Nanogap Engineered Plasmon‐Enhancement in Photocatalytic Solar Hydrogen Conversion

Abstract

of pure g-C 3 N 4 for hydrogen production was relatively low, although the band gap ( E g ≈ 2.7 eV) and band positions of g-C 3 N 4 match well with the intrinsic requisites for photocatalytic water splitting under visible light. [ 6,8 ] To this end, previous attempts have been mainly focused on improving charge carrier migration and separation in g-C 3 N 4 via three aspects: (1) constructing band structure aligned heterojunctions between g-C 3 N 4 and other semiconductor photocatalysts (Cu 2 O, [ 10 ] N-CeO x , [ 11 ] ZnFe 2 O 4 , [ 12 ] CNS, [ 13 ] etc.) for effi cient charge separation, (2) combining g-C 3 N 4 with conductive materials (graphene, [ 14 ] CNTs, [ 15 ] etc.), and (3) designing unique nanostructures (nanorods, [ 16,17 ] nanosheets, [ 18,19 ] mesoporous nanostructures, [20][21][22] etc.) for fast charge carrier migration. However, the photocatalytic effi ciencies of these modifi ed g-C 3 N 4 were still not high enough for practical applications in effi cient solar energy conversion systems.It has been well established that the mismatch between the relatively long penetration depth of photons and the short mean free path of charge carriers signifi cantly account for the high-rate recombination of electrons and holes in semiconductors. [ 23,24 ] Therefore, the charge carrier recombination could be effectively inhibited if the travel distance for charge carriers to transfer to the surface active sites is minimized. Recent development of photocatalysts modifi ed with plasmonic nanostructures of noble metals (such as Au, [25][26][27][28] Ag, [ 29,30 ] etc.) offered a new opportunity to fulfi ll this strategy. These metal nanoparticles (NPs) characteristic of the localized surface plasmon resonance (LSPR) effect can act as nanoantennas for light trapping and form a locally enhanced electromagnetic fi eld in the proximity of the metal NPs. Under irradiation, especially when the LSPR absorption of the metal NPs is partially overlapped with the optical absorption of the semiconductor, [31][32][33] the LSPR induced plasmon resonance energy transfer (PRET) from the plasmonic metal to the nearby semiconductor will preferentially excite charge carriers in the metal/semiconductor interface, namely, the near-surface region of the semiconductor. Then the transfer distance of the photoexcited charge carriers to the surface reactive sites for photocatalytic reactions would be shortened. Watanabe and co-workers demonstrated that the enhanced photocatalytic activity over Ag NPs incorporated TiO 2 photocatalyst was achieved by the LSPR induced electromagnetic fi eld amplitude of Ag NPs. [ 34 ] The consequent PRET effect favored the charge carrier formation in the near-surface region of TiO 2 , thus the

Synergy of Dopants and Defects in Graphitic Carbon Nitride with Exceptionally Modulated Band Structures for Efficient Photocatalytic Oxygen Evolution

“…Note the three kinds of N sites existing in the g‐C 3 N 4 framework (as illustrated in the inset of Figure c), i.e., the N1 site of C–N–C coordination structure in a heptazine unit, the N2 site of N–3C bridging structure connecting with three heptazine units, and the N3 site at the center of a heptazine unit. In the N K‐edge XANES spectra (Figure c), two typical 2p π* resonances are observed at about 400.3 and 403.3 eV, which are correlated with triangular edge N (N1 site) and bridge N (N2 site) of g‐C 3 N 4 , respectively . The intensity change in the N1 and N2 peaks should be originated from the varied numbers of N1 and N2 atoms or amount of unoccupied N 2p states .…”

Highly Efficient Solar‐Catalytic Degradation of Reactive Black 5 Dye Using Mesoporous Plasmonic Ag/g‐C3N4 Nanocomposites

“…A strong and broad emission band from 350 to 600 nm centered at about 440 nm in the blue region is related to the band-to-band transition of the charge carriers in g-C 3 N 4 . [24] The emission peak intensity for Ag/g-C 3 N 4 nanocomposites is less than that of g-C 3 N 4 . Since Ag NPs could accept electron, the rapid recombination of e À /h + pairs is inhibited to some extent.…”

Artificial Photosynthesis with Polymeric Carbon Nitride: When Meeting Metal Nanoparticles, Single Atoms, and Molecular Complexes

“…Chen et al conducted a detailed exploration into the PRET and FRET effects of the SiO 2 insulator layer with controllable thickness on the plasmon‐enhanced photocatalysis. As shown in Figure c, with increasing the thicknesses of SiO 2 shells (8, 12, 17, and 21 nm) synthesized via the sol–gel process, the Ag@SiO 2 core–shell nanoparticles decorated PCN exhibited photocatalytic hydrogen production rates first increased and then decreased . On the other hand, the PRET effect favored the charge excitation in the near‐surface region of PCN for improved photocatalytic activity.…”

“…The PRET and FRET effects gradually become weakened with the widening of the nanogap (i.e., the thickness of the SiO 2 shell). Reproduced with permission . Copyright 2015, Wiley‐VCH.…”

“…As shown in Figure 5c, with increasing the thicknesses of SiO 2 shells (8, 12, 17, and 21 nm) synthesized via the sol-gel process, the Ag@SiO 2 core-shell nanoparticles decorated PCN exhibited photocatalytic hydrogen production rates first increased and then decreased. [71] On the other hand, the PRET effect favored the charge excitation in the near-surface region of PCN for improved photocatalytic activity. The excitation probability of charge carriers increased with the narrowing nanogaps between PCN and Ag nanoparticles, due to the PRET effect strengthened with the decreasing SiO 2 shell thickness (i.e., the distance between PCN and Ag nanoparticles).…”