Carbon‐Modified SnS ₂ /g‐C ₃ N ₄ S‐Scheme Heterostructure with Enhanced Interfacial Charge Transfer for Efficient Photocatalytic Reduction of Cr(VI) and 4‐Nitrophenol

Hexavalent chromium (Cr(VI)) and 4‐nitrophenol (4‐NP) are persistent and highly toxic water pollutants that require efficient treatment under mild conditions. In this work, L‐cysteine‐derived carbon‐modified SnS 2 (SnS 2 ‐C) was prepared hydrothermally and combined with urea‐derived g‐C 3 N 4 to form a 2D/2D heterostructure. CHNS analysis confirmed that SnS 2 ‐C contained 0.53 ± 0.01 wt.% carbon, while ToF‐SIMS depth profiling showed a stronger carbon signal than pristine SnS 2 , confirming successful carbon modification. Carbon modification induced lattice distortion and strain without altering the hexagonal SnS 2 structure and improved its dispersion on g‐C 3 N 4 . The SnS 2 ‐C/g‐C 3 N 4 heterostructure achieved 98.8% Cr(VI) reduction within 10 min (𝑘 app = 0.202 min − 1 ) and 96% 4‐NP reduction within 120 min (𝑘 app = 0.021 min − 1 ). Experimental characterization and density functional theory calculations indicate enhanced interfacial charge redistribution (∼1.03 e transfer) and stronger adsorption of Cr(VI) intermediates. Valence‐band XPS, optical band‐gap measurements, work‐function analysis, and DFT calculations consistently support a direct S‐scheme charge‐transfer pathway, which promotes efficient charge separation and preserves highly reducing electrons for the photocatalytic reduction of both Cr(VI) and 4‐NP. These findings show that carbon modification regulates interfacial electronic interactions and, together with S‐scheme charge separation, enhances photocatalytic reduction of inorganic and organic pollutants.