Separation and migration of the charge carriers to the surface of semiconductor catalysts are of fundamental importance for efficient photocatalytic reactions. The interior recombination of charge carriers is detrimental to photocatalytic efficiency of catalysts. Reduction in particle size of catalysts in principle promotes charge transport to surface by shortening the migration path. The quantum size is promising for dissociating excitons into free electrons and holes in three spatial dimensions. Herein, we report the quantum-size titania (Q-TiO2) particles (2-3 nm) synthesized via a microwave-assisted rout. Combining quantum size and molecular-semiconductor interfacial effect enables more reactive sites exposure and greatly promotes charge transport from interior to surface of Q-TiO2. Hence, the Q-TiO2 catalyst gave rise to significantly improved photocatalytic performances with visible light (lambda > 420 nm): bacteria (E. soli) disinfection and organic pollutant (RhB) degradation. Taken together, this finding highlights the key importance of specific surface states to take into account high charge-carrier transfer and separation for photocatalytic environmental remediation. (C) 2017 Elsevier B.V. All rights reserved.