Degradable Ti₃C₂T_x MXene Nanosheets Containing a Lignin Polyurethane Photothermal Foam (LPUF) for Rapid Crude Oil Cleanup

As two-dimensional (2D) nanomaterials with high photothermal conversion performance, MXenes have great potential for applications in photothermal-assisted crude oil recovery. In this study, MXene nanosheets modified a lignin-based polyurethane foam obtained with solar-to-heat conversion properties for heavy oil recovery. The adsorbent achieved a high solar absorption rate (>95%), and its surface maximum temperature reached up to 83.5 °C owing to the great solar-to-heat effect of MXenes. Due to the superb dispersibility of MXenes in polyol, the resulting bio-based foam adsorbent had a high thermal conductivity. Moreover, with the increase of temperature, the viscosity of the heavy crude oil decreases, which enables the adsorbent to adsorb more than seven times (7.6 ± 0.2 g/g) its weight of crude oil under 1 sun illumination (1.00 kW/m2) in 4 min. In addition, Ti3C2Tx MXene nanosheets containing lignin-based adsorbents readily degraded in alkaline solutions (degradation efficiency > 93%, in a methanol/0.5 mol/L NaOH aqueous solution mixture (1:1, v/v) for 8 h at 60 °C). The molecular dynamics simulation revealed that lignin had lower interaction energy with the solvent solutions when methanol was present, allowing the lignin molecules to unfold and make more contact with the solvent molecules. As a result, the β-O-4 bond of lignin is more likely to be exposed to accelerate the degradation process. The solid residues of degradation were only titanium dioxide (TiO2) nanoparticles, which were harmless to the environment. With their excellent rapid heavy oil removal performance, degradability, and environmental friendliness, these bio-based adsorbents pinpoint a promising solution to clean up high-viscous crude oil spills.