A thorough mechanistic study of ethanol, acetaldehyde, and ethylene adsorption on Cu-MOR via DFT analysis.

A comprehensive study combining the density functional theory (DFT) and ab initio thermodynamic analysis was conducted to unravel the active sites and adsorption mechanisms of ethanol, acetaldehyde, and ethylene on various copper-modified mordenite (Cu-MOR) configurations, including Cu3/MOR, Cu3O3/MOR, and Cu6/MOR. This research involved an exhaustive exploration of structural and formation energies, revealing that the formation energies of these structures are temperature-dependent. Despite all three structures thermodynamically accommodating ethanol adsorption, their respective adsorption mechanisms differ significantly. In Cu3/MOR, weak van der Waals interactions predominate, while strong Cu-OOH interactions in Cu6/MOR facilitate ethanol dehydration. Conversely, Cu3O3/MOR exhibits pronounced Cu3O3-HOH interactions that favor ethanol dehydrogenation. Notably, Cu3O3/MOR displays robust ethylene adsorption, which enhances the potential for further ethylene activation. In-depth Bader charge and density of states analyses underscore the varying strengths and electronic characteristics of these interactions. This research provides a theoretical foundation for the design of highly efficient Cu-MOR catalysts tailored for the selective conversion of ethanol.

Single-Atom MnN5 Catalytic Sites Enable Efficient Peroxymonosulfate Activation by Forming Highly Reactive Mn(IV)-Oxo Species.

Four-nitrogen-coordinated transitional metal (MN4) configurations in single-atom catalysts (SACs) are broadly recognized as the most efficient active sites in peroxymonosulfate (PMS)-based advanced oxidation processes. However, SACs with a coordination number higher than four are rarely explored, which represents a fundamental missed opportunity for coordination chemistry to boost PMS activation and degradation of recalcitrant organic pollutants. We experimentally and theoretically demonstrate here that five-nitrogen-coordinated Mn (MnN5) sites more effectively activate PMS than MnN4 sites, by facilitating the cleavage of the O-O bond into high-valent Mn(IV)-oxo species with nearly 100% selectivity. The high activity of MnN5 was discerned to be due to the formation of higher-spin-state N5Mn(IV)═O species, which enable efficient two-electron transfer from organics to Mn sites through a lower-energy-barrier pathway. Overall, this work demonstrates the importance of high coordination numbers in SACs for efficient PMS activation and informs the design of next-generation environmental catalysts.

Efficient charge separation and transfer in a one-dimensional carbon nanotube/tungsten oxide p-n heterojunction composite for solar energy conversion.

Efficient and cost-effective photocatalysts for solar energy conversion represent a rapidly advancing and compelling area of research. In our study, we employed theoretical calculations to design a novel composite material consisting of a one-dimensional (1D) carbon nanotube (CNT) and tungsten oxide (W18O49) p-n heterojunction. This composite material was successfully synthesized using a straightforward solvothermal method, and we thoroughly investigated the charge separation and transfer mechanism. Our findings revealed that the composite material exhibited a superior photocurrent response. Notably, the CNTs/W18O49-2 sample demonstrated a significantly higher photocurrent under both AM 1.5G and infrared light irradiation, outperforming the individual components under AM 1.5G by a substantial factor of 30. This remarkable enhancement in performance can be attributed to the efficient charge separation and transfer facilitated by the built-in electric field created at the interface through the p-n heterojunction. Our study introduces a pioneering integration of CNTs and 1D tungsten oxide, resulting in a composite structure with a p-n heterojunction-a concept that has not been extensively explored previously. The results confirmed the formation of this unique one-dimensional structure and a p-n heterojunction, which has outstanding properties for various applications. These findings provide a robust foundation for the design of photocatalytic interfaces and offer a fresh approach to the development of high-performance photocatalysts.

CoN1 O2 Single-Atom Catalyst for Efficient Peroxymonosulfate Activation and Selective Cobalt(IV)=O Generation.

High-valent metal-oxo (HVMO) species are powerful non-radical reactive species that enhance advanced oxidation processes (AOPs) due to their long half-lives and high selectivity towards recalcitrant water pollutants with electron-donating groups. However, high-valent cobalt-oxo (CoIV =O) generation is challenging in peroxymonosulfate (PMS)-based AOPs because the high 3d-orbital occupancy of cobalt would disfavor its binding with a terminal oxygen ligand. Herein, we propose a strategy to construct isolated Co sites with unique N1 O2 coordination on the Mn3 O4 surface. The asymmetric N1 O2 configuration is able to accept electrons from the Co 3d-orbital, resulting in significant electronic delocalization at Co sites for promoted PMS adsorption, dissociation and subsequent generation of CoIV =O species. CoN1 O2 /Mn3 O4 exhibits high intrinsic activity in PMS activation and sulfamethoxazole (SMX) degradation, highly outperforming its counterpart with a CoO3 configuration, carbon-based single-atom catalysts with CoN4 configuration, and commercial cobalt oxides. CoIV =O species effectively oxidize the target contaminants via oxygen atom transfer to produce low-toxicity intermediates. These findings could advance the mechanistic understanding of PMS activation at the molecular level and guide the rational design of efficient environmental catalysts.

Ultrahigh Peroxymonosulfate Utilization Efficiency over CuO Nanosheets via Heterogeneous Cu(III) Formation and Preferential Electron Transfer during Degradation of Phenols.

In persulfate activation by copper-based catalysts, high-valent copper (Cu(III)) is an overlooked reactive intermediate that contributes to efficient persulfate utilization and organic pollutant removal. However, the mechanisms underlying heterogeneous activation and enhanced persulfate utilization are not fully understood. Here, copper oxide (CuO) nanosheets (synthesized with a facile precipitation method) exhibited high catalytic activity for peroxymonosulfate (PMS) activation with 100% 4-chlorophenol (4-CP) degradation within 3 min. Evidence for the critical role of surface-associated Cu(III) on PMS activation and 4-CP degradation over a wide pH range (pH 3-10) was obtained using in situ Raman spectroscopy, electron paramagnetic resonance, and quenching tests. Cu(III) directly oxidized 4-CP and other phenolic pollutants, with rate constants inversely proportional to their ionization potentials. Cu(III) preferentially oxidizes 4-CP rather than react with two PMS molecules to generate one molecule of 1O2, thus minimizing this less efficient PMS utilization pathway. Accordingly, a much higher PMS utilization efficiency (77% of electrons accepted by PMS ascribed to 4-CP mineralization) was obtained with CuO/PMS than with a radical pathway-dominated Co3O4/PMS system (27%) or with the 1O2 pathway-dominated α-MnO2/PMS system (26%). Overall, these results highlight the potential benefits of PMS activation via heterogeneous high-valent copper oxidation and offer mechanistic insight into ultrahigh PMS utilization efficiency for organic pollutant removal.

Phosphorus-based metal-free Z-scheme 2D van der Waals heterostructures for visible-light photocatalytic water splitting: a first-principles study.

Direct splitting of water over semiconductors under sunlight irradiation would be a promising approach for hydrogen production and solar energy utilization. In this work, BlueP/PN with a 2D van der Waals (vdW) heterostructure is proposed as a novel catalyst for the Z-scheme photocatalytic system. Its electronic structures, optical properties, and combined configuration were systematically evaluated by hybrid density functional theory (DFT) calculations. It was revealed that the 2D vdW heterostructure of BlueP/PN can play an important role in water splitting under visible light irradiation. This predicts a novel design of P-based vdW heterostructures for efficient photocatalysts.

S-Vacancy induced indirect-to-direct band gap transition in multilayer MoS2.

Two-dimensional (2D) MoS2 has various potential applications due to its attractive band gap of 1.29-1.90 eV and unique photoelectric properties. Furthermore, it is well-known that multilayer and bulk MoS2 structures possess an indirect band gap. In this paper, however, our first-principles calculations demonstrated that the creation of S vacancies in the multilayer and bulk MoS2 structures can achieve indirect-to-direct band gap transition, leading to a decrease in the band gap energies from 0.984-1.542 eV to 0.629-0.971 eV. Although the generation of Mo vacancies cannot cause such indirect-to-direct band gap transition, the Mo vacancies also decrease the band gap energies of the multilayer and bulk MoS2 structures to 0.369-0.460 eV. Furthermore, the band gap energy of the vacancy-defected multilayer MoS2 decreases with the increasing number of layers. Optical properties are also remarkably affected by atomic vacancies, that is, the absorption edges in the defect structures of MoS2 present a redshift and significantly enhance the visible light absorption compared to the corresponding pristine structures. These findings provide a novel approach to tuning the electronic structure and dielectric properties of MoS2 for specific future applications.

Heteroatom substitution enhances generation and reactivity of surface-activated peroxydisulfate complexes for catalytic fenton-like reactions.

Peroxydisulfate (PDS)-based Fenton-like reactions are promising advanced oxidation processes (AOPs) to degrade recalcitrant organic water pollutants. Current research predominantly focuses on augmenting the generation of reactive species (e.g., surface-activated PDS complexes (PDS*) to improve treatment efficiency, but overlooks the potential benefits of enhancing the reactivity of these species. Here, we enhanced PDS* generation and reactivity by incorporating Zn into CuO catalyst lattice, which resulted in 99% degradation of 4-chlorophenol within only 10 min. Zn increased PDS* generation by nearly doubling PDS adsorption while maintaining similar PDS to PDS* conversion efficiency, and induced higher PDS* reactivity than the common catalyst CuO, as indicated by a 4.1-fold larger slope between adsorbed PDS and open circuit potential of a catalytic electrode. Cu-O-Zn formation upshifts the d-band center of Cu sites and lowers the energy barrier for PDS adsorption and sulfate desorption, resulting in enhanced PDS* generation and reactivity. Overall, this study informs strategies to enhance PDS* reactivity and design highly active catalysts for efficient AOPs.

Unexpected catalytic performance in silent tantalum oxide through nitridation and defect chemistry.

This work reports on the preparation of a noble-metal-free and highly active catalyst that proved to be an efficient and green reductant with renewable capacity. Nitridation of a silent Ta1.1O1.05 substrate led to the formation of a series of TaOxNy hollow nanocrystals that exhibited outstanding activity toward catalytic reduction of nitrobenzenes under ambient conditions. ESR and XPS results indicated that defective nitrogen species and oxygen vacancies at the surfaces of the TaOxNy nanocrystals may play synergetic roles in the reduction of nitrobenzenes. The underlying mechanism is completely different from those previously reported for metallic nanoparticles. This work may provide new possibilities for the development of novel defect-meditated catalytic systems and offer a strategy for tuning any catalysts from silent to highly reactive by carefully tailoring the chemical composition and surface defect chemistry.

Breaking scaling relationships in alkynol semi-hydrogenation by manipulating interstitial atoms in Pd with d-electron gain.

Pd catalysts are widely used in alkynol semi-hydrogenation. However, due to the existence of scaling relationships of adsorption energies between the key adsorbed species, the increase in conversion is frequently accompanied by side reactions, thereby reducing the selectivity to alkenols. We report that the simultaneous increase in alkenol selectivity and alkynol conversion is achieved by manipulating interstitial atoms including B, P, C, S and N in Pd catalysts. A negative linear relationship is observed between the activation entropies of 2-methyl-3-butyn-2-ol and 2-methyl-3-buten-2-ol which is highly related to the filling of d-orbital of Pd catalysts by the modification of p-block elements. A catalyst co-modified by B and C atoms has the maximum d charge of Pd that achieves a 17-fold increase in the turn-over frequency values compared to the Lindlar catalysts in the semi-hydrogenation of 2-methyl-3-butyn-2-ol. When the conversion is close to 100%, the selectivity can be as high as 95%.

Palladium catalyzed radical relay for the oxidative cross-coupling of quinolines.

Traditional approaches for transition-metal catalyzed oxidative cross-coupling reactions rely on sp2-hybridized starting materials, such as aryl halides, and more specifically, homogeneous catalysts. We report a heterogeneous Pd-catalyzed radical relay method for the conversion of a heteroarene C(sp3)-H bond into ethers. Pd nanoparticles are supported on an ordered mesoporous composite which, when compared with microporous activated carbons, greatly increases the Pd d charge because of their strong interaction with N-doped anatase nanocrystals. Mechanistic studies provide evidence that electron-deficient Pd with Pd-O/N coordinations efficiently catalyzes the radical relay reaction to release diffusible methoxyl radicals, and highlight the difference between this surface reaction and C-H oxidation mediated by homogeneous catalysts that operate with cyclopalladated intermediates. The reactions proceed efficiently with a turn-over frequency of 84 h-1 and high selectivity toward ethers of >99%. Negligible Pd leaching and activity loss are observed after 7 catalytic runs.

Coupled Heterojunction Sn2Ta2O7@SnO2: Cooperative Promotion of Effective Electron-Hole Separation and Superior Visible-light Absorption.

In this work, a novel heterostructure integrated by two wide-band gap semiconductors, SnO2 and Sn2Ta2O7, is successfully prepared via a hydrothermal approach. Hollow Sn2Ta2O7 spheres were first formed, and small SnO2 particles were then well-dispersed onto the outside surface of the spheres, forming a p-n heterostructure. This heterostructure exhibits a higher potential edge that yielded enhanced photoredox ability. Further, the heterostructure is of Z-type with a consistent internal electric field direction, which effectively separates the photogenerated electron-hole pairs. Although both component semiconductors do not absorb visible light, the resulted p-n heterostructure is surprisingly observed to show an outstanding photocatalytic performance under visible light illumination. Such a visible light response is concluded to be the consequence of the impurity band formed by Sn(2+) doped in SnO2 and Sn(4+) in Sn2Ta2O7 via in situ redox. The existence of coupled Sn(2+) and Sn(4+) ions in p-n heterostructure is responsible for the absence of defects and the regenerated catalytic activities. The findings reported here may provide an approach to fabricate the new types of photocatalysts with a synergetic promotion for visible light absorption and sustained photocatalytic activities by coupling different wide-band semiconductors.

Molecular sensitized GdF3:Eu3+ for color tuning and highly enhanced luminescent properties.

In this work, we report on the preparation of [2,3-f]pyrazino[1,10]phenanthroline-2,3-dicarboxylic anions (PPDB(2-)) modified GdF3:Eu(3+) nanocrystals by a versatile ligand exchange approach for highly enhanced luminescent properties. The samples were carefully characterized by X-ray powder diffraction, transmission electron microscopy, infrared spectra and photoluminescence. It is found that all GdF3:Eu(3+) nanoparticles were entirely composed of homogeneous nano-spheres with an average diameter of about 30-35 nm. After PPDB(2-) capping, GdF3:Eu(3+) nanocrystals exhibited higher color purity and shorter lifetime time, which can be well recognized as a consequence of surface structure modification and local symmetry alteration near Eu(3+) ions. High color purity and short lifetime of PPDB(2-) modified GdF3:Eu(3+) nanocrystals predict highly enhanced red luminescence, which showed the quantum efficiency of ~34%. The highly enhanced luminescent property enables its potential application as chemosensor for detection of heavy metal ions.