Synthesis, characterization, and photocatalytic activity of stannum-doped MgIn2S4 microspheres

Highlights: • A series of Sn²⁺ doped MgIn₂S₄ photocatalysts were prepared. • MgIn₂S₄ doped with Sn²⁺ ions exhibit significantly enhanced photocatalytic activity. • The doping effect of Sn dopant was systematically investigated and discussed. -- Abstract: A series of Sn²⁺ doped MgIn₂S₄ photocatalysts were prepared via a facial hydrothermal method. The Sn dopants substitute the sites of Mg atom in MgIn₂S₄ unit cell, but not alter the crystal structure, demonstrated by the results of XRD and XPS. Compared to pristine MgIn₂S₄, Sn-doped MgIn₂S₄ samples exhibit significantly enhanced photocatalytic CO₂ reduction activity. With increasing the Sn dopant content, the CO₂ conversion rate first ascends, achieving the maximum rate at Sn-MgIn₂S₄-2 sample, and then decreases. After illumination for 4 h, the highest yield of CO and CH₄ for Sn-MgIn₂S₄-2 sample reaches about 3.35 and 3.33 times higher than that of pristine MgIn₂S₄. The theoretical results based on density functional theory calculations reveal that Sn doping in MgIn₂S₄ tunes the band structure from the direct-transition of MgIn₂S₄ to indirect-transition, diminishes band gap and extends the light absorption range, reduces the effective masses of holes and promotes the migration of photoinduced carriers. The experimental results also demonstrate the positive role of Sn dopant in accelerating the separation and transportation of charges, and improving CO₂ adsorption ability. This work systematically investigates and discusses the Sn²⁺ doping effect in MgIn₂S₄ on crystal structure, lattice variations, electronic band structures, CO₂ adsorption ability, and photocatalytic CO₂ reduction activity, which can provide a new hint for the fabrication of efficient photocatalyst by metal ion doping.