Comparative Adsorption Removal of Sildenafil and Tadalafil Using Biomass-Derived Activated Carbon and DDAB-Modified Montmorillonite

This study evaluated and compared two distinct adsorbent systems for removing the phosphodiesterase type-5 (PDE-5) inhibitors sildenafil (SILD) and tadalafil (TAD) from water, using biomass-derived activated carbon (AC) and montmorillonite (MMT) in either its raw or didodecyldimethylammonium bromide (DDAB)-modified form. Spent brewery grains (SBG) were used as a renewable precursor to produce AC via conventional and microwave-assisted pyrolysis, while raw MMT and DDAB-modified MMT were investigated as alternative surface-engineered adsorbents. Batch adsorption experiments showed that AC produced via microwave-assisted pyrolysis exhibited higher removal efficiency under the investigated conditions compared with AC produced via conventional pyrolysis. Microwave-derived AC reached equilibrium within 2 h, achieving removal efficiencies of 90.3 ± 0.1% for SILD and 95 ± 2% for TAD. Under the specific adsorption conditions studied, the Langmuir-estimated adsorption capacities were 207 ± 10 mg g−1 and 119 ± 6 mg g−1, respectively. The DDAB-modified MMT also significantly outperformed the raw MMT, reaching equilibrium within 1 h, with removal efficiencies of 84.9 ± 0.1% for SILD and 91 ± 3% for TAD, and Langmuir-estimated adsorption capacities of 39 ± 3 and 38 ± 1 mg g−1, respectively. These results demonstrate that microwave-derived AC and DDAB-modified MMT represent adsorbent systems exhibiting different adsorption profiles and provide comparative information on the adsorption behaviour of materially distinct adsorbents for removing pharmaceutical contaminants from water.