Antifouling Ion-Selective Electrode With Self-cleaning Properties And Its Application In Environmental Water Monitoring

Polymeric membrane ion-selective electrodes（ISEs）have been widely used in various fields including industrial analysis,clinical diagnosis,and environmental monitoring owing to their specific merits such as low cost,ease of use and easy to be miniaturized.In many cases of practical relevance,however,when these sensors are applied in complex environmental water samples,they are usually suffered from a problem of fouling which refers to the undesirable attachment of organics and further growth of microorganisms on the surface of the membrane.This may shorten the sensor lifetime and cause the measurement errors.To address this challenge,in this thesis,we describe a series of polymeric membrane ISE techniques with excellent anti-fouling and self-cleaning properties by using surface covalent modification of TiO₂-based coatings.The contents of this thesis are as follows:1.Antifouling TiO₂-coated polymeric membrane ISEs with ultraviolet photocatalytic self-cleaning properties:Although several antifouling ISEs have been previously reported by other researchers,the antifouling efficiencies of these electrodes are usually relatively low.Herein,in this chapater,a TiO₂ coating is proposed to improve the anti-fouling and self-cleaning properties of polymeric membrane ISEs for the first time.In order to achieve surface modification of TiO₂ coating,PDA coating is firstly modified onto the surface of the polymeric membrane.Then TiO₂ nanoparticles（NPs）are covalently grafted onto the PDA layer by using a silane coupling agent.As a proof-of-concept experiment,a polymeric membrane Ca²⁺-ISE has been chosen as a model.Under ultraviolet illumination,the TiO₂-coated Ca²⁺-ISE exhibits remarkably improved anti-biofouling properties with an unprecedented low adhesion rate of 4.74%towards pseudomonas aeruginosa and an inhibition rate of 96.62%.In addition,the proposed electrode displays unique properties of anti-organic dye（methyl orange）fouling and a superior self-cleaning ability even soaking in a concentrated pseudomonas aeruginosa suspension of 10⁹ CFU m L^-1 for 60 days.These results indicate that TiO₂ coating-modified Ca²⁺-ISE displays excellent properties of anti-biofouling,anti-organic fouling and self-cleaning.2.Antifouling polymeric membrane ISEs with visible-light photocatalytic self-cleaning properties:Since TiO₂ has a wide band gap,it mainly can absorb ultraviolet light but has a low utilization of visible light.Therefore,this fact may seriously limit the use of the antifouling TiO₂-coated polymeric membrane ISEs in real enviornments.To further extend the application scope of these electrodes,Cd S with visible-light absorbance properties is employed to improve the characteristics of the above mentioned TiO₂ coating.As a proof-of-concept experiment,Ca²⁺-ISE and CO₃^2--ISE have been selected as models.A Cd S-TiO₂ composite photocatalyst is firstly synthesized.In order to achieve simple coating of such catalyst on surface of the ISE membrane,an aqueous polyurethane coating based on Cd S-TiO₂ is then prepared.After being coated by this coating,two kinds of antifouling ISEs with visible-light photocatalytic properties are finally obtained.Experimental results show that the proposed two electrodes also exhibit excellent antifouling characteristics.Compared to the unmodified electrodes,both the Cd S-TiO₂coating modified Ca²⁺and CO₃^2--ISEs exhibit remarkably improved adhesion rates towards pseudomonas aeruginosa.These rates decrease by 95.51%and 96.82%,respectively,as compared to the unmodified ones.In addition,both electrodes exhibit stable response performances even after soaking in high-level pseudomonas aeruginosa suspension for 7days.The response slopes of two electrodes only increase 0.8 and 1.2 m V?dec^-1.It can be expexted that such sensing system will lay the foundation for the applications of ISEs in real environmental waters.3.Application of antifouling ISEs in environmental waters.To demonatrate the applicability of proposed antifouling coating-based self-cleaning ISEs,these electrodes are finally applied in in-situ monitoring in lake water and seawater.Experimental results show that such electrodes also exhibit stable long-term stability even in complicated lake water and seawater.Within 16 days,no significant changes in the response performance can be observed.Further,to confirm the universality of the proposed antifouling method,such antifouling coating is employed to improve the antifouling properties of other different kinds of sensors.It has been found that this antifouling coating is also applicable for fabcrication of other types of antifouling sensors.