Energy-Efficient MIL-53(Fe)/Sn₃O₄ Nanosheet Photocatalysts for Visible-Light Degradation of Toxic Organics in Wastewater

The fabrication of photocatalysts with preferable degradation ability is critical to purify wastewater. MIL-53(Fe), as a representative Fe-based metal–organic framework (Fe-MOF), has been widely used in photocatalysis due to its excellent intrinsic characteristics. However, the inadequate electron number in MIL-53(Fe) has restricted the ability of photodegradation of organic pollutants. Herein, desirable, energy-efficient, and environmentally friendly MIL-53(Fe)/Sn 3 O 4 nanosheet photocatalysts were first constructed by the solvothermal method. The characterization results indicated that the MIL-53(Fe)/Sn 3 O 4 -5 (5 wt % Sn 3 O 4 ) catalyst exhibited optimal photoelectric properties and maintained a relatively regular morphology. Moreover, the prepared MIL-53(Fe)/Sn 3 O 4 -5 exhibited preferable photodegradation ability for dyes and antibiotics under visible light, and the maximum photodegradation capacity for malachite green, methylene blue, tetracycline, ciprofloxacin, and ofloxacin could reach 96.9, 88.2, 70.3, 83.5, and 88.1%, respectively. The initial pH, photocatalyst dosage, and initial concentration were comprehensively investigated for degrading malachite green. In addition, we also explored the prepared catalyst for the removal of malachite green from different actual wastewater samples. After three cycles, the degradation efficiency of malachite green by MIL-53(Fe)/Sn 3 O 4 -5 decreased very little, exhibiting good reuse performance. The enhanced photodegradation efficiency of MIL-53(Fe)/Sn 3 O 4 -5 could be attributed to the construction of heterojunctions derived from a compact joint interface between Sn 3 O 4 and Fe-MOF, which expedited the separation ability of photogenerated carriers and broadened the visible response range. The active species trapping experiments and electron spin-resonance results determined that many active species (h +, •OH, and •O 2 – ) were involved in the photocatalytic process. Correspondingly, a convincible photodegradation mechanism between Sn 3 O 4 and MIL-53(Fe) was proposed according to the experimental results. This study demonstrates that the fabricated Sn 3 O 4 and MOF composites can provide a feasible solution for the purification of wastewater.