Yuhan Li

Enhancing the photocatalytic activity of bulk g-C3N4 by introducing mesoporous structure and hybridizing with graphene

Bulk graphitic carbon nitride (CN) suffers from small surface area and high recombination of charge carriers, which result in low photocatalytic activity. To enhance the activity of g-C3N4, the surface area should be enlarged and charge carrier separation should be promoted. In this work, a combined strategy was employed to dramatically enhance the activity of bulk g-C3N4 by simultaneously introducing mesoporous structure and hybridizing with graphene/graphene oxide. The mesoporous g-C3N4/graphene (MCN-G) and mesoporous g-C3N4/graphene oxide (MCN-GO) nanocomposites with enhanced photocatalytic activity (NO removal ratio of 64.9% and 60.7%) were fabricated via a facile sonochemical method. The visible light-harvesting ability of MCN-G and MCN-GO hybrids was enhanced and the conduction band was negatively shifted when 1.0 wt% graphene/graphene oxide was incorporated into the matrix of MCN. As electronic conductive channels, the G/GO sheets could efficiently facilitate the separation of chare carriers. MCN-G and MCN-GO exhibited drastically enhanced visible light photocatalytic activity toward NO removal. The NO removal ratio increased from 16.8% for CN to 64.9% for MCN-G and 60.7% for MCN-GO. This enhanced photocatalytic activity could be attributed to the increased surface area and pore volume, improved visible light utilization, enhanced reduction power of electrons, and promoted separation of charge carriers. This work demonstrates that a combined strategy is extremely effective for the development of active photocatalysts in environmental and energetic applications.

Enhanced visible-light photo-oxidation of nitric oxide using bismuth-coupled graphitic carbon nitride composite heterostructures

Abstract Pure bismuth (Bi) metal-modified graphitic carbon nitride (g-C3N4) composites (Bi-CN) with a pomegranate-like structure were prepared by an in situ method. The Bi-CN composites were used as photocatalysts for the oxidation of nitric oxide (NO) under visible-light irradiation. The inclusion of pure Bi metal in the g-C3N4 layers markedly improved the light absorption of the Bi-CN composites from the ultraviolet to the near-infrared region because of the typical surface plasmon resonance of Bi metal. The separation and transfer of photogenerated charge carriers were greatly accelerated by the presence of built-in Mott–Schottky effects at the interface between Bi metal and g-C3N4. As a result, the Bi-CN composite photocatalysts exhibited considerably enhanced efficiency in the photocatalytic removal of NO compared with that of Bi metal or g-C3N4 alone. The pomegranate-like structure of the Bi-CN composites and an explanation for their improved photocatalytic activity were proposed. This work not only provides a design for highly efficient g-C3N4-based photocatalysts through modification with Bi metal, but also offers new insights into the mechanistic understanding of g-C3N4-based photocatalysis.

Mechanism of NO Photocatalytic Oxidation on g-C3N4 Was Changed by Pd-QDs Modification

Quantum dot (QD) sensitization can increase the light absorption and electronic transmission of photocatalysts. However, limited studies have been conducted on the photocatalytic activity of photocatalysts after modification by noble metal QDs. In this study, we developed a simple method for fabricating Pd-QD-modified g-C3N4. Results showed that the modification of Pd-QDs can improve the NO photocatalytic oxidation activity of g-C3N4. Moreover, Pd-QD modification changed the NO oxidation mechanism from the synergistic action of h+ and O2− to the single action of ·OH. We found that the main reason for the mechanism change was that Pd-QD modification changed the molecular oxygen activation pathway from single-electron reduction to two-electron reduction. This study can not only develop a novel strategy for modifying Pd-QDs on the surface of photocatalysts, but also provides insight into the relationship between Pd-QD modification and the NO photocatalytic oxidation activity of semiconductor photocatalysts.

In-situ transformation of Bi 2 WO 6 to highly photoreactive Bi 2 WO 6 @Bi 2 S 3 nanoplate via ion exchange

As a two dimensional (2D) visible-light-responsive semiconductor photocatalyst, the photoreactivity of Bi 2 WO 6 is not high enough for practical application owing to its limited response to visible light and rapid recombination of photogenerated electron-hole pairs. In this paper, 2D core-shell structured Bi 2 WO 6 @Bi 2 S 3 nanoplates were prepared by calcination of a mixture of Bi 2 WO 6 (1.3 g) and a certain amount of Na 2 S·9H 2 O (0–3.0 g) at 350 °C for 2 h. The reactivity of the resulting photocatalyst materials was evaluated by photocatalytic degradation of Brilliant Red X-3B (X3B), an anionic dye, under visible light irradiation ( λ > 420 nm). As the amount of Na 2 S·9H 2 O was increased from 0 to 1.5 g, the degradation rate constant of X3B sharply increased from 0.40 × 10 −3 to 6.6 × 10 −3 min −1 . The enhanced photocatalytic activity of Bi 2 WO 6 @Bi 2 S 3 was attributed to the photosensitization of Bi 2 S 3 , which greatly extended the light-responsive range from the visible to the NIR, and the formation of a heterojunction, which retarded the recombination rate of photogenerated electron-hole pairs. However, further increases in the amount of Na 2 S·9H 2 O (from 1.5 to 3.0 g) resulted in a decrease of the photocatalytic activity of the Bi 2 WO 6 @Bi 2 S 3 nanoplates owing to the formation of a photo-inactive NaBiS 2 layer covering the Bi 2 WO 6 surface.

Efficient and stable photocatalytic NO removal on C self-doped g-C3N4: electronic structure and reaction mechanism

Although graphitic carbon nitride (g-C3N4, CN) has been widely studied for its photocatalytic applications in environmental remediation and solar energy conversion, the electronic structure of CN has not been optimized in terms of reactant activation and ROS generation. In this work, C self-doped g-C3N4 (CN-C) was prepared by co-pyrolysis of urea and saccharose and showed highly enhanced photocatalytic NO removal efficiency in comparison with the pristine CN. Theoretical and experimental methods were highly combined to illustrate the geometric structures of CN-C and reveal the promotion mechanisms in terms of enhanced optical and electron transfer properties. The unique electronic structure of CN-C allows NO and O2 to be more easily activated for the production of reactive radicals to participate in the photocatalytic redox reaction. The enhanced production of reactive radicals and the boosted separation rate of photogenerated carriers could promote the photocatalysis efficiency, leading to efficient and stable photocatalytic oxidation of NO over C self-doped g-C3N4. Importantly, the conversion pathways of photocatalytic NO oxidation over CN and CN-C have been elucidated based on the results of DFT calculations, ESR spectra and in situ DRIFTS spectra. A new absorption band at 2175 cm−1 associated with the NO+ intermediate is discovered for CN-C. The present work could offer new insights into the understanding of the electronic structure and photocatalytic NO oxidation mechanism on typical photocatalysts.