| Nitrogen dioxide(NO2)is highly corrosive and physiologically irritating in the atmosphere;which can generate adverse effects for human health and environment.Even long-term exposure to the surrounding of NO2 with a concentration level of dozens of ppb(parts per billion)that can lead to asthma.The ultra-sensitive ppb-level NO2 sensor detection method is an important means to analyze the formation,harm and protection of NO2.At present,most NO2 sensors are made by metal oxide semiconductor materials,and the operation usually requires high operating temperature to activate the test gas,which greatly limits the practical application of the sensor.Therefore,it is great significance to develop NO2 sensors that can respond linearly within the ppb range at room temperature condition.The strategy of visible light excitation can greatly improve concentration of the carrier for semiconductor materials,and which provide new opportunity for to achieve NO2 detection with highly sensitive at room temperature.Graphitic carbon nitride is a typical semiconductor material of two-dimensional for visible light absorbing,which has great potential in the field of NO2 sensing.However,due to the ability of poor charge separation and lack of adsorption sites,The gas sensing performance of carbon nitride materials reported in the present literature are not ideal.To solve the above problems,semiconductor materials with matching energy bands and rich active sites are selected to construct heterojunction system with interfaces of tightly binding,which is expected to realize ultra-sensitive detection of NO2 gas.The metalorganic frameworks(MOFs)of two-dimensional is beneficial for exposing of active sites,its specific metal nodes can be used as specific adsorption sites of NO2,and which have ultra-high specific surface area and porosity facilitate the diffusion of gas molecules.Therefore,it is considered as an ideal gas sensitive material.Based on relevant literature reports,the Ni2+and Co2+of unsaturated coordination showed higher affinity for NO2.In summary,this paper carries out the following two parts of work:(1)Design and synthesis of NiMOF/CN nanocomposites with defects and optoelectronic detection of NO2 gas.Firstly,NiMOF/CN nanocomposites with a large number of unsaturated coordination Ni2+sites(D-NiMOF/CN)constructed via using an alkali aftertreatment process.The optimized sample has a response value of 627%to NO2 of 1 ppm,with ultra-low limit of detection(LOD)of 1 ppb,and possessing outstanding selectivity and long-term stability(120 days).Time-resolved photoluminescence spectra demonstrated that the introduction of NiMOF and the alkali treatment strategy effectively promoted the charge separation and transfer ability of CN.The in situ X-ray photoelectron spectra showed the direction of electron transfer.In addition,in situ Fourier transform infrared spectra and temperature-programmed desorption disclose that the promotion adsorption of NO2 depends on the strengthened interaction between NO2 and Ni2+node sites at the aid of OH groups from unsaturated coordination.Therefore,excellent detection performance is obtained.(2)Design and synthesis of CoNiMOF/CN nanocomposites and its photoelectric gas sensitive performance detection of NO2.Bimetal CoNiMOF and CoNiMOF/CN nanocomposites were prepared.The optimized sample has a response value of 867%to NO2 of 1 ppm and a detection limit of 1 ppb,exhibiting excellent selectivity for various interfering gas.The mechanism of improving for gas sensing performance has been studied using various characterization methods,the improvement of its activity is mainly attributed to that the constructed heterojunction with dimensionally matched effectively promoted the charge transfer and separation ability of CN.In addition,the synergistic effect of CoNi bimetal greatly enhances the adsorption and activation ability of NO2.This work provides an effective modulation strategy for the development of room temperature CN-based NO2 photoelectric sensing materials with promising prospects. |
PDF Full Text Request