Peanut is an important crop that is worldwide cultivation and brings large economic benefit (Liu et al., 2018a, c). However, considerable quantities of peanut hull are generated each year, which is still currently underutilized, causing a serious waste problem without appropriate disposal. Considerable efforts have been devoted to make use of peanut hull and it has been widely applied for adsorption (Banerjee et al., 2017; Cao et al., 2018a, b; Gülen and Zorbay, 2017; Liu et al., 2018a, b, c; Wang et al., 2017; Wei et al., 2018). Peanut hull as the cellulosic waste material can be used raw to converting unwanted to useful value-added adsorbents, however, it is difficult to collect the raw peanut hull after application and the adsorption ability of raw peanut hull is not great. On the other hand, peanut hull can help save the high preparation cost of the prepared adsorbents. Nevertheless, the prepared adsorbents may be expensive and treated complicatedly (Ali et al., 2016). Thus, it is significant to search for effective and innovative approaches for beneficial use of peanut hull.
The three-dimensional (3D) graphene materials that were constructed by two-dimensional (2D) graphene oxide have attracted considerable attention. They inherit fascinating intrinsic properties of graphene and preserve the larger accessible surface area than graphene sheets, making them more promising for a broad range of applications in adsorption (Chen et al., 2018a, b; Nasiri and Arsalani, 2018; Xiao et al., 2018; Xiong et al., 2017; Xu et al., 2018a, b; Yang et al., 2018; Yao et al., 2017). 3D graphene monoliths have proved promising in oil-water separation (Dai et al., 2018; Huang and Yan, 2018; Ren et al., 2017; Xiao et al., 2018; Xu et al., 2018a, b). However, some problems have restricted their applications, including low absorbed oil-water ratio, bad mechanical properties, being not friendly to the environment and costly. Considerable efforts have been devoted to improve the properties of 3D graphene monoliths. Biocompatible molecules like cellulose, ascorbic acid, tannic acid and dopamine have been reported to fabricate 3D graphene materials successfully (Li et al., 2018a, b; Liu et al., 2018a, b; Luo et al., 2016; Mi et al., 2018), but the high price and the complex extraction process of biocompatible molecules always restricted their application for preparing 3D graphene materials. Therefore, application of cheap, abundant biomaterials would be an alternative of biocompatible molecules for fabricating the 3D graphene materials. Peanut hull consists mainly of cellulose, hemicellulose and lignin, which can not only increase hydrophobicity of 3D graphene materials but also improve their mechanical strength as reported (Dang et al., 2018a, b; Mi et al., 2018). Meanwhile, cellulose, hemicellulose and lignin in peanut hull may improve mechanical strength of 3D graphene monoliths. Above all, peanut hull is recyclable, environmental friendly and low cost. Combining peanut hull with 3D graphene monoliths may greatly improve adsorption performance in oil-water separation.
Herein, we present a very simple, green and low-cost approach for the fabricating three-dimensional self-assembled hydrophobic peanut hull/graphene aerogels (3D-PG), successfully achieved base-induced one-step synthesis of 3D-PG for oil-water separation. In addition, three-dimensional self-assembled graphene aerogels (3D-G) without the aid of powdered peanut hull were also prepared as the indicator. Physicochemical properties of 3D-PG and 3D-G were determined by Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), Brunner−Emmet−Teller measurements (BET), Thermal gravimetric analysis (TGA), X-ray diffraction (XRD), Fourier transformation infrared spectrum (FT-IR), Raman spectrum, X-ray photoelectron spectroscopy (XPS) and Atomic Force Microscope (AFM). In addition, to fully understand the adsorption behavior of 3D-PG, the absorption capacity (Q), the adsorption kinetics and regeneration of 3D-PG was explored. Moreover, a dynamic system and the mechanical tests of 3D-PG were used to make sure its practical application.