Controllable Preparation,Properties And Applications Of Functional Graphene-polyaniline Based Nanocomposites

This thesis is intended to focus on two major issues.The first one is to design a supercapacitor electrode to store harvested energy from renewable energy resources to secure the sustainability of energy and reduce the air and water pollution caused by excessive usage of fossil fuels and oil spill.The second one is to identify an efficient catalyst to degrade the organic pollutants in water polluted by industrial waste and oil spill.To develop promising electrodes for high-performance supercapacitors,a novel3D ternary composite,graphene-Fe₃O₄-polyaniline(rGO/Fe₃O₄/PANI)and core/shell architecture of MnO₂ nanorods and polyaniline(MnO₂@PANI nanocomposite)were designed and developed via in-situ hydrothermal polymerization methods.Transition metal oxides such as MnO₂,Fe₃O₄,etc.have been investigated as electrode materials for supercapacitors.The larger specific surface area and highly porous nature of Fe₃O₄provide favorable environment for redox reactions to induce excellent electrochemical properties as a result high specific capacitance.Moreover,Fe₃O₄ is of low cost and environmentally friendly.Aggregation is the major limitation of Fe₃O₄ nanoparticles as an electrode material for supercapacitors.To overcome the challenges associated with aggregation it was essential anchoring the nanoparticles on the surfaces of graphene nanosheets.Intimate interaction between rGO and Fe₃O₄ nanoparticles enables easier electron transport.Moreover,the Fe₃O₄ nanoparticles would be smaller and uniformly distributed on the surface of rGO nanosheets reducing their restacking possibility that increases the specific surface area of the rGO/Fe₃O₄ nanocomposite which is significant for capacitance enhancement.For further capacitance enhancement,a high capacitance,thermally stable and chemically resistant PANI was chosen to develop a novel 3D ternary composite,graphene-Fe₃O₄-polyaniline(rGO/Fe₃O₄/PANI).The large specific surface area of rGO/Fe₃O₄ nanocomposite was favorable to encompass plenty of nanorod-like PANI.Another attractive transition metal oxide with pseudocapacitive behaviors is MnO₂having high theoretical capacitance value and large potential window.To overcome the challenge of small practical capacitance value,the intrinsic capacitive properties of MnO₂ have been activated by coupling it with conductive species,metal doping,heterojunction configuring,defects engineering,etc.In this thesis,a high capacitance,thermally stable,low volume expansion and high chemical resistant PANI was considered in adopting the conductive species coupling to activate capacitive properties of MnO₂.The design was a unique core/shell structure of MnO₂ nanorods wrapped with polyaniline(MnO₂/PANI)nanocomposite.The electronic interaction between the two components provide numerous electron transfer channels and porous structure of the nanocomposite can facilitate the ion transport which are very significant for capacitance enhancement of the nanocomposite.Structure and performance of the 3D ternary rGO/Fe₃O₄/PANI and core/shell architecture of MnO₂/PANI nanocomposites were characterized by powder X-ray diffraction,scanning electron microscope,high-resolution transmission electron microscopy,Fourier transform infrared spectroscopy,Raman spectroscopy,ultraviolet-visible absorption spectroscopy,Brunauer-Emmett-Teller(BET)and X-ray photo-electron spectroscopy(XPS).Finally,capacitance enhancements of the nanocomposites-based electrodes were explored carefully.Results of the capacitance and stability tests showed that electrochemical properties of rGO/Fe₃O₄/PANI-based electrode were enhanced greatly as compared to the pristine PANI and rGO/PANI nanocomposite attributed to the excellent synergistic effect among Fe₃O₄,PANI and rGO.Capacitance of the electrode was increased by 63%and 31%relative to the PANI and rGO/PANI-based electrodes,respectively.According to the cycle stability test,the rGO/Fe₃O₄/PANI-based electrode has retained 52.1%of its original capacitance after2000 cycles compared to 38.9%of the PANI-based electrode.In the case of MnO₂@PANI40(40%MnO₂ relative to aniline monomer)nanocomposite,it has shown notable capacitance enhancement compared to its pristine components.This is due to the synergistic effect of the core/shell networked hierarchical structure of the nanocomposite.That is,unique structure of the nanocomposite improves the ion transportation efficiency and reduces the ion diffusion path of the electrode.Moreover,uniform coating of PANI over MnO₂ nanorods offers protection against the dissolution of MnO₂ in the acidic electrolyte.High electrical conductivity status of PANI(due to its half oxidation-half reduction status,justified by XPS test)also plays important role in the capacitance enhancement of the nanocomposite.To degrade the organic pollutants in water(polluted by industrial waste and oil spill)through catalytic activities,different shapes of nano-sized copper sulfides(CuS)were prepared by hydrothermal method without any surfactant or template.FESEM and HRTEM results show that four morphologies of highly crystallized pure hexagonal covellite CuS(flower-like nanospheres,cross-linked nanodisks,cross-linked nanoplates and nanosheets)were prepared simply by changing the hydrothermal solvent.The strong absorption in the visible region of UV–vis spectra shows that the CuS nanostructures have potential application in the field of solar cells.According to detailed catalytic activities investigation on model pollutant methylene blue(MB)in the dark,the small and flat crystallites showed rapid degradation rate which is attributed to the numerous active sites on their large specific surface area.CuS nanosheets took only 15 min to degrade MB completely.Total organic carbon(TOC)removal of the samples approved mineralization of the MB pollutant.Thus,CuS is an excellent catalyst for degrading organic pollutants,which does not require light energy for its catalytic activities.