Super light 3D hierarchical nanocellulose aerogel foam with superior oil adsorption

Abstract

In this work, the concentration effect of both nanocellulose and sodium dodecylsulfate (SDS) on the fabrication of a super light 3D hierarchical framework adsorbent nanocellulose aerogel foam (NAF) is exploited through a high speed mechanical foaming and solvent-free method by adding SDS. The results show that the optimal concentration of nanocellulose and SDS for preparation of this 3D NAF/SDS is 0.4 and 0.2 wt%, accordingly. By utilizing unique gridding framework of NAF/SDS, a low density of 1.50 mg cm⁻³ and high adsorption capacity of 206.79, 194.75 and 145.20 g g⁻¹ towards cyclohexane, ethyl acetate, and vacuum pump oil, accordingly, are achieved in the as-prepared NAF/SDS, which is much higher than that of conventional nanocellulose aerogel (NA) (52.07, 81.12 and 34.52 g g⁻¹, respectively). The results illustrate that this NAF/SDS is a promising candidate for preparing 3D hierarchical network structure from natural polymer cellulose in an environmental control for oil adsorption.

Introduction

With the developing of the petroleum industry and chemical industry, the oil spill and chemical leakage is becoming harmful issues to the environment faced by the human being [1], [2]. Consequently, numerous approaches such as chemical dispersant, hydrocarbon degrading microorganisms, adsorption and in-situ burning are applied to deal with these issues [3], [4], [5], [6]. Among these methods, adsorption is an effective method owing to its low cost and simple operation [7], [8], [9], [10], [11], [12]. Therefore, to seek effective adsorbents for the oil pollution is imperatively demanded [13], [14]. Darling et al. [15] prepared sequential infiltration synthesis (SIS) functionalized porous polyurethane and polyimide foams for oil adsorption. Aerogel, as a family of ultra-lightweight as compared with metals and ceramics [16], [17], [18], [19], [20], [21], [22], [23] and 3D hierarchical porous structure material, has been intensively investigated in the applications of supercapacitors [24], [25], batteries [26], [27], catalysts [28], [29], [30], flame retardant materials [31], adsorbents [32] and electromagnetic wave absorption [33] due to the large specific surface area, high porosity, low thermal conductivity and high electrical conductivity arising from their highly interconnected network [34], [35]. As a consequence, numerous materials including carbon nanotubes (CNTs) [36], carbon nanofibers (CNFs) [37], graphene [38], and polyaniline (PANI) [39] have been employed to prepare aerogels. Even though these materials with ultra-low density (<1 mg cm⁻³) and ultra-high oil and organic solvent adsorption capacities [40], the high cost of raw materials and the complicated fabrication process severely restrict their applications for oil and organic solvent adsorption [41].

Cellulose is an abundant natural polysaccharide which is composed of a linear chain of several hundred to many thousands of glucose units [42]. As a green and environment-friendly renewable natural resource, cellulose plays an irreplaceable role in the daily life of human being and has gained increasing and considerable attentions for oil adsorption [43] due to the presence of van der Waals forces interaction between oil phase and cellulose and hydrophobic effect to some extent on the surface of cellulose [44]. Various cellulose from barley straw [45], filter papers [46], papermill sludge [47], and nanocellulse sponge [48] have been reported for the oil adsorption. Especially, the emerging nanocellulose-based aerogels generated from the aqueous solution are flexible and less brittle relative to the inorganic aerogels [49]. These nanocellulose aerogels exhibit promising applications in the oil adsorption since they are low cost, renewable, biodegradable and possess high adsorption capacity [50]. For example, Chin et al. [51] reported cellulose aerogels with a motor oil adsorption capacity up to 40–95 times of its weights. Sai et al. [52] prepared a bacterial cellulose aerogel (BCA) with surface treated by trimethyichlorosilane, which displayed organic solvents and oil adsorption capacities up to 185 g g⁻¹. Nevertheless, the adsorption properties of these nanocellulose aerogels are mainly dominated by their microstructures and porosities [40]. In this case, how to control and optimize the morphologies and network structures of nanocellulose aerogels are the main challenges in designing and developing novel structures of nanocellulose aerogels and increase their oil adsorption ability. Normally, for the purpose of reducing the density and increasing the porosity of nanocellulose aerogels, surfactant alkyl polyglycoside Simulsol [53], [54], and cetyltrimethyl ammonium bromide (CTAB)[55] have been employed, the use of sodium dodecylsulfate (SDS) to fabricate nanocellulose aerogel has been rarely reported so far.

Herein, with the aim of handling the oil spill and chemical leakage, we developed a feasible solvent-free method to prepare a super-light 3D hierarchical nanocellulose aerogel foam (NAF) by using aqueous phase high speed mechanical foaming method with a foaming agent SDS, which exhibits an extremely high oil adsorption property compared with the nanocellulose aerogel (NA) without adding SDS. In addition, we have also provided the oil adsorption capability comparison of our as-prepared NAF/SDS with reported values of cellulose materials to show the advantage of our aerogel.