The　development　of　efficient　photocatalysts　for　the　degradation　of　organic　pollutants　and　production　of　hydrogen　peroxide　(H2O2)　is　an　attractive　two-in-one　strategy　to　address　environmental　remediation　concerns　and　chemical　resource　demands.　Graphitic　carbon　nitride　(g-C3N4)　possesses　unique　electronic　and　optical　properties.　However,　bulk　g-C3N4　suffers　from　inefficient　sunlight　absorption　and　low　carrier　mobility.　Once　exfoliated,　ultrathin　nanosheets　of　g-C3N4　attain　much　intriguing　photocatalytic　activity.　Herein,　a　mussel-inspired　strategy　is　developed　to　yield　silver-decorated　ultrathin　g-C3N4　nanosheets　(Ag@U-g-C3N4-NS).　The　optimum　Ag@U-g-C3N4-NS　photocatalyst　exhibits　enhanced　electrochemical　properties　and　excellent　performance　for　the　degradation　of　organic　pollutants.　Due　to　the　photoformed　valence　band　holes　and　selective　two-electron　reduction　of　O2　by　the　conduction　band　electrons,　it　also　renders　an　efficient,　economic,　and　green　route　to　light-driven　H2O2　production　with　an　initial　rate　of　0.75　×　10−6　m　min−1.　The　improved　photocatalytic　performance　is　primarily　attributed　to　the　large　specific　surface　area　of　the　U-g-C3N4-NS　layer,　the　surface　plasmon　resonance　effect　induced　by　Ag　nanoparticles,　and　the　cooperative　electronic　capture　properties　between　Ag　and　U-g-C3N4-NS.　Consequently,　this　unique　photocatalyst　possesses　the　extended　absorption　region,　which　effectively　suppresses　the　recombination　of　electron–hole　pairs　and　facilitates　the　transfer　of　electrons　to　participate　in　photocatalytic　reactions.　©　2019　WILEY-VCH　Verlag　GmbH　&　Co.　KGaA,　Weinheim