Dynamics of Solvation and Rotational Relaxation of Coumarin 480 in Pure Aqueous-AOT Reverse Micelle and Reverse Micelle Containing Different-Sized Silver Nanoparticles Inside Its Core: A Comparative Study

Femtosecond Upconversion Study of Interfacial Electron Transfer from Photoexcited CsPbBr3 Perovskite Nanocrystal to Rhodamine 6G

Photoinduced electron transfer (PET) from an excited-state CsPbBr₃ nanocrystal (NC) to rhodamine 6G (r6G) is studied in toluene using different fluorescence-based techniques. Because of weak solubility of r6G in toluene, excess r6G molecules adsorb at NC surface which result in a much slower rotational diffusion time scale of r6G in the presence of NCs. Study of intrinsic PET benefits from the soft molecular interactions leading to donor (NC)-acceptor (r6G) complex formation, where solvent diffusion parameters would not play any role in the PET kinetics. Femtosecond transients of NCs are nicely fit to a Poisson expression originally proposed by Tachiya. Conclusive fittings to the temperature dependence quenching data reveal two interesting observations: (1) Even though the average number of surface trap state in a NC does not change with temperature (5-60 °C), the trap-state-induced quenching time scale is accelerated with increase in temperature, pointing toward a more efficient trapping at higher temperature. (ii) In the presence of r6G, a fast (∼150 ps per r6G molecule) interfacial PET time scale is observed, which remains unaffected by temperature (5-60 °C). Our findings demonstrate that even a simple "perovskite NC-electron acceptor" composite like that in the present study can ensure a rapid interfacial charge separation. Such information will help us to realize the actual potential of perovskites NCs in their real applications.

A review on the green and sustainable synthesis of silver nanoparticles and one-dimensional silver nanostructures

The significance of silver nanostructures has been growing considerably, thanks to their ubiquitous presence in numerous applications, including but not limited to renewable energy, electronics, biosensors, wastewater treatment, medicine, and clinical equipment. The properties of silver nanostructures, such as size, size distribution, and morphology, are strongly dependent on synthesis process conditions such as the process type, equipment type, reagent type, precursor concentration, temperature, process duration, and pH. Physical and chemical methods have been among the most common methods to synthesize silver nanostructures; however, they possess substantial disadvantages and short-comings, especially compared to green synthesis methods. On the contrary, the number of green synthesis techniques has been increasing during the last decade and they have emerged as alternative routes towards facile and effective synthesis of silver nanostructures with different morphologies. In this review, we have initially outlined the most common and popular chemical and physical methodologies and reviewed their advantages and disadvantages. Green synthesis methodologies are then discussed in detail and their advantages over chemical and physical methods have been noted. Recent studies are then reviewed in detail and the effects of essential reaction parameters, such as temperature, pH, precursor, and reagent concentration, on silver nanostructure size and morphology are discussed. Also, green synthesis techniques used for the synthesis of one-dimensional (1D) silver nanostructures have been reviewed, and the potential of alternative green reagents for their synthesis has been discussed. Furthermore, current challenges regarding the green synthesis of 1D silver nanostructures and future direction are outlined. To sum up, we aim to show the real potential of green nanotechnology towards the synthesis of silver nanostructures with various morphologies (especially 1D ones) and the possibility of altering current techniques towards more environmentally friendly, more energy-efficient, less hazardous, simpler, and cheaper procedures.

Role of Different States of Solubilized Water on Solvation Dynamics and Rotational Relaxation of Coumarin 490 in Reverse Micelles of Gemini Surfactants, Water/12-s-12.2Br- (s = 5, 6, 8)/n-Propanol/Cyclohexane

The present study demonstrates how the different states of solubilized water viz. quaternary ammonium headgroup-bound, bulklike, counterion-bound, and free water in reverse micelles of a series of cationic gemini surfactants, water/12-s-12 (s = 5, 6, 8).2Br^-/n-propanol/cyclohexane, control the solvation dynamics and rotational relaxation of Coumarin 490 (C-490) and microenvironment of the reverse micelles. The relative number of solubilized water molecules of a given state per surfactant molecule decides major and minor components. A rapid increase in the number of bulklike water molecules per surfactant molecule as compared to the slow increase in the number of each of headgroup- and counterion-bound water molecules per surfactant molecule with increasing water content (W _o) in a given reverse micellar system is responsible for the increase in the rate of solvation and rotational relaxation of C-490. The increase in the number of counterion-bound water molecules per surfactant molecule and the concomitant decrease in the number of bulklike water molecules per surfactant molecule with increasing spacer chain length of gemini surfactants at a given W _o are ascribed to the slower rates of both solvation and rotational relaxation. Relative abundances of different states of water have a role on the microenvironment of the reverse micelles as well. Thus, a comprehensive effect of different states of water on dynamics in complex biomimicking systems has been presented here.

L-cysteine modified silver nanoparticles for selective and sensitive colorimetric detection of vitamin B1 in food and water samples

The use of L-cysteine modified silver nanoparticles (Cys-capped AgNPs) as a colorimetric probe for determination of vitamin B1 (thiamine) is described in the present work. This method is based on the measurement of red shift of localized surface plasmon resonance (LSPR) band of Cys-capped AgNPs in the region of 200–800 nm. The color of Cys-capped AgNPs was changed from yellow to colorless by the addition of vitamin B1. The mechanism for detection of vitamin B1 is based on the electrostatic interaction between positively charged vitamin B1, which causes the red shift of LSPR band from 390 nm to 580 nm. The interaction between Cys-capped AgNPs and vitamin B1 was theoretically explored by density function theory (DFT) using LANL2DZ basis sets with help of Gaussian 09 (C.01) program. The morphology, size distribution and optical properties of Cys-capped AgNPs were characterized by transmission electron microscope (TEM), UV-Visible spectrophotometry, Fourier transform infrared spectroscopy (FTIR) and dynamic light scattering (DLS) techniques. The method is linear in the range of 25–500 μg mL⁻¹ with correlation coefficient (R²) 0.992 and limit of detection of 7.0 μg mL⁻¹. The advantages of using Cys-capped AgNPs as a chemical sensor in colorimetry assay are being simple, low cost and selective for detection of vitamin B1 from food (peas, grapes and tomato) and environmental (river, sewage and pond) water samples.

Mechanistic Insights into the Growth of Anisotropic Nanostructures Inside Reverse Micelles: A Solvation Perspective

Reverse micelles (RMs) as soft templates have been successfully used in tailoring the structural characteristics (size and morphology) of nanomaterials that in turn have been used in various applications. In this work, we have focused on the local perturbations in the different interior domains of the cetyltrimethylammonium bromide-reverse micelle-based soft template en route to nanorod formation by monitoring the solvation response of coumarin-based solvatochromic probes (C343 and C153). We have observed an appreciable retardation of the solvent coordinate during the initial phases of nanorod growth, which we have attributed to the reorientational motion of the water molecules lodged in the interfacial region. Moreover, these rigid nanostructures leave their imprints on the soft interfacial layer as was observed from the direct correlation in the solvation response of RM-containing nanostructures and respective surfactant aggregates in supernatant solution. Supporting data from time-resolved anisotropy studies further reinforced our conclusions from the solvation experiments. Our study proves that the hydration dynamics can be a promising tool in tracking the heterogeneous growth evolution of nanostructure formation in RMs since solvent reorganization provides insights into the intrinsic, molecular-level features of the micellar assemblies.

Synergistic interactions of surfactant blends in aqueous medium are reciprocated in non-polar medium with improved efficacy as a nanoreactor

Efficient soft chemical nanoreactors: a design strategy to improve the performance of a model C–C cross coupling (Heck) reaction under nanoscopic confinement of surfactant blends.

Solvation Dynamics in Different Phases of the Lyotropic Liquid Crystalline System

Reverse hexagonal (HII) liquid crystalline material based on glycerol monooleate (GMO) is considered as a potential carrier for drugs and other important biomolecules due to its thermotropic phase change and excellent morphology. In this work, the dynamics of encapsulated water, which plays important role in stabilization and formation of reverse hexagonal mesophase, has been investigated by time dependent Stokes shift method using Coumarin-343 as a solvation probe. The formation of the reverse hexagonal mesophase (HII) and transformation to the L2 phase have been monitored using small-angle X-ray scattering and polarized light microscopy experiments. REES studies suggest the existence of different polar regions in both HII and L2 systems. The solvation dynamics study inside the reverse hexagonal (HII) phase reveals the existence of two different types of water molecules exhibiting dynamics on a 120-900 ps time scale. The estimated diffusion coefficients of both types of water molecules obtained from the observed dynamics are in good agreement with the measured diffusion coefficient collected from the NMR study. The calculated activation energy is found to be 2.05 kcal/mol, which is associated with coupled rotational-translational water relaxation dynamics upon the transition from "bound" to "quasi-free" state. The observed ∼2 ns faster dynamics of the L2 phase compared to the HII phase may be associated with both the phase transformation as well as thermotropic effect on the relaxation process. Microviscosities calculated from time-resolved anisotropy studies infer that the interface is almost ∼22 times higher viscous than the central part of the cylinder. Overall, our results reveal the unique dynamical features of water inside the cylinder of reverse hexagonal and inverse micellar phases.