Indah, D.R. et al. 2026. Adsorption of Copper (Cu²⁺) Ions from Industrial Wastewater : A Systematic Literature Review on Adsorbent Performance. Hydrogen: Jurnal Kependidikan Kimia. 14, 5 (Oct. 2026). DOI:https://doi.org/10.33394/hjkk.v14i5.23047.