Engineering of Single Atomic Cu-N3 Active Sites for Efficient Singlet Oxygen Production in Photocatalysis

Juxtaposing the antibacterial activities of different ZIFs in photodynamic therapy and their oxidative stress approach

Instigating oxidative stress is a crucial aspect of antibacterial therapy. Yet, its behavior is poorly understood in the context of zeolitic imidazolate frameworks (ZIFs) - a group of highly promising antibacterial agents. To address this gap, a series of ZIF@Ce6 particles were synthesized to investigate the impact of particle shape, size, and metal ion type on oxidative stress and bactericidal activity. For the first time, the interplay between the physicochemical properties and antibacterial activities of different ZIF@Ce6 particles is demonstrated, while unearthing their oxidative stress strategy in photodynamic therapy. Notably, the incorporation of chlorin e6 (Ce6), combined with light irradiation, amplified the bactericidal effect of the ZIFs and achieved a rare minimum inhibition concentration (MIC) of 12.5 µgmL-1 for ZIF-8. We discovered that singlet oxygen (1O2) production varies with particle shape and size, while photodynamic activity reshuffles the antibacterial performance sequence from pristine to modified ZIF-8. Interestingly, reactive oxygen species (ROS) accumulation and glutathione depletion tests revealed that oxidative stress in pristine ZIF-8 is predominantly induced by ROS, whereas both ROS and glutathione contribute to the oxidative stress in ZIF@Ce6 and pristine ZIF-67. When bacteria are preincubated with the antioxidant N-acetyl cysteine, the bactericidal activity of ZIF@Ce6 increases while the activity of pristine ZIF-8 is reduced and that of ZIF-67 remains unchanged. This study deepens our understanding of the antibacterial properties of ZIFs and their oxidative stress paths, paving way for the fabrication of ZIF-based materials with enriched and targeted antibacterial properties.

Walnut shell-based biochar-assisted Fe sites anchored carbon-rich g-C3N4: Boosting photodegradation of 2-Mercaptobenzothiazole though synergistic enhancement of Fe sites and C substitution

To expand the utilization of discarded walnut shells and enhance the photocatalytic activity of graphitic carbon nitride(g-C3N4), the carbon-rich graphitic carbon nitride anchored with Fe sites (FeW-CN) was synthesized via a walnut shell-based biochar-assisted strategy. Unlike the direct thermal copolymerization of melamine for g-C3N4, the iron-loaded walnut shell-based biochar (FeW) was first synthesized, followed by thermal copolymerization of melamine with FeW to form FeW-CN. The C substitution on the triazine ring enhanced the light absorption and electron migration for FeW-CN. And the Fe sites interacting with N-(C)3 further improved the migration and the utilization rate of photogenerated carriers. During the degradation of 2-Mercaptobenzothiazole, FeW-CN showed excellent photocatalytic performance and stability compared with g-C3N4. Moreover, FeW-CN maintained excellent photocatalytic performance in river water. Combination of electron paramagnetic resonance with active species quenching experiments, the synergistic mechanism of singlet oxygen, holes, and superoxide radicals was confirmed in the FeW-CN system. Compared to g-C3N4, the Fe sites and C substitution enhanced the production of singlet oxygen.

Highly Selective Conversion of Carbon Dioxide to Methane by Copper Single Atom Electrocatalysts

Electrocatalytic carbon dioxide reduction into high-value chemicals is one of the important solutions to the greenhouse effect and energy crisis. However, the slow kinetic process of eight electrons requires the development of efficient catalysts to improve the yields. Single atom catalysts (SACs) with high activity and selectivity have become an emerging research frontier in the field of heterogeneous catalysis. Herein, a catalyst comprised of Cu single atoms loaded on carbon substrate (Cu-NC) is developed for highly selective electrocatalytic reduction of CO2 to methane (CH4). The optimal catalyst (Cu-NC-1-4) exhibits a faradaic efficiency (FE) of over 50 % for CH4 within a wide potential window from -1.3 V to -1.8 V (vs. RHE) and the highest FE of CH4 is up to 67.22 % at -1.6 V (vs. RHE). Meanwhile, the product selectivity of CH4 among all the carbon products reaches 93.00 %, and the activity decay can be negligible via the 70-hour-stability-test. The existence of atomic dispersed Cu-N3 sites was verified by high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) and X-ray absorption near edge structure (XANES). Density functional theory (DFT) calculations show that the effective adsorption of the key intermediate *CO on Cu-N3 sites prompts the generation of CH4.

Stable Cu/Cu2O/CuN3@NC Catalysts for Aqueous Phase Reforming of Methanol

Aqueous-phase reforming of methanol represents a promising avenue for hydrogen (H2) production. However, developing highly efficient and low-cost nonprecious catalysts remains challenging. Here, we report the synthesis of Cu-based catalysts with Cu, Cu2O, and CuN3 nanoparticles anchored on the nitrogen-doped carbon, forming Cu0/Cu+/Cu-N3 active sites. This catalyst achieves a H2 production rate of 140.1 μmol/gcat/s at 210 °C, which is several times to 2 orders of magnitude higher than that of Cu-, Ni-, even Pt-based catalysts, demonstrating excellent long-term stability over 350 h at 210 °C. A mechanism investigation reveals that the Cu-N3 site facilitates water dissociation into *OH and improves *CO and *OH conversion, leading to enhanced CO conversion and H2 production kinetics.

Precise Modulation of the Coordination Environment of Single Cu Site Catalysts to Regulate the Peroxymonosulfate Activation Pathway for Water Remediation

Single atom site catalysts (SACs) with atomically dispersed active sites can be expected to be potential ideal catalysts for accurately modulating the persulfate activation pathway during the water remediation process because of their well-defined structure and the maximum metallic atom utilization. In this paper, a series of Cu SACs with different coordination environments were synthesized to elaborately regulate the peroxymonosulfate activation pathway in AOPs to clarify active species generation and transformation in water remediation. The degradation rate constants (kobs) of Cu-N2, Cu-N3, and Cu-N4 were 0.028, 0.021, and 0.015 min-1, respectively. Cu-N2 SACs exhibited a noticeable enhanced performance for bisphenol A (BPA) removal from water compared to that of the Cu-Nx SACs (x = 3, 4), accompanied by peroxymonosulfate (PMS) activation pathway variation. As shown by experimental and theoretical results, the PMS activation pathway was transformed from ROS to electron transfer with nitrogen coordination numbers decreasing from 4 to 2, which can be ascribed to the uneven charge distribution of Cu sites as well as upshifts in the d-band center, and thereby optimized electron transfer for PMS activation. Furthermore, the increasing nitrogen vacancies of single Cu site catalysts can also result in more unoccupied 3d orbitals of Cu atoms in SACs, thereby improving the intermediates' (PMS and BPA) adsorption-desorption process and BPA removal performance. These findings provided a beneficial approach for the coordination number regulation of SACs in water remediation.

Noble-Metal-Free Single- and Dual-Atom Catalysts for Artificial Photosynthesis

Artificial photosynthesis enables direct solar-to-chemical energy conversion aimed at mitigating environmental pollution and producing solar fuels and chemicals in a green and sustainable approach, and efficient, robust, and low-cost photocatalysts are the heart of artificial photosynthesis systems. As an emerging new class of cocatalytic materials, single-atom catalysts (SACs) and dual-atom catalysts (DACs) have received a great deal of current attention due to their maximal atom utilization and unique photocatalytic properties, whereas noble-metal-free ones impart abundance, availability, and cost-effectiveness allowing for scalable implementation. This review outlines the fundamental principles and synthetic methods of SACs and DACs and summarizes the most recent advances in SACs (Co, Fe, Cu, Ni, Bi, Al, Sn, Er, La, Ba, etc.) and DACs (CuNi, FeCo, InCu, KNa, CoCo, CuCu, etc.) based on non-noble metals, confined on an arsenal of organic or inorganic substrates (polymeric carbon nitride, metal oxides, metal sulfides, metal-organic frameworks, carbon, etc.) acting as versatile scaffolds in solar-light-driven photocatalytic reactions, including hydrogen evolution, carbon dioxide reduction, methane conversion, organic synthesis, nitrogen fixation, hydrogen peroxide production, and environmental remediation. The review concludes with the challenges, opportunities, and future prospects of noble-metal-free SACs and DACs for artificial photosynthesis.

Adjusting the Architecture of Heptagonal Metallo-Macrocycles by Embedding Metal Nodes into the Backbone

Coordination-driven self-assembly has been extensively employed for the bottom-up construction of discrete metallo-macrocycles. However, the prevalent use of benzene rings as the backbone limits the formation of large metallo-macrocycles with more than six edges. Herein, by embedding metal nodes into the ligand backbone, we successfully regulated the ligand arm angle and assembled two giant heptagonal metallo-macrocycles with precise control. The angle between two arms at position 4 of the central terpyridine (tpy) extended after complexation with metal ions, leading to ring expansion of the metallo-macrocycle. The assembled structures were straightforwardly identified through multi-dimensional NMR spectroscopy (1 H, COSY, NOESY), multidimensional mass spectrometry analysis (ESI-MS and TWIM-MS), transmission electron microscopy (TEM), as well as scanning tunneling microscopy (STM). In addition, the catalytic performances of metallo-macrocycles in the oxidation of thioanisole were studied, with both supramolecules exhibiting good conversion rates. Furthermore, fiber-like nanostructures were observed from single-molecule heptagons by hierarchical self-assembly.