Na and O Co-doped Carbon Nitride for Efficient Photocatalytic Hydrogen Evolution

doi:10.15541/jim20240345

Abstract

Abstract:

Elemental doping is an effective strategy for tuning the band structure of graphite carbon nitride (CN) to enhance its photocatalytic performance. In this study, sodium (Na) and oxygen (O) co-doped carbon nitride (Na/O-CN_x, x=1.0, 2.0, 3.0, 4.0) was synthesized via solid-phase reaction of sodium citrate (NaCA) and pure CN powder in the Teflon-sealed autoclave under air conditions at 180 ℃. Surface area of Na/O-CN_3.0 is measured to be 18.8 m²/g, increasing by 60.7% compared to that of pure CN (11.7 m²/g). Bandgap energy of Na/O-CN_3.0 is determined to be 2.68 eV, marginally lower than that of pure CN (2.70 eV), thereby enhancing its capacity for sunlight absorption. Meanwhile, the incorporation of Na and O atoms into Na/O-CN_x is found to effectively reduce recombination rates of photogenerated electron-hole pairs. As a result, Na/O-CN_x samples exhibit markedly enhanced photocatalytic hydrogen evolution activity under visible light irradiation. Notably, the optimal Na/O-CN_3.0 sample achieves a photocatalytic hydrogen production rate of 103.2 μmol∙g^-1∙h^-1, which is 8.2 times greater than that of pure CN (11.2 μmol∙g^-1∙h^-1). Furthermore, a series of Na/O-CN_x-yO₂ (y=0, 20%, 40%, 60%, 80%, 100%) samples were prepared by modulating the oxygen content within reaction atmosphere. The catalytic performance evaluations reveal that the incorporation of both Na and O atoms in Na/O-CN_3.0 enhances photocatalytic activity. This study also introduces novel methodologies for synthesis of metal atom-doped CN materials at lower temperature, highlighting the synergistic effect of Na and O atoms in photocatalytic hydrogen production of Na/O-CN_x samples.

Key words: Na and O co-doped carbon nitride, synergistic effect, visible light, photocatalytic hydrogen evolution

CLC Number:

TQ174

CHEN Libo, SHENG Ying, WU Ming, SONG Jiling, JIAN Jian, SONG Erhong. Na and O Co-doped Carbon Nitride for Efficient Photocatalytic Hydrogen Evolution[J]. Journal of Inorganic Materials, 2025, 40(5): 552-562.

Figures/Tables 12

Fig. 1 Synthetic schematic of Na/O-CNx and Na/O-CN3.0-yO2 samples

Fig. 2 Structure analyses of samples (a, b) XRD patterns of (a) pure CN and Na/O-CNx, and (b) Na/O-CN3.0-yO2; (c) FT-IR spectra of pure CN, Na/O-CN3.0 and Na/O-CN3.0-40%O2

Fig. 3 Morphologies of samples (a, b) SEM images of (a) pure CN and (b) Na/O-CN3.0; (c) TEM and (d) HRTEM images of Na/O-CN3.0

Fig. 4 High-resolution XPS spectra of pure CN, Na/O-CN3.0 and Na/O-CN3.0-40%O2 samples (a) C1s; (b) N1s; (c) O1s; (d) Na1s

Fig. 5 Band structure analysis of pure CN and Na/O-CN3.0 (a) UV-Vis DRS spectra; (b) Related Tauc plots; (c) VB XPS spectra; (d) Band structure diagram

Fig. 6 Photocurrent and PL spectra analysis of pure CN and Na/O-CN3.0 samples (a) Photocurrent test; (b) EIS plots; (c) PL spectra; (d) Time-resolved PL spectra

Fig. 7 Photocatalytic hydrogen activity (a, b) Photocatalytic hydrogen evolution of (a) pure CN and Na/O-CNx, and (b) Na/O-CN3.0-yO2; (c) PHER of pure CN, Na/O-CN3.0 and Na/O-CN3.0-40%O2; (d) Cycling performance of Na/O-CN3.0

Fig. 8 Photocatalytic hydrogen evolution mechanism of Na/O-CN3.0 under visible light irradiation

Fig. S1 Nitrogen adsorption-desorption isotherms and corresponding pore diameter distribution curves of pure CN and Na/O-CN3.0

Fig. S2 XPS survey spectra of pure CN, Na/O-CN3.0 and Na/O-CN3.0-40%O2

Fig. S3 ESR spectra of pure CN, Na/O-CN3.0 and Na/O-CN3.0-40%O2 samples

Table S1 Photocatalytic hydrogen evolution performance under visible light irradiation (> 420 nm) and surface area of alkali metal doped carbon nitride[S1-S12]

Catalyst	Synthesis temperature/℃	Catalyst weight/mg	Sacrificial reagent/% (in volume)	Surface area/ (m²·g^-1)	Activity compared with CN (times)	Ref.
Na/O-CN_3.0	180	50	TEOA 10%	18.8	9.2	This work
3% NaCl-CN	550	10	TEOA 17%	76.8	4.3	[S1]
KCN-10	550	50	TEOA 10%	11	5.6	[S2]
K(0.05)-CN	550	50	TEOA 17%	11.1	5	[S3]
LiNa-K-CN2	520	50	TEOA 10%	116.2	15	[S4]
Na(30)-MCN	550	100	TEOA 10%	56.1	12.9	[S5]
Na0.1-CNNTs	650	20	TEOA 10%	94	11	[S6]
CN-Na-7	550	50	TEOA 10%	11.7	9.9	[S7]
CN-100	520	50	TEOA 10%	14.9	9.2	[S8]
(Na,O)g-C₃N₄	160	50	ethyl alcohol 40%	-	7	[S9]
CN_0.05	550	20	TEOA	46.7	1.9	[S10]
GCN-Na-5	550	50	TEOA	10.3	1.5	[S11]
K@C₃N₄	600	100	TEOA	27.5	8	[S12]

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