Bi4O5I2 Nanosheets Research Articles

Self-templated fabrication of porous Bi5O7I nanosheets for enhanced visible light CO2 photoreduction

Photocatalytic CO2 reduction is limited by high reaction barriers of CO2 activation, resulting in low conversion efficiency of light energy to chemical energy, especially within the visible light range. To enhance the performance of photocatalytic CO2 reduction, the rational design of the chemical environment on the catalyst surface is conducive to the activation of reactive molecules. Here, we prepared porous Bi5O7I with surface charge-rich Bi(3−x)+ ions by template calcination. The experimental results show that Bi ions accumulated charges on the surface of Bi5O7I have superior adsorption and activation abilities for CO2 molecules than the precursor BiOIO3. Besides, Bi5O7I exhibits better charge transfer capability and roughly double the catalytic activity under visible light irradiation for CO production. This work developed a new facile approach for fabrication of high-performance photocatalysts and provided new insight on the mechanism of CO2 photoreduction.

Synthesis of Bi4O5I2 for bacterial inactivation with visible light exposure

Bi4O5I2 nanosheets were successfully prepared by the alkaline solvothermal method. On account of the greater redox capacity and more efficient photogenerated charge separation, the photocatalytic performance of Bi4O5I2 for E. coli inactivation was superior to BiOI, and E. coli (106 cfu/mL) was entirely inactivated within 125 min. •OH and h+ destroyed the E. coli cell and led to the apoptosis. This work develops the application of bismuth-rich BiOI to water disinfection.

Facile construction of novel Z-scheme Bi4O5I2/CuFe2O4 heterojunctions for NO2-inhibited and robust photocatalytic removal of NO under visible light

Photocatalytic oxidation has been confirmed as a promising manner to control and treat low-concentration NO, during which the generation of hazardous intermediate NO2 is unavoidable, causing more severe health concerns and environmental pollution issues than NO itself. In this research, the photocatalytic removal of NO was studied over novel Bi4O5I2/CuFe2O4 (BCF) binary composites that were constructed by a straightforward solvothermal route. CuFe2O4 nanoparticles and Bi4O5I2 nanosheets were coexisted in composites and merged into heterojunction structures with compatible morphologies. Under visible light, these resultant composites exhibited reinforced photocatalytic NO removal efficiency in comparison to bare components. Specifically, the best sample BCF3, defined as the composite with the mass percent of CuFe2O4 to Bi4O5I2 as 3%, presented the toxic intermediate NO2 as 21 ppb (part per billion) and the largest photocatalytic NO removal of 44% that referred to the ratio of removal to initial concentration of NO. NO removal and NO2 generation of BCF3 improved 1.5 times and reduced by half in only 5 min compared to that of pristine Bi4O5I2, which could be attributed to the strengthened visible light harvesting, efficient transfer and separation of charge carriers through intimate interfaces, and the availability of sufficient reactive radicals. Through entrapping experiments and band structure estimation, a Z-scheme model was put forward for the photocatalysis mechanism of these robust n-p heterojunction composites.

Ultrathin Bi4O5I2 nanosheets as an integrated piezo-photocatalyst: Super visible-light piezo-photocatalysis and synergistic catalytic mechanism

Coupling piezocatalysis in the process of photocatalysis has aroused great interests of researchers to depress the serious recombination of photogenerated charge carriers. However, it still suffers from the inefficient catalytic activity and lacks in-depth understanding on their relationship. In this work, we report that outstanding piezo-photocatalytic activity is achieved over ultrathin Bi4O5I2 nanosheets, and disclose the synergistic catalytic mechanism. Piezoelectric force microscopy (PFM) and COMSOL simulation analysis reveal the strong piezoelectricity of the Bi4O5I2. Under simultaneous irradiation of visible light and ultrasonic, Bi4O5I2 ultrathin nanosheets exhibit a piezo-photocatalytic efficiency of tetracycline hydrochloride (TH) degradation of 88.3% within 8 min with a rate coefficient of 0.4703 min−1, which is 2.3-fold of the sum of the single photocatalysis and piezocatalysis, also far exceeding that of other previously reported piezo-photocatalyst. In situ electrochemical and electron paramagnetic resonance (EPR) under light, ultrasonic, and simultaneous light and ultrasonic conditions disclose that the synergistically enhanced charge separation and transfer and evolution of reactive species (superoxide radicals and holes) occur in the piezo-photocatalytic reaction process, which is derived from the piezoelectric field and band bending. This work emphasizes the effect of the piezoelectric field on strengthening the photocatalytic performance and further the understanding on synergistic piezo-photocatalytic mechanism.

Bi4O5I2 nanosheets as a novel nanofiller for fabrication of antifouling polyethersulfone nanocomposite membranes

Bi4O5I2 is one of the bismuth-rich oxyhalides that exhibited impressive activity in the photodegradation of different organic pollutants. In this research, Bi4O5I2 nanosheets were synthesized, characterized, and applied for fabricating a hydrophilic and antifouling polyethersulfone (PES) membrane by blending in the membrane matrix. The prepared nanocomposite membranes exhibited improved antifouling properties especially when UV irradiation was used during the washing of the fouled membranes. Hydrophilicity enhancement and photocatalytic property of the Bi4O5I2 nanosheets have an excellent synergistic effect, which can yield more hydroxyl radicals (•OH) for efficient removal of the foulant from the membrane surface. The pure water flux can achieve 235.4 L/m2 h (3 bar) when 0.5 wt% Bi4O5I2 was used. The addition of the nanosheets to the membrane matrix in low amounts decreased the membrane surface roughness and increased membrane porosity. The BSA, Reactive Orange 16, Reactive Black 5, and Pb(II) filtration tests showed that the 1 wt% Bi4O5I2 PES membranes provided a good performance of 98.3, 70.3, 92.6, and 47.2 % rejection ability, respectively. In this research, for the first time, the Bi4O5I2 photocatalyst was blended into the membrane matrix which provided a new idea for the progress of highly effective self-cleaning ultrafiltration membranes.

The phase regulation of Bi4O5I2 nanosheets through the controlled hydrolysis in polyhydric alcohol for the enhanced photocatalytic performances of BPA

• Bi 4 O 5 I 2 were regulated via controlled hydrolysis of urea in polyhydric alcohol. • Polyhydric alcohol with proper viscosity is the key role of controlled hydrolysis. • Bi 4 O 5 I 2 with tuned band structure showed superior photodegradation activity. • The reaction rate constant of Bi 4 O 5 I 2 is almost 3 times than that of BiOI. In this study, the phase transition of Bi 4 O 5 I 2 was regulated via the controlled hydrolysis of urea in polyhydric alcohol. The systematic conditions of the controlled hydrolysis for Bi 4 O 5 I 2 phase transition were examined. Polyhydric alcohol solution with proper viscosity (such as EG, and mixture of EG and G), temperature over 180 °C, over 3 h, and tetrabutylammonium iodide (TBAI) over 4 mmol could contribute to the controlled hydrolysis of urea (1.0 g) for Bi 4 O 5 I 2 . The band structure of resulted Bi 4 O 5 I 2 was altered, resulting in superior photodegradation performances of BPA removal due to the efficient charge separation and transfer.

The key role of surface hydroxyls on the activity and selectivity in photocatalytic degradation of organic pollutants and NO removal

Herein, we fabricated hydroxyl groups decorated Bi4O5I2 nanosheets, and the contents of hydroxyl groups on the surface could be controlled by changing the reducibility of organic solvents. The stronger reducibility of organic solvents, the more hydroxyl groups on the surface. The hydroxyl groups on the surface of Bi4O5I2 nanosheets have significant effects on photocatalytic activity. For degradation of organic pollutants, the surface hydroxyls form hydrogen bonds with organic pollutants, which is conducive to the adsorption of the substrates. For NO removal, the NO adsorbed on the hydroxyl groups is more oxidized into a toxic by-product NO2 instead of NO3-, so less hydroxyl groups are important for photocatalysts towards NO removal. These new discoveries provide new insights to improve photocatalytic activities by modulating surface functional groups of photocatalysts.

Few-layered Bi4O5I2 nanosheets enclosed by {1 0−1} facets with oxygen vacancies for highly-efficient removal of water contaminants

Few-layered Bi4O5I2 nanosheets (FL-Bi4O5I2) were synthesized by intergrowth with Bi2O2CO3 under room temperature. The photoactivity of FL-Bi4O5I2 was 2.5 and 9.5 times higher than that of Bi4O5I2 nanoflakes (NF-Bi4O5I2, about 30 nm thickness) and standard visible-light-driven N-TiO2, respectively. Moreover, FL-Bi4O5I2 exhibited a wide pH application range (3.0 – 10.0) and excellent photostability. The characterization results showed FL-Bi4O5I2 was consisted of 5 – 8 layers with thickness of 4 – 7 nm and enclosed by {1 0 − 1} facets. The ultrathin characteristics could accelerate the charge transfer to the surface due to the shortened transport distance. Compared to NF-Bi4O5I2, surface oxygen vacancies and the more negative CB potential were formed on FL-Bi4O5I2. The photogenerated electrons were confirmed to be captured by surface oxygen vacancies to effectively reduce surface adsorbed O2 into HO2•/O2•–, leaving more h+ to oxidize organic pollutants. This process was further facilitated by the more negative CB potential of FL-Bi4O5I2, resulting in the highly efficient removal of pollutants.

Boosting Piezo/Photo-Induced Charge Transfer of CNT/Bi4O5I2 Catalyst for Efficient Ultrasound-Assisted Degradation of Rhodamine B.

Strain-induced internal electric fields present a significant path to boosting the separation of photoinduced electrons and holes. In addition, piezo-induced positive/negative pairs could be released smoothly, taking advantage of the excellent electroconductibility of some conductors. Herein, the hybrid piezo-photocatalysis is constructed by combining debut piezoelectric nanosheets (Bi4O5I2) and typical conductor multiwalled carbon nanotubes (CNT). The photocatalytic degradation efficiency that the hybrid CNT/Bi4O5I2 exhibits was remarkably increased by more than 2.3 times under ultrasonic vibration, due to the piezo-generated internal electric field. In addition, the transient photocurrent spectroscopy and electrochemical impedance measurement reveal that the CNT coating on Bi4O5I2 enhances the piezo-induced positive/negative migration. Therefore, the piezocatalytic activity of CNT/Bi4O5I2 could be improved by three times, compared with pure Bi4O5I2 nanosheets. Our results may offer promising approaches to sketching efficient piezo-photocatalysis for the full utilization of solar energy or mechanical vibration.

3D flower-like mesoporous Bi4O5I2/MoS2 Z-scheme heterojunction with optimized photothermal-photocatalytic performance

3D flower-like hierarchical mesoporous Bi4O5I2/MoS2 Z-scheme layered heterojunction photocatalyst was fabricated by oil bath and hydrothermal methods. The heterojunction with narrow band gap of ∼1.95 eV extended the photoresponse to near-infrared region, which showed obvious photothermal effect due to the introduction of MoS2 with broad spectrum response. MoS2 nanosheets were anchored onto the surface of flower-like hierarchical mesoporous Bi4O5I2 nanosheets, thereby forming efficient layered heterojunctions, the solar-driven photocatalytic efficiency in degradation of highly toxic dichlorophenol and reduction of hexavalent chromium was improved to 98.5% and 99.2%, which was ∼4 and 7 times higher than that of the pristine Bi4O5I2, respectively. In addition, the photocatalytic hydrogen production rate reached 496.78 μmol h−1 g−1, which was ∼6 times higher than that of the pristine Bi4O5I2. The excellent photocatalytic performance can be ascribed to the promoted photothermal effect, as well as, the formation of compact Z-scheme layered heterojunctions. The 3D flower-like hierarchical mesoporous structure provided adequate surface active-sites, which was conducive to the mass transfer. Moreover, the high stability of the prepared photocatalyst further promoted its potential practical application. This strategy also provides new insights for fabricating layered Z-scheme heterojunctions photocatalysts with highly photothermal-photocatalytic efficiency.

CuBi2O4 and rGO co-modified 3D hierarchical flower-like Bi5O7I nanoflakes as Z-scheme heterojunction for enhanced photocatalytic performance

The three-dimensional (3D) flower-shaped layered Bi5O7I nanosheets exhibited tremendous potential in wiping out hazardous organics of sewage due to appropriate band structure and rich surface for attachment of reactants, modified with CuBi2O4 (CBO) and reduced graphene oxide (rGO) further enhancing its photocatalytic effects. Herein, a novel, stabilized and efficient CBO/Bi5O7I@rGO photocatalyst was constructed via sequential hydrothermal process, and the microstructures, physicochemical and optical properties were further researched by serial means such as XRD, XPS, FESEM-EDS, TEM, UV–vis DRS, PT, EIS and physical absorption. SEM and TEM manifested that the composite was successfully prepared and gossamer rGO as a co-catalyst, which is not only conducive to the separation of photo-generated carrier but also facilitates photocatalytic removal pollutants. Furthermore, the photodegradation tests indicated that CBO/Bi5O7I@1.5% rGO sample displayed the highest removal rates towards contaminations such as tetracycline hydrochloride (91%), Rhodamine B (77%) and ciprofloxacin (92%) under visible-light, respectively. Besides, the addition of higher initial concentrations and certain anions inhibited photocatalytic efficiency, which perhaps was due to greater competition with contaminations towards active radicals. Finally, the capture experiment and electron spin resonance (ESR) test certified that superoxide radicals (·O2-) are the direct active group, whereas the holes (h+) and hydroxyl radicals (·OH) exert a supporting role. This work could offer an actual and doable design for constructing of efficient Z-scheme system using rGO as an auxiliary catalyst to sewage remediation.

Hydrolysis of urea induces the formation of bismuth-rich Bi4O5I2 nanosheets with promoted visible-light photoreduction of Cr (VI)

Bismuth-rich Bi4O5I2 nanosheets were prepared through progressive hydrolysis of urea in a facile solvothermal route, which is different from the conventional strategies of pH adjusting or calcination. To promote the hydrolysis of urea for the formation of Bi4O5I2 nanosheets, the type of solvents and urea concentration were the distinctive roles. Especially, urea concentration over 1.0 g but less than 3.0 g in the solvent of ethylene glycol could boost the formation of Bi4O5I2 nanosheets. Furthermore, the resulted Bi4O5I2 nanosheets possessing more negative conductive band level of −1.02 eV showed superior visible-light photoreduction activity of Cr (VI) due to the efficient separation of charge carriers.

Novel p-n type porous Ag2O/Bi5O7I heterojunction for Uv–Vis-NIR activated high efficient photocatalytic degradation of bisphenol A: Photoelectric properties and degradation mechanism

Exploring effective strategies to strengthen the photoresponse and charge separation efficiency is crucial for the preparation of photocatalysts with superior-performance. Herein, series of 0D-2D Ag2O/Bi5O7I heterojunctions with UV–Vis-NIR spectrum response were prepared by modifying Ag2O on the surface of porous Bi5O7I nanosheets to boost the photocatalytic degradation of bisphenol A. The modified p-type Ag2O semiconductor not only extends the optical absorbance range of the prepared p-n heterojunction but also improves the separation efficiency of photoinduced charge carriers by the internal electric field. Moreover, the unique porous thin-layer structure can further shorten the transport distance of bulk charges to the surface. In addition, uniformly distributed holes are able to provide more active sites to accelerate charge depletion on Bi5O7I substrate. As a result, the interfacial coulomb electrostatic repulsive force was greatly weakened, making it easier for the charge transferences from Ag2O to Bi5O7I under the internal electric field. Therefore, the prepared p-n heterojunction exhibited excellent performance in photocatalytic degradation of bisphenol A. In particular, 25% Ag2O/Bi5O7I showed the best bisphenol A degradation performance, which was 7.23 and 4.39 times than that of pristine Ag2O and Bi5O7I, respectively. In addition, the prepared samples showed excellent photocorrosion resistance, due to the rapid consumption of enriched electrons by the porous structure. Furthermore, intermediates of bisphenol A degradation reaction were characterized by liquid mass method, and then the degradation pathway was deduced. This work is of significance to the construction and design of efficient photocatalysts with full spectral response and high photoelectric conversion efficiency.

Highly efficient visible/NIR photocatalytic activity and mechanism of Yb3+/Er3+ co-doped Bi4O5I2 up-conversion photocatalyst

Bi4O5I2 has attracted much attention as a visible-light-driven photocatalyst, but its photocatalytic activity should be further improved for future practical application. Herein, we design and prepared Er3+/Yb3+ co-doped Bi4O5I2 nanosheets by a facile solvothermal method. The samples were characterized by XRD, SEM, TEM, XPS, DRS, PL, and EIS. The photocatalytic activities of samples were evaluated by the degradation of RhB and imidacloprid. Among these doped samples, the Bi4O5I2: Er1%,Yb2% exhibits the highest degradation efficiency for RhB and IM under the irradiation of visible or near infrared (NIR) light irradiation. This can be attributed to the up-conversion transition of Er3+, which can convert NIR light beyond the absorption edge of Bi4O5I2 into visible/UV light to excite Bi4O5I2. In addition, the decreased band gap and improved separation efficiency of e−–h+ pairs due to the rare-earth ions as electron traps play roles in the enhanced vis/NIR photoactivity. The h+ and •O2– are the main active species for the degradation of organic pollutants. Based on the experimental results, a plausible mechanism was proposed.

Morphology-dependent photocatalytic activity of Bi5O7I: Different charge separation efficiencies caused by facet synergy and internal electric field

Bi5O7I nanosheets and Bi5O7I nanorods photocatalysts were successfully fabricated by calcination and hydrothermal methods respectively. The different morphologies of Bi5O7I were characterized by XRD, SEM, HRTEM, UV–vis DRS and PL. The as-prepared samples were used to photocatalytic removal of Hg0 under visible-light irradiation. The results indicated that the photocatalytic activity of Bi5O7I nanorods is better than that of Bi5O7I nanosheets. It can be attributed to the synergistic and internal electric field effects of the (0 0 1) and (1 0 0) facets of Bi5O7I nanorods, which improves the photogenerated charge transfer and separation efficiency.

Assembly of large-area reduced graphene oxide films for the construction of Z-scheme over single-crystal porous Bi5O7I nanosheets

In this work, we have firstly achieved the construction of bismuth oxyiodide (Bi5O7I)/reduced graphene oxide (rGO)/ZnO Z-scheme photoelectrochemical (PEC) system without backward reactions through loading large-area ZnO quantum dots (QDs)/rGO films on Bi5O7I nanosheets. Single-crystal porous Bi5O7I nanosheets with numerous oxygen vacancies (OVs) were firstly fabricated through the calcination of BiOI in reductive glycols. The single-crystal facilitates charge transport, nanoporous structure promotes light absorption and OVs improves charge separation efficiency. As a result, single-crystal porous Bi5O7I nanosheets with OVs exhibited higher PEC performance than other morphologies reported before. Moreover, The PEC activity of Bi5O7I can be further enhanced through loading large-area ZnO QDs/rGO films to construct a pure Z-scheme charge transfer system, which not only achieves efficient separation of electron-hole pairs but also retains its excellent redox ability. To the best of our knowledge, the photocurrent density of Bi5O7I/rGO/ZnO heterostructures is the highest among Bi5O7I-based samples. For comparison, an opposite Z-scheme model has also been built up by replacing Bi5O7I with WO3, in which the photocurrent density decreased conversely. Therefore, it can be known that a pure Z-scheme system without backward reactions can be successfully prepared through loading ZnO QDs/rGO films on photoelectrodes.

Molecular adsorption promotes carrier migration: Key step for molecular oxygen activation of defective Bi4O5I2

Oxide defect engineering in semiconductors is of growing interest and considered as an important strategy for promoting photocatalytic performance, as it enables to couple solar energy into oxygen activation. Herein, the surface oxygen vacancies are introduced into bismuth-rich Bi4O5I2 nanosheets (Bi4O5I2-OV) via a facile solvothermal route. By introducing oxygen vacancies into Bi4O5I2, the molecule oxygen adsorption is significantly improved. More importantly, attributed to the molecular oxygen adsorption, an instantaneous surface-bulk homojunction is constructed, which facilitates the separation and transport of photogenerated charge carriers. Therefore, noticeable molecular oxygen activation and N2 fixation are achieved in Bi4O5I2-OV. These findings may shed light on designing highly efficient photocatalysts and provide fresh insights into understanding the charge migration mechanism in oxygen vacancies-related photocatalytic system.

Three-dimensional Ag2O/Bi5O7I p–n heterojunction photocatalyst harnessing UV–vis–NIR broad spectrum for photodegradation of organic pollutants

Ag2O nanoparticles-loaded Bi5O7I microspheres forming a three dimensional Ag2O/Bi5O7I p–n heterojunction photocatalyst with wide-spectrum response were synthesized in this study. The results of transmission electron microscopy observations revealed that the Ag2O nanoparticles with the diameter of ca. 10–20nm were distributed on the surfaces of Bi5O7I nanosheets. The as-synthesized Ag2O/Bi5O7I exhibited an excellent wide-spectrum response to wavelengths ranging from ultraviolet (UV) to near-infrared (NIR), indicating its potential for effective utilization of solar energy. Compared with pure Bi5O7I, the Ag2O/Bi5O7I composite also demonstrated excellent photocatalytic activity for the degradation of Bisphenol A and phenol in aqueous solution under visible LED light irradiation. Among samples, the 20% Ag2O/Bi5O7I composite photocatalyst showed the highest photocatalytic activity for the degradation of Bisphenol A and phenol in aqueous solution. In addition, the 20% Ag2O/Bi5O7I composite also exhibited a photocatalytic activity for the degradation of Bisphenol A under NIR light irradiation. The improved photocatalytic activity is attributed to the formation of a p-n heterojunction between Ag2O and Bi5O7I, allowing the efficient utilization of solar energy (from UV to NIR) and high separation efficiency of photogenerated electron-hole pairs. The present work is desirable to explore a possible avenue for the full utilization of solar energy.

Graphene-like boron nitride induced accelerated charge transfer for boosting the photocatalytic behavior of Bi4O5I2 towards bisphenol a removal

A novel graphene-like BN/Bi4O5I2 2D-2D stacking has been prepared via a facile ionic liquid 1-hexyl-3-methylimidazolium iodide ([Hmim]I) assisted solvothermal method with the proper pH for the first time. Series of characterizations, such as XRD, XPS, FT-IR, TEM, BET, PL, EIS and ESR have been applied to analyze the composition, morphology, structure, optical and electronic properties of the graphene-like BN/Bi4O5I2 composites. The sufficient contact and strong interfacial interaction between the graphene-like BN and Bi4O5I2 nanosheets can be effective constructed. Colorless endocrine disrupter bisphenol A (BPA) was chosen as the target pollutant to evaluate the photocatalytic degradation performance of the pure Bi4O5I2 nanosheets and graphene-like BN/Bi4O5I2 composites under visible light irradiation. The enhanced photocatalytic activity of the graphene-like BN/Bi4O5I2 composites could be attributed to the higher electron transfer ability over the graphene-like BN nanosheet and thus the molecular oxygen can be better activated. Superoxide radical and hole were determined to be the main active species during the photodegradation process. This work will provide a new sight into the design of other two-dimensional atomic level material based composites for photocatalysis.

Improved photocatalytic activity of few-layer Bi4O5I2 nanosheets induced by efficient charge separation and lower valence position

Ultrasmall few-layer Bi4O5I2 nanosheets were controlled prepared via an ionic liquid [Hmim]I (1-hexyl-3-methylimidazolium iodide)-mannitol assisted solvothermal method accompanied by adjusting to the proper pH. Multiple characterizations were employed to investigate the composition, structure, morphology, optical absorption property and photocatalytic performance of the ultrasmall few-layer Bi4O5I2 nanosheets materials. During the synthesis process, ionic liquid acted as solvent, capping agent and provided the I source to form the Bi4O5I2 nanostructure, resulting in the thinnest Bi4O5I2 materials (about 6 layers) reported up to now. DLS analysis indicated the Bi4O5I2 diameter was mainly distributed in the range of 37–52 nm. Organic dye rhodamine B (RhB) and colourless ciprofloxacin (CIP) were used as target pollutants to estimate the photocatalytic performance of as-prepared Bi4O5I2 nanosheets. PL analysis showed that Bi4O5I2 owned the lower recombination rate of the photogenerated charge carriers. The improved photocatalytic activity of Bi4O5I2 nanosheets was attributed to the ultrasmall few-layer structure and varied energy band structure which favored the efficient separation of electron-hole pairs and the lower valence position of Bi4O5I2 greatly increased the oxidizing ability. Different from the active species of BiOI, the photogenerated holes and ·OH were determined to be the main active species of Bi4O5I2 during the photodegradation process.