The ordered porous anodic aluminum oxide (AAO) is one of the famous nano-templates usedas etching mask for pattern transfer and for synthesis of nanocomposite materials for wideapplications. Conventional AAO templates were synthesized using two-step potentiostaticmethod of direct current anodization (DCA) at low temperature (0-10°C) to avoid dissolutioneffect. In this talk, the synthesis and characteristics of AAO using conventionallow-temperature anodization and an effective method of room-temperature hybrid pulseanodization (HPA) are presented for the comparison. The HPA with normal-positive andsmall-negative voltages for AAO synthesis can be accomplished at relatively hightemperature of 15-25°C for enhancing AAO characteristics from both the cheap low-purity(99%) and costly high-purity (99.997%) aluminum foils. The pore distribution uniformity andcircularity of AAO by HPA is much better than DCA due to its effective cooling at hightemperature. The impurity effect on AAO characteristics is also discussed. HPA is differentfrom the traditional pulse-anodization with alternating both high and low positive potentialdifferences (/currents) or both one-positive and one-zero potential differences. HPA not onlymerits manufacturing convenience and cost reduction but also promotes pore distributionuniformity of AAO at severe conditions of low-purity Al foils and high temperature. Someapplication in humidity sensing, photoluminescence and SERS will be presented.
Zeolitic imidazolate frameworks (ZIFs), a subclass of metal-organic frameworks (MOFs), havebeen recently employed in various fields such as gas separation, catalysis, water purification anddrug delivery.1 Their high importance is due to their chemical and thermal stability in addition tothe flexibility of their design. ZIFs have been synthesized solvothermally or at room temperatureusing organic solvents (e.g. methanol, DMF) or pure water.2 The control of size and morphologyof crystals has been achieved using reverse microemulsion methods, microwave, ultrasoundassistedsyntheses and coordination modulation methods.1-3 Herein, we investigate a newsynthesis method where ZIF crystals are produced using the reaction-diffusion framework (RDF)in a gel medium at room temperature. The method is based on the diffusion of an outer solutionof the organic linker or mixed linkers into an agar gel containing the inner metal ions Zn(II)and/or Co(II) where a precipitation reaction takes place leading to the formation of the ZIFcrystals. A propagating supersaturation wave, initiated at the interface between the outer solutionand the gel matrix leads to a precipitation front endowed with a gradient of crystal sizes rangingbetween 100 nm and 55 μm along the same reaction tube. While the precipitation fronts of ZIF-8 and ZIF-67 travel the same distance for the same initial conditions, ZIF-8 crystals therein areconsistently smaller than the ZIF-67 crystals due to the disparity of their rate of nucleation andgrowth. The effects of temperature, the concentration of the reagents, and the thickness of thegel matrix on the growth of the ZIF crystals are investigated. We also show that by using RDF,we can envisage the formation mechanism of the ZIF crystals, which consists of the aggregationof ZIF nanospheres to form the ZIF-8 dodecahedrons. Moreover, using RDF the formation of asolid-solution ZIF via the incorporation of Co(II) and Zn(II) cations within the same frameworkis achieved in a controlled manner. Finally, we demonstrate that doping ZIF-8 by Co(II)enhances the photodegradation of methylene blue dye under visible light irradiation in theabsence of hydrogen peroxide.
Lasienthra africanum (LA) leaf extract was employed for nano-silver synthesis. The reducing effect of the plant extract was investigated at different times, pH, temperatures and concentrations. The effect of various kinetic parameters was studied using UV–vis spectroscopy. Blue-shifted surface plasmon bands indicating smaller sized nanoparticles were obtained at neutral pH (6.8–7.0), temperature of 65◦C and concentration ratio of 1:10 (leaf extract: AgNO3) with increasing reaction times under the reaction conditions. The kinetics of the reaction followed pseudo-first- and -second-order rate equations, and was thermodynamically favoured at higher time. Spherically shaped nanoparticles were obtained at different reaction conditions.
The current interest of our research group is largely focused on the development and understanding of precipitated crystalline organometallic compounds. We are placing a strong emphasis in the study of the synthetic procedures, the morphology, and on the structural determination of such compounds. Special importance is engaged in the preparation coordination polymers crystallized from solutions of supercritical CO2, (scCO2), where the use of a co-solvent is occasionally employed depending on reagents solubility [1-3]. The correct selection of experimental conditions in the scCO2 reactive crystallization technique, allows a precipitation known from other methodologies, as well as new crystalline phases. This procedure leads to the crystallization of stable hierarchical nanoestructures involving micro and mesoporosity. As the preparation of the crystalline materials is carried out in scCO2, these obtained with microporous structures were recovered activated, i.e., with open volume, since the removal of any guest molecules from the framework is carried out by simple depressurization. This method is expected to have many potential applications in the development of green crystallization techniques for coordination polymers synthesis.
Title of Talk:
Plant-mediated biosynthesis of silver nanoparticles by leaf extracts of Lasienthra africanum and a study of the influence of kinetic parameters
Title of Talk: Plant-mediated biosynthesis of silver nanoparticles by leaf extracts of Lasienthra africanum and a study of the influence of kinetic parameters
Title of Talk: Influence of the support used on the morphology of the template synthesized intermetallic (Co-Sn, Ni-Sn, Co-Ni) nanopareticles
Inorganic semiconductors have recently drawn a huge attention due to their low cost of synthesis and multifunctional applications. Since nickel and titanium oxides have shown to exhibit unique properties separately, nickel titanate was synthesized demonstrating synergistic behavior. Afterwards, it was linked with the reduced graphene oxide, which displays large surface area, high electrical conduction, good electron transport rates and improves dispersity of the inorganic semiconductors. The proposed composite material was utilized for the construction of the glucose sensitive electrochemical sensor of the increased electrocatalytic performance. Applicability of the designed biosensor was shown towards glucose determination in human body fluids.