Bimetallic phosphide decorated Mo–BiVO4 for significantly improved photoelectrochemical activity and stability

Bismuth vanadate photoanode has shown great potential for photoelectrochemical (PEC) catalysis, but it needs to be further modified because of its relatively low charge-separation efficiency and poor stability. Herein, the bimetallic phosphide NiCoP decorated Mo–BiVO₄ is fabricated through the electrodeposition and drop-casting method, which significantly improves the charge separation and surface oxidation reaction. Therefore, the fabricated NiCoP/Mo–BiVO₄ photoanode exhibits a low onset potential of 0.21 V (vs. RHE) and high photocurrent of 3.21 mA cm⁻² at 1.23 V (vs. RHE), which is 3.12 times higher than that of pure BiVO₄. Importantly, the decoration of NiCoP significantly improve the stability of BiVO₄ photoanode.

Bimetallic phosphide NiCoP decorated Mo–BiVO₄ photoanode was fabricated, and showed significantly improved photoelectrochemical activity and stability.     

Efficient photoelectrochemical water oxidation using a TiO2 nanosphere-decorated BiVO4 heterojunction photoanode

Constructing heterojunctions by coupling dissimilar semiconductors is a promising approach to boost charge separation and charge transfer in photoelectrochemical (PEC) water splitting. In this work, we fabricated a highly efficient TiO₂/BiVO₄ heterojunction photoanode for PEC water oxidation via a simple hydrothermal method. The resulting heterojunction photoanodes show enhanced PEC performance compared to the bare BiVO₄ due to the simultaneous improvements in charge separation and charge transfer. Under simulated sunlight illumination (AM 1.5G, 100 mW cm⁻²), a high photocurrent of 3.3 mA cm⁻² was obtained at 1.23 V (vs. the reversible hydrogen electrode (RHE)) in a neutral solution, which exceeds those attained by the previously reported TiO₂/BiVO₄ heterojunctions. When a molecular Co–cubane catalyst was immobilized onto the electrode, the performance of the TiO₂/BiVO₄ heterojunction photoanode can be further improved, achieving a higher photocurrent density of 4.6 mA cm⁻² at 1.23 V, an almost three-fold enhancement over that of the bare BiVO₄. These results engender a promising route to designing an efficient photoelectrode for PEC water splitting.

Constructing heterojunctions by coupling dissimilar semiconductors is a promising approach to boost charge separation and charge transfer in photoelectrochemical (PEC) water splitting.     

Highly efficient hamburger-like nanostructure of a triadic Ag/Co3O4/BiVO4 photoanode for enhanced photoelectrochemical water oxidation

The combination of a semiconductor heterojunction and oxygen evolution cocatalyst (OEC) is an important strategy to improve photoelectrochemical (PEC) water oxidation. Herein, a novel hamburger-like nanostructure of a triadic photoanode composed of BiVO₄ nanobulks, Co₃O₄ nanosheets and Ag nanoparticles (NPs), that is, Ag/Co₃O₄/BiVO₄, was designed. In our study, an interlaced 2D ultrathin p-type Co₃O₄ OEC layer was introduced onto n-type BiVO₄ to form a p–n Co₃O₄/BiVO₄ heterojunction with an internal electric field (IEF) in order to facilitate charge transport. Then the modification with Ag NPs can significantly facilitate the separation and transport of photogenerated carriers through the surface plasma resonance (SPR) effect, inhibiting the electron–hole recombination. The resulting Ag/Co₃O₄/BiVO₄ photoanodes exhibit largely enhanced PEC water oxidation performance: the photocurrent density of the ternary photoanode reaches up to 1.84 mA cm⁻² at 1.23 V vs. RHE, which is 4.60 times higher than that of the pristine BiVO₄ photoanode. The IPCE value is 2.83 times higher than that of the pristine BiVO₄ at 400 nm and the onset potential has a significant cathodic shift of 550 mV for the ternary well-constructed photoanode.

A novel hamburger-like nanostructure of a triadic photoanode Ag/Co₃O₄/BiVO₄ was designed to enhance photoelectrochemical water splitting, providing a fascinating pathway to efficiently improve the PEC conversion efficiency.     

Efficient charge separation and transfer of a TaON/BiVO4 heterojunction for photoelectrochemical water splitting

The separation and transfer of photogenerated electron–hole pairs in semiconductors is the key point for photoelectrochemical (PEC) water splitting. Here, an ideal TaON/BiVO₄ heterojunction electrode was fabricated via a simple hydrothermal method. As BiVO₄ and TaON were in well contact with each other, high performance TaON/BiVO₄ heterojunction photoanodes were constructed. The photocurrent of the 2-TaON/BiVO₄ electrode reached 2.6 mA cm⁻² at 1.23 V vs. RHE, which is 1.75 times as that of the bare BiVO₄. TaON improves the PEC performance by simultaneously promoting the photo-generated charge separation and surface reaction transfer. When a Co-Pi co-catalyst was integrated onto the surface of the 2-TaON/BiVO₄ electrode, the surface water oxidation kinetics further improved, and a highly efficient photocurrent density of 3.6 mA cm⁻² was achieved at 1.23 V vs. RHE. The largest half-cell solar energy conversion efficiency for Co-Pi/TaON/BiVO₄ was 1.19% at 0.69 V vs. RHE, corresponding to 6 times that of bare BiVO₄ (0.19% at 0.95 V vs. RHE). This study provides an available strategy to develop photoelectrochemical water splitting of BiVO₄-based photoanodes.

TaON/BiVO₄ heterojunction electrodes exhibited significant enhancement in the photoelectrochemical water oxidation.     

Ag2O-decorated electrospun BiVO4 nanofibers with enhanced photocatalytic performance

Semiconductor photocatalysts are emerging as tools for pollutant degradation in industrial wastewater, air purification, antibacterial applications, etc. due to their use of visible light, which is abundant in sunlight. Here, we report a new type of p–n junction Ag₂O/BiVO₄ heterogeneous nanostructured photocatalyst with enhanced photocatalytic performance. P-type Ag₂O nanoparticles were in situ reduced and assembled on the surface of electrospun BiVO₄ nanofibers using ultraviolet (UV) irradiation; this process hindered the recombination of localized photogenerated electron–hole pairs, and hence resulted in the enhanced photocatalytic activity of the BiVO₄/Ag₂O nanocomposites. The photocatalytic activities of the obtained BiVO₄ and BiVO₄/Ag₂O nanocomposites were assessed by measuring the degradation of rhodamine B (RhB) under visible light. The 10 wt% Ag₂O/BiVO₄ sample yielded the optimum degradation of RhB (98.47%), much higher than that yielded by pure BiVO₄ nanofibers (64.67%). No obvious change in the XRD pattern of an Ag₂O/BiVO₄ sample occurred as a result of its use in the photocatalytic reaction, indicating its excellent stability. The high photocatalytic performance observed was attributed to the large surface-to-volume ratio of the essentially one-dimensional electrospun BiVO₄ nanofibers and to the in situ growth of p-type Ag₂O on the surface of the n-type BiVO₄ nanofibers.

Ag₂O doped electrospun BiVO₄ nanofibers with p–n junction heterogeneous structures show enhanced photocatalytic activity under visible light (photocatalytic efficiency: 98.47% within 100 min) and good cycling stability.     

Insight into the PEC and interfacial charge transfer kinetics at the Mo doped BiVO4 photoanodes

BiVO₄ is a promising photoanode material for the photoelectrochemical (PEC) oxidation of water; however, its poor charge transfer, transport, and slow surface catalytic activity limit the expected theoretical efficiency. Herein, we have investigated the effect of Mo doping on SnO₂ buffer layer coated BiVO₄ for PEC water splitting. SnO₂ and Mo doped BiVO₄ layers are coated with layer by layer deposition through a precursor solution based spin coating technique followed by annealing. At 5% doping of Mo, the sample (SBM5) shows a maximum current density of 1.65 mA cm⁻² at 1.64 V vs. RHEl in 0.1 M phosphate buffer solution under AM 1.5 G solar simulator, which is about 154% improvement over the sample without Mo (SBM0). The significant improvement in the photocurrent upon Mo doping is due to the improvement of various bulk and interfacial properties in the materials as measured by UV-vis spectroscopy, electrochemical impedance spectroscopy (EIS), Mott–Schottky analysis, and open-circuit photovoltage (OCPV). The charge transfer kinetics at the BiVO₄/electrolyte interface are investigated to simulate the oxygen evolution process in photoelectrochemical water oxidation in the feedback mode of scanning electrochemical microscopy (SECM) using 2 mM [Fe(CN)₆]³⁻ as the redox couple. SECM investigation reveals a significant improvement in effective hole transfer rate constant from 2.18 cm s⁻¹ to 7.56 cm s⁻¹ for the hole transfer reaction from the valence band of BiVO₄ to [Fe(CN)₆]⁴⁻ to oxidize into [Fe(CN)₆]³⁻ with the Mo doping in BiVO₄. Results suggest that Mo⁶⁺ doping facilitates the hole transfer and suppresses the back reaction. The synergistic effect of fast forward and backward conversion of Mo⁶⁺ to Mo⁵⁺ expected to facilitate the V⁵⁺ to V⁴⁺ which has an important step to improve the photocurrent.

BiVO₄ is a promising photoanode material for the photoelectrochemical (PEC) oxidation of water; however, its poor charge transfer, transport, and slow surface catalytic activity limit the expected theoretical efficiency.     

Surfactant-assisted microwave processing of ZnO particles: a simple way for designing the surface-to-bulk defect ratio and improving photo(electro)catalytic properties

ZnO nanopowders were produced using microwave processing of a precipitate and applied as a photoanode for photoelectrochemical water splitting. Two different surfactants, cetyltrimethylammonium bromide (CTAB) as the cationic and Pluronic F127 as the non-ionic one, were employed to in situ adjust the surface-to-bulk defect ratio in the ZnO crystal structure and further to modify the photo(electro)catalytic activity of the ZnO photoanode. The crystal structure, morphological, textural, optical and photo(electro)catalytic properties of ZnO particles were studied in detail to explain the profound effects of the surfactants on the photoanode activity. The ZnO/CTAB photoanode displayed the highest photocurrent density of 27 mA g⁻¹, compared to ZnO (10.4 mA g⁻¹) and ZnO/F127 photoanodes (20 mA g⁻¹) at 1.5 V vs. SCE in 0.1 M Na₂SO₄ under visible illumination of 90 mW cm⁻². A significant shift of the overpotential toward lower values was also observed when photoanodes were illuminated. The highest shift of the overpotential, from 1.296 to 0.248 V vs. SCE, was recorded when the ZnO/CTAB photanode was illuminated. The ZnO/CTAB photoanode provides efficient charge transfer across the electrode/electrolyte interface, with a longer lifetime of photogenerated electron–hole pairs and reduced possibility of charge recombination. The photoconversion efficiency was improved from 1.4% for ZnO and 0.9% for ZnO/F127 to 4.2% for ZnO/CTAB at 0.510 mV. A simple procedure for the synthesis of ZnO particles with improved photo(electro)catalytic properties was established and it was found that even a small amount of CTAB used during processing of ZnO increases the surface-to-bulk defect ratio. Optimization of the surface-to-bulk defect ratio in ZnO materials enables increase of the absorption capacity for visible light, rendering of the recombination rate of the photogenerated pair, as well as increase of both the photocurrent density and photoconversion efficiency.

Employing CTAB in the microwave synthesis of ZnO particles enables improvement of their visible light absorption capacity and photo(electro)catalytic activity.     

Facile and rapid synthesis of a novel spindle-like heterojunction BiVO4 showing enhanced visible-light-driven photoactivity

A spindle-like monoclinic–tetragonal heterojunction BiVO₄ was successfully synthesized by a pressure-controllable microwave method. The as-prepared BiVO₄ samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV-vis diffuse reflectance spectroscopy (DRS), photoluminescence (PL) spectroscopy, transient photocurrent responses and electrochemical impedance spectroscopy (EIS). The visible-light-driven photocatalytic activity of the BiVO₄ samples was evaluated for the degradation of Rhodamine B (RhB) and tetracycline (TC). The synthesis process needs microwave irradiation for only 10 min without the addition of any auxiliary reagent, pH adjustment, and calcination. The as-prepared spindle-like monoclinic–tetragonal heterojunction BiVO₄ exhibits excellent photocatalytic activity for the degradation of both RhB and TC. The photocatalytic degradation rates of RhB and TC over spindle-like BiVO₄ are 1.77 and 1.64 times higher, respectively, than that measured over monoclinic BiVO₄. The enhanced photocatalytic activity is mainly attributed to the fact that the existence of a heterojunction effectively promotes the separation of photo-generated carriers and extends the visible-light absorption of BiVO₄.

A novel spindle-like monoclinic–tetragonal BiVO₄ heterojunction is rapidly synthesized via a pressure-controllable microwave method.     

Superior visible light photocatalytic performance of reticular BiVO4 synthesized via a modified sol–gel method

Reticular BiVO₄ catalysts were successfully synthesized via a modified sol–gel method. Here, citric acid (CA) was used as the chelating agent and ethylenediaminetetraacetic acid (EDTA) was used as the chelating agent and template. Furthermore, the effects of pH values and EDTA on the structure and morphology of the samples were studied. We determined that EDTA and pH played important roles in the determination of the morphology of the as-prepared BiVO₄ samples. Photocatalytic evaluation revealed that the reticular BiVO₄ exhibited superior photocatalytic performance characteristics for the degradation of methylene blue (MB) under visible-light (λ > 400 nm) exposure, about 98% of the MB was found to degrade within 50 min. Moreover, the degradation kinetics of MB was in good agreement with pseudo-first-order kinetics. The obtained apparent reaction rate constant k_app of reticular BiVO₄ was much higher than that of BiVO₄ synthesized by the citric acid sol–gel method.

Reticular BiVO₄ catalysts with superior visible light photocatalytic performance were successfully synthesized via a modified sol–gel method.     

The design and growth of peanut-like CuS/BiVO4 composites for photoelectrochemical sensing

In this study, the CuS/BiVO₄-X (where X represents the mass percentage of CuS associated with CuS/BiVO₄; X = 2%, 5% and 7%) p–n heterostructures were fabricated using a two-step hydrothermal method. The structural and morphological features were ascertained in great detail using several physical characterization processes. According to the results of the photoelectrochemical (PEC) experimental processes, the PEC properties of CuS/BiVO₄-5% were much more obvious as compared to those of pure BiVO₄, CuS and CuS/BiVO₄-X. Moreover, the photoluminescence (PL) and UV-vis diffuse reflection spectra (DRS) affirmed that the CuS/BiVO₄-5% demonstrates an excellent capacity for absorbing visible light and low electron recombination rate as compared with the other composites. Accordingly, PEC sensors with CuS/BiVO₄-5% were fabricated for the detection of dopamine (DA) and bisphenol A (BPA) with outstanding selectivity and stability. For DA, it implied a broad linear range from 0.01–10 μM and 10–120 μM, and for BPA, the broad linear range was 0.01–90 μM. Thus, the PEC sensor has significant potential application when it comes to DA and BPA detection.

In this study, the CuS/BiVO₄-X (where X represents the mass percentage of CuS associated with CuS/BiVO₄; X = 2%, 5% and 7%) p–n heterostructures were fabricated using a two-step hydrothermal method.     

Green fabrication of nanoporous BiVO4 films on ITO substrates for photoelectrochemical water-oxidation

A new green method was developed to prepare nanoporous BiVO₄ films on ITO substrates for photoelectrochemical (PEC) water-oxidation under visible light irradiation. The films can be prepared by simple drop-casting of a stable aqueous solution of Bi³⁺ and V⁵⁺ complexes with tartaric acid and ethylenediaminetetraacetic acid, followed by drying and calcination in air. Thanks to these ligands, the aqueous precursor solution is remarkably stable over a wide range of pH (pH 4–9). The BiVO₄ films on ITO substrates possess a 3D-network structure comprised of nanoparticles with a scheelite–monoclinic phase and a diameter of ca. <100 nm, after calcination at 450–500 °C for 1 h. The PEC performance clearly depended on the film thickness that can be controlled by coating times, and calcination conditions (temperature and time). The CoPi-loaded BiVO₄ electrodes exhibited relatively high performance for PEC water oxidation (ABPE of 0.35% at 0.8 V vs. RHE) under simulated sunlight irradiation.

Nanoporous BiVO₄ photoanodes for efficient water oxidation were directly fabricated on an ITO substrate using an aqueous solution of mild pH.     

Free-standing graphene/bismuth vanadate monolith composite as a binder-free electrode for symmetrical supercapacitors

Preparation of new types of electrode material is of great importance to supercapacitors. Herein, a graphene/bismuth vanadate (GR/BiVO₄) free-standing monolith composite has been prepared via a hydrothermal process. Flexible GR sheets act as a skeleton in the GR/BiVO₄ monolith composites. When used as a binder-free electrode in a three-electrode system, the GR/BiVO₄ composite electrode can provide an impressive specific capacitance of 479 F g⁻¹ in a potential window of −1.1 to 0.7 V vs. SCE at a current density of 5 A g⁻¹. A symmetrical supercapacitor cell which can be reversibly charged–discharged at a cell voltage of 1.6 V has been assembled based on this GR/BiVO₄ monolith composite. The symmetrical capacitor can deliver an energy density of 45.69 W h kg⁻¹ at a power density of 800 W kg⁻¹. Moreover, it ensures rapid energy delivery of 10.75 W h kg⁻¹ with a power density of 40 kW kg⁻¹.

A symmetrical supercapacitor with a high energy density has been assembled based on a free-standing GR/BiVO₄ monolith composite.     

Black Si-doped TiO2 nanotube photoanode for high-efficiency photoelectrochemical water splitting

Black Si-doped TiO₂ (Ti–Si–O) nanotubes were fabricated through Zn metal reduction of the Ti–Si–O nanotubes on Ti–Si alloy in an argon atmosphere. The nanotubes were used as a photoanode for photoelectrochemical (PEC) water splitting. Both Si element and Ti³⁺/oxygen vacancies were introduced into the black Ti–Si–O nanotubes, which improved optical absorption and facilitated the separation of the photogenerated electron–hole pairs. The photoconversion efficiency could reach 1.22%, which was 7.18 times the efficiency of undoped TiO₂. It demonstrated that a Si element and Ti³⁺/oxygen vacancy co-doping strategy could offer an effective method for fabricating a high-performance TiO₂-based nanostructure photoanode for improving PEC water splitting.

Black Si-doped TiO₂ (Ti–Si–O) nanotubes were fabricated through Zn metal reduction of the Ti–Si–O nanotubes on Ti–Si alloy in an argon atmosphere.     

Annealing temperature effects on photoelectrochemical performance of bismuth vanadate thin film photoelectrodes

The effects of annealing treatment between 400 °C and 540 °C on crystallization behavior, grain size, electrochemical (EC) and photoelectrochemical (PEC) oxygen evolution reaction (OER) performances of bismuth vanadate (BiVO₄) thin films are investigated in this work. The results show that higher temperature leads to larger grain size, improved crystallinity, and better crystal orientation for the BiVO₄ thin film electrodes. Under air-mass 1.5 global (AM 1.5) solar light illumination, the BiVO₄ thin film prepared at a higher annealing temperature (500–540 °C) shows better PEC OER performance. Also, the OER photocurrent density increased from 0.25 mA cm⁻² to 1.27 mA cm⁻² and that of the oxidation of sulfite, a hole scavenger, increased from 1.39 to 2.53 mA cm⁻² for the samples prepared from 400 °C to 540 °C. Open-circuit photovoltage decay (OCPVD) measurement indicates that BiVO₄ samples prepared at the higher annealing temperature have less charge recombination and longer electron lifetime. However, the BiVO₄ samples prepared at lower annealing temperature have better EC performance in the absence of light illumination and more electrochemically active surface sites, which are negatively related to electrochemical double-layer capacitance (C_dl). C_dl was 0.0074 mF cm⁻² at 400 °C and it decreased to 0.0006 mF cm⁻² at 540 °C. The OER and sulfide oxidation are carefully compared and these show that the efficiency of charge transport in the bulk (η_bulk) and on the surface (η_surface) of the BiVO₄ thin film electrode are improved with the increase in the annealing temperature. The mechanism behind the light-condition-dependent role of the annealing treatment is also discussed.

The effects of annealing treatment on crystallization behavior, grain size, electrochemical (EC) and photoelectrochemical (PEC) oxygen evolution reaction (OER) performances of bismuth vanadate (BiVO₄) thin films are investigated in this work.     

Efficient photocatalytic degradation of dyes using photo-deposited Ag nanoparticles on ZnO structures: simple morphological control of ZnO

In this work, morphology-controlled ZnO structures were prepared via a hydrothermal method by simple adjustments in the NaOH concentration. The NaOH concentration variation from 0.2 to 1.2 M resulted in the formation of ZnO structures in shapes such as walnut, spherical flower, flower, rod, and urchin-like. The extent of OH⁻ ions is the main factor influencing the growth of ZnO structures. Well-defined morphologies, good crystallinity, and optical properties were obtained for all ZnO structures. Among these ZnO structures, ZnOsf (spherical flower-like) structure showed a greater percentage of photodegradation of methyl orange and rhodamine B dyes. Surface plasmon resonance was achieved by modifying the surface of ZnO with Ag nanoparticles. ZnOsf was loaded with Ag nanoparticles by a facile photo-deposition method. Ag–ZnOsf showed superior photoactivity and recyclability for the degradation of methyl orange and rhodamine B. Therefore, modification of different ZnO structures can help realize potential catalysts for future environmental applications.

Morphology control of ZnO structures were fabricated by hydrothermal method with simple adjustments of NaOH concentration and Ag–ZnO composite showed superior photoactivity and recyclability for the degradation of MO and RhB.     

2D–2D ZnO/N doped g-C3N4 composite photocatalyst for antibiotics degradation under visible light

ZnO and g-C₃N₄ provide excellent photocatalytic properties for degradation of antibiotics in pharmaceutical wastewater. In this work, 2D–2D ZnO/N doped g-C₃N₄ (NCN) composite photocatalysts were prepared for degradation of tetracycline (TC), ciprofloxacin (CIP) and ofloxacin (OFLX). The addition of ZnO resulted in higher separation efficiency and lower recombination rate of photogenerated charge under visible light. The composite photocatalyst showed better degradation performance compared to ZnO or NCN alone. The TC degradation reached 81.3% in 15 minutes by applying the prepared 20% ZnO/NCN composite photocatalyst, showing great competitiveness among literature reported g-C₃N₄ based photocatalysts. After 30 minutes, the degradation rate of TC, CIP and OFLX reached 82.4%, 64.4% and 78.2%, respectively. The TC degradation constant of the composite photocatalyst was 2.7 times and 6.4 times higher than NCN and CN, respectively. Radical trapping experiments indicated that ·O₂⁻ was the dominant active substance. The transference of excited electrons from the conduction band (CB) of NCN to ZnO enhanced the separation of photogenerated electron–hole pairs and simultaneously suppressed their recombination. This study provides a possibility for the design of high-performance photocatalysts for antibiotics degradation in wastewater.

2D–2D ZnO/N doped g-C₃N₄ (NCN) composite photocatalysts were prepared for degradation of antibiotics with high efficiency.     

In situ synthesis of C-doped BiVO4 with natural leaf as a template under different calcination temperatures

In this work, a series of C-doped BiVO₄ (BiVO₄-T) with natural leaf structures were synthesized by a dipping-calcination method with the leaf of Chongyang wood seedling as a template under different calcination temperatures. The structures and morphologies of BiVO₄-T were observed by FE-SEM observations. The doped carbon in BiVO₄-T was formed in situ from the natural leaf during the calcination process and the amount of doping could be regulated from 0.51–1.16 wt% by controlling the calcination temperature. It was found that the sample calcined at 600 °C (BiVO₄-600) with a C-doping content of 1.16 wt% showed the best photocatalytic degradation activity. After 120 min visible light irradiation, the photocatalytic decomposition efficiency of RhB for BiVO₄-600 is 2.2 times higher than that of no template BiVO₄. The enhanced photocatalytic performance is ascribed to the combined action of the unique morphology and doped-carbon. It is considered that the unique structures and carbon doping of BiVO₄-600 are in favor of the enhancement of visible light absorption, which was supported by UV-vis DRS. Furthermore, the C-doping can enhance the efficient separation and transfer of the photo-generated electron–hole pairs, as proved by PL measurements. This study provides a simple dipping-calcination method and found the best calcination temperature to fabricate a high-performance BiVO₄, which simultaneously achieves morphology and C-doping control in one step.

A series of C-doped BiVO₄ with natural leaf as a template were synthesized under different calcination temperatures by the dipping-calcination method, which simultaneously achieves morphology and C-doping control in one step.     

Rational design of magnetically separable core/shell Fe3O4/ZnO heterostructures for enhanced visible-light photodegradation performance

Magnetically separable core/shell Fe₃O₄/ZnO heteronanostructures (MSCSFZ) were synthesized by a facile approach, and their application for enhanced solar photodegradation of RhB was studied. The formation mechanism of MSCSFZ was proposed, in which Fe₃O₄ nanoparticles served as a template for supporting and anchoring the ZnO crystal layer as the shells. The morphology of MSCSFZ can be varied from spherical to rice seed-like structures, and the bandgap was able to be narrowed down to 2.78 eV by controlling the core–shell ratios. As a result, the MSCSFZ exhibited excellent visible-light photocatalytic activity for degradation of rhodamine B (RhB) in aqueous solution as compared to the controlled ZnO nanoparticles. Moreover, MSCSFZ could be easily detached from RhB solution and maintained its performance after 4 cycles of usage. This work provides new insights for the design of high-efficient core/shell recyclable photocatalysts with visible light photocatalytic performance.

Magnetically separable core/shell Fe₃O₄/ZnO heteronanostructures (MSCSFZ) were synthesized by a facile approach, and their application for enhanced solar photodegradation of RhB was studied.     

Enhancing the photocatalytic hydrogen production activity of BiVO4 [110] facets using oxygen vacancies

The activity of the hydrogen evolution reaction (HER) during photoelectrochemical (PEC) water-splitting is limited when using BiVO₄ with an exposed [110] facet because the conduction band minimum is below the H⁺/H₂O potential. Here, we enhance the photocatalytic hydrogen production activity through introducing an oxygen vacancy. Our first-principles calculations show that the oxygen vacancy can tune the band edge positions of the [110] facet, originating from an induced internal electric field related to geometry distortion and charge rearrangement. Furthermore, the induced electric field favors photogenerated electron–hole separation and the enhancement of atomic activity. More importantly, oxygen-vacancy-induced electronic states can increase the probability of photogenerated electron transitions, thus improving optical absorption. This study indicates that oxygen-defect engineering is an effective method for improving the photocatalytic activity when using PEC technology.

An oxygen-vacancy-induced internal electric field enhances the photocatalytic hydrogen production activity of a BiVO₄ [110] facet.