| The research and development of methods and instruments that can directly and quickly detect ammonia nitrogen are of great significance to develop smart agriculture,protect water resource and ensure the safety of drinking water.Electrochemical sensors have the characteristics of high sensitivity,fast response speed and simple operation.Therefore,they are suitable for on-site detection and online monitoring.As the main part of the electrochemical sensor,the sensitive electrode has an important influence on the performance of the electrochemical sensor.Therefore,the design and construction of electrode material that can be used as a sensitive electrode are very important to realize the electrochemical detection of ammonia nitrogen.It is one of the common detection principles that electrocatalyst play a role as electrode materials to catalyze oxidation/reduction reaction of analyte for realizing the quantitative determination of the analyte.The platinum（Pt）is one catalyst with excellent catalytic activity.Therefore,Pt-based materials may exhibit great detection ability.Conductive polymers not only have good conductivity,but have absorption capacity for ammonia,to further show great synergistic effect with Pt nanoparticles.Therefore,fabricating composite materials based on conductive polymers and Pt nanoparticles not only reduce the cost of sensitive electrodes and but also improve the catalytic ability and detection ability.Based on above analysis,in order to obtain sensitive electrode with excellent performance for detection of ammonia nitrogen,this paper adopts an in situ growth strategy to fabricate a series of composite materials based on Pt nanoparticles and conductive polymers（polypyrrole（PPy）/polyaniline（PANI））supported by conductive substrate（Ni foam/carbon cloth（CC））.The detection abilities of these electrode materials were studied.The possible detection mechanisms were analyzed.And finally,several self-supporting ammonia-nitrogen-sensitive electrodes with great performances were obtained.The main research contents are given as follows:1:Ni foam acted as conductive substrate,Pt-Ag/PPy-Ni foam has been fabricated based on chemical polymerization and electrodeposition methods.SEM results indicated that Ag/PPy has evenly grown on the surface of Ni foam and Pt nanoparticles have well dispersed on Ag/PPy surface.XPS results confirmed the existence of Pt,Ag and PPy.The reaction time and temperature of Ag NO3 and Py were optimized and their influences on Ag/PPy-Ni foam were analyzed.The cycles were optimized during the process of growth of Pt nanoparticles by CV,and its effects to detection performance were measured.The optimized Pt-Ag/PPy-Ni foam has exhibited great electrochemical detection ability with a sensitivity of 44.5μAμM-1,a linear range from 100 n M to 100μM and a detection limit of 37.3 n M（S/N=3）.Pt-Ag/PPy-Ni foam has also showed anti-interference ability,good reusability,reproducibility and stability.This work illustrated that it is feasible to realize ammonia nitrogen detection on the basis of electrocatalytic activity of Pt and electrochemical oxidation reaction of ammonia,and to fabricate Ni foam-supported Pt-based sensitive materials for detecting ammonia nitrogen.2:In this work,in order to save the synthesis time and cost of PPy,PPy was deposited on the surface of Ni foam by amperometric measurement and Pt-PPy-Ni foam was constructed via further depositing Pt nanoparticles on PPy-Ni foam by CV.The morphologies of different samples have been observed by SEM,and it was found that too many deposition cycles would cause corrosion of Ni foam during the deposition process of Pt nanoparticles.The crystal structure,surface composition and valence state of the sample were characterized by XRD and XPS.The effects of the deposition time of PPy and deposition cycles of Pt nanoparticles were studied and analyzed.The measurement results of DPV illustrated that the optimized Pt-PPy-Ni foam showed great detection ability of detecting ammonia nitrogen with a sensitivity of 4.19μAμM-1,a linear range from 500 n M to 400μm and a detection limit of 12.36 n M（S/N=3）.In addition,Pt-PPy-Ni foam exhibited good anti-interference ability and stability.3:In order to overcome the corrosion of Ni foam and enhance the stability of the electrode material,in this work,CC was chosen as conductive substrate and Pt-PPy-CC was prepared by two-step amperometric measurements.Based on SEM images of samples,PPy was not uniformly dispersed on the surface of CC,morphology of Pt nanoparticles showed sheet-like characteristics and CC has no obvious corrosion phenomenon during electrodeposition process of Pt nanosheets.The crystal structure,surface composition and valence state of Pt-PPy-CC were characterized by XRD and XPS.The deposition time of PPy and Pt were optimized and their effects on the electrochemical detection ability were analyzed.The measurement results of DPV proved that the optimized Pt-PPy-CC has a sensitivity of 6.67μAμM-1 and a detection limit of 0.24μM（S/N=3）with the ammonia nitrogen concentration from 1 to 450μM.In addition,the sample also showed satisfactory anti-interference ability and stability.4:In order to avoid the influence of the uneven growth of PPy on the sensitive properties,in this work,PPy was replaced by PANI,and the Pt-PANI-CC composite material was prepared by a two-step electrodeposition method.The SEM results showed that PANI not only successfully grew on the surface of the CC,but also formed an array structure.The deposition time of Pt have been optimized and the sample obtained at 800 s showed the best catalytic ability and sensitivity.This Pt-PANI-CC was further tested for detection ability of ammonia nitrogen using DPV.The measurement results of DPV proved that this Pt-PANI-CC has a sensitivity of6.60μAμM-1 and a detection limit of 77.2 n M（S/N=3）with the ammonia nitrogen concentration from 0.5 to 550μM.After testing anti-interference ability,stability,reproducibility and reusability,it is found that its comprehensive performance is great.In conclusion,four Pt-conductive polymer composite materials which supported by conductive substrates（Ni foam,CC）were fabricated by in situ growth methods of electrochemistry deposition and chemical polymerization and used as sensitive electrodes to detect ammonia nitrogen.Experimental results showed that the four sensitive electrodes have good detection capabilities.Above results demonstrate that it is feasible strategy to detect ammonia nitrogen based on the catalytic ability of Pt towards electrochemical oxygen reaction of ammonia,prove that the conductive substrate-supported Pt-conducting polymer composite materials can be fabricated via in situ growth methods,and indicate that the synergistic effect between Pt and conducting polymers has a positive effect on improving catalysis and detection capabilities.Above results provide new reference and strategy for designing sensitive electrode of novel electrochemical sensor for detecting ammonia nitrogen. |
