1 2D Materials: catalysis applications, opportunities, and challenges 1 It has been discovered that two-dimensional (2D) materials possess tunable electronic properties and abundant active sites, making them ideal for catalysis. This comprehensive review examines the use of 2D materials as catalysts and catalyst supports in energy conversion and environmental remediation. This field is characterized by the ability to enhance catalytic activity and selectivity through the engineering of defects, heterostructures, and hybrid composites. Despite these advances, challenges remain in scaling up synthesis, achieving structural stability under reaction conditions, and translating laboratory discoveries into industrial applications. By developing advanced characterization techniques and understanding structure-activity relationships, we can fully exploit the potential of 2D materials for catalysis. 1 5 Bhekumuzi Sfundo Khanyile MRD-Tandetron Accelerator and Nanosciences African Network, iThemba LABS-National Research Foundation, P O Box 722, Somerset West, 7129, Western Cape Province Faculty of Applied Sciences, Mathematics and Physics, Cape Peninsula University of Technology, PO Box 1906, Bellville 7535 South Africa sfundob@gmail.com 2D Materials Catalysis Energy Conversion Environmental Remediation [1] F.R. Fan, R. Wang, H. Zhang, W. Wu, Emerging beyond-graphene elemental 2D materials for energy and catalysis applications, Chemical Society Reviews 50(19) (2021) 10983-11031.##[2] X. Mei, W. Xu, Recent advances in two-dimensional materials as catalysts for the electrochemical reduction of carbon dioxide, Iscience 26(12) (2023).##[3] L.X. Chen, Z.W. Chen, M. Jiang, Z. Lu, C. Gao, G. Cai, C.V. Singh, Insights on the dual role of two-dimensional materials as catalysts and supports for energy and environmental catalysis, Journal of Materials Chemistry A 9(4) (2021) 2018-2042.##[4] L. Zhao, B. Wang, R. Wang, A critical review on new and efficient 2D materials for catalysis, Advanced Materials Interfaces 9(29) (2022) 2200771.##[5] M.H. Shahavi, N. Ayrilmis, Advancements in Energy Storage: Exploring the Impact of Graphene Composites, Journal of Composites and Compounds 5(16) (2023) 208-209.##[6] Y. Yin, X. Kang, B. Han, Two-dimensional materials: synthesis and applications in the electro-reduction of carbon dioxide, Chemical Synthesis 2(4) (2022) N/A-N/A.##[7] D. Lu, X. Fu, D. Guo, W. Ma, S. Sun, G. Shao, Z. Zhou, Challenges and opportunities in 2D high‐entropy alloy electrocatalysts for sustainable energy conversion, SusMat 3(6) (2023) 730-748.##[8] D. Deng, K. Novoselov, Q. Fu, N. Zheng, Z. Tian, X. Bao, Catalysis with two-dimensional materials and their heterostructures, Nature nanotechnology 11(3) (2016) 218-230.##[9] C. Wang, S. Guan, H. Zhang, R. Shen, H. Yuan, B. Li, Perspectives on two-dimensional ultra-thin materials in energy catalysis and storage, APL Materials 11(5) (2023).##[10] L. Xu, R. Iqbal, Y. Wang, S. Taimoor, L. Hao, R. Dong, K. Liu, J. Texter, Z. Sun, Emerging two-dimensional materials: Synthesis, physical properties, and application for catalysis in energy conversion and storage, The Innovation Materials 2(1) (2024) 100060-1-100060-23.##[11] J. Deng, D. Deng, X. Bao, Robust catalysis on 2D materials encapsulating metals: concept, application, and perspective, Advanced Materials 29(43) (2017) 1606967.##[12] C. Tan, X. Cao, X.-J. Wu, Q. He, J. Yang, X. Zhang, J. Chen, W. Zhao, S. Han, G.-H. Nam, Recent advances in ultrathin two-dimensional nanomaterials, Chemical reviews 117(9) (2017) 6225-6331.##[13] F. Song, X. Hu, Exfoliation of layered double hydroxides for enhanced oxygen evolution catalysis, Nature communications 5(1) (2014) 4477.##[14] J. Di, J. Xiong, H. Li, Z. Liu, Ultrathin 2D photocatalysts: electronic‐structure tailoring, hybridization, and applications, Advanced materials 30(1) (2018) 1704548.##[15] A. Abdelaal, F. Banei, A. Fenti, N.A. Maryam, M. Martín Sómer, State of the art review of photocatalytic water treatment, Journal of Composites and Compounds 5(1) (2023).##[16] A.K. Singh, K. Mathew, H.L. Zhuang, R.G. Hennig, Computational screening of 2D materials for photocatalysis, The journal of physical chemistry letters 6(6) (2015) 1087-1098.##[17] Q. Liang, Z. Li, Z.H. Huang, F. Kang, Q.H. Yang, Holey graphitic carbon nitride nanosheets with carbon vacancies for highly improved photocatalytic hydrogen production, Advanced Functional Materials 25(44) (2015) 6885-6892.##[18] X. Yua, W. Lianga, C. Xinga, K. Chena, J. Chena, W. Huangd, N. Xiea, M. Qiue, X. Yanb, Z. Xiea, Rising 2D pnictogens for catalytic applications: Status and challenges, Journal of 6(12) (2018) 4883-5230.##[19] Y. Guo, K. Xu, C. Wu, J. Zhao, Y. Xie, Surface chemical-modification for engineering the intrinsic physical properties of inorganic two-dimensional nanomaterials, Chemical Society Reviews 44(3) (2015) 637-646.##[20] X. Sun, L. Shi, H. Huang, X. Song, T. Ma, Surface engineered 2D materials for photocatalysis, Chemical Communications 56(75) (2020) 11000-11013.##[21] R.K. Chava, J.Y. Do, M. Kang, Smart hybridization of Au coupled CdS nanorods with few layered MoS2 nanosheets for high performance photocatalytic hydrogen evolution reaction, ACS Sustainable Chemistry and Engineering 6(5) (2018) 6445-6457.##[22] S.S. Varghese, S.H. Varghese, S. Swaminathan, K.K. Singh, V. Mittal, Two-dimensional materials for sensing: graphene and beyond, Electronics 4(3) (2015) 651-687.##[23] Y.S. Cho, J. Kang, Two-dimensional materials as catalysts, interfaces, and electrodes for an efficient hydrogen evolution reaction, Nanoscale 16(8) (2024) 3936-3950.##[24] M.A. Basyooni-M. Kabatas, A comprehensive review on electrocatalytic applications of 2D metallenes, Nanomaterials 13(22) (2023) 2966.##[25] Y. Xiao, Theoretical Screening of 2D Materials as High-Efficiency Catalysts for Energy Conversion and Storage Applications, (2022).##[26] H. Meskher, A critical review about metal organic framework-based composites: Potential applications and future perspective, Journal of Composites and Compounds 5(14) (2023) 25-37.##[27] S. Bahadori, M. Sharifianjazi, S. Eskandarinezhad, Photodegradation of Ciprofloxacin, Acetaminophen, and Carbamazepine using g-C3N4-based materials for water treatment, Journal of Composites and Compounds 5(15) (2023) 125-139.##[28] P.K. Sahoo, S.R. Bisoi, Y.-J. Huang, D.-S. Tsai, C.-P. Lee, 2D-layered non-precious electrocatalysts for hydrogen evolution reaction: fundamentals to applications, Catalysts 11(6) (2021) 689.##[29] A. Valluvar Oli, Z. Li, Y. Chen, A. Ivaturi, Near-ultraviolet indoor black light-harvesting perovskite solar cells, ACS Applied Energy Materials 5(12) (2022) 14669-14679.##[30] V. Arivazhagan, F. Gun, R.K.K. Reddy, T. Li, M. Adelt, N. Robertson, Y. Chen, A. Ivaturi, Indoor light harvesting lead-free 2-aminothiazolium bismuth iodide solar cells, Sustainable Energy and Fuels 6(13) (2022) 3179-3186.##[31] H. Tao, Q. Fan, T. Ma, S. Liu, H. Gysling, J. Texter, F. Guo, Z. Sun, Two-dimensional materials for energy conversion and storage, Progress in Materials Science 111 (2020) 100637.##[32] X.-F. Yang, A. Wang, B. Qiao, J. Li, J. Liu, T. Zhang, Single-atom catalysts: a new frontier in heterogeneous catalysis, Accounts of chemical research 46(8) (2013) 1740-1748.##[33] X. Duan, K. O'Donnell, H. Sun, Y. Wang, S. Wang, Sulfur and nitrogen co‐doped graphene for metal‐free catalytic oxidation reactions, Small 11(25) (2015) 3036-3044.##[34] G. Liao, S. Chen, X. Quan, H. Yu, H. Zhao, Graphene oxide modified gC 3 N 4 hybrid with enhanced photocatalytic capability under visible light irradiation, Journal of Materials Chemistry 22(6) (2012) 2721-2726.##[35] F. Schedin, A.K. Geim, S.V. Morozov, E.W. Hill, P. Blake, M.I. Katsnelson, K.S. Novoselov, Detection of individual gas molecules adsorbed on graphene, Nature materials 6(9) (2007) 652-655.##[36] S. Rumyantsev, G. Liu, M.S. Shur, R.A. Potyrailo, A.A. Balandin, Selective gas sensing with a single pristine graphene transistor, Nano letters 12(5) (2012) 2294-2298.##[37] S.G. Chatterjee, S. Chatterjee, A.K. Ray, A.K. Chakraborty, Graphene–metal oxide nanohybrids for toxic gas sensor: A review, Sensors and Actuators B: Chemical 221 (2015) 1170-1181.##[38] G.K. Walia, D.K.K. Randhawa, Density-functional study of hydrogen cyanide adsorption on silicene nanoribbons, Journal of Molecular Modeling 24 (2018) 1-5.##[39] S. Zhou, W. Pei, J. Zhao, A. Du, Silicene catalysts for CO 2 hydrogenation: the number of layers controls selectivity, Nanoscale 11(16) (2019) 7734-7743.##[40] K. Novoselov, S. Morozov, T. Mohinddin, L. Ponomarenko, D.C. Elias, R. Yang, I. Barbolina, P. Blake, T. Booth, D. Jiang, Electronic properties of graphene, physica status solidi (b) 244(11) (2007) 4106-4111.##[41] J. Shim, H.Y. Park, D.H. Kang, J.O. Kim, S.H. Jo, Y. Park, J.H. Park, Electronic and optoelectronic devices based on two‐dimensional materials: From fabrication to application, Advanced Electronic Materials 3(4) (2017) 1600364.##[42] K. Khan, A.K. Tareen, M. Aslam, R. Wang, Y. Zhang, A. Mahmood, Z. Ouyang, H. Zhang, Z. Guo, Recent developments in emerging two-dimensional materials and their applications, Journal of Materials Chemistry C 8(2) (2020) 387-440.##[43] J. Xie, X. Yang, Y. Xie, Defect engineering in two-dimensional electrocatalysts for hydrogen evolution, Nanoscale 12(7) (2020) 4283-4294.##[44] T.A. Shifa, F. Wang, Y. Liu, J. He, Heterostructures based on 2D materials: a versatile platform for efficient catalysis, Advanced Materials 31(45) (2019) 1804828.##[45] J. Mei, T. Liao, Z. Sun, 2D/2D heterostructures: rational design for advanced batteries and electrocatalysis, Energy and Environmental Materials 5(1) (2022) 115-132.##[46] A. Chaves, J.G. Azadani, H. Alsalman, D. Da Costa, R. Frisenda, A. Chaves, S.H. Song, Y.D. Kim, D. He, J. Zhou, Bandgap engineering of two-dimensional semiconductor materials, npj 2D Materials and Applications 4(1) (2020) 29.##[47] M. Zhao, Y. Hao, C. Zhang, R. Zhai, B. Liu, W. Liu, C. Wang, S.H.M. Jafri, A. Razaq, R. Papadakis, Advances in two-dimensional materials for optoelectronics applications, Crystals 12(8) (2022) 1087.##[48] X. Yin, Y. Hua, Z. Gao, Two-dimensional materials for high-performance oxygen evolution reaction: Fundamentals, recent progress, and improving strategies, Renewables 1(2) (2023) 190-226.##[49] S. Hao, X. Zhao, Q. Cheng, Y. Xing, W. Ma, X. Wang, G. Zhao, X. Xu, A mini review of the preparation and photocatalytic properties of two-dimensional materials, Frontiers in Chemistry 8 (2020) 582146.##[50] K.R.G. Lim, A.D. Handoko, S.K. Nemani, B. Wyatt, H.-Y. Jiang, J. Tang, B. Anasori, Z.W. Seh, Rational design of two-dimensional transition metal carbide/nitride (MXene) hybrids and nanocomposites for catalytic energy storage and conversion, ACS nano 14(9) (2020) 10834-10864.##[51] Z. Wang, Q. Jingjing, X. Wang, Z. Zhang, Y. Chen, X. Huang, W. Huang, Two-dimensional light-emitting materials: preparation, properties and applications, Chemical Society Reviews 47(16) (2018) 6128-6174.##[52] K. Khan, A.K. Tareen, M. Aslam, R.U.R. Sagar, B. Zhang, W. Huang, A. Mahmood, N. Mahmood, K. Khan, H. Zhang, Recent progress, challenges, and prospects in two-dimensional photo-catalyst materials and environmental remediation, Nano-Micro Letters 12 (2020) 1-77.##[53] X. Lu, K. Xu, S. Tao, Z. Shao, X. Peng, W. Bi, P. Chen, H. Ding, W. Chu, C. Wu, Engineering the electronic structure of two-dimensional subnanopore nanosheets using molecular titanium-oxide incorporation for enhanced photocatalytic activity, Chemical Science 7(2) (2016) 1462-1467.##[54] X. Xia, B. Li, S. Liu, B. Tang, Recent advances and challenges in 2D metal-free electrocatalysts for N2 fixation, Frontiers in Chemistry 8 (2020) 437.