Nitrogen-Doped Reduced Graphene Oxide as a Bifunctional Material for Removing Bisphenols: Synergistic Effect between Adsorption and Catalysis

Nitrogen modified reduced graphene oxide (N-RGO) was prepared by a hydrothermal method. The nitrogen modification enhanced its adsorption and catalysis ability. For an initial bisphenol concentration of 0.385 mmol L^–1, the adsorption capacity of N-RGO was evaluated as 1.56 and 1.43 mmol g^–1 for bisphenol A (BPA) and 1.43 mmol g^–1 for bisphenol F (BPF), respectively, both of which were about 1.75 times that (0.90 and 0.84 mmol g^–1) on N-free RGO. N-RGO could activate persulfate, producing strong oxidizing sulfate radicals. The apparent degradation rate constant of BPA on N-RGO was 0.71 min^–1, being about 700 times that (0.001 min^–1) on N-free RGO. In mixtures of various phenols, the degradation rate constant of each phenol was linearly increased with its adsorption capacity. A simultaneous use of N-RGO and persulfate yielded fast and efficient removal of bisphenols. The use of N-RGO (120 mg L^–1) and persulfate (0.6 mmol L^–1) almost completely removed the added bisphenols (0.385 mmol L^–1) at pH 6.6 within 17 min. A mechanism study indicated that the adsorption enriched the pollutant, and the catalytically generated sulfate radicals rapidly degrade the adsorbed pollutant, accelerating in turn the adsorption of residual pollutant

Correlation between One-Directional Helical Growth of Polyaniline and Its Optical Activity

A theoretical model for nanofiber growth of polyaniline (PANI) is proposed in consideration of the classical nucleation/growth theory and the structure of electric double layers, and then the correlation between the fibrillar growth of PANI and its optical activity is investigated in the present work. The formation of initial PANI nanofibers is accompanied by formation of electric double layers around the nanofibers due to the positive charges induced by the protonation and/or partial oxidation of PANI chains. The formed electric double layers may protect the initial nanofibers from heterogeneous nucleation but allow their elongation at their two ends. In the presence of optically active camphor sulfonic acid ((+)-CSA), the initial nanoseeds can elongate helically, resulting in highly optically active PANI. PANI products have been prepared under different conditions, followed by the measurements of their circular dichroism spectra. Being consistent with theoretical prediction, the experimental results have confirmed that the conditions favoring the formation of nanofibers would also yield a higher optical activity. Consequently, PANI nanofibers with high chirality are easily prepared under conditions of low aniline concentrations, at higher CSA concentrations, at room temperature, without stirring, and with UV light illumination

Enhanced Photocatalytic Degradation and Selective Removal of Nitrophenols by Using Surface Molecular Imprinted Titania

Poor selectivity of titania (TiO2) photocatalysis is unfavorable to photocatalytic removal of highly toxic low-level organic pollutants in polluted waters in the presence of other less toxic high-level pollutants. A new strategy of increasing this selectivity is the surface modification of TiO2 via coating a thin layer of molecular imprinted polymer (MIP), which provides molecular recognition ability toward the template molecules. By using 2-nitrophenol and 4-nitrophenol as target pollutants, MIP-coated TiO2 photocatalysts were prepared via surface molecular imprinting and were observed to have high activity and selectivity toward the photodegradation of the targets. In the presence of bisphenol A (50 mg L−1) as a nontarget pollutant, the apparent rate constant for the photodegradation of the target 2-nitrophenol and 4-nitrophenol (1.8 mg L−1) over the corresponding MIP-coated TiO2 was 10.73 × 10−3 and 7.06 × 10−3 min−1, being 2.46 and 4.61 times of that (4.36 × 10−3 and 1.53 × 10−3 min−1) over neat TiO2, respectively. The enhanced photocatalytic selectivity was increased when the concentration of the target was decreased and/or when the difference in both the chemical structure and molecule size between the target and nontarget molecules was increased. The increased selectivity was mainly attributed to the special interaction between the target molecules and the footprints polymer via the functional groups (-OH and -NO2)

Synthesis of Organosilanylene−Thienylene Alternating Oligomers Bearing Ether Side Chains. Peculiar Solvatochromic Behavior in Their Fluorescence Spectra

Organosilanylene−thienylene alternating oligomers bearing ether side chains were synthesized, and their optical properties were studied. The oligomers exhibited clear solvatochromic shifts in the fluorescence maxima, probably due to the changes in the oligomer conformations, and the emission maxima moved to longer wavelength as the solvent polarity increased

Ultrarapid and Deep Debromination of Tetrabromodiphenyl Ether over Noble-Metal-Free Cu/TiO₂ Nanocomposites under Mild Conditions

Fast and deep debromination of polybrominated diphenyl ethers (PBDEs) under mild conditions is a challenge in the field of pollution control. A strategy was developed to achieve it by exploiting Cu/TiO2 composites as a noble-metal-free catalyst. Toward the debromination of 2,2′,4,4′-tetrabromodiphenyl ether (BDE47) as a typical PBDE, the use of Cu/TiO2 as a catalyst and hydrazine hydrate (N2H4·H2O) as a reducing agent yielded a degradation removal of 100% and a debromination efficiency of 87.7% in 3 s. A complete debromination of BDE47 at 1500 mg L–1 was possible by successively adding N2H4·H2O. A debromination pathway involving active H atom species was proposed for the catalytic transfer hydrogenation (CTH) of PBDEs according to the identified degradation intermediates. A mechanism was further clarified by density functional theory calculations: electrons are delivered from N2H4·H2O to the metallic Cu atom via a coordination of N in N2H4·H2O with Cu atoms. The electron-trapped Cu atom interacts with adsorbed BDE47 to form a transition complex, and then the debromination of this complex occurs on the surface of Cu nanoparticles due to the hydrogen donation of N2H4·H2O through the CTH process. The new method provides a highly efficient method to remove brominated pollutants

Ligand-Induced Drastic Enhancement of Catalytic Activity of Nano-BiFeO₃ for Oxidative Degradation of Bisphenol A

Effects of chelating agents on the catalytic degradation of bisphenol A (BPA) was studied in the presence of BiFeO3 nanoparticles as a heterogeneous catalyst and H2O2 as a green oxidant. The oxidizing ability of H2O2 in the presence of nano-BiFeO3 alone was not so strong to degrade BPA at neutral pH values, due to the limited catalytic ability of nano-BiFeO3. Once the surface of nano-BiFeO3 was in situ modified by adding proper organic ligands, the BPA degradation was much accelerated in the pH range of 5–9. The enhancing effect of the ligand was observed to have an order of blank –1 EDTA in the H2O2–BiFeO3 system at pH 5.0 and 30 °C increased the BPA removal from 20.4% to 91.2% with reaction time of 120 min. The enhancing effect of the ligand was found to be indifferent of the possible dissolution of iron from nano-BiFeO3, but correlated well with the accelerated •OH formation from the H2O2 decomposition at the BiFeO3 surface, which was confirmed by ESR measurements and density functional theory studies. In general, more addition of EDTA, higher H2O2 concentrations, or higher temperatures were favorable to the BPA degradation. The effect of the EDTA addition on the kinetics of BPA degradation was also clarified

Polyaniline Nanofibers: Their Amphiphilicity and Uses for Pickering Emulsions and On-Demand Emulsion Separation

The wetting property of nanomaterials is of great importance to both fundamental understanding and potential applications. However, the study on the intrinsic wetting property of nanomaterials is interfered by organic capping agents, which are often used to lower the surface energy of nanomaterials and avoid their irreversible agglomeration. In this work, the wetting property of the nanostructured polyaniline that requires no organic capping agents is investigated. Compared to hydrophilic granular particulates, polyaniline nanofibers are amphiphilic and have an excellent capability of creating Pickering emulsions at a wide range of pH. It is suggested that polyaniline nanofibers can be easily wetted by water and oil. Furthermore, the amphiphilic polyaniline nanofibers as building blocks can be used to construct filtration membranes with a small pore size. The wetting layer of the continuous phase of emulsions in the porous nanochannels efficiently prevents the permeation of the dispersed phase, realizing high-efficiency on-demand emulsion separation

Efficient Removal of Organic Pollutants with Magnetic Nanoscaled BiFeO₃ as a Reusable Heterogeneous Fenton-Like Catalyst

BiFeO3 magnetic nanoparticles (BFO MNPs) were prepared with a sol−gel method and characterized as a catalyst. It was found that BFO MNPs effectively catalyzed the decomposition of H2O2 into •OH radicals, being confirmed with electron spin resonance spin-trapping technique and other radical probing techniques. The strong H2O2-activating ability of BFO MNPs showed promising applications in the oxidative degradation of organic pollutants. When BFO MNPs were used as a heterogeneous Fenton-like catalyst to degrade Rhodamine B, the apparent rate constant for the RhB degradation at 25 °C at pH 5.0 in the BFO MNPs-H2O2 system was evaluated to be 2.89 × 10−2 min−1, being about 20 folds of that obtained with Fe3O4 MNPs as the catalyst under similar conditions. Moreover, BFO MNPs were demonstrated to have excellent stability and reusability. The catalytic mechanism of BFO MNPs was also investigated with Monte Carlo simulations and density functional theory calculations

Ring-Opening Reactions of Cyclic Acetals and 1,3-Oxazolidines with Halosilane Equivalents

Reactions of acetal and 1,3-oxazolidine rings were examined using two kinds of iodosilane equivalent reagents, a 1:2 mixture of Me3SiNEt2 and MeI (reagent 1a) and a 1:1 mixture of Et3SiH and MeI containing a catalytic amount of PdCl2 (reagent 1b). In the reactions of alkanone ethylene acetals with reagent 1a, a C−O bond in the acetal ring readily cleaved to give 2-(trimethylsiloxy)ethyl enol ethers. Similarly, the C−O bond of 1,3-oxazolidine rings cleaved to give ring-opened imine or enamine derivatives. The reactions of aromatic ketone ethylene acetals and cyclohexanone trimethylene acetal led to deprotection of the acetal unit to liberate free ketones. With reagent 1b, cycloalkanone ethylene acetal afforded a dimeric product with 2-iodoethyl alkenoate moieties, while aromatic ketone ethylene or trimethylene acetals produced deprotected ketones