Seeking effective strategy to design multifunctional materials for pollutant removal and solar fuel production is of great significance for solving the worldwide environment and energy problems. In this work, two-dimensional porous graphite-like carbon nitride (p-g-C3N4) nanosheets (NSs) decorated with three-dimensional (3D) hierachical TiO2 microflowers (MFs) were constructed through a facile acid hydrothermal route. 3D TiO2 MFs originating from K2Ti6O13 nanobelts were combined with p-g-C3N4 NSs via solid interfacial connections. By chemical exfoliation and etching, the surface area of g-C3N4 was significantly increased along with the formation of porous structures and C vacancies. Interestingly, the hydrothermally produced two-dimensional (2D) p-g-C3N4 NSs showed extraordinarily selective adsorption towards anionic methyl orange via strong electrostatic attraction. More importantly, such 3D/2D TiO2/p-g-C3N4 micro-nano heteroarchitectures exhibited remarkably improved visible-light photocatalytic properties for antibiotic degradation and CO2 reduction, mainly attributed to the enlarged surface areas and pore volumes, increased adsorption/active sites, improved light absorption and higher separation efficiency of photogenerated charge carriers. This one-pot synthesis method opens new possibilities for rational design of multifunctional g-C3N4-based photocatalysts towards environmental purification and solar energy conversion.