Showing papers by "Akira Fujishima published in 2021"

Hierarchical structures hydrogel evaporator and superhydrophilic water collect device for efficient solar steam evaporation

Abstract: Efficient light absorption and trapping are of vital importance for the solar water evaporation by hydrogel-based photothermal conversion materials. Conventional strategies are focused on the development of the composition and structure of the hydrogel's internal network. In our point of view, the importance of the surface structure of hydrogel has usually been underestimated or ignored. Here inspired by the excellent absorbance and water transportation ability of biological surface structure, the hierarchical structured hydrogel evaporators (HSEs) increased the light absorption, trapping, water transportation and water-air interface, which is the beneficial photothermal conversion and water evaporation. The HSEs showed a rapid evaporation rate of 1.77 kg·m-2·h-1 at about 92% energy efficiency under one sun (1 kW·m-2). Furthermore, the superhydrophilic window device was used in this work to collect the condensed water, which avoids the light-blocking caused by the water mist formed by the small droplets and the problem of the droplets stick on the device dropping back to the bulk water. Integrated with the excellent photothermal conversion hydrogel and superhydrophilic window equipment, this work provides efficient evaporation and desalination of hydrogel-based solar evaporators in practical large-scale applications.

Visible light-assisted photocatalysis using spherical-shaped bivo4 photocatalyst

Abstract: In this research work, we reported the synthesis of a spherical-shaped bismuth vanadate (BiVO4) photocatalyst using a cost-effective, simple, chemical hydrothermal method and studied the effect of deposition temperatures on the structural, morphological, optical properties, etc The XRD result confirmed the monoclinic scheelite phase of BiVO4 An XPS study confirmed the occurrence of Bi, V, and O elements and also found that Bi and V exist in +3 and +5 oxidation states, respectively SEM micrographs revealed the spherical-shaped morphology of the BiVO4 photocatalyst Optical investigation showed that the bandgap of the BiVO4 photocatalyst varied between 225 and 232 eV The as-synthesized BiVO4 photocatalyst was used to study the photocatalytic degradation of crystal violet (CV) dye under visible light illumination The photocatalytic degradation experiment showed that the degradation percentage of crystal violet dye using BiVO4 reached 9821% after 120 min Mineralization of crystal violet dye was studied using a chemical oxygen demand analysis

Advanced two-dimensional heterojunction photocatalysts of stoichiometric and non-stoichiometric bismuth oxyhalides with graphitic carbon nitride for sustainable energy and environmental applications

Abstract: Semiconductor-based photocatalysis has been identified as an encouraging approach for solving the two main challenging problems, viz., remedying our polluted environment and the generation of sustainable chemical energy. Stoichiometric and non-stoichiometric bismuth oxyhalides (BiOX and BixOyXz where X = Cl, Br, and I) are a relatively new class of semiconductors that have attracted considerable interest for photocatalysis applications due to attributes, viz., high stability, suitable band structure, modifiable energy bandgap and two-dimensional layered structure capable of generating an internal electric field. Recently, the construction of heterojunction photocatalysts, especially 2D/2D systems, has convincingly drawn momentous attention practicably owing to the productive influence of having two dissimilar layered semiconductors in face-to-face contact with each other. This review has systematically summarized the recent progress on the 2D/2D heterojunction constructed between BiOX/BixOyXz with graphitic carbon nitride (g-C3N4). The band structure of individual components, various fabrication methods, different strategies developed for improving the photocatalytic performance and their applications in the degradation of various organic contaminants, hydrogen (H2) evolution, carbon dioxide (CO2) reduction, nitrogen (N2) fixation and the organic synthesis of clean chemicals are summarized. The perspectives and plausible opportunities for developing high performance BiOX/BixOyXz-g-C3N4 heterojunction photocatalysts are also discussed.

Synthesis of N-doped TiO2 for efficient photocatalytic degradation of atmospheric NOx

Abstract: Titanium oxide (TiO2) is a potential photocatalyst for removing toxic NOx from the atmosphere. Its practical application is, however, significantly limited by its low absorption into visible light and a high degree of charge recombination. The overall photocatalytic activity of TiO2 remains too low since it can utilize only about 4–5% of solar energy. Nitrogen doping into the TiO2 lattice takes advantage of utilizing a wide range of solar radiation by increasing the absorption capability towards the visible light region. In this work, N-doped TiO2, referred to as TC, was synthesized by a simple co-precipitation of tri-thiocyanuric acid (TCA) with P25 followed by heat treatment at 550 degrees C. The resulting nitrogen doping increased the visible-light absorption and enhanced the separation/transfer of photo-excited charge carriers by capturing holes by reduced titanium ions. As a result, TC samples exhibited excellent photocatalytic activities of 59% and 51% in NO oxidation under UV and visible light irradiation, in which the optimum mass ratio of TCA to P25 was found to be 10.

C-doped ZnS-ZnO/Rh nanosheets as multijunctioned photocatalysts for effective H2 generation from pure water under solar simulating light

Abstract: A combined solvothermal method and post-annealing to synthesize highly active ZnS-ZnO nanosheets is presented. ZnO was produced on ZnS nanosheets by thermal annealing ZnS/ethylenediamine in air. From combined studies of experimental and computational works, we revealed that during annealing, carbon (C) element was a major dopant from the decomposition of ethylenediamine, which was unintentionally doped into the ZnS-ZnO, and gave major impacts on enhanced visible-light photocatalysis. Rhodium (Rh) was deposited by in situ photoreduction to form a ZnS-ZnO/Rh catalyst composite. This multijunctioned photocatalyst was outstanding for H2 generation from pure water under solar simulating light due to effective charge separation by Z-scheme heterojunction of ZnS and ZnO and Schottky junction of Rh-cocatalysts/semiconductors. This facile method realizes multijunctioned ZnS-ZnO/Rh photocatalysts with substantial defects that are very promising for solar-energy harvesting applications.

Cobalt-Doped Manganese Dioxide Hierarchical Nanostructures for Enhancing Pseudocapacitive Properties.

Abstract: Herein, overall improvement in the electrochemical performance of manganese dioxide is achieved through fine-tuning the microstructure of partially Co-doped manganese dioxide nanomaterial using facile hydrothermal method with precise control of preparative parameters. The structural investigation exhibits formation of a multiphase compound accompanied by controlled reflections of α-MnO2 as well as γ-MnO2 crystalline phases. The morphological examination manifests the presence of MnO2 nanowires having a width of 70-80 nm and a length of several microns. The Co-doped manganese dioxide electrode displayed a particular capacitive behavior along with a rising order of capacitance concerning with increased cobalt ion concentration suitable for certain limits. The value of specific capacitance achieved by a 5% Co-doped manganese dioxide sample was 1050 F g-1 at 0.5 A g-1, which was nearly threefold greater than that achieved by a bare manganese dioxide electrode. Furthermore, Co-doped manganese dioxide nanocomposite electrode exhibits exceptional capacitance retention (92.7%) till 10,000 cycles. It shows the good cyclability as well as stability of the material. Furthermore, we have demonstrated the solid-state supercapacitor with good energy and power density.

The upsurge of photocatalysts in antibiotic micropollutants treatment: Materials design, recovery, toxicity and bioanalysis

Abstract: The excessive use of antimicrobial agents such as antibiotics and disinfectants for domestic purposes and industries polluted the water bodies severely in the recent past. Thus released antimicrobial agents negatively impact the environment and human health as it induce antimicrobial resistance (AMR) to microbes in the environment. Conventional biodegradation routes showed feasible antibiotics pollutants degradation. Nonetheless, they often demand a long time of operation (usually in days) and a major portion of the antimicrobial agents is left untreated unlike the complete oxidation with advanced oxidation processes. The residues of antibiotics left in the water bodies accelerate growth of microorganisms (bacterial, fungal, and viral) with AMR. In virtue of avoiding the catastrophe of widespread AMR, photocatalysis assisted antibiotic pollutant treatment is recently gaining a great popularity as an advanced oxidation process and has shown to be useful for the removal of antimicrobial compounds, mainly antibiotics. Recent review reports on photocatalytic antibiotic degradation focus on summarizing materials progress and antibiotics pollutants in chronological viewpoints. However, the relationship between photocatalytic materials and antibiotics oxidation reaction pathways and the toxicity of by-products are needed to be shown with better clarity to transfer the photocatalysis technique from lab to market in a safe way. This review critically analyzes the insights of energetic semiconductor structure lacking to achieve hydroxyl and superoxide radicals mediated antibiotics degradation, recommends new materials design (Z scheme) and standardization in the experimental designs, and also informs the influencing parameters on antibiotic degradation. It further assesses the possibility of recovering value-added chemicals from the photocatalytic treatment process and highlights the importance of environmental toxicity analysis. Overall, this review will be a resourceful guide for interdisciplinary researchers working on advanced photocatalysis and pharmaceutical pollutant treatment for achieving a sustainable ecology and initiating a circular economy in chemical industries.

Hydrophilic/Hydrophobic Silane Grafting on TiO2 Nanoparticles: Photocatalytic Paint for Atmospheric Cleaning

Abstract: In this study, anatase titania was utilized to prepare a durable photocatalytic paint with substantially enhanced photoactivity towards NO oxidation. Consequently, to alleviate the choking effect of photocatalytic paint and incorporate self-cleaning properties, the parent anatase titania was modified with Al(OH)3 and a number of organosilane (tetraethyl orthosilicate, propyltrimethoxysilane, triethoxy(octadecyl)silane, and trimethylchlorosilane) coatings. A facile hydrolysis approach in ethanol was employed to coat the parent titania. To facilitate uniform dispersion in photocatalytic paint and strong bonding with the prevailing organic matrix, it is necessary to avail both hydrophobic and hydrophilic regions on the titania surface. Therefore, during the preparation of modified titania, the weight proportion of the total weight of alkyl silane and trimethylchlorosilane was adjusted to a ratio of 1:1. As the parent titania has few hydrophilic portions on the surface, tetraethyl orthosilicate was coated with an organic silane having an extended alkyl group as a hydrophobic group and tetraethyl orthosilicate as a hydrophilic group. When these two silane mixtures are hydrolyzed simultaneously and coated on the surface of parent titania, a portion containing a large amount of tetraethyl orthosilicate becomes hydrophilic, and a part containing an alkyl silane becomes hydrophobic. The surface morphology and the modified titania’s optical attributes were assessed using X-ray powder diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), UV-Vis diffuse reflectance spectroscopy (DRS), and electrochemical impedance spectroscopy (EIS) analysis. Based on the advanced characterizations, the NO removal mechanism of the modified titania is reported. The modified titania coated at 20 wt.% on the ceramic substrate was found to remove ~18% of NO under one h of UV irradiation. An extensive UV durability test was also carried out, whereby the coated surface with modified titania was exposed to 350 W/m2 of UV irradiance for 2 weeks. The results indicated that the coated surface appeared to preserve the self-cleaning property even after oil spraying. Hence, facile hydrolysis of multiple organosilane in ethanol could be a viable approach to design the coating on anatase titania for the fabrication of durable photoactive paint.

Eutectic iodide-based salt as a melem-to-PTI conversion stopping agent for all-in-one graphitic carbon nitride

Abstract: The poor absorption of visible light and rapid recombination of photoexcited charge carriers are the two main factors responsible for the low photocatalytic activities of g-CN under sunlight. To mitigate these technical challenges, we utilize molten-salt synthesis based on alkali metal iodide. The high reactivity of LiI/KI does not allow the polycondensation of triazine dicyanamide intermediates further into PTI, the degree of which depends on the initial weight ratio of eutectic mixture to molecular precursor. This enables the controlled introduction of cyano functional groups with K+-coordination and decomposition of tri-s-triazine into triazine. The resulting all-in-one g-CN-I displays a photocatalytic hydrogen evolution reaction rate of 147 and 60 μmol/h from water under visible light and sunlight, respectively, which are 76 and 7 times higher than those of bulk g-CN. This study demonstrates the significant improvement in the photocatalytic activity of g-CN achievable through the synergistic combination of structural functionalities.

Low Temperature Deposition of TiO2 Thin Films through Atmospheric Pressure Plasma Jet Processing

Abstract: Titanium dioxide (TiO2) has been widely used as a catalyst material in different applications such as photocatalysis, solar cells, supercapacitor, and hydrogen production, due to its better chemical stability, high redox potential, wide band gap, and eco-friendly nature. In this work TiO2 thin films have been deposited onto both glass and silicon substrates by the atmospheric pressure plasma jet (APPJ) technique. The structure and morphological properties of TiO2 thin films are studied using different characterization techniques like X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and field emission scanning electron microscopy. XRD study reveals the bronze-phase of TiO2. The XPS study shows the presence of Ti, O, C, and N elements. The FE-SEM study shows the substrate surface is well covered with a nearly round shaped grain of different size. The optical study shows that all the deposited TiO2 thin films exhibit strong absorption in the ultraviolet region. The oleic acid photocatalytic decomposition study demonstrates that the water contact angle decreased from 80.22 to 27.20° under ultraviolet illumination using a TiO2 photocatalyst.

Probing electrochemical charge storage of 3D porous hierarchical cobalt oxide decorated rGO in ultra-high-performance supercapacitor

Abstract: A 3D porous hierarchical Co3O4-reduced graphene oxide nanosheet (Co3O4-rGO) heterostructure is synthesized by a facile hydrothermal method. Microstructure analysis confirms the decoration of Co3O4 hierarchical structures with an urchin-like spherical microstructure on rGO nanosheet with an average size of about 50 nm. The structural analysis reveals the formation of phase pure spinel Co3O4 and reduced graphene showing their simultaneous existence in the composite. Raman spectroscopy confirms the successful reduction of graphite oxide to reduced graphene oxide and the effectual interaction between Co3O4 and rGO matrix. The Co3O4-rGO composite electrode possesses utmost specific capacitance 688 F g−1, due to effective ion transfer and slight agglomeration of Co3O4 hierarchical structures on the surface of reduced graphene oxide. It is noteworthy that we have demonstrated a flexible solid-state supercapacitor device that exhibits an excellent performance suggesting the possible use of 3D porous hierarchical Co3O4-rGO composite in supercapacitor devices.

Direct Dimethyl Carbonates Synthesis over CeO2 and Evaluation of Catalyst Morphology Role in Catalytic Performance

Abstract: In recent years, direct synthesis of dimethyl carbonate (DMC) from carbon dioxide (CO2) has received considerable attention due to green and sustainable technology. Here, we report a production of DMC from major greenhouse gases and CO2 using various morphologies of cerium oxide (CeO2). Time-dependent synthesis of CeO2, with controlled morphology having various shapes including sphere, nanorods and spindle shape, along with its formation mechanism is proposed. The experimental results indicate the morphology of CeO2 was mostly dependent on the reaction time where crystal growth occurred through Ostwald ripening. The morphology, size and shape of CeO2 were observed using transmission electron microscopy (TEM) and field emission scanning electron microscopy (FESEM).The crystallographic analysis using X-ray diffraction (XRD) shows cubic fluorite phase of CeO2 with crystallite size ~72.0 nm using the Debye–Scherrer equation. The nitrogen adsorption desorption technique suggested the formation of the highly mesoporous framework of CeO2 and the excellent surface area around 104.5 m2/g obtained for CeO2 spindles by Brunauer–Emmett–Teller (BET) method. The DMC synthesis reactions were studied over CeO2 catalyst with different morphologies. The results of catalytic reactions specify that the morphology of catalyst plays an important role in their catalytic performances, where spindle shape CeO2 was the most active catalyst producing of up to13.04 mmol of DMC. Furthermore, various dehydrating agents were used to improve the DMC production at optimized reaction parameters. The overall results reveal that the higher surface area and spindle shape of CeO2 makes it a useful, reusable catalyst for one-pot DMC synthesis.

Hydrogel photocatalysts for efficient energy conversion and environmental treatment

Abstract: Photocatalysts have attracted great research interest owing to their excellent properties and potential for simultaneously addressing challenges related to energy needs and environmental pollution. Photocatalytic particles need to be in contact with their respective media to exhibit efficient photocatalytic performances. However, it is difficult to separate nanometer-sized photocatalytic materials from reaction media later, which may lead to secondary pollution and a poor recycling performance. Hydrogel photocatalysts with a three-dimensional (3D) network structures are promising support materials for photocatalysts based on features such as high specific surface areas and adsorption capacities and good environmental compatibility. In this review, hydrogel photocatalysts are classified into two different categories depending on their elemental composition and recent progresses in the methods for preparing hydrogel photocatalysts are summarized. Moreover, current applications of hydrogel photocatalysts in energy conversion and environmental remediation are reviewed. Furthermore, a comprehensive outlook and highlight future challenges in the development of hydrogel photocatalysts are presented.

Rod-Shaped β-FeOOH Synthesis for Hydrogen Production under Light Irradiation.

Abstract: Renewable energy is spotlighted as a resource to replace fossil fuels, and among the resources, active research on hydrogen energy is ongoing. Various methods have been developed to produce hydrogen energy using photoreduction processes. In this study, we synthesized β-phase iron oxyhydroxide (β-FeOOH) using a hydrothermal method with an optimal synthesis time and investigated its photofunctional properties, including hydrogen production. The obtained samples were characterized and compared with reference data. X-ray powder diffraction results corresponded to the peaks of the reference data. A rod structure was confirmed by scanning electron microscopy, and no impurities were observed. The band-gap energy of β-FeOOH was calculated as 1.8-2.6 eV. A photoreduction process was performed based on a photo-Fenton reaction to produce hydrogen by irradiating ultraviolet (UV) on β-FeOOH. The synthesized β-FeOOH was subjected to UV irradiation for 24 h to produce hydrogen, and we confirmed that hydrogen was successfully produced. The properties of β-FeOOH were evaluated after UV irradiation.

Photocatalytic Water Pollutant Treatment: Fundamental, Analysis and Benchmarking

Abstract: Power-free, light-driven catalysis-based water treatment is a green approach compared to chemical-based water treatment techniques. In this context, a broad range of photocatalytic material is demonstrated for organic water pollutant treatment. However, understanding catalysis reaction at pollutant environment and by-product formation are ambiguous. In this view, this chapter discusses insights of photocatalysis in organic water pollutant treatment at different pollutants (textile dye, pharmaceutical drug and pesticide) using TiO2 as benchmarking photocatalyst. The analytical tools for evaluating the light-active and colourless pollutant before and after photocatalytic experiments are elaborately discussed. A comprehensive discussion on TiO2-based photocatalysis at different strategies such as metal doping, coated on host surface, and varying pH of the solution are clearly explaining the interrelationship between properties of semiconductor catalysts, processing parameters and photocatalytic performance. This chapter is resourceful for fundamental researchers on how to choose the photocatalysis experimental techniques for organic water pollutant treatment.