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Fabrication and Characterization of Porous Carbon-Graphene Composite as an Absorbent for Industrial Pollutants

Alizadeh, Omid | 2020

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 53644 (48)
  4. University: Sharif University of Technology
  5. Department: Institute for Nanoscience and Nanotechnology
  6. Advisor(s): Madaah Hosseini, Hamid Reza; Pourjavadi, Ali; Bahramian, Ahmad Reza
  7. Abstract:
  8. The amount of fresh water suitable for various uses is decreasing day by day. This may be due to evaporation or contamination of water or such. Heavy metal cations, dyes, oils and solvents are the most important substances that contaminate water. There are various ways to remove these contaminants, one of which is the absorption of these substances by suitable absorbents. Carbon compounds have attracted much attention among all the absorbents used so far. The aim of this study is to produce carbon aerogels from an economic and modify its structure and properties by adding graphene nanosheets. In this study, Novalak-graphene oxide (GO) gel was fabricated using solvent-saturated vapor atmosphere method and after drying under environmental conditions and carbonization, it was transformed into carbon-graphene aerogel. The specific surface area of carbon aerogels is more than 500 m2.g-1, which is a large surface area after ambient drying. It has been shown that the size of turbostratic crystallites increases by about 100% by adding 2 wt.% GO due to the presence of thermally-reduced graphene oxide nanosheets (rGO) in the structure that act as a growth template for carbon atoms. The size of turbostratic crystallites has been increased from 24.2% in the GO-free carbon aerogel sample to 49.9% and 60.1% in the carbon aerogels with 2 and 5 wt.% GO. The "modified quasi-percolation" model has been proposed to describe the effect of different GO values on the size of turbostratic crystallites. According to SAXS results mass fractal behavior is observed in all carbon aerogels with fractal dimension between 2.6 to 2.85. Morphological and structural characteristics such as total pore volume, density, average pore size and pore size distribution are affected by the addition of GO. In addition, GO increases the total porosity and reduces the density of carbon aerogel. Although the addition of GO nanoparticles slightly alters the volume of the micro-cavities, it greatly alters the size and structure of the macro- and mesospores. The lowest density (0.167 g.cm-3) belongs to the carbon aerogel with 5 wt.% graphene oxide (C5G), which shows the largest specific surface area with 580.6 m2.g-1. According to the data obtained from the TGA test, the char yield of organic aerogels increases by adding graphene oxide and the char yield at 740 oC increased from 57.3 for pure organic aerogel to 61.4% and 83.0% for organic aerogels with 2 and 5 wt.% graphene oxide, respectively. The highest value of MB adsorption capacity by carbon aerogels is 430.2 mg.g-1. The highest kinetic constant of the pseudo-second order is 5.388 mg.mg-1.min-1. The adsorption capacity increases with increasing temperature and initial dye concentration. As the pH increases from 3 to 8, the adsorption capacity increases but as the pH increases further, the adsorption capacity decreases. The maximum adsorption capacity of carbon aerogels is measured for Pb2+ equal to 220.2 mg.g-1. In general, the lower the temperature and the higher the initial concentration, the higher the Pb2+ adsorption capacity. The highest adsorption capacity is also obtained at pH 7
  9. Keywords:
  10. Graphene Oxide ; Adsorbent ; Activated Carbon ; Solvent-Saturated-Vapor-Atmosphere Method (SSVA) ; Quasi-Percolation Model ; Carbon Aerogel

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