Plasmonic Coupling Architectures for Enhanced Photocatalysis

Ternary heterostructure-driven photoinduced electron-hole separation enhanced oxidative stress for triple-negative breast cancer therapy

Zinc oxide nanoparticles (ZnO NPs) stand as among the most significant metal oxide nanoparticles in trigger the formation of reactive oxygen species (ROS) and induce apoptosis. Nevertheless, the utilization of ZnO NPs has been limited by the shallowness of short-wavelength light and the constrained production of ROS. To overcome these limitations, a strategy involves achieving a red shift towards the near-infrared (NIR) light spectrum, promoting the separation and restraining the recombination of electron-hole (e--h+) pairs. Herein, the hybrid plasmonic system Au@ZnO (AZ) with graphene quantum dots (GQDs) doping (AZG) nano heterostructures is rationally designed for optimal NIR-driven cancer treatment. Significantly, a multifold increase in ROS generation can be achieved through the following creative initiatives: (i) plasmonic Au nanorods expands the photocatalytic capabilities of AZG into the NIR domain, offering a foundation for NIR-induced ROS generation for clinical utilization; (ii) elaborate design of mesoporous core-shell AZ structures facilitates the redistribution of electron-hole pairs; (iii) the incorporation GQDs in mesoporous structure could efficiently restrain the recombination of the e--h+ pairs; (iv) Modification of hyaluronic acid (HA) can enhance CD44 receptor mediated targeted triple-negative breast cancer (TNBC). In addition, the introduced Au NRs present as catalysts for enhancing photothermal therapy (PTT), effectively inducing apoptosis in tumor cells. The resulting HA-modified AZG (AZGH) exhibits efficient hot electron injection and e--h+ separation, affording unparalleled convenience for ROS production and enabling NIR-induced PDT for the cancer treanment. As a result, our well-designed mesoporous core-shell AZGH hybrid as photosensitizers can exhibit excellent PDT efficacy.

Integration of Co Single Atoms and Ni Clusters on Defect-Rich ZrO2 for Strong Photothermal Coupling Boosts Photocatalytic CO2 Reduction

We report a solvothermal method for the synthesis of an oxygen vacancy-enriched ZrO2 photocatalyst with Co single atoms and Ni clusters immobilized on the surface. This catalyst presents superior performance for the reduction of CO2 in H2O vapor, with a CO yield reaching 663.84 μmol g-1 h-1 and a selectivity of 99.52%. The total solar-to-chemical energy conversion efficiency is up to 0.372‰, which is among the highest reported values. The success, on one hand, depends on the Co single atoms and Ni clusters for both extended spectrum absorption and serving as dual-active centers for CO2 reduction and H2O dissociation, respectively; on the other hand, this is attributed to the enhanced photoelectric and thermal effect induced by concentrated solar irradiation. We demonstrate that an intermediate impurity state is formed by the hybridization of the d-orbital of single-atom Co with the molecular orbital of H2O, enabling visible-light-driven excitation over the catalyst. In addition, Ni clusters play a crucial role in altering the adsorption configuration of CO2, with the localized surface plasmon resonance effect enhancing the activation and dissociation of CO2 induced by visible-near-infrared light. This study provides valuable insights into the synergistic effect of the dual cocatalyst toward both efficient photothermal coupling and surface redox reactions for solar CO2 reduction.

Polydopamine-based plasmonic nanocomposites: rational designs and applications

Taking advantage of its adhesive nature and chemical reactivity, polydopamine (PDA) has recently been integrated with plasmonic nanoparticles to yield unprecedented hybrid nanostructures. With advanced architectures and optical properties, PDA-based plasmonic nanocomposites have showcased their potential in a wide spectrum of plasmon-driven applications, ranging from catalysis and chemical sensing, to drug delivery and photothermal therapy. The rational design of PDA-based plasmonic nanocomposites entails different material features of PDA and necessitates a thorough understanding of the sophisticated PDA chemistry; yet, there is still a lack of a systematic review on their fabrication strategies, plasmonic properties, and applications. In this Highlight review, five representative types of PDA-based plasmonic nanocomposites will be featured. Specifically, their design principles, synthetic strategies, and optical behaviors will be elucidated with an emphasis on the irreplaceable roles of PDA in the synthetic mechanisms. Together, their essential functions in diverse applications will be outlined. Lastly, existing challenges and outlooks on the rational design and assembly of next-generation PDA-based plasmonic nanocomposites will be presented. This Highlight review aims to provide synthetic insights and hints to inspire and aid researchers to innovate PDA-based plasmonic nanocomposites.

Solar-Driven Continuous CO2 Reduction to CO and CH4 using Heterogeneous Photothermal Catalysts: Recent Progress and Remaining Challenges

The urgent need to reduce the carbon dioxide level in the atmosphere and keep the effects of climate change manageable has brought the concept of carbon capture and utilization to the forefront of scientific research. Amongst the promising pathways for this conversion, sunlight-powered photothermal processes, synergistically using both thermal and non-thermal effects of light, have gained significant attention. Research in this field focuses both on the development of catalysts and continuous-flow photoreactors, which offer significant advantages over batch reactors, particularly for scale-up. Here, we focus on sunlight-driven photothermal conversion of CO2 to chemical feedstock CO and CH4 as synthetic fuel. This review provides an overview of the recent progress in the development of photothermal catalysts and continuous-flow photoreactors and outlines the remaining challenges in these areas. Furthermore, it provides insight in additional components required to complete photothermal reaction systems for continuous production (e. g., solar concentrators, sensors and artificial light sources). In addition, our review emphasizes the necessity of integrated collaboration between different research areas, like chemistry, material science, chemical engineering, and optics, to establish optimized systems and reach the full potential of this technology.

Fabrication of complexed nanostructure using AAO template for ultrasensitive SERS detection

In the study of surface-enhanced Raman scattering (SERS) processes, a simple and fast approach is needed to ensure the large-scale preparation of SERS substrates. This article uses anodic aluminum oxide (AAO) as a template to assemble gold nanoparticles (Au NPs) into an ordered array. By changing the pore size of AAO and silanizing the pores, the number and density of Au NPs entering the pores through liquid-liquid two-phase self-assembly (LLSA) can be effectively regulated. Using Rh6G (Rhodamine 6G) and CV (Crystal Violet) molecules as probe molecules, substrate sensitivity was evaluated with an enhancement factor of up to 6.34 × 107. In addition, the uniformity of the substrate is good, with a relative standard deviation (RSD) of 9.94%, and the logarithmic concentration and the Raman signal presented significant linear correlations R2 was 0.997 and 0.985, respectively. The detection limit of the substrate for APM (aspartame) as a solvent is as low as 0.0078 g/L. Finally, the substrate was subjected to high sensitivity testing on two types of beverages containing APM sold, proving the practicality of the substrate. It is expected to achieve simple and rapid detection in food additive trace detection in the future.

Dual-Plasmon Resonance Coupling Promoting Directional Photosynthesis of Nitrate from Air

Photocatalysis, particularly plasmon-mediated photocatalysis, offers a green and sustainable approach for direct nitrogen oxidation into nitrate under ambient conditions. However, the unsatisfactory photocatalytic efficiency caused by the limited localized electromagnetic field enhancement and short hot carrier lifetime of traditional plasmonic catalysts is a stumbling block to the large-scale application of plasmon photocatalytic technology. Herein, we design and demonstrate the dual-plasmonic heterojunction (Bi/Csx WO3 ) achieves efficient and selective photocatalytic N2 oxidation. The yield of NO3 - over Bi/Csx WO3 (694.32 μg g-1  h-1 ) are 2.4 times that over Csx WO3 (292.12 μg g-1  h-1 ) under full-spectrum irradiation. The surface dual-plasmon resonance coupling effect generates a surge of localized electromagnetic field intensity to boost the formation efficiency and delay the self-thermalization of energetic hot carriers. Ultimately, electrons participate in the formation of ⋅O2 - , while holes involve in the generation of ⋅OH and the activation of N2 . The synergistic effect of multiple reactive oxygen species drives the direct photosynthesis of NO3 - , which achieves the overall-utilization of photoexcited electrons and holes in photocatalytic reaction. The concept that the dual-plasmon resonance coupling effect facilitates the directional overall-utilization of photoexcited carriers will pave a new way for the rational design of efficient photocatalytic systems.

Promises of Plasmonic Antenna-Reactor Systems in Gas-Phase CO2 Photocatalysis

Sunlight-driven photocatalytic CO2 reduction provides intriguing opportunities for addressing the energy and environmental crises faced by humans. The rational combination of plasmonic antennas and active transition metal-based catalysts, known as "antenna-reactor" (AR) nanostructures, allows the simultaneous optimization of optical and catalytic performances of photocatalysts, and thus holds great promise for CO2 photocatalysis. Such design combines the favorable absorption, radiative, and photochemical properties of the plasmonic components with the great catalytic potentials and conductivities of the reactor components. In this review, recent developments of photocatalysts based on plasmonic AR systems for various gas-phase CO2 reduction reactions with emphasis on the electronic structure of plasmonic and catalytic metals, plasmon-driven catalytic pathways, and the role of AR complex in photocatalytic processes are summarized. Perspectives in terms of challenges and future research in this area are also highlighted.

Recent Advances in Phase-Engineered Photocatalysts: Classification and Diversified Applications

Phase engineering is an emerging strategy for tuning the electronic states and catalytic functions of nanomaterials. Great interest has recently been captured by phase-engineered photocatalysts, including the unconventional phase, amorphous phase, and heterophase. Phase engineering of photocatalytic materials (including semiconductors and cocatalysts) can effectively affect the light absorption range, charge separation efficiency, or surface redox reactivity, resulting in different catalytic behavior. The applications for phase-engineered photocatalysts are widely reported, for example, hydrogen evolution, oxygen evolution, CO₂ reduction, and organic pollutant removal. This review will firstly provide a critical insight into the classification of phase engineering for photocatalysis. Then, the state-of-the-art development of phase engineering toward photocatalytic reactions will be presented, focusing on the synthesis and characterization methodologies for unique phase structure and the correlation between phase structure and photocatalytic performance. Finally, personal understanding of the current opportunities and challenges of phase engineering for photocatalysis will also be provided.

Active Site Engineering on Plasmonic Nanostructures for Efficient Photocatalysis

Plasmonic nanostructures have shown immense potential in photocatalysis because of their distinct photochemical properties associated with tunable photoresponses and strong light-matter interactions. The introduction of highly active sites is essential to fully exploit the potential of plasmonic nanostructures in photocatalysis, considering the inferior intrinsic activities of typical plasmonic metals. This review focuses on active site-engineered plasmonic nanostructures with enhanced photocatalytic performance, wherein the active sites are classified into four types (i.e., metallic sites, defect sites, ligand-grafted sites, and interface sites). The synergy between active sites and plasmonic nanostructures in photocatalysis is discussed in detail after briefly introducing the material synthesis and characterization methods. Active sites can promote the coupling of solar energy harvested by plasmonic metal to catalytic reactions in the form of local electromagnetic fields, hot carriers, and photothermal heating. Moreover, efficient energy coupling potentially regulates the reaction pathway by facilitating the excited state formation of reactants, changing the status of active sites, and creating additional active sites using photoexcited plasmonic metals. Afterward, the application of active site-engineered plasmonic nanostructures in emerging photocatalytic reactions is summarized. Finally, a summary and perspective of the existing challenges and future opportunities are presented. This review aims to deliver some insights into plasmonic photocatalysis from the perspective of active sites, expediting the discovery of high-performance plasmonic photocatalysts.

Plasmonic Metal Mediated Charge Transfer in Stacked Core-Shell Semiconductor Heterojunction for Significantly Enhanced CO2 Photoreduction

Construction of core-shell semiconductor heterojunctions and plasmonic metal/semiconductor heterostructures represents two promising routes to improved light harvesting and promoted charge separation, but their photocatalytic activities are respectively limited by sluggish consumption of charge carriers confined in the cores, and contradictory migration directions of plasmon-induced hot electrons and semiconductor-generated electrons. Herein, a semiconductor/metal/semiconductor stacked core-shell design is demonstrated to overcome these limitations and significantly boost the photoactivity in CO₂  reduction. In this smart design, sandwiched Au serves as a "stone", which "kills two birds" by inducing localized surface plasmon resonance for hot electron generation and mediating unidirectional transmission of conduction band electrons and hot electrons from TiO₂  core to MoS₂  shell. Meanwhile, upward band bending of TiO₂  drives core-to-shell migration of holes through TiO₂ -MoS₂  interface. The co-existence of TiO₂  → Au → MoS₂  electron flow and TiO₂  → MoS₂  hole flow contributes to spatial charge separation on different locations of MoS₂  outer layer for overall redox reactions. Additionally, reduction potential of photoelectrons participating in the CO₂  reduction is elaborately adjusted by tuning the thickness of MoS₂  shell, and thus the product selectivity is delicately regulated. This work provides fresh hints for rationally controlling the charge transfer pathways toward high-efficiency CO₂  photoreduction.

PdAu Nanosheets for Visible-Light-Driven Suzuki Cross-Coupling Reactions

Combining a two-dimensional (2D) morphology and plasmonic photocatalysis represents an efficient design for light-driven organic transformations. We report a one-pot synthesis of surfactant templated PdAu nanosheets (NSs). Transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) analyses show the formation of 2D PdAu structures was initiated through nanoparticle seeds dispersed in the alkyl ammonium salt surfactant which acted as a template for the growth into NSs. The PdAu NSs were used for visible-light-enhanced Suzuki cross coupling. The PdAu bimetallic NSs outperformed monometallic Pd NSs and commercial Pd/C in room-temperature Suzuki cross-coupling reactions. The high catalytic activity is attributed to a combination of the 2D morphology giving rise to plasmon-enhanced catalysis and a high density of surface atoms, the electron-rich Pd surface due to alloying, and the presence of weakly bound amines. A comparative study of surfactant-assisted NSs and CO-assisted NSs was also carried out to assess the influence of surface ligands on the catalytic and photocatalytic enhancement of NSs with similar morphology. The surfactant-assisted NSs showed substantially superior performance compared to the CO-assisted for room-temperature Suzuki coupling reactions.

Solar Energy Catalysis

When it comes to using solar energy to promote catalytic reactions, photocatalysis technology is the first choice. However, sunlight can not only be directly converted into chemical energy through a photocatalytic process, it can also be converted through different energy-transfer pathways. Using sunlight as the energy source, photocatalytic reactions can proceed independently, and can also be coupled with other catalytic technologies to enhance the overall catalytic efficiency. Therefore, sunlight-driven catalytic reactions are diverse, and need to be given a specific definition. We propose a timely perspective for catalytic reactions driven by sunlight and give them a specific definition, namely "solar energy catalysis". The concept of different types of solar energy catalysis, such as photocatalysis, photothermal catalysis, solar cell powered electrocatalysis, and pyroelectric catalysis, are highlighted. Finally, their limitations and future research directions are discussed.

Plasmonic All-Frame-Faceted Octahedral Nanoframes with Eight Engraved Y-Shaped Hot Zones

We report the synthesis of all-frame-faceted octahedral nanoframes containing eight Y-shaped hot zones in a single entity where electromagnetic near-field focusing can be maximized. To realize such state-of-the-art complex nanoframes, a series of multiple stepwise bottom-up processes were executed by exploiting Au octahedral nanoparticles as the initial template. By rationally controlling the chemical reactivity of different surface facets (i.e., vertexes, edges, and terraces), the Au octahedral nanoparticles went through controlled shape transformations, leading to Au-engraved nanoparticles wherein 24 edges wrap the octahedral Au nanoparticle core. Those edges were then selectively decorated with Pt, leading to the formation of eight Pt tripods in a single entity. After etching the central Au, 3D Pt tripod frame-faceted octahedral nanoframes were achieved with high integrity. By harnessing the obtained Pt nanoframes as a scaffold, AuAg alloy-based plasmonic all-frame-faceted nanoframes were obtained after the co-reduction of Ag and Au, which generated multiple hot zones within multiple surface intra-nanogaps, creating a single-particle, surface-enhanced Raman spectroscopy enhancer platform.

Nanoscale thermoplasmonic welding

Establishing direct, close contact between individual nano-objects is crucial to fabricating hierarchical and multifunctional nanostructures. Nanowelding is a technical prerequisite for successfully manufacturing such structures. In this paper, we review the nanoscale thermoplasmonic welding with a focus on its physical mechanisms, key influencing factor, and emerging applications. The basic mechanisms are firstly described from the photothermal conversion to self-limited heating physics. Key aspects related to the welding process including material scrutinization, nanoparticle geometric and spatial configuration, heating scheme and performance characterization are then discussed in terms of the distinctive properties of plasmonic welding. Based on the characteristics of high precision and flexible platform of thermoplasmonic welding, the potential applications are further highlighted from electronics and optics to additive manufacturing. Finally, the future challenges and prospects are outlined for future prospects of this dynamic field. This work summarizes these innovative concepts and works on thermoplasmonic welding, which is significant to establish a common link between nanoscale welding and additive manufacturing communities.

Recent Progress in the Development of MOF-Based Photocatalysts for the Photoreduction of Cr(VI)

There has been a direct correlation between the rate of industrial development and the spread of pollution on Earth, particularly in the last century. The organic and inorganic pollutants generated from industrial activities have created serious risks to human life and the environment. The concept of sustainability has emerged to tackle the environmental issues in developing chemical-based industries. However, pollutants have continued to be discharged to water resources, and finding appropriate techniques for the removal and remedy of wastewater is in high demand. Chromium is one of the high-risk heavy metals in industrial wastewaters that should be removed via physical adsorption and/or transformed into less hazardous chemicals. Photocatalysis as a sustainable process has received considerable attention as it utilizes sunlight irradiation to remedy Cr^(VI) via a cost-effective process. Numerous photocatalytic systems have been developed up to now, but metal-organic frameworks (MOFs) have gained growing attention because of their unique versatilities and facile structural modulations. A variety of MOF-based photocatalysts have been widely employed for the photoreduction of Cr^(VI). Here, we review the recent progress in the design of MOF photocatalysts and summarize their performance in photoreduction reactions.

Plasmonic catalysis with designer nanoparticles

Catalysis is central to a more sustainable future and a circular economy. If the energy required to drive catalytic processes could be harvested directly from sunlight, the possibility of replacing contemporary processes based on terrestrial fuels by the conversion of light into chemical energy could become a step closer to reality. Plasmonic catalysis is currently at the forefront of photocatalysis, enabling one to overcome the limitations of "classical" wide bandgap semiconductors for solar-driven chemistry. Plasmonic catalysis enables the acceleration and control of a variety of molecular transformations due to the localized surface plasmon resonance (LSPR) excitation. Studies in this area have often focused on the fundamental understanding of plasmonic catalysis and the demonstration of plasmonic catalytic activities towards different reactions. In this feature article, we discuss recent contributions from our group in this field by employing plasmonic nanoparticles (NPs) with controllable features as model systems to gain insights into structure-performance relationships in plasmonic catalysis. We start by discussing the effect of size, shape, and composition in plasmonic NPs over their activities towards LSPR-mediated molecular transformations. Then, we focus on the effect of metal support interactions over activities, reaction selectivity, and reaction pathways. Next, we shift to the control over the structure in hollow NPs and nanorattles. Inspired by the findings from these model systems, we demonstrate a design-driven strategy for the development of plasmonic catalysts based on plasmonic-catalytic multicomponent NPs for two types of molecular transformations: the selective hydrogenation of phenylacetylene and the oxygen evolution reaction. Finally, future directions, challenges, and perspectives in the field of plasmonic catalysis with designer NPs are discussed. We believe that the examples and concepts presented herein may inspire work and progress in plasmonic catalysis encompassing the design of plasmonic multicomponent materials, new strategies to control reaction selectivity, and the unraveling of stability and reaction mechanisms.