Research On Photochemical System Of Silica/Methylene Blue/Titanium Dioxide

There were of great significance in the detection of dissolved oxygen in fields of industrial production,aquaculture,food hygiene,biological and medical industry.Thus,the concentration of dissolved oxygen should be efficiently controlled to meet the practical requirements.Methylene blue?MB?exhibited a color variation during the conversion from oxidation to reduction,endowing MB an indicator for the concentration of oxygen.MB with high singlet oxygen yield during illumination could also be employed as a photosensitizer in photodynamic therapy for disease treatment.In this thesis,silica-MB particles were firstly prepared by a modified St?ber method,and the process parameters were varied to obtain silica-MB-Ac.Then,core-shell structured vehicles with photosensitizers of MB were prepared by assembly of coordination complexes of tannic acid?TA?and Fe³⁺ions.Finally,a spraying method was employed to synthesize membrane-like photochemical system composed of silica,methylene blue and titanium dioxide.According to the variation of the concentration of dissolved oxygen,the performance of photochemical reaction under illumination was investigated in detail.The following conclusions were drawn:Firstly,MB molecules were loaded in silica?silica-MB?and followed by encapsulation by coordination complexes of TA and Fe³⁺ions.In comparison with those of silica-MB,decreased condensation of Si-O-Si,shifted infrared absorbance frequencies of chemical bands,delayed thermal degradation and modulated release behavior of MB were observed for silica-MB@TA with a core-shell structure.Although MB dimers were dominantly released from silica-MB,release of MB monomers from silica-MB@TA was significantly promoted,which was described by the Higuchi model.Through monitoring the oxidation of uric acid,generation efficiency of singlet oxygen?¹O₂?by MB released from silica-MB@TA was fairly higher than that from silica-MB.Secondly,silica-MB particles were incubated in acetate buffer solution?pH=3.6?to obtain silica-MB-Ac,and core-shell structured silica-MB-Ac@TA powders were prepared with an assembly of coordination complexes of TA and Fe³⁺ions.Compared with those values for silica-MB,cumulative amount and absorbance ratio of monomer versus dimers of MB released from both silica-MB-Ac and silica-MB-Ac@TA increased obviously as a result of significant decrease of MB self-aggregations with aromatic-aromatic interactions.The generation of singlet oxygen,photodynamic efficiency and stability against in vitro reduction of monomeric MB released from silica-MB-Ac@TA were significantly higher than those for silica-MB-Ac,due to the effective control of aggregation state of MB molecules during outward diffusion through the complexes of TA and Fe?III?ions.Thirdly,MB-loaded silica-MB particles were prepared and treated with acetate?Ac?ions-contained buffer solutions to synthesize silica-MB-Ac.The entrancement of acetate ions destroyed the?-?stacking of MB monomers,resulting in increased release amount of MB monomers from silica-MB-Ac to release solutions.In comapried with MB powders,the emission was enhanced for silica-MB due that fluorescence MB is in locally excited state in aggregation states,which is a characteristic feature for aggregation-induced emission.After the entrance of acetate ions,the large twisted angle makes the charge transfer fast,resulting in the red-shifted emission peak and decreased emission for MB in twisted intramolecular charge transfer state.Meanwhile,the released behaviors from silica-MB and silica-MB-Ac-x are controlled by Fickian's diffusion and degradation of matrix.The simulated n values decreased for silica-MB-Ac-x synthesized with high concentration of acetate ions,as a result of the reduction of the limitation of matrix degradation on the outword diffusion from biodegraded silica-MB-Ac-x.Finally,compared with traditional oxygen absorber,the reduced LMB could visually show the presence of oxygenin the system when it was used as oxygen absorber.Membrane was prepared by MB,silica-MB and nano-titanium dioxide,and the MB could be reduced as LMB by titanium dioxide and tartaric acid,when the membrane was irradiated by ultraviolet light.Although MB-loaded silica-MB particles would reduce the amount of the oxygen uptake of the system?mixed solution or membrane?.The silica matrix is able to effectively limit the diffussion of MB in solutions and protect the MB molecules,and reduce the concentration of MB in solutions.