Metal chlorides-catalyzed selective oxidation of cyclohexane by molecular oxygen under visible light irradiation

Phase-dependent photocatalytic selective oxidation of cyclohexane over copper vanadates

Three copper vanadates with different crystal phases show different abilities for selective oxidation of cyclohexane.

Photoelectrocatalytic C-H halogenation over an oxygen vacancy-rich TiO2 photoanode

Photoelectrochemical cells are emerging as powerful tools for organic synthesis. However, they have rarely been explored for C-H halogenation to produce organic halides of industrial and medicinal importance. Here we report a photoelectrocatalytic strategy for C-H halogenation using an oxygen-vacancy-rich TiO2 photoanode with NaX (X=Cl-, Br-, I-). Under illumination, the photogenerated holes in TiO2 oxidize the halide ions to corresponding radicals or X2, which then react with the substrates to yield organic halides. The PEC C-H halogenation strategy exhibits broad substrate scope, including arenes, heteroarenes, nonpolar cycloalkanes, and aliphatic hydrocarbons. Experimental and theoretical data reveal that the oxygen vacancy on TiO2 facilitates the photo-induced carriers separation efficiency and more importantly, promotes halide ions adsorption with intermediary strength and hence increases the activity. Moreover, we designed a self-powered PEC system and directly utilised seawater as both the electrolyte and chloride ions source, attaining chlorocyclohexane productivity of 412 µmol h-1 coupled with H2 productivity of 9.2 mL h-1, thus achieving a promising way to use solar for upcycling halogen in ocean resource into valuable organic halides.

Novel 2D/2D BiOBr/UMOFNs direct Z-scheme photocatalyst for efficient phenol degradation

A novel 2D/2D BiOBr/ultrathin metal-organic framework nanosheets (UMOFNs) direct Z-scheme photocatalyst was successfully synthesized by using a simple deposition-precipitation method. The photocatalytic performance was evaluated under light irradiation, which revealed that the 2D/2D BiOBr/UMOFNs Z-scheme photocatalyst exhibits higher photocatalytic degradation of phenol compared to pristine BiOBr and UMOFNs. A BiOBr/UMOFNs-40% (mass ratio for BiOBr and UMOFNs of 1:0.4) photocatalyst was found to show the best photocatalytic degradation efficiency and stability, reaching 99% phenol degradation under light irradiation of 270 min and maintaining 97% degradation after 5 recycling runs. Results obtained from a trapping experiment and electron paramagnetic resonance suggest that reactive ·OH and O₂ ^·- play a major role in phenol degradation. Photoluminescence and photocurrent results reveal that the excellent photocatalytic activity of the 2D/2D BiOBr/UMOFNs photocatalyst can be ascribed to the efficient separation of photogenerated electron-hole pairs through a direct Z-scheme system. This article provides a possible reference for designing Z-scheme photocatalysts by using MOFs and semiconductors for practical organic pollutant treatment.

Selective Cl-Decoration on Nanocrystal Facets of Hematite for High-Efficiency Catalytic Oxidation of Cyclohexane: Identification of the Newly Formed Cl-O as Active Sites

Understanding the structure-reactivity relationship at the atomic scale is of great theoretical importance for rational design of highly active catalysts, which has long been a central concern in catalysis communities and interface science. Herein, we developed a high-efficiency catalyst for catalytic oxidation of C₆H₁₂ by poststructural decoration on well-defined single-crystal facets of hematite. Especially for Cl-decorated {012} facets, the conversion and KA oil selectivity are improved about 3.4 times and 2 times, respectively. A better catalytic performance of the newly formed active site is derived from the charge difference between Cl and the neighboring outmost O atoms, which is affected by the geometric and electronic structures of the original catalyst surface. Based on the experimental results and the theoretical analysis, we concluded that the contribution of various O terminations to Cl-decoration follows the order O(I) > O(III) > O(II). Cl-decorated {001} facets show the highest intrinsic activity, whereas Cl-decorated {012} facets show the best catalytic performance because of their more active sites for Cl-decoration.

Visible-Light-Triggered Quantitative Oxidation of 9,10-Dihydroanthracene to Anthraquinone by O2 under Mild Conditions

The development of mild and efficient processes for the selective oxygenation of organic compounds by molecular oxygen (O₂ ) is key for the synthesis of oxygenates. This paper discloses an atom-efficient synthesis protocol for the photo-oxygenation of 9,10-dihydroanthracene (DHA) by O₂ to anthraquinone (AQ), which could achieve quantitative AQ yield (100 %) without any extra catalysts or additives under ambient temperature and pressure. A yield of 86.4 % AQ was obtained even in an air atmosphere. Furthermore, this protocol showed good compatibility for the photo-oxidation of several other compounds with similar structures to DHA. From a series of control experiments, free-radical quenching, and electron paramagnetic resonance spin-trapping results, the photo-oxygenation of DHA was probably initiated by its photoexcited state DHA*, and the latter could activate O₂ to a superoxide anion radical (O₂ ^.- ) through the transfer of its electron. Subsequently, this photo-oxidation was gradually dominated by the oxygenated product AQ as an active photocatalyst obtained from the oxidation of DHA by O₂ ^.- , and was accelerated with the rapid accumulation of AQ. The present photo-oxidation protocol is a good example of selective oxygenation based on the photoexcited substrate self-activated O₂ , which complies well with green chemistry ideals.

HCl and O2 co-activated bis(8-quinolinolato) oxovanadium(iv) complexes as efficient photoactive species for visible light-driven oxidation of cyclohexane to KA oil

Photoactive species (PA) originating from HCl and O₂ co-activated bis(8-quinolinolato) oxovanadium(iv) can effectively modulate the photocatalytic oxidation of cyclohexane.

Deposition of copper from Cu(i) and Cu(ii) precursors onto HOPG surface: Role of surface defects and choice of a precursor

The surface reactivity of two copper-containing precursors, (Cu(hfac)₂ and Cu(hfac)VTMS, where hfac is hexafluoroacetyloacetonate and VTMS is vinyltrimethylsilane), was investigated by dosing the precursors onto a surface of highly ordered pyrolytic graphite (HOPG) at room temperature. The behavior of these precursors on a pristine HOPG was compared to that on a surface activated by ion sputtering and subsequent oxidation to induce controlled surface defects. X-ray photoelectron spectroscopy and energy dispersive X-ray spectroscopy were used to confirm copper deposition and its surface distribution, and to compare with the results of scanning electron microscopy and atomic force microscopy investigations. As expected, surface defects promote copper deposition; however, the specific structures deposited depend on the deposition precursor. Density functional theory was used to mimic the reactions of each precursor molecule on this surface and to determine the origins of this different reactivity.

Synthesis of C–N dual-doped Cr2O3 visible light-driven photocatalysts derived from metalorganic framework (MOF) for cyclohexane oxidation

A series of novel C–N dual-doped Cr₂O₃ photocatalysts were synthesized from MIL-101(Cr), using a two-step method, including initial carbonization in nitrogen atmosphere without adding any carbon source and subsequent calcination in air.