Facile Synthesis of Soybean Oil-Derived Bio-Based Material for Wastewater RemediationModern industrialization has escalated wastewater pollution, with halogenated solvents, synthetic dyes, and toxic chemicals persisting in aquatic ecosystems. Conventional remediation methods rely heavily on petroleum-based adsorbents, which often introduce secondary environmental burdens due to non-degradable residues and fossil resource depletion. This paradox has driven the search for bio-based alternatives—materials derived from renewable resources that combine high adsorption efficiency with minimal ecological impact. Among these, vegetable oil-derived polymers have emerged as promising candidates, leveraging the structural versatility of triglycerides and unsaturated fatty acids for functional modification.
Soybean oil, a globally abundant agricultural byproduct, contains a unique blend of linoleic (54.6%) and oleic (32.5%) acids, whose carbon-carbon double bonds serve as reactive sites for polymerization. Unlike petroleum-based polymers, soybean oil-derived materials offer inherent biodegradability and reduced carbon footprints, aligning with circular economy principles. Recent advancements in green synthesis techniques have now enabled the direct conversion of soybean oil into a solid adsorbent—soybean oil gummy solid (SOGS)—without extensive chemical preprocessing, marking a significant leap in sustainable material science.
Fig 1. Schematic representation of cross-linking reaction of SO in different reaction conditions (A: under microwave irradiation for 1 h, B: normal heat for 12 h, C: normal heat for 3 h). (Barra V., et al., 2025)
The synthesis of SOGS represents a paradigm shift in reducing environmental impact during production. Traditional vegetable oil polymerization requires prolonged heating (12 hours at 110°C) and excessive catalyst usage, undermining sustainability credentials. In contrast, the microwave-assisted approach developed here achieves full conversion in just 1 hour at 110°C using 5 wt% boron trifluoride diethyl etherate (BF3·Et2O) as a catalyst. This method cuts energy consumption by over 90% while maintaining an 80% yield, producing 1.6 g of SOGS from 2 g of soybean oil.
The reaction mechanism hinges on the cationic polymerization of unsaturated fatty acids. 1H NMR spectroscopy reveals a reduction in vinyl protons (5.3–5.4 ppm) from 5 per triglyceride in raw soybean oil to 1.5 in SOGS, indicating cross-linking through double bond reactivity. Gas chromatography-mass spectrometry (GC-MS) further confirms that linoleic acid, abundant in soybean oil, is almost entirely consumed during polymerization, while oleic acid undergoes isomerization to form 6-octadecenoic acid—a key intermediate in Diels-Alder cycloaddition reactions that drive solid network formation. This structural transformation, absent in olive oil (which contains only 6% linoleic acid), explains why SOGS forms exclusively from soybean oil.
SOGS exhibits a unique set of properties that make it ideal for adsorption applications. Morphological analysis via scanning electron microscopy (SEM) and nanotomography reveals a compact matrix with irregular cavities, creating a heterogeneous surface that enhances pollutant trapping. X-ray diffraction (XRD) patterns confirm a semicrystalline structure with a 32% crystallinity index, balancing mechanical stability with flexibility. This structure is further stabilized by intermolecular hydrogen bonds, as evidenced by ATR-FTIR spectroscopy—broad -OH stretching at 3430 cm-1 and shifted carbonyl vibrations at 1710 cm-1 indicate interactions between adsorbed water molecules and ester groups.
Thermal analysis via differential scanning calorimetry (DSC) shows a glass transition temperature (Tg) of 84°C and thermal stability up to 300°C, ensuring functionality across a range of industrial conditions. Swelling tests demonstrate selective solvent affinity: SOGS swells 15-fold in chloroform and 8-fold in tetrahydrofuran (THF) but remains stable in polar solvents like methanol and water. This selectivity arises from hydrophobic interactions between the material's fatty acid chains and non-polar pollutants, a critical feature for targeted adsorption in complex wastewater matrices.
Halogenated Solvent Adsorption: Chloroform Removal
Chloroform (CHCl3), a carcinogenic halogenated solvent widely used in industrial processes, poses severe risks to aquatic life and human health. SOGS demonstrates exceptional efficacy in removing chloroform from water, achieving 62% adsorption within 2 hours and 83% after 24 hours in a saturated solution (8 mg/mL). This performance surpasses many bio-based adsorbents, attributed to the material's high swelling capacity in chloroform, facilitating encapsulation within its porous structure.
The adsorption kinetics, measured via solid-phase microextraction (SPME) coupled with GC-MS, follow a pseudo-second-order model, indicating chemisorption as the dominant mechanism. The large surface area provided by SOGS's cavities, combined with hydrophobic interactions between chloroform and the material's alkyl chains, drives this efficient removal. Importantly, SOGS maintains structural integrity post-adsorption, enabling subsequent regeneration.
Dye Adsorption: Targeting Rhodamine B
Synthetic dyes, such as rhodamine B (RhB), are ubiquitous in textile wastewater, causing water discoloration and disrupting photosynthetic processes in aquatic plants. SOGS shows selective adsorption for cationic dyes, with 45% RhB removal in 24 hours and 57% after 72 hours from a 1.8×10-5 M solution. Adsorption efficiency scales with material dosage, peaking at 60% using 100 mg of SOGS, though 20 mg suffices for practical applications due to marginal gains beyond this threshold.
The material's cationic dye affinity stems from electrostatic interactions between RhB's positively charged amine groups and SOGS's carboxylate residues, formed via partial hydrolysis of ester bonds during synthesis. UV-visible spectroscopy confirms a reduction in RhB's characteristic 554 nm absorption peak over time, with complete decolorization observed in samples with higher SOGS concentrations.
A key advantage of SOGS is its recyclability. Using bio-based solvents like 2-methyltetrahydrofuran (2-MeTHF), adsorbed RhB can be fully desorbed via 3 cycles of sonication (10 minutes each), allowing SOGS to retain 70% of its initial efficiency over 4 reuse cycles. This contrasts with many adsorbents that suffer significant performance drops after the first cycle, reducing long-term costs and waste.
At the end of its lifecycle, SOGS undergoes complete chemical degradation in basic environments. Treatment with 2M KOH at 60°C for 16 hours results in 97% degradation, producing potassium salts of linoleic and oleic acids—non-toxic byproducts that can be further processed or safely disposed of. ATR-FTIR analysis of degraded SOGS confirms ester bond cleavage, with new peaks at 1561 cm-1 corresponding to carboxylate anions. This degradability prevents secondary pollution; a critical feature absents in petroleum-based adsorbents.
For a material used in water treatment, biocompatibility is paramount to avoid ecological harm. In vitro tests on human retinal pigment epithelial (RPE-1) cells show that SOGS concentrations up to 2.4 mg/mL do not affect cell proliferation or metabolic activity. Even at 5 mg/mL—far exceeding typical environmental exposure levels—SOGS only reduces proliferation slightly without inducing cell death, outperforming palmitic acid (a common fatty acid impurity), which causes significant cytotoxicity.
MTT assays confirm that SOGS does not inhibit mitochondrial activity, with optical density values comparable to untreated controls across all tested concentrations. This safety profile ensures that accidental release of SOGS into aquatic ecosystems poses minimal risk to organisms, supporting its use in environmentally sensitive areas.
SOGS represents a milestone in bio-based materials, combining easy synthesis, high adsorption efficiency, and environmental safety. Its derivation from soybean oil—including expired stock—reduces reliance on fossil fuels while valorizing agricultural byproducts. From industrial wastewater treatment to decentralized water purification, SOGS offers a scalable, cost-effective alternative to conventional adsorbents.
Future research could explore modifying SOGS's surface chemistry to enhance heavy metal adsorption or integrating it into filtration membranes for continuous flow systems. As regulatory pressures for green technologies intensify, SOGS stands out as a model for sustainable innovation, proving that environmental protection and industrial efficiency can coexist.
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Reference
This article is for research use only and cannot be used for any clinical purposes.
