Jianghong Zhao

Nitrogen-Promoted Self-Assembly of N-Doped Carbon Nanotubes and Their Intrinsic Catalysis for Oxygen Reduction in Fuel Cells

Nitrogen atoms were found to exhibit a strong ability to promote the self-assembly of nitrogen-doped carbon nanotubes (NCNTs) from gaseous carbons, without an assistance of metal atoms. On the basis of this discovery, pure metal-free CNTs with a nitrogen-doping level as high as 20 atom % can be directly synthesized using melamine as a C/N precursor. This offers a novel pathway for carbon nanotube synthesis. Furthermore, the metal-free and intact characteristics of the NCNT samples facilitate a clear verification of the intrinsic catalytic ability of NCNTs. The results show that the NCNTs intrinsically display excellent catalytic activity for oxygen reduction in fuel cells, comparable to traditional platinum-based catalysts. More notably, they exhibit outstanding stability, selectivity, and resistance to CO poisoning, much superior to the platinum-based catalysts.

Synthesis of highly nitrogen-doped hollow carbon nanoparticles and their excellent electrocatalytic properties in dye-sensitized solar cells

Hollow carbon nanoparticles that have been highly doped with nitrogen (N-HCNPs) are directly prepared by a facile one-pot method based on the detonation-assisted chemical vapor deposition of dimethylformamide without the use of metal catalysts. The N-HCNPs exhibit uniform core-shell microstructures with inner cavities encapsulated by graphitic walls, possessing a narrow size distribution of 10–25 nm. The nitrogen content in N-HCNPs is as high as 20.8% atom ratio, and the nitrogen bonds display pyridine-, pyrrole-, and graphite-like configurations. Defects and dislocations are present in the graphene layers due to highly incorporated nitrogen, leading to the creation of micropores on the carbon shell and a large BET surface area of 454 m2 g−1. The unique N-HCNPs with interconnected hierarchical porous structures and nitrogen-containing defects show excellent electrocatalytic activity for triiodide reduction in dye-sensitized solar cells, superior to conventional platinum catalysts.

Selective oxidation of sacrificial ethanol over TiO2-based photocatalysts during water splitting

The modulation of TiO2 structure can effectively alter the oxidation kinetics and pathway of sacrificial ethanol during the water-splitting reaction and dramatically adjust the selectivity of the valuable coupling product 2,3-butanediol from 0.0% to 96.6%, showing the possibility of photohydrogen production in green and economical indexes.

Nitrogen-doped hollow carbon nanoparticles as efficient counter electrodes in quantum dot sensitized solar cells

The functions of nitrogen-doped hollow carbon nanoparticles (N-HCNPs) as counter electrodes in quantum dot sensitized solar cells (QDSSCs) have been studied in this paper. Electrochemical impedance spectroscopy (EIS) and Tafel-polarization tests reveal a low charge transfer resistance and a high exchange current density between polysulfide electrolyte and the N-HCNPs electrode. Cyclic voltammetry results indicate that the N-HCNPs electrode shows high electrocatalytic activity and excellent tolerance toward the S 2� /Sn 2� electrolyte. A power conversion efficiency of 2.67% is achieved for the QDSSCs based on N-HCNPs counter electrodes, which is clearly higher than those of the QDSSCs based on HCNPs, carbon nanotubes and Pt counter electrodes. The results reveal that the N-HCNPs electrode is a promising counter electrode candidate for QDSSCs.

Construction of Z-scheme carbon nanodots/WO3 with highly enhanced photocatalytic hydrogen production

Carbon nanodots without any modification can drive photocatalytic hydrogen evolution. More importantly, we found that Z-scheme is an effective strategy to improve the photocatalytic performance of carbon nanodots. The photocatalytic H2-evolution rates improve from 4.65 μmol g−1 h−1 to 1330 μmol g−1 h−1 under xenon lamp irradiation.

Intramolecular hydrogen bonds quench photoluminescence and enhance photocatalytic activity of carbon nanodots.

Understanding the photoluminescence (PL) and photocatalytic properties of carbon nanodots (CNDs) induced by environmental factors such as pH through surface groups is significantly important to rationally tune the emission and photodriven catalysis of CNDs. Through adjusting the pH of an aqueous solution of CNDs, it was found that the PL of CNDs prepared by ultrasonic treatment of glucose is strongly quenched at pH 1 because of the formation of intramolecular hydrogen bonds among the oxygen-containing surface groups. The position of the strongest PL peak and its corresponding excitation wavelength strongly depend on the surface groups. The origins of the blue and green emissions of CNDs are closely related to the carboxyl and hydroxyl groups, respectively. The deprotonated COO(-) and CO(-) groups weaken the PL peak of the CNDs and shift it to the red. CNDs alone exhibit photocatalytic activity towards degradation of Rhodamine B at different pH values under UV irradiation. The photocatalytic activity of the CNDs is the highest at pH 1 because of the strong intramolecular hydrogen bonds formed among the oxygen-containing groups.

Graphene Frameworks Promoted Electron Transport in Quantum Dot-Sensitized Solar Cells

Graphene frameworks (GFs) were incorporated into TiO2 photoanode as electron transport medium to improve the photovoltaic performance of quantum dot-sensitized solar cells (QDSSCs) for their excellent conductivity and isotropic framework structure that could permit rapid charge transport. Intensity modulated photocurrent/photovoltage spectroscopy and electrochemical impedance spectroscopy results show that the electron transport time (τ(d)) of 1.5 wt % GFs/TiO2 electrode is one-fifth of that of the TiO2 electrode, and electron lifetime (τ(n)) and diffusion path length (Ln) are thrice those of the TiO2 electrode. Results also revealed that the GFs/TiO2 electrode has a shorter electron transport time (τ(d)), as well as longer electron lifetime (τ(n)) and diffusion path length (Ln), than conventional 2D graphene sheets/TiO2 electrode, thus indicating that GFs could promote rapid electron transfer in TiO2 photoanodes. Photocurrent-voltage curves demonstrated that when incorporating 1.5 wt % GFs into TiO2 photoanode, a maximum power conversion efficiency of 4.2% for QDSSCs could be achieved. This value was higher than that of TiO2 photoanode and 2D graphene sheets/TiO2 electrode. In addition, the reasons behind the sensitivity of photoelectric conversion efficiency to the graphene concentration in the TiO2 were also systematically investigated. Our results provide a basic understanding of how GFs can efficiently promote electron transport in TiO2-based solar cells.

The manufacture of carbon nanotubes decorated with ZnS to enhance the ZnS photocatalytic activity

Abstract Carbon nanotubes with attached ZnS nanocrystals were prepared by a reaction between Zn(NO 3 ) 2 and Na 2 S in an aqueous suspension of carbon nanotubes. Post-refluxing treatment and the order in which the reactants were introduced played a crucial role in the improvement of the interaction between ZnS nanocrystals and carbon nanotubes. Studies on methylene blue degradation revealed that carbon nanotubes could effectively increase the photocatalytic activity of the ZnS nanocrystals. Close contact between carbon nanotubes and the ZnS improved the interfacial electron transfer and restrained the electron/hole (e−/h+) pair recombination of ZnS.

Pure carbon nanodots for excellent photocatalytic hydrogen generation

Pure carbon nanodots (CNDs) without any modification and co-catalyst can drive photocatalytic hydrogen generation. The hydrogen generation rate of CNDs reaches 3615.3 μmol g−1 h−1 when methanol was used as the sacrificial donor, which is 34.8 times higher than that of commercial Degussa P25 photocatalyst under the same conditions. Moreover, the CNDs show good stability; the hydrogen generation rate has negligible change even after four cycles of testing.

Light-induced synthesis of photoluminescent carbon nanoparticles for Fe3+ sensing and photocatalytic hydrogen evolution

We report a new method to prepare photoluminescent carbon nanoparticles (CNPs) by a light-induced process. The obtained CNPs are sensitive to the specific detection of Fe3+ with a detection limit of 0.55 ppm. CNPs also show excellent photocatalytic hydrogen production under xenon lamp irradiation. The hydrogen evolution rate is up to 4.89 μmol h−1 over 2.1 mg CNPs.