Graphitic carbon nitride (C3N4) was synthesised from melamine at 550 °C for 4 h in the argon atmosphere and then was reheated for 1-3 h at 500 °C in argon. Two band gaps of 2.04 eV and 2.47 eV were observed in all the synthetized materials. Based on the results of elemental and photoluminescence analyses, the lower band gap was found to be caused by the formation of vacancies. Specific surface areas of the synthetized materials were 15-18 m2g-1 indicating that no thermal exfoliation occurred. The photocatalytic activity of these materials was tested for hydrogen generation. The best photocatalyst showed 3 times higher performance (1547 μmol/g) than bulk C3N4 synthetized in the air (547 μmol/g). This higher activity was explained by the presence of carbon (VC) and nitrogen (VN) vacancies grouped in their big complexes 2VC + 2VN (observed by positron annihilation spectroscopy). The effect of an inert gas on the synthesis of C3N4 was demonstrated using Graham´s law of ammonia diffusion. This study showed that the synthesis of C3N4 from nitrogen-rich precursors in the argon atmosphere led to the formation of vacancy complexes beneficial for hydrogen generation, which was not referred so far.

Department of Chemistry and Physico Chemical Processes VŠB Technical University of Ostrava 17 listopadu 15 708 00 Ostrava Poruba Czech Republic

Department of Low Temperature Physics Faculty of Mathematics and Physics Charles University 5 Holešovičkách 2 Prague 8 Czech Republic

Institute of Chemical Process Fundamentals Czech Academy of Science Rozvojová 1 165 02 Prague Czech Republic

Institute of Environmental Technology CEET VŠB Technical University of Ostrava 17 listopadu 15 708 00 Ostrava Poruba Czech Republic

Zobrazit více v PubMed

Liu AY, Cohen ML. Prediction of new low compressibility solids. Science. 1989;245:841–842. doi: 10.1126/science.245.4920.841. PubMed DOI

Wang X, et al. A metal-free polymeric photocatalyst for hydrogen production from water under visible light. Nat. Mater. 2009;8:76–80. doi: 10.1038/nmat2317. PubMed DOI

Zhang H, Zuo X, Tang H, Li G, Zhou Z. Origin of photoactivity in graphitic carbon nitride and strategies for enhancement of photocatalytic efficiency: Insights from first-principles computations. Phys. Chem. Chem. Phys. 2015;17:6280–6288. doi: 10.1039/C4CP05288A. PubMed DOI

Wang Y, Wang X, Antonietti M. Polymeric graphitic carbon nitride as a heterogeneous organocatalyst: From photochemistry to multipurpose catalysis to sustainable chemistry. Angew. Chem. Int. Ed. Engl. 2012;51:68–89. doi: 10.1002/anie.201101182. PubMed DOI

Cao S, Low J, Yu J, Jaroniec M. Polymeric photocatalysts based on graphitic carbon nitride. Adv. Mater. 2015;27:2150–2176. doi: 10.1002/adma.201500033. PubMed DOI

Yang Y, et al. Recent advances in application of graphitic carbon nitride-based catalysts for degrading organic contaminants in water through advanced oxidation processes beyond photocatalysis: A critical review. Water Res. 2020;184:116200. doi: 10.1016/j.watres.2020.116200. PubMed DOI

Safaei J, et al. Graphitic carbon nitride (g-C3N4) electrodes for energy conversion and storage: A review on photoelectrochemical water splitting, solar cells and supercapacitors. J. Mater. Chem. A. 2018;6:22346–22380. doi: 10.1039/C8TA08001A. DOI

Dong Y, et al. Graphitic carbon nitride materials: Sensing, imaging and therapy. Small. 2016;12:5376–5393. doi: 10.1002/smll.201602056. PubMed DOI

Wang A, Wang C, Fu L, Wong-Ng W, Lan Y. Recent advances of graphitic carbon nitride-based structures and applications in catalyst, sensing, imaging, and LEDs. Nano-Micro Lett. 2017;9:47. doi: 10.1007/s40820-017-0148-2. PubMed DOI PMC

Wang L, Wang C, Hu X, Xue H, Pang H. Metal/graphitic carbon nitride composites: Synthesis, structures, and applications. Chem. Asian J. 2016;11:3305–3328. doi: 10.1002/asia.201601178. PubMed DOI

Zhou Z, Zhang Y, Shen Y, Liu S, Zhang Y. Molecular engineering of polymeric carbon nitride: Advancing applications from photocatalysis to biosensing and more. Chem. Soc. Rev. 2018;47:2298–2321. doi: 10.1039/C7CS00840F. PubMed DOI

Svoboda L, et al. Graphitic carbon nitride nanosheets as highly efficient photocatalysts for phenol degradation under high-power visible LED irradiation. Mater. Res. Bull. 2018;100:322–332. doi: 10.1016/j.materresbull.2017.12.049. DOI

Wang Y, Liu L, Ma T, Zhang Y, Huang H. 2D graphitic carbon nitride for energy conversion and storage. Adv. Funct. Mater. 2021;31:2102540. doi: 10.1002/adfm.202102540. DOI

Papailias I, et al. Chemical vs thermal exfoliation of g-C3N4 for NOx removal under visible light irradiation. Appl. Catal. B. 2018;239:16–26. doi: 10.1016/j.apcatb.2018.07.078. DOI

Jiang L, et al. Doping of graphitic carbon nitride for photocatalysis: A reveiw. Appl. Catal. B. 2017;217:388–406. doi: 10.1016/j.apcatb.2017.06.003. DOI

Starukh H, Praus P. Doping of graphitic carbon nitride with non-metal elements and its application for photocatalysis. Catalysts. 2020;10:38. doi: 10.3390/catal10101119. DOI

Hasija V, et al. Recent advances in noble metal free doped graphitic carbon nitride based nanohybrids for photocatalysis of organic contaminants in water: A review. Appl. Mater. Today. 2019;15:494–524. doi: 10.1016/j.apmt.2019.04.003. DOI

Fu J, Yu J, Jiang C, Cheng B. g-C3N4-based heterostructured photocatalysts. Adv. Energy Mater. 2018;8:1701503. doi: 10.1002/aenm.201701503. DOI

Miller TS, et al. Carbon nitrides: Synthesis and characterization of a new class of functional materials. Phys. Chem. Chem. Phys. 2017;19:15613–15638. doi: 10.1039/C7CP02711G. PubMed DOI

Ong W-J, Tan L-L, Ng YH, Yong S-T, Chai S-P. Graphitic carbon nitride (g-C3N4)-based photocatalysts for artificial photosynthesis and environmental remediation: Are we a step closer to achieving sustainability? Chem. Rev. 2016;116:7159–7329. doi: 10.1021/acs.chemrev.6b00075. PubMed DOI

Kessler FK, et al. Functional carbon nitride materials—design strategies for electrochemical devices. Nat. Rev. Mater. 2017;2:17030. doi: 10.1038/natrevmats.2017.30. DOI

Kong L, Wang J, Ma F, Sun M, Quan J. Graphitic carbon nitride nanostructures: Catalysis. Appl. Mater. Today. 2019;16:388–424. doi: 10.1016/j.apmt.2019.06.003. DOI

Inagaki M, Tsumura T, Kinumoto T, Toyoda M. Graphitic carbon nitrides (g-C3N4) with comparative discussion to carbon materials. Carbon. 2019;141:580–607. doi: 10.1016/j.carbon.2018.09.082. DOI

Li Y, Li X, Zhang H, Fan J, Xiang Q. Design and application of active sites in g-C3N4-based photocatalysts. J. Mater. Sci. Technol. 2020;56:69–88. doi: 10.1016/j.jmst.2020.03.033. DOI

Barrio J, Volokh M, Shalom M. Polymeric carbon nitrides and related metal-free materials for energy and environmental applications. J. Mater. Chem. A. 2020;8:11075–11116. doi: 10.1039/D0TA01973A. DOI

Zhu B, Zhang L, Cheng B, Yu J. First-principle calculation study of tri-s-triazine-based g-C3N4: A review. Appl. Catal. B. 2018;224:983–999. doi: 10.1016/j.apcatb.2017.11.025. DOI

Wang Y, et al. Catalysis with two-dimensional materials confining single atoms: Concept, design, and applications. Chem. Rev. 2019;119:1806–1854. doi: 10.1021/acs.chemrev.8b00501. PubMed DOI

Lv C, et al. Defect engineering metal-free polymeric carbon nitride electrocatalyst for effective nitrogen fixation under ambient conditions. Angew. Chem. Int. Ed. 2018;57:10246–10250. doi: 10.1002/anie.201806386. PubMed DOI

Niu P, Yin L-C, Yang Y-Q, Liu G, Cheng H-M. Increasing the visible light absorption of graphitic carbon nitride (melon) photocatalysts by homogeneous self-modification with nitrogen vacancies. Adv. Mater. 2014;26:8046–8052. doi: 10.1002/adma.201404057. PubMed DOI

Tu W, et al. Investigating the role of tunable nitrogen vacancies in graphitic carbon nitride nanosheets for efficient visible-light-driven H2 evolution and CO2 reduction. ACS Sustain. Chem. Eng. 2017;5:7260–7268. doi: 10.1021/acssuschemeng.7b01477. DOI

Liao J, et al. Nitrogen defect structure and NO+ intermediate promoted photocatalytic NO removal on H2 treated g-C3N4. Chem. Eng. J. 2020;379:122282. doi: 10.1016/j.cej.2019.122282. DOI

Liang L, et al. Synthesis and photo-catalytic activity of porous g-C3N4: Promotion effect of nitrogen vacancy in H2 evolution and pollutant degradation reactions. Int. J. Hydrogen Energy. 2019;44:16315–16326. doi: 10.1016/j.ijhydene.2019.05.001. DOI

Praus P, et al. The presence and effect of oxygen in graphitic carbon nitride synthetized in air and nitrogen atmosphere. Appl. Surf. Sci. 2020;529:147086. doi: 10.1016/j.apsusc.2020.147086. DOI

Liang L, Shi L, Wang F. Fabrication of large surface area nitrogen vacancy modified graphitic carbon nitride with improved visible-light photocatalytic performance. Diam. Relat. Mater. 2019;91:230–236. doi: 10.1016/j.diamond.2018.11.025. DOI

Barrio J, et al. Unprecedented centimeter-long carbon nitride needles: Synthesis. Charact. Appl. 2018;14:1800633. doi: 10.1002/smll.201800633. PubMed DOI

Jiménez-Calvo P, Marchal C, Cottineau T, Caps V, Keller V. Influence of the gas atmosphere during the synthesis of g-C3N4 for enhanced photocatalytic H2 production from water on Au/g-C3N4 composites. J. Mater. Chem. A. 2019;7:14849–14863. doi: 10.1039/C9TA01734H. DOI

Huang S, et al. Synthesis of carbon nitride in moist environments: A defect engineering strategy toward superior photocatalytic hydrogen evolution reaction. J. Energy Chem. 2021;54:403–413. doi: 10.1016/j.jechem.2020.05.062. DOI

Jiang L, et al. Defect engineering in polymeric carbon nitride photocatalyst: Synthesis, properties and characterizations. Adv. Coll. Interface Sci. 2021;296:102523. doi: 10.1016/j.cis.2021.102523. PubMed DOI

Yu X, et al. Point-defect engineering: leveraging imperfections in graphitic carbon nitride (g-C3N4) photocatalysts toward artificial photosynthesis. Small. 2021;17:2006851. doi: 10.1002/smll.202006851. PubMed DOI

Kumar A, et al. C-, N-Vacancy defect engineered polymeric carbon nitride towards photocatalysis: Viewpoints and challenges. J. Mater. Chem. A. 2021;9:111–153. doi: 10.1039/D0TA08384D. DOI

Yang J, et al. Defective polymeric carbon nitride: Fabrications, photocatalytic applications and perspectives. Chem. Eng. J. 2022;427:130991. doi: 10.1016/j.cej.2021.130991. DOI

Tauc J, Grigorovici R, Vancu A. Optical properties and electronic structure of amorphous germanium. Phys. Status Solidi (b) 1966;15:627–637. doi: 10.1002/pssb.19660150224. DOI

Xu Y, Gao S-P. Band gap of C3N4 in the GW approximation. Int. J. Hydrogen Energy. 2012;37:11072–11080. doi: 10.1016/j.ijhydene.2012.04.138. DOI

Bečvář F, Čížek J, Procházka I, Janotová J. The asset of ultra-fast digitizers for positron-lifetime spectroscopy. Nucl. Instrum. Methods Phys. Res. Sect. A. 2005;539:372–385. doi: 10.1016/j.nima.2004.09.031. DOI

Čížek J. PLRF code for decomposition of positron lifetime spectra. Acta Phys. Pol. A. 2020;137:177–187. doi: 10.12693/APhysPolA.137.177. DOI

Puska MJ, Nieminen RM. Theory of positrons in solids and on solid surfaces. Rev. Mod. Phys. 1994;66:841–897. doi: 10.1103/RevModPhys.66.841. DOI

Puska MJ, Nieminen RM. Defect spectroscopy with positrons: a general calculational method. J. Phys. F Met. Phys. 1983;13:333–346. doi: 10.1088/0305-4608/13/2/009. DOI

Barbiellini B, Puska MJ, Torsti T, Nieminen RM. Gradient correction for positron states in solids. Phys. Rev. B. 1995;51:7341–7344. doi: 10.1103/PhysRevB.51.7341. PubMed DOI

Barbiellini B, et al. Calculation of positron states and annihilation in solids: A density-gradient-correction scheme. Phys. Rev. B. 1996;53:16201–16213. doi: 10.1103/PhysRevB.53.16201. PubMed DOI

Zuo H-W, Lu C-H, Ren Y-R, Li Y, Zhang Y-F, Chen W-K. Pt4 clusters supported on monolayer graphitic carbon nitride sheets for oxygen adsorption: A first-principles study. Acta Phys. Chim. Sin. 2016;32:1183–1190. doi: 10.3866/pku.Whxb201603032. DOI

Zhang X, Zhao M, Wang A, Wang X, Du A. Spin-polarization and ferromagnetism of graphitic carbon nitride materials. J. Mater. Chem. C. 2013;1:6265–6270. doi: 10.1039/C3TC31213E. DOI

Dias EM, Christoforidis KC, Francàs L, Petit C. Tuning thermally treated graphitic carbon nitride for H2 evolution and CO2 photoreduction: The effects of material properties and mid-gap states. ACS Appl. Energy Mater. 2018;1:6524–6534. doi: 10.1021/acsaem.8b01441. DOI

Zhang Y, et al. Synthesis and luminescence mechanism of multicolor-emitting g-C3N4 nanopowders by low temperature thermal condensation of melamine. Sci. Rep. 2013;3:1943. doi: 10.1038/srep01943. PubMed DOI PMC

Wu P, Wang J, Zhao J, Guo L, Osterloh FE. Structure defects in g-C3N4 limit visible light driven hydrogen evolution and photovoltage. J. Mater. Chem. A. 2014;2:20338–20344. doi: 10.1039/c4ta04100c. DOI

Liang X, et al. Graphitic carbon nitride with carbon vacancies for photocatalytic degradation of bisphenol A. ACS Appl. Nano Mater. 2019;2:517–524. doi: 10.1021/acsanm.8b02089. DOI

Wan L, Egerton RF. Preparation and characterization of carbon nitride thin films. Thin Solid Films. 1996;279:34–42. doi: 10.1016/0040-6090(95)08126-7. DOI

Mendes RG, et al. Tailoring the stoichiometry of C3N4 nanosheets under electron beam irradiation. Phys. Chem. Chem. Phys. 2021;23:4747–4756. doi: 10.1039/D0CP06518H. PubMed DOI

Sanagi MM, et al. Comparison of signal-to-noise, blank determination, and linear regression methods for the estimation of detection and quantification limits for volatile organic compounds by gas chromatography. J. AOAC Int. 2009;92:1833–1838. doi: 10.1093/jaoac/92.6.1833. PubMed DOI

Thomas A, et al. Graphitic carbon nitride materials: Variation of structure and morphology and their use as metal-free catalysts. J. Mater. Chem. 2008;18:4893. doi: 10.1039/b800274f. DOI

Komatsu T. The first synthesis and characterization of cyameluric high polymers. Macromol. Chem. Phys. 2001;202:19–25. doi: 10.1002/1521-3935(20010101)202:1<19::AID-MACP19>3.0.CO;2-G. DOI

Li Y, et al. C3N4 with engineered three coordinated (N3C) nitrogen vacancy boosts the production of 1O2 for Efficient and stable NO photo-oxidation. Chem. Eng. J. 2020;389:124421. doi: 10.1016/j.cej.2020.124421. DOI

Wu J, et al. Nitrogen vacancies modified graphitic carbon nitride: Scalable and one-step fabrication with efficient visible-light-driven hydrogen evolution. Chem. Eng. J. 2019;358:20–29. doi: 10.1016/j.cej.2018.09.208. DOI

Niu P, Liu G, Cheng H-M. Nitrogen vacancy-promoted photocatalytic activity of graphitic carbon nitride. J. Phys. Chem. C. 2012;116:11013–11018. doi: 10.1021/jp301026y. DOI

Giannakopoulou T, et al. Tailoring the energy band gap and edges’ potentials of g-C3N4/TiO2 composite photocatalysts for NOx removal. Chem. Eng. J. 2017;310:571–580. doi: 10.1016/j.cej.2015.12.102. DOI

Shen R, Liu W, Ren D, Xie J, Li X. Co1.4Ni0.6P cocatalysts modified metallic carbon black/g-C3N4 nanosheet Schottky heterojunctions for active and durable photocatalytic H2 production. Appl. Surf. Sci. 2019;466:393–400. doi: 10.1016/j.apsusc.2018.10.033. DOI

Kočí K, et al. Photocatalytic decomposition of methanol over La/TiO2 materials. Environ. Sci. Pollut. Res. 2018;25:34818–34825. doi: 10.1007/s11356-017-0460-x. PubMed DOI

Miller TL, Wolin MJ. Oxidation of hydrogen and reduction of methanol to methane is the sole energy source for a methanogen isolated from human feces. J. Bacteriol. 1983;153:1051–1055. doi: 10.1128/jb.153.2.1051-1055.1983. PubMed DOI PMC

Mogensen OE. Positron Annihilation in Chemistry. Springer; 1995.

Hugenschmidt C. Positrons in surface physics. Surf. Sci. Rep. 2016;71:547–594. doi: 10.1016/j.surfrep.2016.09.002. DOI

Tao SJ. Positronium annihilation in molecular substances. J. Chem. Phys. 1972;56:5499–5510. doi: 10.1063/1.1677067. DOI

Eldrup M, Lightbody D, Sherwood JN. The temperature dependence of positron lifetimes in solid pivalic acid. Chem. Phys. 1981;63:51–58. doi: 10.1016/0301-0104(81)80307-2. DOI