Oxygen vacancy-rich 2D/2D BiOCl-g-C3N4 ultrathin heterostructure nanosheets for enhanced visible-light-driven photocatalytic activity in environmental remediation

doi:10.1016/j.apcatb.2017.08.049

Applied Catalysis B: Environmental

Volume 220, January 2018, Pages 290-302

https://doi.org/10.1016/j.apcatb.2017.08.049 Get rights and content

Highlights

•
Oxygen vacancy-rich 2D/2D BiOCl-g-C₃N₄ ultrathin heterostructures were fabricated.
•
The BiOCl-g-C₃N₄ exhibited high photocatalytic activity for non-dye organic contaminants.
•
The synergistic effect between heterostructure and oxygen vacancy led to the excellent photoactivity.
•
Good stability, recyclability and high mineralization were obtained from the BiOCl-g-C₃N₄.

Abstract

Photocatalytic degradation has been unearthed as a promising strategy for environmental remediation, and the calling is endless for more efficient photocatalytic system. In this study, a novel oxygen vacancy-rich two-dimensional/two-dimensional (2D/2D) BiOCl-g-C₃N₄ ultrathin heterostructure nanosheet (CN-BC) is successfully prepared by a facile solvothermal method for degradation of non-dye organic contaminants. HRTEM observes the formation of heterojunction, while ESR and XPS unveil the distinct oxygen vacancy concentrations. Density functional calculations reveal that the introduction of oxygen vacancies (OVs) brings a new defect level, resulting in the increased photoabsorption. Under visible light irradiation, the OVs-rich optimum ratio of CN-BC (50CN-50BC) Exhibits 95% removal efficiency of 4-chlorophenol within 2 h, which is about 12.5, 5.3 and 3.4 times as that of pure BiOCl, g-C₃N₄ and OVs-poor heterostructure, respectively. The photocatalytic mechanism of OVs-rich 50CN-50BC is also revealed, suggesting that the synergistic effect between 2D/2D heterojunction and oxygen vacancies greatly promotes visible-light photoabsorption and photoinduced carrier separation efficiency with a prolonged lifetime, which is confirmed by multiple optical and electrochemical analyses, including DRS, steady-state photoluminescence spectra, electrochemical impedance spectroscopy, photocurrent response and time-resolved fluorescence spectra. This study could bring new opportunities for the rational design of highly efficient photocatalysts by combining 2D/2D heterojunctions with oxygen vacancies in environmental remediation.

Graphical abstract

Introduction

Semiconductor photocatalysis technology has been considered to be a green and benign method to eliminate most environmental contaminations [1]. Thus, exploiting high-efficient and environment-friendly visible-light-driven photocatalysts has attracted explosive attention due to their potential application in solar energy conversion [2], [3], [4]. Among various photocatalysts investigated, triggered by the great success of graphene, two-dimensional (2D) nanosheets have emerged as a new class of photocatalysts, which benefit from their large specific surface areas and unique structural feature of ultimate two-dimensional anisotropy with small thickness. These characters can increase intimate surface to contact with reactants, shorten the transmission path of the photoinduced charges and realize the effective separation of electron-hole pairs [5], [6]. When the thickness of the bulk materials is reduced to nanometer and even subnanometer scale, the surface atomic structures such as coordination number, bond length, and degree of atom disorder will vary [7]. The ultrathin nanosheets will lead to a large fraction of exposed interior atoms and inevitably induce the formation of various defects with structure disorder on the surface, which can enhance the optical absorption and serve as highly active sites for photocatalytic reactions, inducing a nonnegligible enhancement on the photocatalytic activity [7], [8], [9]. Thus, ultrathin 2D nanosheets have been regarded as a new opportunity to synthesize highly efficient photocatalysts.

Bismuth oxychloride (BiOCl), a new type of promising layered materials for photocatalytic environmental remediation, has been intensively investigated due to its stabilized chemical property, nontoxicity, corrosion resistance, indirect-transition band gap and open crystalline structure [10], [11], [12]. The indirect-transition band gap of BiOCl forces the excited electron to travel a certain k-space distance to the valence band (VB), which reduces the recombination probability of the excited electron and the hole [13]. On the other hand, BiOCl has an open layered structure consisting of [Bi2O2]²⁺ layers sandwiched between two slabs of halogen ions, which provides a large space to polarize the related atoms and orbitals, and then enhances the separation of the photoinduced electron-hole pairs [14]. However, despite these excellent advantages, BiOCl is limited by its wide band gap, making it useful only under UV irradiation, which results in its poor visible-light photocatalytic performance. Up to now, many strategies have been employed to regulate and modify BiOCl, such as morphological control [15], [16], exposure of specific crystal faces [11], [17], and heterologous hybridization [18], however, the acquired visible-light photoactivity is generally active in dye photosensitization degradation, and the photocatalytic performance is unsatisfactory [17], [19]. Recently, Xie et al. [20] has synthesized triple-vacancy BiOCl ultrathin nanosheets, which had highly photocatalytic efficiency for Rhodamine B photosensitization degradation under visible light irradiation, while its visible-light photoactivity for colorless non-dye organic contaminant was still moderate. Therefore, it is urgently desirable to design an ideal architecture of 2D ultrathin hybrid nanosheets between BiOCl and other narrow band gap semiconductors, aiming to further imbue BiOCl with higher visible-light photocatalytic activity to non-dye organic contaminants.

Graphitic carbon nitrides (g-C₃N₄) has attracted extensive attention as a potential layered-structure photocatalyst with excellent visible-light response due to its narrow band gap of 2.7eV [21], [22]. Since Wang et al. [23] firstly reported that g-C₃N₄ could be used for hydrogen production from water under visible light irradiation, many followed reports have been booming. However, the photocatalytic performance of bulk g-C₃N₄ is far from optimum because of its poor mass diffusion and fast charge recombination [24]. Fortunately, these short-comings have been overcome through exfoliating bulk g-C₃N₄ into g-C₃N₄ ultrathin nanosheet, which can increase specific surface area, improved electron transport ability along the in-plane direction, and prolong lifetime of photoexcited charge carriers [6], [25]. More importantly, it has been reported that when g-C₃N₄ ultrathin nanosheets were fabricated into 2D/2D heterostructures with other layered semiconductors, its face-to-face contact would form a large interface region, and consequently an enhanced photocatalytic performance would be achieved [26], [27], [28]. Nonetheless, to the best of our knowledge, in 2D/2D heterostructures, the insightful understanding of the impact of vacancies on photocatalytic activity is still missing.

Herein, inspired by the above considerations, in this work we have rational designed an oxygen vacancy (OV)-rich ultrathin g-C₃N₄-BiOCl heterostructure nanosheet with a high visible-light-driven photocatalytic activity via a facile solvothermal method. The visible photocatalytic activity of as-prepared ultrathin g-C₃N₄-BiOCl nanosheets was evaluated by the degradation of 4-chlorophenol (4-CP), and several endocrine disruptors (bisphenol A (BPA), bisphenol S (BPS) and bisphenol F (BPF)). Multiple optical and photoelectrochemical experiments were employed to stuied the degradation mechanism in this system. The enhanced optical absorption and separation efficiency led to the superior visible-light photocatalytic activity, which were originated from the synergistic effect between oxygen vacancies (OVs) and heterojunction in ultrathin hybrid g-C₃N₄-BiOCl nanosheets. The construction of oxygen vacancy-rich ultrathin 2D/2D heterostructures could bring new opportunities for rational design highly active visible light photocatalysts for environmental remediation and other applications.

Section snippets

Materials

All chemical reagents used in this work were analytical reagent grade and without further purification. Bismuth nitrate pentahydrate (Bi(NO₃)₃·5H₂O), sodium chloride (NaCl), urea, polyvinylpyrrolidone (PVP, K-30), glycerol, 4-chlorophenol (4-CP), bisphenol A (BPA), bisphenol S (BPS), bisphenol F (BPF) and ethanol were all obtained from Sinopharm Chemical Reagent Co. Ltd. Deionized water was used throughout the experiments.

Synthesis of graphite carbon nitrogen (g-C₃N₄) nanosheets

Bulk g-C₃N₄ was synthesized by annealing urea at 550 °C for 3 h with the

Morphology and structure

XRD analysis was carried out to investigate the phase structures of the catalysts. Fig. 1a shows the XRD patterns of CN, BC and 50CN-50BC, and those of other ratio xCN-(100-x)BC samples are shown in Fig. S1. The diffraction peak at 27.5° of CN is a characteristic interlayer stacking reflection of conjugated aromatic systems, which indexes to (002) diffraction planes [31]. The small peak at around 13.0° is indexed to (100) diffraction plane [31]. As for the pure BC nanosheets, all diffraction

Conclusion

In this study, we have successfully constructed an oxygen vacancy-rich 2D/2D heterostructure by combining ultrathin BiOCl nanosheets with ultrathin g-C₃N₄ nanosheets through a facile solvothermal reaction. DRS analysis indicated that the formation of 2D/2D heterostructures between BiOCl and g-C₃N₄ nanosheets can enhance the visible-light photoabsorption ability as compared to any single components. XPS and ESR demonstrated the distinct oxygen vacancy concentration in the as-fabricated 50CN-50BC

Acknowledgements

The authors gratefully acknowledge National Natural Science Foundation of China (21304024), State Key Laboratory of Urban Water Resource and Environment in HIT of China (2017TS03), Postdoctoral Science Foundation of Heilongjiang Prov. (LBH-TZ0606 and LBH-Q16012).

References (68)

Y. Li et al.
Hybridization of rutile TiO₂ (rTiO₂) with g-C₃N₄ quantum dots (CN QDs): An efficient visible-light-driven Z-scheme hybridized photocatalyst
Appl. Catal. B: Environ.
(2017)
J. Li et al.
Solar water splitting and nitrogen fixation with layered bismuth oxyhalides
Acc. Chem. Res.
(2017)
X. Zhang et al.
A novel BiOCl thin film prepared by electrochemical method and its application in photocatalysis
Appl. Catal. B: Environ.
(2013)
K. Zhang et al.
Study of the electronic structure and photocatalytic activity of the BiOCl photocatalyst
Appl. Catal. B: Environ.
(2006)
S. Wu et al.
Synthesis and photocatalytic properties of BiOCl nanowire arrays
Mater. Lett.
(2010)
Y. Li et al.
Enhanced visible-light photo-oxidation of nitric oxide using bismuth-coupled graphitic carbon nitride composite heterostructures
Chin. J. Catal.
(2017)
S. Fang et al.
Effect of carbon-dots modification on the structure and photocatalytic activity of g-C₃N₄
Appl. Catal. B: Environ.
(2016)
H. Zhao et al.
Fabrication of atomic single layer graphitic-C₃N₄ and its high performance of photocatalytic disinfection under visible light irradiation
Appl. Catal. B: Environ.
(2014)
J. Wang et al.
Atomic scale g-C₃N₄/Bi₂WO₆ 2D/2D heterojunction with enhanced photocatalytic degradation of ibuprofen under visible light irradiation
Appl. Catal. B: Environ.
(2017)
Z. Zhang et al.
Ultrathin hexagonal SnS₂ nanosheets coupled with g-C₃N₄ nanosheets as 2D/2D heterojunction photocatalysts toward high photocatalytic activity
Appl. Catal. B: Environ.
(2015)

Cited by (505)

Fabrication of oxygen-vacancy-adjustable Yb<sup>3+</sup>/Er<sup>3+</sup> co-doped BiOBr 3D flowerlike hierarchical architectures with enhanced photocatalytic activity under broad spectrum (UV/vis/NIR) excitation
2024, Journal of Molecular Structure
A novel Yb³⁺/Er³⁺ co-doped BiOBr photocatalyst with 3D flowerlike hierarchical architectures were successfully fabricated through self-assembled process without any templates under hydrothermal conditions, and the structure and properties of the photocatalysts were characterized. The results indicate that Yb³⁺ ions and Er³⁺ ions are successfully doped into the lattice of BiOBr, and the as-obtained photocatalyst can respond the NIR light and emit red and green light due to the up-conversion effect of the rare-earth ions. Meanwhile, with co-doped Yb³⁺/Er³⁺ ions content increasing, oxygen vacancy concentration in the photocatalyst rises. The oxygen vacancy will form the intermediate energy band, which can decrease the photon energy required for electronical transition, and thus help to utilize the luminous energy generated by up-conversion luminescence. Moreover, the appropriate introduction of defects (oxygen vacancy defect and impurity atom) can further promote the transfer and separation efficiency of photo-generated carriers. Hence, Yb³⁺/Er³⁺ co-doped BiOBr photocatalyst exhibits enhanced photocatalytic properties under broad spectrum (UV/vis/NIR) excitation, which is about 4 times as high as that of pure BiOBr.
Double defects cooperatively mediated BiOClBr-OV for efficient round-the-clock photocatalytic CO<inf>2</inf> reduction
2024, Fuel
In recent years, the production of high-value solar fuels through photocatalytic reduction of CO₂ has received significant attention. However, the low photocatalytic activity and intermittent nature of solar light contributing to low production rates have hindered its large-scale application. This study successfully constructed BiOClBr-OV with two defects (Cl/Br substitution, oxygen vacancy), which not only enhanced the catalytic activity but also opened the door to round-the-clock photocatalytic reduction of CO₂. Under visible light exposure, the double defects exhibit a synergistic enhancement effect and outstanding electron storage capacity, resulting in 6.8 times and 34.2 times increase in the photocatalytic activity and electron storage capacity, respectively, compared to the pristine BiOCl. Additionally, BiOClBr-OV with surface oxygen defects exhibits frustrated Lewis pair (FLP) catalytic behavior, effectively changing the adsorption mode of CO₂ and enhancing its activation ability. Simultaneously, the unsaturated surface Bi ions of BiOClBr-OV are the electron storage centers, achieving the three-in-one combination of adsorption sites, FLP active sites, and electron storage sites, leading to excellent photocatalytic activity. Finally, the catalytic mechanism and possible reaction pathways are thoroughly explained through in-situ technologies and density functional theory (DFT) calculations. This work introduces a novel multi-sites unified catalyst design strategy, providing deep insight into the photocatalytic CO₂ reduction process and making the application of Bi-based semiconductors in round-the-clock photocatalysis possible.
Facile synthesis method of C self-doped g-C<inf>3</inf>N<inf>4</inf> and its performance in photodegradation of sulfamethoxazole
2024, Separation and Purification Technology
A simple method for preparing C self-doped g-C₃N₄ (CCN) was proposed by calcining urea and barbituric acid to effectively degrade sulfamethoxazole (SMX). X-ray photoelectron spectroscopy and element content analysis implied C atom replaced the original position of the bridging N atom to form CCN. Compared to g-C₃N₄, the absorption edge of CCN was red-shifted. As a result, the band gap of CCN was reduced, which improved the light absorption capacity of CCN and the separation efficiency of photogenerated electron-hole. Ultimately, the photocatalytic activity of CCN was finally boosted. CCN can effectively degrade SMX under visible light. Among CCN with various C dosage, when 0.05 g of barbituric acid was added in the preparation process, the obtained sample (CCN-0.05) exhibited uppermost degradation efficiency on SMX, which can reach 99.0 % after irradiation for 60 min. Additionally, the first-order kinetic reaction rate constant (0.086 min⁻¹) was 8.9 times higher than that of g-C₃N₄ (0.0097 min⁻¹). Electron paramagnetic resonance and trapping experiments showed that the dominant reactive species on SMX degradation were surface ·O₂⁻ and photogenerated holes by CCN-0.05 under visible light. Moreover, CCN-0.05 can still achieve effective removal of SMX under actual water backgrounds and showed selective degradation on sulfonamides.
Construction of 2D/2D BCNS/Ti<inf>3</inf>C<inf>2</inf> heterojunction with boron-doped g-C<inf>3</inf>N<inf>4</inf> and Ti<inf>3</inf>C<inf>2</inf> MXene for enhanced photocatalytic water splitting
2024, Catalysis Today
Graphitic carbon nitride (g-C₃N₄) has attracted great interest in photocatalytic water splitting. However, the poor photogenerated charge carriers transfer and the insufficient driving force for oxygen evolution reaction limit its practical application. In this work, boron-doped g-C₃N₄ nanosheets (BCNS) have been synthesized by calcining a mixture of g-C₃N₄ and NaBH₄. The synthesized BCNS were then combined with Ti₃C₂ MXene using electrostatic self-assembly to construct a 2D/2D BCNS/Ti₃C₂ heterojunction. The resultant BCNS retained the original framework of g-C₃N₄, while the optimized band structure of BCNS induced prominently enhanced visible light absorption, accelerated charge carriers separation, and the increased driving force for water oxidation compared to pure g-C₃N_4. Density functional theory further proved that BCNS can enhance the driving force for photocatalytic O₂ evolution. Moreover, the construction of 2D/2D face-to-face BCNS/Ti₃C₂ heterojunction was carried out to further enhance photocatalytic performance due to the intimate contact interface and the accelerated separation and transfer of photogenerated charge carriers. As a result, the 2D/2D BCNS/Ti₃C₂ hetrojunction exhibited a dramatically improved photocatalytic water-splitting performance compared to pristine g-C₃N₄. This integrated engineering strategy, involving non-metal element doping and 2D/2D heterojunction construction, might provide a unique paradigm for the rational design of efficient photocatalysts for photocatalytic water splitting.
DFT and experimental studies of the facet-dependent oxygen vacancies modulated WS<inf>2</inf>/BiOCl-OV S-scheme structure for enhanced photocatalytic removal of ciprofloxacin from wastewater
2024, Environmental Research
The present study explores visible light-assisted photodegradation of ciprofloxacin hydrochloride (CIP) antibiotic as a promising solution to water pollution. The focus is on transforming the optical and electronic properties of BiOCl through the generation of oxygen vacancies (OVs) and the exposure of (110) facets, forming a robust S-scheme heterojunction with WS₂. The resultant OVs mediated composite with an optimal ratio of WS₂ and BiOCl-OV (4-WS₂/BiOCl-OV) demonstrated remarkable efficiency (94.3%) in the visible light-assisted photodegradation of CIP antibiotic within 1.5 h. The CIP degradation using 4-WS₂/BiOCl-OV followed pseudo-first-order kinetics with the rate constant of 0.023 min⁻¹, outperforming bare WS₂, BiOCl, and BiOCl-OV by 8, 6, and 4 times, respectively. Density functional theory (DFT) analysis aligned well with experimental results, providing insights into the structural arrangement and bandgap analysis of the photocatalysts. Liquid chromatography-mass spectrometry (LC-MS) analysis utilized for identifying potentially degraded products while scavenging experiments and electron paramagnetic resonance (EPR) spin trapping analysis elucidated the S-scheme charge transfer mechanism. This research contributes to advancing the design of oxygen vacancy-mediated S-scheme systems in the realm of photocatalysis, with potential implications for addressing water pollution concerns.
g-C<inf>3</inf>N<inf>4</inf>@CPP/BiOClBr-OV biomimetic fractal heterojunction synergistically enhance carrier dynamics for boosted CO<inf>2</inf> photoreduction activity
2024, Applied Surface Science
In recent years, there has been significant interest in generating high-value solar fuels via the photocatalytic reduction of CO₂. Nonetheless, its large-scale application is impeded by low energy utilization efficiency and limited photocatalytic activity. This study employed carbonized pomelo peel (CPP), a waste biomass material, to successfully craft a CN@CPP/BOCB-OV ternary heterojunction abundant in N/O vacancy defects through secondary calcination and in-situ growth. The construction of the heterojunction and the emergence of defect-induced donor energy levels create a built-in interface electric field (IEF) and an interfacial electron transmission channel respectively, fortifying the separation and transport of photogenerated electrons. Crucially, following the incorporation of CPP, its distinctive 3D porous and heterojunction bionic flower structures expand the spectral absorption range. Acting as a superior electron acceptor, CPP reinforces the IEF, notably boosting carrier transport efficiency. Simultaneously, it operates as a hub for photothermal synergy and CO₂ adsorption activation, achieving multi-site synergistic enhancement of photoreduction CO₂ activity. Hence, the CN@CPP/BOCB-OV heterojunction demonstrates a substantial quantitative enhancement in CO₂ photoreduction activity. Remarkably, it exhibits the capability to catalyze CO₂ reduction even under infrared light excitation, which is of great significance for the cascade utilization of solar energy. Furthermore, employing DFT calculations, we elucidate the electron transfer mechanism at the heterojunction interface and outline potential pathways for photocatalytic CO₂ reduction. The combination of waste biomass utilization, heterostructure construction and defect engineering provides a promising strategy for developing efficient heterostructure photocatalysts.

View all citing articles on Scopus

View full text

Research PaperOxygen vacancy-rich 2D/2D BiOCl-g-C3N4 ultrathin heterostructure nanosheets for enhanced visible-light-driven photocatalytic activity in environmental remediation

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Materials

Synthesis of graphite carbon nitrogen (g-C3N4) nanosheets

Morphology and structure

Conclusion

Acknowledgements

Appl. Catal. B: Environ.

Acc. Chem. Res.

Appl. Catal. B: Environ.

Appl. Catal. B: Environ.

Mater. Lett.

Chin. J. Catal.

Appl. Catal. B: Environ.

Appl. Catal. B: Environ.

Appl. Catal. B: Environ.

Appl. Catal. B: Environ.

Appl. Catal. B: Environ.

Appl. Catal. B: Environ.

Appl. Catal. B: Environ.

J. Photochem. Photobiol. A: Chem.

Appl. Catal. B: Environ.

Catal. Commun.

Appl. Catal. B: Environ.

Nano Energy

Appl. Catal. B: Environ.

Appl. Catal. B: Environ.

Comput. Mater. Sci

Appl. Catal. B: Environ.

Appl. Catal. B: Environ.

Chem. Eng. J.

Sol. Energy Mater. Sol. Cells

Chem. Eng. J.

Semiconductor heterojunction photocatalysts: design, construction, and photocatalytic performances

Chem. Soc. Rev.

Graphitic carbon nitride (g-C3N4)-Based photocatalysts for artificial photosynthesis and environmental remediation: are we a step closer to achieving sustainability?

Chem. Rev.

Hierarchical photocatalysts

Chem. Soc. Rev.

25th anniversary article: hybrid nanostructures based on two-dimensional nanomaterials

Adv. Mater.

Graphene-Like carbon nitride nanosheets for improved photocatalytic activities

Adv. Funct. Mater.

Ultrathin two-dimensional inorganic materials: new opportunities for solid state nanochemistry

Acc. Chem. Res.

Increasing the visible light absorption of graphitic carbon nitride (melon) photocatalysts by homogeneous self-modification with nitrogen vacancies

Adv. Mater.

Defect chemistry of titanium dioxide. application of defect engineering in processing of TiO2-based photocatalysts

J. Phys. Chem. C

Research Paper
Oxygen vacancy-rich 2D/2D BiOCl-g-C₃N₄ ultrathin heterostructure nanosheets for enhanced visible-light-driven photocatalytic activity in environmental remediation

Synthesis of graphite carbon nitrogen (g-C₃N₄) nanosheets

Graphitic carbon nitride (g-C₃N₄)-Based photocatalysts for artificial photosynthesis and environmental remediation: are we a step closer to achieving sustainability?