Magnetic Nanostructured White Graphene for Oil Spill and Water

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Magnetic nanostructured white graphene for oil spill and water cleaning Jose Humberto Ramirez Leyva, Afif Hethnawi, Gerardo Vitale, and Nashaat N. Nassar Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.8b02785 • Publication Date (Web): 07 Sep 2018 Downloaded from http://pubs.acs.org on September 10, 2018

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Industrial & Engineering Chemistry Research

Magnetic Nanostructured White Graphene for Oil Spill and Water Cleaning Jose Humberto Ramirez Leyva, Afif Hethnawi, Gerardo Vitale and Nashaat N. Nassar* Department of Chemical and Petroleum Engineering, University of Calgary, 2500 University Drive NW. Calgary Alberta, Canada. T2N 1N4. Email: [email protected], Tel: 403-210-9772

Abstract Crude oil spills are of global concern because of their potential to cause massive water pollution and the destruction of aquatic life. The current technologies for oilspill clean-up only focuses on impact mitigation and ignores crude oil recovery. There is therefore a need for an innovative technology that generates materials with crude oil recovery capabilities. Since manufactured materials have shown promising capabilities for recovering crude oil and treating water at the same time, this study examines and develops a strategy for manufacturing magnetic hexagonal boron nitride (h-BN) nanostructured composites - a high-performance material that can be used to both clean water and recover crude oil for further use after a crude oil spill. This manufacturing technique is unique as it consists of a single step and contemplates h-BN synthesis at 1300 K compared to 2275 K used previously. The material produced is capable of absorbing crude oil up to 53 times its own weight, employing only a magnetic field for the recovery. Evaluation of adsorption isotherms using model molecules demonstrated that absorption, rather than adsorption, is the dominant mechanism responsible for crude oil uptake.

Keywords: oil spills, nanoparticles, white graphene, hexagonal boron nitride

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1. INTRODUCTION A crude oil spill is a

situation when fluid hydrocarbons are released into the

environment due to anthropogenic activity.1 Since an average of about five million tons of crude oil are transported across the seas around the world annually.2 There is a significant risk of spills from either mechanical failure or human error. These spills represent a latent danger for accidents and a threat to water wildlife. The biggest crude oil spill in history occurred in 2010, when 486,000 tons of crude oil were released into the Gulf of Mexico, affecting 9900 km2 of the sea’s surface. Even worse than the financial losses of $30 billion, this crude oil spill had a profound negative impact on the environment that will be felt for the next 50 years.1 Because of the environmental regulations and economic sanctions that affect business, oil companies are seriously concerned about crude oil spills and interested in methods to mitigate their impact.3 Current technologies such as dispersion,4-5 conventional adsorption,6 biological treatment,7 flotation,8 settling9 and burning,10 have not only showed collateral effects, but also the crude oil cannot be recovered for further use. Absorption by porous materials is a frequently used technology for crude oil spills cleaning up.11 For the successful application of this type of technology there is a compromise between price, efficiency, and environmental impact.6 Current technology for crude oil sorption relies on the oil’s adherence to porous media contained in pillows.3 If the captured crude oil is wanted for further usage, separation processes must be carried out to the spent sorbent; following complicated procedures that are costly, inefficient and antiquated.5, 11 A key property which should therefore be considered is the ease, economy and feasibility with which spent material can be removed from water bodies.12 Research into the application of nanomaterials for crude oil spillage cleaning has increased in 2


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the last decade because of the potential ability for water treatment and crude oil recovery of the developed nanomaterials.13 Magnetic nanoparticles have been reported as promising alternatives for crude oil spillage clean-up and energy recovery.14 Their effectiveness is limited by two main factors: the specific surface area, and particles hydrophobicity.3, 15 Previous studies about magnetic iron oxide nanoparticles have reported specific surface areas around 96 m2/g.16 Regarding hydrophobicity, in some cases the usage of surfactants or grafting polymers around magnetic nanoparticles are needed to introduce oleophilic characteristics to their surface.17 Furthermore, using other magnetic nanomaterial have been also reported for oil spill-clean up, such as graphene aerogel/Fe3O4/ polystyrene composites,18 magnetic macro-porous carbon nanotubes (CNT),19 and magnetic graphene foam.20They showed an outstanding performance in oil spill removal and strong recyclability with oil removal capacities of 40, 56, and 28 g/g, respectively. These materials, even with high efficiencies, showed high biopersistence.21Thus, short or long-term exposure of them might lead to induced sustained inflammation, lung cancer, and gene damage in the lung.21For that reason, Hexagonal boron nitride (h-BN) was suggested as a bio-compatible and less harmful material for human body and many organisms as reported in our previous study.22 This material is commercially called white graphene. It is also a hydrophobic and light material with promising properties for crude oil sorption.23 Those properties are oleophilicity, low density,24 high melting-point,25 oxidation resistance,26 high specific surface area23 and the capability for making hybrid materials with iron oxide.28 h-BN was first synthetized in the laboratory by O´Connor in 1962,29 and its production was patented the same year.24 It has been commercially available since 1969.30 Until cubic boron nitride discovery in 2013, it

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was considered to be a man-made material with no naturally occurring counterparts.31 A versatile material, h-BN is currently being studied because its characteristics points to some promising uses in

medicine,32 electronics,33

cosmetics,34 wastewater treatment,23 pharmaceutical applications,35 and even space technology.36 Companies like General Electric in USA, Showa Denko in Japan, De Beers in South Africa and various companies in Russia are now producing this material for industrial applications.30 h-BN is considered highly thermally stable and resistant to high temperatures and oxidation,37 however, researchers have recently discovered that h-BN could be degraded by biological processes at mild temperatures even inside the human body.38 Nanostructured h-BN can be prepared

by different methods; including chemical

vapor deposition (CVD),39 synthesis from organic precursors40,41and synthesis from inorganic precursors.42 All of those methods are similar in that they use high temperatures (up to 1873 K) and high pressures (up to 5 GPa).43 The preparation method via reduction of melamine diborate (M2B) is considered the safest one as high pressure and flammable or toxic gases such as hydrogen or ammonia are not needed.44 h-BN can take different nanoscale morphologies depending on the applied synthesis method and the conditions used during preparation.45 Different h-BN nanostructures have been reported by other researchers, such as nanotubes,46 nanosheets,47 nano-meshes,48 nanoscrolls,49 nano-flower-shaped materials50 and nanoribbons which have similar characteristics to graphene.51 As the temperature plays a key role in the architecture and surface morphology of h-BN,51 scroll shaped h-BN structures can be engineered by temperature controlling.49 Considering that fact, a tailor-made thermal treatment might help in the development of h-BN economically. With the aforementioned unique properties, much attention has been 4


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paid by many researchers to synthesize a nanostructured h-BN as with excellent sorption capacity for crude oil spill clean-up.23,49-51 For instance, porous boron nitride nano-sheet showed excellent sorption performances toward wide ranges of organic solvents and dyes.21 Besides having high sorption capacity, the nano-sheets have high stability and strong resistance for oxidation.23 However, these materials have limited recyclability from the application perspective, because the need for an efficient separation process after each sorption cycle, and thus, unsatisfactory regeneration can be obtained. On the other hand, the retrieved crude oil requires mechanical handling, filtration, or high rate centrifugation procedures after each sorption cycle, which is unmanageable for continuous separation process in largearea oil spills. Furthermore, applying such physical separation procedures either ineffective or inappropriate for accurately quantification of the removed oil. Applying the physical separation following traditional standards like ASTM F716 and ASTM F726, for instance, have shortcoming in testing the efficiency of various sorbents for crude oil spill clean-up.52 These standards are not suitable to note the terminology used for describing the phenomenon of crude oil sorption. To modify these standards, keeping in mind better recyclability and separation processes, we introduced here magnetic boron nitride (MBN). Herein, we synthesize MBN in a simple procedure as an alternative material for crude oil spill clean-up, starting from M2B precursor. Our alternative material consists of a composite magnetic lyophilic sponge-like material, which can be dispersed in the crude oil spill, forming a magnetic nano-fluid with the oil. Then, the crude oil can be taken up by the high surface area and porosity MBN. After that, the spent sorbent, with applying a magnetic field, can be easily separated, enabling for easy recovery of crude oil as well as high uptake. However, the up-taken crude oil by



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MBN, similar to the BN nano-sheets,18 has unclear sorption phenomenon (surface or bulk).

Using the most general term “sorption” can be considered due to

encompassing both “adsorption” and “absorption” and the concept of both phenomena have unfortunately often been used loosely and interchangeably. When crude oil is taken up, there is no evidence that the removal was due to surface effect (adsorption) or capillary effect (pore filling) of crude oil molecules on a hydrophobic MBN, especially if a structural distortion is carried out for the MBN. By having all these scenarios, it is expected to have various removal phenomena for targeting a wide range of wastes. These phenomena can be observed by testing MBN in the removal of other dyes with opposite charges. Thus, we tested the removal of methylene blue (MB) and amaranth (AR), as commonly used dyes in the textile industry, by MBN. These experiments including adsorption isotherms in order to identify if the main mechanism responsible for the crude oil sorption corresponds to absorption or is due to surface interactions (adsorption). Hence, by development of MBN with its innovative features and understanding the mechanism involved in crude oil sorption, we are looking forward to improving the technology used in crude oil recovery. 2. Experimental Section 2.1 Synthesis of MBN

6


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Figure 1. Schematic representation of porous MBN preparation procedure. Magnetic boron nitride (MBN) was prepared using an in-house modification of the synthesis technique reported by O´Connor.53

Figure 1 shows a schematic

representation of the developed procedure. A stoichiometric ratio of 2:1 boric acid: melamine was employed to produce the melamine diborate (M2B) precursor of boron nitride. 4.6 g of boric acid (99%) from Sigma Aldrich were dissolved in 200 mL of boiling deionized water. Then, 4.3 g of melamine (99%) from Sigma Aldrich was added slowly under magnetic stirring at 350 rpm. At the same time, powdered steel filings were added in proportion of 5% by mass. M2B fast precipitation was induced by adding deionized water ice cubes to cause the precipitation of M2B on the surface of the suspended steel filing particles. By comparing this process with others in the reported literature,15, 54-55 suggests that the use of a smaller volume of water and abrupt quenching is responsible for accelerating the precipitation of the precursor of boron nitride, and facilitating the gathering of the iron particles from the steel filing within the M2B. The obtained iron particles-M2B composites were shaped to get uniform flakes approximately 1x30x50 mm. These flakes were introduced into an alumina crucible and submitted to a thermal treatment protocol. First, the material was heated at a rate of 10 K/min until 773 K and it was kept for 3 h, then the temperature was increased to 1073 K for 4 h. Finally, the material was heated to 1373 K for 6 h under nitrogen atmosphere. During the ramp up temperature protocol, nitrogen flow was employed at 30 psig with a flowrate of 150 mL/min until the end of the thermal protocol and the material was allowed to cool down to room temperature.



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2.2 Characterization of the Prepared Materials 2.2.1 X-ray Diffraction (XRD) Structure and crystalline composition of the materials were determined by using Xray diffraction. An Ultima III Multi-Purpose Diffraction System (Rigaku Corp., The Woodlands, TX) with Cu Kα radiation operating at 40 kV and 44 mA with a θ–2θ goniometer was employed for obtaining the diffraction patterns. The crystalline domain sizes were measured using the Scherrer equation as implemented in the commercial software JADE that came with the diffractometer. 2.2.2 High Resolution Transmission Electron Microscopy (HRTEM) The HRTEM images were collected on a FEI Tecnai F20 FEG TEM using an accelerating voltage of 200 kV. The samples were dispersed in pure ethanol. A pipette was then used to draw and deposit a drop of the suspension on the HRTEM carbon grid sample holder. The drop was then allowed to dry depositing powder particles on the grid holder. 2.2.3 Scanning Electron Microscopy (SEM) SEM images were taken by using a microscope Quanta FEG 250 field emission made by FEI. The X-ray spectrometry system used was a Bruker Quantax system equipped with a Bruker 5030 silicon drift detector (SDD). 2.2.4 X-ray Photo Electron Spectroscopy (XPS) XPS was carried out with a PHI VersaProbe 5000 spectrometer operating under ultra-high vacuum (

Magnetic Nanostructured White Graphene for Oil Spill and Water

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