Design And Construction Of High-Efficient Solar Water Evaporation Device Based On Micro-Nano Photothermal Conversion Materials

With the continuous growth of population and the rapid development of industrialization,the shortage of fresh water resources is becoming more and more serious due to the discharge of industrial wastewater and domestic sewage,which has become one of the great challenges.Interface solar water evaporation technology aims to provide energy with green solar energy,and maximize the use of solar energy by building solar water evaporation devices,so as to achieve efficient water evaporation process.The interface heating strategy is employed to desalinate seawater and treat wastewater to obtain clean fresh water resources.In this paper,the design and application of the solar water evaporation devices are mainly studied.(1)A photothermal conversion device based on interface heating is constructed by coating LaB₆ nanoparticles with photothermal conversion performance on melamine sponge with three-dimensional network structure,low thermal conductivity and better hydrophilicity.Under the illumination intensity of 1 k W·m^-2,the evaporation rate of water reaches 1.13 kg·m^-2·h^-1.In addition,LaB₆ and melamine sponge have high chemical stability(acid and alkali resistance),so they can evaporate water in simulated seawater,acid/alkali wastewater and dye wastewater,which shows remarkable treatment effects,and has broad application prospects in the field of water treatment.(2)Using Loofah biomass as the precursor,carbonized Loofah(CL)was obtained by one-step carbonization,and then CL-CNF was obtained by coating polydopamine and chemical vapor deposition of carbon nanofibers(CNF).After depositing CNF,the microscopic morphology of CL is changed,which is beneficial to enhance the light absorption ability in the whole spectrum range.A solar steam generation device(SSGD)based on interface heating was constructed by using CL/CL-CNF as photothermal conversion material,cotton pad as water transfer layer and EVA foam as heat insulation layer.Under 1 k W·m^-2 light intensity,the water evaporation rate of CL-CNF SSGD can reach 1.72 kg·m^-2·h^-1,and the corresponding photothermal conversion efficiency is 92.5%.In addition,the application of SSGD in seawater desalination,heavy metal ion wastewater and dye wastewater was verified.After treatment,the concentration of ions in purified water is far lower than that in drinking water standard.The color of dye wastewater becomes colorless.Finally,CL-CNF SSGD displayed a stable performance in recycling and longtime usage.(3)A low-cost and high-performance carbonized green algae solar steam generator(CGA SSG)was prepared using biomass green algae(GA)as precursor for gold smelting wastewater treatment.The CGA SSG shows excellent light absorption(98%),better hydrophilicity and high water evaporation rate(1.66 kg·m^-2·h^-1).CGA SSG can achieve the non-selective removal of heavy metal ions(Cu²⁺,Pb²⁺,Zn²⁺,Hg²⁺)and CN^-in wastewater,and the removal rate is up to 99%,the ion concentrations of the heavy metal ions and CN^-are lower than the concentration standard of drinking water.In addition,the p H value of gold smelting wastewater is 8.15,while the p H value of pure water produced by solar steam generator is 7.77,which realizes the transition from weak alkali to neutral.The method can also be used for treating various sewage(dye wastewater and domestic sewage),and the obtained purified water can achieve the purpose of direct drinking.(4)A natural integrated three-dimensional solar vapor generator(3D SVG)based on carbonized cattail(CCT)was fabricated using biomass cattail(CT)as precursor for efficient solar steam generation.The fine morphology of CCT endows it high light absorbance,excellent hydrophilicity,sufficient water transport channel and steam escape channel,which is conducive to improve the water evaporation performance of CCT.The CCT was fixed by the PS foam in the beaker to construct natural integrated SVG and the exposure height of CCT in the environment was 0,5 and 10 cm to verify the enhancement effect of environmental energy on water evaporation.Under the irradiation of 1 k W·m^-2,10 cm-CCT SVG obtained the highest water evaporation rate,the energy efficiency exceeded the theoretical limit(105.8%),and the maximum water evaporation rate was4.12 kg·m^-2·h^-1.This is because in vertical sunlight,the top surface of 10 cm-CCT SVG absorbs sunlight and converts it into heat,which naturally drives the top surface temperature higher than the ambient temperature,resulting in energy dissipation to the environment.At the same time,the side as a cold evaporation surface cannot absorb sunlight,so that the side temperature is lower than the ambient temperature.Therefore,driven by the temperature difference,the energy in the environment is transferred to the side,so as to obtain additional energy other than sunlight,which makes SVG show extremely high water evaporation rate and energy efficiency.In addition,a simple outdoor evaporation water collection device was designed and manufactured to evaluate the daily water yield(8.32 kg·m^-2·d^-1),which can meet the drinking water demand of 40 adults for a day.