Carbon nitrides and metal nanoparticles: from controlled synthesis to design principles for improved photocatalysis

Abstract

The use of sunlight to drive chemical reactions via photocatalysis is of paramount importance towards a sustainable future. Among several photocatalysts, earth-abundant polymeric carbon nitride (PCN, often wrongly named g-C3N4) has emerged as an attractive candidate due to its ability to absorb light efficiently in the visible and near-infrared ranges, chemical stability, non-toxicity, straightforward synthesis, and versatility as a platform for constructing hybrid materials. Especially, hybrids with metal nanoparticles offer the unique possibility of combining the catalytic, electronic, and optical properties of metal nanoparticles with PCN. Here, we provide a comprehensive overview of PCN materials and their hybrids, emphasizing heterostructures with metal nanoparticles. We focus on recent advances encompassing synthetic strategies, design principles, photocatalytic applications, and charge-transfer mechanisms. We also discuss how the localized surface plasmon resonance (LSPR) effect of some noble metals NPs (e.g. Au, Ag, and Cu), bimetallic compositions, and even non-noble metals NPs (e.g., Bi) synergistically contribute with PCN in light-driven transformations. Finally, we provide a perspective on the field, in which the understanding of the enhancement mechanisms combined with truly controlled synthesis can act as a powerful tool to the establishment of the design principles needed to take the field of photocatalysis with PCN to a new level, where the desired properties and performances can be planned in advance, and the target material synthesized accordingly.

Modulation of Bi2MoO6‐Based Materials for Photocatalytic Water Splitting and Environmental Application: a Critical Review

“…φ s and φ m represent the semiconductor work function and the metal work function, respectively. Reproduced with permission . Copyright 2018, Royal Society of Chemistry.…”

“…LSPR‐related mechanisms: d) localized heating; e) near‐field enhancements; f) charge‐transfer processes from metal to semiconductor. Reproduced with permission . Copyright 2018, Royal Society of Chemistry.…”

“…In this case, the light with specific wavelength striking on the surface provides a force for the free electrons to regularly vibrate with an associated resonant frequency, which dramatically enhances the absorption of visible light . Typically, the enhancement mechanisms by LSPR in the generation of excitons at the semiconductor can be concluded as the following: i) localized heating (Figure d), which causes local temperature increase; ii) near‐field enhancements (Figure e), which promotes the photons to transfer toward the semiconductor; iii) charge‐transfer processes from metal to semiconductor (Figure f) . A typical indicator of LSPR effect is that a new absorption band will emerge on the UV–vis diffuse reflectance spectra, suggesting an enhanced light absorption ability.…”

“…Rarely powerful characterization techniques are employed to unravel the charge cascading process and interface effects in detail. Meanwhile, the distance between the semiconductor and the noble metal is decisive to balance the plasmon resonance energy transfer (PRET) and the Förster resonance energy transfer (FRET), which are favorable and harmful for the photoexcited semiconductor, respectively . It is imperative to investigate the optimal distance, as well as the suitable size and shape of metallic particles.…”

Photoexcited charge carrier behaviors in solar energy conversion systems from theoretical simulations

“…It is a consensus that single‐component photocatalysts cannot simultaneously take on wide light absorption range and strong redox ability partially due to, for instance, the fast recombination between conduction band electrons and valence band holes. This can be overcome by designing proper heterogeneous photocatalytic systems . For heterogeneous photocatalytic materials, photoexcited electrons and holes are transferred to opposite components, reducing the charge carrier recombination and thus improving the light–energy conversion efficiency.…”