Preparation And Research Of Vertical Graphene Decorated With SnO₂ Nanoparticles For Highly Sensitive Room Temperature Formaldehyde Sensing

Formaldehyde is one of the most widespread volatile organic compounds(VOCs).It is known that formaldehyde can cause severe damage to human health even at sub-ppm level.In the World Health Organization regulations,the standard for safe exposure of formaldehyde in the workplace is 0.08 ppm for an average of 30 min.To detect and monitor formaldehyde,different methods have been developed,including gas chromatography,polarography,fluorometry and gas sensors.Specifically,gas sensors have attracted considerable attention due to the low-cost and real-time detection.While most of gas sensors presented low detection limit for formaldehyde,the disadvantage is that they need operating at elevated temperatures,resulting in high power consumption and difficulty in integration.For the room temperature formaldehyde sensors,the detection limit is almost at ppm level,which cannot meet the WHO standard.Therefore,it is essential to develop an effective method for detecting formaldehyde at concentrations below 0.08 ppm at room temperature.Graphene has been widely investigated as a promising material for the fabrication of high-performance sensors at room temperature due to their large specific surface area and high sensitivity to electrical perturbations from gas molecule adsorption.Vertical graphene(VG)is a two-dimensional“graphitic”platelet that is typically oriented vertically on a substrate.The vertical orientation and open structures offer large accessible surface areas for gas molecule adsorption and inhibit the agglomeration of graphene sheets during the sensor device fabrication.VG has been reported for sensor applications.For instance,Mao et al.fabricated a field-effect transistor biosensor using VG labeled with Au nanoparticles.Because the vertical orientation and open structure expose entire surface to the surrounding atmosphere,it is believed that VG could offer more reactive surface sites for formaldehyde detection.It is reported that the graphene-gas molecule adsorption also depend on the molecular adsorption configuration.Gas molecules have much stronger adsorption on the doped graphene than that on the pristine graphene.To improve the sensing performance of graphene-based sensors,various metal oxides such as SnO2,ZnO and TiO2,have been explored to modify graphene.Among these metal oxides,SnO2 has attracted tremendous attention due to the high conductivity,good stability and low detection limit for formaldehyde.Considering the unique structure of VG and the excellent formaldehyde sensing performance of SnoO,it would be worthwhile to explore formaldehyde sensor based on VG/SnO2 nanohybrids and investigate its properties.In this work,a novel formaldehyde sensor was fabricated through direct growth of VG networks on the sensor electrodes by microwave plasma-enhanced chemical vapor deposition(MW-PECVD).SnO2 nanoparticles were then deposited on the VG surface by electrochemical deposition.The low limit of detection(LOD)of VG/SnO2 sensor for formaldehyde sensing is 0.02 ppm.The response time and recovery time were 46 s and 95 s for 5 ppm formaldehyde,respectively.Moreover,the sensor showed excellent selectivity and stability.Results from this study present a new method to design and fabricate formaldehyde sensors,and this VG/nanoparticle structure is promising for room temperature VOCs sensing.