3D hollow Bi2O3@CoAl-LDHs direct Z-scheme heterostructure for visible-light-driven photocatalytic ammonia synthesis

In-situ construction of WS2/ZIF-8 composites with an electron-rich interface for enhancing nitrogen photofixation

Photocatalytic nitrogen reduction reaction (PNRR) is an environmentally friendly synthesis method. It has been regarded as a promising approach for future NH3 preparation, which can reduce the natural fuel consumption and pollution of the Haber Bosch process. Nevertheless, this method exists poor activity for mass production, so it is urgent but challenging to explore highly efficient catalysts. Here, the novel WS2/ZIF-8 composites are reported, DFT and XPS indicate the transfer direction of electrons is from ZIF-8 to WS2, forming an electron-rich interface between WS2 and ZIF-8, thus it endows the more powerful photocatalytic nitrogen reduction ability for 2-WS2/ZIF-8 than monomer material. Meanwhile, 2-WS2/ZIF-8 exhibits admirable photocatalytic nitrogen reduction performance under real and simulated sunlight or in tap water, further attesting its excellent stability and practicability.

Nitrogen vacancy-induced spin polarization of ultrathin zinc porphyrin nanosheets for efficient photocatalytic CO2 reduction

Metalloporphyrin compounds have excellent electron transfer and visible light absorption ability, demonstrating broad application prospects in the field of photocatalysis. In this work, the nitrogen vacancies (NVs) were successfully introduced into zinc porphyrin (ZnTCPP) ultrathin nanosheets through surface N2 plasma treatment, which is environmentally friendly and can react in low temperatures. Furthermore, the prepared nitrogen vacancies-zinc porphyrin (NVs-ZnTCPP) materials exhibited excellent photocatalytic CO2 reduction activity and selectivity, specifically, the CO production rate of ZnTCPP-1 (N2 plasma treatment, 1 min) achieved as high as 12.5 µmol g-1h-1, which is about 2.7 times greater than that of untreated ZnTCPP. Based on the experimental and density functional theory calculation (DFT) results, it is found that the promoted photocatalytic performance of NVs-ZnTCPP could be mainly attributed to nitrogen vacancy-induced spin polarization by reducing the reaction barriers and inhibiting the recombination of photoexcited carriers. This work provides a new perspective for the construction of vacancy-based metalloporphyrin, and further explores the intrinsic mechanism between the electron spin property and the performance of the photocatalyst.

Non-noble-metal TiC-nanoparticle-promoted charge separation and photocatalytic degradation performance on Bi2O3 microrods: degradation pathway and mechanism investigation

In the present work, a promising binary TiC/Bi2O3 photocatalyst was obtained via a simple hydrothermal route. In the photodegradation experiment of acid orange 7 (AO7) and tetracycline (TC) irradiated by simulated sunlight, the attachment of TiC nanoparticles on the Bi2O3 microrods leads to an obvious improvement in the photocatalytic removal properties of the Bi2O3 microrods. The optimal removal efficiency of AO7 was achieved by the 7.5%TiC/Bi2O3 sample, which results in about 91.5% dye removal within 75 min of reaction. Meanwhile, the 7.5%TiC/Bi2O3 sample also exhibits favorable photodegradation performance for the degradation of TC, leading to about ∼76.9% TC being degraded after 75 min of irradiation. More importantly, the degradation pathways of AO7 and toxicity analysis of the intermediate products were performed based on liquid chromatography-mass spectrometry detection and theoretical simulation. The superior photocatalytic behavior of the TiC/Bi2O3 composite is attributed to the effective separation and migration of photoexcited electrons and holes in the heterojunction, where the TiC nanoparticles act as an acceptor of photoexcited electrons.

An electrochemiluminescence resonance energy transfer biosensor based on Luminol-LDH and CuS@Pt for detection of alpha-fetoprotein

Alpha-fetoprotein (AFP) is the best diagnostic marker for hepatocellular carcinoma (HCC) and plays an important role in the general surveillance of the population. Therefore, the establishment of an ultra-sensitive AFP assay is essential for the early screening and clinical diagnosis of HCC. In this work, we designed a signal-off biosensor for ultra-sensitive detection of AFP based on an electrochemiluminescent resonance energy transfer (ECL-RET) strategy using luminol intercalated layered bimetallic hydroxide (Luminol-LDH) as an ECL donor and Pt nanoparticles-grown on copper sulfide nanospheres (CuS@Pt) as ECL acceptor. The (Au NPs/Luminol-LDH)_n multilayer nanomembrane synthesized by our intercalation and layer-by-layer electrostatic assembly process not only effectively immobilizes luminol but also significantly enhances the ECL signal. The CuS@Pt composite has well visible light absorption ability and can burst the light emitted from luminol by ECL-RET. The biosensor showed good linearity in the range from 10^-5 ng mL^-1 to 100 ng mL^-1 and a minimum detection limit of 2.6 fg mL^-1. Therefore, the biosensor provides a novel and efficient strategy for the detection of AFP, which is important for the early screening and clinical diagnosis of HCC.

Introducing oxygen vacancies in a bi-metal oxide nanosphere for promoting electrocatalytic nitrogen reduction

The sluggish breakage of the N-N triple bond, as well as the existence of a competing hydrogen evolution reaction (HER), restricts the nitrogen reduction reaction process. Modification of the catalyst surface to boost N₂ adsorption and activation is essential for nitrogen fixation. Herein, we introduced surface oxygen vacancies in bimetal oxide NiMnO₃ by pyrolysis at 450 °C (450-NiMnO₃) to achieve remarkable NRR activity. The NiMnO₃ 3D nanosphere with a rough surface could increase catalytically active metal sites and introduce oxygen vacancies that are able to enhance N₂ adsorption and further improve the reaction rate. Benefiting from the introduced oxygen vacancies in NiMnO₃, 450-NiMnO₃ showed excellent performance for nitrogen reduction to ammonia with a high NH₃ yield of 31.44 μg h^-1 mg_cat^-1 (at -0.3 V vs. RHE) and a splendid FE of 14.5% (at -0.1 V vs. RHE) in 0.1 M KOH. 450-NiMnO₃ also shows high long-term electrochemical stability with excellent selectivity for NH₃ formation. ¹⁵N isotope labeling experiments further verify that the source of produced ammonia is derived from 450-NiMnO₃. The present study opens new avenues for the rational construction of efficient electrocatalysts for the synthesis of ammonia from nitrogen.

Interspersed Bi Promoting Hot Electron Transfer of Covalent Organic Frameworks Boosts Nitrogen Reduction to ammonia

Seeking highly-efficient, non-pollutant, and chemically robust photocatalysts for visible-light-driven ammonia production still remained challenging, especially in pure water. The key bottle-necks closely correlate to the nitrogen activation, water oxidization, and hydrogen evolution reaction (HER) processes. In this study, a novel Bi decorated imine-linked COF-TaTp (Bi/COF-TaTp) through N-Bi-O coordination is reasonably designed to achieve a boosting solar-to-ammonia conversion of 61 µmol^-1  g^-1  h^-1 in the sacrificial-free system. On basis of serial characterizations and DFT calculations, the incorporated Bi is conducive to the acceleration of charge carriers transfer and N₂ activation through the donation and back-donation mode. The N₂ adsorption energy of 5% Bi/COF-TaTp is calculated to be -0.19 eV in comparison with -0.09 eV of the pure COF-TaTp and the electron exchange between N₂ and the modified catalyst is much more intensive. Moreover, the accompanied hydrogen production process is effectively inhibited by Bi modification, demonstrated by the higher energy barrier for HER over Bi/COF-TaTp (2.62 eV) than the pure COF-TaTp (2.31 eV) when using H binding free energy (ΔG_H* ) as a descriptor. This work supplies novel insights for the design of photocatalysts for N₂ reduction and intensifies the understanding of N₂ adsorption and activation over covalent organic frameworks-based materials.

High-Efficiency Photocatalytic Ammonia Synthesis by Facet Orientation-Supported Heterojunction Cu2O@BiOCl[100] Boosted by Double Built-In Electric Fields

In this work, the advantages of in situ loading, heterojunction construction, and facet regulation were integrated based on the poly-facet-exposed BiOCl single crystal, and a facet-oriented supported heterojunction of Cu₂O and BiOCl was fabricated (Cu₂O@BiOCl[100]). The photocatalytic nitrogen reduction reaction (pNRR) activity of Cu₂O@BiOCl[100] was as high as 181.9 μmol·g^-1·h^-1, which is 4.09, 7.13, and 1.83 times that of Cu₂O, BiOCl, and Cu₂O@BiOCl-ran (Cu₂O randomly supported on BiOCl). Combined with the results of the photodeposition experiment, X-ray photoelectron spectroscopy characterization, and DFT calculation, the mechanism of Cu₂O@BiOCl[100] for pNRR was discussed. When Cu₂O directionally loaded on the [100] facet of BiOCl, electrons generated by Cu₂O will be transmitted to the [100] facet of BiOCl through Z-scheme electron transmission. Due to the directional separation characteristics of charge in BiOCl, the electrons transmitted from Cu₂O are enriched on the [001] facet of BiOCl, which will together with the original electrons generated by pristine BiOCl act on pNRR, thus greatly improving the activity of photocatalytic ammonia synthesis. Thus, a new construction scheme of biphasic semiconductor heterojunction was proposed, which provides a reference research idea for designing and synthesizing high-performance photocatalysts for nitrogen reduction.

A minireview on catalysts for photocatalytic N2 fixation to synthesize ammonia

Ammonia (NH3) is an important feedstock in chemical industry. Nowadays NH3 is mainly produced via the industrialized Haber-Bosch process, which requires substantial energy input, since it operates at high temperatures (400-650 °C) and high pressures (20-40 Mpa). From the energy conservation point of view, it is of great significance to explore an alternative avenue to synthesize NH3, which is in line with the concept of sustainable development. Very recently, photocatalytic N2 fixation (PNF) has been discovered as a safe and green approach to synthesize NH3, as it utilizes the inexhaustible solar energy and the abundant N2 in nature to synthesize NH3 under mild conditions. A highly efficient catalyst is the core of PNF. Up to now, extensive studies have been conducted to design efficient catalysts for PNF. Summarizing the catalysts reported for PNF and unraveling their reaction mechanisms could provide guidance for the design of better catalysts. In this review, we will illustrate the development of catalysts for PNF, including semiconductors, plasmonic metal-based catalysts, iron-based catalysts, ruthenium-based catalysts and several other catalysts, point out the remaining challenges and outline the future opportunities, with the aim to contribute to the development of PNF.

A highly active Z-scheme SnS/Zn2SnO4 photocatalyst fabricated for methylene blue degradation

Herein, a highly active Z-scheme SnS/Zn₂SnO₄ photocatalyst is fabricated by a one-step hydrothermal route. The structure, composition, photoelectric and photocatalytic properties of the as-prepared photocatalysts are systematically researched. The results demonstrate that SZS-6 displays a good photocatalytic performance with an efficiency of 94.5% to degrade methylene blue (MB) under visible light irradiation (λ > 420 nm). And its degradation rate constant is up to 0.0331 min⁻¹, which is 3.9 and 4.4 times faster than SnS and Zn₂SnO₄, respectively. The formation of a Z-scheme heterojunction facilitates the separation and transfer of charges, which improves the degradation of MB. The Z-scheme charge transfer pathway of the SnS/Zn₂SnO₄ photocatalyst is verified by the shifted peaks of the X-ray photoelectron spectroscopy (XPS) spectrum, the relative position of the bandgap, work function as well as free radical trapping experiments. The photocatalytic mechanism for the degradation of MB by SnS/Zn₂SnO₄ is proposed.

Herein, a highly active Z-scheme SnS/Zn₂SnO₄ photocatalyst is fabricated by a one-step hydrothermal route.