There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Several industries are using dyes as coloring agents. The effluents from these industries are increasingly becoming an environmental problem. The removal of dyes from aqueous solution has a great potential in the field of environmental engineering. This paper reviews the classification, characteristics, and problems of dyes in detail. Advantages and disadvantages of different methods used for dye removal are also analyzed. Among these methods, Fenton process-based advanced oxidation processes are an emerging prospect in the field of dye removal. Fenton processes have been classified and represented as “Fenton circle”. This paper analyzes the recent studies on Fenton processes. The studies include analyzing different configurations of reactors used for dye removal, its efficiency, and the effects of various operating parameters such as pH, catalyst concentration, H2O2 concentration, initial dye concentration, and temperature of Fenton processes. From the present study, it can be conclude that Fenton processes are very effective and environmentally friendly methods for dye removal.

Degradation of dyes from aqueous solution by Fenton processes: a review

Water purification for human use, ecosystem management, agriculture, and industry is emerging as a leading global priority. Access to sufficient clean water ultimately requires improvements over the current state of water filtration technology. Membrane technologies for water purification have been actively pursued for decades, but with recent innovation of both analytical and fabrication tools, more advanced membrane technologies are surfacing. Here, we review the design, development, and application of new membrane materials, fabrication methods for controlling the filtration size regime, analytical tools for performance testing, and molecular modeling for transport and separation. Membrane chemical stability, fouling, and environmental impact as open questions are also presented.

Membrane materials for water purification: design, development, and application

Polyvinylidene fluoride (PVDF)–oxidized carbon nanotubes (OMWCNTs), PVDF–graphene oxide (GO) and PVDF–OMWCNTs–GO composite ultrafiltration membranes were prepared by solution-blending the ternary mixture of PVDF–oxidized low-dimensional carbon nanomaterials–dimethylacetamide in combination with the phase inversion method. The microscope images of the PVDF matrix microstructure showed that the composite membranes exhibited a bigger mean pore size and higher roughness parameters than pristine membranes. The contact angle of the membranes decreased from 78.5° (PVDF) to 66.8° (PVDF–OMWCNTs), 66.4° (PVDF–GO) and 48.5° (PVDF–OMWCNTs–GO). For the PVDF–OMWCNTs, PVDF–GO and PVDF–OMWCNTs–GO composite membranes, there was a 99.33%, 173.03% and 240.03% increase in permeation flux and a 21.71%, 17.23% and 14.29% increase in bovine serum albumin (BSA) rejection, respectively, compared with those of the pristine membranes. The newly developed composite ultrafiltration membranes demonstrate an impressive prospect for the anti-irreversible fouling performance in multi-cycle operations from BSA treatment. Additionally, the addition of OMWCNTs and GO increased the tensile strength of composite membranes from 1.866 MPa to 2.106 MPa and 2.686 MPa, respectively. Conspicuously, the PVDF composite ultrafiltration membranes endowed with oxidized low-dimensional carbon nanomaterials demonstrated fascinating hydrophilicity, permeability, antifouling and mechanical performance and promising application prospects owing to the rich oxygen-containing functional groups, high specific surface and synergistic effect of inorganic additive.

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Improved hydrophilicity, permeability, antifouling and mechanical performance of PVDF composite ultrafiltration membranes tailored by oxidized low-dimensional carbon nanomaterials

The upper bound of thin-film composite (TFC) polyamide membranes for desalination

Novel functionalized carbon nanotubes for improving the surface properties and performance of polyethersulfone (PES) membrane

Nanostructured polyaniline and its composites with pine cone-based activated carbon were synthesized by the oxidative polymerization of aniline in an aqueous solution of sulfuric acid and in the presence and absence of appropriate surfactant. The prepared activated carbon (AC), AC/polyaniline nanofiber composite (AC–PANI-F) and AC/polyaniline nanosphere composites (AC–PANI-S) were characterized by an N2 adsorption isotherm at 77 K, elemental analysis, thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and acid–base Boehm titration. The equilibrium adsorption of CO2 on AC and nanocomposites were experimentally investigated via a volumetric technique at a temperature range of 298–318 K and pressures up to 16 bar. The CO2 adsorption capacity was remarkably increased from 1.91 mmol g−1 for AC to 2.69 mmol g−1 for AC–PANI-F and 3.16 mmol g−1 for AC–PANI-S at 25 °C and 1 bar. The Sips isotherm presented a perfect fit to the CO2 adsorption data on adsorbents. The relatively fast kinetic adsorption of CO2 on the nanocomposites reflected the presence of more easily accessible adsorption sites toward CO2 for nanocomposites than AC. The isosteric heat of adsorption at relatively low adsorbate coverage was 55 kJ mol−1 for AC–PANI-F and 52 kJ mol−1 for AC–PANI-S, indicating the physico-chemical characteristics and heterogeneity of the adsorbents surface. The selectivity of CO2 over N2 by AC, AC–PANI-F and AC–PANI-S (CO2:N2 = 15:85, 298 K, 1 bar), predicted by the ideal adsorbed solution theory (IAST) model, achieved 1.53, 18.97 and 6.1, respectively. The results indicate that activated carbon/PANI nanocomposites can be used as an effective adsorbent for capture of CO2 from flue gas.

Synthesis of activated carbon/polyaniline nanocomposites for enhanced CO2 adsorption

In this study the equilibrium uptake of methane as the main constituent of natural gas (NG) by the multi-walled carbon nanotubes (MWCNTs) as well as the kinetic of adsorption was investigated at the temperature range 283–318 K and pressure up to 50 bar. The experimental apparatus consisting of a dual adsorption vessel was set up for the measurement of equilibrium adsorption of methane on the adsorbent using a volumetric technique (pressure decay). The average pore diameter, specific surface area and total pore volume of the MWCNT adsorbent were 4.6 nm, 294 m2 g−1 and 0.62 cm3 g−1, respectively. The results indicated that an optimal methane storage capacity up to 34 wt% was achieved at a temperature of 283 K and pressure of 50 bar. Several model isotherms such as Langmuir, Freundlich and Sips were examined to fit the equilibrium uptake data. The best fit was obtained with the Sips model based on the values of the regression correlation coefficient. The kinetics of methane adsorption on MWCNT was also investigated and the results revealed fast sorption kinetics for methane adsorption on MWCNTs. Gas adsorption kinetic data were analyzed in terms of the pseudo-first-order kinetic model and intra-particle diffusion model and the model parameters were recovered through a nonlinear fit to the experimental data. Isosteric heat of adsorption was evaluated based on the Clausius–Clapeyron equation at different temperatures. Small values of isosteric heat of adsorption confirmed the physical nature of the adsorption mechanism. The high capacity for natural gas storage also emphasized that MWCNT can be a good candidate as a porous media for natural gas storage compared to a conventional adsorbent such as activated carbon. However, lower temperatures and higher pressures are required to improve the NG storage capacity on the MWCNT adsorbent.

Equilibria and kinetics of natural gas adsorption on multi-walled carbon nanotube material

In this study, crude multi-walled carbon nanotubes (MWCNT) was functionalized by a two-step process; first using strong mixed acids (H2SO4/HNO3) and then treatment with 1,3-phenylenediamine (mPDA). The equilibrium adsorption of CO2 on pristine MWCNT and amine functionalized MWCNT (MWCNT-NH2) were investigated. Experiments were preformed via application of volumetric method in a dual sorption vessel at temperature range of 298–318 K and pressures up to 40 bars. The results obtained indicated that the equilibrium uptake of CO2 increased after functionalizing of MWCNT. The increase in CO2 capture by MWCNT-NH2 was attributed to the existence of great affinity between CO2 molecules and amine sites on this adsorbent at low pressures. The experimental data were analyzed by means of Freundlich and Langmuir adsorption isotherm models. The data obtained revealed a fast kinetics for the adsorption of CO2 in which most of adsorption occurred at initial period of adsorption experiments. This renders MWCNT as a suitable adsorbent for practical applications. Values of isosteric heat of adsorption were evaluated based on Clausius–Clapeyron equation. The results demonstrated that both chemisorption and physisorption played important role in CO2 adsorption on MWCNT-NH2, whereas the physisorption process was dominant for CO2 adsorption on MWCNT.

Enhancement of Carbon Dioxide Capture by Amine-Functionalized Multi-Walled Carbon Nanotube

In this study, the equilibrium adsorption of CO2 on activated charcoal (AC) and multi-walled carbon nanotube (MWCNT) were investigated. Experiments were performed at temperature range of298-318 K and pressures up to 40 bar The obtained results indicated that the equilibrium uptakes of CO2 by both adsorbents increased with increasing pressure and decreasing temperature. In spite of lower specific surface area, the maximum amount of CO2 uptake achieved by MWCNT at 298 K and 40 bar were twice that of CO2 capture by AC (15 compared to 793 mmol g-1). The higher amount of CO2 captured by MWCNT can be attributed to its higher pore volume and specific structure of MWCNT, such as hollowness and light mass, which had greater influence than specific surface area. The experimental data were analyzed by means of Freundlich and Langmuir adsorption isotherm models. Following a simple acidic treatment procedure, CO2 capture was increased marginally by MWCNT over entire range of pressure, while for AC this effect appeared at higher pressures. Small values of isosteric heat of adsorption were evaluated based on Clausius-CIapeyron equation showed the physical nature of adsorption mechanism. The high amount of CO2 capture by MWCNT renders it as a promising carrier for practical applications such as gas separation.

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Soodabeh Khalili

Papers

Novel functionalized carbon nanotubes for improving the surface properties and performance of polyethersulfone (PES) membrane

Synthesis of activated carbon/polyaniline nanocomposites for enhanced CO2 adsorption

Equilibria and kinetics of natural gas adsorption on multi-walled carbon nanotube material

Enhancement of Carbon Dioxide Capture by Amine-Functionalized Multi-Walled Carbon Nanotube

Carbon dioxide captured by multiwalled carbon nanotube and activated charcoal: A comparative study

Soodabeh Khalili

Papers

Novel functionalized carbon nanotubes for improving the surface properties and performance of polyethersulfone (PES) membrane

Synthesis of activated carbon/polyaniline nanocomposites for enhanced CO2 adsorption

Equilibria and kinetics of natural gas adsorption on multi-walled carbon nanotube material

Enhancement of Carbon Dioxide Capture by Amine-Functionalized Multi-Walled Carbon Nanotube

Carbon dioxide captured by multi­walled carbon nanotube and activated charcoal: A comparative study

Carbon dioxide captured by multiwalled carbon nanotube and activated charcoal: A comparative study