Direct Z-scheme Heterojunction Research Articles

A new approach on visible light assisted oxygen doped g-C3N4/β-Bi2O3 direct Z-scheme heterojunction towards the degradation of bisphenol A: Degradation pathway, toxicity assessment, and continuous mode study

Graphitic carbon nitride (g-C3N4, G) was firstly doped with oxygen atom and then bismuth oxide nanoparticles (β-Bi2O3, B) were embedded into the modified G to enhance its photocatalytic activity. The photocatalytic performance of the as-prepared composite (β-Bi2O3/O-G, BOG) was evaluated towards bisphenol A (BPA) degradation under visible light irradiation in both batch and continuous-flow reactors. A series of catalyst characterization tests, including XRD, FTIR, FESEM, HRTEM, XPS, TGA, EDX, BET, DRS, PL, EIS, transient photocurrent, CV, and LSV, revealed the significant improvement in photocatalytic activity of G after oxygen doping and its combination with B. Under optimum conditions, 98.7% BPA and 76.8% total organic carbon (TOC) removals were achieved. A direct Z-scheme heterojunction system was described via a series of photochemical tests as well as the identified oxidizing reactive species. The visible light-assisted BOG system also exhibited excellent performance for purifying real BPA-laden water samples. Moreover, BOG composite showed noticeable reusability, implying its cost-effective potential for practical applications. The mechanistic degradation pathway of BPA was proposed based on the identified transformation products (TPs). Furthermore, the toxicity of TPs was evaluated by the Ecological Structure-Activity Relationships (ECOSAR) predictive model. This study gives a new point of view on as-prepared BOG composite potential with highly-efficient photocatalytic performance towards degradation of emerging refractory contaminants and treatment of contaminated effluents.

Construction of CdS/CdSnO3 direct Z-scheme heterostructure for efficient tetracycline hydrochloride photodegradation

Photocatalytic technology is one of the promising methods for solving the environmental crisis caused by antibiotics. In this work, CdS/CdSnO3 direct Z-scheme heterojunctions were fabricated through soft-chemistry routes. Various characterizations were performed to analyze the intrinsic properties of the constructed photocatalysts. The photocatalytic activity of the as-prepared catalysts was assessed via tetracycline hydrochloride (TCH) photodegradation. Compared with the bare CdSnO3 and CdS, all the obtained CdS/CdSnO3 heterojunctions exhibited improved photocatalytic performance. Meanwhile, the kinetic constant of CdS/CdSnO3 heterojunction with optimized mass ratio was about 57.5 and 1.85 times as high as the bare CdSnO3 and CdS. The upgraded photocatalytic activity can be attributed to the enhanced light absorption and unique charge transfer path. Based on the systematic analysis, the possible direct Z-scheme photocatalytic mechanism was put forward.

Mechanistic study of two-dimensional CrS2/Sc2CF2 direct Z-scheme heterojunction as the solar-driven water-splitting photocatalyst

Direct Z-scheme based on biomimetic artificial photosynthesis is a promising strategy to enhance photocatalytic activity. The search for direct Z-scheme photocatalysts is imperative, and the photocatalytic efficiency is mainly influenced by the separation rate of photogenerated electron–hole (e--h+) pairs and the light capture ability. Herein, a two-dimensional (2D) van der Waals (vdW) heterostructure consisting of a monolayer of CrS2 and Sc2CF2 is predicted based on density functional theory (DFT) as a promising direct Z-scheme photocatalyst for water splitting. The CrS2/Sc2CF2 heterojunction possesses a large energy band interleaving arrangement and a small interlayer band gap, and the orientation of the built-in electric field promotes interlayer carrier complexes, with electrons and holes localized at the highest redox energy level, respectively. In addition, the CrS2/Sc2CF2 heterojunction possesses a high overpotential driving force and excellent light harvest ability. Our calculations indicate that the CrS2/Sc2CF2 heterojunction is a promising new photocatalyst.

A novel direct Z-scheme heterojunction BiFeO3/ZnFe2O4 photocatalyst for enhanced photocatalyst degradation activity under visible light irradiation

In recent years, inhibition of photoinduced electron and hole recombination is considered as a breakthrough to improve the photocatalytic degradation of pollutants. In this study, we successfully loaded ZnFe 2 O 4 (ZFO) microsphere onto BiFeO 3 (BFO) microcubes via a simple hydrothermal method, and intimate interface between BFO and ZFO was constructed. Under the effect of heterojunction between BFO and ZFO, the recombination rate of photogenerated electron-hole pairs was decreased significantly, leading to the enhanced photocatalytic effect. The photocatalytic experiments show that the degradation efficiency of BFO/ZFO-10% composite for tetracycline and methylene blue are 1.63 and 1.38 times higher than that of pure BFO. In addition, four cycles experiment also proved that BFO/ZFO has good stability and excellent magnetic recovery properties. A possible carrier transfer path on the base of the direct Z-scheme mechanism in composite was proposed. This study provides a useful guide toward the design of the highly efficient and magnetic collectable photocatalysts by the introduction of magnetic component and the construction of heterojunction, and as-synthesized BFO/ZFO was proved to be a promising photocatalyst for the elimination of toxic organic molecules in groundwater. • 3D/3D BFO/ZFO photocatalyst were prepared by simple hydrothermal method. • Direct Z-scheme photocatalytic system promotes the separation efficiency of carriers. • Charge carriers were separated efficiently due to the BFO/ZFO heterojunction. • Magnetic BFO/ZFO can be recovered under the external magnetic field.

Direct observation of carrier migration in heterojunctions to discuss the p–n and direct Z-scheme heterojunctions

Type II p–n heterojunction and direct Z-scheme heterojunction are identical staggered band alignments, but were reported ambiguously in many composite photocatalysts because their carriers migrate in opposite directions. In this research, metal oxides CuO, NiO and Co3O4-based heterojunctions with Na0.9Mg0.45Ti3.55O8 (NMTO) were synthesized via a simple hydrothermal method. The CuO/NMTO heterojunction was demonstrated as a direct Z-scheme heterojunction, whereas the NiO/NMTO and Co3O4/NMTO heterojunctions showed type II p–n band alignment, distinguished by the direct observation of carrier migration under light illumination, and confirmed by the x-ray photoelectron spectroscopy, Mott–Schottky measurements, ultraviolet photoelectron spectra and capture experiments. These all heterojunctions enjoyed better photocatalytic performance to degrade methylene blue and antibiotics (Enrofloxacin, Metronidazole and tetracycline) than the pure NMTO, attributed to their effective separation of the photoinduced electron–hole pairs owing to the staggered band alignment. Prominently, the NiO/NMTO and Co3O4/NMTO p–n heterojunctions exhibited superior degradation ability to the CuO/NMTO Z-scheme heterojunction. The initial relative Fermi position of two semiconductors is the prerequisite to determine whether the p–n heterojunction or direct Z-scheme heterojunction is built because the electrons diffuse from one semiconductor with a higher Fermi level to another with a lower Fermi level while the holes diffuse reversely until a united Fermi level when they combine. The built-in electric field at the heterojunction interface is determined by the difference in the initial Fermi levels or work functions of two semiconductors, regulating the separation ability of photogenerated electrons and holes to affect the photocatalytic performance. Thus, the high difference in the initial Fermi levels of semiconductors is crucial in the development of heterojunctions with staggered band alignment to obtain high performance in photocatalytic reactions.

A Direct Z-Scheme AgBr/CuBi2O4 Photocathode for Ultrasensitive Detection of Ciprofloxacin and Ofloxacin by Controlling the Release of Luminol in Self-Powered Microfluidic Photoelectrochemical Aptasensors.

An innovative self-powered microfluidic photoelectrochemical (PEC) aptasensor was developed that uses photoactive AgBr/CuBi2O4 (ACO) composites as the photocathode matrix for ultrasensitive detection of ciprofloxacin (CIP) and ofloxacin (OFL). The formation of direct Z-scheme heterojunctions in ACO composites greatly aided electron/hole pair separation. Meanwhile, ZnIn2S4-decorated CdS nanorod arrays (CZIS) as the photoanode were used instead of a platinum counter electrode to provide electrons. The "signal-off" CIP detection was accomplished through the steric hindrance effect in the photoanode due to the combination of aptamer(CIP) and CIP. To increase the cathodic photocurrent intensity for OFL determination, controlled release of luminol was first used. Luminol molecules were successfully embedded in the porous structure of silicon dioxide nanospheres (PSiO2) by the electrostatic adsorption between PSiO2 and aptamer(OFL). The luminol released by specific recognition between OFL and aptamer(OFL) could not only react with •O2- but also produce chemiluminescence emission, resulting in the "signal-on" state. Because of the signal "on-off-on", the proposed aptasensor exhibited wide linear ranges for CIP (0.001-100 ng/mL) and OFL (0.0005-100 ng/mL) detection. Furthermore, the low detection limits of CIP (0.06 pg/mL) and OFL (0.022 pg/mL) could achieve the ultrasensitive analysis.

Direct Z-scheme heterojunction rutile-TiO2/g-C3N4 catalyst constructed by solid grinding method for photocatalysis degradation

Schematic illustration of RhB photocatalytic reaction mechanism over the rutile-TiO 2 /g-C 3 N 4 photocatalyst. • The rutile-TiO 2 /g-C 3 N 4 photocatalyst is constructed by a simple solid grinding method. • The optimized rutile-TiO 2 /g-C 3 N 4 photocatalyst has more excellent photocatalytic performance than the pure rutile-TiO 2 and g-C 3 N 4 . • The direct Z-scheme heterojunction mechanism is proposed over the rutile-TiO 2 /g-C 3 N 4 photocatalyst. Constructing a direct Z-scheme heterojunction is an effective method to improve the catalytic performance of photocatalyst. Here, the direct Z-scheme heterojunction rutile-TiO 2 /g-C 3 N 4 photocatalyst was constructed by a simple solid grinding method. This method can not only avoid the weak activity of rutile-TiO 2 in high synthesized temperature condition, but also precisely control the amount of g-C 3 N 4 . The evaluation of photodegradation reaction suggests that the rutile-TiO 2 /g-C 3 N 4 photocatalyst exhibits higher photodegradation efficiency than the pure rutile-TiO 2 and the pure g-C 3 N 4 under simulated sunlight irradiation, and the optimal photocatalytic performance is achieved when the mass ratio of rutile-TiO 2 to g-C 3 N 4 is 2:5. The experimental results prove that a direct Z-scheme heterojunction is formed over the rutile-TiO 2 /g-C 3 N 4 photocatalyst, which promotes the effective electron-hole separation and the higher redox potential over the rutile-TiO 2 /g-C 3 N 4 photocatalyst. This work provides an attractive strategy to construct the direct Z-scheme photocatalyst consisted of rutile-TiO 2 and g-C 3 N 4 .

Dual Direct Z-Scheme Heterojunction with Growing Photoactive Property for Sensitive Photoelectrochemical and Colorimetric Bioanalysis.

A dual direct Z-scheme heterojunction photoactive material of CoTiO3/g-C3N4/Bi2O3 was designed based on calcination and in situ illumination-assisted process for sensitivity bioproteins detection which combined with MnO2 nanoflowers to achieve signal quenching strategy. The complex consists of two direct Z-scheme heterojunctions of g-C3N4 and two photoactive materials CoTiO3 and Bi2O3. This great structure could augment the migration of photogenerated electrons obviously, which boost the photocurrent greatly and prefer the photoelectric application of perovskite oxide. To improve sensitivity, the nanoflower like MnO2 with oxidation performance is introduced into the system and used as a label fixed on secondary antibody to oxidize electron donor (AA) to achieve an enlarged signal quenching value. Interestingly, MnO2 also showed an effective oxidation activity for TMB oxidation, leading to a chromogenic reaction. With the change of antigen concentration, the color of the test electrolyte also changes. Herein, the designed smart photoelectrochemical sensor shows a wide detection range (neuron specific enolase as an example) from 0.00005 to 200 ng/mL with a detection limit as low as 28 fg/mL. And the colorimetric assay for target detection owns a liner range from 0.1 to 20 ng/mL accompany with a detection limit of 0.05 ng/mL. These two designed sensing modes offer a new strategy for signal amplification of perovskite oxide and the possibility of real-time detection.

Mechanism of photocatalytic water splitting of 2D WSeTe/XS2 (X = Hf, Sn, Zr) van der Waals heterojunctions under the interaction of vertical intrinsic electric and built-in electric field

Finding photocatalytic materials with high hydrogen production efficiency is an effective way to solve the problem of the energy crisis. We use density functional theory (DFT) to predict the 2D WSeTe/XS2 (X = Hf, Sn, Zr) van der Waals (vdW) heterojunctions as the potential direct Z-scheme heterojunction photocatalysts and discuss the mechanism of photocatalytic water splitting under the interaction of vertical intrinsic electric field and built-in electric field. The WSeTe/XS2 heterojunctions have large band-edge staggered alignment, small interlayer bandgap, and good interlayer carrier recombination, which predict the direct Z-scheme charge transfer path formation. Meanwhile, the small bandgap of the 2D WSeTe/XS2 direct Z-scheme heterojunctions enables it to obtain a wide light absorption range. The built-in electric field from WSeTe to XS2 changes the charge transfer mode of the heterojunction and improves the separation efficiency of photo-generated carriers, and the vertical intrinsic electric field not only improves the hydrogen evolution reaction (HER) ability but also reduces the bandgap limitation of photocatalytic materials. In this paper, the 2D WSeTe/XS2 heterojunctions show significant advantages as photocatalytic materials, providing unique insights for researching and developing this kind of heterojunction.

Z-Scheme Heterojunction of SnS2/Bi2WO6 for Photoreduction of CO2 to 100% Alcohol Products by Promoting the Separation of Photogenerated Charges.

Using sunlight to convert CO2 into solar fuel is an ideal solution to both global warming and the energy crisis. The construction of direct Z-scheme heterojunctions is an effective method to overcome the shortcomings of single-component or conventional heterogeneous photocatalysts for photocatalytic CO2 (carbon dioxide) reduction. In this work, a composite photocatalyst of narrow-gap SnS2 and stable oxide Bi2WO6 were prepared by a simple hydrothermal method. The combination of Bi2WO6 and SnS2 narrows the bandgap, thereby broadening the absorption edge and increasing the absorption intensity of visible light. Photoluminescence, transient photocurrent, and electrochemical impedance showed that the coupling of SnS2 and Bi2WO6 enhanced the efficiency of photogenerated charge separation. The experimental results show that the electron transfer in the Z-scheme heterojunction of SnS2/Bi2WO6 enables the CO2 reduction reactions to take place. The photocatalytic reduction of CO2 is carried out in pure water phase without electron donor, and the products are only methanol and ethanol. By constructing a Z-scheme heterojunction, the photocatalytic activity of the SnS2/Bi2WO6 composite was improved to 3.3 times that of pure SnS2.

Energy band engineering of Bi2O2.33CdS direct Z-scheme heterojunction for enhanced photocatalytic reduction of CO2

In this work, a Bi 2 O 2.33 CdS direct Z-scheme heterojunction was fabricated based on energy band engineering. The Bi 2 O 2.33 core nanoflakes were first synthesized by electrodeposition which was followed by an annealing process to fabricate this heterojunction. Then the CdS shell was deposited on Bi 2 O 2.33 nanoflakes utilizing the solution method, during which a suitable concentration of CdCl 2 solution was used for forming a homogeneous and continuous integrated CdS shell. A space charge region and an internal electric field from CdS (+) to Bi 2 O 2.33 (−), which drove a direct Z-scheme charge transfer process, were formed at the interface. The Bi 2 O 2.33 CdS exhibited excellent photocatalytic performance for CO 2 reduction mainly attributed to the satisfactory photoinduced charge separation and transport efficiency in the direct Z-scheme heterojunction. The photocatalytic CO 2 reduction ability of Bi 2 O 2.33 CdS was significantly enhanced compared with single Bi 2 O 2.33 or CdS, with a CO yield rate of ca. 2.9 μmol/(cm 2 h) under a 300 W Xe lamp. The reduction of CO 2 to CO demonstrated 94.0% selectivity. Bi 2 O 2.33 CdS direct Z-scheme heterojunction with excellent photocatalytic performance for CO 2 reduction was fabricated based on energy band engineering.

Light-assisted room temperature gas sensing performance and mechanism of direct Z-scheme MoS2/SnO2 crystal faceted heterojunctions

Light assistance and construction of heterojunctions are both promising means to improve the room temperature gas sensing performance of MoS2 recently. However, enhancing the separation efficiency of photo-generated carriers at interface and adsorption ability of surface have become the bottleneck problem to further improve the room temperature gas sensing performance of MoS2-based heterojunctions under light assistance. In the present study, a novel direct Z-scheme MoS2/SnO2 heterojunction was designed through crystal facets engineering and its room temperature gas sensing properties under light assistance was studied. It was found that the heterojunction showed outstanding room temperature NO2 sensing performance with a high response of 208.66 toward 10 ppm NO2, together with excellent recovery characteristics and selectivity. The gas sensing mechanism study suggested that high-energy {221} crystal facets of SnO2 and MoS2 directly formed Z-scheme heterojunction, which could greatly improve the separation efficiency of photo-generated carriers with high redox capacity. Moreover, {221} facets greatly enhanced adsorption ability towards NO2. This work not only opens up the application of Z-scheme heterojunctions in gas sensing, which will greatly promotes the development of room temperature light-assisted gas sensors, but also provides a new idea for the construction of direct Z-scheme heterojunctions through crystal facets engineering.

Z-scheme SnC/HfS2 van der Waals heterojunction increases photocatalytic overall water splitting

Designing a direct Z-scheme system is one of the effective ways to develop a high-efficient photocatalyst. In this paper, we designed the SnC/HfS2 heterojunction and explored its electronic structure and photocatalytic properties for water splitting based on first-principles calculations. Our results suggest that SnC/HfS2 heterostructure is a typical direct Z-scheme heterojunction, which can effectively separate carriers and possesses strong oxidation and reduction capabilities. The valence band maximum of SnC is close to the conduction band minimum of HfS2, which is in favor of the recombination of inter-layer carriers. The very small interlayer band gap and appropriate built-in electric field direction make the migration of electrons and holes along the Z-path. The photo-generated electrons on SnC make the hydrogen evolution reaction happen continuously, while the photo-generated holes on HfS2 make the oxygen evolution reaction happen continuously. The calculation of the reaction energy barrier indicates that the procedure of photocatalytic water splitting on the SnC/HfS2 heterojunction can be spontaneous. Our results show that SnC/HfS2 heterojunction is a potential direct Z-scheme photocatalyst for the overall decomposition of water.

Microwave-assisted hydrothermal synthesis of broadband Yb3+/Er3+ co-doped BiOI/Bi2O4 photocatalysts with synergistic effects of upconversion and direct Z-scheme heterojunction

Constructing full spectrum photocatalyst is an effective strategy to improve the conversion efficiency of solar energy. In this work, BiOI:Yb3+,Er3+/Bi2O4 (BYE/BO) direct Z-scheme heterojunction photocatalysts were successfully synthesized by a fast and simple microwave-assisted hydrothermal method. XRD, XPS, FE-SEM, TEM, PL, DRS, and BET were used to investigate the physical and chemical properties of samples. Compared to pure BYE and BO, as-synthesized BYE/BO samples had significantly improved photocatalytic activity in the degradation of Ciprofloxacin and Rhodamine B when exposed to visible or near infrared light (NIR) light. Among them, 20% -BYE/BO has the best photocatalytic activity, and its NIR-light degradation ratio of Ciprofloxacin is as high as 66 and 103 times that of BO and BYE, respectively. The enhanced photoactivity of as-synthesized BYE/BO heterojunction is attributed to synergistic effects of the upconversion and the direct Z heterojunction. Moreover, capture experiment showed that the·O2- and h+ were main active species, and the directive Z-scheme mechanism was proposed.

Direct Z-scheme charge transfer of Bi2WO6/InVO4 interface for efficient photocatalytic CO2 reduction

InVO4 possesses great potential in photocatalytic CO2 conversion. It is still highly desired to develop efficient strategies of photocatalyst fabrication to prevent its attenuated activity caused by the rapid recombination of photogenerated electron-hole. Herein, a direct Z-scheme heterojunction of Bi2WO6/InVO4 nanosheets is constructed via two-step hydrothermal synthesis. The Bi2WO6/InVO4 composite exhibits a superior photocatalytic performance toward CO2 reduction into CO and CH4 under visible light irradiation. The CO evolution rate reaches up to 17.97 μmol g−1 h−1, while the CH4 production rate is 1.13 μmol g−1 h−1, which are higher than those catalyzed by bare InVO4 and bare Bi2WO6. Based on the photoelectrochemical results, hydroxyl radical test, Scanning Kelvin Probe (SKP) and electron spin resonance (ESR) investigation, the enhanced activity of CO2 reduction can be attributed to a Z-scheme electron transfer at the interface to promote spatial charge separation, which effectively preserves the reduction ability of photoelectron on the conduction band of InVO4 for CO2 conversion.

Facile Synthesis with TiO2 Xerogel and Urea Enhanced Aniline Aerofloat Degradation Performance of Direct Z-Scheme Heterojunction TiO2/g-C3N4 Composite.

Different TiO2/g-C3N4 (TCN) composites were synthesized by a simple pyrolysis method with TiO2 xerogel and urea. The structure and physicochemical properties of TCN were characterized by X-ray diffraction, scanning electron microscope, transmission electron microscope, ultraviolet-visible diffuse reflectance spectrum, X-ray photoelectron spectroscopy, N2-adsorption isotherms and electrochemical impedance spectroscopy. Aniline Aerofloat was chosen as a typical degradation-resistant contaminant to investigate the photodegradation activity of TCN under UV irradiation. The results indicated that TCN had higher light absorption intensity, larger specific surface area and smaller particle size compared to pure TiO2. Furthermore, TCN had great recycling photocatalytic stability for the photodegradation of Aniline Aerofloat. The photocatalytic activity depends on the synergistic reaction between holes (h+) and hydroxyl radicals (·OH). Meanwhile, the direct Z-scheme heterojunction structure of TiO2 and g-C3N4 postpones the recombination of h+ and electrons to enhance UV-light photocatalytic activity.

Facilely fabrication of the direct Z-scheme heterojunction of NH2-UiO-66 and CeCO3OH for photocatalytic reduction of CO2 to CO and CH4

NH2-UiO-66 is recently regarded as a potential photocatalyst for CO2 reduction reaction due to the high CO2 adsorption capacity, high UV–vis light absorption capacity and chemical stability. Aiming to further improve its activity, in this paper, a composite of NH2-UiO-66 and CeCO3OH (NU/CC) was fabricated via an in-situ growth method of NH2-UiO-66 on CeCO3OH. The X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and electron spin resonance (ESR) characterizations indicated that a direct Z-scheme heterojunction between CeCO3OH and NH2-UiO-66 was formed via the formation of O-Zr-CO32- bond. The CO2 adsorption measurement, UV–vis DRS spectra and photo(electro)chemical measurements indicated that the optimal composite NU/CC-1.6–90 exhibited the higher CO2 adsorption capacity, stronger respond and wider absorption range to UV–vis light, as well as the significantly delayed recombination of photogenerated electron-hole pairs, compared with other control samples. As a result, NU/CC-1.6–90 delivered the obviously enhanced photocatalytic activity of CO2 to both CO and CH4, and the rate of electron consumption reached 152.8 μmol/g h, 5-fold of that of NH2-UiO-66.

Visible-light-responsive Z-scheme heterojunction MoS2 NTs/CuInS2 QDs photoanode for enhanced photoelectrocatalytic degradation of tetracycline

A direct Z-scheme heterojunction coupling hierarchical nanosheet MoS2 nanotubes with CuInS2 quantum dots was successfully prepared to fabricate MoS2 NTs/CuInS2 QDs photoanodes for enhanced photoelectrocatalytic (PEC) activity. The MoS2 NTs with stacked nanosheets and tubular structure have high surface area and abundant basal edges, which can create more active reaction sites. Simultaneously, the continuous and broad photo-absorption range of MoS2 NTs improved the utilization of visible-light and increased the separation efficiency of photo-induced electron-hole pairs. The integration of MoS2 NTs with CuInS2 QDs onto Cu foil yielded direct Z-scheme heterojunction photoanode. The formation of Z-scheme heterojunction inhibited the recombination of photo-induced electron-hole pairs and produced more active electrons and holes to facilitate the generation of highly active species. Under visible light illumination, the prepared MoS2 NTs/CuInS2 QDs photoanode showed superior PEC activity by applying a suitable bias voltage. In PEC process, the generated holes, hydroxyl radicals and superoxide radicals with strong oxidative were employed to achieve highly efficient degradation of tetracycline. The prepared photoanode exhibited high stability, reusability, and broad application potential in PEC degradation of organic pollutants. Moreover, a possible mechanism of the transfer pathway of photo-induced electron-hole pairs on the MoS2 NTs/CuInS2 QDs photoanode was proposed based on a direct Z-scheme heterojunction.

Unique multi-hierarchical Z-scheme heterojunction of branching SnIn4S8 nanosheets on ZnIn2S4 nanopetals for boosted photocatalytic performance

Multinary metal sulfides are receiving more and more attention in the field of photocatalysis due to their excellent photoelectronic properties, but they usually suffer from the low photogenerated carrier separation efficiency and poor photostability. In this work, a dual multinary metal sulfides composite system is developed to address these issues. A unique multi-hierarchical Z-scheme heterojunction is successfully constructed by in-situ growth of branched SnIn4S8 nanosheets on nanopetals of flower-like ZnIn2S4. The prepared optimal composite photocatalyst displays significantly enhanced visible-light photocatalytic activity with H2 evolution rate of 2.988 mmol g−1h−1, Cr(VI) reduction rate constant of 0.094 min−1 and dye degradation rate constant of 0.152 min−1, which are 4.5, 9.4 and 19 times of bare SnIn4S8, and 2.9, 4.3 and 3.5 times of bare ZnIn2S4, respectively. The improved photocatalytic performance is primarily attributed to the abundant porous channels of the novel hierarchical flower-shaped architecture and the formation of the direct Z-scheme heterojunction, guaranteeing the richer active sites, better light harvesting, stronger redox capability, and more efficient charge transfer. This work demonstrates the promising applications of the SnIn4S8/ZnIn2S4 hybrid in energy and environmental photocatalysis fields, and should be instructive for the design and modification of multinary sulfide photocatalysts.

Direct Z-scheme MoSe2/TiO2 heterostructure with improved piezoelectric and piezo-photocatalytic performance

Nano-semiconductor materials coupled with piezoelectric effect have received extensive attention due to their wide application in catalysis. In this work, few-layered MoSe2 nanosheets were grown vertically on TiO2 nanorods (TNr) to synthesize a direct Z-scheme heterojunction, exhibiting efficient piezocatalytic and piezo-photocatalytic performance. The MoSe2/TNr heterostructure exhibited superior piezoelectric degradation efficiency, successfully removing over 98% of RhB within 360 s under continuous magnetic stirring in dark. Compared with piezocatalysis, the piezo-photocatalytic system possessed higher degradation efficiency and cycle stability. Furthermore, a piezo-photoelectric synergistic effect of nanocomposites was observed by current outputs. Under stirring conditions, the current density of depleted MoSe2/TNr and MoSe2 nanosheets were respectively 6.3 μA/cm2 and 5.5 μA/cm2. When light and stirring were applied, the MoSe2/TNr current density increased twice to 13.2 μA/cm2, while the MoSe2 nanosheets didn’t exhibit improvement. Through the direct Z-scheme heterojunction of MoSe2/TNr, photoexcitation and piezoelectric polarization work together to effectively replenish carriers under light irradiation, and then rapidly separate free charges through piezopotential. This work broadens the application prospects of piezocatalysis and piezo-photocatalysis in renewable energy harvesting and water purification.