Directional construction of magnetic high-entropy LDHs from scandium-rich bauxite residue: Magnetic field-photo-thermal synergistic catalysis for CO2 reduction

Addressing dual environmental challenges of global red mud accumulation (>150 million tons/year globally) and lithium battery waste disposal, this study proposes an innovative “solid waste synergy and energy-field coupling” strategy. Utilizing Sc-rich red mud from Boshan bauxite (Shandong Provience, P. R. China) (containing Ca 2+ , Al 3+ , Fe 3+ , Ga 3+ , Sc 3+ ) synergistically with Co 2+ from battery liquid waste, we constructed high-entropy layered double hydroxide CoCaAlFeGaSc-LDHs via co-precipitation. The material exhibits broadband near-infrared absorption through Co 2+ d - d transitions, enabling instantaneous photothermal response under NIR laser irradiation and enhancing CH 4 conversion by 7.9-fold. Fe 3+ /Ga 3+ facilitates ultraviolet and visible-light harvesting, while Sc 3+ effectively suppresses the formation of hydroxyl (•OH) and superoxide (•O 2 − ) radicals. This synergistic mechanism significantly enhances both the CH 4 production yield (2.1×) and selectivity (reaching 89 %), driving the CO 2 reduction pathway efficiently along the critical intermediates •HCOO and •CH 3 O toward CH 4 formation. The ferromagnetism ( M s  = 76.7 emu·g −1 ) enables the material to markedly enhance the separation and suppress the recombination of photogenerated charge carriers under a 500 mT magnetic field, which in turn leads to a substantial gain in photocatalytic efficiency. CH 4 yield reaches 36.8 μmol·h −1 ·g −1 —1.46-fold enhancement compared to non-magnetic field conditions. The terminal residue contains no residual heavy metal ions, and insoluble SiO 2 and TiO 2 can be safely returned to the environment, establishing a closed-loop solution for waste valorization while pioneering magnetic field-enhanced photothermal catalysis.