苯甲醛是一类重要化学品，在医药、化学合成和食品等领域具有广泛应用。然而，苯甲醛的生产过程通常涉及三氟甲苯或乙腈等危险溶剂的使用，并且，苯甲醛在水相反应体系中的转化率，尤其是选择性一直是难点。因此，开发一种环境友好的苯甲醛合成工艺具有极其重要的意义。在本文中，我们通过在磷酸功能化的石墨相氮化碳（g-C₃N₄）纳米片上负载磷钨酸成功制备了新型光催化剂（PW₁₂-P-UCNS，其中，PW₁₂为H₃PW₁₂O₄₀·xH₂O，P-UCNS为磷酸修饰的超薄石墨相氮化碳）。选取水相中苯甲醇光氧化制备苯甲醛的反应为模型反应，在室温条件下，对PW₁₂-P-UCNS的催化性能进行了系统探究。所制备的PW₁₂-P-UCNS光催化剂在2 h内的转化率为58.3%，选择性为99.5%，可重复使用5次以上，且活性未发生明显损失。同时，本文揭示了PW₁₂-P-UCNS催化模型反应的Z型机理，系统分析了催化剂的光电流和光化学阻抗性能，并通过电子自旋共振测试和自由基捕获实验证明了超氧自由基和光生空穴是其主要反应活性物质。基于此，所设计的PW₁₂-P-UCNS光催化剂对于在温和条件下通过水相光氧化反应生产苯甲醛具有广阔的应用前景。

Benzaldehyde is a highly desirable chemical due to its extensive application in medicine, chemical synthesis and food sector among others. However, its production generally involves hazardous solvents such as trifluorotoluene or acetonitrile, and its conversion, especially selectivity in the aqueous phase, is still not up to expectations. Hence, developing an environmentally benign, synthetic process for benzaldehyde production is of paramount importance. Herein, we report the preparation of a photocatalyst (PW₁₂-P-UCNS, where PW₁₂ is H₃PW₁₂O_40·xH₂O and P-UCNS is phosphoric acid-modified unstack graphitic carbon nitride) by incorporating phosphotungstic acid on phosphoric acid-functionalised graphitic carbon nitride (g-C₃N₄) nanosheets. The performance of PW₁₂-P-UCNS was tested using the benzyl alcohol photo-oxidation reaction to produce benzaldehyde in H2O, at room temperature (20 °C). The asprepared PW₁₂-P-UCNS photocatalyst showed excellent photocatalytic performance with 58.3% conversion and 99.5% selectivity within 2 h. Moreover, the catalyst could be reused for at least five times without significant activity loss. Most importantly, a proposed Z-scheme mechanism of the PW₁₂-P-UCNScatalysed model reaction was revealed. We carefully investigated its transient photocurrent and electrochemical impedance, and identified superoxide radicals and photogenerated holes as the main active species through electron spin-resonance spectroscopy and scavenger experiments. Results show that the designed PW₁₂-P-UCNS photocatalyst is a highly promising candidate for benzaldehyde production through the photo-oxidation reaction in aqueous phase, under mild conditions.