No abstract

The present work deals with the preparation of graphene oxide (GO) using Hummers-Offeman method in the presence of ultrasonic irradiations. Further loading of TiO photocatalyst on prepared GO was accomplished which is basically oxidation reduction reaction between graphene oxide and titanium isopropoxide that leads to the formation of graphene-TiO nanocomposite. Graphene-Ce-TiO and Graphene-Fe-TiO nanocomposites were prepared using one step in-situ ultrasound assisted method using GO, titanium isopropoxide, cerium nitrate, ferric nitrate, and 2-propanol. The successfully prepared graphene-TiO, Graphene-Ce-TiO, Graphene-Fe-TiO nanocomposites were then characterized using XRD, SEM and TEM analysis. The obtained XRD patterns clearly indicates the formation of anatase TiO on graphene nanosheets and it also indicates the presence of Ce and Fe in the Graphene-Ce-TiO and Graphene-Fe-TiO nanocomposite respectively. Further the use of the prepared nanocomposites as a photocatalyst have been studied for the degradation of crystal violet dye. The effect of various parameters such as catalyst doping, catalyst loading and initial concentration of dye on its degradation were studied. The effectiveness of the prepared catalysts were compared for the degradation of crystal violet dye. It has been observed that Graphene-Fe-TiO exhibits maximum photocatalytic activity compared to Graphene-Ce-TiO and Graphene-TiO nanocomposite photocatalyst.

Sonolytic degradation kinetics of non-volatile surfactant perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) were investigated over a range of concentration, considering active cavity as a catalyst. The Michaelis-Menten type kinetic model was developed to empirically estimate the concentration of active cavity sites during reactions. Sonolytic degradation of PFOA and PFOS, as well as the formation of its inorganic constituents, fluoride, and sulfate, follows saturation kinetics of pseudo-first order at lower concentration (<2.34 µM) and zero order at higher concentration (>23.60 µM). Nitrate and hydrogen peroxide formations were 0.53 ± 0.14 µM/min and 0.95 ± 0.11 µM/min, respectively. At a power density of 77 W/L and frequency of 575 kHz, the empirically estimated maximum number of active cavity sites that could lead to the sonolytic reaction were 89.25 and 8.8 mM for PFOA and PFOS, respectively. This study suggests that a lower number of active cavity sites with higher temperature needed to degrade PFOS might be the reason for lower degradation rate of PFOS compared to that of PFOA. Diffusion of non-volatile surfactants at the cavity-water interface is found to be the rate-limiting step for the mineralization of perfluoroalkyl substances.

The Meter model (a four-parameter model) captures shear viscosityshear stress relationship (S-shaped type) of polymeric non-Newtonian fluids. We devise an analytical solution for radial velocity profile, average velocity and volumetric flow rate of steady state laminar flow of non-Newtonian Meter model fluids through a circular geometry. The analytical solution converts to the Hagen-Posseuille equation for the Newtonian fluid case. We also develop the formulations to determine effective viscosity, Reynolds number and Darcy's friction factor using measurable parameters as available rheological models do not correctly define these parameters for a given set of flow condition in circular geometry. The analytical solution and formulations are validated against experimental data. The results suggest that the effective Reynolds number and effective friction factor estimated using the proposed formulation helps to characterise non-Newtonian fluid flow through a circular geometry in laminar and turbulent flow.

No abstract