Structural Design And Photothermal Conversion Properties Of WO_3-x/Ag/PbS Composites

Solar steam conversion technology is a green and sustainable technology that collects solar energy to evaporate water.With the rapid development of industrialization,human beings are facing the embarrassing situation of energy depletion and water shortage.Solar steam conversion technology can play an important role to solve the above problems.In the past,the solar evaporation technology mainly absorbed the solar energy and heated all volume of water.However,the heated all volume of water can cause the large heat losses.In order to solve this problem,the interfacial heating was proposed in the early nineteenth century,which heating only a small portion of the water at the interface to generate steam.The development of interface heating technology has greatly improved the efficiency of steam conversion,and further promoted the application of solar steam conversion technology in daily life.Due to the poor photothermal conversion efficiency and unreasonable design of most solar evaporators,their industrial promotion is greatly restricted.Therefore,how to select suitable materials,optimize the structure and stabilize the device are important issues in this field.In recent years,inorganic semiconductors,such as Ti O₂,Co S,Cu_2-xS,and WO_3-x,are widely used in the field of photothermal.Among them,the semiconductor WO₃is considered to be a strong photothermal candidate due to its nontoxicity,small band gap,and wide light absorption range.In this work,the effects of oxygen vacancy-rich WO₃decorated nickel foam（NF）and WO_3-x/Ag/PbS decorated NF solar evaporators on their light absorption rate and photothermal conversion efficiency were investigated.The main research contents are as follows:（1）Through a simple hydrothermal and annealing method.a WO_3-xwith rich in oxygen vacancies and a unique structure of"nanorod arrays grown on nanosheets"was designed on the NF surface and used as a light absorbing material.The unique three-dimensional（3D）hierarchical porous structure of WO_3-x/NF solar vaporizer can provide channel vapor escape and enhance optical trapping through multiple scattering effects,and the localized surface plasmon resonance（LSPR）effect of WO_3-xalso contributes to increase light absorption in the full solar spectrum.The prepared WO_3-x/NF solar evaporator has a high solar absorption rate（95%）,and the evaporation rate at one solar light intensity(1 k W m^-2)is 1.50 kg m^-2h^-1.The photothermal conversion efficiency is about 88%.The results of water purification show that the WO_3-x/NF solar evaporator has a significant effect on seawater desalination,and there is no obvious salt accumulation.First-principles calculations suggest that the narrower bandgap of WO₃containing oxygen vacancies is more favorable to absorbe solar energy across the entire spectrum.（2）Silver nanoparticles（Ag NPs）were mounted on WO_3-x/NF by photoreduction method,and then PbS quantum dots were sprayed on one side of WO_3-x/Ag/NF by spraying method to form Janus-type WO_3-x/Ag/PbS/NF heterocomposite structure.Ag NPs have strong absorption in the ultraviolet range,PbS quantum dots have strong absorption near visible light,and WO_3-xhas strong absorption near visible light and near-infrared.The combination of the three as light absorbers can improve the overall Absorbance in the solar spectral range.The Janus structure WO_3-x/Ag/PbS/NF is conducive to the escape of steam,avoids the accumulation of salt,and has a certain self-cleaning ability.The evaporation rate under 1 Sun is 1.9 kg m^-2h^-1,and the photothermal conversion efficiency is as high as 94%.It also has excellent performance in heavy ion water desalination and organic matter treatment.The first-principles calculations of the photo-generated carrier migration process between the heterocomposite structures indicate that the three have a certain synergistic ability and promote light absorption.