1. Cambridge Institute for Sustainability Leadership (CISL), University of Cambridge , Cambridge, CB2 1QA , UK
2. Energy and Climate Change Division, Faculty of Engineering and Physical Science, The University of Southampton , Southampton, SO17 1BJ , UK
3. Institute of Engineering Research and Material Technology, National Centre for Research , Khartoum , Sudan / , Sudan
4. University of Khartoum , Khartoum , Sudan / , Sudan
5. University of California , Davis, 1 Shields Ave, Davis, CA 95616 , USA
6. School of Chemistry, Faculty of Engineering and Physical Sciences, The University of Southampton , Southampton, SO17 1BJ , UK