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Highly ordered TiO2 nanotubes (TNTs) decorated with a series of lanthanide ions (Ln3+ = Ho3+, Tb3+, Eu3+, Yb3+, and Er3+) were prepared through an electrochemical process and anodization. The composition, structure, and chemical bond of the as-prepared photocatalysts were characterized through scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, and ultraviolet diffuse reflectance spectroscopy. Furthermore, the electrochemical characteristics of the catalysts were analyzed and photoelectrochemical properties were investigated through water splitting. All samples were prepared in the anatase phase without changing the crystal structure. The holmium-doped TNT photocatalyst exhibited the best performance with a hydrogen evolution rate of 90.13 μmol cm−2h−1 and photoconversion efficiency of 2.68% (0 V vs. RHE). Photocatalytic efficiency increased because of the expansion of the absorption wavelength range attributed to the appropriate positioning of the band structure and reduced electron/hole pair recombination resulting from the unhindered electron movement. This study demonstrated the preparation of high-potential solar-active photocatalysts through the synergetic effects of the work function, band edge, and bandgap changes caused by the series of lanthanide combinations with TNTs.

Highly ordered TiO[sub.2] nanotubes (TNTs) decorated with a series of lanthanide ions (Ln[sup.3+] = Ho[sup.3+] , Tb[sup.3+] , Eu[sup.3+] , Yb[sup.3+] , and Er[sup.3+] ) were prepared through an electrochemical process and anodization. The composition, structure, and chemical bond of the as-prepared photocatalysts were characterized through scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, and ultraviolet diffuse reflectance spectroscopy. Furthermore, the electrochemical characteristics of the catalysts were analyzed and photoelectrochemical properties were investigated through water splitting. All samples were prepared in the anatase phase without changing the crystal structure. The holmium-doped TNT photocatalyst exhibited the best performance with a hydrogen evolution rate of 90.13 μmol cm[sup.−2] h[sup.−1] and photoconversion efficiency of 2.68% (0 V vs. RHE). Photocatalytic efficiency increased because of the expansion of the absorption wavelength range attributed to the appropriate positioning of the band structure and reduced electron/hole pair recombination resulting from the unhindered electron movement. This study demonstrated the preparation of high-potential solar-active photocatalysts through the synergetic effects of the work function, band edge, and bandgap changes caused by the series of lanthanide combinations with TNTs.

Iron cation impurities reportedly enhance the oxygen evolution reaction (OER) activity of Ni-based catalysts, and the enhancement of OER activity by Fe cations has been extensively studied. Meanwhile, Fe salts, such as iron hydroxide and iron oxyhydroxide, in the electrolyte improve the OER performance, but the distinct roles of Fe cations and Fe salts have not been fully clarified or differentiated. In this study, NiO electrodes were synthesized, and their OER performance was evaluated in KOH electrolytes containing goethite (α-FeOOH). Unlike Fe cations, which enhance the performance via incorporation into the NiO structure, α-FeOOH boosts OER activity by adsorbing onto the electrode surface. Surface analysis revealed trace amounts of α-FeOOH on the NiO surface, indicating that physical contact alone enables α-FeOOH to adsorb onto NiO. Moreover, interactions between α-FeOOH and NiO were observed, suggesting their potential role in OER activity enhancement. These findings suggest that Fe salts in the electrolyte influence OER performance and should be considered in the development of OER electrodes.

In this study, we investigated the oxygen evolution reaction (OER) characteristics of Ni–Zn–Fe electrodes by varying plating current density and Ni:Fe ratio in a plating bath. The activity of the OER increased up to the plating current density of 160 mA/cm2, as the Fe content of the deposited electrode increased and electrochemical surface area (ECSA) increased after Zn dealloying. However, for the plated electrode with higher than 160 mA/cm2 of current density, the change in composition caused by underpotential deposition led to decreased activity due to decreasing Fe content and diminishing Zn dealloying. Moreover, when the Ni:Fe ratio in the plating bath was varied, outstanding OER activity was observed at Ni:Fe = 2:1. When the Fe content of the bath increased beyond this ratio, Fe could not restrain Ni oxidation and formed Fe oxides in OER reaction, and oxygen vacancy decreased. These caused a degradation of the OER activity.

Coprocessing of waste plastics with coal and petroleum resid was investigated to determine the effect of resid on reactivity and conversion. This study includes five experimental chapters: (1) use of petroleum resid as a solvent in coprocessing waste plastics with coal and its feasibility and synergistic effect; (2) details of the effect of varying the reaction time on systems including LDPE; (3) factorial design to determine the significance of the factors such as catalyst type, time, and temperature on the product distribution and boiling point distribution of hexane solubles from reactions; (4) use of a two-stage process to which fractional factorial design was applied, and consists of two sets of experiments, which include the selection of reaction temperature and time and reactant loading sequence and a detailed study of the effect of coal content and H$\\sb2$ pressure on the conversion of coal and LDPE; (5) fractional factorial design of two-stage coprocessing using different kinds of reactants. Summaries of these five experimental chapters follow. First of all, the feasibility of using resid as a solvent in coprocessing waste plastics with coal was determined using the defined coprocessing effect factor $(f\\sb{i}).$ Increasing LDPE reaction times from 60 to 300 min resulted in an increase of conversion from 39.5% to 90.2%. After 360 min the conversion declined to 70.9%. Similar results were obtained with the LDPE and coal reactions; increased reaction time resulted in increased LDPE conversion as well as increased overall conversion. The results from the catalyst study showed that catalytic coprocessing of LDPE, coal, and resid was affected by the type of catalyst used. Introduction of 10 wt% hydrocracking catalyst to NiMo/Al$\\rm\\sb2O\\sb3$ increased conversion and improved the overall product slate. The hydrocracking catalysts themselves were most effective for converting the solid reactants to THF soluble material and producing lower boiling point products. By contrast, the different types of catalysts gave very similar results in LDPE/coal reactions and did not produce substantial improvements in conversion. From an analysis of the variance of the first set of experiments of fractional factorial design of two-stage coprocessing for reaction parameter selection, extraction after the first stage turned out to be significant for all gas, hexane solubles (KXs), and conversion, with a confidence level of 97.5 $\\sim$ 99%, while no two-factor interactions investigated in this study had a significant effect on the response variables. The weight percent of coal present in the reaction had an effect on the amount of hexane solubles with a 99% confidence level. Hydrogen pressure in the second stage affected the amount of gas produced, while hydrogen pressure in the first stage affected the amount of hexane solubles produced with 90% confidence. Interactions of weight percent and hydrogen pressure at the second stage did not affect the response variables. Low H$\\sb2$ pressure at the second stage with a high coal weight percent was the worst case for producing HXs. The effect of catalyst sequence and types of reactants turned out to be significant for HXs and conversion.