Efficient　degradation　of　sulfur　mustard　is　essential　owing　to　its　extreme　toxicity　and　widespread　use　as　a　chemical　warfare　agent.　However,　current　degradation　methods　often　lack　selectivity　and　generate　highly　toxic　by-products.　Herein,　we　demonstrate　an　approach　for　the　selective　photodegradation　of　a　sulfur　mustard　simulant　using　singlet　oxygen　(1O2)　produced　by　a　methylene　blue　(MB)-modified　UiO-66-(COOH)2　(UC,　a　classical　metal-organic　framework)　composite,　termed　as　MB@UC.　The　composite　was　prepared　via　adsorption　of　MB　onto　the　surface　of　UC　through　strong　electrostatic　interactions.　The　MB@UC　composite　demonstrates　high　1O2　generation,　enabling　selective　detoxification　of　a　sulfur　mustard　simulant　(2-chloroethyl　ethyl　sulfide)　into　relatively　non-toxic　sulfoxide,　with　a　half-life　of　1.8　minutes　under　ambient　conditions.　Compared　to　traditional　detoxifying　agents,　the　MB@UC　composite　offers　superior　selectivity,　rapid　degradation,　and　excellent　recyclability,　maintaining　its　performance　over　multiple　cycles.　This　work　presents　a　promising　strategy　for　the　development　of　advanced　heterogeneous　photosensitizers　for　the　detoxification　of　chemical　warfare　agents.　©　2025　The　Royal　Society　of　Chemistry.