It　is　of　vital　significance　to　explore　effective　and　economical　multifunctional　materials　for　the　detection,　remediation　and　recycling　of　heavy　metal　(Cr(VI)).　Herein,　two-dimensional　(2D)　phenyl-modified　carbon　nitride　(PCN)　polymer　was　prepared　through　thermal　polymerization　of　phenylguanidine　carbonate.　The　incorporation　of　phenyl　groups　endowed　PCN　polymer　with　both　strong　green　fluorescence　and　high　photocatalytic　activity　for　the　reduction　of　Cr(VI).　An　multifunctional　gel　for　simultaneous　detection,　adsorption,　photo-reduction　and　recycling　of　Cr(VI)　was　further　prepared　by　assembling　PCN　with　polyethyleneimine–N,N’-methylenebisacrylamide　(PEI-MBA)　gel.　PCN-PEI-MBA　gel　showed　a　sensitive　fluorescence　/　colorimetric　dual-mode　detection　of　Cr(VI).　Meanwhile,　PCN-PEI-MBA　gel　displayed　preeminent　adsorption　capacity　of　3055.9　mg　g−1,　surpassing　previously　reported　adsorbents.　Under　visible-light　irradiation,　the　absorbed　Cr(VI)　in　PCN-PEI-MBA　gel　was　photocatalytically　reduced　into　Cr(III)　with　visual　real-time　monitoring　the　detoxification　process　and　Cr(III)　can　be　further　recycled　as　Cr2O3　by　calcination　of　PCN-PEI-MBA　gel.　Finally,　PCN-PEI-MBA　gel　was　utilize　to　adsorb　and　recycle　Cr(VI)　from　the　chromium-plating　wastewater　and　detect　the　concentration　of　remaining　Cr(VI)　in　the　wastewater.　This　work　provides　an　all-in-one　treatment　strategy　for　the　detection,　remediation　and　resource　recycling　of　Cr(VI)　in　practical　wastewater.　©　2024　Elsevier　B.V.