Promoted solubilization and desorption of petroleum hydrocarbons to remediate contaminated soils using Pickering emulsions stabilized by cellulose nanocrystals†

Abstract

Surfactant-based treatment, particularly Pickering emulsion-based treatment, is becoming an attractive technique to remediate the globally concerning petroleum hydrocarbon-related soil pollution. Cellulose nanocrystals (CNCs) are promising natural materials to enhance the stability and performance of Pickering emulsions. In this study, rice straw was hydrolyzed through sulfuric acid (SCNCs) and combined HCOOH/H₂SO₄ (FSCNCs) to prepare CNCs, respectively. The yield of FSCNCs (73.2%) was significantly higher than that of SCNCs (44.6%), which largely reduced the consumption of H₂SO₄. Notably, the as-prepared FSCNCs had a smaller particle size and more hydrophobic formyl groups than the SCNCs, enabling FSCNCs to exhibit better emulsification, stability, and amphiphilicity. The Pickering emulsions stabilized by FSCNCs were able to remove up to 59.1% of tetradecane, which was used as a representative molecule of petroleum hydrocarbons from soils across a wide range of ambient temperatures and ionic strengths. In the presence of surfactants, such as Tween-80 and a plant biosurfactant, the droplet size decreased distinctly, further promoting the removal efficiency of tetradecane from soil. The large amount of oxygen-containing groups in FSCNCs favored the electrostatic attractions between FSCNCs and the minerals or metals in soils. The superior emulsification effect of FSCNCs greatly promoted the transfer of tetradecane into the aqueous phase, thus enhancing the remediation efficiency. The findings provide novel insights into the utilization of Pickering emulsions stabilized by FSCNCs in remediation of soils contaminated by petroleum hydrocarbons.