Jiangtao Feng

Influence of metal oxides on the adsorption characteristics of PPy/metal oxides for Methylene Blue.

In this paper, the pure PPy and PPy/metal oxide composites including PPy/SiO2, PPy/Al2O3, and PPy/Fe3O4 as well as PPy coated commercial SiO2 and Al2O3 (PPy/SiO2(C) and PPy/Al2O3(C)) were successfully synthetized via chemical oxidative polymerization in acid aqueous medium to investigate the influence of metal oxides on adsorption capacity and their adsorption characteristics for Methylene Blue (MB). The composites were characterized by Zeta potential analysis, BET analysis, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA) and scanning electron microscope (SEM). The results indicate that the metal oxides have great impact on textural properties, morphology, Zeta potential and PPy polymerization on their surface, further influence the adsorption capacity of their composites. The PPy/Al2O3(C) composite owns the highest specific surface area, rougher surface and most PPy content, and show the highest monolayer adsorption capacity reaching 134.77mg/g. In the adsorption characteristic studies, isotherm investigation shows an affinity order of PPy/metal oxides of PPy/Al2O3(C)>PPy/Al2O3>PPy/SiO2(C)>PPy/SiO2>PPy/Fe3O4>PPy, stating the affinity between PPy and MB was greatly improved by metal oxide, and Al2O3 owns high affinity for MB, followed by SiO2 and Fe3O4. Kinetic data of the composites selected (PPy/SiO2(C), PPy/Al2O3(C) and PPy/Fe3O4) were described more appropriately by the pseudo-second-order model, and the order of K2 is PPy/Al2O3>PPy/SiO2>PPy/Fe3O4, further showing a fast adsorption and good affinity of PPy/Al2O3(C) for MB. The regeneration method by HCl-elution and NaOH-activation was available, and the composites selected still owned good adsorption and desorption efficiency after six adsorption-desorption cycles.

Adsorbent synthesis of polypyrrole/TiO2 for effective fluoride removal from aqueous solution for drinking water purification: Adsorbent characterization and adsorption mechanism

More than 20 countries are still suffering problems of excessive fluoride containing water, and greater than 8mg/L fluoride groundwater has been reported in some villages in China. In order to meet the challenge in the drinking water defluoridation engineering, a high efficiency and affinity defluoridation adsorbent PPy/TiO2 composite was designed and synthetized by in-situ chemical oxidative polymerization. Fourier Transform Infrared Spectroscopy (FTIR), X-ray diffraction Investigator (XRD), X-ray photoelectron spectroscopy (XPS), Thermogravimetric analysis (TG), N2 isotherm analysis, Scanning Electron Microscopy (SEM) and Zeta potential analysis were conducted to characterize surface and textural properties of the as-prepared PPy/TiO2, and the possibility of fluoride adsorption was carefully estimated by adsorption isotherm and kinetic studies. Characterization investigations demonstrate the uniqueness of surface and textural properties, such as suitable specific surface area and abundant positively charged nitrogen atoms (N+), which indicate the composite is a suitable material for the fluoride adsorption. Adsorption isotherms and kinetics follow better with Langmuir and pseudo-second-order model, respectively. The maximum adsorption capacity reaches 33.178mg/g at 25°C according to Langmuir model, and particular interest was the ability to reduce the concentration of fluoride from 11.678mg/L to 1.5mg/L for drinking water at pH of 7 within 30min. Moreover, the adsorbent can be easily recycled without the loss of adsorption capacity after six cycles, greatly highlighting its outstanding affinity to fluoride, low-cost and novel to be used in the purification of fluoride containing water for drinking. Furthermore, the adsorption mechanism was extensively investigated and discussed by FTIR investigation and batch adsorption studies including effect of pH, surface potential and thermodynamics. The adsorption is confirmed to be a spontaneous and exothermic process with decreasing entropy, which is prominently conducted through electrostatic attraction, and ionic exchange, and chelation may be also involved. Hydroxyls and positively charged nitrogen atoms play important roles in the adsorption.

Synthesis of polyaniline/TiO2 composite with excellent adsorption performance on acid red G

A polyaniline-modified TiO2 (PANI/TiO2) composite was designed and synthesized via the in situ chemical polymerization of aniline monomer in the as-prepared TiO2 solution. The composite was employed as a novel reusable adsorbent based on the unique doping–dedoping properties of polyaniline. Fourier transform infrared (FT-IR) spectra, scanning electron microscopy (SEM) and X-ray diffraction (XRD) were combined to characterize the chemical structure and morphology of PANI/TiO2. The adsorption–desorption characteristics of polyaniline/TiO2 (PANI/TiO2) on Acid Red G (ARG) were further investigated. The prepared adsorbent possessed excellent adsorption and regeneration performances with the adsorption equilibrium time in about 5 min and the maximum adsorption capacity at 454.55 mg g−1. The possible adsorption mechanism was proposed to be associated with the doping–dedoping behaviors of the PANI chain.

Facile synthesis of a polythiophene/TiO2 particle composite in aqueous medium and its adsorption performance for Pb(II)

A polythiophene/TiO2 (PTh/TiO2) particle composite was synthesized by a facile and green method via (NH4)2S2O8-catalyzed oxidative polymerization of thiophene in acidic aqueous medium to adsorb Pb2+ ions from aqueous solution, and the synthesis mechanism was proposed. The particle composite was carefully characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), thermogravimetric (TG) analysis, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and zeta potential analysis, and it showed that the composite prepared had a high specific surface area of 229.66 m2 g−1. Various factors such as adsorbent dosage and solution pH influencing the adsorption were investigated. The isotherm results indicated that the adsorption performance of Pb2+ on the composite fitted the Langmuir model, and the maximum adsorption capacity reached 151.52 mg g−1 at 25 °C, 170.36 mg g−1 at 35 °C and 173.61 mg g−1 at 45 °C. The present adsorption system can be described most favorably by a pseudo-second-order model, confirming that chemisorption such as chelation may be the adsorption rate-limiting step. Meanwhile, adsorption was a spontaneous and endothermic process with increased entropy. In addition, regeneration by HCl-elution and NaOH-activation was possible, and the composite could be used repeatedly without any significant reduction in its adsorption capacity after 6 adsorption–desorption cycles. Furthermore, the adsorption mechanisms were investigated.

Self-assembly of tetra(aniline) nanowires in acidic aqueous media with ultrasonic irradiation

An environmentally friendly method is developed to explore the self-assembly of Ph/NH2-capped tetra(aniline), TANI, nanowires in acidic aqueous media with ultrasonic irradiation. Ultrasonic irradiation is demonstrated to be an effective method to achieve self-assembled thermodynamic equilibrium for nanostructure formation in only 2 minutes. Further assembly, i.e., the formation of thicker TANI nanowires in acidic solution left undisturbed for 96 h without the addition of any organic solvent, is also investigated. The self-assembly behaviour of TANI is studied using FT-IR, Raman, UV-Vis spectroscopy, thermogravimetric analysis, X-ray diffraction, and scanning electron microscopy. Investigations suggest that extra hydrogen bonding associated with the protonation, electrostatic interactions and π–π stacking interaction are important for the self-organization of TANI nanowires. Furthermore, the assembly behaviour of TANI nanowires is dependent on the properties of the dopant, including size and concentration, and reflected in the conductivity of the assembled structures. These results provide insight to understand and tune the self-assembly behaviour of nanostructured oligo(aniline)s in complex dopant-containing systems, and form the basis for further detailed mechanistic studies.

Enhanced adsorption capacity of polypyrrole/TiO2 composite modified by carboxylic acid with hydroxyl group

It was reported in our previous work that polypyrrole/TiO2 (PPy/TiO2) composite exhibited excellent adsorption ability for organic contaminants, and modification of the composite by different acids could greatly impact the adsorption performance. Herein, AC-PPy/TiO2, SU-PPy/TiO2, TA-PPy/TiO2 and CI-PPy/TiO2 composites were prepared in acetate (with only one carboxylic group), succinic (with two carboxylic groups), tartaric (with two hydroxyl and two carboxylic groups) and citric (with one hydroxyl and three carboxylic groups) acids, respectively. Acid Red G (ARG) as the typical anionic dye and Methylene Blue (MB) as the typical cationic dye were employed as the target removals to investigate the adsorption behavior of the as-prepared composites. It was found that the hydroxyl group in the employed carboxylic acids significantly affected the surface physicochemical properties and further the adsorption capacity of PPy/TiO2 composite. TA-PPy/TiO2 and CI-PPy/TiO2 prepared in the carboxylic acids with hydroxyl group displayed enhanced adsorption capacity for either ARG or MB, which was 3–4 times higher than that of AC-PPy/TiO2 and SU-PPy/TiO2 prepared in the carboxylic acids without hydroxyl group. Furthermore, all the composites could rapidly reach adsorption equilibrium within 30 min and could be reused at least 4 times without losing the adsorption capacity. The adsorption kinetic and thermodynamic data proved that the adsorption process of the employed dyes onto the composites mainly depended on the chemisorption.

Electrochemical potential-responsive tetra(aniline) nanocapsules via self-assembly

A simple and effective approach is developed to obtain electroactive TANI nanocapsules via self-assembly. The carboxylic acid doped TANI molecules can self-assemble into nanocapsules through a simple dialysis process. The average diameter of the nanocapsules can be tuned using hydrophilic dopant acids with different alkyl lengths. Furthermore, those electroactive nanocapsules can be disrupted by applying a reducing voltage at −0.1 V.

Enhanced capacitance of rectangular-sectioned polypyrrole microtubes as the electrode material for supercapacitors

Rectangular-sectioned polypyrrole microtubes (R-PPy) were synthesized in aqueous solution with β-cyclodextrin (β-CD)/I2 inclusion compound and FeCl3 by chemical oxidation. Field emission scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD) were used to characterize the formation and molecular structure of R-PPy. From the results of the characterization, Complexes of β-CD/I2–Fe2+ acted as the soft-template during the synthesis process of rectangular-sectioned polypyrrole microtubes. Some I− ions retained in the backbone of the as-prepared PPy served as the counter ions after rinsing. Furthermore, R-PPy demonstrated higher conductivity and better electrochemical properties than PPy particles synthesized by the conventional method (C-PPy). The specific capacitance of R-PPy (322.5 F g−1 at the current of 1 A g−1) is almost twice as large as that of C-PPy. The original specific capacitance of R-PPy can be maintained at around 83.3% whereas it was only about 61.5% for the C-PPy after 2000 charge–discharge cycles. The larger specific capacitance and relatively high cycling stability of R-PPy make it a more attractive candidate for energy storage electrodes than C-PPy.

Application of chemically synthesized polypyrrole with hydro-sponge characteristic as electrode in water desalination†

In this article, the chemical oxidative approach was employed to synthesize bulk sponge-like polypyrrole; p-toluenesulfonate (pTSNa), sodium benzene-sulfonate (BSNa) and sodium nitrate (NaNO3) were chosen, respectively, as doping agents to modify the sponge polypyrrole. The microstructure, specific surface area and electrochemical activity of doped polypyrrole samples were characterized. Through repeated expansion and contraction tests, it was proved that the bulk polypyrrole samples exhibited excellent sponge property. To investigate the potential desalination ability, this type of sponge-characteristic polypyrrole was processed into electrodes, and applied in saline solution to remove sodium ions by the electrochemical approach. The results showed that the sponge polypyrrole performed wonderful desalination effect with above 20 mg Na+ for per gram polypyrrole.

Insight into the Synergistic Effect on Selective Adsorption for Heavy Metal Ions by a Polypyrrole/TiO2 Composite

Polymer/metal oxide composites are promising candidates for the treatment of water pollution. Adsorption selectivity as well as a large adsorption capacity are two key factors for treating wastewater containing multiple ions. Herein, a PPy+/TiO2(O-) composite with a heterojunction structure was first discovered to have novel selectivity toward heavy metal ions. An interesting self-doping nature of TiO2(O-) together with SO42- for PPy+ was reported. This interesting structure contributed to an impressive selective adsorption capability with an ascending order of Zn2+ > Pb2+ ≫ Cu2+ in a ternary ion system, where the adsorption for Cu2+ could be almost suppressed. Through the designed adsorption experiments and characterization techniques including Fourier transform infrared, thermogravimetric analysis, and X-ray photoelectron spectroscopy, a universal synergistic mechanism for PPy+/TiO2(O-) composite was first proposed and confirmed. The doping and dedoping of metal oxide (dopant) from the polymer dictates the adsorption selectivity, where the selectivity is determined by the interaction between TiO2 and heavy metal ions. This work may provide some useful guidelines for designing adsorbents with selectivity toward specific heavy metal ions.