A review on plasmonic-based heterojunction photocatalysts for degradation of organic pollutants in wastewater

Abstract

Organic pollutants in wastewater are the biggest problem facing the world today due to population growth, rapid increase in industrialization, urbanization, and technological advancement. There have been numerous attempts to use conventional wastewater treatment techniques to address the issue of worldwide water contamination. However, conventional wastewater treatment has a number of shortcomings, including high operating costs, low efficiency, difficult preparation, fast recombination of charge carriers, generation of secondary waste, and limited light absorption. Therefore, plasmonic-based heterojunction photocatalysts have attracted much attention as a promising method to reduce organic pollutant problems in water due to their excellent efficiency, low operating cost, ease of fabrication, and environmental friendliness. In addition, plasmonic-based heterojunction photocatalysts contain a local surface plasmon resonance that enhances the performance of photocatalysts by improving light absorption and separation of photoexcited charge carriers. This review summarizes the major plasmonic effects in photocatalysts, including hot electron, local field effect, and photothermal effect, and explains the plasmonic-based heterojunction photocatalysts with five junction systems for the degradation of pollutants. Recent work on the development of plasmonic-based heterojunction photocatalysts for the degradation of various organic pollutants in wastewater is also discussed. Lastly, the conclusions and challenges are briefly described and the direction of future development of heterojunction photocatalysts with plasmonic materials is explored. This review could serve as a guide for the understanding, investigation, and construction of plasmonic-based heterojunction photocatalysts for various organic pollutants degradation.

Graphical abstract: Herein, the plasmonic effects in photocatalysts, such as hot electrons, local field effect, and photothermal effect, as well as the plasmonic-based heterojunction photocatalysts with five junction systems for the degradation of pollutants are explained. Recent work on plasmonic-based heterojunction photocatalysts for the degradation of various organic pollutants in wastewater such as dyes, pesticides, phenols, and antibiotics is discussed. Challenges and future developments are also described.

Figure 1

Plasmonic hot electron transfer routes a indirect and b direct transfer in metal to a semiconductor. Adapted with permission from [58]

Figure 2

Schematic diagram of photoinduced charge transfer and photocatalytic processes using an Au/KCNO photocatalyst to degrade TC. Adapted with permission from [62]

Figure 3

Possible photodegradation mechanism of the W₁₈O₄₉/BiOBr photocatalyst to degrade MO and TC pollutants. Adapted with permission from [63]

Figure 4

Local electric field distributions at Ag/Ag₂CO₃ interfaces were calculated by the FDTD method. Adapted with permission from [71]

Figure 5

Possible photocatalytic mechanism of Ag-CoWO₄/CdWO₄ photocatalyst. Adapted with permission from [72]

Figure 6

Possible photodegradation mechanism of Ce@15-AC photocatalyst. Adapted with permission from [74]

Figure 7

a Shows infrared images of α-Fe₂O₃, α-Fe₂O₃/defective MoS₂, and α-Fe₂O₃/defective MoS₂/Ag, and b illustration of the photothermal mechanism in a semiconductor with a narrow-bandgap and a normal. Adapted with permission from [88]

Figure 8

Schematic diagram of plasmonic heterojunctions: a type-I, b type-II, and c type-III

Figure 9

Possible mechanism of photoinduced charge carrier migration in the CeO₂/ZnO@Au photocatalyst. Adapted with permission from [104]

Figure 10

Mechanism of the plasmonic type-II heterojunction Ag/BSO-BCN photocatalyst for TC degradation. Adapted with permission from [101]

Figure 11

Schematic representation of plasmonic p–n junction

Figure 12

A possible mechanism for photodegradation of MO by Ag/α-Bi₂O₃/Bi₂O₂CO₃ photocatalyst [34]

Figure 13

Schematic illustration of the charge carrier transfer in a plasmonic Schottky junction

Figure 14

Photocatalytic mechanism of the Ag/Bi₂WO₆/TiO₂ photocatalyst for RhB degradation. Adapted with permission from [122]

Figure 15

Schematic representation of the plasmonic Z-scheme heterojunction

Figure 16

Proposed photocatalytic mechanism of Ag₂MoO₄/Ag/Ag₃VO₄ photocatalyst. Adapted with permission from [133]

Figure 17

The charge transfer path in plasmonic S-scheme heterojunction

Figure 18

The possible charge transfer of Pg-C₃N₄/Ag₃VO₄ photocatalyst. Adapted with permission from [141]

Figure 19

The sources and pathways of various dye pollutants in water systems. Adapted with permission from [153]

Figure 20

a The fabrication process of Ag–Ag₂MoO₄/PAN photocatalyst, b photocatalytic performance of the as-prepared photocatalyst for the removal of MO, and c possible photocatalytic mechanism of the Ag–Ag₂MoO₄/PANI photocatalyst. Adapted with permission from [154]

Figure 21

a The photocatalytic performance of Ag/AgCl/Ag₂MoO₄ photocatalyst for the removal RhB, and b MB. Adapted with permission from [156]

Figure 22

a The photocatalytic degradation of MO by HBPP photocatalyst with different Pd %wt and b photocatalytic degradation mechanism of MO by HBPP photocatalyst. Adapted with permission from [158]

Figure 23

a The fabrication process of the plasmonic heterojunction g-C₃N₄/Ag₂WO₄/Ag photocatalyst, and b photocatalytic degradation of MB by g-C₃N₄/Ag₂WO₄/Ag photocatalyst. Adapted with permission from [159]

Figure 24

a Photodegradation of TCP pesticide and b degradation mechanism of TCP pesticide by PZn₈Cu photocatalyst. Adapted with permission from [170]

Figure 25

Photocatalytic degradation performance of phenol by Bi–Bi₇O₉I₃/Ag–AgI photocatalyst. Adapted with permission from [177]

Figure 26

a The fabrication process of the g-C₃N₄/Ag/LaFeO₃ photocatalyst, b photodegradation of phenol by g-C₃N₄/Ag/LaFeO₃ photocatalyst and c photocatalytic mechanism of phenol by g-C₃N₄/Ag/LaFeO₃ photocatalyst. Adapted with permission from [178]

Figure 27

The sources and pathways of antibiotic pollutants in the environment. Adapted with permission from [187]

Figure 28

Photocatalytic degradation of TC by BFTO/Ag/UCN photocatalyst with different wt% of Ag. Adapted with permission from [188]

Figure 29

a Schematic diagram of the preparation process of Ag/Ag₂S/Bi₂MoO₆ photocatalyst, and b, c photocatalytic degradation of LEV and TC by Ag/Ag₂S/Bi₂MoO₆ photocatalyst. Adapted with permission from [116]

Figure 30

a The preparation process of the Ag-C₃N₄/SnS₂ photocatalyst, and b photocatalytic efficiency of Ag-C₃N₄/SnS₂ photocatalyst for the removal of TC. Adapted with permission from [189]

Figure 31

The photocatalytic performance of as-prepared photocatalysts for the degradation of a CIP, b TC, and c photocatalytic degradation mechanism of AASO/BMO photocatalyst. Adapted with permission from [190]

Figure 32

Schematic representation of the mechanism of plasmonic-based heterojunction photocatalysts for organic pollutants degradation