Direct sunlight-active Na-doped ZnO photocatalyst for the mineralization of organic pollutants at different pH mediums

•Na-doped ZnO (Na-ZnO) nanosheet was prepared and used as a photocatalyst for methylene blue dye photocatalytic degradation.•Density functional theory (DFT) calculations used for proving the electronic and crystal structures of Na-ZnO.•Na-ZnO has high photocatalytic activity and stability at different pH's.•Under direct sunlight, Na-ZnO decolorized more than 99.5% and mineralized 98.3% of MB.•Na-ZnO have high photostability reach to 7 recycle with the same efficiency.