Influence of zinc doping on the photocatalytic activity of nanocrystalline SnO₂ particles synthesized by the polyol method for enhanced degradation of organic dyes

Undoped and Zn-doped SnO₂ nanocrystals were prepared using a straightforward polyol method and the influence of the doping on the structural, textural, and optical properties was carefully studied. X-ray diffraction (XRD) patterns revealed after annealing the formation of cassiterite, i.e. rutile-like, tetragonal SnO₂ crystallites and the absence of any crystalline zinc phase whatever the doping concentration. However, the average crystallite size decreased from 9 to 6.5 nm when the doping concentration increased from 0 to 10 at%, respectively. Furthermore, Transmission Electron Microscopy (TEM) and N₂ sorption porosimetry showed that all samples prepared were made of an aggregated network of almost spherical nanoparticles, the size of which decreased when increasing the doping concentration up to 10 at%. The presence of SnO₂ and zinc oxide species was assessed by EDX (Energy Dispersive X-ray spectroscopy) analysis. According to UV–visible absorption measurements, this decrease in nanoparticle size was accompanied by a decrease in the band gap value from 3.50 eV for undoped SnO₂ to 3.17 eV for 10 at% Zn-doped SnO₂. The photocatalytic properties of undoped and Zn-doped SnO₂ nanoparticles were evaluated by studying the photodecomposition of methylene blue (MB) and methyl orange (MO) as organic pollutant models. The 10 at% Zn-doped SnO₂ nanoparticles showed the highest photocatalytic activity for both MB and MO decomposition and led to an almost complete discoloration of MB solutions, i.e. 98%, after irradiation of 120 min and to an apparent MB degradation constant rate reaching 0.058 min⁻¹. - Highlights: • Nanocrystalline and nanoporous Zn-doped SnO₂ materials prepared by the polyol route. • Fine tuning of the textural and optical properties by varying the zinc content. • Efficient photocatalysts for anionic and cationic organic dyes degradation in water. • The 10 at% Zn-doped SnO₂ material showed the best photocatalytic performances.