Thermoelectric Effect Of PANI/CNTs Composite And Its Effect And Mechanism Of Regulating Hexavalent Chromium Reduction

The applied electric field can change the carrier concentration,Fermi level and density of states distribution,etc.,thus changing the electronic structure of the solid catalyst and further regulating the catalytic activity.But this requires external power supply,consumes energy and complicates the process equipment.Based on thermoelectric effect,this study directly converts unused thermal energy(such as solar heat)widely existing in the environment into electric energy,generating in-situ electric field to regulate chemical reactions.On the one hand,waste heat is utilized,power-on equipment is simplified;on the other hand,the concept and practice of electrically regulating the surface charge state of the material to enhance the catalytic efficiency are developed and enriched.In this work,polyaniline/carbon nanotubes(PANI/CNTs)composite thermoelectric materials were prepared by chemical oxidation and electrochemical synthesis methods.Photothermal and thermoelectric properties of sheet samples were characterized by self-built photothermal and thermoelectric testing devices.Taking the reduction of hexavalent chromium [Cr(Ⅵ)] as the model reaction and the light source as the heat source,the regulation process and performance of the thermoelectric effect of PANI/CNTs composites on the chemical reaction were explored investigated,thus realizing the multilevel conversion and in-situ utilization of light energy,thermal energy,electric energy and chemical energy.The experimental results show that the PANI/CNTs composites prepared by chemical oxidation have good photothermal performance and are also good p-type thermoelectric materials,and their Seebeck coefficient increase with the increase of carbon nanotube content.100 W iodine-tungsten lamp irradiation can cause a temperature difference of about 10 ℃ on both sides of the sheet-like PANI/CNTs sample.Under the driving of this temperature difference,a significant thermoelectric voltage is generated on both sides of the PANI/CNTs material,and Cr(VI)reduction reaction is obviously promoted.Based on the characterization of PANI/CNTs composites before and after the reaction or illumination by X-ray photoelectron spectroscopy,the mechanism of thermoelectric effect regulating Cr(Ⅵ)reduction reaction is preliminarily proved: the reducing group in polyaniline reduced Cr(Ⅵ)and changed itself from a reduced state to oxidized state;while the electrons generated by thermoelectric effect can make polyaniline return from oxidation state to reduced state,in this way,the electrons that reduce Cr(Ⅵ)are actually provided by thermoelectric effect.