Construction of Indium Oxide/N-Doped Titanium Dioxide Hybrid Photocatalysts for Efficient and Selective Oxidation of Cyclohexane to Cyclohexanone

Abstract

Photocatalytic oxidation of cyclohexane (CHA) to generate cyclohexanone (CHA-one) is one of the most important strategic links for the production of nylon-6 and nylon-66. Herein, an indium oxide/N-doped titanium dioxide (In2O3/N-TiO2) hybrid photocatalyst with a p–n heterointerface was successfully constructed by a two-step strategy of the hydrothermal N-doped method and impregnation method with structural reconstruction. Under green and mild reaction conditions (room temperature, atmospheric pressure, and solvent-free), the In2O3/N-TiO2 hybrid catalyst achieved the desired photocatalytic performance for the production of CHA-one at simulated solar light. Compared with bare TiO2, the 5% In2O3/N-TiO2 composite achieved a 4-fold increase for producing CHA-one in catalytic activity and an increase in selectivity to the CHA-one of approximately 90%. Moreover, the In2O3/N-TiO2 composites exhibited a desirable cycling durability and recoverability. According to the photoelectrochemical tests and density functional theory (DFT) calculations, the enhanced photocatalytic performance of In2O3/N-TiO2 can be attributed to high visible-light absorption derived from N-doping and fast separation of photoformed electron–hole pairs caused by the p–n heterointerface. A possible photo-oxidation mechanism of CHA over the In2O3/N-TiO2 catalyst was proposed and verified by the trapping detection of active species. Thereby, the present approach provides a green and prospective strategy for extending the application of the TiO2-based photocatalyst for selective photo-oxidation.

Solvent-free aerobic photocatalytic oxidation of alcohols to aldehydes over ZnO/C3N4

“…In order to explore the mechanism of selective oxidation of benzyl alcohol over ZnO/C 3 N 4 , the photocatalytic reaction is conducted with the addition of different active species scavengers, such as tert -butanol ( t -BuOH, scavengers for ˙OH), butylated hydroxytoluene (BHT, scavengers for ˙O 2 − ), trichloro-bromomethane (CBrCl 3 , scavengers for an alcohol cation radical), silver nitrate (AgNO 3 , scavengers for electrons e − ), ethylenediamine tetraacetic acid disodium salt (EDTA-2Na, scavengers for holes h + ), and 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO, scavengers for free radicals). 35–38 As shown in Fig. 5a, the activity decreases when TEMPO, BHT, and AgNO 3 are added to the reaction system.…”

“…-oxyl (TEMPO, scavengers for free radicals). [35][36][37][38] As shown in Fig. 5a, the activity decreases when TEMPO, BHT, and AgNO 3 are added to the reaction system.…”

“…As shown in Fig. 6b, the band energy (E g ) of g-C 3 N 4 and ZnO-A can be estimated as 2.70 and 3.07 eV based on the UV-vis spectra according to the equation: αhν = A(hν − E g ) n/2 , 23,37 in which α is the absorption coefficient, h is Planck's constant, v is the light frequency, A represents a constant, and E g represents the bandgap energy. n is 1 and 4 for g-C 3 N 4 and ZnO, respectively.…”

“…7a, ZnO/C 3 N 4 -600 has a higher photocurrent than g-C 3 N 4 and ZnO-A, indicating that ZnO/ C 3 N 4 -600 possesses a higher separation efficiency of photogenerated charge carriers. 37 The electron and excitation photoexcitation behaviors of the g-C 3 N 4 , ZnO/C 3 N 4 -600, and ZnO-A catalysts were studied to gain further understanding of the notable photocatalytic activity of ZnO/C 3 N 4 . As shown by the steady-state photoluminescence (PL) spectra in Fig.…”

Selective photocatalytic oxidation of cyclohexene coupled with hydrogen evolution from water splitting over Ni/NiO/CdS and mechanism insight

“…Under the optimum yield conditions of cyclohexanol and cyclohexanone, 18.8 μmol CO 2 can still be produced. 16 The study of the photocatalytic reaction mechanism is crucial to improve the activity and selectivity of the catalyst and avoid the mineralization of organic molecules. 17,18 The oxidation of cyclohexene can occur on the CC double bond or the allylic C-H bond of cyclohexene, but the research on how oxidants affect the reaction pathway of cyclohexene to generate specific products is still relatively rare.…”