Selective Photoelectrochemical Analysis Of Polychlorinated Biphenyls

Polychlorinated biphenyls（PCBs）are a kind of typical persistent organic pollutants with 209 homologs.Since the 20th century,PCBs have attracted widespread attention because of their serious threat to human health.Due to the high toxicity and low lethal dose of PCBs,many countries have enacted laws to prohibit their production and use.However,due to its excellent chemical stability,PCBs can still be detected in surface water,atmosphere and soil,which may enter and enrich in human body through the food chain,and inevitably damage the endocrine,nervous and reproductive system.Therefore,it is of great significance to establish a rapid,simple and sensitive method for the detection and removal of PCBs in the environment.The photoelectrochemical（PEC）method has shown a wider application prospect in the field of biosensing owing to the advantages of high sensitivity,low cost,simple instrument,convenient operation and on-line detection.However,during the PEC detection,a large number of highly oxidized substances are usually produced,such as hydroxyl radicals and superoxide anions,which can oxidize most of the compounds in the environment.Therefore,PEC technology has poor selectivity.In order to achieve highly selective detection of target analytes in complex environments,a large number of specific recognition elements have been used for PEC detection,such as molecularly imprinted polymers,enzymes,antibodies,and nucleic acid aptamers.Among them,aptamers,as a new type of biological recognition elements,have attracted more and more attention in the field of biosensing due to their low-cost in vitro synthesis,mass production,low immunogenic response,and high specific recognition performance.Therefore,in this paper,a series of photoelectrochemical aptasensors have been constructed to detect PCBs with high sensitivity and selectivity by the combination of the ultra-sensitive photoelectrochemical method with the aptamer that specifically recognizes PCBs.On this basis,a photoactive material with excellent performance was designed as the photoelectrode for photoelectrocatalysis degradation and removal of PCBs in the environment.This paper includes the following research:（1）A photoelectrochemical sensor was constructed based on BiVO₄nanoparticles/TiO₂ nanotubes for detection of PCB72In this work,a photoelectrochemical aptasensor based on BiVO₄nanoparticles（NPs）/TiO₂ nanotubes（NTs）composite materials was prepared to detect PCB72.The BiVO₄ NPs/TiO₂ NTs composites were synthesized by a simple one-step hydrothermal method.The composite materials showed strong visible light absorption,high PEC response and good stability.Then,gold nanoparticles（Au NPs）are deposited on BiVO₄ NPs/TiO₂ NTs by electrochemical deposition technology,and the SH-aptamer is modified on the surface of the composite material by S-Au bond.At the same time,the conductivity of the composite can be further improved via the modification of Au NPs.The PEC aptasensor shows high sensitivity and selectivity to PCB72 with a linear detection range of 1 ng/L-500 ng/L and a detection limit as low as 0.23 ng/L.In addition,the prepared PEC sensor was applied to the determination of PCB72 in environmental water samples,which verified the practical application ability of the sensor.Therefore,the PEC sensing platform can be used to evaluate the content of PCBs in the environment,and has potential application ability.（2）A photoelectrochemical sensor was constructed based on Cd Te@Cd S core@shell QDs sensitized TiO₂ NTs for detection of PCB72The uniform and upright TiO₂ NTs were in situ synthesized on the titanium sheet by anodizing method.The inherent band gap of TiO₂ NTs limits its absorption of visible light,and its photogenerated electrons and holes have a high recombination rate,which affects its photoelectric conversion efficiency.In this work,the hydrothermally synthesized Cd Te@Cd S core@shell QDs was modified on TiO₂ NTs by direct adsorption technology,and Cd Te@Cd S core@shell QDs sensitized TiO₂NTs were prepared.The composites can enhance the absorption capacity of light,extend the absorption range of visible light,and effectively improve the photoelectric conversion efficiency.Subsequently,a photoelectrochemical aptasensor based on Cd Te@Cd S core-shell QDS sensitized TiO₂ NTs was constructed by anchoring aptamer with end-modified amino group on the composite material through covalent reaction.When PCB72 was added,due to the specific recognition of the aptamer to PCB72,PCB72 was captured on the sensing interface to form a poorly conductive PCB72-aptamer complex that hindered the electron transfer between the solution and the sensing interface,and reduced the photocurrent density.The quantitative relationship established between the change of photocurrent density and the concentration of PCB72 was used to analyze PCB72.The results show that the sensor exhibits excellent analytical performance for PCB72 with a linear range of0.1-500 ng/L and a detection limit of 0.03 ng/L（S/N=3）.It can be seen the sensor can be successfully used to evaluate the content of PCB72 in environmental pollutants.（3）Photoelectrocatalytic degradation and removal of PCB72 based on g-C₃N₄/Mo-BiVO₄/FTO compositeThe Mo-doped BiVO₄/FTO（Mo-BiVO₄/FTO）was synthesized by simple electrochemical deposition and spin coating methods.Afterwards,g-C₃N₄ was modified on the Mo-BiVO₄/FTO by physical adsorption and in-situ calcination to prepare the g-C₃N₄/Mo-BiVO₄/FTO.The composites were characterized by transmission electron microscopy（TEM）,scanning electron microscopy（SEM）,UV-visible diffuse reflectance spectroscopy（DRS）,X-ray photoelectron spectroscopy（XPS）,and X-ray diffraction（XRD）.