Efficient Adsorption of Food Colorants onto Activated Carbon Derived from Haematococcus pluvialis Residue: Performance and Mechanism
Azo food colorants are persistent aquatic pollutants posing risks to ecosystems and human health. Utilizing biomass waste to produce low-cost activated carbon offers a sustainable strategy for their removal. In this study, activated carbon (HPR-AC) was synthesized from Haematococcus pluvialis residue via phosphoric acid activation, and its adsorption performance was evaluated using Sunset Yellow (SY), Ponceau 4R (P4R), and Tartrazine (TY) as model pollutants. The effects of solution pH, adsorbent dosage, initial dye concentration, and temperature on adsorption efficiency were systematically examined. Characterization by BET, FTIR, XRD, and XPS revealed that HPR-AC possesses a high specific surface area and an abundant mesoporous structure. The adsorption process was well described by the Langmuir isotherm and pseudo-second-order kinetic models, indicating monolayer chemisorption and an endothermic nature. At pH 5 and 55 °C, the maximum adsorption capacities reached 67.12, 79.72, and 72.75 mg·g−1 for SY, P4R, and TY, respectively. Statistical physics modeling further suggested a multilayer physical adsorption mechanism, primarily governed by pore filling, electrostatic interactions, hydrogen bonding, π-π stacking, and charge transfer. These findings provide both theoretical insights and empirical data for the valorization of H. pluvialis residue and the development of efficient, sustainable adsorbents for azo dye removal from water.