There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

A critical review in strategies to improve photocatalytic water splitting towards hydrogen production

Graphitic carbon nitride (g-C3N4) is a metal-free conjugated polymer constructed from two-dimensional sheets with a bandgap energy of 2.7 eV, which makes it an applicable and efficient visible-active photocatalyst for H2 production. In the present study, the basic concepts and principles of photocatalytic water splitting have been discussed, and a guide for the selection of appropriate photocatalysts, focusing on the g-C3N4 nanomaterials, has been proposed. Our approach is mainly concentrated on evaluating two factors, namely the solar-to-hydrogen (STH) conversion and apparent quantum yield (AQY) for different photocatalysts, to provide an in-depth analysis and a framework for solar H2 production for future research directions. We compared hydrogen production from an economic viewpoint and performance of g-C3N4 nanomaterials through photochemical (PC) and photoelectrochemical (PEC) methods. Various approaches for efficient solar H2 generation over a modified g-C3N4 surface with the possibility for commercialization have been introduced. The promising approaches for the effective utilization of g-C3N4 are categorized into three proposed methods: electronic structure tuning, hybrid and nanocomposite fabrication, and finally geometric structure manipulation. Finally, we compared the recent findings and key achievements for g-C3N4-based photocatalysts modified based on the abovementioned three approaches to propose two possible scenarios for their use in the future development of efficient solar H2 generation.

Graphitic carbon nitride (g-C3N4)-based photocatalysts for solar hydrogen generation: recent advances and future development directions

Impact of the annealing temperature on Pt/g-C3N4 structure, activity and selectivity between photodegradation and water splitting

Metal/semiconductor interactions affect electron transfer rates and this is central to photocatalytic hydrogen ion reduction. While this interaction has been studied in great detail on metal oxide semiconductors, not much is known of Au particles on top of polymeric semiconductors. The effects of gold nanoparticle size and dispersion on top of g-C3N4 were studied by core and valence level spectroscopy and transmission electron microscopy in addition to catalytic tests. The as-prepared, non-calcined catalysts displayed Au particles with uniform dimension (mean particle size = 1.8 nm) and multiple electronic states: XPS Au 4f7/2 lines at 84.9 and 87.1 eV (each with a spin–orbit splitting of 3.6–3.7 eV). These particles, which did not show localized surface plasmon resonance (LSPR), before the reaction, doubled in size after the reaction giving a pronounced LSPR at about 550 nm. The effect of the heating environment on these particles (in air or in H2) was further investigated. While heating in H2 gave Au nanoparticles of different shapes, heating under O2 gave exclusively spherical particles. Similar activity towards photocatalytic hydrogen ion reduction under UV excitation was seen in both cases, however. XPS Au 4f analyses indicated that an increase in deposition time, during catalyst preparation, resulted in an increase in the initial fraction of oxidized gold particles, which were easily reduced under hydrogen. The valence band region for Au/gC3N4 was further studied in an effort to compare it to what is already known for Au/metal oxide semiconductors. A shift of over 2 eV for the Au 5d doublets was noticed between reduced and oxidized gold particles with mean particle sizes between 2 and 6 nm, which is consistent with the final state effect. A narrow range of gold loading for optimal catalytic performance was seen, where it seems that a density of one Au particle per 10 × 10 nm2 is the most suitable. Particle size and shape had a minor effect on performance, which may indicate the absence of a plasmonic effect on the reaction rate.

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Photo-catalytic hydrogen production over Au/g-C3N4: effect of gold particle dispersion and morphology.

Many drinking water reservoirs can contain organic pollutants such as artificial synthesized dye and drugs. On the other hand, some naturally occurring microorganisms such as cyanobacteria, are capable of producing toxic secondary metabolites (cyanotoxins) causing detrimental health effects in humans and animals are also present in water reservoirs. Photocatalytic destruction of organic pollutants in-reservoir requires not only good photo-catalytically activity but also efficacy of distribution and recycling. We report here, a facile calcination method of coating graphitic carbon nitride (g-C3N4) onto porous glass beads. Influences of precursor and heating temperature on photocatalytic activity were evaluated by photocatalytic degradation of methyl orange. The yellow floating beads show comparable activity to P25 (TiO2) coated beads in the removal of two of the most frequently occurring cyanobacterial toxins, microcystin-LR and cylindrospermopsin, in artificial freshwater under UV light irradiation. Microcystin-LR was destroyed within 60 min and cylindrospermopsin was removed after 100 min UV irradiation. The coated g-C3N4 layer is very robust and shows negligible degradation on photocatalytic performance when recycled. The recycling of the photocatalyst is very simple because of the large size of the catalyst-coated beads. A large batch was successfully produced in a lab tube furnace. For further application, the ability of g-C3N4 absorbing visible light could pave the way to utilise sunlight for the destruction of toxins in the water.

/pdf/graphitic-c3n4-coated-floating-glass-beads-for-1x8yoe0b6y.pdf

Marine Caux

Papers

Impact of the annealing temperature on Pt/g-C3N4 structure, activity and selectivity between photodegradation and water splitting

Photo-catalytic hydrogen production over Au/g-C3N4: effect of gold particle dispersion and morphology.

Graphitic-C3N4 coated floating glass beads for photocatalytic destruction of synthetic and natural organic compounds in water under UV light