Efficient Z-scheme Photocatalysts Research Articles

A highly efficient bifunctional Z-scheme photocatalyst with spatially-separated and synergistically-enhanced adsorption and photodegradation

Adsorption-enhanced photodegradation and its unique kinetics are studied in a bifunctional Z-scheme photocatalyst. MoS2 nanoflakes are selectively deposited on the edges of TiO2 nanosheets to form an edge-connected MoS2/Au/TiO2 Z-scheme heterostructured photocatalyst, with rapid pollutant adsorption on MoS2 surfaces and subsequent degradation on TiO2 surfaces. The spatial separation of two components promotes the formation of Z-scheme charge transfer and maintains the effective bifunctions. As a result, the optimal system (10 %MoS2/Au/TiO2) could remove up to 90 % of pollutant within 30 mins and subsequently eliminates the residue to a level below ppm. Detailed study on the synergistic effects of adsorption and photodegradation indicates that the system exhibits an adsorption-enhanced photodegradation due to the pre-concentration effect by MoS2 and a surface-diffusion mechanism of pollutant molecules migrating from MoS2 to TiO2. This work provides a novel strategy in designing the bifunctional photocatalyst for effective water treatment.

Facile construction of a novel dual Z-scheme mixed phases BiFeO3 heterojunction: For peroxymonosulfate activation toward efficient photodegradation of 4-nitrophenol and mechanistic insights

This study proposes a novel approach for preparing bismuth ferrite (BiFeO3, BFO) with controlled crystal phase purity and morphology via a one-pot hydrothermal process using specific mineralizers (NaOH or KOH). The effects of these mineralizers on the crystal purity and photocatalytic efficiency of the catalyst were investigated. The XRD results revealed that KOH produced pure BFO, whereas NaOH yielded mixed-phase BFO (m-BFO) with secondary phases, including Bi2O3 and Bi2Fe4O9. SEM analysis revealed that m-BFO exhibited a flake-like structure assembled into cubes, whereas pure BFO consisted of irregularly shaped agglomerated nanoparticles. The photocatalytic efficiency of the two catalysts was evaluated for the degradation of 4-nitrophenol (4-NP). The results showed that m-BFO exhibited outstanding photocatalytic degradation performance (92%) for 4-NP compared with pure BFO (22%). The enhanced photocatalytic efficiency of m-BFO was attributed to the construction of a dual-heterojunction Z-scheme within its structure and the presence of abundant surface oxygen vacancies. This study provides valuable insights into the synthesis of efficient dual-heterojunction Z-scheme photocatalysts via one-pot hydrothermal synthesis.

Direct Z-scheme ZrS2/InP heterostructure as an efficient photocatalyst for overall water-splitting under acidic, alkaline and neutral environments

Photocatalytic water-splitting for hydrogen production by building heterostructure is an efficient approach to resolve the current environmental pollution problem. Here, the ZrS2/InP heterostructure with a direct Z-scheme have been constructed, and the first-principles calculations with Heyd-Scuseria-Ernzerhof (HSE06) hybrid function and density functional dispersion correction (DFT-D3) have been used to study their structural stabilities, electronic properties, photocatalytic mechanisms and optical features. The findings reveal that the ZrS2/InP heterostructure is a direct bandgap semiconductor having a type-II energy band alignment, where electrons mobilize from InP to ZrS2 monolayer at the interface of the heterostructure, leading to the creation of a build-in electric field pointing from InP to ZrS2. The ZrS2/InP heterostructure is competent for photocatalytic water-splitting owing to its advantageous band edge positions. In addition, the ZrS2/InP heterostructure possesses superior visible light absorption properties than the two monolayers structures, with a solar-to-hydrogen (STH) efficiency of 7.11 % and useable in acidic, alkaline and neutral environments. These excellent properties enable ZrS2/InP heterostructure to be an efficient photocatalyst for overall water-splitting. This effort not only proves the possibility of applying heterostructure in photocatalytic water-splitting but also has important implications for designing efficient direct Z-scheme photocatalysts.

Zinc indium sulfide coupling with graphitic carbon nitride containing non-intrinsic oxygen vacancies to form Z-scheme heterojunction for boosting photodegradation of tetracycline

A novel graphitic carbon nitride containing non-intrinsic oxygen vacancies (Vo-CN) is interfacial coupling with zinc indium sulfide (ZIS) to form Z-scheme heterojunction (VCZ) for efficient tetracycline (TC) degradation. The TC removal rate by VCZ-1 (mass ratio of Vo-CN: ZIS is 1:20, 0.2 g/L) achieves 99.86 %. VCZ-1 reveals outstanding reusability and stability with an unchanged TC degradation rate after undergoing five cycles. VCZ-1 achieves high-efficiency TC degradation in various water matrices. The experimental and DFT calculations indicate that the built-in electric field drives charges on Vo-CN transfer to ZIS, forming a Z-scheme VCZ-1 heterojunction. The strong electronic coupling effect between Vo-CN and ZIS facilitates charge exchange at the heterojunction interface. Non-intrinsic oxygen vacancies in VCZ, as binding sites for electrons and holes, effectively lower the energy barrier for singlet excitons converting to triplet excitons. The triplet excitons are induced to transfer energies to dissolved oxygen and expedite 1O2 production. 1O2 synergizes with •O2– and •OH to attack O-containing groups and hexatomic rings in TC, inducing demethylation, hydroxylation, dihydroxylation, and ring-opening reactions. Three possible degradation pathways are inferred by UPLC/MS/MS and Fukui index of TC. The ecotoxicity evaluation of intermediate products highlights the benefits of VCZ-1 photocatalytic oxidation in ensuring environmental safety. This work proposes a novel idea for constructing efficient Z-scheme photocatalysts for environmental remediation.

Constructed black phosphorus quantum dots/BiVO4 Z-scheme heterojunction catalysis for efficient Rhodamine b degradation and DFT study

Black phosphorus (BP) is highly regarded in photocatalysis for its bandgap thickness dependency, high hole mobility, and broad visible light absorption. This study introduces a simple hydrothermal method to construct a BP QDs/BiVO4 direct Z-scheme heterojunction. The composite’s crystal structure, morphology, and photochemical properties were comprehensively characterized. The photocatalytic activity was evaluated using Rhodamine B (RhB) degradation under visible light. Notably, BP QDs0.12%/BiVO4 exhibited exceptional performance, achieving a 95.4 % RhB degradation after 100 min, three times higher than BiVO4 alone. The direct Z-scheme heterojunction played a pivotal role in facilitating O2− and h+ involvement in the degradation process. The interfacial interaction between BP QDs and BiVO4 significantly enhanced BiVO4′s visible light absorption, preserving its strong oxidation–reduction capacity. This enhancement was further corroborated by DFT simulation calculations. Overall, this study presents a novel approach for constructing efficient Z-scheme photocatalysts based on BP QDs, laying a solid foundation for their application in the field of photocatalytic degradation.

A novel MXene-bridged Z-scheme ZnO@Nb2CTx MXene@carbon nitride nanosheets photocatalyst for efficient enrofloxacin degradation

A Z-scheme photocatalyst, ZnO@Nb2CTx MXene@carbon nitride nanosheets (ZNC), is synthesized by the hydrothermal and electrostatic self-assembly strategy. The degradation test shows that ZNC photocatalyst has an enhanced photocatalytic efficiency of Enrofloxacin (ENR) degradation under visible light irradiation. The ENR removing rate has reached 98.2 % after 40 min light irradiation and has a degradation rate of 0.0961 min−1, which is 4.78 times higher than pure ZnO and 3.987 times higher than CNNS. Besides, a possible ENR degradation pathway was studied via LC-MS method. Furthermore, in-situ high resolution XPS spectroscopy and DFT calculation confirmed the direction of electron flow in the ZNC photocatalyst, highlighting that its improved degradation efficiency primarily stems from the introduction of the MXene electron transport layer, which promotes efficient charge transfer and separation of electron-hole pair. This study provides a guidance to design highly efficient Z-scheme photocatalyst for ENR degradation.

Janus PtSSe-based van der Waals heterostructures for direct Z-scheme photocatalytic water splitting

The semiconductor photocatalysts based on van der Waals heterostructures (vdWHs) and direct Z-scheme mechanism are viable candidates for water splitting using sunlight. In this study, we exploit the combined effects of the inherent dipole in a Janus PtSSe monolayer and the intrinsic electric field present at the interface of Janus PtSSe-based vdWHs for water splitting. These vdWHs exhibit type-II band edge position, narrow band gap and intrinsic electric fields, establishing them as prototypical direct Z-scheme systems. Remarkably, the density functional theory-based results find the potential drop of ∼0.2–3.2 eV across the interface of vdWHs, promoting the interlayer photogenerated carrier's recombination while suppressing the intralayer charge transfer, which leads to a direct Z-scheme charge transfer pathway with robust redox capabilities. In conjunction with redox reactions, the built-in electric field at the interface generates sufficient driving force for the photogenerated carrier's separation. Also, these Janus PtSSe-based vdWHs possess exceptional abilities in capturing visible light with high solar-to-hydrogen (STH) conversion efficiency. The results obtained from this study are important to designing efficient direct Z-scheme photocatalysts for splitting water under sunlight and offer valuable insights for potential commercial implementations.

Visible-Light Photocatalytic Overall Water Splitting on a B4C3/CxNy Z-Scheme Heterojunction: Role of Ultrafast Carrier Recombination-Transfer Kinetics.

Herein, combining density functional theory (DFT) calculations with nonadiabatic molecular dynamics (NAMD), we built a computational framework to rationally screen from a series of 2D conjugated carbon nitrides (CNs) to match with B4C3, resulting in the excellent direct Z-scheme photocatalyst (B4C3/C6N6) for overall water splitting (OWS). Studies on interface engineering and ultrafast dynamics of carrier recombination-transfer show that in the B4C3/C6N6 system, compared with the slower interlayer migration process of carriers, strong nonadiabatic coupling and longer quantum decoherence time accelerates weak carrier interlayer recombination on a subpicosecond time scale, enabling simultaneous triggering of hydrogen evolution reaction (HER) with ΔG = -0.23 eV and spontaneous oxygen evolution reaction (OER) in the absence of sacrificial or cocatalysts. In general, our work will promote the design of efficient direct Z-scheme photocatalysts from an ultrafast dynamics perspective.

Controllable construction of direct Z-scheme Mo2C-CdxZn1−xIn2S4 heterojunction via defect-mediated modulation for enhanced visible-light photocatalysis

Direct Z-scheme semiconductor heterostructures possess fascinating merits for solar photocatalysis, including increased light harvesting, spatially isolated photogenerated charge carriers, and well-preserved strong redox capability. However, steering Z-scheme charge transfer of semiconductor heterojunction in a controllable manner is still a challenging task. In this work, unique direct Z-scheme Mo2C-CdxZn1−xIn2S4 heterojunction is constructed via a defect-mediated modulating strategy, where Cd-doping switches the charge transfer mode of Mo2C-CdxZn1−xIn2S4 heterojunction from type-I to Z-scheme through increasing S vacancies, up-shifting conduction band level, and narrowing bandgap of CdxZn1−xIn2S4 component. Moreover, the defect-induced Mo-S bond affords fast channels for built-in electric field-induced Z-scheme photo-electrons transporting from Mo2C conduction band to CdxZn1−xIn2S4 valence band, supporting by X-ray photoelectron spectroscopy, surface photovoltage spectroscopy, and radical testing results. Noticeably, under irradiation of visible light (λ > 400 nm), Mo2C-CdxZn1−xIn2S4 Z-scheme heterojunction displays an excellent and stable photocatalytic H2-evolving activity, reaching an outstanding H2 generation rate of 28.12 mmol·g−1·h−1 with the corresponding high apparent quantum efficiency of 21.1% at 400 nm, far surpassing that of Pt-loaded C0.25ZIS and most documented ZnIn2S4-containing photocatalysts. The present work could inspire the crafty design of efficient Z-scheme photocatalysts through defect-mediated heterostructure construction and energy band engineering.

Direct Z-scheme GaTe/SnS2 van der Waals heterojunction with tunable electronic properties: A promising highly efficient photocatalyst

The production of hydrogen through photocatalytic water splitting offers a secure and eco-friendly approach. In this study, the application of GaTe/SnS2 heterojunction in the field of photocatalysis was studied in depth by using the first-principles calculation method. Based on single-layer GaTe and SnS2, a novel two-dimensional GaTe/SnS2 van der Waals heterojunction (vdwH) was constructed. Through analytical calculations, it is obvious that the GaTe/SnS2 heterojunction has an indirect bandgap of 0.85eV. Furthermore, its type-II band alignment facilitates efficient separation of photogenerated electrons and holes across different layers. The application of Bader charge analysis revealed an intriguing observation: the GaTe layer transferred a charge of 0.058e to the SnS2 layer. This charge transfer led to the creation of a robust built-in electric field, which played a pivotal role in efficiently inhibiting the recombination of photogenerated electrons and holes. Under the condition of pH = 0, GaTe/SnS2 heterojunction can promote redox reaction and realize water splitting. In addition, when the biaxial strain of -3%–3 % is applied to the GaTe/SnS2 heterojunction, the band edge position and light absorption properties are effectively changed, and more photons participate in the water splitting process. More importantly, the solar-to-hydrogen (STH) efficiency of GaTe/SnS2 heterojunction reaches 56.6 %, and when ε = 3 %, ηSTH increases to 58.21 %. Hence, our research showcases the GaTe/SnS2 heterojunction's potential as a highly efficient Z-scheme photocatalyst for water splitting, offering promising prospects for hydrogen production.

Electron bridge rGO synergized with Z-scheme ZnTe/WO3 heterojunction for simultaneous and efficient tetracycline degradation and Cu (II) reduction

Z-scheme heterojunction photocatalysts can restrain carriers’ recombination while retaining high redox capacity. Herein, a novel ZnTe/rGO/WO3 (ZRW) Z-scheme heterojunction was constructed for simultaneous removal of TC and Cu (II) from wastewater. The highly conductive rGO served as a bridge connecting the ZnTe and WO3 whereby forming a tight interaction interface, beneficial to carriers transfer and separation. The removals of TC and Cu (II) using the optimized ZRW-10% achieved 90.6% and 89.5% within 150 min of light exposure, which were much higher than those from the ZnTe and WO3. Results of free radical trapping experiments and electron spin resonance analysis suggested that·O2- and·OH were the key active species for TC oxidation while e- dominated Cu (II) reduction. Based on the identified TC degradation intermediates, two possible degradation pathways for TC were proposed, and the ecotoxicity of most intermediates were less than TC. This study can advance research development of designing efficient Z-scheme photocatalyst and elimination of complex pollutants.

Fabrication of Z-scheme ZnO/g-C3N4 heterojunction modified by silver nanoparticles for photocatalytic removal of Norfloxacin and Rhodamine B

A novel ternary photocatalyst with a Z-scheme heterojunction was successfully synthesized through the deposition of Ag nanoparticles onto the surface of a ZnO/g-C3N4 composite. The prepared photocatalysts were characterized by XRD, FT-IR, XPS, HRSEM, TEM, DRS, PL, EIS, TPC, and M-S. The photocatalytic performance of the as-synthesized photocatalysts was systematically investigated through the photodegradation of norfloxacin (NOR) and rhodamine B (RhB) under visible light irradiation. The photodegradation efficiency of 5% Ag/ZnO/g-C3N4 (5AZCN) composite photocatalyst reached 86.7% (480 min) and 98.0% (60 min) for NOR and RhB, respectively. Moreover, the apparent rate constants of the 5AZCN composite photocatalysts for NOR and RhB were found to be 3.4 and 22.2 times higher than that of the ZCN composite photocatalysts, respectively. The significantly enhanced photocatalytic performance was ascribed to the widened range of visible light response and the efficient separation and migration of carriers facilitated by the introduction of Ag nanoparticles that functioned as electron transfer mediators. Based on the free radicals quenching experiment and electron spin resonance (ESR) spectroscopy characterization, superoxide radicals (·O2−) were the main reactive species in the photodegradation process. Furthermore, the charge transfer process was proved to be a Z-scheme transfer mechanism. This work provides a promising approach to simply constructing novel efficient Z-scheme photocatalysts for the elimination of environmental pollutants.

Preparation of LSPR enhanced Z-scheme Pd/WO3@SnO2 for photocatalytic decomposition of organic compounds under simulated sunlight

The decoration of semiconductor photocatalysts with metal nanoparticles (NPs) is an efficient strategy for improving their performance via localized-surface-plasma-resonance (LSPR). For this study, a LSPR enhanced Z-scheme Pd/WO3@SnO2 photocatalyst was synthesized, which revealed excellent photocatalytic performance and reusability against Rhodamine B (RhB) with degradation rate of 100 % after 1 h under simulated sunlight. The reaction rate constants (k) of the Pd/WO3@SnO2 were ∼4.9, 3.5, and 2.1 times higher than those of the WO3, SnO2, and WO3@SnO2, respectively. In this Z-scheme-structure, the transfer efficacy of photogenerated electrons was significantly promoted due to integrated electric-field between the SnO2 and WO3, which was supported by experimental results and theoretical calculations. The deposited Pd nanoparticles served as an electron-transfer-bridge, as well as a LSPR excitation source, which played significant role in the degradation of RhB. The photodecomposition pathway of RhB was explored, and the toxicities of the intermediates were evaluated. Moreover, tetracycline (TC), chlortetracycline-hydrochloride (CTC), doxycycline-hydrate (DOX), and oxytetracycline (OTC) were tested as common antibiotic models to verify the effectiveness of the catalysts. The degradation efficiencies for TC, CTC, DOX, and OTC over Pd/WO3@SnO2 attained 90.98 %, 96.33 %, 75.37 %, and 50.90 %, respectively, under simulated sunlight, which confirmed its strong potential for the removal of recent pollutants. Experiments and electron paramagnetic resonance (EPR) tests indicated that •O2– served as the major active species in the photocatalysis process, while •OH and h+ played secondary roles. Finally, an LSPR enhanced direct Z-scheme mechanism was proposed. This study provides a rational design strategy for the development of more efficient Z-scheme photocatalysts that exploit the LSPR-effect for photodecomposition of organic pollutant compounds.

Ternary rGO decorated W18O49 @g-C3N4 composite as a full-spectrum-responded Z-scheme photocatalyst for efficient photocatalytic H2O2 production and water disinfection

Integrating g-C3N4 with narrow-band semiconductor to construct a Z-scheme structured heterojunction has been regarded as a common strategy to improve the photocatalytic performance of g-C3N4. However, limited catalytic activity increment is achieved due to the contradiction of expanding the light absorption scope of traditional photo-oxidation semiconductors (PS II) and preserving their valance band oxidative abilities. Herein, to extend the light absorption range of g-C3N4 based Z-scheme photocatalyst to the whole solar spectra while without losing the high oxidative ability of this system, we select the heavy doped W18O49 as PS II and provide a facile in situ hydrothermal method to elaborately fabricate an rGO decorated W18O49 @g-C3N4 (r-CNW) Z-scheme photocatalyst. The prepared r-CNW-2 (with optimal W18O49 to g-C3N4 weight ratio of 1:2) exhibits improved photocatalytic performance with H2O2 generation rates of 71, 58.5 and 6.3 μmol g−1 h−1 obtained under the simulated solar light, visible light (>400 nm) and NIR light (>800 nm) irradiation, respectively, which is 1.3 and 2 times higher than those of the g-C3N4 counterparts (54, 29 μmol g−1 h−1 and even not detected).such outstanding performance of r-CNW-2 could be associated with the broader light absorption, fast charge separation, and rapid redox reactions. Moreover, the r-CNW-2 also displays an excellent E-coli inactivation activity, comparable to most g-C3N4-based photocatalysts. Our work gives a new insight through trading off light absorption and redox ability to fabricate efficient Z-scheme photocatalyst for photocatalytic H2O2 generation and environmental remediation.

Simultaneous photocatalytic tetracycline oxidation and Cr(VI) reduction by a 0D/3D hierarchical Bi2WO6@CoO Z-scheme heterostructure: In situ interfacial engineering and charge regulation mechanism

Constructing visible-light driven semiconductor heterojunction with high redox bifunctional characteristics is a promising approach to deal with the increasingly serious environmental pollution problems, especially the coexistence of organic/heavy metal pollutants. Herein, a simple in-situ interfacial engineering strategy for the fabrication of 0D/3D hierarchical Bi2WO6@CoO (BWO) heterojunction with an intimate contact interface was successfully developed. The superior photocatalytic property was reflected not only in individual tetracycline hydrochloride (TCH) oxidation or Cr(VI) reduction, but also in their simultaneous redox reaction, which could be predominantly attributed to the outstanding light-harvesting, high carrier separation efficiency and enough redox potentials. In the simultaneous redox system, TCH acted as a hole-scavenger for Cr(VI) reduction, replacing the additional reagent. Interestingly, superoxide radical (·O2−) played the role as oxidants in TCH oxidation but as electron transfer media in Cr(VI) reduction. On account of the interlaced energy band and tight interfacial contact, a direct Z-scheme charge transfer model was established, which was verified by the active species trapping experiments, spectroscopy, and electrochemical tests. This work provided a promising strategy for the design/fabrication of highly efficient direct Z-scheme photocatalysts in environmental remediation.

Construction of Ternary Bismuth-Based Heterojunction by Using (BiO)2 CO3 as Electron Bridge for Highly Efficient Degradation of Phenol.

Inspired by nature, it has been considered an effective approach to design artificial photosynthetic system by fabricating Z-scheme photocatalysts to eliminate environmental issues and alleviate the global energy crisis. However, the development of low cost, environment-friendly, and high-efficient photocatalysts by utilizing solar energy still confronts huge challenge. Herein, we constructed a Bi2 O3 /(BiO)2 CO3 /Bi2 MoO6 ternary heterojunction via a facile solvothermal method and calcination approach and used it as a photocatalyst for the degradation of phenol. The optimized Bi2 O3 /(BiO)2 CO3 /Bi2 MoO6 heterojunction delivers a considerable activity for phenol photodegradation with an impressive removal efficiency of 98.8 % and about total organic carbon (TOC) of 68 % within 180 min under visible-light irradiation. The excellent photocatalytic activity was ascribed to the formation of a Z-scheme heterojunction, more importantly, the presence of (BiO)2 CO3 as an electron bridge greatly shortens the migration distance of photogenerated electron from ECB of Bi2 O3 to EVB of Bi2 MoO6 , thus prolonging the lifetime of photogenerated electrons, which is verified by trapping experiments, electron spin-resonance spectroscopy (ESR) results, and density functional theory (DFT) calculations. This work provides a potential strategy to fabricate highly efficient Bi-based Z-scheme photocatalysts with wide application prospects in solar-to-fuel conversion and environmental protection.

Construction of Cu7 S4 @CuCo2 O4 Yolk-Shell Microspheres Composite and Elucidation of Its Enhanced Photocatalytic Activity, Mechanism, and Pathway for Carbamazepine Degradation.

Water pollution caused by the massive use of medicines has caused significant environmental problems. This work first reports the synthesis and characterization of the Cu7 S4 /CuCo2 O4 (CS/CCO) yolk-shell microspheres via hydrothermal and annealing methods, and then investigates their photocatalytic performance in removing organic water pollutants. The 10-CS/CCO composite with yolk-shell microspheres exhibits the highest photodegradation rate of carbamazepine (CBZ), reaching 96.3% within 2h. The 10-CS/CCO also demonstrates more than two times higher photodegradation rates than the pure (Cu7 S4 ) CS and (CuCo2 O4 ) CCO. This outstanding photocatalytic performance can be attributed to the unique yolk-shell structure and the Z-scheme charge transfer pathway, reducing multiple reflections of the acting light. These factors enhance the light absorption efficiency and efficiently transfer photoexcited charge carriers. In-depth, photocatalytic degradation pathways of CBZ are systematically evaluated via the identification of degradation intermediates with Fukui index calculation. The insights gained from this work can serve as a guideline for developing low-cost and efficient Z-scheme photocatalyst composites with the yolk-shell structure.

Insights into Photoinduced Carrier Dynamics and Overall Water Splitting of Z-Scheme van der Waals Heterostructures with Intrinsic Electric Polarization

Using first-principles calculations in combination with nonadiabatic molecular dynamics (NAMD), we propose novel heterostructures of carbon nitride (C7N6) and the Janus GaSnPS monolayer as promising direct Z-scheme photocatalysts for solar-driven overall water splitting. The out-of-plane electric field due to the electric polarization which is dependent on the stacking pattern alters the band alignment and catalytic activity of the heterostructures. The relatively strong interfacial nonadiabatic coupling and long quantum coherence time accelerate the interlayer carrier recombination, enabling a direct Z-scheme photocatalytic mechanism. More importantly, the redox ability of the remanent photogenerated carriers in the Z scheme is strong enough to trigger both the hydrogen evolution reaction (HER) and oxygen reduction reaction (OER) simultaneously without the help of sacrificial agents. Our work reveals a fundamental understanding of ultrafast charge carrier dynamics at vdW heterointerfaces as well as new design prospects for highly efficient direct Z-scheme photocatalysts.

Highly porous BiOBr@NU-1000 Z-scheme heterojunctions for synergistic efficient adsorption and photocatalytic degradation of tetracycline.

Designing an effective photoactive heterojunction having dual benefits towards photoenergy conversion and pollutant adsorption is regarded as an affordable, green method for eliminating tetracycline (TC) from wastewater. In this regard, a series of BiOBr@NU-1000 (BNU-X, X = 1, 2 and 3) heterojunction photocatalysts are constructed. BNU-X preserves the original skeleton structure of the parent NU-1000, and its high porosity and specific surface area enable superior TC adsorption. At the same time, BNU-X is an effective Z-scheme photocatalyst that improves light trapping, promotes photoelectron-hole separation, and shows excellent photocatalytic degradation efficiency towards TC with the value of the photodegradation kinetic rate constant k being 2.2 and 24.8 times those of NU-1000 and BiOBr, respectively. The significant increase in the photocatalytic activity is ascribed to the construction of an efficient Z-scheme photocatalyst, which promotes the formation of superoxide radicals (˙O2-) and singlet oxygen (1O2) as the main oxidative species in the oxidation system. This research has the advantage of possibilities for the development of porous Z-scheme photocatalysts based on photoactive MOF materials and inorganic semiconductors for the self-purification and photodegradation of organic contaminants.

Synergetic interfacial charge transfer with Z-scheme heterostructure and S–Mo–S linkage in one-pot synthesized SnIn4S8/MoS2 for efficient photocatalytic activity

Construction of high-efficiency scheme towards interfacial charge transfer is of great value to suppress the spatial carrier recombination and thus to develop advanced heterogeneous photocatalysts for environmental remediation. Herein, a novel Z-scheme SnIn4S8/MoS2 with interfacial S–Mo–S bond was synthesized by a facile one-step hydrothermal method. The prepared optimal SnIn4S8/MoS2 heterostructure (SIS/MS-24) exhibited significantly enhanced visible-light photocatalytic activities for crystal violet degradation and Cr(VI) reduction compared with individual materials. The boosted photocatalytic performance was primarily attributed to the Z-scheme charge transfer mechanism certificated by the trapping experiments, ESR (electron spin resonance) test, and DFT (density functional theory) calculation. What’s more, the formation of S–Mo–S bond between SnIn4S8 and MoS2 acted as a specific bridge to further promote the Z-scheme channel for charge transport at the interface. This synergy of Z-scheme heterostructure and covalent S–Mo–S linkage greatly accelerated the separation of electron-hole pairs. Additionally, the SIS/MS-24 composite also displayed good stability even after five cycles of testing experiments. This work provides a novel way to design and fabricate efficient Z-scheme photocatalysts for water purification.