Determination of phenolic compounds using spectral and color transitions of rhodium nanoparticles

This work reports a new approach for the determination of phenolic compounds based on their interaction with citrate-capped rhodium nanoparticles. Phenolic compounds (i.e., catechins, gallates, cinnamates, and dihydroxybenzoic acids) were found to cause changes in the size and localized surface plasmon resonance of rhodium nanoparticles, and therefore, give rise to analyte-specific spectral and color transitions in the rhodium nanoparticle suspensions. Upon reaction with phenolic compounds (mainly dithydroxybenzoate derivatives, and trihydroxybenzoate derivatives), new absorbance peaks at 350 nm and 450 nm were observed. Upon reaction with trihydroxybenzoate derivatives, however, an additional absorbance peak at 580 nm was observed facilitating the speciation of phenolic compounds in the sample. Both absorbance peaks at 450 nm and 580 nm increased with increasing concentration of phenolic compounds over a linear range of 0–500 μM. Detection limits at the mid-micromolar levels were achieved, depending on the phenolic compound involved, and with satisfactory reproducibility (<7.3%). On the basis of these findings, two rhodium nanoparticles-based assays for the determination of the total phenolic content and total catechin content were developed and applied in tea samples. The obtained results correlated favorably with commonly used methods (i.e., Folin-Ciocalteu and aluminum complexation assay). Not the least, the finding that rhodium nanoparticles can react with analytes and exhibit unique localized surface plasmon resonance bands in the visible region, can open new opportunities for developing new optical and sensing analytical applications.     

Heterogeneous activation of oxone using Co3O4

This study explores the potential of heterogeneous activation of Oxone (peroxymonosulfate) in water using cobalt oxides. Two commercially available cobalt oxides, CoO and Co3O4 (CoO.Co2O3) were tested for the activation of peroxymonosulfate and the consequent oxidation of 2,4-dichlorophenol (2,4-DCP) via a sulfate radical mechanism. Both systems, CoO/Oxone and Co3O4/Oxone, were tested at acidic and neutral pH and compared with the homogeneous Co(NO3)2/Oxone. The activity of these systems was evaluated on the basis of the induced transformation of 2,4-DCP as well as the dissolution of cobalt occurred after 2 h of reaction. It was observed that only Co3O4 activates peroxymonosulfate heterogeneously, with its heterogeneity being more pronounced at neutral pH. Both CoO and Co2O3 contained in Co3O4 might be responsible for the observed heterogeneity, and the relative mechanisms are further discussed here. To our knowledge, this is perhaps the first study that documents the heterogeneous activation of peroxymonosulfate with cobalt, the best-known catalyst-activator for this inorganic peroxide.     

Numerical Simulation of Diesel Spray Evaporation in a “Stabilized Cool Flame” Reactor: A Comparative Study

The major objective of this work is to numerically investigate the interacting physical and chemical phenomena that characterize the flow in a stabilized cool flame diesel fuel spray evaporation system. A two-phase RANS computational fluid dynamics code has been developed and used to predict the characteristics of the developing turbulent, multiphase, multi-component, reactive flow-field. The code employs a Eulerian–Lagrangian approach, taking into account the mass, momentum, thermal and turbulent energy exchange between the phases. A variety of physical phenomena, such as turbulent dispersion, droplet evaporation, droplet-wall collision, conjugate heat transfer, drift correction, two-way coupling are taken into account by implementing respective sub-models. Two alternative modelling approaches for the simulation of cool flame reactions have been validated and evaluated by comparing numerical predictions with experimental data from two atmospheric pressure, evaporating Diesel spray, Stabilized Cool Flame reactors. Both models have achieved good quantitative agreement in the majority of the considered test cases. The results have been used to estimate the local physical and chemical characteristic time scales of the occurring phenomena, thus allowing, for the first time, the classification of stabilized cool flames.