Eco-friendly sorbents for petroleum and diesel based on macadamia nutshell waste in castor oil-based polyurethane foam for oil spill

Aquatic environments have faced significant and severe impacts in recent years due to oil spills and chemical leaks in oceanic and river ecosystems. Because of this, several studies have aimed to develop sustainable adsorbents with hydrophobic characteristics. This research focuses on creating eco-friendly sorbents using macadamia nutshell waste (MW) incorporated into castor oil-based polyurethane foam at different proportions (5, 10, 15, and 20 wt%). The study also evaluates the absorption efficiency of these sorbents for different oil types, including crude oils (crude oil CB, crude oil SB, diesel S10, and diesel S500). The eco-friendly sorbents (biocomposites) were characterized by optical microscopy, scanning electron microscopy, density, and contact angle analyses. Results revealed that the pore morphology of sorbents changed to a partial closed-cell structure with a smaller pore size. Additionally, the biocomposites exhibited a higher contact angle (119.1º ± 0.4) compared to pure polyurethane (PU). The oil absorption efficiency by biocomposites showed maximum sorption of 7.3, 7.1, 5.1, and 3.9 g.g⁻¹ for crude oils (SB and CB), S10, and S500 diesel, respectively. The absorption results showed that the biocomposites showed good removal of heavy oils (crude oil) compared to light oils (diesel S10 and S500). Among the isotherm models used, the Langmuir model demonstrated the most accurate fit and estimated a maximum adsorption capacity of 5.39, 4.23, 3.24, and 2.69 g.g⁻¹ for crude oil CB, crude oil SB, S10, and S500 diesel respectively, using PU + 20% MW. Additionally, PU + 20% MW showed excellent reusability during 30, 30, 30, and 10 cycles of sorption–desorption for crude oil CB, crude oil SB, S10, and S500 diesel, respectively.