Microwave synthesis and photocatalytic activity of Tb 3+ doped BiVO 4 microcrystals

Green light all the way: Triple modification synergistic modification effect to enhance the photoelectrochemical water oxidation performance of BiVO4 photoanode

The recombination of photogenerated electron-hole pairs of the photoanode seriously impairs the application of bismuth vanadate (BiVO4) in photoelectrochemical water splitting. To address this issue, we prepared a Yb:BiVO4/Co3O4/FeOOH composite photoanode by employing drop-casting and soaking methods to attach Co3O4/FeOOH cocatalysts to the surface of ytterbium-doped BiVO4. The prepared Yb:BiVO4/Co3O4/FeOOH photoanode demonstrates a high photocurrent density of 4.89 mA cm-2 at 1.23 V versus the reversible hydrogen electrode (RHE), which is 5.1 times that of bare BiVO4 (0.95 mA cm-2). Detailed characterization and testing demonstrated that Yb doping narrows the band gap and significantly enhances the carrier density. Furthermore, Co3O4 serves as a hole transfer layer to expedite hole migration and diminish recombination, while FeOOH offers additional active sites and minimizes surface trap states, thus boosting stability. The synergistic effects of Yb doping and Co3O4/FeOOH cocatalyst significantly improved the reaction kinetics and overall performance of PEC water oxidation. This work provides a strategy for designing efficient photoanodes for PEC water oxidation.

Snow-like BiVO4 with rich oxygen defects for efficient visible light photocatalytic degradation of ciprofloxacin

The overuse of ciprofloxacin (CIP), causing serious environment pollution, has drawn great attentions. To provide alternative solution to this problem, we synthesized a snow-like BiVO₄ with rich oxygen vacancy by adjusting the amounts of cetyltrimethyl ammonia bromide (CTAB) surfactant. Various characterizations were performed to investigate the morphology and surface properties of the synthesized BiVO₄. Interestingly, both the morphology and the amount of oxygen vacancy were related to the concentration of additional CTAB, and the most oxygen vacancies were generated when specific amount of CTAB (molar ratio of CTAB to Bi³⁺ of 0.2) was introduced. Photoluminescence and photoelectrochemical tests demonstrated that the presence of oxygen vacancy significantly enhanced the separation efficiency of photo-generated carriers in BiVO₄. Subsequently, CIP photodegradation was significantly enhanced in the presence of snow-like BiVO₄. Both quenching experiments and EPR tests demonstrated that photogenerated holes and •O₂^- were the main active species contributing to CIP degradation. Furthermore, CIP transformation pathway was proposed based on the identified transformation products. Our study developed a novel method to synthesize a BiVO₄ material with snow-like morphology and abundant oxygen vacancy by simply varying the amount of surfactant. This study would shed light on designing the next generation photocatalyst with the assistant of surfactant to control the surface properties.

Investigation on Al3+ and Al2O3 Coexist in BiVO4 for Efficient Methylene Blue Degradation: Insight into Surface States and Charge Separation

A series of Al-doped BiVO₄ composites have been synthesized via the hydrothermal method for methylene blue (MB) degradation application. The reasons for the improvement of photocatalytic performance was explained from the perspective of optics. Transient photovoltage (TPV) measurements suggested that the surface states have the priority to capture photogenerated carriers, and the Al₂O₃ surface passivation layer can prolong the lifetime of charge carrier. The results of surface photovoltage (SPV), transient photovoltage (TPV), and surface photocurrent (SPC) measurements suggested that the coexistence of Al³⁺ and Al₂O₃ caused by the appropriate doping would improve the transfer property and prolong the lifetime of photogenerated carriers. Finally, the possible photocatalytic mechanism is expounded to illustrate the photogenerated charge behavior under visible light irradiation. This work provides a better understanding of the synergistic effect of Al-doping and Al₂O₃ passivation layer on enhancing the photocatalytic performance.

Surfactants-assisted preparation of BiVO4 with novel morphologies via microwave method and CdS decoration for enhanced photocatalytic properties

The development of a highly efficient and rapid method for the accurate preparation of photocatalysts with novel morphologies is a hot research topic. The different morphologies of BiVO₄ was prepared using surfactants-assisted microwave method, and demonstrated irregular (no surfactant), octahedral (sodium dodecyl benzene sulfonate), olive-like (polyvinylpyrrolidone) and hollow structures (ethylenediaminetetraacetic acid), respectively. The BiVO₄-CdS were synthesized using the chemical-bath-deposition method with different morphologies of BiVO₄ as the substrates. The hollow structure of BiVO₄ displayed the highest photocatalytic performance. Moreover, the photodegradation rates of the hollow structure BiVO₄-CdS on tetracycline hydrochloride and ciprofloxacin were about 1.8 and 1.5 times higher than the corresponding BiVO₄, indicating that the Z-scheme heterojunction can improve the photogenerated electron pairs separation efficiency. Furthermore, the regulation mechanism of morphology and energy-band position, as produced using the surfactants, has also been thoroughly investigated in this work, which provides a novel insight into the efficient and rapid preparation of photocatalysts with special morphology and high performance.

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.

Co2+ substituted for Bi3+ in BiVO4 and its enhanced photocatalytic activity under visible LED light irradiation

We investigated the fabrication of Co-doped BiVO₄ (Bi_1−xCo_xVO_4+δ, 0.05 < x < 0.5) by the substitution of Co ions for Bi sites in BiVO₄. The X-ray diffraction (XRD), Raman, and X-ray photoelectron spectroscopy (XPS) results indicated that the substitution of Co²⁺ ions for Bi³⁺ sites in BiVO₄ was successful, although a change in the crystal phase of BiVO₄ did not occur. UV-vis DRS and PL results suggested that the Co-incorporation could slightly improve the visible light absorption of BiVO₄ and induce the separation of photoinduced electron–hole pairs; therefore, a significant enhancement of photocatalytic performance was achieved. The Bi_0.8Co_0.2VO_4+δ sample showed superior photocatalytic activity in comparison with other samples, achieving 96.78% methylene blue (MB) removal within 180 min. In addition, the proposed mechanism of improved photocatalytic activities and the stability of the catalyst were also investigated.

We investigated the fabrication of Co-doped BiVO₄ (Bi_1−xCo_xVO_4+δ, 0.05 < x < 0.5) by the substitution of Co ions for Bi sites in BiVO₄.

BiVO4-rGO with a novel structure on steel fabric used as high-performance photocatalysts

A high-performance and novel photocatalyst of BiVO4-reduced Graphene Oxide (BiVO4-rGO) nanocomposite was prepared by a facile hydrothermal method. The photocatalyst was characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electronic microscopy, UV-Vis diffusion reflectance spectroscopy, photoluminescence spectroscopy and UV-Vis adsorption spectroscopy, respectively. The visible-light photocatalytic activity was evaluated by oxidation of methyl orange (MO) under simulated sunlight irradiation. The results show that the BiVO4-rGO nanocomposites exhibit enhanced photocatalytic performance for the degradation of MO with a maximum removal rate of 98.95% under visible light irradiation as compared with pure BiVO4 (57.55%) due to the increased light absorption intensity and the degradation of electron-hole pair recombination in BiVO4 with the introduction of the rGO.