Oluwatobi S. Oluwafemi

Completely green synthesis of dextrose reduced silver nanoparticles, its antimicrobial and sensing properties

We herein report the green synthesis of highly monodispersed, water soluble, stable and smaller sized dextrose reduced gelatin capped-silver nanoparticles (Ag-NPs) via an eco-friendly, completely green method. The synthesis involves the use of silver nitrate, gelatin, dextrose and water as the silver precursor, stabilizing agent, reducing agent and solvent respectively. By varying the reaction time, the temporal evolution of the growth, optical, antimicrobial and sensing properties of the as-synthesised Ag-NPs were investigated. The nanoparticles were characterized using UV-vis absorption spectroscopy, Fourier transform infra-red spectroscopy (FT-IR), X-ray diffraction (XRD), transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HR-TEM). The absorption maxima of the as-synthesized materials at different reaction time showed characteristic silver surface plasmon resonance (SPR) peak. The as-synthesised Ag-NPs show better antibacterial efficacy than the antibiotics; ciproflaxin and imipenem against Pseudomonas aeruginosa with minimum inhibition concentration (MIC) of 6 μg/mL, and better efficacy than imipenem against Escherichia coli with MIC of 10 μg/mL. The minimum bactericidal concentration (MBC) of the as-synthesised Ag-NPs is 12.5 μg/mL. The sensitivity of the dextrose reduced gelatin-capped Ag-NPs towards hydrogen peroxide indicated that the sensor has a very good sensitivity and a linear response over wide concentration range of 10(-1)-10(-6)M H2O2.

A facile completely 'green' size tunable synthesis of maltose-reduced silver nanoparticles without the use of any accelerator

A simple, straightforward, cost effective and environmentally benign method for the synthesis of highly stable and small sized silver nanoparticles (Ag-NPs) with narrow size distribution without the use of an accelerator is reported. Silver nitrate, gelatin and maltose, a non-toxic disaccharide sugar were used as silver precursor, stabiliser and reducing agent. By varying the precursor concentration and reaction time, we monitored the temporal evolution of the optical and structural properties of the as-synthesised Ag-NPs. The as-synthesised Ag-NPs were characterised using UV-vis absorption spectroscopy, Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD). The absorption maxima of the surface plasmon resonance (SPR) were blue-shifted as the reaction time increased indicating decrease in particle size. The TEM images showed that, the particles are small, well dispersed and spherical in shape. The smallest particles with an average particle diameter of 3.76±1.00 nm and 4.09±1.83 nm were obtained at 24h for the 1.0M and 0.5M silver ion precursor solution concentration respectively. The smaller particles produced were attributed to the higher concentration of the reducing saccharides in the reaction system, which in turn increases the formation of stable silver ions in the reaction system. The HRTEM images confirmed the crystalline nature of the material while the FTIR confirmed the stabilisation of the Ag-NPs by the gelatin.

Facile synthesis of transparent and fluorescent epoxy–CdSe–CdS–ZnS core–multi shell polymer nanocomposites

A facile and environmentally benign approach for the synthesis of highly transparent and fluorescent CdSe–CdS–ZnS core–multi-shell polymer nanocomposites is presented. The CdSe–CdS–ZnS core–multi-shell quantum dots (QDs) were prepared via a continual precursor injection and phosphine free method in paraffin liquid and oleic acid without a protective atmosphere. The as-prepared core–multi-shell QDs were dispersed directly in an epoxy polymer matrix via a melt mixing technique. The QDs showed better dispersibility and good optical properties in the epoxy matrix. The transmission electron microscopy (TEM) images showed that the as-synthesized QDs are small, spherical and are well dispersed inside the polymer matrix without any change in morphology. It was found that the nanocomposite filled with yellow-emitting QDs had more transparency compared to the neat epoxy. The luminescence of the neat polymer shifted from the blue region to the yellow region in the nanocomposite. The fluorescent lifetime analysis of the as-prepared core–multi shell and the polymer nanocomposite showed a decrease compared to the core while the tensile measurements showed an increase in the tensile properties of the nanocomposite in comparison with the neat polymer.

Synthesis of copper–isonicotinate metal–organic frameworks simply by mixing solid reactants and investigation of their adsorptive properties for the removal of the fluorescein dye

The formation of [Cu(INA)2] (INA = isonicotinate) metal–organic frameworks (MOFs) by a highly efficient and environmentally benign method simply by mixing and heating solid reactants without milling has been investigated. The materials were characterized using elemental analysis, FT-IR spectroscopy and powder X-ray diffraction (PXRD) and scanning electron microscopy (SEM). Comparison of PXRD patterns of the materials with patterns simulated from single crystal X-ray diffraction data allowed identification of the products. The adsorption properties of [Cu(INA)2] were studied using the fluorescein dye (FS). The adsorption data followed both Langmuir and Freundlich equations but was best suited to the Langmuir model. The adsorption data were also correlated with the Temkin and Dubinin–Radushkevich adsorption model and the results showed that the adsorption process is physical. These results indicate that the adsorption of FS on [Cu(INA)2] is partly due to electrostatic interaction between fluorescein and the adsorbent. Compared with the traditional synthetic techniques, this method for the synthesis of MOFs was found to be highly efficient, environmentally benign and useful for the large-scale production.

Effect of some nitrogen donor ligands on the optical and structural properties of CdS nanoparticles

The cadmium complex of N-ethyl-N-phenyl dithiocarbamate, 1, and its 2,2′-bipyridine and 1,10-phenanthroline adducts, 2, and 3, respectively, have been used as single source precursors for the synthesis of CdS nanoparticles. The formation of CdS nanoparticles was achieved by thermal decomposition of the complexes (pyrolysis) and thermolysis in the presence of hexadecylamine – HDA (solvothermal). Scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and high resolution transmission electron microscopy (HRTEM) analyses were carried out to study the structural properties of the nanoparticles. Complex 1 afforded rod-shaped nanoparticles while star-shaped nanoparticles were obtained from complexes 2 and 3. The optical property of the CdS nanoparticles was studied by UV–visible and fluorescence spectroscopy. The spectral features for the nanoparticles prepared via the solvothermal route were significantly sharper and blue shifted to a greater extent relative to the corresponding bulk semiconductor, compared to the observed shift in the nanoparticles prepared via pyrolysis. All the as-synthesized material exhibited band edge luminescence.

A facile “green” synthesis of ascorbic acid-capped ZnSe nanoparticles

A simple, green room temperature synthesis of ascorbic acid-capped ZnSe nanoparticles is hereby reported. By varying the pH of the solution, the temporal evolution of the optical properties and shape of the nanocrystals was investigated. The nanoparticles were characterized by UV-vis absorption and photoluminescence spectroscopy (PL), transmission electron microscope (TEM) and infra-red spectroscopy (IR). All the particles exhibited quantum confinement in their optical spectra. An atypical optical spectrum was observed at pH 11 after 5h attributed to digestive ripening and shrinkage of ZnSe core. From the TEM image we inferred that the reaction is kinetically driven at pH 7 producing elongated particles as the reaction times increases, while spherical particles are produced at pH 4 and 11. The IR spectroscopy confirmed the capping of ascorbic acid and its deprotonation to give ascorbate ions.

Interface engineered ferrite@ferroelectric core-shell nanostructures: A facile approach to impart superior magneto-electric coupling

The electric field control of magnetism in multiferroics is attractive for the realization of ultra-fast and miniaturized low power device applications like nonvolatile memories. Room temperature hybrid multiferroic heterostructures with core-shell (0–0) architecture (ferrite core and ferroelectric shell) were developed via a two-step method. High-Resolution Transmission Electron Microscopy (HRTEM) images confirm the core-shell structure. The temperature dependant magnetization measurements and Mossbauer spectra reveal superparamagnetic nature of the core-shell sample. The ferroelectric hysteresis loops reveal leaky nature of the samples. The results indicate the promising applications of the samples for magneto-electric memories and spintronics.

Biopolymer-mediated Green Synthesis of Noble Metal Nanostructures

Polymer-coated noble metal nanoparticles are currently of particular interest to investiga‐ tors in the fields of nanobiomedicine and fundamental biomaterials. These materials not only exhibit imaging properties in response to stimuli but also efficiently deliver various drugs and therapeutic genes. Even though a large number of polymer-coated noble metal nanoparticles have been fabricated over the past decade, most of these materials still present some challenges emanating from their synthesis. The metal nanoparticles when encapsulated in a polymer and taken up by human cells might show a lower degree of toxicity; however, the degree of toxicity for some of the starting materials and precursors has raised serious concerns. Hence, there is a need to implement the principle of green chemistry in the synthesis of nanomaterials. The use of environmentally benign materials for the synthesis of metal nanoparticles provides numerous benefits ranging from bio‐ compatibility, availability, cost-effectiveness, amenable scale-up to eco-friendliness. The biopolymer-based nanovehicles have been found to be more suitable in the field of nano‐ technology owing to their high reproducibility, ease of manufacture, functional modifica‐ tion and safety (they are not carcinogenic). Unlike synthetic polymers where the raw material can be derived from petrochemicals or chemical industrial processes, biopoly‐ mers are produced from renewable resources such as plant and/or living organism. They are degradable by natural processes down to elemental entities that can be resorbed in the environment. Furthermore, they can also be modified to serve a particular purpose which explains the myriad of their potential applications. The macromolecular chain of these biopolymers possesses a large number of hydroxyl groups which can easily com‐ plex with metal ions. Additionally, these biopolymers also contain supramolecular struc‐ tures that can lead to new functionalities of their composites with metal and semiconductor nanoparticles. In this chapter, a comprehensive discussion on different bi‐ opolymers, green synthesis of noble metal nanostructures, mechanisms, characterization and application in various fields is presented.

A Facile One-Pot Synthesis of MSe (M = Cd or Zn) Nanoparticles Using Biopolymer as Passivating Agent

In recent years, semiconductor quantum dots (QDs) sometimes also referred to as nanoparticles (NPs) or nanocrystals (NCs) have attracted much attention for many potential applications due to their unique physical and chemical properties such as size-dependent band gap, size dependent excitonic emission, enhanced nonlinear optical properties and size-dependent electronic properties attributed to quantum size-effect and enormously high specific surface area. Hence they are different from those of the corresponding bulk materials and contain a relatively large percentage of surface atoms which makes them extremely active (Alivastos, 1996; Bruchez et al., 1998). They have been extensively studied over the past decade and are useful in many wider areas of applications hence, they have become an important class of material for the photonic, electronic, biological and other technological industries in the 21st century (Bruchez et al., 1998; Chan & Nie, 1998; Coe et al., 2003; Murphy, 2002). The applicative utility of QDs as seen in various field are: medicine for diagnostics, drug delivery and tissue engineering, chemistry and environment -for catalysis and filtration, energy for reduction of energy consumption, increasing the efficiency of energy production, the use of more environmentally friendly energy systems, recycling of batteries, information and communication novel semiconductor devices, novel optoelectronic devices, displays, quantum computers, heavy industryaerospace, refineries, vehicle manufacturers to mention a few. Compared with conventional organic fluorophores, QDs exhibit bright fluorescence, narrow emission, broad UV excitation, high quantum yield and high photostability (Coastal –Fernandez et al., 2006; Ozkan, 2004; Derfus et al., 2004).