Visible Light Absorption Capacity Research Articles

Preparation of a ternary g-C3N4-CdS/Bi4O5I2 composite photocatalysts with two charge transfer pathways for efficient degradation of acetaminophen under visible light irradiation

It is a challenge to explore highly efficient photocatalysts for the degradation of pharmaceutical contaminant under visible light. In this work, a series of g-C3N4-CdS/Bi4O5I2 composites were prepared by a simple self-assembly and calcination method. The photocatalysts showed good photocatalytic activity and stability for acetaminophen degradation. The enhanced activity and stability can be ascribed to the reason that the formed ternary heterojunctions provided multi-channel for the transfer of photogenerated charges. Meanwhile, the visible light absorption capacity was improved effectively because of the addition of Bi4O5I2. Furthermore, the transfer of holes from CdS to g-C3N4 prohibited the photocorrosion of CdS, thus improving the stability of the composites. The apparent rate constant of the optimal sample (g-C3N4-CdS/Bi4O5I2-3) for acetaminophen degradation was 5 and 2.5 times as that of g-C3N4-CdS and pure Bi4O5I2. The degradation pathway of acetaminophen was proposed based on the detected intermediates. This work provided an idea to design multi-heterojunction photocatalysts with high performance for the degradation of drug pollutants.

Carbonized polymer dots modified ultrathin Bi12O17Cl2 nanosheets Z-scheme heterojunction for robust CO2 photoreduction

How to achieve efficient photocatalytic CO2 reduction has received widespread attention. Herein, 0D carbonized polymer dots are evenly loaded on ultrathin 2D Bi12O17Cl2 nanosheets (CPDs/Bi12O17Cl2), which construct the Z-scheme carrier migration system with effectively increased photocatalytic CO2 conversion to CO. The structure and morphology of these samples were investigated by XRD, Raman, XPS, TEM, photocurrent, etc. The reaction mechanism was proposed through in situ FT-IR spectrometry. Under visible light irradiation, the CO evolution rate of 3 wt% CPDs/Bi12O17Cl2 composites is 4.1 times higher than that of pure Bi12O17Cl2 material. The improved photo-reduction CO2 conversion rate of CPDs/Bi12O17Cl2 is ascribed to promoted absorption capacity of visible light, enhanced carrier separation efficiency and increased activity specific surface area. CPDs act as the enrichment center for photo-generated electrons in the Z-scheme system and capture sites for CO2, while also strengthen the adsorption and activation of intermediate products COOH*, thereby promoting CO production.

Facile fabrication of vanadium sensitized silver titanium oxides (V–Ag/TiO2) photocatalyst nanocomposite for pollutants removal in river water

Vanadium sensitized silver titanium mixed metal (V–Ag/TiO2) oxides photocatalyst nanocomposite was prepared by a sol-gel, hydrothermal route. Lattice fringes for both anatase and rutile in its crystalline phase was depicted by X-Ray Diffraction (XRD) structural analysis. Surface areas (SBET) analysis shows that synthesized V–Ag/TiO2 has a huge surface area of 74.58 m2g-1, compare to TiO2 94.77 m2g-1, Ag–TiO2 89.32 m2g-1 and V–TiO2 82.59 m2g-1. Optical absorption results demonstrated by UV–Visible Spectroscopy (UV–Vis) shows a reduced bandgap energy of 2.3 eV and a shift in spectrum to the visible light region, enhancing the visible light absorption capacity of the synthesized photocatalyst. Binding energies of species were presented by X-ray photoelectron spectroscopy (XPS). Scanning electron microscope (SEM) image shows the formation of a closely stacked cluster composed of rod-like aggregated particles of non-uniform diameter while Transition Electron Microscope (TEM) shows particle size distribution range between 15 and 25 nm. Synthesized V–Ag/TiO2 showed tremendous photocatalytic abilities under visible light irradiation as gas chromatography–mass spectrometry (GC–MS) analysis of surface water from Lepelle River Limpopo province of South Africa demonstrate the selective removal of organic pollutant.

Tuning Photocatalytic Performance of Multilayer ZnO for Water Splitting by Biaxial Strain Composites

Novel two-dimensional (2D) materials have received extensive attention in the field of photocatalysis due to their unique properties. Traditional ZnO material with wurtzite structure transforms into a stable graphite-like structure that has the characteristics of 2D material when its thickness is less than a few atomic layers. In this work, using first-principles calculations, we investigated the potential of multilayer graphite-like ZnO as a photocatalyst for water splitting. The results showed that multilayer ZnO is a series of direct bandgap semiconductors, and their band edge positions all straddle the redox potential of water. Increasing with the number of layers, the bandgap of multilayer ZnO decreased from 3.20 eV for one layer to 2.21 eV for six layers, and visible light absorption capacity was significantly enhanced. Hence, multilayer ZnO was indeed promising for photocatalytic water splitting. Furthermore, suitable biaxial tensile strain could decrease the bandgap and maintain the stable graphite-like structure at a broader thickness range. In contrast, excessive biaxial tensile strain could change the redox capacity of multilayer ZnO and prevent it from catalyzing water splitting. Our theoretical results show that six-layer ZnO under 1% biaxial strain had direct bandgap of 2.07 eV and represents the most excellent photocatalytic performance among these multilayer ZnO materials.

Fabrication and characterization of BiOBr-SnWO4 heterojunction nanocomposites with boosted photodegradation capability

Novel BiOBr-SnWO4 heterojunction nanocomposites were fabricated by chemical precipitation method using as-prepared SnWO4 nanoparticles, bismuth nitrate as a source of bismuth, KBr as a source of Br, and ethylene glycol as solvent. The prepared BiOBr-SnWO4 heterojunction nanocomposites were examined for phase structure, chemical composition, surface morphology, optical properties, and charge transport by XRD, XPS, TEM, UV-Visible NIR, photoluminescence (PL), time-resolved fluorescence spectroscopy, electrochemical impedance spectroscopy (EIS), and Brunauer-Emmett-Teller (BET) analysis. X-ray diffractogram of BiOBr-SnWO4 nanocomposites revealed the diffraction peaks corresponding to orthorhombic SnWO4 nanoparticles in the tetragonal BiOBr which indicated that they exist in the mixed-phase in the composite. TEM pictures confirmed the existence of SnWO4 nanostructure in the BiOBr particles yielding core-shell particles. PL, fluorescence lifetime, and EIS investigations of the prepared samples showed a good charge separation efficiency in the BiOBr-SnWO4–1 nanocomposite. The application of BiOBr-SnWO4 nanocomposites as a photocatalyst was investigated via the decomposition of an aqueous solution of rhodamine B (RhB) and brilliant green (BG) dyes in the natural sunlight. Among the prepared materials, the BiOBr-SnWO4–1 nanocomposite presented robust photodegradation capability towards the degradation of RhB and BG dyes. The degradation efficiency touched to 97.85% and 95.5% for RhB and BG, respectively. The superior performance of BiOBr-SnWO4–1 is attributed to the existence of heterojunction between p-type BiOBr and n-type SnWO4 nanoparticles along with an improved visible light absorption capacity of heterojunction and the efficient interfacial charge transfer/ separation. The radical scavenger investigations showed that photogenerated h+, O2∙−, and ∙OH radicals generated by the photocatalyst were responsible for RhB and BG degradation.

Design of a novel carbon/BiOBr nanosheet photoanode and its photoelectrochemical application

A novel carbon/BiOBr (C/BiOBr) photoanode with interesting electronic structure is designed. Carbon atoms are connected with bismuth (Bi) and bromine (Br) atoms by electron interaction. Such an electron interaction changes the chemical environments of Bi and Br, so that results in enhanced visible light absorption capacity and high transfer rate of charge carriers. Photoelectrochemical cell (PEC) system has been constructed to study the photoelectrochemical property of C/BiOBr photoanode. The short-circuit current (Jsc) and open-circuit voltage (Voc) of C/BiOBr are measured to be 0.057 mA/cm2 and 0.296 V, which are higher than that in PEC with the pristine BiOBr photoanode. The proposed chemically bonded C/BiOBr photoanode offers potential for electricity generation and pollutants degradation.

Synthesis of Ag2O Coated TiO2 Nanoparticles by Sonochemically Activated Methods for Enhanced Photocatalytic Activities

TiO2 nanoparticles were successfully synthesized by sol-hydrothermal (SH) method using sonochemically activated precursors. Sonochemical activation yields product bearing desirable crystallinity at relatively lower temperature in comparison with conventional SH method. Glycine was used as a mineralizer in the ultrasound activation process which suppress the formation of brookite phase (of TiO2) observed in the sonochemically activated sample. TiO2 sample synthesized in presence of Glycine [SA-SH(GLY)] was further modified by coating Ag2O nanoparticles by sonochemical (SD-Ag) and photochemical (PD–Ag) methods. The deposition by sonochemical method yields product with better crystallinity, high surface area and improved optical properties. Morphological investigations confirm the formation of rounded cube and cube shaped Ag2O particles in the sonochemical and photochemical methods respectively. Photoactivities of the catalysts were investigated in terms of degradation of methyl orange (MO) dye contaminated aquatic waste. Equilibrium of MO photo-degradation was achieved within about 90 min with removal efficiencies of 99.9, 67.1, and 44.4% for SD-Ag, PD–Ag, and SA-SH-(GLY) samples, respectively at 50 mg/L of MO dye concentration. The high photo-catalytic activity of SD-Ag sample was observed for MO photo-degradation, which is attributed to the improved properties like crystallinity, visible light absorption capacity and higher surface area. Advance route of sonochemical activation process for synthesis of Ag2O co-capped TiO2 nanocomplex for MO photo-degradation

Electronic and optical properties of Zn-S, Ag-C, Ag-N and Ag-S co-doped K2Ti6O13 with different doping concentrations

K2Ti6O13 is a wide band gap semiconductor photocatalytic material. Its absorption spectrum is concentrated in the ultraviolet band, which limits its application as a photocatalyst. Doping can effectively improve its light absorption. Based on the first principles and the density functional theory, crystallographic properties, electronic properties and optical properties of pure K2Ti6O13 and of Zn-S, Ag-C, Ag-N and Ag-S co-doped K2Ti6O13 with different doping concentrations have been calculated and compared. The results show that K2Ti4Ag2O12N (Ag’s doping concentration is 33.33 % and that of N is 7.69 %) has the best absorption capacity of visible light. This study provides a valuable theoretical reference for the application and preparation of potassium titanate photocatalyst materials. Certain doping concentrations and doping atoms can be selected according to different needs to prepare potassium titanate with specific characteristics.

Facile green route sol–gel synthesis of nano-titania using bio-waste materials as templates

Titania semiconductor is being used in a wide range of fields; however, the poor surface properties and meagre visible light absorption capacity of it stand as barriers for being used as an effective visible light active photocatalyst. To overcome these limitations, various strategies have been adopted, among which the usage of templates has been the topic of research for the past 10 years. Usage of the template during the synthesis of titania increases the surface area by reducing the agglomeration of nanoparticles and also shifts the absorption edge to the visible range. Nowadays, green synthesis has gained substantial attention as an effective, safe and environmentally friendly practice for the synthesis of nano-titania. Bio-waste pista shells, corn pith, and tamarind seeds which are regarded as unproductive have been used in the sol–gel synthesis of Pista Shell Templated Titania (PST), Corn Pith Templated Titania (CPT) and Tamarind Seed Templated Titania (TST). The synthesized templated titania was subjected to morphological, crystallite, surface characteristic and photocatalytic studies. XRD results of synthesized CPT, PST and TST exhibited that they possessed anatase form. The crystallite size of PST, CPT and TST was found to be 12.26 nm, 12.28 nm and 15.55 nm, respectively, proving the reduction in crystallite size than in non-templated titania. Efficient photocatalytic activity of templated titania was observed via the degradation of methyl orange, which proved the larger surface area of templated titania than that of non-templated titania. Pista shells, corn pith and tamarind seeds were found to grant a decisive support in the controlled growth of titania and in photocatalytic applications which stands out as a reason to be looked upon as an effective bio-waste green template in the synthesis of nano-titania.

Synthesis and photocatalytic performance of Ag-TiVOX nanocomposite

A silver, vanadium and silver/vanadium doped titanium dioxide (TiO2, Ag-TiO2, V-TiO2 and Ag-TiVOX) nanocomposite photocatalyst was achieved via a modify sol–gel and hydrothermal method. Structural analysis by X-Ray Diffraction (XRD) depicted the lattice fringes for both anatase and rutile in its crystalline phase in the synthesized nanocomposites. Surface areas (SBET) analysis shows that surface area of synthesized Ag-TiVOX is 46.01 m2/g, compare to TiO2 64.75 m2/g, Ag-TiO2 61.33 m2/g and V-TiO2 62.73 m2/g. Optical absorption results demonstrated by UV–Visible Spectroscopy (UV–Vis) shows that the effects of Ag and V doping was a shift in spectrum to the visible light region, enhancing the visible light absorption capacity of the synthesized photocatalyst. The optical absorption of Ag-TiVOX achieved a reduced bandgap energy of 2.2 eV, as compared to Ag-TiO2 (2.8 eV), V-TiO2 (2.3 eV) and TiO2 (2.9 eV). Morphological characterization by Transition Electron Microscope (TEM) and Scanning Electron Microscope (SEM), depicting a cluster composed of spherical aggregates particles of non-uniform diameter nanoparticles with particle size ranging between 10 and 50 nm. Synthesized Ag-TiVOx demonstrated remarkable photocatalytic capabilities under visible light irradiation, as 99.83 percent of methylene blue (MB) degradation was accomplished during the first 15 min. Impact of Ag and V doping of TiO2 showed enhancement in the photocatalytic activity, reporting excellent removal rates and achieving well desirable decline in the band gap energy.

Microwave synthesized nano-photosensitizer of CdS QD/MoO3–OV/g–C3N4 heterojunction catalyst for hydrogen evolution under full-spectrum light

In this study, facile solid-state CdS quantum dots (QDs) supported MoO3/g-C3N4 nanostructure photocatalysts were prepared via an innovative in-situ deposition protocol with consecutive ionic layer adsorption and reaction. The CdS QDs-anchored MoO3/g-C3N4 heterostructure photocatalysts demonstrated enhanced visible-light absorption capacity, which was realized by the quantum confinement of the CdS QDs. The maximum photocatalytic hydrogen (H2) production rate with the CdS QDs-anchored MoO3/g-C3N4 heterostructure photocatalysts reached 294.32 μmol g− 1 h−1, which was 76.84, 215.21, 27.12, and 3.64 folds superior as compare to bare g-C3N4, MoO3, CdS, and MoO3/g-C3N4 catalysts, respectively. The enriched photocatalytic performance was mainly credited to the high surface area and MoO3 with oxygen vacancies (OV), ultra-thin g-C3N4 and high optical adsorption ability of CdS QDs. Thus, forming a dual Z-scheme system in the CdS QDs-supported MoO3-OV/g-C3N4 nanostructures not only facilitated efficient interfacial charge transfer but also preserved the robust redox ability of the photoinduced electrons and holes.

Laser-assisted synthesis of Z-scheme TiO2/rGO/g-C3N4 nanocomposites for highly enhanced photocatalytic hydrogen evolution

Constructing nanocomposite structures with favorable charge transfer routes is an effective way to obtain highly efficient photocatalysts. Herein, fabrication of indirect and noble metal-free Z-scheme photocatalytic architecture is demonstrated using pulsed laser ablation in liquids (PLAL) technique for the first time. The as-prepared ternary photocatalyst (denoted as TiO2/rGO/g-C3N4) comprises titanium dioxide (TiO2) nanotubes, reduced graphene oxide (rGO) nanosheets, and graphitic carbon nitride (g-C3N4) nanosheets. The photocatalytic activity of the as-synthesized composite is evaluated by monitoring water splitting. Various analytical techniques were employed to investigate the compositional, morphological, structural, and optical properties of the photocatalysts. The system of TiO2/rGO/g-C3N4 with the weight ratio of TiO2 to g-C3N4 of 2:4 and 1% rGO exhibited the highest hydrogen production rate of 32 ± 1 mmol g−1h−1, which is about 93, 3.8 and 2.6 times higher than those of pure g-C3N4, TiO2, and TiO2/rGO, respectively. This enhanced performance can be ascribed to the strong interfacial bonding (TiO2-rGO-g-C3N4), extended visible light absorption capacity due to higher photo-responsiveness of rGO and g-C3N4, the synergetic effect between TiO2 and g-C3N4 and direct contact between TiO2 and rGO which facilitated efficient separation and transfer of photogenerated charges. This study opens opportunities for the fabrications of different Z-scheme systems for various applications.

A new carbon allotrope: T5-carbon

A novel carbon allotrope is predicted by first-principles calculations. This allotrope is obtained by replacing one of the two atoms in the primitive cell of diamond with a carbon tetrahedron, thus it contains five atoms in one primitive cell, termed T5-carbon. The stabilities of T5-carbon are checked in structural, thermal and vibrational calculations. T5-carbon is a wide band gap semiconductor with an indirect band gap of 4.30 eV, and has a lattice thermal conductivity of 409 W/mK. Mechanical analyses reveal that T5-carbon shows good mechanical performances. Furthermore, by modifying T5-carbon with replacing some carbon atoms with Si or Ti atoms, we can obtain SiC4 or TiC4 structures. Importantly, the TiC4 system has a moderate conduction and valance band edges, comparable larger absorption capacity of visible light and smaller effective masses of electron and hole carriers than TiO2, confirming its photocatalysis applications.

Tailoring the CdS surface structure for photocatalytic applications

Semiconductor mediated photocatalysis is envisaged as a promising approach to initiate the diverse redox reactions under the ambient conditions. Although titania still remains as benchmark photocatalyst, its wide band gap and rapid charge carrier recombination blights their utility under natural solar light. Thus, search of functional materials with narrow gap and suitable band edge potentials has drawn significant attention for photocatalytic applications. Towards this end, CdS have been impressive as prime nanomaterial which is mainly attributed to their visible light absorption capacity, more negative conduction band edge potential, and simplistic preparation with diverse morphologies and their proficiency to form stable heterostructure with variety of co-catalysts. However, photocorrosion vulnerability of CdS becomes the origin of intimidation for long term operations and massive charge carrier recombination constrains their performance. In this review article, surface structure of the CdS modified with various co-catalysts such as metal NPs, metal oxides, sulfides, phosphides, carbides, g-C3N4, polymers and carbon materials to overcome the aforementioned drawbacks is discussed. Besides, fundamental aspects concerning the relationship between the crystal structure and morphological effects of CdS on the photocatalytic property is emphasized. The preparative methods, charge carrier dynamics and performance of CdS-based binary and ternary composites benefitting the model reactions such as pollutant degradation, hydrogen evolution and organic functional group transformation is reviewed in detail. The literature survey concludes that the surface modifications with co-catalysts can be the constructive approach for exploring the CdS based nanomaterials for broader environmental applications.

One-pot synthesis of BiOCl microflowers co-modified with Mn and oxygen vacancies for enhanced photocatalytic degradation of tetracycline under visible light

Visible light photocatalysis is one of the promising green strategies to settle the global energy and environmental crisis. Herein, BiOCl microflowers co-modified with oxygen vacancies (OVs) and Mn2+ were synthesized via a simple one-pot solvothermal method. The phase structures, morphologies, chemical states, light absorption properties and photoelectrochemical behaviors of the prepared materials were systematically characterized. The photocatalytic activity was evaluated by degrading tetracycline under visible light irradiation. It was revealed that the BiOCl samples fabricated by the solvothermal method showed the morphology of 3D microflowers. Compared with the BiOCl prepared via the hydrothermal route, these microflowers had lower crystallinity and higher visible light absorption capacity. Additionally, both the degradation of tetracycline and the photocurrent response were significantly improved in the case of co-modified BiOCl. This was because the shift of absorption edge towards longer wavelength could promote to generate more charge carriers. Another reason might be that the defect/impurity energy levels introduced by forming OVs/doping Mn2+ could capture the photoexcited electrons and holes to retard their recombination. Furthermore, the conduction band and valence band of BiOCl could be concurrently adjusted to narrow its band gap. Therefore, the improved photocatalytic performance might derive from the enhancement of visible light absorption and the effective separation of photo-generated charge carriers.

Enhancing visible-light driven photocatalytic performance of BiOBr by self-doping and in-situ deposition strategy: A synergistic effect between Bi5+ and metallic Bi

A novel composite photocatalyst of Bi/BiOBr-Bi5+ was successfully developed via a facile two-step procedure. The co-existence of self-doped Bi5+ and in-situ deposited Bi(M) was evidenced by X-ray diffraction, field-emission transmission electron microscope and X-ray photoelectron spectra. Its photocatalytic performance on the Rhodamine B (RhB) degradation under visible light irradiation displayed a significant improvement compared with that of Bi/BiOBr or BiOBr-Bi5+, which was mainly attributed to the synergistic effect between Bi(M) and Bi5+. For Bi(M), enhancement of visible-light absorption capacity was beneficial from surface plasmon resonance (SPR) effect while the promoted separation of photoinduced charge carriers was attributed to the formation of oxygen vacancies (OVs) and Schottky-barrier. Besides, Bi(M) induced a predominant exposure of (010) facet, further enhancing photocatalytic performance. Differently, Bi5+ brought a narrowed bandgap of BiOBr in increasing the carrier density. A plausible mechanism towards RhB degradation was proposed based on analysis of electron transfer pathway and determination of dominant active species. The work offers new routes to enhance the photocatalytic performance of Bi-based materials without introducing any impurities.

In-situ self-assembly construction of hollow tubular g-C3N4 isotype heterojunction for enhanced visible-light photocatalysis: Experiments and theories

A highly reactive hollow tubular g-C3N4 isotype heterojunction (SCN-CN) was designed to enhance visible light absorption and manipulate the directed transfer of electrons and holes. The results of UV–vis DRS, XPS valence band and DFT theoretical calculations indicated S doping increases the visible-light absorption capacity and changed the ba nd gap structure of g-C3N4 (CN), resulting in the transfer of electrons from the CN to the SCN and holes from the SCN to the CN under visible light. In addition, the tubular structure of the SCN-CN facilitated the transfer of electrons in the longitudinal direction, which reduced charge carrier recombination. Furthermore, the optical properties, electronic structure, and electron transfer of SCN-CN were also studied by experiments and theoretical calculations. The antibiotic tetracycline hydrochloride (TCH) and dye Rhodamine B (RHB) were subjected to evaluate the photocatalytic performance of SCN-CN. The scavenger tests and ESR data showed that the h+, ·O2− and ·OH worked together in the photocatalytic process. Moreover, the photocatalytic degradation pathway was analyzed by LC-MS. This study synthesized a hollow tubular CN isotype heterojunction with high visible-light photocatalytic performance and provided a theoretical basis for CN isotype heterojunction.

Hydrothermal deposition of AgCl/AgBr co-sensitizers to modify TiO2 NTs for enhanced photocatalytic performance

AgCl/AgBr co-sensitizers were prepared on TiO2 nanotube arrays (TiO2 NTs/AgCl/AgBr) by the hydrothermal method. The composition, morphology, optical absorption, photoelectric and photoelectrocatalytic (PEC) performances of TiO2 NTs/AgCl/AgBr were influenced by the concentration ratio of KCl/KBr. The investigation results revealed that the TiO2 NTs/AgCl/AgBr photocatalyst exhibited dramatically strong visible light absorption and outstanding photoelectrochemical capacity. The photoelectrode produced high visible light surface photovoltage (-0.43 V), transient photocurrent (0.47 mA/cm2) and carrier concentration (4.39 × 1020 cm-3). The sample also showed high PEC activity in the organic dye and Cr(VI) removal, and the photocatalytic mechanism and charge carrier transfer path were described based on PEC results. The investigation would offer prospective insight to the sensitization of TiO2 NTs, which would result in extensive attraction in the preparation and application of semiconductor materials as photoelectrodes and photocatalysts with superior photoelectrochemical performances.

Facile synthesis of Ag/Zn1-xCuxO nanoparticle compound photocatalyst for high-efficiency photocatalytic degradation: Insights into the synergies and antagonisms between Cu and Ag

By carefully balancing synergies and antagonisms that arise from incorporating Cu and Ag within a single ZnO-based catalytic platform, the photocatalytic activity of Ag/ZnO based on three-dimensional modified ceramic structures can be further significantly enhanced. The performance of Ag/ZnO heterostructure (Z0) was significantly improved by only 0.2 mol% Cu incorporation (Z0.2) and the first-order degradation kinetics constants (K) of Z0.2 were 2 and 1.5 times higher than that of Z0 under simulated sunlight and UV light. The synergies between Cu dopants and metallic Ag were mainly the significantly enhanced visible light absorption capacity and the prolonged photo-excited charge lifetime. However, with the excessive introduction of Cu precursors, the surface Cu2+ was found to inhibit the interfacial charge transfer between Ag and ZnO NPs under UV and visible light irradiation, but the transformation from Cu2+ to Cu+ was also presumed to be a driving factor for the improvement of photocatalytic efficiency. These interactions may provide a useful pathway for enhancing photocatalytic efficiency of low-cost ZnO-based catalytic platforms.

2D/2D Z-scheme BiO1-XBr/g-C3N4 heterojunction with rich oxygen vacancies as electron mediator for enhanced visible-light degradation activity

Typically, Z-scheme heterojunctions with excellent photodegradation capability need electron mediator to assist electron transfer, such as redox water mediator and noble metal nanoparticles, but redox water mediators usually cause weak photoabsorption capability and constancy of the photocatalyst, and the noble metal nanoparticles as electron transfer mediator are costly and suffer from various reverse reactions between the redox mediators and the photocatalysts. In this work, oxygen vacancies (OVs)-assisting 2D/2D Z-scheme BiO1-XBr/g-C3N4 (OV-BOB-CN) photocatalysts were synthesized successfully via a simple hydrothermal treatment. Notably, the introduction of OVs is not only to improve visible-light absorption capacity of photocatalyst reflected by UV–vis DRS, but more importantly, it can act as electron mediator in capturing and shuttling electrons of Z-scheme heterostructure to accelerate the separation rate of photogenerated carriers, which was demonstrated by transient photocurrent analysis, EIS, and PL results. The suitable ratio of OV-BOB-CN (OV-50BOB-50CN) showed optimal photodegradation activity for RhB, which was mainly owed to the synergistic reaction between 2D/2D Z-scheme heterostructure and OVs. The photocatalytic mechanism of OV-BOB-CN was revealed by free radical trapping experiments. In conclusion, this work provided a new protocol to design 2D/2D Z-scheme photocatalyst involved OVs, thus guiding a new way to further enhance degradation activity of photocatalyst.