Jian Kang

Nitrogen-doped graphene for generation and evolution of reactive radicals by metal-free catalysis.

N-Doped graphene (NG) nanomaterials were synthesized by directly annealing graphene oxide (GO) with a novel nitrogen precursor of melamine. A high N-doping level, 8-11 at. %, was achieved at a moderate temperature. The sample of NG-700, obtained at a calcination temperature of 700 °C, showed the highest efficiency in degradation of phenol solutions by metal-free catalytic activation of peroxymonosulfate (PMS). The catalytic activity of the N-doped rGO (NG-700) was about 80 times higher than that of undoped rGO in phenol degradation. Moreover, the activity of NG-700 was 18.5 times higher than that of the most popular metal-based catalyst of nanocrystalline Co3O4 in PMS activation. Theoretical calculations using spin-unrestricted density functional theory (DFT) were carried out to probe the active sites for PMS activation on N-doped graphene. In addition, experimental detection of generated radicals using electron paramagnetic resonance (EPR) and competitive radical reactions was performed to reveal the PMS activation processes and pathways of phenol degradation on nanocarbons. It was observed that both (•)OH and SO4(•-) existed in the oxidation processes and played critical roles for phenol oxidation.

Nitrogen-doped bamboo-like carbon nanotubes with Ni encapsulation for persulfate activation to remove emerging contaminants with excellent catalytic stability

Abstract Nitrogen-doped bamboo-like carbon nanotubes encapsulated with nickel nanoparticles (Ni@NCNTs) were feasibly fabricated by a one-pot pyrolysis route. The characterization techniques revealed the surface morphology, structure and chemical composition of the as-prepared catalysts synthesized in different conditions. Ni@NCNTs were employed as both adsorbents and catalysts for activating persulfate to remove an emerging pollutant, antibiotic sulfachloropyridazine. The nitrogen modification enhanced both adsorption capacity and catalytic ability of Ni@NCNTs and proved to be a promising alternative to metal oxides and other carbon catalysts. Moreover, Ni@NCNTs showed an excellent stability because of nitrogen heteroatom doping and Ni nanoparticle encapsulation. Electron paramagnetic resonance (EPR) and classical radical quenching tests discovered a simultaneous radical/non-radical mechanism in Ni@NCNTs/persulfate system. The results indicated that the novel nano-architectured catalyst materials can show emerging functionalities for environmental remediation processes.

Ferric carbide nanocrystals encapsulated in nitrogen-doped carbon nanotubes as an outstanding environmental catalyst

Nitrogen-doped carbon nanotubes encapsulating iron carbide (Fe3C) nanocrystals (Fe3C@NCNT) were fabricated by a simple and direct pyrolysis method using melamine and ferric chloride as the C, N and Fe precursors. The surface morphology, structure and composition of the Fe3C@NCNT materials were thoroughly investigated. The nanomaterials were employed as novel catalysts for peroxymonosulfate (PMS) activation; outstanding efficiency, high stability and excellent reusability were observed in the catalytic oxidation of organics. The encapsulated Fe3C nanoparticles played a key role in the emerging synergetic effects of the carbide and the protective graphitic layers. In addition, the quaternary N and trace amounts of iron on the CNT surface acted as the active sites. Various quenching experiments were carried out to elucidate the catalytic mechanism of Fe3C@NCNT. It was found that singlet oxygen, superoxide, sulfate and hydroxyl radicals worked together to degrade phenol solutions. Due to their simple synthesis method, low-cost precursors, unique structure and excellent catalytic activity and stability, these novel iron-carbide-based composites have great potential as new strategic materials for environmental catalysis.

Efficient removal of organic and bacterial pollutants by Ag-La 0.8 Ca 0.2 Fe 0.94 O 3-δ perovskite via catalytic peroxymonosulfate activation

Removal of toxic organics and bacterial disinfection are important tasks in wastewater treatment. Most heavy metal-based catalysts for degradation of aqueous organic pollutants in heterogeneous Fenton-like processes suffer from the toxicity of leached metals. The present work reports environmentally benign systems for both degradation of organics and bacterial disinfection. Calcium substituted LaFeO3-δ perovskite was demonstrated as an efficient catalyst to activate peroxymonosulfate (PMS) for degradation of phenol, methylene blue and rhodamine 6 G. Compared to LaFeO3-δ and nanocrystal Fe3O4, the lattice oxygen vacancies in B-site cation-deficient perovskite of La0.8Ca0.2Fe0.94O3-δ (LaCaFeO3-δ) particles renders this material a greatly improved catalytic performance. Electron paramagnetic resonance (EPR) suggested that both sulfate (SO4-) and hydroxyl radicals (OH) played critical roles in the advanced oxidation processes. Moreover, silver doped perovskite (Ag-LaCaFeO3-δ)/PMS successfully inhibited the growth of waterborne pathogen Escherichia coli and Methicillin-resistant Staphylococcus aureus (MRSA) at a lower dose than silver ions, proving a synergetic effect between free radicals and Ag+ in killing the bacteria. Therefore, Ag-LaCaFeO3-δ/PMS would be promising for practical wastewater treatment.

Pt-Free microengines at extremely low peroxide levels

Herein, we demonstrate that iron oxide modified MnO2 (FeOx-MnO2) catalyzed micromotors can be fabricated via electrochemical co-reduction and exhibit exceptional high performance at an extremely low hydrogen peroxide (H2O2) fuel concentration. We observed that graphene/FeOx-MnO2 microtubes could show motion behaviors at fuel concentration as low as 0.03% H2O2, which is nearly one order of magnitude lower than Pt-based micromotors (normally at above 0.2% H2O2). Moreover, the micromotors exhibit higher speeds than any other reported catalytic micro/nanomotors (MNMs) at low peroxide levels. The FeOx-MnO2 systems are better catalytic MNMs, due to their excellent catalytic activity, easy fabrication, robust structure and movement, as well as low-cost, biocompatible and abundance nature, showing great potential for future applications.

High-speed graphene@Ag-MnO2 micromotors at low peroxide levels

Platinum (Pt) free micro/nanomotors (MNMs) using a low content of fuels are highly desired for many applications. Herein, we demonstrate that cathodic electrofabrication can produce modified MnO2 based microtubes and microrods as highly efficient MNMs in hydrogen peroxide (H2O2) as low as 0.2%. The speed of graphene/Ag-MnO2 micromotors could be smartly regulated using a surfactant and the maximum speed of an individual micromotor exceeds 1.3 mm s-1 in 0.5% H2O2. The propelling force and output power of the micromotors are 3.4 and 10 times as high as those of the best Pt-based micromotors reported. These Ag-MnO2 based micromotors are envisioned to be a great promise for practical applications from biomedical delivery to environmental decontamination.