Robust superhydrophobicity: mechanisms and strategies.

Superhydrophobic surfaces hold great prospects for extremely diverse applications owing to their water repellence property. The essential feature of superhydrophobicity is micro-/nano-scopic roughness to reserve a large portion of air under a liquid drop. However, the vulnerability of the delicate surface textures significantly impedes the practical applications of superhydrophobic surfaces. Robust superhydrophobicity is a must to meet the rigorous industrial requirements and standards for commercial products. In recent years, major advancements have been made in elucidating the mechanisms of wetting transitions, design strategies and fabrication techniques of superhydrophobicity. This review will first introduce the mechanisms of wetting transitions, including the thermodynamic stability of the Cassie state and its breakdown conditions. Then we highlight the development, current status and future prospects of robust superhydrophobicity, including characterization, design strategies and fabrication techniques. In particular, design strategies, which are classified into passive resistance and active regeneration for the first time, are proposed and discussed extensively.

Durable radiative cooling against environmental aging.

To fight against global warming, subambient daytime radiative cooling technology provides a promising path to meet sustainable development goals. To achieve subambient daytime radiative cooling, the reflection of most sunlight is the essential prerequisite. However, the desired high solar reflectance is easily dampened by environmental aging, mainly natural soiling and ultraviolet irradiation from sunlight causing yellowish color for most polymers, making the cooling ineffective. We demonstrate a simple strategy to use titanium dioxide nanoparticles, with ultraviolet resistance, forming hierarchical porous morphology via evaporation-driven assembly, which guarantees a balanced anti-soiling and high solar reflectance, rendering anti-aging cooling paint based coatings. We challenge the cooling coatings in an accelerated weathering test against simulated 3 years of natural soiling and simulated 1 year of natural sunshine, and find that the solar reflectance only declined by 0.4% and 0.5% compared with the un-aged ones. We further show over 6 months of aging under real-world conditions with barely no degradation to the cooling performance. Our anti-aging cooling paint is scalable and can be spray coated on desired outdoor architecture and container, presenting durable radiative cooling, promising for real-world applications.

Is Heat Really Beneficial to Water Evaporation-Driven Electricity?

Water evaporation-driven electricity (EDE) has attracted a great deal of attention in recent years as a novel renewable energy. Previous works have demonstrated that a high evaporation rate leads to a large output voltage. Hence, it is believed that heating is beneficial to EDE by enhancing the evaporation rate. However, experimental verification is lacking. This study demonstrates that heat induces a thermodiffusion effect that drives hydrated ions in the opposite direction of the evaporation-driven water flow, which reduces the output voltage as a synergistic effect. Our findings could be useful for designing a multifunction EDE generator and provide insight into the electricity generation mechanism.

Harvesting Electricity from Water Evaporation through Microchannels of Natural Wood.

When external pressure drives an electrolyte solution in a capillary tube with a charged inner surface, we obtain a streaming potential/current. This effect is also manifested when water flows through the microchannels of a tree, which is driven by capillary pressure and natural evaporation. Thus, by making use of natural evaporation, we took advantage of the anisotropic three-dimensional wood structures to fabricate nanogenerators drawing electricity from the streaming potential/current. As a result, direct current can be harvested continuously, simply through a piece of wood. A 300 mV open-circuit voltage and a 10 µA short-circuit current (ISC) were recorded from a single device, which surpassed the ISC values of most previous works by an order. By connecting five wood nanogenerators in series, a calculator can be completely functional, as a demonstration for practical application.

Degradation of 3,4-dichlorobenzotrifluoride by the Fenton-like process using zirconia-coated magnetite magnetic nanoparticles as an effective heterogeneous catalyst.

In this study, zirconia-coated magnetite magnetic nanoparticles (ZrO2/Fe3O4 MNPs) were prepared, characterized, and used as an effective and reusable heterogeneous catalyst for 3,4-dichlorobenzotrifluoride (3,4-DCBTE) degradation. The catalytic potential of the Fe3O4/ZrO2-H2O2 system for the removal of 3,4-DCBTE was tested in comparison with several other systems, and the effects of various operating parameters, including initial solution pH, catalyst addition, H2O2 concentrations, and reaction temperature, were also evaluated with respect to the degradation efficiency of 3,4-DCBTE. Results showed that the Fe3O4/ZrO2 composite could effectively enhance the oxidation of 3,4-DCBTE by the Fenton-like process, and there might be a synergetic effect in the Fe3O4/ZrO2 composite. When the mass ratio of Fe3O4 and ZrO2 was 1:1, the Fe3O4/ZrO2 exhibited the best catalytic activity, and the catalyst-driven Fenton process achieved high removal of 3,4-DCBTE (98.5%) and total organic carbon (TOC) (52.7%) at the operating conditions: pH 3.0, catalyst 2.0 g/L, H2O2 30 mM, temperature 30 °C, and reaction time 1 h. Furthermore, five successive runs of the Fenton oxidation using the same Fe3O4/ZrO2 composite resulted in the steady removal of 3,4-DCBTE, further confirming the high stability of the catalyst. In addition, the possible catalytic mechanism and degradation pathways of 3,4-DCBTE were also investigated.

[Degradation of 3,4- Dichlorobenzotrifluoride by Fe3O4/CeO2-H2O2 Heterogeneous Fenton-Like Systems].

The 3,4-Dichlorobenzotrifluoride (3,4-DCBTE) was dehalogenated with oxidation treatment by heterogeneous Fenton-like system, using nanoscale Fe304/CeO2 as a catalyst. This nanoscale catalyst was prepared by the impregnated method. As a highly active new heterogeneous Fenton-like catalyst, nanoscale Fe304/CeO2 not only has the characteristics of the traditional Fenton-like catalyst but also can prevent the secondary pollution which caused by Fe2+. To find the optimum catalytic conditions for nanoscale Fe3O4/CeO2, the influence factors were investigated. The results indicated that the degradation ratio of 3,4-DCBTE was significantly improved by adding nanoscale Fe3O4/CeO2, with the removal ratio reaching 97.76% in 120 minutes and 79.85% in 20 minutes. As the temperature increasing, the catalytic effect of nanoscale Fe3O4/CeO2 catalyst had been constantly improved obviously. As the pH decreased, the degradation ratio of 3,4-DCBTE increased. With the increase of dosage of hydrogen peroxide (H2O2), the degradation efficiency of 3,4-DCBTE initially increased and then decreased, because oxygen (O2) was generated in preferential self-reaction when an excess of (H2O2) was added. The optimum removal efficiency was observed with the dosage of 15 mg x L(-1). With the increased amount of catalyst, there was a same trend as dosage of hydrogen peroxide (H2O2). The degradation ratio of 3,4-DCBTE initially increased and then decreased, the optimum amount of catalyst was 0.5 g x L(-1). The results also suggested that the reaction process followed the first-order kinetics and the thermodynamic analysis demonstrated that the reaction was only needed low reaction activation energy.