Wenguo Xu

Preparation of Superhydrophobic Coatings on Zinc as Effective Corrosion Barriers

Stable superhydrophobic films with a contact angle of 151 +/- 2 degrees were prepared on zinc substrates by a simple immersion technique into a methanol solution of hydrolyzed 1H,1H,2H,2H-perfluorooctyltrichlorosilane [CF3(CF2)5(CH2)2SiCl3, PFTS] for 5 days at room temperature followed by a short annealing at 130 degrees C in air for 1 h. The superhydrophobic film provides an effective corrosion-resistant coating for the zinc interface when immersed in an aqueous solution of sodium chloride (3% NaCl) for up to 29 days. The corrosion process was investigated by following the change of the water contact angle over time and by electrochemical means. The results are compared to those of unprotected zinc interfaces.

Fabrication of Superhydrophobic Surfaces with Hierarchical Structure through a Solution-Immersion Process on Copper and Galvanized Iron Substrates

Superhydrophobic surfaces were obtained on copper and galvanized iron substrates by means of a simple solution-immersion process: immersing the clean metal substrates into a methanol solution of hydrolyzed 1H,1H,2H,2H-perfluorooctyltrichlorosilane (CF3(CF2)5(CH2) 2SiCl3, FOTMS) for 3-4 days at room temperature and then heated at 130 degrees C in air for 1 h. Both of the resulting surfaces have a high water contact angle (CA) of larger than 150.0 degrees as well as a small sliding angle (SA) of less than 5 degrees . The formation and structure of the superhydrophobic surfaces were characterized by means of scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and energy-dispersive X-ray spectrometry (EDX). SEM images showed that both of the resulting surfaces exhibited special hierarchical structure. The special hierarchical structure along with the low surface energy leads to the high surface superhydrophobicity.

Preparation of Superhydrophobic Coatings on Zinc, Silicon, and Steel by a Solution-Immersion Technique

Zinc, silicon, and steel superhydrophobic surfaces were prepared by a simple solution-immersion technique. In the case of zinc, the method consists of dipping of the substrate in a prehydrolyzed methanol solution of 1H,1H,2H,2H-(perfluorooctyl)trichlorosilane [CF(3)(CF(2))(5)(CH(2))(2)SiCl(3), PFTS] for 24 h at 50 degrees C. Micron-sized spheres (1.7-2 microm in diameter) were formed on the zinc substrate at 50 degrees C, while a featureless coating was obtained when the solution-immersion process was conducted at room temperature. When the reaction was performed at room temperature, the formation of superhydrophobic coatings took several days (up to 5 days). In contrast, immersion of silicon or steel substrates in the PFTS/methanol solution led to the formation of hydrophobic interfaces even for a prolonged immersion period at 50 degrees C. The formation of superhydrophobic surfaces on silicon and steel surfaces was only possible if a zinc foil was added in the PFTS/methanol solution containing the silicon or steel substrate. X-ray photoelectron spectroscopy analysis was used to characterize the resulting surfaces and to underline a plausible reaction mechanism.

Fabrication of superhydrophobic Au–Zn alloy surface on a zinc substrate for roll-down, self-cleaning and anti-corrosion properties

Superhydrophobic Au–Zn alloy surfaces have been fabricated successfully on a zinc substrate via chemical substitution deposition and subsequent annealing treatment. The resulting surfaces exhibited remarkable superhydrophobicity with a WCA of 170 ± 2° and a WSA smaller than 1° without any organic modification. The surface morphologies and chemical compositions were investigated using field emission scanning electron microscopy (FESEM), energy-dispersive spectroscopy (EDS), X-ray powder diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), and the surface roughness was analyzed by atomic force microscopy (AFM). The theoretical mechanism for superhydrophobicity and wettability were also analyzed. The surface wettability changed from superhydrophilicity to superhydrophobicity with a stable Cassie–Baxter state via thermal treatment, which caused the generation of Au–Zn alloys (including AuZn3 and AuZn) and ZnO, and the formation of micro-/nano-binary architectures. The resulting superhydrophobic Au–Zn alloy surfaces exhibited exquisite roll-down, self-cleaning, and excellent anti-corrosion properties, and also had a firm mechanical property about 10 N, and this might have important values for more potential applications. The corrosion current density was reduced by more than 2 orders of magnitude for the resulting superhydrophobic surface in comparison with the untreated zinc surface and this should be ascribed to the contribution of Au–Zn alloys on the surface.

Controllable wettability of micro- and nano-dendritic structures formed on aluminum substrates

A superhydrophilic surface with a static water contact angle of 4° ± 2° via two-step immersion process and a superhydrophobic surface with a static water contact angle of 169° ± 2° and a sliding angle of almost 0° via successive thermal treatment have been successfully fabricated on aluminum substrates. Surface morphologies and chemical compositions were investigated using field emission scanning electron microscopy, X-ray powder diffraction and X-ray photoelectron spectroscopy, and the formation mechanism was also analyzed. The thermal treatment, which causes the generation of oxides and the appearance of nano-sized particles, is very important for the surface characteristic transformation from superhydrophilicity to superhydrophobicity. The effects of various experimental parameters on wettability, corrosion resistance, anti-icing and deicing properties, stability and large-area preparation were also studied. The corrosion rate of the as-prepared superhydrophobic surface decreases by about 57.6 times compared with that of the untreated aluminum surface and about 34.8 times compared with that of the pure copper surface. These excellent properties of the superhydrophobic surface may be favorable for its potential applications and industrialization.

Efficient photocatalytic degradation of bisphenol A and dye pollutants over BiOI/Zn2SnO4 heterojunction photocatalyst

BiOI/Zn2SnO4 composites with a heterostructure have been synthesized via a chemical deposition method under mild conditions by tuning the BiOI mass ratios. The physicochemical characteristics were investigated by X-ray diffraction (XRD), diffuse reflectance ultraviolet-visible light spectroscopy (DRS), scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HRTEM). The XRD results show that two phases of BiOI and Zn2SnO4 co-existed in the composites. The HRTEM image showing clear lattice fringes proves the formation of a heterojunction at the interfaces of BiOI and Zn2SnO4. The photocatalytic degradation of the endocrine disruptor bisphenol A and dyes (MB and RhB) indicated that the BiOI/Zn2SnO4 composites were more photoactive than pure BiOI and Zn2SnO4. The activity enhancement was mainly ascribed to the formation of a heterojunction between BiOI and Zn2SnO4, which facilitated the transfer and separation of photogenerated electron–hole pairs. The photoelectrochemical measurement has also confirmed the enhancement of the separation efficiency of electron–hole pairs.

Facile synthesized highly active BiOI/Zn2GeO4 composites for the elimination of endocrine disrupter BPA under visible light irradiation

A simple chemical bath approach for the facile synthesis of a BiOI/Zn2GeO4 composite has been demonstrated. The as-prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and UV-vis diffuse reflectance spectroscopy (UV-vis DRS). The XRD results indicate that the BiOI and Zn2GeO4 co-exist in the composite. The HRTEM image, showing clear lattice fringes, proves the formation of a heterojunction between BiOI and Zn2GeO4. The photo-degradation of bisphenol A indicates that the BiOI/Zn2GeO4 composites are more photoactive than BiOI and Zn2GeO4. The photocatalytic activity enhancement, which is mainly ascribed to the strong sensitization of BiOI to Zn2GeO4, broadened the photoabsorption of Zn2GeO4, and the heterojunction of BiOI/Zn2GeO4 facilitated the transfer and separation of photo-generated charge carriers. In addition, the active species trapping experiments showed that h+ and ˙O2− were the dominant reactive species, while molecular oxygen plays a fatal role for photocatalytic interactions. Subsequently, a possible degradation mechanism is proposed. Furthermore, the BiOI/Zn2GeO4 photocatalysts exhibit a higher mineralization capacity for bisphenol A, suggesting hopeful prospects for its use in practical applications for the decomposition of organic pollutants.

Controlled growth of CuO–Cu3Pt/Cu micro-nano binary architectures on copper substrate and its superhydrophobic behavior

A facile, simple and novel method for controllable fabrication of a superhydrophobic surface was developed by spontaneous deposition and subsequent annealing on a copper substrate. The surface morphologies, chemical compositions and hydrophobicity of the as-prepared surfaces were investigated using field emission scanning electron microscopy, X-ray diffractometry, X-ray photoelectron spectroscopy and contact angle measurements. The superhydrophobic surface was composed of a hierarchical structure of CuO–Cu3Pt/Cu. At the optimal conditions, the surface showed good superhydrophobicity with a water contact angle of about 170 ± 2° and a sliding angle of approximately 0 ± 2°. Additionally, the formation mechanism of the superhydrophobic surface was studied. The as-prepared superhydrophobic surface exhibited good nonsticking behavior, long-term stability, and a large buoyancy force, which offers possibilities for potential applications.

First-principles study of electronic structures and photocatalytic activity of low-Miller-index surfaces of ZnO

First-principles calculations have been performed to investigate the electronic structures and optical properties of the main low-Miller-index surfaces of ZnO: nonpolar (101¯0) and (112¯0) surfaces as well as polar (0001)-Zn and (0001¯)-O surfaces. According to the structure optimization results, there are similar relaxation behaviors for the (101¯0) and (112¯0) surfaces, both with a strong tilting of the surface Zn-O dimers and an obvious contraction of the surface bonds. For the polar surfaces, the surface double layers both tend to relax inwards, but the largest relaxation is found on the (0001¯)-O surfaces. The calculated band gaps are 0.56, 0.89, 0.21, and 0.71 eV for (101¯0), (112¯0), (0001)-Zn and (0001¯)-O surfaces, respectively. For the nonpolar (101¯0) and 112¯0 surfaces, the Fermi levels locate at the valence band maximum, which are similar to that of bulk ZnO. The surface states in the conduction band lead to the increased Fermi level and cause the n-type conduction behavior for (0001)-Zn surf...

Fabrication of Au–AlAu4–Al2O3 superhydrophobic surface and its corrosion resistance

Superhydrophobic Au–AlAu4–Al2O3 surfaces have been successfully fabricated on aluminum substrate via immersion in chloroauric acid (HAuCl4) aqueous solution and subsequent annealing treatment. The morphologies of the surfaces exhibit dendritic structures. The surface with remarkable superhydrophobic properties has a water contact angle of 171 ± 2° and a sliding angle of approximately 0°. The effects of the immersion time, immersion concentration, annealing time and annealing temperature on surface wettability were investigated in detail. The corrosion resistance of the untreated aluminum surface and the resulting Au–AlAu4–Al2O3 surface were also investigated via the Tafel extrapolation method. The corrosion current densities are reduced by more than 1 order of magnitude for the resulting surface in comparison with the untreated aluminum surface. The anticorrosion properties of the surfaces get better over the immersion time and this may be due to the generation of corrosion products, which can prevent the corrosion process and protect the substrates. Moreover, the low current density of the resulting superhydrophobic surface demonstrates its excellent corrosion resistance.