Chemical Functionalization Of Carbon Nanotubes By Hydroxyl Radical

As a new molecular form of carbon in the fullerene family, there has been increasing interest in carbon nanotubes (CNTs) because of their structural, electronic and mechanical properties. The initial studies focused on preparation and purification techniques, as well as on understanding the structure and physical properties of the pristine nanotubes. In recent years, however, chemical functionalization of CNTs has attracted great attention and efforts to modify their chemical and physical properties, and expand their application areas.It is well known that Fenton oxidation system is a kind of advanced oxidation process (AOP) for existence of hydroxyl radical (HO) which can be generated by Fenton's reagents (Fe²+/H₂O₂). Noticeably, HO has double properties of oxidisability and electrophilic reactivity. On the one hand, HO is known as one of the most active oxidants which has a higher oxidation potential than other oxidants except for fluorine. On the other hand, HO can attack the high electron density sites as an electrophilic reagent and easily carry out electrophilic addition reaction with the unsaturated substances abundant with Ï€ -bonding electrons, such as alkenes, alkynes, aromatic compounds and fullenes as well. Furthermore, considering that CNTs are assemblies of concentric sp² bonded carbon tubules made of rolled-up graphite sheets. So there are plentiful Ï€ -bonding electrons in nanotube framework. Hereby we conclude that functionalization of CNTs could be achieved via electrophilic addition and oxidation reaction of HO This paper mainly consists of five parts as follows: Part one: Preparation and purification of carbon nanotubesIn our paper, the pristine CNTs synthesized by catalytic chemical vapour deposition (CCVD) method contains catalytic particles and the carbonaceous impurities. So it is necessary to eliminate these impurities before the experiment. In this work, we developed a two-step purification method to remove the above-mentioned impurities. The purification procedure was as follows: Firstly, the pristine MWNTs sample was calcined in air at certain temperature for some time. The temperature of air oxidation of CNTs was determined by TGA. Thus the carbonaceous impurities were removed effectively. After air oxidation treatment, the residual powders were submerged into an acid solution and simultaneously sonicated for some time, then the solution was centrifuged and filtered. In this step, the catalytic particles were removed. The experimental results were investigated by SEM, TEM, TG-DTG, EA and XRD.Part two: Chemical functionalization of multi-walled carbon nanotubes (MWNTs) by hydroxyl radicalAfter purification pretreatment, multi-walled carbon nanotubes (MWNTs) was treated with Fenton's reagents and concentrated H2SO4/HNO3 mixture, respectively. The results of FT-IR spectra showed that hydroxyl groups and carbonyl groups could be brought into the MWNTs after Fenton chemical treatment. However, both carbonyl groups and carboxylic groups could be produced at broken sites when MWNTs was treated by concentrated H2SO4/HNO3 mixture. The original graphene structure of MWNTs was disordered/destroyed and some holes were formed on the end caps and sidewalls, as expected, which was in accordance with gradual enhancement of I_D/I_G in Raman spectra with the increase of oxidative treatment time. When MWNTs was treated with Fenton's reagents, the following factors: molar ratio of H2O2 and Fe²+, pH value and reaction time, could affect modification outcome of MWNTs. The experimental results indicated that when molar ratio of H2O2 and Fe2+ was maintained at 10 and pH value at 3 under acidic condition, more carbonyl groups could be produced on the MWNTs after the treatment was carried out for 1 Oh. In other words, MWNTs could be modified very effectively in the optimized conditions. Part three: Chemical functionalization of multi-walled carbon nanotubes synthesized in different preparation conditions by CCVD methodAfter purification pretreatment, in the same experimental conditions two kinds...