Role of polyaniline in accomplishing a sustainable environment: recent trends in polyaniline for eradicating hazardous pollutants

Attaining a sustainable environment has become a prime area of research interest, as it is an utmost necessity for a healthy life. Hence, ample studies have been carried out in adopting different processes and utilizing various materials to attain the goal. Herein, we present an exclusive discussion on one such material, i.e., polyaniline (PANI) and its derivatives. Being an intrinsic conducting type, it has grabbed more attention due to its durability in different doped/un-doped states, promptness in structural alteration, and solution processability. This review presents an exhaustive discussion on published reports showing utilization of PANI and its derivative in various forms like pure and composites, for cleaning the environment through adsorption, photodegradation, etc., and the various methods adopted in order to achieve an optimum operating condition to obtain the maximum outcome. In addition to these merits and demerits, various technical challenges faced with materials have been also presented. Therefore, it is expected that this piece of work, presenting the exhaustive discussion on PANI and; its derivatives would help to develop a better understanding of this excellent conducting polymer PANI and provide a state of art on the role of this material for attaining sustainable surroundings for the living beings.

Smart Synthesis of Hollow Microporous Organic Capsules with a Polyaniline Modified Shell

In this work, novel hypercrosslinked polymer-based hollow microporous organic capsules with a polyaniline (PANI)-modified shell (PANI@S-HMOCs) are prepared by in-situ polymerization of aniline in the porous structure of the sulfonated hollow microporous organic capsules (S-HMOCs). PANI@S-HMOC1, PANI@S-HMOC2, and PANI@S-HMOC3 are made by adjusting S-HMOCs and aniline weight ratios of 4:1 and 3:1, and 2:1, respectively. The characterizations of PANI@S-HMOCs demonstrate that electrostatic interaction between aniline and sulfonic acid groups plays an important role in encapsulating PANI in the pores of the shell. The content of PANI showed an evident effect on the porosity of PANI@S-HMOCs, and an appropriate polyaniline loading amount may increase the surface area. PANI@S-HMOC1 and PANI@S-HMOC2 have higher BET surface areas (529 and 503 m² g^-1 ) than S-HMOCs (424 m² g^-1 ), but PANI@S-HMOC3 has lower BET surface area (380 m² g^-1 ). Based on the structural and textural features, PANI@S-HMOC2 shows good adsorption performance for Cr(VI) from aqueous media (156 mg g^-1 , pH = 2, and 27 mg g^-1 , pH = 7).

Surface modified polythiophene/Al2O3 and polyaniline/Al2O3 nanocomposites using poly(vinyl alcohol) for the removal of heavy metal ions from water: kinetics, thermodynamic and isotherm studies

In this study, polythiophene/Al₂O₃ (PTh/Al₂O₃) and polyaniline/Al₂O₃ (PAn/Al₂O₃) nanocomposites in the presence of poly(vinyl alcohol) (PVA) as the surfactant were synthesized via in situ chemical oxidative polymerization method in aqueous medium. The synthesized nanocomposites were characterized by scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD). Results indicated that the Al₂O₃ and poly(vinyl alcohol) influenced the properties of synthesized nanocomposites. The aim of this research was to investigate the sorption characteristics of polythiophene and polyaniline nanocomposites for the removal of heavy metal cations including Pb(II), Zn(II) and Cd(II) from aqueous solution. The factors that affected the adsorption equilibrium as well as the removal efficiency of the nanoadsorbents, i.e., contact time, metal ion concentration, pH and adsorption conditions were investigated in detail. From the kinetic results, it was concluded that the pseudo-second-order kinetic model was found to be the best at describing the adsorption process for Pb(II), Zn(II) and Cd(II) on PTh-PVA/Al₂O₃ and PAn-PVA/Al₂O₃. In addition, thermodynamic analysis suggests the endothermic and spontaneous nature of the present adsorption process with increased entropy on PTh-PVA/Al₂O₃ and PAn-PVA/Al₂O₃. The results suggest polythiophene, polyaniline and their nanocomposites have great potential to be used as efficient absorbent for the removal of heavy metal ions from water.

Enhanced adsorptive composite foams for copper (II) removal utilising bio-renewable polyisoprene-functionalised carbon derived from coconut shell waste

A bio -renewable polyisoprene obtained from Hevea Brasiliensis was used to produce functionalised carbon composite foam as an adsorbent for heavy metal ions. Functionalised carbon materials (C-SO₃H, C-COOH, or C-NH₂) derived from coconut shell waste were prepared via a hydrothermal treatment. Scanning electron microscopy images showed that the functionalised carbon particles had spherical shapes with rough surfaces. X-ray photoelectron spectroscopy confirmed that the functional groups were successfully functionalised over the carbon surface. The foaming process allowed for the addition of carbon (up to seven parts per hundred of rubber) to the high ammonia natural rubber latex. The composite foams had open pore structures with good dispersion of the functionalised carbon. The foam performance on copper ion adsorption has been investigated with regard to their functional group and adsorption conditions. The carbon foams achieved maximum Cu(II) adsorption at 56.5 \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\text{mg g}}_{\text{foam}}^{-1}$$\end{document}mg gfoam-1 for C-SO₃H, 55.7 \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\text{mg g}}_{\text{foam}}^{-1}$$\end{document}mg gfoam-1 for C-COOH, and 41.9 \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\text{mg g}}_{\text{foam}}^{-1}$$\end{document}mg gfoam-1 for C-NH₂, and the adsorption behaviour followed a pseudo-second order kinetics model.

Noble metal-based sorbents: A way to avoid new waste after mercury removal

The development of technologies to control mercury emissions is now a legal requirement imposed by recent international agreements. The use of regenerable sorbents is consistent with this requirement as it allows mercury to be captured from industrial gases without generating new mercury-containing toxic waste. Because regenerable sorbents based on noble metals are often questioned due to the heavy investment they entail, this study assesses the viability of their use in terms of efficiency and cost. Its primary aim is to develop new regenerable sorbents based on an activated carbon support impregnated with Ag in order to compare their cost and behavior in a CO₂ enriched gas stream with that of similar materials containing Au. Mercury retention efficiencies of 100 % can be achieved over several adsorption-desorption cycles depending on the type of noble metal used, particle size and impurities in the gas atmosphere. The results suggest that the Hg-Ag amalgamation process differs from the Hg-Au one, in that they show different kinetics of adsorption and temperatures of desorption. The Ag and Au regenerable sorbents developed in this study would be competitive given the environmental and health benefits they offer compared to the single-use activated carbons employed until now at industrial scale.

Step-Adsorption of Vanadium (V) and Chromium (VI) in the Leaching Solution with Melamine

The vanadium (V) and chromium (VI) was hard to separate directly due to the similar nature. In this paper, separation and recovery of vanadium (V) and chromium (VI) from a leaching solution was investigated by adsorption of vanadium (V) with melamine, followed by electro-reduction of chromium (VI) and adsorption of chromium (III) with melamine, respectively. The effects of experimental parameters including dosage of melamine, reaction temperature and reaction time on the adsorption process were investigated. The results showed that melamine was a good sorbent for adsorption of vanadium (V) and chromium (III). 99.89% of vanadium (V) was adsorbed by melamine at the optimal conditions, the adsorption kinetic was followed the pseudo-second-order model and the adsorption isotherm conformed to the Langmuir model. While the adsorption of chromium (III) was followed the pseudo-first-order model and the adsorption isotherm was conformed to the Freundlich model as the adsorption efficiency was 98.63% under optimal conditions.

Macroscopic Poly Schiff Base-Coated Bacteria Cellulose with High Adsorption Performance

Here, a nanofiber-exfoliated bacteria cellulose aerogel with improved water affinity and high mass transfer was synthesized. Consequently, poly Schiff base can be uniformly coated within the body of bacteria cellulose aerogel without the traditional dispersion treatment. The composite aerogel has adequate mechanical and thermal stability and high mass transfer efficiency. Such an aerogel can serve as a superior adsorbent for flow through adsorption of pollution. Typically, the adsorption capacity towards Cr(VI), Cu(II), Re(VII), Conga red, and Orange G reaches as high as 321.5, 256.4, 153.8, 333.3, and 370.3 mg g-1, respectively. Moreover, the adsorption by this composite aerogel is very fast, such that, for example, at just 2 s, the adsorption is almost finished with Cr(VI) adsorption. Moreover, the composite aerogel exhibits a good adsorption-desorption capability. This research will hopefully shed light on the preparation of bacteria cellulose-derived macroscopic materials powerful in not only environmental areas, but also other related applications.

Synthesis of core-shell UiO-66-poly(m-phenylenediamine) composites for removal of hexavalent chromium

The present research developed a direct in situ heterogeneous method to synthesize UiO-66-poly(m-phenylenediamine) core-shell nanostructures by inducing assembly of m-phenylenediamine radical on UiO-66 surfaces. The strong interaction between negative charged UiO-66 and positive radical from the oxidation of monomer is the major driving force. The produced UiO-66-poly(m-phenylenediamine) composites exhibited a distinct core-shell morphology with controllable surface features. The UiO-66₁-PmPD_0.5 showed a uniform PmPD shell with a thickness of 40-60 nm and the nanocomposite exhibited a high specific surface area of 319.77 m² g^-1. Moreover, the Cr(VI) adsorption amount of the polymeric shell in the nanocomposites can reach as high as 745 mg g^-1, far beyond the performance of the original PmPD. The adsorption tends to be equilibrium within 300 min. This research opens a hopeful window for facile and large-scale fabrication of core-shell nanostructures with controllable core-shell configuration, exhibiting high prospect in heavy metal removal from water.

Influence of Selective Conditions on Various Composite Sorbents for Enhanced Removal of Copper (II) Ions from Aqueous Environments

Numerous pollutants, including dyes, heavy metals, pesticides, and microorganisms, are found in wastewater and have great consequences when discharged onto natural freshwater sources. Heavy metals are predominantly reported in wastewater. Heavy metals are persistent, non-biodegradable and toxic, transforming from a less toxic form to more toxic forms in environmental media under favourable conditions. Among heavy metals, copper is dominantly found in wastewater effluent. In this review, the effects of high concentration of copper in plants and living tissues of both aquatic animals and humans are identified. The performance of different polymer adsorbents and the established optimum conditions to assess the resultant remediation effect as well as the amount of copper removed are presented. This procedure allows the establishment of a valid conclusion of reduced time and improved Cu (II) ion removal in association with recent nano-polymer adsorbents. Nano-polymer composites are therefore seen as good candidates for remediation of Cu ions while pH range 5-6 and room temperature were mostly reported for optimum performance. The optimum conditions reported can be applied for other metal remediation and development of potent novel adsorbents and process conditions.

Recyclable functionalized polymer films for the efficient removal of hexavalent chromium from aqueous solutions

In this study, polyethylenimine-functionalized poly(vinyl alcohol) (PEI-PVA) films were prepared for the first time to remove aqueous Cr(vi). The results indicate that our PEI-PVA films have an excellent potential for Cr(vi) removal and their maximum removal capacity was 396.83 mg g-1. The optimized pH value was 2, the adsorption of Cr(vi) was fitted to the Langmuir model, and the kinetics of uptake could be described well by a pseudo-second-order rate model. Taking into account the simplified separation method of adsorbents and solutions, we used a PVA film as a carrier in which PEI-PVA microspheres were filled to obtain a PEI-PVA functionalized film (PPF). The PPF shows a great efficiency in the removal of Cr(vi) ions in solution, which can absorb and reduce the Cr(vi) ion concentration in the solution in 90 min. PPF has excellent selectivity and the removal efficiency of Cr(vi) ions in the presence of co-existing ions is not reduced. It also has good recycling properties; the removal efficiency remains at 77% over four cycles. The removal mechanism of Cr(vi) ions by PEI-PVA microspheres involves the reduction of the adsorbed Cr(vi) ions to Cr(iii) ions, which are less toxic.

Fabrication of Hydrazone-Linked Covalent Organic Frameworks Using Alkyl Amine as Building Block for High Adsorption Capacity of Metal Ions

There are several researches on the preparation and application of hydrazone-linked covalent organic frameworks (COFs), and all of them generally necessitate rigid aromatic amines. Herein, we report a strategy for design and synthesis of COF with flexible alkyl amine as a building block and intramolecular hydrogen bonding as a knot in the network. The proof-of-concept design was demonstrated by exploring 1,3,5-triformylphloroglucinol and oxalyldihydrazide (ODH) as precursors to synthesize a novel COF material (TpODH), in which different organic building units are combined through hydrazone bonds to form two-dimensional porous frameworks. It should be pointed that irreversible enol-to-keto tautomerism and intramolecular N-H···O═C hydrogen bonding of TpODH would enhance the crystallinity and chemical stability, leading to large specific surface area of 835 m² g^-1. However, another COF synthesized with 1,3,5-triformylbenzene and ODH exhibited less crystallinity and low special surface area (94 m² g^-1). Representatively, the resulting TpODH afforded Cu(II) and Hg(II) capacities of 324 and 1692 mg g^-1, respectively, which exceeded that of most COFs previously reported. Moreover, the Fourier-transform infrared and X-ray photoelectron spectroscopy spectra analyses were taken to demonstrate the adsorption mechanism. These results suggested that the materials could be applied to the removal of metallic ions in the future.

Reusable and removable PmPD/PVA membrane for effective Cr(vi) adsorption and reduction

The PmPD/PVA membranes with facile reusability for and highly effective removal of Cr(vi).

Nanoadsorbents based on conducting polymer nanocomposites with main focus on polyaniline and its derivatives for removal of heavy metal ions/dyes: A review

Water contamination by toxic heavy metal ions and dyes remains a serious public health problem for humans, so attention on specific methods and technologies to remove heavy metal ions and dyes from wastewaters/aqueous solutions are desired. Numerous adsorbents have been reported for the removal of heavy metal ions/dyes from wastewaters/aqueous solutions. Polyaniline (PANI) and its derivatives, as conducting polymers, are good adsorbents to remove various kinds of heavy metal ions and dyes from wastewaters/aqueous solutions. The nanoadsorbents based on PANI and its derivatives have received much consideration, and are extensively reported in literature. This review focuses on the PANI and its derivatives based on nanoadsorbents for water purification. Various types of these nanoadsorbents used for the removal of heavy metal ions/dyes from wastewaters/aqueous solutions are also briefly compared in this review.

Facile Synthesis, Characterization of Poly-2-mercapto-1,3,4-thiadiazole Nanoparticles for Rapid Removal of Mercury and Silver Ions from Aqueous Solutions

Industrial pollution by heavy metal ions such as Hg2+ and Ag⁺ is a universal problem owing to the toxicity of heavy metals. In this study, a novel nano-adsorbent, i.e., poly-2-mercapto-1,3,4-thiadiazole (PTT), was synthesized and used to selectively adsorb mercury and silver ions from aqueous solutions. PTT nanoparticles were synthesized via chemical oxidative dehydrogenation polymerization under mild conditions. Oxidant species, medium, monomer concentration, oxidant/monomer molar ratio, and polymerization temperature were optimized to obtain optimum yields. The molecular structure and morphology of the nanoparticles were analyzed by ultraviolet-visible (UV-Vis), Fourier transform infrared (FT-IR), matrix-assisted laser desorption/ionization/time-of-flight (MALDI/TOF) mass and X-ray photoelectron (XPS) spectroscopies, wide-angle X-ray diffraction (WAXD), theoretical calculations and transmission electron microscopy (TEM), respectively. It was found that the polymerization of 2-mercapto-1,3,4-thiodiazole occurs through head-to-tail coupling between the S(2) and C(5) positions. The PTT nanoparticles having a peculiar synergic combination of four kinds of active groups, S⁻, ⁻SH, N⁻N, and =N⁻ with a small particle size of 30⁻200 nm exhibit ultrarapid initial adsorption rates of 1500 mg(Hg)·g-1·h-1 and 5364 mg(Ag)·g-1·h-1 and high adsorption capacities of up to 186.9 mg(Hg)·g-1 and 193.1 mg(Ag)·g-1, becoming ultrafast chelate nanosorbents with high adsorption capacities. Kinetic study indicates that the adsorption of Hg2+ and Ag⁺ follows the pseudo-second-order model, suggesting a chemical adsorption as the rate-limiting step during the adsorption process. The Hg2+ and Ag⁺-loaded PTT nanoparticles could be effectively regenerated with 0.1 mol·L-1 EDTA or 1 mol·L-1 HNO₃ without significantly losing their adsorption capacities even after five adsorption⁻desorption cycles. With these impressive properties, PTT nanoparticles are very promising materials in the fields of water-treatment and precious metals recovery.

Highly Flexible and Porous Nanoparticle-Loaded Films for Dye Removal by Graphene Oxide-Fungus Interaction

Highly flexible and porous films with the ability to load various nanoscale adsorbents are of particular importance in the purification field. Herein, we report the sustainable and large-scale fabrication of a porous and flexible hybrid film based on the graphene oxide/hyphae interaction at a relatively low temperature of 130 °C. Under identical conditions, such films cannot be constructed with solely graphene oxide or hyphae. Moreover, through the addition of nanoscale building blocks [e.g., nanoscale poly(m-phenylenediamine) (PmPD) adsorbents] in the interaction process, the nanoparticles can be in situ loaded into the film. According to FTIR and XPS analyses, the film formation mechanisms mainly involve redox and cross-linking reactions between graphene oxide and fungus hyphae. In a proof-of-concept study, a PmPD nanoparticle-loaded hybrid film was used as a superior key component to build a flow-through adsorption device that displayed a promising adsorption performance toward dye pollutants.

Electrospun Poly(acrylic acid)/Silica Hydrogel Nanofibers Scaffold for Highly Efficient Adsorption of Lanthanide Ions and Its Photoluminescence Performance

Combined with the features of electrospun nanofibers and the nature of hydrogel, a novel choreographed poly(acrylic acid)-silica hydrogel nanofibers (PAA-S HNFs) scaffold with excellent rare earth elements (REEs) recovery performance was fabricated by a facile route consisting of colloid-electrospinning of PAA/SiO2 precursor solution, moderate thermal cross-linking of PAA-S nanofiber matrix, and full swelling in water. The resultant PAA-S HNFs with a loose and spongy porous network structure exhibited a remarkable adsorption capacity of lanthanide ions (Ln(3+)) triggered by the penetration of Ln(3+) from the nanofiber surface to interior through the abundant water channels, which took full advantage of the internal adsorption sites of nanofibers. The effects of initial solution pH, concentration, and contact time on adsorption of Ln(3+) have been investigated comprehensively. The maximum equilibrium adsorption capacities for La(3+), Eu(3+), and Tb(3+) were 232.6, 268.8, and 250.0 mg/g, respectively, at pH 6, and the adsorption data were well-fitted to the Langmuir isotherm and pseudo-second-order models. The resultant PAA-S HNFs scaffolds could be regenerated successfully. Furthermore, the proposed adsorption mechanism of Ln(3+) on PAA-S HNFs scaffolds was the formation of bidentate carboxylates between carboxyl groups and Ln(3+) confirmed by FT-IR and XPS analysis. The well-designed PAA-S HNFs scaffold can be used as a promising alternative for effective REEs recovery. Moreover, benefiting from the unique features of Ln(3+), the Ln-PAA-S HNFs simultaneously exhibited versatile advantages including good photoluminescent performance, tunable emission color, and excellent flexibility and processability, which also hold great potential for applications in luminescent patterning, underwater fluorescent devices, sensors, and biomaterials, among others.

Biosorptive uptake of Fe(2+), Cu(2+) and As(5+) by activated biochar derived from Colocasia esculenta: Isotherm, kinetics, thermodynamics, and cost estimation

The adsorptive capability of superheated steam activated biochar (SSAB) produced from Colocasia esculenta was investigated for removal of Cu(2+), Fe(2+) and As(5+) from simulated coal mine wastewater. SSAB was characterized by scanning electron microscopy, Fourier transform infrared spectroscopy and Brunauer-Emmett-Teller analyser. Adsorption isotherm indicated monolayer adsorption which fitted best in Langmuir isotherm model. Thermodynamic study suggested the removal process to be exothermic, feasible and spontaneous in nature. Adsorption of Fe(2+), Cu(2+) and As(5+) on to SSAB was found to be governed by pseudo-second order kinetic model. Efficacy of SSAB in terms of metal desorption, regeneration and reusability for multiple cycles was studied. Regeneration of metal desorbed SSAB with 1 N sodium hydroxide maintained its effectiveness towards multiple metal adsorption cycles. Cost estimation of SSAB production substantiated its cost effectiveness as compared to commercially available activated carbon. Hence, SSAB could be a promising adsorbent for metal ions removal from aqueous solution.

Morphology-dependent enhancement of template-guided tunable polyaniline nanostructures for the removal of Cr(vi)

Three nanostructured polyanilines (PANIs) with different morphologies, including nanofibers, nanotubes and nanosheets, have been successfully synthesized using MnO₂ with tunable morphologies as the reactive templates.

Efficient synthesis of oligofluoranthene nanorods with tunable functionalities

Strongly fluorescence-emitting oligofluoranthene nanorods efficiently synthesized by template-free oligomerization of fluoranthene in nitromethane demonstrate tunable conductivity and porous carbon formability.

Strongly fluorescence-emitting oligofluoranthene (OFA) nanorods are readily synthesized by a direct template-free chemical oxidative oligomerization of fluoranthene in nitromethane containing ferric chloride as an oxidant. The OFAs likely consist of five fluoranthene units containing cyclic pentamers with crystalline order and tunable electrical conductivity across 12 orders of magnitude. The OFA nanorods are heat-resistant materials and efficient precursors for macroporous carbon materials with high carbon yield in argon at 1100 °C. In particular, the optimal ring-like pentamer shows 12.2 times stronger cyan fluorescence-emission than recognized highly fluorescent fluoranthene under the same conditions, which makes the OFAs into ideal strong fluorescent emitters, tunable conductors, and high carbon-yield precursors for the preparation of sensors and carbon materials. These findings demonstrate an advance in the direct synthesis of oligomers from fused-ring aromatic hydrocarbons and provide a potential direction to optimize the synthesis and functionalities of wholly aromatic nanomaterials.

Controlled growth of polyhedral and plate-like Ag nanocrystals on a nanofiber mat as a SERS substrate

We report chemical deposition of silver nanocrystals (AgNCs) of different sizes and morphologies, such as polyhedra and plates, on a polyacrylonitrile (PAN) nanofiber mat. High performance surface-enhanced Raman scattering (SERS) substrates are achieved. The effect of the experimental parameters, such as the temperature, concentration and pH of [Ag(NH3)2]OH aqueous solution, on the morphology evolution and density of AgNCs is systematically investigated. The results suggest that the optimized nanofiber mat exhibits a significant SERS performance with superior stability and reproduction, and the SERS enhancement factor (EF) can reach as high as 10(8) for 4-mercaptobenzoic acid (4-MBA). The optimized nanofiber mat also shows high SERS activity for p-aminothiophenol (4-ATP) over the whole nanofiber mat demonstrating the feasibility for detection of both analytes. The detection limit of 4-MBA and 4-ATP is as low as 10(-9) M and 10(-10) M respectively, making the nanofiber mat a promising candidate for SERS detection of chemical pollutants.