Cr-Doped CuTi-Layered Double Hydroxide Nanoarchitectures Grown on 3D Ni Foam: Boosting Charge Separation for Photocatalytic Mineralization of Refractory Organics

Immobilized photocatalytic membranes that integrate efficient charge separation with structural robustness are highly desirable for the sustainable removal of refractory organic pollutants, yet they remain challenging to construct due to limited interfacial activity and sluggish carrier transport. Herein, Cr-doped CuTi-layered double hydroxide (Cr-CuTi-LDH) nanoarchitectures are rationally grown in situ on three-dimensional nickel foam (NF) via a facile one-step hydrothermal strategy, yielding a self-supported photocatalytic membrane with intimate interfacial contact and enhanced electronic conductivity. Chromium incorporation induces pronounced nanosheet refinement and ordered stacking, which effectively regulates nucleation kinetics, maximizes accessible surface sites, and promotes the separation and migration of photogenerated charge carriers. Systematic photoelectrochemical analyses, including electrochemical impedance spectroscopy, transient photocurrent response, and Mott–Schottky measurements, reveal that Cr doping significantly reduces charge-transfer resistance and facilitates electron–hole separation without substantially altering the bandgap structure. Benefiting from these interfacial and electronic advantages, the optimized Cr-CuTi-LDH/NF membrane exhibits significantly enhanced photocatalytic activity for the mineralization of Rhodamine B and Methylene Blue under simulated solar irradiation. It degraded 82.8% and 76.9% of Rhodamine B and Methylene Blue, respectively, within 180 min, while demonstrating excellent reaction kinetics and outstanding cycling stability. Mechanistic investigations indicate that the synergistic participation of photogenerated holes and superoxide radicals (•O2–), promoted by Cr-mediated charge regulation, dominates the degradation pathway. This work not only elucidates the critical role of heteroion doping in governing interfacial charge dynamics within LDH-based membranes, but also provides a scalable design paradigm for high-performance, recyclable photocatalytic systems for water purification.