Photocatalytic Activity Of Semiconductors Research Articles

Size dependent photogeneration charge carrier density of hollow ZnIn2S4 microspheres for enhanced photocatalytic activity

The effect of the morphology of semiconductors on the photocatalytic performance is commonly observed but ambiguous due to the other structural changes usually occur simultaneously along with morphology variation. In this work, we have successfully constructed a series of ZnIn2S4 hollow microspheres (named ZIS-x, x = 0.6, 0.2, 0.15, 0.1, 0.06.) with systematically decreased size in both shell thickness and diameter of the sphere and comparable band structures, degree of crystallinity and density of defects as confirmed by extensive characterizations. Taking advantage of the above features, the decoupled effect of size on photocatalytic activity is investigated and established, which displays a volcano-type relationship. The best performed ZIS-0.1 displays a hydrogen evolution rate of 3.76 mmol g-1h−1, which is 2.66 times that of the worst performed ZIS-0.6. Further mechanistic studies disclose that the observed size dependent hydrogen evolution rate originates from the ability of charge carrier generation under light, which increases with the light harvesting ability of the hollow microspheres. This work explicitly reveals the effect of the morphology on the photocatalytic activity of semiconductors, which highlights the route to improve the photocatalytic performance morphologically.

Built-in electric field intensified by SPR effect to drive charge separation over Ag-AgI/Sb2S3 heterojunction for high-efficiency photocatalytic metronidazole mineralization

The photocatalytic activity of semiconductor is extremely limited due to the rapid recombination of photo-generated carriers and low utilization of solar energy. Herein, a novel Ag-AgI/Sb2S3 (A-S) heterojunction with superior photocatalytic activity was synthesized, in which the optimal Ag-AgI/Sb2S3 heterojunction exhibited 31 times photocatalytic activity of metronidazole removal than that of than that of Sb2S3. The excellent performance of the prepared photocatalysts could be attributed to the synergy of surface plasmon resonance effect by in situ-generated Ag nanoparticles and the built-in electric field of heterostructure, which would broaden the response range of solar light and accelerate the transfer of photogenerated carriers. Besides, characterization and theoretical calculations confirm Ag atoms acquire abundant electrons from Sb atoms of Sb2S3, allowing Ag+ to reduce to Ag0. Meanwhile, a portion of the Ag0 plasma-induced hot electrons reduce O2 to ·O2–, while the remaining portion flows to AgI and circulates in AgI and Ag0 to form a closed loop, thus eliminating the photo-corrosion of AgI. The stability of A-S photocatalyst was also confirmed by five cycle-tests. Furthermore, a reasonable photocatalytic mechanism was proposed by analyzing the intermediates of metronidazole. This work has implications for designing efficient photocatalysts using high-performance materials based on Ag nanoparticles.

Photocatalytic Activity of BaAl2O4 for Water Purification.

Degradation of dyes under natural light sources is one of the most active research areas in basic science for greener technology. In this context, the photocatalytic activity of semiconductors has received massive attention in solving water treatment-related issues as these possess enormous potential for degrading organic impurities. Here, we report that barium aluminate (BaAl2O4, BAO), which has been extensively studied for photoluminescence applications, is found to be a highly potent candidate for photocatalytic activities. We have explored the degradation of dyes (meant for water purification) by using the photocatalytic properties of pure and Dy- and Yb-codoped BAO. Crystal structure, electron microscopy, and Raman analysis of the autocombustion-synthesized pure and codoped BAO samples revealed significant morphological changes such as increased particle size and stabilization of rod-like structures. UV-vis absorbance measurements confirm the presence of multiple bandgaps in the BAO samples, which is substantiated by X-ray absorption spectroscopy measurements. Photocatalytic degradation studies of methylene blue (MB) dye (with different catalyst concentrations, dopings, and MB dye concentrations) have been carried out by using BAO. The kinetics of the photocatalytic degradation measurements has been explained by the Boltzmann distribution function, and the fastest (in less than 40 min), with more than 99% degradation of MB impurity, is reported here for the first time in BAO compounds. Synthesized BAO samples show excellent cyclic stability, which is essential for their potential applications in environmental remediation. The trade-off between the enhancement of surface area and increased particle size is considered the key parameter for controlling the photocatalytic performance of the BAO catalyst after Dy and Yb codopings.

Do potential dependent kinetics play a role in photocatalytic rate trends?

Higher order trends in the photocatalytic activity of semiconductors, concerning environmental remediation and energy applications, under increasing light illumination may originate in part or in whole from potential dependent kinetics.

Near Infrared Light-to-Heat Conversion for Liquid-Phase Oxidation Reactions by Antimony-Doped Tin Oxide Nanocrystals.

Effective utilization of the sunlight for chemical reactions is pivotal for dealing with the growing energy and environmental issues. So far, much effort has been focused on the development of semiconductor photocatalysts responsive to UV and visible light. However, the near infrared and infrared (NIR-IR) light occupying ∼50 % of the solar energy has usually been wasted because of the low photon energy insufficient for the band gap excitation. Antimony doping into SnO2 (ATO) induces strong absorption due to the conduction band electrons in the NIR region. The absorbed light energy is eventually converted to heat via the interaction between hot electrons and phonons. This Concept highlights the photothermal effect of ATO nanocrystals (NCs) on liquid-phase oxidation reactions through the NIR light-to-heat conversion. Under NIR illumination even at an intensity of ∼0.5 sun, the reaction field temperature on the catalyst surface is raised 20-30 K above the bulk solution temperature, while the latter is maintained near the ambient temperature. In some reactions, this photothermal local heating engenders the enhancement of not only the catalytic activity and selectivity but also the regeneration of catalytically active sites. Further, the photocatalytic activity of semiconductors can be promoted. Finally, the conclusions and possible subjects in the future are summarized.

Development of highly-efficient 0D/1D/0D dual Z-scheme CdS/ZnWO4/ZnS heterojunction photocatalysts in pollutant removal and involved mechanism

Rational design of heterostructures is an important strategy for improving photogenerated-carrier separation and photocatalytic activity of semiconductors. Herein, zero-dimensional (0D) CdS and ZnS quantum dots were assembled onto one-dimensional (1D) ZnWO4 (ZWO) nanorods to construct 0D/1D/0D dual Z-scheme CdS/ZWO/ZnS heterojunction photocatalysts. The photodegradation capacities of the photocatalysts were compared by using methylene blue as target pollutant under simulated-sunlight irradiation. The photocatalytic experiments reveal that the dual Z-scheme heterojunction photocatalyst with composition 40 %ZnS/(40 %CdS-ZWO) exhibits an extremely high photodegradation activity with η(50 min) = 99.9 % and kapp = 0.14867 min−1, which is higher than that of bare ZWO, CdS and ZnS as well as that of binary CdS/ZWO and ZnS/ZWO heterojunctions. Multiple measurement techniques, response surface methodology and density functional theory calculation were used to elucidate the characteristics and photocatalytic mechanism of the CdS/ZWO/ZnS photocatalysts. Moreover, the potential application of the CdS/ZWO/ZnS photocatalysts in degrading various organic pollutants (including organic dyes, antibiotics and other serious organic pollutants) was also investigated.

(Invited) Endohedral Fullerene Hybrids: From Gold Nanoparticles to Graphene

Endohedral fullerenes are at the forefront of nanotechnology due to their rich electronic structure. In this talk I will focus on some examples of endohedral fullerenes used in hybrid nanostructures with other nanomaterials. For example, gold nanoparticles have been found to significantly increase or alternatively quench the photoluminescence of dyes, enhance the Raman scattering of organic molecules and the photocatalytic activity of semiconductors. We have reported for the first time the use of the singlet oxygen sensor green for the evaluation of the generation of singlet oxygen from a series of fullerenes (including endohedral fullerenes) and gold nanoparticle hybrids. The C70 mono adducts appear to be more efficient sensitizers compared to C60 in accordance with previous studies that were based on the 1270 nm emission of the singlet oxygen. Lu3N@C80 had a performance somewhat between the two empty cages. Overall, pyrene derivatives appeared to be efficient photo-sensitizers, especially when coupled with gold nanoparticles, with the 2.24 and 3.48 times increase on the fluorescence intensity.I will also elaborate on how Gd-based metallofullerene (Gd3N@C80) molecules can be used to create single adatoms and nanoclusters on a graphene surface. We have shown that endohedral metallofullerenes can adhere to graphene surfaces at temperatures well above their bulk sublimation point, indicating that the surface bound metallofullerenes have strong adhesion to dangling bonds on graphene surfaces. The ability to create dispersed single Gd adatoms, and Gd nanoclusters on graphene may have impact in spintronics and magnetism.Endohedral metallofullerenes continue to fascinate us with their versatility and attractive electronic properties.

Adsorption and Photocatalytic Reduction of Carbon Dioxide on TiO2

The photocatalytic activity of TiO2 depends on numerous factors, such as the chemical potential of electrons, charge transport properties, band-gap energy, and concentration of surface-active sites. A lot of research has been dedicated to determining the properties that have the most significant influence on the photocatalytic activity of semiconductors. Here, we demonstrated that the activity of TiO2 in the gas-phase reduction of CO2 is governed mainly by the desorption rate of the reaction intermediates and final products. This indicates that the specific surface area of TiO2 and binding strength of reaction intermediates and products are the main factors affecting the photocatalytic activity of TiO2 in the investigated process. Additionally, it was shown that rutile exhibits higher photocatalytic activity than anatase/rutile mixtures mainly due to its high efficiency in the visible portion of the electromagnetic spectrum.

Synergetic Hybridization Effect of Homogeneously Mixed Inorganic and Graphene Nanosheets on the Photocatalytic Activity of Semiconductor

Using the homogeneous colloidal mixture of conductive metal oxide nanosheet (NS) and reduced graphene oxide (rGO) NS as hybridization matrices provides universal way of optimizing the photocatalyst functionality of semiconductor nanocrystals. A self‐assembly between CdS quantum dots (QDs) and RuO2/rGO NSs yields strongly coupled ternary nanohybrids with enhanced photocatalytic activity and increased porosity. Even with its lower RuO2 content, the ternary CdS−RuO2/rGO nanohybrid exhibits notably higher photocatalytic activities for visible‐light‐induced H2 evolution and photocurrent generation than binary CdS−RuO2/rGO homologues, underscoring the synergetic hybridization effect of flexible rGO and hydrophilic RuO2 NSs. In comparison with single RuO2/rGO NSs, their homogeneous mixture can play better roles of photosensitizers and cocatalysts, which is mainly responsible for remarkable improvement of photocatalytic activity upon the cohybridization with mixed RuO2/rGO NSs. The current study underscores that cohybridization with complementary inorganic and graphene NSs can provide an efficient and economically feasible methodology to explore novel high‐performance catalyst materials.

Enhanced Antibacterial Photocatalytic Activity of Porous Few-Layer C₃N₄.

Nowadays, antibacterial photocatalytic activity of semiconductors has attracted great attention due to its excellent stability, good biocompatibility and no disinfection byproducts. Herein, a porous few-layer C₃N₄ was successfully fabricated via a simple and low-cost bottom-up method. The asprepared porous few-layer C₃N₄ exhibits large specific surface areas, which is about 4.8 times than bulk C₃N₄. Under the light (<430 nm) irradiation, reactive oxygen species (ROS) (singlet oxygen (1O₂), hydroxyl radicals (·OH), and superoxide (O·-₂)) can be generated. The porous few-layer C₃N₄ was used as an antibacterial agent to kill gram-positive bacterium S. Aureus with an anibacterial efficiency up to 99.7%. The log removal rate of the porous few-layer C₃N₄ is more than 50 times than the bulk C₃N₄. The material shows a potential application in water purification and antibacterial photocatalytic therapy.

(Invited) Endohedral Fullerene Hybrids: From Gold Nanoparticles to Graphene

Endohedral fullerenes are at the forefront of nanotechnology due to their rich electronic structure. In this talk I will focus on some examples of endohedral fullerenes used in hybrid nanostructures with other nanomaterials. For example, gold nanoparticles have been found to significantly increase or alternatively quench the photoluminescence of dyes, enhance the Raman scattering of organic molecules and the photocatalytic activity of semiconductors. We have reported for the first time the use of the singlet oxygen sensor green for the evaluation of the generation of singlet oxygen from a series of fullerenes (including endohedral fullerenes) and gold nanoparticle hybrids. The C70 mono adducts appear to be more efficient sensitizers compared to C60 in accordance with previous studies that were based on the 1270 nm emission of the singlet oxygen. Lu3N@C80 had a performance somewhat between the two empty cages. Overall, pyrene derivatives appeared to be efficient photo-sensitizers, especially when coupled with gold nanoparticles, with the 2.24 and 3.48 times increase on the fluorescence intensity.I will also elaborate on how Gd-based metallofullerene (Gd3N@C80) molecules can be used to create single adatoms and nanoclusters on a graphene surface. We have shown that endohedral metallofullerenes can adhere to graphene surfaces at temperatures well above their bulk sublimation point, indicating that the surface bound metallofullerenes have strong adhesion to dangling bonds on graphene surfaces. The ability to create dispersed single Gd adatoms, and Gd nanoclusters on graphene may have impact in spintronics and magnetism.Endohedral metallofullerenes continue to fascinate us with their versatility and attractive electronic properties.

GaN nanowire arrays for photocatalytic applications II: influence of a dielectric shell and liquid environments

GaN nanowires (NWs) are promising candidates for photocatalytic devices due to their large surface-to-volume ratio and their waveguide character. Protective coatings and nanoparticle co-catalysts are widely used to improve the stability and the photocatalytic activity of semiconductors in liquid electrolytes. Here, we present a systematic experimental study of the influence of a dielectric shell and liquid environments on the interaction of light with GaN NW arrays related to photocatalytic applications. Transmission measurements on bare GaN NWs and core–shell NWs with varying shell thickness and refractive index of the shell reveal a shift of the transmission minima that originate from the coupling of light to various waveguide modes supported within the NWs. This shift is a result of the shift of the dispersion relations of the modes for core–shell NWs. The transmission spectra of GaN NWs in liquid environments show a spatial and spectral shift. These results are explained by the dependence of both, the waveguide properties of the single NWs and the photonic crystal characteristics of the NW array, on the refractive index of the environment. A comparison of the experimental findings with numerical simulations shows a good agreement.

Band-gap engineering and comparative investigation of Ti2Nb10O29 photocatalysts obtained by Various synthetic routes

Ti2Nb10O29 photocatalysts were successfully synthesized by three different methods. Ti2Nb10O29 fabricated by the solvothermal method (ST-TNO) exhibited unique microspheres compared to the larger irregular particles observed for the samples annealed in air (Air-TNO) and Ar (Ar-TNO). X-ray Photoelectron Spectroscopy (XPS) results revealed that a partial reduction process from Ti4+ into Ti3+ occurs in Ar-TNO, because of the introduction of oxygen defects. Ar-TNO exhibited visible-light absorption with a band gap of 2.85 eV, while the absorption edges of Air-TNO and ST-TNO were approximately 400 nm. Under UV light irradiation (λ < 420 nm), Ar-TNO exhibited a photocatalytic activity 2.1 times greater than that of Air-TNO, corresponding to the highest activity. The results indicated that the preparation method is crucial for determining the band gap and photocatalytic activity of semiconductors. Moreover, the novel semiconductor photocatalyst can be further applied for constructing the heterojunction and designing the band structure.

The origin of enhanced photocatalytic activities of hydrogenated TiO2 nanoparticles.

The photocatalytic activity of semiconductors is largely governed by their light absorption, separation of photoinduced charge carriers and surface catalytically active sites, which are primarily controlled by the morphology, crystalline size, structure, and especially the electronic structure of photocatalysts. Black TiO2 is recognized as one of the most promising visible-light photocatalysts, due to its significantly enhanced visible-light photocatalytic performance in comparison to intrinsic TiO2. In this work, black TiO2 is synthesized through the hydrogenation process. The sample shows a TiO2@TiO2-x core/shell structure which is attributed to hydrogenation. By using X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), and nuclear magnetic resonance (NMR) spectroscopy, we identified the featured midgap electronic states in black TiO2, which gave rise to the TiO2-x shell layer. These states lead to the improvement of visible-light absorption and the separation of photoinduced charge carriers, which consequently result in remarkable enhanced photocatalytic activities in black TiO2.

An initiative, simple vacancy remedy method and the effect on photochemical properties

Recently, an increasing attention is paid to crystal defects due to the significant influence on the catalytic properties of material. Herein, the WO3 and fluorinated WO3 (F-WO3) samples have been prepared by an in situ hydrothermal method. On one hand, we have found that under visible light irradiation (λ≥420nm), the photocatalytic activities of F-WO3 samples are obviously reduced, which has been mainly attributed to the generation of W vacancies by fluorination. This finding is obviously distinct from the previous reports, in which the photocatalytic activities of semiconductors can be effectively improved by fluorination. On the other hand, after being further processed by H2O2 again, the generated W vacancies by fluorination can be remedied easily; moreover, the WO3/WO3·0.333H2O heterojunctions have formed with a novel flower shape (H2O2-F-WO3). It is amazing that under visible light irradiation (λ≥420nm), the activity of H2O2-F-WO3 sample is 4.3 and 3.0 times higher than that of F-WO3 and WO3, respectively. The significantly improved activity is mainly attributed to the remedy of W vacancy and the formation of the WO3/WO3·0.333H2O heterojunction. Compared with conventional defect remedy method (e.g., calcination), this vacancy remedy method with H2O2 is facile, energy-saving, which could be extended to develop the other efficient photocatalysts.

Photoactivity enhancement of the CdxZn1−xS nanoparticles by immobilizing on the graphene under visible light irradiation

The photocatalytic activity of semiconductor is strongly dependent on the efficient separation of photogenerated electron–hole pairs. In the present work, the graphene-immobilized CdxZn1−xS nanoparticles with a uniform and small diameter have been prepared by one-step solvothermal route. After dispersing CdxZn1−xS on the graphene surface well, the composites of CdxZn1−xS and graphenes show better photocatalytic activity than pure CdxZn1−xS nanoparticles. And the issue of photocorrosion, a disadvantage of CdxZn1−xS photocatalysts, has also been solved partly. The mechanisms on enhancement of photocatalytic activity were further investigated. Under visible light irradiation, photogenerated electrons of CdxZn1−xS can be transferred into the graphene, and the electron and hole was effectively separated, leading to the photoactivity enhancement.

Bactericidal Activity of TiO2on Cells ofPseudomonas aeruginosaATCC 27853

The photocatalytic activity of semiconductors is increasingly being used to disinfect water, air, soils, and surfaces. Titanium dioxide (TiO2) is widely used as a photocatalyst in thin films, powder, and in mixtures with other semiconductors or metals. This work presents the antibacterial effects of TiO2and light exposure (at 365 nm) onPseudomonas aeruginosaATCC 27853. TiO2powder was prepared from a mixture of titanium isopropoxide, ethanol, and nitric acid using a green and short time sol-gel technique. The obtained gel annealed at 450°C was characterized by X-ray diffraction, Raman spectroscopy, ultraviolet-visible spectroscopy, diffuse reflectance, scanning electron microscopy, and transmission electron microscopy. The nanocomposite effectively catalyzed the inactivation ofPseudomonas aeruginosa. Following 90 minutes exposure to TiO2and UV light, logarithm of cell density was reduced from 6 to 3. These results were confirmed by a factorial design incorporating two experimental replicates and two independent factors.

MgO–TiO2mixed oxide nanoparticles: Comparison of flame synthesis versus aerogel method; characterization, and photocatalytic activities

Abstract