Comparative study of the behavior of anions in polypyrrole films

Remediation of Cr(VI)-contaminated soil by CS/PPy coupling with Microbacterium sp. YL3

In this research, a new material, chitosan/polypyrrole (CS/PPy), was synthesized and linked with the Cr(VI)-reducing bacterial strain YL3 to treat Cr(VI)-polluted soil. The findings demonstrated that the synergistic application of strain YL3 and CS/PPy achieved the greatest reduction (99.6 %). During the remediation process, CS/PPy served as a mass-storage and sustained release agent in the soil, which initially decreased the toxic effects of high concentrations of Cr(VI) on strain YL3, thereby enhancing the Cr(VI) reduction efficiency of strain YL3. These combined effects significantly mitigated Cr(VI) stress in the soil and restored enzyme activities. Furthermore, wheat growth in the treated soil also significantly improved. High-throughput sequencing of the microorganisms in the treated soil revealed that CS/PPy was not only effective at removing Cr(VI) but also at preserving the original microbial diversity of the soil. This suggests that the combined treatment using strain YL3 and CS/PPy could rehabilitate Cr(VI)-contaminated soil, positioning CS/PPy as a promising composite material for future bioremediation efforts in Cr(VI)-contaminated soils.

In situ self-sacrificial synthesis of polypyrrole/biochar composites for efficiently removing short- and long-chain perfluoroalkyl acid from contaminated water

Efficient removal of perfluoroalkyl acids (PFAAs), especially short-chain ones, from contaminated water is of great challenge and is urgently called for so as to safeguard the ecosystem and human health. Herein, polypyrrole (PPy) functionalized biochar (BC) composites were innovatively synthesized by an in situ self-sacrificial approach to allow efficient capture of PFAAs with different chain lengths. Compared with conventional PPy-based composites synthesized by direct polymerization using FeCl3 as an oxidizing agent, PPy/BC composites were fabricated utilizing freshly generated Fe3+ as an oxidizing agent from self-sacrificial Fe3O4 for pyrrole monomers in situ polymerizing on BC. As a result, with the support of BC and gradual release of Fe3+, PPy overcame its tendency to aggregate and became uniformly dispersed on BC, and meanwhile, PPy could well tailor the surface chemistry of BC to endow its positively charged surface. Consequently, the composites exhibited strong sorption capacities of 3.89 and 1.53 mmol/g for short-chain perfluorobutanoic acid (PFBA) and perfluorobutane sulfonic acid (PFBS), 2.55 and 1.22 mmol/g for long-chain perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS), respectively, which were superior to those of pristine BC, commercial activated carbon, and anion exchange resins reported. Additionally, they could effectively remove 17 different classes of per- and polyfluoroalkyl substances (PFAS) (removal >95%) from actual PFAS-contaminated water, and the spent sorbent could be well regenerated and reused at least 5 times. An integrated analysis indicated that such an outstanding PFAA sorption performance on PPy/BC composites could be mainly attributed to surface adsorption enhanced by electrostatic attractions (anion exchange interaction) with the traditional hydrophobic interaction and pore filling of less contribution, particularly for short-chain analogues. These results are expected to inform the design of BC with greater ability to remove PFAS from water and the new sorbent could help water facilities comply with PFAS regulations.

Durable underwater super-oleophobic/super-hydrophilic conductive polymer membrane for oil-water separation

Oily sewage has made serious impact on environment and people's life, and its treatment has become a global problem to be urgently solved. Oil-water separation has been considered to be an effective method to treat oily sewage at present. In this work, an underwater super-oleophobic/super-hydrophilic membrane with oil-water separation and self-cleaning properties was fabricated by electrochemical oxidation of sodium lignosulfonate doped polypyrrole. The membrane showed super-hydrophilicity for water-removal in air and super-hydrophilicity for oil-removal underwater in both oxidation and reduction states. The oil-water separation efficiency of the membranes for different organics exceeded 98.44%, no matter in oxidation or reduction state. Moreover, the membrane still exhibited excellent performance in terms of the oil-water separation efficiency and flux after 70 cycles, which were greater than 97.18% and 70.14 L·m-2·h-1, respectively. Simultaneously, through exploration of the mechanism, it was found that the larger anion kept intact in the membrane during the redox process, which made the stability of composition and performance. Thus, the membrane with advantageous properties, including underwater super-oleophobic/super-hydrophilicity, high oil-water separation efficiency, high circulating rate and stability, has significant potential in separation and collection of oily sewage.

A nanoporous gold film sensor modified with polypyrrole/CuO nanocomposite for electrochemical determination of piroxicam and tramadole

In this paper, an electrochemical sensor was developed to determine piroxicam (PX) and tramadole (Tr) based on their enhanced electrochemical responses at the surface of the polypyrrole/CuO nanocomposite-modified nanoporous gold film (NPGF) electrode. The experimental results showed that PX provide an oxidation peak at 0.65 V in pH = 8.0. The DPV results were linearly affiliated on PX concentration within the two closed windows (C1_PX = 0.05-30.0 μM, correlation coefficient of 0.9905, and C2_PX = 50.0-300.0 μM, correlation coefficient of 0.9927). From voltammetric curves, the detection limit (LOD = 3S_b/m) for PX at a surface of PPY-CuO-NPGF electrode was appeared to be 0.01 μM. Furthermore, the ability of PPY-CuO-NPGF electrode for simultaneous measurement of PX and Tr was investigated. The suggested sensor shows a long-time stability, good repeatability, and rapid response in the mixture media of PX and Tr.

Application of polypyrrole-based adsorbents in the removal of fluoride: a review

When fluoride levels in water exceed permitted limits (>1.5 mg L−1), water pollution becomes a major concern to humans.

Insight into the ion exchange in the adsorptive removal of fluoride by doped polypyrrole from water

In this study, the polypyrrole (PPy) samples doped with Cl^- (PPy-Cl), SO₄^2- (PPy-SO4) and SO₄^2-+Cl^- (PPy-SO4+Cl) were synthesized by chemical polymerization for the adsorptive removal of fluoride ion from water. The structure and morphology of the as-prepared PPy samples were characterized by FT-IR, BET, SEM, XPS, and zeta potential. The adsorption experiments revealed that the PPy-Cl exhibited faster kinetics and higher adsorption capacity (13.98 mg/g), more than 4 times that of PPy-SO4 (3.08 mg/g) and PPy-SO4+Cl (3.17 mg/g). The kinetics of the adsorption followed the pseudo-second-order model and the adsorption isotherm data fitted well to the Langmuir model. FT-IR, EDX, and XPS tests for PPy samples before and after fluoride adsorption demonstrated that anion exchange between F^- and Cl^- or SO4^2- was the prior mechanism for fluoride ion removal from water. Cl^- was more favorable than SO₄^2- in the ion exchange with F^-. Meanwhile, the Cl^- or SO₄^2- exchanged with F^- was mainly bound to the active nitrogen that accounts for 6% of the total nitrogen in PPy molecular matrix. Further study of zeta potential and pH influence experiment demonstrated the electrostatic interaction is auxiliary interaction for the fluoride removal by doped PPy samples.

Toxic heavy metals: impact on the environment and human health, and treatment with conducting organic polymers, a review

Water pollution by heavy metals has many human origins, such as the burning of fossil fuels, exhaust gases of vehicles, mining, agriculture, and incineration of solid and liquid wastes. Heavy metals also occur naturally, due to volcanoes, thermal springs activity, erosion, infiltration, etc. This water contamination is a threat for living beings because most heavy metals are toxic to humans and to aquatic life. Hence, it is important to find effective techniques for removing these contaminants in order to reduce the level of pollution of the natural waters. In this work, we have reviewed the toxicity of several heavy metals (mercury, lead, cadmium, chromium, nickel), their impact on the environment and human health, and the synthesis and characterization methods of conducting organic polymers (COPs) utilized for the removal of heavy metals from the environment. Therefore, this review was essentially aimed to present recent works and methods (2000-2020) on the environmental impact and toxicity of heavy metals and on the removal of toxic heavy metals, using chemically and/or electrochemically synthesized COPs. We have also stressed the great interest of COPs for the removal of toxic heavy metals from waters.

Selective uptake and sensing of nitrate in poly(3,4-ethylenedioxythiophene)

Nitrogen (N) as a nutrient, in the form of nitrate (NO3-), is essential for plant growth. Chemical fertilizers are used to increase crop yields, but overuse can lead to forms of environmental pollution necessitating methods to detect and monitor the level of NO3- in-situ in agricultural soils. Herein we report for the first time the NO3- selectivity of the inherently conducting polymer poly (3,4-ethylenedioxythiophene) (PEDOT). This selectivity occurs when PEDOT thin films are exposed to an aqueous environment containing not only NO3-, but a mixture of other ions present in concentrations (ppm) typical of real agricultural soil. The PEDOT sensitivity to absorb NO3- from solution is determined to be <1 ppm.

Electronic properties of the polypyrrole-dopant anions ClO4- and MoO42-: a density functional theory study

The conductive properties of polypyrrole chains doped with ClO₄^- or MoO₄^2- anions and the existence of polarons and bipolarons in these doped polypyrrole chains were investigated by performing computational calculations based on density functional theory (DFT). Doping with these anions was found to decrease the band gap of the polypyrrole. Theoretical calculations revealed that changing the type of oxidative agent applied does not affect the conversion of polypyrrole into a conducting polymer, but the conductivity of the doped polypyrrole does depend on the ratio of oxidant to polypyrrole.

Adsorptive removal of sulfate from acid mine drainage by polypyrrole modified activated carbons: Effects of polypyrrole deposition protocols and activated carbon source

Polypyrrole modified activated carbon was used to remove sulfate from acid mine drainage water. The polypyrrole modified activated carbon created positively charged functionality that offered elevated sorption capacity for sulfate. The effects of the activated carbon type, approach of polymerization, preparation temperature, solvent, and concentration of oxidant solution over the sulfate adsorption capacity were studied at an array of initial sulfate concentrations. A hardwood based activated carbon was the more favorable activated carbon template, and this offered better sulfate removal than when using bituminous based activated carbon or oak wood activated carbon as the template. The hardwood-based activated carbon modified with polypyrrole removed 44.7 mg/g sulfate, and this was five times higher than for the pristine hardwood-based activated carbon. Various protocols for depositing the polypyrrole onto the activated carbon were investigated. When ferric chloride was used as an oxidant, the deposition protocol that achieved the most N⁺ atomic percent (3.35%) while also maintaining the least oxygen atomic percent (6.22%) offered the most favorable sulfate removal. For the rapid small scale column tests, when processing the AMD water, hardwood-based activated carbon modified with poly pyrrole exhibited 33 bed volume compared to the 5 bed volume of pristine activated carbons.

Polypyrrole-grafted peanut shell biological carbon as a potential sorbent for fluoride removal: Sorption capability and mechanism

In this study, an effective defluoridation adsorbent was developed by depositing polypyrrole (PPy) on granular peanut shell biological carbon (BC) via in situ chemical oxidative polymerization. The variables of defluoridation process (i.e., adsorbent dosage, fluoride solution pH, and anionic interference) were tested. The mechanism was determined by isotherm and kinetic studies, Brunauer-Emmett-Teller (BET) method, scanning electronic microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy and automatic titration. The PPy-grafted BC (PPy/BC) composite performed commendably from pH 2.0 to 10.0, and exhibited high selectivity for fluoride in the presence of several co-existing anions. The experimental data were described well by a Langmuir isotherm curve, and the maximum adsorption capacity was 17.15 mg g(-1). Kinetic studies illustrated the adsorption process was accomplished via surface adsorption as well as by intraparticle diffusion. In addition, mesoporous diffusion was the rate-controlling step in intraparticle diffusion process. BET and SEM analysis revealed the sponge-like polymer adhered to the BC and plugged the pores. XPS, FTIR, and SEM confirmed that fluoride removal was accomplished via the replacement of doped ionizable chloride ions (Cl(-)) coupled with positively charged nitrogen (N(+)), computation of XPS data enabled the formulation of a three-layer-deep hypothesis for PPy.

Graphene-polypyrrole nanocomposite as a highly efficient and low cost electrically switched ion exchanger for removing ClO₄⁻ from wastewater

Perchlorate (ClO(4)(-)) contamination is a widespread concern affecting water utilities. In the present study, functionalized graphene sheets were employed as the scaffold to synthesize a novel graphene-polypyrrole (Ppy) nanocomposite, which served as an excellent electrically switched ion exchanger for perchlorate removal. Scanning electron microscopy and electrochemical measurements showed that the 3D nanostructured graphene-Ppy nanocomposite exhibited a significantly improved uptake capacity for ClO(4)(-) compared with Ppy film alone. X-ray photoelectron spectroscopy confirmed the uptake and release process of ClO(4)(-) in graphene-Ppy nanocomposite. In addition, the presence of graphene substrate resulted in high stability of graphene-Ppy nanocomposite during potential cycling. The present work provides a promising method for large scale water treatment.

Control of neural stem cell survival by electroactive polymer substrates

Stem cell function is regulated by intrinsic as well as microenvironmental factors, including chemical and mechanical signals. Conducting polymer-based cell culture substrates provide a powerful tool to control both chemical and physical stimuli sensed by stem cells. Here we show that polypyrrole (PPy), a commonly used conducting polymer, can be tailored to modulate survival and maintenance of rat fetal neural stem cells (NSCs). NSCs cultured on PPy substrates containing different counter ions, dodecylbenzenesulfonate (DBS), tosylate (TsO), perchlorate (ClO₄) and chloride (Cl), showed a distinct correlation between PPy counter ion and cell viability. Specifically, NSC viability was high on PPy(DBS) but low on PPy containing TsO, ClO₄ and Cl. On PPy(DBS), NSC proliferation and differentiation was comparable to standard NSC culture on tissue culture polystyrene. Electrical reduction of PPy(DBS) created a switch for neural stem cell viability, with widespread cell death upon polymer reduction. Coating the PPy(DBS) films with a gel layer composed of a basement membrane matrix efficiently prevented loss of cell viability upon polymer reduction. Here we have defined conditions for the biocompatibility of PPy substrates with NSC culture, critical for the development of devices based on conducting polymers interfacing with NSCs.

Investigations on the mechanical properties of conducting polymer coating-substrate structures and their influencing factors

This review covers recent advances and work on the microstructure features, mechanical properties and cracking processes of conducting polymer film/coating- substrate structures under different testing conditions. An attempt is made to characterize and quantify the relationships between mechanical properties and microstructure features. In addition, the film cracking mechanism on the micro scale and some influencing factors that play a significant role in the service of the film-substrate structure are presented. These investigations cover the conducting polymer film/coating nucleation process, microstructure-fracture characterization, translation of brittle-ductile fractures, and cracking processes near the largest inherent macromolecule defects under thermal-mechanical loadings, and were carried out using in situ scanning electron microscopy (SEM) observations, as a novel method for evaluation of interface strength and critical failure stress.