Design strategies of two-dimensional metal-organic frameworks toward efficient electrocatalysts for N2 reduction: cooperativity of transition metals and organic linkers

Advancing electrocatalytic reactions through mapping key intermediates to active sites via descriptors

Descriptors play a crucial role in electrocatalysis as they can provide valuable insights into the electrochemical performance of energy conversion and storage processes. They allow for the understanding of different catalytic activities and enable the prediction of better catalysts without relying on the time-consuming trial-and-error approaches. Hence, this comprehensive review focuses on highlighting the significant advancements in commonly used descriptors for critical electrocatalytic reactions. First, the fundamental reaction processes and key intermediates involved in several electrocatalytic reactions are summarized. Subsequently, three types of descriptors are classified and introduced based on different reactions and catalysts. These include d-band center descriptors, readily accessible intrinsic property descriptors, and spin-related descriptors, all of which contribute to a profound understanding of catalytic behavior. Furthermore, multi-type descriptors that collectively determine the catalytic performance are also summarized. Finally, we discuss the future of descriptors, envisioning their potential to integrate multiple factors, broaden application scopes, and synergize with artificial intelligence for more efficient catalyst design and discovery.

A DFT Investigation of B-Doped C3 N as Single Atom Electrocatalysts for N2 -to-NH3 Conversion

The NH3 synthesis from N2 plays an important role in the ecological cycle and industrial production. Different from industrial NH3 synthesis with high pollution and energy consumption, electrocatalytic NH3 synthesis is favored because of its environmental protection, energy saving, ambient reaction conditions and other characteristics. However, due to the low efficiency and poor reaction selectivity of the existing electrocatalysts, which can not be used actually, the development of new electrocatalysts for nitrogen reduction reaction (NRR) is particularly urgent. Herein, we designed a series of transition metal atoms anchored B-doped defective C3 N surface (TM@B2 C3 N) as single-atom catalysts. Through the screening process of N2 adsorption activation, N2 H formation and NH3 desorption, finally the excellent electrocatalysts with strong stability and high activity (Cr@B2 C3 N and Mn@B2 C3 N) were obtained. After simulating the entire pathway, it was found that the NRR process on Cr@B2 C3 N and Mn@B2 C3 N via consecutive and distal pathways with the lowest limiting potential of -0.42 and -0.52 V, which have the good ability to inhibit hydrogen evolution reaction. Finally, the electronic properties were analyzed, and the reason for their high catalytic activity was summarized. This work provides a new idea for the rational design of NRR electrocatalysts and promotes the practical application of electrocatalysts.

Structural Design of π-d Conjugated TMx B3 N3 S6 (x=2, 3) Monolayer Toward Electrocatalytic Ammonia Synthesis

Single-atom catalysts (SACs) have attracted wide attention to be acted as potential electrocatalysts for nitrogen reduction reaction (NRR). However, the coordination environment of the single transition metal (TM) atoms is essential to the catalytic activity for NRR. Herein, we proposed four types of 3-, 4-coordinated and π-d conjugated TMx B3 N3 S6 (x=2, 3, TM=Ti, V, Cr, Mn, Fe, Zr, Nb, Mo, Tc, Ru, Hf, Ta, W, Re and Os) monolayers for SACs. Based on density functional theory (DFT) calculations, I-TM2 B3 N3 S6 and III-TM3 B3 N3 S6 are the reasonable 3-coordinated and 4-coordinated structures screening by structure stable optimizations, respectively. Next, the structural configurations, electronic properties and catalytic performances of 30 kinds of the 3-coordinated I-TM2 B3 N3 S6 and 4-coordinated III-TM3 B3 N3 S6 monolayers with different single transition metal atoms were systematically investigated. The results reveal that B3 N3 S6 ligand is an ideal support for TM atoms due to existence of strong TM-S bonds. The 3-coordinated I-V2 B3 N3 S6 is the best SAC with the low limiting potential (UL ) of -0.01 V, excellent stability (Ef =-0.32 eV, Udiss =0.02 V) and remarkable selectivity characteristics. This work not only provides novel π-d conjugated SACs, but also gives theoretical insights into their catalytic activities and offers reference for experimental synthesis.

Transition Metal Catalysts for Atmospheric Heavy Metal Removal: A Review of Current Innovations and Advances

Atmospheric heavy metal pollution presents a severe threat to public health and environmental stability. Transition metal catalysts have emerged as a potent solution for the selective capture and removal of these pollutants. This review provides a comprehensive summary of current advancements in the field, emphasizing the efficiency and specificity of nanostructured transition metals, including manganese, iron, cobalt, nickel, copper, and zinc. Looking forward, we delve into the prospective trajectory of catalyst development, underscoring the need for materials with enhanced stability, regenerability, and environmental compatibility. We project that advancements in computational materials science, nanotechnology, and green chemistry will be pivotal in discovering innovative catalysts that are economically and environmentally sustainable. The integration of smart technologies for real-time monitoring and adaptive control is anticipated to revolutionize heavy metal remediation, ensuring efficient and responsive pollution abatement strategies in the face of evolving industrial scenarios and regulatory landscapes.

The novel π-d conjugated TM2B3N3S6 (TM = Mo, Ti and W) monolayers as highly active single-atom catalysts for electrocatalytic synthesis of ammonia

Recently, single-atom catalysts (SACs) are receiving significant attention in electrocatalysis fields due to their excellent specific activities and extremely high atomic utilization ratio. Effective loading of metal atoms and high stability of SACs increase the number of exposed active sites, thus significantly improving their catalytic efficiency. Herein, we proposed a series (29 in total) of two-dimensional (2D) conjugated structures of TM2B3N3S6 (TM means those 3d to 5d transition metals) and studied the performance as single-atom catalysts for nitrogen reduction reaction (NRR) using density functional theory (DFT). Results show that TM2B3N3S6 (TM = Mo, Ti and W) monolayers have superior performance for ammonia synthesis with low limiting potentials of -0.38, -0.53 and -0.68 V, respectively. Among them, the Mo2B3N3S6 monolayer shows the best catalytic performance of NRR. Meanwhile, the π conjugated B3N3S6 rings undergo coordinated electron transfer with the d orbitals of TM to exhibit good chargeability, and these TM2B3N3S6 monolayers activate isolated N2 according to the "acceptance-donation" mechanism. We have also verified the good stability (i.e., Ef < 0, and Udiss > 0) and high selectivity (Ud = -0.03, 0.01 and 0.10 V, respectively) of the above four types of monolayers for NRR over hydrogen evolution reaction (HER). The NRR activities have been clarified by multiple-level descriptors (ΔG*N2H, ICOHP, and Ɛd) in the terms of basic characteristics, electronic property, and energy. Moreover, the aqueous solution can promote the NRR process, leading to the reduction of ΔGPDS from 0.38 eV to 0.27 eV for the Mo2B3N3S6 monolayer. However, the TM2B3N3S6 (TM = Mo, Ti and W) also showed excellent stability in aqueous phase. This study proves that the π-d conjugated monolayers of TM2B3N3S6 (TM = Mo, Ti and W) as electrocatalysts show great potentials for the nitrogen reduction.

Preparation of 2D Materials and Their Application in Oil-Water Separation

The problems of environmental pollution are increasingly severe. Among them, industrial wastewater is one of the primary sources of pollution, so it is essential to deal with wastewater, especially oil and water mixtures. At present, biomimetic materials with special wettability have been proven to be effective in oil-water separation. Compared with three-dimensional (3D) materials, two-dimensional (2D) materials show unique advantages in the preparation of special wettable materials due to their high specific surface area, high porosity, controlled structure, and rich functional group rich on the surface. In this review, we first introduce oil-water mixtures and the common oil-water separation mechanism. Then, the research progress of 2D materials in oil-water separation is presented, including but not limited to their structure, types, preparation principles, and methods. In addition, it is still impossible to prepare 2D materials with large sizes because they are powder-like, which greatly limits the application in oil-water separation. Therefore, we provide here a review of several ways to transform 2D materials into 3D materials. In the end, the challenges encountered by 2D materials in separating oil-water are also clarified to promote future applications.

Nitrogen Reduction Reaction Catalyzed by Diatomic Metals Supported by N-Doped Graphite

In this article, for the transition metal-nitrogen ligand Mn-M@N6-C (M = Ag, Bi, Cd, Co, Cr, Cu, Fe, Hf, Ir, Mo, Nb, Ni, Os, Pd, Pt, Re, Rh, Ru, Sc, Ta, Tc, V, Y, Zn, Zr, Ti, W), by comparing the amount of change in the length of the N-N triple-bond, and calculating the adsorption energy of N2 and the change of charge around N2, it is shown that the activation effect of Sc, Ti, Y, Nb-Mn@N6-C on the single-atomic layer of graphite substrate is relatively good. The calculation of structural stability shows that the Mn-M@N6-C (M = Sc, Ti, Y) load is relatively stable when it is on the single-atomic layer of the graphite substrate. Through calculations, a series of data such as the adsorption free energy and reaction path are obtained, and the final results show that the preferred reaction mechanism of NRR is the alternating path on Mn-Ti@N6-C, and the reaction limit potential is only 0.16 eV, Mn-Ti@N6-C and has good NRR activity. In addition, the vertical path on Mn-Y@N6-C has a reaction limit potential of 0.39 eV. Mn-Y@N6-C also has good NRR catalyzing activity.

In silico design of single transition metal atom anchored defective boron carbide monolayers as high-performance electrocatalysts for the nitrogen reduction reaction

Development of low-cost and high-efficiency single atom catalysts (SACs) is essential for catalyzing nitrogen reduction reactions (NRR) under ambient conditions. Current SACs suffer from low selectivity and poor activity, making it hard for them to meet the requirements of industrial applications. Here, we present a graphene-like BC₃ monolayer as a substrate for single metal atoms. The catalytic performance of 4d and 5d metal atoms anchored in a vacancy containing BC₃ monolayer for NRR is systematically investigated by first-principles calculations. We find that Re@V_B is outstanding among all candidates, exhibiting high catalytic activity and selectivity, with a low limiting potential of -0.28 V. A new descriptor involving the active site and its environment is proposed, which has a volcano relationship with several factors in the catalytic process, establishing a link between the intrinsic properties of the active site and the catalytic performance. This study opens a new route to designing efficient catalysts with BC₃ as a substrate.

Blue energy generation by the temperature-dependent properties in funnel-shaped soft nanochannels

Salinity energy generation (SEG) studies have only been done under isothermal conditions at ambient temperature. The production of salinity energy can be improved under non-isothermal conditions, albeit preserving the energy efficiency. In the current study, the effects of gradients of temperature and concentration on the salinity energy generation process were examined simultaneously. Based on the temperature-dependent properties resulting from both temperature and concentration gradients, a numerical study was carried out to determine the maximum efficiency of salinity energy generation in funnel-shaped soft nanochannels. It was presumed that a dense layer of negative charge, called a polyelectrolyte layer (PEL), is coated on the walls of the nanochannels. Co-current and counter-current modes were used to obtain temperature and concentration gradients. Under steady-state conditions, the Poisson-Nernst-Planck, Stokes-Brinkman, and energy equations were numerically solved using equivalent approaches. The results revealed that by increasing the temperature and concentration ratios in both co-current and counter-current modes of operation, the salinity energy generation increased appreciably. The salinity energy generation increased from 30 to 80 pW upon increasing the temperature ratio from 1 to 8 at a constant concentration ratio of 1000 in counter-current mode. As verified from this analysis, low-grade heat sources (<100 °C) provide considerable energy conversion in PEL grafted nanofluidic confinement when placed between electrolyte solutions of different temperatures.

The identification of byproducts from the catalytic reduction reaction of 4-nitrophenol to 4-aminophenol: A systematic spectroscopic study

Acetaminophenol, commonly recognized as paracetamol (considered safer than aspirin) is formed by nitration of phenol (4-nitrophenol (4-NP)) for its conversion to 4-aminophenol (4-AP), followed by the acetylation for the final product. As 4-NP is an intermediate product in acetaminophenol (paracetamol) production from phenol the dynamic analysis of acetylation of amine group is important. This study focuses on the feasibility of spectroscopic studies to monitor the removal of 4-NP using sodium borohydride (NaBH₄) probe reaction in the presence of silver, gold, and bimetallic Ag/Au nanoparticles. UV-visible absorbance and fluorescence spectroscopy measurements reveal the formation of 1,4-benzoquinone (BQ), hydroquinone (HQ), and phenol (Ph) as the final products, in addition to the formation of typically reported 4-AP. The intermediates of NaBH₄ seem to play a significant role in the formation of BQ, which converts to HQ in the basic medium followed by the formation of phenol in an acidic medium. Complete kinetic analysis with respect to spectroscopic studies of the standard compounds is presented. Similar results were obtained with 4-NP spiked river and seawater samples. The present findings may lead to catalytic benchmarking that can differ from most of the current practices and highlight the importance of adopting a holistic approach towards the fundamental understanding of 4-NP catalytic reduction that must take into account the concentration of NaBH₄ and pH interdependencies.

Metal-organic framework grown in situ on chitosan microspheres as robust host of palladium for heterogeneous catalysis: Suzuki reaction and the p-nitrophenol reduction

In this study, the metal-organic framework ZIF-8 has been successfully planted on the surface of chitosan microspheres (CS/PDA@ZIF-8) using polydopamine as connecting material for the first time, which avoids the use of expensive, non-renewable, and non-biodegradable polystyrene microspheres commonly used as templates to prepare core-shell structures. Moreover, the metal-organic framework ZIF-8 was prepared specially by three different methods and all characterized by SEM, TEM, and BET, and the ZIF-8 shell prepared at room temperature presents a regular morphology, uniform size, large specific surface area (353.1 m²/g) than the shells prepared by the other methods including. The CS/PDA@ZIF-8₂₅@Pd with high catalytic activity and high stability was especially prepared by encapsulating Pd nanoparticles into the pores of CS/PDA@ZIF-8₂₅. Notably, the fabricated catalyst performed well in an array of reactions, for example the Kapp value of the p-nitrophenol reduction reaction reached 0.0426 s^-1, and the TOF of the Suzuki coupling reaction reached 128 h^-1. In addition, the ZIF-67, UiO-66, UiO-66-NH₂, HKUST-1, and NH₂-MIL-53(Al) were also grown on chitosan microcapsules successively to prepare the core-shell microspheres, which prove the universal applicability of this strategy. And beyond that, the introduction of chitosan microspheres endows the material with biodegradable properties and excellent recycling properties.

Construction of manganese-based metal organic frameworks derived from aromatic dicarboxylic acids and application for the adsorption of iodine

In this work, we selected terephthalic acid or 2-amino-terephthalic acid as ligand, transition metal manganese salt as metal source under the solvothermal conditions to successfully construct two kinds of manganese-based metal-organic frameworks (Mn-MOFs): Mn3(BDC)3(H2O)2 (1) and Mn3(NH2-BDC)3(DMF)4 (2) (H2BDC = terephthalic acid; NH2-BDC = 2-amino terephthalic acid; DMF = N, N-dimethyl formamide). It was characterized by elemental analysis, IR spectrum, thermogravimetric analysis (TG), X-ray powder diffraction (PXRD) and UV-vis absorption spectrum. It was found that the packing structures of compounds 1 and 2 were constructed by the trinuclear Mn3O16 building block and exhibited different spatial structure: compound 1 was a three-dimensional structure, and 2 was a two-dimensional network structure. The iodine adsorption in cyclohexane solution properties of compounds 1 and 2 were investigated. Research results showed that the uncoordinated amino group in the structure of framework compounds has a great influence on the iodine adsorption capacity and compound 2 had good adsorption property and reusability.

Catalytic nanoparticles and magnetic nanocatalysts in organic reactions: A mini review

Nanocatalysts, as a part of nanotechnology, have been seen very useful for various fileds of applications capturing a large contribution of the world market. Indeed, several unsolved issues of catalysts have been reconsidered by employing the new nanocatalysts including single core metal atoms and ions with surrounding holes. Moreover, it was expected that the future of catalytic reactions, especially those organic ones, will deal with the nanocatalyst applications. To this aim, the features of catalytic nanoparticles and magnetic nanocatalysts regarding evaluation of their advantages and applications in organic reactions were investigated in this work. Developments of catalytic nanoparticles and magnetic nanocatalysts were discussed in this work regarding the novel applications of such materials at the nanoscale for approaching advantageous features. Increased availability, activity, and stability are very important for applications of the catalysts in various organic reactions. Therefore, it is a must to discuss features of such nanocatalytic systems to provide more information about their advantages and even disadvantages of their applications.