The removal of toxic hexavalent chromium (Cr(VI)) from polluted water by magnetic polyaniline (PANI) polymer nanocomposites (PNCs) was investigated. The PNCs were synthesized using a facile surface initiated polymerization (SIP) method and demonstrated unique capability to remove Cr(VI) from polluted solutions with a wide pH range. Complete Cr(VI) removal from a 20.0 mL neutral solution with an initial Cr(VI) concentration of 1.0–3.0 mg L⁻¹ was observed after a 5 min treatment period with a PNC load of 10 mg. The PNC dose of 0.6 g L⁻¹ was found to be sufficient for complete Cr(VI) removal from 20.0 mL of 9.0 mg L⁻¹ Cr(VI) solution. The saturation magnetization was observed to have no obvious decrease after treatment with Cr(VI) solution, and these PNCs could be easily recovered using a permanent magnet and recycled. The Cr(VI) removal kinetics were determined to follow pseudo-first-order behavior with calculated room temperature pseudo-first-order rate constants of 0.185, 0.095 and 0.156 min⁻¹ for the solutions with pH values of 1.0, 7.0 and 11.0, respectively. The Cr(VI) removal mechanism was investigated by Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS) and energy-filter transmission electron microscopy (EFTEM). The results showed that PANI was partially oxidized after treatment with Cr(VI) solution, with Cr(VI) being reduced to Cr(III). The EFTEM observation indicated that the adsorbed Cr(III) had penetrated into the interior of the PNCs instead of simply adsorbing on the PNC surface. This synthesized material was found to be easily regenerated by 1.0 mol L⁻¹p-toluene sulfonic acid (PTSA) or 1.0 mol L⁻¹ hydrochloric acid (HCl) and efficiently reused for further Cr(VI) removal.

The high performance multi-walled carbon nanotubes (MWNTs) reinforced epoxy polymer nanocomposites (PNCs) have been synthesized at different MWNT loading levels. The surface functionalization of MWNTs with conductive PANI was achieved by using a facile surface initiated polymerization method with the aid of the oxidations of CNTs and subsequent anilines by hexavalent chromium (Cr(VI)) oxidant. The effects of MWNT loading, surface functionalization and temperature on the rheological behaviors of liquid epoxy resin nanosuspensions and on the physicochemical properties of cured solid PNCs were systematically investigated. The glass transition temperature (T_g) of the cured epoxy PNCs filled with functionalized MWNTs obtained from the dynamic mechanical analysis (DMA) test was increased about 6–25 °C than that of cured pure epoxy. The PNCs reinforced with functionalized MWNTs demonstrated an enhanced tensile strength than either cured pure epoxy or its PNCs filled with the as-received MWNTs. The electrical conductivity of cured epoxy PNCs with functionalized MWNTs was improved by 5.5 orders of magnitude compared with cured pure epoxy. Thermogravimetric analysis (TGA) revealed an enhanced thermo-stability in the cured epoxy PNCs filled with functionalized MWNTs than that of cured pure epoxy and its PNCs filled with the as-received MWNTs. The observed strong interfacial interaction between MWNTs and the epoxy resin matrix was responsible for the enhanced mechanical tensile strength. The nanocomposite formation mechanism is proposed based on the analysis from Fourier transform infrared (FT-IR), thermogravimetric analysis (TGA), Raman and differential scanning calorimetry (DSC) tests.