Energy-Efficient Molten-Salt-Shielded Synthesis of Ti3C2Tx MXene from Low-Cost Precursors and Its Integration into a Carbonized Luffa Sponge Composite for High-Performance Solar-Driven Interfacial Evaporation and Desalination

Abstract

Scalable, energy-passive desalination technologies are urgently needed to address the growing freshwater crisis, particularly in off-grid and resource-constrained communities. This study develops an integrated materials pathway spanning the energy-efficient synthesis of Ti₃C₂Tₓ MXene from low-cost precursors to its application in a high-performance solar desalination platform. The Ti₃AlC₂ MAX phase was synthesized at 1100°C through a molten-salt-shielding synthesis (MS3) route using titanium dioxide (TiO₂), aluminum, and activated carbon in a NaCl–KCl eutectic medium with a 7:3 salt-to-precursor ratio, reducing the synthesis temperature by approximately 600°C relative to conventional solid-state routes. Selective HF/HCl etching subsequently converted the MAX phase into multilayer Ti₃C₂Tₓ MXene. Successful conversion was confirmed by a characteristic (002) diffraction shift to 7°, accordion-like morphology, disappearance of Al–C bonds, and a localized surface plasmon resonance peak at 792 nm. The MXene was deposited onto a carbonized luffa sponge (CLS) through controlled dip coating to produce an MC-CLS photothermal evaporator. Characterization revealed uniform MXene coverage, broadband solar absorptance of ≥0.95 across 200–1100 nm, retained hydrophilic surface terminations, and substantially enhanced thermal stability. Under one-sun illumination (1 kW m⁻²), MC-CLS achieved an average evaporation rate of 2.12 kg m⁻² h⁻¹ and a solar-to-steam conversion efficiency of 95%. The evaporation rate increased near-linearly to 7.79 kg m⁻² h⁻¹ at 5 kW m⁻², while the evaporator retained more than 94% of its performance after 21 wetting–drying cycles. Inductively coupled plasma optical emission spectrometry further confirmed that condensate produced from simulated seawater consistently met World Health Organization drinking-water standards for Na⁺, K⁺, Ca²⁺, and Mg²⁺. These findings establish an integrated pathway from low-cost MXene synthesis to solar water purification, offering a promising approach to scalable, durable, and energy-autonomous freshwater production.