Zinc oxide (ZnO) has been known as an excellent photocatalyst for the degradation of a variety of organic pollutants under UV irradiation. This work describes a synthesis of ZnO nanoparticles via a facile precipitation method, and Ag was doped into Ag/ZnO nanocomposite to improve the photocatalytic degradation of BPA under visible light irradiation. The obtained ZnO nanoparticles were 20 nm in size and had a relatively high surface area and pore volume, 26.2 m2/g and 0.48 cm3/g, respectively. The deposition of Ag led to a decrease in the surface area, pore volume, and band gap energy ( E g ) of ZnO nanoparticles. However, the photocatalytic activity of Ag/ZnO composite in the case increased. The performance of ZnO was compared with Ag/ZnO composites at the different molar ratios, and the kinetic reaction of BPA in these catalysts was investigated by the first-order kinetic model. The sample of Ag/ZnO-10 composite had the highest catalytic activity and showed the degradation efficiency, reaction rate, and degradation capacity of 100% in 120 min, 0.014 min-1, and 40 mg/g, respectively. In comparison, the effects of Ag/ZnO molar ratio, catalyst dosage, solution pH, and concentration of BPA on photocatalytic degradation were investigated. Additionally, the photocatalytic performance of Ag/ZnO-10 composite was evaluated by the degradation of other persistent organic compounds such as phenol, tartrazine, and methylene blue and compared to other catalysts in literature.

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Zinc oxide (ZnO) has been shown as a potential photocatalyst under ultraviolet (UV) light but its catalytic activity has a limitation under visible (Vis) light due to the wide bandgap energy and the rapid recombination of electrons and holes. Thus, hierarchical structure Au/ZnO composites were fabricated by the hydrothermal method and chemical reduction method for enhanced photocatalytic performance under visible light. As-prepared composites were characterized by UV-vis diffuse reflectance spectra (DR/UV-Vis), field emission scanning electron microscope (FESEM), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and electron paramagnetic resonance (EPR). The Au/ZnO-5 composite showed the highest adsorption among as-prepared samples in the range of 250-550 nm, having bandgap energy of 0.13 eV. Au nanoparticles of about 3-5 nm were well dispersed on hierarchical flower ZnO with approximately 10-15 μm. The EPR signal at g = 1.965 on both ZnO and Au/ZnO samples was attributed to oxygen vacancy Vo•, but the presence of Au led to a decrease in signal strength of Au/ZnO composite, showing the degradation efficiency (DE) and reaction rate of 99.2% and 0.109 min-1, respectively; these were larger than those of other samples. The effects of reaction parameters and oxidizing agents on photocatalytic performance were investigated and showed that the presence of H2O2 and O2 could improve the reaction of composite. In addition, the kinetic and photocatalytic mechanism of tartrazine (TA) on catalysts were studied by the first-order kinetic model and characterized analyses.

The effect of varying additions of metakaolin (MK) on the mechanical properties of lateritic soil to be utilized in the construction of pavement foundations has been studied. The preliminary test results show that the soil is highly plastic and lacks the sufficient mechanical ability to be used as a compacted subgrade/subbase for flexible pavement foundation. The kaolin was calcinated to form MK, which was utilized in proportions of 3%, 6%, 9%, and 12% by weight of the dry lateritic soil to stabilize it. California bearing ratio and unconfined compressive strength tests were conducted on the MK-treated lateritic soil to determine the suitability of the treated materials in the construction of compacted subgrade and / or subbase layers of flexible pavement. The stabilization test results show that MK has the potential to be utilized to strengthen the CBR and UCS of lateritic soil with a peak proportion of 6% MK by weight of dry soil beyond which the soil experiences a decline in strength formation.

Suffusion is an internal erosion mechanism, which means the transport of fine particles within the soil due to hydraulic interflows. With the objective to characterize this mechanism and to study a scale effect presented in literature, a specific centrifuge bench is designed. Test specimens of mixture of sand and kaolinite are compacted in rigid walled cells. The specimen height is selected according to the applied gravity and the chosen effective stress. After saturation, specimens are subjected to centrifugal acceleration and to a vertical downward flow under a constant hydraulic head. The effect of the applied hydraulic gradient is examined and the study underlines that the increase of specimen height induces the decrease of critical hydraulic gradient and the increase of erosion rate. A new energy analysis of tests is developed, linking the expended power to the erosion rate. This method permits to avoid the effect of specimen height.