* Corresponding authors

^a School of Energy and Environment, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong, China
E-mail: jinshang@cityu.edu.hk
Fax: +852 3442 0688
Tel: +852 3442 7714

^b State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of Chemistry, Jilin University, Changchun 130012, China
E-mail: lijiyang@jlu.edu.cn, jihong@jlu.edu.cn
Fax: +86 431 8516 8608
Tel: +86 431 8516 8608

^c City University of Hong Kong Shenzhen Research Institute, 8 Yuexing 1st Road, Shenzhen Hi-Tech Industrial Park, Nanshan District, Shenzhen, China

^d The Australian Synchrotron (ANSTO), 800 Blackburn Road, Clayton, VIC 3168, Australia

^e Korea Biochar Research Center, O-Jeong Eco-Resilience Institute (OJERI) & Division of Environmental Science and Ecological Engineering, Korea University, Seoul 02841, Republic of Korea

^f Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, China
E-mail: dan.tsang@polyu.edu.hk
Fax: +852 2334 6389
Tel: +852 2766 6045