Synthesis And Photothermal Properties Investigation Of Hollow Cu₇S₄ Micro-/Nanoparticles And Its Composites

Copper sulfides(Cu_2-xS),a non-stoichiometric p-type semiconductor,exhibit strong absorptivity for solar radiation in the near infrared range due to its localized surface plasmon resonance(LSPR)property,which makes them widely used in a broad range of photothermal conversion devices and technologies.Since the physical and chemical properties of inorganic micro-/nanomaterials can be significantly affected by their morphology and size,the controlled synthesis of Cu_2-xS is necessary for studying the relationship between its properties and morphology,size.In addition,some disadvantages of copper sulfides,such as poor thermal conductivity as well as narrow absorption spectrum,limit their applications in such fields as energy storage and photothermal conversion.Therefore,combining Cu_2-xS with carbon-based nanostructures,which is a kind of materials with good thermal conductivity,high photothermal conversion efficiency as well as excellent photothermal stability can greatly widen the applications of this composites.In this paper,we managed to fabricate uniform cubic cuprous oxide(Cu₂O)and Cu₇S₄ micro-/nanocrystals by facile aqueous wet-chemical methods.At first,cubic Cu₂O micro-/nanocrystals with different sizes were obtained by changeing the concentration of sodium hydroxide in the reaction solution.Then,hollow Cu₇S₄ micro-/nanocrystals were synthesized by template methods with the as-prepared cubic Cu₂O as sacrificial templates.By controlling the type of sulfides,the release rate of sulfur ions and the size of Cu₂O templates,Cu₇S₄ micro-/nanocrystals with different morphologies and different particle sizes can be obtained.Specifically,we prepared flower-liked,nanosheets-constructed,spherical and polyhedral hollow Cu₇S₄ crystals,and spherical Cu₇S₄ particles with the diameter in the range from 32 nm to 715 nm.We investigated the photothermal properties of Cu₇S₄ micro-/nanocrystals with different sizes.It was founded that the light absorption rate of Cu₇S₄ increases as the decrease of its particle sizes.When the particle diameter is about 32 nm,the light absorption rate of Cu₇S₄reach 97%.When the propous,super-hydrophilic composite films,fabricated by depositing as-prepared Cu₇S₄ particles on filter paper through vocumn filtration,was used for light-induced water evaporation,the maximum evaporation rate was 1.355 kgm^-2h^-1 under a simulated solar irradiation,and the corresponding photothermal conversion efficiency was 85.0%.By utilizing the electrostatic adsorption between copper ions and the oxygen-containing functional groups of graphene oxide(GO)and hydroxyl multi-walled carbon nanotubes(CNTs),Cu₇S₄crystals were successfully grown on reduced graphene oxide(r GO)and on the outside wall of the CNTs in situ.Thus,Cu₇S₄/r GO composite with sandwich-liked structure and Cu₇S₄/CNTs composite with bead-string structure were prepared,respectively.Similarly,those composites were assembled with filter paper to form composite films for photothermal property characterization.Among them,the light absorption rate of Cu₇S₄/r GO composite can reach 95%.When this composite was used for light-induced water evaporation,its solar photothermal conversion efficiency is 78.1%under a simulated solar irradiation.The light absorption rate of Cu₇S₄/CNTs composite is over 97%,and its photothermal conversion efficiency is 80.9%under the same condition.