Hybrid multiwalled carbon nanotube − Laponite sorbent for removal of methylene blue from aqueous solutions

Adsorption of methylene blue from aqueous solution onto viscose-based activated carbon fiber felts: Kinetics and equilibrium studies

Two viscose-based activated carbon fiber felts (VACFF-1300 and VACFF-1600) with different specific surface areas and pore structures were prepared via two-step carbonization and steam activation and characterized by SEM observation, N2 adsorption/desorption isotherms, Fourier-transform infrared, X-ray diffraction and X-ray photoelectron spectroscopy analysis. They were used as adsorbents for the removal of methylene blue dye from aqueous solution, and the adsorption equilibrium and kinetics were studied via batch adsorption experiments and the adsorption mechanisms were investigated. Results showed that the equilibrium data for methylene blue adsorption onto VACFF-1300 and VACFF-1600 fitted well to the Langmuir isotherm model, with maximum monolayer adsorption capacity of 256.1 mg/g and 325.8 mg/g, respectively. Besides, the adsorption kinetics study showed that the adsorption of methylene blue onto the two VACFF samples could be best described by the pseudo second-order model. Moreover, the intraparticle diffusion modelling showed that intraparticle diffusion is rate-controlling for both VACFF-1300 and VACFF-1600, and external diffusion is also a rate-controlling step for the latter.

Application of Synthetic Layered Sodium Silicate Magadiite Nanosheets for Environmental Remediation of Methylene Blue Dye in Water

The removal of methylene blue (MB) dye from water was investigated using synthetic nano-clay magadiite (SNCM). SNCM was synthesized by a hydrothermal treatment under autogenous pressure. A rosette-shaped single mesoporous magadiite phase with 16.63 nm average crystallite size and 33 m²∙g⁻¹ Braunauer-Emmet-Teller (BET)-surface area was recorded. The adsorption results indicated the pronounced affinity of the SNCM to the MB dye molecules, which reached an adsorption uptake of 20.0 mg MB dye/g of SNCM. The elimination of MB dye by the SNCM was kinetically and thermodynamically considered; a pseudo-second-order kinetic model was attained, and its spontaneous, chemical, and endothermic nature was verified. SNCM was shown to be robust without a detectable reduction in the adsorption capacity after up to four times re-use.

Selective Adsorption and Separation through Molecular Filtration by Hyperbranched Poly(ether amine)/Carbon Nanotube Ultrathin Membranes

In response to the increasing public awareness of serious dye-contained wastewater contamination, we herein fabricated a novel anthracene-containing hyperbranched poly(ether amine) (hPEA-AN)/carbon nanotube (CNT) ultrathin membrane (UTM), which combined both the merits of the conventional dye adsorption strategy and membrane filtration process, to implement efficient selective adsorption of dye molecules and also the separation of dye mixtures by molecular filtration. Taking advantage of the π-π stacking interactions between anthracene and CNT sidewalls and hydrophobic interactions, CNTs were coated tightly with hPEA-AN to form the hPEA-AN@CNT complex, which can be well-dispersed very stably in water. The formation of the hPEA-AN@CNT complex was confirmed using X-ray photoelectron spectroscopy, Raman spectra, fluorescence spectra, and thermogravimetric analysis. Meanwhile, a simple filtration process was applied to prepare hPEA-AN@CNT UTMs with a thickness of 1.5 μm, which can be further cross-linked through photodimerization of anthracene moieties. The UTMs represented selective adsorption behaviors toward hydrophilic dyes even with similar backbones and the same charge states, namely, they showed high adsorption capacities (Q_eq) toward eosin B, erythrosin B (ETB), 4',5'-dibromofluorescein, and Evans blue (EVB) dyes up to 300 μmol/g while showing low adsorption capacities toward calcein (Cal), methyl red, and Ponceau S dyes. On the basis of this unique selective adsorption, molecular filtration was then realized toward mixed ETB/Cal and EVB/Cal dyes, with a separation efficiency of up to 100% and regeneration without an obvious efficiency decrease.

Mechanism of Methylene Blue adsorption on hybrid laponite-multi-walled carbon nanotube particles

The kinetics of adsorption and parameters of equilibrium adsorption of Methylene Blue (MB) on hybrid laponite-multi-walled carbon nanotube (NT) particles in aqueous suspensions were determined. The laponite platelets were used in order to facilitate disaggregation of NTs in aqueous suspensions and enhance the adsorption capacity of hybrid particles for MB. Experiments were performed at room temperature (298 K), and the laponite/NT ratio (Xl) was varied in the range of 0-0.5. For elucidation of the mechanism of MB adsorption on hybrid particles, the electrical conductivity of the system as well as the electrokinetic potential of laponite-NT hybrid particles were measured. Three different stages in the kinetics of adsorption of MB on the surface of NTs or hybrid laponite-NT particles were discovered to be a fast initial stage I (adsorption time t=0-10 min), a slower intermediate stage II (up to t=120 min) and a long-lasting final stage III (up to t=24hr). The presence of these stages was explained accounting for different types of interactions between MB and adsorbent particles, as well as for the changes in the structure of aggregates of NT particles and the long-range processes of restructuring of laponite platelets on the surface of NTs. The analysis of experimental data on specific surface area versus the value of Xl evidenced in favor of the model with linear contacts between rigid laponite platelets and NTs. It was also concluded that electrostatic interactions control the first stage of adsorption at low MB concentrations.

Photo-Catalytic Properties of TiO2 Supported on MWCNTs, SBA-15 and Silica-Coated MWCNTs Nanocomposites

Mesoporous silica, specifically SBA-15, acid-treated multi-walled carbon nanotubes and a hybrid nanocomposite of SBA-15 coated onto the sidewalls acid-treated multi-walled carbon nanotubes (CNTs) were prepared and used as supports for anatase TiO2. Sol-gel methods were adapted for the synthesis of selected supports and for coating the materials with selected wt% loading of titania. Physical and chemical properties of the supports and catalyst composite materials were investigated by powder X-ray diffraction (XRD), Raman spectroscopy, thermogravimetric analysis, scanning electron microscope (SEM), high-resolution transmission electron microscope (HRTEM), UV-vis diffuse reflectance spectroscopy and fluorescence spectroscopy. The photo-activity of the catalyst composites were evaluated on the decolorisation of methylene blue as a model pollutant. Coating CNTs with SBA-15 improved the thermal stability and textural properties of the nanotubes. All supported titania composites had high surface areas (207-301 m(2)/g), altered band gap energies and reduced TiO2 crystallite sizes. The TiO2/SBA-CNT composite showed enhanced photo-catalytic properties and activity than the TiO2/SBA-15 and TiO2/CNT composites. In addition, an interesting observation was noted with the TiO2/SBA-15 nanocomposites, which had a significantly greater photo-catalytic activity than the TiO2/CNT nanocomposites in spite of the high electron-hole recombination phenomena observed with the photoluminescence results. Discussions in terms of morphological, textural and physical-chemical aspects to account for the result are presented.