Defective MIL-88B(Fe) nanorods are exploited as exemplary iron-bearing metal-organic framework (MOF) catalyst for molecular oxygen (O2) activation at ambient temperature, triggering effective catalytic oxidation of formaldehyde (HCHO), one of the major indoor air pollutants. Defective MIL-88B(Fe) nanorods, growing along the [001] direction, expose abundant coordinatively unsaturated Fe-sites (Fe-CUSs) along extended hexagonal channels with a diameter of ca. 5 A, larger enough for the diffusion of O2 (3.46 A) and HCHO (2.7 A). The Lewis acid-base interaction between Fe-CUSs and accessible HCHO accelerates the FeIII/FeII cycle, catalyzing Fenton-like O2 activation to produce reactive oxidative species (ROSs), including superoxide radicals (•O2-), hydroxyl radicals (•OH), and singlet oxygen (1O2). Consequently, adsorbed HCHO can be oxidized into CO2 with a considerable mineralization efficiency (over 80%) and exceptional recyclability (4 runs, 48 h). Dioxymethylene (CH2OO), formate (HCOO-) species, and formyl radicals (•CHO) are recorded as the main reaction intermediates during HCHO oxidation. HCHO, H2O, and O2 are captured and activated by abundant FeIII/FeII-CUSs as acid/base and redox sites, triggering synergetic ROS generation and HCHO oxidation, involving cooperative acid-base and redox catalysis processes. This study will bring new insights into exploiting novel MOF catalysts for efficient O2 activation and reliable indoor air purification at ambient temperature.

Synergetic Molecular Oxygen Activation and Catalytic Oxidation of Formaldehyde over Defective MIL-88B(Fe) Nanorods at Room Temperature.

DFT calculations: A powerful tool for better understanding of electrocatalytic oxygen reduction reactions on Pt-based metallic catalysts

Solar-induced overall water splitting to produce hydrogen is inspiring towards energy sustainability, but it is also formidable due to its limited efficiency seriously hindering its scale up for practical application. CdS is an important transition metal sulfide with low-work-function. However, its photostability is often deteriorated due to photocorrosion influence. To overcome this issue, single-atom Pd was employed here to decorate CdS to form a CdS-Pd nanocatalyst through a simple and controllable photoinduced reduction strategy. The synergetic semiconductor (CdS)-metal (Pd) interaction promotes the fast bulk-to-surface electron migration, thereby the resultant CdS-Pd (3.83‰) nanocatalyst shows considerable structural stability and dramatically improved solar-induced HER activity in overall water splitting, about 110-fold higher than that of pristine CdS. Meanwhile, high apparent quantum yields (AQYs) of 4.47%/1.81% and 33.92%/27.49% were respectively achieved with this decorated nanocatalyst under the light of 420 nm/500 nm in absence and presence of scavenger, demonstrating the high-efficiency under broadband light illumination. Density functional theory (DFT) calculation supports that the easy formation of H* intermediates on the decorated nanocatalyst due to low energy barriers accounts for the internal promoted mechanism for hydrogen production. This study provides important insight to gain stable CdS-based photocatalysts for high-efficient hydrogen production by overall water splitting. 

Pd single-atom decorated CdS nanocatalyst for highly efficient overall water splitting under simulated solar light

An account of the strategies to enhance the water splitting efficiency of noble-metal-free electrocatalysts

In situ electrochemical reduced Au loaded black TiO2 nanotubes for visible light photocatalysis

Photocatalysis is a promising technology for energy and environment applications. Herein, a dual-defect heterojunction system of TiO2 hierarchical microspheres with oxygen vacancies modified with ultrathin MoS2−x nanosheets (MoS2−x @TiO2-OV) is designed for simultaneously degrading pollutants and evolving hydrogen. MoS2−x @TiO2-OV exhibits a dramatically enhanced photocatalytic activity with a H2 evolution rate of 2985.16 μmol g−1h−1. In treating the simulated pharmaceutical wastewater, MoS2−x @TiO2-OV is capable of purifying various refractory contaminants, with the highest H2 evolution rate of 41.59 μmol g−1h−1 during enrofloxacin degradation. While treating the simulated coking wastewater, the catalyst achieves a H2 evolution rate of 102.72 μmol g−1h−1 and a mineralization rate of 50%. Computational studies suggest that the dual-defect is superior for the adsorption of H* and producing·OH (‘dual-defect boosted dual-function’). Also, the dual-defect sites significantly boosted the charge-carrier separation and transfer efficiencies. This work highlights the crucial role of defect engineering to develop the energy-recovering wastewater treatment approaches.

Photocatalytically recovering hydrogen energy from wastewater treatment using MoS2 @TiO2 with sulfur/oxygen dual-defect

In this study, we construct the surface Lewis pairs, involving electron-rich nitrogen (Lewis base) sites and electron-deficient carbon (Lewis acid) sites, on carbon-based catalysts to enhance the catalytic activity towards the room-temperature decomposition of formaldehyde (HCHO). Density functional theory (DFT) calculation results show that the Lewis pairs, especially pyrrolic nitrogen species, contributed to the efficient HCHO adsorption ability. After the adsorbed HCHO molecules are oxidized into CO2 and H2O, and the Lewis acid-base catalytic sites finally get re-exposed, further initiating the next round of HCHO adsorption-decomposition process. Experimental measurements found that the typical sample exhibits an excellent catalytic HCHO oxidation activity, with the maximum HCHO removal efficiency of about 98.0 %, and the catalytic activity remains relatively unchanged after five cycles of reuse. This study may also open a new strategy to construct novel Lewis pairs for the removal of HCHO from other heteroatom-doped (e.g., B, S, F) porous carbon-based materials.

Enhancing the room-temperature catalytic degradation of formaldehyde through constructing surface lewis pairs on carbon-based catalyst

Exploring a novel approach for the synthesis of oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) catalysts with inexpensive and high-activity is desirable. Herein, we report a bubble templating method to synthesize the graphene-like mesoporous carbon sheets with point defects as ORR/HER bifunctional electrocatalysts. The typical product shows excellent ORR performance including the positive onset potential (740 mV) and high diffusion-limiting current density (4.07 mA cm−2). Along with small Tafel slopes, the overpotential is determined to be about −453 and −378 mV at 10 mA cm−2 in both alkaline and acidic media, which suggests a good candidate for HER reaction as well. The superior catalytic activities are derived from the abundant point defects on the mesoporous carbon sheets surface, especially the existence of pyridinic and pyrrolic nitrogen species. This study may be an alternative route to prepare the novel functional materials for the applications of ORR and HER.

Point-Defect-Rich Carbon Sheets as the High-Activity Catalyst Toward Oxygen Reduction and Hydrogen Evolution

https://iopscience.iop.org/article/10.1149/1945-7111/ab6978/pdf

Wenjing Yuan

Papers

Photocatalytically recovering hydrogen energy from wastewater treatment using MoS2 @TiO2 with sulfur/oxygen dual-defect

Enhancing the room-temperature catalytic degradation of formaldehyde through constructing surface lewis pairs on carbon-based catalyst

Point-Defect-Rich Carbon Sheets as the High-Activity Catalyst Toward Oxygen Reduction and Hydrogen Evolution

Engineering Nanowire Array Structure of Copper Oxide/Cuprous Oxide for Enhanced Oxygen Evolution Reaction