Photocatalytic　CO2　reduction　conjugated　with　H2O　oxidation　is　regarded　as　a　promising　artificial　photosynthesis　system　because　it　can　simultaneously　solve　energy　and　environment　problems.　Here,　a　novel　solid　solution,　Zn2Ti1−xGexO4　(0　≤　x　≤　0.15),　with　high　photocatalytic　activity　for　the　reaction　was　successfully　synthesized　via　a　facile　molten　salts　route.　The　Zn-based　solid　solutions　with　size　about　200　nm　have　a　homogeneous　inverted　cubic　spinel　structure　(Fd3m)　and　a　continuously　modulated　band　gap　with　the　Ge　content.　For　the　CO2　reduction　reaction　with　H2O　under　simulated　solar　irradiation,　the　Zn2Ti1−xGexO4　solid　solutions　display　not　only　high　activity　for　the　conversion　of　CO2　into　CH4　and　CO　fuels,　but　also　long-term　stability　(>60　h　of　catalytic　reaction).　Experimental　results　and　theoretical　calculations　indicated　that　the　conduction　and　the　valence　bands　of　the　cubic　spinel　Zn2TiO4　are　positively　shifted　by　introducing　Zn2GeO4　with　a　pseudocubic　inverse　spinel　structure,　but　the　band　gaps　of　solid　solutions　are　simultaneously　modulated　with　the　introduction　of　germanium.　Nevertheless,　the　Zn2TiO4　affords　a　light-carrier　effective　mass　and　strong　electron　delocalization　by　forming　a　solid　solution　with　Zn2GeO4,　which　is　beneficial　to　improving　migration　of　photogenerated　electrons　and　holes.　As　a　synergistic　result　of　band　gap　narrowing　and　high　carrier　diffusion,　good　conversion　efficiencies　for　production　of　solar　fuels　through　the　reactions　of　CO2　reduction　with　H2O　are　achieved.　©　2019　Elsevier　Inc.