Design Of Z-scheme Research Articles

Rational design of Z-scheme configured polymeric carbon nitride-decorated ZnWO4 nanofibers for enhanced visible-light-driven photodegradation of antibiotics

In this study, a Z-scheme heterostructure was meticulously engineered between zinc tungstate (ZnWO4) nanofibers and polymeric carbon nitride (PCN) nanosheets to augment the photocatalytic degradation of tetracycline (TC) under visible light irradiation. A cohesively integrated PCN/ZnWO4 photocatalyst structure was synthesized through an in-situ gas-solid reaction. The quantity and spatial distribution of PCN nanosheets were modulated by fine-tuning the gas precursor and reaction parameters. Relative to pristine ZnWO4 nanofibers and PCN photocatalysts, the distinct three-dimensional PCN/ZnWO4 heterostructure manifests a notable enhancement in photocatalytic performance, attributed to its plethora of active sites and a Z-scheme configuration that bolsters charge separation efficiency, achieving a tetracycline degradation rate of 95.4% upon exposure to simulated sunlight for 160 minutes. The employment of gas-solid reaction as a design paradigm pioneers a fresh paradigm in the strategic assembly of Z-scheme heterostructured photocatalysts, thereby illuminating a promising pathway for advancements in environmental remediation technologies.

Rational design of Z-scheme CoS@NC/CdS heterojunction with N doped carbon (NC) as an electron mediator for enhanced photocatalytic H2 evolution

Rational construction of Z-scheme heterojunction photocatalysts have been regarded as a promising approach for enhanced hydrogen generation performance from splitting water. Herein, a Z-scheme heterojunction CoS@NC/CdS using N doped carbon (NC) as an electron mediator bridge was fabricated by coupling CdS with CoS@NC prepared via solid-state self-sulfuring a novel cationic cobalt (Co) based metal–organic framework (namely PZH-42) under argon atmosphere. Notably, the H2 production activity could be optimized by regulating the sulfurization temperature and the content of CoS@NC. The 20-CoS@NC−700/CdS with sulfurization temperature of 700 ℃ and the content for CoS@NC−700 of approximately 20 wt% exhibited the highest H2 generation activity of 20.56 mmol h−1 g−1 with an apparent quantum efficiency (AQE) of 23.98 %, which was 70 and 10-folds as high as that of CdS and CdS/CoS. Such improvement might be attributed to the four synergisms of rapidly separating the electrons and holes by the NC electron mediator bridge in Z-scheme system, retaining electrons at the higher position conduction band (CB) of Z-scheme heterojunction more than that of the type-II heterojunction, increasing the specific surface area and enhancing light absorption range and intensity. More significantly, this rare idea can not only provide a promising strategy for designing highly efficient Z-scheme heterojunction photocatalysts, but also expand the photocatalytic H2 production applications of Co-based metal–organic framework.

Design of Z-scheme UIO-66-NH2/BiOBr heterojunctions for efficient visible-light-driven selenite removal from water: Performance and mechanism studies

Excess existence of the selenite (Se(IV)) is hazardous to water resources. Therefore, a need still exists for the removal of Se(IV) from the wastewater in the renewable, environmentally friendly, and low-cost way. This paper presents a novel way to design a Z-type heterojunction of UIO-66-NH2/BiOBr using co-precipitation technology for efficiently removal of Se(IV) from wastewater using the adsorption-visible photocatalytic synergy. The UIO-66-NH2 presents an enhanced adsorption of Se(IV) due to the expose of abundant linker defects, as the active sites. The Z-type heterojunction (UB-2) showed 96.4% removal of Se(IV) at an initial concentration of 100 mg/L under visible light conditions due to its higher charge transfer capacity and electron-hole separation ability. The photocatalytic removal rate of UB-2 toward Se(IV) was 4.12 times and 9.93 times higher than that of UIO-66-NH2 and BiOBr, respectively. UB-2 could be reused and showed a good removal capacity in real-world water samples. The used UB-2 was superior to the nano-selenium in the scavenging of superoxide radical and DPPH, revealing a potential of biological antioxidant. This work will be beneficial for the efficient decontamination of Se(IV)-containing wastewater.

Simultaneous degradation of methyl orange and indigo carmine dyes from an aqueous solution using nanostructured WO3 and CuO supported on Zeolite 4A

In this study, a novel composite catalyst system, Zeolite 4A/WO3/CuO with a Z-scheme design, was synthesized for photocatalysis, sonocatalysis, and sono-photocatalysis methyl orange (MO) and indigo carmine (IC) dyes simultaneously. The properties of the Zeolite 4A/WO3/CuO composite were thoroughly investigated using various techniques, and the results confirmed the synthesis of the desired catalyst system. In the sono-photocatalytic process, using the Zeolite 4A/WO3/CuO composite, the maximum efficiency for MO (99.12 %) and IC (97.24 %) was achieved at pH of 2 and 3, with a catalyst dosage of 0.15 g/L, a dye concentration of 10 mg/L, a contact time of 25 min, and H2O2 dosage of 30 µL/100 mL. The dye elimination efficiency using the sono-photocatalytic process was reduced in the presence of Cl- and PO43- in the distilled water. The efficiency also declined in the medium of river and well water resources. Moreover, the Zeolite 4A/WO3/CuO catalyst maintained over 90 % of its performance even after five reuse cycles. Based on the kinetic study, the sono-photocatalytic process exhibited higher activation for the removal of MO (k: 0.1946 min−1 and t1/2: 3.561) and IC (k: 0.1433 min−1 and t1/2: 4.836) than other processes. The synergy values for the MO and IC degradation using the Zeolite 4A/WO3/CuO composite were determined to be 2.167 and 2.303, respectively. The impact of various scavengers demonstrated that in the degradation processes of the target dyes using the sono-photocatalytic process, different active species like OH•, e-, h+, and O2–• are involved. The purification of dye-laden water using the sono-photocatalytic process was not toxic for plant germination, microorganisms, and fish, highlighting the successful biocompatibility of the process for dye removal.

Enhanced Photocatalytic Performance of Z-Scheme Design of Bi2O2CO3/Ag/g-C3N4 Photocatalyst

Enhanced Photocatalytic Performance of Z-Scheme Design of Bi2O2CO3/Ag/g-C3N4 Photocatalyst

Creation and Plasmon-Assisted Photosensitization of Annealed Z-Schemes for Sunlight-Only Water Splitting.

Solely light-induced water splitting represents a promising avenue for a carbon-free energy future, based on reliable energy sources. Such processes can be performed using coupled semiconductor materials (the so-called direct Z-scheme design) that facilitate spatial separation of (photo)excited electrons and holes, prevent their recombination, and allow water-splitting half-reactions proceeding at each corresponding semiconductor side. In this work, we proposed and prepared a specific structure, based on WO3g-x/CdWO4/CdS coupled semiconductors, created by annealing of a common WO3/CdS direct Z-scheme. WO3-x/CdWO4/CdS flakes were further combined with a plasmon-active grating for the creation of the so-called artificial leaf design, making possible complete utilization of the sunlight spectrum. The proposed structure enables water splitting with high production of stoichiometric amounts of oxygen and hydrogen without undesirable catalyst photodegradation. Several control experiments confirm the creation of electrons and holes participating in the water splitting half-reaction in a spatially selective manner.

A mesh cladding-structured Sr-doped LaFeO3/Bi4O5Br2 photocatalyst: Integration of oxygen vacancies and Z-scheme heterojunction toward enhanced CO2 photoreduction

Solar-driven conversion of CO2 into beneficial chemical fuels using photocatalysts is a sustainable approach for obtaining renewable energy. However, the poor photoabsorption, low charge separation efficiency, and sluggish interfacial reaction due to a paucity of active sites limit the photocatalytic activity. Herein, a mesh cladding structure of Sr-doped LaFeO3/Bi4O5Br2 (Sr-LFO/BOB) Z-scheme heterojunction with abundant surface oxygen vacancies (OVs) is developed to improve the CO2 photoreduction. Sr doping in LFO introduce OVs, which captures more photoinduced electrons contributing to the surface adsorption of CO2 molecules and narrows the LFO band gap extending the light absorption range to the whole visible spectrum. Particularly, the unique mesh cladding heterostructure composed of Sr-LFO particles wrapped with BOB nanowires provides ample Z-scheme charge-transfer pathways at the Sr-LFO/BOB and sufficiently exposes Sr-LFO surface for CO2 adsorption. Benefiting from the OVs and design of Z-scheme, the optimized photocatalyst (0.05Sr-LFO/BOB(2)) with appropriate Sr doping (5%) and BOB content demonstrates a considerable CH4 generation of 10.14 μmol g−1, which is approximately 48.3-fold higher than that of the pristine LFO. This study provides an insight into the design and fabrication of high-performance perovskite oxide-based photocatalysts by constructing a Z-scheme heterojunction with abundant active sites for CO2 photoreduction.

Rational design of Z-scheme ZnFe2O4/Ag@Ag2CO3 hybrid with enhanced photocatalytic activity, stability and recovery performance for tetracycline degradation

The occurrence of pharmaceutical and personal care products (PPCPs) in the ambient environment has raised serious concerns. Herein, a dispersed ZnFe2O4 nanoparticle loaded Ag@Ag2CO3 nanorod hybrid (ZnFe2O4/Ag@Ag2CO3) was facile prepared, and used as a solar light driven photocatalyst for the degradation of tetracycline (TC), a typicalPPCPs. The hybrids were characterized by XRD, SEM, EDS, HRTEM, DRS, PL, TRPL, M−H, BET, XPS, ESR and photoelectrochemical testing. The ZnFe2O4 was evenly dispersed on the surface of Ag@Ag2CO3 nanorods of which diameter was about 100 nm. The obtained ZnFe2O4/Ag@Ag2CO3 composites exhibited high TC degradation efficiency after 150 min Xe light illumination, which was much better than those of pure Ag@Ag2CO3 and ZnFe2O4. The photodegradation reaction rate constant (k) of the optimum ternary photocatalyst (ZnFe2O4 loading 5% wt) increased 4.04 times and 2.48 times than those of pure ZnFe2O4 and Ag2CO3@Ag, respectively. More importantly, the stability and recovery capacity of the ZnFe2O4/Ag@Ag2CO3 photocatalyst improved obviously than those of Ag@Ag2CO3. The reactive oxygen species (ROS) experiment indicated that •OH、h+ and •O2− involved in the photocatalytic reaction process, and the ROS contributes order was •O2− > h+ >•OH. The band positions of individual ZnFe2O4 and Ag2CO3 were elucidated via DRUV–Vis spectra and Mott-Schottky plots. Based on the results of ROS experiment and band structure of ZnFe2O4 and Ag2CO3, it could be inferred that the photocatalytic reaction of ZnFe2O4/Ag@Ag2CO3 abided by Z-scheme mechanism, that is, Ag acted as the electronic bridge between Ag2CO3 and ZnFe2O4, and the •OH and •O2− were formed on the valence band (VB) of Ag2CO3 and conduction band (CB) of ZnFe2O4, respectively, and then TC was further oxidized. The sufficient photocatalytic degradation of TC in ambient water revealed that a sunlight-driven ZnFe2O4/Ag@Ag2CO3 photocatalytic process may be efficiently applied for the remediation of PPCPs contaminated natural waters.

Improving photocatalytic activity by construction of immobilized Z-scheme CdS/Au/TiO2 nanobelt photocatalyst for eliminating norfloxacin from water

To improve the photocatalytic activity of TiO2 NBs under irradiation of solar light, an immobilized Z-scheme composite photocatalyst CdS/Au/TiO2 NBs has been constructed. For the unique architectures, the TiO2 NBs provide more absorption and reaction sites, the CdS nanoparticles enhance overall light harvesting, and Au acts as the electron transfer mediator, promoting the interfacial charge transfer and efficient separation of electrons and holes. The morphology, elements, crystal structure, optical and photoelectrochemical properties, and photocatalytic activity of CdS/Au/TiO2 NBs were characterized. Results showed that CdS/Au/TiO2 NBs possesses higher photocatalytic activity toward the degradation of antibiotic norfloxacin under irradiation of simulated sunlight, which is attributed to the synergetic interaction of increased light absorption and separation of photogenerated electrons and holes. Besides, the degradation of norfloxacin was promoted by HCO3−, but inhibited by NO3− and Cl−. The radicals trapping experiments proved that superoxide radicals (O2−) was the dominating active species during the photocatalysis process. The photocatalytic degradation products of norfloxacin was analyzed, and nine intermediates were identified. Moreover, the photocatalytic degradation mechanism and photostability of CdS/Au/TiO2 NBs were analyzed in detail. The matched energy levels and unique ternary Z-scheme design are the key for improved photocatalytic activity. The deactivation of CdS/Au/TiO2 NBs after recycles mainly due to the release of CdS by photocorrosion and the loss of deposited Au.

Enhanced photocatalytic performance of TiO2 through a novel direct dual Z-scheme design

A novel ternary TiO2/MoO3/g-C3N4 nanocomposite photocatalyst has been synthesized and shown to exhibit a direct dual Z-scheme photodegradation mechanism. The TiO2/MoO3/g-C3N4 nanocomposite catalyst outperforms its constituents for methylene blue degradation. The highest degradation rate constant of 0.0303 min−1 is about 3.9 times greater than that of TiO2. The improved photocatalytic activity is attributed to the enhanced visible light absorption from the g-C3N4 and α-MoO3, enhanced photogenerated hole/electron separation primarily in the TiO2 and α-MoO3, and enhanced fast charge transfer due to the existence of oxygen vacancies. The photodegradation mechanism is explained using a direct dual Z-scheme. This work affords a new insight towards designing highly efficient Z-scheme photocatalysts with enhanced visible light absorption, efficient photogenerated hole/electron separation, and strong redox ability.

Novel application of a Z-scheme photocatalyst of Ag3PO4@g-C3N4 for photocatalytic fuel cells

A composite of Ag3PO4@g-C3N4 with the Z-scheme structure was synthesized, and used as the photoanode in a photocatalytic fuel cell (PFC). With the help of the Z-scheme design, both the degradation of tetracycline and the output of maximum power density (Pmax) were greatly enhanced in this PFC system. The degradation rate of tetracycline in the Ag3PO4@g-C3N4 PFC was 2.53 times and 3.65 times that in the PFC systems with the Ag3PO4 photoanode and the g-C3N4 photoanode, respectively. The Pmax of the Ag3PO4@g-C3N4 PFC was 6.06 μW cm−2, which was 1.46 times and 90.4 times that of the Ag3PO4 PFC (4.16 μW cm−2) and the g-C3N4 PFC (0.067 μW cm−2), respectively. The possible mechanism was proposed. The Z-scheme photoanode could not only contribute to the separation of photogenerated carriers to achieve a high photocatalytic activity, but also reserve a good redox capacity. Additionally, aeration played an important role on the PFC performance. It was demonstrated that N2 purging facilitated the electricity generation, while O2 purging promoted the pollutant degradation.

Z-scheme design of Ag@g-C3N4/ZnS photoanode device for efficient solar water oxidation: An organic-inorganic electronic interface

Abstract Herein, we demonstrate a design of a composite photoanode comprising a very thin layer of ZnS NPs onto a dense layer of Ag@g-C3N4 to form a dual absorber tandem device based on organic-inorganic electronic interface for photo water-splitting. The XRD pattern of Ag@g-C3N4 showed both the diffraction peaks of cubic Ag and main peak of g-C3N3. The XPS survey spectrum confirms the existence of the C, N, Ag, Zn, and S elements on the surface of the Ag@g-C3N4/ZnS photoelectrode. With incorporating Ag in g-C3N4 structure, the band gap decreased from 2.90 for g-C3N4 to 2.55 eV for Ag@g-C3N4 and also light absorption ability increased. The device based on the architecture of TiO2/Ag@g-C3N4/ZnS/Ni(OH)2 showed a photocurrent of about 0.1 and 0.2 mA cm−2 at potential of 1.23 and 1.7 V vs. RHE. The Ag@g-C3N4/ZnS photoanode exhibited a photocurrent turn-on potential of 0.45 V vs. RHE. In this photoanode device, Ag@g-C3N4 as a second absorber layer could absorb the photons of visible light which are transparent to ZnS layer and transforms into additional photovoltage. This architecture introduces a successful band alignment for high efficiency water-splitting through organic-inorganic junction.

Strategic modulation of electron migration in the TiO2-Au-CdS: Z-scheme design for the enhancement in hydrogen evolution reaction

The Z-scheme design was employed to strategically modulate the transfer process of photogenerated charges for hydrogen evolution reaction. The hydrothermally treated Au nanoparticles were introduced as the Z-scheme bridge, which was advantageous in the separation and transportation of active charges. Comparing with pristine samples, the TiO2-Au-CdS nanorods exhibited superior performance for solar water splitting.

Rational design of Z-scheme LaFeO3/SnS2 hybrid with boosted visible light photocatalytic activity towards tetracycline degradation

Abstract Visible-light-driven photocatalytic degradation of organic pollutants is considered as one of the promising and effective strategies for water purification. Extensive efforts have been devoted to explore various inorganic and organic semiconductor materials as photocatalysts for the degradation of organic pollutants under visible light irradiation in the past few decades. Among them, artificial Z-scheme photocatalyst has recently attracted considerable attention in water purification owing to it can not only effective transfer and separation of the photogenerated charge carriers, but also retain prominent redox ability. Herein, a direct Z-scheme LaFeO3/SnS2 hybrid was successfully constructed via a facile hydrothermal method. The structure, composition, photoelectric and photocatalytic properties of the as-obtained samples were systematically characterized by X-ray diffraction, Fourier transform infrared spectrum, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, UV–Vis diffuse reflectance spectroscopy, photoluminescence spectroscopy, transient photocurrent response, electrochemical impedance spectroscopy and photocatalytic degradation of tetracycline (TC). These characterizations revealed that the LaFeO3 nanoparticles were well dispersed on the surface of SnS2 nanosheets. The photoelectrochemical characterizations demonstrated that the promoted transfer and separation of charge carrier in the LaFeO3/SnS2 hybrid was achieved. As expected, compared to bare LaFeO3 and SnS2, all the LaFeO3/SnS2 hybrids displayed boosted the photocatalytic performances for the degradation of TC under visible light irradiation (λ > 420 nm). In particular, the photocatalytic degradation of TC over all the as-obtained samples obeyed pseudo-first-order kinetics equation, and the optimal photodegradation rate constant over the LaFeO3(10.0 wt%)/SnS2 hybrid for TC degradation was up to 0.0028 min−1, which was about 3.5 and 2.2 times larger than those of SnS2 and LaFeO3, respectively. Such an enhancement could be mainly ascribed to the formation of the Z-scheme LaFeO3/SnS2 heterojunction, which not only promoted the visible light absorption, but also facilitated the charge separation and transfer efficiency and prolonged lifetime of charge carriers as a result of the closely contacted Z-scheme heterojunction interface effect between LaFeO3 and SnS2. Furthermore, results from the radical trapping experiments confirmed that there existed the Z-scheme charge transfer mechanism, and the synergistic effect of superoxide radicals and holes was favorable for the photodegradation of TC under visible light irradiation. This work will provide a new insight for the rational design and construction of highly efficient SnS2-based Z-scheme heterojunction hybrid photocatalysts for applying in environmental remediation and energy conversion.

Spatially Separated Photosystem II and a Silicon Photoelectrochemical Cell for Overall Water Splitting: A Natural-Artificial Photosynthetic Hybrid.

Integrating natural and artificial photosynthetic platforms is an important approach to developing solar-driven hybrid systems with exceptional function over the individual components. A natural-artificial photosynthetic hybrid platform is formed by wiring photosystem II (PSII) and a platinum-decorated silicon photoelectrochemical (PEC) cell in a tandem manner based on a photocatalytic-PEC Z-scheme design. Although the individual components cannot achieve overall water splitting, the hybrid platform demonstrated the capability of unassisted solar-driven overall water splitting. Moreover, H2 and O2 evolution can be separated in this system, which is ascribed to the functionality afforded by the unconventional Z-scheme design. Furthermore, the tandem configuration and the spatial separation between PSII and artificial components provide more opportunities to develop efficient natural-artificial hybrid photosynthesis systems.