Surface modification of activated carbon and fullerene black by Diels–Alder reaction

Abstract

Activated carbon and fullerene black react with cyclopentadiene at room temperature or slightly elevated temperature. At higher temperature a retro-Diels–Alder reaction takes place. The reaction with the diene and the retro-Diels–Alder reaction could be repeated. As a consequence of the reaction with cyclopentadiene or other suitable dienes and the retro reaction, the surface structure of different carbons changed considerably. The surface area of micropores on fullerene black was much higher than for the original sample. The influence on the surface area of porosity is reported for two different types of carbon.

Appendix: SAXS by disperse porous systems

When X-rays are scattered by colloidal particles owing to differences in electron density caused by inhomogeneities, the intensity of scattered radiation is a function of the scattering vector h=4π/λsinΘ [7, 8, 9]:

$$ I{\left( h \right)} = \eta ^{2} {\left( 0 \right)}V{\int\limits_0^\infty {4\pi \,r^{2} \gamma _{0} } }{\left( r \right)}\frac{{\sin \;hr}} {{hr}}{\text{d}}r, $$

(1)

where V is the volume of the system in which X-rays are scattered by electrons. η ²(0) is defined by [7, 8, 9]

$$ \eta ^{2} {\left( 0 \right)} = \frac{1} {V}{\int\limits_0^\infty {{\left[ {\rho _{{\text{e}}} {\left( r \right)} - \rho _{{\text{e}}} } \right]}^{2} } }\,{\text{d}}^{3} r, $$

(2)

where ρ _e(r) is the local electron density at a given point r and ρ _e is the average electron density.

The correlation function contains significant information on the geometry and structural arrangement of the scattering particles. The function is calculated from the scattering function [7, 10]. The following relationship holds for the tailing region of the scattering function (the so-called Porod range) [7]:

$$ I{\left( h \right)} = \eta ^{2} {\left( 0 \right)}\,2\,\pi \frac{S} {{h^{4} }}, $$

(3)

where S is the surface area of the particles. The specific surface area of the particles (relative to unit volume V) is [7]

$$ \frac{S} {V} = \pi \,\frac{{{\mathop {\lim I{\left( h \right)}\,h^{4} }\limits_{h \to \infty \quad \quad \quad } }}} {Q} = \pi \frac{{K_{{\text{p}}} }} {Q}, $$

(4)

where K _p is the tail-end constant.

The correlation length is calculated directly from the scattering function by the following integration [7, 8, 9]:

$$ l_{{\text{c}}} = \pi \,\frac{{{\int\limits_0^\infty {I{\left( h \right)}\,h\,{\text{d}}h} }}} {Q}. $$

(5)

From the middle section of the scattering curve the mass fractal dimension D _m of the particles can be determined [10, 11], when the scattering curve is linear in a relatively wide range of h:

$$ \log I{\left( h \right)} = p\log h. $$

(6)

From the value of the tangent p, D _m is calculated by the relationship D _m=∣p∣+1 (for 1≤D _m≤3).