Detection Of Emerging Contaminants Based On Functional Photoelectrochemical Sensor Constructed By Nano-composited Photoactive Materials

Emerging contaminants pose significant ecological and health risk due to their low exposure concentration,variety,wide distribution and complex composition.The development of corresponding detection methods can provide a basis for analysing the environmental behaviour and migration laws of emerging contaminants,and play an important role in maintaining environmental health and ecological security.Although many analytical methods have been developed and applied to the detection of emerging contaminants,it is still a big challenge to develop low-cost,high-sensitive,and easy-to-operate detection methods for the low concentration,high toxicity and increasing quantities of emerging contaminants in the environment.Photoelectrochemical（PEC）sensing technology is a new analytical method with simple instrumentation,low cost,high sensitivity,low energy consumption,and easy miniaturization.However,this technology is still in the initial stage of development and is far from being applied to the sensitive detection of emerging contaminants in the real environment.In order to meet the ever-changing detection requirements,it is necessary to further improve the photoelectric conversion efficiency of photoelectrodes,enhance the stability accuracy of detection,and achieve the portability,miniaturization,and automation of sensing devices.This work adheres to the concept of interdisciplinary,combining the expertise and knowledge of Environmental science,Chemistry,Materials,Biology,Physics and Mechanology to inject inspiration and vitality for the development of PEC sensors from the aspects of the preparation of high-efficiency photoelectric active materials,the design of new sensing strategies,the innovations in electrode substrates and modification processes,and the simplification and integration of detection systems.We deeply explore the electron transfer mechanism of the sensing system and effectively improve the detection performance,providing a new detection strategy and sensing platform for emerging contaminants,as well as providing a reference and basis for the future practical application of PEC sensors.The main works include the following:（1）To address the problem of narrow signal response range and high probability of“false positive”of"signal-off"PEC sensors,and the fact that most"signal-on"sensors are limited by the activity of biological enzymes.We have developed an enzyme-free"signal-on"PEC sensor by coupling the high activity of Ce O₂/Au/g-C₃N₄ternary heterojunction materials with the high specificity of aptamers.The built-in electric field coupled surface plasmon resonance（SPR）effect can inhibit the recombination of photogenerated electron-hole pairs and promote charge separation and transfer.Highly active carriers and free radicals under photoexcitation can directly oxidize microcystin-LR（MC-LR）,resulting in corresponding electrical signal changes.Based on it,the proposed sensor avoids the shortcomings of biological and"signal-off"detection mode successfully,and shows excellent analytical performance towards MC-LR with a wide detection range（0.05～1×10⁵ p M）,low detection limit（0.01 p M）and good anti-interference ability.（2）The construction of ternary heterojunction can enhance the carrier separation efficiency of photoactive materials and improve the detection sensitivity of PEC sensors to a certain extent,but its preparation process is tedious,and the components are complex.In order to achieve higher photoelectric activity with simplicity and low cost,a direct Z-type heterojunction material ofα-Fe₂O₃/d-C₃N₄ was prepared.The special"Z"carrier transfer path can effectively avoid the drawbacks of the carrier migration to the low potential energy band inside the conventional type II heterojunction,retaining a high redox activity.On the other hand,to address the problem of low specific surface area and low flexibility caused by planar rigid electrode substrates（e.g.FTO）,a novel flexible photoelectrode was developed by modifyingα-Fe₂O₃/d-C₃N₄ on the three-dimensional（3D）carbon fiber textile（CFT）.The unique 3D layer structure of flexible CFT provide a larger specific surface area and higher mechanical strength than FTO,providing more reactive sites to improve the sensitivity of the sensor.The photocurrent signal of the sensor showed a good linearity with the concentration of penbritin,demonstrating excellent performance with low detection limit（0.0125 p M）over a wide concentration range（0.5 p M-50n M）.（3）The application of flexible electrode substrates can provide an avenue for the development portable and flexible sensors,but more specialised optimization of electrode integration and device miniaturization processes is required to obtain integrated PEC sensing devices.We have combined PEC and micro-nano 3D printing technology to develop a miniaturized PEC self-powered sensing device,which overcomes the shortcomings of traditional detection technology that require external electricity and a three-electrode system.However,this puts forward higher demands to the performance of photoactive materials.Herein,bismuth vanadate（Bi VO₄）with nitrogen doping and oxygen vacancies（O_v）was grown on the surface of the FTO electrode substrate by in-situ self-assembly.The obtained N/O_v/Bi VO₄ exhibit a unique fern-like biomimetic structure,which can provide abundant recognition sites and improve the mass transfer efficiency on the photoanode surface.The bandgap and photoactivity of Bi VO₄ can modulated by doping of nitrogen,and the introduction of O_v brings impurity energy levels,which effectively promote the light utilization and the effective separation of carriers.A dual-electrode self-powered sensing system was constructed by using N/O_v/Bi VO₄ modified FTO as the photoanode and Pt electrode as the photocathode,and a portable self-powered PEC sensing device was integrated with micro-nano 3D printing technology.Based on it,a low detection limit（0.025 nM）and excellent detection range（0.1 n M～100μM）for bisphenol A（BPA）were achieved,and excellent detection reproducibility performance and stability were demonstrated.（4）The development of a self-powered miniaturized sensor with dual-electrode system can greatly simplify the detection system and broaden the development of portable devices.However,this dual-electrode system still relies on Pt electrodes,which is costly and limits the development of photoanode materials.Therefore,a dual-photoelectrode self-powered system was developed by two photoactive materials（n-type Au NPs/g-C₃N₄ nanotubes and p-type 3D reticular Ni/Zn In₂S₄）with difference energy band potential,which was further combined with micro-nano 3D printing technology to construct a PEC miniaturized sensing device.While reducing the overall cost,the photoelectric activity of photoactive materials and the potential difference between the two photoelectrodes can be modulated through morphology control,element doping and other strategies to obtain a higher-performance sensing system.The self-bias caused by the Fermi level difference between the photoanode/cathode enables the directional transfer of photogenerated carriers,which can generate electricity and provide the corresponding detection signals under visible light irradiation.The pattern of signal output was simplified by using open-circuit voltage as the detection signal.The proposed dual-photoelectrode self-powered sensing device displayed an ultra-sensitive detection of ciprofloxacin over a wide detection range with a detection limit as low as 0.03 ng/m L.（5）All of the above research work relies on an external physical light sources that provide stable incident light,which violates the original intention of the miniaturization of PEC sensing devices.Replacing the external physical light source with a built-in chemiluminescent light source is a promising way to simplify the equipment.In this work,an innovative self-luminescent PEC sensing system was developed by peroxalate chemiluminescence system with a highly active photoelectrode for the detection of biogenic amines.Firstly,Au NPs-modified S-vacancy Sn S₂（Au/S_v/Sn S₂）nanoflowers photoactive materials was prepared based on the SPR light absorption and defect engineering strategy of surface noble metal nanoparticles.The material shows significantly improved light absorption capacity and photoelectric conversion efficiency,which greatly optimizes the basic photocurrent signal and response sensitivity of the PEC system.On the other hand,bioamine molecules can be oxidized to generate H₂O₂ with the presence of diamine oxidase,which triggers the luminescence reaction of the peroxalate chemiluminescence system and simultaneously induces PEC reactions on the Au/Sv/Sn S₂ photoanode acts as a hole-scavenger,and thereby realizing the highly sensitive detection of bioamine.The results showed that the proposed self-luminescence sensor achieved a wide detection range（10-1000μg/m L）and a low detection limit（0.07μg/m L）by using histamine as the representative bioamine substance.