Study Of Bionic Water-harvesting Surface For Ph Sensor Of Cultivated Substrates

In the production of facility agriculture,the realization of online detection of ion concentration of cultivated substrate is one of the bases to promote the automation and intelligence of cultivation in China.The group proposes to build an integrated bionic sensor（IBS）for the difficult problem of poor detection accuracy due to insufficient water around the electrode and difficulty in forming a saturated hydrogen ion solution on the electrode surface during the online detection of p H of cultivated substrate.The water in air and soil is collected and stored by bionic leaves and bionic roots,and water is replenished around the electrode during online detection to form the ionic solution required for detection.In this paper,we synthesize the current research on bionic water collection surfaces and construct a bionic leaf water collection surface for capturing water mist in the air by means of theoretical analysis and experimental studies to investigate the influence of process parameters of surface preparation and surface structure parameters on water collection performance.The main research contents and conclusions are as follows.（1）Structural design of the bionic leaf water-collecting surface and theoretical analysis of the factors influencing water-collection performance:A bionic desert beetle water-collecting surface with non-uniform wettability was designed by studying the water-collection mechanisms of plant and animal surfaces and non-uniform wettability surfaces.The water collection surface consists of a square hydrophilic matrix and hydrophobic channels.According to the Wenzel model of the basic theoretical model of surface wettability,the larger the ratio of hydrophobic channel width to hydrophilic square side length,the higher the water collection rate of the water collection surface.In addition,according to the analysis of the characteristics of the actual agricultural production environment,it is obtained that the water mist composition and p H value in the air will affect the water collection performance of the surface,and the surface will be corroded to a certain extent under acidic and alkaline conditions,leading to changes in the surface microstructure,which in turn leads to a decrease in the water collection performance of the surface.（2）Preparation and performance characterization of bionic leaf water collection surface:The bionic leaf water collection surface was prepared based on magnetron sputtering and chemical etching method.The hydrophobic PDMS and superhydrophobic NC-317 coatings were firstly prepared on the glass substrate by coating method and treated with stainless steel mesh mask with mesh size of 200～500,and then the hydrophilic Ti matrix was prepared on the surface by magnetron sputtering method;finally,the superhydrophobic Ti O₂ matrix surface was prepared by Na OH etching treatment to form a non-uniform wettability water collection surface.Through SEM,XPS,contact angle measurement and other methods of comparative observation and test analysis,it was determined that the suitable parameters of the preparation process were obtained:magnetron sputtering coating thickness of 150 nm,Na OH alkali etching time of 30 min,and concentration of 6 M.According to the different wettability,four kinds of non-uniform wettability were prepared:hydrophilic-hydrophobic,superhydrophilic-hydrophobic,hydrophilic-superhydrophobic,and superhydrophilic-superhydrophobic bionic leaf water collection surfaces.（3）Water collection performance and stability tests of the bionic leaf water collection surfaces:Referring to the current test methods for measuring the water collection rate of non-uniform wettability surfaces,water collection tests were conducted on the four types of bionic leaf water collection surfaces,and it was found that the superhydrophilic-superhydrophobic surface had the highest water collection rate,and the higher the number of mask plate mesh,the higher the water collection rate,reaching a maximum of 3.455 g cm^-2 h^-1.However,after 7 days of continuous water collection,the water collection rate decreases due to the destruction of the surface microstructure and the residue of surface materials.The water collection performance of the bionic leaf surface placed in outdoor environment for 8 weeks was tested:the surface could maintain a good water collection rate for 3 weeks,and still meet the minimum requirement of water collection rate(1.47 g cm^-2 h^-1)at 6 weeks,and the water collection rate decreased to about 1.1 g cm^-2 h^-1 after 7-8 weeks.Tests by scanning electron microscopy（SEM）and X-ray photoelectron spectroscopy（XPS）showed that the main reasons for the decrease in water collection performance were the damage to the surface microstructure to some extent and the thinning of the thickness,the adhesion of impurities and organic matter,and the failure of superhydrophobicity.In this paper,we propose a method to prepare a bionic leaf water collection surface,which can effectively collect water mist in the air and has good stability,and can provide sufficient water source for the bionic leaf of the cultivated substrate p H sensor,thus solving the problem of low accuracy of measurement due to insufficient water around the electrode.On this basis,the causes of the degradation of the water collection performance on the collecting surface are investigated,which to a certain extent remedy the deficiencies in the current research and provide the theoretical basis and experimental basis for further development of the bionic leaf and integrated bionic sensor.