# Super-Hydrophobic Polyurethane/Activated Biochar Composites with Polydimethylsiloxane Coating for High-Efficiency Organic Liquid Uptake

## TL;DR

Scientists created a new foam material that efficiently absorbs organic pollutants using a combination of polyurethane, biochar, and a hydrophobic coating.

## Contribution

The novel hybrid composite combines activated biochar and PDMS coating to significantly enhance PU foam's oil absorption and reusability.

## Key findings

- The hybrid PU-AC/PDMS composite achieved oil uptake capacities of 44–56 g/g and solvent uptake up to 35 g/g.
- PDMS coating increased surface hydrophobicity from 88.53° to 148.25°, while preserving open-cell structure.
- The composite showed improved thermal stability through silica-rich char formation from PDMS.

## Abstract

The aim of this work is to develop structurally enhanced and highly hydrophobic polyurethane (PU) foams for the efficient remediation of liquid organic pollutants. For this purpose, PU foams were modified with renewable activated biochar derived from marine algae (AC) and a hydrophobic polydimethylsiloxane (PDMS) coating, producing four systems: pristine PU, PU-AC, PU/PDMS, and the hybrid PU-AC/PDMS composite. The study evaluates how AC incorporation and PDMS surface functionalization influence the microstructure, chemical composition, wettability, thermal stability, and sorption behavior of the foams. SEM images revealed progressive reductions in pore size from 420 ± 80 μm (PU) to 360 ± 85 μm (PU-AC/PDMS), with AC introducing heterogeneity while PDMS preserved open-cell morphology. FTIR confirmed the presence of urethane linkages, carbonaceous structures, and PDMS siloxane groups. Surface hydrophobicity increased markedly from 88.53° (PU) to 148.25° (PU-AC/PDMS). TGA results showed that PDMS improved thermal stability through silica-rich char formation, whereas AC slightly lowered degradation onset. Sorption tests using petroleum-derived oils and hydrophobic organic liquids demonstrated a consistent performance hierarchy (PU < PU/PDMS < PU-AC < PU-AC/PDMS). The ternary composite achieved the highest uptake capacities, reaching 44–56 g/g for oils and up to 35 g/g for hydrophobic solvents, while maintaining reusability. These findings demonstrate that combining activated biochar with PDMS significantly enhances the functional properties of PU foams, offering an efficient and sustainable material for oil–water separation and organic pollutant remediation.