OICC Press Journal of Nanostructure in Chemistry 2193-8865 13 2 (April 2023) 2022 01 11 Photocatalytic transition-metal-oxides-based p–n heterojunction materials: synthesis, sustainable energy and environmental applications, and perspectives 10.1007/s40097-021-00462-1 EN Vatika Soni School of Advanced Chemical Sciences, Faculty of Basic Sciences, Shoolini University, Solan, Himachal Pradesh, 173229, IN Pardeep Singh School of Advanced Chemical Sciences, Faculty of Basic Sciences, Shoolini University, Solan, Himachal Pradesh, 173229, IN Aftab Aslam Parwaz Khan Center of Excellence for Advanced Materials Research, King Abdulaziz University, Jeddah, 21589, SA Chemistry Department, Faculty of Science, King Abdulaziz University, Jeddah, 21589, SA Arachana Singh Advanced Materials and Processes Research Institute, Bhopal, Madhya Pradesh, 462026, IN Ashok Kumar Nadda Department of Biotechnology and Bioinformatics, Jaypee University of Information Technology, Solan, Himachal Pradesh, 173 234, IN Chaudhery Mustansar Hussain Department of Chemistry and Environmental Science, New Jersey Institute of Technology, Newark, NJ, 07102, US Quyet Van Le Department of Materials Science and Engineering, Korea University, Seoul, 02841, KR Stanislav Rizevsky Biology Faculty, Belarusian State University, Minsk, BY Faculty of Biotechnology, Binh Duong University, Thu Dau Mot, VN Van-Huy Nguyen Faculty of Biotechnology, Binh Duong University, Thu Dau Mot, VN Pankaj Raizada School of Advanced Chemical Sciences, Faculty of Basic Sciences, Shoolini University, Solan, Himachal Pradesh, 173229, IN Journal Article 2022 01 11 Abstract In recent years, photocatalysis has gained particular attention due to its crucial potential applications in addressing many essential energy and environmental challenges. Considerable efforts have been devoted to developing photocatalysts to understand the fundamental processes and enhance photocatalytic efficiencies. The rate of photoinduced e − –h + reassembly is one of the difficulties encountered in semiconductor photocatalysis. Various alternative photosystems were designed to overcome this problem and thereby improve the efficiency of the heterojunction photocatalyst. Among the explored methods, the charge carrier separation using a built-in electric field attracts considerable attention as a new concept. The present review highlights the development of p–n heterojunctions to overcome the existing challenges in rigorously explored type-I, II, and III heterojunctions. Herein, reports on widely explored TiO 2 , ZnO, and various other transition metal oxides based p–n heterojunctions are extensively deliberated. This review pinpoints the benefits of constructing p–n junctions, including their impact on optical absorption, physical, and chemical properties over other n–n and p–p heterojunctions. The mechanistic route followed to construct effective p–n heterojunction and practical work carried out by generated internal electric field in isolating the charge carriers is also highlighted. Transition-metal-oxides based p–n heterojunction shows promising practical applications in various fields, including H 2 evolution, CO 2 reduction, overall water splitting, photo-reforming, and photodegradation of harmful pollutants. The various challenges and future perspectives for developing metal oxides-based p–n heterojunction materials are also summarized. Graphical abstract