Conspectus From size-dependent luminescence to localized surface plasmon resonances, the optical properties that emerge from common materials with nanoscale dimensions have been revolutionary. As ...nanomaterials get smaller, they approach molecular electronic structures, and this transition from bulk to molecular electronic properties is a subject of far-reaching impact. One class of nanomaterials that exhibit particularly interesting optoelectronic features at this size transition are coinage metal (i.e., group 11 elements copper, silver, and gold) nanoparticles with core diameters between approximately 1 to 3 nm (∼25–200 atoms). Coinage metal nanoparticles can exhibit red or near-infrared photoluminescence features that are not seen in either their molecular or larger nanoscale counterparts. This emission has been exploited both as a probe of electronic behavior at the nanoscale as well as in critical applications such as biological imaging and chemical sensing. Interestingly, it has been demonstrated that their photoluminescence figures of merit such as emission quantum yield, energy, and lifetime are largely independent of particle diameter. Instead, emission from particles at this size range depends heavily on the particle surface chemistry, which includes both its metallic composition and the capping ligand architecture. The strong influence of surface chemistry on these emergent optoelectronic phenomena has powerful implications for both the study and use of these particles, primarily due to the theoretically limitless possible surface ligand architectures and metallic compositions. In this Account, we highlight recent work that studies and uses surface chemistry-mediated photoluminescence from coinage metal nanoparticles. Specifically, we emphasize the distinct, as well as synergistic, roles of the nanoparticle capping ligand and the nanoparticle core for controlling and/or enhancing their near-infrared photoluminescence. We then discuss the implications of surface chemistry-mediated photoluminescence as it relates to downstream applications such as energy transfer, sensing, and biological imaging. We conclude by discussing current challenges that remain in the field, including opportunities to develop new particle synthetic routes, analytical tools, and physical frameworks with which to understand small nanoparticle emission. Taken together, we anticipate that these materials will be foundational both in understanding the unique transition from molecular to bulk electronic structures and in the development of nanomaterials that leverage this transition.
We use nuclear magnetic resonance spectroscopy methods to quantify the extent of ligand exchange between different types of thiolated molecules on the surface of gold nanoparticles. Specifically, we ...determine ligand density values for single-moiety ligand shells and then use these data to describe ligand exchange behavior with a second, thiolated molecule. Using these techniques, we identify trends in gold nanoparticle functionalization efficiency with respect to ligand type, concentration, and reaction time as well as distinguish between functionalization pathways where the new ligand may either replace the existing ligand shell (exchange) or add to it (“backfilling”). Specifically, we find that gold nanoparticles functionalized with thiolated macromolecules, such as poly(ethylene glycol) (1 kDa), exhibit ligand exchange efficiencies ranging from 70% to 95% depending on the structure of the incoming ligand. Conversely, gold nanoparticles functionalized with small-molecule thiolated ligands exhibit exchange efficiencies as low as 2% when exposed to thiolated molecules under identical exchange conditions. Taken together, the reported results provide advances in the fundamental understanding of mixed ligand shell formation and will be important for the preparation of gold nanoparticles in a variety of biomedical, optoelectronic, and catalytic applications.
The syntheses, properties, and broad utility of noble metal plasmonic nanomaterials are now well-established. To capitalize on this exceptional utility, mitigate its cost, and potentially expand it, ...non-noble metal plasmonic materials have become a topic of widespread interest. As new plasmonic materials come online, it is important to understand and assess their ability to generate comparable or complementary plasmonic properties to their noble metal counterparts, including as both sensing and photoredox materials. Here, we study plasmon-driven chemistry on degenerately doped copper selenide (Cu2–x Se) nanoparticles. In particular, we observe plasmon-driven dimerization of 4-nitrobenzenethiol to 4,4′-dimercaptoazobenzene on Cu2–x Se surfaces with yields comparable to those observed from noble metal nanoparticles. Overall, our results indicate that doped semiconductor nanoparticles are promising for light-driven chemistry technologies.
What are the effects of perceiving peers' higher performance? Social-cognitive theory emphasizes the positive influence that perceiving higher performers can have on observer task and job performance ...(because observational learning from role models enhances self-efficacy). Social comparison theory emphasizes the negative self-evaluations that accompany perceiving higher performers, which should under many circumstances reduce self-efficacy and subsequent task and job performance. To more fully understand the effects of perceiving higher performance, we argue the effects of perceived higher performers on observer task and job performance depend on individuals' disposition in how they cognitively process coworkers' performance. Drawing on goal orientation theory, we suggest individuals with higher levels of performance prove goal orientation (PPGO) primarily interpret perceived higher performers as comparative referents rather than as instructive role models, inhibiting social learning and reducing self-efficacy. Results from a 2 studies (a field study of 110 corporate employees as well as an experimental study with 107 undergraduate students) support these ideas: Individuals with higher levels of PPGO have decreased self-efficacy and performance when observing higher performing coworkers, and individuals with lower levels of PPGO have increased self-efficacy and performance when observing higher performing coworkers.
Rare earth elements (REEs) are widely used in high-performance technologies including wind turbine magnets, electric vehicle batteries, lighting displays, circuitry, and national defense systems. A ...combination of projected increasing demand for REEs, monopolistic economic conditions, and environmental hazards associated with the mining and separation of REEs has led to significant interest in recovering REEs from alternative sources such as coal waste streams. However, rapidly locating high-value waste streams in the field remains a significant challenge primarily because of slow analytical methods, and existing techniques with low limits of detection such as inductively-coupled plasma mass spectrometry suffer from high equipment and operating costs and a lack of portability. Alternatively, luminescence-based sensors for REEs present a potential path for sensitive, portable, low-cost detection. The development and design of materials suitable for the luminescence-based detection of REEs are crucial to realizing this potential. Here, we review a broad range of materials used (or that have the potential to be used) for REE luminescence-based detection, including organic compounds, biomolecules, polymers, metal complexes, nanoparticles, and metal-organic frameworks. A general overview of REE optoelectronic properties and luminescent sensing protocols is first presented, followed by analyses of material-specific sensing mechanisms, emphasizing sensing figures of merit including sensitivity, selectivity, reusability and portability. The review concludes with a discussion of remaining barriers to luminescent REE sensing, how each sensor class may be best deployed, and directions for future material and spectrometer design. Taken together, this review provides a broad overview of sensing materials and methods that should be foundational for the continued development of high-performance sensors.
A range of materials are evaluated for their ability to detect and quantify rare earth elements
via
luminescence techniques.
Colloidal inorganic nanoparticles are being used in an increasingly large number of applications ranging from biological imaging to television displays. In all cases, nanoparticle surface chemistry ...can significantly impact particle physical properties, processing, and performance. The first step in leveraging this tunability is to develop analytical approaches to describe surface chemical features. Some of the most basic descriptors of particle surface chemistry include the quantity, identity, and arrangement of ligands appended to the particle core. Here, we review approaches to quantify molecular ligand densities on nanoparticle surfaces and consider fundamental barriers to the accuracy of this analysis including parameters such as dispersity in colloidal nanoparticle samples, particle-ligand interactions, and currently available analytical techniques. Techniques reviewed include widely studied methods such as optical, atomic, vibrational, and nuclear magnetic resonance spectroscopies as well as emerging or niche approaches including electrospray-differential mobility analysis, pH-based methods, and X-ray photoelectron spectroscopy. Collectively, these studies elucidate surface chemistry architectures that accelerate both fundamental understanding of nanoscale physical phenomena and the implementation of these materials in a wide range of technologies.
Rare earth elements (REEs) are critical to numerous technologies; however, a combination of increasing demand, environmental concerns, and monopolistic marketplace conditions has spurred interest in ...boosting the domestic REE production from sources such as coal utilization byproducts. The economic viability of this approach requires rapid, inexpensive, and sensitive analytical techniques capable of characterizing the REE content during resource exploration and downstream REE processing (e.g., analyzing REE separation, concentration, and purification production steps). Luminescence-based sensors are attractive because many REEs may be sensitized to produce element-specific emission. Hence, a single material may simultaneously detect and distinguish multiple REEs. Metal–organic frameworks (MOFs) can sensitize multiple REEs, but their viability has been hindered by sensitivity and selectivity challenges. Understanding how the MOF structure impacts the REE sensing efficacy is critical to the rational design of new sensors. Here, we evaluate the sensing performance of seven different anionic zinc-adeninate MOFs with different organic linkers and/or structures for the visible-emitting REEs Tb, Dy, Sm, and Eu. The choice of a linker determines which REEs are sensitized and significantly influences their sensitivity and selectivity against competing species (here, Fe(II) and HCl). For a given linker, structural changes to the MOF can further fine-tune the performance. The MOFs produce some of the lowest detection limits (sub-10 ppb for Tb) reported for the aqueous sensitization-based REE detection. Importantly, the most selective MOFs demonstrated the ability to sensitize the REE signal at sub-ppm levels in a REE-spiked acid mine drainage matrix, highlighting their potential for use in real-world sensing applications.
Small gold nanoparticles (∼1.4–2.2 nm core diameters) exist at an exciting interface between molecular and metallic electronic structures. These particles have the potential to elucidate fundamental ...physical principles driving nanoscale phenomena and to be useful in a wide range of applications. Here, we study the optoelectronic properties of aqueous, phosphine-terminated gold nanoparticles (core diameter = 1.7 ± 0.4 nm) after ligand exchange with a variety of sulfur-containing molecules. No emission is observed from these particles prior to ligand exchange, however the introduction of sulfur-containing ligands initiates photoluminescence. Further, small changes in sulfur substituents produce significant changes in nanoparticle photoluminescence features including quantum yield, which ranges from 0.13 to 3.65% depending on substituent. Interestingly, smaller ligands produce the most intense, highest energy, narrowest, and longest-lived emissions. Radiative lifetime measurements for these gold nanoparticle conjugates range from 59 to 2590 μs, indicating that even minor changes to the ligand substituent fundamentally alter the electronic properties of the luminophore itself. These results isolate the critical role of surface chemistry in the photoluminescence of small metal nanoparticles and largely rule out other mechanisms such as discrete (Au(I)SR) n impurities, differences in ligand densities, and/or core diameters. Taken together, these experiments provide important mechanistic insight into the relationship between gold nanoparticle near-infrared emission and pendant ligand architectures, as well as demonstrate the pivotal role of metal nanoparticle surface chemistry in tuning and optimizing emergent optoelectronic features from these nanostructures.
Metal-organic frameworks (MOFs) have been widely investigated as chemical sensing materials due to their periodic porosity, tunable chemical functionalities such as Lewis acid/base sites, potential ...conductivity and/or sensitive optical properties. However, most sensor devices require the integration of the sensing material as a thin film, which presents significant synthetic and stability challenges for MOF materials. In this review, we provide a background on why MOFs are excellent candidates for the chemical sensing of various analytes (
i.e.
gases, ions, pH), as well as different techniques for MOF thin film growth and the challenges associated with each method. Examples of different MOF thin film chemical sensor devices will be discussed, as well as their various transduction mechanisms: electrical, optical, and acoustic. The review concludes with an outlook on potential future innovations for MOF thin film chemical sensors, and the remaining challenges associated with real-world implementation.
This review discusses the fabrication, deployment, challenges, and future directions of metal-organic framework thin film sensing platforms, which are of particular interest due to their tunable porosity, chemical functionalities, optical and electrical properties.
Metal–organic frameworks (MOFs) are useful for thin film-based device integration as they show high adsorption capacity for selected gases. However, optimized device integration of MOFs for various ...platforms requires high-quality, well controlled thin film growth techniques that are flexible, scalable, and manufacturable. For this reason, there is a critical need for the ability to grow MOFs in the form of dense and uniform thin films efficiently on a wide range of substrates. In this work, copper benzene-1,3,5-tricarboxylate (Cu–BTC) MOF thin films are rapidly produced at room temperature by using a conductive aluminum-doped zinc oxide (AZO) as a seed layer to template Cu–BTC growth, with growth only occurring on the AZO layer via a hydroxy double salt intermediate. The formation pathway of the Cu–BTC films was investigated in detail because of the significant importance of improving the Cu–BTC film growth from the perspective of optimized device integration. We demonstrate that the structure of the resultant Cu–BTC film could be fine-tuned via alterations to the solvents used during growth conditions, pH, and the identity of the Cu salt anion. The technique described here is rapid, tunable, selective, and applicable to a variety of substrates.
PDF
