Structural rearrangement of mesostructured silica nanoparticles incorporated with ZnO catalyst and its photoactivity: effect of alkaline aqueous electrolyte concentration

ZnO-incorporated mesostructured silica nanoparticles (MSN) catalysts (ZM) were prepared by the introduction of Zn ions into the framework of MSN via a simple electrochemical system in the presence of various concentrations of NH4OH aqueous solution. The physicochemical properties of the catalysts were studied by XRD, 29Si MAS NMR, nitrogen adsorption-desorption, FE-SEM, TEM, FTIR, and photoluminescence spectroscopy. Characterization results demonstrated that the alkaline aqueous electrolyte simply generated abundant silanol groups on the surface of the catalysts as a consequence of desilication to form the hierarchical-like structure of the MSN. Subsequent restructuring of the silica network by the creation of oxygen vacancies and formation of Si-O-Zn during the electrolysis, as well as formation of new Si-O-Si bonds during calcination seemed to be the main factors that enhanced the catalytic performance of photodecolorization of methyl orange. A ZM prepared in the presence of 1.0 M NH4OH (ZM-1.0) was determined to be the most effective catalyst. The catalyst displays a higher first-order kinetics rate of 3.87 × 10-1 h-1 than unsupported ZnO (1.13 × 10-1 h-1) that prepared under the same conditions in the absence of MSN. The experiment on effect of scavengers showed that hydroxyl radicals generated from the three main sources; reduced O2 at the conduction band, decomposed water at the valence band and irradiated H2O2 in the solution, are key factors that influenced the reaction. It is also noted that the recycled ZM-1.0 catalyst maintained its activity up to five runs without serious catalyst deactivation

Tailoring the metal introduction sequence onto mesostructured silica nanoparticles framework: effect on physicochemical properties and photoactivity

Cu with variable weight loading (1-5wt%) was introduced to 5wt% Zn mixed mesostructured silica nanoparticles (MSN) via an electrochemical method to synthesize CuO-ZnO/MSN (C-ZM) catalysts. The physicochemical properties of the catalysts were characterized by XRD, FTIR, XPS, N2 adsorption-desorption, ESR, and cyclic voltammetry. 3 wt% Cu and 5 wt% Zn were also introduced alternately to MSN (3C-ZM and Z-3CM) to study the metal introduction sequence effect on the properties and catalytic activity. The characterization data showed that an altered arrangement of the silica network was observed with a different structure, particularly in the numbers of SiOSi, SiOZn, and SiOCu bonds as well as oxygen vacancies. The catalytic activity regarding the photodecolorization of methyl orange (MO) was in the following order: 3C-ZM > 5C-ZM > Z-3CM > 1C-ZM. The higher numbers of SiOZn, oxygen vacancies, and the higher pore volume of the 3C-ZM catalyst seemeed to be the main factors behind its higher photoactivity compared to the other catalysts. Further optimization by response surface methodology (RSM) with a central composite design (CCD) model was performed for the decolorization of MO. RSM demonstrated that the experimental value (99.89%) was reasonably close to the predicted value (99.99%) with only 0.1% error for MO decolorization at pH 3.5 using 1.6 g L-1 catalyst with 4 wt% Cu loading

Recovery of synthetic dye red 3BS from simulated wastewater using supported liquid membrane process containing immobilized kerosene-tridodecylamine liquid membrane

The discharge of reactive dyes into the environment has led to the toxicity problems especially to the aquatic organism. Therefore, there is a necessity for treatment of the reactive dyes from wastewater. In this work, Red 3BS reactive dye was separated using supported liquid membrane process. Commercial polypropylene (PP) membrane was used as a support of kerosene-tridodecylamine liquid membrane. Several important parameters such as flow rate, pH of feed phase, initial concentration of feed phase and stripping agent concentration were investigated. The result shows that for 50 ppm Red 3BS solution containing 0.00001M Na2SiO3 almost 100 and 89% of Red 3BS was removed and recovered respectively at the favorable condition of 0.1 M NaOH as a stripping agent, pH 3 of feed phase and 100 ml/min of flow rate