Enhanced adsorption of cationic and anionic dyes from aqueous solutions by polyacid doped polyaniline

A new high surface area polyaniline (PANI) adsorbent was synthesized by matrix polymerization of aniline in the presence of a polyacid, poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPSA). Morphological and physicochemical properties of PANI-PAMPSA were characterized by field emission scanning electron microscope (FESEM), Fourier transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD), nitrogen adsorption/desorption and zeta potential measurement. Adsorption properties were evaluated using methylene blue (MB) and rose bengal (RB) as model dyes.The results showed that PANI-PAMPSA obtained a well-defined porous structure with a specific surface area (126 m2 g−1) over 10 times larger than that of the emeraldine base PANI (PANI-EB) (12 m2 g−1). The maximum adsorption capacities were 466.5 mg g−1 for MB and 440.0 mg g−1 for RB, higher than any other PANI-based materials reported in the literature. The FTIR analysis and zeta potential measurement revealed that the adsorption mechanisms involved π-π interaction and electrostatic interaction. The adsorption kinetics were best described by a pseudo-second-order model, and the adsorption isotherms followed the Langmuir model. The thermodynamic study indicated that the adsorption was a spontaneous endothermic process. Overall, the convenient synthesis and the high adsorption capacity make PANI-PAMPSA a promising adsorbent material for dye removal

Exploiting the electrical conductivity of poly-acid doped polyaniline membranes with enhanced durability for organic solvent nanofiltration

We have developed stable organic solvent nanofiltration (OSN) membranes that are electrically conductive. These membranes overcome key issues with current tuneable membranes: molecular weight cut off (MWCO) limited to the UF-range and lack of filtration stability. Polyaniline (PANI) was in-situ doped by poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPSA) using chemical oxidative polymerization that leads to formation of interpolymer complex. The PANI-PAMPSA membranes were prepared by phase inversion method and the pore sizes were shrunk by annealing the membranes at temperatures lower than the crosslinking temperature. The membranes were systematically evaluated using visual and chemical analysis and in-filtration experiments. The developed membranes were solvent stable, reusable, had a denser structure and lower MWCO and there was no thermal crosslinking as seen by IR. The solvent permeance obtained were: 0.46, 0.60 and 0.74 Lm −2 h −1 bar −1 for acetone, 2-propanol and methanol respectively, with MWCO below 300 Da and 266 Da for methanol. For the tuneability investigation, when applying an electrical potential (20 V) in a custom-made cross-flow membrane cell, an increase in MWCO and permeance (10.4% and 55.6%, respectively) was observed. These results show that this simple in-situ doping method with heat treatment can produce promising and stable PANI membranes, for OSN processes in different solvents, with the distinctive feature of in-situ performance control by applying external electrical potential. </p

Effect of polyacid dopants on the performance of polyaniline membranes in organic solvent nanofiltration

Polyaniline (PANI) has been widely explored as a promising membrane material, but the trade-off between porosity and stability limits its widespread application in organic solvent nanofiltration (OSN). Here we present a simple approach to prepare PANI membranes with excellent chemical stability and rejection performance in OSN by employing polyacids as PANI dopants for the first time. The PANI membranes were doped with two polyacids with different molecular weights (MW) and acid dissociation constants (pKa): namely poly(4-styrenesulfonic acid) (PSSA, MW: 75000 g mol −1, pKa: 0.94) and poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPSA, MW: 800000 g mol −1, pKa: 0.87), and were compared with a small acid (HCl) doped PANI membrane. The polyacid doped membranes, PANI-PSSA and PANI-PAMPSA, obtained dense structures with increased hydrophilicity due to strong intermolecular interactions between the PANI and the polyacids. Stability tests showed that the PANI-PSSA and PANI-PAMPSA were stable in a wide range of polar and nonpolar solvents, while the undoped PANI and PANI-HCl had poor stability in these solvents. The swelling degree and permeance of the doped membranes decreased with the increase of the dopant MW. The PANI-PAMPSA membrane exhibited a molecular weight cut-off (MWCO) in the nanofiltration (NF) range of 400 g mol −1 in methanol and isopropanol, while the PANI-HCl and PANI-PSSA membranes were in the ultrafiltration (UF) range. This study demonstrates that polyacid doping can make stable and nanoporous PANI membranes for OSN applications without the need for crosslinking. This simple approach can be used to design new classes of OSN membranes for challenging separation processes in the future. </p