Atomic layer deposition (ALD) is proposed to synthesize ZnS-coated g-C3N4 photocatalysts which form an effective heterojunction for charge separation by reducing carrier recombination. It also, enables decrease in processing time from few days to several hours and circumvents collection process of synthesized powder which leads improvement in the productivity. In ZnS/g-C3N4 heterojunction composite, ZnS quantum-dots are uniformly distributed on g-C3N4 rather than conformal ZnS film due to hydrophobic nature of g-C3N4 surface. Photocatalytic activity of the ZnS/g-C3N4 heterojunction composites is enhanced up to 2.6 times compared to pristine g-C3N4 by tailoring ZnS ALD cycles. A range of ALD cycles from 2 to 50 have applied, out of which 5 cycles are found optimum for best efficiency, above and below 5 cycles it becomes either saturated or less potent, respectively. (C) 2017 Elsevier B.V. All rights reserved.