Preparation And Performance Of Organic Thin Film Gas Sensors Based On Squaraines

With the rapid development of social economy,increasingly serious air pollution promotes an urgent demand for efficient gas sensor equipment.The common gas sensing materials are mainly metal oxides semiconductors,but these materials has many defects,such as high working temperature,poor selectivity and low sensitivity.In this merit,organic thin film-based resistor and transistor has gradually attracted considerable attention for gas sensing due to their intrinsic advantages including structural diversity,high selectivity,high sensitivity and low working temperature.Exploring new organic sensory materials is critical to continuously improve the sensing performance and thus attracts increasing attention.Squaraines are classical organic dyes of resonant zwitterionic properties,which usually are of high molar extinction coefficients,low band gap,and broad absorption in Vis-Near infrared spectral regions.But these materials have not been applied in the field of gas sensing,and we demonstrated their potential application in gas sensing.In this thesis,a series of organic compounds based on squaraines were designed and synthesized.The sensory films were prepared by squaraine molecules,polymers,and polymer doped by gold nanoparticles.We tested the sensing performance of these squaraines on the detection of ammonia and humidity.The following contents are included.(1)A novel conjugated organic small molecule based on squaraine was designed and fabricated into an organic thin film gas sensor.The fabricated sensor has a lowest detection limit of 40 ppb for ammonia,which is the lowest among the currently reported organic ammonia sensors.In addition,this molecule has a response / recovery time as short as 44 s / 135 s with excellent selectivity and good time stability.(2)A conjugated polymer(PMPS)based on the squaraines was designed and synthesized.The electrical properties of the polymer were enhanced by introducing new donor and acceptor.The results show that the humidity can be detected in the range of 33% RH-95% RH.The response time and the recovery time are 3 s / 16 s,and the overall humidity hysteresis is less than 4%.The impedance map and the simulated circuit diagram were used to explain the sensing mechanism.(3)A novel humidity sensing polymer(PPPS)with the donor and acceptor structure is designed and synthesized.In order to improve the sensing capacity,gold nanoparticles were doped on the surface of the polymer.The results show that this novel material can detect a wide range of humidity(RH11%-RH95%).The response time/recovery time are 1 s / 3 s which are the lowest among all reported humidity sensing polymers.The humidity hysteresis at any humidity is less than 2%.A portable apparatus with rapid detection of breath was fabricated based on this material.This enhancement by doping gold nanoparticles opens the door for the future development of organic gas sensor.