Polypyrrole Nanomaterials: Structure, Preparation and Application

In the past decade, nanostructured polypyrrole (PPy) has been widely studied because of its many specific properties, which have obvious advantages over bulk-structured PPy. This review outlines the main structures, preparation methods, physicochemical properties, potential applications, and future prospects of PPy nanomaterials. The preparation approaches include the soft micellar template method, hard physical template method and templateless method. Due to their excellent electrical conductivity, biocompatibility, environmental stability and reversible redox properties, PPy nanomaterials have potential applications in the fields of energy storage, biomedicine, sensors, adsorption and impurity removal, electromagnetic shielding, and corrosion resistant. Finally, the current difficulties and future opportunities in this research area are discussed.

Metal-Free Organo-Theranostic Nanosystem with High Nitroxide Stability and Loading for Image-Guided Targeted Tumor Therapy

The desire for all-organic-composed nanoparticles (NPs) of considerable biocompatibility to simultaneously diagnose and treat cancer is undeniably interminable. Heretofore, metal-based agents dominate the landscape of available magnetic resonance imaging (MRI) contrast agents and photothermal therapeutic agents, but with associated metal-specific downsides. Here, an all-organic metal-free nanoprobe, whose appreciable biocompatibility is synergistically contributed by its tetra-organo-components, is developed as a viable alternative to metal-based probes for MRI-guided tumor-targeted photothermal therapy (PTT). This rationally entails a glycol chitosan (GC)-linked polypyrrole (PP) nanoscaffold that provides abundant primary and secondary amino groups for amidation with the carboxyl groups in a nitroxide radical (TEMPO) and folic acid (FA), to obtain GC-PP@TEMPO-FA NPs. Advantageously, the appreciably benign GC-PP@TEMPO-FA features high nitroxide loading (r₁ = 1.58 mM^-1 s^-1) and in vivo nitroxide-reduction resistance, prolonged nitroxide-systemic circulation times, appreciable water dispersibility, potential photodynamic therapeutic and electron paramagnetic resonance imaging capabilities, considerable biocompatibility, and ultimately achieves a 17 h commensurate MRI contrast enhancement. Moreover, its GC component conveys a plethora of PP to tumor sites, where FA-mediated tumor targeting enables substantial NP accumulation with consequential near-complete tumor regression within 16 days in an MRI-guided PTT. The present work therefore promotes the engineering of organic-based metal-free biocompatible NPs in synergism, in furtherance of tumor-targeted image-guided therapy.

A Hybrid Organo-Nanotheranostic Platform of Superlative Biocompatibility for Near-Infrared-Triggered Fluorescence Imaging and Synergistically Enhanced Ablation of Tumors

The quest for an all-organic nanosystem with negligible cytotoxicity and remarkable in vivo tumor theranostic capability is inescapably unending. Hitherto, the landscape of available photothermal agents is dominated by metal-based nanoparticles (NPs) with attendant in vivo negatives. Here, an all-organic-composed theranostic nanosystem with outstanding biocompatibility for fluorescence image-guided tumor photothermal therapy, and as a potential alternative to metal-based photothermal agents is developed. This is rationally achieved by compartmentalizing indocyanine green (ICG) in glycol chitosan (GC)-polypyrrole (PP) nanocarrier to form hybrid ICG@GC-PP NPs (≈65 nm). The compartmentalization strategy, alongside the high photothermal conversion ability of PP jointly enhances the low photostability of free ICG. Advantageously, ICG@GC-PP is endowed with an impeccable in vivo performance by the well-known biocompatibility track records of its individual tri organo-components (GC, PP, and ICG). As a proof of concept, ICG@GC-PP NPs enables a sufficiently prolonged tumor diagnosis by fluorescence imaging up to 20 h post-injection. Furthermore, owing to the complementary heating performances of PP and ICG, ICG@GC-PP NPs-treated mice by one-time near-infrared irradiation exhibit total tumor regression within 14 days post-treatment. Therefore, leveraging the underlying benefits of this study will help to guide the development of new all-organic biocompatible systems in synergism, for safer tumor theranostics.

Removal of Cr(VI) from Aqueous Solution by Polypyrrole/Hollow Mesoporous Silica Particles

The removal of Cr(VI) in wastewater plays an important role in human health and environment. In this work, polypyrrole/hollow mesoporous silica particle (PPy/HMSNs) adsorbents have been newly synthesized by in-situ polymerization, which prevent the aggregation of pyrrole in the process of polymerization and exhibit highly selective and powerful adsorption ability for Cr(VI). The adsorption process was in good agreement with the quasi-second-order kinetic model and the Langmuir isotherm model. And the maximum adsorption capacity of Cr(VI) was 322 mg/g at 25 °C. Moreover, the removal rate of Cr(VI) by PPy/HMSNs was ~100% in a number of binary systems, such as Cl⁻/Cr(VI), NO₃⁻/Cr(VI), SO₄²⁻/Cr(VI), Zn²⁺/Cr(VI), Fe³⁺/Cr(VI), Sn⁴⁺/Cr(VI), and Cu²⁺/Cr(VI). Thus, the PPy/HMSNs adsorbents have great potential for the removal of Cr(VI) in wastewater.

Highly Efficient Removal of Cr(VI) from Aqueous Solutions by Polypyrrole/Monodisperse Latex Spheres

Pyrrole (Py) is easily agglomerated during the polymerization process, affecting its performance. In this paper, polypyrrole/monodispersed latex sphere (PPy/MLS) composites were prepared using in-situ polymerization for the adsorption of hexavalent chromium (Cr(VI)). The specific surface area of PPy/MLS (39.30 m²/g) was increased relative to that of PPy (24.82 m²/g), thus providing more effective adsorption sites. In addition, the adsorption properties of Cr(VI) under different conditions, including Py content, pH of the aqueous solution, and PPy/MLS dosage, were investigated to reveal the adsorption mechanism. The results showed that PPy/MLS possessed high Cr(VI) adsorption capacities when the Py content was 50 wt %. The maximum adsorption capacity was 343.64 mg/g at pH 2.0 and 25 °C. Remarkably, the adsorbents exhibited an excellent removal rate of Cr(VI) after three cycles of adsorption-desorption (over 99%), suggesting that the adsorbents had exceptional recyclability. Furthermore, the adsorption process followed quasi-second-order kinetics and Langmuir isothermal adsorption model. The high adsorption performance, sustainability, and cost-efficiency make this adsorbent a promising candidate for large-scale Cr(VI) contaminant removal.

Construction of novel graphene-based materials GO@SiO2@C@Ni for Cr(VI) removal from aqueous solution

A series of novel sandwich-like GO@SiO₂@C@Ni composites were developed. The morphologies and adsorption capacities of the materials sintered at different carbonization temperatures were investigated. The formed GO@SiO₂@C@Ni-400 possessed of wonderful dispersion, large surface area (229.88 m²/g) and high saturation magnetization. Batch experimental results revealed that maximum adsorption capacities of these materials towards Cr(VI) were as follows: GO@SiO₂@C@Ni-400 (299.20 mg/g) > GO@SiO₂@C@Ni-500 (244.05 mg/g) > GO (202.39 mg/g) > Graphene@C@Ni (188.80 mg/g) > GO@SiO₂@C@Ni-600 (165.51 mg/g) > GO@SiO₂@C@Ni-700 (93.36 mg/g). Moreover, the influence of hydrochemistry, such as contact time, pH, co-existing ions and solution temperature, on Cr(VI) adsorption was researched as well. It was demonstrated that GO@SiO₂@C@Ni-400 had remarkable adsorption capacity for Cr(VI) removal under the acidic condition, hardly disturbed by other anions, and showed better adsorption performance at 328 K. Besides, On the base of X-ray photoelectron spectroscopy analysis, mechanisms of adsorption could be explained that Cr(VI) was reduced to Cr(III) by nitrogen dopant, and the complexation was existed between Cr(VI) and oxygen-containing functional groups. Additionally, GO@SiO₂@C@Ni-400 could be easily separated under the external magnetic field and displayed outstanding reusability. Herein, GO@SiO₂@C@Ni-400 opens up the possibility of future practical applications.

Graphene oxide-based materials for efficient removal of heavy metal ions from aqueous solution: A review

Graphene with atomic layer of sp²-hybridized carbon atoms in a hexagonal structure has attracted multidisciplinary attention since its discovery. Due to the inherent advantages of large specific surface area and abundant functional groups, its derivative graphene oxide (GO) nanomaterials have achieved large-scale development in effective pollution treatment. In the past few years, novel GO-based nanomaterials through coupling with other nanomaterials have been synthesized with significant process and applied for efficient elimination of different kinds of pollutants. This paper aims to summarize recent research results on the excellent removal ability of GO-based nanomaterials for various heavy metal ions in aqueous solutions. The synthesis, adsorption process characteristics and interaction mechanism of the adsorbent are emphasized and discussed. The effects of various environmental conditions are outlined. At last, a brief summary, perspective and outlook are presented. This review is intended to provide some thrilling information for the design and manufacture of GO-based nanomaterials for the elimination of heavy metal ions from wastewater in environmental pollution management.

Clay based nanocomposites for removal of heavy metals from water: A review

The exponential increment in world population, recent industrialization, civilization, agricultural and household activities leads to greater levels of water pollution in terms of organic and inorganic contaminants. However, numerous workers have done research for the removal of these pollutants and various types of clays and/or modified clays have been extensively used for this purpose. But all identified adsorbent materials are not able to remove pollutants after certain concentration and sometimes these contaminants are left as such in environment which may create other environmental issues. This paper presents comprehensive information for the adsorption of heavy metal ions from water and waste water using various nanostructured adsorbents such as different clay minerals (kaolinite, montmorillonite) and clay (bentonite), carbon nanotube and nanocomposites. In addition to this, the efficiency of developed materials for the removal of heavy metals is also discussed in details along with comparison of their adsorption efficiencies, pH and change in specific surface area, initial metal ion concentration and contact time. This paper also states the future directions which could be followed to challenge the situation of removal of traces of heavy metals from water, hence protecting water bodies from high pollution load.

One-Step Synthesis of Iodinated Polypyrrole Nanoparticles for CT Imaging Guided Photothermal Therapy of Tumors

Theranostic materials are of great significance to a personalized precise medicine. However, conventional theranostic agents are mainly fabricated by combining presynthesized independent imaging probes and therapeutic agents, suffering from multiple synthesis procedures, poor morphological control, and time/reagent-consuming process. Herein, iodinated polypyrrole (I-PPy) nanoparticles are fabricated via a one-step synthesis strategy combining chemical oxidation and iodination for computed tomography (CT) imaging-guided photothermal therapy. Iodic acid with a high standard electrode potential enables the chemical oxidation polymerization of pyrrole monomers. Meanwhile, the iodination of PPy induced by the corresponding reduction product I₂ takes place during the polymerization process to generate I-PPy nanoparticles. The prepared I-PPy nanoparticles possess a uniform size, excellent colloidal stability, intense near-infrared absorption, strong X-ray attenuation ability, and favorable biocompatibility. The as-synthesized I-PPy nanoparticles not only guarantee remarkable contrast-enhanced CT imaging of blood pool and tumors, but also realize effective tumor suppression in vitro and in vivo by I-PPy nanoparticles-mediated CT imaging-guided photothermal therapy. To the best of the authors' knowledge, it is the first time that multifunctional PPy nanoparticles are fabricated through a one-step synthesis process. The proposed strategy opens up a new way for the fabrication of high-performance theranostic agents via a one-step strategy under mild conditions.

Facile synthesis of hierarchical nickel (III) oxide nanostructure: A synergistic remediating action towards water contaminants

Heavy metal ion removal from consumable water is an indispensable need to maintain healthy life. Therefore cost effective and highly efficient sorbents are strongly needed to pose threat to real water pollution. Nanomaterials are widely used to maintain clean aqueous system in a very cost effective way with high removal efficiency. In this present work, pure coral like Ni₂O₃ nanostructures were prescribed for Cr(VI) remediation which were prepared by two step synthesis procedure at room temperature. The single hierarchical morphology as confirmed from HRTEM (size∼200 nm) were subjected to toxic Cr(VI) ion removal experiments. They were found to remove ∼65% Cr(VI) ions that was higher than that of pure Ni₂O₃ nanoparticles of comparable size. The enhanced properties were explained on the basis of the defect states present within the nanostructure, investigated by positron annihilation lifetime spectroscopy (PALS). It was found that the hierarchical nanostructure had more number of di-vacancies and vacancy-clusters as compared to the particles. On performing isotherm fitting, it was found that the coral like morphology had a high heterogeneity factor that aided to a high adsorption rate when compared to the pure Ni₂O₃ nanoparticles (which had a homogenous surface). The synthesized nanostructure was severely toxic to bacterial community having minimum inhibitory concentration (MIC) of ∼300 μg/L. Also the nanostructure exhibited dual functionality towards Cr(VI) and bacteria contaminated water at 200 μg/ml. The maximum Cr(VI) removal efficiency for this dual system is found to be 39% whereas antibacterial activity was turned out to be 30% which was extensively higher than that of toxic Cr(VI) ions. A plausible mechanism for the dual functionality was also predicted.

Synthesis of graphene/SiO2@polypyrrole nanocomposites and their application for Cr(VI) removal in aqueous solution

A novel hybrid nanocomposite, polypyrrole nanoparticles (PPy) anchored on the graphene/silica nanosheets with the high specific surface area (polypyrrole-graphene/silica, GS-PPy), was synthesized by a facile in situ polymerization and shows great potential to remove hexavalent chromium [Cr(VI)] in aqueous solutions. Characterizations by XRD, TEM, SEM, BET, FT-IR and XPS, have confirmed that the PPy nanoparticles were well-distributed on the surface of GS nanosheets. The effects of pH, contact time, the concentration of Cr(VI), temperature, coexisting ions and the number of adsorption-desorption cycles were studied. The maximum adsorption capacity of the GS-PPy for Cr(VI) was 429.2 mg g^-1 at 298 K at pH 2, which was much higher than PPy nanoparticles and other related materials. The adsorption data fitted to the pseudo-second-order model and Langmuir isotherm model. The removal mechanism involved in electrostatic attraction, ion exchange and reduction process that partial adsorbed Cr(VI) was reduced to Cr(III). And Cr(III) was still retained on the surface of GS-PPy. The GS-PPy nanocomposite will be a potential candidate for the removal of Cr(VI) from the industrial waste water.

Efficient removal of hexavalent chromium from water by an adsorption–reduction mechanism with sandwiched nanocomposites

Hexavalent chromium Cr(vi), one of the most toxic contaminants, is released in the environment due to various anthropogenic activities. This study presents a novel sandwiched nanocomposite synthesized using graphene oxide (GO), manganese dioxide (MnO₂) nanowires, iron oxide (Fe₃O₄) nanoparticles and polypyrrole (PPy) to remove hexavalent chromium ion Cr(vi) from water by an adsorption–reduction mechanism. In the sandwiched nanocomposites, GO provided enough surface area, functional groups, and hydrophilic surface for efficient absorption. Fe₃O₄ nanoparticles with excellent magnetic properties make it easy to separate and recover from water. Under acidic conditions, MnO₂ nanowires act as both template and oxidant to initiate the polymerization of pyrrole monomers on its freshly activated surface to obtain GO/MnO₂/Fe₃O₄/PPy (designated as GMFP) nanocomposite. GMFP could effectively adsorb Cr(vi) through electrostatic attraction, and the adsorbed Cr(vi) ions were partly reduced to trivalent chromium Cr(iii) (62%), resulting in the efficient adsorption and high removal of Cr(vi) from water. Hexavalent chromium adsorption by GMFP is strongly pH dependent and the adsorption kinetics followed the pseudo-second-order model. The Langmuir isothermal model described the adsorption isotherm data well and the maximum adsorption capacity was up to 374.53 mg g⁻¹ at pH 2.0. These experimental results suggested that GMFP had great potential as an economic and efficient adsorbent of hexavalent chromium from wastewater, which has huge application potential.

A sandwiched nanocomposite has been developed to remove hexavalent chromium ion Cr(vi) from water by an adsorption–reduction mechanism.

Polymer-based nanocomposites for heavy metal ions removal from aqueous solution: a review

A review of versatile polymer-based composites containing different functional organic and/or inorganic counterparts for the removal of hazardous metal ions from wastewater solutions.

Facile fabrication of PS/Fe3O4@PANi nanocomposite particles and their application for the effective removal of Cu2+

Herein we reported a facile approach to fabricating polystyrene/Fe₃O₄@polyaniline nanocomposite particles with high adsorption capacity and good recyclability for Cu²⁺.

Synthesis of polypyrrole–polystyrene composite microspheres via pseudo-multicomponent heterophase polymerization and the potential application on Cr(vi) removal

Polypyrrole–polystyrene (PPy–PS) composite hollow microspheres with a dry-plum-like morphology were prepared via pseudo-multicomponent heterophase polymerization in an aqueous dispersion system.

Enhanced selective photocatalytic properties of a novel magnetic retrievable imprinted ZnFe2O4/PPy composite with specific recognition ability

The process of the selective photocatalytic degradation of different organic contaminants over imprinted ZnFe₂O₄/PPy composite.

The removal of heavy metal ions from wastewater/aqueous solution using polypyrrole-based adsorbents: a review

Water pollution caused by heavy metal ions is becoming a serious threat to human and aquatic lives day by day.

Microstructured macroporous adsorbent composed of polypyrrole modified natural corncob-core sponge for Cr(vi) removal

A high-performance, cost-effective and spongy adsorbent is rationally designed for Cr(vi) removal based on polypyrrole modified corncob-core natural microsheets.

Sulfuric acid doped poly diaminopyridine/graphene composite to remove high concentration of toxic Cr(VI)

Sulfuric acid doped diaminopyridine polymers are synthesized in situ on graphene oxide surface via mutual oxidation-reduction technique. Exploiting large and highly porous surface, we have used this polymer composite as an adsorbent to remove high concentration of toxic Cr(VI) from water. It shows very high adsorption capacity (609.76 mg g(-1)) during removal process. The composite takes only 100 min to remove high concentration of 500 mg L(-1) Cr(VI) from water. Interesting features for this material is the enhancement of removal efficiency at lower acidic condition due to the formation of acid doped emeraldine salt during polymerization. XPS and AAS measurements reveal that our prepared material mainly follows reduction mechanism at higher acidic condition while anions exchange mechanism at lower acidic condition during the removal experiments. Good recycling ability with ∼ 92% removal efficiency after fifth cycle is also noticed for this material. Easy preparation, superior stability in acidic condition, remarkable removal efficiency and excellent recycling ability make this polymer composite an efficient material for modern filtration units in waste water purification.

Graphene oxide coated coordination polymer nanobelt composite material: a new type of visible light active and highly efficient photocatalyst for Cr(vi) reduction

GO/CPNB was fabricated successfully, which displays excellent photocatalytic activity in visible light. Furthermore, the influence of GO on photocatalytic activity is discussed.

Synthesis of pure nickel(iii) oxide nanoparticles at room temperature for Cr(vi) ion removal

Ni₂O₃ nanoparticles of various sizes (25.8 to 49.7 nm), obtained by a facile oxidation process using Ni(NO₃)₂·6H₂O and alkaline NaOCl as precursor at various temperatures (0, 25, 50 and 70 °C), are found to remove toxic Cr(vi) from aqueous solution.

Fabrication of well-defined electromagnetic Fe3O4/polyaniline hollow microspheres and their application in Pb2+ uptake

Magnetic polyaniline hollow spheres with the functionality of lead uptake were fabricated by using citric acid to decorate ferroferric oxide.

Applications of conjugated polymer based composites in wastewater purification

This review describes the application of conjugated polymer (polyaniline, polypyrrole, and polythiophene) based composites in wastewater purification.

Polymeric sorbents for removal of Cr(VI) from environmental samples

Chromium (Cr) is an important raw material in some chemical industries including paint, pigments, textiles, leather tanning, steel fabrication, electroplating, cement preservation, and canning industries. Once in the environment, Cr exists in various oxidation states depending on pH and concentration. Trivalent [Cr(III)] and hexavalent [Cr(VI)] forms are the most common with Cr(VI) being the most toxic to biota. The review discusses various types of polymeric sorbents that have been prepared for the extraction of Cr(VI) from environmental samples, mostly aqueous samples. Sorbents are categorized into biosorbents, hybrid sorbents, synthetic polymeric, and modified natural polymeric sorbents. Most of the emphasis will be on the advantages and disadvantages of different synthetic polymeric sorbents. Important parameters that define the performance of the sorbents, that is, binding capacity, equilibration time, optimum sample pH, and selectivity, are compared.

Polyacrylonitrile/polypyrrole core/shell nanofiber mat for the removal of hexavalent chromium from aqueous solution

Polyacrylonitrile/polypyrrole (PAN/PPy) core-shell structure nanofibers were prepared via electrospinning followed by in situ polymerization of pyrrole monomer for the removal of hexavalent chromium (Cr(VI)) from aqueous solution. Attenuated total reflections Fourier transform infrared (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS) results confirmed the presence of the polypyrrole (PPy) layer on the surface of PAN nanofibers. The morphology and structure of the core-shell PAN/PPy nanofibers were studied by scanning electron microscopy (SEM) and transmission electron microscope (TEM), and the core-shell structure can be clearly proved from the SEM and TEM images. Adsorption results indicated that the adsorption capacity increased with the initial solution pH decreased. The adsorption equilibrium reached within 30 and 90 min as the initial solution concentration increased from 100 to 200mg/L, and the process can be described using the pseudo-second-order model. Isotherm data fitted well to the Langmuir isotherm model. Thermodynamic study revealed that the adsorption process is endothermic and spontaneous in nature. Desorption results showed that the adsorption capacity can remain up to 80% after 5 times usage. The adsorption mechanism was also studied by XPS.