In-situ pressure-induced BiVO4/Bi0.6Y0.4VO4 S-scheme heterojunction for enhanced photocatalytic overall water splitting activity

Platinum-induced nanolization and electron-deficient gold in platinum@gold cocatalyst for efficient photocatalytic hydrogen peroxide production

Simultaneous optimization of the number and intensity of oxygen (O2) adsorption on gold (Au) cocatalyst is highly required to greatly improve their interfacial hydrogen peroxide (H2O2)-production activity. However, it is a great challenge to realize the above effective modulation of Au by traditional photodeposition route. In this study, a platinum (Pt)-induced selective photodeposition method was designed to simultaneously regulate the particle size and electronic structure of Au cocatalyst for boosting the photocatalytic H2O2-production activity of bismuth vanadate (BiVO4) via the selective deposition of Pt@Au core-shell cocatalyst. The photocatalytic results indicate that the as-prepared BiVO4/Pt0.1@Au photocatalyst achieves a considerable H2O2-production activity with a rate of 2752.13 μmol L-1 (AQE = 13.76 %), which is obviously higher than that of BiVO4/Pt (137.63 μmol L-1) and BiVO4/Au (475.33 μmol L-1). It was found that the introduction of Pt successfully induced the formation of Au nanoparticles for enhancing the number of O2 adsorption. Meanwhile, the spontaneous transfer of free electrons of Au to Pt induces the generation of electron-deficient Auδ+ sites, which spontaneously enhances the O2-adsorption intensity for facilitating the 2-electron oxygen reduction reaction (ORR), resulting in efficient H2O2 production. The present strategy may be useful for more comprehensively regulating the intensity and number of O2 adsorption on cocatalysts to facilitate artificial photosynthesis.

Charge self-regulation over in-plane two-dimensional/two-dimensional hetero-cocatalyst for robust photocatalytic hydrogen generation

The rationally designing and constructing atomic-level heterointerface of two-dimensional (2D) chalcogenides is highly desirable to overcome the sluggish H2O-activation process toward efficient solar-driven hydrogen evolution. Herein, a novel in-plane 2D/2D molybdenum disulfide-rhenium disulfide (ReS2-MoS2) heterostructure is well-designed to induce the charge self-regulation of active site by forming electron-enriched Re(4-δ)+ and electron-deficient S(2-δ)- sites, thus collectively facilitating the activation of adsorbed H2O molecules and its subsequent H2 evolution. Furthermore, the obtained in-plane heterogenous ReS2-MoS2 nanosheet can powerfully transfer photoexcited electrons to inhibit photocarrier recombination as observed by advanced Kelvin probe measurement (KPFM), in-situ X-ray photoelectron spectroscopy (XPS) and femtosecond transient absorption spectroscopy (fs-TAS). As expected, the obtained ReS2-MoS2/TiO2 photocatalyst achieves an outperformed H2-generation rate of 6878.3 μmol h-1 g-1 with visualizing H2 bubbles in alkaline/neutral conditions. This work about in-plane 2D/2D heterostructure with strong free-electron interaction provides a promising strategy for designing novel and efficient catalysts for various applications.

A novel visible-light-driven Z-scheme C3N5/BiVO4 heterostructure with enhanced photocatalytic degradation performance

As a visible-light response semiconductor materials, bismuth vanadate (BiVO4) is extensively applied in photodegradation organic dye field. In this study, we synthesized C3N5 nanosheets and coupled with decahedral BiVO4 to construct a Z-scheme C3N5/BiVO4 heterostructure with close interface contact. By introducing C3N5 into BiVO4, the built Z-scheme transfer pathway provides silky channel for charge carrier migration between different moieties and enables photoexcited electrons and holes accumulated on the surface of BiVO4 and C3N5. The accelerated separation of charge carriers ensures C3N5/BiVO4 heterostructures with a powerful oxidation capacity compared with pure BiVO4. Due to the synergistic effect in Z-scheme heterostructure, the C3N5/BiVO4 demonstrated an improved photodegradation ability of rhodamine B (RhB) and methylene blue (MB) that of bare BiVO4.

Efficient Degradation of Rhodamine B with the BiOCl/Bi2Fe4O9 Heterojunction Photocatalyst

BiOCl/Bi2Fe4O9 photocatalyst was prepared by a coprecipitation-hydrothermal method. The heterojunction structure generated by the composite of BiOCl and Bi2Fe4O9 reduced the electron-hole recombination efficiency and improved the degradation rate of RhB. At 240 min, 20% BiOCl/Bi2Fe4O9 represented the excellent degradation effect on 10 mg/L RhB; the degradation efficiency reached 99.56%; and the reaction rate constant was 0.01534 min-1, which was 5.76 times and 6.06 times that of Bi2Fe4O9 and BiOCl, respectively. The main active substance of the photocatalytic degradation of dyes was superoxide radical O2-·. Five cycles of the experiment proved the relative stability of BiOCl/Bi2Fe4O9.

2D/2D MgO/g-C3N4 S-scheme heterogeneous tight with Mg-N bonds for efficient photo-Fenton degradation: Enhancing both oxygen vacancy and charge migration

Construction of S-scheme heterojunction is an efficient strategy to enhance photocatalytic efficiency. Besides the retained redox ability, the wide work function gap and intimate interface contact are essential for efficient degradation. Nontoxic magnesium oxide (MgO) with two dimensional (2D) structures and high work function is a potential material for S-scheme photocatalysts. Herein, MgO was used to in-situ grown on graphitic carbon nitride (g-C3N4) for constructing the strongly connected MgO/g-C3N4 S-scheme photocatalyst with tight Mg-N bonds. Meanwhile, the presence of Mg-N bonds induces the formation of oxygen vacancy in MgO, which enhances the Fenton-like degradation. Furthermore, the Mg-N bond promotes the charge migration between MgO and g-C3N4. Consisting of the enhanced Fenton-like process and photocatalysis, the MgO/g-C3N4 shows a higher photo-Fenton degradation activity (80.01%) for degradation of organic pollutants (Rhodamine B, 100 mg L-1) in water, than g-C3N4 (28.46%) and MgO (55.64%). Therefore, the interfacial chemical bonds in heterojunction photocatalysts provide an efficient strategy for further enhancing the photocatalysis of S-scheme photocatalysts.

Efficient Photocatalytic Reduction of Hexavalent Chromium by BiVO4-Decorated MXene Photocatalysts and Their Charge Carrier Dynamics

The synergistically MXene (Ti3C2Tx) co-catalyst-decorated BiVO4-based heterostructured photocatalysts have been synthesized by a hydrothermal approach with varied loading concentrations of MXene (Ti3C2Tx) to drive the hexavalent chromium reduction efficiently. The formation of the heterostructured photocatalyst was confirmed by the appearance of X-ray diffraction (XRD) peaks corresponding to the monoclinic BiVO4 phase and MXene (Ti3C2Tx) and also the antisymmetric (834 cm-1) and symmetric stretching (715 cm-1) of tetrahedral VO4 and D (1330 cm-1) and G (1570 cm-1) bands corresponding to MXene (Ti3C2Tx) in the Raman spectrum. The worm-like structures of BiVO4 nanocrystals grew onto the lamellar sheets of MXene (Ti3C2Tx), as shown by field emission scanning electron microscopy (FESEM), and has an increased surface area of 15.62 m2g-1 in the case of BVO-20-TC. X-ray photoelectron spectroscopy (XPS) analysis confirms the presence of V5+ and Ti3+states, and the uniform distribution of BiVO4 nanocrystals over lamellar sheets of MXene (Ti3C2Tx) is evident from energy-dispersive X-ray (EDX) analysis. The ultraviolet-diffuse reflectance spectroscopy (UV-DRS) spectra suggest a decrease in the band gap energy of BVO-20-TC to 2.335 eV, promoting a higher degree of visible light harvesting. Upon optimization, by varying the pH, the amount of the photocatalyst, and the concentration of Cr(IV), BVO-20-TC exhibits the highest photocatalytic efficiency (96.39%) while using a Cr(VI) concentration of 10 ppm at pH 2 and 15 mg of the photocatalyst, and the photoreduction of Cr(VI) to Cr(III) follows the pseudo-first-order reaction. The decrease in the PL intensity in BVO-20-TC reveals a faster transfer of electrons from MXene (Ti3C2Tx) to BiVO4. Further, the higher degree of band bending at the BiVO4/MXene (Ti3C2Tx) heterojunction, revealed from the Mott-Schottky analysis, facilitates efficient charge transfer and eventually faster and efficient photoreduction of Cr(VI) to Cr(III). The reusability and stability test undertaken for BVO-20-TC reveals that even after five cycles, the Cr (VI) photoreduction efficacy is retained. This work provides insights into photoreduction of Cr (VI) by using such heterostructures.

Construction of an La-BiVO4/O-Doped g-C3N4 Heterojunction Photocatalyst Embedded in Electrospinning Nanofibers

BiVO₄ has been widely used in the field of photocatalysis due to its nontoxic and moderate band gap. However, single BiVO₄ has the disadvantages of a high recombination rate of photogenerated carriers and weak response to visible light, inhibiting its photocatalytic applications. To explore viable solutions, a hybrid material composed of lanthanum-doped bismuth vanadate (La-BiVO₄) and oxygen-doped porous graphite carbon nitride (O-doped g-C₃N₄), i.e., La-BiVO₄/O-doped g-C₃N₄ powder, was prepared by a facile hydrothermal reaction and low-temperature calcination. Then, the powder was loaded on polyacrylonitrile nanofibers (NFs) through the electrospinning fiber technique. Various surface science characterizations, including transmission electron microscopy and nitrogen absorption and desorption analysis, confirmed the successful synthesis of a mesoporous heterojunction material. The La³⁺-doping as well as the porous morphologies and larger specific surface area of the O-doped g-C₃N₄ ultimately improve the photocatalytic abilities via a proposed Z-scheme heterojunction mechanism. The roles of La³⁺-doping and morphology modification in promoting the separation of the photogenerated carriers and broadening the optical absorption range were experimentally discussed. The RhB degradation experiment indicated that the La-BiVO₄/O-doped g-C₃N₄ powder has excellent photocatalytic activity, which is about 2.85 and 2 times higher than that of the pure BiVO₄ and O-doped g-C₃N₄, respectively. Meanwhile, the La-BiVO₄/O-doped g-C₃N₄ NF shows good stability and recoverability after a 10-cycle testing. Such a hybrid photocatalyst with a proposed Z-scheme heterojunction mechanism and good plasticity might pave a feasible way to fabricate a new library of photocatalysts.

Microwave-Assisted Synthesis of MoS2/BiVO4 Heterojunction for Photocatalytic Degradation of Tetracycline Hydrochloride

Compared with traditional hydrothermal synthesis, microwave-assisted synthesis has the advantages of being faster and more energy efficient. In this work, the MoS₂/BiVO₄ heterojunction photocatalyst was synthesized by the microwave-assisted hydrothermal method within 30 min. The morphology, structure and chemical composition were characterized by X-ray diffraction (XRD), Raman, X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), and high-resolution transmission electron microscopy (HRTEM). The results of characterizations demonstrated that the synthesized MoS₂/BiVO₄ heterojunction was a spherical structure with dimensions in the nanorange. In addition, the photocatalytic activity of the samples was investigated by degrading tetracycline hydrochloride (TC) under visible light irradiation. Results indicated that the MoS₂/BiVO₄ heterojunction significantly improved the photocatalytic performance compared with BiVO₄ and MoS₂, in which the degradation rate of TC (5 mg L^-1) by compound where the mass ratio of MoS₂/BiVO₄ was 5 wt% (MB5) was 93.7% in 90 min, which was 2.36 times of BiVO₄. The active species capture experiments indicated that •OH, •O₂^- and h⁺ active species play a major role in the degradation of TC. The degradation mechanism and pathway of the photocatalysts were proposed through the analysis of the band structure and element valence state. Therefore, microwave technology provided a quick and efficient way to prepare MoS₂/BiVO₄ heterojunction photocatalytic efficiently.

Towards the Sustainable Production of Ultra-Low-Sulfur Fuels through Photocatalytic Oxidation

Nowadays, the sulfur-containing compounds are removed from motor fuels through the traditional hydrodesulfurization technology, which takes place under harsh reaction conditions (temperature of 350–450 °C and pressure of 30–60 atm) in the presence of catalysts based on alumina with impregnated cobalt and molybdenum. According to the principles of green chemistry, energy requirements should be recognized for their environmental and economic impacts and should be minimized, i.e., the chemical processes should be carried out at ambient temperature and atmospheric pressure. This approach could be implemented using photocatalysts that are sensitive to visible light. The creation of highly active photocatalytic systems for the deep purification of fuels from sulfur compounds becomes an important task of modern catalysis science. The present critical review reports recent progress over the last 5 years in heterogeneous photocatalytic desulfurization under visible light irradiation. Specific attention is paid to the methods for boosting the photocatalytic activity of materials, with a focus on the creation of heterojunctions as the most promising approach. This review also discusses the influence of operating parameters (nature of oxidant, molar ratio of oxidant/sulfur-containing compounds, photocatalyst loading, etc.) on the reaction efficiency. Some perspectives and future research directions on photocatalytic desulfurization are also provided.

Interface Engineering of a 2D/2D BiVO4/Bi4V2O10 Heterostructure with Improved Photocatalytic Photoredox Activity

Bismuth vanadate (BiVO₄) is a promising photocatalyst for water pollution degradation and photocatalytic oxygen evolution. In this work, we prepared 2D/2D BiVO₄-Bi₄V₂O₁₀ heterostructure with tight interfacial contact via a facile one-step hydrothermal process. The crystal structure and morphology of the samples could be easily regulated by changing the pH values of the solution. The BiVO₄-Bi₄V₂O₁₀ heterostructure exhibited an enhanced photodegradation rate of Cr(VI) and oxygen evolution that of bare BiVO₄, indicating that the synergistic effect and the interfacial fusions between BiVO₄ and Bi₄V₂O₁₀ can effectively promote the migration and separation rate of photoexcited charge carriers.

Insight into the enhanced photocatalytic activity mechanism of the Ag3VO4/CoWO4 p–n heterostructure under visible light

A novel Ag3VO4/CoWO4 p–n heterostructure was designed and prepared by an in situ growth method. The physicochemical properties were characterized by multiple techniques, and the photocatalytic performances in Cr(vi) reduction and TC degradation were also evaluated under visible-light irradiation.