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Materials and Interfaces 2
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Regenerable CuO/#-AlO-Reduced Graphene Oxide Adsorbent with a High Adsorption Capacity for Dibenzothiophene from Model Diesel Oil Hongqin Ma, Xiao Sun, Meijie Wang, and Jiasheng Zhang Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.8b00407 • Publication Date (Web): 16 Jul 2018 Downloaded from http://pubs.acs.org on July 18, 2018
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Industrial & Engineering Chemistry Research
Regenerable CuO/γ-Al2O3-Reduced Graphene Oxide Adsorbent with a High Adsorption Capacity for Dibenzothiophene from Model Diesel Oil Hongqin Ma,*,u
Xiao Sun,u Meijie Wang,u Jiasheng Zhangu
u
( School of Chemical Engineering and Technology, Tianjin University, Tianjin 300350, China) ABSTRACT: This research focused on the removal of dibenzothiophene (DBT) from model diesel oil using
CuO-loaded γ-Al2O3-reduced graphene oxide (CuO/γ-Al2O3-RGO) as an adsorbent, which possesses the highest adsorption capacity among reported regenerable graphene-related materials. The boehmite-RGO supports were synthesized using a one-pot hydrothermal synthesis method. As the RGO sheet surfaces are completely covered and isolated by boehmite nanorods formed via hydroxyl condensation of [Al(OH)x](3-x)+ or Al(OH)3 and the -OH of graphene oxide (GO), the specific surface area of boehmite-RGO increased to 378 m2/g, which is 20.8% higher than that of RGO (313 m2/g). CuO/γ-Al2O3-RGO adsorbents with different CuO contents were prepared, and their DBT adsorption desulfurization properties were evaluated. With a 2% mass ratio of CuO to boehmite-RGO, CuO/γ-Al2O3-RGO displays the highest DBT adsorption capacity (6.0 mg S/g) under ambient conditions, which improved by 53.8% in comparison with that of pure RGO (3.9 mg S/g). Moreover, the regeneration of the CuO/γ-Al2O3-RGO adsorbent is much more practical than that of the pure RGO adsorbent.
1. INTRODUCTION A growing population with increased needs has caused serious environmental problems.1,2 Among the variety of pollutants, SOx emissions from the combustion of sulfur compounds contained in fuel oil have received wide attention. In recent years, many countries have required sulfur concentrations in diesel to be less than 10 ppm.3,4 Hence, numerous technologies have been developed to sustain a green atmosphere.5,6 The conventional desulfurization technology is catalytic hydrodesulfurization (HDS). Nevertheless, HDS has a few disadvantages, such as expensive hydrogen, rigorous high-pressure and high-temperature reaction conditions, and negligible removal rates for bulky sulfur compounds, such as dibenzothiophene (DBT) and benzothiophene (BT), due to their low hydrogenation reactivity.7-9 Therefore, many studies have focused on ultra-deep desulfurization technology, which could produce “zero” sulfur fuels. Among several effective desulfurization processes, selective adsorption desulfurization provides a promising alternative approach for the removal of thiophene derivatives from hydrocarbon fuels with the potential to realize low sulfur levels under normal pressure and temperature conditions.10,11 On this basis, various new adsorbents, such as zeolites,12 activated carbon,13,14 and boron nitride,15 have been investigated for their ability to efficiently remove sulfur from fuels. Moreover, π-complexation adsorbents, which have interactions stronger than van der Waals interactions, were reported to be superior to all other adsorbents.16-18 The studies on complexation adsorbents have shown that Cu2+ ions have the potential to strongly bind aromatic organosulfur compounds via sulfur-metal σ-bonds and π-interactions.12,19 As discussed by Seredych et al,20 copper oxides and metallic copper have a positive effect on the performance of polymer-derived carbon in the desulfurization process of diesel fuel. The desulfurization performance under ambient conditions using fluid catalytic cracking (FCC) fuel was evaluated and has been shown to have a significant increase upon modification of SBA-15 with CuO. However, this increase decreases slowly as the concentration of CuO increases.21 Recently, exfoliated graphene has attracted considerable attention due to its unique two-dimensional (2D) structure and excellent functional properties, which include a high specific surface area (a theoretical value of 2630 3
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m2/g), mechanical robustness, chemical inertness, and remarkable electrical and thermal conductivities.22-28 Among numerous multidisciplinary research activities,29 the utilization of graphene-related materials as support frameworks for functional nanoparticles has emerged as a promising research field.30 Hybrid materials based on inorganic nanoparticles and graphene or its hydrophilic derivative, graphene oxide, have been shown to significantly enhance functional performance in a wide range of applications,31 including sensors,32-35 tribological properties,36,37 metal-free electrocatalysis,38 and photocatalysis10. Graphene layers are prone to re-aggregation due to intrinsic van der Waals forces, which can result in a reduction of the interfacial area of RGO. In the open literature, there is relatively little work devoted to improving the bonding between graphene/graphene oxide nanoplatelets and other nanoparticles, which can effectively overcome the enormous interlayer van der Waals forces and have positive effects on the surface area and porous structure of RGO. As an important hydrated alumina, boehmite (γ-AlOOH) has been widely used in catalysis,39 adsorption,40 catalyst supports41 and the preparation of alumina-based materials. Recent reports suggest that boehmite-modified RGO is a promising support material owing to its unique properties, including a high surface area and abundant anchoring sites (hydroxyl groups).42 Graphene is also known to have an sp2 configuration and contain free π bonds for interactions with DBT rings.22 The strong π-π bonds can form face-to-face between RGO and DBT molecules when DBT is adsorbed on the RGO surface, leading to difficulty in desorbing DBT from the RGO surface during regeneration. Herein, we developed a novel procedure to synthesize RGO modified with boehmite using ammonium hydroxide as a precipitator with a one-pot hydrothermal synthesis method and applied it to prepare a new adsorbent material as a support. In this case, the surface of the RGO can be covered and isolated by boehmite, and the regeneration of the adsorbent can be easily achieved in comparison with that of pure RGO. Then, boehmite-RGO samples loaded with different amounts of CuO were produced to access the capability of adsorption desulfurization from model diesel, and CuO was used as the active component. The pure RGO and CuO/γ-Al2O3-RGO adsorbents loaded with different contents of CuO were tested in batch experiments to evaluate the saturated adsorption capacity of DBT from isooctane (model diesel) at normal temperature and pressure conditions by a static adsorption method, and the adsorption-desorption recyclability was quantified. To the best of our knowledge, this is the first report on the application of a CuO/γ-Al2O3-RGO material as a desulfurization adsorbent.
2. EXPERIMENTAL SECTION 2.1.
Materials. The chemicals used in this work are as follows: graphite powder (Aladdin,
