Elsevier

Chemosphere

Volume 249, June 2020, 126141
Chemosphere

Reduced graphene oxide composites and its real-life application potential for in-situ crude oil removal

https://doi.org/10.1016/j.chemosphere.2020.126141Get rights and content

Highlights

  • Graphene based composite provided an alternative strategy to achieve in situ crude oil removal.

  • Reduced graphene oxide converted sunlight into heat, which reduced the viscosity of crude oil to allow faster adsorption.

  • A 3D-printed mounting platform was designed and fabricated to achieve easy retrieval of the composites after usage.

  • The strategy shown in this study was easy-to-apply, safe-to-use, and highly effective.

Abstract

Crude oil pollution can cause severe and long-term ecological damage and oil cleanup has become a worldwide challenge. Conventional treatment strategies like in-situ burning, manual skimmer and bioremediation were labor-intensive and time-consuming. The high viscosity of crude oil also posed difficulty for traditional absorbents. Herein, to address these limitations, we designed and fabricated a floating absorbent that was comprised of reduced graphene oxide (RGO), melamine sponge (MS), and a 3D-printed mounting platform. Through a facile one-pot hydrothermal method, graphene oxide (GO) was simultaneously reduced to RGO and loaded in MS (RGO-MS). The resulted RGO-MS composites possess desirable hydrophobicity/oleophilicity for oil absorption with a water contact angle of 122°. The effective light-to-heat conversion allowed the RGO-MS composite to absorb approximately 95 times its own weight of crude oil within 12 min under light irradiation. A 3D-printed mounting platform for RGO-MS composites was further fabricated to improve its applicability and allow easy retrieval. Taking advantages of the RGO’s hydrophobicity/oleophilicity and photothermal property, the floating ability of MS, this study demonstrated the real-life applicability of RGO-MS composites for in-situ crude oil cleanup.

Introduction

In recent years, frequent oil spill has exerted great threat to the environment, especially the sea and coastal places, therefore has become a worldwide environmental issue (Peterson et al., 2003; Jernelov, 2010; Brette et al., 2014). Conventional cleanup approaches, such as oil skimmer (Broje and Keller, 2006), bioremediation (Macnaughton et al., 1999), and in-situ burning (Beyer et al., 2016) have been widely used to remove the oil contamination. But most of these approaches were either labor-intensive or time-consuming. The negative impact on the air quality due to in-situ burning made it not desirable for future oil pollution treatment. Since most of the oil density is lower than water, floating absorbents offered an alternative cleanup approach by in-situ oil absorption (Adebajo et al., 2003). Typical naturally-occurring absorbents (such as straw, zeolites, and wool fibers) (Liu et al., 2015) and common synthetic absorbents (such as polyurethane and polyethylene) (Ke et al., 2014; Ali et al., 2018, 2019a) were used for this purpose. However, these absorbents usually suffer from lack of reusability or low absorption efficiency (Gupta et al., 2017; Ali et al., 2019b; Nodeh et al., 2016).

Recently, novel adsorbing materials with improved performance have been reported (Wang et al., 2015a; Zhang et al., 2013; Hayase et al., 2013; Mu et al., 2015; Yu et al., 2015; Ferrero et al., 2019; Basheer, 2018). Through silylation modification, a hydrophilic sponge could be turned into a hydrophobic absorbent for oil-water separation (Zhang et al., 2013). A superhydrophobic and superoleophilic “sponge-like” aerogel could be obtained via sol–gel reaction, in which methyltriethoxysilane (MTES) and dimethyldiethoxysilane (DMDES) were used as co-precursors (Yu et al., 2015). Functional nanoparticles integrated into material matrix (such as polymers) could provide additional surface roughness and increased hydrophobicity for oil absorption (Gupta et al., 2017). But most of these methods were not applicable for crude oil absorption due to its high viscosity (100–10000 mPa s at room temperature) (Chang et al., 2018; Zhang et al., 2018; Ge et al., 2017). Therefore, besides hydrophobicity/oleophilicity, the key for crude oil absorption is to decrease oil viscosity for better fluidity (Yang et al., 2018). In this regard, Ge et al. recently demonstrated a Joule-heated graphene-wrapped sponge that was able to convert electricity into thermal energy to reduce the crude oil viscosity (Ge et al., 2017). However, since the electro-thermal conversion would require additional electric power input, materials with photothermal properties might be a better candidate for in-field applications. In fact, photothermal materials with the ability to convert light to heat efficiently have been used in desalination, clean water production, catalysis and cancer therapy (Jain et al., 2008; Liu et al., 2013; Zhang et al., 2015, 2017a; Xu et al., 2017; Wang, 2018; Jiang et al., 2018). Recently, photothermal oil absorbents were fabricated through coating photothermal materials (such as polydopamine and polypyrrole) on the sponge (Chang et al., 2018; Zhang et al., 2018; Wu et al., 2018). However, the time-consuming preparation process and instability of polymers in heat continued to be a challenge (Wang et al., 2019). Although graphene could be a suitable substitution due to its heat stability, hydrophobic/oleophilic characteristic and photothermal property, its high hydrophobicity could pose difficulty in applying in aqueous environment (Yang et al., 2010, 2013; Hu et al., 2017; Chung et al., 2013; Robinson et al., 2011; Fojtu et al., 2017).

Against this background, this study set out to explore the use of graphene-based photothermal nanomaterials in combination with floating matrix to achieve in situ crude oil absorption. A facile one-step hydrothermal synthesis method was used to achieve graphene oxide (GO) to reduced graphene oxide (RGO) conversion and loading to melamine sponge (MS) simultaneously. The resulted RGO-MS composite possesses desirable hydrophobicity and oleophilicity. Upon light irradiation, the photothermal property of RGO enabled fast temperature rise thus lowered the crude oil viscosity. Moreover, by designing and fabricating a mounting platform through 3D-printing, multiple RGO-MS composites could be applied, retrieved, and replaced after usage. The reusability of such composite was also evaluated.

Section snippets

Fabrication and characterization of RGO-MS composites

The commercially available MS was selected as the substrate material due to its characteristics, including low cost, low density (<10 mg/cm3), high porosity (>99%), high compressibility, and thermal stability (Gao et al., 2018; Zhang et al., 2017b; Stolz et al., 2016). The schematic illustration of the fabrication process of RGO-MS composites is shown in Fig. S1. The ammonia solution played an important role of promoting the stability of GO suspension through electrostatic repulsion and l

Conclusion

In conclusion, the RGO-MS composite fabricated by simultaneously reducing GO to RGO and loading to melamine sponge has excellent hydrophilicity/oleophilicity and photothermal property that enabled effective crude oil absorption. Upon light irradiation, the RGO-MS composite achieved in-situ crude oil absorption 95 times of its own weight within 12 min. And 3D-printed mounting platform provided easy retrieval of the composites for reuse purpose. Our study has demonstrated a facile synthesis

Materials

Graphene oxide (GO, >99%, leaf size of 0.5–3 μm, thickness of 0.55–1.2 nm) was purchased from Aladdin Bio-Chem Co. Ltd. (Shanghai, China). l-Ascorbic acid (L-AA) was obtained from Sinopharm Chemical Reagent Co. Ltd. (Shanghai, China). ammonia solution (28.0–30.0%) was produced by InnoChem Science & Technology Co. Ltd. (Beijing, China). The crude oil and diesel were both obtained from China National Petroleum Corporation. Other light oils and organic solvents, including castor oil, soybean oil,

CRediT authorship contribution statement

Xiaoxiao Wang: Data curation, Formal analysis, Writing - original draft. Guotao Peng: Formal analysis. Mengmeng Chen: Visualization. Mei Zhao: Data curation. Yuan He: Data curation, Formal analysis. Yue Jiang: Data curation. Xiaozhen Zhang: Data curation. Yao Qin: Conceptualization. Sijie Lin: Conceptualization, Writing - review & editing.

Declaration of competing interest

The authors declare no conflict of interest.

Acknowledgements

This work was financially supported by the National Key R&D Program of China (Grant No. 2018YFC1803100), National Science Foundation of China (Grant No. 21777116) and the Fundamental Research Funds for the Central Universities.

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      The contact angle on bottom side was 57° (Fig. 4c), confirming its hydrophilicity, while the contact angle on top side was 100° (Fig. 4c), confirming its hydrophobicity. The hydrophobic nature may possibly arise from the hydrophobicity of the rGO surface, which has been confirmed by many reports [24–29]. The hydrophilic nature may arise from the hydrophilicity of the coated AuNPs, which possess high surface energy and are usually hydrophilic [30–33].

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