Abstract: Enrichment of pollutants is a crucial step in the photocatalytic degradation of organic contaminants. Development of photocatalysts with both superior adsorption capacity and high photocatalytic activity is of great significance. In this work, a WO₃·H₂O/g-C₃N₄ (WH/CN) heterojunction was successfully constructed via a one-step hydrothermal method using g-C₃N₄ as the substrate. The structure and physicochemical properties of the WH/CN were systematically characterized by XRD, SEM, TEM, FTIR, XPS, UV-Vis DRS, and PL. The results revealed that nanosheet-structured WO₃·H₂O was uniformly anchored on the g-C₃N₄ lamellar surface, forming a compact heterostructure that effectively facilitated the separation of photogenerated carriers and enhanced visible-light absorption. Moreover, the incorporation of WO₃·H₂O introduced abundant oxygen-containing functional groups, which significantly improved the adsorption and enrichment of organic pollutants during the photocatalytic process. Specifically, when the molar ratio of Na₂WO₄·2H₂O to g-C₃N₄ was 1:5, the obtained WH1/CN5 composite exhibited equilibrium adsorption capacities of 48.2% for methylene blue (MB) and 20.3% for gaseous formaldehyde, much higher than those of pristine g-C₃N₄ (8.8% and 5.6%, respectively). Upon visible-light irradiation, WH1/CN5 also demonstrated superior photocatalytic activity, achieving an 85.9% degradation rate of MB within 30 min, and a degradation efficiency of 83.9% for formaldehyde after 4 h. Furthermore, the composite retained high catalytic efficiency over cyclic experiments, confirming its excellent stability. This study provides new insights and experimental evidence for the design of efficient visible-light-driven photocatalysts with synergistic adsorption-photocatalysis properties.