Preparation Of Nickel Black Photothermal Materials And Study On Solar Desalination Performance

Water is the source of life and the artery of social and economic development.Although 70%of the earth's area is covered by water,the fresh water that people rely on for survival only accounts for 2.5%to 3%.With the rapid population growth,global environmental changes and the large-scale development of industry,the whole world today faces a serious shortage of fresh water resources.According to the current situation,about 70%of humans live in less than 120 kilometers from the sea,so the vast sea is used as a source of fresh water,and desalinated seawater is a favorable supplementary measure for existing water sources.Under certain conditions,it can satisfy people's living water demand.In recent years,renewable energy as a clean and friendly energy source,the use of renewable energy to operate small-scale desalination devices has received increasing attention,and in the future will be an important means of emergency water supply for coastal cities with difficult water transfer.Combining renewable energy such as solar energy,wind energy and geothermal energy with desalination technology system is expected to solve the problem of water shortage and is a feasible solution to the problem of climate change and water shortage.Solar thermal water evaporation is a clean,sustainable and energy-saving way to generate fresh water compared with the traditional way.Electro-blacks,for example,nickel black have been commercialized for the solar water heater,but it has not been used in the field of seawater desalination,Inspired by this,We have studied the synthesis process of nickel black photothermal materials and seawater desalination properties in ordert to achieve energy savings and reducing global environmental pollution.In this paper,nanostructured nickel hydroxide Ni?OH?₂ was grown on a foamed nickel substrate?NF?by hydrothermal synthesis at a ratio of nickel nitrate to hexamethyl enetetramine of 1:2.After that,the precursor of nickel-hydroxide foam Ni?OH?₂/NF composite porous material was treated with high temperature including explore different calcination temperature and time,so that the Ni?OH?₂ could be transformed into NiO nanostructures with different thickness,and a series of physical characterization and performance tests were carried out to find the optimal calcination temperature and time.Finally,the hydrothermal reduction method is used to reducethe NiO/NF to form a nanostructural Ni-NiO_x/NF.These include adjusting the concentration and time of the reducing agent hydrazine hydrate.SEM and TEM test Ni-NiOX/NF showed two morphologies,which is composed of Ni metal nanoparticles and NiO_x with defects.On the one hand,The Ni-NiO_x/NF exhibits high solar absorbance due to the plasmonic effect of metallic Ni nanoparticles and surface carrier migration caused by defective NiO_x,the absorption rate reaches90.31%.On the other hand,it shows a low thermal conductivity which minimizes heat transfer from the foamed nickel layer to a large number of water bodies below,that will beneficial to the generation of the localized high temperature.The as-prepared Ni-NiO_x/NF can self-float on the water surface without any materials due to the high contact angle.It has the ability to heat the self-sustaining interface on the water surface,there by improving the photothermal conversion efficiency.The high porosity of the nickel foam substrate not only achieves high light capturing ability,but also promotest fluid flow into the structure to supplement surface water evaporation.Various advantages the average water evaporation rate of as-prepared Ni-NiO_x/NF reaches 1.41 kg m^-2 h^-1 and the average solar conversion efficiency is about 93.88%.The best sample exhibits 1.45 kg m^-2 h^-1 and 96.30%for the water evaporation rate and solar conversion efficiency,respectively.And the obtained material Ni-NiO_x/NF has obvious effect on the desalination of Bohai Sea water,and the concentration of each ion is reduced by about 3 orders of magnitude,which is lower than the standards of World Health Organization?WHO?and US Environmental Protection Agency?EPA?.And through the cycle stability test,it shows it has good stability and high evaporation rate in both seawater and fresh water.Therefore,this paper presents a high-efficiency solar water evaporation material that maximizes the use of solar energy and minimizes thermal energy loss.It can be applied to seawater desalination on a large scale and solve the problem of lack of fresh water resources.