Hierarchical Z-scheme Research Articles

Attapulgite-intercalated g-C3N4/ZnIn2S4 3D hierarchical Z-scheme heterojunction for boosting photocatalytic hydrogen production

Construction of hierarchical architecture with suitable band alignment for graphitic carbon nitride (g-C3N4) played a pivotal role in enhancing the efficiency of photocatalysts. In this study, a novel attapulgite-intercalated g-C3N4/ZnIn2S4 nanocomposite material (ZIS/CN/ATP, abbreviated as ZCA) was successfully synthesized using the freeze-drying technique, thermal polymerization, and a simple low-temperature hydrothermal method. Attapulgite (ATP) was intercalated into g-C3N4 to effectively regulate its interlayer structure. The results reveal a substantial enlargement of its internal space, thereby facilitating the provision of additional active sites for improved dispersibility of ZnIn2S4. Notably, the optimized photocatalyst, comprising a mass ratio of ATP, g-C3N4, and ZnIn2S4 at 1:1:2.5 respectively, achieves an outstanding hydrogen evolution rate of 3906.15 μmol g−1h−1, without the need for a Pt co-catalyst. This rate surpasses that of pristine g-C3N4 by a factor of 475 and ZnIn2S4 by a factor of 5, representing a significant improvement in performance. This significant enhancement can be primarily attributed to the higher specific surface area, richer active sites, broadened light response range, and efficient interfacial charge transfer channels of the ZCA composite photocatalyst. Furthermore, the Z-scheme photocatalytic mechanism for the sandwich-like layered structure heterojunction was thoroughly investigated using diverse characterization techniques. This work offers new insights for enhancing photocatalytic performance through the expanded utilization of natural minerals, paving the way for future advancements in this field.

Synthesis and characterization of a novel MnO2@MXene-based 2D/3D hierarchical Z-scheme for sustainable environmental applications

A wet chemical synthesis of a novel 2D/3D hierarchical Z-scheme that utilizes manganese oxide decorated 2D Ti3C2 MXene (MnO2@MXene), which is designed for effective utilization in environmentally sustainable applications, is presented in this study. The synergistic role of 20 nm thick MnO2 nanopetals (NPTs) and MXene sheets, which inhibited the electron/hole pair recombination and improved the surface activity, enhanced the catalytic properties of the material. This was facilitated by the unique 3D/2D structural characteristics of MnO2 NPTs and MXene. The MnO2 nanopetals NPTs integrated the MXene-based photocatalyst, which was synthesized using the ultrasonication approach, removed ∼99 % of the methylene blue dye (MB) and 75 % of the phenol within 30 min. The antibacterial test of the as-prepared MnO2@MXene simultaneously confirmed its admirable antibacterial efficacy. The recyclability test verified that the synthesized material can be recycled multiple times without a significant loss, which was only a 3 % loss in this case, in photocatalytic activity. The results imply that MnO2@MXene has significant promise as an eco-friendly material that is suitable for utilization in photocatalytic and antibacterial applications.

Preparation of direct Z-scheme hierarchical MoS2/MnO2 composite for efficient adsorption and wide spectrum photocatalytic degradation of organic pollutants in water

Developing semiconductor-based heterogeneous photocatalysts with high adsorption performance and wide light response range is a significant technology for removing organic pollutants from water. Herein, a novel hierarchical dendritic-like direct Z-scheme MoS2/MnO2 composite with MoS2 hollow tubular decorated by MnO2 nanosheets was successfully fabricated by vacuum freeze-drying. When the mass ratio of MoS2/MnO2 is 3:1, the highest adsorption-photocatalytic removal rate of 94.5% and 95.1% in 120 min for RhB was attained under visible (Vis) and ultraviolet (UV) light irradiation, respectively. After three repeated uses, the removal rate of RhB still reached 91.1%. The enhanced adsorption-photocatalytic performance of the composite can be well illustrated according to the hierarchical composite structure, production of •OH, •O2− and h+ active species, oxygen-doping in the MoS2 and the direct Z-scheme photocatalytic mechanism. This work gives a good strategy to frame hierarchical Z-scheme photocatalysts for efficient adsorption and wide-spectrum photocatalytic removal of organic pollutants from water.

Boosted Light-Excited NO2 Detection Based on Hierarchical Z-Scheme MoS2/SnO2 Heterostructure Microspheres at Room Temperature

Light excitation has been developed as an economical way to realize room-temperature gas sensing recently. However, the high recombination rate of photogenerated carriers in semiconductor gas sensing materials leads to very limited carriers that can effectively take part in sensing reactions, which greatly restricts the further performance improvement of gas sensing under light excitation. Here, a hierarchical Z-scheme heterostructure microsphere of MoS2/SnO2 is designed and prepared. The heterostructure demonstrates an outstanding NO2 sensing performance at room temperature with the excitation of a low-power LED light (0.06 W), which exhibits an ultrahigh sensitivity of 264.2 to 10 ppm of NO2 along with acceptable response/recovery properties. The physical mechanism of NO2 sensing is analyzed. The results suggest that the construction of the Z-scheme heterostructure between MoS2 and SnO2 can greatly promote the separation of photogenerated carriers so that more photogenerated carriers can take part in the NO2 sensing reaction. Furthermore, the designing of a hierarchically porous structure can provide abundant active sites for gas sensing reactions. The work not only expands the development of Z-scheme heterostructures in gas sensing but also provides a strategy to promote the performance of light-excited gas sensors by designing a Z-scheme heterostructure with a hierarchically porous structure.

Interfacial chemical bond modulated Z-scheme mechanism in In2−xS3/Cd1+xIn2−xS4 heterojunction for enhanced photocatalytic CO2 reduction and wastewater treatment

An interfacial CdS bond modulated hierarchical Z-scheme heterostructure composed by indium vacancies-rich In2-xS3 and Cd-rich Cd1+xIn2-xS4 (In2-xS3/Cd1+xIn2-xS4) is rationally designed and fabricated by using MIL-68 (In) as precursor and template, and used for efficient photocatalytic wastewater treatment and CO2 reduction. The in-situ ion-exchange derived CdS bond at the heterointerface induced the Z-scheme charge transfer mechanism in hierarchical In2-xS3/Cd1+xIn2-xS4 photocatalyst, which is verified by the X-ray photoelectron spectroscopy, electron paramagnetic resonance and density functional theory calculations. Moreover, the hierarchical ultrathin and loose two-dimensional nanosheet structure is conducive to expose more active sites and adsorb more reactants. By integrating the efficient adsorption capacity and Z-scheme mechanism, the In2-xS3/Cd1+xIn2-xS4 photocatalyst shows superior photocatalytic CO2 reduction activity and high removal efficiency of dyes and heavy metal. For example, under visible light illumination, it removed almost 100 % of various dyes within 10 min operation, and reduced 100 % Cr(VI) within 1 h, and it also manifested state-of-the-art production rates of 132.5 and 392.1 μmol h−1 g−1 for CH4 and CO, respectively, in reducing CO2 without co-catalyst. A useful inspiration on purposive modulating Z-scheme charge transfer by atomic-level interface engineering was proposed to significantly promote the photocatalytic performance.

MnIn2S4 nanosheets growing on rods-like β-MnO2 via covalent bonds as high-performance photocatalyst for boosting Cr(VI) photocatalytic reduction under visible light irradiation: Behavior and mechanism study

It is an urgent and onerous task to develop catalysts for photocatalytic reduction of Cr(VI) in wastewater under wide pH range. In this work, a novel hierarchical Z-scheme MnO2/MnIn2S4 (MISO) heterojunction photocatalyst with MnIn2S4 nanosheets growing on the surface of β-MnO2 nanorods is constructed for efficient photocatalytic reduction of Cr(VI). The optimized 2.0-MISO photocatalyst exhibits the almost 100% reduction efficiency in the pH range of 2.1–5.6 under visible light irradiation, and the apparent rate constant is 0.05814 min−1, which is 29.96 and 3.27 times higher than the pure β-MnO2 and MnIn2S4, respectively. A efficient photocatalytic reduction of Cr(VI) to Cr(III) species on 2.0-MISO photocatalyst in actual industry wastewater (286.7 mg/L) up to 99.8% is achieved. Under natural light, the 2.0-MISO photocatalyst also shows rapid reduction of Cr(VI) species. The photocorrosion of MnIn2S4 was significantly hindered by the construction of heterojunction. And the O2− and e− species are the main active species during the Cr(VI) photoreduction process. The connection mode between MnIn2S4 and β-MnO2 is verified by DFT calculations and a possible photocatalytic mechanism is also proposed.

Ultrathin Two-Dimensional BiOCl with Oxygen Vacancies Anchored in Three-Dimensional Porous g-C3N4 to Construct a Hierarchical Z-Scheme Heterojunction for the Photocatalytic Degradation of NO

Ultrathin Two-Dimensional BiOCl with Oxygen Vacancies Anchored in Three-Dimensional Porous g-C₃N₄ to Construct a Hierarchical Z-Scheme Heterojunction for the Photocatalytic Degradation of NO

Piezotronic effect and hierarchical Z-scheme heterostructure stimulated photocatalytic H2 evolution integrated with C-N coupling of benzylamine

Photocatalytic hydrogen generation represents a potential approach to address global energy and environmental issues for artificial photosynthesis. Generally, the inevitable use of the holes scavengers leads to increased cost and production of waste. The integration of H2-producing half-reaction with value-added organic molecule oxidation reaction provides a promising strategy to cope with this issue. However, owing to the low separation efficiency of photo-generated charge carriers and sluggish kinetics of the surface reaction, the photocatalytic activity without a co-catalyst is unsatisfying. Herein, the hierarchical and piezoelectric Z-scheme BaTiO3@ZnIn2S4 heterostructure without any co-catalyst were dexterously constructed. The Z-scheme electron transfer paths maintain the strong redox ability of the photo-generated electrons and holes, also offer spatial separation of both charge carriers and the surface redox regions. The well-designed redox regions endow BaTiO3@ZnIn2S4 with the lowest energy barriers of hydrogen production and C-N coupling of benzylamine than that of pure BaTiO3 or ZnIn2S4. Significantly, piezotronic effect can further accelerate the separation and transfer of photo-generated charge carriers in Z-scheme BaTiO3@ZnIn2S4 heterostructure. Thus, by the feat of the multiple advantages of the piezotronic effect and Z-scheme heterostructure, the high photocatalytic activity for the co-production of C-N coupling products (5593 umol g−1) and H2 (8041 umol g−1) was achieved through coupling utilization of mechanical energy and solar energy.

Construction of magnetically separable hierarchical Z-scheme NiFe2O4@Bi2Sn2O7 heterojunction with enhanced visible-light photocatalytic activity

Construction of magnetically separable hierarchical Z-scheme NiFe2O4@Bi2Sn2O7 heterojunction with enhanced visible-light photocatalytic activity

Hierarchical Z-scheme Bi2S3/CdS heterojunction: Controllable morphology and excellent photocatalytic antibacterial

The hierarchical nanostructure can significantly increase photocatalytic centers and enhance light harvesting. In this study, a series of hierarchical Z-scheme Bi2S3/CdS heterojunctions with solvent-dependent morphologies are synthesized by a solvothermal method. The Bi2S3/CdS nanostructures synthesized in ethylene glycol (BC-EG) and N, N-dimethylformamide (BC-DMF) are assembled by Bi2S3 nanowires and CdS nanoparticles. Notably, the photocatalytic efficiency of BC-DMF for the antibacterial of E.coli and S.aureus is 100.00 % and 93.85%, respectively. The improvement of photocatalytic activity by BC-DMF is mainly ascribed to the increased photocatalytic active centers, enhanced photo-induced carriers separation and transfer between Bi2S3 and CdS as a Z-scheme heterojunction and the relatively suitable Bi2S3/CdS ratio. This study can provide an insight into constructing Z-scheme hierarchical photocatalysts for antibacterial.

Spatially Separating Redox Centers on Z-Scheme ZnIn2 S4 /BiVO4 Hierarchical Heterostructure for Highly Efficient Photocatalytic Hydrogen Evolution.

Photocatalysis technology using solar energy for hydrogen (H2 ) production still faces great challenges to design and synthesize highly efficient photocatalysts, which should realize the precise regulation of reactive sites, rapid migration of photoinduced carriers and strong visible light harvest. Here, a facile hierarchical Z-scheme system with ZnIn2 S4 /BiVO4 heterojunction is proposed, which can precisely regulate redox centers at the ZnIn2 S4 /BiVO4 hetero-interface by accelerating the separation and migration of photoinduced charges, and then enhance the oxidation and reduction ability of holes and electrons, respectively. Therefore, the ZnIn2 S4 /BiVO4 heterojunction exhibits excellent photocatalytic performance with a much higher H2 -evolution rate of 5.944 mmol g-1 h-1 , which is about five times higher than that of pure ZnIn2 S4 . Moreover, this heterojunction shows good stability and recycle ability, providing a promising photocatalyst for efficient H2 production and a new strategy for the manufacture of remarkable photocatalytic materials.

All solid-state Z‑scheme CeO2/ZnIn2S4 hybrid for the photocatalytic selective oxidation of aromatic alcohols coupled with hydrogen evolution

The solar-driven transformation of alcohols into hydrogen and value-added products is a promising strategy for the green synthesis of fuels and fine chemicals. However, achieving these reactions via photocatalysts with efficient photo-adsorption and charge‑separation is challenging. Herein, a novel all-solid-state Z‑scheme catalyst was constructed. In this system, ZnIn2S4 nanosheets were grown in situ on the surfaces of CeO2 nanorods. Such 2D/1D composites showing intimate contact can form solid Z-scheme heterostructures that combine the excellent visible-light absorption of ZnIn2S4 nanosheets, and the fast charge transport of CeO2 nanorods, while retaining the strong reducibility of electrons in the CB of ZnIn2S4 nanosheets and the oxidizability of holes in the VB of CeO2 nanorods. These synergistic advantages enhanced the photocatalytic performance, and the benzaldehyde and hydrogen yields reached 664.1 and 1496.6 μmol gcat−1. h−1 respectively. Moreover, a high benzaldehyde selectivity was achieved. These findings provide new opportunities for application of hierarchical Z-scheme metal-oxide-based photocatalysts.

Visible-light-induced water splitting on a hierarchically constructed Z-scheme photocatalyst composed of zinc rhodium oxide and bismuth vanadate

A hierarchical Z-scheme photocatalyst composed of BiVO4, ZnRh2O4, and Au was synthesized for visible-light-induced water splitting.

Surprise in the phosphate modification of BiOCl with oxygen vacancy: In situ construction of hierarchical Z-scheme BiOCl-OV-BiPO4 photocatalyst for the degradation of carbamazepine

Phosphate modification is a general strategy for improving the photocatalytic activities of semiconductors. Ion exchange can be occurred during the phosphate modification process. This would give a surprise for a new phase formed on the surface of the parent photocatalyst. More importantly, this is conductive to form close contact and continuous interface favoring the charge transfer between two phases. Here, a novel BiOCl-OV-BiPO4 photocatalyst was fabricated using a facile in situ phosphate modification method. BiOCl-OV-BiPO4 displayed a maximum carbamazepine (CBZ) degradation efficiency of 81.70% after 30 min Xe lamp irradiation, with a reaction kinetics rate constant (k) of 5.75 times higher than ordinary BiOCl samples. Oxygen vacancy (OV) is important for the construction of Z-scheme BiOCl-OV-BiPO4: OV benefits the generation of BiPO4 on the surface of BiOCl; furthermore, OV acting as electron mediator, promotes the separation of photogenerated charge carriers between BiOCl and BiPO4. Based on the results from PL tests, photocurrent density, EIS Nyquist plots, and cyclic voltammetry, it can be demonstrated that Z-scheme structure of BiOCl-OV-BiPO4 not only increases the photogenerated electrons-holes separation rate but also retains their strong redox ability. This significantly facilitates the production of superoxide radical (O2−) and holes (h+), which dominates the CBZ photodegradation. This work provides a new sight for the fabrication of Z-scheme photocatalysts to improve the photocatalytic performance.

Fabrication of multiple hierarchical heterojunction Ag@AgBr/BiPO4/r-GO with enhanced visible-light-driven photocatalytic activities towards dye degradation

Novel hierarchical Z-scheme photocatalyst Ag@AgBr/BiPO4/r-GO was synthesized by in situ deposition of AgBr onto the surface of BiPO4/r-GO precursor and followed by photo-reduction of AgBr into Ag@AgBr. The as-synthesized photocatalyst was characterized with X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), energy dispersive spectrometry (EDS), UV–vis diffuse reflectance spectroscopy (DRS) and infrared spectroscopy (IR). The photocatalytic activity of the Ag@AgBr/BiPO4/r-GO was evaluated by degrading reactive blue 19 (RB-19) under visible-light irradiation. The results showed that Ag@AgBr/BiPO4/r-GO composite exhibited much better photocatalytic performance than BiPO4 and Ag@AgBr/BiPO4 due to the efficient visible-light utilization. The construction of Z-scheme kept the photo-generated electrons and holes having high reduction and oxidation capabilities. Ag nanoparticles and r-GO acted as the electron mediators to form the charge transmission bridge for the AgBr/BiPO4 heterojunction, promoting the efficient separation of photo-induced electron-hole pairs and inhibiting the electron-hole recombination. Finally, a possible photocatalytic mechanism for the degradation of RB-19 by Ag@AgBr/BiPO4/r-GO was proposed based on the free radical and hole scavenging experiments.

A Hierarchical Z-Scheme α-Fe2 O3 /g-C3 N4 Hybrid for Enhanced Photocatalytic CO2 Reduction.

The challenge in the artificial photosynthesis of fossil resources from CO2 by utilizing solar energy is to achieve stable photocatalysts with effective CO2 adsorption capacity and high charge-separation efficiency. A hierarchical direct Z-scheme system consisting of urchin-like hematite and carbon nitride provides an enhanced photocatalytic activity of reduction of CO2 to CO, yielding a CO evolution rate of 27.2 µmol g-1 h-1 without cocatalyst and sacrifice reagent, which is >2.2 times higher than that produced by g-C3 N4 alone (10.3 µmol g-1 h-1 ). The enhanced photocatalytic activity of the Z-scheme hybrid material can be ascribed to its unique characteristics to accelerate the reduction process, including: (i) 3D hierarchical structure of urchin-like hematite and preferable basic sites which promotes the CO2 adsorption, and (ii) the unique Z-scheme feature efficiently promotes the separation of the electron-hole pairs and enhances the reducibility of electrons in the conduction band of the g-C3 N4 . The origin of such an obvious advantage of the hierarchical Z-scheme is not only explained based on the experimental data but also investigated by modeling CO2 adsorption and CO adsorption on the three different atomic-scale surfaces via density functional theory calculation. The study creates new opportunities for hierarchical hematite and other metal-oxide-based Z-scheme system for solar fuel generation.

Hierarchical Z-scheme photocatalyst of g-C3N4@Ag/BiVO4 (040) with enhanced visible-light-induced photocatalytic oxidation performance

The preferred exposure of (040) crystal facet of BiVO4 is conductive to optimizing its photocatalytic performance. And the great separation of photoinduced electron-hole pairs is also a critical factor for semiconductor photocatalyst. Herein we designed a hierarchical g-C3N4@Ag/BiVO4 (040) hybrid photocatalyst, in which Ag was photodeposited on the (040) facets of BiVO4 and subsequently g-C3N4 was covered on the surface of Ag/BiVO4 (040). The physical and chemical properties of the synthetic samples were analyzed by several characterization techniques. SEM spectrum clearly reveals the morphology and structure of g-C3N4@Ag/BiVO4 (040), suggesting the existence of the hierarchical composite photocatalyst. The visible light absorption wavelength of the composite is increased due to the surface plasmon resonance (SPR) effect of metal Ag nanoparticles, displayed in UV–vis spectrum. The photogenerated electron-hole pairs are also greatly enhanced through the Z-scheme g-C3N4@Ag/BiVO4 (040) system with the Ag nanoparticles as the electron mediator. The above synergistic effects of the hybrid photocatalyst result in higher photocatalytic oxidation performance not only for water splitting but also for NO oxidation in gas phase compared with pure BiVO4.

Improved photoelectrochemical performance of Z-scheme g-C3N4/Bi2O3/BiPO4 heterostructure and degradation property

In g-C3N4/Bi2O3/BiPO4, the p–n junction between p-type Bi2O3 and n-type BiPO4 was encapsulated by g-C3N4 and a direct Z-scheme was built between g-C3N4 and Bi2O3. The optical, morphological and photoelectrochemical (PEC) properties of BiPO4, g-C3N4/BiPO4, Bi2O3/BiPO4 and g-C3N4/Bi2O3/BiPO4 hierarchical Z-scheme system were studied. More than 90% photodegradation of methyl orange (MO) with the exposure of simulated solar light was achieved within 160min with the g-C3N4/Bi2O3/BiPO4, which displayed remarkably promoted photocatalytic activities than other samples. The electrochemical impedance spectra and photocurrent results also proved that efficient charge separation and better electron transport properties were achieved by g-C3N4/Bi2O3/BiPO4. In general, the addition of g-C3N4 can guide the residual electrons on p-type Bi2O3 to recombine with photoholes of g-C3N4 and make sure the left carries exhibit stronger oxidation and reduction ability to boost the production of active groups.

Photoelectrochemical performance of g-C3N4/Au/BiPO4Z-scheme composites to improve the mineralization property under solar light

g-C3N4/Au/BiPO4as a hierarchical Z-scheme system was prepared through three steps at different reaction temperatures, using thiourea as a precursor to synthesize g-C3N4.

Fabrication of Z-scheme photocatalyst Ag–AgBr@Bi20TiO32 and its visible-light photocatalytic activity for the degradation of isoproturon herbicide

A novel hierarchical Z-scheme photocatalyst Ag–AgBr@Bi20TiO32 was synthesized by in situ deposition of AgBr onto the surface of mesoporous metastable Bi20TiO32 template and followed by photoreduction of AgBr to Ag–AgBr. The as-synthesized photocatalyst was characterized by X-ray diffraction spectra (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N2 adsorption–desorption analysis and UV–vis diffuse reflectance spectra (UV–vis DRS). The photocatalytic activity of Ag–AgBr@Bi20TiO32 was evaluated by the degradation of isoproturon herbicide under visible-light irradiation. Results showed that Ag–AgBr@Bi20TiO32 photocatalyst exhibited much better photocatalytic activity than Ag–AgBr, or Bi20TiO32, or the physical mixture of AgBr and Bi20TiO32, due to its efficient visible-light utilization and the construction of Z-scheme keeping photo-generated electrons and holes with high reduction and oxidation capability. A possible catalytic mechanism for Ag–AgBr@Bi20TiO32 photocatalyst was put forward based on band gap structure of AgBr and Bi20TiO32 and free radical and hole scavenging experiments. The degradation pathway of isoproturon herbicide was also proposed according to the intermediates identified in the reaction system.