Carbon nanomaterials are prominent building blocks in the synthetic van der Waals (vdW) heterostructures with desired properties. Scientific understanding of their interfacial interactions is the premise to design this kind of vdW heterostructures with optimal performance. We here study the mechanism of enhanced photocatalytic activity of SnO2 by fullerene modification at electronic level, to explore the interfacial interaction and its correlation with photocatalytic activity. The results show that the interfacial interaction increases with the number of C atom of fullerene, and leads to some of C atoms be positively/negatively charged, making the fullerene a highly active co-catalyst in heterostructures. Compared to pristine SnO2, the band gap of the heterostructures is much smaller, leading to their absorption wavelength extending the entire visible region. Interestingly, a staggered type-II band alignment in the C-20 (C-60)/SnO2 (101) heterostructures results into the robust separation of photoexcited charge carriers between the two constituents, indicating that the fullerene is an effective sensitizer, and thus enhanced photocatalytic activity. These findings can rationalize the available experiment and will be of broad interest in developing the highly efficient semiconductor photocatalysts via fullerene modification. (C) 2017 Elsevier B.V. All rights reserved.