Citrate-silver nanoparticles and their impact on some environmental beneficial fungi

Opportunities and Challenges in the Synthesis of Noble Metal Nanoparticles via the Chemical Route in Microreactor Systems

The process of noble metal nanoparticle synthesis is complex and consists of at least two steps: slow nucleation and fast autocatalytic growth. The kinetics of these two processes depends on the reductant "power" and the addition of stabilizers, as well as other factors (e.g., temperature, pH, ionic strength). Knowing these parameters, it is possible to synthesize materials with appropriate physicochemical properties, which can be simply adjusted by the type of the used metal, particle morphology and surface property. This, in turn, affects the possibility of their applications in various areas of life, including medicine, catalysis, engineering, fuel cells, etc. However, in some cases, the standard route, i.e., the chemical reduction of a metal precursor carried out in the batch reactor, is not sufficient due to problems with temperature control, properties of reagents, unstable or dangerous intermediates and products, etc. Therefore, in this review, we focused on an alternative approach to their chemical synthesis provided by microreactor systems. The use of microreactors for the synthesis of noble metal nanomaterials (e.g., Ag, Au, Pt, Pd), obtained by chemical reduction, is analyzed, taking into account investigations carried out in recent years. A particular emphasis is placed on the processes in which the use of microreactors removed the limitations associated with synthesis in a batch reactor. Moreover, the opportunities and challenges related to the synthesis of noble nanomaterials in the microreactor system are underlined. This review discusses the advantages as well as the problems of nanoparticle synthesis in microreactors.

Graphitic carbon nitride supported silver nanoparticles (AgNPs/g-C3N4): synthesis and photocatalytic behavior in the degradation of 2,4-dichlorophenoxyacetic acid

Graphitic carbon nitride supported silver nanoparticles (AgNPs/g-C3N4) with 1%, 3%, and 5% AgNPs were successfully synthesized by an "ex situ" method with ultrasound of a mixture of AgNP solution and g-C3N4. The AgNP solution was prepared by chemical reduction with trisodium citrate, and g-C3N4 was synthesized from the urea precursor. The supported nanoparticles were characterized by X-ray diffraction spectroscopy (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen adsorption-desorption (BET), Fourier transformation infrared (FTIR) and Raman spectroscopy, ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS), photoluminescence spectroscopy (PL), electron paramagnetic resonance (EPR) and electrochemical impedance spectroscopy (EIS) Nyquist plots. The visible light-driven photocurrent measurement was performed by three on-off cycles of intermittent irradiation. The analyses show that AgNPs were evenly dispersed on g-C3N4, and have sizes ranging from 40 to 50 nm. The optical properties of the AgNPs/g-C3N4 material were significantly enhanced due to the plasmonic effect of AgNPs. The photocatalytic activity of catalysts was evaluated by 2,4-D degradation under visible light irradiation (λ > 420 nm). In the reaction conditions: pH 2.2; C o (2,4-D) 40 ppm; a m/v ratio of 0.5 g L-1, AgNPs/g-C3N4 materials exhibit superior photocatalytic activity compared to the pristine g-C3N4. The studies on the influence of free radicals and photogenerated holes, h+, show that ˙OH, O2˙-, and h+ play decisive roles in the photocatalytic activity of AgNPs/g-C3N4. The TOC result indicates the minimal toxicity of the by-products formed during the 2,4-D degradation. In addition, the AgNPs/g-C3N4 catalytic activity under direct sunlight irradiation was similar to that under artificial UV irradiation. Based on these results, a possible mechanism is proposed to explain the enhanced photocatalytic activity and stability of AgNPs/g-C3N4. Theoretical calculations on the interaction between 2,4-D and g-C3N4, Ag/g-C3N4 was also performed. The calculated results show that the adsorption of 2,4-D on Ag-modified g-C3N4 is significantly more effective compared to pristine g-C3N4.

Spectroscopic/colorimetric dual-mode rapid and ultrasensitive detection of reactive oxygen species based on shape-dependent silver nanostructures

Excessive production of reactive oxygen species (ROS) from endogenous and exogenous pathways is linked to oxidative stress and various diseases. Although a variety of ROS probes have been developed, their multistep synthesis strategies and complicated instrumental operating procedures limit their frequent use. In this work, different shaped silver nanostructures including nanoparticles, nanoprisms, and nanocubes were utilized to demonstrate simple spectroscopic and colorimetric techniques for sensitive ROS detection. The nanostructures displayed different sensing behaviours recorded via plasmon tuning with morphological changes upon exposure to ROS. Among the nanostructures, silver nanocubes were found to be extremely efficient in recognising a particular ROS, namely hypochlorite ions. The detection limits of this ROS were calculated to be 23.76 nM, 85.71 nM, and 36.37 nM for silver nanoparticles, nanoprisms, and nanocubes, respectively. A time-dependent microscopic examination was carried out and revealed that the presence of hypochlorite ions deteriorates structural morphologies. The formation of highly reactive chlorite, chlorate, and chloride ions in hypochlorite ion solution was ascribed to the significant spectroscopic and microscopic changes in all the nanostructures. The attenuation of plasmonic peaks and etching of nanostructures by ROS were supported by the increment of the oxidation state of silver. In addition, silver nanocubes were successfully applied to recognize ROS in Spinacia oleracea and real water samples. The results confirm the potentiality of silver nanostructures for sensitive detection of ROS in biological and environmental systems.

Evaluation of Sclerotinia sclerotiorum MTCC 8785 as a biological agent for the synthesis of silver nanoparticles and assessment of their antifungal potential against Trichoderma harzianum MTCC 801

INTRODUCTION

Owing to loads of industrial development and advancements, there is an unmet need for green-ecosystem support as well as safe technologies. For cost-cutting and eco-friendly applications, biosynthetic pathways for nanoparticle synthesis from microbes like bacteria, and fungi have attracted the global attention of researchers.

METHODS

In the present research work, silver nanoparticles (AgNPs) from fungus (mycogenic) were extracellularly synthesized with cell-free filtrates of fungal phytopathogen Sclerotinia sclerotiorum MTCC 8785 harvested from broth culture in Potato dextrose broth (CFF-PDB) and Amylase production media (CFF-AMP). The synthesis was carried out at pH 7, 28 °C under dark conditions. The synthesized AgNPs were characterized using UV spectrophotometer and transmission electron microscopy (TEM). Furthermore, the antifungal efficacy of AgNPs was evaluated against the Trichoderma harzianum MTCC 801 strain by radial inhibition assay.

RESULTS

Primarily, the process of biosynthesis was inferred by the characteristic change of color and spectral peak at 420 nm recorded with UV spectrophotometer further approved the nano silver production in CFF-AMP which approves the role of amylases in reduction mediated capping process. TEM analysis revealed that the AgNPs synthesized using S. sclerotiorum MTCC 8785 grown in PDB were spherical with variable size ranges from 10 to 50 nm in diameter whereas, the AgNPs synthesized using S. sclerotiorum MTCC 8785 grown in APM were in the size ranges from 40 to 50 nm.

CONCLUSIONS

This is the first investigatory concern where nano-silver from fungal phytopathogen S. sclerotiorum MTCC 8785 has been prospected as new age antifungal alternatives against evolving threats from T. harzianum strain.

Silver Nanoparticle Synthesis via Photochemical Reduction with Sodium Citrate

The aim of this paper is to provide a simple and efficient photoassisted approach to synthesize silver nanoparticles, and to elucidate the role of the key factors (synthesis parameters, such as the concentration of TSC, irradiation time, and UV intensity) that play a major role in the photochemical synthesis of silver nanoparticles using TSC, both as a reducing and stabilizing agent. Concomitantly, we aim to provide an easy way to evaluate the particle size based on Mie theory. One of the key advantages of this method is that the synthesis can be "activated" whenever or wherever silver nanoparticles are needed, by premixing the reactants and irradiating the final solution with UV radiation. UV irradiance was determined by using Keitz's theory. This argument has been verified by premixing the reagents and deposited them in an enclosed space (away from sunlight) at 25 °C, then checking them for three days. Nothing happened, unless the sample was directly irradiated by UV light. Further, obtained materials were monitored for 390 days and characterized using scanning electron microscopy, UV-VIS, and transmission electron microscopy.

Nitrapyrin Addition Mitigated CO2 Emission from a Calcareous Soil Was Closely Associated with Its Effect on Decreasing Cellulolytic Fungal Community Diversity

Application of nitrification inhibitors (NIs) has been widely used to inhibit nitrification and reduce N₂O emissions. However, the impacts of NI addition on soil carbon transformation and carbon-degrading microbial communities have not been well explored. Here, a microcosm experiment was carried out, and four treatments were designed: (i) unfertilized control, (ii) urea alone, (iii) urea plus cattle manure, and (iv) urea plus cattle manure with nitrapyrin. The influence of nitrapyrin on soil CO₂ emissions, carbon-degrading extracellular enzyme activities, and the abundance and diversity of the cbhI community was investigated. Compared to the treatment of urea plus cattle manure, nitrapyrin significantly decreased cumulative CO₂ emissions by 51.8%. Moreover, cbhI community gene copies and their α-diversities (P < 0.05) were also significantly reduced by nitrapyrin application. A partial least squares path model showed that CO₂ emission was positively associated with cbhI community α-diversity but negatively associated with nitrapyrin addition. We conclude that the mitigation of soil CO₂ emissions by nitrapyrin can be ascribed to its effects on decreasing of cellulose-degrading gene community diversity. Our findings provide new insights into the side-effects of nitrapyrin on abating CO₂ emission.

Synthesis of Sodium Alginate-Silver Nanocomposites Using Plasma Activated Water and Cold Atmospheric Plasma Treatment

In this study, sodium alginate (SA)-based, eco-friendly nanocomposites films were synthesized for potential food packaging applications using silver nitrate (AgNO₃) as the metal precursor, reactive nitrogen and oxygen species (RNOS) created within plasma activated water (PAW), or through cold plasma treatment (CP) as reducing agent and SA as stabilizing agent. The formation of silver nanoparticles (AgNPs) was confirmed via the absorption peaks observed between 440 and 450 nm in UV-vis spectroscopy. The tensile strength (TS) and tensile modulus (TM) of the nanocomposite films were significantly higher than those of the SA films. An increase in the TS was also observed as the AgNP concentration was increased from 1 to 5 mM. The storage modulus (G’) of the nanocomposite solution was higher than that of the SA solution. The synthesis of AgNPs resulted both in a higher solution viscosity and a more marked shear-thinning effect. The synthesized AgNPs showed antimicrobial activity against both Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria. The AgNPs were spherical in shape with an average size of 22 nm.

Photochemical Synthesis of Gold and Silver Nanoparticles-A Review

Nanomaterials have supported important technological advances due to their unique properties and their applicability in various fields, such as biomedicine, catalysis, environment, energy, and electronics. This has triggered a tremendous increase in their demand. In turn, materials scientists have sought facile methods to produce nanomaterials of desired features, i.e., morphology, composition, colloidal stability, and surface chemistry, as these determine the targeted application. The advent of photoprocesses has enabled the easy, fast, scalable, and cost- and energy-effective production of metallic nanoparticles of controlled properties without the use of harmful reagents or sophisticated equipment. Herein, we overview the synthesis of gold and silver nanoparticles via photochemical routes. We extensively discuss the effect of varying the experimental parameters, such as the pH, exposure time, and source of irradiation, the use or not of reductants and surfactants, reagents' nature and concentration, on the outcomes of these noble nanoparticles, namely, their size, shape, and colloidal stability. The hypothetical mechanisms that govern these green processes are discussed whenever available. Finally, we mention their applications and insights for future developments.