The Preparation And Investigation Of Graphene Quantum Dots Based Composites Humidity Sensitive Film

As one of the most important physical parameters of environmental monitoring,humidity is of great important in the field of meteorological detection,industrial production,agricultural planting and smart home.The development and preparation of high performance humidity sensitive films and humidity sensors are important prerequisites for real-time monitoring of humidity with high precision.Along with the development of materials science,various advanced materials have attracted lots of researchers.Among them,as a new type of zero dimensional graphene materials,graphene quantum dots owns the quantum confinement effect and boundary effect,as well as many excellent characteristics of graphene.Graphene oxide is one of important graphene derivatives and its abundant surface-modified hydrophilic oxygen-containing functional groups make it a high-performance sensing material for humidity.In this paper,quartz crystal microbalance(QCM)was used as transducer to fabricate polymer/graphene oxide quantum dots and zinc oxide/graphene quantum dot composite film QCM humidity sensors.The properties and humidity sensing performance of as-fabricated sensing films were measured.Based on the results,the sensing mechanism was further analyzed and the sensing model were also established.The main content of this paper is as follows:1?Polyethyleneimine/graphene oxide quantum dots(PEI/GOQDs)and Polyvinyl alcohol graphene oxide quantum dots(PVA/GOQDs)humidity sensitive films were deposited on the electrodes of QCM through spray method.The properties of hybrid composite,layered composite films of PEI and GOQD were measured and compared with it of pristine material films.The results showed that the sensitivity of PEI/GOQDs layered humidity sensitive membrane was 16.59 Hz/%RH,the humidity hysteresis was 2.88%RH and the minimum response time reached to 2s,the minimum recovery time reached to 2s.The characteristics of sensing films were measured through transmission electron microscopy(TEM)and Fourier transform infrared spectrum(FTIR).It showed that there was acylation reaction between PEI and GOQDs.Based on the results of measurement,the humidity sensing mechanism of PEI/GOQDs layered film QCM humidity sensor in low humidity,mid humidity and high humidity environment was presented,as well as the mechanism of humidity hysteresis.In addition,a preliminary exploration of QCM sensors humidity sensing properties was carried out by PVA / goqds in different volume ratio.It was found that when the volume ratio was 1: 1,the maximum response was 1683 Hz at 97.3 %RH.The sensitivity was 17.92 Hz/%RH and hysteresis was 2.416667 %RH.The etherification reaction between PVA and GOQDs was proved by FTIR spectra,and the cause of hysteresis was analyzed.2?Spray method was employed to deposit ZnO seed layer on the electrodes of QCM devices.Then,ZnO nanorods arrays,ZnO/PEI nanorods arrays,ZnO/PEI/GOQDs nanorods arrays were grown through hydrothermal method.The sensing films with different structures were characterized and measured to compare their properties.Results showed that ZnO/PEI/GOQDs nanorods film obtained an optimum response value of 1354 Hz at 97.3%RH and a sensitivity of 14.89 Hz/% RH.The characterization of the films revealed that the structure of ZnO/PEI/GOQDs film owned more compact and uniform in diameter for ZnO nanorods and the Zn O nanorods were covered by PEI film.It can be inferred by FTIR spectra that PEI and GOQDs were attached to the ZnO nanorods.Based on the characterization and measurement results,the sensing performance enhancement of composite film can be attributed to more water adsorption sites that provided by PEI and GOQDs that attached on the ZnO nanorods.The humidity sensing and hysteresis mechanism of ZnO/PEI/GOQDs nanorods in low humidity,mid humidity and high humidity conditions were presented.