Bismuth-based Photocatalysts Research Articles

Construction of Hexagonal Prism-like Defective BiOCL Hierarchitecture for Photocatalytic Degradation of Tetracycline Hydrochloride.

Oxygen vacancy manipulation and hierarchical morphology construction in oxygen-containing semiconductors have been demonstrated to be effective strategies for developing high efficiency photocatalysts. In most studies of bismuth-based photocatalysts, hierarchical morphology and crystal defects are achieved separately, so the catalysts are not able to benefit from both features. Herein, using boiling ethylene glycol as the treatment solution, we developed an etching-recrystallization method for the fabrication of 3D hierarchical defective BiOCl at ambient pressure. The target hierarchical 3D-BiOCl is composed of self-assembled BiOCl nanosheets, which exhibit a hexagonal prism-like morphology on a micron scale, while simultaneously containing numerous oxygen vacancies within the crystal structure. Consequently, the target catalyst was endowed with a higher specific surface area, greater light harvesting capability, as well as more efficient separation and transfer of photo-excited charges than pristine BiOCl. As a result, 3D-BiOCl presented an impressive photocatalytic activity for the degradation of tetracycline hydrochloride in both visible light and natural white light emitting diode (LED) irradiation. Moreover, an extraordinary recycling property was demonstrated for the target photocatalyst thanks to its hierarchical structure. This study outlines a simple and energy-efficient approach for producing high-performance hierarchically defective BiOCl, which may also open up new possibilities for the morphological and crystal structural defect regulation of other Bi-based photocatalysts.

Accelerating transfer of photogenerated charge carriers by loading PtOx on Cr2Bi3O11 nanorods to enhance photocatalytic activity in water detoxification and splitting

As a new type of visible-light-driven bismuth-based photocatalyst, Cr2Bi3O11 exhibited potentials in photodegradation of organic pollutants and water splitting for oxygen evolution. However, its photocatalytic activity still needs to be further improved. Herein, an in-situ photoreduction route was employed to anchor PtOx onto the surface of Cr2Bi3O11 for improved carrier transport and enhanced photocatalytic activity. The high crystallinity and uniform crystal structure of the Cr2Bi3O11 nanorods matrix were beneficial to evenly deposit the PtOx nanodots (diameter: 0.5 nm–2.0 nm). The optimal PtOx modified Cr2Bi3O11 (1.0Pt-Cr2Bi3O11) exhibited higher photocatalytic activity in organic pollutants (i.e. phenol, chlorophenol and tetracycline) removal than other noble metals (Ag, Au, and Pd) modified Cr2Bi3O11. Besides, 1.0Pt-Cr2Bi3O11 also exhibited enhanced activity in oxygen evolution (210.5 μL/gcat/h, 4.3 times higher than pristine Cr2Bi3O11). The PtOx can effectively capture the photogenerated electrons, hence repressing electron/hole recombination and providing active sites for charge-transfer reactions.

Myth or reality? A disquisition concerning the photostability of bismuth-based photocatalysts

Photocatalysis is a well-known and extensively investigated field within advanced oxidation processes. Numerous papers have been reported that the semiconductors applied were photostable and potentially reusable based on the degradation efficiencies observed. However, researchers did not attach enough importance to investigate the residual catalysts in most cases. Here, we report on some important alterations that occurred during photocatalytic experiments, such as acid-induced and light-assisted structure break-down and complete transformation of catalysts, which could place their photostability into a new perspective. In this work, the photostability of five, increasingly popular bismuth-based oxides (Bi2WO6, BiVO4, BiOI, BiOCl, and BiOBr) were investigated in the presence of various carboxylic acids (oxalic acid, formic acid, salicylic acid, malonic acid, and ascorbic acid), focusing on the crystallographic and morphological alterations of the residual photocatalysts. When investigating the resistance of the photocatalysts to oxalic acid, the formation of bismuth oxalate hydroxide was observed in all cases. At the same time, most components of the catalysts appeared in the liquid phase in high amounts. Similar transformations occurred to a lesser extent for the other acids, which was deduced to be related to the acidic strength and proton concentration. We also highlighted that in some instances, during photocatalytic processes, the occurrence of light-assisted acid-induced reactions must be considered as well.

N-CQDs from reed straw enriching charge over BiO2−x/BiOCl p-n heterojunction for improved visible-light-driven photodegradation of organic pollutants

Green bismuth-based photocatalysts have attracted extensive attention in the field of PPCPs photodegradation. The improved carrier separation efficiency still remains a key factor to enhance photocatalytic performance. Herein, N-doped biomass carbon quantum dots (N-CQDs) decorated p-n heterojunction photocatalyst BiO2−x/BiOCl was prepared using a facile ion-etching strategy, and it displayed a markedly enhanced catalytic activity in the photodegradation of sulfonamide antibiotics. Calculated by the differential charge density, the doped N-CQDs could gather photogenerated electrons, which indicated that the introduction of N-CQDs into BiO2−x/BiOCl would effectively inhibit the recombination of photogenerated charge carriers. In addition, photocatalytic performance and density functional theory (DFT) calculation results revealed that the photogenerated electrons tended to transfer from p-BiOCl to n-BiO2−x through N-CQDs, which could generate ·O2- and photogenerated h+ to oxidize the target pollutants. Benefiting from the synergistic effect of accelerated separation of e--h+ in p-n heterojunction and the electron-rich performance of N-CQDs, the superb TOC removal efficiencies (89.40% within 120 min visible-light irradiation) and toxicity reduction performance of photodegradation intermediates were achieved. As a consequence, this work will provide a design of high-quality photocatalysts and a green-promising strategy for bismuth-based photocatalysts in the water treatment of PPCPs.

Co-precipitation synthesis of BiOI/(BiO)2CO3: Brief characterization and the kinetic study in the photodegradation and mineralization of sulfasalazine

A binary BiOI/(BiO)2CO3 catalyst was prepared via the co-precipitation process as a typical bismuth-based photocatalyst. The XRD data confirmed the tetragonal crystals of BiOI and (BiO)2CO3 had been produced. The crystallite size of BiOI, (BiO)2CO3, and BiOI/(BiO)2CO3 samples were 28.94, 23.24, and 25.11 ​nm (Scherrer formula), and 86.26, 28.28, and 39.60 ​nm (Williamson formula), respectively. FTIR bands for the Bi–O and Bi–I in BiOI, the stretching vibrations bands of the Bi–O, the C–O and CO bonds in (BiO)2CO3 were detected, confirming the formation of the proposed semiconductors. DRS results showed the absorption wavelength edges of 684, 362, and 509 ​nm correspond to the band gap values of 1.81, 3.43, 2.44 ​eV for BiOI, (BiO)2CO3, and BiOI/(BiO)2CO3, respectively. This confirms that the binary catalyst is a visible-light-driven photocatalyst. Some lump and plate-like segments were depicted in the SEM images. About 1% and 5% of a 10 ​ppm SSZ solution were removed by direct photolysis and surface adsorption, while photodegradation by BiOI, (BiO)2CO3, and BiOI/(BiO)2CO3 catalysts removed 62, 75, and 81% SSZ molecules during 30 ​min visible irradiation, confirming the high efficiency of the photocatalysis in SSZ removal by the proposed photocatalyst, especially the binary system. The Hinshelwood formula studied the kinetics of the photodegradation process, and a rate constant of 0.106 min−1 (slope) with a t1/2 value of 7.1 ​min was obtained. When the photodegraded SSZ solutions were subjected to the COD experiment y= −0.085–0.106x, r2=0.9725, and k= 0.106 min−1 (t1/2 ​= ​6.5 ​min) were obtained for the mineralized SSZ molecules.

Polyoxometalates-doped Bi2O3–x/Bi photocatalyst for highly efficient visible-light photodegradation of tetrabromobisphenol A and removal of NO

Bismuth-based photocatalysts are a class of excellent visible-light photocatalysts; however, their redox activity is relatively poor and the efficiency of photogenerated carrier separation is low, limiting their development and application in the field of photocatalysis. To address these issues, a series of polyoxometalate PW12O403–-doped Bi2O3–x/Bi Schottky photocatalysts PW12@Bi2O3–x/Bi-n (PBOB-n, where n is the amount of NaBH4, i.e., 6, 12, 18, 24, and 48 mg) were prepared by a simple electrospinning/calcination/in-situ NaBH4 reduction method. In this composite photocatalyst, the doping of PW12 could effectively adjust the electronic structure of Bi2O3–x and improve its redox properties. As a shallow electron trap, PW12 promoted the separation of the photogenerated carriers. Furthermore, desirable Schottky junction between the metal Bi nanoparticles and PW12@Bi2O3–x further accelerated the separation of the photogenerated carriers. The synergistic effect of the aforementioned factors endowed PBOB-n with excellent photocatalytic activity. Among the samples, PBOB-18 exhibited superior photocatalytic activity. Under visible-light irradiation, 93.7% (20 mg catalyst) of 20 ppm tetrabromobisphenol A (TBBPA, 20 mL) was degraded in 60 min. Its activity was 4.4 times higher than that of Bi2O3. PBOB-18 also exhibited an ultrahigh photocatalytic performance for the removal of NO. Its removal rate (600 ppb) reached 83.3% in 30 min, making it one of the most active Bi-based photocatalysts. Furthermore, the photocatalytic mechanisms of PBOB-18 for TBBPA and NO have been proposed. This work provides a new direction and reference for the design of low-cost, efficient, stable, and versatile photocatalysts.

Ammonia-dependent synthesis of (BiO)2OHCl@Bi24O31Cl10 heterostructures with enhanced visible-light induced photocatalytic activities on levofloxacin removal

Designing semiconductor photocatalyst with high visible-light sensitivity and good photocatalytic performance is still a key issue for pollutant remediation and energy storage. In this work, a series of (BiO)2OHCl@Bi24O31Cl10 composite photocatalysts were synthesized through an ammonia-dependent aqueous strategy with (BiO)2OHCl as the in-situ formed precursor. More ammonia introduction in the synthetic system led to faster transformation of (BiO)2OHCl to Bi24O31Cl10 component and resulted in composites with controllable compositions. The Bi-based heterostructures extended good visible-light absorption ability and strengthened internal electric field (IEF) to induce the generation of charge carriers and promote bulk-charge separation (BCS) efficiency for antibiotic removal. (BiO)2OHCl@Bi24O31Cl10 composites with optimum compositions exhibited superior photocatalytic activities on levofloxacin (LEV) degradation under visible-light irradiation, roughly two times higher than that of individual (BiO)2OHCl or Bi24O31Cl10 powders. The high degradation efficiency and rapid reaction kinetics would be ascribed to the valid charge transfer from the bulk interior to the surface of composite catalysts. The sheet-like Bi24O31Cl10 at catalyst surface and matched band structures of two components in (BiO)2OHCl@Bi24O31Cl10 heterostructures are also proposed as vital factors to influence the photocatalytic performances. This study hopes to provide new insights for the design of visible-light induced bismuth-based photocatalysts for practical applications.

Strategies based review on near-infrared light-driven bismuth nanocomposites for environmental pollutants degradation

Recently, solar energy has been considered the most vulnerable source to resolve environmental pollution and energy scarcity problems. Researchers have made intense research efforts to convert solar energy into chemical energy through photocatalysis processes as it is a green, clean and renewable energy source. Numerous discovered photocatalysts show absorption in the ultraviolet–visible (UV∼5% and visible ∼43%) region and are devoid of near-infrared (NIR ∼52%) light utilization. As infrared (IR) light contains a top portion of the solar spectrum; therefore, many alluring and attractive practical strategies have been explored to improve photocatalytic reactions and to harness full solar spectrum (including NIR light). Among those strategies, bandgap engineering, coupling with carbon quantum dots, heterostructure formation, mingling with plasmonic and upconversion (UC) NPs are more worthwhile. In different visible light-assisted photocatalysts, bismuth typically covers a distinctive, favorable, and earth-abundant group of freshly discovered innovative photocatalytic nanomaterials. Bi-based photocatalysts have suitable/good optoelectronic properties, crystalline geometric conformations, amendable electronic structure, and outstanding visible-light responsive range, helpful in environmental remediation and energy transformation. Due to the outstanding photo-oxidization/photodegradation capability of NIR-driven photocatalysts, bismuth-based nanomaterials have been considered suitable photocatalysts for inclusive solar energy utilization. Henceforth, keeping in mind the benefits of bismuth nanomaterials, the present review is focused on NIR-based modification strategies to upgrade solar light absorption of bismuth-based photocatalysts in the NIR region by making it NIR responsive photocatalyst. We have also discussed the photocatalytic applications of bismuth-based NIR responsive photocatalysts in pollutant degradation.

Vacancy-engineered bismuth-based semiconductor with enhanced photocatalytic activity: A review

The introduction of vacancies has been increasingly attracted attentions to improve photocatalytic activity of semiconductors including bismuth-based photocatalysts. Theoretically, vacancies cannot only narrow the band gap to enable the semiconductor to capture more visible light in the solar light spectrum, but also provide more reactive sites on the surface of photocatalysts. In this review, recent progress on vacancy-engineered bismuth-based semiconductors in photocatalysis has been comprehensively summarized and discussed, including the fabrication methods, characterization approaches to detect the vacancies, and functions of vacancy in improving the photocatalytic activity in various applications. Finally, we proposed the challenges and suggested strategies for future work on vacancy-engineered bismuth-based semiconductor in photocatalysis.

Effective promotion of g–C3N4 photocatalytic performance via surface oxygen vacancy and coupling with bismuth-based semiconductors towards antibiotics degradation

In this research, the potential of bismuth chromate (BCO), a new bismuth-based semiconductor belongs to the family of Bi2XO6 (X = Mo, W, or Cr), was introduced by a novel 1D/2D structure consist of BCO nanobelts and N2-freezed ultra-wrinkled graphitic carbon nitride (N–CN) nanosheets. To enhance intimate contact between BCO and N–CN (BCO/N–CN composite), surface oxygen vacancy (VO) was created as an efficient electron transfer highway using a simple alkaline-treatment-assisted method. Various characterization techniques, including XRD, FT-IR, EPR, FE-SEM, TEM, BET, DRS, PL, EIS, and photocurrent transient analyses were conducted to elucidate the physicochemical aspects of catalysts. The synthesized catalysts were subjected to levofloxacin (LVFX) photodegradation and optimum conditions were found under LED irradiation. Under optimum conditions, about 92.5% of LVFX was catalytically degraded over VO-rich BCO/N–CN heterojunction after 120 min of reaction, which was 2.3 folds higher than that of VO-free composite. The obtained heterojunction maintained superior performance after five consecutive runs with no noticeable changes in the XRD and FT-IR patterns, demonstrating the high stability of synthesized nanocomposite. Thus, the proposed interfacial engineering in this study opens new insight for ameliorating the insufficient interfacial contact between components of heterojunctions. This study not only presents a new bismuth-based photocatalyst for antibiotic degradation but also sheds light on the charge migration behavior in favor of efficient Z-type heterojunction.

Construction of novel MWCNTs/Bi4O5I2 nanosheets with enhanced adsorption and photocatalytic performance for the degradation of tetracycline: Efficiency, mechanism and regeneration

Bismuth oxyhalide-based photocatalysts with anisotropic sandwiched-structure present excellent photoactivity in water purification. However, rapid recombination of photogenerated charge carriers and regeneration are two significant challenges of bismuth-based photocatalyst. Herein, a novel multiwalled carbon nanotubes (MWCNTs)/Bi4O5I2 heterostructure with narrow band-gap and high reactive species (RSs) production capacity were firstly designed via interfacial amidation linkage. Photoelectrochemical analysis confirmed that the interfacial amidation linkage significantly boosted the surface charge effective transfer (45 times vs Bi4O5I2) and broadened the visible light adsorption (555 nm), resulting in the enhanced photocatalytic activity. As expected, the optimized MWCNTs/Bi4O5I2 photocatalyst exhibited remarkable adsorption and photocatalytic performance for Tetracycline (TC) degradation under visible light with respect to that of Bi4O5I2 (2.32 times). Radical trapping experiments and Electron spin resonance (ESR) results clarified that h+ and •O2− contributed 34.48% and 93.97% of TC photodegradation, respectively. Density Functional Theory (DFT) calculation including frontier electron densities (FEDs) and Fukui methods further revealed the possible attack sites of RSs for TC. More insights for the decrease of stability showed that main adsorption sites and iodine dissolution were considered to be the key parameters for application of MWCNTs/Bi4O5I2 photocatalyst. Afterwards, we firstly proposed a facile regeneration strategy to solve the deactivation of bismuth oxyhalide-based photocatalysts. This study provided a potential approach to design novel bismuth oxyhalide-based photocatalysts with the high efficiency and possibility of regeneration.

Oxygen vacancy-enriched Bi2O3/BiFeO3 p-n heterojunction nanofibers with highly efficient photocatalytic activity under visible light irradiation

The construction of heterojunctions is considered an effective way to improve the photocatalytic performance of bismuth-based photocatalysts. In this research, Bi2O3/BiFeO3 heterojunction nanofibers with rich oxygen vacancies were successfully synthesized via the in-situ growth of Bi2O3 nanosheets on the surface of BiFeO3 nanofibers, and were then reduced in N, N-dimethylformamide (DMF) via the solvothermal method for different times. The composite ratios and oxygen vacancy concentrations were then systematically optimized. The optimal composite with the molar ratio of BiFeO3:Bi2O3 = 1:1 and solvothermally reducted in DMF for 3 h was found to completely degrade the tetracycline hydrochloride (TC) solution within 120 min, and its photodegradation rate was 8.7 and 5.4 times higher than those of pure BiFeO3 and Bi2O3, respectively. The enhancement can be ascribed to the synergistic effect of the p-n heterojunction formed at the interface and oxygen vacancies produced on the surface, which significantly increased the absorption of visible light, inhibited the recombination of photogenerated electron-hole pairs, and accelerated the separation and transfer of photogenerated charges. Moreover, the obtained oxygen vacancy-enriched Bi2O3/BiFeO3 heterojunction nanofibers exhibited good cyclic stability and magnetic separation capability, and therefore have potential applications in practical sewage treatment.

LAYERED BISMUTH TUNGSTATE – HETEROGENEOUS PHOTOCATALYSIS FOR ENVIRONMENTAL REMEDIATION

Air and water pollution has been one of the challenging environmental issues in modern society. Since the Honda-Fujishima effect was first reported in 1972, a semiconductor-based photocatalysis has been regarded as one of the most green and economical processes for potential application in environmental remediation. Bismuth-based semiconductors are regarded as a promising group of advanced photocatalytic materials due to their suitable band gap for visible light response, an increased mobility of photo-generated charge carriers because of well-dispersed Bi 6s orbital, non-toxicity, and easy tailoring of their morphologies. To utilize its full potential in environmental remediation, various studies have been carried out to enhance the photocatalytic performance of layered Bi2WO6, one of the simplest members of the Aurivillius oxide family of layered perovskites. This review introduces past achievements, the state of the art, and future perspectives in heterogeneous photocatalysis and its application in environmental remediation, particularly in photocatalytic air and water purification. The layered compounds, bismuth-based photocatalysts, and composite photocatalysts and their application in environmental remediation are discussed.

A review of bismuth-based photocatalysts for antibiotic degradation: Insight into the photocatalytic degradation performance, pathways and relevant mechanisms

The intensive production and utilization of antibiotics worldwide has inevitably led to releases of very large amounts of these medicines into the environment, and numerous strategies have recently been developed to eliminate antibiotic pollution. Therefore, bismuth-based photocatalysts have attracted much attention due to their high adsorption of visible light and low production cost. This review summarizes the performance, degradation pathways and relevant mechanisms of typical antibiotics during bismuth-based photocatalytic degradation. First, the band gap and redox ability of the bismuth-based catalysts and modified materials (such as morphology, structure mediation, heterojunction construction and element doping) were compared and evaluated. Second, the performance and potential mechanisms of bismuth oxides, bismuth sulfides, bismuth oxyhalides and bismuth-based metal oxides for antibiotic removal were investigated. Third, we analysed the effect of co-existing interfering substances in a real water matrix on the photocatalytic ability, as well as the coupling processes for degradation enhancement. In the last section, current difficulties and future perspectives on photocatalytic degradation for antibiotic elimination by bismuth-based catalysts are summarized. Generally, modified bismuth-based compounds showed better performance than single-component photocatalysts during photocatalytic degradation for most antibiotics, in which h+ played a predominant role among all the related reactive oxygen species. Moreover, the crystal structures and morphologies of bismuth-based catalysts seriously affected their practical efficiencies.

Palladium-Free Suzuki–Miyaura Coupling with a Bismuth-Based Composite Photocatalyst

Palladium-Free Suzuki–Miyaura Coupling with a Bismuth-Based Composite Photocatalyst

Influence of different solvents on the performance of bismuth-based photocatalyst for mercury removal

The BiOIO3 nanosheets and Bi7O9I3 nanoflowers were successfully prepared by solvothermal method with different solvents for Hg0 photocatalytic oxidation. XRD, SEM, XPS, FTIR, UV–vis DRS and PL were used to analyze the physical and chemical characteristics of BiOIO3 and B7O9I3. It was discovered that Bi7O9I3 has superior visible light absorption capacity and carrier separation and transport properties, which allows it to use a wider spectrum of visible light to promote the separation and transport of electrons and holes, thereby facilitating photocatalytic activity.

Recent advances in bismuth-based multimetal oxide photocatalysts for hydrogen production from water splitting: Competitiveness, challenges, and future perspectives

The efficient utilization of photocatalytic technology is essential for clean energy. Bismuth-based multimetal oxides (Bi2WO6, Bi2MoO6, BiVO4 and Bi4Ti3O12) have aroused widespread attention as a visible light responsive photocatalyst for hydrogen evolution due to their low cost, nontoxicity, modifiable morphology, and outstanding optical and chemical properties. Nevertheless, the photocatalytic activities of pure materials are unsatisfactory because of their relative small specific surface area, poor quantum yield, and the rapid recombination of photogenerated carriers. Therefore, some modification strategies, including morphological control, semiconductor combination, doping, and defect engineering, have been systematically studied to enhance photocatalytic H2 evolution activity in the past few years. Herein, we summarize the recent research progress on bismuth-based photocatalysts, pointing out the prospects, opportunities and challenges of bismuth-based photocatalysts. Eventually, we aims to put forward valuable suggestions for designing of bismuth-based photocatalysts applied in hydrogen production on the premise of consolidating the existing theoretical basis of photocatalysis.

Facile synthesis of CeO2/carbonate doped Bi2O2CO3 Z-scheme heterojunction for improved visible-light photocatalytic performance: Photodegradation of tetracycline and photocatalytic mechanism

CeO2 nanoparticles are successfully loaded on carbonate doped Bi2O2CO3 (CBOC) nanosheets by a facile hydrothermal and low-temperature calcination method. CeO2/CBOC heterojunction shows significantly enhanced photocatalytic activity, when 35 mg of CeO2/CBOC photocatalyst is added to tetracycline (TC) solution (20 mg/L, 100 mL), about 79.5% TC is degraded within 90 min under visible light irradiation, which is much higher than that of original CeO2 and CBOC. According to photoelectrochemical characterization and active radical capture experiments, the Z-scheme electron transfer mechanism is the reason for the significant enhancement of photocatalytic activity. Besides, the XPS results indicate that Ce4+/Ce3+ redox pairs are formed at the contact interface between CeO2 and CBOC, which is conducive to the transfer of photoexcited electrons and production of superoxide radicals. Additionally, the photocatalytic mechanism and possible degradation pathway of TC is proposed through free radical trapping experiments and liquid chromatography-mass (LC-MS) analysis. This study will accumulate experience for the combination of CeO2 and bismuth-based nanomaterials, and provide a feasible way to design wide band-gap bismuth-based photocatalysts, thereby achieving efficient visible light degradation of environmental pollutants.

Facet-selective charge separation in two-dimensional bismuth-based photocatalysts

In this review, we summarize recent advances in the facet design of bismuth-based single-crystal plates based on facet-dependent charge separation for photocatalytic reactions, and the manipulation of the spatial charge separation is highlighted.

Surface and interface engineering of two-dimensional bismuth-based photocatalysts for ambient molecule activation

This review endeavors to reveal the inherent functionality of the surface and interface to the reactivity and selectivity of photocatalytic ambient molecule activation, with 2D Bi-based photocatalysts as the platform.