Optimizing electronic structure and charge transport of sulfur/potassium co‐doped graphitic carbon nitride with efficient photocatalytic hydrogen evolution performance

Abstract

Recently, graphitic carbon nitride (CN) has been widely investigated for solar energy conversion through water splitting, but its low photocatalytic activity needs to be further improved and optimized. Herein, S/K co‐doped CN photocatalysts have been fabricated by condensation of thiourea and dithiooxamide followed by post‐treatment in molten salt. As evidenced by XRD patterns and UV–vis DRS plots, the engineering crystalline and electronic structure of all as‐prepared samples have been explored through tailoring the mass ratio of thiourea and dithiooxamide as well as ratio of molten salt/the precursor. After optimization, the as‐prepared S/K co‐doped CN photocatalysts with needle‐like nanorods structure exhibit excellent hydrogen evolution rate of 1962.10 μmol−1 g−1 h−1. While its photocatalytic activity is lower than that of pure CN by molten salt treatment (K‐doped CN) (2066.40 μmol−1 g−1 h−1), which results from that the K content of S/K co‐doped CN photocatalyst is lower than that of K‐doped CN. Moreover, compared with K‐doped CN, S/K co‐doped CN photocatalyst possesses higher photocatalytic performance when irradiated by a light source (λ > 520 nm). This might be ascribed to the fact that the introduction of sulfur can expand light absorption region (λ > 520 nm), whereas K cannot improve light absorption of CN in this wavelength region. Furthermore, DFT calculation reveals that both S and K atoms can offer more electrons to band gap, leading to the formation of metallic‐character band structure. In addition, K atom can intercalate in the interlayer of CN and bridge the adjacent two layers, leading to the formation of charge delivery channels. These results demonstrate that S/K co‐doped CN photocatalysts facilitate the separation and transport of photogenerated charge carries, resulting in the efficient photocatalytic activity for hydrogen evolution. Besides, a competition between sulfur and potassium atom during the synthesis process is also discussed in details.

Binary Type-II Heterojunction K7HNb6O19/g-C3N4: An Effective Photocatalyst for Hydrogen Evolution without a Co-Catalyst

“…The characteristic peaks of g-C 3 N 4 in Nb–CN-0.4 appeared at different wavebands in the absorption region. The wide peak between 3000 and 3600 cm −1 was caused by the stretching vibration of N–H and O–H of the physical absorption water molecules [ 37 ]. The peaks at 1630 cm −1 are attributed to the stretching vibration of C=N in g-C 3 N 4 , while the peaks at 1405, 1321, 1246 and 807 cm −1 belonged to a typical C–N heterocyclic stretching vibration for triazinyl units [ 23 , 38 ].…”

Effect of molten-salt modulation on the composition and structure of g-C3N4-based photocatalysts

“…[45][46][47][48] More importantly, the dopant and alkali-metal co-doping can achieve unexpected effects. [49][50][51] For instance, He et al 52 synthesized red carbon/ potassium-doped polymeric carbon nitride (RPCN) using melamine as a precursor, 2,4,6-triamine-pyrimidine (TAP) as a carbon dopant, and KCl as a K dopant. As revealed in Fig.…”

Non-Metal-Doped Porous Carbon Nitride Nanostructures for Photocatalytic Green Hydrogen Production

“…Table 6 summarizes diverse mono-heteroatoms including phosphorus [ 76 , 89 , 90 , 91 , 92 , 93 , 94 , 95 , 96 , 97 , 98 , 99 , 100 , 101 , 102 , 103 ], sulfur [ 104 , 105 , 106 , 107 , 108 , 109 , 110 , 111 , 112 , 113 , 114 ], boron [ 115 , 116 , 117 , 118 , 119 , 120 , 121 ], oxygen [ 122 , 123 , 124 , 125 , 126 , 127 , 128 , 129 , 130 , 131 , 132 , 133 , 134 ], carbon [ 135 , 136 , 137 , 138 , 139 ], nitrogen [ 140 , 141 , …”

“…Sulfur doping has also been used to tune the bandgap and electronic structure of g-C 3 N 4 for enhanced visible light absorption, improved charge separation and transfer, and consequently, photocatalytic performance [ 104 , 107 , 111 , 148 ]. For instance, Xu’s group fabricated S-doped mesoporous g-C 3 N 4 (mpgCNS) by using thiourea as a precursor and SiO 2 nanoparticles as a template [ 113 ].…”