Preparation And Modification Of Silicon Based Photothermal Conversion Membrane And Interfacial Evaporation Properties

Solar interface evaporation technology has the advantages of energy conservation,environmental protection and a wide range of water treatment.So,it is considered to have great application potential in the fields of seawater desalination and sewage purification.Unfortunately,due to the high cost and instability of light absorption materials,large heat loss and serious salt deposition,the interface evaporation technology is difficult to achieve efficient and stable evaporation,which hinders the development of this technology.In response to the above problems,a series of studies have been carried out in this paper from the perspectives of solar energy absorption,heat management and salt precipitation prevention.The specific work as following:Black silicon powders with porous structure were prepared by etching commercially inexpensive micron Al Si alloy with acid or alkali.Then,black silicon photothermal conversion membranes were constructed with black silicon powders.And a solar interfacial evaporation system with a one-dimensional water transport structure was constructed.The partially broken spherical particles and porous structure after etching were beneficial to enhance the refraction of light inside the material.And the oxide and hydroxide produced by etching could enhance the hydrogen bond between the materials and water molecules,which could reduce the evaporation enthalpy of water.As a result,the black silicon membranes（Si-Na OH）prepared by alkali had the lowest evaporation enthalpy,and achieved an average absorbance of 93.96%in the range of 300 nm-2500nm.Due to the small contact area between the one-dimensional water transport channel and the photothermal membranes,the heat conduction loss was suppressed.Under the continuous illumination of 1 k W·m^-2（1 sun）for 1 h,The interface temperature of the Si-Na OH photothermal conversion membranes increased to 46.9°C,while the water temperature increase was only 1.2°C.Benefiting from the light absorption and effective thermal management,the interfacial evaporation system achieved a water evaporation rate of 2.18 kg·m^-2·h^-1（5.74 times that of bulk water）and an energy efficiency of 90.76%.Then,the stability of light absorption performance of the photothermal conversion membranes was verified by ball milling test.And the effects of the concentration and type of etchant,the composition and particle size of Al Si alloy on properties of black silicon were investigated.The results proved that the etching strategy had strong applicability,feasibility and stability.In order to enable the interfacial evaporation system to efficiently and stably evaporate seawater,the interface hydrophilicity and hydrophobicity of black silicon powder and photothermal conversion membranes were regulated by Polydimethylsiloxane（PDMS）,respectively.The test results showed that both strategies could prepare superhydrophobic membranes.The superhydrophobic interface combined with a superhydrophilic bottom surface could form a photothermal membranes with Janus properties（The substance had two diametrically opposed properties）.The degree of hydrophobicity of the membrane interface could be regulated by controlling the amount of PDMS.The research showed that with the enhancement of the hydrophobicity of the evaporation interface,the negative impact of salt deposition on the interfacial evaporation system was gradually weakened.And the PDMS/b-Si membranes prepared by membrane hydrophobic modification could achieve a light absorption rate of 94.55%.When 3.5%brine was evaporated continuously for 8 h under 1sun,the evaporation rate of the system was kept above 2.07 kg·m^-2·h^-1.The structural design of water transport is an effective strategy to inhibit salt precipitation.Therefore,the effects of water transport rate and water diffusion path in the photothermal conversion membranes on salt precipitation were investigated with PDMS/b-Si as the light-absorbing layer.The water transport rate was regulated by the number of cotton swabs.As the water transport rate increased,the precipitation of salt was significantly inhibited.The water diffusion path was regulated by the positional distribution of the cotton swab,so that the salt was precipitated directionally.Benefiting from the significantly increased additional evaporation area,the PDMS/b-Siφ6x9 system could obtain a higher evaporation rate of pure water(2.27 kg·m^-2·h^-1)when using a large number of cotton swabs with small diameters.The interface regulation and the water transport structure design synergize,and the salt precipitation was effectively suppressed.The 10%Na Cl solution was continuously evaporated for 8 hours under 1 sun light,and the cycle test was performed for 7 days.The results showed that the evaporation rate remained above2.10 kg·m^-2·h^-1.In addition,the interfacial evaporation system could remove 99.7%of dye molecules in the printing and dyeing wastewater.The removal rate of metal ion in wastewater containing heavy metals ion and simulated seawater was over 99.9%.When it was used to purify the tailings pond wastewater,it showed a better removal rate of organic matter,and the removal rate of 9 metal ions such as Mn²⁺,Al³⁺,Fe³⁺and Zn²⁺could reach99.6%.In addition,the concentration of Mn²⁺decreased from 15.51 g·L^-1to 2.25×10^-5 g·L^-1.