Metal‐ and Additive‐Free Oxidation of Sulfides into Sulfoxides by Fullerene‐Modified Carbon Nitride with Visible‐Light Illumination

Abstract

Photocatalytic selective oxidation has attracted considerable attention as an environmentally friendly strategy for organic transformations. Some methods have been reported for the photocatalytic oxidation of sulfides into sulfoxides in recent years. However, the practical application of these processes is undermined by several challenges, such as low selectivity, sluggish reaction rates, the requirement of UV-light irradiation, the use of additives, and the instability of the photocatalyst. Herein, a metal-free C /graphitic carbon nitride (g-C N ) composite photocatalyst was fabricated by a facile method, and well characterized by TEM, SEM, FTIR spectroscopy, XRD, X-ray photoelectron spectroscopy, diffuse reflectance spectroscopy, and photoluminescence spectroscopy. The C /g-C N catalyst exhibited a high photocatalytic activity at room temperature for the selective oxidation of sulfides into the corresponding sulfoxides in the presence of other functional groups, due to the synergetic roles of C and g-C N . Several important parameters have been screened, and this method afforded good to excellent yields of sulfoxides under optimal conditions. The superoxide radical ( O ) and singlet oxygen ( O ) were identified as the oxidative species for the oxidation of sulfides into sulfoxides by exploring EPR experiments, and hence, a plausible mechanism for this oxidation was proposed. Moreover, the C /g-C N catalyst can be easily recovered by filtration and then reused at least four times without loss in activity.

Oxygen‐Functionalized and Ni+x (x=2, 3)‐Coordinated Graphitic Carbon Nitride Nanosheets with Long‐Life Deep‐Trap States and their Direct Solar‐Light‐Driven Hydrogen Evolution Activity

“…[ 22,23] The peak at 404.19 eV corresponded to the p-excitationo nt he exposed surfaces of g-C 3 N 4 . [32] The O1ss pectrum( Figure 4c)w as deconvoluted into five peaks at 530.58, 531.59, 532.56, 533.53,a nd 535.6 eV.T he peak at 530.58 eV was attributedt oC ÀO/NÀCÀOb onds in g-C 3 N 4 , clearly confirming the oxygen functionalization of the g-C 3 N 4 matrix. [27,28,[33][34][35] The oxygen functionalization occurred owing to thermal condensation of melaminei na na ir atmosphere.…”

“…The main peak at 398.35 eV was attributed to sp 2 ‐hybridized nitrogen in the aromatic ring (C=N−C), whereas the peaks at 399 and 400.87 eV were attributed to sp 3 ‐hybridized N‐C 3 and C‐N‐H groups in the g‐C 3 N 4. The peak at 404.19 eV corresponded to the π‐excitation on the exposed surfaces of g‐C 3 N 4 . The O 1s spectrum (Figure c) was deconvoluted into five peaks at 530.58, 531.59, 532.56, 533.53, and 535.6 eV.…”

Imine‐Based Covalent Organic Frameworks as Photocatalysts for Metal Free Oxidation Processes under Visible Light Conditions

“…In order to stablish the influence of crystallinity in the catalytic activity, crystalline materials 1 a-c were evaluated under the optimized conditions (entry 9). Full and 69 % conversions were obtained under crystalline 1 a and 1 c catalysis, respectively, after 48 h (entries [13][14][15]. Remarkably, the crystalline laminar-COF 1 b showed the highest catalytic activity, showing full conversion after 24 h (entry 14).…”

“…Moreover, the overoxidation process to sulfone has been also described as a limitation to be overcome. However, although the use of materials in the sulfoxidation reactions has been explored, [14][15][16][17][18][19][20][21][22] several limitations have been frequently described, such as the use of high powered light energy (> 150 W), [14] materials decorated with toxic metals, [16] non-green solvents and moderate recyclability. [8][9][10][11][12][13] Therefore, an alternative oxidation for the use of peracids and peroxides is the application of gaseous reagents that allows the development of greener processes by reducing the waste from purification, because excess of gas can be easily removed from the reaction.…”

“…Although in most cases the use of oxygen for the oxidation of sulfides has been carried out with homogeneous systems, the use of heterogeneous materials, especially those containing porosity in their structure, seems one of the most logical approaches for the use of gases in catalysis. However, although the use of materials in the sulfoxidation reactions has been explored, [14][15][16][17][18][19][20][21][22] several limitations have been frequently described, such as the use of high powered light energy (> 150 W), [14] materials decorated with toxic metals, [16] non-green solvents and moderate recyclability. [16] Overcoming such drawbacks would be highly desirable in order to achieve a green process.…”