| As an extension of human sensory organs,sensors can help people acquire a variety of complex external information beyond the range of human perception.Among them,gas sensor can act as an "electronic nose" and play an essential role in environmental pollution,industrial and agricultural safety production and human life and health monitoring.At present,existing sensors still face problems,such as simple signal sensing function,limited multi-signal recognition and low intelligent integration,which cannot meet the requirements of multifunctional applications.Metal-organic framework(MOF)materials have potential prospects in the field of gas sensing due to their advantages such as large surface area,rich topological network,high porosity,customized and adjustable cavity structure as well as highly active metal sites.However,for the actual needs of environmental monitoring and early disease physiological signal screening,single-phase MOF materials have many shortcomings such as poor conductivity,sensitivity and stability,which limit their application in multi-scene gas detection.The main line of this paper is to design novel functional MOF composites,explore new sensing mechanisms and develop new integrated technologies.The multifunctional micro/nano MOF@SMO gas sensor series integrated with enrichment/filtration/sensing functions and the bionic MOF@MXene multi-mode sensor series with a realistic mimesis both in the "structure and sense" are designed,respectively.Furthermore,the application of multi-functional sensor in environmental monitoring,early-screening of disease and intelligent wearable human health monitoring is further explored.The main research contents are as follows:(1)Aiming at the problem of single function,low sensitivity and low selectivity of traditional semiconductor metal oxide(SMO)gas sensors,a high-performance micro/nano sensor integrated with the function of gas enrichment /filtration/sensing is constructed for efficient,rapid and specific detection of H2 S gas.In this study,by strategically combining a three-dimensional inverse opal(3DIO)macroporous Zn O substrate and a ZIF-8 outer filter membrane,two series of sensors with Pt NPs loaded at different locations are developed.In the optimal 3DIO Zn O@ZIF-8/Pt sensor,the existence of small Pt NPs in ZIF-8 cavities can effectively accelerate the absorption of H2 S,capture electrons from the N site of ZIF-8,and donate the electron to the S site of H2 S,as indicated by density functional theory simulations,leading to a significantly increased response to H2 S.Together with the molecular-sieving effect that ZIF-8 exerts on gas molecules with larger kinetic diameters,the 3DIO Zn O@ZIF-8/Pt sensor exhibits a high response to H2S(118 to 5.5 ppm),a detection limit of 40 ppb,and importantly,a 59-fold higher selectivity to H2 S against typical interference gases.In addition,the 3DIO Zn O@ZIF-8/Pt sensor is developed as a multi-platform sensor to evaluate trace concentrations of H2 S in meat quality assessment,halitosis diagnosis,and automobile exhaust assessment.(2)The low sensitivity and selectivity of SMO gas sensors caused by its open active sites are the key problems,which restrict the practical application of the sensors in complex environments.Using metal-organic frameworks(MOF)materials as a filter membrane is an innovative method to improve the response and selectivity of gas sensors by adjusting the size of the pores and cavities;however,the active sensing surface and dynamic sensing processes are inevitably negatively affected.A facile but effective strategy for gas sensitization is performed in this work by integrating Co ions as catalysts into the inner three-dimensional Zn O skeleton and outer MOF filter membrane.The appropriate incorporation of Co cations was found to increase the surface area,facilitate the adsorption of oxygen species onto the zeolitic imidazolate framework(ZIF)surface,and promote the catalytic oxidation of H2 S.In the optimised Zn Co O2%@BM-ZIF gas sensor,an enhanced response of H2S(260 to 5 ppm),a low detection limit(70 ppb)and 130-fold increase in H2 S selectivity(among various interfering gases)at 180°C were obtained because of the catalytic action of appropriate amounts of Co.In addition,beyond the molecular sieve effect to exclude interference from larger gas molecules,the incorporation of Co catalysts can adjust the number of base sites in the ZIF filter(from 1.592 to 3.325 mol/g),which further assists in avoiding basic-type interference from gas molecules with smaller kinetic diameters.Moreover,the sensor was demonstrated to be a powerful platform for assessing trace amounts of H2 S in pesticide volatile gas identification and protein food quality evaluation.(3)Designing multifunctional MOF composite sensitive materials plays an important role in realizing the acquisition of multiple signals(such as gas,pressure and strain,etc.)and reducing the dependence of devices on circuit integration.Elaborately constructing synapse-inspired materials provides a crucial guidance for designing highperformance sensors toward multiplex stimuli response.However,a realistic mimesis both in the "structure and sense" of biological synapses to obtain advanced multifunctions is still challenging but essential for simplifying subsequent circuit and logic programs.Herein,an ionic artificial synapse integrated with Ti3 CNTx nanosheets insitu grown with zeolitic imidazolate framework flowers(ZIF-L@Ti3CNTx composite)is constructed to concurrently mimic the structure and working mechanism of the synapse.The flexible sensor of the bio-inspired ZIF-L@Ti3CNTx composite exhibits excellent dual-mode dimethylamine(DMA)and strain-sensitive response with nonoverlapping resistance variations.The specific ions conduction working principle triggered by DMA gas or strain with the assistance of humidity is confirmed by the density functional theory simulation.Finally,an intelligent wearable system is selfdeveloped by integrating the dual-mode sensor into flexible printed circuits.This device is successfully applied in pluralistic monitoring abnormal physiological signals of Parkinson’s sufferers,including real-time and accurately assessment of simulated DMA expiration and kinematic tremor signals.This work provides a feasible routine to develop intelligent multifunctional devices for upsurging telemedicine diagnosis.(4)Aiming at the problems of single detection function of sensor and poor electrical conductivity of MOF material,a multi-mode bionic flexible sensor that integrated with high-conductivity Ti3C2Tx@Cu3(HHTP)2 composite material with hollow sphere structure is constructed by simulating human sensory system.And it is further implanted into intelligent wearable system for motion signal monitoring.Due to the three-dimensional hierarchical hollow sphere structure,high conductivity,fast electron transmission dynamics,long-term stability and ultra-high hydrophobicity,the bionic Ti3C2Tx@Cu3(HHTP)2 sensor can independently detect NO2 gas and pressure.Since that the prepared sensor has dual-mode sensing characteristics and the same resistance signal output,it is further implanted into flexible circuits for portable wearable electronic health monitoring and sound and vibration recognition. |
PDF Full Text Request