| Clay minerals have been widely used in the fields of adsorption,catalysis,energy storage and biomedicine because of their layered structure,special morphology,low cost,rich reserves,good thermal and chemical stability,and strong adsorption.In recent years,with the development of nanotechnology,nano functional modification of minerals for the preparation of mineral functional composites have become a frontier research field.Among them,clay minerals and their derivatives are mainly used as carriers to load,disperse,and enhance nano functional bodies.Based on its typical carrier function,this thesis studies the inducible regulating function of clay minerals and their derivatives on nano functional bodies,and assembles mineral functional composites with high catalytic performance.Specifically,two-dimensional montmorillonite(Mt)and kaolinite-derived silica nanosheets(SiNSs)were used as carriers to induce the in-situ assembly of nano g-C3N4 and metal-particle by using the pores and interlayers,surface hydroxyls and interlayer cations of Mt,as well as the surface structure and defec-tinduced optical properties of SiNSs,and then explored the environmental catalytic performance of functional composites.The main contents of the research are as follows:(1)A new insight into the inducer role of Mt in structure-tuning of CN at nano-and molecular scales were researched.Results showed that the pores and interlayers of Mt induced the spatial-confined polymerization of precursors urea(U)/melamine(M),obtaining the highly dispersed CN nanosheets;simultaneously,the Al/Mg–OH groups and interlayer Na cations of Mt induced the self O,Na,Mg,Al elements from Mt to dope into the CN framework.It is found that the advantage of urea in nanostructure construction of CN nanosheets for the CN-U/Mt composite with larger specific surface area,and the superiority of melamine in multi-element doping for CN-M/Mt with a narrowed band gap.Therefore,the optimal CN-UM/Mt composite showed the highest activity for Rhodamine B(Rh B)photodegradation with a reaction time of 60 min and an apparent rate constant of 0.053 min-1,which is better than most other g-C3N4/clay minerals composites.The enhanced activity could be owing to the high adsorption of Mt,large specific surface area of CN nanosheets,and the adjusted band structure originated from the comprehensive effects of CN nanosheets,nonmetal O-and metal cations doping induced by Mt,enabling a narrowed band gap with strengthened visible-light adsorption and an enhanced photogenerated carrier separation efficiency.Furthermore,in terms of the semiconductor mechanism,it showed more reactive oxygen species of ~1O2(main)and·O2-(secondary)for effective Rh B degradation,but without the typical holes.(2)Kaolinite-derived silica nanosheets(SiNSs)with excellent structure advantages have been used as a support to disperse silver nanoparticles(Ag NPs)via chemical reduction methods.Herein,the special defect-induced optical properties of SiNSs were revealed by comparing with kaolinite(Kaol)and fumed silica nanoparticles(SiNPs).Results showed that the SiNSs harvested more UV light than SiNPs owing to the more defect sites of E?-centres,nonbridging oxygen hole centers(NBOHC),and peroxy radicals(POR),and then the POR sites contributed a bandgap of 2.46 e V in the light region of330–400 nm.Moreover,the SiNSs exhibited higher photogenerated carrier separation efficiency than SiNPs and Kaol.These can be attributed to the Si O4 tetrahedral sheet structure of SiNSs with high specific surface area.Therefore,in the photochemical assembly process,the precursor silver-ammonia complex(Ag(NH3)2+)absorbed by the negatively charged Si–OH of SiNSs,was efficiently reduced by the photogenerated electrons(e-)of SiNSs excited under UV irradiation.The resultant Ag/SiNSs nanocomposite offered the highly dispersed and uniform Ag NPs(?8.48 nm),which showed higher activity and stability for 4-nitrophenol catalytic reduction than Ag/Kaol,Ag/SiNPs,and most other Ag NPs/nanosilica catalysts.(3)Based on the above work,we continued to make use of the optical properties and structural advantages of SiNSs to study its wide applicability towards the photochemical reduction induced assembly of transition metal Cu particles(Cu NPs)and Ag-Cu nanoalloys.The results show that the Cu/SiNSs composite has highly dispersed Cu NPs,and the average size is only 2.67 nm,which is obviously smaller than that of Ag NPs(8.48 nm),indicating that the photochemical reduction of SiNSs to transition metal Cu is lower than that of precious metal Ag.In the Ag-Cu/SiNSs composite,the highly dispersed homogeneous Ag-Cu nanoalloy(11.36 nm)was successfully loaded because of the uniform adsorption of surface silanol groups and micropores of SiNSs to the precursors Ag(I)and Cu(II).In the catalytic reduction reaction of 4-NP,the synergistic effect of Ag-Cu nanoalloy reduces its work function and the Schottky barrier height of its interface with SiNSs,and significantly promotes the transfer of electrons from the surface of Ag-Cu to the conduction band of SiNSs,thus enhancing the catalytic activity of Ag-Cu/SiNSs.The reaction is completed rapidly within 90 s,and the apparent rate constant kapp is 37.45×10-3 s-1,which is significantly higher than that of the single metal composites Ag/SiNSs(26.87×10-3 s-1)and Cu/SiNSs(20.08×10-3 s-1). |
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