Organic Electron Donors as Powerful Single-Electron Transfer Reducing Agents in Organic Synthesis Essay

This hydrate is relatively stable and exhibits all the triphenylene properties. 2,3,6,7,10,11-hexamethoxytriphenylene (HMTP), a product from substitution of methyl group reaction is used as a new organic cathode material (Figure 2.6), which exhibit similar reduction and oxidation potentials as poly(2,2,6,6-tetramethylpiperidinyloxy-4-yl methacrylate) (PTMA) and have high rate capability and stable cycling. However, HMTP is less prone to self-discharge due to the delocalization of the free electron over the whole molecule, compared to other organic cathode material containing free radicals, where the charge is localized [16-17]. 2.4 Mesoporous Silicon Based Material/Carbon Composite as Anode System of Lithium Ion Battery Recently, a variety of methods were used to synthesize nano-scale materials. In order to improve their properties, the nanomaterials have been fabricated. The nanomaterials can be fabricated via laser-assisted catalytic growth (LCG) processes, single-wall carbon nanotubes (SWCNT), capillary growth methods, template synthesis, and self assembly. Between the methods stated, template synthesis is more preferred because the size and shape of the desired materials can be controlled using a well-defined template matrix [2]. Generally, mesoporous materials that have pore diameter between 2 to 50 mm were used in the template synthesis method. Some examples of mesoporous materials that can be used are SBA (Santa Barbara USA)-n, MCF (Mesostructured Cellular Foams), MCM (Mobil Composition of Matters)-41, FSM (Folded Sheet material)-16, MCM-48, mesoporous silica (MS) spheres, and others. These mesoporous materials work as a host where the mesopores are filled with metal nanoparticles or nanowires [19-20]. Some properties of mesoporous material are having high surface area, controllable pore size, easy functionalization, low acidity, and high thermal stability [19, 21]. Mesoporous substances have create many opportunities to be applied in catalysis, catalyst support, separation, drug delivery, protein encapsulation, semiconductor nanoparticles adsorbents, size-selective reaction, energy conversion, and energy storage because of these properties [19, 22]. In general, silicon based material/carbon composite combine the appealing properties of both Si nanoparticles (high lithium storage capacity) and carbon (mechanical stability, chemical electrolyte compatibility and good electronic conductivity) and they show high reversible capacity and coulombic efficiency. Silicon based material/carbon composite also exhibited modified cycle stability with the contribution of nanosized pores in Si particles. Inchul et al. stated that an initial discharge capacity of about 1500 mAh/g at 0.1 C and tends to plateau around 600 mAh/g after 100 cycles was obtained for mesoporous Si/C composite, while Xueyang et al. reported the performance of Si/mesoporous carbon composite, which exhibits an initial reversible capacity of 1220.9 mAh/g and a modified cycleability having the capacity of 594 mAh/g in 50 cycles [23-24]. Mesoporous silicon based material/carbon composite (Figure 2.7) can be prepared by several ways carbothermal reduction of silica, sol-gel process, decomposition of organic silicon compounds, chemical vapour deposition, and direct combustion synthesis [25]. However, the most common used method nowadays for the synthesis of mesoporous silicon based material/carbon composite is by using sol-gel process. Sol-gel methods generally can be defined as the preparation of ceramic material through the preparation of a sol, gelation of the sol, and removal of the solvent.