Silver nanoparticles of variable morphology synthesized in aqueous foams as novel templates

In this paper, we describe the synthesis of silver nanocrystals within aqueous foams as a template. More specifically, we show that aqueous Ag⁺ions may be electrostatically complexed with the anionic surfactants aerosol OT (sodiumbis-2-ethylhexyl-sulfosuccinate, (AOT) and sodium dodecyl sulphate (SDS)) in a highly stable liquid foam. After drainage of the foam, the silver ions are reducedin situby introducing sodium borohydride into the foam by capillary flow. This leads to the formation of silver nanoparticles of spherical, tape-and sheet-like morphology in the foam. The structure of the foam is extremely complex and presents reaction sites of different spatial extent. The differences in foam reaction-site geometry are believed to be responsible for the morphology variation in the silver nanoparticles observed. The silver nanoparticles are observed to be extremely stable in solution suggesting that the AOT or SDS molecules stabilize them. This approach appears promising for application in large-scale synthesis of nanoparticles and may be readily extended to other chemical compositions.     

Density maximum effect on buoyancy-driven convection of water in a porous cavity with variable side wall temperatures

The buoyancy-driven convection in a square cavity filled with water-saturated porous medium is studied numerically. While the right and left side wall temperatures vary linearly from θ_a to θ_o and θ_o to θ_b, respectively with height and θ_o is the mean of θ_a and θ_b,  the top and bottom walls of the cavity are thermally insulated. The Brinkman–Forchheimer extended Darcy model is considered to study the effects of density maximum, Grashof numbers, porosity and Darcy numbers on the buoyancy-induced flow and heat transfer. The finite volume method is used to discretize the governing equations, which are solved by Gauss–Seidel and successive over relaxation methods. The temperature distribution and flow fields are presented in the form of streamlines, isotherms and mid-height velocity profiles. It is found that the effect of density maximum is to slow down the natural convection and reduce the average heat transfer. The strength of convection and heat transfer rate become weak due to more flow restriction in the porous medium for small porosity.     

Combined buoyancy and thermocapillary convection of cold water around its density maximum temperature

Summary Combined buoyancy and thermocapillary flow of cold water is investigated in an open square cavity. The investigations are carried out to determine the effect of density maximum temperature on the fluid motions and thereby resulting thermal transport. The air-water interface is assumed to be either flat or concave. Numerical solutions of the governing equations are obtained using Alternating Direction Implicit (ADI) and Successive Over Relaxation (SOR) methods.     

Recent progress on graphene quantum dots-based fluorescence sensors for food safety and quality assessment applications

The versatile photophysicalproperties, high surface-to-volume ratio, superior photostability, higher biocompatibility, and availability of active sites make graphene quantum dots (GQDs) an ideal candidate for applications in sensing, bioimaging, photocatalysis, energy storage, and flexible electronics. GQDs-based sensors involve luminescence sensors, electrochemical sensors, optical biosensors, electrochemical biosensors, and photoelectrochemical biosensors. Although plenty of sensing strategies have been developed using GQDs for biosensing and environmental applications, the use of GQDs-based fluorescence techniques remains unexplored or underutilized in the field of food science and technology. To the best of our knowledge, comprehensive review of the GQDs-based fluorescence sensing applications concerning food quality analysis has not yet been done. This review article focuses on the recent progress on the synthesis strategies, electronic properties, and fluorescence mechanisms of GQDs. The various GQDs-based fluorescence detection strategies involving Förster resonance energy transfer- or inner filter effect-driven fluorescence turn-on and turn-off response mechanisms toward trace-level detection of toxic metal ions, toxic adulterants, and banned chemical substances in foodstuffs are summarized. The challenges associated with the pretreatment steps of complex food matrices and prospects and challenges associated with the GQDs-based fluorescent probes are discussed. This review could serve as a precedent for further advancement in interdisciplinary research involving the development of versatile GQDs-based fluorescent probes toward food science and technology applications.