Particle Size And Mophology Controlling Of Urea Formaldehyde Microspheres And Application In Supercapacitors

Urea formaldehyde resin microspheres (UFMs) have drawn widely attention due to their good mechanical property, riched surface functional groups and high nitrogen content. They have been widely used in chromatographic column, catalyst support, template agent for composite microspheres, precursor of carbon materials and so on. So far, the study of UFMs mainly focused on the application. There were few people noticing the nature of the reaction between urea and formaldehyde, which may affect the size and morphology of UFMs significantly.In this thesis, pH value, surfactant and inorganic salt was added in the polymerization system of UFMs. Their effects on the particle size and morphology of UFMs were studied carefully. SEM and precipitation time was used to characterize the effects of reaction conditions on UFMs. The results showed that pH value was the key for controlling the reaction rate between urea and formaldehyde. Precipitation time enlarged along with the increasing pH value. The morphology of UFMs became rougher with the increasing pH value. The morphology of UFMs could be controlled by controlling pH value and adding HEC in the system. The particle size and the roughness of the surface of UFMs could be decreased by adding inorganic salt in the system.Submicro-size UFMs (300 nm) could be obtained in the presence of 7 g(NH4)2SO4 and 0.3 g HEC. Well-defined marigold-like UFMs could be obtained in the presence of 0.1 g HEC at pH 4. The formation mechanism could be proposed by tracing the formation process of flower-like UFMs and be convinced by FTIR and XRD results. The formation mechanism of flower-like UFMs was as follows. The low reaction time provided enough conditions for crystallization and self-assembly of UF oligomers.Then, thermogravimetry method was used to study the thermal degradation kinetics of three typical UFMs (normal UFMs, submicro-size UFMs and flower-like UFMs). The thermogravimetry process was characterized by TGA measurements. FR method, FWO method, KAS method and AICM method was employed to calculate the relationship between thermal degradation activate energy (Ea) and conversion pecent (a). The results were as follows. Firstly, the thermal gravimetry of normal UFMs?submicro-size UFMs?flower-like UFMs could be separated into three parts.The first part (< 150 ?) was the removal of little molecular like H2O and formaldehyde. The second part (150-400 ?) was the fast gravimetry part. The third part (> 400 ?) was the part with low gravimetry rate. In the second part,Ea of normal UFMs decreased at first and increased later. Ea of submicro-size UFMs increased then decreased then increased and decreased in the end. Ea of flower-like UFMs decreased former and increased later. The degradation regulation of these three typical UFMs was similar. Secondly, Ea of submicro-size UFMs was the smallest among them. With the increasing of conversion, Ea of normal UFMs was smaller than that of flower-like UFMs former and bigger than that of flower-like UFMs later. Thirdly, submicro-size UFMs possessed the highest curing degree and the lowest crystal property and flower-like UFMs possessed the lowest curing degree and highest crystal property when we combined the results of thermal degradation kenetic with the results of FTIR.At last, submicro-size UFMs and flower-like UFMs were used as the precursors of carbon materials. Nitrogen-doped porous carbon materials(NPCs) and hierarchical porous carbon materials (HPCs) were fabricated by KOH activation method. SEM, Raman, N2 adsorption and desorption test and XPS was used to characterize the effect of KOH/C weight ratio on the structure of NPCs and HPCs. CV curves, Galvanostatic charge/discharge curves and Nyquist plots was used to characterization the electrochemical properties of NPCs and HPCs. The results were as follows. Firstly, the specific surface area and pore volume of NPCs and HPCs changed with the change of KOH/C weight ratio. NPCs2 showed the biggest specific surface area of 3386 m2·g-1 and pore volume of 1.967 cm3·g-1. HPCs2 showed the biggest specific surface area of 3223 M2·g-1 and pore volume of 1.929 cm3·g-1. Secondly,nitrogen content on the surface of NPCs and HPCs decreased with the increase of KOH/C weight ratio. Thirdly, NPCs 1.5 performed excellent electrochemical properties (specific capacity: 343 F·g-1 at the current density of 0.5 A·g-1 in 1M H2SO4, rate capability of 68% at the current density of 30 A·g-1). HPCs1.5 performed good electrochemical properties (specific capacity:288 F·g-1 at the current density of 0.5 A/g in 1M H2SO4, rate capability of 71%at the current density of 30 A·g-1). They all could maintain 100% long-cycle retention after 5000 cycle.