An integrated approach for Cr(VI)-detoxification with polyaniline/cellulose fiber composite prepared using hydrogen peroxide as oxidant

A Novel Biosorbent From Hardwood Cellulose Nanofibrils Grafted With Poly(m-Aminobenzene Sulfonate) for Adsorption of Cr(VI)

Cellulose from different lignocellulosic biomass can be used to prepare various materials. In this work, the cellulose nanofibrils were produced from hardwood bleached kraft pulp. Then, a novel biosorbent from cellulose nanofibrils grafted with poly(m-aminobenzene sulfonate) (PABS) was prepared for effective detoxification and adsorption of Cr(VI) in an aqueous medium. 6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized cellulose nanofibrils (TOCNF) with a high aspect ratio was used as an adsorbent matrix. PABS, an amine-rich conductive polymer, was grafted onto TOCNF via a successive two-step reaction. The analyses of Fourier transform infrared (FT-IR) spectroscopy and X-ray photoelectron spectroscopy (XPS) confirmed the successful grafting reaction between TOCNF and PABS. The biosorbent from TOCNF-bonded PABS with the nitrogen content of 7.0% was synthesized. It exhibited excellent Cr(VI) adsorption capacity at a solution pH below 3, and almost 100% Cr(VI) can be removed. The adsorption of Cr(VI) on the biosorbent was described by a pseudo-second-order model and obeyed the Langmuir model. The Cr(VI) adsorption capacity of the biosorbent from TOCNF-bonded PABS was almost 10 times higher than that of TOCNF. It was interesting to note that part of Cr(VI) ions had been reduced to Cr(III) during the adsorption process. It indicated that the biosorbent from TOCNF grafted with PABS could detoxify and adsorb Cr(VI) synchronously.

Density functional theory simulation for Cr(VI) removal from wastewater using bacterial cellulose/polyaniline

Herein, for the first time, the adsorption mechanism of HCrO₄^- and CrO₄^2- (as models of Cr(VI)) by bacterial cellulose (BC), polyaniline (PANI), and BC/PANI was performed using Density Functional Theory (DFT) in both acidic and neutral pH. For this purpose, three forms of neutral, partially (pp), and fully protonated (fp) were assumed for PANI in neutral and acidic media to elucidate the influence of pH. The results indicated that the formation of hydrogen bonds (H-bond) had the main contribution in the adsorption of CrO₄^2- and HCrO₄^- onto both BC and PANI. Besides, the adsorption energy of PANI was nearly 3 times as much as BC in both acidic and neutral pH. The design of the BC/PANI complex improved the stability of PANI by increasing in HOMO-LUMO energy gap from 1.1 eV to 1.97 eV. The establishment of more H-bonds, and the appearance of two different types of H-bonds, O⋯H and N⋯H, and their smaller distances (average 1.5 Å), were observed in HCrO₄^-/BC-fp-PANI complexes, while one type of hydroxyl H-bond (average 2 Å) was detected in CrO₄^2-/BC-pp-PANI. It proved the adsorption of Cr(VI) is more favorable in acidic pH. The small value of charge transferred (-0.001-0.01) showed that interfacial interaction was governed by physisorption.

Ultra-low pressure cellulose-based nanofiltration membrane fabricated on layer-by-layer assembly for efficient sodium chloride removal

Cellulose is a renewable, biodegradable, biocompatible, and sustainable material. A bamboo cellulose-based nanofiltration membrane (LBL-NF-CS/BCM) was prepared with a combination of layer-by-layer assembly and spraying methods. The chemical structure, morphology, and surface charge of the resultant LBL-NF-CS/BCM composite membranes were characterized based on Thermo Gravimetric Analysis (TGA), X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), and X-ray Photoelectron Spectroscopy Scanning (XPS). The nanofiltration performance of the LBL-NF-CS/BCM composite membranes was evaluated using 500 ppm NaCl solutions under 0.3 MPa pressure. It was found that the LBL-NF-CS/BCM composite membranes had a rejection rate of about 36.11 % against a 500 ppm NaCl solution under the conditions tested, and membrane flux of about 12.08 L/(m² h) was reached. The combined layer-by-layer assembly and spraying provides a scalable and convenient process concept for nanofiltration membrane fabrication.

Polyaniline-based adsorbents for removal of hexavalent chromium from aqueous solution: a mini review

Hexavalent chromium (Cr(VI)) is a common hazardous contaminant in the environment and carcinogenic or mutagenic to aquatic animals and human beings. Therefore, the removal and detoxification of Cr(VI) have been attracting increasing attention of researchers. Among various conducting polymers, polyaniline (PANI)-based adsorbents have shown an excellent performance on the removal of Cr(VI) because of their redox properties, eased synthesis, and favorable biocompatibility. In this review, the characteristics of various PANI-based adsorbents were described, including PANI-modified nanofiber mats and membranes, PANI/bio-adsorbents, PANI/magnetic adsorbents, PANI/carbon adsorbents, PANI-modified clay composites, and PANI-inorganic hybrid composites. The mechanisms for the detoxification and adsorption of Cr(VI) were also discussed. The results indicated the potential applications of PANI-based adsorbents for the removal of Cr(VI). Graphical abstract ᅟ.

A process of applying polypyrrole-engineered pulp fibers prepared using hydrogen peroxide as oxidant to detoxification of Cr(VI)-contaminated water

In this study, different from previous reports, an alternative process for detoxification of Cr(VI)-contaminated water with polypyrrole-engineered pulp fibers prepared using low cost hydrogen peroxide as oxidant was proposed. The process conditions in preparation of the engineered fibers as well as the water treatment conditions were optimized, and the behavior of Cr desorption from the engineered fibers was evaluated. The results showed that the proposed process was highly efficient in Cr(VI)-detoxification via the integration of adsorption with reduction. Compared with the previously reported polyaniline-engineered fibers prepared with hydrogen peroxide as oxidant, the engineered fibers studied in this work was much more effective.