| Silver-based photocatalysts have been extensively investigated due to their good light responsiveness and simple synthesis method,but their light stability is not satisfactory.This dissertation focuses on the researches about the design and photocatalytic activity of silver-based nanocomposites,emphasizing the adjustment of the photo-response and photo-generated carrier transfer mechanism of silver-based photocatalysts,and then constructing silver-based composite photocatalysts with efficient visible light response and excellent photostability catalysts.Various characterization methods were used to systematically study the crystal phase structure,micro-nano structure,chemical composition,specific surface area,optical properties,electrochemical properties,photocatalytic performance and possible photocatalytic mechanism of the synthesized photocatalysts.The main contributions involved in this dissertation are as follows:1.Surfactant-assisted synthesis of direct Z-scheme Ag Br/?-Ag2WO4 composite photocatalysts and their photocatalytic performanceUsing surfactant as dispersant and bromine source,a series of Ag Br/?-Ag2WO4composite photocatalysts with different Ag Br content were successfully prepared by one-pot method at room temperature.The phase structure,micro-nano structure,optical properties,surface element composition and the interaction between the components of the composite catalyst sample were systematically studied.Photodegradation of rhodamine B(Rh B)under visible light was used to evaluate the photocatalytic activity of the composite.The results imply that under visible light irradiation,when the composite system contains30 wt%Ag Br nanoparticles,the as-prepared composite catalyst(Ag Br/?-Ag2WO4-30%)exhibits the best photocatalytic activity toward Rh B degradation.Its apparent kinetic constant is 135.9 times and 1.7 times that of pure?-Ag2WO4 and pure Ag Br,respectively.A possible photocatalytic mechanism is proposed based on the XPS analysis,active species trapping experiments,qualitative analysis of hydroxyl radicals and measurement of energy band positions.2.Preparation and photocatalytic performance of dual Z-scheme Ag Br/?-Ag2WO4/g-C3N4 ternary compositeA series of Ag Br/?-Ag2WO4/g-C3N4 ternary composite photocatalysts were successfully fabricated by combining precipitation method and ion exchange method at room temperature.The photocatalytic performance of the obtained catalysts was evaluated by degrading the colored dye Rh B and the colorless antibiotic tetracycline hydrochloride(TCH)under visible light irradiation.Among all the samples,CNAWAB7 shows the best degradation performance of Rh B and TCH.It also exhibits relatively high photostability.The rate constants of Rh B degradation are 5.2 times,519.3 times and 4 times of Ag Br,?-Ag2WO4 and g-C3N4,respectively.For TCH degradation,the rate constants of CNAWAB7 are 1.9,12.8 and 3.9 times that of Ag Br,?-Ag2WO4 and g-C3N4,respectively.This is mainly because the heterogeneous interface formed between the three will affect the separation of photo-generated holes and electrons,thereby affecting the photocatalytic activity.Aiming at the capture of active species in the photocatalytic process,the quantitative detection of superoxide radical anions(·O2-),the qualitative detection of hydroxyl radicals(·OH)and the analysis of energy band positions,the Ag Br/?-Ag2WO4/g-C3N4 ternary composite material is inferred to be a double Z-scheme photocatalyst.3.In situ synthesis of visible-light-responsive Ag3PO4/C3N5 Z-scheme heterojunctions for antibiotics removalAg3PO4/C3N5 composites with different Ag3PO4 content were prepared via room temperature precipitation strategy.The phase structure,micro-nano structure,surface element composition,optical properties,electrochemical properties,etc.of the prepared composite materials were fully investigated.The photocatalytic activity of the obtained samples was evaluated by degrading TCH under visible light irradiation.Among all the as-prepared samples,C3N5AP3 exhibits the best photocatalytic performance,and its apparent rate constant is 2.6 times and 373.2 times that of pure Ag3PO4 and C3N5.Recycling experiment indicates it possesses relatively high stability.The intermediate products and degradation pathways in the degradation process of TCH were analyzed by high performance liquid chromatography-mass spectrometry.Electrochemical tests show that the composite catalyst has higher carrier separation efficiency,which is an important reason for its enhanced photocatalytic performance.Through XPS analysis,free radical trapping experiment,energy band position and electron paramagnetic resonance spectrum analysis,it is judged that Ag3PO4/C3N5 composite material is a Z-scheme photocatalyst.4.Ag3PO4/Ni Al-LDH direct Z-scheme photocatalyst with low Ag3PO4 loading for efficient antibiotic degradationA room temperature precipitation strategy was used to deposit different content of ultrafine Ag3PO4 nanoparticles on the surface of Ni Al-LDH.The obtained samples were systematically characterized via X-ray diffraction,scanning electron microscope(SEM),transmission electron microscope(TEM),ultraviolet-visible diffuse reflectance spectroscopy(UV-vis DRS),X-ray photoelectron spectroscopy(XPS),etc.The photocatalytic performance of the as-prepared photocatalysts was evaluated by TCH degradation under visible light illumination.The results show that the pure Ag3PO4particles are large and easy to agglomerate.In Ag3PO4/Ni Al-LDH nanocomposites,Ag3PO4 nanoparticles have good dispersibility on the surface of Ni Al-LDH nanosheets.This highly dispersed supported type structure is of great significance to the improvement of the photocatalytic activity of Ag3PO4/Ni Al-LDH composites.Compared with a single component,the Ag3PO4/Ni Al-LDH composite exhibits better photocatalytic activity toward TCH degradation.Among all the fabricated samples,NAAP20 has the best photocatalytic performance,and its rate constant is 61.6 and 3.1 times that of Ni Al-LDH and Ag3PO4,respectively.Through XPS,energy band position,free radical capture experiment and qualitative analysis of hydroxyl radicals,it is inferred that the transfer pathway of the charge carriers in Ag3PO4/Ni Al-LDH composite is a Z-scheme mechanism. |
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