Photocatalytic Superamphiphobic Coatings and the Effect of Surface Microstructures on Superamphiphobicity

Transition metal compounds: From properties, applications to wettability regulation

Transition metal compounds (TMCs) have the advantages of abundant reserves, low cost, non-toxic and pollution-free, and have attracted wide attention in recent years. With the development of two-dimensional layered materials, a new two-dimensional transition metal carbonitride (MXene) has attracted extensive attention due to its excellent physicochemical properties such as gas selectivity, photocatalytic properties, electromagnetic interference shielding and photothermal properties. They are widely used in gas sensors, oil/water separation, wastewater and waste-oil treatment, cancer treatment, seawater desalination, strain sensors, medical materials and some energy storage materials. In this view, we aim to emphatically summarize MXene with their properties, applications and their wettability regulation in different applications. In addition, the properties of transition metal oxides (TMOs) and other TMCs and their wettability regulation applications are also discussed.

Fabrication of durable self-cleaning photocatalytic coating with long-term effective natural light photocatalytic degradation performance

The practical application of photocatalytic coating has been greatly challenged in terms of its long-term effective natural light photocatalytic degradation due to its vulnerability and easy contamination caused by poor self-cleaning properties. In this work, photocatalytic coating with self-cleaning properties was prepared by spraying fluorinated dual-scale TiO₂ on the inorganic lithium silicate adhesive, enabling excellent durability and long-term effective photocatalytic degradation performance under natural light. The coating exhibits superhydrophobic properties even after abrasion testing, acid and alkali immersion testing, and UV aging, laying a foundation for the practical use. Moreover, the coating can be applied to various substrates and its excellent self-cleaning properties make it resistant to particulate and liquid contamination that may occur in the environment. Besides, we evaluated the photocatalytic stability of the coating by subjecting it to acidic and alkaline environments and high pollution concentrations. Furthermore, benefiting from the synergistic effect of photocatalytic and self-cleaning properties, the coating achieves long-term effective photocatalytic degradation of dye wastewater under natural light, which still has a high removal rate of 95.8% for methylene blue even after 30 cycles of use. Meanwhile, due to the coating's excellent durability, the long-term quality loss rate of the coating still remained below 0.3%, which avoids the risk of secondary environmental pollution caused by nanoparticle leakage. Therefore, these excellent properties enable the coating to have a broad range of application prospects for the treatment of pollutants in water.

A review of self-cleaning photocatalytic surface: Effect of surface characteristics on photocatalytic activity for NO

Self-cleaning surface has attracted much attention in the field of photocatalytic degradation of NO due to its dirt pickup resistance and self-cleaning effect under the action of rainwater. In this review, the factors affecting NO degradation efficiency were analyzed in terms of photocatalyst characteristics and environmental conditions combined with the photocatalytic degradation mechanism. The feasibility of photocatalytic degradation of NO on superhydrophilic, superhydrophobic and superamphiphobic surfaces was discussed. Furthermore, the effect of special surface characteristics of self-cleaning on photocatalytic NO was highlighted and the improvement of the long-term effect using three self-cleaning surfaces on photocatalytic NO was evaluated and summarized. Finally, the conclusion and outlook were proposed related to the self-cleaning surface for photocatalytic degradation of NO. In future research, the comprehensive effects of the characteristics of photocatalytic materials, self-cleaning characteristics and environmental factors on the photocatalytic degradation of NO and the actual application effects of such self-cleaning photocatalytic surfaces should be further clarified in combination with the engineering. It is believed that this review can provide some theoretical basis and support for the development of self-cleaning surfaces in the field of photocatalytic degradation of NO.

A WO3-TiO2 nanorod/CaCO3 photocatalyst with degradation-regeneration double sites for NO2-inhibited and durable photocatalytic NO

As a promising cleaner technology for nitric oxide degradation, photocatalysis has attracted extensive attention, while the main limitations of photocatalytic nitric oxide are that the toxic NO₂ is produced easily and the photocatalytic durability was inferior due to the accumulation of photocatalytic products. In this paper, a WO₃-TiO₂ nanorod/CaCO₃ (TCC) insulating heterojunction photocatalyst with degradation-regeneration double sites was prepared by simple grinding and calcining. The effects of CaCO₃ loading on the morphology, microstructure and composition of TCC photocatalyst were investigated by SEM, TEM, XRD, FT-IR and XPS etc. Also, TCC exhibits NO₂-inhibited and durable characteristics for NO degradation. DFT calculation, the detection of active radicals by EPR, capture test and the NO degradation pathway characterized by in-situ FT-IR spectra showed that the electron-rich region formed and the existence of regeneration sites are the main reasons for promoting the NO₂-inhibited and durable NO degradation. Furthermore, the mechanism of NO₂-inhibited and durable NO degradation by TCC was revealed. Finally, TCC superamphiphobic photocatalytic coating was prepared, which still exhibits similar NO₂-inhibited and durable characteristics for NO degradation to TCC photocatalyst. It may provide new application value and development prospects in the field of photocatalytic NO.

Lignin self-assembly and auto-adhesion for hydrophobic cellulose/lignin composite film fabrication

Large amounts of lignin are produced as a by-product of paper pulping, resulting in a tremendous waste of natural resources with potential uses across various areas. To achieve the value-added utilization of agricultural waste and lignin, we developed a method for the fabrication of a lignin structure-designed hydrophobic film (LSHF) directly through solvent/anti-solvent self-assembly (acetic acid aqueous solution/n-hexane) and auto-adhesion of acetic acid lignin (AL) on the surface of a lignocellulose film (LCF). As the morphology structure revealed, the LSHF had a rough surface composed of lignin colloidal spheres, which significantly improved the water contact angle (WCA) from ~80° to ~130°. Furthermore, benefiting from the auto-adhesion of lignin, the WCA was more stable in 240 s, demonstrating that the LSHF had a lower WCA decrease (15.53 % - 25.55 % decrease) than the LCF (41.97 % - 61.11 % decrease) and the sample without auto-adhesion (100 % decrease). Simultaneously, auto-adhesion endowed the LSHF with a ~50 % increase in tensile strength. This work provides a novel strategy for the fabrication of hydrophobic cellulose/lignin composite films via lignin self-assembly and auto-adhesion.

Selective Fabrication of Robust and Multifunctional Super Nonwetting Surfaces by Diverse Modifications of Zirconia-Ceria Nanocomposites

The creation of surfaces with various super nonwetting properties is an ongoing challenge. We report diverse modifications of novel synthesized zirconia-ceria nanocomposites by different low surface energy agents to fabricate nanofluids capable of regulating surface wettability of mineral substrates to achieve selective superhydrophobic, superoleophobic-superhydrophilic, and superamphiphobic conditions. Surfaces treated with these nanofluids offer self-cleaning properties and effortless rolling-off behavior with sliding angles ≤7° for several liquids with surface tensions between 26 and 72.1 mN/m. The superamphiphobic nanofluid coating imparts nonstick properties to a solid surface whereby liquid drops can be effortlessly displaced on the coating with a near-zero tilt and conveniently lifted off using a needle tip, leaving no trace. Further, the superamphiphobic surface demonstrates good oil repellency toward ultralow surface tension liquids such as n-hexane and n-heptane. The superoleophobic-superhydrophilic surface repels oil droplets well regardless of whether it is in the air or underwater conditions. In addition, reaping the benefits of the ZrO₂-CeO₂ nanocomposites' photocatalysis feature, the superoleophobic-superhydrophilic coating exhibits self-cleaning ability by the degradation of color dyes. Modification of the wettability of substrates is carried out by a cost-effective and facile solution-immersion approach, which creates surfaces with hierarchical nano-submicron-scaled structures. The multipurpose coated surfaces have outstanding durability and mechanical stability. They also resist well high-temperature-high-pressure conditions, which will provide various practical applications in different fields, including the condensate banking removal in gas reservoirs or the separation of oil/water mixtures.

Improvement mechanism of NO photocatalytic degradation performance of self-cleaning synergistic photocatalytic coating under high humidity

Photocatalytic coating has been widely studied as a promising material to remove air pollutants. However, the effectiveness and long-term effect of photocatalysis in high relative humidity environment is still the main challenge in this field. In this study, a fluorinated WO₃-TiO₂ nanorods/SiO₂ epoxy photocatalytic superamphiphobic coating (FTSE coating) was prepared using a simple spraying method. The micromorphology and chemical composition of FTSE coating was characterized by SEM, EDS, FT-IR, XPS and TGA techniques. The advanced contact angle and hysteresis angle test show that the FTSE coating had excellent superamphiphobicity. The mechanical abrasions, corrosion resistance and UV aging tests show that the FTSE coating exhibited reasonable durability. Besides, the NO degradation efficiency of hydrophilic and superamphiphobic coatings with contact angles of 20.19°, 87.74°, 162.93° and 164.47° was tested in different humidity environment. The results showed that the superamphiphobic coating exhibited more superior photocatalytic degradation efficiency (84.02%) than the hydrophilic coating (51.38%) at a high relative humidity (RH=98%). Finally, FTSE coating exhibited prominent photocatalytic stability and the synergistic effect of photocatalysis and self-cleaning. After 30 d outdoor weathering test, the NO degradation efficiency decreased by 13.07% and recovered to the original level after flushing. The improvement mechanism of NO degradation performance was proposed based on the characteristics of superamphiphobic surface.