Interfacial solar desalination using plasmonic metal semiconductors is a valuable process for freshwater production. However, the design of a sustainable and efficient photothermal evaporator is still challenging. In the present research, polyethylene terephthalate waste bottles were upcycled into carbon foam (CF) and further functionalized with CuS nanoflakes as a photothermal layer. Analytical characterizations (X-ray diffraction, Fourier transform infrared spectroscopy, Scanning electron microscopy, and scanning transmission electron microscopy–high-angle annular dark field) demonstrated the successful decoration of two-dimensional Covellite CuS nanoflakes on graphitic CF having microporous channels. UV/vis spectroscopy measurements show enhanced optical absorption with CuS/CF of up to 95% compared to bare CF (72%). The photothermal desalination experiment displayed an improved evaporation rate of 1.90 kg m⁻² h⁻¹ for the CuS–CF compared to 1.58 kg m⁻² h⁻¹ for the bare CF and CuS 1.41 kg m⁻² h¹, reveling the excellent water evaporation efficiency of 91%. The obtained results suggested that the design of CuS-functionalized CF derived from waste plastic for solar desalination is a useful strategy to produce fresh water from the upcycling of waste materials and a good example of circular economy through the development of engineered composite systems.