Electrochemical Co-reduction of N2 and CO2 to Urea Using Bi2S3 Nanorods Anchored to N-Doped Reduced Graphene Oxide.

Producing "green urea" using renewable energy, N2, and CO2 is a long-considered challenge. Herein, an electrocatalyst, Bi2S3/N-reduced graphene oxide (RGO), was synthesized by loading the Bi2S3 nanorods onto the N-RGO via a hydrothermal method. The Bi2S3/N-RGO composites exhibit the highest yield of urea (4.4 mmol g-1 h-1), which is 12.6 and 3.1 times higher than that of Bi2S3 (0.35 mmol g-1 h-1) and that of N-RGO (1.4 mmol g-1 h-1), respectively. N-RGO, because of its porous and open-layer structure, improves the mass transfer efficiency and stability, while the basic groups (-OH and -NH2) promote the adsorption and activation of CO2. Bi2S3 promotes the absorption and activation of inert N2. Finally, the defect sites and the synergistic effect on the Bi2S3/N-RGO composites work simultaneously to form urea from N2 and CO2. This study provides new insights into urea synthesis under ambient conditions and a strategy for the design and development of a new material for green urea synthesis.

Facile preparation of novel nickel sulfide modified KNbO3 heterojunction composite and its enhanced performance in photocatalytic nitrogen fixation.

This work was designed to prepare a novel NiS/KNbO3 p-n heterojunction composite for efficient photocatalytic nitrogen fixation under simulated sunlight. The NiS/KNbO3 photocatalyst was prepared through a two-step hydrothermal method. X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy analyses proved that NiS nanoparticles were closely decorated on the surface of KNbO3 nanorods, to facilitate the migration of electrons between the two semiconductors. Mott-Schottky analysis indicated that the Femi level of KNbO3 is higher than that of NiS. Thus, the electron migration from KNbO3 to NiS occurs naturally. This migration elevates the band potential of NiS, makes NiS/KNbO3 form a type-II photocatalyst, and generates an internal electric field in the composite. The synergetic effect of the internal electric field and the type-II band structure endows NiS/KNbO3 with high efficiency in the spatial separation of photogenerated electron-hole pairs, verified by electrochemical impedance spectroscopy and transient photocurrent experiments. Therefore, NiS/KNbO3 presents good efficiency in photocatalytic N2 reduction with an NH3 production rate of 155.6 µmol·L-1·g-1·h-1, which is 1.9 and 6.8 times higher than those of KNbO3 and NiS, respectively. UV-visible diffuse reflectance spectroscopy and N2-adsorption experiments were also performed to investigate the effect of light absorption and surface area on the photocatalytic reaction. Nevertheless, compared with the great promotion effect in charge separation, the contribution of the two factors can be ignored.

Facile fabrication of novel Ag2S/K-g-C3N4 composite and its enhanced performance in photocatalytic H2 evolution.

This work synthesized a novel Ag2S/K-g-C3N4 photocatalyst which was effective in photocatalytic hydrogen production under simulated sunlight and visible light. Systematic investigation including TG, XRD, FT-IR, DRS, XPS, N2-adsorption, SEM, TEM, PL, and photoelectrochemical analyses was executed to examine the structure, optical property and charge separation efficiency of the as-prepared photocatalysts. Result indicated that potassium was successfully doped into the g-C3N4 framework via direct heating the mixture of melamine and potassium iodide at 520 °C, which increases the BET surface area, broadens the visible light response region, and elevates the separation efficiency of electron-hole pairs. The modification of Ag2S nanoparticles on the optimal K-g-C3N4 sample further improves the surface charge separation efficiency via a type-II mechanism, which was believed to be the key role in photocatalytic reaction. The best Ag2S/K-g-C3N4 hybrid shows a photocatalytic H2 generation rate of 868 and 96 µmol·g-1·h-1 under simulated sunlight and visible light, respectively. This value is 2.7 and 1.3 times greater than that of g-C3N4 and K-g-C3N4, respectively. Meanwhile, the Ag2S/K-g-C3N4 displayed high photocatalytic stability. A probable mechanism of the synthesized photocatalyst was also suggested.

Effectively H2 generation over CdS/KTa0.75Nb0.25O3 composite via water splitting.

The present work reports a novel CdS/KTa0.75Nb0.25O3 (KTN) composite photocatalyst which was synthesized via a facile deposition method. The photocatalytic reaction in Na2S solution indicated that the as-synthesized composite presented excellent performance in water splitting under simulated sunlight and visible light. A thorough investigation was performed to reveal the origin of the high performance. X-ray diffraction (XRD), Raman, X-ray photoelectron spectroscopy (XPS), Scanning electron microscopy (SEM), and Transmission electron microscopy (TEM) experiments proved that CdS nanopartilces were uniformly dispersed on the surface of KTN naocubes. UV-visible diffuse reflection spectroscopy (DRS) analysis indicated that the addition of CdS improved the ability to absorb visible light. N2-adsorption analysis showed that the difference in surface area of the CdS/KTN composites was very small. Photoluminescence (PL) spectroscopy, electrochemical impedance spectroscopy (EIS), and transient photocurrent response (PC) analyses suggested that the added CdS greatly elevated the charge separation efficiency, which was considered as the key character of the composite. On the basis of the characterization results and the band structure of the two semiconductors, it is deduced that the CdS/KTN composite works according to a type-II mechanism under simulated sunlight. The optimal sample demonstrated a H2-generation rate of 1252 µmol·g-1·h-1, which is 260 and 48 times higher than that of KTN and CdS, respectively. Under visible light, photosensitization mechanism works in the composite. The synergetic effect of CdS and KTN in H2 production was also observed. Meanwhile, the composite also presented high photocatalytic stability. Considering the high activity and stability, the CdS/KTN may have potential application in photocatalytic H2 generation.

In-situ synthesis of AgNbO3/g-C3N4 photocatalyst via microwave heating method for efficiently photocatalytic H2 generation.

This paper is designed for elevating the photocatalytic H2-evoultion performance of g-C3N4 through the modification of AgNbO3 nanocubes. Via the microwave heating method, g-C3N4 was in-situ formed on AgNbO3 surface to fabricate a close contact between the two semiconductors in forty minutes. X-ray diffraction (XRD), Fourier transform-infrared (FT-IR), X-ray photoelectron spectroscopy (XPS) experiments were performed to confirm the binary structure of the synthesized AgNbO3/g-C3N4 composite. N2-adsorption and visible diffuse reflection spectroscopy (DRS) analyses indicated that the addition of AgNbO3 to g-C3N4 showed nearly negligible influence on the specific surface area and the optical property. Photoluminescence (PL) spectroscopy experiment suggested that the AgNbO3/g-C3N4 displayed reduced PL emission and longer lifetime of photoexcited charge carriers than g-C3N4, which could be ascribed to the suitable band potential and the intimate contact of g-C3N4 and AgNbO3. This result was also confirmed by the transient photocurrent response experiment. The influence of the enhanced charge separation was displayed in their photocatalytic reaction. AgNbO3/g-C3N4 sample showed enhanced performance in photocatalytic H2-generation under visible light illumination. The H2-evolution rate is determined to be 88 µmol·g-1·h-1, which reaches 2.0 times of g-C3N4. This study provides a feasible and rapid approach to fabricate g-C3N4 based composite.