Biogenic Approach Research Articles

Quantitative nucleation and growth kinetics of gold nanoparticles via model-assisted dynamic spectroscopic approach

Lacking of quantitative experimental data and/or kinetic models that could mathematically depict the redox chemistry and the crystallization issue, bottom-to-up formation kinetics of gold nanoparticles (GNPs) remains a challenge. We measured the dynamic regime of GNPs synthesized by l-ascorbic acid (representing a chemical approach) and/or foliar aqueous extract (a biogenic approach) via in situ spectroscopic characterization and established a redox–crystallization model which allows quantitative and separate parameterization of the nucleation and growth processes. The main results were simplified as the following aspects: (I) an efficient approach, i.e., the dynamic in situ spectroscopic characterization assisted with the redox–crystallization model, was established for quantitative analysis of the overall formation kinetics of GNPs in solution; (II) formation of GNPs by the chemical and the biogenic approaches experienced a slow nucleation stage followed by a growth stage which behaved as a mixed-order reaction, and different from the chemical approach, the biogenic method involved heterogeneous nucleation; (III) also, biosynthesis of flaky GNPs was a kinetic-controlled process favored by relatively slow redox chemistry; and (IV) though GNPs formation consists of two aspects, namely the redox chemistry and the crystallization issue, the latter was the rate-determining event that controls the dynamic regime of the whole physicochemical process.

Highly visible light active Ag@TiO2 nanocomposites synthesized using an electrochemically active biofilm: a novel biogenic approach

Titanium dioxide (TiO2) nanoparticles were decorated with different amounts of silver nanoparticles (AgNPs) using an electrochemically active biofilm (EAB), which is a biogenic approach that leads to the formation of Ag@TiO2 nanocomposites. UV-vis spectroscopy, photoluminescence, X-ray diffraction and electron microscopy showed AgNPs, 2-5 nm in size, well-dispersed and anchored to the TiO2 surface and overall synthesis of Ag@TiO2 nanocomposites. The photocatalytic performance of the as-synthesized Ag@TiO2 nanocomposites was evaluated in terms of their efficiency for the photodecomposition of methylene blue (MB) in an aqueous solution under visible light irradiation. The nanocomposites showed exceptionally high photodecomposition efficiency (>7 times) compared to commercial TiO2 (Sigma). The enhanced photocatalytic activity was attributed to the synergistic contribution of both a delayed charge recombination rate caused by the high electronic mobility of the AgNPs and the increased surface area originating from the nanometer sized AgNPs on TiO2. The nanocomposites also showed exceptionally high stability and reusability under similar experimental conditions.

Positively Charged Gold Nanoparticles Synthesized by Electrochemically Active Biofilm—A Biogenic Approach

Positively charged gold nanoparticles [(+) AuNPs] of 5-20 nm were synthesized by using electrochemically active biofilm (EAB) formed on a stainless steel mesh, within 30 minutes, in aqueous solution containing HAuCl4 as a precursor and sodium acetate as an electron donor. Electrochemically active bacteria present on biofilm oxidize the sodium acetate by producing electrons. Simultaneously, stainless steel also provides electrons because of the Cl- ions penetration into the stainless steel. Combined effect of both the EAB and stainless steel mesh enhances the availability of electrons for the reduction of Au3+ in the solution, which makes this synthesis efficient and fast. Therefore, small size, positively charged (+32.72 mV), monodispersed, controlled, easy separation and extracellular synthesis of (+) AuNPs makes this protocol highly significant. As-synthesized AuNPs were characterized by UV-vis, DLS, XRD, TEM, HRTEM, EDX and SAED. (+) AuNPs shows remarkable enhancement in the rate of reduction of methyl orange by NaBH4 because of the electron relay effect.

Oxygen vacancy induced band gap narrowing of ZnO nanostructures by an electrochemically active biofilm

Band gap narrowing is important and advantageous for potential visible light photocatalytic applications involving metal oxide nanostructures. This paper reports a simple biogenic approach for the promotion of oxygen vacancies in pure zinc oxide (p-ZnO) nanostructures using an electrochemically active biofilm (EAB), which is different from traditional techniques for narrowing the band gap of nanomaterials. The novel protocol improved the visible photocatalytic activity of modified ZnO (m-ZnO) nanostructures through the promotion of oxygen vacancies, which resulted in band gap narrowing of the ZnO nanostructure (Eg = 3.05 eV) without dopants. X-ray diffraction, UV-visible diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy, electron paramagnetic resonance spectroscopy, Raman spectroscopy, photoluminescence spectroscopy and high resolution transmission electron microscopy confirmed the oxygen vacancy and band gap narrowing of m-ZnO. m-ZnO enhanced the visible light catalytic activity for the degradation of different classes of dyes and 4-nitrophenol compared to p-ZnO, which confirmed the band gap narrowing because of oxygen defects. This study shed light on the modification of metal oxide nanostructures by EAB with a controlled band structure.

Biocompatible Synthesis Of Silver And Gold Nanoparticles Using Leaf Extract Of Dalbergia Sissoo

This report presents a rapid, reproducible and a green biogenic approach for the biosynthesis of gold and silver nanoparticles using leaf extract of Dalbergia sissoo. The biomolecules present in the plant induced the reduction of Au 3+ and Ag + ions from HAuCl4 and AgNO3 respectively, which resulted in the formation of Dalbergia conjugated nanoparticles. The growth of nanoparticles was monitored by UV-vis spectrophotometer that demonstrated a peak at 545 and 425 nm corresponding to Plasmon absorbance of gold and silver nanoparticles respectively. The leaf extract was found to direct different shape and sized gold nanoparticles. Gold nanoparticles were 50-80 nm in size and their shape varied from spherical to few triangular and hexagonal polyshaped. While silver nanoparticle synthesized were spherical, in the range of 5-55 nm in size. X-ray diffraction studies corroborated that the biosynthesized nanoparticles were crystalline gold and silver. Fourier transform infra-red spectroscopy analysis revealed that biomolecules were involved in the synthesis and capping of silver nanoparticles and gold nanoparticles.

Dioscorea batatas Rhizome-Assisted Rapid Biogenic Synthesis of Silver and Gold Nanoparticles

Development of biologically inspired experimental process for the synthesis of nanoparticles is an important branch of nanotechnology. Here the authors have synthesized silver and gold nanoparticles (AgNPs and AuNPs) by using rhizome extract of Dioscorea batatas at 50°C (AuNps), AgNPs was carried out at 80°C as well as room temperature (25°C). The reductions of Ag and Au ions were observed by the color changes from colorless to brownish yellow, and dark yellow and dark red wine, respectively. The reaction was followed with the help of UV-visible spectrometer. The synthesized nanoparticles were characterized using Fourier transform infrared spectroscopy, X-ray diffraction, and scanning electron microscope analysis. The authors did not find, formation of gold nanoparticles at room temperature. Furthermore, this green biogenic approach is rapid and simple alternative to chemical synthesis methods.

Trends in belichaamde cognitie

Embodied cognition has come of age and is now diversifying. In this paper, I discuss four different approaches within embodied cognition: a biogenic approach, an enactive approach, a sensorimotor approach and a scaffolding approach. The four approaches can be differentiated according to their commitments to either biology (biogenic and enactive approaches) and/or experience (enactive and sensorimotor approaches). I will argue that these differences are substantial, but that a reconciliation is possible and even desirable. Seen in this light, embodied cognition can remain a comparatively unified field, these diverging approaches notwithstanding.

The biogenic approach to cognition

After half a century of cognitive revolution we remain far from agreement about what cognition is and what cognition does. It was once thought that these questions could wait until the data were in. Today there is a mountain of data, but no way of making sense of it. The time for tackling the fundamental issues has arrived. The biogenic approach to cognition is introduced not as a solution but as a means of approaching the issues. The traditional, and still predominant, methodological stance in cognitive inquiry is what I call the anthropogenic approach: assume human cognition as the paradigm and work 'down' to a more general explanatory concept. The biogenic approach, on the other hand, starts with the facts of biology as the basis for theorizing and works 'up' to the human case by asking psychological questions as if they were biological questions. Biogenic explanations of cognition are currently clustered around two main frameworks for understanding biology: self-organizing complex systems and autopoiesis. The paper describes the frameworks and infers from them ten empirical principles--the biogenic 'family traits'--that constitute constraints on biogenic theorizing. Because the anthropogenic approach to cognition is not constrained empirically to the same degree, I argue that the biogenic approach is superior for approaching a general theory of cognition as a natural phenomenon.

A biogenic approach for green synthesis of silver nanoparticles using extract of Foeniculum vulgare and its activity against Staphylococcus aureus and Escherichia coli

Abstract. Bonde S. 2011. A biogenic approach for green synthesis of silver nanoparticles using extract of Foeniculum vulgare and its activity against Staphylococcus aureus and Escherichia coli. Nusantara Bioscience 3: 59-63. We report green synthesis of silver nanoparticles from extract of Foeniculum vulgare (fennel, saunf). The synthesis of silver nanoparticles was detected by changing color from green to brown after treatment with AgNO3 (1mM) and the UV-visible spectrophotometer analysis showed the absorbance peak at about 427 nm, which indicates the synthesis of silver nanoparticles. Nanoparticle Tracking and Analysis (NTA) by LM-20 was used for multi-parameter analysis, allowing for characterization of particle size and particle distribution of silver nanoparticles synthesized from extract of F. vulgare. NTA revealed the polydispersed nanoparticles in the range of 18-83 nm. Phytosynthesized silver nanoparticles showed antibacterial activity against the Staphylococcus aureus (ATCC-25923) and Escherichia coli (ATCC-39403). The silver nanoparticles also demonstrated remarkable antibacterial activity against two human pathogenic bacteria when used in combination with commercially available antibiotics. The bactericidal activity of the standard antibiotics was significantly enhanced in presence of silver nanoparticles against pathogenic bacteria, viz. E. coli-JM-103 (ATCC-39403) and S. aureus (ATCC-25923). Silver nanoparticles in combination with vancomycin showed maximum activity against E. coli (increase in fold area 5.76. and followed by S. aureus (1.08) and Gentamicin showed the maximum activity S. aureus (2.6) while E. coli (0.96). The approach of phytosynthesized silver nanoparticles using F. vulgare appears to be cost-efficient, eco-friendly and easy alternative to conventional methods of synthesis.