Preparation and characterization of gold nanoparticles prepared with aqueous extracts of Lamiaceae plants and the effect of follow-up treatment with atmospheric pressure glow microdischarge

AbstractThe unique properties of gold nanoparticles (AuNPs) make them attractive for use in a number of fields, ranging from cosmetology to medicine. If AuNPs are to be widely used in industrial and medical applications, it is necessary to develop environmentally friendly methods for their synthesis. This can be accomplished by replacing the traditional chemical compounds for the reduction of the Au(III) ions to Au0 during AuNPs synthesis with natural plant extracts or with atmospheric pressure plasmas. Here, the properties of three aqueous plant extracts (Mentha piperita, Melissa officinalis, and Salvia officinalis) in the synthesis of AuNPs were compared and optimized under standardized conditions. The effects of the type of plant extract, the reaction temperature, and the precursor concentration on the production and size of the obtained AuNPs were examined using UV–Vis absorption spectrophotometry, dynamic light scattering (DLS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). It was observed that the size of the produced AuNPs was dependent on the aqueous plant extract used, and that under the optimized conditions, the aqueous leaf extract of M. piperita resulted in the production of AuNPs with the smallest volume-weighted diameter. Additionally, the bioactive compounds present in each extract were studied. Attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) indicated that different chemical groups could be involved in the AuNPs synthesis, while a Folin–Ciocalteu (FC) assay revealed a clear role of phenolic compounds. Finally, it was shown that the treatment of the synthesized AuNPs, which were obtained after bioreduction using the plant extracts, with atmospheric pressure glow microdischarge (μAPGD) resulted in their agglomeration and enlargement

Central composite design application in oil agglomeration of talc

Talc has many applications in various branches of industry. This material is an inert one with a naturally hydrophobic surface. Talc agglomeration is within the wide interest of pharmaceutical industry. Oil agglomeration experiments of talc were carried out to find out and assess the significance of experimental factors. Central composite design (CCD) was used to estimate the importance and interrelation of the agglomeration process parameters. Four experimental factors have been evaluated, i.e. concentration of cationic surfactant and oil, agitation intensity as well as time of the process. The median size of agglomerates (D50) and the polydispersity span (PDI) were used as the process responses. Logarithmic transformations of the responses provide better description of the model, than untransformed responses, with the reduced cubic model for D50 and quadratic model for PDI. This was supported by the Box-Cox plots. It was shown that there were many statistically important factors, including the concentration of cationic surfactant and stirring rate for D50, concentration of oil and stirring rate for PDI, as well as various interactions, up to third order for D50. Optimal conditions for minimum values of reagent amounts as well as mixing time and intensity for the maximum size of agglomerates but of rather narrow size distribution were found

Calcium carbonate mineralization. Part 1, The effect of poly(ethylene glycol) concentration on the formation of precipitate

In this study, the role of polymer in precipitation has been examined by studying the effect of poly(ethylene glycol) (PEG) on the formation of calcium carbonate particles. The CaCO3 particles were characterized by several techniques, such as FTIR, XRD, SEM, and particle size distribution analysis. In the absence of polymer, the mixing of reagents in an aqueous solution led to the formation of calcite crystals. Introduction of poly(ethylene glycol) molecules reduced the rate of crystallization process, and the effect was concentration dependent. In the presence of 0.05, 0.1, and 0.5 % of PEG, after 5 minutes of precipitation initiation, vaterite microspheres appeared in the system and which were transformed into calcite crystals after 24 hours. The calcium carbonate obtained with PEG was characterized by smaller sized particles in comparison with the ones without polymer

Calcium carbonate mineralization. Part II: effect of poly(ethylene glycol) and block copolymers molecular weight on formation of precipitate

In this study the role of PEG and PEO-PPO-PEO block copolymers molecular weight in precipitation of calcium carbonate was examined. The CaCO3 particles were characterized by FTIR spectroscopy, X-ray, SEM and particle size distribution analysis. In absence and presence of modifiers, mixing of the reagents led to the formation of calcite crystals. The calcium carbonate obtained with poly(ethylene glycol) and block copolymers was characterized by smaller diameter in comparison with the one without modifiers. It was observed that using compounds with different molecular weights has no obvious effect on the form and properties of precipitated calcium carbonate particles

Effect of Layered Double Hydroxide, Expanded Graphite and Ammonium Polyphosphate additives on thermal stability and fire performance of polyisocyanurate insulation foam

This work examines the effect of Layered Double Hydroxides (LDHs), Expandable Graphite (EG) and Ammonium Polyphosphate (APP) on the thermal stability and behaviour under fire conditions of polyisocyanurate (PIR) insulation foams. Virgin materials’ and char residues’ morphologies were analyzed with a variety of experimental techniques including field emission scanning electron and optical microscopy along with Raman spectroscopy. Thermal stability and burning behaviour were examined using thermogravimetric (TGA) coupled with Fourier Transform Infrared (FTIR) spectrometer and cone calorimeter. TGA results suggested a decrease in degradation temperature upon introduction of fillers in PIR samples. FTIR spectra were used to determine the absorbance intensity of the different pyrolysis gases. Cone calorimeter data analysis established a limited effect on reducing the rate of heat release rate and smoke production with the inclusion of LDHs. However, EG or EG + APP addition, caused a considerable decrease in heat release rate, owing to the increased char strength and the release of non-combustible gases. The positive effect of EG or EG + APP in the fire behaviour of PIR foams was further supported by the morphological evaluation of their residual char samples