PREPARATION AND CHARACTERIZATION OF HYDROPHOBIC NANOCELLULOSE COMPOSITES FOR OIL SPILL CLEANUP

Abstract

Water is necessary for life, the environment, and the industrial revolution. Pollution and inadequate water management exacerbate the supply of fresh water. Wastewater treatment is becoming increasingly important for sustaining life due to the emission of volatile organic compounds (VOCs) and synthetic organic compounds (SOCs) from diverse sources like oil spills and the petroleum industry that occurred in exploration/transportation activities. The estimated risk of environmental hazards of oil and chemical pollutants is enormously high. The techniques used to treat the catastrophic oil spills of the last decades include in-situ burning, physical methods, chemical methods, and bioremediation. Among all these methods, physical sorption stands out due to its simplistic operability, significant capacity for oil capture, and high cost-efficiency, creating less secondary pollution. A wide variety of sorbent materials have been utilized for oil spill cleanup, such as inorganic minerals, synthetic organics, and natural organics. However, these materials have several drawbacks, including low efficiency, non-renewability, secondary pollution, and lack of eco-friendliness. Our strategy involves utilizing a 3D structure based on nanocellulose (NFC) as a sorbent material. It is not only the pristine cellulose material; using different approaches, we converted the hydrophilic cellulose composite to hydrophobic for selective sorption of oil/organic solvent from the aquatic environment. First, we used stearic acid chloride as the modifying agent through a dip-coating strategy. Incorporating a long fatty chain on the hydroxyl group of NFC composites gives a tremendous change in the water contact angle (WCA) study. The hydrophilic surface (WCA ∼ 0°) turns to superhydrophobic (WCA ∼ 159°) by anchoring a long fatty chain on the hydroxyl group. The surface analysis study using field emission scanning electron microscopy (FE-SEM) and X-ray microtomography (XMT) showed the uniform cellular porous structure and was unaffected after modification. The specimen was used to sift a wide range of oil/organic solvents from a water mixture of 35-105 g/g. Further, we used the different chain lengths (C8, C12, C18, and C22) for functionalization in the next study. The chain length study shows that the hydrophobic wettability properties increase with increasing the side chain length, and the pore structure was affected at a higher chain length. The C18 modified aerogel performs better with high crude oil removal efficiency (98%) and excellent reusability for at least 15 cycles. The adsorption isotherm analysis for crude oil revealed that it follows the Langmuir models with a maximum sorption capacity of 61 g/g. In our subsequent research, we employed rice straw (RS), an agricultural waste material, to extract cellulose. We utilized polylactic acid (PLA) to modify the extracted cellulose hydrophobically via a spray Abstract

coating technique. The FE-SEM analysis shows that the incorporation of PLA on the aerogel did not affect the internal porous structure, while the surface wettability shows a WCA of around ∼ 120°. The PLA-coated aerogel removes different oil/organic solvents from water within 33-70 g/g. In the fourth approach, we developed the organic solvent-free insitu modification strategy using natural rubber latex (NRL). The synergistic effect of 20% NRL in the NFC matrix improves the WCA of hydrophilic NFC to ∼ 110°. The prepared composite was tested for continuous oil removal and shows that it separates the oil continuously with negligible water uptake. The prepared composite sample widely absorbs a different range of organic solvents/oil from an aquatic environment with a sorption capacity of 36-68 g/g. Reusability analysis shows that it could be reused for at least 10 cycles for oil/organic solvent with 85% efficiency. Instead of using a nanocellulose 3D structure in the fifth approach, we used 2D filter paper (FP). The smooth surface of FP tuned to the rough structure with the incorporation of Fe2O3 nanoparticles in combination with myristic acid (MA). The synergistic effect of nanoparticles combined with low surface energy MA gives the lotus effect. The modified FP removed the different organic solvent from water with a flux rate of 800-500 L/m2h for chloroform/water andDMF/water, respectively. The modified FP also separates the different emulsion types effectively. The tentative cost analysis of all the prepared specimens was estimated and compared with the reported literature. With the urgent need for sustainable materials, this research presents a promising path toward a more sustainable future.