Metal-organic framework-based S-scheme heterojunction photocatalysts

Photocatalysis is a promising technology to resolve energy and environmental issues, where the design of high-efficiency photocatalysts is the central task. As an emerging family of photocatalysts, semiconducting metal-organic frameworks (MOFs) with remarkable features have demonstrated great potential in various photocatalytic fields. Compared to MOF-based photocatalysts with a single component, construction of S-scheme heterojunctions can render MOFs with enhanced charge separation, redox capacity and solar energy utilization, and thus improved photocatalytic performance. Herein, an overview of the recent advances in the design of MOF-based S-scheme heterojunctions for photocatalytic applications is provided. The basic principle of S-scheme heterojunctions is introduced. Then, three types of MOF-based S-scheme heterojunctions with different compositions are systematically summarized including MOF/non-MOF, MOF-on-MOF and MOF-derived heterojunctions. Afterwards, the enhanced performances of MOF-based S-scheme heterojunctions in hydrogen production, CO2 reduction, C-H functionalization, H2O2 production and wastewater treatment are highlighted. Lastly, the current challenges and future prospects regarding the design and applications of MOF-based S-scheme heterojunctions are discussed to inspire the further development of this emerging field.

In situ Hg2+ improved the peroxidase-like activity and triggered "ON" the oxidase-like activity of yolk-shell Co3S4 microspheres for the detection of Hg2

Exploring highly active nanozymes is an important task to realize the real-time detection of some heavy metal ions in water. In this work, yolk-shell Co3S4 microspheres have been verified to possess excellent peroxidase-like activity, which can be further improved by adding Hg2+. Very interestingly, Hg2+ can trigger "ON" the oxidase-like activity of Co3S4 microspheres. The dual peroxidase-/oxidase-like activity of the yolk-shell Co3S4 microspheres is evaluated by using the chromogenic substrate 3,3',5,5'-tetramethylbenzidine (TMB). Furthermore, comprehensive studies verify that the enhanced peroxidase-like activity, together with the "ON" oxidase-like activity of the yolk-shell Co3S4 microspheres, is attributed to the in situ generation of HgS on the surface of Co3S4 microspheres and then the release of more active sites. Importantly, the in situ generated HgS on the surface of Co3S4 microspheres can form a heterojunction, which also accelerates the catalytic process. During the catalytic reaction, some active species (O2- and h+) can be detected by ESR. Thus, a colorimetric sensing platform based on Hg2+-triggered signal amplification has been successfully constructed, which can be validated by the detection of Hg2+ residue in environmental water.

Synthesis of Metal-Organic Framework-Based ZIF-8@ZIF-67 Nanocomposites for Antibiotic Decomposition and Antibacterial Activities

Toxic antibiotic effluents and antibiotic-resistant bacteria constitute a threat to global health. So, scientists are investigating high-performance materials for antibiotic decomposition and antibacterial activities. In this novel research work, we have successfully designed ZIF-8@ZIF-67 nanocomposites via sol-gel and solvothermal approaches. The ZIF-8@ZIF-67 nanocomposite is characterized by various techniques that exhibit superior surface area enhancement, charge separation, and high light absorption performance. Yet, ZIF-8 has high adsorption rates and active sites, while ZIF-67 has larger pore volume and efficient adsorption and reaction capabilities, demonstrating that the ZIF-8@ZIF-67 nanocomposite outperforms pristine ZIF-8 and ZIF-67. Compared with pristine ZIF-8 and ZIF-67, the most active 6ZIF-67@ZIF-8 nanocomposite showed higher decomposition efficacy for ciprofloxacin (65%), levofloxacin (54%), and ofloxacin (48%). Scavenger experiments confirmed that •OH, •O2-, and h+ are the most active species for the decomposition of ciprofloxacin (CIP), levofloxacin (LF), and ofloxacin (OFX), respectively. In addition, the 6ZIF-67/ZIF-8 nanocomposite suggested its potential applications in Escherichia coli for growth inhibition zone, antibacterial activity, and decreased viability. Moreover, the stability test and decomposition pathway of CIP, LF, and OFX were also proposed. Finally, our study aims to enhance the efficiency and stability of ZIF-8@ZIF-67 nanocomposite and potentially enable its applications in antibiotic decomposition, antibacterial activities, and environmental remediation.

ZIF template-based Fe-doped defect-rich hierarchical structure Co3S4/MoS2 as a bifunctional electrocatalyst for overall water splitting

To replace the current expensive precious metal catalysts for water electrolysis, it is important to develop inexpensive and powerful bifunctional catalysts for hydrogen production. It is an effective way to improve catalytic performance using excellent templates and elemental doping. Here, a hierarchical structure Fe-Co3S4/MoS2 was synthesized using an Fe-ZIF precursor prepared by ion exchange, followed by hydrothermal sulfuration and annealing. It required overpotentials of only 93 mV and 243 mV to achieve a current density of 10 mA cm-2 in the HER and OER, respectively. It also showed excellent catalytic performance for overall water splitting, requiring only 1.42 and 1.71 V to achieve current densities of 10 and 100 mA cm-2 in 1 M KOH. The catalyst also demonstrated excellent ultra-long-term stability. The superb catalytic performance and stability can be attributed to the Fe doping, exposing more active sites while retaining the highly stable framework of the ZIF. The component modulation of Co3S4 and MoS2 by Fe doping induced high intrinsic activity and excellent transfer coefficients. This work presents a novel approach to prepare noble metal-free catalysts with highly stable rich interfaces and defects for overall water splitting.

"d-electron interactions" induced CoV2O6-Fe-NF for efficient oxygen evolution reaction

The investigation of cost-effective, highly efficient, and environmentally friendly non-noble-metal-based electrocatalysts is imperative for oxygen evolution reactions (OER). Herein, CoV₂O₆ grown on nickel foam (NF) was selected as the fundamental material, and Fe²⁺ is introduced through a simple Fe³⁺ immersion treatment to synthesize CoV₂O₆-Fe-NF. Fe²⁺ is transformed into high oxidation state Fe^(2+δ)+ due to interactions between the 3d electrons of transition metals. In situ Raman spectroscopy analysis reveals the specific process of OER in the presence of Fe^(2+δ)+. Being in a higher oxidation state, Fe^(2+δ)+ provides more active sites, which is beneficial for the reaction between water molecules and the reactive sites of the electrocatalyst, ultimately enhancing the accelerated OER process. CoV₂O₆-Fe-NF exhibited an overpotential of only 298 mV at 100 mA cm^-2 in 1 M KOH electrolyte, which is lower than that of CoV₂O₆-NF (348 mV), as well as the comparative samples: Fe-NF (390 mV) and NF (570 mV). The exploration of high performance, triggered synergistically by the cooperative effect of transition metal 3d electrons, provides insights into the design of transition metal electrocatalysts for highly efficient OER.