Novel Carbon-Based Nanoadsorbents for Removal of Synthetic Textile Dyes from Wastewaters - Green Chemistry for Dyes Removal from Wastewater - page 36

TGA: Thermogravimetric analysis
XPS: X-ray photoelectron spectroscopy
2.1 Introduction
Textile manufacturing involves several processes (e.g., desizing, scour-
ing, bleaching, rinsing, mercerizing, dyeing and finishing) which generate
large volumes of colored effluents [1]. The presence of dyes and pigments
in water, even at very low concentrations, is highly undesirable and rep-
resents a serious environmental problem due to their negative ecotoxi-
cological effects and bioaccumulation in wildlife [2]. The removal of
dyes from textile effluents is thus of prime importance. During the past
three decades, several physical, chemical, and biological methods have
been developed for decoloration of textile wastewaters with varying lev-
els of success. These include coagulation, flocculation, microfiltration,
ultrafiltration, reverse osmosis, adsorption, ion-exchange, irradiation,
sonochemical degradation, photocatalytic degradation, oxidation using
chlorine, chlorine dioxide, hydrogen peroxide and Fenton's reagent,
ozonation, electrocoagulation, electrochemical destruction, aerobic or
anaerobic treatment, and microbial degradation [3-5]. Amongst these
techniques, adsorption is widely acknowledged as the most promising
and efficient method because of its low capital investment, simplicity of
design, ease of operation, insensitivity to toxic substances and complete
removal of pollutants even from dilute solutions [6-11]. Adsorption treat-
ment also does not result in any harmful substances and produces a high
quality treated effluent.
Activated carbon, a crude form of graphite, is undoubtedly the most
preferred adsorbent because of its highly porous structure and large
surface area [10,12]. However, its widespread use is restricted due to
economic considerations [13]. Attempts have thus been made by many
researchers to find inexpensive alternative substitutes to activated car-
bon. Most research undertaken for this purpose has focused on the use
of waste/byproducts from industries (e.g., fly ash, bottom ash, steel-
plant slag, red mud, metal hydroxide sludge) and agricultural operations
(e.g., rice husk, orange peel, banana peel, sawdust, soybean hull), natu-
ral materials (e.g., bentonite, kaolinite, diatomite, zeolites, dolomite), or
microbial and non-microbial biomass [4,10,14-19]. Nevertheless, these
low-cost adsorbents have been largely criticized for their low adsorp-
tion capacities and potential disposal problems and have thus not been
applied at an industrial scale [16]. Therefore, the exploration of new