Alkali treatment of cellulose II fibres and effect on dye sorption
ABSTRACT To understand the effect of alkali treatment on sorption behaviour of cellulose II fibres, samples were continuously pre-treated using NaOH over a concentration range of 0.0–7.15 mol dm−3, with varying tension; treated substrates were dyed with hydrolysed C. I. Reactive Red 120. Greatest adsorption of dye occurs for cellulose II fibres treated with 2.53 and 3.33 mol dm−3 aqueous NaOH solution. Correlation to sorption isotherms is most closely associated with a Langmuir type isotherm, but correlation to the Freundlich isotherm is still significant, indicating sorption via a combination of Langmuir and Freundlich isotherms. Adsorption energy (ΔG0) increases with increasing NaOH concentration to a maxima between 2.53 and 3.33 mol dm−3 NaOH and then decreases with further increase in NaOH concentration. Equilibrium dye sorption shows good correlation with water sorption as assessed by the reactive structural fraction (RSF) theory. Theoretical monolayer capacity (q0) increases with increasing NaOH concentration to a maxima at 3.33 mol dm−3 NaOH and then decreases with further increase in NaOH concentration; q0 is significantly in excess of the number of available specific sites (–COO−Na+) in the substrate, indicating non-site-specific interactions, more typical of a Freundlich isotherm. Pores in the fibre significantly affected by alkali treatment (<20 Å diameter) and accessibility of dye (14 Å) sorption into those pores account the differences observed herein; maximum qe, q0 and ΔG0 are observed for cellulose II fibre treated with 2.53–3.33 mol dm−3 NaOH as this concentration range affects the greatest increase in accessible pore volume in the fibres.
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ABSTRACT: This study was conducted in order to understand the mechanism of Cd and Pb adsorption in aqueous solutions by raw and modified saw dust (SD) of Alstonia macrophylla. The biosorbent was characterized by Boehm titration, specific surface area, scanning electron microscopy (SEM), X-ray energy dispersion (EDAX), and Fourier transform infrared (FTIR) analyses. SD was treated using organic acids and bases. Batch studies were conducted for raw and modified SD to determine the effect of initial concentration, pH, ionic strength, and contact time on metal adsorption. The specific surface area and total basic and acidic groups of SD were 77 m2/g and 1521 and 2312 μmol/g, respectively. The adsorption of both metals onto SD was pH dependent. No ionic strength dependency was observed in adsorption of Cd and Pb at pH >6, indicating inner sphere surface complexation. Monolayer adsorption is dominant in both metal sorptions by SD. Furthermore, there is no competition between metals on adsorption and raw SD was found to be suitable for removal of Cd and Pb as compared to organic acid– or base-treated SD. Maximum adsorption capacity of SD for Cd and Pb were 30.6 and 204.2 mg/g, respectively. Results indicate that the A. macrophylla SD can be considered as a potential material for metal ion removal from wastewater.Bioremediation Journal 01/2012; 16(2):113-124. DOI:10.1080/10889868.2012.665963 · 0.71 Impact Factor
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ABSTRACT: Cellulose is a linear 1,4-β-glucan polymer where the units are able to form highly ordered structures, as a result of extensive interaction through intra- and intermolecular hydrogen bonding of the three hydroxyl groups in each cellulose unit. Alkali has a substantial influence on morphological, molecular and supramolecular properties of cellulose II polymer fibres causing changes in crystallinity. Lyocell fibres pre-treated with 0.0, 2.0, and 4.0moldm−3 aqueous NaOH solution were dyed with hydrolyzed reactive dyes that had different molecular shapes and sizes. Overall exhaustion (q e), value of K, and −ΔG increased for lyocell samples pre-treated with aqueous NaOH solution in the following order: 2.0>4.0>0.0moldm−3 NaOH. The same trends were observed for colour strength (K/S) values of the dyeings. Pre-treatment of lyocell with 2.0moldm−3 NaOH creates the substrate that achieves the most thermodynamically favourable system for sorption of hydrolyzed reactive dyes, as at this concentration crystallinity decreases (with respect to 0.0moldm−3 NaOH treated lyocell) to afford higher sorption; however, at higher alkali concentrations the macro-sorbent forms a compacted unit that limits diffusion within the sorbent interior. Molecular size of the sorbate dye has a significant effect on the sorption process: for the largest dye structure the sorption isotherm is most closely correlated to a Langmuir isotherm; as the size of the dye decreases correlation to a Langmuir isotherm is observed, but with good correlation to the Freundlich isotherm; as the size of the dye is decreased further sorption is more typical of a Freundlich isotherm. KeywordsFreundlich isotherm–Langmuir isotherm–Adsorption–Polysaccharides–Lyocell–Sodium hydroxide–Adsorption–Hydrolyzed reactive dyeCellulose 08/2011; 18(4):1063-1072. DOI:10.1007/s10570-011-9540-0 · 3.03 Impact Factor
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ABSTRACT: This study is an attempt to investigate the feasibility of alkali pre-treatment to activate surface hydroxyl groups of cellulose fibers in order to enhance the deposition efficiency of silver nanoparticles (AgNPs) onto cotton fabrics. Cotton samples were pre-treated with various alkali solutions containing different earth metal hydroxides (LiOH, NaOH, and KOH). The as-prepared samples were then treated with aqueous silver nitrate followed by reduction treatment with aqueous ascorbic acid, which caused in situ formation of AgNPs on fiber surfaces. The surface structure of the fabrics was characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD) analysis, and colorimetric data. The amount of silver was measured by using inductively coupled plasma-optical emission spectrometer (ICP-OES). Antimicrobial activity was measured against Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli bacteria. It was established that alkali pre-treatment had a substantial effect on the formation and adsorption of AgNPs on the fibers. Alkali pre-treated samples were homogeneously coated by AgNPs with high surface coverage. Alkali type had significant effect not only on the amount of AgNPs on the surface but also on its size. High antibacterial activity against both Gram-positive and Gram-negative strains was also demonstrated, even after 10 cycles washing.Fibers and Polymers 11/2012; 13(9). DOI:10.1007/s12221-012-1170-0 · 1.11 Impact Factor