•Ag-introduced CN was designed to photocatalytically eliminate organic pollutant.•Weakening planar H bonding of CN can be achieved by Ag introduction.•Ag introduction improved electronic structures and O2-adsorption state of CN.•AgCN presented remarkable activity for eliminating organic pollutant.•The remarkable activity of AgCN was explored experimentally and theoretically.Owing to the unique electronic and optical properties, carbon nitride (CN) materials have attracted widespread interest for photocatalytic application in the field of environment and energy. However, low carrier mobility and insufficient sunlight absorption limit the efficient application, which is attributed to the planar hydrogen bonding between strands of polymeric melon units with NH/NH2. Herein, Ag-introduced CN (AgCN) samples were designed as photocatalysts by introducing Ag into CN to weaken the planar hydrogen bonding for photocatalytically eliminating methyl orange pollutant. Spectroscopy, electrochemistry and computational studies revealed that AgCN photocatalyts presented a significantly enhanced sunlight absorption, efficient carrier mobility as well as improved O2 adsorption state. As a result, photoreactivity for methyl orange photooxidation elimination over AgCN was significantly enhanced, with apparent rate of 0.13 min−1 for optimal AgCN-4 under visible-light irradiation, which was 6.50, 8.13, 2.60, and 4.33 times that of Bi2WO6, BiOCl, Ag/CN, and Ag2CO3, respectively. The result supplied an efficient approach for constructing effective visible-light-irradiation photocatalysts for environmental purification.Download high-res image (247KB)Download full-size image

•Graphene-like SC3N4 was prepared to phtocatalytically eliminate UO22+ pollutant.•Weakening planar hydrogen bonding of g-C3N4 can obtain graphene-like structure.•Graphene-like structure modified the electronic structures of g-C3N4.•SC3N4 showed remarkable performance in the photocatalytic reduction of UO22+.•The good activity of SC3N4 was explored both experimentally and theoretically.Owing to the unique electronic and optical properties, the graphene-like carbon nitride (C3N4) materials have attracted widespread interest. However, the exfoliation of bulk C3N4 into graphene-like structure is inhibited by the planar hydrogen bond between strands of polymeric melon units with NH/NH2, due to the higher electronegativity of N with respect to C atoms. Herein, graphene-like sulfur-doped C3N4 (SC3N4) samples were successfully prepared by introducing sulfur into C3N4 to weaken the planar hydrogen bonding, and investigated as catalysts to photoreductively eliminate uranyl ion in aqueous media. Both experimental and computational perspectives confirmed that S-doping in SC3N4 can modify its electronic structure, reflected by the elevated conduction and valence band levels, as well as the improved transportation capability of photogenerated electrons. As a result, the photoactivity for UO22+ photocatalytic reduction over the optimal SC3N4 was significantly improved, with apparent rate value reaching 0.16 min−1 under visible-light irradiation, which was 2.28 times that over C3N4. This study provides an effective strategy for designing efficient visible-light-responsive photocatalysts for environmental remediation.Download high-res image (210KB)Download full-size image

Computational studies have been applied to gain insight into the mechanism of Pd(II) catalyzed α-C–H functionalization of N-methoxy cinnamamide. The results show that the whole catalytic cycle proceeds via sequential six steps, including (i) catalyst Pd(t-BuNC)2 oxidation with O2, (ii) O–H deprotonation, (iii) t-BuNC migratory insertion to the Pd–C bond, (iv) acyl migration, (v) C–H activation and (vi) reductive elimination. The regioselectivity for different C–H activation sites depends on the coordination structures of α-C or β-C to the palladium(II) center. The coordination of α-C to the palladium(II) center shows a regular planar quadrilateral structure, which is stable. However, the β-C coordinating to the palladium(II) center mainly exhibits a distorted quadrilateral structure, which is relatively unstable. Thus, the barrier of α-C–H activation is much lower than that of β-C–H activation. The present results provide a deep understanding of the site-selectivity of C–H activation.

The detailed mechanism of the double hydrophosphination of terminal arylacetylenes catalyzed by an iron complex was studied by density functional theory. The calculated results suggest that the reaction proceeds in three steps: active species generation, single hydrophosphination reaction (Cycle 1), double hydrophosphination reaction, viz., active species regeneration (Cycle 2). The results uncovered the selectivity of the iron complex for double hydrophosphination of terminal arylacetylenes. The symmetry of frontier molecular orbitals determines the effectiveness of the catalyst. We also discuss the formation mechanism of the single hydrophosphination product with Z configuration.

The reaction mechanism for electrocatalytic reduction of CO2 to formate by water-stable iridium dihydride pincer complex is studied using density functional theory (DFT). The reaction pathways are investigated in detail. The results suggest that the reaction proceeds in three steps: insertion of carbon dioxide into the Ir(III) pincer dihydride, elimination of formate ligand from the hydridoformatoiridium complex, and catalyst regeneration. The reduction potential of the electrode reaction is calculated and accords well with the experimental value. The solvent effect of MeCN and water on the reaction is explored. The results indicate that water has an important effect on CO2 transforming to HCOO−. In addition, it also plays a critical role for regeneration of the catalyst via non-classical intermolecular hydrogen bonding.

The reaction mechanism for electrocatalytic reduction of CO2 to formate by water-stable iridium dihydride pincer complex is studied using density functional theory (DFT). The reaction pathways are investigated in detail. The results suggest that the reaction proceeds in three steps: insertion of carbon dioxide into the Ir(III) pincer dihydride, elimination of formate ligand from the hydridoformatoiridium complex, and catalyst regeneration. The reduction potential of the electrode reaction is calculated and accords well with the experimental value. The solvent effect of MeCN and water on the reaction is explored. The results indicate that water has an important effect on CO2 transforming to HCOO−. In addition, it also plays a critical role for regeneration of the catalyst via non-classical intermolecular hydrogen bonding.

The detailed mechanism of the double hydrophosphination of terminal arylacetylenes catalyzed by an iron complex was studied by density functional theory. The calculated results suggest that the reaction proceeds in three steps: active species generation, single hydrophosphination reaction (Cycle 1), double hydrophosphination reaction, viz., active species regeneration (Cycle 2). The results uncovered the selectivity of the iron complex for double hydrophosphination of terminal arylacetylenes. The symmetry of frontier molecular orbitals determines the effectiveness of the catalyst. We also discuss the formation mechanism of the single hydrophosphination product with Z configuration.

Computational studies have been applied to gain insight into the mechanism of Pd(II) catalyzed α-C–H functionalization of N-methoxy cinnamamide. The results show that the whole catalytic cycle proceeds via sequential six steps, including (i) catalyst Pd(t-BuNC)2 oxidation with O2, (ii) O–H deprotonation, (iii) t-BuNC migratory insertion to the Pd–C bond, (iv) acyl migration, (v) C–H activation and (vi) reductive elimination. The regioselectivity for different C–H activation sites depends on the coordination structures of α-C or β-C to the palladium(II) center. The coordination of α-C to the palladium(II) center shows a regular planar quadrilateral structure, which is stable. However, the β-C coordinating to the palladium(II) center mainly exhibits a distorted quadrilateral structure, which is relatively unstable. Thus, the barrier of α-C–H activation is much lower than that of β-C–H activation. The present results provide a deep understanding of the site-selectivity of C–H activation.