Z-scheme Type Research Articles

The ZnO–Au-Titanium oxide nanotubes (TiNTs) composites photocatalysts for CO2 reduction application

The presence of gold nanoparticles (Au) on the zinc oxide (Zn)-titanium oxide nanotubus (TiNTs) composites to form the Z-scheme type photocatalysts has been investigated for photocatalytic reduction of CO2 to methanol. In this study, the commercial titanium dioxide powder (P-25) was first treated under a strong basic environment and applied a hydrotherrmal method to systhsize TiNTs, and calcined to use as a support. Then, various ratios of ZnO and TiNTs from 0.1 to 0.5 were also prepared by hydrothermal method to form TiNTs-ZnO-X (TZ-X, X is equal to the ZnO/TiNTs weight ratio) composites, and 1 to 5 wt % of Au were impregnated on the TiNTs-ZnO support to form the ZnO–Au-TiNTs composite photocatalysts.The catalysts will be characterized by x-ray diffraction spectroscopy (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–visible spectroscopy (UV–Vis) and photoluminescence spectroscopy (PL) techniques to determine the structures and morphology of the ZnO–Au-TiNTs composites. The catalytic results have revealed that the TZ-0.20–2 wt% Au catalyst has the best photocatalysis activity with a 7777.1μmole/(g-cat) (hr) CH3OH production yield.The formation of the ZnO–Au-TiNTs Z-scheme type heterostructure results in an efficient electron transfer pathway and electron-hole separation inside the composite catalyst which lead to a highly efficient CO2 reduction and excellent improvement in methanol yield.

Z-scheme transition metal bridge of Co9S8/Cd/CdS tubular heterostructure for enhanced photocatalytic hydrogen evolution

Narrow band gap semiconductors heterojunction with superior coupling and composition matching can enhance light absorption, reduce carrier recombination and increase redox activity. Here, we report Co9S8/Cd/CdS Z-scheme type heterojunctions with hierarchical tubular heterostructure and inexpensive transition metallic electronic bridge between two distinct semiconductors by a simultaneous immobilization and in-situ reduction strategy. The designed heterostructure greatly promotes the redox activity owing to high-density catalytic sites, excellent visible light capture by small band gap Co9S8/CdS and hollow framework in conjunction with fast charge separation and smooth transfer through intermediary conductive Cd. The optimized photocatalyst exhibits a hydrogen generation rate up to 10.42 μmol h−1 without obvious drop in performance over multiple cycles. The structural design, matching tandem constituent and continuous phase mediator are the pivotal factors to engender an efficient solid-state Z-scheme photocatalysis. The facile synthetic approach and noble metal free tandem structure of this work provide alternative avenues for the development of heterojunction photocatalysts for efficient solar-to-chemical conversion.

Highly Efficient InGaN Nanorods Photoelectrode by Constructing Z-scheme Charge Transfer System for Unbiased Water Splitting.

Unbiased photoelectrochemical water splitting for the promising InGaN nanorods photoelectrode is highly desirable, but it is practically hindered by the serious recombination of charge carrier in bulk and surface of InGaN nanorods. Herein, an unbiased Z-scheme InGaN nanorods/Cu2 O nanoparticles heterostructured system with boosted interfacial charge transfer is constructed for the first time. The introduced Cu2 O nanoparticles pose double-sided effect on photoelectrochemical (PEC) performance of InGaN nanorods, which enables a robust hybrid structure and induces weakened light absorption capability simultaneously. As a result, the optimized InGaN/Cu2 O-1.5C photoelectrode with the uniform morphology exhibits an enhanced photocurrent density of ≈170 µA cm-2 at 0 V versus Pt, with 8.5-fold enhancement compared with pure InGaN nanorods. Comprehensive investigations into experimental results and theoretical calculations reveal that the electrons accumulation and holes depletion of Cu2 O facilitate to form a typical Z-scheme band alignment, thus providing a large photovoltage to drive unbiased water splitting and enhancing the stability of Cu2 O. This work provides a novel and facile strategy to achieve InGaN nanorods and other catalyst-based PEC water splitting without external bias, and to relieve the bottlenecks of charge transfer dynamics at the electrode bulk and electrode/electrolyte interface by constructing Z-scheme heterostructure.

Development of Cu-Doped ZIF-8/g-C3N4 Photocatalyst and Hydrogen Generation from Water Splitting

Energy and environmental issues are serious problems and early solution is desired. In particular, the impact of using fossil fuels is significant. Although it is somewhat affected by technological innovation, their usable years tend to decrease. In addition, greenhouse gases such as CO2 emitted from their use have greatly contributed to environmental problems. Meanwhile, the demand for renewable and alternative energy as a clean energy source is increasing. Hydrogen is used as an energy source for fuel cells, and is a substance that attracts attention because of its portability, no emission of carbon dioxide after use, and its high energy density. However, the current steam supply method, which is a hydrogen supply method, has a problem that a large amount of CO2 is simultaneously emitted when hydrogen is generated. Therefore, it is strongly desired to establish another technology capable of supplying hydrogen stably and cleanly.Photocatalysts are famous materials that attract attention from a hydrogen supply perspective. They are used as materials for artificial photosynthesis, and artificial photosynthesis is an effective method for energy and environmental issues due to the following advantages; using water that is abundant on the earth as a raw material, using sunlight that infinitely falls on the earth as a supply energy source and emitting no gas that is harmful to the environment. However, photocatalysts have a serious drawback of poor hydrogen generation efficiency, and many researchers are working to solve this problem for practical use. However, researches on highly efficient photocatalysts often use expensive metals such as Rh complexes and Pt cocatalysts, or sulfides containing highly toxic and unstable Cd. From an environmental and biological point of view, these solutions are problematic in the long term use of photocatalysts, and the development of safe and stable photocatalysts while generating hydrogen with high efficiency is desired.Metal-organic Frameworks (MOFs) are also attracting materials as new porous materials applied to drug delivery, catalysis, sensors, etc. MOFs have unique structures formed by coordinating central metals and organic linkers and have photocatalytic functions because of its band structures. MOFs have been actively studied in the photocatalyst field due to large surface area and property of easily modifying structure. In many MOFs, Zeolitic Imidazole Framework-8 (ZIF-8) has high alcohol adsorption and UV-excited photocatalytic function i.e. band gap energy = 5.1 eV. Since ZIF-8 has properties that photocatalysts should have, such as heat resistance and pH resistance, there is great interest in improving its wide band gap.In this study, we improve the photocatalytic efficiency by Cu doping and composite with g-C3N4. g-C3N4 is one of the popular visible-light-driven photocatalysts and we introduce this material for the purpose of supplementing the absorption band near 480 nm where ZIF-8 could not absorb. Although simple g-C3N4 has a shortcoming of low hydrogen generation efficiency due to fast charge recombination, we also aim to reduce the amount of bulk g-C3N4 by combining and dispersing it using the porosity of ZIF-8. Cu-doped ZIF-8 carrying Cu is synthesized by partially changing Zn, which is the raw material of ZIF-8, to Cu. g-C3N4 is gained by a simple method of calcining melamine in air. The sample of Cu-doped ZIF-8 and g-C3N4 composite, named XCZGC (X is value of prepared Cu weight percentage) is synthesized by dispersing in water at a weight ratio of 1: 1 and drying overnight. 40CZGC shows 2.5 and 16 times higher efficient (32.2 μmolH2 g-1 h-1 and 213.3 μmolH2 g-1 h-1, respectively) by Cu doping and combining as-Cu-doped ZIF-8 with g-C3N4. The former improves efficiency due to the small amount of Cu2+ dope and the deposition of metallic Cu on the surface of ZIF-8, and the latter improves due to the formation of Z-scheme type charge separation structure with g-C3N4. The structure and absorption light are analyzed by XRD and UV-vis DRS, and the added amount of copper is measured by XPS and ICP-OES. The hydrogen generation experiment is performed in a closed circulation system, and changes over time are observed under 300 W Xe lamp irradiation.Through this study, we propose a novel Z-scheme-type composite photocatalyst using Cu-doped ZIF-8. The above is just an expectation considered from action spectrum experiment since the transient absorption spectrum could not be measured at the time of submission. Therefore, the near goal is to confirm the Z-Scheme structure with analyzing the transient absorption spectrum. As a long goal, we consider further improvement in efficiency by using alcohol as a sacrificial reagent. Figure 1

Enhanced photocatalytic reduction of mercuric cations endorsing fabricated mesoporous BiFeO3/g-C3N4 heterojunction under Vis light irradiation

In this probe, enhanced photocatalytic reduction of mercuric cations has been achieved endorsing a novel mesoporous BiFeO3/g-C3N4 heterojunction accommodating various percentages of BiFeO3 nanoparticles (NPs) under Vis light irradiation. Formic acid was adopted as holes sacrificial correlated with pure g-C3N4 nanosheet or BiFeO3 nanoparticles. BiFeO3 NPs of particle dimension of 4–6 nm were homogeneously spread over the surface of the g-C3N4 nanosheet. The superior photocatalytic reduction of mercuric cations endorsing BiFeO3/g-C3N4 heterojunction has been affirmed since enlarging the dopant content (BiFeO3 NPs) from 1 up to 4% brings about an enhancement in the efficacy of the photocatalytic reduction of mercuric cations(Hg) from 38 up to 88% after 1 h of illumination. Obviously, the rate of the photocatalytic removal of mercuric cations endorsing mesoporous BiFeO3/g-C3N4 heterojunction accommodating 4% BiFeO3 NPs was found to be 5.3 and 7.9 times larger when correlated to those of neat BiFeO3 NPs and g-C3N4 nanosheet, accordingly. The superior photocatalytic reduction of mercuric cations under Vis light irradiation via adopting the synthesized BiFeO3/g-C3N4 heterojunction could be appropriated to the very finite particle sizes of BiFeO3 NPs in addition to their excellent dispersion over the g-C3N4 nanosheet surface. Besides, the extensive area, little band gap, and the excellent crystallinity of the synthesized photocatalyst are considered crucial aspects in the photocatalytic achievement of the synthesized BiFeO3/g-C3N4 heterojunction. Interestingly, the stability of the synthesized BiFeO3/g-C3N4 heterojunction towards the photocatalytic reduction of mercuric cations has been affirmed via recycling the photocatalyst up to five runs without pronounced loss in the photocatalytic performance towards mercuric cations reduction. In conclusion, the attained data brings about establishing a novel photocatalyst of Z-scheme type that could be successfully applied for photocatalytic remediation of toxic contaminants under Vis light irradiation.

An efficient Z-scheme (Cr, B) codoped g-C3N4/BiVO4 photocatalyst for water splitting: A hybrid DFT study

A systematic theoretical research on the geometrical, electronic, optical, charge transfer, and photocatalytic mechanisms of pure, Cr-doped, B-doped, and (Cr, B) codoped g-C3N4/BiVO4 heterostructures using a hybrid density functional approach has been carried out. The face-to-face g-C3N4/BiVO4 composed of two-dimensional materials of g-C3N4 and BiVO4 (010) surface, can introduce a built-in electric field, which promotes interface charge transfer and prevents the electron-hole pair recombination, and causing g-C3N4 monolayer with negative charge and BiVO4 (010) surface with positive charge. Under visible light irradiation, electrons are excited to the conduction band minimum (CBM) of the BiVO4 (010) surface undergoing the hydrogen evolution reaction (HER), while the holes remain in the valence band maximum (VBM) of g-C3N4 monolayer aiding the oxygen evolution reaction (OER). The band edge potentials of BiVO4 (010) surface is higher than that of g-C3N4 monolayer, which ensures a stronger redox reaction potential and therefore belongs to a typical Z-scheme heterostructure. In addition, the Cr or/and B (co)doping introduces the Cr-3d or/and B-2p states to reduce the bandgap and generate impurity levels, thus enhancing solar energy utilization rate and expanding the optical absorption in the visible-light range. The optical absorption intensity of the (Cr, B) codoped g-C3N4/BiVO4 is superior to pure and Cr or B doped g-C3N4/BiVO4, confiriming the synergistic effect of Cr-3d and B-2p states. Thus, this research is helpful to design a novel and potential Z-scheme photocatalyst useful for the photocatalytic water splitting.

Synthesis of cadmium sulfide-tungsten trioxide nanocomposites for photo-catalytic degradation of organic pollutants and growth retardation of waterborne bacteria and biofilms

Nanocomposites of cadmium sulfide-tungsten trioxide (CdS@WO3), with different CdS content (2.5 %, 5 % and 10 %) in WO3 were synthesized by laser defect engineering in liquid (LDL). In the characterization studies, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), transmission electron microscope (TEM) and high-resolution transmission electron microscope (HR-TEM) studies showed the perfect anchoring of CdS nanoparticles on the surface of bigger WO3 nanoparticles in CdS@WO3 nanocomposites. In the optical characterization, ultra-violet diffuse reflectance spectra (UV-DRS) indicated the narrowing down of band gap energy in CdS@WO3, and consequent enhancement of visible light absorption compared to pure WO3. Also photoluminescence (PL) implied the reduced charge recombination in CdS@WO3, compared to that of pure WO3, which can be attributed to the typical Z-scheme charge transfer between the composite partners. The LDL synthesized CdS@WO3 nanocomposites were used as (i) a photocatalyst for the degradation of Rhodamine B dye in water, (ii) anti-microbial agent against multi drug-resistant Pseudomonas aeruginosa (MDR-PA) and Methicillin-resistant Staphylococcus aureus (MRSA) bacteria, (iii) biofilm growth retardation agent against biofilm-producing strains of MRSA and MDR-PA. In all the three applications CdS@WO3 nanocomposite in general revealed a better performance than pure WO3, particularly 5 % CdS content in the composite (5 %-CdS@WO3), was the optimum for photocatalytic degradation and 10 % CdS content in CdS@WO3 showed the best performance in antibacterial and biofilm growth retardation applications for both bacterial strains.

Z-scheme-type conductive-polymer-P3HT/KTa(Zr)O3 heterojunction composites for enhancing the photocatalytic activity of water splitting

Photocatalytic water splitting on Pt/KTa(Zr)O3 modified with poly(3-hexylthiophene-2,5-diyl) (P3HT) as a photoconductive organic polymer is investigated. The photocatalyst powder of Pt/P3HT/KTa(Zr)O3 was synthesized by evaporation to dryness method. The H2/O2 production ratio of the unmodified catalyst was 2.90, whereas the H2/O2 production ratio become close to 2 (1.66–2.26) with loading P3HT (0.1 wt% to 0.8 wt%). The optimum amount of P3HT added was 0.4 wt% and the H2/O2 production ratio was 2.00, which increased the hydrogen production rate by 476 % compared to the unmodified photocatalyst. As a result of the fluorescence lifetime measurement, when the dye and platinum were supported on KTa(Zr)O3, charge separation into the dye and platinum was confirmed in both UV and visible light irradiation. Irradiation with visible light in addition to UV light increased the water splitting activity, while water decomposition was not performed only with visible light, suggests Z-scheme type water splitting reaction.

Facile approach for Z-scheme type Pt/g-C3N4/SrTiO3 heterojunction semiconductor synthesis via low-temperature process for simultaneous dyes degradation and hydrogen production

The platinum/graphite-like carbon nitride/strontium titanate (Pt/g-C3N4/SrTiO3) heterojunction semiconductor was synthesized using a facile approach for simultaneous photocatalytic dye degradation and hydrolysis of hydrogen production from simulated dyeing wastewater. Using SrTiO3, trace Pt, and the addition of an appropriate amount of electron donors, it can effectively absorb sunlight and achieve 93% dye degradation and 471 μmol h−1 g−1 hydrogen yield. The analysis result indicates that the semiconductor is a Z-scheme type composite. It was also showed that the addition of electron donors effectively promoted the degradation rate, whereas the addition of Pt changed the photocatalytic reaction pathway, which resulted in a reduced degradation rate and a significant improvement of hydrogen evolution. A reaction mechanism for this phenomenon is also proposed.

Ag NPs modified plasmonic Z-scheme photocatalyst Bi4Ti3O12/Ag/Ag3PO4 with improved performance for pollutants removal under visible light irradiation

In a typical Z-scheme photocatalytic system, the visible light responsive component typically plays a crucial role and is often confined to materials sensitive to visible light. In addition, metallic nanodots or quantum dots are used as effective cocatalysts in the construction of plasmonic Z-scheme photocatalysts because of their strong light harvesting capacities under visible light illumination. In the present study, Bi4Ti3O12 nanosheets dominated with (001) crystal planes were successfully prepared via a facile molten-salt method, and BTO/Ag/APO composite samples were prepared by a simple precipitation method followed by photoreduction. The obtained BTO/Ag/APO composite exhibits improved photocatalytic activity for the decontamination of two typical organic pollutants, compared to bare Bi4Ti3O12 and Ag3PO4. Based on various characterization techniques, a Z-scheme electron transfer mechanism induced by the plasmonic effect was hypothesized to clarify the enhanced catalytic performances in this system. On the other hand, the LSPR effect of deposited silver nanoparticles can boost the molecular oxygen activation process and generate more superoxide radicals. This study provides a promising approach to apply highly effective photocatalytic degradation for environmental remediation.

A novel solar photo-Fenton system with self-synthesizing H2O2: Enhanced photo-induced catalytic performances and mechanism insights

To solve problems of consecutive H2O2 external supplement and reutilization difficult of free Fe2+ ion in traditional homogeneous photo-Fenton, an efficient solar photo-Fenton system with self-supplying H2O2 was developed based on a heterogeneous catalyst of α-Fe2O3/g-C3N4. The microstructure, physicochemical and photoelectric properties of the optimal α-Fe2O3/g-C3N4 were characterized. It was found that the introduced α-Fe2O3 significantly enhanced the photoeletrochemical performances of g-C3N4. Rhodamine B and tetracycline hydrochloride were degraded in this solar photo-Fenton system with α-Fe2O3/g-C3N4, and the corresponding degradation rates reached to 96% (in 90 min) and 95% (in 150 min) at neutral pH circumstance respectively, which were much higher than that of single g-C3N4 and α-Fe2O3. The efficient degradation performance was attributed to the effective separation and rapid transfer of photo-generated charge carriers derived from classic Z-scheme type. Accordingly, it was deduced that H2O2 can produce on the g-C3N4 surface firstly under simulated solar irradiation, and the efficient removal of contaminant could be ascribed to oxidation by amount of ·OH predominantly derived from H2O2 decomposition on the α-Fe2O3, which was verified by trapping experiments and EPR analysis. In addition, ·O2− and h+ also played supporting roles. The main significance of this study gives a new insight into photo-Fenton.

WO3 nanocrystals decorated Ag3PO4 tetrapods as an efficient visible-light responsive Z-scheme photocatalyst for the enhanced degradation of tetracycline in aqueous medium

A series of WO3/Ag3PO4 composites with varying amounts of WO3 were successfully synthesized by a surfactant-free hydrothermal method and utilized for the photocatalytic degradation of tetracycline (TC) under visible-light irradiation. The formation of a composite structure with the decoration of WO3 nanocrystals on the surface of tetrapod-like Ag3PO4 was clearly seen in the materials characterization. The surface of Ag3PO4 tetrapods was found to be homogenously decorated with WO3 nanocrystals depending on their incremental amount, and an adjacent contact between the coupling materials was resulted that instigated the formation of heterointerfaces in the composites. The visible light absorption of WO3 was significantly improved by its coupling with Ag3PO4 tetrapods. The photoluminescence, electrochemical impedance and photocurrent density analyses indicated the increased life time of the charge carriers with reduced electron-hole pair recombination rate. The photocatalytic activity results had shown that within 24 min of visible light irradiation, the 50 % WO3/Ag3PO4 composite achieved ∼96 % TC degradation with a TC mineralization efficiency of 15.4 %. The enhanced photocatalytic activity of the composites could be attributed to the facile separation of the photoinduced charge carriers through a Z-scheme type charge transfer mechanism at the heterointerface. The scavenger studies specified the primary role of holes and hydroxyl radicals in the oxidative degradation of TC. Additionally, the 50 % WO3/Ag3PO4 composite was effectively reused for four cycles of TC degradation with a gradual loss in its activity, whereas the Ag3PO4 tetrapods suffered a rapid photocorrosion. It validates the superior role of charge transfer process in the photocorrosion inhibition of Ag3PO4 tetrapods.

Stabilizing CuGaS2 by crystalline CdS through an interfacial Z-scheme charge transfer for enhanced photocatalytic CO2 reduction under visible light.

CuGaS2 is one of the most excellent visible-light-active photocatalysts for CO2 reduction and water splitting. However, CuGaS2 suffers from serious deactivation in photocatalytic reactions, which is mainly due to the photo-oxidation induced self-corrosion (Cu+ to Cu2+). Here, we constructed a CuGaS2/CdS hybrid photocatalyst dominated by a Z-scheme charge transfer mechanism. The transfer of photo-generated electrons from excited nanocrystalline CdS to CuGaS2 across the coherent interface reduces Cu2+ formation and favors Cu+ regeneration. This process suppresses the deactivation of CuGaS2 and maintains high performance. Both the activity and stability of photocatalytic CO2 reduction to produce CO over the CuGaS2/CdS hybrid were remarkably improved, which was approximately 4-fold higher than CuGaS2 and 3-fold higher than CdS in converting CO2 into CO. Our study demonstrates that even using the semiconductors prone to photo-corrosion, it is possible to obtain satisfactory catalytic activity and stability by designing efficient Z-scheme-charge-transfer-type photocatalysts.

Z-scheme assisted ZnO/Cu2O-CuO photocatalysts to increase photoactive electrons in hydrogen evolution by water splitting

Multi-component photocatalysts have been considered as promising candidates to overcome fast charge recombination phenomena in solar water splitting process, which improve electron utilizations in reductive hydrogen generation. However, most reported multi-component systems have been rarely fabricated by aids with z-scheme type components. Thus, cuprous and cupric oxides are proposed as an excellent example for a z-scheme system with ZnO base materials. The ZnO particles are firstly synthesized by a precipitation method, and CuS components are added on the ZnO particle surfaces in various compositions. The ZnO/CuS materials are then thermally treated under controlled oxygen atmosphere to form cuprous and cupric oxides. To enhance photoactive electrons for reductive water splitting in conduction bands of the photocatalyst system, optimum content of cuprous oxides in the z-scheme components is a critical factor. At the optimum cuprous content (14.3%) in the copper oxides, the highest hydrogen production rate of 1092.5 μmolg-1h-1 is achieved at about 3% apparent quantum yield under the standard solar irradiation.

Accelerated photocatalytic degradation of quinolone antibiotics over Z-scheme MoO3/g-C3N4 heterostructure by peroxydisulfate under visible light irradiation: Mechanism; kinetic; and products

Abstract The advanced oxidation processes (AOPs) was regarded as one of the effective strategies for the degradation of organic pollutant. Herein, anovel Z-scheme type MoO3/g-C3N4 composite photocatalyst synergize with peroxydisulfate (PDS) to enhanced photocatalytic activity. Systematic studies indicated that the synergistic MoO3/g-C3N4/PDS photocatalyticsystem exhibited significantly enhanced photocatalytic activity for the degradation of ofloxacin (OFLX) in contrast to MoO3/g-C3N4 and pure g-C3N4. A 94.4% removal efficiency could be accomplished with 0.6 g/L catalyst and 5 mM peroxydisulfate (PDS) under visible light within 120 min.The enhanced photocatalytic performance of MoO3/g-C3N4/PDS could be attributed to the capture of the photoinduced electrons of PDS as well as the generation of SO4•− which can oxidize water to generate •OH. Quenching experiments revealed that O2•− and h+were the dominant active species involved in the MoO3/g-C3N4/PDS system under visible light irradiation. Degradation pathways of OFLX were then proposed based on the identification of intermediates. Reactions in inorganic anions aqueous solutions showed that MoO3/g-C3N4/PDS system provided a superior approach for the remediation of OFLX from aqueous solutions.

Novel rugby-like g-C3N4/BiVO4 core/shell Z-scheme composites prepared via low-temperature hydrothermal method for enhanced photocatalytic performance

Novel rugby-like g-C3N4/BiVO4 (xCN/BVO, x = 3, 5, and 10) Z-Scheme type composite photocatalyst was fabricated using g-C3N4 nanosheets as raw materials of the morphology directing and heterojunction construction via one-step low-temperature hydrothermal method. The results showed that this fabrication method is effective to control the morphology of BiVO4 from irregular shape to regular rugby-like with g-C3N4 nanosheets addition and construct a Z-Scheme type heterojunction with intimate and wide interfaces between g-C3N4 and BiVO4. The rugby-like CN/BVO exhibited better photocatalytic activity for methyl orange (MO) degradation than single irregular BiVO4. The optimal 5CN/BVO sample can degraded 94.2% of MO in 50 min under visible light illumination, being about 8.78 higher than pure BiVO4. The improved photocatalytic efficiency for CN/BVO is mainly due to the strengthen visible light utilization ability, the special rugby-like morphology, intimate interface, and the efficient Z-Scheme type heterojunction formation.

Photocathodic Protection Performance of ZnS-CdS-Ag@TiO2 for 403SS Under Visible Light

Up to date, TiO2 nanotubes have attracted extensive interest in photocatalysts [1], dye-sensitized solar cells [2], photocatalytic decomposition of water into hydrogen [3], and sensors [4]. In addition, some researchers have reported that the photoelectrochemical properties of TiO2 could be applied to the cathodic protection of metals [5-7]. Compared with conventional cathodic protection, the photocathodic protection technology has no need to supply current or sacrificial anodes, and can achieve green and nonpolluting protection of metals [5]. However, there are two key drawbacks to the practical application of photocathodic protection of bare TiO2 films. In this work, an all-solid-state Z-scheme type CdS-Ag@TiO2 nanocomposite was fabricated by pulse electrodeposition and the successive ion layer adsorption and reaction (SILAR) technique. To suppress CdS photocorrosion, a ZnS shell was provided by the SILAR method. The CdS was chosen to sensitize the TiO2, and Ag acted as a transporter of electrons. This nanocomposite shows an impressive photocathodic protection performance for the 403 stainless steel (SS). The morphologies were observed using field-emission scanning electron microscope Hitachi FE-SEM S4800. The results showed that the film possessed a porous network morphology and the network consisted of scrolled-up nanowires. It can be observed that CdS and ZnS particles were uniformly distributed on the nanowire surface. The EDX spectrum and XPS measurement revealed that the ZnS-CdS-Ag@TiO2 films were composed of Ti, O, Ag, Cd, Zn and S. The UV-vis absorption spectra showed that the photoabsorption spectrum of the composite film was expanded into the visible light region. The corrosion performances of 403 stainless steel in a 0.5 M NaCl solution coupled to a titanate film photoanode in 1.0 M NaOH solutions were evaluated by photogenerated potential and electrochemical impedance spectroscopy (EIS). The steel was coupled to the composite photoanode under illumination and dark conditions. Under irradiation, the stabilized potential of 403SS coupled to the composite photoanode was recorded at approximately -1174 mV (vs.SCE). Under dark condition, the composite photoanode still provides the certain cathodic protection for the steel. To further study the corrosion process of 403SS under photocathodic protection, EIS was performed under illumination. It was found that the impedance arc of the 403SS coupled to the composite photoanode was markedly smaller. This may be due to a larger number of photogenerated electrons being transferred from the photoanode to the the surface of 403SS, leading to the cathodic current density increase for the steel. The EIS result revealed composite film could provide a good photocathodic protection effect for 403SS. Acknowledgements This work was supported by the the National Natural Science Foundation of China (Nos. 51801013) and the Natural Science Foundation of Shandong Province of China (ZR2016BP11) and A Project of Shandong Province Higher Educational Science (J16LC18).

Efficient photo-electrochemical water splitting based on hematite nanorods doped with phosphorus

The realization of an efficient photocatalytic water splitting in the absence of sacrificial agent is an important step to achieve the sustainable production of hydrogen using solar energy. Heterostructure-based photocatalysts are used to mitigate charge recombination, thus leading to the improved photoactivity. In a traditional electrochemical system, it works similarly as the heterostructure of z-scheme type which transports the photoinduced electrons to the cathode. Herein, by using a photo-electrochemical process, the production of oxygen and hydrogen was achieved with improved photocatalytic faradaic efficiency. The oxygen evolution process (OER) was improved upon modifying the hematite with phosphorous. The phosphorous doping led to a shift of the band structure toward more positive potentials, resulting in higher OER rates. The optimized electrode achieved a plateau photocurrent of 2.5 mA/cm2 at 100 mW/cm2 illumination.

A novel Z-scheme Ag3VO4/BiVO4 heterojunction photocatalyst: Study on the excellent photocatalytic performance and photocatalytic mechanism

Aabstract A novel three-dimensional microspheres mediator-free Z-scheme Ag3VO4/BiVO4 heterojunction photocatalyst was successfully obtained for the first time. The photocatalytic performance of the as-prepared photocatalyst was systematically examined via the photocatalytic reduction of Cr6+ and oxidation of Bisphenol S under visible-light irradiation. Among these samples, 0.24-Ag3VO4/BiVO4 exhibits the highest photocatalytic performances, the photocatalytic reduction and oxidation efficiency of 74.9 and 94.8%, respectively, can be achieved. The enhanced photocatalytic performance is attributed to the build-in electric field assisted charge transfer between the Ag3VO4 and BiVO4, and the increasing lifetime of the charge carrier confirmed by the results of time-resolved fluorescence spectra and photoelectrochemical measures. Moreover, based on the results of free radical scavenging activity test, and EPR experiments, it has been verified that the Ag3VO4/BiVO4 heterostructures follow a typical Z-scheme charge transfer mechanism rather than conventional type-II heterojunction charge transfer mechanism. Furthermore, the theoretical understanding of the underlying mechanism was also supported, while the energy band structure, and Fermi level were systematically calculated using the density functional theory approach. The results show that a built-in electric field directed from Ag3VO4 to BiVO4 surface was established as an equalized Fermi level was reached, which benefits the separation of photogenerated charge carriers in the way of a Z-scheme charge transfer mechanism. The strategy to form the three-dimensional microspheres Z-scheme heterojunction photocatalyst may offer new insight into the Z-scheme charge transfer mechanism for applications in the field of solar energy conversion.

Visible-Light Overall Water Splitting by CdS/WO3/CdWO4 Tricomposite Photocatalyst Suppressing Photocorrosion

Photocatalytic water splitting under visible light has attracted attention as a possible solution to the energy exhaustion problem. Hitherto, water splitting has been generally achieved using several oxynitrides, oxysulfides, and nitrides, and only a few studies report water splitting using cadmium sulfide (CdS) as a photocatalyst. A major reason for this is that CdS undergoes photocorrosion. In this study, we achieved an overall water splitting under visible light using a CdS/WO3/CdWO4 tricomposite photocatalyst. In the process, photocorrosion of CdS was suppressed by covering it with WO3 and CdWO4, and the oxidation reaction progressed in WO3 by the Z-scheme type photocatalytic reaction.