An "on-off-on" G-C₃N₄ Nanosheets Fluorescent Sensor For The Detection Of 5-Br-PADAP And Co²⁺ Based On The Inner Filter Effect

Cobalt is an important trace element in the human body and played an important role in physiological activities,but exposure to excessive Co²⁺and cobalt compounds would cause serious threats to human health;(2-（5-Bromo-2-pyridylazo）-5（diethylamino）phenol（abbrev.5-Br-PADAP）had a wide range of applications in metal ion detection and dyes research due to its unique azo-pyridine-phenol hydroxyl structure and good color rendering ability.However,the toxic degradation products after its discharge would also pose a serious threat to human health and the environment.Therefore,it is necessary to develop a sensitive,reliable,and highly selective detection method for Co²⁺and 5-Br-PADAP in the environment.Fluorescent sensors are currently attracting attention in the fields of environmental monitoring,food safety,and medical technology due to its advantages of high sensitivity,good selectivity,low cost and fast response speed.In the past,small organic molecules were generally used to construct fluorescent sensors,but two-dimensional nanomaterials have attracted widespread attention because of their low toxicity and abundant optical properties in recent years.Therefore,two-dimensional nanomaterials and fluorescence analysis methods were combined in this paper.Firstly,the graphite phase g-C₃N₄ was prepared by burning method and then g-C₃N₄nanosheets were obtained by liquid phase exfoliation method.Subsequently,the fluorescent sensor based on g-C₃N₄ nanosheets was successfully constructed and used to the detection of 5-Br-PADAP and Co²⁺.The main research content included the following parts:The first part:the bulk g-C₃N₄ was prepared by burning the mixture of melamine and urea,and then the bulk g-C₃N₄was treated by liquid exfoliation method to obtain g-C₃N₄nanosheets.Later,it was confirmed that the g-C₃N₄ nanosheets with a size of about 100 nm had been successfully prepared by some characterization techniques（such as TEM,SEM,XRD,XPS,FTIR）.The second part:the prepared g-C₃N₄ nanosheets were used to construct"turn-off"fluorescent sensor and applied it to the detection of 5-Br-PADAP.The experimental results exhibited that the sensor had a good fluorescence response to 5-Br-PADAP with the linear detection range was0-15μM and the detection limit was 64 n M.Besides,the sensor possessed good selectivity.The third part:the g-C₃N₄-5-Br-PADAP nanosheets were used to construct"turn-on"fluorescent sensor and applied it to the detection of Co²⁺.The experimental results exhibited that the sensor achieved the quantitative detection of Co²⁺under strong acidity conditions,and had a good linear response（R²=0.991）in the concentration range of Co²⁺was 0-10μM and the detection limit was 44 n M.Ultimately,the sensors achieved the detection of environmental water samples and simulated nuclear wastewater,and possessed good selectivity and anti-interference ability.This paper systematically studied and discussed the construction and application of"on-off-on"fluorescent sensor based on g-C₃N₄ nanosheets,which provided a good platform for the detection of Co²⁺and 5-Br-PADAP.