UV induced reduction of graphene oxide (GO) filled pristine and oxidized CNF composites

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Fabrication of graphene oxide (GO) filled pristine and oxidized cellulose nanofibrils (CNF) composites

The composite films were fabricated by mixing graphene oxide dispersion with CNF and TCNF followed by solution casting. The GO dispersions were prepared by mixing 200 mg of graphene oxide in 100 ml of deionized water and treated by ultrasonically for 1 hr to get homogeneous dispersion. The GO solutions having 0.003/0.006/0.0125/0.019 g were mixed with 50 ml of 1.2 wt% of CNF and TCNF, respectively using magnetic stirrer (Tehtnica Rotamix SHP-10) and cast on to Petri dishes for drying at room temperature. The fabricated films of GO with CNF were named as CGO-0.5, CGO-1, CGO-2, and CGO-3, whereas films of GO with TCNF as TCGO-0.5, TCGO-1 TCGO-2 and TCGO-3, respectively.

Fabrication of reduced graphene oxide (RGO) filled cellulose nanofibrils (CNF) as film like xerogels and cryogels

Various quantity of RGO (0.0003, 0.0008, 0.0013, 0.0025, 0.005, 0.0125 g) was mixed with 15 ml of DMSO using ultrasonic processor (CV 334) for 1 hour to obtain a stable solution.
20 ml of 1.2 wt% CNF solution were mixed with each of the RGO solutions by stirring for another 30 minutes to get homogeneous CNF-RGO (CRGO) dispersions. The resultant CRGO dispersions were vacuum filtered to remove DMSO and dried at room temperature to obtained film-like xerogel. The composite films were termed as CNF, CRGO-0.1, CRGO-0.3, CRGO-0.5, CRGO-1, CRGO-2 and CRGO-5. In parallel, the solvent-removed CRGO-5 water-dispersion was put into Teflon Petri dishes of 50 mm and placed on a temperature-controlled (by the software programme Supercool®) Cu-plate of a self-constructed cryo-unit with a temperature set to -50 ̊ C and -80 ̊ C, respectively, for about 3 hours to allow the cryogelation process and formation of the porous structure, followed by lyophilisation for 48 hours using a Christ Alpha 1-2 LD plus freeze-dryer to remove water.

Attenuated Total Reflectance – Fourier Transform Infrared (ATR-FTIR)

Attenuated Total Reflectance – Fourier Transform Infrared (ATR-FTIR) spectroscopic analysis was performed to identify the spectral differences associated with the molecular structure of the films, as well as to identify the nature of their interaction. For that purpose, a Perkin–Elmer IR spectrophotometer was used with a Golden Gate Attenuated Total Reflection (ATR) attached to a diamond crystal. The spectra were accumulated under ambient conditions from obtaining 16 scans at resolutions of 4 cm-1 within a region of 4000-500 cm-1, with air spectrum subtraction performed in parallel as a background. The Spectrum 5.0.2 Software Programme was applied for the data acquisition analysis.
In the case of composites with NGO and GO, a linear baseline was subtracted, and the resulting (absorbance) spectra were normalised before performing the spectral deconvolution in the OH region (3000–3700 cm−1) as well as the carbonyl region (1500-1800 cm-1), only for GO based composites, followed by the Gaussian curve fitting procedure, being processed by using Peakfit 4.12 software (Galactic Industries Corporation, New Hampshire, USA). Band position and area were assessed and compared.

X-Ray diffraction (XRD) analysis

X-ray Diffraction (XRD) technique were employed to confirm the reduction of graphene oxide and to study the crystallinity of the composite films. The X-ray equatorial diffraction patterns of the composite films were obtained with an X-ray Diffractometer (Bruker Diffractomer D8 Advance Model) using Cu Kα radiation (λ= 0.1539 nm) at the operating voltage and current of 40 KV and 40 mA, respectively, at room temperature (23±1 °C) at a scan rate of 2◦ min−1.

UV-Visible spectroscopy analysis

The transmittance curves of the NGO based composite films within the 250-750 nm wavebands were recorded using a Lambda 900 UV- Vis spectrophotometer (Perkin Elmer) with an integrated sphere of the scanning speed of 450 nm/min.

Contact angle and surface energy analysis

Film surface free energy and surface energy components were determined from Contact Angle (CA) measurements with four pure liquids of different polarities, namely water, formamide, diiodomethane, and glycerol. Contact Angle (CA) measurements of the NGO based films were performed using an SCA20 contact angle measurement system from Dataphysics (Germany). All measurements were conducted at room temperature on two independent surfaces with a test liquid volume of 3 mL. Each CA value was the average of at least eight drops of liquid per surface. The Surface Free Energy (SFE) of the films was calculated from the Contact Angle values of the test liquids by the van Oss and Good method [6-7]. The values of the surface tension and the components of the probe liquids used for CA measurements were taken from the Dataphysics database. The total SFE (γsTOT) was calculated using the acid-base approach of van Oss and Good, which divides the total SFE into the dispersive Lifshitz–van der Waals interaction (γsLW) and the polar Lewis acid–base interactions (γsAB) according to the following Equations:
γsTOT = γsLW + γsAB (1).
γsAB = 2 √(γs+ γs-) (2).

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Table of contents :

Contents
Acknowledgements
Chapter 1: Graphene-cellulose composites for energy storage applications
1. Introduction
1.1 Energy storage systems
1.1.1 Conventional capacitors
1.1.2 Batteries
1.1.3 Electrochemical capacitors
1.2 Selection of materials for high charge storage capacity
1.2.1 Polymer composites
1.2.1.1 Graphene as a filler material
1.2.1.2 Synthesis of graphene based fillers
1.2.1.3 Cellulose as a matrix
1.2.1.4 Chemical modifications on cellulose
1.3 Graphene- cellulose composites for energy storage applications
1.4 Objectives of research
1.5 References
Chapter 2: Materials and methods
2.1 Introduction
2.2 Materials
2.3 Methods of fabrication of different nanocomposites
2.3.2 Fabrication of ammonia functionalized graphene oxide (NGO) filled pristine and oxidized cellulose nanofibrils (CNF) composites
2.3.3 Fabrication of graphene oxide (GO) filled pristine and oxidized cellulose nanofibrils (CNF) composites
2.3.4 Fabrication of thermally reduced graphene oxide (RGO) filled cellulose nanofibrils (CNF) composites as film like xerogels and cryogels
2.4 Characterization techniques
2.4.1 Potentiometric titration
2.4.2 Raman spectroscopy
2.4.3 Attenuated Total Reflectance – Fourier Transform Infrared (ATR-FTIR)
2.4.4 X-Ray diffraction (XRD) analysis
2.4.5 UV-Visible spectroscopy analysis
2.4.6 Contact angle and surface energy analysis
2.4.7 Transmission Electron Microscopy (TEM)
2.4.8 Scanning Electron Microscopy (SEM)
2.4.9 Tensile strength analysis
2.4.10 Dynamic mechanical analysis (DMA)
2.4.11 Thermal Gravimetric Analysis (TGA)
2.4.12 Dielectric studies
2.4.13 Cyclic voltammetry (CV) analysis
2.4.14 Electrochemical impedance spectroscopy (EIS)
2.5 Conclusions
2.6 References
Chapter 3: Oxidization of pristine CNF using TEMPO reagent and synthesis, reduction and characterization of graphene oxide (GO)
3.1 Summary
3.2 Oxidization of pristine cellulose nanofibrils
3.3 Characterization of pristine and oxidized CNF
3.3.1 Potentiometric titration analysis
3.3.2 ATR-FTIR analysis
3.3.3 XRD studies
3.3.4 UV-Visible spectroscopy analysis
3.3.5 Scanning Electron Microscopy (SEM)studies
3.4 Synthesis of graphene oxide
3.5 Characterization of synthesized graphene oxide
3.5.1 Transmission Electron Microscopy (TEM) studies
3.5.2 XRD analysis
3.5.3 Raman spectroscopy
3.5.4 ATR-FTIR analysis
3.6 UV induced reduction of graphene oxide (GO) filled pristine and oxidized CNF composites
3.6.1UV irradiation experiment
3.9 Thermal reduction of graphene oxide (GO)
3.10 Characterization of thermally reduced graphene oxide (RGO)
3.10.1 Transmission Electron Microscopy (TEM) studies
3.10.2 XRD analysis
3.10.3 Raman spectroscopy
3.10.4 ATR- FTIR analysis
3.11 Conclusions
3.12 References
Chapter 4: Structure, morphology, mechanical, dielectric and electrochemical storage properties of ammonia functionalized graphene oxide (NGO) filled pristine and oxidized cellulose nanofibrils (CNF) composites
4.1 Summary
4.2 ATR-FTIR spectroscopy analysis
4.3 XRD studies
4.4 UV-visible spectra analysis
4.5 Contact angle and surface energy studies
4.6 Scanning Electron Microscopy (SEM) studies
4.7 Mechanical properties
4.8 Thermal properties
4.9 Dielectric properties
4.10 Electrochemical properties
4.11 Conclusions
4.12 References
Chapter 5: Structure, morphology, mechanical, dielectric and electrochemical properties of untreated and UV treated composites of graphene oxide (GO) filled pristine and oxidized cellulose nanofibril composites
5.1 Summary
5.3 Potentiometric titration studies
5.4 ATR-FTIR spectroscopy analysis
5.5 XRD analysis
5.6 UV-Visible spectra studies
5.7 Dynamic mechanical analysis (DMA) studies
5.8 Dielectric properties of untreated composites
5.9 Dielectric properties of UV treated composites with different treatment time
5.10 Electrochemical properties of untreated and UV treated composites
5.11 Conclusions
5.12 References
Chapter 6: Structure. morphology, dielectric and electrochemical storage properties of thermally reduced graphene oxide (RGO) filled cellulose nanofibrils based xerogels and cryogels
6.1 Summary
6.2 ATR-FTIR spectroscopy analysis
6.3 XRD analysis
6.4 Scanning Electron Microscopy (SEM) studies of composite films
6.5 Temperature dependent dielectric properties of films
6.6 SEM analysis of aerogel composites
6.7 BET analysis of film and aerogels
5.9 Electrochemical properties of film and aerogel composites
5.10 Conclusions
5.11 References
Chapter 7: Conclusions and Perspectives

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