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The solubility of solid phenanthrene (PHE) powder in aqueous solutions of surfactant and chitosan (CS) was evaluated by varying the composition of aqueous mixtures. Cetyltrimethyl ammoniumbromide (CTAB) and sodium dodecyl sulfate (SDS) were used as model cationic and anionic surfactants, respectively. CS at a particular concentration in the mixture especially above the CMC value of the anionic surfactant exhibited somewhat higher PHE solubility values than surfactant itself. CS (20 mg/l)-SDS (20 g/l) solution showed higher PHE solubility (422.05 mg/l) than that of 20 g/l SDS (377.92 mg/g). However, CS-CTAB did not show any additional enhancing effect on PHE solubilization, and CS (5 mg/l)-CTAB (10 g/l) solution showed almost similar PHE solubility (867.23 mg/l) of 10 g/l CTAB (865.25 mg/g). The maximum increase in absorbance value of a 20 ml CS solution (5, 20 and 100 mg/l) at 540 nm with stepwise addition of SDS (10 g/l) was found at a SDS concentration much less than its CMC value (2.33 g/l) in...

Chitosan hydrogel beads (CSB) formed by sodium dodecyl sulphate (SDS) gelation were used for the removal of a cationic dye, methylene blue (MB), from aqueous solutions. The adsorption capacity of chitosan beads (CB) formed by alkali gelation was low because of charge repulsions between the chitosan (CS) and the MB. The adsorption capacity of CSB (4 g/L SDS gelation) for MB (100 mg/L) was 129.44 mg/g, and it decreased significantly with increasing SDS concentration during gelation. This decrease was a result of increased density of the CSB membrane materials. The CSB membrane materials formed with the 4 g/L SDS gelation showed the highest volumetric adsorption capacity. The MB adsorption on to CB and CSB increased with increasing values for the initial pH of solution. Data from both CB and CSB showed good fit to Sips isotherm models, and the maximum adsorption capacity of CSB (226.24 mg/g) was higher than that of CB (99.01 mg/g).

The effect of cetyltrimethylammonium bromide (CTAB) and triton X-100 (TX100) impregnation into chitosan hydrogel beads formed by sodium dodecyl sulfate (SDS) gelation (CSB) was investigated for the adsorption of Congo red (CR) from aqueous solutions. An impregnation of CTAB at 0.1 wt% into CSB increased adsorption from 97.46 mg/g to 113.24 mg/g, while 0.5 wt% TX100 impregnation into CSB registered a very small increase from 112.56 mg/g to 115.64 mg/g. CSB/CTAB exhibited similar adsorption at all pH levels (4-9), but CSB and CSB/TX100 showed lower adsorption at higher pH values. The Sips isotherm model was the best fit for all bead varieties, and the Sips maximum adsorption capacity value of CSB/CTAB (271.74 mg/g) was higher than that for CSB/TX100 (242.72 mg/g) or CSB without surfactant impregnation (174.83 mg/g). The experimental kinetic values of all varieties of beads for CR adsorption followed a pseudo-first-order rate model better than a pseudo-second-order rate model.

Effective coagulation and separation of particles in a soil-washed solution is required for a successful soil washing process. The effectiveness of chitosan (CS), a polycationic biodegradable polymer, as a coagulant was compared to polyacrylamide (PAA) and polyaluminium chloride (PAC) for the coagulation of a soil suspension (5 g L −1 ). The effect of surfactants in the coagulation process was investigated using Triton X-100 (TX-100), a nonionic surfactant, and sodium dodecyl sulfate (SDS), an anionic surfactant. CS (5 mg L −1 ) removed 86% and 63% of the suspended soil in the presence of TX-100 (5 g L −1 ) and SDS (5 g L −1 ), respectively, after 30 min at a pH of 6. The results prove that coagulation in the presence of TX-100 is more effective than with SDS. CS was found to be more efficient compared to PAA and PAC under all coagulation conditions. The optimum concentration of CS required for maximum coagulation of soil suspension was 5 mg L −1 . PAA and PAC could not achieve the same degree soil removal as CS even after increasing their concentrations up to 50 mg L −1 . Maximum levels of 50% and 60% soil removal were achieved using PAA (50 mg L −1 ) and PAC (50 mg L −1 ), respectively, after 30 min from a 5 g L −1 suspension containing TX-100 (5 g L −1 ). The soil coagulation process was found to decrease with an increase in the pH of the suspension, and maximum coagulation was achieved with an acidic pH.

Chitosan, a biodegradable compound, is used as an eco-friendly coagulant in water and wastewater treatment to avoid production of the large amounts of sludge using conventional chemical coagulants. Conditioning of chitosan using four different salts (Na2SO4, NaHSO4, (NH4)2SO4, and KHSO4) along with H2SO4 and treatment condition optimization were investigated to enhance coagulating efficiency for bentonite suspension. Chitosan dissolved in acetic acid was used for coagulation of 5 g/l bentonite suspension. The optimum concentration of chitosan required for maximum coagulation of bentonite suspension was 5 mg/l. Among the five additives used for conditioning, NaHSO4, at all concentrations, was found to be the most effective for enhancing the coagulating efficiency of chitosan and it was at its maximum when conditioned by 0.05 mM NaHSO4. NaHSO4 conditioned chitosan showed better coagulating efficiency than unconditioned chitosan at all pHs (3–8) tested in this study. The coagulation of bentonite by chitosan was found to decrease with increase in pH of the suspension. Using 5 mg/l of NaHSO4 conditioned chitosan at pH 6, the removal percentage of bentonite was increased from 76% to 88 % compared to unconditioned chitosan.

The adsorption performance of chitosan (CS) hydrogel beads (CSBs) generated by sodium dodecyl sulfate (SDS) gelation with multi-walled carbon nanotube (CNT) impregnation was investigated for Congo red removal as a model anionic dye. CNT-impregnated CSBs were prepared by four different strategies for dispersing CNTs: (a) in CS solution (CSBN1), (b) in SDS solution (CSBN2), (c) in CS solution containing cetyltrimethylammonium bromide (CTAB) (CSBN3), and (d) in SDS solution for gelation with CTAB-containing CS solution (CSBN4). It was observed from FE-SEM study that depending on nature of CNT dispersion, CNTs were found on the outer surface of CSBN2 and CSBN4 only. The adsorption capacity of the CSBs varied with the strategy used for CNT impregnation, and CSBN4 exhibited the highest maximum adsorption capacity (375.94 mg/g) from the Sips model. The lowest Sips maximum adsorption capacity by CSBN3 (121.07 mg/g) suggested significant blocking of binding sites of CS by CNT impregnation.

A new type of chitosan hydrogel beads (CSB) with a core–shell membrane structure was generated by sodium dodecyl sulfate (SDS) gelation process. CSB exhibited higher mechanical strength and acid stability than chitosan hydrogel beads (CB) formed by alkali gelation. The effect of SDS concentration variation during gelation on the adsorption capacity of CSB for congo red (CR) as a model anionic dye showed that CSB formed by 4 g l −1 SDS gelation had the highest adsorption capacity. The maximum adsorption capacity of CSB (208.3 mg g −1 ) obtained from the Sips model was found slightly higher than that of CB (200.0 mg g −1 ). Membrane materials of CSB obtained after squeezing core water from the beads showed approximately 25 times higher volumetric adsorption capacity than CB.