Photocatalytic And Controlled Release Properties Of Structured Composites Constructed Based On ZnCr-LDHs

Layer double hydroxides(LDHs)have attracted widespread attention and research due to their layered composition,interlayer confinement environment,and adjustable microstructure.Their excellent controllability provides various possibilities for constructing functional materials with ordered structures and controllable properties.Based on the microstructure design of LDHs materials at the micro scale,multiple functional guest materials were combined with LDHs through intercalation assembly technology to achieve interface optimization and structural regulation of LDHs with guest materials,and constructed highly functional LDHs-based composites.In this work,we have constructed ferroelectric photocatalytic materials with lead titanate(PbTiO3)by surface modification and slow-released materials with cinnamic acid(CA)by intercalation based on ZnCr-LDHs.The interface and confinement effects of LDHs were studied,and their applications in visible light catalysis and controlled release of spices were explored.The thesis mainly includes the following two aspects:(1)By combining the ferroelectricity of ferroelectric material PbTiO3 with ZnCr-LDHs through interface interaction,four kinds of hydrotalciteferroelectric composites(ZnCr-LDHs/x%-PbTiO3)in different mass ratios(1:0.25,1:0.5,1:1,1:2)with self-polarized built-in electric field were constructed.Rich interfaces between ZnCr-LDHs and PbTiO3 were observed by TEM.XRD patterns showed that the combination of ZnCr-LDHs and PbTiO3 resulted in a crystal orientation transition in PbTiO3,which affected the built-in electric field of ZnCr-LDHs/x%-PbTiO3.Under visible light radiation,the photo-generated carriers produced in ZnCr-LDHs were affected by PbTiO3 ferroelectrics,which inhibited the recombination of photogenerated carriers,prolongated the lifetime of electrons and holes,and fully participated in the redox reaction of photocatalytic water splitting.The oxygen production rate of ZnCr-LDHs/32.8%-PbTiO3 in visible light water splitting reaction was 1.016 mmol·g-1·h-1,which is about two times higher than that of pure ZnCr-LDHs(0.571 mmol·g-1·h-1).This work proved that the existence of ferroelectrics plays an important role in improving the carrier lifetime and photocatalytic performance of materials.(2)Aromatic cinnamic acid(CA)was introduced into the interlayer of ZnCr-LDHs through ion exchange(IE),coprecipitation(CM),and nucleation crystallization(NC)methods,and three kinds of hydrotalcite-fragrances composites CA@LDHs were constructed respectively.The results indicated that the contents of CA in the three materials were basically the same,but their interlayer confinement environment and host-guest interaction depended on different synthesis methods:The CA@LDHs composites constructed by the nucleation crystallization method showed the strongest conjugate interaction between the guests,while the CA@LDHs constructed by coprecipitation method exhibited the strongest electrostatic interaction between the host and the guests.Thermogravimetric analysis showed a significant improvement in thermal stability of CA after intercalation,the maximum weight loss rates of the three materials constructed by ion exchange,coprecipitation and nucleation crystallization method were 354℃,356℃ and 359℃respectively,which was consistent with the differences in the release properties of the materials in aqueous solutions.The results of TG-MS analysis showed that the intercalated CA could also decompose into aromatic benzene and butadiene.In comparison,the pure CA was converted into carbon dioxide during thermal decomposition.This method was also suitable for the intercalation of benzoic acid fragrances.This work exhibited excellent application prospects in the construction of sustained-release materials for fragrances.