A multi-dimensional (1D/2D/3D) carbon/g-C3N4 composite photocatalyst (CCN) was successfully prepared by a facile method with carbon from cheap absorbent cotton wool. The activities and stabilities of CCN were evaluated by photo-degrading Rhodamine B (RhB) under visible light irradiation. The effect of carbon content in composite on the catalytic activities was investigated. The results show that a good interfacial contact can be observed between g-C3N4 and carbon materials in CCN. It reveals an enhanced photocatalytic activity in photocatalytic decomposition of RhB compared with g-C3N4. The carbon content has obvious effect on the performance of CCN, and the optimal carbon content in CCN is 1 wt% (CCN1.0). The first-order rate constant (k) of CCN1.0 is approximately 5.5 and 3.4 times those of g-C3N4 and AC1.0/gC(3)N(4). The CCN1.0 catalyst also shows the excellent photocatalytic stability in the recycling experiments. The enhanced catalytic performance of CCN is mainly due to an increase in electron-hole pair separation efficiency and visible light adsorption after coupling carbon. The hole and center dot O2- radicals are the main active species, and center dot O2- plays a more important role than h(+). The photocatalytic mechanism over CCN1.0 was proposed. This work will provide a new insight to prepare highly-efficient g-C3N4-based photocatalysts. (C) 2020 Elsevier Inc. All rights reserved.