Madhumita Bhaumik

Enhanced removal of Cr(VI) from aqueous solutions using polypyrrole wrapped oxidized MWCNTs nanocomposites adsorbent.

Polypyrrole wrapped oxidized multiwalled carbon nanotubes nanocomposites (PPy/OMWCNTs NCs) were prepared via in situ chemical polymerization of pyrrole (Py) monomer in the presence of OMWCNTs using FeCl3 as oxidant for the effective removal of hexavalent chromium [Cr(VI)]. The as-prepared PPy/OMWCNTs NCs were characterized by FE-SEM, HR-TEM, ATR-FTIR, XRD, XPS and BET method. Characterization results suggested that PPy was uniformly covered on the OMWCNTs surface and resulted in enhanced specific surface area. Adsorption experiments were carried out in batch sorption mode to investigate the effect of pH, dose of adsorbent, contact time, concentration of Cr(VI) and temperature. The adsorption of Cr(VI) on the nanocomposite surface was highly pH dependent and the kinetics of the adsorption followed the pseudo-second-order model. The adsorption isotherm data were in good conformity with the Langmuir isothermal model. The maximum adsorption capacity of the PPy/OMWCNTs NCs for Cr(VI) was 294mg/g at 25°C. The calculated values of the thermodynamic parameters such as ΔG(0) (-0.237kJ/mol), ΔH(0) (13.237kJ/mol) and ΔS(0) (0.0452kJ/mol/K) revealed that the adsorption process is spontaneous, endothermic and marked with an increase in randomness at the solid-liquid interface. The presence of co-existing ions slightly affected the Cr(VI) removal efficiency of the PPy/OMWCNTs.

Polyaniline nanofibers as highly effective re-usable adsorbent for removal of reactive black 5 from aqueous solutions.

Polyaniline nanofibers (PANI NFs) with 50-80 nm in diameter were successfully prepared at room temperature (22 °C) using ferric chloride (FeCl3) as an oxidant via a simple rapid mixing polymerization method. The prepared PANI NFs were characterized by FE-SEM, HR-TEM, BET, ATR-FTIR and by Zeta potential measurement method. The adsorption of azo dye Reactive Black 5 (RB5) onto PANI NFs from aqueous solutions was investigated. Adsorption studies were carried out at different initial dye concentrations, initial solution pH and adsorbent doses. The kinetic data fitted well with the pseudo-second-order model while the equilibrium data were satisfactorily described by the Langmuir isotherm model. The Langmuir maximum adsorption capacity of RB5 at pH 6.0 was found to be 312.5, 389.1 and 434.7 mg/g at 25 °C, 35 °C and 45 °C, respectively. Thermodynamic parameters including the Gibbs free energy (ΔG°), enthalpy (ΔH°), and entropy (ΔS°) changes indicated that the adsorption of RB5 onto PANI NFs was feasible, spontaneous, and endothermic. Moreover, desorption experiments revealed that the PANI NFs can be reused effectively for five consecutive adsorption-desorption cycles without any loss of its original capacity.

Selective removal of toxic Cr(VI) from aqueous solution by adsorption combined with reduction at a magnetic nanocomposite surface

The adsorption of toxic hexavalent chromium (Cr(VI)) and its reduction to trivalent chromium (Cr(III)) are important processes for the treatment of industrial wastewater. Conducting polymers can adsorb and reduce Cr(VI) to less toxic Cr(III) but have low adsorption capacities due to agglomeration of particles and are difficult to separate from treated water. In this study, magnetic polypyrrole (PPy)-polyaniline (PANI)/iron oxide (Fe3O4) nanocomposite was synthesized for the selective removal of Cr(VI) in aqueous solution. PPy-PANI/Fe3O4 nanocomposite was characterized using various techniques including ATR-FTIR, FE-SEM, HR-TEM, EDX, TGA, XRD, VSM and XPS analyses. PPy-PANI/Fe3O4 nanocomposite (0.05g) removed 99% of Cr(VI) from aqueous solution (100mg/L, pH 2). Speciation studies confirmed Cr(VI) adsorption and reduction to Cr(III) by the PPy-PANI/Fe3O4 nanocomposite in solutions with initial pH of 2 and 3 and that no Cr(VI) reduction occurred at pH values of 4 and above. The Langmuir maximum adsorption capacity for Cr(VI) removal by PPy-PANI/Fe3O4 nanocomposite at pH 2 was 303mg/g at 25°C. PPy-PANI/Fe3O4 nanocomposite was highly selective for Cr(VI) removal and could be used for three consecutive treatment cycles without loss of adsorption capacity. Moreover, the magnetic nanocomposite could be separated from the reaction fluid using an external magnet. PPy-PANI/Fe3O4 nanocomposite is therefore a promising magnetic adsorbent for the treatment of industrial wastewater.

Selective removal of Cr(VI) from aqueous solution by polypyrrole/2,5-diaminobenzene sulfonic acid composite

A polypyrrole/2,5-diaminobenzenesulfonic acid (PPy/DABSA) composite, synthesised by the in situ oxidative polymerization of pyrrole in the presence of DABSA, was studied as an adsorbent for the removal of Cr(VI) from aqueous solution. The structure and morphology of the composite were investigated by ATR-FTIR, FE-SEM, EDX, TGA, XRD and XPS studies. The adsorption of Cr(VI) by PPy/DABSA composite was highly pH dependent and optimum removal was achieved at pH 2. Adsorption of Cr(VI) was confirmed by EDX and XPS studies. The isotherm data fitted the linear Langmuir model well, with a maximum adsorption capacity of 303mg/g at 25°C. Thermodynamic parameters (ΔG°, ΔH° and ΔS°) were calculated using isotherm data and confirmed that the adsorption process was spontaneous and endothermic. Adsorption kinetics was best described by the pseudo-second-order model. The activation energy of the adsorption process suggested that Cr(VI) was chemisorbed by PPy/DABSA composite. PPy/DABSA composite could be used for three consecutive adsorption-desorption cycles without loss of its original adsorption capacity. Highly selective removal of Cr(VI) was observed even when co-existing ions such as Cu(2+), Zn(2+), Ni(2+), Cl(-), SO4(2)(-) and NO3(-) were present in the solution. In summary, the potential of PPy/DABSA composite for remediating industrial wastewater contaminated by Cr(VI) has been demonstrated.

Sonocatalytic rapid degradation of Congo red dye from aqueous solution using magnetic Fe0/polyaniline nanofibers

Nano-sized magnetic Fe0/polyaniline (Fe0/PANI) nanofibers were used as an effective material for sonocatalytic degradation of organic anionic Congo red (CR) dye. Fe0/PANI, was synthesized via reductive deposition of nano-Fe0 onto the PANI nanofibers at room temperature. Prepared catalyst was characterized using HR-TEM, FE-SEM, XRD, FTIR instruments. The efficacy of catalyst in removing CR was assessed colorimetrically using UV-visible spectroscopy under different experimental conditions such as % of Fe0 loading into the composite material, solution pH, initial concentration of dye, catalyst dosage, temperature and ultrasonic power. The optimum conditions for sonocatalytic degradation of CR were obtained at catalyst concentrations=500mg.L-1, concentration of CR=200ppm, solution pH=neutral (7.0), temperature=30°C, % of Fe0 loading=30% and 500W ultrasonic power. The experimental results showed that ultrasonic process could remove 98% of Congo red within 30min with higher Qmax value (Qmax=446.4 at 25°C). The rate of degradation of CR dye was much faster in this ultrasonic technique rather than conventional adsorption process. The degradation efficiency declined with the addition of common inorganic salts (NaCl, Na2CO3, Na2SO4 and Na3PO4). The rate of degradation suppressed more with increasing salt concentration. Kinetic and isotherm studies indicated that the degradation of CR provides pseudo-second order rate kinetic and Langmuir isotherm model compared to all other models tested. The excellent high degradation capacity of Fe0/PANI under ultrasonic irradiation can be explained on the basis of the formation of active hydroxyl radicals (OH) and subsequently a series of free radical reactions.

Synthesis and characterization of Fe0/TiO2 nano-composites for ultrasound assisted enhanced catalytic degradation of reactive black 5 in aqueous solutions

In the present study, nanocomposites (NCs) of zero valent iron nanoparticles (Fe0 NPs) and titanium dioxide nanoparticles (Fe0/TiO2 NCs) were prepared by coating Fe0 NPs onto the surface of TiO2 NPs through borohydride reduction of Fe(II) salt for the ultrasound assisted removal/ degradation of reactive black 5 (RB5) dye from aqueous solutions. Morphological and structural characterizations of the Fe0/TiO2 NCs were performed by FE-SEM, HR-TEM, XRD, XPS and Brunauer-Emmett-Teller (BET) method. The Fe0/TiO2 NCs exhibited highly efficient ultrasonic degradation/decolourization of RB5, compared to TiO2 NPs counterpart. In the presence of ultrasonic irradiation, 0.25g/L of Fe0/TiO2 NCs showed complete removal of 100mg/L RB5 dye within 10min of reaction. An increase in RB5 removal efficiency was obtained with decrease in initial concentration and solution pH, whereas it was decreased with decrease in the amount of Fe0/TiO2 NCs. The rate of RB5 degradation was in good agreement with the pseudo-first-order kinetic model. Higher RB5 removal efficiency was observed at a higher ultrasonic power level. Coexisting NO3- and SO42- ions had only a minor impact on the removal of RB5, whereas, CO32- ions considerably affected the% removal of RB5 using Fe0/TiO2 NCs. Regeneration/reusability experiments revealed that Fe0/TiO2 NCs could be reused efficiently up to 7th removal cycle without considerable loss of their original RB5 removal performance. Liquid chromatography-mass spectrometry (LC-MS) study, used for the detection of the RB5 degradation products showed that the degradation mechanism proceeds via the reductive cleavage of the azo linkage of the dye which produced 1-sulfonic, 2(4-aminobenzenesulfonyl) ethanol as the stable end product.

Fe-polyaniline composite nanofiber catalyst for chemoselective hydrolysis of oxime

A facile chemoselective one-pot strategy for the deprotection of oxime has been developed using Fe0-polyaniline composite nanofiber (Fe0-PANI), as a catalyst. Nano material based Fe0-PANI catalyst has been synthesized via in-situ polymerization of ANI monomer and followed by reductive deposition of Fe0 onto PANI matrix. The catalyst was characterized by FE-SEM, HR-TEM, BET, XRD, ATR-FTIR, XPS and VSM techniques. The scope of the transformation was studied for aryl, alkyl and heteroarylketoxime with excellent chemoselectivity (>99%). Mechanistic investigations suggested the involvement of a cationic intermediate with Fe3+ active catalytic species. Substituent effect showed a linear free energy relationship. The activation energy (Ea) was calculated to be 17.46 kJ mol-1 for acetophenone oxime to acetophenone conversion. The recyclability of the catalyst demonstrated up to 10 cycles without any significant loss of efficiency. Based on the preliminary experiments a plausible mechanism has been proposed involving a carbocationic intermediate.

Hydrous CeO2-Fe3O4 decorated polyaniline fibers nanocomposite for effective defluoridation of drinking water

Hydrous CeO2-Fe3O4 (HCeFe) decorated polyaniline nanofibers (HCeFe NFs) were obtained through a simple co-precipitation deposition approach on pre-synthesized polyaniline nano-fibers (PANI NFs), and evaluated as adsorbents for fluoride removal from synthetic and real water samples. Field emission scanning electron microscopy/energy dispersive X-ray spectroscopy (FE-SEM/EDS), high resolution-transmission electron microscopy (HR-TEM), Braunauer-Emmett-Teller (BET), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric-differential thermal analysis (TGA-DTA), X-ray photoelectron spectroscopy (XPS) and dynamic mechanical analysis (DMA) techniques were used to characterize the hybrid nanomaterials. The optimised HCeFe NFs adsorbent with specific surface area 66 m2/g, exhibited excellent adsorption efficiency towards fluoride ions (F-) via both electrostatic interactions and ion exchange mechanisms. F- adsorption followed the pseudo-second-order rate model and best fitted the Langmuir isotherm, with the maximum capacities within 93.46-117.64 mg/g over a broad pH range 3-10, respectively. The determined thermodynamic parameters, including enthalpy (ΔH° - 15.1 kJ/mol) and Gibbs free energies change (ΔG° < 0) indicated to the exothermic and a spontaneous nature of the sorption process. The regeneration of HCeFe NFs showed a considerable adsorption-desorption efficiency over three consecutive cycles. Ultimately, the adsorbent was tested on spiked F- containing groundwater and the obtained results demonstrated its potential utility for defluoridation of natural water.