Search

[Display omitted] • Active site engineering in MOFs is first explored for photocatalytic N 2 fixation. • Acetic acid is added to expose and regulate the (1 0 0) facet with more active sites. • The FeIII/FeII ratio is controlled to improve active site reduction ability. • The photocatalytic NH 3 production rate of optimal MOFs reaches 164 μmol h−1 g−1. Photocatalytic ammonia synthesis from N 2 is a carbon neutral approach, its efficiency is yet impeded by the lack of abundant and efficient active sites on catalyst surface. Herein, we explore active site engineering strategy via employing MOF-235-based heterovalent metal organic frameworks (HMOFs) with FeIII/FeII clusters to break this dilemma. Acetic acid was added in solvothermal process, which was adsorbed on (1 0 1) facet of HMOF(FeIII/FeII) to restrain its further growth. The (1 0 0)/(1 0 1) facet ratio of HMOFs was regulated by the acetic acid content. Meanwhile, the FeIII/FeII ratio was regulated by the Fe3+/Fe2+ feeding ratio. It is found that the (1 0 0) facet of HMOFs exists more abundant Fe active sites, exposing (1 0 0) facet can increase the amount of active sites. On the other hand, the FeIII active site is favourable of N 2 adsorption, while the FeII active site is favourable for N 2 activation. The excellent balance between N 2 adsorption and N 2 activation can promote the reduction ability of active sites. At the optimal FeIII/FeII ratio of 1:1 and (1 0 0)/(1 0 1) facet ratio of 4.84, the photocatalytic activity of HMOF(FeIII/FeII)-10 reached 164 μmol g−1 h−1, more than 20 times compared to HMOF(FeIII/FeII)-0 without exposing the (1 0 0) facet. Our strategy may provide a reference in exploiting advanced photocatalysts based on organic framework-based materials. [ABSTRACT FROM AUTHOR]

• Nitrogenase-inspired MIL-53(FeII/FeIII) is first synthesized for N 2 photo fixation. • Mixed-valence FeII/FeIII clusters mimic the active center in nitrogenase. • FeII are in-situ formed by ethylene glycol reductant in solvothermal process. • FeII/FeIII ratio is vital to coordinate catalytic activity and framework stability. • MIL-53(FeII/FeIII) stably yields 306 μmol h−1 g−1 NH 3 under visible light. Biological nitrogenases exhibit superior nitrogen fixation efficiency owing to their unique multi-iron metallocluster (Fe2+ 3 Fe3+ 4 M3+, M = Mo, V, Fe) coordinated by organic polypeptide. Herein, we design a kind of metal organic framework (MOF) photocatalyst, MIL-53(FeII/FeIII) (MIL = Material from Institute Lavoisier), in which the FeII and FeIII constitute the mixed-valence metalloclusters to mimic the Fe2+ active sites and high-valence metal ions in nitrogenases, respectively. Both the FeII and FeIII are coordinated by organic ligands (terephthalic acid), which afford the electron transfer chains as well as the support of monodispersed FeII active sites. The FeIII in MIL-53(FeII/FeIII) is partly in-situ reduced into FeII by ethylene glycol (EG) via one-step solvothermal method, and the FeII/FeIII ratio is regulated from 0.18:1 to 1.21:1 by varying the EG content. Our results show that the FeII/FeIII ratio can significantly affect the photocatalytic activity and structure stability, and MIL-53(FeII/FeIII)-1 with optimal FeII/FeIII ratio (1.06:1) achieves the highest ammonia evolution rate up to 306 μmol h−1 g−1, nearly 10-fold higher than that of other framework-based materials, while remaining stable after 24 h irradiation. Such nitrogenase-like design in MIL-53(FeII/FeIII) endows the efficient electron transfer, exposed active sites, and in particular rational synergy between the catalytic function and non-catalytic function. This work may open a new avenue to the rational design of nitrogen fixation photocatalysts based on framework materials. [ABSTRACT FROM AUTHOR]

• NM@NHM hetero-framework photocatalysts are designed and constructed. • The optimal photocatalyst exhibits a H 2 evolution rate of 2.25 mmol g−1 h−1 under visible light. • Both dual-ligand push-pull effect and heterojunction structure promote the electron transfer. • This study provides a new strategy to intensify the electron transfer in photocatalysis. The efficient transfer of photogenerated carriers is essential to the photocatalytic H 2 evolution. Herein, we designed and synthesized a kind of novel NH 2 -MIL-125@NH 2 /H-MIL-125 hetero-frameworks with nanopore structure to drive efficient charge transfer for photocatalytic H 2 evolution. Single-ligand NH 2 -MIL-125 (NM) and dual-ligand NH 2 /H-MIL-125 (NHM), which have similar composition, structure and well-matched energy band, were selected as the core and shell to prepare the NM@NHM hetero-framework as a proof-of-principle system. The hetero-framework strategy is proposed to intensify the charge transfer and thus enhance the photocatalytic activity. The H 2 evolution rate of optimal NM@NHM hetero-framework can reach 2.25 mmol g−1 h−1 under visible light, much higher than pristine NM (0.726 mmol g−1 h−1) and NHM (1.27 mmol g−1 h−1). Such high performance can be attributed to the hetero-framework structure consisting of NM and NHM with similar composition and structure, which reduces the interfacial resistance in the charge transfer, thus facilitating the photocatalytic H 2 evolution. Our work may provide a new strategy for the rational design of high-performance photocatalysts. [Display omitted] [ABSTRACT FROM AUTHOR]

• Porous cPTA/CNT/CNU nanorod is prepared by using PTA as both template and adhesive. • A g-C 3 N 4 isotype heterojunction forms on the cPTA nanorod surface in cPTA/CNT/CNU. • Optimal cPTA/CNT/CNU nanorod can degrade 95% RhB within 1 h under visible light. • A multistep electron transfer path from CNU, CNT to cPTA forms in cPTA/CNT/CNU. • Porous cPTA nanorod increases light harvesting, active sites and molecule channels. Graphite carbon nitride (g-C 3 N 4) has a huge application potential in the photocatalysis field due to its unique conjugated structure. Inspired by the mussel adhesion protein, the cPTA/CNT/CNU (cPTA, carbonized poly(tannic acid); CNT, g-C 3 N 4 prepared by thiourea); CNU, g-C 3 N 4 prepared by urea) nanorod was synthesized by using PTA as the adhesive and template, and thiourea and urea as g-C 3 N 4 precursors. The CNT/CNU isotype heterojunction is assembled on the surface of porous cPTA nanorod, which effectively solves the problem of high photogenerated electron-hole recombination of pure g-C 3 N 4. The optimal cPTA/CNT/CNU photocatalyst can degrade 95% of rhodamine B (RhB) within 1 h under visible light, which is much higher than CNT, CNU and CNT/CNU. With the conduction band potential difference of cPTA, CNT and CNU, a multistep electron transfer path forms in the cPTA/CNT/CNU, which can accelerate the electron transfer through the interface, thereby increasing the photocatalytic activity. [ABSTRACT FROM AUTHOR]

[Display omitted] • Porous cPTA/CN nanorod was prepared by using PTA as both template and adhesive. • In such a nanocomposite, the CN nanolayer forms on the surface of cPTA nanorods. • cPTA/CN degrades 97% RhB in 80 min and 78% tetracycline in 3 h under visible light. • cPTA facilitates the photoinduced carrier separation and afford more active sites. • This study offers a generic method for making nanorod photocatalysts. Solar energy-driven photocatalysis has become a promising green technology to degrade organic pollutants discharged into water environment in recent years. In this study, a kind of novel cPTA/CN nanorod photocatalysts were prepared by using poly(tannic acid) as both template and adhesive, in which the g-C 3 N 4 (CN) nanolayer formed on the surface of carbonized poly(tannic acid) (cPTA) nanorods, similar to the adhesion of marine mussel foot silk protein on the solid surface. The porous cPTA/CN nanorods with about 400 nm in width and 2–4 μm in length can degrade 97% Rhodamine B within 80 min and 78% tetracycline within 3 h under visible light irradiation. Porous cPTA nanorods play an important role for promoting the photocatalytic activity, which can not only accelerate the separation of photogenerated carriers, but also afford more active sites and molecule diffusion channels. This kind of nanocomposite photocatalysts may find broad application potential in the treatment of organic pollutants in aqueous solution. [ABSTRACT FROM AUTHOR]

[Display omitted] • Nitrogenase-inspired modular synthesis is designed to construct bimetallic UiO-66. • Zr-Hf clusters are constructed to coordinate the electron transfer and utilization. • U(0.5Hf)-2SH with TPA-2SH as the ligand can absorb and utilize the visible light. • A tandem ligand-to-metal-to-metal charge transfer mechanism (LMMCT) is proposed. • The resultant bimetallic UiO-66 yields 116.1 μmol h−1 g−1 NH 3 under visible light. Inspired by nitrogenase, we designed a kind of metal-organic framework (MOF) photocatalysts, U(Zr-Hf)-X, composed of bimetallic Zr-Hf nodes and different functional ligands. In the Zr-Hf bimetallic cluster, the Zr species serves as the active site of nitrogen fixation, while the Hf species acts as electron buffer tank to optimize electron transfer and utilization. In the organic ligands, the light absorption and utilization of MOFs is improved via introducing target functional groups to efficiently generate electrons. Notably, the organic ligand containing two thiol groups (-SH) can extend the absorption edge to the visible region. The optimal U(0.5Hf)-2SH (metal nodes: 0.5Zr: 0.5Hf; linkers: TPA-2SH) photocatalyst exhibits nitrogen fixation rate up to 116.1 μmol g−1 h−1 under visible-light, attributed to the ligand-to-metal-to-metal electron transfer (LMMET) pathway and Zr-based π-backbonding mechanism. Our nitrogenase-inspired strategy establishes a novel paradigm for rational design of visible-light-driven nitrogen fixation catalysts. [ABSTRACT FROM AUTHOR]

• CNNS/PDA/CdS is prepared via bioinspired adhesion and metal chelation of PDA. • CdS nanoparticles about 5−10 nm in size are in-situ anchored on the CNNS surface. • CNNS/PDA/CdS can degrade 97 % RhB within 80 min under visible light irradiation. • CNNS constructs type II heterostructure with CdS to improve energy band matching. • PDA layer facilitates the visible-light absorption and interfacial charge transfer. By utilizing the bioinspired adhesion and metal chelation of polydopamine (PDA), a kind of ternary nanocomposites that consist of the graphitic carbon nitride nanosheet (CNNS), PDA layer and cadmium sulfide (CdS) nanocrystals were synthesized. In the resultant CNNS/PDA/CdS nanocomposites, CdS nanocrystals about 5−10 nm in diameter are scattered on the CNNS surface in the presence of the PDA layer. Due to the energy band matching, CNNS constructs a type II heterostructure with CdS nanoparticles via the mediation of the electroconductive PDA layer, thus enhancing the photocatalytic activity. Compared with pristine CdS and CNNS, the CNNS/PDA/CdS nanocomposite conspicuously shows superior photocatalytic performance under visible light above 420 nm, which can degrade 97 % Rhodamine B (RhB) molecules within 80 min. The introduction of a PDA layer between CNNS and CdS not only promotes the photon energy absorption but also facilitates the separation of photoinduced electron-hole pairs. [ABSTRACT FROM AUTHOR]

• Highlights: Porous N-deficient g-C3N4 was fabricated with acetic acid-treated melamine as precursor. • Acetic acid plays a key role in the formation of porous structure and N deficiency. • PNCN can degrade almost 100 % RhB within 2.0 h and generate 257.5 μmol g−1 h−1 H2. • DFT calculation indicates that N deficiency can lead to bandgap narrowing and activity elevating. • This study affords a facile and scalable strategy to fabricate efficient g-C3N4 photocatalysts. Porous nitrogen-deficient graphic carbon nitride (PNCN) was fabricated by using acetic acid (HAc)-treated melamine as precursor via one-pot method. The as-prepared PNCN photocatalysts possess a loose porous structure with nitrogen deficiencies due to the decomposition of HAc during calcination process. The PNCN photocatalyst exhibits the rate constant of RhB degradation (1.92 h−1) and H 2 evolution rate (257.5 μmol g−1 h−1) for ∼4.6 and ∼2.5 times of pristine g-C 3 N 4 under visible light irradiation, respectively. The mesoporous structure can increase the specific surface area of PNCN (19.24 m2 g-1), thereby rendering ample active sites and facilitating visible-light utilization. The moderate nitrogen deficiencies can not only substantially enhance photocurrent density and interfacial charge transfer, but also restrain the recombination of photo-generated carriers. In addition, the density functional theory (DFT) calculation further provides insight into the photocatalytic mechanism over PNCN. This study may present a facile and scalable method to fabricate PNCN with superior photocatalytic performance, which may hold great promise in practical applications. [ABSTRACT FROM AUTHOR]