Research On Preparation Of MoS₂ Printing Ink And Its Humidity Sensing

Graphene-analogues transition metal sulfides molybdenum disulfide?MoS₂?,due to its abundant reserves,easy lamination and distinctive physical and chemical properties,is expected to be used for applications such as field effect transistors,photodetectors,sensors and hydrogen evolution reaction.However,when fabricating devices with layered MoS₂,there are problems such as complicated processes,uneven film formation,and poor device performance.This thesis developed a simple and low-cost preparation technology of flexible paper-based MoS₂ humidity sensor.The research results are as follows:?1?Using liquid-phase exfoliation,an appropriate mixture solvent system with 50%volume ethanol-water solution was selected based on the theory of Hansen solubility.The effects on the concentration of the MoS₂ nanosheet dispersion were investigated by exploring the ultrasonic power,ultrasonic time,and the initial concentration of MoS₂powder.The optimizations were:350 W,48 h,10 mg/m L for the ultrasonic power,the ultrasonic time,and the initial concentration of MoS₂ powder,respectively,and the concentration of the dispersion was 0.16 mg/mL.Because of the poor stability of dispersion,polyvinyl pyrrolidone?PVP?was selected as stabilizer.The results showed that PVP could effectively improve the stability of the dispersion as no sediment occurred for two months.At the same time,due to the intercalation of PVP in the exfoliation process,the concentration of the dispersion greatly increased,and was up to 0.42 mg/m L.?2?Based on the obtained MoS₂ dispersion,the viscosity and surface tension of the ink were adjusted by the addition of physical property modifiers?ethylene glycol,n-propanol and glycerin?to obtain the printing ink.The viscosity and surface tension of the final ink were 2.8 mPa·s and 30.2 mN/m,respectively.The parameter Z of ink hydrodynamic characteristic was 8.86,indicating that the ink had a good printability,meanwhile,the ink also had an excellent long-term stability.?3?A interdigitated electrode pattern was fabricated on a pretreated paper using inkjet printing-chemical deposition technique.The surface morphology and composition of the copper interdigitated electrodes were analyzed by SEM and EDS.The uniform copper particles formed a continuous and compact copper layer,and the purity of the copper layer was high.The copper interdigitated electrode had a low resistivity with a value of 2.62×10^-8?·m.?4?MoS₂ humidity-sensing functional layer was formed on the paper-based copper interdigitated electrodes using inkjet printing technique.The moisture sensitivity characteristics of the Mo S₂ humidity sensor were investigated.The results showed that the humidity sensor had a wide humidity range?RH=11%^RH=95%?,low hysteresis?4.49%RH?and long-term stability?the sensor worked functionally after 3 months?.The response/recovery time of sensor from RH=11%to RH=95%were 2 s and 3 s,respectively.The humidity sensor could also be used to monitor the human respiratory rate.The work of this thesis showed that the fabrication of large area humidity sensors with excellent humidity-sensing characteristics on a flexible substrate could be quickly and cheaply realized by inkjet printing technique.