Photocatalytic transition-metal-oxides-based p–n heterojunction materials: synthesis, sustainable energy and environmental applications, and perspectives Vatika Soni, Pardeep Singh, Aftab Aslam Parwaz Khan, Arachana Singh, Ashok Kumar Nadda, Chaudhery Mustansar Hussain, Quyet Van Le, Stanislav Rizevsky, Van-Huy Nguyen, Pankaj Raizada*, 10.1007/s40097-021-00462-1 XML