Preparation And Properties Of The Ternary Silver-based Solid Solution α-AgAl_0.3Ga_xIn_0.7-xO₂ And Its Composite

The rapid development of industry had caused environmental pollution,semiconductor photocatalytic technology was widely used in environmental remediation because of no secondary polluting and low-cost characteristics.However,traditional semiconductor photocatalysts were limited in their application due to their narrow spectral response range and low photon quantum efficiency.The band gap of semiconductor could be controlled by doped elements,the spectral response range can be expanded,and the photocatalytic activity can be enhanced.At the same time,the semiconductor heterojunction（composite）could inhibit the recombination of photoinduced electrons and holes pairs,enhanced the photocatalytic efficiency.In this paper,α-Ag Al_0.3Ga_0.7O₂,α-Ag Al_0.3Ga_0.3In_0.4O₂ andα-Ag Al_0.3Ga_0.5In_0.2O₂were synthesized by hydrothermal method.Ternary silver-solid solutionα-Ag Al_0.3Ga_0.3In_0.4O₂ coupled with Ag₂CO₃ and CQDs achieved the Ag₂CO₃/α-Ag Al_0.3Ga_0.3In_0.4O₂ and C/α-Ag Al_0.3Ga_0.3In_0.4O₂ composites.The crystal structure,energy band structure and electronic behavior of the composites were systematically analyzed by using a variety of characterization techniques,and the regulating effect of the composites on the semiconductor energy band was studied in detail.The reaction process and degradation mechanism of the composites in phenol and methyl blue were also studied under visible light irradiation.The main research contents this thesis are as follows:（1）Ternary silver-base solid solutionα-Ag Al_0.3Ga_xIn_0.7-xO₂ was synthesized by hydrothermal method.X-ray diffractometry（XRD）confirmed the successful preparation ofα-Ag Al_0.3Ga_0.7O₂,α-Ag Al_0.3Ga_0.3In_0.4O₂ andα-Ag Al_0.3Ga_0.5In_0.2O₂.Scanning electron microscopy（SEM）showed that the ternary silver-solid solutionα-Ag Al_0.3Ga_0.5In_0.2O₂ has irregular polygonal lamellar structure.By adjusting the molar ratio of Ga and In,the UV-vis absorption range of the sample was extended from 550nm to 752 nm.For the fluorescence spectra,the luminescence intensity of silver solid solution doped with In was lower.The results showed that the photoinduced electrons and holes pairs ofα-Ag Al_0.3Ga_0.3In_0.4O₂ andα-Ag Al_0.3Ga_0.5In_0.2O₂ had higher separation efficiency.Compared with the binary silver solid solutionα-Ag Al_0.3Ga_0.7O₂,the ternary silver solid solutionα-Ag Al_0.3Ga_0.3In_0.4O₂ andα-Ag Al_0.3Ga_0.5In_0.2O₂showed better performance in degradation of phenol.The photocatalytic degradation rate ofα-Ag Al_0.3Ga_0.5In_0.2O₂ was 0.04109 min^-1,and the reaction rate ofα-Ag Al_0.3Ga_0.3In_0.4O₂ was 0.00375 min^-1.The reaction rate ofα-Ag Al_0.3Ga_0.7O₂ was0.00168 min^-1.Electrochemical analysis showed thatα-Ag Al_0.3Ga_0.3In_0.4O₂ andα-Ag Al_0.3Ga_0.5In_0.2O₂ inhibited the recombination of photoinduced electrons and holes pairs.（2）Ag₂CO₃/α-Ag Al_0.3Ga_0.3In_0.4O₂ composites with different molar ratios were prepared by precipitation reaction.XRD confirmed the formation of Ag₂CO₃/α-Ag Al_0.3Ga_0.3In_0.4O₂ composites.The results of SEM and TEM showed that the polyhedral Ag₂CO₃ polyhedrons were dispersed on the surface ofα-Ag Al_0.3Ga_0.3In_0.4O₂sheets.UV-vis absorption of the composites was effectively regulated from 530 nm to644 nm by controlling the molar ratio ofα-Ag Al_0.3Ga_0.3In_0.4O₂ to Ag₂CO₃.Compared with pure-phase sample,the absorption edge of the composites exhibited obvious red shift.Photoelectrochemical analysis showed that the separation efficiency of photoinduced electrons and holes was promoted in the composites which inhibited the recombination of charges.While eliminating methyl blue under visible light,the photocatalytic activity of the composites was higher than that of bareα-Ag Al_0.3Ga_0.3In_0.4O₂ and Ag₂CO₃.Especially,the 0.3-Ag₂CO₃/α-Ag Al_0.3Ga_0.3In_0.4O₂eliminated 90%of methyl blue within 90 min.This was mainly due to the formation of an internal electric field between p-type semiconductorα-Ag Al_0.3Ga_0.3In_0.4O₂ and n-type semiconductor Ag₂CO₃,which enhanced the separation and migration of photoinduced electrons and holes pairs.In addition,the possible photodegradation process of methyl blue under Ag₂CO₃/α-Ag Al_0.3Ga_0.3In_0.4O₂ composites was proposed.C/α-Ag Al_0.3Ga_0.3In_0.4O₂ composites were successfully prepared by mechanical mixing method（The CQDs were prepared by electrochemical etching of graphite rods）.The formation of C/α-Ag Al_0.3Ga_0.3In_0.4O₂ composites was confirmed by XRD.By adjusting the molar ratio of CQDs andα-Ag Al_0.3Ga_0.3In_0.4O₂,the UV-vis absorption edge of the composites showed red shift.The photoluminescence intensity of the composite was lower than that of theα-Ag Al_0.3Ga_0.3In_0.4O₂.In comparison with theα-Ag Al_0.3Ga_0.3In_0.4O₂,the separation efficiency of the photoinduced electrons and holes pairs of the C/α-Ag Al_0.3Ga_0.3In_0.4O₂ composites was effectively improved.The small arc radius in electrochemical impedance spectroscopy and the higher photocurrent intensity for C/α-Ag Al_0.3Ga_0.3In_0.4O₂ composite also confirm this result.