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

Twofold Interpenetrated Cationic Metal-Organic Framework with Hydrophobic Channels for Effectively Trapping Toxic Oxo-Anions

Sequestration of toxic oxo-anions (such as ⁹⁹TcO₄^- and ClO₄^-) from wastewater has received constant attention due to the existing serious threat to public health and the sustainability of the environment. In view of the low energy of hydration of TcO₄^- and ClO₄^-, cationic metal-organic framework (MOF) materials with the hydrophobic microenvironment are preferred in the selection of sorbents. Herein, a twofold interpenetrated cationic MOF (ZJU-X15) with double-helical chains was constructed by tetrakis[4-(pyridin-4-yl)phenyl]ethene (TPPE) and Cd²⁺ for the elimination of ⁹⁹TcO₄^- and ClO₄^-. Profiting from hydrophobic channels, ZJU-X15 could remove most of ReO₄^- (a surrogate for ⁹⁹TcO₄^-) and ClO₄^- in less than 10 and 20 min, respectively. As the result of batch experiments, ZJU-X15 could capture 356 mg of ReO₄^- and 221 mg of ClO₄^- per 1 g of sorbent, showcase decent selectivity, and still maintain high removal efficiency for anions after four recycles. Furthermore, the process of anion-exchange was confirmed by ion chromatography, Fourier-transform infrared spectroscopy, scanning electron microscopy combined with an energy-dispersive X-ray spectrometer, and X-ray photoelectron spectroscopy, indicating that target anions successfully entered into the body of ZJU-X15 through anion exchange.

Treatment of nitrate containing wastewater by adsorption process using polypyrrole-modified plastic-carbon: Characteristic and mechanism

Polypyrrole-modified plastic-carbon (PET-PPy) composite was prepared by using high porosity plastic-carbon materials and a special doping mechanism of polypyrrole to remove nitrate from water to achieve waste recycling. As a result, PET-PPy-500 showed remarkable nitrate adsorption in both acidic and alkaline wastewater. The pseudo-second-order kinetic and Langmuir isotherm models were fit for the nitrate adsorption by PET-PPy-500, and the maximum adsorption capacity predicted by the Langmuir model was 10.04 mg NO₃-N/g (45.18 mg NO₃^-/g) at 30 °C. The ion exchange and electrostatic attraction were the main mechanisms of removing NO₃^- by PET-PPy-500, which was demonstrated by the interface characterization and theoretical calculation. The doped ions (Cl^-) and/or other anions produced by charge transfer interaction were the main exchange ions in the process of NO₃^- adsorption. The main binding sites in the electrostatic adsorption process were nitrogen-containing functional groups, which can be confirmed by the results of XPS and density functional theory (DFT). Furthermore, DFT results also showed that the adsorption of nitrate by PET-PPy was a spontaneous exothermic process, and the adsorption energy at the nitrogen site was the lowest. The findings of this study provide a feasible strategy for the advanced treatment of nitrate containing wastewater.

Selective Removal of Perfluorobutyric Acid Using an Electroactive Ion Exchanger Based on Polypyrrole@Iron Oxide on Carbon Cloth

Perfluorobutyric acid (PFBA) is one type of perfluoroalkyl and polyfluoroalkyl substances (PFASs) and is widely used as an industrial compound. The removal of PFBA has attracted considerable scientific interests in recent decades because it causes environmental pollution and human diseases. Currently, the adsorption method has been used commonly to remove PFASs from wastewater. However, it is usually limited by the inevitable "secondary waste" produced in this treatment process. In this work, PFBA can be effectively removed by synergistic electrical switching ion exchange (ESIX) and a new type of nanostructured ion exchanger. Herein, the nanostructured ion exchanger has been designed and synthesized by coating a polypyrrole (PPy)@Fe₂O₃ nanoneedle on carbon cloth (PPy@Fe₂O₃ NN-CC). Results show that the PPy@Fe₂O₃ NN-CC nanocomposite enhances ion exchange speed and efficiency, which ensures its high adsorption capacity and rapid regeneration property, thereby reducing secondary waste. Moreover, ESIX based on the PPy@Fe₂O₃ NN-CC nanocomposite has high selectivity for adsorption of PFBA over other common anions in water, such as Cl^-, SO₄^2-, and NO₃^-.

Synthesis and Characterization of Hollow-Sphered Poly(N-methyaniline) for Enhanced Electrical Conductivity Based on the Anionic Surfactant Templates and Doping

Poly(N-methylaniline) (PNMA) is a polyaniline derivative with a methyl substituent on the nitrogen atom. PNMA is of interest owing to its higher solubility in organic solvents when compared to the unsubstituted polyaniline. However, the electrical conductivity of polyaniline derivatives suffers from chemical substitution. PNMA was synthesized via emulsion polymerization using three different anionic surfactants, namely sodium dodecylsulfate (SDS), sodium dodecylbenzenesulfonate (SDBS), and dioctyl sodium sulfosuccinate (AOT). The effects of surfactant structures and concentrations on electrical conductivity, doping level, crystallinity, morphology, and thermal stability were investigated. The re-doping step using perchloric acid (HClO₄) as a dopant was sequentially proceeded to enhance electrical conductivity. PNMA synthesized in SDBS at five times its critical micelle concentration (CMC) demonstrated the highest electrical conductivity, doping level, and thermal stability among all surfactants at identical concentrations. Scanning electron microscopy (SEM) images revealed that the PNMA particle shapes and sizes critically depended on the surfactant types and concentrations, and the doping mole ratios in the re-doping step. The highest electrical conductivity of 109.84 ± 20.44 S cm⁻¹ and a doping level of 52.45% were attained at the doping mole ratio of 50:1.

Synthesis of Three-Dimensional Graphene-Based Hybrid Materials for Water Purification: A Review

Graphene-based nanostructures and nanomaterials have been widely used for the applications in materials science, biomedicine, tissue engineering, sensors, energy, catalysis, and environmental science due to their unique physical, chemical, and electronic properties. Compared to two-dimensional (2D) graphene materials, three-dimensional (3D) graphene-based hybrid materials (GBHMs) exhibited higher surface area and special porous structure, making them excellent candidates for practical applications in water purification. In this work, we present recent advances in the synthesis and water remediation applications of 3D GBHMs. More details on the synthesis strategies of GBHMs, the water treatment techniques, and the adsorption/removal of various pollutants from water systems with GBHMs are demonstrated and discussed. It is expected that this work will attract wide interests on the structural design and facile synthesis of novel 3D GBHMs, and promote the advanced applications of 3D GBHMs in energy and environmental fields.

Electrochemical Evaluation of Selenium (IV) Removal from Its Aqueous Solutions by Unmodified and Modified Graphene Oxide

The removal of selenium from superficial and waste water is a worldwide problem. The maximum limit according to the World Health Organization (WHO) for the selenium in the water is set at a concentration of 10 μg/L. Carbon based adsorbents have attracted much attention and recently demonstrated promising performance in removal of selenium. In this work, several materials (iron oxide based microparticles and graphene oxides materials) and their composites were prepared to remove Se(IV) from water. The graphene oxides were prepared according to the simplified Hummer's method. In addition, the effect of pH, contact time and initial Se(IV) concentration was tested. An electrochemical method such as the differential pulse cathodic stripping voltammetry was used to determine the residual selenium concentration. From the experimental data, Langmuir adsorption model was used to calculate the maximum adsorption capacity. Graphene oxide particles modified by iron oxide based microparticles was the most promising material for the removal of Se(IV) from its aqueous solution at pH 2.0. Its adsorption efficiency reached more than 90% for a solution with given Se(IV) concentration, meanwhile its maximal recorded adsorption capacity was 18.69 mg/g.

Electrically Switched Ion Exchange Based on Carbon-Polypyrrole Composite Smart Materials for the Removal of ReO4- from Aqueous Solutions

A simple and rapid process of ReO₄^- (as a surrogate of TcO₄^-) removal from aqueous solutions based on the electrically switched ion exchange (ESIX) method has been demonstrated in this work. Activated carbon-Polypyrrole (AC-PPy) was synthesized from activated carbon and pyrrole by electrodeposition method which was served as an electrically switched ion exchanger for ReO₄^- removal. The characterization results show that the AC-PPy composite exhibited an excellent loading capacity and a high stability for ions uptake and release. Chronoamperometric studies show that the ESIX treatment could be completed within 60 s, demonstrating the rapid uptake and release of ions. Uptake and release of ReO₄^- was verified by electrochemical quartz crystal microbalance with dissipation shift (EQCMD) studies. By modulating the electrochemical potential of the AC-PPy, the uptake and release of ReO₄^- ions can be controlled. Similar trends of uptake and release of ReO₄^- were observed in cyclic voltammetry (-0.4 to 0.8 V) for five cycles with the EQCMD. X-ray photoelectron spectroscopy (XPS) confirmed the process of ReO₄^- removal in the AC-PPy composite. Conclusively, the smart material shows excellent efficiency and selectivity for the removal of ReO₄^- from aqueous solutions.

Synthesis of catalytically active bimetallic nanoparticles within solution-processable metal–organic-framework scaffolds

Bimetallic alloy nanoparticles are synthesized by in situ reduction of mixed metal ions inside CD-MOFs.

Synthesis, characterization and application of polypyrrole-cellulose nanocomposite for efficient Ni(II) removal from aqueous solution: Box-Behnken design optimization

The role of polypyrrole-cellulose (PPy-Ce) nanocomposite for the removal of Ni(II) from aqueous solution was investigated by batch experiments. The PPy-Ce nanocomposite was prepared by chemical oxidate polymerization of pyrrole monomer with cellulose. Transmission electron micrography (TEM) showed the size of the particles varied from 80 to 95 nm. The characteristic C-O, O-H, C-N and C-C vibrations in the Fourier transform infrared (FTIR) spectra indicate that the cellulose successfully integrated with the pyrrole. Influence of experimental variables such as pH, contact time, adsorbent dose and initial Ni(II) concentration were optimized using the response surface methodology (RSM) based Box-Behnken design (BBD). The optimal conditions for maximum removal of Ni(II) were pH 8, time 65 min, adsorbent dose 0.3 mg/l and Ni(II) concentration 50 mg/l. The maximum removal efficiency under optimized conditions was >94%. The results indicate that BBD could be used to optimize experimental conditions for metal removal from aqueous solution.

A green method based on electro-assisted and photo-assisted regeneration for removal of chromium(VI) from aqueous solution

In general, spent adsorbent is regenerated using high-concentration chemicals. Although chemical regeneration is efficient, it often leads to adsorbent damage and secondary waste. To overcome these problems, electro-assisted and photo-assisted regeneration were proposed in this study for the remediation of hexavalent chromium (Cr(VI)). Filter paper was decorated with polyethylene glycol (PEG) and polypyrrole (PPy) to fabricate a FP/PEG/PPy nanocomposite, which could be used as an adsorbent for Cr(VI) with a high adsorption capacity. Moreover, it could be regenerated by electro-assisted or photo-assisted regeneration to reduce eluent use. As a result, secondary waste could be greatly reduced.

Radioactive iodine capture and storage from water using magnetite nanoparticles encapsulated in polypyrrole

The effective capture and storage of radioactive iodine is of importance for nuclear waste storage during nuclear power station accidents. Here we report Fe₃O₄@PPy powder containing ∼12nm magnetite (Fe₃O₄) nanoparticles encapsulated in the polypyrrole (PPy) matrix. It shows 1627mg/g uptake of iodine dissolved in water, within 2h at room temperature. Fe₃O₄@PPy is ferromagnetic in nature and can be separated from water using external magnetic field. The nitrogen gas sweeping test at 30°C shows release of 2% iodine from iodine adsorbed Fe₃O₄@PPy, revealing stable storage of iodine for a moderate period. The iodine-adsorbed magnetic powder can be regenerated by washing with ethanol. The XPS spectrum of iodine adsorbed Fe₃O₄@PPy confirmed the presence of polyiodides (I₃^- and I₅^-) bound to the PPy surface. This excellent iodine capture and storage from iodine contaminated water is an environment friendly, inexpensive and large scale method.

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.

Gas adsorption properties of graphene-based materials

Clean energy sources and global warming are among the major challenges of the 21st century. One of the possible actions toward finding alternative energy sources and reducing global warming are storage of H₂ and CH₄, and capture of CO₂ by using highly efficient and low-cost adsorbents. Graphene and graphene-based materials attracted a great attention around the world because of their potential for a variety applications ranging from electronics, gas sensing, energy storage and CO₂ capture. Large specific surface area of these materials up to ~3000m²/g and versatile modification make them excellent adsorbents for diverse applications. Here, graphene-based adsorbents are reviewed with special emphasis on their adsorption affinity toward CO₂, H₂ and CH₄. This review shows that graphene derivatives obtained mainly via "chemical exfoliation" of graphite and further modification with polymers and/or metal species can be very effective sorbents for CO₂ and other gases and can compete with the currently used carbonaceous or non-carbonaceous adsorbents. The high adsorption capacities of graphene-based materials are mainly determined by their unique nanostructures, high specific surface areas and tailorable surface properties, which make them suitable for storage or capture of various molecules relevant for environmental and energy-related applications.

Polymer-supported CuPd nanoalloy as a synergistic catalyst for electrocatalytic reduction of carbon dioxide to methane

Developing sustainable energy strategies based on CO2 reduction is an increasingly important issue given the world's continued reliance on hydrocarbon fuels and the rise in CO2 concentrations in the atmosphere. An important option is electrochemical or photoelectrochemical CO2 reduction to carbon fuels. We describe here an electrodeposition strategy for preparing highly dispersed, ultrafine metal nanoparticle catalysts on an electroactive polymeric film including nanoalloys of Cu and Pd. Compared with nanoCu catalysts, which are state-of-the-art catalysts for CO2 reduction to hydrocarbons, the bimetallic CuPd nanoalloy catalyst exhibits a greater than twofold enhancement in Faradaic efficiency for CO2 reduction to methane. The origin of the enhancement is suggested to arise from a synergistic reactivity interplay between Pd-H sites and Cu-CO sites during electrochemical CO2 reduction. The polymer substrate also appears to provide a basis for the local concentration of CO2 resulting in the enhancement of catalytic current densities by threefold. The procedure for preparation of the nanoalloy catalyst is straightforward and appears to be generally applicable to the preparation of catalytic electrodes for incorporation into electrolysis devices.

Three dimensional graphene based materials: Synthesis and applications from energy storage and conversion to electrochemical sensor and environmental remediation

With superior electrical/thermal conductivities and mechanical properties, two dimensional (2D) graphene has become one of the most intensively explored carbon allotropes in materials science. To exploit the inherent properties fully, 2D graphene sheets are often fabricated or assembled into functional architectures (e.g. hydrogels, aerogels) with desired three dimensional (3D) interconnected porous microstructures. The 3D graphene based materials show many excellent characteristics including increased active material per projected area, accessible mass transport or storage, electro/thermo conductivity, chemical/electrochemical stability and flexibility. It has paved the way for practical requirements in electronics, adsorption as well as catalysis related system. This review shows an extensive overview of the main principles and the recent synthetic technologies about fabricating various innovative 3D graphene based materials. Subsequently, recent progresses in electrochemical energy devices (lithium/lithium ion batteries, supercapacitors, fuel cells and solar cells) and hydrogen energy generation/storage are explicitly discussed. The up to date advances for pollutants detection and environmental remediation are also reviewed. Finally, challenges and outlooks in materials development for energy and environment are suggested.

Environmental applications of three-dimensional graphene-based macrostructures: adsorption, transformation, and detection

Just as graphene triggered a new gold rush, three-dimensional graphene-based macrostructures (3D GBM) have been recognized as one of the most promising strategies for bottom-up nanotechnology and become one of the most active research fields during the last four years. In general, the basic structural features of 3D GBM, including its large surface area, which enhances the opportunity to contact pollutants, and its well-defined porous structure, which facilitates the diffusion of pollutant molecules into the 3D structure, enable 3D GBM to be an ideal material for pollutant management due to its excellent capabilities and easy recyclability. This review aims to describe the environmental applications and mechanisms of 3D GBM and provide perspective. Thus, the excellent performance of 3D GBM in environmental pollutant adsorption, transformation and detection are reviewed. Based on the structures and properties of 3D GBM, the removal mechanisms for dyes, oils, organic solvents, heavy metals, and gas pollutants are highlighted. We attempt to establish "structure-property-application" relationships for environmental pollution management using 3D GBM. Approaches involving tunable synthesis and decoration to regulate the micro-, meso-, and macro-structure and the active sites are also reviewed. The high selectivity, fast rate, convenient management, device applications and recycling utilization of 3D GBM are also emphasized.

Environmental applications of graphene-based nanomaterials

A critical assessment of recent developments in environmental applications of graphene and graphene-based materials.

Graphene nanosheets as novel adsorbents in adsorption, preconcentration and removal of gases, organic compounds and metal ions

Due to their high adsorption capacities, carbon-based nanomaterials such as carbon nanotubes, activated carbons, fullerene and graphene are widely used as the currently most promising functional materials. Since its discovery in 2004, graphene has exhibited great potential in many technological fields, such as energy storage materials, supercapacitors, resonators, quantum dots, solar cells, electronics, and sensors. The large theoretical specific surface area of graphene nanosheets (2630 m(2)·g(-1)) makes them excellent candidates for adsorption technologies. Further, graphene nanosheets could be used as substrates for decorating the surfaces of nanoparticles, and the corresponding nanocomposites could be applied as novel adsorbents for the removal of low concentrated contaminants from aqueous solutions. Therefore, graphene nanosheets will challenge the current existing adsorbents, including other types of carbon-based nanomaterials.

Facile preparation of ion-imprinted composite film for selective electrochemical removal of nickel(II) ions

A facile unipolar pulse electropolymerization (UPEP) technique is successfully applied for the preparation of ion-imprinted composite film composed of ferricyanide-embedded conductive polypyrrole (FCN/PPy) for the selective electrochemical removal of heavy metal ions from wastewater. The imprinted heavy metal ions are found to be easily removed in situ from the growing film only by tactfully applying potential oscillation due to the unstable coordination of FCN to the imprinted ions. The obtained Ni(2+) ion-imprinted FCN/PPy composite film shows fast uptake/release ability for the removal of Ni(2+) ions from aqueous solution, and the adsorption equilibrium time is less than 50 s. The ion exchange capacity reaches 1.298 mmol g(-1) and retains 93.5% of its initial value even after 1000 uptake/release cycles. Separation factors of 6.3, 5.6, and 6.2 for Ni(2+)/Ca(2+), Ni(2+)/K(+), and Ni(2+)/Na(+), respectively, are obtained. These characteristics are attributed to the high identification capability of the ion-imprinted composite film for the target ions and the dual driving forces resulting from both PPy and FCN during the redox process. It is expected that the present method can be used for simple preparation of other ion-imprinted composite films for the separation and recovery of target heavy metal ions as well.

An intelligent displacement pumping film system: a new concept for enhancing heavy metal ion removal efficiency from liquid waste

A concept of electrochemically switched ion exchange (ESIX) hybrid film system with piston-like proton pumping effect for the removal of heavy metal ions was proposed. Based on this concept, a novel ESIX hybrid film composed of layered alpha zirconium phosphate (α-Zr(HPO4)2; α-ZrP) nanosheets intercalated with a potential-responsive conducting polyaniline (PANI) was developed for the removal of Ni(2+) ions from wastewater. It is expected that the space between α-ZrP nanosheets acts as the reservoir for the functional ions while the intercalated PANI works as the potential-sensitive function element for piston-like proton pumping in such ESIX hybrid films. The prepared ESIX hybrid film showed an excellent property of rapid removal of Ni(2+) ions from wastewater with a high selectivity. The used film was simply regenerated by only altering the applied potential. The ion pumping effect for the ESIX of Ni(2+) ions using this kind of film was proved via XPS analysis. The proposed ESIX hybrid film should have high potential for the removal of Ni(2+) ions and/or other heavy metal ions from wastewater in various industrial processes.

Fabrication of polypyrrole/graphene oxide composite nanosheets and their applications for Cr(VI) removal in aqueous solution

In this paper, we report on the simple, reliable synthesis of polypyrrole (PPy)/graphene oxide (GO) composite nanosheets by using sacrificial-template polymerization method. Herein, MnO₂ nanoslices were chosen as a sacrificial-template to deposit PPy, which served as the oxidant as well. During the polymerization of pyrrole on surface of GO nanosheets, MnO₂ component was consumed incessantly. As a result, the PPy growing on the surface of GO nanosheets has the morphology just like the MnO₂ nanoslices. This method can provide the fabrication of PPy nanostructures more easily than conventional route due to its independence of removing template, which usually is a complex and tedious experimental process. The as-prepared PPy/GO composite nanosheets exhibited an enhanced properties for Cr(VI) ions removal in aqueous solution based on the synergy effect. The adsorption capacity of the PPy/GO composite nanosheets is about two times as large as that of conventional PPy nanoparticles. We believe that our findings can open a new and effective avenue to improve the adsorption performance in removing heavy metal ions from waste water.