Efficient Z-scheme Research Articles

Fabrication and characterization of high efficient Z-scheme photocatalyst Bi2MoO6/reduced graphene oxide/BiOBr for the degradation of organic dye and antibiotic under visible-light irradiation

A novel Bi2MoO6/reduced graphene oxide/BiOBr (Bi2MoO6/RGO/BiOBr) composite was successfully synthesized via a facile solvothermal synthesis and precipitation method. The Bi2MoO6/RGO/BiOBr composite was characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, UV–vis diffuse reflectance spectroscopy (UV–vis DRS) and photoelectrochemical measurements. The photocatalytic properties were explored for removal of methylene blue (MB) and norfloxacin (NFX) under visible-light irradiation. The Bi2MoO6/RGO/BiOBr composite exhibits the highest degradation rate compared with Bi2MoO6, BiOBr and Bi2MoO6/BiOBr composite, and that removal ratios of MB and NFX were 96.93% and 78.12%, respectively. A Z-scheme catalytic mechanism suitable for the system was proposed based on the results of UV–vis DRS, free radical trapping experiments and M–S carve analysis, in which RGO as an electronic medium can accelerate electron transfer. It is noteworthy that the close contact interface structure promotes the separation of electrons and holes and improves the photocatalytic performance.

Unraveling the Interfacial Charge Migration Pathway at the Atomic Level in a Highly Efficient Z-Scheme Photocatalyst.

A highly efficient Z-scheme photocatalytic system constructed with 1D CdS and 2D CoS2 exhibited high photocatalytic hydrogen-evolution activity of 5.54 mmol h-1 g-1 with an apparent quantum efficiency of 10.2 % at 420 nm. More importantly, its interfacial charge migration pathway was unraveled: The electrons are efficiently transferred from CdS to CoS2 through a transition atomic layer connected by Co-S5.8 coordination, thus resulting in more photogenerated carriers participating in surface reactions. Furthermore, the charge-trapping and charge-transfer processes were investigated by transient absorption spectroscopy, which gave an estimated charge-separation yield of approximately 91.5 % and a charge-separated-state lifetime of approximately (5.2±0.5) ns in CdS/CoS2 . This study elucidates the key role of interfacial atomic layers in heterojunctions and will facilitate the development of more efficient Z-scheme photocatalytic systems.

Alkali-assisted synthesis of direct Z-scheme based Bi2O3/Bi2MoO6 photocatalyst for highly efficient photocatalytic degradation of phenol and hydrogen evolution reaction

Semiconductor based photocatalytic technology has attracted substantial research attention based on its potential to overcome environmental and energy crisis. The conventional photocatalysts with their issues such as rapid charge recombination are considered unfavorable candidates for practical applications. Herein, a novel direct Z-scheme based photocatalyst composed of Bi2O3/Bi2MoO6 hetrojunction is proposed for efficient photo-degradation of phenol and hydrogen (H2) production reaction. The hetrojunction comprises of ultra-thin (2D) Bi2O3 nanosheets, in-situ grown over 3D Bi2MoO6 microspheres via simple alkali treatment of Bi2MoO6 succeeded by air calcination step. The relative mass ratio of Bi2O3 and Bi2MoO6 could be fine-tuned by controlling the alkali dosage (i.e. NaOH or KOH). Unlike the conventional Bi2O3/Bi2MoO6 hetrojunction, the proposed catalyst follow a direct Z-scheme charge transfer mechanism which permits superior photocatalytic activity with 96.4% phenol degradation efficiency and high hydrogen evolution rate of 52 μmol·g−1 under visible light irradiation. The exuberant performance is accredited to the spatially separated redox charge carriers, excellent light harvesting capability and fast-charge transportation characteristics of the proposed photocatalyst. The present work serves as a primary pathway to design and develop efficient Bi2MoO6-based direct Z-scheme photocatalysts with promising applications in environmental remediation and solar fuel production.

One-step impregnation method to prepare direct Z-scheme LaCoO3/g-C3N4 heterojunction photocatalysts for phenol degradation under visible light

Abstract A series of efficient and stable Z-scheme LaCoO3/g-C3N4 heterojunction photocatalysts with different weight contents of g-C3N4 had been first successfully fabricated by a facile one-step impregnation method. The crystal structure, surface state, element distribution and photoelectronic properties of the as-prepared samples were characterized by XRD, FT-IR, XPS, SEM, TEM, UV–Vis DRS, PL, photocurrent testing and EPR technique. The results show that Z-scheme heterostructures have formed on the interfaces between the perovskite-type oxides LaCoO3 and the flake-like g-C3N4, which enhance the visible-light absorption, separation of the photogenerated electron-hole pairs and transformation of the photogenerated electrons. Moreover, the LaCoO3/g-C3N4-60 wt% composite photocatalyst presented the highest photocatalytic activity for the degradation of phenol under visible light, whose phenol degradation rate is 85% after 5 h under visible light irradiation, which is about 5.2 and 7.5 times higher than that of bare LaCoO3 and g-C3N4, respectively. What's more, the LaCoO3/g-C3N4-60 wt% composite also shows an excellent stability. The highest photocatalytic activity can mainly attribute to high charge carrier separation efficiency as well as the improved dispersity via the Z-scheme LaCoO3/g-C3N4 heterostructure and a possible mechanism for photodegradation process over the Z-scheme LaCoO3/g-C3N4 heterojunction photocatalysts has been proposed.

Facile construction of hierarchical flower-like Z-scheme AgBr/Bi2WO6 photocatalysts for effective removal of tetracycline: Degradation pathways and mechanism

A novel hierarchical flower-like AgBr/Bi2WO6 Z-scheme photocatalyst was prepared through the simplified hydrothermal and deposition-precipitation method. The as-prepared photocatalysts exhibited excellent photocatalytic performance for tetracycline (TC) degradation. Especially, AgBr (20 wt%)/Bi2WO6 displayed the optimal TC removal efficiency (87.5%) within 60 min of visible light illumination. Besides, no obvious decrease in photocatalytic performance was observed after four cycles. The excellent photocatalytic performance could be ascribed to the synergistic effect between electron mediator Ag nanoparticles (Ag NPs) and Z-scheme heterojunction charge transfer mechanism, which enhanced the light harvest capability, separation efficiency of photo-generated carriers and redox ability. Moreover, three-dimensional excitation-emission matrix fluorescence spectroscopy (3D EEMs) and liquid chromatography-mass spectrometry (LC-MS) analyses shed light on the mineralization behavior and the detailed decomposition pathway of TC. This work opened up a new road to efficient Z-scheme heterojunction design and provided novel insights into antibiotics elimination mechanism in photocatalysis.

Curcumin functionalized CuO/Ag nanocomposite: Efficient visible light Z-scheme photocatalyst for methyl orange degradation

An aqueous green synthesis protocol was used to prepare two different curcumin functionalized CuO/Ag photocatalysts. The procedure involved the precipitation of fine spherical nanostructures of Ag on ˜250 nm long (needle-shaped) CuO with curcumin as the reducing and functionalizing agent. Synthesized photocatalysts were characterized by XRD and TEM. In contrast to CuO nanocatalysts, these nanocomposites are efficient visible light photocatalysts for aerobic methyl orange (MO) degradation. There is almost five times increase in photocatalytic activity on the incorporation of a suitable amount of Ag in this nanocomposite. Moreover, these photocatalysts also demonstrate good recyclability for this reaction. Appropriate reactive species trapping experiments confirmed that superoxide radicals were the main active species responsible for the degradation reaction. On the other hand, the water oxidation transfers electrons to photo-generated valence band holes. The results suggest that the photocatalyst works by a Z-scheme charge transfer from the CuO to curcumin through the plasmonic Ag component.

Optimal construction of WO3·H2O/Pd/CdS ternary Z-scheme photocatalyst with remarkably enhanced performance for oxidative coupling of benzylamines

In this work, an all-solid-state Z-scheme photocatalyst of WO3·H2O/Pd/CdS ternary heterostructures was constructed by introducing a small amount of Pd into the optimized WO3·H2O/CdS binary system, where Pd nanoparticles (NPs) were sandwiched between WO3·H2O nanosheets and CdS NPs. The WO3·H2O/Pd/CdS ternary heterostructures exhibited remarkably enhanced photocatalysis towards the oxidative coupling of benzylamines to imines, compared with the other photocatalysts of WO3·H2O, CdS, WO3·H2O/CdS, WO3·H2O/Pd, and WO3·H2O/CdS/Pd. The wavelength-dependent photocatalysis of WO3·H2O/Pd/CdS is in good agreement with its light-harvesting intensity at the corresponding wavelengths. The photoelectrochemical results reflected the enhanced charge carrier separation in WO3·H2O/Pd/CdS, and the photocatalytic H2 evolution confirmed the highly efficient Z-scheme charge transfer in this ternary photocatalyst. Therefore, the WO3·H2O/Pd/CdS ternary heterostructures possess distinct advantages of extended light harvesting region, spatial separation of electron and holes, and elevated redox power, which synergistically contribute to the superior photocatalysis. The Pd NPs sandwiched between WO3·H2O and CdS acted as not only an electron mediator to facilitate the interfacial charge separation but also a cocatalyst to accelerate the selective oxidation of benzylamine. This work demonstrates a rational design of highly efficient Z-scheme photocatalysts and presents some revelations about the photocatalytic mechanism for selective organic transformations.

Highly efficient visible-light-driven photocatalytic activity of g-C3N4@Ag/AgVO3 composites for dye degradation and bacterial inactivation

In this study, g-C3N4@Ag/AgVO3 composite have been successfully synthesized and characterized by XRD, FESEM, TEM, XPS and UV–DRS. Compared with bare g-C3N4, Ag/AgVO3 and g-C3N4@AgVO3, the as-prepared ternary g-C3N4@Ag/AgVO3 composites exhibit higher photocatalytic activity for RhB degradation under visible light irradiation. Antibacterial experiments reveal that g-C3N4@Ag/AgVO3 composite also displays superior photocatalytic disinfection efficiency and 3.05 log of E. coli are inactivated under 100 min visible light exposure. The greatly improved photocatalytic activities are derived from efficient Z-scheme charge transfer with Ag nanoparticles as charge transmission-bridge. Moreover, after three cycling experiment, the composites maintain high stability and good reusability. It is expected that the Z-scheme photocatalyst could be used in the water treatment for the degradation of organic pollutants and disinfection of bacteria.

Preparation of a direct Z-scheme α-Fe2O3/MIL-101(Cr) hybrid for degradation of carbamazepine under visible light irradiation

A series of direct Z-scheme α-Fe2O3/MIL-101(Cr) hybrids were successfully prepared through a facile hydrothermal method in this work. And, the materials were characterized by some technologies including X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), N2 adsorption-desorption, photoluminescence (PL) spectroscopy, Ultraviolet-visible (UV–vis) diffuse reflectance spectroscopy (DRS) and electron spin resonance (ESR). The photocatalytic activities of the hybrids were evaluated by degradation of carbamazepine (CBZ) under visible light irradiation. It is found that 100% of CBZ was able to be removed after 180 min irradiation over the optimum α-Fe2O3 (0.3)/MIL-101(Cr) hybrid. The superior activity was engendered from good textural properties and the formation of a direct Z-scheme heterojunction in the hybrid. The decomposition process of CBZ and the formation of intermediate products were analyzed through liquid chromatography-tandem mass spectrometry (LC–MS) and a possible photodegradation pathway of the CBZ was proposed. Also, the possible mechanism for the photodegradation process was provided to illustrate the excellent performance. The work has paved a new way for the application of MOF materials in the design of efficient Z-scheme system for organic pollution degradation in wastewater.

0D/2D Z-scheme heterojunctions of g-C3N4 quantum dots/ZnO nanosheets as a highly efficient visible-light photocatalyst

Constructing Z-scheme heterojunctions comprising of constituents with different dimensionality is an effective strategy to spatially separate electron and hole. To fully utilize the synergistic coupling effect of dimensionality, herein, we first immobilize g-C3N4 quantum dots (CNQDs) onto ZnO nanosheets with oxygen vacancies (OV-ZnO) to create a 0D/2D hybrid via a facile and cost-effective approach. The CNQDs/OV-ZnO heterojunctions display CNQDs content-dependent performance in visible-light photocatalytic activity. The optimal CNQDs/OV-ZnO heterojunction exhibits high photocatalytic activity for degradation of methyl blue and bisphenol A, where the kinetic constant is 11.4 and 32.5 fold of pure OV-ZnO, respectively. Photoluminescence, electrochemical impedance spectroscopy and photocurrent verify that the photogenerated electron-hole pairs in this 0D/2D Z-scheme heterojunction have been effectively separated. The enhanced photocatalytic activity could be attributed to the synergistic effect of efficient Z-scheme charge separation, highly dispersed 0D CNQDs, coordinating sites of 2D OV-ZnO nanosheets and the strong coupling between them. In addition, the 3D flower-like structure constructed by 2D nanosheets greatly inhibits the leaching and loss of the photocatalyst in the recycling process, and ensures the high recycling ability of CNQDs/OV-ZnO. This work paves the way toward designing novel visible-light 0D/2D photocatalysts in the application of solar energy.

3D/2D direct Z-scheme heterojunctions of hierarchical TiO2 microflowers/g-C3N4 nanosheets with enhanced charge carrier separation for photocatalytic H2 evolution

Constructing a 3D/2D direct Z-scheme heterojunction is a practical way to promote charge separation for attaining efficient solar hydrogen production. In the present work, hybrid 3D TiO2 microflowers/2D g-C3N4 nanosheets with a direct Z-scheme heterostructure is designed and fabricated through a hydrothermal and calcination process. The photocatalytic properties of the hybrid photocatalysts are evaluated by water splitting under solar light irradiation. The optimal ratio of g-C3N4 in the hybrid is found to be 50% (wt), and the resulting TiO2/g-C3N4 composite shows the highest photocatalytic activity among the experimental samples, which is 7.7 and 1.9 times higher than that of bare g-C3N4 and TiO2, respectively. The outstanding H2 production activity benefits from the synergistic effects of highly dispersed 3D TiO2 microflowers, extended photo-response to visible light through coordinating with 2D g-C3N4 nanosheets and the strong coupling effect resulting from an efficient direct Z-scheme structure. Photoluminescence and photocurrent response results reveal that the photoinduced e−-h+ pairs in this 3D/2D direct Z-scheme heterojunction can be separated efficiently, which also accounts for the obtained outstanding performance. Our results suggest that constructing a 3D/2D Z-scheme heterojunction in photocatalysts could be an efficient way to realize high speed solar H2 production.

Rational construction of plasmon Au assisted ferroelectric-BaTiO3/Au/g-C3N4 Z-scheme system for efficient photocatalysis

Abstract Application of Z-scheme heterojunction systems toward mimicking natural photosynthesis is an efficient methodology to improve solar energy conversion. Herein, we successfully develop a Z-scheme heterojunction photocatalyst by using Au nanoparticles as electron mediator to couple ferroelectric-BaTiO3 nanowires and g-C3N4. This rationally constructed Z-scheme system with the extra surface plasmon resonance (SPR) effect of Au nanoparticles and ferroelectricity of BaTiO3 shows the significantly enhanced generation and separation efficiency of photogenerated carriers and the high reduction ability of elections. Accordingly, it exhibits the high photocatalytic performance for both H2 evolution and RhB degradation. In particular, its H2 evolution rate is about 18 times to that of g-C3N4 alone. The reasonable interfacial charge transfer mechanism discovered in this work provides a new approach to understanding and designing other efficient Z-scheme heterojunction systems.

Rationally designed Fe2O3/GO/WO3 Z-Scheme photocatalyst for enhanced solar light photocatalytic water remediation

A novel ternary Fe2O3/GO/WO3 all-solid-state Z-Scheme photocatalyst was rationally designed. Structural, morphological, optical and electronic properties of the synthesized nanocomposite were investigated by XRD, SEM, TEM, UV–vis Diffuse Reflectance and Raman spectroscopy. The results revealed the successful synthesis of the nanocomposite materials. Uniquely, double absorption edges at 2.0 and 2.3 eV for Fe2O3/WO3 and triple absorption edges at 1.5, 1.8 and 2.1 eV for Fe2O3/GO/WO3 were investigated for the first time. Lower absorption band edges dominated for both Fe2O3/WO3 and Fe2O3/GO/WO3, while higher absorption edges dominated for pure nanomaterials. The enhanced interaction among GO, Fe2O3 and WO3 matrix explained the reduction in the CB energy leading to efficient electron separation and transformation and consequently improving the photocatalytic activity. The visible light photocatalytic performance of Fe2O3/GO/WO3 nanocomposites were evaluated for degradation of methylene blue (MB) and crystal violet (CV) dyes as model water pollutants. The photocatalytic activity for degradation of both dyes was found to be greatly enhanced in the presence of ternary Fe2O3/GO/WO3 nanocomposite as compared to nanocomposite systems of Fe2O3/WO3, WO3/GO and Fe2O3/GO or pure Fe2O3 and WO3 nanomaterials. The enhancement in the photocatalytic performance of the ternary Fe2O3/GO/WO3 nanocomposite was expected to be due to the all-solid-state Z-Scheme in which the photogenerated electrons in the CB of photosystem I (WO3) transferred through GO mediator and recombined with the photogenerated holes in the VB of Fe2O3 (photosystem II). So that, the electron-hole pair recombination can be suppressed in both systems. Moreover, the photocatalytic activity of Fe2O3/GO/WO3 nanocomposite has been tested for the degradation of phenol. The results show that 95.4% of phenol was degraded in 120 min. This study provides an efficient green Z-Scheme photocatalyst for water remediation utilizing solar light.

Z-scheme structure SnS2–Au–CdS with excellent photocatalytic performance for simultaneous removal of Cr(VI) and methyl orange

A highly efficient Z-scheme photocatalyst SnS2–Au–CdS was fabricated by photoreduction and thiourea medium deposition methods. It was found that Au nanoparticles were successfully anchored on the surface of SnS2, and CdS nanoparticles were further deposited on the surface Au nanoparticles by the strong interaction of S–Au. Compared to SnS2, CdS, SnS2–Au, and SnS2–CdS, Z-scheme structure SnS2–Au–CdS shows the best photocatalytic performance for methyl orange (MO) degradation and Cr(VI) reduction under visible light irradiation. The outstanding photocatalytic performance of SnS2–Au–CdS can be ascribed to the special Z-scheme structure which not only improves the separation of photogenerated charge carriers but also preserves its high redox ability. In addition, SnS2–Au–CdS exhibited synergistic effects in photocatalytic removal of Cr(VI) and MO.

Highly efficient Z-scheme structured visible-light photocatalyst constructed by selective doping of Ag@AgBr and Co3O4 separately on {010} and {110} facets of BiVO4: Pre-separation channel and hole-sink effects

To improve the visible-light photocatalytic activity and photo-carriers separation of BiVO4, highly efficient Z-scheme structured visible-light photocatalyst Ag@AgBr/BiVO4/Co3O4 was constructed by selective doping of Ag@AgBr and Co3O4 on {010} and {110} facets of BiVO4. Due to the different energy levels of conduction band (CB) and valence band (VB) between {010} facet and {110} facet, BiVO4 could act as the ‘pre-separation channel’ to achieve spatial charge separation. Such pre-separation channel effect improved photo-electrons transfer from BiVO4{010} facets to electron mediator (Ag°) for subsequent recombination with holes of AgBr. Thus, the photo-induced electrons of AgBr could be accumulated on CB for reduction of O2 to O2−. On the other hand, holes of BiVO4 accumulated on {110} facets were captured by deriving-hole-type co-catalysts Co3O4 for organics oxidation. In addition, Ag° not only served as the electron mediator of Z-scheme but also improve the visible-light utilization due to SPR-effect. Being attributed to the synergistic effect of pre-separation channel and deriving-hole-type co-catalysts, Z-scheme structured Ag@AgBr/BiVO4/Co3O4(0.15 wt%) achieved high photodegradation rate of organics. Even after 9th cycles, Ag@AgBr/BiVO4/Co3O4(0.15 wt%) could still photodegraded more than 90% of OTC within 24 min. DRS, PL and photoelectrochemical analyses also confirmed the improvement of visible-light utilization and charge separation of Ag@AgBr/BiVO4/Co3O4. The radical trapping experiments and EPR demonstrated that both superoxide radical (O2−) and holes (h+) were main active species for organics photodegradation. In summary, this work not only constructed a highly efficient Z-scheme structured visible-light photocatalyst, but also provided a new method to diminish the photo-carriers recombination by pre-separation channel and hole-sink effects.

AgxH3-xPMo12O40/Ag nanorods/g-C3N4 1D/2D Z-scheme heterojunction for highly efficient visible-light photocatalysis.

Reasonably designing Z-scheme photocatalysts has been deemed to be an ideal and prospective way to develop new and highly efficient photocatalytic materials for removing environmental pollutants. Herein, a new type of AgxH3-xPMo12O40/Ag nanorods/g-C3N4 1D/2D Z-scheme photocatalyst (abbr. APM/C3N4) was fabricated by a simple self-assembly procedure. Transmission electron microscopy (TEM) images revealed that the 1D silver polyoxometalate (POM) nanorods loaded with Ag nanoparticles (AgxH3-xPMo12O40/Ag = APM) were well dispersed on the plicated 2D g-C3N4 nanosheets. Photocatalytic experiments demonstrated that these composite catalysts exhibited an excellent and durable photocatalytic performance for the degradation of methyl orange (MO) and tetracycline (TC) and the photoreduction of Cr(vi) under visible light, which was significantly higher than that of the individual components and most of the previous reported materials. The photocatalytic mechanism suggests that superoxide and holes are the main active species in MO photodegradation, demonstrating its Z-scheme photocatalytic process. The synergistic effects of the enhanced light absorption, unique 1D/2D hybrid heterojunction structure, good and efficient interfacial contact and Z-scheme process endowed the as-prepared APM/C3N4 composites with excellent performance. This study may provide a new comprehension into the design of polyoxometalate-based Z-scheme hybrid materials for photocatalytic applications in the removal of organic and inorganic pollutants from wastewater.

Enhanced Rhodamine B and coking wastewater degradation and simultaneous electricity generation via anodic g-C3N4/Fe0(1%)/TiO2 and cathodic WO3 in photocatalytic fuel cell system under visible light irradiation

Degradation of pollutants can be integrated with electricity generation in Photocatalytic fuel cell under light irradiation or self-powered fuel cell in the dark. In fuel cell driven by electrode reactions, the electrode reduction and oxidation transforms chemical energy in pollutants into electrical energy. In this work, Rhodamine B and coking wastewater were treated, using an efficient Z-scheme g-C3N4/Fe0(1%)/TiO2 as an anodic catalyst and WO3 as a cathodic catalyst. After 100 min of reaction in a single chamber fuel cell with 10 Ω of external resistance, in 0.05 M Na2SO4 electrolyte, the paired stainless-steel electrodes loaded respectively with g-C3N4/Fe0(1%)/TiO2 and WO3, degraded 98% Rhodamine B and generated 0.95 V cell voltage under 50 W visible-light irradiation, while removed 60% RhB and generated 0.5 V without light. To investigate the PFC performance of g-C3N4/Fe0(1%)/TiO2 in treating real coking wastewater, at optimal pH 2, 91% chemical oxygen demand (COD) and 89% total organic carbon (TOC) were removed and generated 0.3 V cell voltage. The influence of pH on photocatalytic degradation performance and cell voltage are evaluated. The high cell voltage is attributed to the very low impedance of the g-C3N4/Fe0(1%)/TiO2 loaded anode. The excellent electrochemical properties of paired electrodes help in generating higher current density, due to the increased photocatalyst activity of the tridimensional catalyst as proved by electron spinning resonance spectrum, photoluminescence, and Electric Impedance Spectrum analysis.

Ultrathin Visible-Light-Driven Mo Incorporating In2 O3 -ZnIn2 Se4 Z-Scheme Nanosheet Photocatalysts.

Inspired by natural photosynthesis, the design of new Z-scheme photocatalytic systems is very promising for boosting the photocatalytic performance of H2 production and CO2 reduction; however, until now, the direct synthesis of efficient Z-scheme photocatalysts remains a grand challenge. Herein, it is demonstrated that an interesting Z-scheme photocatalyst can be constructed by coupling In2 O3 and ZnIn2 Se4 semiconductors based on theoretical calculations. Experimentally, a class of ultrathin In2 O3 -ZnIn2 Se4 (denoted as In2 O3 -ZISe) spontaneous Z-scheme nanosheet photocatalysts for greatly enhancing photocatalytic H2 production is made. Furthermore, Mo atoms are incorporated in the Z-scheme In2 O3 -ZISe nanosheet photocatalyst by forming the MoSe bond, confirmed by X-ray photoelectron spectroscopy, in which the formed MoSe2 works as cocatalyst of the Z-scheme photocatalyst. As a consequence, such a unique structure of In2 O3 -ZISe-Mo makes it exhibit 21.7 and 232.6 times higher photocatalytic H2 evolution activity than those of In2 O3 -ZnIn2 Se4 and In2 O3 nanosheets, respectively. Moreover, In2 O3 -ZISe-Mo is also very stable for photocatalytic H2 production by showing almost no activity decay for 16 h test. Ultraviolet-visible diffuse reflectance spectra, photoluminescence spectroscopy, transient photocurrent spectra, and electrochemical impedance spectroscopy reveal that the enhanced photocatalytic performance of In2 O3 -ZISe-Mo is mainly attributed to its widened photoresponse range and effective carrier separation because of its special structure.

Visible-light degradation of sulfonamides by Z-scheme ZnO/g-C3N4 heterojunctions with amorphous Fe2O3 as electron mediator

ZnO grafted amorphous Fe2O3 matrix (ZnO/Fe2O3) was coupled with g-C3N4 to synthesize heterojunction photocatalysts with a loosened multilayered structure. The ZnO/Fe2O3/g-C3N4 exhibited enhanced photocatalytic performance in the degradation of sulfamethazine under visible-light irradiation (λ > 420 nm), with an optimum photocatalytic degradation rate approximately 3.0, 2.4 times that of pure g-C3N4 and binary ZnO/g-C3N4. Moreover, the target sulfonamides spiked in actual surface water samples could be efficiently photodegraded by ZnO/Fe2O3/g-C3N4 after 8 h of irradiation, demonstrating its practical potential. An amorphous Fe2O3-mediated Z-scheme mechanism was proposed for the charge transfer at the heterojunction surface, which involved a Fe(III)/Fe(II) oxidation-reduction center that favored the retarded charge recombination and improved photocatalytic activity. Such a mechanism was well supported by the direct detection of surface generated O2− and OH reactive species. Finally, detailed transformation pathways were proposed based on the photodegradation products identified by QToF-MS analyses. This work provides an illustrative strategy for developing efficient Z-scheme photocatalysts for water purification, by taking advantage of amorphous Fe-based oxides in the semiconductor lattice matching.

Non-additional carbon source one-step synthesis of Bi2O2CO3-based ternary composite for efficient Z-scheme photocatalysis

Bi2O2CO3-based ternary composite materials are generally synthesized by two- or multi-step method and special precursor of CO32− is usually utilized in synthesis of Bi2O2CO3, which are time-consuming, laborious and relatively costly. In this paper, for the first time, a facile one-step solvothermal method is used to fabricate Z-scheme Bi2O2CO3/Bi/Bi2WO6 ternary composites. Interestingly, ethylene glycol not only acts as solvent for the reaction system, but also reduced Bi3+ into metallic Bi and itself is oxidized to CO32−, which could construct Bi2O2CO3. On this occasion, Bi2O2CO3/Bi/Bi2WO6 ternary composites are obtained after one-step method. High resolution transmission electron microscopy clearly reveals each component in composites. The as-prepared samples could be applied in various photocatalytic activities. Under solar light irradiation, Bi2O2CO3/Bi/Bi2WO6 composites exhibited prominent photodegradation performances for both ciprofloxacin and bisphenol A. Meanwhile, these composites could also be used in efficient photoreduction of CO2. The efficient photocatalytic activity could be mainly ascribed to Z-scheme electron transfer mechanism in ternary composites, which is determined by surface redox reactions, active species trapping experiment, electron spin resonance spectrum.