Composite nanofibers for highly efficient photocatalytic degradation of organic dyes from contaminated water.

In this study highly efficient photocatalyst based on composite nanofibers containing polyacrylonitrile (PAN), carbon nanotubes (CNT), and surface functionalized TiO2 nanoparticles was developed. The composite nanofibers were fabricated using electrospinning technique followed by chemical crosslinking. The surface modification and morphology changes of the fabricated composite nanofibers were examined through SEM, TEM, and FTIR analysis. The photocatalytic performance of the composite nanofibers for the degradation of model molecules, methylene blue and indigo carmine, under UV irradiation in aqueous solutions was investigated. The results demonstrated that high photodegradation efficiency was obtained in a short time and at low power intensity compared to other reported studies. The effective factors on the degradation of the dyes, such as the amount of catalyst, solution pH and irradiation time were investigated. The experimental kinetic data were fitted using pseudo-first order model. The effect of the composite nanofibers as individual components on the degradation efficiency of MB and IC was evaluated in order to understand the overall photodegradation mechanism. The results obtained showed that all the components possess significant effect on the photodegradation activity of the composite nanofibers. The stability studies demonstrated that the photodegradation efficiency can remain constant at the level of 99% after five consecutive cycles.

Nanocomposite functionalized membranes based on silica nanoparticles cross-linked to electrospun nanofibrous support for arsenic(v) adsorption from contaminated underground water.

Nanocomposite functionalized membranes were synthesized using surface functionalized mesoporous silica nanoparticles (MCM-NH2 or MCM-PEI) cross-linked to a modified polyacrylonitrile (mPAN) nanofibrous substrate for the removal of 1 mg L-1 of As(v); a concentration much higher than what has been reported for underground water in Argentina. Adsorption studies were carried out in batch mode at pH 8 with nanoparticles in colloidal form, as well as the nanoparticles supported on the modified PAN membranes (mPAN/MCM-NH2 and mPAN/MCM-PEI). Results indicate a twenty-fold improvement in As(v) adsorption with supported nanoparticles (nanocomposite membranes) as opposed to their colloidal form. The adsorption efficiency could be further enhanced by modifying the nanocomposite membrane surface with Fe3+ (mPAN/MCM-NH2-Fe3+ and mPAN/MCM-PEI-Fe3+) which resulted in more than 95% arsenic being removed within the first 15 minutes and a specific arsenic adsorption capacity of 4.61 mg g-1 and 5.89 mg g-1 for mPAN/MCM-NH2-Fe3+ and mPAN/MCM-PEI-Fe3+ nanocomposite membranes, respectively. The adsorption characteristics were observed to follow a pseudo-first order behavior. The results suggest that the synthesized materials are excellent for quick and efficient reduction of As(v) concentrations below the WHO guidelines and show promise for future applications.

Surface modified composite nanofibers for the removal of indigo carmine dye from polluted water.

Surface coated magnetite nanoparticles (Fe3O4 NPs) with 3-mercaptopropionic acid were immobilized on amidoximated polyacrilonitrile (APAN) nanofibers using electrospinning followed by crosslinking. The prepared composite nanofibers were characterized with Scanning Electron Microscopy (SEM), and Fourier Transform Infrared analysis (FTIR). The composite nanofiber was evaluated for the removal of indigo carmine dye from aqueous solutions. The effects of contact time, initial dye concentration, solution pH and adsorption equilibrium isotherms were studied. The adsorption of indigo carmine was found to be greatly affected by solution pH. The maximum loading capacity was determined to be 154.5 mg g-1 at pH = 5. The experimental kinetic data were fitted well using a pseudo-first order model. The adsorption isotherm studies showed that the adsorption of indigo carmine fits well with the Langmuir model. The reuse of the composite nanofiber was also investigated in which more than 90% of indigo carmine was recovered in 5 min. The results of stability studies showed that the adsorption efficiency can remain almost constant (90%) after five consecutive adsorption/desorption cycles.

Surface functionalized composite nanofibers for efficient removal of arsenic from aqueous solutions.

A novel composites nanofiber was synthesized based on PAN-CNT/TiO2-NH2 nanofibers using electrospinning technique followed by chemical modification of TiO2 NPs. PAN-CNT/TiO2-NH2 nanofiber were characterized by XRD, FTIR, SEM, and TEM. The effects of various experimental parameters such as initial concentration, contact time, and solution pH on As removal were investigated. The maximum adsorption capacity at pH 2 for As(III) and As(V) is 251 mg/g and 249 mg/g, respectively, which is much higher than most of the reported adsorbents. The adsorption equilibrium reached within 20 and 60 min as the initial solution concentration increased from 10 to 100 mg/L, and the data fitted well using the linear and nonlinear pseudo first and second order model. Isotherm data fitted well to the linear and nonlinear Langmuir, Freundlich, and Redlich-Peterson isotherm adsorption model. Desorption results showed that the adsorption capacity can remain up to 70% after 5 times usage. This work provides a simple and an efficient method for removing arsenic from aqueous solution.

Removal of chromium (VI) from aqueous solutions using surface modified composite nanofibers.

A novel material composite nanofibers (PAN-CNT/TiO2-NH2) based on adsorption of Cr(VI) ions, was applied. Polyacrylonitrile (PAN) and carbon nanotube (CNTs)/titanium dioxide nanoparticles (TiO2) functionalized with amine groups (TiO2-NH2) composite nanofibers have been fabricated by electrospinning. The nanostructures and the formation process mechanism of the obtained PAN-CNT/TiO2-NH2 composite nanofibers are investigated using FTIR, XRD, XPS, SEM, and TEM. The composite nanofibers were used as a novel adsorbent for removing toxic chromium Cr(VI) in aqueous solution. The kinetic study, adsorption isotherm, pH effect, initial concentration, and thermodynamic study were investigated in batch experiments. The composite nanofibers had a positive effect on the absorption of Cr(VI) ions under neutral and acidic conditions, and the saturated adsorption reached the highest when pH was 2. The adsorption equilibrium reached within 30 and 180min with an initial solution concentration increasing from 10 to 300mg/L, and the process can be better described using nonlinear pseudo first than nonlinear pseudo second order model and Intra-particle diffusion. Isotherm data fitted well using linear and nonlinear Langmuir, Freundlich, Redlich-Peterson, and Temkin isotherm adsorption model. Thermodynamic study showed that the adsorption process is exothermic. The adsorption capacity can remain up to 80% after 5 times usage, which show good durability performance. The adsorption mechanism was also studied by UV-vis and XPS.

Arsenate removal with 3-mercaptopropanoic acid-coated superparamagnetic iron oxide nanoparticles.

In the present work, superparamagnetic iron oxide nanoparticles (SPION) surface-coated with 3-mercaptopropanoic acid (3-MPA) were prepared and their feasibility for the removal of arsenate from dilute aqueous solutions was demonstrated. The synthesized 3-MPA-coated SPION was characterized using transmission electron microscopy (TEM), thermogravimetric analysis (TGA) and Fourier transform infra-red spectrometry (FTIR). Separation efficiency of the coated nanoparticles and the equilibrium isotherm of arsenate adsorption were investigated. The obtained results reveal the arsenate adsorption to be highly pH-dependent, and the maximum adsorption was attained in less than 60 min. The resulting increase of 3-MPA-coated SPION adsorption capacity to twice the adsorption capacity of SPION alone under the same conditions is attributed to the increase of active adsorption sites. An adsorption reaction is proposed. On the other hand, efficient recovery of arsenate from the loaded nanoparticles was achieved using nitric acid (HNO3) solution, which also provides a concentration over the original arsenate solution.

Studies on the adsorption of chromium(VI) onto 3-Mercaptopropionic acid coated superparamagnetic iron oxide nanoparticles.

Chromium (Cr) in the form of Cr(VI) is deemed toxic in water due to its mutagenic and carcinogenic properties. For the successful removal of Cr(VI), we demonstrate a novel adsorbent consisting of superparamagnetic iron oxide nanoparticles (SPION) functionalized with 3-Mercaptopropionic acid (3-MPA). Fourier transform infrared spectroscopy (FT-IR) confirmed the functionalization of nanoparticles and presence of sulfonate groups. Batch adsorption experiments showed that the functionalized adsorbent recovered 45 mg of Cr(VI)/g of 3-MPA coated SPION at initial concentration of 50mg/L aqueous solution at pH 1 with less than 1% of Fe dissolution from SPION. The results from X-ray photoelectron spectroscopy confirmed that Cr(VI) chemisorbed onto the adsorbent. Hence, the XPS spectra did not indicate any reduction of Cr(VI) to Cr(III) upon adsorption. The adsorption data were better fitted for the Freundlich model. Moreover, the Cr(VI) adsorption kinetics on functionalized SPION followed a pseudo-second order rate, revealing chemisorption as the dominant mechanism. The high Cr(VI) removal, rapid adsorption kinetics and stability of adsorbent indicate that 3-MPA coated SPION could be an efficient adsorbent for the removal of Cr(VI).