Synthesis of modified hydrophobic hybrid biopolymer alginate/soy protein isolates aerogels via scCO2 drying for oil removal

Oil pollution poses significant environmental challenges, necessitating the development of effective and sustainable solutions for oil absorbents. In this work, sodium alginate (ALG) and soy protein isolate (SPI) were combined via a sol–gel method, followed by surface functionalization using methyltrimethoxysilane (MTMS) and tetraethyl orthosilicate (TEOS) and dried by supercritical carbon dioxide (scCO2) to produce a hybrid aerogel oil absorbent. ALG concentration was varied from 1 to 3% w/w, while SPI concentrations were constant at 0.5 and 1.5% w/w. Results showed that the one-step surface modification successfully changed the ALG/SPI aerogel to hydrophobic. ALG/SPI aerogels are capable of absorbing model pollutants (i.e., waste engine oil, heavy-duty oil and chloroform) ranging from 1.34 to 10.3 g/g, with the highest absorption efficiency reaching 91%. Notably, ALG/SPI 1_1.5 appears as the most effective, absorbing waste oil at temperatures from 40 to 80 °C, has a high surface area (210 m2∙g−1), lightweight (0.107 g·cm−3), thermally stable over 196 °C, and is reusable up to four times. ALG/SPI aerogel remains afloat, retaining absorbed pollutants and is biodegradable, hence reducing post-use environmental impact. This study demonstrated that the hybrid ALG/SPI aerogels are promising materials as oil absorbents in the oil/water separation industry.