Solar water oxidation is a crucial process in light-driven reductive synthesis, providing electrons and protons for various chemical reductions. Despite advances in light-harvesting materials and cocatalysts, achieving high efficiency and stability remains challenging. In this study, we present a simple yet effective strategy for immobilizing natural photosystems (PS) made of abundant and inexpensive elements, using amine-rich polyethylenimine (PEI) hydrogels, to fabricate organic/inorganic hybrid photoanodes. Natural PS II extracted from spinach was successfully immobilized on inverse opal TiO2 photoanodes in the presence of PEI hydrogels, leading to greatly enhanced solar water oxidation activity. Photoelectrochemical (PEC) analyses reveal that PS II can be immobilized in specific orientations through electrostatic interactions between the positively charged amine groups of PEI and the negatively charged stromal side of PS II. This specific orientation ensures efficient photogenerated charge separation and suppresses undesired side reactions such as the production of reactive oxygen species. Our study provides an effective immobilization platform and sheds light on the potential utilization of PS II in PEC water oxidation.
Efficient electrochemical hydrogen production and biomass refinery are crucial for the decarbonization of various sectors. However, their energy-intensive nature and low efficiency have hindered their practical application. In this study, earth-abundant and non-toxic photocatalysts that can produce hydrogen and reform biomass efficiently, utilizing unlimited solar energy, are presented. The approach involves using low-bandgap Si flakes (SiF) for efficient light-harvesting, followed by modification with Ni-coordinated N-doped graphene quantum dots (Ni-NGQDs) to enable efficient and stable light-driven biomass reforming and hydrogen production. When using kraft lignin as a model biomass, SiF/Ni-NQGDs facilitate record-high hydrogen productivity at 14.2 mmol gcat -1 h-1 and vanillin yield of 147.1 mg glignin -1 under simulated sunlight without any buffering agent and sacrificial electron donors. SiF/Ni-NQGDs can be readily recycled without any noticeable performance degradation owing to the prevention of deactivation of Si via oxidation. This strategy provides valuable insights into the efficient utilization of solar energy and practical applications of electro-synthesis and biomass refinement.
This study aimed to examine the prevalence and risk factors of depression among patients with rheumatic diseases (RDs) during the coronavirus disease 2019 (COVID-19) pandemic. This study adopted a cross-sectional design, and 160 outpatients with RDs in one university hospital in South Korea were sampled using the convenience sampling method. Data were collected from May to July 2021 using a structured questionnaire. The risk factors of depression were analyzed using descriptive statistics and multiple logistic regression analyses. The prevalence rates of post-traumatic stress disorder (PTSD), insomnia, and depression were 37.5%, 20.0%, and 24.4%, respectively. Multiple logistic regression analyses confirmed that employment status, monthly income, perceived health, PTSD, and insomnia were significant risk factors of depression. The findings highlight the urgent need to assist patients with RDs who are at risk of depression during the COVID-19 pandemic, especially individuals who are unemployed or have low incomes and poor perceived health, individuals with high PTSD, and individuals with severe insomnia. There is a need to provide disease-specific interventions to effectively alleviate depression among these individuals during the COVID-19 pandemic.
Photocatalytic sustainable fuel production attracted extensive attention because of the urgent need of the society to shift from fossil fuels to solar fuels. Herein, the synthesis of hexagonal rosettes of g-C3N4 with an efficient performance toward hydrogen evolution and hydrogen peroxide production as the two kinds of solar fuels were reported. The hexagonal rosettes of g-C3N4 were simply fabricated via controlled solid-state polymerization of three-dimensional hexagonal rosettes of cyanuric acid-melamine adduct at 500 °C. The hexagonal rosettes of g-C3N4 showed an amorphous nature with an extremely high surface area of 400 m2 g-1. Also, the as-obtained catalyst demonstrated remarkable photocatalytic activity in hydrogen production of 1285 µmol g-1 h-1 and hydrogen peroxide production of 150 µmol g-1 h-1. The mechanism for the polymerization process of the cyanuric acid-melamine (CM) complex to hexagonal rosettes of g-C3N4 was thoroughly described employing electron microscopy tools. This study identified that the CM complex condensation is accomplished via a dehydration process by producing a highly condensed and active structure of g-C3N4, which is different from the previously reported condensation mechanism of the melamine and its derivatives performed through a deamination process.
We studied the kinetics of photoelectrochemical (PEC) water oxidation using a model photoanode BiVO4 modified with various water oxidation catalysts (WOCs) by electrochemical impedance spectroscopy. In particular, we prepared BiVO4 photoanodes with catalytic multilayers (CMs), where cationic polyelectrolytes and anionic polyoxometalate (POM) WOCs were assembled in a desired amount at a nanoscale precision, and compared their performance with those with well-known WOCs such as cobalt phosphate (CoPi) and NiOOH. Our comparative kinetics analysis suggested that the deposition of the CMs improved the kinetics of both the photogenerated charge carrier separation/transport in bulk BiVO4 due to passivation of surface recombination centers and water oxidation at the electrode/electrolyte interface due to deposition of efficient molecular WOCs. On the contrary, the conventional WOCs were mostly effective in the former and less effective in the latter, which is consistent with previous reports. These findings explain why the CMs exhibit an outstanding performance. We also found that separated charge carriers can be efficiently transported to POM WOCs via a hopping mechanism due to the delicate architecture of the CMs, which is reminiscent of natural photosynthetic systems. We believe that this study can not only broaden our understanding on the underlying mechanism of PEC water oxidation but also provide insights for the design and fabrication of novel electrochemical and PEC devices, including efficient water oxidation photoanodes.
An efficient water oxidation photoanode based on hematite has been designed and fabricated by tailored assembly of graphene oxide (GO) nanosheets and cobalt polyoxometalate (Co-POM) water oxidation catalysts into a nacre-like multilayer architecture on a hematite photoanode. The deposition of catalytic multilayers provides a high photocatalytic efficiency and photoelectrochemical stability to underlying hematite photoanodes. Compared to the bare counterpart, the catalytic multilayer electrode exhibits a significantly higher photocurrent density and large cathodic shift in onset potential (â¼369 mV) even at neutral pH conditions due to the improved charge transport and catalytic efficiency from the rational and precise assembly of GO and Co-POM. Unexpectedly, the polymeric base layer deposited prior to the catalytic multilayers improves the performance even more by facilitating the transfer of photogenerated holes for water oxidation through modification of the flat band potential of the underlying photoelectrode. This approach utilizing polymeric base and catalytic multilayers provides an insight into the design of highly efficient photoelectrodes and devices for artificial photosynthesis.
We report the development of semiconducting melanin-based organic/inorganic hybrid photoanodes for solar water oxidation. Synthetic melanin thin-film incorporating polyoxometalate (POM) water oxidation catalysts (WOCs) are readily deposited on the surface of various n-type inorganic semiconductors (e.g., Fe2 O3 , BiVO4 , and TiO2 ) by electropolymerization. The deposition of melanin and POM hybrid (MP) thin-film results in the remarkably improved performance of an underlying semiconductor photoanode for solar water oxidation with a significantly increased photocurrent density and decreased onset potential for water oxidation through the formation of a melanin-based p-n heterojunction structure. We believe that this study can provide insights into the design and fabrication of various melanin-based optoelectronic devices by utilizing its unique physicochemical properties.
An efficient and stable heterojunction photoanode for solar water oxidation was fabricated by hybridization of WO3 and conducting polymers (CPs). Organic/inorganic hybrid photoanodes were readily prepared by the electropolymerization of various CPs and the codeposition of tetraruthenium polyoxometalate (Ru4POM) water-oxidation catalysts (WOCs) on the surface of WO3. The deposition of CPs, especially polypyrrole (PPy) doped with Ru4POM (PPy:Ru4POM), resulted in a remarkably improved photoelectrochemical performance by the formation of a WO3/PPy p-n heterojunction and the incorporation of efficient Ru4POM WOCs. In addition, there was also a significant improvement in the photostability of the WO3-based photoanode after the deposition of the PPy:Ru4POM layer due to the suppression of the formation of hydrogen peroxide, which was responsible for corrosion. This study provides insight into the design and fabrication of novel photosynthetic and photocatalytic systems with excellent performance and stability through the hybridization of organic and inorganic materials.
In this study, immobilized TiO(2) electrode is applied to reduce toxic Cr(VI) to non-toxic Cr(III) in aqueous solution under UV irradiation. To overcome the limitation of powder TiO(2), a novel technique of immobilization based on anodization was applied and investigated under various experimental conditions. The anodization was performed at 20V-5 degrees C for 45min with 0.5% hydrofluoric acid, and then the anodized samples were annealed under oxygen stream in the range 450-850 degrees C. Based on the results of the experiments, the photocatalytic Cr(VI) reduction was favorable in acidic conditions, with approximately 98% of the Cr(VI) being reduced within 2h at pH 3. Among the samples tested under same anodizing condition, the nanotubular TiO(2) annealed at 450 and 550 degrees C showed highest reduction efficiencies of Cr(VI). In addition, the surface characterizations (zeta potential, XRD, and SEM) of these samples proved that the Cr(VI) reduction efficiency was higher under acidic conditions and at a lower annealing temperature. From this research, it was concluded that the anodized TiO(2) has the potential to be a useful technology for environmental remediation as well as photocatalytic hydrogen production from water.
Chromium/chemistry , Hydrogen/chemistry , Titanium/chemistry , Water/chemistry , Catalysis , Chemistry Techniques, Analytical/methods , Hydrofluoric Acid/chemistry , Hydrogen-Ion Concentration , Microscopy, Electron, Scanning , Photochemistry/methods , Powders , Temperature , Time Factors , X-Ray Diffraction
