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In this work, ZnO, SnO₂, and their mixed ZnO-SnO₂(25%) nanoparticles (NPs) were successfully green synthesized in a straightforward manner with a low-cost and environmentally friendly approach using a banana peel extract. The synthesized nanophotocatalysts were characterized using various techniques including FTIR, XRD, UV-Vis, TEM, SEM, BET, PL, EDS, and TGA. The characterization results showed that the ZnO and SnO₂ powders were crystallized in a hexagonal wurtzite and rutile-type tetragonal structures, respectively, and their mixed ZnO-SnO₂(25%) NPs contain both structures. Also, it was found that the addition of SnO₂ into the ZnO structure reduces the PL intensity of the latter, confirming better separation of electron/hole pairs. The average particle size of a ZnO-SnO₂(25%) NP photocatalyst was found to be 7.23 nm. The cationic dyes methylene blue (MB) and crystal violet (CV) as well as the anionic dyes naphthol blue black (NBB) and Coomassie brilliant blue R 250 (CBB) were employed as model dyes to assess the dye removal efficiencies of the biosynthesized nanophotocatalysts under sunlight. In all cases, the mixed ZnO-SnO₂(25%) NP photocatalyst showed much better photocatalytic activity than individual photocatalysts. The degradation percent of dyes using ZnO-SnO₂(25%) NPs ranged between 92.2% and 98%. The efficient photocatalytic activity of ZnO-SnO₂(25%) NPs is attributed to the effective charge separation and reduced electron/hole recombination rate. The kinetic study results conformed to a pseudo first-order reaction rationalized in terms of the Langmuir–Hinshelwood model. Furthermore, the results showed that the ZnO-SnO₂(25%) NP photocatalyst is highly stable and could be recycled several times without a noticeable reduction in its catalytic activity towards dye removal. Full article

The crystal structures of red and blue-black tin(II) oxide, SnO, have been determined for the first time by single-crystal X-ray diffraction. Blue-black SnO crystallizes in the tetragonal space group P4/nmm, representing a layer structure consisting of the square–pyramidally coordinated tin and slightly distorted tetrahedrally coordinated oxygen atoms, in accordance with previous results. In contrast, red SnO crystallizes in the orthorhombic centrosymmetric space group Pbca rather than in the non-centrosymmetric space group Cmc2₁, as assumed for a long time. Its layer structure consists of very regular, trigonal–pyramidally coordinated tin atoms as well as trigonal–planar coordinated oxygen atoms. Special care was taken on space group determination, including lattice centering. C-centering could be excluded because of systematic absence violations detected when collecting and processing a primitive triclinic dataset and by generating precession images. In the absence of meaningful extinction conditions resulting from the very small crystal under examination, the structure was initially solved and refined in the triclinic space group P1. Subsequently, the observed atom coordinates were used to reconstruct the actual symmetry skeleton. The various possibilities to identify the correct space group starting from the triclinic solution are demonstrated, and the unique structural features of the crystal structure are visualized. Full article