2D BiOBr Research Articles

Design of BiOBr nanosheets decorated SiC whisker hybrid structure with enhanced photocatalytic performance

Although BiOBr exhibits unique layer structures and good visible light response features as photocatalysts, it has been limited by low surface area and poor carries separation. Herein, a simple hydrothermal approach is reported for planting 2D BiOBr nanosheets on 1D SiC whiskers to obtain the binary hybrid structure. By further controlling the hydrothermal temperature, the loading content of BiOBr on SiC whiskers surface, the band structure of BiOBr/SiCw hybrids could be finely tuned to optimize photodegradation activity. Results demonstrate that the construction of BiOBr/SiC hybrid structure not only increases surface area to provide more activity sites, but also improves photo-induced carriers transfer for strengthening the separation of the photo-induced carrier, which favors photodegradation activity. More importantly, the electron spin resonance and capture experiment reveals that holes are the main species responsible for the oxidation of contaminants. Benefited from the above characteristics, the optimized BS160 exhibits efficient photodegradation ability, where 97% Rhodamine B (RhB) is eliminated after 15 min and 60% tetracycline hydrochloride is degraded after 60 min under visible light irradiation, respectively. Moreover, the optimized BS160 also displays excellent photocatalytic stability after 5 reusability cycles. This work paves a new route for the development of photocatalysts based on BiOBr.

Enhanced photocatalytic degradation of glyphosate over 2D CoS/BiOBr heterojunctions under visible light irradiation

Two-dimensional (2D) heterojunction photocatalysts can shorten the carrier transfer pathway. In this study, CoS nanoparticles were deposited on the surface of 2D BiOBr nanosheets to fabricate novel ultrathin and intimate-contact 2D heterojunction photocatalysts by a two-step solvothermal route. Under visible-light (λ > 400 nm) irradiation, the apparent reaction rate constant of glyphosate degradation over 10%CoS/BiOBr reaches 0.0074 min–1 (74.7% glyphosate was degraded within 3 h), which is about 5.3 times that of pure BiOBr (0.0014 min–1). The extraordinary photocatalytic performance is attributed to the strong visible-light absorption, the effective charge separation and low charge transfer resistance. The possible photocatalytic reaction process and mechanism over CoS/BiOBr heterojunctions are proposed. Moreover, the 10%CoS/BiOBr sample shows good reusability and stability. This work could provide a new insight for the design and development of 2D heterojunction photocatalysts.

Controllable preparation of ultrathin 2D BiOBr crystals for high-performance ultraviolet photodetector

Ternary layered compound materials (bismuth oxyhalides and metal phosphorus trichalcogenides) stand out in electronic and optoelectronic fields due to their interesting physical properties. However, few studies focus on the preparation of high-quality two-dimensional (2D) BiOBr crystals with a typical layered structure, let alone their optoelectronic applications. Here, for the first time, high-quality 2D BiOBr crystals with ultrathin thicknesses (less than 10 nm) and large domain sizes (∼100 µm) were efficiently prepared via a modified space-confined chemical vapor deposition (SCCVD) method. It is demonstrated that a moderate amount of H2O molecules in the SCCVD system greatly promote the formation of high-quality 2D BiOBr crystals because of the strong polarity of H2O molecules. In addition, a linear relationship between the thickness of BiOBr nanosheets and Raman shift of $${\rm{A}}_{1{\rm{g}}}^{\left( 1 \right)}$$ mode was found. Corresponding theoretical calculations were carried out to verify the experimental data. Furthermore, the BiOBr-based photodetector was fabricated, exhibiting excellent performances with a responsivity of 12.4 A W−1 and a detectivity of 1.6×1013 Jones at 365 nm. This study paves the way for controllable preparation of high quality 2D BiOBr crystals and implies intriguing opportunities of them in op toelectronic applications.

Vanadate-Rich BiOBr/Bi Nanosheets for Effective Adsorption and Visible-Light-Driven Photodegradation of Rhodamine B.

Two-dimensional (2D) BiOBr nanosheets (NSs) have attracted considerable interest as photocatalysts. The surface active sites of BiOBr NSs are crucial in determining the photocatalytic performance of these materials under visible light. The modification of the surface state of BiOBr NSs with multiple charged groups has been scarcely studied as a way to increase the number of surface active sites and the corresponding photocatalytic activity. Herein, vanadate-rich 2D BiOBr/Bi NSs were in-situ fabricated without adding strong reductants and subsequently used for visible-light-driven photocatalysis. Even under reductant-free condition, we were able to simultaneously deposit Bi0 and vanadate groups on the surface of pristine BiOBr NSs. The corresponding formation mechanism was also explored in a subsequent step. Compared to pristine BiOBr NSs and BiOBr/Bi NSs, the vanadate-rich BiOBr/Bi NSs prepared herein exhibited superior adsorption and enhanced photodegradation of Rhodamine B (RhB) under visible light illumination.

NaOH-induced formation of 3D flower-sphere BiOBr/Bi4O5Br2 with proper-oxygen vacancies via in-situ self-template phase transformation method for antibiotic photodegradation.

In this study, a novel 3D flower-sphere BiOBr/Bi4O5Br2 with proper-oxygen vacancies (OV) was successfully synthesized by using 3D BiOBr as a self-sacrificed template, NaOH as a structure-driving reagent and midwifery agent of OV. The synthesis mechanism was systematically studied. It revealed that Bi4O5Br2 lamina generated via in-situ phase transfer tightly interspersed in the interior and surface of 3D BiOBr hierarchical structures; calcination temperature, stirring time and -OH concentration can optimize the composition and structure of materials. Also, the calcination conditions (temperatures and air or N2 atmosphere) can regulate the OV's concentration. Ultimately, 3D hierarchical architectures, the optimal heterojunction composition and OV with proper concentrations three positive factors synergistically promoted the photoelectric activity of BiOBr/Bi4O5Br2-OV, making it exhibit ultrahigh photocatalytic activity for antibiotic photodegradation (tetracycline, TC; ciprofloxacin, CIP). We believe the synthesis methods and design idea mentioned in this paper have high instructive significance to prepare high-performance materials.

Direct Z-scheme hierarchical WO3/BiOBr with enhanced photocatalytic degradation performance under visible light

A visible light-driven 3D hierarchical photocatalyst WO3/BiOBr (WB) was prepared by solvothermal method, through which 2D BiOBr ultra-thin nanosheets grew on 1D WO3 nanotube bundles. The as-prepared WB-0.5 (i.e. W:Bi with a mole ratio of 0.5:1) had the highest photocatalytic degradation efficiency of 94.7% for ciprofloxacin hydrochloride under visible light irradiation (λ > 400 nm) within 120 min; such efficiency was about 5.2 and 1.6 times higher than that of individual WO3 and BiOBr, respectively. Its removal rate of total organic carbon was 41.2%. Moreover, WB-0.5 showed high reusability and photostability, and its photocatalytic activity did not show any obvious decrease even after five cycles. The characterisation of WB-0.5’s crystal structure, morphology, and surface elemental state confirmed its 3D hierarchical structure and formation of heterojunction. Its direct Z-scheme system was tested by analysing the active species, photocurrent characteristics, Mott–Schottky plots, UV-vis diffuse reflection spectroscopy and in situ irradiation XPS. The 3D hierarchical structure may provide increased active sites and enhanced light absorption efficiency. The direct Z-scheme configuration is particularly beneficial for improving photocatalytic activity. Therefore, this work may provide a feasible strategy for designing a Z-scheme 3D hierarchical photocatalyst.

Bi-modified 3D BiOBr microsphere with oxygen vacancies for efficient visible-light photocatalytic performance

Flower-like Bi that deposited BiOBr with oxygen vacancies (OVs) has been successfully fabricated via a simple solvothermal method followed by an easy hydrogenated treatment. The characterization results show that three-dimensional (3D) H-1.0Bi@BiOBr microspheres with the diameter about 1.2–1.5 μm were self-assembled by countless two-dimensional (2D) interlaced BiOBr nanosheets. Bi-deposited and oxygen vacancies endowed the H-1.0Bi@BiOBr samples with a dramatically enhanced photocatalytic performance for the degradation of organic pollutants (Rhodamine B and Ofloxacin) and the solar-energy nitrogen fixation. It disclosed that the photocatalytic performance order of the photocatalyst was H200-1.0Bi@BiOBr > H250-1.0Bi@BiOBr > H150-1.0Bi@BiOBr > 1.0Bi@BiOBr > 2.0Bi@BiOBr > 0.5Bi@BiOBr > BiOBr. Particularly, the enhanced photocatalytic activity was ascribed to higher BET specific area, enhanced visible-light absorption, effective photoinduced charge separation and suitable amounts of oxygen vacancies. The H-1.0Bi@BiOBr samples also showed good photochemical stability under repeated visible-light irradiation. This work could shed light on exploring high-photocatalytic-property materials and stimulating the development of OVs-Bi@BiOBr photocatalysts, which had great potential for the solar-energy conversion, environmental purification and organic pollution treatment in water.

Controlled synthesis of bifunctional 3D BiOBr:Eu3+ hierarchitectures with tunable thickness for enhanced visible light photocatalytic activities and mechanism insight

Bifunctional 3D BiOBr:Eu3+ hierarchical nanostructures assembled by nanosheets with tunable thickness have been successfully synthesized.

Facile synthesis of Bi decorated 2D and 3D BiOBr micro‐nanostructures with enhanced photocatalytic activity

BiOBr nanoplates and microflowers decorated with Bi nanoparticles were synthesised by a one-pot catalytic-solvothermal method. Using SbCl3 as additive agent, it can not only shorten the synthesis time but also control the morphology and composition of the product. The samples were characterised by various analytical techniques, indicating enhanced optical absorption and effective charge separation properties as well as abundant oxygen vacancies. The products were employed for the degradation of rhodamine B and phenol solution under visible-light irradiation, exhibiting significantly improved photocatalytic efficiency in comparison with pure BiOBr. An investigation into the photocatalytic mechanism of Bi/BiOBr showed that peroxy radical was the main active species in the degradation process. This study provided a facile and energy saving preparation of controllable Bi/BiOBr heterojunction with oxygen vacancies.

Enhanced photocatalytic activity in hybrid composite combined BiOBr nanosheets and Bi2S3 nanoparticles

To improve photocatalytic activity of 2D BiOBr nanosheets, Bi2S3 nanoparticles were introduced to fabricate the hybrid composite using co-precipitation method. The Bi2S3 loading 15 wt% amount of as-prepared composite shows the optimal visible light-driven photocatalytic activity for the degradation of Rhodamine B (RhB), tetracycline hydrochloride (TC) and ciprofloxacin (CIP). Radicals trapping experiments are further conducted to detect the reactive active species generated during the irradiation of BiOBr/Bi2S3-15 photocatalyst. It demonstrated that h+ and ∙O2− play the key role in photocatalytic degradation of pollutants. Photocurrent response, EIS and PL spectra reveal that the enhanced photocatalytic performance of BiOBr/Bi2S3 hybrid material shows higher separation efficiency of the photo-generated electron–holes pairs.

Enhanced photoelectrocatalytic performance of temperature-dependent 2D/1D BiOBr/TiO2-x nanotubes

A p-n junction with oxygen vacancy and excellent visible light response based on 1D TiO2-x nanotubes and 2D BiOBr nanosheets was prepared successfully. BiOBr nanosheets are well distributed on the outer walls of TiO2-x nanotubes by chemical bath deposition method. The fabricated intimately connected interfacial p-n junction between 2D BiOBr nanoplates and 1D TiO2-x nanotubes offers an interfacial nanochannel, which can promote efficient interfacial charge migration and separation. The construct of TiO2-x extends the photoresponse to visible light due to the introducing of oxygen vacancy. The B/T-80 °C exhibits excellent visible light photoelectrocatalytic activities and stable performance for Rhodamine B (λ = 420 nm), which is caused by the enhanced visible light response, the intimately connect of 2D BiOBr and 1D TiO2-x, and the formation of p-n junction. Furthermore, the quantity and dimension of BiOBr nanoplates decorated on TiO2-x nanotubes has been well controlled by adjusting the dipping temperature.

Optimized design of novel Pt decorated 3D BiOBr flower-microsphere synthesis for highly efficient photocatalytic properties

3D BiOBr flower-microspheres decorated with small amount (0.02–0.5 wt%) of Pt nanoparticles were successfully prepared via new electrostatic-adsorption-assisted light-reduction route. The as-prepared samples were characterized by XRD, SEM, HRTEM, EDS, XPS, UV–Vis DRS, PL, and photocurrent measurements. The photocatalytic activities were tested through the photocatalytic degradation of Bisphenol A (BPA) under visible light (420 nm < λ < 680 nm) and simulated sunlight (320 nm < λ < 680 nm) irradiation. The results indicate that Pt loading do not change the structural morphologies and particle sizes of BiOBr flower-microspheres, but there exists an enhanced photocurrent effect, greatly achieving the highly efficient photocatalytic activity of BiOBr under visible-light and simulated sunlight irradiation. 0.2 wt% Pt/BiOBr sample reveals the highest photocatalytic activity for the degradation on BPA with almost 92% under 10 min, much better than pure BiOBr and (P25) TiO2. The presence of synergistic effect between Pt4+ and Pt0 has vital impact on the electron capture and transfer from the semiconductor to noble metal, preventing the fast electron/hole recombination and participating in the multi-electron reduction of O2, and, consequently, achieving the formation of effective photocatalytic active species. Our findings should provide the fundamental data for making further research efforts in the hot topic on the monatomic Pt-modified photocatalyst systems.

Template-Free Solvothermal Synthesis of Flower-Like BiOBr Microspheres in Ethanol Medium for Photocatalytic Applications

Three-dimensionally (3D) BiOBr microflowers were prepared by a simple solvothermal method, employing Bi(NO3)3 · 5H2O and NaBr as starting reagents in ethanol. The structural, light absorption and morphological properties of as-prepared BiOBr microspheres were determined by X-ray diffraction (XRD), scanning electron microscopy (SEM), and UV–Vis diffuse reflectance spectroscopy (DRS), etc. The results showed that ethanol acted not only as a solvent but also as a template in 3D BiOBr preparation. The BiOBr microspheres exhibited superior photocatalytic activity compared with 2D BiOBr nanosheets, far exceeding that of TiO2 (Degussa, P25). It was found that both superoxide radical (O2•-) and holes (h+) played a key role in the degradation of RhB by BiOBr microflowers.

Visible light-enhanced electrocatalytic alcohol oxidation based on two dimensional Pt-BiOBr nanocomposite

Photoelectrocatalytic oxidation based on noble/semiconductor has been a renewed interest in the past decades. The lack of high-performance semiconductor support remains a challenge for the harvesting and conversion of solar energy. Here, we report the syntheses of two dimensional (2D) BiOBr nanosheets with the superiorities of suitable band gaps, nontoxic, corrosion resistant and so on. These features enable them unprecedented performance for acting as the visible-light-driven support towards alcohol oxidation. Firstly, the pure BiOBr nanosheet has negligible activity towards alcohol oxidation. After the deposition of Pt nanoparticles (NPs), the as-prepared Pt-BiOBr composites show superior electrocatalytic activities towards ethanol and methanol oxidation reaction under visible light irradiation, with the mass activities of 929.8 mA mg−1Pt and 751.7 mA mg−1Pt, 6.0 and 28.4-fold enhancements than those under dark condition, respectively. The great enhancement in the photoelectrocatalytic performances can be attributed to the unique 2D nanostructure, synergistic and photocatalytic effects. This work may pave up a new route for designing the desirable semiconductor supports for the decoration of the noble metal catalysts, showing significant promise for the application of fuel cells.

Construction of 2D lateral pseudoheterostructures by strain engineering

Two-dimensional (2D) lateral heterostructures host unconventional physical properties due to their controllable band-offset tuning and interfacial sensitive characteristic. The lattice mismatch results in the difficulties to construct the perfect atomic interface in such 2D lateral heterostructures, which in turn limits their desirable properties and performances in applications. In this work, strain-modulated 2D lateral pseudoheterogeneous structures are designed and realized in the single-component 2D BiOBr nanosheets by taking advantage of their strain-sensitive crystal and electronic structures. The pseudoheterogeneous interface without atomic mismatch can be feasibly modulated by local strain distribution, which exhibits similar local electronic band structure of corresponding heterostructures. Significant enhancement in charge separation at the pseudoheterostructure was demonstrated under visible light irradiation, which is given rise to the controllable electronic band alignment across the interface. The construction of the lateral pseudoheterostructure offers a feasible and promising way to build unprecedented 2D systems with exciting properties.

Synthesis of 3D BiOBr microspheres for enhanced photocatalytic CO2 reduction

In this work, 3D BiOBr microspheres were successfully synthesized via a solvothermal method with different bromine source. The as-fabricated samples were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), UV–vis diffuse reflectance spectroscopy (DRS), and X-ray photoelectron spectroscopy (XPS). Compared their photocatalytic performance for CO2 reduction, BiOBr-IL showed the highest activity and selectivity. It suggested that the [Bmim]Br ionic liquids assisted synthesis method was an successful way to improve the photocatalytic performance for CO2 reduction of BiOBr.

Synthesis of novel 2D-2D p-n heterojunction BiOBr/La2Ti2O7 composite photocatalyst with enhanced photocatalytic performance under both UV and visible light irradiation

In the present work, an efficient composite photocatalyst composed of 2D BiOBr nanoplates and 2D La2Ti2O7 thin nanosheets was synthesized. The photocatalytic performance of the as-obtained samples was investigated by the degradation of dye Rhodamine B and phenol under both UV and visible light irradiation. The results demonstrated that the La2Ti2O7 modified with proper amount of BiOBr nanosheets exhibited high efficiency in the photocatalytic process, and the holes took part in the photo-decomposition reaction as the main radicals. The morphology, crystallization, photo-response and electrochemical properties of the obtained catalysts were characterized to understand the mechanism of high photocatalytic activity. The results illustrated that the high photocatalytic performance could be ascribed to the following reasons. First of all, the decoration of BiOBr enlarged the photoresponce of La2Ti2O7 to visible light region, thus the composite can be activated to generate more electron and hole pairs. Secondly, the formed BiOBr/La2Ti2O7 p-n heterojunction promoted the transfer rate of electrons through the interface and improved the separation efficiency of electron-hole pairs. It is expected that this novel 2D-2D p-n heterostructured photocatalyst would be a promising candidate for environmental remediation.

Enhanced photocatalytic performance of BiOBr/NH2-MIL-125(Ti) composite for dye degradation under visible light.

Metal-organic frameworks (MOFs) are considered as suitable materials for various applications in the area of photocatalysis. On the other hand, 2D BiOBr materials are efficient for the photodegradation of organic dyes under visible light illumination. In this work, BiOBr/NH2-MIL-125(Ti) composite photocatalysts with different NH2-MIL-125(Ti) content were prepared by incorporating NH2-MIL-125(Ti) with BiOBr using a co-precipitation method. A series of characterizations confirmed the strong synergistic effect between BiOBr and NH2-MIL-125(Ti). In rhodamine B (RhB) degradation experiments, the composite photocatalyst with a mass percent of 7 wt% NH2-MIL-125(Ti) exhibited an improved photocatalytic activity compared to pristine BiOBr and NH2-MIL-125(Ti). Furthermore, the enhanced photocatalytic performance under visible light illumination could be attributed to the Ti3+-Ti4+ intervalence electron transfer and synergistic effect between NH2-MIL-125(Ti) and BiOBr, and also resulted in a separation efficiency of photo-generated electron-hole pairs during the photocatalytic reaction. This study can open up numerous opportunities for the development of various MOF-based visible light photocatalysts when combined with 2D bismuth oxyhalide materials for applications in environmental cleaning.

Modulation of Photocatalytic Properties by Strain in 2D BiOBr Nanosheets

BiOBr nanosheets with highly reactive {001} facets exposed were selectively synthesized by a facile hydrothermal method. The inner strain in the BiOBr nanosheets has been tuned continuously by the pH value. The photocatalytic performance of BiOBr in dye degradation can be manipulated by the strain effect. The low-strain BiOBr nanosheets show improved photocatalytic activity. Density functional calculations suggest that strain can modify the band structure and symmetry in BiOBr. The enhanced photocatalytic activity in low-strain BiOBr nanosheets is due to improved charge separation attributable to a highly dispersive band structure with an indirect band gap.

Investigation on the upconversion emission in 2D BiOBr:Yb3+/Ho3+ nanosheets

As lanthanide doped upconverting host, two dimensional (2D) nanostructure materials have remarkable advantages compare with the bulk materials, but excellent 2D upconversion nanohost is still few up to date. In this work, Yb3+/Ho3+ co-doped BiOBr nanosheets have been successfully prepared via a facile hydrothermal method, which were characterized by X-ray diffraction, transmission electron microscopy, Atomic Force Microscope, Raman spectra, Fourier transform infrared absorption and UC luminescence spectra. Under excitation at 980nm, bright green UC emission centered at 550nm accompanied with weak red (663nm) and near infrared (NIR) UC emissions (760nm) were observed. Power dependence studies revealed that NIR and red UC emissions were both dominated by a two and one-photon process due to saturation effects that is related to the special crystal structure of BiOBr nanosheets, and a different UC mechanism of NIR emission from Ho3+ was proposed accordingly.