here, we present Au-Cu nanofoams and Au-Cu-Pd macrobeams synthesized from salt precursors. Salt precursors formed from the precipitation of square planar ions resulted in short- and long-range ordered crystals that, when reduced in solution, form nanofoams or macrobeams that can be dried or pressed into freestanding monoliths or films. Metal composition was determined with X-ray diffraction and energy dispersive X-ray spectroscopy. Nitrogen gas adsorption indicated an Au-Cu nanofoam specific surface area of 19.4 m²/g. Specific capacitance determined with electrochemical impedance spectroscopy was 46.0 F/g and 52.5 F/g for Au-Cu nanofoams and Au-Cu-Pd macrobeams, respectively. The use of salt precursors is envisioned as a synthesis route to numerous metal and multi-metallic nanostructures for catalytic, energy storage, and sensing applications.

Low-temperature biosynthesis of silver nanoparticles using mango leaf extract: catalytic effect, antioxidant properties, anticancer activity and application for colorimetric sensing

Aqueous mango leaf extract was used as a reducing and capping agent for the biosynthesis of silver nanoparticles (AgNPs)viaa single-step, low cost and green process.

Natural iron ore as a novel substrate for the biosynthesis of bioactive-stable ZnO@CuO@iron ore NCs: a magnetically recyclable and reusable superior nanocatalyst for the degradation of organic dyes, reduction of Cr(vi) and adsorption of crude oil aromatic compounds, including PAHs

For the first time, stable ZnO@CuO@iron ore nanocomposites (NCs) were green synthesized using magnetic iron ore as a natural substrate through an eco-friendly, simple and cost-effective method.

Green Adeptness in the Synthesis and Stabilization of Copper Nanoparticles: Catalytic, Antibacterial, Cytotoxicity, and Antioxidant Activities

Copper nanoparticles (CuNPs) are of great interest due to their extraordinary properties such as high surface-to-volume ratio, high yield strength, ductility, hardness, flexibility, and rigidity. CuNPs show catalytic, antibacterial, antioxidant, and antifungal activities along with cytotoxicity and anticancer properties in many different applications. Many physical and chemical methods have been used to synthesize nanoparticles including laser ablation, microwave-assisted process, sol-gel, co-precipitation, pulsed wire discharge, vacuum vapor deposition, high-energy irradiation, lithography, mechanical milling, photochemical reduction, electrochemistry, electrospray synthesis, hydrothermal reaction, microemulsion, and chemical reduction. Phytosynthesis of nanoparticles has been suggested as a valuable alternative to physical and chemical methods due to low cytotoxicity, economic prospects, environment-friendly, enhanced biocompatibility, and high antioxidant and antimicrobial activities. The review explains characterization techniques, their main role, limitations, and sensitivity used in the preparation of CuNPs. An overview of techniques used in the synthesis of CuNPs, synthesis procedure, reaction parameters which affect the properties of synthesized CuNPs, and a screening analysis which is used to identify phytochemicals in different plants is presented from the recent published literature which has been reviewed and summarized. Hypothetical mechanisms of reduction of the copper ion by quercetin, stabilization of copper nanoparticles by santin, antimicrobial activity, and reduction of 4-nitrophenol with diagrammatic illustrations are given. The main purpose of this review was to summarize the data of plants used for the synthesis of CuNPs and open a new pathway for researchers to investigate those plants which have not been used in the past. Graphical abstract Proposed Mechanism for Antibacterial activity of copper nanoparticles.

Synthesis paradigm and applications of silver nanoparticles (AgNPs), a review

Nanoscience is an inspiring and influential discipline of science which have accessible numerous novel and cost-effective yields and applications. Currently, nanotechnology research has been empowering more in agricultural sector, food process and medicinal industries. The surface area to volume ratio of nanoparticles is quite large which have 1–100 nm size. Nanomaterials have superior bioavailability than larger particles, resulting in greater utilization in single cells, tissues and organs. Referable to the growing demand of nanoparticles, it is essential to build up synthetic method which is profitable, environmentally sustainable and which can substitutes with effective and competent technology to synthesis environmentally benign nanoparticles (NPs). Nanomaterials are “deliberately engineered” to direct the enhancement of special properties at the nanoscale. Nanoparticles have been known to be used for abundant physical, biological, and pharmaceutical applications. Nano-silver is the most studied and utilized nanoparticle. Silver nanoparticles (AgNPs) have been the topics of researchers because of their unique properties. Thus, this review presents various synthesis methods of AgNPs and its application in different sectors.

Novel synthesis and characterization of pristine Cu nanoparticles for the non-enzymatic glucose biosensor

Non enzymatic electrochemical glucose sensing was developed based on pristine Cu Nanopartilces (NPs)/Glassy Carbon Electrode (GCE) which can be accomplished by simple green method via ocimum tenuiflorum leaf extract. Then, the affect of leaf extract addition on improving Structural, Optical and electrochemical properties of pristine cu NPs was investigated. The synthesized Cu NPs were characterized with X-ray diffraction (X-ray), Uv-Visible spectroscopy (Uv-Vis), Fourier transformation infrared spectroscopy (FTIR), Particle size distribution (PSA), Scanning electron microscopy (SEM), Energy dispersive X-ray spectroscopy (EDS), Transmission electron microscopy (TEM) for structural optical and morphological studies respectively. The synthesized Cu NPs were coated over glassy carbon electrode (GCE) to study the electrochemical response of glucose by cyclic voltammetry and ampherometer. The results indicates that the modified biosensor shows a remarkable sensitivity (1065.21 μA mM^-1 cm^-2), rapid response time (<3s), wide linear range (1 to 7.2 mM), low detection limit (0.038 μM at S/N = 3). Therefore, the prepared Cu NPs by the Novel Bio-mediated route were exploited to construct a non-enzymatic glucose biosensor for sustainable clinical field applications.

Green methods for the synthesis of metal nanoparticles using biogenic reducing agents: a review

Metal nanoparticles are being extensively used in a variety of sectors, including drug delivery, cancer treatment, wastewater treatment, DNA analysis, antibacterial agents, biosensors and catalysts. Unlike chemically produced nanoparticles, biosynthesized metal nanoparticles based on green chemistry perspectives impose limited hazards to the environment and are relatively biocompatible. This review is therefore focused on green methods for nanoparticle synthesis by emphasizing on microbial synthesis using bacteria, fungi, algae, and yeasts, as well as phytosynthesis using plant extracts. Furthermore, a detailed description of bioreducing and capping/stabilizing agents involved in the biosynthesis mechanism using these green sources is presented.

Effect of Gelatin-Stabilized Copper Nanoparticles on Catalytic Reduction of Methylene Blue

The synthesis of copper nanoparticles was carried out with gelatin as a stabilizer by reducing CuSO₄.5H₂O ions using hydrazine. Ascorbic acid and aqueous NaOH were also used as an antioxidant and pH controller, respectively. The effects of NaOH, hydrazine, and concentration of gelatin as stabilizer were studied. The synthesized copper nanoparticles were characterized by UV-vis spectroscopy, XRD, zeta potential measurements, FTIR, EDX, FESEM, and TEM. The formation of CuNPs@Gelatin is initially confirmed by UV-vis spectroscopic analysis with the characteristic band at 583 nm. XRD and TEM reports revealed that CuNPs@Gelatin (0.75 wt.%) is highly crystalline and spherical in shape with optimum average size of 4.21 ± 0.95 nm. FTIR studies indicated the presence of amide group on the surface of the CuNPs indicating the stability of CuNPs which is further supported by zeta potential measurements with the negative optimum value of -37.90 ± 0.6 mV. The CuNPs@G4 showed a good catalytic activity against methylene blue (MB) reduction using NaBH₄ as a reducing agent in an aqueous solution. The best enhanced properties of CuNPs@G4 were found for the 0.75 wt.% gelatin concentration. Thermodynamic parameters (ΔH and ΔS) indicate that under the studied temperature, the reduction of MB by CuNPs@G4 is not feasible and had endothermic in nature.

Photocatalytic decomposition behavior and reaction pathways of organic compounds using Cu nanoparticles synthesized via a green route

Green, facile and environmentally friendly biosynthetic methodology for the fabrication of Cu nanoparticles using an aqueous extract ofAnas platyrhynchosegg shells.

One-pot microwave-assisted in situ reduction of Ag+and Au3+ions by Citrus limon extract and their carbon-dots based nanohybrids: a potential nano-bioprobe for cancer cellular imaging

In situreduction and microwave-assisted synthesis of Ag/C-dot and Au/C-dot nanohybrids using natural lemon extract for cancer cellular imaging applications.

Synthesis of copper nanoparticles supported on a microporous covalent triazine polymer: an efficient and reusable catalyst for O-arylation reaction

Cu NPs immobilized on a microporous covalent triazine polymer obtained by a cost-effective synthesis method were evaluated as a catalyst for Ullmann coupling of O-arylation.

Green synthesis of CuO nanoparticles using aqueous extract of Thymus vulgaris L. leaves and their catalytic performance for N-arylation of indoles and amines

Copper oxide (CuO) nanoparticles (NPs) were synthesized by biological method using aqueous extract of Thymus vulgaris L. leaves as a reducing and capping agent. The progress of the reaction was monitored using UV-visible spectroscopy. The advantages of this procedure are simple operation, use of cheap, natural, nontoxic and benign precursors, absence of toxic reagents and mild and environmentally friendly conditions. The green synthesized CuO NPs was characterized by transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), fourier-transform infrared (FT-IR) spectroscopy, X-ray diffraction analysis (XRD), thermogravimetric analysis (TGA) and differential thermal analysis (DTA). More importantly, the green synthesized CuO NPs was found to be an excellent heterogeneous catalyst for ligand-free N-arylation of indoles and amines. The N-arylated products were obtained in good to excellent yield and the catalyst can be recovered and reused for further catalytic reactions with almost no loss in activity.

Pd nanoparticles synthesized in situ with the use of Euphorbia granulate leaf extract: Catalytic properties of the resulting particles

For the first time the extract of the plant of Euphorbia granulate was used to green synthesis of Pd nanoparticles (NPs) as a heterogeneous catalyst for the phosphine-free Suzuki-Miyaura coupling reaction at room temperature. This method is a facile and eco-friendly way in organic synthesis using the plant extract as biomedia, bioreductant and capping ligand which considerably stabilizes the surface of Pd NPs. The presence of flavonoid and phenolics acids in the extract could be responsible for the reduction of Pd(2+) ions and formation of the corresponding Pd NPs.

Green synthesis of copper nanoparticles using Ginkgo biloba L. leaf extract and their catalytic activity for the Huisgen [3+2] cycloaddition of azides and alkynes at room temperature

During this study, we report the green synthesis of copper nanoparticles (Cu NPs) using Ginkgo biloba L. leaf extract as a reducing and stabilizing agent under surfactant-free conditions. The formation of Cu NPs is monitored by recording the UV-vis absorption spectra. The green synthesized Cu NPs are characterized by TEM, EDS, FT-IR and UV-visible techniques. According to UV-vis results, the synthesized Cu NPs by this method are quite stable even after one month indicating the stability of Cu NPs. In terms of environmental impact and economy, metallic Cu NPs offer several advantages over homogeneous and traditional heterogeneous catalysts. In addition, due to the increased metal surface area, Cu NPs shows very high catalytic activity for the Huisgen [3+2] cycloaddition of azides and alkynes at room temperature. Furthermore, the catalyst can be simply recovered and reused several times with almost no loss in activity.

Green synthesis of Pd/CuO nanoparticles by Theobroma cacao L. seeds extract and their catalytic performance for the reduction of 4-nitrophenol and phosphine-free Heck coupling reaction under aerobic conditions

We report the green synthesis of palladium/CuO nanoparticles (Pd/CuO NPs) using Theobroma cacao L. seeds extract and their catalytic activity for the reduction of 4-nitrophenol and Heck coupling reaction under aerobic conditions. The catalyst was characterized using the powder XRD, TEM, EDS, UV-vis and FT-IR. This method has the advantages of high yields, elimination of surfactant, ligand and homogeneous catalysts, simple methodology and easy work up. The catalyst can be recovered from the reaction mixture and reused several times without any significant loss of catalytic activity.

Tamarix gallica leaf extract mediated novel route for green synthesis of CuO nanoparticles and their application for N-arylation of nitrogen-containing heterocycles under ligand-free conditions

We report the green synthesis of CuO nanoparticles (CuO NPs) using Tamarix gallica leaf extract and their catalytic activity for N-arylation of nitrogen-containing heterocycles with aryl halides under ligand-free conditions.

Preparation of carbon supported CuPd nanoparticles as novel heterogeneous catalysts for the reduction of nitroarenes and the phosphine-free Suzuki–Miyaura coupling reaction

This paper reports on the synthesis and use of C/CuPd bimetallic NPs as heterogeneous catalysts for the phosphine-free Suzuki–Miyaura coupling and the reduction of nitroarenes.

Barberry fruit extract assisted in situ green synthesis of Cu nanoparticles supported on a reduced graphene oxide–Fe3O4 nanocomposite as a magnetically separable and reusable catalyst for the O-arylation of phenols with aryl halides under ligand-free conditions

In situ synthesis of copper nanoparticles (NPs) supported on a reduced graphene oxide (RGO)–Fe₃O₄ nanocomposite was carried out with barberry fruit extract as a reducing and stabilizing agent.

Green synthesis of a Cu/reduced graphene oxide/Fe3O4 nanocomposite using Euphorbia wallichii leaf extract and its application as a recyclable and heterogeneous catalyst for the reduction of 4-nitrophenol and rhodamine B

Herein, we describe a green and eco-friendly synthesis method for preparing a Cu/RGO/Fe₃O₄ nanocomposite through biological reduction of graphene oxide and Cu²⁺, Fe³⁺ ions using Euphorbia wallichii leaf extract as a reducing and stabilizing agent.

Green synthesis of a natrolite zeolite/palladium nanocomposite and its application as a reusable catalyst for the reduction of organic dyes in a very short time

A natrolite zeolite/palladium (natrolite zeolite/Pd) nanocomposite has been successfully synthesized applying a simple in situ reduction method using an aqueous extract of fruits of Piper longum as a reducing and stabilizing agent.