Photocatlytic decomplexation provides an effective way to tackle the problem of heavy metal contamination. By far, the exploration of more efficient photocatalysts with low environmental risk is still an important but challenging issue. In this study, the feasibility of using metal-free carbon nitride as environmental-friendly catalysts for photocatalytic decomplexation was demonstrated, using Cu(II)-EDTA as a model contaminant. A facile oxygen doping strategy could significantly enhance the interfacial separation of photogenerated holes, which was determined to be the most effective reactive species for decomplexation reactions. Compared to pristine g-C3N4, oxygen doped sample exhibited 2.5-fold enhanced photoactivity. The hypothesis of using decomplexation solution as sustainable resource for fabricating copper modified photocatalysts was further investigated. The in-situ formation of Cu or Cu2O resulted in the significantly improved activity for hydrogen evolution over recycled photocatalysts. According to the component analysis, chemical reduction strategy was beneficial for the sufficient recovery of copper ions, while the photoreduction method led to the most efficient utilization of copper metals. This study not only presents a promising method for the treatment of heavy metal-contaminated water, but also provides a sustainable way to utilize decomplexation solution as valuable resource for clean energy production.