Polysaccharide Derived Mesoporous Carbonaceous Materials for Bulky Dyes and Metals Adsorption from Wastewater (Green Chemical Technology for The Production of Polysaccharide Derived Mesoporous Carbonaceous Materials for Wastewater Treatment)

The current world crisis in the demand for water is a real problem for all forms of life on our
planet. For years, scientists have tried to propose various technologies which might be able to
clean and reuse contaminated water. It is crucial to develop a sustainable low cost form of
technology. This is especially important for Third World countries, where the ability to get high
level technology is difficult and ideally, the form of technology should be cheap, simple and
based on the local resources. One of the most available local resources is a polysaccharide
such as starch, pectin, cellulose or alginic acid. The major goal of this dissertation is to develop
a green form of technology to capture potentially harmful, toxic or valuable compounds from
waste water using mesoporous carbonaceous materials based on the local polysaccharide
resources.
To achieve this target, a novel and improved method of synthesis of mesoporous carbonaceous
materials from starch (hereafter referred to as Starbon® ) and alginic acid (hereafter referred to
as Algibon) was established at the beginning of the project. Based on this method, a number of
mesoporous materials with different textural and surface properties have been generated and
characterised by various techniques including nitrogen porosimetry, solid state NMR, DRIFT
spectroscopy, electron microscopy, elemental analysis and ash content tests.
Some of the major water pollutants in industrial wastes are dyes from textile industry and heavy
metals from mining, steel industry, welding, batteries, refinery, fertiliser and other processes.
Therefore, the produced materials were systematically tested as dye adsorbers. Bulky azodyes,
which represent 75% of the current cotton industry market, were selected as model
absorbates. A wide range of Algibons and Starbons materials with different properties (from the
completely hydrophilic to completely hydrophobic and with different micro/mesopore volumes
and ratios) enabled the optimum material to be found for certain types of adsorption process. It
was found that in this type of adsorption, Starbons materials cannot compete with commercially
available adsorbents. In contrast, Algibon has demonstrated great potential and significantly
outperformed the commercially available adsorbents such as activated carbon (up to 6 times
more) for the uptake of a range of bulky dyes.
The adsorption data reveals that the BET specific surface area (N2-adsorption) was not the only
governing factor and that the dominant mesoporous character of these materials, the
accessibility of the pores versus the bulkiness of the dyes and the nature of the surface
functionality (hydrophobic versus hydrophilic) also played key roles.
The maximum adsorption capacity of Algibon prepared at 800o C (A800) is markedly higher than
the one recorded for A450 and outperforms Norit as a commercially available activated carbon
(AC) adsorbent. It was found that the higher adsorption capacity of A800 relates to a higher
surface area in the mesoporous region. Moreover, it was found that the energy of adsorption is
smaller for A800 than for AC. This shows that A800 is not only the preferred adsorbent but will
also enable a more effective and easier recovery of the dyes.
In addition, the project involved the use of the developed Starbon materials to recover metals.
This application is crucial not only for the cleaning of waste waters but also for recovering the
valuable and critical metals from solid wastes. Some of these metals are in the EU critical list of
elements due to their significant demand in modern economy technologies or are substantial
components of industrial waste. These elements are in short supply because of their large
demand in growing economy and their scarce abundance in the world. Therefore, a variety of
Starbons were screened to test the selectivity of the polysaccharide derived carbonaceous
materials towards the high value metals from digested solid wastes consisting of Pulverised fly
ash (PFA), Red Mud (RM), Bottom ash (BA), Titano gypsum (TiG), Red Titano gypsum (RTiG)
and Phospho Gypsum (PG).
Further investigation of metals adsorption based on Algibon was systematically conducted.
A800 which demonstrated the most promising results early on and was found to be the most
stable material, and was used as the adsorber. A solution containing four high value metal ions
(i.e. Co, Cu, Ag and Cd) were selected for the adsorption experiment. Investigation focused on
the nature of the metal ions and how they affect the kinetic parameters of adsorption in a
detailed experimental analysis of the model system. Different types of adsorption isotherms
were applied. The maximum adsorption capacity for each metal was found from the fit isotherm
type. Kinetic adsorption was tested and kinetic order model study was carried out.