The present investigation examined how substituting some Cu²⁺ ions for Zn²⁺ ions could increase zinc oxide (ZnO) photocatalytic activity toward the reduction of Rhodamine B. Phase composition, the presence of functional groups, optical properties, emission spectra, and surface morphology of ZnO nanoflakes (NFs) were evaluated using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), UV-visible spectroscopy (UV-vis), photoluminescence (PL) spectrophotometer, and scanning electron microscopy (SEM). To investigate the photocatalytic capabilities of Cu-doped ZnO NFs driven by visible light/sunlight, Rhodamine B dyes were photocatalytically degraded in water using UV-visible absorption spectroscopy. Using Williamson-Hall analysis of the XRD data, it was discovered that the internal strain of the Cu-doped ZnO NFs was altered. UV-vis absorption showed that the energy gap of the semiconducting ZnO NFs shrank when Cu was substituted. FT-IR studies revealed that the surface of the Cu-doped ZnO NFs contained greater amounts of reactive oxidizing species. PL studies revealed that the ZnO NFs' surface defects were being caused by the Cu substitution. According to SEM research, more surface fault NFs formed when the concentration of Cu increased. The photocatalytic activity was enhanced by the production of these NFs. The UV-vis absorption spectra showed that Cu-doped ZnO NFs were more effective than pure ZnO at degrading the rhodamine B dye (RhB). Finally, it was shown that replacing Zn²⁺ ions with Cu²⁺ ions improved the photodegradation of the rhodamine B dye. According to this study, Cu-doped ZnO NFs are an excellent choice for wastewater treatment.

Three-dimensional hierarchical mesoporous structures of titanium dioxide (3D-HPT) were synthesized by self-assembly emulsion polymerization. Polymethyl methacrylate (PMMA) and pluronic 123 (P123) were used as the soft templates and co-templates for assisting the formation of hierarchical 3D porous structures. The TiO₂ crystal structure, morphology, and Remazol red dye degradation were investigated. The 3D-HPT and normal three-dimensional titanium dioxide (3D-T) presented the good connection of the nanoparticle-linked honeycomb within the form of anatase. The 3D-HPT structure showed greatly enhanced adsorption of Remazol dye, and facilitated the efficient photocatalytic breakdown of the dye. Surprisingly, 3D-HPT can adsorb approximately 40% of 24 ppm Remazol dye in the dark, which is superior to 3D-T and the commercial anatase at the same condition (approx. 5%). Moreover, 3D-HPT can completely decolorize Remazol dye within just 20 min, which is more than three folds faster than the commercial anatase, making it one of the most active photocatalysts that have been reported for degradation of Remazol dye. The superior photocatalytic performance is attributed to the higher specific surface area, amplified light-harvesting efficiency, and enhanced adsorption capacity into the hierarchical 3D inverse opal structure compared to the commercial anatase TiO₂.

A bifunctional oxygen evolution reaction and oxygen reduction reaction (OER/ORR) electrocatalyst, macroporous cerium‐doped LaCoO₃, was designed based on a dual strategy that included (1) constructing a three‐dimensionally ordered macroporous (3DOM) structure to increase the electrochemical surface area and (2) varying amount of cerium substitution from 0.02 to 0.15 mole fraction of the A site to alter the intrinsic activity of LaCoO₃. The catalytic activity of 3DOM La_0.95Ce_0.05CoO₃ (3DOM LCCO‐0.05) is significantly improved over that of the unmodified LaCoO₃, with the OER overpotential to reach 10 mA cm⁻² lowered by 190 mV, the ORR limiting current density doubled, and the OER‐ORR potential gap reduced by 220 mV to 1.07 V. This enhanced activity is attributed to the increased electrochemical surface area and specific activity, as evidenced by the greater double‐layer capacitances and the lower charge transfer resistances determined by electrochemical impedance spectroscopy (EIS). Furthermore, X‐ray diffraction (XRD) and X‐ray photospectroscopy (XPS) results reveal that these enhanced OER/ORR activities are possibly related to the transformation of the cobalt(III) spin state from low to intermediate or high‐spin, and the increasing amount of surface oxygen species and oxygen vacancies.