Nanoscale Spatial Distribution of Supported Nanoparticles Controls Activity and Stability in Powder Catalysts for CO Oxidation and Photocatalytic H2 Evolution

Deconvoluting the Individual Effects of Nanoparticle Proximity and Size in Thermocatalysis

Nanoparticle (NP) size and proximity are two physical descriptors applicable to practically all NP-supported catalysts. However, with conventional catalyst design, independent variation of these descriptors to investigate their individual effects on thermocatalysis remains challenging. Using a raspberry-colloid-templating approach, we synthesized a well-defined catalyst series comprising Pd12Au88 alloy NPs of three distinct sizes and at two different interparticle distances. We show that NP size and interparticle distance independently control activity and selectivity, respectively, in the hydrogenation of benzaldehyde to benzyl alcohol and toluene. Surface-sensitive spectroscopic analysis indicates that the surfaces of smaller NPs expose a greater fraction of reactive Pd dimers, compared to inactive Pd single atoms, thereby increasing intrinsic catalytic activity. Computational simulations reveal how a larger interparticle distance improves catalytic selectivity by diminishing the local benzyl alcohol concentration profile between NPs, thus suppressing its readsorption and consequently, undesired formation of toluene. Accordingly, benzyl alcohol yield is maximized using catalysts with smaller NPs separated by larger interparticle distances, overcoming activity-selectivity trade-offs. This work exemplifies the high suitability of the modular raspberry-colloid-templating method as a model catalyst platform to isolate individual descriptors and establish clear structure-property relationships, thereby bridging the materials gap between surface science and technical catalysts.

Regulating the spatial arrangement of CuO and MgO within activated carbon matrix to maximize their room temperature H2S removal

Adsorbents with dual-component active phases have attracted much attention owing to their potential application in synergistic H2S removal. The influence of spatial arrangements of two components within a support matrix on their desulfurization performance was investigated through regulating the mutual arrangements of CuO and MgO on an activated carbon surface. Their spatial locations were found to remarkably affect interfacial interactions, local pH, the conductivity of adsorbents, and electronic structure of copper oxide. A close contact of CuO with the carbon surface led to strong interactions of both components, inhibiting the reduction of CuO and decreasing its reactivity with H2S. On the other hand, a proximity of MgO to the carbon surface increased local pH, promoting the oxidation of H2S into elemental S, instead of sulfates. Cu+ in the copper oxide phase increased the desulfurization performance due to its ability to activate oxygen and to accelerate a lattice diffusion. Enhanced surface conductivity due to the interfacial interactions improved the desulfurization efficiency and favored the formation of elemental S through promoting an electron transfer in redox reactions.

Catalyzing Artificial Photosynthesis with TiO2 Heterostructures and Hybrids: Emerging Trends in a Classical yet Contemporary Photocatalyst

Titanium dioxide (TiO2) stands out as a versatile transition-metal oxide with applications ranging from energy conversion/storage and environmental remediation to sensors and optoelectronics. While extensively researched for these emerging applications, TiO2 has also achieved commercial success in various fields including paints, inks, pharmaceuticals, food additives, and advanced medicine. Thanks to the tunability of their structural, morphological, optical, and electronic characteristics, TiO2 nanomaterials are among the most researched engineering materials. Besides these inherent advantages, the low cost, low toxicity, and biocompatibility of TiO2 nanomaterials position them as a sustainable choice of functional materials for energy conversion. Although TiO2 is a classical photocatalyst well-known for its structural stability and high surface activity, TiO2-based photocatalysis is still an active area of research particularly in the context of catalyzing artificial photosynthesis. This review provides a comprehensive overview of the latest developments and emerging trends in TiO2 heterostructures and hybrids for artificial photosynthesis. It begins by discussing the common synthesis methods for TiO2 nanomaterials, including hydrothermal synthesis and sol-gel synthesis. It then delves into TiO2 nanomaterials and their photocatalytic mechanisms, highlighting the key advancements that have been made in recent years. The strategies to enhance the photocatalytic efficiency of TiO2, including surface modification, doping modulation, heterojunction construction, and synergy of composite materials, with a specific emphasis on their applications in artificial photosynthesis, are discussed. TiO2-based heterostructures and hybrids present exciting opportunities for catalyzing solar fuel production, organic degradation, and CO2 reduction via artificial photosynthesis. This review offers an overview of the latest trends and advancements, while also highlighting the ongoing challenges and prospects for future developments in this classical yet rapidly evolving field.

A Water-Promoted Mars-van Krevelen Reaction Dominates Low-Temperature CO Oxidation over Au-Fe2O3 but Not over Au-TiO2

We provide experimental evidence that is inconsistent with often proposed Langmuir-Hinshelwood (LH) mechanistic hypotheses for water-promoted CO oxidation over Au-Fe2O3. Passing CO and H2O, but no O2, over Au-γ-Fe2O3 at 25 °C, we observe significant CO2 production, inconsistent with LH mechanistic hypotheses. Experiments with H218O further show that previous LH mechanistic proposals cannot account for water-promoted CO oxidation over Au-γ-Fe2O3. Guided by density functional theory, we instead postulate a water-promoted Mars-van Krevelen (w-MvK) reaction. Our proposed w-MvK mechanism is consistent both with observed CO2 production in the absence of O2 and with CO oxidation in the presence of H218O and 16O2. In contrast, for Au-TiO2, our data is consistent with previous LH mechanistic hypotheses.

Copper Single-Atom Catalysts-A Rising Star for Energy Conversion and Environmental Purification: Synthesis, Modification, and Advanced Applications

Future renewable energy supply and green, sustainable environmental development rely on various types of catalytic reactions. Copper single-atom catalysts (Cu SACs) are attractive due to their distinctive electronic structure (3d orbitals are not filled with valence electrons), high atomic utilization, and excellent catalytic performance and selectivity. Despite numerous optimization studies are conducted on Cu SACs in terms of energy conversion and environmental purification, the coupling among Cu atoms-support interactions, active sites, and catalytic performance remains unclear, and a systematic review of Cu SACs is lacking. To this end, this work summarizes the recent advances of Cu SACs. The synthesis strategies of Cu SACs, metal-support interactions between Cu single atoms and different supports, modification methods including modification for carriers, coordination environment regulating, site distance effect utilizing, and dual metal active center catalysts constructing, as well as their applications in energy conversion and environmental purification are emphatically introduced. Finally, the opportunities and challenges for the future Cu SACs development are discussed. This review aims to provide insight into Cu SACs and a reference for their optimal design and wide application.

Defects Healing of the ZnO Surface by Filling with Au Atom Catalysts for Efficient Photocatalytic H2 Production

Healed defects on photocatalysts surface and their interaction with plasmonic nanoparticles (NPs) have attracted attention in H2 production process. In this study, surface oxygen vacancy (Vo ) defects are created on ZnO (Vo -ZnO) NPs by directly pyrolyzing zeolitic imidazolate framework. The surface defects on Vo -ZnO provide active sites for the diffusion of single Au atoms and as nucleation sites for the formation of Au NPs by the in situ photodeposition process. The electronically healed surface defects by single Au atoms help in the formation of a heterojunction between the ZnO and plasmonic Au NPs. The formed Au/Vo -Au:ZnO-4 heterojunction prolongs photoelectron lifetimes and increases donor charge density. Therefore, the optimized photocatalysts of Au/Vo -Au:ZnO-4 has 21.28 times higher H2 production rate than the pristine Vo -ZnO under UV-visible light in 0.35 m Na2 SO4 and 0.25 m Na2 SO3 . However in 0.35 m Na2 S and 0.25 m Na2 SO3 , the H2 production rate is 25.84 mmole h-1 g-1 . Furthermore, Au/Vo -Au:ZnO-4 shows visible light activity by generating hot carries via induced surface plasmonic effects. It has 48.58 times higher H2 production rate than pristine Vo -ZnO. Therefore, this study infers new insight for defect healing mediated preparation of Au/Vo -Au:ZnO heterojunction for efficient photocatalytic H2 production.

A PtPdCoCuNi high-entropy alloy nanocatalyst for the hydrogenation of nitrobenzene

High-entropy alloys (HEAs) with multiple elements in near-equiatomic proportions hold great promise in heterogeneous catalysis because of their exceptional physicochemical properties governed by synergy. Herein, we prepared PtPdCoCuNi HEA nanoparticles via a one-step colloid-based route and tested their catalytic performance for nitrobenzene hydrogenation to aniline. The SiO₂ supported PtPdCoCuNi displays 93.9% yield of aniline at 80 °C, which is 2.11 times that of PtPd/SiO₂. Even at room temperature, a 47.4% yield of aniline is attained with the PtPdCoCuNi/SiO₂ catalyst. DRIFTS experiments indicate formation of isolated Pt and Pd sites after alloying the transition metals and evidence a stronger interaction between the HEA catalyst and nitrobenzene. Both XPS data and DFT calculations disclose charge transfer to Pt and Pd species, which eventually enhance the interaction between nitrobenzene and the isolated metal sites and the hydrogenation activity as well. The experimental and theoretical results shed light on mechanistic understanding of the unique catalytic performance of the HEA nanocatalyst and pave a new avenue to realize the high catalytic performance of nitrobenzene hydrogenation over well-isolated noble metal sites with specific geometries.

High-entropy alloys (HEAs) with multiple elements in near-equiatomic proportions hold great promise in heterogeneous catalysis because of their exceptional physicochemical properties governed by synergy.

Reciprocal regulation of NRF2 by autophagy and ubiquitin-proteasome modulates vascular endothelial injury induced by copper oxide nanoparticles

NRF2 is the key antioxidant molecule to maintain redox homeostasis, however the intrinsic mechanisms of NRF2 activation in the context of nanoparticles (NPs) exposure remain unclear. In this study, we revealed that copper oxide NPs (CuONPs) exposure activated NRF2 pathway in vascular endothelial cells. NRF2 knockout remarkably aggravated oxidative stress, which were remarkably mitigated by ROS scavenger. We also demonstrated that KEAP1 (the negative regulator of NRF2) was not primarily involved in NRF2 activation in that KEAP1 knockdown did not significantly affect CuONPs-induced NRF2 activation. Notably, we demonstrated that autophagy promoted NRF2 activation as evidenced by that ATG5 knockout or autophagy inhibitors significantly blocked NRF2 pathway. Mechanically, CuONPs disturbed ubiquitin–proteasome pathway and consequently inhibited the proteasome-dependent degradation of NRF2. However, autophagy deficiency reciprocally promoted proteasome activity, leading to the acceleration of degradation of NRF2 via ubiquitin–proteasome pathway. In addition, the notion that the reciprocal regulation of NRF2 by autophagy and ubiquitin–proteasome was further proven in a CuONPs pulmonary exposure mice model. Together, this study uncovers a novel regulatory mechanism of NRF2 activation by protein degradation machineries in response to CuONPs exposure, which opens a novel intriguing scenario to uncover therapeutic strategies against NPs-induced vascular injury and disease.

CuONPs exposure activates NRF2 signaling in vascular endothelial cells and mouse thoracic aorta.

KEAP1 is dispensable for NRF2 activation in CuONPs-treated vascular endothelial cells.

CuONPs-induced autophagy facilitates NRF2 activation in vascular endothelial cells and mouse thoracic aorta.

Autophagy and ubiquitin–proteasome reciprocally regulate NRF2 activation in CuONPs-treated vascular endothelial cells and mouse thoracic aorta.

Electrochemical α-fetoprotein immunosensor based on Fe3O4NPs@covalent organic framework decorated gold nanoparticles and magnetic nanoparticles including SiO2@TiO2

The early diagnosis of major diseases such as cancer is typically a major issue for humanity. Human α-fetoprotein (AFP) as a sialylated glycoprotein is of approximately 68 kD molecular weight and is considered to be a key biomarker, and an increase in its level indicates the presence of liver, testicular, or gastric cancer. In this study, an electrochemical AFP immunosensor based on Fe₃O₄NPs@covalent organic framework decorated gold nanoparticles (Fe₃O₄ NPs@COF/AuNPs) for the electrode platform and double-coated magnetic nanoparticles (MNPs) based on SiO₂@TiO₂ (MNPs@SiO₂@TiO₂) nanocomposites for the signal amplification was fabricated. The immobilization of anti-AFP capture antibody was successfully performed on Fe₃O₄ NPs@COF/AuNPs modified electrode surface by amino-gold affinity, while the conjugation of anti-AFP secondary antibody on MNPs@SiO₂@TiO₂ was achieved by the electrostatic/ionic interactions. Transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) analysis, cyclic voltammetry (CV), square wave voltammetry (SWV), and electrochemical impedance spectroscopy (EIS) techniques were used to characterize the nanostructures in terms of physical and electrochemical features. The limit of detection (LOD) was 3.30 fg mL^-1. The findings revealed that the proposed electrochemical AFP immunosensor can be effectively used to diagnose cancer.

Porous Fe3O4@COF-Immobilized gold nanoparticles with excellent catalytic performance for sensitive electrochemical detection of ATP

In this work, a "signal-off" electrochemical biosensor was established for sensitive detection of adenosine triphosphate (ATP) based on Fe₃O₄@covalent organic framework-immobilized gold nanoparticles (Fe₃O₄@COF-Au NPs) porous composite material as a nanocarrier. The proposed Fe₃O₄@COF-Au NPs could effectively confine Au NPs in the uniform channels of the Fe₃O₄@COF, which successfully avoided Au NPs aggregation to a certain extent and provided a comparatively independent and stable micro-environment via its hydrophobic porous nanochannels, thereby owning excellent electro-catalytic performance for the reduction of 4-nitrophenol. Moreover, the Fe₃O₄@COF-Au NPs nanomaterials were served as functional platform for immobilizing DNA substrate (S0), which was used to bind with the conversion product (S1) of the target ATP for subsequent branched hybridization chain reaction (b-HCR) to form dendritic DNA strands to hinder electron transfer between Fe₃O₄@COF-Au NPs and 4-nitrophenol, finally achieving sensitive detection of ATP with a wide linear range of 5 pM-50 μM and a low detection limit of 1.6 pM. Such strategy provides a multifunctional immobilized platform for the sensitive detection of ATP and a versatile strategy for monitoring other biomolecules.

Structural Insights into Multi-Metal Spinel Oxide Nanoparticles for Boosting Oxygen Reduction Electrocatalysis

Multi-metal oxide (MMO) materials have significant potential to facilitate various demanding reactions by providing additional degrees of freedom in catalyst design. However, a fundamental understanding of the (electro)catalytic activity of MMOs is limited because of the intrinsic complexity of their multi-element nature. Additional complexities arise when MMO catalysts have crystalline structures with two different metal site occupancies, such as the spinel structure, which makes it more challenging to investigate the origin of the (electro)catalytic activity of MMOs. Here, uniform-sized multi-metal spinel oxide nanoparticles composed of Mn, Co, and Fe as model MMO electrocatalysts are synthesized and the contributions of each element to the structural flexibility of the spinel oxides are systematically studied, which boosts the electrocatalytic oxygen reduction reaction (ORR) activity. Detailed crystal and electronic structure characterizations combined with electrochemical and computational studies reveal that the incorporation of Co not only increases the preferential octahedral site occupancy, but also modifies the electronic state of the ORR-active Mn site to enhance the intrinsic ORR activity. As a result, nanoparticles of the optimized catalyst, Co_0.25 Mn_0.75 Fe_2.0 -MMO, exhibit a half-wave potential of 0.904 V (versus RHE) and mass activity of 46.9 A g_oxide ^-1 (at 0.9 V versus RHE) with promising stability.

Boosting the catalytic behavior and stability of a gold catalyst with structure regulated by ceria

In this work, a series of colloidal gold nanoparticles with controllable sizes were anchored on carbon nanotubes (CNT) for the aerobic oxidation of benzyl alcohol. The intrinsic influence of Au particles on the catalytic behavior was unraveled based on different nanoscale-gold systems. The Au/CNT-A sample with smaller Au sizes deserved a faster reaction rate, mainly resulting from the higher dispersion degree (23.5%) of Au with the available exposed sites contributed by small gold particles. However, monometallic Au/CNT samples lacked long-term stability. CeO₂ was herein decorated to regulate the chemical and surface structure of the Au/CNT. An appropriate CeO₂ content tuned the sizes and chemical states of Au by electron delivery with better metal dispersion. Small CeO₂ crystals that were preferentially neighboring the Au particles facilitated the generation of Au–CeO₂ interfaces, and benefited the continuous supplementation of oxygen species. The collaborative functions between the size effect and surface chemistry accounted for the higher benzaldehyde yield and sustainably stepped-up reaction rates by Au-Ce₅/CNT with 5 wt% CeO₂.

In this work, a series of colloidal gold nanoparticles with controllable sizes and CeO₂ promotion were anchored on carbon nanotubes (CNT) for the aerobic oxidation of benzyl alcohol.

Dual promotional effect of CuxO clusters grown with atomic layer deposition on TiO2 for photocatalytic hydrogen production

The promotional effects on photocatalytic hydrogen production of Cu_xO clusters deposited using atomic layer deposition (ALD) on P25 TiO₂ are presented. The structural and surface chemistry study of Cu_xO/TiO₂ samples, along with first principles density functional theory simulations, reveal the strong interaction of ALD deposited Cu_xO with TiO₂, leading to the stabilization of Cu_xO clusters on the surface; it also demonstrated substantial reduction of Ti⁴⁺ to Ti³⁺ on the surface of Cu_xO/TiO₂ samples after Cu_xO ALD. The Cu_xO/TiO₂ photocatalysts showed remarkable improvement in hydrogen productivity, with 11 times greater hydrogen production for the optimum sample compared to unmodified P25. With the combination of the hydrogen production data and characterization of Cu_xO/TiO₂ photocatalysts, we inferred that ALD deposited Cu_xO clusters have a dual promotional effect: increased charge carrier separation and improved light absorption, consistent with known copper promoted TiO₂ photocatalysts and generation of a substantial amount of surface Ti³⁺ which results in self-doping of TiO₂ and improves its photo-activity for hydrogen production. The obtained data were also employed to modify the previously proposed expanding photocatalytic area and overlap model to describe the effect of cocatalyst size and weight loading on photocatalyst activity. Comparing the trend of surface Ti³⁺ content increase and the photocatalytically promoted area, calculated with our model, suggests that the depletion zone formed around the heterojunction of Cu_xO–TiO₂ is the main active area for hydrogen production, and the hydrogen productivity of the photocatalyst depends on the surface coverage by this active area. However, the overlap of these areas suppresses the activity of the photocatalyst.

The depletion zone formed around the Cu_xO clusters is the main photocatalytically active area, and the H₂ production rate depends on surface coverage with this area; however, the overlap of these areas suppresses the photocatalyst activity.

Photocatalytic Activity of Supported Metal Nanoparticles and Single Atoms

Photocatalysis has been known as one of the promising technologies due to its eco-friendly nature. However, the potential application of many photocatalysts is limited owing to their large bandgaps and inefficient use of the solar spectrum. One strategy to overcome this problem is to combine the advantages of heteroatom-containing supports with active metal centers to accurately adjust the structural parameters. Metal nanoparticles (MNPs) and single atom catalysts (SACs) are excellent candidates due to their distinctive coordination environment which enhances photocatalytic activity. Metal-organic frameworks (MOFs), covalent organic frameworks (COFs) and carbon nitride (g-C₃ N₄ ) have shown great potential as catalyst support for SACs and MNPs. The numerous combinations of organic linkers with various heteroatoms and metal ions provide unique structural characteristics to achieve advanced materials. This review describes the recent advancement of the modified MOFs, COFs and g-C₃ N₄ with SACs and NPs for enhanced photocatalytic applications with emphasis on environmental remediation.

Template-assisted synthesis of Ag/AgCl hollow microcubes and their composition-dependent photocatalytic activity for the degradation of phenol

Plasmonic photocatalysts with hollow structures and tunable composition exhibit significant advantages due to their high efficiency in light collection and effective charge transfer across the tight contact heterojunction interface. Herein, hollow Ag/AgCl microcubes were developed by treating nanosheet-assembled hollow Ag microcubes with FeCl₃, where a part of Ag at the interface could be in situ transformed and oxidized into AgCl. Equally, by adjusting the concentration of Fe³⁺ ions, Ag/AgCl hollow microcubes with different compositions could be easily achieved. Electron transfer was favored by a lot of tiny Ag/AgCl heterojunctions induced by the in situ oxidation of the multicrystalline Ag hollow microcube template containing a number of grain boundaries. The designed hollow Ag/AgCl microcubes exhibited strong visible-light adsorption owing to the surface plasmon resonance effect of Ag nanoparticles, in addition to the multiple light-reflections inside the hollow structure. The as-obtained products were then used as visible-light photocatalysts, where the results indicated that 91.6% of phenol was degraded within 150 min under visible light by the as-obtained sample with a Ag to AgCl ratio of 1 : 3. The superior visible-light photocatalytic activity resulted from the enhancement of the visible light-harvesting and the efficient charge separation at the Ag and AgCl contact interfaces.

Ag/AgCl hollow microcubes with enhanced visible-light photocatalytic activity were synthesized by the template method, and the charge transfer process was proposed.

Ru Nanoworms Loaded TiO2 for Their Catalytic Performances toward CO Oxidation

Ruthenium nanocrystals with small size and special morphology are of great interest in various catalytic reactions due to their high activities. However, it is still a great challenge to downsize these nanocatalysts to a sub-nano scale (<2 nm). Herein, we reported a synthesis of ultrasmall size and uniform Ru nanoparticles through a rapid one-pot method. The prepared Ru nanocrystal shows a wormlike shape, in which the diameter is as thin as 1.6 ± 0.3 nm and the length is 13.6 ± 4.4 nm. These Ru nanoworms (NWs) are quite steady during the synthetic process even though the reaction time was further prolonged. We also examined their catalytic activity toward CO oxidation by loading Ru NWs on TiO₂ to form Ru NWs/TiO₂ catalysts. These catalysts exhibit a high activity of 100% CO conversion at 150 °C, which is much lower than the normal Ru NPs/TiO₂ nanostructures. Based on our detailed investigations, we proposed that the small size, special morphology, and TiO₂ support are the keys for their significantly improved catalytic activity. We believed that these reasonable discoveries provide a methodology and opportunity to get highly active catalysts for CO oxidation by a detailed increase in their active sites.