Advanced electrocatalysts based on two-dimensional transition metal hydroxides and their composites for alkaline oxygen reduction reaction

Ultrasensitive PD-L1-Expressing Exosome Immunosensors Based on a Chemiluminescent Nickel-Cobalt Hydroxide Nanoflower for Diagnosis and Classification of Lung Adenocarcinoma

Programmed death ligand-1 (PD-L1)-expressing exosomes are considered a potential marker for diagnosis and classification of lung adenocarcinoma (LUAD). There is an urgent need to develop highly sensitive and accurate chemiluminescence (CL) immunosensors for the detection of PD-L1-expressing exosomes. Herein, N-(4-aminobutyl)-N-ethylisopropanol-functionalized nickel-cobalt hydroxide (NiCo-DH-AA) with a hollow nanoflower structure as a highly efficient CL nanoprobe was synthesized using gold nanoparticles as a "bridge". The resulting NiCo-DH-AA exhibited a strong and stable CL emission, which was ascribed to the exceptional catalytic capability and large specific surface area of NiCo-DH, along with the capacity of AuNPs to facilitate free radical generation. On this basis, an ultrasensitive sandwich CL immunosensor for the detection of PD-L1-expressing exosomes was constructed by using PD-L1 antibody-modified NiCo-DH-AA as an effective signal probe and rabbit anti-CD63 protein polyclonal antibody-modified carboxylated magnetic bead as a capture platform. The immunosensor demonstrated outstanding analytical performance with a wide detection range of 4.75 × 103-4.75 × 108 particles/mL and a low detection limit of 7.76 × 102 particles/mL, which was over 2 orders of magnitude lower than the reported CL method for detecting PD-L1-expressing exosomes. Importantly, it was able to differentiate well not only between healthy persons and LUAD patients (100% specificity and 87.5% sensitivity) but also between patients with minimally invasive adenocarcinoma and invasive adenocarcinoma (92.3% specificity and 52.6% sensitivity). Therefore, this study not only presents an ultrasensitive and accurate diagnostic method for LUAD but also offers a novel, simple, and noninvasive approach for the classification of LUAD.

Rational Design of Stimuli-Responsive Inorganic 2D Materials via Molecular Engineering: Toward Molecule-Programmable Nanoelectronics

The ability of electronic devices to act as switches makes digital information processing possible. Succeeding graphene, emerging inorganic 2D materials (i2DMs) have been identified as alternative 2D materials to harbor a variety of active molecular components to move the current silicon-based semiconductor technology forward to a post-Moore era focused on molecule-based information processing components. In this regard, i2DMs benefits are not only for their prominent physiochemical properties (e.g., the existence of bandgap), but also for their high surface-to-volume ratio rich in reactive sites. Nonetheless, since this field is still in an early stage, having knowledge of both i) the different strategies for molecularly functionalizing the current library of i2DMs, and ii) the different types of active molecular components is a sine qua non condition for a rational design of stimuli-responsive i2DMs capable of performing logical operations at the molecular level. Consequently, this Review provides a comprehensive tutorial for covalently anchoring ad hoc molecular components-as active units triggered by different external inputs-onto pivotal i2DMs to assess their role in the expanding field of molecule-programmable nanoelectronics for electrically monitoring bistable molecular switches. Limitations, challenges, and future perspectives of this emerging field which crosses materials chemistry with computation are critically discussed.

Cu-based catalysts with the co-existence of single atoms and nanoparticles for basic electrocatalytic oxygen reduction reaction

Developing efficient and stable oxygen reduction reaction (ORR) catalysts to replace the precious Pt/C is very important for the industrial application of proton-exchange membrane fuel cells. Herein, using bismuth-based metal-organic frameworks as the substrate to disperse copper ions, we prepared a catalyst containing both Cu single atoms and Cu nanoparticles (CuSACuNP/BiCN) by a pyrolysis method. In 0.1 M KOH electrolyte, the electrocatalytic ORR performance of CuSACuNP/BiCN was superior to that of commercial Pt/C. With a hierarchical porous architecture, CuSACuNP/BiCN displayed a half-wave potential of 0.86 V vs. RHE and a diffusion-limiting current density of 5.82 mA cm-2 with a four-electron transfer process. In addition, it was stable during a 12-hour durability test. This study provides guidance for the synthesis of advanced Cu-based nano-single-atom catalytic materials for ORR applications.

Advanced hematite nanomaterials for newly emerging applications

Because of the combined merits of rich physicochemical properties, abundance, low toxicity, etc., hematite (α-Fe2O3), one of the most chemically stable compounds based on the transition metal element iron, is endowed with multifunctionalities and has steadily been a research hotspot for decades. Very recently, advanced α-Fe2O3 materials have also been developed for applications in some cutting-edge fields. To reflect this trend, the latest progress in developing α-Fe2O3 materials for newly emerging applications is reviewed with a particular focus on the relationship between composition/nanostructure-induced electronic structure modulation and practical performance. Moreover, perspectives on the critical challenges as well as opportunities for future development of diverse functionalities are also discussed. We believe that this timely review will not only stimulate further increasing interest in α-Fe2O3 materials but also provide a profound understanding and insight into the rational design of other materials based on transition metal elements for various applications.

FeOOH nanosheet assisted metal ion coordination with porphyrins for rapid detection and removal of cadmium ions in water

Excessive cadmium ions in water bodies pose a severe challenge to ecology and human health, and the development of cadmium metal ion sensors is imperative. Here, we showed a dual-signal sensor based on colorimetry and fluorescence that was self-assembled from FeOOH nanosheets and TMPyP4. This nanocomposite enabled quick, selective cadmium ion detection. The Soret band at 442 nm in the UV absorption spectrum represented the coordination of cadmium ions with FeOOH@TMPyP4, and the absorbance increased linearly with increasing cadmium ion concentration (R² = 0.989 and linear range: 0.5-10 μM). In the presence of FeOOH nanosheets, the coordination of cadmium ions with FeOOH@TMPyP4 took only 70 min, and the detection limit of cadmium ions was as low as 0.24 μM. In addition, Cd²⁺ could be effectively removed from the nanocomposite due to its easy separation from water. This research developed a simple and efficient approach for detecting and removing heavy metal ions from water bodies.

Achieving a highly efficient oxygen reduction reaction via a molecular Fe single atom catalyst

Molecular Fe phthalocyanine (FePc) is successfully anchored on a defective mesoporous carbon framework for the highly efficient oxygen reduction reaction (ORR) with a half-wave potential of 0.86 V (vs. RHE) and a limited current density of 5.40 mA cm^-2. DFT calculations further suggest that the non-planar structure incorporating FePc can promote charge polarization and decrease the energy barrier.

Prussian blue analogues derived electrocatalyst with multicatalytic centers for boosting oxygen reduction reaction in the wide pH range

Due to the complex of oxygen reduction reaction (ORR), designing catalysts with multicatalytic centers is considered as a promising way for boosting the ORR. Herein, a multicatalytic centers electrocatalyst Fe₃C/Mn₃O₄ encased by N-doped graphitic layers (FeMn PDA-900) is synthesized using iron manganese Prussian blue analogues and dopamine as the precursor. It exhibits a half-wave potential (E_1/2) of 0.86 V for ORR and yields of H₂O₂ lower than 5% in 0.1 M KOH. Moreover, the prepared catalyst has also shown high catalytic ORR performance in both acidic and neutral electrolyte solutions, which exhibits the potential application in both the proton exchange membrane fuel cell and the microbial electrolysis cell. It is found that the good performance can be well explained by proton-coupled electron transfer mechanism due to the multicatalytic centers from Fe-N_x, Fe₃C and Mn₃O₄ for providing enough active sites at the same time and the N-doped graphitic layers as a bridge for facilitating the electron transfer between the interfaces of Fe₃C/Mn₃O₄ nanoparticles, which paves the way for protons and electrons transfer simultaneously and rapidly, and thus lowing the energy barrier and facilitating the ORR process. Therefore, FeMn PDA-900 is a promising candidate to replace precious metal-based ORR electrocatalysts at the whole pH range.

Layered FeCoNi double hydroxides with tailored surface electronic configurations induced by oxygen and unsaturated metal vacancies for boosting the overall water splitting process

Two-dimensional (2D) layered double hydroxides (LDH) with excellent hydrophilic ability and rapid hydroxyl insertion are regarded as one of the most promising electrocatalysts for both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) for overall water splitting to produce hydrogen. However, the electrocatalytic HER/OER activities can be restricted by the inert basal plane due to the poor conductivity, deficient active sites and inferior durability despite there being efficient active sites in the material edge. Thus, capturing many more exposed reactive sites to facilitate the rapid reaction kinetics is a crucial strategy. In this paper, both oxygen and unsaturated metal vacancies with FeCoNi LDH materials are generated through a surface activation approach by pre-covering of fluoride and a post-boronizing process. Such a material is grown on Ni foam to form an F-FeCoNi-Ov LDH/NF electrocatalyst. The activated surface of the electrocatalyst with oxygen vacancies and unsaturated metal sites shows enhanced electroconductivity for regulating the surface electronic structure and optimizing the surface adsorption energy for intermediates during HER/OER processes. As a result, this electrocatalyst exhibits excellent electrocatalytic performance for both the HER and OER with low overpotentials, small Tafel slopes and long durability. The enhancement mechanism is also studied deeply for fundamental understanding. For performance validation, an F-FeCoNi-Ov LDH/NF∥F-FeCoNi-Ov LDH/NF water splitting cell is fabricated and needs only 1.54 V and 1.81 V to reach current densities of 10 and 100 mA cm^-2, respectively. This work provides a practicable strategy to develop 2D LDH nanomaterials with boosted electrocatalytic activity for sustainable and clean energy storage systems.

Layered double hydroxide based materials applied in persulfate based advanced oxidation processes: Property, mechanism, application and perspectives

Recently, persulfate-based advanced oxidation processes (persulfate-AOPs) are booming rapidly due to their promising potential in treating refractory contaminants. As a type of popular two-dimensional material, layered double hydroxides (LDHs) are widely used in energy conversion, medicine, environment remediation and other fields for the advantages of high specific surface area (SSA), good tunability, biocompatibility and facile fabrication. These excellent physicochemical characteristics may enable LDH-based materials to be promising catalysts in persulfate-AOPs. In this work, we make a summary of LDHs and their composites in persulfate-AOPs from different aspects. Firstly, we introduce different structure and important properties of LDH-based materials briefly. Secondly, various LDH-based materials are classified according to the type of foreign materials (metal or carbonaceous materials, mainly). Latterly, we discuss the mechanisms of persulfate activation (including radical pathway and nonradical pathway) by these catalysts in detail, which involve (i) bimetallic synergism for radical generation, (ii) the role of carbonaceous materials in radical generation, (iii) singlet oxygen (¹O₂) production and several special nonradical mechanisms. In addition, the catalytic performance of LDH-based catalysts for contaminants are also summarized. Finally, challenges and future prospects of LDH-based composites in environmental remediation are proposed. We expect this review could bring new insights for the development of LDH-based catalyst and exploration of reaction mechanism.

High-Level Oxygen Reduction Catalysts Derived from the Compounds of High-Specific-Surface-Area Pine Peel Activated Carbon and Phthalocyanine Cobalt

Non-platinum carbon-based catalysts have attracted much more attention in recent years because of their low cost and outstanding performance, and are regarded as one of the most promising alternatives to precious metal catalysts. Activated carbon (AC), which has a large specific surface area (SSA), can be used as a carrier or carbon source at the same time. In this work, stable pine peel bio-based materials were used to prepare large-surface-area activated carbon and then compound with cobalt phthalocyanine (CoPc) to obtain a high-performance cobalt/nitrogen/carbon (Co-N-C) catalyst. High catalytic activity is related to increasing the number of Co particles on the large-specific-area activated carbon, which are related with the immersing effect of CoPc into the AC and the rational decomposed temperature of the CoPc ring. The synergy with N promoting the exposure of CoNx active sites is also important. The Eonset of the catalyst treated with a composite proportion of AC and CoPc of 1 to 2 at 800 °C (AC@CoPc-800-1-2) is 1.006 V, higher than the Pt/C (20 wt%) catalyst. Apart from this, compared with other AC/CoPc series catalysts and Pt/C (20 wt%) catalyst, the stability of AC/CoPc-800-1-2 is 87.8% in 0.1 M KOH after 20,000 s testing. Considering the performance and price of the catalyst in a practical application, these composite catalysts combining biomass carbon materials with phthalocyanine series could be widely used in the area of catalysts and energy storage.