Key Takeaways & Executive Findings
- •• ZnO-rGO/CMF composite exhibits superhydrophobicity with a water contact angle of 151.5° and superoleophilicity, enabling efficient oil-water separation. • The composite achieves a maximum adsorption capacity of 120.2 g/g for soybean oil, outperforming most previously reported MF-derived carbon-based adsorbents. • The material demonstrates excellent recyclability, maintaining stable adsorption performance over 20 separation cycles and retaining 70% capacity after five combustion cycles. • The fabrication method combines hydrothermal treatment and pyrolysis, yielding a composite with high compression resistance and flame retardancy, suitable for practical oily wastewater treatment.
Abstract
Oily wastewater discharge severely endangers the environment and hinders energy conservation efforts, necessitating the development of high-performance oil-water separation materials. We report the formation of a superhydrophobic and superoleophilic composite by integrating ZnO with reduced graphene oxide (rGO) on a carbonized melamine foam (CMF) using pristine melamine foam (MF) as the starting substrate. The fabrication involved two key steps: hydrothermal treatment and high-temperature pyrolysis. Characterization showed that the resultant ZnO-rGO/CMF composite had a water contact angle of 151.5°, indicating excellent superhydrophobicity. Both static adsorption and continuous dynamic separation tests verified the composite’s superior oil-water separation performance. It had remarkable adsorption capacities for various oils and organic solvents, with a maximum adsorption capacity of 120.2 g/g for soybean oil, surpassing the values for most previously reported MF-derived carbon-based adsorbents. After 20 consecutive separation cycles, the composite maintained a stable adsorption performance, demonstrating good recyclability. It also had an excellent compression resistance and good flame retardancy. It retained 70% of its original adsorption capacity for gasoline after five combustion cycles, confirming its reusability under high-temperature conditions. Hydrophobic carbon-based porous sponges were developed, providing valuable insights for the design and development of advanced carbon-based superhydrophobic materials for environmental remediation, particularly in oily wastewater treatment.
1. Introduction
Frequent leakage accidents during petroleum extraction, transportation, and refining, along with the increasing discharge of industrial oily wastewater, have led to serious issues such as energy waste, environmental pollution, and ecological damage[1−2]. Meanwhile, oil pollutants in domestic sewage cause pipeline blockages by forming a floating oil layer on water surfaces, thereby hindering reoxygenation and disrupting ecological cycles[3]. Traditional oil-water separation methods, such as mechanical skimming, chemical dispersion, and biodegradation, generally suffer from drawbacks including low separation efficiency, potential secondary pollution, complicated operation, and high costs[4–8]. These limitations make it difficult to meet the practical demands of large-scale industrial oily wastewater treatment and domestic sewage purification in complex environments[9–12]. Therefore, there is an urgent need to develop novel materials capable of absorbing, removing, and transferring oil contaminants from water effectively.
Adsorption is an effective approach for oil-water separation. A material is considered suitable for oil-water separation if its surface exhibits opposite wettability toward oil and water[13]. Melamine foam (MF) has emerged as a promising substrate for developing novel hydrophobic oil-absorbing materials due to its low cost, excellent elasticity, high thermal stability, outstanding flame retardancy and eco-friendliness[14–16]. However, pristine MF is amphiphilic. The lack of selective adsorption capacity for oil precludes meeting the requirements of oil-water separation. Thus, surface modification is essential to construct a superhydrophobic and superoleophilic interface[17]. Currently, carbonization under an inert gas atmosphere is used to remove hydrophilic groups (e.g.,―NH2, ―OH) from the surface of MF, forming carbonized melamine foam (CMF) with significantly enhanced hydrophobicity and lipophilicity[18]. For instance, Niu et al. prepared superhydrophobic CMF by pyrolysis at 1000 °C, with an adsorption capacity of 60–150 g/g. However, the material exhibited poor adsorption performance for low-viscosity organic solvents at room temperature and required photothermal or Joule heating to achieve effective adsorption. Additionally, the impact of repeated heating-cooling cycles on its adsorption performance has not been evaluated[19].
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YANG Shifang, YU Peng (2025). Construction of a superhydrophobic ZnO-rGO/CMF composite and its high-efficiency oil adsorption-separation performance. SinoTechIntel Verified Research. https://doi.org/10.1016/S1872-5805(NCM2026-41-03-12)
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Frequently Asked Questions
What is the water contact angle of the ZnO-rGO/CMF composite?
The ZnO-rGO/CMF composite exhibits a water contact angle of 151.5°, indicating excellent superhydrophobicity.
What is the maximum adsorption capacity of the composite for soybean oil?
The composite achieves a maximum adsorption capacity of 120.2 g/g for soybean oil, surpassing most previously reported MF-derived carbon-based adsorbents.
How is the ZnO-rGO/CMF composite fabricated?
The fabrication involves two key steps: hydrothermal treatment of melamine foam with GO and Zn2+ at 90°C for 9 hours, followed by high-temperature pyrolysis at 400°C for 2 hours under inert atmosphere.
Does the composite maintain its adsorption performance after multiple cycles?
Yes, the composite maintains stable adsorption performance over 20 consecutive separation cycles and retains 70% of its original adsorption capacity for gasoline after five combustion cycles, demonstrating good recyclability.
What are the key properties of the composite besides oil adsorption?
The composite also exhibits excellent compression resistance and good flame retardancy, making it suitable for practical applications in oily wastewater treatment.
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