Plasmonic behaviour and plasmon-induced charge separation of nanostructured MoO3-x under near infrared irradiation

Understanding Metal-Semiconductor Plasmonic Resonance Coupling through Surface-Enhanced Raman Scattering

Although there has been intense research on plasmon-induced charge transfer within metal/semiconductor heterostructures, previous studies have all focused on the surface plasmonic resonance (SPR) of only noble metals. Herein and for the first time, we observe and take into account the plasmonic coupling between SPR of both noble-metal and semiconductor nanostructures. A W₁₈O₄₉/Ag heterostructure composed of metallic Ag nanoparticles (Ag NPs) and semiconducting W₁₈O₄₉ nanowires (W₁₈O₄₉ NWs) is designed and fabricated, which exhibits a broad and strong SPR absorption in the visible wavelength range. This SPR band is attributed to the SPR coupling between the SPR of both Ag NPs and W₁₈O₄₉ NWs. Surface-enhanced Raman scattering (SERS) is then used to reveal the interactions between the metal SPR, semiconductor SPR, and the heterostructure's charge transfer (CT) process, demonstrating that such coupled SPR enhanced the heterostructure's internal CT and SERS signals. Finally, we proposed a new coupled-plasmon-induced charge transfer mechanism to interpret the improved CT efficiency between the SERS substrate and molecules. Our work provides insight for further studies on plasmonic effects and interfacial charge transfer in metal/semiconductor heterostructures.

Plasmonic metal oxides and their biological applications

Metal oxides modified with dopants and defects are an emerging class of novel materials supporting the localized surface plasmon resonance across a wide range of optical wavelengths, which have attracted tremendous research interest particularly in biological applications in the past decade. Compared to conventional noble metal-based plasmonic materials, plasmonic metal oxides are particularly favored for their cost efficiency, flexible plasmonic properties, and improved biocompatibility, which can be important to accelerate their practical implementation. In this review, we first explicate the origin of plasmonics in dopant/defect-enabled metal oxides and their associated tunable localized surface plasmon resonance through the conventional Mie-Gans model. The research progress of dopant incorporation and defect generation in metal oxide hosts, including both in situ and ex situ approaches, is critically discussed. The implementation of plasmonic metal oxides in biological applications in terms of therapy, imaging, and sensing is summarized, in which the uniqueness of dopant/defect-driven plasmonics for inducing novel functionalities is particularly emphasized. This review may provide insightful guidance for developing next-generation plasmonic devices for human health monitoring, diagnosis and therapy.

Plasmonic Oxygen Defects in MO3- x (M = W or Mo) Nanomaterials: Synthesis, Modifications, and Biomedical Applications

Nanomedicine is a promising technology with many advantages and provides exciting opportunities for cancer diagnosis and therapy. During recent years, the newly developed oxygen-deficiency transition metal oxides MO_{3- x} (M = W or Mo) have received significant attention due to the unique optical properties, such as strong localized surface plasmon resonance (LSPR) , tunable and broad near-IR absorption, high photothermal conversion efficiency, and large X-ray attenuation coefficient. This review presents an overview of recent advances in the development of MO_{3- x} nanomaterials for biomedical applications. First, the fundamentals of the LSPR effect are introduced. Then, the preparation and modification methods of MO_{3- x} nanomaterials are summarized. In addition, the biological effects of MO_{3- x} nanomaterials are highlighted and their applications in the biomedical field are outlined. This includes imaging modalities, cancer treatment, and antibacterial capability. Finally, the prospects and challenges of MO_{3- x} and MO_{3- x} -based nanomaterial for fundamental studies and clinical applications are also discussed.

Current and future perspectives on catalytic-based integrated carbon capture and utilization

There exist several well-known methods with varying maturity for capturing carbon dioxide from emission sources of different concentrations, including absorption, adsorption, cryogenics and membrane separation, among others. The capture and separation steps can produce almost pure CO₂, but at substantial cost for being conditioned for transport and final utilization, with high economical risks to be considered. A possible way for the elimination of this conditioning and cost is direct CO₂ utilization, whether on-site in a further process but within the same plant, or in-situ, coupling both capture and conversion in the same unit. This approach is usually called integrated carbon capture and utilization (ICCU) or integrated carbon capture and conversion (ICCC), and has lately started receiving considerable attention in many circles. As CO₂ is already industrially employed in other sectors, such as food preservation, water treatment and conversion to high added-value chemicals and fuels such as methanol, methane, etc., among others, it is of great interest to explore the global ICCC approach. Catalytic-based processes play a key role in CO₂ conversion, and different technologies are gaining great attention from both academia and industry. However, the 'big picture of ICCU' and in which technology the efforts should focus on at large scale is still unclear. This review analyzes some promising concepts of ICCU specifically on CO₂ catalytic conversion, highlighting their current commercial relevance as well as challenges that have to be faced today and in the next future.

Ultrasensitive Sensing of Volatile Organic Compounds Using a Cu-Doped SnO2 -NiO p-n Heterostructure That Shows Significant Raman Enhancement*

Surface enhanced Raman scattering (SERS) based on chemical mechanism (CM) attracts tremendous attention for great selectivity and stability. However, low enhancement factor (EF) limits its practical applications for trace detection. Here, a novel sponge-like Cu-doping SnO₂ -NiO p-n semiconductor heterostructure (SnO₂ -NiO_x /Cu), was first created as a CM-based SERS substrate with a significant EF of 1.46×10¹⁰ . This remarkable EF was mainly attributed to the enhanced charge-separation efficacy of p-n heterojunction and charge transfer resonance resulted from Cu doping. Moreover, the porous structure enriched the probe molecules, resulting in further SERS signals magnification. By immobilizing CuPc as an inner-reference element, SnO₂ -NiO_x /Cu was developed as a SERS nose for selective recognition of multiple lung cancer related VOCs down to ppb level. The information of VOCs was recorded in a barcode, demonstrating practical potential of a desktop SERS device for biomarker screening.

Controlling the oxidation state of molybdenum oxide nanoparticles prepared by ionic liquid/metal sputtering to enhance plasmon-induced charge separation

Nanoparticles composed of molybdenum oxide, MoO x , were successfully prepared by room-temperature ionic liquid (RTIL)/metal sputtering followed by heat treatment. Hydroxyl groups in RTIL molecules retarded the coalescence between MoO x NPs during heat treatment at 473 K in air, while the oxidation state of Mo species in MoO x nanoparticles (NPs) could be modified by changing the heat treatment time. An LSPR peak was observed at 840 nm in the near-IR region for MoO x NPs of 55 nm or larger in size that were annealed in a hydroxyl-functionalized RTIL. Photoexcitation of the LSPR peak of MoO x NPs induced electron transfer from NPs to ITO electrodes.

Plasmonic hole ejection involved in plasmon-induced charge separation

Since the finding of plasmon-induced charge separation (PICS) at the interface between a plasmonic metal nanoparticle and a semiconductor, which has been applied to photovoltaics including photodetectors, photocatalysis including water splitting, sensors and data storage in the visible/near-infrared ranges, injection of hot electrons (energetic electrons) into semiconductors has attracted attention almost exclusively. However, it has recently been found that behaviours of holes are also important. In this review, studies on the hot hole ejection from plasmonic nanoparticles are described comprehensively. Hole ejection from plasmonic nanoparticles on electron transport materials including n-type semiconductors allows oxidation reactions to take place at more positive potentials than those involved in a charge accumulation mechanism. Site-selective oxidation is also one of the characteristics of the hole ejection and is applied to photoinduced nanofabrication beyond the diffraction limit. Hole injection into hole transport materials including p-type semiconductors (HTMs) in solid-state cells, hole ejection through a HTM for stabilization of holes, hole ejection to a HTM for efficient hot electron ejection, voltage up-conversion by the use of hot carriers and electrochemically assisted hole ejection are also described.

Formation of Surface Silver Nano-network Structures through Hot Electron Regulated Diffusion-limited Aggregation

A surface Ag nano-network pattern is formed by first depositing Ag nanoparticles (NPs) on a conductive template, which has a certain defect structure, and then illuminating the Ag NPs with ultraviolet (UV) light in a moist environment. Such an Ag nano-network pattern consists of multiple connected Brownian trees (BTs), which are produced through the diffusion-limited aggregation (DLA) process. In the DLA process, diffuse Ag⁺ ions, which are generated by UV light illumination and dissolved by a thin adsorbed water layer on the surfaces of the Ag NPs and used GaN template, settle to form a BT through the combination with excited hot electrons migrating into the template from the Ag NPs. The lateral transport of hot electrons in the template is regulated by the distributions of threading dislocation and point defect cluster in the template, which eventually become the centers of BTs. The structure of a surface Ag nano-network can potentially serve as a transparent conductor.

Energy transfer from Er to Nd ions by the thermal effect and promotion of the photocatalysis of the NaYF4:Yb,Er,Nd/W18O49 heterostructure

The NaYF4:Yb,Er/W18O49 heterostructure is an excellent photocatalyst that can promote H2 evolution by hydrolyzing BH3NH3 under near-infrared (NIR) light irradiation. At the same time, the photothermal effect can be produced in photocatalytic reactions, which will cause the luminescence efficiency and photocatalytic activity to decrease. Determining how to take advantage of that photothermal effect becomes a major problem. Moreover, the energy transfer (ET) process from Er ions to Nd ions in NaYF4 co-doped with Yb/Er/Nd ions (NaYF4:Yb,Er,Nd) occurred at high temperature. Herein, the NaYF4:Yb,Er,Nd/W18O49 quasi-core-shell heterostructure was designed to achieve better H2 production capacity; this heterostructure exhibits a 1.5-fold enhancement of photocatalytic activity for H2 evolution as compared with the NaYF4:Yb,Er/W18O49 heterostructure. This study provides a new way to explore the catalytic activities in the NIR field for application in the development of a sustainable energy source.

Plasmon-induced charge separation at the interface between ITO nanoparticles and TiO2 under near-infrared irradiation

Plasmon-induced charge separation (PICS) by continuous electron injection from plasmonic compound nanoparticles to a semiconductor was achieved by using solid-state cells based on tin-doped indium oxide (ITO) nanoparticles with a short capping agent and a TiO2 film. The cells extended the PICS range to longer wavelengths and exhibited photoresponses to 1500-2200 nm near-infrared light.

Growth behavior of Au/Cu2−xS hybrids and their plasmon-enhanced dual-functional catalytic activity

The growth behavior of Au/Cu_2−xS hybrids was investigated, and the obtained half-shell Au(nanospheres)/Cu_2−xS exhibited dual-plasmon enhanced bifunctional catalytic activity.