Plasmonic Enhanced Reactive Oxygen Species Activation on Low-Work-Function Tungsten Nitride for Direct Near-Infrared Driven Photocatalysis

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

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.

Multicomponent Composite Membrane with Three-Phase Interface Heterostructure as Photocatalyst for Organic Dye Removal

A multicomponent composite membrane (P-S-T/C) with three-phase interface heterostructure is ingeniously designed. A polydopamine (PDA)-modified conductive carbon fiber cloth (C_FC) is used as the substrate. Activated poly(vinylidene fluoride) (PVDF) with titanium dioxide (TiO₂) and a silicon dioxide (SiO₂) aerogel are electrospun as the top layer. The three-phase interface heterostructure was formed by TiO₂, conductive C_FC, and the SiO₂ aerogel. Its photocatalytic performance is validated by photodegradation of organic dyes in a low-oxygen (O₂) water environment. On combining with the capillary condensation of a bilayer structure, P-S-T/C exhibits excellent removal capability for anionic and cationic dyes. Moreover, P-S-T/C exhibits excellent stability and recyclability under simulated sunlight. The mechanism study indicates that the separated photogenerated carriers diffuse to the composite membrane surface rapidly on the three-phase interface of P-S-T/C. The abundant O₂ adsorbed on the porous SiO₂ aerogel surface acts as an electron (e^-)-trapping agent, which can also decrease the work function of the composite materials. Superoxide radicals (^•O₂ ^-) play a dominant role in the reaction of photodegradation supported by a free radical-trapping experiment. This work paves a way to design a membrane with photocatalytic performance by constructing the interface heterostructure.

Co4N-WNx composite for efficient piezocatalytic hydrogen evolution

A dual-phase transition metal nitride (TMN) based Co₄N-WN_x system has been fabricated using nitridation of CoWO₄. The interface between centrosymmetric Co₄N and non-centrosymmetric WN_x promotes charge carrier separation. This system also shows piezoelectric behavior. The piezoelectric property has been proved using piezoelectric force microscopy (PFM) measurements. In addition, modulating the non-centrosymmetric structure of Co₄N-WN_x allows a hydrogen production rate of about 262.7 μmol g^-1 h^-1 in pure water. We also show that the piezocatalytic hydrogen evolution efficiency is satisfactory. Co₄N-WN_x can also help achieve simultaneous piezocatalytic hydrogen production and RhB degradation. This work provides a novel strategy for designing efficient piezocatalytic materials.

In-Situ Monitoring the SERS Spectra of para-Aminothiophenol Adsorbed on Plasmon-Tunable Au@Ag Core–Shell Nanostars

Plasmon-induced photocatalysis on noble metal surfaces has attracted broad attention due to its application in sunlight energy conversion, while the selectivity of plasmonic platforms remains unclear. Herein, we present the controlled plasmon-mediated oxidation of para-aminothiophenol (p-ATP) by employing Au@Ag core–shell nanostars with tunable tip plasmons in visible–near-infrared range as reactors. In-situ Raman measurements indicate that Au@Ag core–shell nanostars essentially promote the conversion of p-ATP to 4,4′-dimercaptoazobenzene (DMAB) due to hot carriers excited by localized surface plasmon resonance. Au@Ag nanostars with plasmon modes under resonant light excitation suggested higher catalytic efficiency, as evidenced by the larger intensity ratios between 1440 cm⁻¹ (N=N stretching of DMAB) and 1080 cm⁻¹ shifts (C–S stretching of p-ATP). Importantly, the time-dependent surface-enhanced Raman scattering spectra showed that the conversion efficiency of p-ATP was mainly dictated by the resonance condition between the tip plasmon mode of Au@Ag core–shell nanostars and the excitation light, as well as the choice of excitation wavelength. These results show that plasmon bands of metal nanostructures play an important role in the efficiency of plasmon-driven photocatalysis.

The Z-scheme transfer of photogenerated electrons for CO2 photocatalytic reduction over g-ZnO/2H-MoS2 heterostructure

Effective separation of the photogenerated electrons and holes is critical to improve photocatalytic efficiency. To achieve this, we design a Z-scheme g-ZnO/2H-MoS₂ heterostructure to spatially separate the photogenerated carriers promoting the reduction of CO₂ on the surface of the heterostructure, through density functional theory (DFT) calculations. The g-ZnO/2H-MoS₂ heterostructure has a narrow band gap, which is beneficial to speed up the transport of carriers. Simultaneously, the designed heterostructure forms a built-in electric field between the layers to cause band bending, which is very conducive to separate the photogenerated electrons on g-ZnO and the photogenerated holes on 2H-MoS₂, and suppress their recombination effectively. Furthermore, the reaction mechanism of photocatalytic reduction of CO₂ to CH₄ on g-ZnO/2H-MoS₂ is studied. The calculation results show that the Z-scheme charge transfer mechanism reduces the barrier of the potential energy control step compared with pristine g-ZnO and 2H-MOS₂. Our calculations lay a theoretical foundation for designing and developing high performance photocatalysts for the photocatalytic reduction of CO₂.

Low-work-function LaB6 for realizing photodynamic-enhanced photothermal therapy

There is great potential for photodynamic therapy (PDT)-enhanced photothermal therapy (PTT) to be used for tumor therapy, especially for the single material-mediated process that could greatly simplify the experimental arrangements. This study presents a new cancer phototherapeutic agent consisting of low-work-function lanthanum hexaboride particles, which are excellent light absorbers in the near-infrared (NIR) region. The photothermal effect and reactive oxygen species production were realized by LaB6 under NIR light irradiation. Theoretical calculations based on density functional theory confirmed that the strong NIR light absorption by LaB6 was attributed to the local plasmonic resonance effect and the excellent photodynamic effect derived from the low work function. In vivo treatment of HepG2 tumor-bearing mice revealed that LaB6-mediated phototherapy resulted in excellent tumor inhibitory effects, and no adverse effects on mice were observed. These results indicate that LaB6 is a promising phototherapeutic agent for cancer synergetic phototherapy.