Folic Acid-Polyaniline Hybrid Hydrogel for Adsorption/Reduction of Chromium(VI) and Selective Adsorption of Anionic Dye from Water

Abstract

A porous 3D folic acid (F)-polyaniline (PANI) hybrid hydrogel (F-PANI), produced by in situ polymerization of aniline, exhibit highest compressive stress (15.1 kPa), 3D hierarchical network morphology with BET surface area 236 m2/g. Here, PANI is present in emeraldine salt (ES) state, which facilitates excellent adsorption of anionic pollutants. It exhibits an extremely high adsorption capacity for Cr­(VI) and during adsorption Cr­(VI) is reduced to Cr­(III).The electrical impedance spectra of the Cr­(VI) adsorbed xerogel, support the conversion of PANI chains from ES to pernigraniline base­(PB) making the xerogel more resistive. It also selectively adsorbs anionic dyes, the adsorption capacity increases with decrease of pH. Both the adsorption data are found to be well explained through pseudo-second-order kinetic model, and they obey Langmuir adsorption isotherm. F-PANI2 showed high adsorption capacities selectively toward anionic pollutants, for example, Cr­(VI), eosine yellow, rose bengal, methyl orange, and low adsorption capacities for Hg­(II), Pb­(II), rhodamineB, bismark brownY methylene blue, and neutral red. The removal of Cr­(VI) and anionic dyes are very much effective at neutral and acidic pH. After dye/Cr­(VI) adsorption the Nyquist plot indicate significant decrease in the capacitance of xerogels. Cyclic experiments show that, F-PANI xerogels can be effectively reused to remove Cr­(VI) from different contaminated water.

Carbohydrate-supramolecular gels: Adsorbents for chromium(VI) removal from wastewater

“…The chemisorption process for Cr(VI) removal has also been observed for some polyaniline hydrogels and it has been ascribed to oxidation of the aryl amine -NH sites of the polymer into imine groups. [16,59] However, those studies were carried out under acidic pH conditions, so in our case, it is likely that another functionality is responsible for the reduction process. Remembering the high potential of aldaric acid to form complexes with metal species, [39,[60][61][62] we tested the ability of saccharic acid potassium salt to reduce Cr(VI) as a model of what could occur on our carbohydrate-based gels after Cr (VI) adsorption causes the colour to change (Figure 4c).…”

“…A similar behaviour has been previously observed for some polymeric xerogels, which are able to remove the oxyanionic pollutant Cr 2 O 7 2− , but not cationic ones such as Hg 2+ and Pb 2+ . [16] This selectivity has been ascribed to the electrostatic interactions between the oppositely charged adsorbent and adsorbate. However, for the hydrogels in this work, other factors can cooperate in the adsorption process, because the gelator comprises both cationic and anionic components and the anion features multiple hydrogen bonding groups.…”

“…Recently, polymeric and hybrid gels have been used to remove Cr(VI) from aqueous solution. For example, a redox-responsive copper(I) metallogel, [14] a sponge-like porous composite chitosan hydrogel formed with reduced graphene oxide and montmorillonite [15] and a porous 3D folic acid-polyaniline hybrid hydrogel [16] have been reported. In all cases, high efficiency was observed, especially in acidic conditions.…”

Engineering of MoS2 Quantum Dots/PANI Aerogel for High Performance Supercapaciator

“…The adsorption band at 339 and 342 nm for D‐PANI and D‐MoS 2 ‐PANI are ascribed to π–π* transition in the benzenoid rings, respectively. In contrast, the peak at ≈440 nm corresponds to polaron to π* band transition and the peak at 842 nm and 851 nm for D‐PANI and D‐MoS 2 ‐PANI aerogel correspond to π‐band to the polaron‐band transition of the PANI chain, respectively . This result confirms that PANI is produced in the doped emaraldine salt (ES) state because D dopes PANI well.…”

“…The UV–Vis spectra of MoS 2 QDs, D‐PANI, and D‐MoS 2 ‐PANI are presented in Figure a MoS 2 QDs exhibit four peaks; the two peaks at 384 and 446 nm correspond to valence band to the conduction band transition, and next two peaks at 605 and 668 nm are assigned to the Brillouin zone of K point . UV–Vis spectra of D‐PANI and D‐MoS 2 ‐PANI aerogels (Figure a) show three peaks.…”