Engineering selective pathways for photocatalytic methyl mercaptan oxidation via spatially separated redox centers in Sr-modified carbon nitride

Abstract

Photocatalytic oxidation of methyl mercaptan (CH₃SH) often suffers from inefficient degradation and the generation of odorous byproducts such as dimethyl disulfide (DMDS), leading to secondary pollution and catalyst deactivation. In this study, we engineer a Sr-doped polymeric carbon nitride (CN) catalyst featuring spatially separated redox centers constructed via Sr–N coordination and nitrogen vacancies (N_V). The optimized Sr-CN-N_V material achieves stable > 99% CH₃SH removal over 50 h of continuous operation while completely suppressing DMDS formation. Mechanistic studies indicate that the spatially segregated charge carriers enhance reactive oxygen species (ROS) generation and promote the deep oxidation of adsorbed intermediates. This work provides a spatial-site engineering strategy for designing robust and selective photocatalysts toward efficient and sustainable air purification.

Graphical abstract

Keywords

Photocatalytic air purification / Methyl mercaptan oxidation / Spatial charge separation / Strontium-doped carbon nitride / Reaction pathway control

Highlight

	● Sr-CN-NV with separated redox sites achieves > 99% CH3SH removal for 50 h.
	● Sr sites and nitrogen vacancies steer complete oxidation, suppressing DMDS.
	● Weak sulfur affinity allows catalyst regeneration by simple water washing.
	● Spatial-site engineering provides a general strategy for selective air purification.

References

[1] Bai K T , Yu X H , Wen G Z , Yang Y Q , Lin Y X , Zhang L L , Rong J , Yin L C , Qi W , Bonn M . et al. (2025). Spontaneous dissociation of excitons in polymeric photocatalysts for overall water splitting. Nature Communications, 16(1): 8577

[2] Cao X H , Lu J C , Zheng X Q , He D D , Zhu W J , Zhao Y T , Zhang W J , Tian R , Luo Y M . (2022). Regulation of the reaction pathway to design the high sulfur/coke-tolerant Ce-based catalysts for decomposing sulfur-containing VOCs. Chemical Engineering Journal, 429: 132473

[3] Chen Y Q , Wang P L , Qu W Q , Shen Y J , Tang Y , Mariani E , Ni Y B , Hu X N , Wang F L , Zhang J . et al. (2025). Cu-Ce dual-atom sites embedded in zeolites boost resistance to impurity interference for environmental catalysis. Angewandte Chemie International Edition, 64(49): e202517918

[4] Dong X A , Li J Y , Xing Q , Zhou Y , Huang H W , Dong F . (2018). The activation of reactants and intermediates promotes the selective photocatalytic NO conversion on electron-localized Sr-intercalated g-C₃N₄. Applied Catalysis B: Environmental, 232: 69–76

[5] Guo B , Tang Y Q , Liu Z X , Zhu Z , Yan G Q . (2021). Numerical study on optoelectronic properties of alkaline-earth metal doped g-C₃N₄. Chemical Physics, 544: 111104

[6] Guo F S , Li S R , Hou Y D , Xu J K , Lin S , Wang X C . (2019). Metalated carbon nitrides as base catalysts for efficient catalytic hydrolysis of carbonyl sulfide. Chemical Communications, 55(75): 11259–11262

[7] He D D , Wan G P , Hao H S , Chen D K , Lu J C , Zhang L , Liu F , Zhong L P , He S F , Luo Y M . (2016). Microwave-assisted rapid synthesis of CeO₂ nanoparticles and its desulfurization processes for CH₃SH catalytic decomposition. Chemical Engineering Journal, 289: 161–169

[8] Kong J J , Tang M Q , Luo Y J , Song S N , Xiang Z W , Guo Y L , Zhang W P , Li G Y , An T C . (2025). Pyroelectric Pt-supported S-scheme heterojunction catalyst for effective photocatalytic degradation of VOCs containing soot driven by visible light. Applied Catalysis B: Environment and Energy, 365: 124858

[9] Kong J , Zhang W , Li G , Huo D Y J , Guo Y Y , Niu X M , Wan Y , Tang B , Xia A D . (2020). Excited-state symmetry-breaking charge separation dynamics in multibranched perylene diimide molecules. The Journal of Physical Chemistry Letters, 11(24): 10329–10339

[10] Lan H C , Tang Q W , Hou Z A , Zhu K , An X Q , Liu H J , Qu J H . (2023). Hydrogen-induced defective crystalline carbon nitride with enhanced bidirectional charge migration for persulfate photoactivation. ACS ES&T Engineering, 3(4): 580–589

[11] Li S R , Wang J L , Cai X , Li S , Liang X C , Ye H F , Xiong R , Yang C , Lin W , Yu Z Y . et al. (2026). From amorphous to ordered: ammonia-mediated structural evolution in melon-based carbon nitride photocatalyst. Applied Catalysis B: Environment and Energy, 381: 125807

[12] Li S S , Zhang Y F , Li Y J , Xue J , Deng C Y , Song W J , Chen C C , Zhao J C . (2024). Modulating the photooxidation selectivity on graphitic carbon nitride by tuning edge functional groups. Applied Catalysis B: Environmental, 340: 123180

[13] Li W X , Wang W J , Wang C , Huang Y M , Liu W H , Zhao W N , Xu Z , Li G Y , An T C . (2025). Synergy of dual dopants and nitrogen defects in graphitic carbon nitride for boosting sustainable photocatalytic inactivation efficiency towards antibiotic-resistant bacteria. Chemical Engineering Journal, 507: 160404

[14] Lin L H , Yu Z Y , Wang X C . (2019). Crystalline carbon nitride semiconductors for photocatalytic water splitting. Angewandte Chemie International Edition, 58(19): 6164–6175

[15] Liu F , Li W C , Wang L , Rao X , Zheng S H , Zhang Y P . (2022). Sulfur-and strontium-doped graphitic carbon nitride for efficient photocatalytic hydrogen evolution. ACS Applied Energy Materials, 5(12): 15834–15843

[16] Liu W Q , Xing C Z . (2024). Needs and challenges of optical atmospheric monitoring on the background of carbon neutrality in China. Frontiers of Environmental Science & Engineering, 18(6): 73

[17] Lu J C , Mu W H , Qin C Y , Liu T , Xu Z Z , Zhu W J , Fang J , Ai T H , Tian R , Zhang L . et al. (2024). Synchronous catalytic elimination of malodorous mercaptans based VOCs: controlling byproducts and revealing sites-pathway relationship. Applied Catalysis B: Environment and Energy, 357: 124253

[18] Lu J C , Tian R , Zhang W J , Zhang Y L , Yang Y J , Xu Z Z , He D D , Ai T H , Luo Y M . (2023). An ultra-long stability of lanthanum (La) modified molecular sieve for catalytic degradation of typical sulfur-containing VOCs in a near-real environment. Applied Catalysis B: Environmental, 339: 123114

[19] Lu P , Hu X L , Li Y J , Zhang M , Liu X P , He Y Z , Dong F , Fu M , Zhang Z . (2018). One-step preparation of a novel SrCO₃/g-C₃N₄ nano-composite and its application in selective adsorption of crystal violet. RSC Advances, 8(12): 6315–6325

[20] Luo R , Liu S G , Tian S L , Li C , Ning P . (2025). N-doped activated carbon promoting sulfur-containing VOC removal in three-dimension electrode system. Frontiers of Environmental Science & Engineering, 19(5): 71

[21] Lyu S H , Wang J L , Zhou Y Q , Wei C G , Liang X C , Yu Z Y , Lin W , Hou Y D , Yang C . (2024). Structural lithium incorporated with the crystalline poly (triazine imide) frameworks for selective catalytic oxidative desulfurization. Advanced Functional Materials, 34(10): 2310286

[22] Maung N . (1999). The evaluation of bond dissociation energies for simple sulphur containing molecules using ab initio and density functional methods. Journal of Molecular Structure: THEOCHEM, 460(1−3): 159–166

[23] Sebastian E , Sunny J , Hariharan M . (2022). Excimer evolution hampers symmetry-broken charge-separated states. Chemical Science, 13(36): 10824–10835

[24] Su R D , Zhu Y F , Gao B Y , Li Q . (2024). Progress on mechanism and efficacy of heterogeneous photocatalysis coupled oxidant activation as an advanced oxidation process for water decontamination. Water Research, 251: 121119

[25] Tian R , Lu J C , Xu Z Z , Zhang W J , Liu J P , Wang L L , Xie Y B , Zhao Y T , Cao X H , Luo Y M . (2023). Unraveling the synergistic reaction and the deactivation mechanism for the catalytic degradation of double components of sulfur-containing VOCs over ZSM-5-Based materials. Environmental Science & Technology, 57(3): 1443–1455

[26] Wang J L , Chen B Q , Zeng F H , Lu X F , Hou Y D , Lin W , Yang C . (2024). Boosting oxygen activation by CoP/carbon nitride photocatalyst in low-concentration H₂S oxidation. Journal of Materials Chemistry A, 12(24): 14508–14516

[27] Wang X C , Maeda K , Thomas A , Takanabe K , Xin G , Carlsson J M , Domen K , Antonietti M . (2009). A metal-free polymeric photocatalyst for hydrogen production from water under visible light. Nature Materials, 8(1): 76–80

[28] Wei Z D , Yan J W , Guo W Q , Shangguan W F . (2023). Nanoscale lamination effect by nitrogen-deficient polymeric carbon nitride growth on polyhedral SrTiO₃ for photocatalytic overall water splitting: synergy mechanism of internal electrical field modulation. Chinese Journal of Catalysis, 48: 279–289

[29] Wu J D , Huang Z A , He Z , Zairov R , He X T , Huang Y , Fu M Y , Yuan C D , Sinyashin O G , Zhou Y . (2025). Unraveling the role of CH₃S* intermediates for efficient methane and hydrogen sulfide reforming over Mo/Al₂O₃ catalysts. Journal of Catalysis, 448: 116168

[30] Xu Z L , Li J , Zhan D Y , Liu Y , Xu W H , Wang J F , Yu Z W . (2024). The n-π* electronic transition induced by nitrogen vacancies enhances photocatalytic hydrogen production in carbon nitride. Chemical Engineering Journal, 501: 157670

[31] Yang H , Sun S D , Lyu J L , Yang Q , Cui J . (2024). Mechanism insight into triple S-scheme intermolecular carbon nitride homojunction with robust built-in electric field for highly enhanced photocatalytic hydrogen evolution. Chemical Engineering Journal, 481: 148297

[32] Yang P J , Wang L , Zhuzhang H Y , Wang R R , Titirici M M , Wang X C . (2019). Photocarving nitrogen vacancies in a polymeric carbon nitride for metal-free oxygen synthesis. Applied Catalysis B: Environmental, 256: 117794

[33] Yang Z C , Xu Y Y , He L , Lu X K , Yao X L , Li C M , Gao H N , Yao Z L , Wu C . (2025). Construction of superhydrophilic/superhydrophobic composite photocatalysts for efficient gas-liquid-solid photocatalytic degradation of methyl mercaptan. Chemical Engineering Journal, 513: 162913

[34] Ye H F , Zhao F , Lyu S H , Wen Z Q , Wu D P , Yang C . (2026). Continuously selective oxidation of hydrogen sulfide over carbon-nitrogen catalysts for sustainable environment-a review. Global Environmental Science, 2(1): 1–22

[35] Zhang G G , Zhang J S , Zhang M W , Wang X C . (2012). Polycondensation of thiourea into carbon nitride semiconductors as visible light photocatalysts. Journal of Materials Chemistry, 22(16): 8083–8091

[36] Zhang W N , Zheng D Y , Lao J L , Li R J , Chen B H , Chen J Y , Zhong J , Ji Y M , Li G Y , Francisco J S . et al. (2025). Sulfate promotes amine salt ozonation in atmospheric aerosols. Journal of the American Chemical Society, 147(38): 34327–34338

[37] Zhu H , Wang Y J , Jiang Z Q , Deng B L , Xin Y , Jiang Z J . (2024). Defect engineering promoted ultrafine Ir nanoparticle growth and Sr single-atom adsorption on TiO₂ nanowires to achieve high-performance overall water splitting in acidic media. Advanced Energy Materials, 14(14): 2303987

RIGHTS & PERMISSIONS

Higher Education Press 2026