Adsorption of reactive dye from aqueous solution and synthetic dye bath wastewater by Eucalyptus bark/magnetite composite

Adsorption of Reactive Black 5 Dye from Aqueous Solutions by Carbon Nanotubes and its Electrochemical Regeneration Process

: Removal of Reactive Black 5 (RB5) dye from aqueous solutions was investigated by adsorption onto Multi-walled Carbon Nanotubes (MWCNTs) and Single-walled Carbon Nanotubes (SWCNTs). A Taguchi orthogonal design including pH, initial RB5 concentration, contact time, and CNTs dose, was used in 16 experiments. The results showed that all four factors were statistically significant, and the optimum conditions for both adsorbents were as follows: pH of 3, adsorbent dose of 1000 mg/L, RB5 concentrations of 25 mg/L, and contact time of 60 min. An equilibrium study by Isotherm Fitting Tool (ISOFIT) software showed that Langmuir isotherm provided the best fit for RB5 adsorption by CNTs. The maximum predicted adsorption capacities for the dye were obtained as 231.84 and 829.20 mg/g by MWCNTs and SWCNTs, respectively. The results also indicated that the adsorption capacity of SWCNTs was about 1.21 folds higher than that of MWCNTs. Studies of electrochemical regeneration were conducted, and the results demonstrated that RB5-loaded MWCNTs and SWCNTs could be regenerated (86.5% and 77.3%, respectively) using the electrochemical process. Adsorbent regeneration was mostly due to the degradation of the dye by the attack of active species such as chlorate, H2O2, and, •OH, which were generated by the electrochemical oxidation process with Ti/RuO2-IrO2-TiO2 anodes. The results of Gas Chromatography-Mass Spectrometry (GC-MS) analysis showed that acetic acid, 3-chlorobenzenesulfonamide, and 1,2-benzenedicarboxylic acid were produced after adsorbent regeneration by the electrochemical process in the solution of regeneration. The adsorption and regeneration cycles showed that the electrochemical process with Ti/RuO2-IrO2-TiO2 and graphite is a good alternative method for the regeneration of CNTs and simultaneous degradation of the dye.

Biosorption of methylene blue by nonliving biomass of the brown macroalga Sargassum hemiphyllum

The ability of Sargassum hemiphyllum to remove methylene blue (MB) from aqueous solution was evaluated. Batch experiments were conducted to examine the effects of parameters such as initial pH, contact time, biomass dose and initial dye concentration on adsorption capacity. S. hemiphyllum before and after MB adsorption was characterized by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The Langmuir isotherm model provided the best correlation with experimental data, and the monolayer biosorption capacity was 729.93 mg·g-1 within 120 min using 0.5 g·L-1 algal biomass and pH of 5. The pseudo-second-order kinetic model accurately described the adsorption kinetics data. Thermodynamic parameters (ΔG0, ΔH0 and ΔS0) at temperature ranges of 293-313 K demonstrated that biosorption is an endothermic and spontaneous reaction. FT-IR analysis showed that the hydroxyl, amine and carboxyl functional groups on the surface of the algae were the most important functional groups for biosorption of MB. XPS analysis indicated that the algal biomass combined with MB molecules through -NH2 groups. These results suggest that S. hemiphyllum is a favorable biosorbent for removing MB dye from wastewater.