Photothermal and Joule heating-assisted thermal management sponge for efficient cleanup of highly viscous crude oil

https://doi.org/10.1016/j.jhazmat.2020.124090Get rights and content

Highlights

  • Superhydrophobic/oleophilic m-CNT/PPy@MS were rationally constructed by in-situ polymerization and dipping method.

  • m-CNT/PPy@MS exhibits excellent mechanical properties and durability.

  • m-CNT/PPy@MS shows efficient and stable heating performance.

  • m-CNT/PPy@MS significantly reduces the viscosity of crude oil via photothermal and Joule heating for oil spills recovering.

Abstract

Fast and efficient cleanup of high-viscosity oil spills on the sea is still a global challenge today. Traditional recycling methods are either energy demanding or inefficient. Hydrophobic/oleophilic sorbents are promising candidates to handle oil spills, but they have limited ability to recover high viscosity oil. In this work, we report a superhydrophobic/oleophilic carbon nanotubes (CNT) and polypyrrole (PPy) coated melamine sponge (m-CNT/PPy@MS). The CNT/PPy coating enables the sponge to convert light and electricity to heat, ensuring that the absorbent can adapt to various working environments. The rapid heat generation on the sponge surface can significantly reduce the viscosity of crude oil and accelerate the absorption rate, thereby achieving the purpose of rapid recovery of oil spills. Under one sun illumination (1.0 kW/m2) and an applied voltage (8 V), the surface temperature of the m-CNT/PPy@MS can reach 118.6 °C. The complete penetration time of oil droplets is 93.5% less than that of an unheated sponge. In addition, under half sun irradiation intensity and 11 V, the porous sponge absorbed 6.92 kg/m2 of crude oil in the first minute, which is about 31 times as much as that of an unheated sponge. Finally, we demonstrate a continuous absorption system, consisting of a self-heating m-CNT/PPy@MS and peristaltic pump, that can continuously recover oil spills on the sea surface. In view of its unique design, lower cost and fast oil absorption speed, this work provides a new option to tackle large-scale oil spill disasters on the sea surface.

Introduction

With the continuous development of the global economy, huge energy demand has accelerated the rapid development of the offshore oil exploration and transportation. This has led to increased risk of oil spills, which not only leads to catastrophic damages to the marine environment and human health, but also causes huge resource losses. According to statistics, 120 million gallons of crude oil and its refined products leak into the marine environment every year, causing a lot of marine pollution Peterson et al., 2003, Li et al., 2020. Example 2010, Oil spill in the Gulf of Mexico caused about 5 million barrels of crude oil to flow continuously into the sea Ji et al., 2014, Valentine et al., 2014. For recovery of spilled oil, several key requirements are necessary, including quick cleaning of spilled oil to reduce the spread and aging of spilled oil, excellent oil–water separation efficiency, low cost, and easy operation in large areas and various harsh working conditions. Traditional oil spill recovery methods, such as controlled combustion, chemical dispersion, and bioremediation, are slow and inefficient, and often cause secondary pollution. Therefore, new strategies are needed for the restoration of oil spills on the sea.

In recent years, porous hydrophobic/oleophilic adsorption materials, including common aerogels (Chen et al., 2016, Hayase et al., 2013), polyurethane foams (Nikkhah et al., 2015), modified commercial sponges (Feng et al., 2017, Weinstein et al., 2015, Ge et al., 2014, Sun et al., 2013, Li et al., 2011, Xu et al., 2015, Duc Dung et al., 2012), and biomass materials (Doshi et al., 2018), have become potential candidates for oil spill remediation due to their low cost and environmental friendliness. Not only can they recover oil quickly, they are also suitable for a variety of complex environments. However, these sorbents are limited to recovering low-viscosity light oils. On the other hand, about 40% of the world's oil reserves are heavy crude oils (Ge et al., 2017). Due to their high viscosity (typically from 103 to 105 mPa s at room temperature), traditional absorbents become inefficient in their recovery. Since the viscosity of crude oil decreases with increasing temperature (Luo and Gu, 2007), a number of researches have been focused on heated hydrophobic absorbents (Chang et al., 2018, Ge et al., 2017, Huang et al., 2020, Kuang et al., 2019, Li et al., 2020, Wang et al., 2020, Wang et al., 2019, Wu et al., 2018, Wu et al., 2019, Zhang et al., 2018). These materials are capable of heating the surrounding crude oil, reducing its viscosity, thereby increasing its diffusion coefficient. For example, Yu et al. proposed Joule-heated graphene-wrapped sponges for cleaning high-viscosity crude oils (Ge et al., 2017). They found that Joule heating can significantly reduce the viscosity of crude oil and increase its diffusion coefficient. However, supplying the needed electricity at the scene of many oil spill sites poses a huge challenge. Later, it was discovered that the use of solar energy can reduce the viscosity of crude oil. Therefore, many researchers have prepared materials with good light-to-heat conversion properties. Wang et al. wrapped polypyrrole on melamine sponge (MS) (Wu et al., 2018) and carbon nanotubes on polyurethane sponge (Chang et al., 2018). Xu et al. used the photothermal properties of polydopamine (PDA) to prepare hydrophobic melamine sponges (Zhang et al., 2018). Hu et al. prepared porous heating absorbent by carbonizing logs (Kuang et al., 2019). Yuan et al. prepared hydrophobic graphene-coated melamine sponges (Wang et al., 2019). However, using solar energy alone to recover oil spills has a severe limitation, because the solar lighting time is restricted in a day and the light intensity varies in different locations. Constant provision of heat is necessary, but this is not guaranteed even during daytime due to the presence of cloud or rain.

We propose a new strategy to develop a heating sorbent that can use both electrical energy and solar energy to ensure constant heat generation under any working environment. We made use of the excellent photothermal conversion and electrical conductivity of PPy (Bae et al., 2019, Jung et al., 2018, Lyu et al., 2019, Zhang et al., 2015a) and CNT (Chen et al., 2017, Mu et al., 2019, Yang et al., 2017). PDA and polydimethylsiloxane (PDMS) were used as binders to attach CNT/PPy onto a melamine sponge to prepare a self-heating superhydrophobic/oleophilic absorbent (denoted as m-CNT/PPy@MS). The m-CNT/PPy@MS is able to selectively absorb oil in water due to its excellent superhydrophobicity. When a voltage is applied to or sunlight is shone on the functionalized sponge, a large amount of heat is rapidly generated on its surface to heat up the surrounding crude oil, as a result, the viscosity of the crude oil is reduced and its diffusion coefficient increases. When solar light and the electrical voltage are applied simultaneously, the recovery of crude oil will be better. The hot oil absorbed in the sponge will not be cooled immediately, which is conducive to subsequent rapid recovery and transportation. The materials reported in this work, due to their novel design, low cost, and suitability for large-scale operations, provide an efficient and environmentally-friendly solution for remediating crude oil spills in marine systems.

Section snippets

Materials and reagents

Dopamine hydrochloride, pyrrole (Py), and multi-walled carbon nanotubes (> 95% carbon basis, O.D × I.D × L = 10–20 nm × 5–10 nm × 10–30 µm) were purchased from Macleans. PDMS prepolymer (Sylgard 184) and silicone elastomer curing agent (with weight ratio of: 10:1) were provided by Dow Corning. Conductive silver glue was provided by Shanghai Synthetic Rubber Research Institute. The remaining chemicals were obtained commercially. All the chemicals were used as received without further purification. Melamine

Preparation of superhydrophobic/oleophilic m-CNT/PPy@MS

Fig. 1a illustrates the preparation process of the functionalized sponge by sequentially depositing PPy and CNT on the skeleton of melamine sponge. The main reason for choosing melamine sponge as the oil-absorbing substrate lies with its low cost, good mechanical strength, and high porosity (Viet Hung and Dickerson, 2014). The pristine white sponge exhibits a three-dimensional porous structure (Fig. 1b and c), and the surface of the interconnected skeletons is smooth, providing a large surface

Conclusions

We have demonstrated a novel multifunctional sponge by attaching conductive light-to-heat conversion materials CNT and PPy to commercial sponges and rationally designing their wettability. The sponge adsorbent demonstrates stable superhydrophobicity and oleophilicity, and can maintain its properties under a variety of harsh environments, thereby ensuring the continuous and stable oil and water separation for practical applications. The adsorbent has demonstrated efficient light-to-heat

CRediT authorship contribution statement

Jianying Huang, Lin Teng and Yuekun Lai: conceived the idea and designed the experiment. Xingwang Wu, Yonggang Lei and Shuhui Li: performed the experiment and data collection. Xingwang Wu, Jianying Huang, Lin Teng, Zhong Chen and Yuekun Lai: contributed to scientific discussion. Xingwang Wu, Zhong Chen and Yuekun Lai: wrote the paper.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

The authors thank the National Natural Science Foundation of China (51972063, 21501127 and 51502185), Natural Science Foundation of Fujian Province (2019J01256), 111 Project (No. D17005).

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