TiO2 and SiO2 encapsulated metal nanoparticles: Synthetic strategies, properties, and photocatalytic applications

Comparison of the antimicrobial photocatalytic activities of SiO2 and Au@SiO2 nanostructures in water decontamination

Photocatalytic disinfection of Escherichia coli suspension by silicon dioxide nanoparticles and silicon dioxide/gold nanocomposite in a batch reactor is investigated experimentally and results are compared. Silica nanoparticles were synthesized by Stöber method and pulsed laser ablation method was employed to prepare gold nanoparticles in distilled water. Composition of two nanoparticles species was carried out, using the second harmonic pulse of Nd:YAG laser, whose wavelength is in the absorption spectra of gold nanoparticles. Results confirm a decrease in the bandgap energy of silica nanoparticles after composition. Escherichia coli were selected as an indicator of the microbial water contamination. Disk diffusion method was used to evaluate the antimicrobial potential of SiO2 and Au@SiO2 nanostructures. Photocatalytic activities of both nanostructures were examined in dark, and under the irradiation of UV and visible light. In all conditions, the performance of Au@SiO2 nanocomposites was higher than SiO2 nanoparticles. In dark condition the higher biocidal nature and activity of Au nanoparticles and for the case of UV radiation, decreasing the bandgap energy and recombination rate of SiO2 nanoparticles after composition with Au increased the efficiency. For the case of visible light radiation, surface plasmon resonances effects, and local heat of Au nanoparticles were responsible for increasing the efficiency. RESEARCH HIGHLIGHTS: Doping large bandgap semiconductors nanostructures, such as silica with metal nanoparticles, such as gold will improve their photocatalytic activity to work in visible light. In this mechanism, gold nanoparticles act as effective traps to prevent the recombination of photogenerated electron-hole pairs. Other mechanisms, such as Schottky barrier formation, surface plasmon resonance absorption of gold nanoparticles, and biocidal nature of the gold nanoparticles are effective in increasing the efficiency of Au doped silica nanostructures.

Synthesis and characterization of Fe3O4@SiO2 -supported metal-organic framework PAEDTC@MIL-101 (Fe) for degradation of chlorpyrifos and diazinon pesticides

In this study, a new core-shell Fe3O4@SiO2/PAEDTC@MIL-101 (Fe) photocatalyst was prepared by sol-gel method and used to degrade diazinon (DZN) and chlorpyrifos (CPS) from aqueous solutions. The characteristics analyzed by various techniques indicate that the core-shell photocatalyst with a specific surface area of 992 m2/g, pore size of 1.35 nm and saturation magnetization of nanocomposite was 12 emu/g has been successfully synthesized and can be separated from the reaction solution by a magnetic field. The maximum efficiencies of DZN (98.8%) and CPS (99.9%) were provided at pH of 5, photocatalyst dosage of 0.6 g/L, pollutant concentration of 25 mg/L, radiation intensity of 15 W, and time of 60 min. The presence of anions such as sulfate, nitrate, bicarbonate, phosphate, and chloride had a negative effect on the performance of the photocatalysis system. Compared to the adsorption and photolysis systems alone, the photocatalytic process based on Fe3O4@SiO2/PAEDTC@MIL-101 (Fe) under two UV and visible light sources showed a high efficiency of 90% in the reaction time of 60 min. The BOD5/COD ratio improved after 50 min to above 0.4 with TOC and COD removal rates >80%. Scavenging tests showed that •OH radical, hole (h+), electron (e-), and O2•- anion were produced in the reaction reactor, and the •OH radical was the dominant species in the degradation of DZN and CPS. The stability tests confirmed the recyclability of the photocatalyst in 360 min of reactions, with a minimum reduction of 7%. Energy consumption for the present system during different reactions was between 15.61 and 25.06 kWh/m3 for DZN degradation and 10-22.87 kWh/m3 for CPS degradation.