Z-scheme Mechanism Research Articles

Phase transition guided V2O5/β-Bi2O3 Z-scheme heterojunctions for efficient photocatalytic Hg0 oxidation

The incorporation of vanadium during the synthesis process induced a spontaneous and complete thermal phase transition from α-Bi2O3 to β-Bi2O3. This phase transition facilitated the development of intrinsic electric field at the interface between V2O5 and β-Bi2O3, consequently establishing a novel carrier transfer pathway. As a result, the fabricated V2O5/β-Bi2O3 heterojunction exhibited an outstanding removal efficiency of over 98 % for gaseous mercury (Hg0) under UV light, and this efficiency of 95.0 % even after 35 h of testing. Introducing vanadium enhanced the light absorption capacity in the ultraviolet region and effectively separated photoinduced charge carriers. As revealed by density functional theory calculations, the photoinduced electron–hole transfer in the V2O5/β-Bi2O3 heterojunction followed the Z-scheme mechanism. This mechanism significantly contributed to the long-term stability of photocatalytic Hg0 removal, even when H2O and NO were present. This study presents a novel material composited by a thermal phase transition technique, aimed at the highly effective and green removal of Hg0 in the environment.

Enhanced photocatalytic activities of ZnO/Bi2O3 hollow composites via the Z-scheme mechanism through p–n heterojunctions

Constructing Z-scheme heterojunctions by establishing a unique charge transfer pathway at the interface has garnered growing attention in photocatalytic technology. In this study, a p-n heterojunction of Z-scheme was developed by employing an in-situ annealing strategy following the electrostatic self-assembled chemistry, with n-type ZnO and p-type Bi2O3 as the constituent materials. Upon AM 1.5 G irradiation, the optimal ZnO/Bi2O3(Zn/BO) photocatalysts achieved a remarkable H2-evolution reaction (HER) rate of 458.3 μmol∙h−1, which was 10.5 times higher than that of the original ZnO and 5 times higher than that of Bi2O3, respectively. Moreover, its efficiency in degrading 100 mg∙L−1 rhodamine B (RhB) reached 100% within a 60-minute period. Its rate constant was 24.70 and 11.71 times higher compared to ZnO and Bi2O3, respectively. The proposed Z-scheme mechanism of electron transfer was put forward to explain the observed enhancement in photocatalytic performance, as determined by in-situ XPS experiments. Furthermore, the Zn/BO photocatalyst exhibited exceptional catalytic activity when exposed to visible light (λ > 420 nm). The remarkable cycle stability of the hollow Z-scheme catalyst further suggests its potential for facilitating the industrialization of photocatalytic technology.

Activation of persulfate ions by QDs-sized Z-scheme TiO2−x/Cu3Mo2O9 photocatalysts in visible-light detoxification of organic contaminants

As known, colored TiO2−x is a promising material in the photocatalytic detoxification of water pollutants. Herein, brown TiO2−x was combined with Cu3Mo2O9 nanoparticles to fabricate quantum dot-sized photocatalysts through hydrothermal method preceded calcination at 350 °C. The optical, electrochemical, textural, structural, and morphological features of the prepared photocatalysts were explored via various techniques. The photocatalytic ability of the materials was studied in the presence of persulfate ions (PS) upon visible light to remove different pollutants. After adding PS, the TiO2−x/Cu3Mo2O9 (1%)/PS system represented an efficient performance for the degradation of tetracycline (TC), cephalexin (CFX), fuchsine (FS), and methyl orange (MO). The rate constants of TC oxidation in the TiO2−x/Cu3Mo2O9 (1%)/PS system were respectively 333, 245, 198, 190, 95.2, 92.9, 77.9, and 2.03 times higher than the TiO2, PS, TiO2/PS, Cu3Mo2O9, Cu3Mo2O9/PS, TiO2−x, TiO2−x/PS, and TiO2−x/Cu3Mo2O9 (1%) systems. So, the synergistic effect of PS and heterogeneous photocatalysis was confirmed by the TiO2−x/Cu3Mo2O9 (1%) material in the removal reactions. The quenching tests demonstrated that the •O2−, h+, •OH, and •SO4− are key reactive species. Finally, a Z-scheme mechanism was suggested for the degradation reactions by TiO2−x/Cu3Mo2O9 /PS system.

Oxygen vacancies mediated enhanced visible-light-driven photocatalytic oxidation of biomass derived 5-hydroxymethylfurfural over V2O5·nH2O/g-C3N4 composite

A series of V2O5·nH2O/g-C3N4 (HVO/CN) heterogeneous composites were synthesized using an ultrasonic method and employed in the photocatalytic oxidation of 5-hydroxymethylfurfural (HMF) towards 2,5-diformylfuran (DFF). The HVO/CN-5 catalyst exhibited the highest photocatalytic performance with a 35.7 % yield and a 84 % of selectivity of DFF under visible light irradiation. A thorough investigation on the synthesized HVO/CN composite was executed to reveal the origin of the high photoactivity. The research results showed that the incorporation of HVO into CN widened the range of the visible-light response and improved the ability to separate the photo-induced charge carriers via a Z-scheme mechanism. Meanwhile, an increased concentration of oxygen vacancies was also observed in the composite, which enhanced the surface OH− content and facilitated the generation of hydroxyl radicals. This change is beneficial to the photocatalytic reaction since that hydroxyl and superoxide radicals are the main reactive species. A possible reaction pathway for the photocatalytic oxidation of 5-HMF to DFF was also suggested. This work may provide insights on the green and sustainable conversion of HMF to DMF via photocatalysis.

Construction of Z-scheme CoFe2O4@ZnIn2S4 p-n heterojunction for enhanced photocatalytic hydrogen production

The p-n heterojunction’s construction is considered a valid and prominent method to accelerate photogenerated carriers’ separation and transfer rate, enhancing the efficiency of photocatalytic hydrogen production. In this work, the core–shell CoFe2O4@ZnIn2S4 (CFO@ZIS) p-n heterojunction photocatalyst is designed and fabricated by growing ZIS nanosheets on yolk-shelled CFO surfaces by hydrothermal and calcination method followed by oil bath process for the first time. Notably, the CFO@ZIS-2 photocatalyst exhibits excellent cycle applicability and chemical stability and exhibits a remarkable hydrogen evolution rate of 1576.5 μmol∙g−1∙h−1 without Pt as a co-catalyst. However, the hydrogen evolution rates of pristine ZIS and CFO products are just 344.3 and 0 μmol∙g−1∙h−1, respectively. Furthermore, the analysis of structural, morphological, optical and photo/electrochemical characterizations further manifested the existence of p-n heterojunction in CFO@ZIS core–shell structure is beneficial to facilitate the separation and migration of photoinduced carriers. Meanwhile, the Z-Scheme mechanism of CFO@ZIS p-n heterojunction in photocatalytic hydrogen production has been discussed in detail. This work provides a feasible and resultful strategy to design the core–shell p-n heterojunction for the promotion of photocatalytic H2 production.

An experimental design study of photocatalytic activity of the Z-scheme silver iodide/tungstate binary nano photocatalyst.

A binary AgI/ Ag2WO4 photocatalyst was fabricated and characterized by SEM, XRD, UV-Vis DRS, and FT-IR. It was then used to photodegrade sodium ceftriaxone (CTX) in an aqueous solution. The band gap energies of 2.95, 2.78, and 2.62eV were obtained by the Kubelka-Munk model for Ag2WO4, AgI, and AgI/Ag2WO4 catalysts. The samples have pHPZC values of 6.9, 4.2, and 6.6, respectively. The synergistic photocatalytic activity of the coupled system depended on the AgI:Ag2WO4 mole ratio and grinding time (optimums:mole ratio of 4:1 and time 30min). The experimental design was used for optimizing the conditions and a quadratic model well-processed the data based on the model F value of 131.87 > F0.05,14,13 = 2.55 and LOF F value of 0.78 < F0.05,10,3 = 8.78. The optimized RSM run included the irradiation time of 85min, 3.5mg/L of CTX sample at pH 9, and a catalyst dose of 1.0g/L. Under the optimized conditions, about 63% of CTX molecules were photodegraded. In the study of the scavenging agents, the direct Z-scheme mechanism accumulated electrons in the CB-AgI and the holes in the VB-Ag2WO4 level, as stronger reducing and oxidizing centers than the accumulated electrons and holes of the type (II) heterojunction mechanism. Compared to a CTX oxidation potential of about 0.06V, the direct Z-scheme mechanism is more favorable to reduce or oxidize it.

Enhanced photocatalytic degradation activity of ZIF-8 doped with Ag2WO4 photocatalyst

BackgroundMethylene blue (MB) is a carcinogenic pollutant that is widely known for its dangerous effects on humans and marine life. MethodsHerein, Ag2WO4-supported ZIF-8 hybrid photocatalyst has been constructed simple using a hydrothermal method. The constructed photocatalysts were described by XRD, FESEM, EDX, UV–visible DRS, TEM, and BET surface area methods. FindingsThe Ag2WO4/ZIF-8 photocatalyst established high photocatalytic degradation performance under visible light toward MB dye, giving 98.3 % photodegradation of 30 mg/l MB and 0.1 g/l photocatalyst dosage in 120 min of irradiation. Also, the photostability was excellent after five rounds. The boosted photodegradation performance was attributed to the synergic mechanism, which proposed the efficient charge separation efficiency and the presence of plasmon Ag in the Ag2WO4/ZIF-8 Z-scheme heterojunction. The trapping experiments illustrated that ·O2- was primary reactive radicals in the photodegradation process of MB. This research opens a new insight into assembling new heterojunction photocatalyst with improved behavior and stability, and presents a new understanding of Surface Plasmon Resonance (SPR)-supported Z-scheme mechanism for environmental application.

ZnO/black phosphorus/C3N4 composite: An effective photocatalyst for Cr (VI) reduction and degradation of rhodamine B

The utilization of photocatalysts offers a promising approach for the removal of Cr (VI) and rhodamine dyes. Through the generation of reactive species and subsequent degradation reactions, photocatalysis provides an efficient and environmentally friendly method for the remediation of wastewater. In this study, we have synthesized an n-p-n heterojunction of carbon nitride (C3N4), zinc oxide (ZnO), and black phosphorus (BP) through the sonication-stirring method. The photocatalytic ability of this composite was examined for the decomposition rhodamine B (RhB) and detoxification of hexavalent chromium ion (up to 97% during 80 min) under Xenon irradiation. The results of trapper experiments indicated that the active species were hydroxyl radical (˙OH), electron (e−), and superoxide anion radical (˙O2−). Based on the obtained potential of the lowest unoccupied molecular orbitals (LUMO) and the highest occupied molecular orbital (HOMO) for the mentioned semiconductors, through Mutt-Schottky results, the double Z-scheme mechanism was proposed for the studied process. The electrochemical impedance spectroscopy data exhibited good charge transfer for the evaluated composite versus the pure compounds. The impressive separation of holes and electrons along with the low recombination were confirmed by the responses of photocurrent and quenching the photoluminescence (pl) intensity for the composite, respectively. The current density of the composite recorded 66.6%, 87.3%, and 92% higher than those of BP, C3N4, and ZnO, indicating an excellent electron-hole separation for the ternary composite compared to the pure semiconductors. Diffuse reflectance spectra (DRS) data revealed 2.9, 3.17, 1.15, and 2.63 eV as the band gap values for C3N4, ZnO, BP, and composite. The rate constant of the new composite to remove RhB and reduce hexavalent chromium were about 4.79 and 2.64 times higher than that of C3N4, respectively.

Enhanced Antibacterial Activity at Ag-Cu Nanojunctions: Unveiling the Mechanism with Simple Surfaces of CuNPs-on-Ag Films.

Deposition of CuNPs on silver film gives rise to the formation of active Ag-Cu interfaces leading to dramatic enhancements in antibacterial activity against Escherichia coli. Transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDAX) analyses reveal that CuNPs are covered in a thin Cu2O shell, while X-ray photoelectron spectroscopy measurements (XPS) reveal that the Ag film samples contain significant amounts of Ag2O. XPS analyses show that the deposition of CuNPs on Ag films leads to the formation of a photoactive Ag2O-Cu2O heterostructure. Following a Z-scheme mechanism, electrons from the conduction band of Ag2O recombine with photogenerated holes from the valence band of Cu2O. Consequently, electrons at Cu2O's conduction band render Cu reduced and cause reductive activation of surface oxygen species on Cu forming reactive oxygen species (ROS). Interaction between metallic Cu and ROS species leads to the formation of a Cu(OH)2 phase. Both ROS and Cu(OH)2 species have previously been reported to lead to enhanced antibacterial properties. Holes on Ag2O produce a highly oxidized AgO phase, a phase reported to exhibit excellent antibacterial properties. Quantitative analysis of Cu and Ag high-resolution X-ray photoelectron spectroscopy (HR-XPS) spectra directly reveals several-fold increases in these active phases in full agreement with the observed increase in antibacterial activities. This study provides insight and surface design parameters by elucidating the important roles of Ag and Cu's bifunctionality as active antibacterial materials.

Enhanced photo-degradation of organic contaminants on CdS/magnetic aluminum fumarate metal-organic framework as a novel Z-scheme photocatalyst under visible light: A comprehensive study

In the current study, Fe3O4/aluminum fumarate (AlFu) magnetic nanocomposite has been synthesized through the sol-gel procedure to be used as a novel support for CdS nanorods in photocatalytic degradation of Congo red (CR) and crystal violet (CV) dyes in aqueous media under visible light irradiation, separately. The CdS nanorods were solvothermally decorated on magnetic AlFu. The physicochemical properties of the synthesized samples were examined by multiple techniques. In comparison to pure CdS, the photocatalytic performance of magnetical separable Cd/magnetic AlFu is striking. This could be attributed to improving the recombination rate, charge transfer resistance, and adsorption site, which are figured out through characterization data. Removal of contaminants has been statistically optimized and modeled based on operational parameters, including catalyst dosage, initial dye concentration, and pH. At optimum conditions, the removal of CR and CV dyes was 99.5 % and 86.17 %, respectively. Moreover, the photocatalyst exhibited satisfactory performance in TOC removal and remarkable stability during six successive cyclic operations. At several dye concentrations, kinetic experiments have been undertaken, and results revealed that the photo-degradation reaction of CR and CV corresponds well with the Langmuir-Hinshelwood model. Furthermore, the Z-scheme mechanism was suggested based on characterization data and quenching experiments, which revealed that •O2- plus h+ in CR photo-degradation, and •O2- plus •OH in CV photo-degradation play pivotal roles.

Biowaste derived UV–Visible-NIR active Z-scheme CaO/MoS2 photocatalyst as a low-cost, waste-to-resource strategy for rapid wastewater treatment

There is a need for industries to adopt greener strategies to minimise the environmental impact and overuse of natural resources. In the light of alarming environmental conditions, there is an expanding and progressing centre around the concept of waste to resource strategy. With this inspiration, a low-cost marine biowaste-based CaO/MoS2 photocatalyst synthesized by ball milling is proposed with a viable green route for water remediation. The mass ratio of CaO and MoS2 were optimized for the photocatalytic reduction of cationic methylene blue (MB) as a probe dye and an actual industrial dye wastewater. It was found that 45CaO/55MoS2 (45-CaMo) outperformed all the proportions including the conventionally popular TiO2. 70% of MB got discoloured in 10 min of exposure to natural sunlight following Langmuir-Hinshelwood model with a rate constant of 0.064 min−1 and exhibiting good photo-stability. The morphology and crystallinity were studied by scanning electron microscopy (SEM) and X-ray diffraction (XRD). UV–Visible-NIR spectroscopy and calculations reveal the activity of the synthesized photocatalyst in UV, visible and IR regions with a direct Z-scheme mechanism as its probable charge modulation technique. This work offers new perspectives and directions for future research using waste-derived resources and renewable energy.

Magnetically separable NiZn-ferrite/CeO2 nanorods/CNT ternary composites for photocatalytic removal of organic pollutants

Water scarcity and contamination are the foremost global one health challenges, which require immediate nano/biotechnology–based innovative interventions. Hybrid nanocomposites have emerged as novel nanoplatforms for wastewater remediation through photocatalytic degradation of persistent organic pollutants. This unprecedented study reports the economical fabrication of novel nanoplatforms based on Ni0.5Zn0.5Fe2O4 and CeO2 (using the modified hydrothermal method) and their binary and ternary hybrid nanocomposites of Ni0.5Zn0.5Fe2O4/CeO2 and Ni0.5Zn0.5Fe2O4/CeO2/multi-walled carbon nanotubes (MWCNT) (using facile ultra-sonication method) respectively, for water health management. The engineered nanocomposites were evaluated for the Z-scheme mechanism using morphological (SEM, TEM), structural (XRD), optical (UV–Visible spectroscopy), magnetic (VSM), electronic and compositional (XPS) analyses and employed for wastewater remediation. The ternary hybrid composites exhibit excellent photocatalytic degradation efficacy (93.5%) for removing rose bengal (RB) dye from wastewater on UV illumination. The high dye-removal efficacy of ternary hybrid is attributed to the suitable band gap positions of Ni0.5Zn0.5Fe2O4 and CeO2 metal oxides enhancing its photodegradation efficiency on UV illumination, and to the MWCNT enhancing the recombination time of photogenerated electron-hole pairs during dye-removal phenomena. Owing to their excellent performance and robust stability, the engineered ternary composites possess enormous potential for degrading diversified organic pollutants for wastewater treatment and contribute to One Health management, where photocatalytic degradation attributes are a prerequisite.

Effective graphene incorporation of strontium niobate–doped titanium oxide for photocatalytic hydrogen production

To meet the increasing global demand for clean energy and mitigate the impact of CO2 emissions on climate change, the production of photocatalytic hydrogen through water splitting is a compelling scientific and technological objective. Despite considerable efforts, the establishment of a reliable and highly efficient system for hydrogen generation powered by visible light remains challenging. In this study, we developed a solar-active strontium niobate-doped titanium oxide incorporated with graphene (Sr2Nb2O7–rGO–TiO2), characterized by various analytical techniques such as optical, morphological, HR-TEM, XPS, and XRD. Sr2Nb2O7–rGO–TiO2 demonstrated enhanced photocatalytic H2 evolution under solar irradiation without requiring precious-metal doping. The maximum H2 production performance rate of 1769 μmol/g/h was attained with the Sr2Nb2O7–rGO–TiO2 composites, significantly surpassing those of the bare (TiO2: 210 μmol/g/h, Sr2Nb2O7: 88 μmol/g/h) and binary (TiO2–rGO: 430 μmol/g/h, Sr2Nb2O7–rGO: 176 μmol/g/h, and Sr2Nb2O7–TiO2: 880 μmol/g/h) photocatalysts. The enhanced performance of the Sr2Nb2O7–rGO–TiO2 composite is attributable to the synergistic effect of rGO acting as an electron-transfer bridge. Thus, with the integration of rGO, absorption is attainable in an extended range up to 445 nm (2.90 eV), suggesting that the composite material could enable the catalyst to absorb more visible light. Additionally, the composite exhibited minor degradation after five consecutive cycles, demonstrating its excellent stability and reusability for hydrogen generation. Based on a comprehensive evaluation of the ESR and transient photocurrent response, a potential Z-scheme mechanism for the photocatalytic H2 generation activity over Sr2Nb2O7–rGO–TiO2 was suggested. The Z-scheme processability allows more electrons to contribute to the H2 evolution reduction. In this study, we developed a non-toxic, cost-effective, highly efficient, and recyclable photocatalyst for H2 production.

Z-scheme MnO2/Mn3O4 heterojunctions with efficient peroxymonosulfate activation for organic pollutant removal

The exploration of efficient heterogeneous catalysts for persistent organic pollutant removal is extremely attractive. In the present work, MnO2/Mn3O4 photo-Fenton catalysts were designed by a facile hydrothermal route to activate peroxymonosulfate (PMS) under visible light irradiation for organic pollutant degradation. The optimized MnO2/Mn3O4 heterojunction shows excellent Rhodamine B (RhB) removal efficiency, whose apparent kinetic constant is 11.9 and 5.36 times as high as the MnO2 and Mn3O4. Meanwhile, there is a neglectable attenuation in catalytic performance after 5 recycling runs. Based on the active species trapping experiments, the non-radical process contributes more than the radical process during RhB degradation. Moreover, factors including the dosage of PMS, initial RhB concentration, initial pH, the presence of various anions, different organic pollutants, and water sources are investigated. Systematical characterizations reveal that the enlarged specific surface areas and the efficient charge separation aroused from the Z-scheme mechanism are attributed to the enhanced photo-Fenton performance. The present work contributes to the construction of the Mn-based photo-Fenton catalyst with efficient PMS activation capacity for environmental remediation.

GQD@NiFe-LDH Nanosheets for Photocatalytic Activity towards Textile Dye Degradation via Lattice Contraction.

The functionalized NiFe-LDH with photosensitized GQDs were synthesized through the hydrothermal route by differing the amount of GQDs solution and studied its efficacy towards the mineralization of textile dyes under visible light. The synthesized samples were characterized by XRD, FESEM, HRTEM, DRUV-Vis, RAMAN, XPS, and BET. The combined effect of the hexagonal carbon lattice in GQD and open layered porous structure of NiFe-LDH nanosheets results in the contraction of the lattice. Different reactive and conventional dyes were taken as representative dyes to evaluate the activity of the as-synthesized photocatalysts. The enhanced electron absorption/donor effect between GQDs and NiFe-LDH, and the growth of oxygen-bridged Ni/Fe-C moieties enable the composite to exhibit better photocatalytic activity. Both photocatalytic activity and characterization results confirmed that the GQD@NiFe-LDH nanocomposite heterostructure synthesized at 160 °C by taking 10 mL of GQDs aqueous solution named GNFLDH10 has a higher degree of crystallinity and has the best photocatalytic efficiency compared to other reported visible light catalysts. Specifically, the above optimized GQD@NiFe-LDH photocatalyst is capable of photo-mineralizing 50 ppm of Reactive Green in 20 min, Reactive Red in 20 min, and Congo Red in 25 min respectively following a direct Z-scheme mechanism with substantial reusability.

One-step preparation of novel Bi-Bi2O3/CdWO4 Z-scheme heterojunctions with enhanced performance in photocatalytic NH3 synthesis

This study focuses on the design and synthesis of a novel ternary composite photocatalyst, Bi-Bi2O3/CdWO4, using a one-step solvothermal method. A comprehensive investigation was conducted to analyze the morphology, specific surface area, structure, optical property, and photoelectric chemical property of the composite. The incorporation of Bi-Bi2O3 was found to significantly impact the growth of CdWO4 crystals, resulting in a morphological transformation into nanoparticles. This morphological change has been shown to enhance the specific surface area of the catalyst, thereby improving its catalytic performance. Furthermore, the incorporation of Bi-Bi2O3 has been demonstrated to greatly enhance the light absorption capability of CdWO4, which also favored the photocatalytic N2 fixation (PNF) reaction. However, after conducting a comprehensive analysis of different Bi-BiO3/CdWO4 and two reference samples Bi/CdWO4 and Bi2O3/CdWO4, it was determined that the improvement of photogenerated charge carrier separation efficiency is the decisive factor determining the performance of the ternary composite catalyst. The closely bound Bi-Bi2O3 on the CdWO4 surface triggers the formation of a heterojunction structure at their interface. By analyzing the band structure of CdWO4 and Bi2O3, it is suggested that the heterojunction operates through a Z-scheme mechanism. The Bi metal serves as a bridge that intimately binds CdWO4 and Bi2O3, facilitating the rapid migration of electrons and improved charge separation. Therefore, the Bi-Bi2O3/CdWO4 composite exhibits high performance in PNF reactions. The optimal 7.5% Bi-Bi2O3/CdWO4 catalyst presents a PNF rate of 434.9 μmol L−1 g−1 h−1 under simulated sunlight irradiation, which is 4.9 times that of pure CdWO4. These findings from this study may offer valuable insights into the design and synthesis of new photocatalysts for PNF.

Sn and dual-oxygen-vacancy in the Z-scheme Bi2Sn2O7/Sn/NiAl-layered double hydroxide heterojunction synergistically enhanced photocatalytic activity toward carbon dioxide reduction

Photocatalytic conversion of carbon dioxide (CO2) into high value-added chemicals is an attractive yet challenging process, primarily due to the readily recombination of hole-electron pairs in photocatalysts. Herein, dual-oxygen-vacancy mediated Z-scheme Bi2Sn2O7/Sn/NiAl-layered double hydroxide (VO,O-20BSL) heterojunctions were hydrothermally synthesized and subsequently modified with Sn monomers to enhance photocatalytic activity toward CO2 reduction. The abundance of oxygen vacancies endowed the VO,O-20BSL with extended optical adsorption, enhanced charges separation, and superior CO2 adsorption and activation. The interfacial charges transfer of the VO,O-20BSL was demonstrated to follow a Z-scheme mechanism via photochemical deposition of metal/metal oxide. Under visible light irradiation, the VO,O-20BSL exhibited the highest yields of carbon monoxide (CO) and methane (CH4), with values of 72.03 and 0.85 umol·g−1·h−1, respectively, which were 2.66 and 1.57 times higher than that of the VO-NiAl-layered double hydroxide (VO-1LDH). In situ diffuse reflectance infrared fourier transform spectroscopy (DRIFTS) revealed that carboxylic acid groups (COOH*) and aldehyde groups (CHO*) were the predominant intermediates during CO2 reduction, and accordingly, possible CO2 reduction pathways and mechanism were proposed. This study presents a feasible approach to incorporate dual vacancies into Z-scheme heterojunctions for CO2 reduction.

Construction of Z-Scheme MoS2/ZnFe2O4 heterojunction photocatalyst with enhanced photocatalytic activity under visible light

Construction of direct Z-scheme heterostructure photocatalysts with improved photogenerated charge carriers has gained considerable attention during the past few years. In this work, a direct Z-scheme MoS2/ZnFe2O4 heterostructure photocatalyst was synthesized via a facile hydrothermal method. The photocatalytic activity of this photocatalyst was evaluated through degradation of methylene blue (MB) dye under visible light irradiation. The MZF-25 catalyst showed high catalytic activity with a degradation efficiency of 92.3%, higher than that of pristine MoS2 and ZnFe2O4. Further, the reusability of the MoS2/ZnFe2O4 heterostructure was analysed and there was no significant loss in the photocatalytic activity even after four cycles. Finally, the Z-scheme mechanism of the MoS2/ZnFe2O4 photocatalyst was determined for the degradation of MB. This work provides a promiosing strategy for designing MoS2/ZnFe2O4-based Z-scheme heterostructures for removal of organic pollutants.

Visible light photocatalysis: efficient Z-scheme LaFeO3/g-C3N4/ZnO photocatalyst for phenol degradation.

In this work, a Z-scheme LaFeO3/g-C3N4/ZnO heterojunction photocatalyst with large specific surface (68.758 m2/g) and low cost (0.00035 times the cost of per gram of Au) was easily synthesized by glucose-assisted hydrothermal method. The structure, surface morphology, and optical properties of the photocatalyst were investigated. The constructed Z-scheme heterojunction catalysts can enhance the visible light absorption and carrier separation efficiency. Among these photocatalysts, the 10%-LaFeO3/g-C3N4/ZnO composite possesses the premium performance for efficient degrading 97.43% of phenol within 120 min. Even after 5 cycles, it still sustains an excellent photocatalytic stability (92.13% phenol degradation). According to the XPS surface states and the capture of active species on LaFeO3/g-C3N4/ZnO, the electrons would be transferred from ZnO and LaFeO3 to g-C3N4. In addition, ·OH plays an important role in photocatalytic reactions for phenol degradation. Thus, the proposed possible photocatalytic reaction mechanism of Z-scheme LaFeO3/g-C3N4/ZnO can provide a more economical and efficient conception for phenol degradation.

Photocatalytic degradation of bisphenol A by temperature-sensitive magnetic hydrogel with enhanced service life

Easy diffusion and low reusability limit the practicality of photocatalysts. In this study, a hollow sphere (HS) heterojunction was synthesized based on oxygen-doped carbon nitride (OCN) and layered double hydroxides (LDHs). A thermosensitive HS hydrogel (HS Gel) was prepared by mixing HS with N-isopropylacrylamide. Bisphenol A (BPA), being widely manufactured and used in commercial and domestical products and its high toxicity, was chosen as the target pollutant to demonstrate the photocatalytic ability and practicality of the HS Gel. HS Gel presented effective BPA degradation (95% degradation in 70 mins, 4.2 × 10−2 min−1 of kobs) at ambient temperature which is much better than kobs = 1.8 × 10−2 min−1 of OCN and kobs = 0.08 × 10−2 min−1 of LDH), and increased by two-fold the recycling service life (retention of >80% degradation efficiency after 13 usage cycles) compared to other carbon-based photocatalysts (retention of >80% degradation efficiency after 5–6 usage cycles). This is due to its multifunctional characteristics (magnetic property and thermal sensitivity). Under ambient temperature, the hydrophilic HS Gel swelled in the aqueous solution, which promoted the photocatalytic reaction between HS and BPA in the gel state. After the reaction, the HS Gel was subjected to shrinkage by high temperature heating to enhance the mechanical strength for recovery. The magnetic recovery was realized by the paramagnetic properties of layered double oxide to reduce environmental interference. Detailed studies of HS gel related to enhanced service life were conducted including structural changes, catalyst leaking and magnetic changing. A new kind of type Ӏ plus Z-scheme mechanism was also proposed based on the Kubelka-Munk equation, UV diffuse reflectance spectroscopy and Mott-Schotty technique.