Adsorption of crystal violet dye by biochar made from coffee groundLe Hong Phuc, Nguyen Quan Hien, Bui Thi Hoa, Nguyen Ngoc Truc My, Thai Thi Kim Ngan and Bui Xuan VuongE3S Web Conf., 626 (2025) 03001DOI: https://doi.org/10.1051/e3sconf/202562603001