Synthesis Of Covalent Multifunction Nanoparticles For Application In Optical Imaging The Pore Structure In Geomaterials

As an important research content of reservoir geology,pore structure of rock has always been one of the basic key issues in geological research.At present,the characterization of rock pore structure has accumulated a large number of analytical methods.Among them,imaging analysis provides an intuitive characterization strategy for the analysis of rock pore structure.Because of its low cost,simple operation and accurate and reliable analysis results,it is one of the most widely used pore structure characterization methods.The traditional optical imaging technology of rock pore is to inject markers?plexiglass or epoxy resin?into rock pore under high temperature and pressure,which will destroy the primary pore structure of rock to a certain extent,and influence the accuracy of the results.In our previous work,bifunctional nanoparticles were introduced into the analysis of rock pore structure,and injected into rock pore by external magnetic field,which avoided the damage of rock pore structure caused by high temperature and high pressure.The dark field imaging analysis of rock pore was realized by using the fluorescence characteristics of nanoparticles.However,because the dual-functional nanoparticles only encapsulate the fluorescent molecules Rhodamine B?RhB?and magnetic particles in the SiO₂shell by simple physical encapsulation,their fluorescence intensity is weak and stability is poor,which will be greatly limited in practical applications.Based on this,a chemical bonding method is proposed to couple the fluorescent dye RhB with the magnetic particle Fe₃O₄ in order to obtain bifunctional nanoparticles with high fluorescence intensity and good stability.The main research contents are as follows:?1?Preparation of magnetic fluorescent Fe₃O₄/SiO₂/APTES-RhB nanoparticles by step-by-step modification.The effects of experimental conditions in different synthetic steps on the morphology and particle size of the products were investigated,and the experimental process was optimized.The formation of amide bonds in composite nanoparticles was discussed and verified in detail by X-ray photoelectron spectroscopy.The morphology,composition,structure,magnetic and fluorescence properties of the composite nanoparticles were characterized.The results show that the Fe₃O₄/SiO₂/APTES-RhB composite nanoparticles are spherical,with an average particle size of 62 nm,superparamagnetic and can be effectively controlled by an external magnetic field.Compared with the coated Fe₃O₄/SiO₂/RhB composite nanoparticles,the prepared Fe₃O₄/SiO₂/APTES-RhB composite nanoparticles have better stability and higher fluorescence intensity.?2?Two types of rock materials were used in the study:carbonatite and sandstone.The fluorescence images obtained under different impregnation time were compared and the result indicating that the saturation time of composite particles in rock pore was 6 hours.Meanwhile,through the image analysis software,the face porosity statistics and analysis of fluorescent images are determined.The deviation of the statistical results of the face porosity of carbonate rock and sandstone is less than 1%by comparing with the gas porosity measurement,which proves the accuracy of the rock pore imaging method based on nanoprobe.Compared with coated nanoparticles,bonded nanoparticles can provide a clearer field of vision under fluorescence microscopy due to their stronger fluorescence,and obtain fluorescence images with strong contrast between rock matrix?black?and pore?bright?.It makes the rock image analysis process based on nanoparticle labeling more practical and effectively improves the accuracy of rock pore analysis.