Receptor-mediated activation of nitric oxide synthesis …
inhibits nitric oxide synthesis
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.
An improved Hummers method for eco-friendly synthesis …
Heterogeneous photo-catalysis is an advanced oxidation process (PAO), which has been the subject of numerous studies and applications, particularly using the commercial oxide of TiO2 (P25, Evonik). Zinc oxide (ZnO) has often been considered a valid alternative to TiO2 due to its good opto-electronic, catalytic and photochemical characteristics along with its low cost. In order to improve the photocatalytic performance of ZnO for practical applications, various types of synthetic approaches have been developed, including, among others, the hydrothermal / solvothermal growth method, sol-gel method, ultrasonic assisted method, deposition chemistry in vapor phase, etc. with the aim of preparing ZnO particles with different sizes and morphologies. However, all of these methods require relatively severe reaction conditions such as high temperature, sophisticated techniques, high purity of gases, adjustable gas flow, expensive raw materials, etc. Therefore, it is important to find a simple and cost-effective method for the synthesis of crystalline nano-particles of ZnO. For this reason, in the present work, the ZnO has been synthesized by three different procedures: conventional aqueous precipitation method, hydrothermal method (H) and microwave assisted method (MW). In all three processes, the same material is obtained, hydrocincite [Zn5(CO3) 2(OH)6], which evolves to crystalline ZnO after calcination thermal treatments. We investigated the effect of the calcination temperature, at the same time (2 h), on the optical, textural and structural properties. Photo-catalytic studies were performed using two selected substrates, Methyl Orange and Phenol, as toxic model substrates (one colorant and the other transparent). The catalysts prepared were characterized by several techniques: DRX, SBET, FE-SEM, TEM and UV-Vis (in diffuse reflectance mode).From the results of XRD, it has been possible to establish that a minimum difference between the relative intensities of exposed faces (I100 and I002) is a crucial factor to obtain good photocatalytic properties. This minimum difference is achieved, in our cases by thermal treatments of calcination at 400ºC, 2 h. When this temperature is chosen, there is no appreciable variation between the photocatalytic activities of the oxides of zinc obtained by the three processes, and there are small differences depending on the nature of the substrate chosen, which can be attributed to the textural differences between the oxides. In any case, the obtained zinc oxides show, for each substrate, photo-catalytic activities in the UV that are superior to those presented by the widely used commercial oxide TiO2 (P25) used as reference.