Efficient Photocatalytic Water Research Articles

Ta3N5–LaTaON2 heterojunction with matched interfaces to accelerate charge separation for efficient photocatalytic water oxidation

Charge separation is generally considered as the most critical step to achieve efficient photocatalytic reactions. Although charge separation can be promoted by a semiconductor heterojunction, its efficacy is inherently restrained by the mismatched atomic arrangements across the heterojunction interfaces. Here, Ta3N5–LaTaON2 heterojunction with matched interfaces has been fabricated by one-step ammonolysis treatment of KLaTa2O7. The match interfaces are formed by nearly perfect adhesion of Ta3N5 (010) and LaTaON2 (101¯) facets whose interatomic distance is similar. Compared with conventional heterojunction, the so-formed Ta3N5–LaTaON2 heterojunction are extremely efficient in accelerating charge separation which in turn enables a high photocatalytic activity. An apparent quantum efficiency as high as 11.6% at 420 ± 20 nm has been reached by Ta3N5–LaTaON2 heterojunction, which is almost three times higher than Ta3N5/LaTaON2 mixtures. These results signify the importance of matched heterojunction interfaces for charge separation and provide a paradigm in the design of efficient heterojunction-based semiconductor photocatalysts.

Enhanced photocatalytic degradation of organic contaminants in water by highly tunable surface microlenses

Photocatalysis is one of the dominant technologies used to enhance the efficiency of water decontamination with light-based treatments. However, the effectiveness of photocatalysts is usually limited by the irradiation conditions and the properties of the water matrix. In this work, we have demonstrated the capability of surface microlenses (MLs) as a clean technology for more efficient photocatalytic water decontamination. Random or ordered surface MLs were fabricated from simple polymerization of nanodroplets produced in a solvent exchange process. Both random microlenses (MLR) and microlenses array (MLA) could enhance the photocatalytic degradation efficiency (η) of four representative organic pollutants, including methyl orange (MO), norfloxacin (NFX), sulfadiazine (SFD), sulfamethoxazole (SMX), spiked in ultra-pure water, synthetic natural water, or real river water. By controlling the conditions of light treatment, η could be enhanced by up to 402%. The effectiveness of surface MLs was validated under both visible LED light and simulated solar light and for two photocatalysts zinc oxide (ZnO) and titanium dioxide (TiO2). By reducing the concentration of the photocatalysts from 100 to 5 mg/L and the intensity of irradiation intensity from 1 Sun to 0.3 Sun, our findings suggest that the enhancement factor by MLs was higher at lower catalyst concentration, or at lower light intensity. Based on optical simulations and experimental results, we demonstrated that surface MLs optimize the light distribution and promote the formation of active species, which results in the enhancement of η. The use of MLs may serve as a novel strategy to improve the photocatalytic degradation of micropollutants, especially in places where the available light source is weak, such as indoors or in cloudy regions.Synopsis: MLs-enhanced photocatalysis degradation of organic contaminants in different water matrices.

2D co-catalyst leads the charge in efficient photocatalytic water splitting

2D co-catalyst leads the charge in efficient photocatalytic water splitting

Engineering high-coordinated cerium single-atom sites on carbon nitride nanosheets for efficient photocatalytic amine oxidation and water splitting into hydrogen

Developing highly-active rare-earth single atom photocatalysts have attracted extensive attention due to their excellent catalytic properties. Herein, we prepared a single-atom Ce-SA-C3N4 catalyst composed of atomically dispersed rare-earth cerium (Ce) on C3N4 nanosheets by the pyrolysis of cerium-incorporated layered precursor. The atomic distribution and high-coordinated environment of Ce sites were disclosed by aberration-corrected scanning transmission electron microscopy, electron energy-loss spectra, X-ray absorption spectroscopy, and theoretical calculations. In Ce-SA-C3N4, Ce single atoms are coordinated by four N atoms and six O atoms (Ce-N4/O6). The cooperation of single-atom Ce-N4/O6 active sites in C3N4 nanosheets tunes the electronic structure and the surface trap states, resulting in accelerated charge transfer/separation and extended lifetime of photoinduced electrons. Meanwhile, the high-coordinated Ce-N4/O6 active sites could promote the production of superoxide radicals (•O2−) and C = N bond, thus, the optimized single-atom Ce-SA-C3N4 photocatalyst exhibits highly efficient photocatalytic oxidation of amines under visible light irradiation. Furthermore, the fabricated single-atom Ce-SA-C3N4 photocatalysts are applied to split water into hydrogen, producing the maximum hydrogen yield of 33.5 mmol h−1 g−1. The apparent quantum efficiency for hydrogen evolution achieves 32.6% at 420 nm. This study provides a guideline for rationally designing efficient high-coordinated rare-earth single-atom active sites for efficient solar energy conversion and utilization.

Rh-doped ultrathin NiFeLDH nanosheets drive efficient photocatalytic water splitting

NiFeLDH (Layered double hydroxide) semiconductors are promising for harnessing light energy. The development of transition metal-based photocatalysts consisting of rhodium building blocks is not only beneficial for the separation and transfer of photo-generated carriers in photocatalytic reactions but also an effective means of widening the optical window of light absorption. In this report, a facile hydrothermal approach is employed in modulating NiFeLDH nanosheets arrays with optimal molar ratio of Rhodium (Rh) in LDH to engineer a robust hierarchical NiFeLDH-Rh photocatalytic system towords efficient hydrogen evolution reaction (HER) under visible light. In a systematic investigation, the NiFeLDH is grown on nickel foam and controlled doping of Rhodium led to fine-tuning of their electronic structure and efficient visible light-driven proton reduction system due to its multiple accessible active sites boosting the photocatalytic performance. Furthermore, the 2D hierarchical nanosheet arrays can speed up electron diffusion and assure fast electron/mass transfer while maintaining high photocatalytic stability. The NiFeLDH-Rh composite demonstrated an enhanced hydrogen generation rate of 2.09 mmolg−1h−1 (AQY = 6.1%). The photocurrent density and transient photocurrent curve show rapid charge transfer as well as the unique electron transfer paths through the contact surface, resulting in efficient charge separation. Moreover DFT and photoelectrochemical studies reveal higher HER activity due to the augmented electric field between Rh and NiFeLDH complex. This research offers a novel strategy and new insights into the investigation of highly active photocatalysts for overall water splitting.

Construction of TiO2 /SrTiO3 Heterojunction Derived from Monolayer Ti3 C2 MXene for Efficient Photocatalytic Overall Water Splitting.

Construction of heterojunction at the atomic scale to ensure efficient charge separation for improvement of photocatalytic water splitting is challenging. Herein, a facile hydrothermal method has been applied for the in situ fabrication of TiO2 /SrTiO3 heterojunction, using the monolayer Ti3 C2 MXene as the template and reactant. It is found that the sample with the hydrothermal reaction time of 60 min exhibits the highest H2 evolution rate with the sacrificial reagent, due to the efficient charge separation of TiO2 /SrTiO3 heterojunction as Ti3 C2 derivative. In addition, the sample shows the best overall water splitting performance at a hydrothermal reaction time of 120 min, where TiO2 is nearly converted to SrTiO3 , due to the fast kinetic process and low structural defects of SrTiO3 . This work not only provides a simple strategy for the fabrication of heterojunction photocatalysts but also demonstrates the difference in optimization of half-reaction and overall water splitting reaction.

Synthesis of PDI/Zn0.8Cd0.2S composites for efficient visible light-driven photocatalytic overall water splitting

BackgroundOverall water splitting based on particulate photocatalysts under visible light irradiation is a cost-effective technology for the conversion of solar energy into renewable energy (hydrogen and oxygen). MethodsHerein, the perylene diimide (PDI)/Zn0.8Cd0.2S composite photocatalyst is synthesized for application in visible light driven photocatalytic overall water splitting. Significant findingsThe PDI/Zn0.8Cd0.2S composite with 10 wt% PDI loading exhibits superior H2-evolution rate of 71.98 μmol·g−1·h−1 and O2-evolution rate of 32.44 μmol·g−1·h−1, which in a perfect stoichiometric ratio close to 2:1. The PDI/Zn0.8Cd0.2S with remarkable enhanced photocatalytic activity have the advantages of high charge separation efficiency and strong redox capacity. This work provided a new approach for the design of new type composite photocatalysts with efficient photocatalytic overall water splitting.

Construction of ternary RuP2/Ti4P6O23@TiO2 photocatalysts for efficient photocatalytic biomass selective oxidation and water splitting

Construction of ternary RuP2/Ti4P6O23@TiO2 photocatalysts for efficient photocatalytic biomass selective oxidation and water splitting.

CdS-POM nanosheets for highly efficient visible-light-driven H2 evolution

Polyoxometalates/metal-sulfide heterojunction can efficient photocatalytic split water to produce hydrogen to alleviate environmental pollution and the energy crisis.

Janus β-Te2X (X = S, Se) monolayers for efficient excitonic solar cells and photocatalytic water splitting

In this work, we have investigated the novel 2D allotropes i.e., β-Te2X (X = S, Se) using first-principles calculations and study their potential applications in light harvesting devices.

Multiple strategies of improving photocatalytic water splitting efficiency in 2D arsenic sesquichalcogenides.

Improving the solar-to-hydrogen efficiency has always been a significant topic in the field of photocatalysis. Based on first-principles calculations, herein, we propose multiple strategies to improve the photocatalytic properties of 2D arsenic sesquichalcogenides for full water splitting. The new configurations As2STe2 and As2SeTe2 monolayers, derived from the As2Te3 monolayers by surface modification, are manifested to be typical infrared-light driven photocatalysts. Notably, under the built-in electric field, As2STe2 and As2SeTe2 monolayers can fulfil overall water splitting and the predicted solar-to-hydrogen efficiencies even reach up to 36.19% and 29.36%, respectively. The Gibbs free energy calculations indicate that the OER can be successfully driven under light irradiation. In addition, the overpotentials can provide most of the energy for HER when illuminated, especially for As2STe2 with the . In addition, both As2S3 and As2Se3 monolayers are capable of satisfying the conditions for photocatalytic water splitting. Furthermore, the band gaps of As2Se3 and As2S3 can dramatically be narrowed by increasing the number of layers and doping, respectively. These findings provide a theoretical basis for As2X3 monolayers to achieve efficient photocatalytic water splitting.

Fabrication of In(OH)3–In2S3–Cu2O nanofiber for highly efficient photocatalytic hydrogen evolution under blue light LED excitation

This study synthesized the In(OH)3–In2S3 nanosheet via a simple hydrothermal method. The different amounts of In(OH)3–In2S3 nanosheet used to synthesize In(OH)3–In2S3–Cu2O composite by a wet chemical method. FESEM, FETEM, XRD, XPS, BET, UV–vis DRS, and PL spectroscopy characterized the In(OH)3–In2S3–Cu2O composite. Compared with In(OH)3–In2S3 nanosheet, In(OH)3–In2S3–Cu2O composite can exhibit the synergistic effects of higher specific surface area, higher light-harvesting capacity, and accelerating the separation and migration of photogenerated charge carriers. In addition, In(OH)3–In2S3–Cu2O nanofiber was fabricated via a facile electrospinning process at the different amounts of In(OH)3–In2S3 nanosheet. The manufacturing process offers many advantages, such as simplicity, low temperature, and without templates. The effect of operational parameters (such as the reaction conditions of photocatalysts, pH values, sacrificial reagents, and light sources) on the photocatalytic hydrogen production of In(OH)3–In2S3–Cu2O nanofiber was investigated. The results indicate that the appropriate reaction conditions of In(OH)3–In2S3–Cu2O nanofiber can reveal higher efficient photocatalytic water splitting than commercial TiO2 or ZnO nanofiber under blue light LED excitation. Furthermore, In(OH)3–In2S3–Cu2O nanofiber can provide a simple fabrication process, high photocatalytic activity, and high reusability shall be beneficial for the practical application of photocatalytic hydrogen production.

Homogeneously Nitrogen Doped BaLa4Ti4O15Extending Visible Light Responsive Range for Photocatalytic Oxygen Evolution

Homogeneous nitrogen doping is a promising strategy for narrowing the band gap of layered metal oxides without altering the crystal structures and microstructures of precursors. In this work, BaLa4Ti4O15, a (111) plane-type layered perovskite metal oxide with a band gap of about 3.77 eV, was doped with nitrogen by a thermal treatment in an ammonia atmosphere. The nitrogen dopants are homogeneously distributed in the layered perovskite framework, resulting in an extended band-to-band visible light absorption edge up to 600 nm, corresponding to a band gap of 2.07 eV. It is worth noting that the nitrogen doping process has trivial impact on the crystal structure, microstructure, and chemical states of the BaLa4Ti4O15, which minimizes the side effect of photogenerated carrier separation and surface chemical reaction. BaLa4Ti4O15–xNy exhibited efficient photocatalytic water oxidation activity under visible light. This work highlights the usefulness of homogeneous doping for tuning wide band gap layered metal oxides.

Highly efficient photocatalytic overall water splitting in two-dimensional van der Waals MoS2/Hf2CO2 heterostructure

Two-dimensional (2D) van der Waals (vdW) heterostructures have attracted much attention due to their unique properties in photocatalysis, electronics, and energy storage. This work comprehensively analyzed the electronic properties and photocatalytic efficiency properties of 2D vdW MoS2/Hf2CO2 heterostructure by first-principles calculations and molecular dynamics simulation. An ideal band gap of 1.44 eV was found for visible light absorption. Meanwhile, a high solar-to-hydrogen efficiency of 17.14% is obtained from the calculated band-edge positions, and a high power conversion efficiency of 13.84% is also confirmed by spectroscopy limited maximum efficiency simulation. We estimate the time scale for electron–hole transfer and recombination times using a combination of non-adiabatic molecular dynamics and time-dependent density functional theory. A suitable e-h recombination time of 1.86 ns and electron (hole) transfer time of 331 (978) fs are obtained in the 2D MoS2/Hf2CO2 heterostructure, which is expected to ensure high photocatalytic efficiency. Therefore, the constructed MoS2/Hf2CO2 heterostructures provide a new example for the prediction of high-performance nano optoelectronic devices.

Formation of buried 2D Aluminium Gallium Nitride structures with enhanced piezoelectric modulus by xenon ion implantation

Two-Dimensional (2D) III-V nitrides are anticipated to exhibit exceptional material properties with wide-ranging technological significance. We report, ion beam synthesis of buried 2D Aluminium Gallium Nitride structures with enhanced piezoelectric modulus. We propose three criteria for the formation of 2D AlGaN layers by ion implantation. The 2D layers were synthesized by Xe implantation into epitaxially grown, strain-free Al0.5Ga0.5N thin films and their presence was confirmed by scanning transmission electron microscopy. Alternating planar and buckled 2D III-Nitride layers in conjunction with a rapid change of polarity of the buckled layer confirms the weak interaction between the individual layers. Rutherford backscattering, in conjunction with piezoelectric force microscopy was used to identify the optimum Xe dose to induce maximum enhancement of piezoelectric modulus. Our results are supported by X-ray diffraction to quantify the macroscopic strain of the implanted film and Monte-Carlo simulations of ion-solid interactions. Fabrication of this material on a large scale may lead to highly efficient energy harvesters, communication devices, power devices and photocatalytic water splitting technologies.

Surface Coating of Amorphous TiOx Enables Efficient Vapor-fed Photocatalytic Overall Water Splitting with Substantial Apparent Quantum Yield.

Photocatalytic overall water splitting represents a promising strategy for sustainable hydrogen production. However, photocorrosion and dissolution of photocatalysts and cocatalysts are common concern for the solid-liquid phase reaction. Recently, the above issues could be addressed by Domen and coworkers, when the photocatalytic water splitting was conducted in the presence of water vapor, which dramatically restrain the undesired corrosion of the photocatalysts and cocatalysts. Besides, surface decoration of hygroscopic TiOx layer promotes adsorption of water molecules and prevents the corrosion process. In addition, vapor-fed photocatalytic water splitting remains considerable apparent quantum yield compared with the liquid water photocatalytic overall water splitting at pressurized condition, which endows great potential in practical application.

Two-dimensional ABC3 (A = Sc, Y; B = Al, Ga, In; C = S, Se, Te) with intrinsic electric field for photocatalytic water splitting

Hydrogen production from water photolysis is considered to be one of the main approaches to obtain clean energy in the future. Two-dimensional (2D) materials with intrinsic vertical electric field can break the band gap limitation (>1.23 eV) of photocatalysts in traditional theory, and broaden the spectrum that can be used for photocatalytic water splitting, such as infrared light. Inspired by the ferroelectric phase α-B2C3 (B = Al, Ga, In; C = S, Se, Te), we replaced one of the B atoms with IIIB elements (namely Sc and Y) of the same valency, and successfully predicted 18 kinds of ABC3 (A = Sc, Y; B = Al, Ga, In; C = S, Se, Te) monolayers with high stability. Encouragingly, 15 predicted ABC3 monolayers possess direct band gap features in contrast to that of α-B2C3, which all exhibit indirect band gap feature. Due to the large intrinsic vertical electric field, the ABC3 monolayers hold great potential for efficient photocatalytic water splitting in acidic and alkaline as well as neutral environments. The rectified solar-to-hydrogen (STH) efficiencies of 14 ABC3 MLs were larger than 20%. Excitingly, the STH efficiency limits of YGaTe3 and YInTe3 even reach 35.97% and 36.94% using the full solar spectrum, which breaks the conventional theoretical efficiency limit. In addition, considerable light absorption and large carrier mobility are confirmed in ABC3 MLs. These interesting findings render ABC3 monolayers a strong candidate for future photovoltaic and nanoelectronic applications.

2D WSe2/MoSi2N4 type-II heterojunction with improved carrier separation and recombination for photocatalytic water splitting

The use of semiconductor photocatalysis for hydrogen production is an ideal approach for achieving solar energy and conversion. In this work, we systematically examine the photocatalytic properties of WSe2/MoSi2N4 van der Waals heterojunctions using first-principles calculation and nonadiabatic molecular dynamics. The results demonstrate that the WSe2/MoSi2N4 heterojunction possesses a 1.81 eV indirect band gap and type-II band alignment, which ensures that the photoexcited electron–hole (e–h) pairs are spatially separated. The carrier lifetime of the photoexcited e–h pairs is 278 ps significantly longer than the interlayer hole transfer time of 335 fs, implying that the heterojunction has the high quantum efficiency. In addition, this heterojunction possesses superior optical absorption (105 cm−1), low overpotential for OER (0.60 V), and outstanding light absorption properties. These findings indicate that this heterojunction can achieve highly efficient and spontaneous photocatalytic water splitting.

Molten salt-assisted synthesis of nitrogen-vacancy crystalline graphitic carbon nitride with tunable band structures for efficient photocatalytic overall water splitting

The photocatalytic overall water splitting performance of graphitic carbon nitride (g-C3N4) has still been restricted by its inefficient charge separation efficiency. Herein, nitrogen-vacancy crystalline g-C3N4 nanosheets (g-C3N4-D) with tunable band structures were successfully prepared by the alkali-molten salt-assisted method for efficient photocatalytic overall water splitting. Among them, g-C3N4-D2 not only combines the advantages of the amorphous and crystalline state of two-dimensional g-C3N4 nanosheets, but also introduces nitrogen vacancy to adjust the bandgap structures of crystalline g-C3N4 by an alkali etching, thus improving the light energy utilization and charge separation efficiency. TEM and EPR spectrum prove the existence of N defects in the crystalline g-C3N4. The excellent and stable photocatalytic overall water splitting activity with H2 and O2 evolution rate of 49.60 μmol g−1 h−1 and 24.71 μmol g−1 h−1 was obtained over g-C3N4-D2 with Pt and Co3O4 nanorods as cocatalysts (Pt/g-C3N4-D2/3%Co3O4 NRs) under AM 1.5G simulated light irradiation. In the half-reaction experiments, the maximum H2 evolution rate of Pt/g-C3N4-D2/3%Co3O4 NRs is 3.78 mmol g−1 h−1 with a significant quantum efficiency of 11.94 % at 400 nm, and the solar-hydrogen conversion efficiency (STH) is 1.48 %. The photocatalytic water oxidation activity of Pt/g-C3N4-D2/5%Co3O4 NRs is 42.34 μmol g−1 h−1. Additionally, the potential mechanism of photocatalytic overall water splitting was testified by in-situ XPS. This work provides a simple strategy for further advancing the potential application of g-C3N4 by molten salt-assisted alkali etching to introduce N vacancies to regulate the band gap of crystalline g-C3N4 for photocatalytic overall water splitting.

Single-atomic Co-N4-O site boosting exciton dissociation and hole extraction for improved photocatalytic hydrogen evolution in crystalline carbon nitride

Single atom co-catalyst loading has been demonstrated to be an effective strategy for achieving efficient photocatalytic water splitting. Unfortunately, the origins of the high activity of the single atom sites remain unrevealed owing to the lack of deep insight on their coordination environment. Herein, single-atom Co was loaded on crystalline g-C3N4 (CCN) nanorod in the form of five-coordination (Co-N4-O) at the heptazine cavities. Both experimental and theoretical evidences revealed that single-atomic Co-N4-O sites in CCN-Co played a key role in exciton dissociation and photogenerated charge carrier separation as well as subsequent hole extraction and transfer. Under visible light irradiation, the photogenerated holes in CCN directionally transferred to Co-N4-O sites and were rapidly extracted by hole sacrificial agent. As a result, the obtained CCN-Co sample with 0.32 wt. % Co and 1.0 wt. % Pt exhibited significantly improved photocatalytic hydrogen production rate of 32.1 mmol g−1 h−1, nearly 4 times and 38 times higher than that of CCN and bulk g-C3N4, respectively. The apparent quantum yield as high as 49.5 % was achieved at 420 nm. This work opens new insights for understanding the effect of single-atom active sites in promoting photocatalytic hydrogen production.