Xinyu Song

Construction of reduced graphene oxide-supported Ag–Cu2O composites with hierarchical structures for enhanced photocatalytic activities and recyclability

Ternary spherical Ag–Cu2O/reduced graphene oxide (rGO) nanohybrids with excellent hierarchical structures are developed through a simple one-pot, two-stage reduction synthetic route at room temperature without any surfactant. In the resultant complex heterostructures, both Ag and rGO are in direct contact with Cu2O, and Ag nanocrystals are mainly deposited on the surface of Cu2O spheres. The resultant ternary spherical Ag–Cu2O/rGO composite exhibits excellent photocatalytic activity in photocatalytic degradation of methyl orange (MO) under visible light irradiation, which is much higher than that of either the single component (Cu2O) or two component systems (spherical Cu2O/rGO and Ag–Cu2O). In particular, the resultant ternary composites possess excellent stability and extend the light absorption range. The PL spectrum results have demonstrated that not only Ag but also rGO could capture the photogenerated electrons from Cu2O, thus leading to effective separation of electrons and holes. In particular, it is found that the direct junction and interaction between Ag and Cu2O in the ternary composites are more beneficial for charge transportation than the direct contact between Ag and rGO (labeled as sample Ag-rGO-Cu2O), and thereby the resultant Ag–Cu2O/rGO composites with such complex heterostructures exhibit a better photoactivity than the sample Ag-rGO-Cu2O. This work provides an insight into designing and synthesizing new Cu2O-based hybrid materials for effectively improving the photocatalytic performance.

Multi-zinc-expanded graphene patches: Tetraradical versus diradical character

Three classes of multi‐Zn‐expanded graphene patches in different shapes are computationally designed through introducing a Zn chain into the corresponding middle benzenoid chain. Both density functional theory and complete active space self‐consistent field calculations predict that molecules of nnn‐quasi‐linear and nnn‐slightly bent series have the open‐shell broken‐symmetry (BS) singlet diradical ground states, whereas those of n(n+1)n species possess quintet tetraradical as their ground state and become open‐shell BS singlet tetraradicals when they are in a higher energy state. These results offer the first theoretical attempt to introduce multi‐Zn into the small graphene patches to form Zn‐expanded graphene patches, leading them to polyradical structures. This work provides an executable strategy to yield molecules which have stable polyradicaloid character and enhanced electronic properties of multi‐Zn‐expanded graphene patches.

Reduced graphene oxide-stabilized copper nanocrystals with enhanced catalytic activity and SERS properties

Well-defined Cu/reduced graphene oxide (rGO) hybrid materials are successfully synthesized by controlling the amount of ascorbic acid and maintaining an appropriate pH value. We found that graphene oxide (GO) served not only as the precursor for graphene, but also as an effective surfactant to hamper the aggregation of copper nanoparticles, resulting in a small size of the copper nanoparticles. Furthermore, the as-prepared copper composites can serve as an effective catalyst for 4-nitrophenol in aqueous conditions and exhibit surface enhanced Raman scattering in the detection of crystal violet (CV). Notably, the obtained copper nanoparticle hybrids with rGO have extremely high air stability after exposure to air. Density functional theory calculations firstly reveal that rGO can effectively prevent Cu nanoparticles from spontaneous oxidation due to its slightly lower ionization potential than that of Cu nanoparticles. We expect the as-prepared rGO-stabilized copper nanocrystals with small size to meet the increasing demands of industrial applications at reduced costs.

Computational design of the magnetism-tunable oligobenzylic carbanion complexes

Unrestricted density functional theory calculations in combination with the broken symmetry approach have been employed to study several benzylic carbanions. As a free anion, 2-(3,5-dinitrophenyl)-1,3-dithiane carbanion has near-degenerate singlet and triplet states and appears to be a promising magnetism-tunable species. In this work, we computationally design some of its derivatives in two ways: expanding the π-conjugated structures and introducing Lewis acids (Li+, Na+, and K+, and polar molecules are considered here) with different acidities. Calculations reveal that ring expansion does not change its open-shell broken symmetry singlet diradical ground state and antiferromagnetic character, but decreases its magnetism, whereas introduction of Lewis acids can lead to different ground states (triplet vs. singlet) and different magnetism, depending on the binding sites of the Lewis acid. That is, they show closed-shell singlet ground states without magnetism when a cation locates near the anionic center of the 1,3-dithiane ring, but convert to triplet as their ground states with ferromagnetic character when the cation moves to one nitro group of the 3,5-dinitrophenyl-based π-conjugation-expanded fragment. These findings regarding modulation through ring expansion and Lewis acid-binding ways make the magnetisms of 2-(3,5-dinitrophenyl)-1,3-dithiane-based carbanions tunable, and thus provide prospects of a new extension of the results from the previous study for designing magnetism-tunable building blocks for novel electromagnetic materials.

Magnetism‐Tunable Oligoacene Dioxide Diradicals: Promising Magnetic Oligoacene‐Like Molecules

Graphene oxide has attracted intense research interest recently because the graphene oxide synthesis route, as a promising alternative for cost-effective mass production of graphene, has been explored. To further study the oxidation process and possible mechanism and to explore applicability of the oxidized products, we have performed a computational study on three series of oligoacene dioxides, focusing on their structures and electronic properties. Taking 1,5-dioxidized naphthalene as a starting point, three series of oligoacene dioxides are considered as follows: 1) middle insertion by 1-2 benzene rings; 2) single-side expansion using 1-2 benzene rings; 3) double-side expansion using two benzene rings. On the basis of density functional theory and complete active space self-consistent field (CASSCF) calculations, we reveal that oligoacene dioxides in the middle insertion series have a triplet ground state, whereas those in the single-side expansion series and the double-side expansion series have open-shell broken-symmetry singlet diradical ground states except for their common origin naphthalene-1,5-dioxide whose ground state is triplet and which is also viewed as the origin of the middle insertion series. Magnetic coupling interactions of these oligoacene dioxides are also determined. This work should help people toward an atomistic understanding of the electronic structures and properties of possible intermediates or products and even the oxidation mechanism of graphene sheets, and provides a reasonable strategy of designing novel graphene-oxide-based magnetic materials.

Facile and economical synthesis of ZnS nanotubes and their superior adsorption performance for organic dyes

Developing a green and economical synthetic strategy for ZnS nanotubes is of great interest. In this work, ZnS nanotubes are successfully fabricated using only three raw materials (Zn(CH3COO)2, NaHCO3 and Na2S) through a simple two step synthetic route at ambient temperature. It is worth noting that the process is economical and environmentally friendly, without the need for high pressure or elevated temperature conditions. Interestingly, a very obvious feature is the existence of abundant sulfur surface defects on the as-prepared ZnS nanotubes, which not only produces strong defect-related fluorescence properties, but also leads to abundant water adsorbed on the surface of zinc sulfide. Furthermore, the as-prepared ZnS nanotubes as an adsorbent are exploited in the adsorption of organic dyes. Notably, the resultant products display superior selective adsorption ability for anionic dyes with amine (–NH2/NH) functional groups over a wide pH range through the synergistic effect of hydrogen bonding and electrostatic attraction between the dye molecules and the adsorbent. Taking CR dye as an example, the maximum adsorption capacity for the removal of Congo red reaches 724.6 mg g−1 in water, much higher than many composite adsorbents reported in the literature. Thus, the present study not only presents a promising strategy for fabrication of ZnS nanotubes but also indicates their great potential application as environmentally friendly adsorbents in organic dye separation technologies or dye removal.

Tuning the Spin Coupling Interactions in the Nitroxide‐Based Bisphenol‐Like Diradicals

The intramolecular spin coupling interactions of bisphenol-like trinary-bridged diradicals [nitroxide-(para/meta)phenylene-X-phenylene(para/meta)-nitroxide, X=C=CH2 , O, BH, NH and SO2 ] were explored with an emphasis on the tuning role of the X coupler at the (U)B3LYP/6-311++G(d,p) level. Our results indicate that all designed trinary-bridged diradicals featuring a V-type structure with a bending angle of 104-130° and torsional angles of two phenylene rings being 20-90° exhibit different diradical character and magnetism, depending on the structures and properties of the X bridges. More interestingly, although meta/para-phenylene supports a ferromagnetic (FM)/antiferromagnetic (AFM) coupling, their combinations by using X as a trinary bridge can mediate spin coupling, but the coupling magnitude strongly depends on X. In general, a para/para or meta/meta combination with X leads to an open-shell singlet ground state and thus AFM, but the meta/meta combination considerably decreases the spin coupling interaction. In contrast, a para/meta combination with X produces a triplet ground state and FM. Their combination with a single-electron conjugation end coupler (C=CH2 ) leads to an inverse coupling regularity. All results can be reasonably explained by the spin alternation rule, molecular structures, and properties. In particular, detailed spin coupling mechanisms are suggested to involve cooperative through-space and through-bond pathways with different levels of cooperativity. This is rationalized with the X-induced bending of the diradicals not only modifying the through-bond (extended π conjugation) pathway but also provididng a through-space (face-to-face vs. side-to-side π-π interaction) possibility for spin coupling, in conjunction with twisting of the phenylene rings. Different contributions of the through-space and through-bond couplings are quantitatively distinguished and depend on the structure and property of the X coupler. Clearly, this work reports interesting aspects of the trinary bridged diradicals and also provides important information for the design of molecules for functional magnetic materials and tuning their magnetic properties.