Plasmonic Hybrid Nanostructures in Photocatalysis: Structures, Mechanisms, and Applications

(Sun)Light is an abundantly available sustainable source of energy that has been used in catalyzing chemical reactions for several decades now. In particular, studies related to the interaction of light with plasmonic nanostructures have been receiving increased attention. These structures display the unique property of localized surface plasmon resonance, which converts light of a specific wavelength range into hot charge carriers, along with strong local electromagnetic fields, and/or heat, which may all enhance the reaction efficiency in their own way. These unique properties of plasmonic nanoparticles can be conveniently tuned by varying the metal type, size, shape, and dielectric environment, thus prompting a research focus on rationally designed plasmonic hybrid nanostructures. In this review, the term "hybrid" implies nanomaterials that consist of multiple plasmonic or non-plasmonic materials, forming complex configurations in the geometry and/or at the atomic level. We discuss the synthetic techniques and evolution of such hybrid plasmonic nanostructures giving rise to a wide variety of material and geometric configurations. Bimetallic alloys, which result in a new set of opto-physical parameters, are compared with core-shell configurations. For the latter, the use of metal, semiconductor, and polymer shells is reviewed. Also, more complex structures such as Janus and antenna reactor composites are discussed. This review further summarizes the studies exploiting plasmonic hybrids to elucidate the plasmonic-photocatalytic mechanism. Finally, we review the implementation of these plasmonic hybrids in different photocatalytic application domains such as H₂ generation, CO₂ reduction, water purification, air purification, and disinfection.

Synthesis of Ag and AgCl co-doped ZIF-8 hybrid photocatalysts with enhanced photocatalytic activity through a synergistic effect

Recently, Ag/AgCl composites with different structures have been widely studied and used as photocatalysts to degrade dye pollutants, due to their high separation efficiency of electron-hole pairs under visible light irradiation. Herein, we adopted a nucleation, precipitation, growth and photoreduction method to prepare Ag and AgCl co-doped ZIF-8 hybrid photocatalysts and explored the influence of Ag content on their physical and chemical properties. All as-prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET) measurements, energy dispersive spectroscopy (EDS), UV-vis diffuse reflectance and X-ray photoelectron spectroscopy (XPS). XRD indicated that ZIF-8 and AgCl were formed and some of the AgCl was reduced into Ag0 after 30 min of UV light irradiation. SEM and TEM images verified that Ag/AgCl nanoparticles were inlaid in the body of ZIF-8 and Ag ions could hinder the growth of the ZIF-8 crystal. BET data indicated that Ag/AgCl nanoparticles did not alter the pore size of ZIF-8. The UV-vis diffuse reflectance spectra showed that Ag/AgCl@ZIF-8 has excellent ability to absorb visible light, indicating the high efficiency of the electron-hole pair separation of Ag/AgCl@ZIF-8. Finally, the photocatalytic activities of all of the as-synthesized samples were evaluated by degradation of RhB under visible light irradiation. Ag and AgCl co-doped ZIF-8 hybrid photocatalysts exhibited high photocatalytic activity due to the synergistic effect of ZIF-8, AgCl and Ag. After 60 min of visible light irradiation, Ag/AgCl(15)@ZIF-8 exhibited the best photocatalytic activity and could degrade 99.12% RhB, which was higher than Ag/AgCl (94.24%) and ZIF-8 (5.17%). Additionally, a photocatalytic mechanism for dye pollutant degradation over the Ag and AgCl co-doped ZIF-8 hybrid photocatalysts was proposed.

Free-standing and flexible 0D CeO2 nanodot/1D La(OH)3 nanofiber heterojunction net as a novel efficient and easily recyclable photocatalyst

Novel 0D CeO₂ nanodot/1D La(OH)₃ nanofiber heterojunction net with in-built Ce⁴⁺/Ce³⁺ redox centers was fabricated, which exhibits excellent photocatalytic performance and remarkable recoverability.

Novel La(OH)3-integrated sGO-Ag3VO4/Ag nanocomposite as a heterogeneous photocatalyst for fast degradation of agricultural and industrial pollutants

The composite described couples the benefits of hydroxyl radical formation from sunlight-inactive La(OH)₃ and strong sunlight absorption by Ag₃VO₄.

Vacancy induced photocatalytic activity of La doped In(OH)3 for CO2 reduction with water vapor

A possible mechanism to explain the impact of La doping on electron transfer process in wide band gap semiconductor In(OH)₃.

Ag loading induced visible light photocatalytic activity for pervoskite SrTiO3 nanofibers

The synthesis and photocatalytic activities of Ag-SrTiO₃ nanofibers were reported in this work. The fabricated Ag-SrTiO₃ nanofibers were characterized by TG-DSC, XRD, IR, XPS, SEM, TEM, DRS and ESR techniques. The XRD and IR results show that Ag-SrTiO₃ nanofibers have a perovskite structure after the heat treatment at 700°C. The XPS result shows that Ag element exists as Ag⁰ in the fabricated Ag-SrTiO₃ nanofibers. The SEM and TEM images indicate the obtaining of nanofibers with porous structure. The photocatalytic activity of Ag-SrTiO₃ nanofibers was evaluated by degrading RhB and MB under visible light irradiation. The Ag-SrTiO₃ nanofibers show excellent photocatalytic activity under visible light irradiation because of the surface plasmon resonance effect of Ag⁰. In the photocatalysis process of RhB and MB, lots of hydroxyl radicals were generated, which plays the key role in the decomposition of organic pollutants.

Unraveling the Mechanisms of Visible Light Photocatalytic NO Purification on Earth-Abundant Insulator-Based Core-Shell Heterojunctions

Earth-abundant insulators are seldom exploited as photocatalysts. In this work, we constructed a novel family of insulator-based heterojunctions and demonstrated their promising applications in photocatalytic NO purification, even under visible light irradiation. The heterojunction formed between the insulator SrCO₃ and the photosensitizer BiOI, via a special SrCO₃-BiOI core-shell structure, exhibits an enhanced visible light absorbance between 400-600 nm, and an unprecedentedly high photocatalytic NO removal performance. Further density functional theory (DFT) calculations and X-ray photoelectron spectroscopy (XPS) analysis revealed that the covalent interaction between the O 2p orbital of the insulator (SrCO₃, n-type) and the Bi 6p orbital of photosensitizer (BiOI, p-type) can provide an electron transfer channel between SrCO₃ and BiOI, allowing the transfer of the photoexcited electrons from the photosensitizer to the conduction band of insulator (confirmed by charge difference distribution analysis and time-resolved fluorescence spectroscopy). The •O₂^- and •OH radicals are the main reactive species in photocatalytic NO oxidation. A reaction pathway study based on both in situ FT-IR and molecular-level simulation of NO adsorption and transformation indicates that this heterojunction can efficiently transform NO to harmless nitrate products via the NO → NO⁺ and NO₂⁺ → nitrate or nitrite routes. This work provides numerous opportunities to explore earth-abundant insulators as visible-light-driven photocatalysts, and also offers a new mechanistic understanding of the role of gas-phase photocatalysis in controlling air pollution.

Synergistic effect of CoPi-hole and Cu(ii)-electron cocatalysts for enhanced photocatalytic activity and photoinduced stability of Ag3PO4

CoPi–Cu(ii)/Ag₃PO₄ not only exhibited much higher photocatalytic activity than Ag₃PO₄, Cu(ii)/Ag₃PO₄ and CoPi/Ag₃PO₄ but could also maintain excellently stable performance.

Pt quantum dots deposited on N-doped (BiO)2CO3: enhanced visible light photocatalytic NO removal and reaction pathway

The reaction pathway for visible light photocatalytic NO removal with Pt quantum dots/N-doped (BiO)₂CO₃ was revealed with in situ FT-IR and ESR spectroscopy.