Hehe Wei

Direct Blow-Spinning of Nanofibers on a Window Screen for Highly Efficient PM2.5 Removal

Particulate matter (PM) pollution has caused many serious public health issues. Whereas indoor air protection usually relies on expensive and energy-consuming filtering devices, direct PM filtration by window screens has attracted increasing attention. Recently, electrospun polymer nanofiber networks have been developed as transparent filters for highly efficient PM2.5 removal; however, it remains challenging to uniformly coat the nanofibers on window screens on a large scale and with low cost. Here, we report a blow-spinning technique that is fast, efficient, and free of high voltages for the large-scale direct coating of nanofibers onto window screens for indoor PM pollution protection. We have achieved a transparent air filter of 80% optical transparency with >99% standard removal efficiency level for PM2.5. A test on a real window (1 m × 2 m) in Beijing has proven that the nanofiber transparent air filter acquires excellent PM2.5 removal efficiency of 90.6% over 12 h under extremely hazy air conditions (PM2.5 mass concentration > 708 μg/m3). Moreover, we show that the nanofibers can be readily coated on the window screen for pollution protection and can be easily removed by wiping the screen after hazardous days.

Iced photochemical reduction to synthesize atomically dispersed metals by suppressing nanocrystal growth

Photochemical solution-phase reactions have been widely applied for the syntheses of nanocrystals. In particular, tuning of the nucleation and growth of solids has been a major area of focus. Here we demonstrate a facile approach to generate atomically dispersed platinum via photochemical reduction of frozen chloroplatinic acid solution using ultraviolet light. Using this iced-photochemical reduction, the aggregation of atoms is prevented, and single atoms are successfully stabilized. The platinum atoms are deposited on various substrates, including mesoporous carbon, graphene, carbon nanotubes, titanium dioxide nanoparticles, and zinc oxide nanowires. The atomically dispersed platinum on mesoporous carbon exhibits efficient catalytic activity for the electrochemical hydrogen evolution reaction, with an overpotential of only 65 mV at a current density of 100 mA cm−2 and long-time durability (>10 h), superior to state-of-the-art platinum/carbon. This iced-photochemical reduction may be extended to other single atoms, for example gold and silver, as demonstrated in this study.Photochemical synthesis is a popular approach to fabricate metallic nanoparticles, however stabilizing individually-dispersed atoms by this method remains challenging. Here, the authors freeze their precursor solution prior to UV irradiation to obtain atomically-dispersed platinum catalysts with high electrocatalytic performance.

Defective molybdenum sulfide quantum dots as highly active hydrogen evolution electrocatalysts

Molybdenum disulfide (MoS2), a promising non-precious electrocatalyst for the hydrogen evolution reaction with two-dimensional layered structure, has received increasing attention in recent years. Its electrocatalytic performance has been limited by the low active site content and poor conductivity. Herein, we report a facile and general ultrafast laser ablation method to synthesize MoS2 quantum dots (MS-QDs) for electrocatalytic HER with fully exposed active sites and highly enhanced conductivity. The MS-QDs were prepared by ultrafast laser ablation of the corresponding bulk material in aqueous solution, during which they were partially oxidized and formed defective structures. The as-prepared MS-QDs demonstrated high activity and stability in the electrocatalytic HER, owing to their very large surface area, defective structure, abundance of active sites, and high conductivity. The present MS-QDs can also find application in optics, sensing, energy storage, and conversion technologies.

Ice Melting to Release Reactants in Solution Syntheses

Aqueous solution syntheses are mostly based on mixing two solutions with different reactants. It is shown that freezing one solution and melting it in another solution provides a new interesting strategy to mix chemicals and to significantly change the reaction kinetics and thermodynamics. For example, a precursor solution containing a certain concentration of AgNO3 was frozen and dropped into a reductive NaBH4 solution at about 0 °C. The ultra-slow release of reactants was successfully achieved. An ice-melting process can be used to synthesize atomically dispersed metals, including cobalt, nickel, copper, rhodium, ruthenium, palladium, silver, osmium, iridium, platinum, and gold, which can be easily extended to other solution syntheses (such as precipitation, hydrolysis, and displacement reactions) and provide a generalized method to redesign the interphase reaction kinetics and ion diffusion in wet chemistry.

Aerodynamic levitated laser annealing method to defective titanium dioxide with enhanced photocatalytic performance

Defective TiO2 has attracted increasing attention for use in photocatalytic and electrochemical materials because of its narrowed band-gap and improved visible-light photocatalytic activity. However, a facile and efficient approach for obtaining defect-rich TiO2 still remains a challenge. Herein, we demonstrate such an approach to narrow its bandgap and improve visible-light absorption through implanting abundant defects by aerodynamic levitated laser annealing (ALLA) treatment. Note that the ALLA method not only provides rapid annealing, solidifying and cooling process, but also exhibits high efficiency for homogeneous and defective TiO2 nanoparticles. The laser-annealed TiO2 achieves a high hydrogen evolution rate of 8.54 mmol·h–1·g–1, excellent decomposition properties within 60 min, and outstanding recyclability and stability, all of which are superior to the corresponding properties of commercial P25.

Enhanced Electrocatalytic Activity for Water Splitting on NiO/Ni/Carbon Fiber Paper

Large-scale growth of low-cost, efficient, and durable non-noble metal-based electrocatalysts for water splitting is crucial for future renewable energy systems. Atomic layer deposition (ALD) provides a promising route for depositing uniform thin coatings of electrocatalysts, which are useful in many technologies, including the splitting of water. In this communication, we report the growth of a NiO/Ni catalyst directly on carbon fiber paper by atomic layer deposition and report subsequent reduction and oxidation annealing treatments. The 10–20 nm NiO/Ni nanoparticle catalysts can reach a current density of 10 mA·cm−2 at an overpotential of 189 mV for hydrogen evolution reactions and 257 mV for oxygen evolution reactions with high stability. We further successfully achieved a water splitting current density of 10 mA·cm−2 at 1.78 V using a typical NiO/Ni coated carbon fiber paper two-electrode setup. The results suggest that nanoparticulate NiO/Ni is an active, stable, and noble-metal-free electrocatalyst, which facilitates a method for future water splitting applications.

Defective MoS2 electrocatalyst for highly efficient hydrogen evolution through a simple ball-milling method

Molybdenum disulfide (MoS2) has attracted extensive attention as an alternative to replace noble electrocatalysts in the hydrogen evolution reaction (HER). Here, we highlight an efficient and straightforward ball milling method, using nanoscale Cu powders as reductant to reduce MoS2 engineering S-vacancies into MoS2 surfaces, to fabricate a defectrich MoS2 material (DR-MoS2). The micron-sized DR-MoS2 catalysts exhibit significantly enhanced catalytic activity for HER with an overpotential (at 10 mA cm−2) of 176 mV in acidic media and 189 mV in basic media, surpassing most of Mo-based catalysts previously reported, especially in basic solution. Meanwhile stability tests confirm the outstanding durability of DR-MoS2 catalysts in both acid and basic electrolytes. This work not only opens a new pathway to implant defects to MoS2, but also provides low-cost alternative for efficient electrocatalytic production of hydrogen in both alkaline and acidic environments.摘要通过电催化将水分解可大量制备高纯度氢气, 这一过程需要高效能低成本的电催化剂材料. 二硫化钼价格低廉、 资源丰富, 且具有类似贵金属铂的氢吸附自由能, 是一种潜在的高效制氢电催化剂. 然而其仍面临着析氢过电位偏高、 稳定性差、 难以批量制备、 在碱性环境下催化析氢活性较低等问题, 限制了其实际应用. 目前, 大量文献证实制造缺陷是一种有效的优化二硫化钼电催化活性的方法. 本文通过球磨还原法制备了一种富含缺陷的二硫化钼析氢反应电催化剂. 这种新型的富缺陷二硫化钼催化剂在酸碱性条件下都显示出较高的催化活性, 在酸性条件下, 过电位为176 mV时其电流密度可达10 mA cm−2; 在碱性条件下, 过电位为189 mV时其电流密度可达10 mA cm−2, 超过了大部分报道的析氢反应电催化剂. 此外, 富缺陷二硫化钼材料显示出较小的塔菲尔斜率和良好的电化学稳定性, 进一步证实了析氢反应催化活性的增强. 这种通过球磨还原制造缺陷的思路为未来催化剂的设计与性能优化开辟了一条新的道路, 且该方法简单, 适于大规模的工业生产.