Controllable Preparation Of Ag/AgCl Nanostructures And Their Application In The Treatment Of Pollutants

Today,environmental pollution has become a major problem that human society urgently needs to solve.Among treatment methods of pollutants,the photocatalytic degradation of pollutants has been widely concerned and studied for its advantages of solar energy utilization,high efficiency and no secondary pollution.Compared with the traditional TiO₂ photocatalysts,Ag/AgCl photocatalysts exhibit high photocatalytic degradation activity for organic pollutants under visible light excitation due to their plasmon resonance effect,which makes them a hot research spot.However,the rapid recombination of photogenerated carriers and instability of Ag/AgCl materials have greatly limited their application in the field of photocatalysis.In order to improve the photocatalytic degradation performance of Ag/AgCl,rod-like Ag/AgCl photocatalysts and net-like AgCl-Ag/g-C₃N₄ composite photocatalysts were prepared by morphology control and semiconductor compounding.Both rod-like Ag/AgCl and net-like AgCl-Ag/g-C₃N₄ showed high photocatalytic activity in degradation of pollutants and the corresponding photocatalytic mechanism was proposed.The specific research contents are as follows:In chapter 2,rod-like Ag/AgCl photocatalysts were synthesized by a two-step method?supramolecular assembly and displacement method?.First,the Ag-melamine nanowire precursors were synthesized by the supramolecular assembly of melamine and Ag⁺.Then the precursors of Ag-melamine nanowires were used as templates to prepare rod-like Ag/AgCl photocatalysts with different concentrations of cetyltrimethylammonium chloride?CTAC?.The photocatalytic degradation of Rhodamine B showed that the performance of the rod-like Ag/AgCl photocatalysts were greatly improved compared with the Ag/AgCl sample prepared by directly mixing CTAC and AgNO₃ solution.When the concentration of CTAC was controlled to 0.1 mol L^-1,rod-like Ag/AgCl?0.1?sample showed the highest degradation activity with a rate constant of 0.12 min^-1,which was clearly higher than the Ag/AgCl sample by a factor of 4.6 times.From the analysis of specific surface area data,it is known that the specific surface area of the rod-like Ag/AgCl?0.1?sample(1.86 m² g^-1)was 18.5 times that of the base Ag/AgCl sample(0.10 m² g^-1).It can be seen from the solid ultraviolet diffuse reflectance spectrum that the rod-like Ag/AgCl samples exhibited the enhanced visible-light absorption and a stronger plasmon resonance absorption peak.According to the above data analysis,the improved activity of the rod-like sample can be attributed to the following two points.One is that the specific surface area of the rod-like Ag/AgCl was significantly increased,which enhanced the ability of the to adsorb organic pollutants and increased the active sites of the reaction.The other is that the rod-like Ag/AgCl photocatalyst showed the enhanced visible-light absorption.These two factors improved the performance of the rod-like Ag/AgCl in photocatalytic degradation of organic pollutants.In chapter 3,net-like AgCl-Ag/g-C₃N₄ photocatalysts were synthesized by a three-step method?supramolecular assembly,calcination and redox methods?.First,the Ag-melamine nanowire precursors were synthesized by the supramolecular assembly of melamine and Ag⁺.Then the Ag-melamine nanowire precursors were calcined at high temperature in tubular furnace to obtain net-like Ag/g-C₃N₄.Finally,FeCl₃ solution was added to the Ag/g-C₃N₄ and Ag was in-situ oxidized to form AgCl,resulting in th final formation of net-like AgCl-Ag/g-C₃N₄ composite photocatalysts.The photocatalytic degradation of methyl orange showed that the performance of the net-like AgCl-Ag/g-C₃N₄ composite photocatalysts were greatly improved compared with the g-C₃N₄ and Ag/g-C₃N₄.When the concentration of FeCl₃ was controlled to 0.25 mol L^-1,the net-like AgCl-Ag/g-C₃N₄?0.25?sample displayed the highest degradation activity,which was clearly higher than that of g-C₃N₄ and Ag/g-C₃N₄ by a factor of 126 and 5.4 times,respectively.The enhanced photocatalytic activity of AgCl-Ag/g-C₃N₄ can be attributed to the net-like structure of AgCl-Ag/g-C₃N₄ composite with the strong-coupling interface among the three phases?AgCl,Ag and g-C₃N₄?,which is beneficial to the rapid transfer and separation of the photogenerated electron-hole pairs and enable AgCl-Ag/g-C₃N₄ to exhibit good photocatalytic degradation activity.