Display omitted •Mesoporous Ag3VO4/C3N4 heterojunction photocatalysts was performed via a sol–gel.•The Hg(II) reduction was completely achieved within 60 min through illumination.•2.4%Ag3VO4/C3N4 photocatalyst indicated much better photoreduction performance.•It was 4.3 and 5.4 fold larger Hg(II) reduction than that Ag3VO4 NPs and g-C3N4.•Mesoporous Ag3VO4/C3N4 showed high stability and recyclability for five times runs. A facile and highly efficient mesoporous Ag3VO4/C3N4 heterojunction photocatalysts were synthesized by accommodating Ag3VO4 nanoparticles (NPs) onto the porous g-C3N4 nanosheets. The findings showed that mesoporous Ag3VO4 NPs uniformly disseminated onto the g-C3N4 with a small particle size (5 nm). Compared to pristine g-C3N4 and Ag3VO4 NPs, the mesoporous Ag3VO4/C3N4 photocatalysts displayed much higher photocatalytic Hg(II) reduction. It was found that among all the synthesized nanocomposites, the synthetic mesoporous 2.4%Ag3VO4/C3N4 photocatalyst indicated much better photoreduction performance. The Hg(II) reduction was completely achieved within 60 min (100%) through illumination by visible light, which was 4.3 and 5.4 fold larger photocatalytic performance than that Ag3VO4 NPs and g-C3N4, in that order. The enhancement Hg(II) reduction performance of mesoporous Ag3VO4/C3N4 photocatalysts could be explained by a synergetic effect of S-scheme heterojunction structure with high surface area and promotion light harvest, suggesting to efficacious of the photoinduced charges separation. The recycling performance of the nanocomposites exhibited superior stability, durability and reusability. S-scheme charge transfer route accomplished of mesoporous Ag3VO4/C3N4 with improved stronger redox ability and separation of photoinduced carriers. This research work clarifies an outstanding approach to promote a novel and facile S-scheme photocatalytic system to oxidize environmental contaminants and reduce toxic heavy metals.