Research On Airborne Redox-Active Compounds Detection And Electrocatalytic CO₂ Reduction Based On Gold Nanoparticles And Fiber Membranes

With the increased human activities such as fossil fuel combustion,industrial production and vehicle exhaust,global atmospheric pollution and excessive greenhouse gas emissions have emerged.Airborne redox-active compounds（ARC）and carbon dioxide（CO₂）,as typical atmospheric pollutants and greenhouse gases,can negatively impact on ecological environment and display damage to human health.The development of methods for ARC detection and CO₂conversion is thus of great significance for the reduction of pollution and carbon emissions.However,conventional ARC detection techniques rely on complex,expensive equipment and complex procedures.Additionally,the method for CO₂catalyst is complex and the substrate for catalyst deposition is limited.To address these challenges,heating-induced Au NPs optical sensing method in the solution system for ARC determination is developed based on the filtration performance of fiber membranes and local surface plasmon resonance（LSPR）of gold nanoparticles（Au NPs）.On this basis,wearable masks are employed as passive samplers for simplifying the sampling process and the applicability of mask as a dosimeter for quantifying personal exposure to ARC is explored.Subsequently,the light-induced Au NPs smartphone-based colorimetric method for on-site ARC detection is further developed to simplify the detection procedures transforming from the solution system to filter-based solid system.Furthermore,waterproof conductive cellular gold-coated PVDF nanofiber membranes are designed based on the catalytic activity of Au NPs and the mass transport of fiber,and explored practical suitability as gas diffusion electrode in the electrocatalytic CO₂reduction.The details are as follows.1.Based on the redox ability of ARC and LSPR response of Au NPs,the Au NPs colorimetric sensor was constructed to achieve the rapid determination of ARC under heating-induced reaction by utilizing UV-Vis spectrophotometer.Humic acid（HA）and Suwanee River fulvic acid（SRFA）were chosen as standard ARC models.Upon optimizing reaction conditions,the absorbance intensity of Au NPs was in a linear relationship both with the concentration of HA and SRFA.Under the optimal reaction conditions,the linear dynamic range of ARC was 0.005-100 ppm,and the detection limit was 0.005 ppm.Additionally,ARC was determined qualitatively using the naked eye without resorting to any complex analytical instrument due to the color of Au NPs.Furthermore,the real-world samples from three typical cities in Switzerland were collected by quartz filter and analyzed by the Au NPs colorimetric sensor.The results were verified by the standard Total Organic Carbon method and had a good correlation with that by TOC,thus demonstrating the practical application of the Au NPs colorimetric sensor in real-world aerosol detection.2.To simply the sampling process and detect ARC rapidly,Au NPs colorimetric sensor in combination of mask sampling based on human breathing was developed.The blank disposable PP masks had the least background signals among different masks,thus were selected as passive samplers.For the sampling time within 1-7 h indoor,the absorbance intensity of Au NPs was in a linear relationship with the concentration of water-soluble particles trapped in the middle and outer layer of masks collected by machine simulation.The developed method was to monitor indoor and outdoor ARC in Shanghai.The average exposure(37.11μg m^-3)and the average potential exposure dose(27.84μg h^-1)on the campus were then calculated using the"Time-activity profile"method.Finally,the deposition fraction of different particle sizes in the respiratory tract was predicted based on a multiple path particle dosimetry model（MPPD）,where the PM2.5 deposition fraction in the lung was high and the corresponding ARC concentration was up to 6.05μg m^-3for an individual in the campus based on ARC exposure results above.In combination of passive mask sampler,Au NPs colorimetric method and MPPD model,prediction of personal exposure risk to ARC is achieved.3.A portable smartphone-based colorimetric sensor was developed in combination of the filter membranes,ARC-induced photochemistry,colorimetric Au NPs for in situ ARC detection directly on filter membrane.QF can be either employed for aerosols collection and the reaction site to store reactants within the fiber network.Airborne BQ particles on the QF was deposited and subsequently achieved in-situ reduction of gold ions through light irradiation.The ARC concentration could be either directly quantified by measuring the reflectance of filters through a UV–Vis spectrophotometer or by a portable smartphone-based software for the read-out RGB（Red,Green.Blue）values of filter.This smartphone-based approach offers outstanding advantages over the conventional ARC analysis techniques,including the simple operation,exemption of complex instrumentation and elimination of sample extraction.The smartphone-based method demonstrated good linear dynamic range of 0.026-0.49μg/mm²,low detection limit of 0.05μg/mm²,good reproducibility and practical application in real-world aerosols collected from Switzerland,especially suitable for rapid on-site detection and remote areas.4.A conformal gold-coated electrospun PVDF fibers（Au-PVDF-NFMs）via electrospinning and electroless plating were designed.The deposition of a conformal and fully interconnected gold layer with an average thickness of circa 38 nm and sheet resistance of 1.2Ωsq^-1was achieved.Besides,integrated functionalities were discovered such as hydrophobicity and gas permeability.Notably,the NFMs also showed excellent mechanical durability under both stretching and bending,with negligible conductivity losses after 1000 cycles.Thanks to these structure and properties,the Au-PVDF-NFMs demonstrated practical suitability as gas diffusion electrodes（GDEs）for electrochemical CO₂reduction.The Au-PVDF-NFMs exhibited a Faradaic efficiency towards CO,as high as～85%at-0.7 V vs RHE and were able to reach current densities of 100m A cm^-2at-0.95 V vs RHE.In contrast with other methods,the membranes by electrospinning technique are potentially scalable and microstructurally controllable,while the metal deposition achieves a three-dimensional,conformal coating on hydrophobic and nonplanar substrates,with no plasma treatment,requiring only energetically efficient p DA treatment,environmentally friendly reagents and simple procedures.In summary,the sensing performance,detection time,sampling process and detection procedures of Au NPs sensor based on fiber filter for ARC determination can be effectively improved upon the optimization of sensing conditions,the sensor mechanism and fiber structural characteristics.Meanwhile,the structural tunability of nanofiber membranes and the optimization of gold nanoparticle coating can be employed to enhance the mass transport of gas diffusion electrodes and catalysis activity,which in turn improves the catalytic performance of CO₂.This research provides novel and feasible approach to combining fiber membranes and Au NPs for ARC determination and gas diffusion electrode,which are helpful to promote in the fields of environmental detection and catalytic conversion.