Nugroho, F. L., D. Rusmaya, and A. Deviliana. “Removal of Reactive Yellow 4R Azo Dye from Synthetic Aqueous Solution by Alkali Hydrothermally Activated Fly Ash ”. Journal of Engineering and Technological Sciences, vol. 54, no. 3, June 2022, p. 220312, doi:10.5614/j.eng.technol.sci.2022.54.3.12.