Advanced 3D Polymeric Sponges Offer Promising Solutions for Addressing Environmental Challenges in Qatar’s Marine Ecosystems ^†

Abstract

The increasing incidence of oil contamination in many aquatic ecosystems, particularly in oil-rich regions such as Qatar, poses significant threats to marine life and human activities. Our study addresses the critical need for effective and eco-friendly oil-water separation techniques, focusing on developing graphene and chitosan-based three-dimensional (3D) polymeric sponges. These materials have demonstrated potential due to their high porosity and surface area, which can be enhanced through surface treatment to improve hydrophobicity and oleophilicity. This study introduces a new technique dependent on the optimization of the graphene oxide (GO) concentration within the composite sponge to achieve a superior oil uptake capacity (51.4 g oil/g sponge at 3% GO), and the detailed characterization of the material’s performance in separating heavy oil-water emulsions. Our study seeks to answer key questions regarding the performance of these modified sponges and their scalability for industrial applications. This research directly aligns with Qatar’s environmental goals and develops sustainable oil-water separation technologies. It addresses the pressing challenges of oil spills, ultimately contributing to improved marine ecosystem protection and efficient resource recovery.

1. Introduction

The global problem of oil contamination in aquatic ecosystems has become increasingly critical in recent years, particularly in areas concerned with substantial oil production and transportation activities like Qatar. The unintentional release of oil into water bodies through various means, including spills, industrial waste, and offshore drilling operations, presents significant threats to marine life, human well-being, and economic activities [1,2]. Consequently, there is a pressing demand for effective, economical, and eco-friendly ways to separate oil from water, especially in persistent oil-in-water emulsions.

Materials science and environmental engineering researchers have been intensely focused on developing advanced materials for oil-water separation. Among the various strategies investigated, using porous materials with hydrophobic and oleophilic properties has shown considerable potential [3,4]. Three-dimensional (3D) polymeric sponges have emerged as promising candidates for oil absorption and separation due to their high porosity, extensive surface area, and potential for surface modification [5,6]. Graphene and chitosan have garnered considerable interest as components in these 3D polymeric sponges. Graphene, a two-dimensional carbon allotrope, exhibits exceptional mechanical strength, thermal conductivity, and electrical properties [7]. Its integration into polymeric matrices can significantly enhance the overall performance of the resulting composites. Chitosan, a natural polysaccharide derived from chitin, offers biocompatibility, biodegradability, and numerous functional groups for further modification [7]. The combination of graphene and chitosan in 3D sponges presents a unique opportunity to leverage the strengths of both materials for oil-water separation applications. However, the efficacy of graphene and chitosan-based 3D polymeric sponges in oil-water separation relies heavily on their surface properties. The inherent hydrophilicity of chitosan and graphene’s tendency to aggregate in aqueous environments can hinder their performance in oil absorption and separation [4]. Therefore, surface treatment and decoration of these sponges are vital steps in optimizing their functionality for oil-water separation. In this context, the novelty of the present work lies in introducing a new technique that focuses on the strategic optimization of the graphene oxide (GO) concentration within the chitosan-based 3D polymeric sponge. This optimization is demonstrated to achieve a superior oil uptake capacity, specifically 51.4 g oil/g sponge at an optimal GO concentration of 3%. It is further supported by a detailed characterization of the material’s performance in separating challenging heavy oil-water emulsions. This study seeks to answer key questions regarding the performance of these modified sponges and their scalability for industrial applications. This research aligns with Qatar’s environmental goals by developing sustainable oil-water separation technologies. It addresses the pressing challenges of oil spills, ultimately contributing to improved marine ecosystem protection and efficient resource recovery.

2. Experimental Method

The study aimed to assess the efficacy of 3D polymeric sponges made from graphene and chitosan for separating heavy oil-water emulsions in the laboratory. The research concentrated on enhancing the sponges’ hydrophobicity and oil absorption capabilities through surface modification and decoration. Figure 1 illustrates the process flow for coating polyurethane sponges with a graphene oxide (GO)-chitosan solution. Graphene Oxide (GO) Synthesis: GO was produced from graphite powder using a modified Hummers’ technique. The process involved oxidizing graphite with a mixture of H₂SO₄ and H₃PO₄, along with KMnO₄. H₂O₂ was subsequently added to eliminate excess permanganate [8]. The resulting product underwent multiple washing and centrifugation cycles before being dried at 90 °C to obtain powdered GO. Polyurethane Sponge Coating with Chitosan: A PU sponge was submerged in a solution of chitosan dissolved in acetic acid. The sponges were then treated with glutaraldehyde for cross-linking to improve their structural integrity. Graphene Application and Reduction: The sponges were immersed in a GO suspension following the chitosan coating. The GO was then converted to reduced graphene oxide (rGO) using hydrazine hydrate. Finally, the sponges were dried and subjected to testing.

3. Results and Discussion

3.1. Scanning Electron Microscopy (SEM)

SEM analysis (Quanta 650 FEG, FEI Company, OR, USA) specific surface area and abundant oxygen-containing functional groups, including hydroxyl (OH⁻) and carboxyl (COOH⁻) moieties (Figure 2a). These structural features facilitate GO’s role as an effective functional additive for enhancing material properties in composite formation, particularly for applications requiring high surface activity and adsorption capacity [9]. The unmodified polyurethane sponge displays a well-defined three-dimensional network with interconnected pores with smooth pore walls (Figure 2b). While this architecture ensures adequate fluid permeability and mechanical stability, the inherent hydrophobicity and absence of functional groups limit its efficiency in oil-water separation applications. The GO/chitosan-modified polyurethane sponge exhibits significant morphological alterations compared to the unmodified substrate (Figure 2c). SEM micrographs reveal increased surface roughness and heterogeneity along the pore walls, attributed to the successful deposition of GO sheets and chitosan. This modification synergistically combines GO’s enhanced surface area and hydrophilicity with chitosan’s abundant amino (NH⁻²) and hydroxyl (OH⁻) functionalities, resulting in superior adsorption characteristics. The modified structure demonstrates enhanced oil-water separation efficiency through selective oil droplet adsorption while maintaining water permeability. The increased surface roughness facilitates improved oil trapping, while enhanced hydrophilicity ensures efficient water transport through the structure, making this composite particularly suitable for environmental remediation applications, including oily wastewater treatment and marine oil spill management [10].

3.2. Preliminary Test of Oil and Water Adsorption

Figure 3 visually demonstrates the modified sponge’s selective absorption capabilities, illustrating the material’s interaction with distinct oil and water phases. The GO-chitosan-coated PU sponge exhibited preferential oil absorption while maintaining minimal interaction with the aqueous phase, as evidenced by the unperturbed water surface. This observation validates the successful development of a dual-functional interface characterized by hydrophobic and oleophilic properties [11]. The enhanced separation performance can be attributed to the synergistic effects of the GO-chitosan composite coating. The functionalized surface demonstrates a strong affinity towards oil molecules while exhibiting water-repellent characteristics, facilitating efficient oil-water separation. This selective absorption mechanism minimizes water uptake during operation, a critical parameter for maintaining separation efficiency in practical applications. The qualitative observations from Figure 3 complement quantitative performance data, visually confirming the composite’s functionality. These findings suggest significant potential for scale-up and practical implementation across various applications, from environmental remediation to industrial wastewater treatment. The demonstrated selective absorption capabilities validate the composite design strategy and indicate its viability for addressing real-world oil-water separation challenges.

3.3. Analysis of Adsorption Capacity

The oil adsorption performance of GO-chitosan modified PU sponges was systematically evaluated using a 1% oil-in-water emulsion (10,000 ppm).

Table 1. Adsorption test results showing the weight changes of a modified sponge with graphene oxide and chitosan, before and after oil adsorption from a 1% oil-water mixture.

GO Loading (%)	Weight of Sponge (g)	Weight the Modified Sponge with GO/Chitosan (g)	Weight After oil Adsorption (g)	Weight of Oil Adsorbed (g)	Adsorption Capacity (g/g)
3%	0.1120	0.1431	7.4976	7.3545	51.4
6%	0.1353	0.1441	3.0733	2.9292	20.3
9%	0.1330	0.1722	3.5056	3.3334	19.4
12%	0.1260	0.1300	3.4517	3.3217	25.6

presents comprehensive weight measurements at critical stages: initial dry weight, post-modification weight, and post-adsorption weight, along with calculated oil uptake values across varying GO concentrations (3%, 6%, 9%, and 12%). The successful surface modification was evidenced by consistent weight increases after GO-chitosan deposition, indicating effective functionalization of the PU substrate. The modified sponges demonstrated significant oil uptake capacity, with performance varying notably across GO concentrations [12]. Quantitative analysis revealed that the 3% GO-modified sample exhibited superior performance, achieving an oil uptake of 7.3545 g (initial weight: 0.1431 g; post-adsorption weight: 7.4976 g), corresponding to an exceptional adsorption capacity of 51.4 g oil/g sponge. Higher GO concentrations showed reduced efficiency: 6% GO samples demonstrated an uptake of 2.9292 g (initial: 0.1441 g; post-adsorption: 3.0733 g), yielding 20.3 g oil/g sponge capacity; 9% GO samples captured 3.3334 g oil (initial: 0.1722 g; post-adsorption: 3.5056 g), achieving 19.4 g oil/g sponge capacity; and 12% GO samples adsorbed 3.3217 g oil (initial: 0.1300 g; post-adsorption: 3.4517 g), resulting in 25.6 g oil/g sponge capacity. The adsorption performance was calculated using Equations (1) and (2) [13]:

Weight of oil adsorbed = Weight after adsorption − Weight of modified sponge

(1)

Adsorption capacity = Weight of oil adsorbed/Weight of modified sponge

(2)

The superior performance of the 3% GO-modified sponge can be attributed to optimal surface functionalization, maintaining an effective balance between porosity and composite loading. The observed decrease in adsorption capacity at higher GO concentrations (6–12%) suggests that excessive GO loading may compromise performance through reduced pore accessibility or increased surface hydrophilicity. These findings indicate that precise control of GO concentration is crucial for optimizing oil-water separation efficiency. The demonstrated high adsorption capacity, particularly at 3% GO loading, validates the potential of these modified sponges for environmental remediation applications, specifically in oily wastewater treatment and oil spill management. Further investigation of ecological parameters and optimization of the modification process could enhance the material’s practical implementation potential. The experimental findings reveal complex relationships between material composition, structure, and performance in oil-water separation applications. Our results of optimal oil adsorption at a 3% GO concentration underscore the importance of a balanced approach to surface modification. This finding aligns with previous research by Ahmed et al. [6], who also reported that a moderate graphene concentration in polymeric sponges yielded the highest oil uptake, suggesting that an optimal ratio exists between the active material and the sponge substrate. However, our results diverge from those of Kahya and Erim [14], who found a continuous increase in adsorption capacity with increasing GO content in chitosan composites. This discrepancy might be attributed to the differences in the sponge’s 3D structure in our study, compared to the 2D composite films used by Kahya and Erim, which could influence GO dispersion and accessibility. The decrease in separation efficiency we observed at higher GO concentrations (6%, 9%, and 12%) indicates a threshold effect [14]. This is likely due to excessive surface coating that restricts pore accessibility, hindering oil absorption, and potentially altering the material’s hydrophilic-oleophilic balance. This is likely due to excessive surface coating that restricts pore accessibility, hindering oil absorption, and potentially altering the material’s hydrophilic-oleophilic balance. This interpretation is supported by Zhu et al. [4], who highlighted that excessive surface modification can reduce the porosity of separation materials, thus limiting their capacity for oil uptake. This phenomenon can be explained through multiple mechanisms: the reduced pore volume limiting oil absorption capacity, modified surface chemistry increasing water affinity, and potentially compromised structural integrity of the porous network affecting overall performance. The synergistic interaction between GO and chitosan emerges as a crucial factor, where GO contributes to mechanical reinforcement and provides anchoring sites for chitosan attachment. In contrast, chitosan enhances biocompatibility and structural stability. This combination creates an optimal interface for selective oil absorption while maintaining water repellency, demonstrated through the material’s high absorption capacity and selectivity. SEM analysis confirms successful surface modification and reveals the hierarchical porous structure essential for efficient oil capture. At the same time, the maintained structural integrity after multiple absorption-desorption cycles validates the robust material design. However, several critical aspects warrant further investigation, including the impact of environmental parameters such as temperature, pH, and salinity on absorption performance, particularly under Gulf region conditions. The molecular-level mechanisms of oil-water separation require detailed examination to optimize future material designs and enhance performance. Cost-effectiveness and scalability considerations suggest process optimization, potentially through modified coating techniques, alternative fabrication methods, or automated regeneration processes [15]. Technology’s potential extension to other environmental contaminants and comprehensive life cycle assessment would provide valuable insights for broader applications. The material’s performance under various oil types and concentrations, alongside its behavior in complex mixtures containing suspended solids or emulsified oils, represents another critical area for investigation. Integration of additional functional materials or surface modifications could enhance selectivity and efficiency, while developing in situ regeneration methods could improve practical applicability. These findings advance our understanding of oil-water separation mechanisms and highlight crucial areas for future research to optimize real-world implementation and maximize environmental impact.

4. Conclusions

This investigation focused on developing and evaluating graphene oxide (GO) and chitosan-modified polyurethane (PU) sponges for oil-water separation applications in Qatar’s marine environment. Experimental results demonstrated optimal performance at 3% GO concentration, achieving an oil adsorption capacity of 51.4 g oil/g sponge. The synergistic interaction between GO and chitosan enhanced the composite’s hydrophobicity, oleophilicity, and porous architecture. However, GO concentrations exceeding 3% (6%, 9%, and 12%) showed marginally decreased efficiency, potentially due to excessive surface coating that restricted pore accessibility and increased hydrophilic character. Morphological characterization through SEM confirmed that the modified surface structure facilitated selective oil absorption while maintaining water repellency. Preliminary adsorption studies validated the material’s high selectivity and practical functionality. The composite sponges demonstrated robust cyclic stability and reusability, indicating suitability for practical implementation. This research presents an environmentally sustainable and scalable solution for oil spill remediation, aligned with Qatar’s environmental preservation initiatives. Future investigations should optimize coating methodologies, evaluate field performance, and expand applications to diverse contaminants.