SYNTHESIS AND CHARACTERIZATION OF CARBON AEROGELS FOR CHROMIUM ION REMOVAL

Chromium is one of the heavy metals (HMs) that may cause lung cancer, irritation or
damage to nose, throat, eyes and skin at high concentrations. One of the effective
separation methods of HMs from aqueous solution is adsorption using carbon aerogels
(CAs). These CAs are known to have the potential ability to remove HMs; but to date
there is no documented scientific literature on justification, methodologies and practices
of chromium removal. Since CAs specific to remove chromium are not commercially
available, and CAs development is still in its infancy at the research stage, therefore it is
of critical importance to synthesize these CAs before hand in order to satisfy the
commercial needs. This is scientifically attainable since CAs work is well developed in
many other applications, for instance in the fields of capacitors, insulators, and medical
applications.
In this work CAs were synthesized and characterized in order to obtain the best material
for the removal of chromium. CAs development is influenced by many factors; one of the
most important factors is the catalyst. Three types of catalyst were normally used to
synthesis CAs namely sodium carbonate, sodium hydroxide, and acetic acid. In this work
CAs were developed by stirring resorcinol, formaldehyde, and water with the selected
catalysts. The solutions were then cured in an oven at 85±50C for three hours followed by
supercritical drying, and finally carbonization at 8000C in inert environment. The
materials were then characterized in order to understand the parameters affecting the
sorption process using x-ray diffraction (XRD) for degree of crystallinity, scanning
electron microscope (SEM) for porous surface morphology, nitrogen adsorption tests to
obtain Brunauer-Emmett-Teller (BET) surface area and pore size distribution, and Fourier
transform infra-red (FTIR) spectroscope for functional group. The results showed that the
developed CAs have high surface area and they are porous, amorphous, and have a
hydroxyl group which is known to strongly bind metal cations in aqueous solution. The
sorption system was found to be affected by the sorbent dose, initial chromium
concentration, and the pH of the solution. The kinetic data showed that the sorption
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capacity of the three types of carbon aerogels for the chromium increased with increasing
initial chromium concentration, while a reverse trend was observed when the effect of
sorbent dosage was studied. Analysis of the data obtained from the different sorption
studies for the three types of carbon aerogels revealed that the data fitted better to the
pseudo-second order model than the first order kinetic model. The results showed that the
CA prepared by acetic acid has the highest removal percentage followed by those prepared
using sodium hydroxide and finally sodium carbonate. The CAs removal performance was
analyzed using two different known isotherm models for solid-liquid interference
(Langmuir, and Freundlich). The highest values of linearity error (R2) were obtained
when the experimental data were fitted into Langmuir model.