Ethanol Sensing Performance Of Au And Cl Comodified LaFeO₃ And ZnO Nanoparticles

With the increasing demand for monitoring combustible,explosive and toxic gases by various social departments,the development and application of various gas sensors had attracted extensive attention by researchers.The pure semiconductor metal oxides?SMOs?material has some disadvantages that are unfavorable to practical application,such as low gas response,slow response recovery and poor selectivity.Therefore,researchers keep improving the gas response by doping the material,surface modification,composite modification and changing the experimental methods.In this paper,Au and Cl comodified SMOs nanoparticles were prepared by a citric sol-gel method to improve the gas response to ethanol,the main contents of this paper are summarized as follows:Firstly,Au and Cl comodified LaFeO₃ nanoparticles were prepared through the addition of HAuCl₄ into precursor.As evidenced by XRD and TEM,the addition of HAuCl₄ suppressed the growth of LaFeO₃ crystallite but hardly influenced the average particle size.XPS indicated that chlorine existed in the forms of organics and chlorides,while Au existed in the form of Au⁰.The simultaneous existence of Au and Cl on the surface suppressed the adventitious carbon contamination,whereas it favored the formation of La carbonate and the adsorption of oxygen species which were both beneficial for the improvement of gas sensing performance.At the prime working temperature of 120°C,the Au and Cl comodified LaFeO₃ sensor with the addition of 1wt%HAuCl₄ exhibited the highest gas response?220.7?reported so far to 100 ppm ethanol.Ab initio calculations on the Fe-O terminated LaFeO₃?001?surface pre-adsorbed by O atom demonstrated that more charge transferred from the ethanol to the surface additionally adsorbed by Au and Cl,resulting in higher gas response as observed.Secondly,the same method was adopted to prepare Au and Cl comodified ZnO nanoparticles with different proportion of HAuCl₄ into precursor.at the temperature of 220°C,the Au and Cl comodified ZnO with the addition of 1wt%HAuCl₄ had the highest gas response to ethanol?19.64?,Moreover,the gas response of the sample was significantly improved compared with that Au modified ZnO and Cl modified ZnO nanoparticles that ensure the addition amount of Au and Cl is the same.XRD and TEM conformed that the impurity phase of Au in single substance suppressed the growth of ZnO crystallite or particle.XPS indicates that Cl exists in the form of chloride,while 88.05%of Au exists in the form of Au³⁺and the rest in the form of Au⁰.The substitution of chlorine for oxygen atom either in the lattice or at the adsorption site may resulted in more transferred charge from the ethanol molecular to the ZnO surface,which speculated by our previous analysis on the enhanced ethanol sensing performance of Cl modified LaFeO₃ nanoparticles.For the adsorption of Au atoms on the surface promoted the decomposition of O₂,The electronic mechanism considers formation of depletion regions around Au nanoparticles and the modulation of the nano-Schottky barriers?and hence the conduction channel width?due to changes in the oxidation state of the Au accompanying oxygen adsorption and desorption.The chemical mechanism is based on the highly effective dissociation catalytic ability of Au,which is a far better oxygen dissociation catalyst than ZnO and catalytically activates the dissociation of molecular oxygen.Therefore,the synergistic effect of Au and Cl for the modified nano-particles resulted in the significantly higher gas response to ethanol gas than pure ZnO.