Rationally constructing of a novel dual Z-scheme composite photocatalyst with significantly enhanced performance for neonicotinoid degradation under visible light irradiation

https://doi.org/10.1016/j.apcatb.2020.118918Get rights and content

Highlights

  • Mediator-free direct dual-Z-scheme g-C3N4/WO3/AgI hybrid photocatalysts were rationally constructed.

  • The photocatalyst was prepared by electrostatic self-assembly plus selective deposition method.

  • The photocatalyst exhibited high performance for the degradation of nitenpyram.

  • The rate constant improved by a factor of 12.4 and 21.8 compared to g-C3N4 and WO3.

  • A deductive degradation pathway of nitenpyram was proposed.

Abstract

A novel dual Z-scheme g-C3N4/WO3/AgI photocatalyst was rationally constructed via a two-step method (electrostatic self-assembly plus selective deposition). Firstly, binary g-C3N4/WO3 system was fabricated by electrostatic self-assembly method. Then, Ag ions were selectively adsorbed on the surface of negatively charged WO3 and reacted with I ions to form AgI nanoparticles. Compared with pure g-C3N4, WO3, AgI and their binary composites, the ternary composites showed significantly enhanced photocatalytic performance for nitenpyram (NTP) degradation under visible light. The enhanced performance can be ascribed to the increased charge transferring/separation efficiency and remaining high reduction/oxidation ability of the photo-generated electrons/holes in the dual Z-scheme system. Furthermore, the possible degradation pathway of NTP was deduced based on the results of high-performance liquid chromatography mass spectrometry (HPLC-MS). This work would broaden insight into the rationally construction of highly efficient Z-scheme composite photocatalysts.

Graphical abstract

A novel dual Z-scheme photocatalyst was rationally constructed via a two-step method (electrostatic self-assembly plus selective deposition). Firstly, binary g-C3N4/WO3 system was fabricated by electrostatic self-assembly method. Then, Ag ions were selectively adsorbed on the surface of negatively charged WO3 and reacted with I ions to form AgI nanoparticles. The as constructed composites showed significantly enhanced visible light responsive photocatalytic performance for nitenpyram (NTP) compared to pure g-C3N4, WO3, AgI and their binary composites.

  1. Download : Download high-res image (299KB)
  2. Download : Download full-size image

Introduction

Micropollutants, including high-effective neonicotinoid pesticides, have attracted considerable attention due to their widespread transmissibility and persistent presence in water [1]. Neonicotinoids are difficult to self-degrade in the environment, and their long-term existence and accumulation in water or soil will have a serious impact on ecology and human health [[2], [3], [4]]. Many groups have studied a variety of degradation methods, but they have various defects. For example, the microbial method has a high requirement for reaction environments and a low efficiency [5,6]. The electrocatalysis method and the low-temperature plasma technique have special demands for reaction conditions and high energy consumption [7,8]. While photocatalysis has attracted more and more attention on account of its simple operation, low environmental hazard and high efficiency [[9], [10], [11]]. Previous researches have shown that photocatalysts absorbing ultraviolet light have low utilization of sunlight, with a difficulty in realizing practical application [12,13]. Therefore, many people devote to developing high-efficient photocatalysts for visible light response.

Nonmetallic photocatalyst g-C3N4 is a widely studied material [14,15]. It has an adaptive band gap energy with a widened response range of light wavelength, and its potential energy of conduction band electron is negative enough with strong reducibility [[16], [17], [18]]. However, the photocatalytic activity of a single component photocatalyst is impeded by the fast recombination of photo-generated carriers [19]. Now, many methods have been explored to solve this problem. One of the most widely used is to construct heterojunction [[20], [21], [22]]. In traditional heterojunctions, e transfers from PC I (a semiconductor with a higher CB position) to PC II (a semiconductor with a lower CB position), while h+ transfers in the opposite direction. This will lead to the weakening of the reducibility/oxidizability of photo-generated carriers after migrating [23,24]. While Z-scheme heterojunction can retain the reducibility and oxidizability of the photo-generated carriers due to its unique Z-type channel which can adjust the transfer path of the photo-generated carriers [[25], [26], [27]]. Recently, many g-C3N4 based Z-scheme heterojunctions have been studied, such as g-C3N4/ZnIn2S4 [12], Ag3PO4/g-C3N4 [28], TiO2/g-C3N4 [29], Ag2CrO4/g-C3N4 [30] and the like. As mentioned above, enough efforts have been made on binary Z-scheme photocatalysts, while their photocatalytic activities still have an improvement room. Some people are trying to construct dual Z-scheme composites, which have three components can broaden light response range. Furthermore, two Z-type channels would improve the separation/transfer efficiency of photogenerated carriers [31,13]. As we all know, photogenerated e transfers faster than h+. Therefore, two PC I are needed in a dual Z-scheme system [32,33]. Photogenerated e on CB of PC II can adequately transfer to VB of PC I, and the photogenerated carriers can retain their reducibility and oxidizability better, leading an improvement of the photocatalytic performance [32,24]. Some studies reported that successfully synthesized ternary Z-scheme photocatalysts showed enhanced photocatalytic activities [34]. WO3, a material with a narrow band gap and good stability, owns a good photocatalytic activity [35,36]. Its CB and VB positions are close to 0.74 eV and 3.44 eV, respectively, which can match g-C3N4 bandgap positions [37,23]. Therefore, Jiang et al. fabricated a dual Z-scheme WO3/g-C3N4/Bi2O3 composite to degrade tetracycline. The k of tetracycline degradation by ternary WCB composite exhibited much higher activity than the corresponding single ones [13]. In a dual Z-scheme system, the containing three components would contact to each other inevitably. If the synthesis method is not appropriate, it would affect the performance of the composites. Thus, it is indispensable to develop an effective method to rationally construct novel dual Z-scheme photocatalysts, in which the two PC I parts contact with PC II selectively.

In the designed dual Z-scheme structure, considering that the surface of WO3 is full of negative charge [38], it can occupy the PC II position. According to the energy band configuration, g-C3N4 can occupy a PC I position, so a positive material with a higher CB and VB position is required to locate in another PC I position. Due to silver-based materials are positive photocatalytic materials with superior photocatalytic activity, AgI with a higher CB and VB position was selected [[40], [41], [42]]. According to the existing reports and bandgap matching principle, the formation of a dual Z-scheme heterojunction containing these three components is possible. In addition, photocatalytic degradation of dye and pharmaceutical wastewater has been researched a lot, but the photocatalytic degradation of refractory pesticide wastewater is still rare. Thus, it is important to probe the mechanism of such pesticides by photocatalytic degradation.

Under the instruction of above concepts, we synthesized a direct ternary dual Z-scheme g-C3N4/WO3/AgI composite via a facile electrostatic self-assembly plus selective deposition method. The photocatalytic performance of g-C3N4/WO3/AgI was assessed by the degradation of NTP under visible light. The fabricated ternary composites showed an improved photocatalytic performance compared to pure g-C3N4, WO3, AgI and their binary composites. Besides, the morphologies, chemical compositions and optical properties of the prepared samples were determined by various characterization methods in detail, and a possible photocatalytic mechanism was further proposed.

Section snippets

Materials

A variety of analytical grade chemical reagents, such as dicyandiamide, silane coupling agent KH550 (APTES), ethyl alcohol, sodium tungstate dehydrate, sodium chloride, hydrochloric acid, silver nitrate (AgNO3), potassium iodide (KI), nitenpyram (NTP), p-benzoquinone (BZQ), tert-butanol (TBA), ethylenediamine tetraacetic acid disodium (Na2-EDTA) and the like, were used directly in the experiment.

Preparation of g-C3N4/WO3/AgI photocatalyst

g-C3N4 was prepared by two-step calcination. The specific preparation steps are the same as the g-C3N

Characterizations of g-C3N4/WO3/AgI

The micromorphologies of WO3, CW and 75CWA were characterized by TEM and HRTEM (Fig. 2). From Fig. 2a, it can be seen that the WO3 sample is composed of nanorods. From Fig. 2b, it can be seen that many WO3 rods are scattered on the folded sheets of g-C3N4 [45]. From Fig. 2c and d, some AgI nanoparticles adhere to the surface of WO3 nanorods. From Fig. 2e, uniform lattice fringes with a space of 0.317 nm are in keeping with the (2 0 0) crystal plane of hexagonal WO3. From Fig. 2f, the lattice

Conclusions

A novel dual Z-scheme photocatalytic material g-C3N4/WO3/AgI was prepared by a simple electrostatic self-assembly plus selective deposition method. Compared with bare g-C3N4, WO3, AgI and their binary composites, the ternary composite 75CWA has an improved photocatalytic activity for photocatalytic degradation of a neonicotinoid pesticide NTP. The enhanced photocatalytic activity of 75CWA is mainly assigned to the two photogenerated carrier transmission paths, which greatly enhances the

CRediT authorship contribution statement

Mengling Tang: Methodology, Software, Validation, Visualization, Writing - original draft. Yanhui Ao: Conceptualization, Writing - review & editing, Supervision, Funding acquisition, Data curation, Validation, Formal analysis. Chao Wang: Formal analysis. Peifang Wang: Funding acquisition, Formal analysis.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

We are grateful for grants from National Science Funds for Creative Research Groups of China (No. 51421006), Natural Science Foundation of China (51979081, 51679063), Major Science and Technology Program for Water Pollution Control and Treatment (2017ZX07203002), the National Key Plan for Research and Development of China (2016YFC0502203), and PAPD.

References (59)

  • S.W. Cao et al.

    Solar-to-fuels conversion over In2O3/g-C3N4 hybrid photocatalysts

    Appl. Catal. B: Environ.

    (2014)
  • G. Mamba et al.

    Graphitic carbon nitride (g-C3N4) nanocomposites: A new and exciting generation of visible light driven photocatalysts for environmental pollution remediation

    Appl. Catal. B: Environ.

    (2016)
  • G. Zhou et al.

    Synthesis and characterizations of metal-free semiconductor/MOFs with good stability and high photocatalytic activity for H2 evolution: a novel Z-scheme heterostructured photocatalyst formed by covalent bonds

    Appl. Catal. B: Environ.

    (2018)
  • H.T. Yu et al.

    TiO2-carbon nanotube heterojunction arrays with a controllable thickness of TiO2 layer and their first application in photocatalysis

    J. Photochem. Photobiol: A Chem.

    (2008)
  • M.M. Zhang et al.

    Rational design 2D/2D BiOBr/CDs/g-C3N4 Z-scheme heterojunction photocatalyst with carbon dots as solid-state electron mediators for enhanced visible and NIR photocatalytic activity: kinetics, intermediates, and mechanism insight

    J. Catal.

    (2019)
  • L.F. Cui et al.

    Facile preparation of Z-scheme WO3/g-C3N4 composite photocatalyst with enhanced photocatalytic performance under visible light

    Appl. Surf. Sci.

    (2017)
  • J. Li et al.

    Enhanced molecular oxygen activation of Ni2+ -doped BiO2-xnanosheets under UV, visible and near-infrared irradiation: mechanism and DFT study

    Appl. Catal. B

    (2018)
  • C.D. Song et al.

    Enhanced performance of direct Z-scheme CuS-WO3 system towards photocatalytic decomposition of organic pollutants under visible light

    Appl. Surf. Sci.

    (2017)
  • Y.C. Deng et al.

    Facile fabrication of a direct Z-scheme Ag2CrO4/g-C3N4 photocatalyst with enhanced visible light photocatalytic activity

    J. Mol. Catal. A: Chem.

    (2016)
  • J. Yan et al.

    Fabrication of TiO2/C3N4 heterostructure for enhanced photocatalytic Z-scheme overall water splitting

    Appl. Catal. B: Environ.

    (2016)
  • F. Chen et al.

    Novel ternary heterojunction photcocatalyst of Ag nanoparticles and g-C3N4 nanosheets co-modified BiVO4 for wider spectrum visible-light photocatalytic degradation of refractory pollutant

    Appl. Catal. B: Environ.

    (2017)
  • W.K. Jo et al.

    Fabrication and efficient visible light photocatalytic properties of novel zinc indium sulfide (ZnIn2S4)-graphitic carbon nitride (g-C3N4)/bismuth vanadate (BiVO4) nanorod-based ternary nanocomposites with enhanced charge separation via Z-scheme transfer

    J. Colloid Interface Sci.

    (2016)
  • Q.L. Xu et al.

    Direct Z-scheme photocatalysts: Principles, synthesis, and applications

    Mater. Today

    (2018)
  • Z.F. Dong et al.

    Double Z-scheme ZnO/ZnS/g-C3N4 ternary structure for efficient photocatalytic H2 production

    Appl. Surf. Sci.

    (2018)
  • J. Cao et al.

    Thermodecomposition synthesis of WO3/H2WO4 heterostructures with enhanced visible light photocatalytic properties

    Appl. Catal. B: Environ.

    (2012)
  • S.F. Chen et al.

    Study on the separation mechanisms of photogenerated electrons and holes for composite photocatalysts g-C3N4-WO3

    Appl. Catal. B: Environ.

    (2014)
  • X. Liu et al.

    Synergy of adsorption and visible-light photocatalytic degradation of methylene blue by a bifunctional Z-scheme heterojunction of WO3/g-C3N4

    Appl. Surf. Sci.

    (2017)
  • M. Tang et al.

    Facile synthesis of dual Z-scheme g-C3N4/Ag3PO4/AgI composite photocatalysts with enhanced performance for the degradation of a typical neonicotinoid pesticide

    Appl. Catal. B: Environ.

    (2020)
  • M. Tang et al.

    All-solid-state Z-scheme WO3 nanorod/ZnIn2S4 composite photocatalysts for the effective degradation of nitenpyram under visible light irradiation

    J. Hazard. Mater.

    (2020)
  • Cited by (160)

    View all citing articles on Scopus
    View full text