Dephosphorylation that removes a phosphate group from substrates is an important reaction for living organisms and environmental protection. Although CeO2 has been shown to catalyze this reaction, ...cerium is low in natural abundance and has a narrow global distribution (>90 % of these reserves are located within six countries). It is thus imperative to find another element/material with high worldwide abundance that can also efficiently extract the phosphate out of agricultural waste for phosphorus recycle. Using para‐nitrophenyl phosphate (p‐NPP) as a model compound, we demonstrate that TiO2 with a F‐modified (001) surface can activate p‐NPP dephosphorylation at temperatures as low as 40 °C. By probe‐assisted nuclear magnetic resonance (NMR), it was revealed that the strong electron‐withdrawing effect of fluorine makes Ti atoms (the active sites) on the (001) surface very acidic. The bidentate adsorption of p‐NPP on this surface further promotes its subsequent activation with a barrier ≈20 kJ mol−1 lower than that of the pristine (001) and (101) surfaces, allowing the activation of this reaction near room temperature (from >80 °C).
We demonstrate for the first time that TiO2 with a F‐modified (001) surface can activate p‐NPP dephosphorylation near room temperature. The electron‐withdrawing effect of fluorine imposed on the TiO2(001) surface strongly manipulates the electronic state of surrounding Ti5C atoms by making them very acidic, facilitating not only the bidentate adsorption of p‐NPP but also its subsequent activation.
Amides are crucial components of biomolecules and are extensively used in polymer, pharmaceutical, and agrochemical production. Their direct hydrolysis offers great potential for exploring protein ...structures and producing valuable carboxylic acids in biological and industrial applications. Nevertheless, activating the resonance‐stabilized C−N bond in amides poses a formidable challenge. Extensive research over the past decades has reported various transition metal‐based complexes and solid catalysts that catalyze this reaction. These catalysts possess Lewis acid (LA) sites and exhibit enhanced activity when further combined with Brönsted acid (BA) sites. In this study, we present the first demonstration of amide hydrolysis on TiO2, a rock‐forming material, offering valuable insights into its surface activity. By using acetamide as the model compound, we observed that the thermodynamically stable (101) surface of TiO2 remained inert up to 95 °C. Surprisingly, the high‐energy (001) surface of TiO2 activated amide hydrolysis at a temperature as low as 25 °C. Contrary to previous reports, the fluorine‐modified (001) surface with additional BA sites required temperatures above 70 °C likely due to hydrogen bond stabilization by nearby fluorine atoms. These findings provide guidance for the development of cost‐effective catalysts with improved activity.
We report the first case of amide hydrolysis on a rock‐forming material, TiO2, with insights into its surface activity. Amide hydrolysis at room temperature was achieved on TiO2 with (001) surface, which is much lower than fluorine‐modified (001) surface (>70 °C). The former surface follows the Lewis acid‐catalyzed pathway, while the additional Brönsted acid sites induced by fluorine atoms on the latter one unexpectedly hindered the reaction.
Among reported nanozymes, CeO2 seems to be the only transition metal oxide that can mimic phosphatase and peroxidase by catalyzing substrate dephosphorylation and oxidation (with H2O2). However, no ...consensus on the key Ce species was reached in the literature using spherical CeO2 enclosed by (111) and (100) surfaces, not to mention the further control of its reaction specificity. In this study, octahedral and cubic CeO2 preferentially terminated by (111) and (100) surfaces were found to exhibit high reaction specificity (and activity) towards each of the above reactions. Spectroscopic evidence suggests that this is closely associated with the Lewis acidity (or electron density) of surface Ce species. The acidic Ce species on (111) surface can catalyze substrate dephosphorylation at room temperature but do not for substrate oxidation with H2O2. This correlation was further evidenced by the electron‐rich Ce species on (100) surface, hindering the first reaction while promoting the latter.
CeO2 nanosphere enclosed by (100) and (111) surfaces has been reported to mimic phosphatase and peroxidase by catalyzing substrate dephosphorylation and oxidation (with H2O2). We herein successfully boost the reaction specificity for this material by shape control. The acidic Ce species on octahedron (111) surface was found to selectively catalyze substrate dephosphorylation while its electron rich counterpart on cube (100) surface only promotes substrate oxidation.
Single‐atom catalysts have attracted attention in the past decade since they maximize the utilization of active sites and facilitate the understanding of product distribution in some catalytic ...reactions. Recently, this idea has been extended to single‐atom nanozymes (SAzymes) for the mimicking of natural enzymes such as horseradish peroxidase (HRP) often used in bioanalytical applications. Herein, it is demonstrated that those SAzymes without constructing the reaction pocket of HRP still undergo the OH radical‐mediated pathway like most of the reported nanozymes. Their positively charged single‐atom centers resulting from support electronegative oxygen/nitrogen hinder the reductive conversion of H2O2 to OH radicals and hence display low activity per site. In contrast, it is found that this step can be facilitated over their metallic counterparts on cluster nanozymes with much higher site activity and atom efficiency (cf. SAzymes with 100% atom utilization). Besides the mimicking of HRP in glucose detection, cluster nanozymes are also demonstrated as a better oxidase mimetic for glutathione detection.
Although single‐atom nanozymes have been reported to mimic peroxidases, they undergo the OH radical‐mediated pathway like most of nanozymes. In fact, OH radical generation (from H2O2) over those cationic single‐atom centers is much slower than their metallic counterparts on conventional nanozymes. A cluster nanozyme with optimized site reactivity and utilization is demonstrated here to be a better candidate for peroxidase/oxidase mimicking.
Comprehensive Summary
We have compiled eight promising strategies for enhancing the specificity and selectivity of nanozymes, as depicted in the comprehensive summary above. Enzymes exhibit intricate ...and sophisticated structures, including substrate channels and active sites, which can inform the design of nanozymes. Replication of these structural features and the application of facet engineering/doping techniques can significantly enhance the catalytic specificity of nanozymes. Alternatively, the use of Molecularly Imprinted Polymers (MIPs) to coat nanozymes represents an effective approach to impart substrate specificity. Furthermore, several straightforward stopgap strategies have been devised to improve nanozyme specificity for analytical applications, such as the integration of biorecognition elements and nanozyme sensor arrays through surface modification.
Key Scientists
A comprehensive overview was conducted on the design strategies for nanozymes with intrinsic catalytic specificity. Additionally, supplemental strategies were summarized to achieve the selectivity of nanozymes for analytical applications.
Emerging non‐noble metal 2D catalysts, such as molybdenum disulfide (MoS2), hold great promise in hydrogen evolution reactions. The sulfur vacancy is recognized as a key defect type that can activate ...the inert basal plane to improve the catalytic performance. Unfortunately, the method of introducing sulfur vacancies is limited and requires costly post‐treatment processes. Here, a novel salt‐assisted chemical vapor deposition (CVD) method is demonstrated for synthesizing ultrahigh‐density vacancy‐rich 2H‐MoS2, with a controllable sulfur vacancy density of up to 3.35 × 1014 cm−2. This approach involves a pre‐sprayed potassium chloridepromoter on the growth substrate. The generation of such defects is closely related to ion adsorption in the growth process, the unstable MoS2‐K‐H2O triggers the formation of sulfur vacancies during the subsequent transfer process, and it is more controllable and nondestructive when compared to traditional post‐treatment methods. The vacancy‐rich monolayer MoS2 exhibits exceptional catalytic activity based on the microcell measurements, with an overpotential of ≈158.8 mV (100 mA cm−2) and a Tafel slope of 54.3 mV dec−1 in 0.5 m H2SO4 electrolyte. These results indicate a promising opportunity for modulating sulfur vacancy defects in MoS2 using salt‐assisted CVD growth. This approach represents a significant leap toward achieving better control over the catalytic performances of 2D materials.
Sulfur vacancy engineering is a vital strategy to activate the hydrogen evolution activity of the MoS2 basal plane. Unlike traditional costly post‐treatment methods, this work demonstrates a novel salt‐assisted chemical vapor deposition method for synthesizing vacancy‐rich 2H‐MoS2 electrocatalysts with exceptional catalytic activity. The generation of such defects is closely related to ion adsorption in the growth process.
Since Fe3O4 was reported to mimic horseradish peroxidase (HRP) with comparable activity (2007), countless peroxidase nanozymes have been developed for a wide range of applications from biological ...detection assays to disease diagnosis and biomedicine development. However, researchers have recently argued that Fe3O4 has no peroxidase activity because surface Fe(III) cannot oxidize tetramethylbenzidine (TMB) in the absence of H2O2 (cf. HRP). This motivated us to investigate the origin of transition metal oxides as peroxidase mimetics. The redox between their surface M n+ (oxidation) and H2O2 (reduction) was found to be the key step generating OH radicals, which oxidize not only TMB for color change but other H2O2 to produce HO2 radicals for M n+ regeneration. This mechanism involving free OH and HO2 radicals is distinct from that of HRP with a radical retained on the Fe-porphyrin ring. Most importantly, it also explains the origin of their catalase-like activity (i.e., the decomposition of H2O2 into H2O and O2). Because the production of OH radicals is the rate-limiting step, the poor activity of Fe3O4 can be attributed to the slow redox of Fe(II) with H2O2, which is two orders of magnitude slower than the most active Cu(I) among common transition metal oxides. We further tested glutathione (GSH) detection on the basis of its peroxidase-like activity to highlight the importance of understanding the mechanism when selecting materials with high performance.
Bio-oil, produced by the destructive distillation of cheap and renewable lignocellulosic biomass, contains high energy density oligomers in the water-insoluble fraction that can be utilized for ...diesel and valuable fine chemicals productions. Here, we show an efficient hydrodeoxygenation catalyst that combines highly dispersed palladium and ultrafine molybdenum phosphate nanoparticles on silica. Using phenol as a model substrate this catalyst is 100% effective and 97.5% selective for hydrodeoxygenation to cyclohexane under mild conditions in a batch reaction; this catalyst also demonstrates regeneration ability in long-term continuous flow tests. Detailed investigations into the nature of the catalyst show that it combines hydrogenation activity of Pd and high density of both Brønsted and Lewis acid sites; we believe these are key features for efficient catalytic hydrodeoxygenation behavior. Using a wood and bark-derived feedstock, this catalyst performs hydrodeoxygenation of lignin, cellulose, and hemicellulose-derived oligomers into liquid alkanes with high efficiency and yield.Bio-oil is a potential major source of renewable fuels and chemicals. Here, the authors report a palladium-molybdenum mixed catalyst for the selective hydrodeoxygenation of water-insoluble bio-oil to mixtures of alkanes with high carbon yield.
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•“Clean surface” for photocatalysis is not always ensured, affecting each facet which possesses distinctive intrinsic energy.•Adsorbates remain on the facets can influence adsorption ...of reactant molecules and chemical states of surface active features.•Many characterization techniques are not facet-specific, causing difficulty to unambiguously correlate facet-dependent properties.•The new chemical probe-assisted NMR technique can differentiate surface features from various facets.
Semiconductive metal oxides are of great importance in environmental remediation and electronics because of their ability to generate charge carriers when excited with appropriate light energy. The electronic structure, light absorption and charge transport properties of the metal oxides have made possible their applications as photocatalysts. Recently, facet-engineering by morphology control has been intensively studied as an efficient approach to further enhance their photocatalytic performance. However, various processing steps and post-treatments used during the preparation of facet-engineered particles may generate different surface active sites which may affect their photocatalysis. Moreover, many traditional techniques (PL, EPR, XPS and Raman) used for materials characterization (oxygen vacancy, hydroxyl group, cation…etc.) are not truly surface specific but the analyses range from top few layers to bulk. Accordingly, they can only provide very limited information on the chemical states of the surface active features and distributions among facets, causing difficulty to unambiguously correlate facet-dependent results with activity. As a result, this always leads to different interpretations amongst researchers during the past decades. In this article, we will review on the controversies generated among researchers, when they correlated the performance of two most popular photocatalysts, ZnO and TiO2 with their facet activities based on characterization from the traditional techniques. As there are shortcomings of these techniques in producing truly facet-dependent features, some results can be misleading and with no cross-literature comparison. This review is also focussed on the new capability of probe-molecule-assisted NMR which allows a genuine differentiation of surface active sites from various facets. This surface-fingerprint technique has been demonstrated to provide both qualitative (chemical shift) and quantitative (peak intensity) information on the concentration and distribution of truly surface features. In light of the new technique this article will revisit the facet-dependent photocatalytic properties and shed light on these issues.
The use of surface-directing species and surface additives to alter nanoparticle morphology and physicochemical properties of particular exposed facets has recently been attracting significant ...attention. However, challenges in their chemical analysis, sometimes at trace levels, and understanding their roles to elucidate surface structure-activity relationships in optical (solar cells) or (photo)catalytic performance and their removal are significant issues that remain to be solved. Here, we show a detailed analysis of TiO
facets promoted with surface species (OH, O, SO
, F) with and without post-treatments by
P adsorbate nuclear magnetic resonance, supported by a range of other characterization tools. We demonstrate that quantitative evaluations of the electronic and structural effects imposed by these surface additives and their removal mechanisms can be obtained, which may lead to the rational control of active TiO
(001) and (101) facets for a range of applications.Metal oxide nanocrystals can be grown with different facets exposed to give variations in reactivity, but the chemical state of these surfaces is not clear. Here, the authors make use of a phosphine probe molecule allowing the differences in surface chemistry to be mapped by NMR spectroscopy.
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