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In this study, we examined whether catalysts with many defects have excellent photoactivity. We prepared ZnO nanoplates with varying degrees of defects in a short time of 4 h by varying the crystal growth temperature at 50, 100, 150, and 200 °C under a strong alkali NaOH atmosphere of 4.0 M. During high-temperature preparation of ZnO, crystal defects were reduced and crystallinity was further increased. In crystallized systems over 100 °C, rhombic nanoplates were used to control particle shape and induce growth in only two axes. The PL, Raman, and XPS analyses confirmed the presence of strong oxygen vacancies in all ZnO nanoplates, and the vacancies decreased with increasing crystallization temperatures. Methylene blue (MB) dye was initially fixed at 50 mg/L with a peak decrease in absorption at 600–700 nm, confirming its decomposition over time. For the 5 h reaction, the MB removal concentration follows the following order: ZnO-50 < ZnO-100 < ZnO-150 < ZnO-200. The study confirms that ZnO-200 nanoplates with fewer oxygen vacancies decompose MB more quickly. ZnO-200 nanoplates synthesized at 200 °C provided the best sterilization performance when tested against gram-positives and gram-negatives, Escherichia coli and Staphylococcus aureus, respectively. ZnO-200 nanoplates after 3 h showed a high sterilization performance of 96.95% (86.67% in a dark room) for staphylococcus aureus and 95.82% (74.66% in a dark room) for Escherichia coli when irradiated with light. Particularly noteworthy in this study is that ·OH and ·O2− radicals are generated more strongly in ZnO-200 than in ZnO-50 nanoplates. These results show that too-strong oxygen vacancies rather inhibit the antibacterial performance, and that the virtue of moderation also exists in the catalytic activity.

This study focused on developing an efficient phase change material (PCM) with a stable shape that can be applied in a wide range of industries. To prevent leakage of the PCM liquid at a temperature above the melting point, we used an encapsulation method by making use of an interfacial polycondensation reaction, and attempted to develop a new PCM with excellent thermal conductivity and thermal energy storage capacity. In order to improve the functionality of the PCM in latent thermal storage applications, a magnetic material, Fe3O4, was mixed with n-eicosane and a shape-stable phase change microcapsule with a silica shell was successfully prepared. In this study, we loaded Cu metal nanoparticles on the outer wall of the capsule with the aim of improving the thermal conductivity of the material for efficient heat transfer. The results indicated that the n-eicosane-Fe3O4@SiO2@Cu microcapsule has excellent heat transfer ability owing to its high thermal conductivity and exhibits efficient thermal energy storage–release performance by suppressing supercooling. The n-eicosane-Fe3O4@SiO2@Cu microcapsule showed an encapsulation efficiency (Een) of 61.48%, an energy storage efficiency (Ees) of 61.47%, and a thermal storage capacity (Ces) of 99.99%. Moreover, the multi-cycle differential scanning calorimetry scan showed excellent thermal reliability and shape stability, even in repetitive melting–cooling processes, suggesting that it is a promising PCM that can be used in industrial applications.

In order to improve the electrochemical performance of the NiCo2O4 material, Ni ions were partially substituted with Cu2+ ions having excellent reducing ability. All of the electrodes were fabricated by growing the Ni1−xCuxCo2O4 electrode spinel-structural active materials onto the graphite felt (GF). Five types of electrodes, NiCo2O4/GF, Ni0.875Cu0.125Co2O4/GF, Ni0.75Cu0.25Co2O4/GF, Ni0.625Cu0.375Co2O4/GF, and Ni0.5Cu0.5Co2O4/GF, were prepared for application to the oxygen evolution reaction (OER). As Cu2+ ions were substituted, the electrochemical performances of the NiCo2O4-based structures were improved, and eventually the OER activities were also greatly increased. In particular, the Ni0.75Cu0.25Co2O4/GF electrode exhibited the best OER activity in a 1.0 M KOH alkaline electrolyte: the cell voltage required to reach a current density of 10 mA cm−2 was only 1.74 V (η = 509 mV), and a low Tafel slope of 119 mV dec−1 was obtained. X-ray photoelectron spectroscopy (XPS) analysis of Ni1−xCuxCo2O4/GF before and after OER revealed that oxygen vacancies are formed around active metals by the insertion of Cu ions, which act as OH-adsorption sites, resulting in high OER activity. Additionally, the stability of the Ni0.75Cu0.25Co2O4/GF electrode was demonstrated through 1000th repeated OER acceleration stability tests with a high faradaic efficiency of 94.3%.

One dimensional (1D) metal sulfide nanostructures are one of the most promising materials for photocatalytic water splitting reactions to produce hydrogen (H2). However, tuning the nanostructural, optical, electrical and chemical properties of metal sulfides is a challenging task for the fabrication of highly efficient photocatalysts. Herein, 1D CdS nanorods (NRs) were synthesized by a facile and low-cost solvothermal method, in which reaction time played a significant role for increasing the length of CdS NRs from 100 nm to several micrometers. It is confirmed that as the length of CdS NR increases, the visible photocatalytic H2 evolution activity also increases and the CdS NR sample obtained at 18 hr. reaction time exhibited the highest H2 evolution activity of 206.07 μmol.g−1.h−1. The higher H2 evolution activity is explained by the improved optical absorption properties, enhanced electronic bandstructure and decreased electron-hole recombination rate.

This study introduces NiWO4 as a main photocatalyst, where the Ni component promotes methanation to generate a WO3-based catalyst, as a new type of catalyst that promotes the photoreduction of carbon dioxide by slowing the recombination of electrons and holes. The bandgap of NiWO4 is 2.74 eV, which was expected to improve the initial activity for the photoreduction of carbon dioxide. However, fast recombination between the holes and electrons was also expected. To overcome this problem, attempts were made to induce structural defects by partially replacing the Ni2+ ions in NiWO4 with Li+. The resulting CO2 conversion reaction was greatly enhanced with the Ni1-xLi2xWO4 catalysts containing Li+, compared to that of the pure NiWO4 catalysts. Notably, the total amount of CO and CH4 produced with the Ni0.8Li0.4WO4 catalyst was 411.6 nmol g−1. It is believed that the insertion of Li+ ions into the NiWO4 skeleton results in lattice defects due to charge and structural imbalance, which play a role in the capture of CO2 gas or excited electrons, thereby inhibiting recombination between the electrons and holes in the Ni1-xLi2xWO4 particles.

We synthesized cerium-doped cobalt-alumina (CoxCey/Al2O3) catalysts for the propane steam reforming (PSR) reaction. Adding cerium introduces oxygen vacancies, and the oxygen transfer capacity of the Ce promoter favors CO to CO2 conversion during PSR, inhibiting coke deposition and promoting hydrogen production. The best PSR activity was achieved at 700 °C using the Co0.85Ce0.15/Al2O3 catalyst, which showed 100% propane (C3H8) conversion and about 75% H2 selectivity, and 6% CO, 5% CO2, and 4% CH4 were obtained. In contrast, the H2 selectivity of the base catalyst, Co/Al2O3, is 64%. The origin of the difference in activity was the lower C3H8 gas desorption temperature of the Co0.85Ce0.15/Al2O3 catalyst compared to that of the Co/Al2O3 catalyst; thus, the PSR occurred at low temperatures. Furthermore, more CO was adsorbed on the Co0.85Ce0.15/Al2O3 catalyst, and subsequently, desorbed as CO2. The activation energy for water desorption from the Co0.85Ce0.15/Al2O3 catalyst was 266.96 kJ/mol, higher than that from Co/Al2O3. Furthermore, the water introduced during the reaction probably reacted with CO on the Co0.85Ce0.15/Al2O3 catalyst, increasing CO2 generation. Finally, we propose a mechanism involving the Co0.85Ce0.15/Al2O3 catalyst, wherein propane is reformed on CoxCey sites, forming H2, and CO, followed by the conversion of CO to CO2 by water on CeO2 sites.