Ulvan-based composite aerogels for efficient methylene blue adsorption

Developing polymer composite aerogels from macroalgae biomass efficiently eliminates water contaminants and mitigates the environmental issues associated with their disposal. We synthesized Ulvan and Ulvan/polyvinyl alcohol (Ulvan/PVA) composite aerogels employing a chemical crosslinking method utilizing borate ions and freeze-drying to enhance porosity. Ulvan/PVA composite aerogels were characterized through water solubility, SEM, FTIR, XRD, TGA and Brunauer, Emmett and Teller (BET) surface area measurements. The resultant Ulvan/PVA composite aerogels possess a resilient chemically cross-linked network with strong hydrogen bonds, significantly improving their mechanical and thermal properties. They exhibit a low density of 0.053 g/cm³, a surface area (BET) of 1.398 m²/g, and demonstrate exceptional mechanical properties with a strength of 4.7 MPa at 80 % strain. The synergistic effects of critical independent variables, including contact time and initial methylene blue (MB) concentration (1-20 mg/L), on MB adsorption capacity (mg/g) and removal efficiency (%) were optimized. The porous Ulvan/PVA composite aerogels demonstrated a strong affinity for methylene blue (MB), with a maximum adsorption capacity of 526.5 mg/g. The adsorption process was found to follow pseudo-second-order kinetics and was well described by the Langmuir isotherm model. Moreover, the adsorption capacity was investigated for three consecutive cycles, with 510, 496.54 and 483.26 mg/g in the first, second, and third cycles, respectively. The higher adsorption capacity of the adsorbent may be due to the synergistic interplay of electrostatic interactions, π-π conjugation, hydrogen bonding, and physicochemical properties. This synthesis strategy can provide an effective and facile pathway to prepare stable and porous polysaccharide-based composite aerogel with methylene blue (MB) uptake, reusability, and eco-friendliness as potential systems for pollutant treatment fields.