Efficient Photocatalytic Degradation of Tetracycline on the MnFe2O4/BGA Composite under Visible Light.

In this work, the MnFe2O4/BGA (boron-doped graphene aerogel) composite prepared via the solvothermal method is applied as a photocatalyst to the degradation of tetracycline in the presence of peroxymonosulfate. The composite's phase composition, morphology, valence state of elements, defect and pore structure were analyzed by XRD, SEM/TEM, XPS, Raman scattering and N2 adsorption-desorption isotherms, respectively. Under the radiation of visible light, the experimental parameters, including the ratio of BGA to MnFe2O4, the dosages of MnFe2O4/BGA and PMS, and the initial pH and tetracycline concentration were optimized in line with the degradation of tetracycline. Under the optimized conditions, the degradation rate of tetracycline reached 92.15% within 60 min, whereas the degradation rate constant on MnFe2O4/BGA remained 4.1 × 10-2 min-1, which was 1.93 and 1.56 times of those on BGA and MnFe2O4, respectively. The largely enhanced photocatalytic activity of the MnFe2O4/BGA composite over MnFe2O4 and BGA could be ascribed to the formation of type I heterojunction on the interfaces of BGA and MnFe2O4, which leads to the efficient transfer and separation of photogenerated charge carriers. Transient photocurrent response and electrochemical impedance spectroscopy tests offered solid support to this assumption. In line with the active species trapping experiments, SO4•- and O2•- radicals are confirmed to play crucial roles in the rapid and efficient degradation of tetracycline, and accordingly, a photodegradation mechanism for the degradation of tetracycline on MnFe2O4/BGA is proposed.

Ho2C2 Cluster with Flexible Configurations inside a Large C2(61)-C92 Cage.

Carbide clusterfullerenes (CCFs) have been of great concern due to their potential applications in materials science, in which the internal carbide cluster plays vital roles in the stability and properties of CCF. However, there still remains a debate about what configuration is ideal for the internal carbide cluster. In this work, we isolated two isomers (I and II) of Ho2C94 and studied them by means of mass spectrometry, UV-vis-NIR spectroscopy, and cyclic/differential pulse voltammetry. A combined study of single-crystal X-ray diffraction (SC-XRD) and density functional theory (DFT) computation ascertains isomer-I as Ho2C2@C2(61)-C92, in which the Ho2C2 cluster displays variable configurations from planar zigzag to folded butterfly with very small distortion energy (∼10 kJ/mol). This study hence confirms that the internal carbide cluster is intrinsically flexible over a broad geometrical range in a relatively large fullerene cage, where the nanoscale compression effect is almost negligible.

Favorite Orientation of the Carbon Cage and a Unique Two-Dimensional-Layered Packing Model in the Cocrystals of Nd@C82(I,II) Isomers with Decapyrrylcorannulene.

To date, the experimental studies on Nd-based metallofullerenes are only limited to spectroscopic characterizations. In this work, the molecular structures of Nd@C82(I,II) isomers, including the isomeric symmetry of the C cage and the position of endohedral Nd atom, as well as their unique two-dimensional (2D)-layered crystallographic packing structures were initially and unambiguously elucidated, based on the X-ray structural analyses of the cocrystals of Nd@C82(I) or Nd@C82(II) with cocrystallizing agent decapyrrylcorannulene (DPC). In the V-shaped unit cell, the endohedral Nd atom prefers a site as far away from the DPC molecules as possible because of the unevenly distributed charge on the C cage mainly related to the charge transfers from the endohedral Nd atom, cocrystallizing agent DPC, and solvent toluene molecules to the C82 cage. Apart from charge transfers, multiple C-H···π intermolecular interactions are also confirmed to play important roles both for the orientation of the C cage correlated with the preferential sites of the endohedral Nd atom and for the 2D-layered packing structures within the cocrystals. Density functional theory computations offered theoretical support for the molecular structures of Nd@C82(I,II) isomers, the valence of the endohedral Nd atom (between II+ and III+), and the global ground state, i.e., the Nd@C2v(9)-C82 isomer in the quintet state.

Ho2O@D3(85)-C92: Highly Stretched Cluster Dictated by a Giant Cage and Unexplored Isomerization.

For endohedral metallofullerenes (EMFs), it has been well established that the cage shape and size should match those of the endohedral cluster. As a result, sufficient cluster-cage interaction can be achieved, which is essential for mutual stabilization. Nevertheless, how a small endohedral cluster nests in a giant fullerene has been less explored. Herein, we report a pair of large oxide-cluster fullerene (OCF) isomers, denoted as Ho2O@C92-I and -II. Crystallographic studies reveal that major isomer-I possesses a D3(85)-C92 cage with a highly stretched Ho2O cluster inside, which contributes to achieving regular metal-cage contacts. Density functional theory (DFT) computations also reveal the predominant abundance of the D3(85) isomer relative to the other two possible minor species including C1(67) and C2(64) isomers. Moreover, electrochemical (EC) studies verify that the isomers exhibit almost identical redox behaviors, indicating their similar cage structures. On the basis of the remarkable topological similarity of D3(85) and C1(67) isomers, isomer-II is likely to be Ho2O@C1(67)-C92, though it remains to be confirmed. Our studies thus provide new insights into the cage-cluster interplay and cage isomerization, both contributing to a better understanding of large EMFs.

An Explosive Bomb-Inspired Method to Prepare Collapsed and Ruptured Fe2 O3 /Nitrogen-Doped Carbon Capsules as Catalyst Support.

Compared with integrated capsules, ruptured ones have better mass diffusion and transport properties due to large gaps in the shells. However, most studies focus on integrated capsules, whereas little attention has been paid to the ruptured counterparts. Herein, an explosive bomb-inspired method was employed to prepare collapsed and ruptured Fe2 O3 /nitrogen-doped carbon (CR-Fe2 O3 /NC) capsules by using polystyrene (PS) nanoparticles (NPs) as a hard template, and polypyrrole (PPy) with embedded Prussian blue (PB) NPs as the shell. During pyrolysis, PB is converted into Fe2 O3 , and PPy is carbonized to form NC. Importantly, the PS core decomposes into gas molecules, leading to high pressure inside of the capsule, which explodes the thin shell into pieces. The roles of shell thickness and amount of Fe2 O3 on determining the spherical or collapsed, and integrated or ruptured morphology were revealed. Taking advantage of structural merits, including large gaps, thin shells, low density, and high surface area, CR-Fe2 O3 /NC capsules were used as supports for Pd NPs. These capsules exhibited better catalytic activity than that of integrated ones. Due to the magnetic properties, they could be reused at least five times.

Adamantylidene Addition to M3 N@Ih -C80 (M=Sc, Lu) and Sc3 N@D5h -C80 : Synthesis and Crystallographic Characterization of the [5,6]-Open and [6,6]-Open Adducts.

Additions of adamantylidene (Ad) to M3 N@Ih -C80 (M=Sc, Lu) and Sc3 N@D5h -C80 have been accomplished by photochemical reactions with 2-adamantyl-2,3'-[3H]-diazirine (1). In M3 N@Ih -C80 , the addition led to rupture of the [6,6]- or [5,6]-bonds of the Ih -C80 cage, forming the [6,6]-open fulleroid as the major isomer and the [5,6]-open fulleroid as the minor isomer. In Sc3 N@D5h -C80 , the addition also proceeded regioselectively to yield three major isomeric Ad mono-adducts, despite the fact that there are nine types of C-C bonds in the D5h -C80 cage. The molecular structures of the seven Ad mono-adducts, including the positions of the encaged trimetallic nitride clusters, have been unambiguously determined through single-crystal XRD analyses. Furthermore, results have shown that stepwise addition of Ad to Lu3 N@Ih -C80 affords several Ad bis-adducts, two of which have been isolated and characterized. The X-ray structure of one bis-adduct clearly revealed that the second Ad addition took place at a [6,6]-bond close to an endohedral metal atom. Theoretical calculations have also been performed to rationalize the regioselectivity.

D2d(23)-C84 versus Sc2C2@D2d(23)-C84: Impact of Endohedral Sc2C2 Doping on Chemical Reactivity in the Photolysis of Diazirine.

We compared the chemical reactivity of D2d(23)-C84 and that of Sc2C2@D2d(23)-C84, both having the same carbon cage geometry, in the photolysis of 2-adamantane-2,3'-[3H]-diazirine, to clarify metal-atom doping effects on the chemical reactivity of the carbon cage. Experimental and computational studies have revealed that the chemical reactivity of the D2d(23)-C84 carbon cage is altered drastically by endohedral Sc2C2 doping. The reaction of empty D2d(23)-C84 with the diazirine under photoirradiation yields two adamantylidene (Ad) adducts. NMR spectroscopic studies revealed that the major Ad monoadduct (C84(Ad)-A) has a fulleroid structure and that the minor Ad monoadduct (C84(Ad)-B) has a methanofullerene structure. The latter was also characterized using X-ray crystallography. C84(Ad)-A is stable under photoirradiation, but it interconverted to C84(Ad)-B by heating at 80 °C. In contrast, the reaction of endohedral Sc2C2@D2d(23)-C84 with diazirine under photoirradiation affords four Ad monoadducts (Sc2C2@C84(Ad)-A, Sc2C2@C84(Ad)-B, Sc2C2@C84(Ad)-C, and Sc2C2@C84(Ad)-D). The structure of Sc2C2@C84(Ad)-C was characterized using X-ray crystallography. Thermal interconversion of Sc2C2@C84(Ad)-A and Sc2C2@C84(Ad)-B to Sc2C2@C84(Ad)-C was also observed. The reaction mechanisms of the Ad addition and thermal interconversion were elucidated from theoretical calculations. Calculation results suggest that C84(Ad)-B and Sc2C2@C84(Ad)-C are thermodynamically favorable products. Their different chemical reactivities derive from Sc2C2 doping, which raises the HOMO and LUMO levels of the D2d(23)-C84 carbon cage.

The Unanticipated Dimerization of Ce@C2v (9)-C82 upon Co-crystallization with Ni(octaethylporphyrin) and Comparison with Monomeric M@C2v (9)-C82 (M = La, Sc, and Y).

We report that Ce@C2v (9)-C82 forms a centrosymmetric dimer when co-crystallized with Ni(OEP) (OEP = octaethylporphyrin dianion). The crystal structure of {Ce@C2v (9)-C82 }2 ⋅2[Ni(OEP)]⋅4 C6 H6 shows that a new C-C bond with a bond length of 1.605(5) Šconnects the two cages. The high spin density of the singly occupied molecular orbital (SOMO) on the cage and the pyramidalization of the cage are factors that favor dimerization. In contrast, the treatment of Ni(OEP) with M@C2v (9)-C82 (M = La, Sc, and Y) results in crystallization of monomeric endohedral fullerenes. A systematic comparison of the X-ray structures of M@C2v (9)-C82 (M = Sc, Y, La, Ce, Gd, Yb, and Sm) reveals that the major metal site in each case is located at an off-center position adjacent to a hexagonal ring along the C2  axis of the C2v (9)-C82 cage. DFT calculations at the M06-2X level revealed that the positions of the metal centers in these metallofullerenes M@C2v (9)-C82 (M = Sc, Y, and Ce), as determined by single-crystal X-ray structure studies, correspond to an energy minimum for each compound.

An experimentally observed trimetallofullerene Sm3@I(h)-C80: encapsulation of three metal atoms in a cage without a nonmetallic mediator.

We report the synthesis, isolation, and characterizations of the novel trimetallofullerene Sm3@I(h)-C80. Importantly, the experimental X-ray structure of Sm3@I(h)-C80 verified for the first time that three metal atoms can be stabilized in a fullerene cage without a nonmetal mediator. Furthermore, computational studies demonstrated the electronic features of Sm3@I(h)-C80, which are similar to that of theoretically studied Y3@I(h)-C80. Electrochemical studies of Sm3@I(h)-C80 showed a major difference from those of the well-studied isoelectronic species Sc3N@I(h)-C80 and La2@I(h)-C80.

The Improved Microwave Absorption Performance of the 3D Porous (Ni@NO-C)n/NO-C Composite Absorber.

Microwave absorbers that are lightweight and have good stability and high efficiency have attracted much attention for their applications in many contemporary fields. In this work, a 3D porous (Ni@NO-C)n/NO-C composite absorber was prepared using a wet chemistry method with Ni chains and melamine as precursors, in which NO-C (N,O-doped carbon)-encapsulated Ni particles are homogenously dispersed in the 3D porous networks of NO-C in the form of (Ni@NO-C)n chains. The special microstructure of the as-prepared material is proven to be beneficial for the improvement of its microwave absorption performance. The as-synthesized (Ni@NO-C)n/NO-C composite absorber exhibited an effective absorption bandwidth of 4.1 GHz and an extremely large reflection loss of -72.3 dB. The excellent microwave-absorbing performances can be ascribed to the cooperative consequences of dielectric loss and magnetic loss, along with the balance between attenuation capability and impedance matching.

Influences of different surface oxygen species on oxidation of toluene and/or benzene and their reaction pathways over Cu-Mn metal oxides.

Catalytic oxidation is considered as the most effective and economical method to remove low concentration volatile organic compounds (VOCs). Activation of oxygen to form active oxygen species on metal oxides catalyst plays a key role in the process. Three copper-manganese oxide catalysts with cubic Cu1.5Mn1.5O4 phases were prepared by microwave heating (CM-MW), sol-gel (CM-SG) and co-precipitation (CM-CP) methods, and applied for the elimination of toluene and benzene as representative aromatic VOCs. These catalysts exhibit different catalytic oxidation performance due to their different physicochemical properties. Various characterizations were used to clarify the role of different oxygen species in the oxidation of VOCs, and the reaction pathway. In situ DRIFTS were carried out to explore the function of surface adsorbed oxygen, oxygen vacancy, and surface lattice oxygen in the catalytic oxidation of VOCs over three catalysts. Various types of intermediate species and detailed reaction pathways are also explored by combining in situ DRIFTS and mass spectrometry. Among these catalysts, CM-MW with nanosheet morphology shows the best catalytic oxidation performance of toluene and/or benzene with/without H2O due to the most abundant active oxygen species, and the highest oxygen vacancy concentration which is beneficial to activate oxygen. Meanwhile, toluene and benzene do not interfere with each other during the mixture oxidation. This study can provide new inspiration for rational design of metal oxide catalysts to remove VOCs.

The Various Packing Structures of Tb@C82 (I, II) Isomers in Their Cocrystals with Ni(OEP).

Soot-containing terbium (Tb)-embedded fullerenes were prepared by evaporation of Tb4O7-doped graphite rods in an electric arc discharge chamber. After 1,2,4-trichlorobenzene extraction of the soot and rotary evaporation of the extract, a solid product was obtained and then dissolved into toluene by ultrasonication. Through a three-stage high-pressure liquid chromatographic (HPLC) process, Tb@C82 (I, II) isomers were isolated from the toluene solution of fullerenes and metallofullerenes. With the success of the growth of cocrystals of Tb@C82 (I, II) with Ni(OEP), the molecular structures of Tb@C82 (I) and Tb@C82 (II) were confirmed to be Tb@C2v(9)-C82 and Tb@Cs(6)-C82, respectively, based on crystallographic data from X-ray single-crystal diffraction. Moreover, it was found that Tb@C82 (I, II) isomers demonstrated different packing behaviors in their cocrystals with Ni(OEP). Tb@C2v(9)-C82 forms a 1:1 cocrystal with Ni(OEP), in which Tb@C2v(9)-C82 is aligned diagonally between the Ni(OEP) bilayers to form zigzag chains. In sharp contrast, Tb@Cs(6)-C82 forms a 2:2 cocrystal with Ni(OEP), in which Tb@Cs(6)-C82 forms a centrosymmetric dimer that is aligned linearly with Ni(OEP) pairs to form one-dimensional structures in the a-c lattice plane. In addition, the distance of a Ni atom in Ni(OEP) to the Cs(6)-C82 cage is much shorter than that to the C2v(9)-C82 one, indicative of a stronger π-π interaction between Ni(OEP) and the C82 carbon cage in the cocrystal of Tb@CS(6)-C82 and Ni(OEP). Density functional theory calculations reveal that the regionally selective dimerization of Tb@CS(6)-C82 is the result of a dominant unpaired spin existing on a particular C atom of the CS(6)-C82 cage.

Access to an unexplored chiral C82 †cage by encaging a divalent metal: structural elucidation and electrochemical studies of Sm@C2(5)-C82.

Access to a chiral C(82)  cage: Encaging a divalent samarium atom has provided access to an unexplored chiral cage of C(2)(5)-C(82) that has never been reported for trivalent M@C(82) or empty fullerenes. Inside this cage, a wandering Sm atom has been identified using crystallographic methods. In addition, electrochemical studies of Sm@C(2)(5)-C(82) have been performed to explore its oxidation properties (see figure).

Controllable deposition of platinum nanoparticles on single-wall carbon nanohorns as catalyst for direct methanol fuel cells.

Uniform and well dispersed platinum nanoparticles were successfully deposited on single-walled carbon nanohorns with the assistance of 4,4-dipydine and ion liquids, respectively. In particular, the size of platinum nanoparticles could be controlled in a very narrow range (2.2 to 2.5 nm) when ion liquids were applied. The crystalline nature of these platinum nanoparticles was confirmed by high resolution transmission electron microscopy observation and X-ray power diffraction analysis, and two species of platinum Pt(0) and Pt(II) were detected by X-ray photoelectron spectroscopy. Electrochemical studies revealed that thus obtained nanocomposites had much better electrocatalytic activity for the methanol oxidation than those prepared with carbon nanotubes as supporter.

Determination of Organophosphorus Pesticides Using Solid-Phase Extraction Followed by Gas Chromatography-Mass Spectrometry.

In this study, a method was developed for determination of three organophosphorus pesticides (OPPs) using graphene aerogel solid-phase extraction (SPE) combined with gas chromatography-mass spectrometry (GC-MS). The experimental results showed that the target analytes could be extracted on packed SPE cartridges and then eluted with tetrahydrofuran. The final sample solution was analyzed by GC-MS, which demonstrated good linearity between 0.5 and 500 µg L-1 with a correlation coefficient (r) of 0.9991-0.9998. The limits of detection (S/N = 3) and the limits of quantification (S/N = 10) for the three OPPs ranged from 0.38 to 0.82 µg L-1 and 1.32 to 2.75 µg L-1, respectively. The accuracy of the proposed method was evaluated by measuring the recovery of the spiked samples, which ranged from 91.2 to 103.7%, with relative standard deviations of 2.1-7.2%. This method was successfully applied for the determination of the target analytes in water samples taken from tap, wetlands and canal water.

Polymethyl(1-Butyric acidyl)silane-Assisted Dispersion and Density Gradient Ultracentrifugation Separation of Single-Walled Carbon Nanotubes.

Individual single-walled carbon nanotubes (SWNTs) with distinct electronic types are crucial for the fabrication of SWNTs-based electronic and magnetic devices. Herein, the water-soluble polymethyl(1-butyric acidyl)silane (BA-PMS) was synthesized via the hydrosilylation reaction between 3-butenoic acid and polymethylsilane catalyzed by 2,2'-azodibutyronitrile. As a new dispersant, BA-PMS displayed a quite good dispersing capacity to arc-discharged SWNTs and moderate selectivity for metallic species. The application of sucrose-DGU, the density gradient ultracentrifugation with sucrose as the gradient medium, to the co-surfactants (BA-PMS and sodium dodecyl sulfonate) individually dispersed SWNTs yielded metallic SWNTs of 85.6% purity and semiconducting SWNTs of 99% purity, respectively. This work paves a path to the DGU separation of the SWNTs dispersed by polymer-based dispersants with hydrophobic alkyl chains.

Crystallographic X-ray analyses of Yb@C(2v)(3)-C80 reveal a feasible rule that governs the location of a rare earth metal inside a medium-sized fullerene.

Single crystal X-ray diffraction studies of Yb@C(2v)(3)-C(80)·Ni(II)(OEP)·CS(2)·1.5C(6)H(6) (OEP = octaethylporphinate) reveal that a relatively flat region of the fullerene interacts with the Ni(II)(OEP) molecule, featuring shape-matching interactions. Surprisingly, it is found that the internal metal is located under a hexagonal carbon ring apart from the 2-fold axis of the C(2v)(3)-C(80) cage, presenting the first example of metallofullerenes with an asymmetrically positioned metal. Such an anomalous location of Yb(2+) is associated with its strong ability to pursue a large coordination number and the lack of hexagon along the C(2) axis of C(2v)(3)-C(80). It is accordingly assumed that a suitable cage hexagon is most likely to be preferred by the single rare earth metal to stay behind inside a medium-sized fullerene, such as C(80) and C(82).

Interaction between fullerenes and single-wall carbon nanotubes: the influence of fullerene size and electronic structure.

A series of fullerenes and endohedral metallofullerenes peapods have been synthesized by supercritical method in high filling rate. The interaction between SWNTs and various kinds of fullerenes (C60, C70, C78, C84) and metallofullerenes (Gd@C82, Er@C82, Ho@C82, Y@C82) has been further investigated. The slight blue shift of G-band in Raman spectra with respect to pristine SWNTs was attributed to the charge transfer from SWNTs to fullerenes cage. The obvious RBM shift strongly depended on the distance between the inner wall of the SWNTs and the fullerene cage and also partly associated with the electronic structure of the fullerene. These results indicated that the interaction between fullerenes and SWNTs, which was considered to be the van de walls interaction, can be influenced by the cage size and the kind of fullerenes.

The Efficient Photocatalytic Degradation of Organic Pollutants on the MnFe2O4/BGA Composite under Visible Light.

The MnFe2O4/BGA (boron-doped graphene aerogel) composite was prepared by hydrothermal treatment of MnFe2O4 particles, boric acid, and graphene oxide. When applied as a photo-Fenton catalyst for the degradation of rhodamine B, the MnFe2O4/BGA composite yielded a degradation efficiency much higher than the sum of those of individual MnFe2O4 and BGA under identical experimental conditions, indicating a strong synergetic effect established between MnFe2O4 and BGA. The catalytic degradation of rhodamine B was proved to follow pseudo first-order kinetics, and the apparent reaction rate constant on the MnFe2O4/BGA composite was calculated to be three- and seven-fold that on BGA and MnFe2O4, respectively. Moreover, the MnFe2O4/BGA composite also demonstrated good reusability and could be reused for four cycles without obvious loss of photocatalytic activity.

Enhanced Catalytic Oxidation of Toluene over Manganese Oxide Modified by Lanthanum with a Coral-Like Hierarchical Structure Nanosphere.

Coral-like lanthanum manganese oxides (LayMnOx) with a hierarchical structure nanosphere were successfully prepared using a simple method, which presented a high-efficiency catalytic performance for toluene combustion. Among them, La0.08MnOx with the Mn3O4 phase exhibits superior catalytic activity, such as a lower T95 value (218 °C), excellent H2O resistance, and catalytic stability. The effects of La addition on the bulk and surface physicochemical properties of LayMnOx were investigated by sorts of characterization including X-ray diffraction, scanning electron microscopy, transmission electron microscopy, N2 adsorption-desorption, temperature-programmed reduction with H2, temperature-programmed desorption of O2, X-ray photoelectron spectroscopy, and so forth. The results demonstrate that the doping of La can induce the variation of physicochemical properties and the formation of more surface oxygen species and high valence state amorphous manganese oxides, improving low-temperature reducibility, which facilitates good catalytic activity for La0.08MnOx. A series of in situ diffuse reflectance infrared Fourier transform spectroscopy experiments for toluene adsorption were performed on the La0.08MnOx catalyst pretreated under different atmosphere conditions to investigate the role of oxygen species and the reaction processes. The results indicate that the abundant surface oxygen species over La0.08MnOx can make the rapid formation of benzoic acid species, further transfer into CO2 and H2O, which is considered as the key factor in the activation and oxidation of toluene.