Tuning the properties of hydrothermally synthesized Cu2ZnSnSe4 (CZTSe) nanopolygons by sulphur doping for visible-light-driven photocatalytic degradation of cationic and anionic dyes

Sulphur (S) doping in kesterite CZTSe has been performed via a hydrothermal method. X-ray diffraction (XRD) study indicated the particles have grown in a tetragonal phase and the shift towards higher two theta values upon S doping confirmed the formation of Cu₂ZnSn(SSe)₄ (CZTSSe) alloy. Raman analysis corroborated the XRD results, ruling out the possible presence of secondary phases. Polygonal-shaped nanoparticles of varying dimensions are formed, agglomerated as cauliflower-like structures (scanning electron microscopy). The transmission electron microscopic (TEM) images provided enhanced view about the morphology revealing 2D nature of the nanopolygons. Average particle dimensions of CZTSe particles are ~ 20 nm and that of CZTSSe are ~ 15 nm. Both CZTSe (E_g ~ 1.2 eV) and CZTSSe (E_g ~ 1.45 eV) are visible light active, with CZTSSe nanoparticles band gap blue shifted. CZTSSe photodegraded 98% methylene blue (MB) and 80% methyl orange (MO) under visible light illumination in just 120 min. The use of a convex lens enhanced the catalysts activity, degrading whole of MB dye in just 90 min. The active species corresponding to the photocatalysts are superoxide free radicals which were confirmed by the scavenger test. High efficiency, better rate constant values together with good stability and reusability make the photocatalysts prospective material for futuristic environmental remediation.