Enhanced Photothermal Conversion through 2D/0D Nano-Heterojunction Engineering for Highly Efficient Solar Desalination

Two-dimensional (2D) materials are promising candidates for solar-driven desalination. However, conventional photothermal 2D materials like transition metal carbides and nitrides (MXenes) as well as transition metal dichalcogenides (TMDs) suffer from major limitations such as their complex synthesis and low photothermal conversion efficiency. In contrast, metal phosphorus trichalcogenides (MPCh₃) do not display the same drawbacks and possess widely tunable bandgaps (1.2-3.5 eV), making them ideal candidates for solar desalination. Moreover, their properties and applications related to light-matter interactions can be further enhanced by coupling with other low-dimensional nanostructures, tailoring hybrid van der Waals heterostructures of mixed dimensionality. Herein, we report the synthesis of FePS₃ nanosheets/carbon nanodots (CNDs) 2D/0D nanoheterojunctions and their photothermal response when integrated into a 3D photothermal evaporator. These nanoheterojunctions exhibited high photothermal conversion performance, with an average absorbance of 90.6% from the UV to the NIR and a temperature increase of 42 °C over the blank control under 1 sun illumination for 300 s. A high water evaporation rate of 1.68 kg m^-2 h^-1 was observed under the same condition. Photothermal conversion and water evaporation experiments, along with femtosecond transient absorption spectroscopy (fs-TAS), photoluminescence (PL) analysis, and finite-difference time-domain (FDTD) simulations, revealed that the incorporation of CNDs and formation of the nanoheterojunction synergistically enhance localized heating and light absorption, improve trapping efficiency, and optimize nonradiative transition pathways. This study demonstrates the disruptive potential of the rational design of high-performance 2D material hybrids through MPCh₃-based nanoheterojunction engineering, unveiling its transformative capability for use in solar desalination and photothermal technologies.