Development Of An All-solid-state Ion Sensor And Its Application In Hydrothermal Exploration At The Southwest Indian Ridge

Resulting from the development of industry and agriculture in recent years,water pollution has become more and more serious,and ion monitor in water has attracted the attention of many scientists.The all-solid-state ion sensor is an important method for in-situ and continuous ion monitor in various waters.It shows its unique advantages during the monitoring of marine environment,especially for ion detection in deep sea complex environments.Submarine hydrothermal fluid is a huge treasure in the ocean,and it contains many resources needed for human life.However,there are few chemical methods that can be used for hydrothermal ion determination due to the harsh chemical environment near the seabed hydrothermal vent.Therefore,the development of an all-solid-state ion sensor that can be used for in-situ ion monitor in different fields and for hydrothermal detection in harsh seabed environments is of great significance for water pollution assessment and marine resource development.On the one hand,an all-solid Ag/Pb/PbSiO₃ silicate ion sensor was prepared by electrochemical method with Pb film as the intermediate layer and PbSiO₃ as the sensitive membrane.The sensor response mechanism is derived from a reversible ion exchange reaction between the surface of the sensitive membrane and the solution to be tested and a reversible electron exchange reaction between the metal and the membrane.The performance characterization of the sensor by electronic scanning electron microscopy and electrochemical analysis revealed that the sensor showed a particle film with a diameter of about 0.2-0.5 ?m.The linear range of the sensor response to silicate is 10^-1-10^-5M with a performed superior reversibility.Its response time is less 5 s due to its low impedance of 65 ?.The sensor behaved good selectivity to several anions,such as NO3^-,SO₄^2-,CH₃COO^-,CO₃^2-,PO₄^3-and so on.In addition,the Ag/Pb/PbSiO₃ silicate ion sensor could be used to self-contained/online in-situ monitoring in the field environment with its small in size?about 0.4 mm in diameter and 2-3 cm in length?,easy to operate and integrate.It has broad application prospects.On the other hand,the assembly and calibration methods for all-solid-state pH,Eh,H₂S and Ag/AgCl reference sensors were described in this paper.During the Chinese Dayang 341 and 4911 cruises at the Southwest Indian Ridge,the assembled multi-parameter chemical sensor?MPCS?,equipped with a deep-sea towed camera system,was continuously monitored in-situ at depths exceeding 2,000 m.The potential anomalies of the Eh,H₂S,and pH electrodes were 49,98,and 18 mV,respectively,in the Longqi hydrothermal plume area.In the undetected area,the MPCS showed slight anomalies,indicating the presence of an unknown hydrothermal plume at the site.All potential anomalies of the MPCS were consistent with those of commercial sensors?methane,turbidity,and temperature sensors?.The test results suggested that the MPCS can sensitively detect changes in chemical quantities caused by hydrothermal fluid,and it provides an effective technique for exploring hydrothermal vents.