Visible light active MgO/g-C ₃ N ₄ composites for 4-nitrophenol degradation and selective oxidation of benzyl alcohol.

Despite their many advantages, issues remain unresolved over the variability in catalytic activities in supported gold nanoparticle (AuNP)-based catalysts, which requires precise characterization to unravel the presence of any fine features. Herein, upon analyzing the Au 4f core-level spin-orbit components in many as-synthesized AuNP-based catalysts, we observed that like deviations in the Au 4f_7/2 binding energy positions, both the Au 4f_7/2-to-Au 4f_5/2 peak intensity and linewidth ratios varied largely from the standard statistical bulk reference values. These deviations were observed in all the as-synthesized supported AuNPs irrespective of different synthesis conditions, variations in size, shape or morphology of the gold nanoparticles, and different support materials. On the other hand, the spin-orbit-splitting values remained almost unchanged and did not show any appreciable deviations from the atomic or bulk standard gold values. These deviations could originate due to alterations in the electronic band structures in the supported AuNPs and might be present in other NP-based catalyst systems as well, which could be the subject of future research interest.

The air annealing induced grain growth from nano to microscale and a transformation sequence from Bi → β-Bi₂O₃ → γ-Bi₂O₃ → α-Bi₂O₃ was evident. All the annealed samples are oxygen-deficient, resulting in the appearance of a strong red emission band.

As it is now well established that oxygen vacancies are spontaneously introduced during nitrogen doping of anatase ${\text{TiO}}_2$ , there is a lively debate on whether nitrogen dopant or oxygen vacancy contributes to the visible light photoactivity of the doped catalyst. We showed that the coordinately unsaturated Ti site is integral to the visible light photoactivity in anatase oxygen-deficient ${\text{TiO}}_2$ catalyst. Accordingly, oxygen vacancies may contribute to the visible light photoactivities in N-doped ${\text{TiO}}_2$ and other nonmetallic ion-doped ${\text{TiO}}_2$ as well. A redox active visible light photocatalyst has been developed based on oxygen-deficient structure in anatase ${\text{TiO}}_2$ .

In this study, Fe-doped graphitic carbon nitride (Fe-MCNC) with varying Fe contents was synthesized via a supramolecular approach, followed by thermal exfoliation, and was then used for accelerated photocatalytic hydrogen evolution and nitrogen fixation. Various techniques were used to study the physicochemical properties of the MCN (g-C₃N₄ from melamine) and Fe-MCNC (MCN for g-C₃N₄ and C for cyanuric acid) catalysts. The field emission scanning electron microscopy (FE-SEM) images clearly demonstrate that the morphology of Fe-MCNC changes from planar sheets to porous, partially twisted (partially developed nanotube and nanorod) nanostructures. The elemental mapping study confirms the uniform distribution of Fe on the MCNC surface. The X-ray photoelectron spectroscopy (XPS) and UV-visible diffuse reflectance spectroscopy (UV-DRS) results suggest that the Fe species might exist in the Fe³⁺ state and form Fe-N bonds with N atoms, thereby extending the visible light absorption areas and decreasing the band gap of MCN. Furthermore, doping with precise amounts of Fe might induce exfoliation and increase the specific surface area, but excessive Fe could destroy the MCN structure. The optimized Fe-MCNC nanostructure had a specific surface area of 23.6 m² g⁻¹, which was 8.1 times greater than that of MCN (2.89 m² g⁻¹). To study its photocatalytic properties, the nanostructure was tested for photocatalytic hydrogen evolution and nitrogen fixation; 2Fe-MCNC shows the highest photocatalytic activity, which is approximately 13.3 times and 2.4 times better, respectively, than MCN-1H. Due to its high efficiency and stability, the Fe-MCNC nanostructure is a promising and ideal photocatalyst for a wide range of applications.