Controlled Synthesis Of Manganese Oxide Nanoparticles Integrated Hollow Mesoporous Silica Nanoreactors And Their Application In Dye Degradation

The thesis aims to controllably synthesize hollow mesoporous silica nanoreactors with small manganese oxide nanoparticles(NPs)in their cavities(MnxOy@HMSNs),and enhance the degradation performance in the presence of hydrogen peroxide.The synthesized MnxOy@HMSNs show greatly enhanced catalytic degradation efficiency and stability for a series of dyes in the presence of H2O2.The results indicate that mesoporous silica shells protect the inner MnxOy NPs with an increased stability and the residence of small MnxOy NPs inside hollow cavity increases the collision times of reactant molecules with an increased activity.The detailed results are as follows:(1)Controlled Synthesis of MnxOy@HMSNs.This work developed a new preparation method to employ charge-driven self-assembly micelles containing metal ions,triple ligands and diblock copolymers as templates.Following deposition of silica onto micelles and subsequent treatment will give hollow mesoporous silica nanoreactors with small MnxOy NPs inside their cavities(MnxOy@HMSNs).Characterization results by a series of techniques such as XRD,FT-IR and HAADF-STEM suggest that,compared with double ligands(L2),using triple ligands(L3)can have a wider pH range for synthesis(3.5-8.0);the calcination temperature range from 400-900? not only completely remove organic staffs to obtain hollow mesoporous nanostructures but also could maintain the intact hollow nanostructures.With adjusting the ratios of silica resource/Mn(90/1-300/1),the total size and wall thickness of the nanoreactors can be adjusted from 24.2 nm to 33.7 nm,and from 4.5 nm to 8.5 nm,respectively.(2)Application of MnxOy@HMSNs in dye degradation.This study first investigates the influences of synthetic parameters of MnxOy@HMSNs on the catalytic degradation performance for methylene blue.The optimal synthetic conditions of MnxOy@HMSNs for dye degradation were determined:the pH is 4.50;the calcination temperature is 400?;the TMOS/Mn ratio is 90/1.The effects of dye degradation reaction conditions and the presence of radical scavengers on dye degradation were also investigated,and a carbonate-assisted hydroxyl radical mechanism is confirmed.The MnxOy@HMSNs demonstrate a wide adaptability for a series of dyes.Due to their unique nanostructures,MnxOy@HMSNs show a superior catalytic performance relative to supported MnxOy/SiO2 catalysts.The stability test shows that MnxOy@HMSNs still exhibit above 95%of methylene blue degradation after five cycle reactions,and the leaching of manganese ions into the solution is only 0.88 ppm,indicating that the materials not only have good stability but also their hollow mesoporous nanostructures can protect the active components inside their cavities.