<![CDATA[This study investigates the selective adsorption behavior of freshwater macroalgae Cladophora sp. for the removal of mixed dye systems containing cationic (rhodamine B (RB), malachite green (MG), and methylene blue (MB)) and anionic dyes (congo red (CR) and remazol red (RR)). The biomass was characterized using Fourier-transform infrared spectroscopy (FTIR), Brunauer–Emmett–Teller (BET) analysis, and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM–EDX), confirming the presence of abundant functional groups and a porous surface structure suitable for adsorption. The point of zero charge (pHpzc) was determined to be 6.5, indicating that the adsorbent surface becomes negatively charged under near-neutral conditions. Selective adsorption was evaluated using UV–Visible spectrophotometry combined with Gaussian peak deconvolution to distinguish individual dye contributions in mixed systems. The results showed a significantly higher adsorption efficiency for cationic dyes, with methylene blue exhibiting the highest removal efficiency (93.56%), followed by malachite green (91.48%) and rhodamine B (51.09%). In contrast, anionic dyes showed considerably lower adsorption, with congo red (33.99%) and remazol red (32.68%). The enhanced selectivity toward cationic dyes is primarily attributed to electrostatic attraction between the negatively charged adsorbent surface and positively charged dye molecules, supported by additional interactions such as π–π stacking and hydrogen bonding. These findings demonstrate that Cladophora sp. is a promising low-cost and sustainable bioadsorbent with selective adsorption capability, making it suitable for the treatment of complex dye-contaminated wastewater.]]>
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