Efficient photoreduction of carbon dioxide to ethanol using diatomic nitrogen-doped black phosphorus.

Successful conversion of CO2 into C2 products requires the development of new catalysts that overcome the difficulties in efficient light harvesting and CO-CO coupling. Herein, density functional theory (DFT) is used to assess the photoreduction properties of nitrogen-doped black phosphorus. The geometric structure, redox potential, first step of hydrogenation activation, CO desorption, and CO-CO coupling are systematically calculated, based on which the diatomic nitrogen-doped black phosphorus (N2@BPV) stands out. The calculated results of the CO2RR pathway demonstrate that N2@BPV has excellent selectivity and high activity for CH3CH2OH production. The results of the time-dependent ab initio nonadiabatic molecular dynamics simulation show that the diatomic N active sites of N2@BPV facilitate charge separation and inhibit electron-hole recombination. In addition, the activation mechanism of CO2 is studied. The main reason for CO2 activation is attributed to the imbalance in electron transfer that destroys the symmetry of CO2. We expect that our study will offer some theoretical guidance in CO2 conversion.

NiFe Nanoparticle-Encapsulated Ultrahigh-Oxygen-Doped Carbon Layers as Bifunctional Electrocatalysts for Rechargeable Zn-Air Batteries.

There is an urgent demand for developing highly efficient bifunctional electrocatalysts with excellent stability toward the oxygen evolution and reduction reactions (OER and ORR, respectively) for rechargeable Zn-air batteries (ZABs). In this work, NiFe nanoparticles encapsulated within ultrahigh-oxygen-doped carbon quantum dots (C-NiFe) as bifunctional electrocatalysts are successfully obtained. The accumulation of carbon layers formed by carbon quantum dots results in abundant pore structures and a large specific surface area, which is favorable for improving catalytic active site exposure, ensuring high electronic conductivity and stability simultaneously. The synergistic effect of NiFe nanoparticles enriched the number of active centers and naturally increased the inherent electrocatalytic performance. Benefiting from the above optimization, C-NiFe shows excellent electrochemical activity for both OER and ORR processes (the OER overpotential is only 291 mV to achieve 10 mA cm-2). Furthermore, the C-FeNi catalyst as an air cathode displays an impressive peak power density of 110 mW cm-2, an open-circuit voltage of 1.47 V, and long-term durability over 58 h. The preparation of this bifunctional electrocatalyst provides a design idea for the construction of bimetallic NiFe composites for high-performance Zn-air batteries.

Enhancing photocatalytic overall water-splitting performance on dual-active-sites of the Co-P@MoS2 catalysts: a DFT study.

The rational construction of photocatalysts possesses tremendous potential to solve the energy crisis and environmental pollution; however, designing a catalyst for solar-driven overall water-splitting remains a great challenge. Herein, we propose a new MoS2-based photocatalyst (Co-P@MoS2), which skillfully uses the cobalt (Co) atom to stimulate in-plane S atoms and employs the phosphorus (P) atom to stabilize the basal plane by forming the Co-P bands. Using density functional theory (DFT), it was found that oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) can occur at the P site and S2 site of the Co-P@MoS2, respectively, and the dual-active sites successfully makes a delicate balance between the adsorption and dissociation of hydrogen. Furthermore, the improved overall water-splitting performance of Co-P@MoS2 was verified by analyzing the results of the electron structure and the dynamics of photogenerated carries. It was found that the imbalance of electron transfer caused by the introduction of the Co atom was the main contributor to the catalytic activity of Co-P@MoS2. Our study broadens the idea of developing photocatalysts for the overall water-splitting.

Efficient Removal of Pb(â ¡) by Highly Porous Polymeric Sponges Self-Assembled from a Poly(Amic Acid).

Lead (II) (Pb(II)) is widespread in water and very harmful to creatures, and the efficient removal of it is still challenging. Therefore, we prepared a novel sponge-like polymer-based absorbent (poly(amic acid), PAA sponge) with a highly porous structure using a straightforward polymer self-assembly strategy for the efficient removal of Pb(II). In this study, the effects of the pH, dosage, adsorption time and concentration of Pb(II) on the adsorption behavior of the PAA sponge are investigated, revealing a rapid adsorption process with a removal efficiency up to 89.0% in 2 min. Based on the adsorption thermodynamics, the adsorption capacity increases with the concentration of Pb(II), reaching a maximum adsorption capacity of 609.7 mg g-1 according to the Langmuir simulation fitting. Furthermore, the PAA sponge can be efficiently recycled and the removal efficiency of Pb(II) is still as high as 93% after five adsorption-desorption cycles. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analyses reveal that the efficient adsorption of Pb(II) by the PAA sponge is mainly due to the strong interaction between nitrogen-containing functional groups and Pb(II), and the coordination of oxygen atoms is also involved. Overall, we propose a polymer self-assembly strategy to easily prepare a PAA sponge for the efficient removal of Pb(II) from water.

First-principles calculations of 0D/2D GQDs-MoS2 mixed van der Waals heterojunctions for photocatalysis: a transition from type I to type II.

The fabrication of type II heterojunctions is an efficient strategy to facilitate charge separation in photocatalysis. Here, mixed dimensional 0D/2D van der Waals (vdW) heterostructures (graphene quantum dots (GQDs)-MoS2) for generating hydrogen from water splitting are investigated based on density functional theory (DFT). The electronic and photocatalytic properties of three heterostructures, namely, C6H6-MoS2, C24H12-MoS2 and C32H14-MoS2 are estimated by analyzing the density of states, charge density difference, work function, Bader charge, absorption spectra and band alignment. The results indicated that the built-in electric fields from GQDs to MoS2 boost charge separation. Meanwhile, all the GQDs-MoS2 exhibit strong absorption in the visible light region. Surprisingly, the transition of heterojunctions from type I to type II is realized by tuning the size of GQDs. In particular, C32H14-MoS2 with enhanced visible-light absorption and an appropriate band edge position, as a type II heterostructure, may be a promising photocatalyst for generating hydrogen from water splitting. Thus, in this work a novel type II 0D/2D nanocomposite as a photocatalyst is constructed that provides a strategy to regulate the type of heterostructure from the perspective of theoretical calculation.

Sandwich Photothermal Membrane with Confined Hierarchical Carbon Cells Enabling High-Efficiency Solar Steam Generation.

Solar-driven vaporization is a sustainable solution to water and energy scarcity. However, most of the present evaporators are still suffering from inefficient utilization of converted thermal energy. Herein, a universal sandwich membrane strategy is demonstrated by confining the hierarchical porous carbon cells in two energy barriers to obtain a high-efficiency evaporator with a rapid water evaporation rate of 1.87 kg m-2 h-1 under 1 sun illumination, which is among the highest performance for carbon-based and wood-based evaporators. The significantly enhanced evaporation rate is mainly attributed to the inherently optimized porous evaporation mode derived from the hierarchical hollow structures of pollen carbon cells, and the synergistically regulated water transporting and thermal management performance of the sandwich membrane. Moreover, the constructed sandwich membrane also exhibits excellent self-regenerating performance in simulated seawater and high salinity water. The developed device can maintain an average evaporation rate of 4.3 L m-2 day-1 in a 25 day consecutive outdoor test.

Theoretical insight into the photophysical properties of long-lifetime Ir(iii) and Rh(iii) complexes for two-photon photodynamic therapy.

Two-photon photodynamic therapy (TP-PDT) plays crucial roles in curing tumors because it involves deep penetration of drugs into the tissue and has minimal damage to the surrounding cells. Our theoretical study was aimed at providing fresh insights into photosensitizers, such as [Ir(N^C)2(N^N)]+ (N^C = 2-phenylpyridine, N^N = bis-benzimidazole) and [Rh(N^C)2(N^N)]+, to treat cancer via the TP-PDT route. To better understand the properties of the complexes [Ir(N^C)2(N^N)]+ and [Rh(N^C)2(N^N)]+, the one-photon and two-photon absorption electronic spectra, energy gap (ΔES-T), strength of two-photon absorption cross-section (δ), spin-orbit matrix element (S1|HSO|Tj), and phosphorescence lifetimes (τ) were calculated by DFT and TD-DFT. The calculation results suggested that both complexes met the criteria (i.e. an efficient ISC process, enough energy to produce 1O2 and phototherapeutic window of the absorption wavelength) of photosensitizers; importantly, the designed complex [Rh(N^C)2(N^N)]+ had better performance than [Ir(N^C)2(N^N)]+, especially in the long-lived triplet excited state. It is expected that our research can make quite a few contributions to the development of photosensitizers and establish some guidelines for experiments based on TP-PDT.

Simultaneous Electrochemical Detection of Nitrite and Hydrogen Peroxide Based on 3D Au-rGO/FTO Obtained Through a One-Step Synthesis.

In this paper, Au and reduced graphene oxide (rGO) were successively deposited on fluorine-doped SnO2 transparent conductive glass (FTO, 1 × 2 cm) via a facile and one-step electrodeposition method to form a clean interface and construct a three-dimensional network structure for the simultaneous detection of nitrite and hydrogen peroxide (H2O2). For nitrite detection, 3D Au-rGO/FTO displayed a sensitivity of 419 µA mM-1 cm-2 and a linear range from 0.0299 to 5.74 mM, while for the detection of H2O2, the sensitivity was 236 µA mM-1 cm-2 and a range from 0.179 to 10.5 mM. The combined results from scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, X-ray diffraction measurements (XRD) and electrochemical tests demonstrated that the properties of 3D Au-rGO/FTO were attributabled to the conductive network consisting of rGO and the good dispersion of Au nanoparticles (AuNPs) which can provide better electrochemical properties than other metal compounds, such as a larger electroactive surface area, more active sites, and a bigger catalytic rate constant.

Theoretical study on photophysical properties of three high water solubility polypyridyl complexes for two-photon photodynamic therapy.

Two-photon photodynamic therapy (TP-PDT) is a very promising treatment that has drawn much attention in recent years due to its ability to penetrate deeper into tissues and minimize the damage to normal cells. Here, the properties of three highly water soluble Ru(ii) and Zn(ii) polypyridyl complexes as photosensitizers (PSs) were examined, including the one-photon and two-photon absorption (OPA and TPA) spectra, singlet-triplet energy gap (ΔH-L), TPA cross-section and spin-orbit coupling constant via Density Function Theory (DFT) and Time-Dependent Density Functional Theory (TD-DFT). Their potential therapeutic use as photosensitizers in TP-PDT is proposed, where the reasoning is as follows: first, they possess strong absorption in the therapeutic window; second, the vertical excitation energy is greater than 0.98 eV, which can generate a singlet oxygen species and the remarkable coupling between the S1 and T1 states. Moreover, the spin-orbit matrix elements are greater than 0.24 cm-1 for Ru-bpy and Zn-tpy, indicating that the intersystem spin crossing processes are efficient. It is expected that these complexes will be applied to PSs in TP-PDT, and we hope this research can serve as a guideline for the development of efficient two-photon PSs.

Rapid synthesis of rGO conjugated hierarchical NiCo2O4 hollow mesoporous nanospheres with enhanced glucose sensitivity.

NiCo2O4 nanospheres, a type of conjugated reduced graphene oxide (rGO), are compounded by a simple and easy synthesis of Cu2O/GO and fabricated NiCo2O4/rGO nanocomposites based on a Cu2O/GO template. The structure and morphology of the hierarchical NiCo2O4/rGO are characterized by x-ray diffraction, x-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy. The electrochemistry properties of NiCo2O4/rGO composites toward glucose are determined based on a glassy carbon electrode, and the results indicate that the hollow nanospheres of NiCo2O4/rGO could achieve high-sensitivity detections of glucose. The NiCo2O4/rGO composite has a detection range of 0.04 mM to 1.28 mM, a sensitivity of 2082.57 µA mM-1 cm-2, and a detection limit of 0.7 µM. The composite further exhibits obvious stability, superior reproducibility, and excellent selectivity. This study demonstrates that NiCo2O4/rGO is a unique and material with high potential in glucose sensing.

Hierarchical NiCo2O4 Hollow Sphere as a Peroxidase Mimetic for Colorimetric Detection of H2O2 and Glucose.

In this work, the hierarchical NiCo2O4 hollow sphere synthesized via a "coordinating etching and precipitating" process was demonstrated to exhibit intrinsic peroxidase-like activity. The peroxidase-like activity of NiCo2O4, NiO, and Co3O4 hollow spheres were comparatively studied by the catalytic oxidation reaction of 3,3,5,5-tetramethylbenzidine (TMB) in presence of H2O2, and a superior peroxidase-like activity of NiCo2O4 was confirmed by stronger absorbance at 652 nm. Furthermore, the proposed sensing platform showed commendable response to H2O2 with a linear range from 10 µM to 400 µM, and a detection limit of 0.21 µM. Cooperated with GOx, the developed novel colorimetric and visual glucose-sensing platform exhibited high selectivity, favorable reproducibility, satisfactory applicability, wide linear range (from 0.1 mM to 4.5 mM), and a low detection limit of 5.31 µM. In addition, the concentration-dependent color change would offer a better and handier way for detection of H2O2 and glucose by naked eye.

Multi-shelled hollow micro-/nanostructures.

Great progress has been made in the preparation and application of multi-shelled hollow micro-/nanostructures during the past decade. However, the synthetic methodologies and potential applications of these novel and interesting materials have not been reviewed comprehensively in the literature. In the current review we first describe different synthetic methodologies for multi-shelled hollow micro-/nanostructures as well as their compositional and geometric manipulation and then review their applications in energy conversion and storage, sensors, photocatalysis, and drug delivery. The correlation between the geometric properties of multi-shelled hollow micro-/nanostructures and their specific performance in relevant applications are highlighted. These results demonstrate that the geometry has a direct impact on the properties and potential applications of such materials. Finally, the emerging challenges and future development of multi-shelled hollow micro-/nanostructures are further discussed.

Enhanced conversion of CO2 into C2H4 on single atom Cu-anchored graphitic carbon nitride: Synergistic diatomic active sites interaction.

Single atom metal-nitrogen-carbon materials have emerged as remarkably potent catalysts, demonstrating unprecedented potential for the photo-driven reduction of CO2. Herein, a unique Cu@g-C3N5 catalyst obtained by cooperation of single atom Cu and nitrogen-rich g-C3N5 is proposed. The particular CuN diatomic active sites (DAS) in Cu@g-C3N5 contribute to the formation of highly stable CuOCN adsorption, a key configuration for CO2 activation and CC coupling. The synergistic diatomic active sites interaction is found responsible for the efficient photoreduction of CO2 to C2H4 which has been demonstrated in our Gibbs free energy calculation and COHP analysis. The CO2 activation mechanism was studied, the charge density difference and DOS analysis show that the low oxidation state Cu atom significantly affects the electronic structure of g-C3N5 and then enhance the catalytic activity of CO2 hydrogenation.

Facile one-step solvothermal synthesis of iron oxide/polypyrrole nanocomposites and their magnetic properties.

Iron oxide/polypyrrole (PPy) nanocomposites (NCs) were prepared by a facile one-step solvothermal process using FeCl3 x 6H2O and pyrrole as starting materials. The resultant products were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), differential scanning calorimetry (DSC) and superconducting quantum interference device magnetometer (SQUID). TEM image suggested the mesoporosity of the iron oxide/polypyrrole nanocomposites and pyrrole is found to play an important role in controlling the final morphology and porosity of the products. Magnetic hysteresis measurement reveals that nanocomposite shows a superparamagnetic behavior, and possesses a larger saturation magnetization strength (M(s)) of about 15.06 emu/g at room temperature, which allows its application in adsorption or separation as magnetically recyclable materials.

Synthesis and characterization of hollow cadmium oxide sphere with carbon microsphere as template.

Cadmium Oxide (CdO) hollow spheres have been synthesized by using carbon microsphere as sacrificial template. The products were characterized by X-ray powder diffraction (XRD), scanning electronic microscopy (SEM) and transmission electron microscopy (TEM). The average diameter and shell thickness of as-prepared hollow spheres are about 600 nm and 50 nm, respectively. The formation of hollow spheres was investigated and it was found that the shell formed when the heating temperature reached about 673 K and the sequential heat treatment could remove the carbon template. Moreover, the influence of other experimental parameters including concentration (0.1-5 M) and type of cadmium salts (cadmium chloride, cadmium acetate and cadmium nitrate, etc.) as well as type of solvents (water, ethanol and dimethylfomamide) were also investigated.

A novel and highly efficient photocatalyst based on P25-graphdiyne nanocomposite.

Titania nanoparticles (P25) are successfully chemically bonded with graphdiyne (GD) nanosheets by a facile hydrothermal treatment, to form a novel nanocomposite photocatalyst. The as-prepared P25-GD nanocomposite exhibits higher photocatalytic activity for degrading methylene blue under UV irradiation than not only P25 and P25-carbon nanotube composite but also the current well-known P25-graphene composite photocatalysts. Moreover, P25-GD also shows considerable visible-light-driven photocatalytic activity, since the formation of chemical bonds between P25 and GD effectively decreases the bandgap of P25 and extends its absorbable light range. The photocatalytic activity of P25-GD can be adjusted by changing the content of GD in composites and the optimized value is about 0.6 wt%. Such a nanocomposite photocatalyst might find potential application in a wide range of fields including air purification and waste water treatment.

Water-soluble monodispersed lanthanide oxide submicrospheres: PVP-assisted hydrothermal synthesis, size-control and luminescence properties.

We report a facile hydrothermal synthetic route to prepare a class of monodispersed lanthanide-based compound submicrospheres with controllable size, which employs raw lanthanide oxides as starting material, urea as precipitator and poly(N-vinyl-2-pyrrolidone) (PVP) as surfactant. Dependent on the intrinsic properties of respective lanthanide, the resulting products could be in the form of oxide, hydroxide or basic carbonate. These lanthanide hydroxides or basic carbonates can be easily transformed into their corresponding oxides by calcination, retaining the same morphology and size dispersion. The formation mechanism of these lanthanide-based compound submicrospheres is investigated and PVP plays a critical role in forming uniform and well-dispersed products. Furthermore, this method could be extended to a binary system by using two kinds of lanthanide oxides as starting material, resulting in doped-type lanthanide oxide submicrospheres (such as Y(2)O(3):Eu(3+)). The Y(2)O(3):Eu(3+) submicrospheres exhibit nearly uniform spherical morphology and narrow size distribution as well as good water solubility and sharp spectral emission at 610 nm (corresponding to the 5D(0)-7F(2) transition of Eu(3+)). This makes them attractive materials for applications in fields such as fluorescent lamps, field emission displays (FEDs) or LCDs, or as biomedical labels and molecular probes.

Highly porous nitrogen-doped carbon superstructures derived from the intramolecular cyclization-induced crystallization-driven self-assembly of poly(amic acid).

Hierarchically porous carbon nanomaterials have shown significant potential in electrochemical energy storage due to the promoted charge and mass transfer. Herein, a facile template-free method is proposed to prepare nitrogen-doped carbon superstructures (N-CSs) with multi-level pores by pyrolysis of polymeric precursors derived from the intramolecular cyclization-induced crystallization-driven self-assembly (ICI-CDSA) of poly(amic acid) (PAA). The excellent thermal stability of PAA enables the N-CSs to inherit the hierarchical structure of the precursors during pyrolysis, which facilitates the formation of meso- and macropores while the decomposition of the precursors promotes the creation of micropores. Electrochemical tests demonstrate the ultrahigh surface-area-normalized capacitance (76.5 µF cm-2) of the N-CSs facilitated by the hierarchically porous structure, promoting the charge and mass transfer, as well as the high utilization of pyridinic and pyrrolic nitrogen (12.9%) to provide significant pseudocapacitance contribution up to 40.6%. Considering the diversity of monomers of PAA, this ICI-CDSA strategy could be extended to prepare carbon nanomaterials with various morphologies, pore structures and chemical compositions.

A Photoelectrochemical Platform Based on Polyaniline-Modified Titanium Dioxide Facet Heterostructure.

A photoelectrochemical (PEC) electrode for glucose detection was built based on polyaniline (PANI) modified titanium dioxide heterojunction (FH-TiO2) structures. Ultrathin titanium dioxide (TiO2) nanosheets are assembled onto rutile nanorods (TiO2 NRs). Experiments show that the main exposed faces of these nanosheets are (101) or (111) crystal planes. Proven by theoretical calculation, the bottom of the conduction band (CB) of (111) is 0.15 eV lower than the bottom of the conduction band of (101). Therefore, when the material is excited by light, photogenerated electrons are able to transfer from the conduction band of (101) to the conduction band of (111). PANI was introduced as a medium to effectively conduct photogenerated charges between glucose oxidase and titanium dioxide. A photoelectric detection electrode for glucose was fabricated by loading glucose oxidase onto PANI@FH-TiO2. This electrode showed excellent performance in 0.2-1.0 mM linear range with a sensitivity 15.63 µA mM-1 cm-2 and 1.0-15.0 mM linear range with a sensitivity of 1.42 µA mM-1 cm-2.

One-pot synthesis of porous hematite hollow microspheres and their application in water treatment.

Alpha-Fe2O3 hollow micospheres have been successfully synthesized by solvothermal method at 200 degrees C. The synthesized products are characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and the nitrogen adsorption-desorption isotherm technique. The alpha-Fe2O3 hollow microspheres have an average diameter of 2-3 microm, the shell consists of numerous aligned nanorods with length of about 200-400 nm. The effects of solvent and reaction time have been studied. The Ostwald ripening mechanism is proposed to account for the formation of alpha-Fe2O3 hollow microspheres. Because of the porous hollow microstructure and large specific surface area, the microspheres were found to be effective sorbents for the removal of Cr(VI) ions from wastewater.