Synthesis of geopolymer spheres with photocatalytic activity Patricia Isabel Bravo, Roy Alvin Malenab, Eiza Shimizu, Derrick Ethelbhert Yu and Michael Angelo Promentilla MATEC Web Conf., 268 (2019) 04007 Published online: 20 February 2019 DOI: 10.1051/matecconf/201926804007