One step synthesis of novel CuS-ZnS/SiO2@n-octadecane nanocapsules with full spectral absorption range and high photothermal conversion efficiency

•CuS-ZnS coated SiO2 shell PCM nanocapsules were synthesized.•One step hydrothermal codeposition method is simple and effective.•Efficient absorption and transformation of full spectrum benefits from CuS-ZnS. In this manuscript, CuS-ZnS/SiO2@n-octadecane nanocapsules were prepared by a simple one-step Cu2+ and Zn2+ co-deposition method. The results of XRD, SEM, TEM, FTIR and XPS show that nanocapsules composed of CuS-ZnS/SiO2 shell and n-octadecane core material were successfully prepared, and the particles deposited was proved to be composite structure of CuS-ZnS. The solution concentration, reaction temperature and pH value have significant effects on the morphology of the nanocapsules prepared. The appropriate conditions are 0.02 mol/L CuSO4, 0.02 mol/L Zn(CH3COO)2, 60 °C, and no additional pH adjustment. Under the optimum conditions, the melting enthalpy reached 45.11 J/g, and after 100 times of cold and hot cycles, the melting enthalpy of the sample only decreased by 3.2%, showing good thermal stability. The CuS-ZnS composite structure makes CuS-ZnS/SiO2 nanocapsules exhibit a wider spectrum absorption performance. The absorption effect of CuS-ZnS/SiO2 nanocapsules to ultraviolet light is significant, compared to the slight reducing of the visible light, while the absorption of near-infrared light is strong. The photothermal conversion efficiency of the samples is significantly improved from 9.7% to 86.6%. Hence, the prepared nanocapsules achieve full spectral absorption, which has a broad application prospect in solar thermal utilization.