In this paper, the chromium, Cr (VI), ion adsorption ability of oyster shell samples collected from two sea regions in Vietnam (Phu Yen province and Quang Ninh province) was investigated and compared. The oyster shell samples were calcined at different temperatures and denatured by using ethylenediaminetetraacetic acid (EDTA). The Cr (VI) ion adsorption ability of the prismatic (PP) and nacreous (NP) shell layers of oysters was also evaluated. The characteristics of oyster shell samples before and after treatment were determined by using analysis methods including XRD, IR, BET, UV-Vis, and FESEM. The Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich models and fit statistic equations were used to study the adsorption isotherms of Cr (VI) ion adsorption by oyster shells. The Cr (VI) ions adsorption kinetic has been set up using four reaction models consisting of first-order, pseudo-first-order, second-order, and pseudo-second-order reaction models. Effects of experimental factors on the Cr (VI) ion adsorption process using oyster shells were also investigated and discussed in this work.

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Effect of titania nanoparticles modified with 3 wt% [3‐(methacrylloxy)propyl]trimethoxysilane (m‐TiO2 NPs) and zirconia nanoparticles modified with 3 wt% (3‐glycidyloxypropyl)triethoxysilane (m‐ZrO2 NPs) on properties and morphology of acrylic emulsion polymer coating was investigated. With suitable weight ratio of m‐TiO2/m‐ZrO2 NPs, the acrylic coating could be improved abrasion resistance, weather durability, reflectance index (400–1400 nm) as well as thermal‐oxidation stability in comparison with the coatings having the same content of single modified nanoparticles. The starting thermal degradation temperature of acrylic coating filled by mixture of m‐TiO2 NPs and m‐ZrO2 NPs was approximately 10°C higher than that of the acrylic coating contained separately modified nanoparticles. The mixture of m‐TiO2 NPs and m‐ZrO2 NPs were used in solar reflective paint. Replacement of rutile TiO2 microparticles by 1 wt% mixture of modified nanoparticles, the solar reflective paint (SRP) could be improved water resistance and cooling performance. The water permeability of the SRP coating with mixture of modified nanoparticles was reduced by nearly 50%. The results of cooling performance test indicated that SRP loaded 1 wt% (m‐TiO2 NPs and m‐ZrO2 NPs) (weight ratio of 1/1) replaced 1 wt% TiO2 microparticles could reduce outside temperature of chamber test by nearly 11°C and ambient inside temperature of chamber test by 7.5°C. This novel solar reflective paint is considered as promising material for outdoor applications.

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Effect of zirconia nanoparticles (zirconia NPs/ZrO2 NPs) modified by 3 wt.% (glycidyloxypropyl) triethoxysilane – GPTES (m-ZrO2 NPs) on some properties of epoxy coating such as mechanical properties, thermal stability and anti-corrosion performance was investigated. The obtained results indicated that the addition of zirconia nanoparticles to epoxy coating could enhance the properties of this coating. The addition of 2 wt.% of pure ZrO2 NPs (u-ZrO2 NPs) to the epoxy matrix could increase the mechanical properties (hardness and adhesion to the steel substrate) by approximately 10 %, the onset temperature of thermal degradation of the epoxy/u-ZrO2 NPs coating was 4.4 oC higher, and the anti-corrosion performance of epoxy coating was improved in comparison with the neat epoxy coating. Organically modified ZrO2 NPs had higher improvement for epoxy coating’s properties than pure ZrO2 NPs. The epoxy coating filled with m-ZrO2 NPs had 19.7 % higher in relative hardness, 88.73 % more in adhesion to steel substrate, 25.6 oC higher in the onset temperature of thermal degradation, and higher anti-corrosion performance in comparison with the epoxy coating filled with 2 wt.% of pure zirconia nanoparticles. The cross-section FESEM images of the epoxy/m-ZrO2 NPs coating showed that m-ZrO2 NPs could regularly disperse in epoxy polymer matrix while unmodified zirconia nanoparticles (u-ZrO2 NPs) were agglomerated to big cluster in the epoxy coating. This was the reason for the high performance of the epoxy coating filled with zirconia NPs modified by GPTES.