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Simultaneous Preparation of Meso/macroporous Graphene Aerogels and Bright Green Photoluminescent Graphene Quantum Dots by a Simple Solvothermal Method Jiajie Yu, Siyu Liu, Shuai Chen, and Tianhe Wang Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.7b01954 • Publication Date (Web): 15 Aug 2017 Downloaded from http://pubs.acs.org on August 17, 2017
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Industrial & Engineering Chemistry Research
Simultaneous Preparation of Meso/macroporous Graphene Aerogels
and
Bright
Green
Photoluminescent
Graphene
Quantum Dots by a Simple Solvothermal Method Jiajie Yua, Siyu Liua, Shuai Chenb, Tianhe Wanga* a
Chemicobiology and Functional Materials Institute, Nanjing University of Science
and Technology, Nanjing, 210094, China b
School of Management, Chengdu University of Information Technology, Chengdu,
610225, China The corresponding author e-mail address:
[email protected] Abstract: In this work, we report a simple one-step solvothermal method using DMF as solvent to fabricate simultaneously meso/macroporous graphene aerogels (GAs) and strong green photoluminescent graphene quantum dots (GQDs). A black monolithic graphene organogel was formed under solvothermal condition and further freeze-dried to obtain GA. In addition, the residual DMF solvent was filtered, dialyzed and diluted to produce GQDs. The resulting GAs exhibited\ an average mesopore size of 3.98 nm, while the GQDs had a mean diameter of 4.92 nm. The interconnected macropores were derived from assembled GA, while the mesopores on GAs were probably formed by a result of “chipping” GQDs off the GA sheets under solvothermal condition. The as-prepared GAs exhibited an amazing adsorption capacity of not only oil products, but also toxic solvents like chloroform and toluene. 1
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In addition, GAs also showed excellent abilities for dyes removal from water. The GQDs exhibited bright green photoluminescent properties with high quantum yield of 11.2%. The solid GQDs were capable of being redissolved in water and most polar organic solvents, and showed typical excitation- and solvent-dependent properties. Keywords ： Graphene aerogels; Graphene quantum dots; Solvothermal method; DMF; Oil adsorption
1. INTRODUCTION Graphene has attracted intense interest because of its distinctive band structure and physical properties,1,
2
and wide potential applications in nanoelectronics, energy
storage and conversion, chemical sensors and biotechnology.3-5 Recently, three dimensional (3D) graphene macrostructures like hydrogels, organogels and aerogels have been widely developed, primarily due to the fact that they not only retain the large surface area of graphene nanosheets, but also have highly porous structures.6 As a result, they provide a functional platform characterized by light weight and high porosity,7 thus offering a variety of potential applications in areas of catalysis,8 oil adsorption and water treatment.9 So far, there have been several methods to produce 3D graphene architectures including cross-linking method,10 chemical vapor deposition method (CVD),11 self-assembly method12 and hydrothermal/solvothermal method.13 Chemical or physical cross-linkers such as organic binders,14 DNA molecules15 and ion linkages10 2
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Industrial & Engineering Chemistry Research
were used in the cross-linking method to promote the assembly of 3D graphene macrostructures, but these cross-linkers normally resulted in a decrease of electric conductivity of graphene. CVD method was also attempted to deposit graphene into 3D nickel foams under high temperatures.16,
17
The self-assembly technique was
reported to produce 3D graphene under mild conditions.18 Hydrothermal/solvothermal method is a simple method for the preparation of 3D graphene, although it is usually achieved under high pressure or using a large amount of reducing agents.13, 19 It is still widely adopted in synthesis owing to the unique feature of self-generated high pressure in sealed vessels.20 However, three dimensional GAs and zero dimensional GQDs are usually separately prepared and there is no literature reporting a method capable of fabricating them together in a single step. For the first time, to our best knowledge, we demonstrate a simple solvothermal method to produce simultaneously meso- and macroporous GAs and bright photoluminescent GQDs. We used DMF as a solvent and reducing agent, with no additional added chemicals. Organic pollutants or oil leakages have caused serious environmental and ecological issues in recent years.21 Traditional adsorbents like zeolites, perlites and activated carbon usually have low oil adsorption capacities and have difficulties in efficient separation of dye pollutants from waste water.22 Many efforts have been applied to prepare new advanced adsorbents for the fast and efficient separation of organic pollutants or oil from water.23 Graphene aerogels, due to their ultralight weight, high porosity and large surface area, have been proved to exhibit excellent oil removal capacity and good reusability. GQDs are usually few layers or tens of layers 3
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of graphene with a size less than 30 nm.24, 25 They have emerged as a fascinating quantum dot system due to their remarkable optical, electronic and spin properties induced by quantum confinement and edge effects.26-28 Therefore, GQDs have promising applications in cell imaging,29 biosensing,30 photovoltaic31 and light emitting device.32 In this paper, we provide a simple solvothermal method to fabricate simultaneously meso/macroporous GAs and bright green photoluminescent GQDs. This simple solvothermal method was achieved by using DMF as solvent and no additional chemical agent was added. The obtained GAs possessed excellent adsorption capacities for oil products and were reusable for up to ten times without obviously decreased oil capacities. It was also efficient for organic dyes removal from water. The GQDs were shown strong green photoluminescent with high quantum yields of 11.2%. The novelty of this study lies in: (a) we put forward a simple solvothermal method to produce GAs and GQDs simultaneously, (b) a plausible “chipping” mechanism was proposed for this simple method, (c) the obtained GAs with mesoand macroporous structures exhibited excellent properties for oils adsorption and dyes removal from water, and (d) GQDs exhibited strong green photoluminescent with high quantum yields.
2. MATERIALS AND CHARACTERIZATION Chemicals.
Natural
graphite
powder
(
