Promising Applications In Photocatalysis Research Articles

Visible light photocatalytic performance of Co/Ag bimetallic coordination polymer catalysts designed from hard and soft acid-base theory

Heterometallic coordination polymers have promising applications in photocatalysis, and the design and selection of suitable organic ligands and coordination metals is the key to improve the catalytic activity of polymer photocatalysts. Herein, a novel Co/Ag bimetallic coordination photocatalyst, designed based on the hard and soft acid-base (HSAB) theory, has been successfully prepared by a stepwise method with Ag-S coordination as the main component and Co-N/Co-S as the complementary component. The obtained Co/Ag photocatalyst demonstrates excellent performance in the photocatalytic degradation (visible light) of halogenated phenolic pollutants. Degradation of 10 ppm of 4-chlorophenol could reach 100 % in 4 h, and 70 % degradation of 4-fluorophenol, which is even more difficult to degrade, could also be achieved. In addition, hydrogen production experiments conducted under visible light irradiation showed that the hydrogen production could reach 36.95 μmol h−1 g−1 for 6 h, which strongly demonstrated the excellent reduction ability of Co/Ag photocatalysts. The photocatalyst exhibits enhanced photocatalytic activity which is ascribed to the formation of Ag-S and Co-N/Co-S coordination, which greatly increases the charge density and facilitates charge transfer. Thus, the photogenerated electrons can induce both the conversion of O2 to •O2- for oxidation reactions, as well as the direct attack of the C-Cl bond for reduction reactions. This study demonstrates the successful design of the synergistic Co/Ag bimetallic coordination photocatalysts based on the HSAB theory, thereby offering a promising research avenue for the fabrication of heterometallic coordination photocatalysts.

Hollow spherical covalent organic framework supported gold nanoparticles for photocatalytic H2O2 production

Covalent organic frameworks (COFs) are porous crystalline materials with promising applications in photocatalysis, but their performance is greatly hampered by the fast recombination of photogenerated carriers. Herein, a hollow spherical COF was synthesized via the condensation polymerization of 1,3,5-tris(4-aminophenyl)benzene and 1,3,5-benzenetricarbaldehyde, and Au nanoparticles were in-situ deposited onto the COF through NaBH4 reduction to ameliorate the photocatalytic performance. The composite exhibits impressive photocatalytic H2O2-production performance with the highest H2O2-evolution rate of 6067 μmol g−1 h−1 under visible light irradiation, which is about 1.9 times that of the pristine COF. The enhanced photocatalytic activity was ascribed to improved light absorption, abundant active Au sites, and efficient transfer and separation of photogenerated carriers in space. This work provides an avenue for designing high-performance H2O2-production photocatalysts by decorating porous COFs with active noble-metal sites.

Probing the Optoelectronic Properties and Energy Conversion of Boron Nitride Quantum Dots: Impact of Oxygen Doping and Chemical Functionalization

Boron nitride quantum dots (BNQDs) are emerging nanomaterials with promising applications in photocatalysis and optoelectronics. Chemical functionalization effectively tunes the optoelectronic properties and photocatalytic performance of BNQDs. This study investigates the impact of oxygen doping and functionalization with urea, thiourea, and p‐phenylenediamine (PPD) on BNQD properties. Density functional theory calculations reveal that these functional groups introduce new electronic states within the bandgap, shifting absorption spectra and reducing the bandgap due to ligand molecular orbital contributions. Functionalization also adjusts the energy‐level alignment between BNQDs and cocatalysts, enhancing interfacial charge transfer. Oxygen‐doped, chemically functionalized BNQDs exhibit significantly higher first‐order hyperpolarizability, up to 17 times greater than pristine BNQDs, enabling superior optical nonlinearities. Additionally, PPD functionalization leads to a remarkable 18.2% photocatalytic energy conversion efficiency under simulated solar irradiation. These achieved quantum yields result from bandgap engineering, expanded light harvesting, increased exciton densities, prolonged exciton lifetimes, and improved charge separation and transfer dynamics. This study provides crucial insights into property tuning mechanisms, establishing the promising potential of chemically functionalized BNQDs for energy conversion and optoelectronic technologies.

Efficient spatial separation of charge carriers over Sv-ZnIn2S4/NH2-MIL-88B(Fe) S-scheme heterojunctions for enhanced photocatalytic H2 evolution and antibiotics removal performance

The exploration of highly efficient sunlight-assisted photocatalyst for photodegradation of organic contaminants or energy conversion is strongly encouraged. In this work, we designed a novel three-dimensional spindle-like Sv-ZIS@NMFe heterojunction made of amino functionalized NH2-MIL-88B(Fe) (NMFe) and ZnIn2S4 nanosheets with abundant sulfur vacancies (Sv-ZIS). The structural properties of NMFe materials, such as a clearly defined system of pores and cavities, were retained by the Sv-ZIS@NMFe composites. Additionally, the incorporation of sulfur vacancies, –NH2 functional groups, and well-matched energy level positions led to various synergistic effects that considerably enhanced internal electron transformation and migration, as well as improved adsorption performance. Consequently, under visible light irradiation, the optimized sample exhibited superior hydrogen production activity and tetracycline hydrochloride photodegradation performance. At last, density functional theory calculations was used to further elucidated the possible photoreactivity mechanism. This study demonstrates that the Sv-ZIS@NMFe heterojunction materials formed by ZnIn2S4 with suitable sulfur vacancies and amino functionalized Fe-MOFs have promising applications in photocatalysis.

One-step solvothermal method synthesizes petal-like Cu2WSx supported on carbon paper used in dye-sensitized solar cells

Sheet-like transition metal sulfides have promising applications in photocatalysis and energy conversion. This study provides a petal-like Cu2WSx nanosheet structure supported on carbon paper (CP) synthesized by a simple one-step solvothermal method. Cu2WSx microstructures with different morphologies were synthesized by solvothermal vulcanization of thioacetamide (TAA) at different concentrations. The Cu2WSx/CP was used as the counter electrode of DSSCs and compared with the Pt FTO electrode. It was proved that Cu2WSx-7 M/CP had the best electrocatalytic performance and obtained 9.01% photoelectric conversion efficiency. The different sulfide concentration changes the morphology of Cu2WSx and continuously affects the specific surface area and catalytic activity of the material. The better electrochemical performance shows that Cu2WSx/CP is expected to become a substitute for expensive Pt CE materials in dye-sensitized solar cells (DSSCs).

An azine-linked 2D porphyrinic covalent organic framework for red light photocatalytic oxidative coupling of amines

The construction of two-dimensional covalent organic frameworks (2D COFs) with robust stability for photocatalysis has gained intensive attention recently. Herein, we report the design and synthesis of a highly crystalline azine-linked porphyrinic 2D COF (Por-HZ-COF). Our results clearly show that Por-HZ-COF adopts an eclipsed AA stacking structure with a high Brunauer-Emmett-Teller (BET) specific surface area of 1586 m2/g. In addition, Por-HZ-COF is chemically stable under various conditions, even in 12 M sodium hydroxide aqueous solution or 9 M hydrochloric acid. Moreover, Por-HZ-COF can be used for the photocatalytic aerobic oxidative coupling of benzylamines under red light irradiation with high activity and good reusability. This study demonstrates a novel robust 2D COF with azine linkage that has promising applications in photocatalysis.

Recent progress on van der Waals heterojunctions applied in photocatalysis

Progress on the applications of van der Waals heterojunctions in photocatalysis.

Enabling photocatalytic hydrogen production over Fe-based MOFs by refining band structure with dye sensitization

Fe-based metal-organic frameworks (MOFs) have shown promising applications in photocatalysis, yet they are incapable of photocatalytic H2 production due to their inappropriate conduction band (CB) position and large overpotential for H2 evolution. Herein, we present a facile strategy enabling the photocatalytic H2 production over Fe-based MOFs through dye sensitization. A combination of characterization techniques with theoretical simulation reveals that dye sensitization can effectively inject energetic electrons into Fe-MOFs and elevate their quasi-Fermi level under light irradiation, overcoming the surface overpotential for H2 production from water. Furthermore, deposition of Pt nanoparticles on Fe-MOFs can lower the overpotential for H2 evolution toward further enhanced photocatalytic activity. This work provides insights into MOF band structure engineering at electronic level, and proves a concept that harnesses MOF materials for targeted photocatalytic applications they are originally not fit for.

Construction of Novel Polyoxometalate/Perylenediimide Hybrid Heterostructures for Enhanced Photocatalytic Oxidation of Mustard Gas Simulants

Developing and designing novel materials for effective sulfur mustard detoxification are of great importance given their threat to human health. Crystalline donor–acceptor (D–A) hybrid heterostructures as an emerging class of materials are composed of semiconducting organic and inorganic components with enhanced charge-separated properties and thus promising applications in photocatalysis and photovoltaic cells. Herein, we demonstrated that the combination of three perylene diimide derivatives (PDIs) as electron-deficient acceptors with polyoxometalate (POM) anion [SiW12O40]4– as electron-rich donors resulted in three crystalline D–A hybrid heterostructures, namely, (Me4-PDI)2·SiW12O40 (1), (Me4-Br2-PDI)1.5·(HSiW12O40) (2), and (Me4-Cl4-PDI)2·SiW12O40 (3). Due to the considerable electrostatically assisted noncovalent interactions (lone pair−π, π–π, anion−π, and hydrogen-bonding interactions) between electron donors and acceptors, POMs, and PDIs, these hybrids displayed a significant enhancement in the photochemical stability and selective photocatalytic oxidation of the sulfur mustard simulant, 2-chloroethyl ethyl sulfide (CEES).

Two-dimensional H-TiO2/MoS2(WS2) van der Waals heterostructures for visible-light photocatalysis and energy conversion

Titanium dioxide (TiO2) has promising applications in photocatalysis and energy-conversion devices due to its low cost, outstanding conductivity, and excellent electrochemical activity. However, its large band gap and insufficient-sized surface hinder its applications under visible-light radiation, so designing a highly efficient TiO2-based electrode structure is challenging. Herein, we constructed novel van der Waals (vdW) heterostructures using two-dimensional hexagonal TiO2 (H-TiO2) and 2D MoS2 (WS2) components. By density functional theory, we found that the 2D H-TiO2 has robust stability in energy and mechanics, as well as higher ductility than graphene and MoS2. The estimated indirect band gap ranged within 4.30–4.62 eV, resulting in hardly any visible-light absorbance. The vdW heterostructures of MoS2/TiO2 and WS2/TiO2 had the following characteristics: direct band gap, type-II band alignment, built-in electronic field, mobility as high as that of MoS2 (WS2), and remarkably improved visible-light absorption. These features enabled the heterostructures to have highly improved photocatalytic performance and solar-to-electric power conversion efficiency. Thus, these materials have high potential application in photocatalytic water splitting and solar energy-conversion devices.

Insight into efficient photocatalytic elimination of tetracycline over SrTiO3(La,Cr) under visible-light irradiation: The relationship of doping and performance

Antibiotic has become an important organic contaminant in surface water, which poses a huge threat to human health and ecosystem. SrTiO3 is an attractive perovskite structured semiconductor material and shows promising applications in photocatalysis. Herein, a series of lanthanum and chromium codoped SrTiO3 (denoted as SrTiO3(La,Cr)-x) with different dopant amount of La and Cr have been successfully fabricated via a facile sol-gel hydrothermal method and employed as efficient photocatalysts for the elimination of tetracycline (TC) from aqueous solution under visible-light irradiation. It indicates that the photocatalytic performance is highly dependent on the La and Cr content in the samples. Among the catalysts, the porous SrTiO3(La,Cr)-6 spheres with a moderate dopant amount exhibit the best photocatalytic activity for TC removal, which is approximately 4.4 and 2.3 times as superior as SrTiO3(La,Cr)-2 with the least dopants and SrTiO3(La,Cr)-8 with the most dopants, respectively. Detailed characterizations reveal that the significant improvement of photocatalytic activity is attributed to the increasing molar ratio of Cr3+/Cr6+, which can be facilely adjusted by tuning the doping amount of La and Cr during the synthesis process. In addition, the catalyst shows excellent photocatalytic stability and can be recycled over ten times with negligible activity decline. Active species trapping experiments demonstrate that superoxide radicals, holes and hydroxyl radicals are responsible for TC degradation. On the basis of the intermediate products identified using HPLC-MS, four possible reaction pathways and TC degradation mechanism have been put forward. This study offers an effective strategy to modulate the photocatalytic properties of SrTiO3 by simple tuning the dopant content for environment and energy applications, which can be facilely extended to the modification of other semiconductors.

Improved visible-light catalytic activities of novel Au/P-doped g-C3N4 photocatalyst for solar fuel production and mechanism

The noble metal decorated photocatalytic materials have received marvelous attention in recent decade owing to their exceptional applications in energy conversion and environmental remediation. Herein, we have successfully fabricated Au decorated phosphorus doped graphitic carbon nitride (Au/P-CN) photocatalyst for the first time via ionic liquid and in situ photo-reduction methods. The resultant photocatalyst exhibits significant visible-light activities for water splitting to evolve H2 and CO2 conversion to CH4. The amount of H2 evolved over Au/P-CN photocatalyst is 97 μmol, ∼12-fold enhanced compared to that of the bare CN (8 μmol). Similarly, the amount of CH4 produced over Au/P-CN photocatalyst is 24 μmol, about 6-fold enhanced compared to that of the bare CN (4 μmol). The calculated quantum efficiencies for H2 evolution and CH4 production are ∼3.60% and ∼2.83%, respectively at λ = 420 nm. The exceptional photocatalytic activities are attributed to the extended visible-light absorption and improved charge carriers separation via the dopant induced surface states and the well decorated Au nanoparticles. This work demonstrate that the Au decorated CN-based photocatalysts show promising applications in photocatalysis for water splitting to evolve H2 and CO2 conversion to CH4 under visible-light irradiation.

Research advances of polyoxotantalates

Polyoxometalates (POMs), as early transition metal-oxo clusters of V, Mo, W, Nb, and Ta, have been attracting extensive interest owing to their structural variety associated with interesting structural characteristics such as high negative charge, oxygen-rich surface, and rich redox properties. In the past two centuries, the main success was achieved in POM chemistry of V, Mo, and W. In contrast, the advancement of polyoxotantalate (POTa) chemistry falls far behind that of POM chemistry of V, Mo, and W. The reasons lie in the narrow working pH region, the slight solubility, and the low reaction activity of tantalum species. Despite these hurdles, as an important subclass of POMs, POTas have received more and more intense interest and attentions because of their promising applications in photocatalysis and the base-catalyzed reactions. In recent years, considerable advancements in POTa chemistry have been made. During the past two decades, POM chemistry of polyoxovanadates, polyoxoniobates, polyoxomolybdates, and polyoxotungstates has been reviewed extensively. While, no review about POTas has been known to our knowledge. We are thus very interested in making a summary on the research advances of POTa chemistry with attempt to provide some insight into the syntheses of new POTa clusters, in particular brand-new and high-nuclearity POTas, which is a subject of current intense investigation. In this review, we systematically summarized the research progress in structural types, synthetic methods, and related applications of POTas, which were achieved in recent two decades. This review aims to be not only a snapshot of the recent developments of design, architecture, and application of POTas, but also to be employed as a guide to understand the different cluster types of POTas. The main content of the review includes the following four parts: (1) Isopolyoxotantalate species with different counter cations (Li, Na, K, Cs, and organic amines) and different aggregations (hexamer and decamer); (2) Tantalum-based polyoxometalates, including Ta-substituted polyoxotungstates derived from different structures such as Keggin-, Linqvist- and Dawson-type configurations; (3) Heteropolyoxotantalate species, including Ti- and P-containing POTas; and (4) Organic-inorganic hybrid polyoxotantalates constructed from lindqvist-type Ta6 decorated by various organic species (e.g., organometallic complexes and metal-organoamine complexes). According to the above four aspects, we not only summarized the different classifications of POTas but also their corresponding synthetic strategies. Especially, the synthetic methods of POTas has been summarized from the traditional hydrothermal method to a variety of synthetic strategies such as solvothermal, diffusion, and steam-heat. Further, on the issue of how to improve the aggregation degree of Ta atoms, we analyze the difficulties in constructing high-nuclearity POTas and the key factors affecting the construction of high-nuclearity POTas. Additionally, the review also represents that POTas have a variety of excellent properties and exciting application prospects in photocatalytic hydrogen production and degradation of organic pollutant. In summary, this review provides a personal view on the research in the area of POTa chemistry. From the review, it can be found that, even after more than decades of research, known POTas species are really very limited compared to POMs of V, Mo, W, and even Nb on the one hand. And on the other hand, alomost all known POTas are in the small nuclearity range ( 20). Obviously, the design and synthesis of POTas are of great challenge. Nevertheless, it is believed that the current state of POTas will continue to evolve, leading to a variety of expected and unexpected new species with fascinating structures and properties. It could be expected that the review may initiate more extensive research on the discovery of novel POTa materials and open up new perspectives for the development of POTa chemistry.

Density functional theory study of atomic and electronic properties of defects in reduced anatase TiO2 nanocrystals

Anatase TiO2 nanocrystals have received considerable attention owing to their promising applications in photocatalysis, photovoltaics, and fuel cells. Although experimental evidence has shown that the performance of nanocrystals can be significantly improved through reduction, the mechanistic basis of this enhancement remains unclear. To shed a light on the chemistry of reduced anatase TiO2 nanocrystals, density functional theory were used to investigate the properties of defects and excess electrons. We demonstrated that oxygen vacancies are stable both on the surface and at the sub-surface of the nanocrystal, while titanium interstitials prefer sub-surface sites. Different defect locations possessed different excess electron structures, which contributed to deep and shallow states in the band gap of the nanocrystals. Furthermore, valence band tailing was observed, resulting in band gap narrowing. The theoretical results presented here deepen our understanding, and show the potential of defects to considerably change the macroscopic properties of anatase TiO2 nanocrystals.

CuO–MMT nanocomposite: effective photocatalyst for the discoloration of methylene blue in the absence of H2O2

Copper oxide (CuO) nanoparticles are of particular interest because of their interesting properties and promising applications in photocatalysis and purification of water. In this work, CuO–montmorillonite (CuO–MMT) nanocomposite was synthesized by a thermal decomposition method and characterized by diffuse reflectance spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy and transmission electron microscopy. The resultant particles were nearly spherical, and particle size in MMT was in the range of ∼3–5 nm. The powder X-ray reflection patterns indicate that MMT has a d-spacing higher (1.22 nm) than CuO–MMT nanocomposite (0.97 nm). The shrinkage probably is related to the conformation of CuO nanoparticles on the clay surface. The diffuse reflectance spectrum of CuO–MMT showed band around 340–360 nm corresponding to presence of [Cu–O–Cu]n-type clusters over the support surface. The band gaps of the resulting CuO nanoparticles and CuO–MMT nanocomposite were widened from 1.70 to 1.80 eV for an indirect allowed band gap and from 3.70 to 3.82 eV for a direct allowed inter band transition owing to the quantum size effect, respectively. The nanocomposite exhibited an enhanced and stable photoactivity for the discoloration of methylene blue (MB) aqueous solution under visible light. The result showed that MB discoloration was observed after 20 min light irradiation in the absence of H2O2. The several parameters were examined, such as the catalyst amount, pH and initial concentration of MB. The mechanism of separation of the photogenerated electrons and holes of the CuO–MMT nanocomposite was discussed.

Facile ion-exchange synthesis of mesoporous Bi2S3/ZnS nanoplate with high adsorption capability and photocatalytic activity

Novel Bi2S3/ZnS nanoplates have been successfully prepared by simple reflux and cation exchange reaction between the preformed ZnS spheres and Bi(NO3)3·5H2O. The synthesized Bi2S3/ZnS nanoplates are mesoporous structures, possess a high specific surface area of 101.30m2/g and exhibit high adsorption capability and photocatalytic activity for methylene blue (MB) degradation under UV light irradiation. The high adsorption capability and photocatalytic activity can be ascribed to the fact that the formation of Bi2S3/ZnS nanoplates with large specific surface area provides more reactive sites and facilitates the separation of photogenerated electron–hole pairs. The possible formation mechanism of Bi2S3/ZnS nanoplates is proposed based on the time-dependent observation. Moreover, a tentative mechanism for degradation of MB over Bi2S3/ZnS has been proposed involving OH radical and photoinduced holes as the active species, which is confirmed by using methanol or ammonium oxalate as scavengers. This work provides a cost-effective method for large-scale synthesis of composite with controlled architectural morphology and highly promising applications in photocatalysis.

Selective patterned growth of ZnO nanowires/nanosheets and their photoluminescence properties

Zinc oxide (ZnO) demonstrates promising applications in photocatalysis, photodetectors and light-emitting devices. The shape of the ZnO nanoparticles plays an important role in determining their mechanical and optical properties. Here we report facile and controllable synthesis of ZnO nanowires and nanosheets with hydrothermal synthesis on patterned aluminum substrates prepared by colloidal lithography. The nanowire areas and nanosheet areas were well-defined in micron scale and they displayed dramatically different photoluminescence properties: while nanowires showed strong band-edge emission at 382 nm with a moderate orange emission at 600 nm, nanosheets only showed broad and intense green emission in the 547 nm range. The method demonstrated here enables periodic ZnO nanowire/nanosheet patterning with well-controlled morphology and luminescence property, which would provide a large-scale facile fabrication technique to tailor the substrate’s optical properties by using ZnO as the only constituent oxide component.

Graphene-wrapped ZnO nanospheres as a photocatalyst for high performance photocatalysis

In this work, graphene-wrapped ZnO nanospheres (ZnO–graphene nanocomposites) were prepared by a simple facile lyophilization method, followed by thermal treatment process. ZnO nanospheres with the size of about 100–400nm, composed of numerous nanocrystals with hexagonal wurtzite structure, were well separated from each other and wrapped with transparent graphene sheets. Compared to ZnO nanospheres, the ZnO–graphene nanocomposites showed a significant enhancement in the photodegradation of methylene blue. This enhanced photocatalytic activity could be attributed to their favorable dye-adsorption affinity and increased optical absorption as well as the efficient charge transfer of the photogenerated electrons in the conduction band of ZnO to graphene. Thus, this work could provide a facile and low-cost method for the development of graphene-based nanocomposites with promising applications in photocatalysis, solar energy conversion, sensing, and so on.

Electrochemical and Optical Properties of ZnO Nanowires Modified with Ag Nanoparticles by Electrodeposition

The electrochemical and optical properties of ZnO nanowires modified with Ag nanoparticles by electrodeposition are studied. The results of cyclic voltammetry and chronoamperometry show that the radiated, well-crystallized ZnO-nanowire electrode, with a spacial architecture, allows fast Ag(I) ion diffusion, rapid electron transfer, and high Ag deposition rate. Numerous Ag nanoparticles deposited on the nanowires induce a redshift of 0.23 eV in the ZnO optical bandgap while without causing a large decrease in optical absorption intensity. However, a great decrease in photoluminescence intensity occurs in the modified structure, mainly resulting from the charge transfer between ZnO and Ag. The composite structure has promising applications in photocatalysis and photovoltaics.

Enhancing photocatalytic activity of one-dimensional KNbO3 nanowires by Au nanoparticles under ultraviolet and visible-light

A novel photocatalyst was prepared by anchoring Au nanoparticles (NPs) onto one-dimensional potassium niobate (KNbO3) nanowires. Photocatalytic activity towards rhodamine B degradation over Au/KNbO3 appears to be much greater than that of KNbO3 nanowires, nanorods and commercial Alfa Aesar. In terms of reaction rate constant (k), ultraviolet excitation (λ = 365 nm) is higher than that of visible-light (λ > 420 nm) and increasing the size of Au NPs from 5 to 10 nm significantly improves the reactivity. Notably, Au NPs with a size of ca. 10 nm supported on KNbO3 nanowires display the greatest photoreactivity, with k exceeding that of commercial KNbO3 by a factor of 15. The mechanism responsible for the enhancement of photocatalytic activity was discussed, highlighting the crucial role of surface plasmon resonance as well as interband transitions on Au NPs. This study is potentially applicable to a range of low-dimensional niobate-based nanostructures combined with Au and other plasmonic NPs with promising applications in photocatalysis and relevant areas.