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There is a significant drive to identify alternative materials that exhibit room temperature phosphorescence for technologies including bio-imaging, photodynamic therapy and organic light-emitting diodes. Ideally, these materials should be non-toxic and cheap, and it will be possible to control their photoluminescent properties. This was achieved here by embedding carbon nanodots within crystalline particles of alkaline earth carbonates, sulphates and oxalates. The resultant nanocomposites are luminescent and exhibit a bright, sub-second lifetime afterglow. Importantly, the excited state lifetimes, and steady-state and afterglow colours can all be systematically controlled by varying the cations and anions in the host inorganic phase, due to the influence of the cation size and material density on emissive and non-emissive electronic transitions. This simple strategy provides a flexible route for generating materials with specific, phosphorescent properties and is an exciting alternative to approaches relying on the synthesis of custom-made luminescent organic molecules. Materials exhibiting room temperature phosphorescence (RTP) with short afterglow are desirable for bio-medical applications. Here the authors synthesise a library of compounds with tunable RTP properties, embedding carbon nanodots in non-toxic alkaline-earth carbonate, sulphate and oxalate hosts.

The nucleation of ice crystals in clouds is poorly understood, despite being of critical importance for our planet’s climate. Nucleation occurs largely at rare “active sites” present on airborne particles such as mineral dust, but the nucleation pathway is distinct under different meteorological conditions. These give rise to two key nucleation pathways where a particle is either immersed in a supercooled liquid water droplet (immersion freezing mode) or suspended in a supersaturated vapor (deposition mode). However, it is unclear if the same active sites are responsible for nucleation in these two modes. Here, we directly compare the sites that are active in these two modes by performing immersion freezing and deposition experiments on the same thin sections of two atmospherically important minerals (feldspar and quartz). For both substrates, we confirm that nucleation is dominated by a limited number of sites and show that there is little correlation between the two sets of sites operating in each experimental method: across both materials, only six out of 73 sites active for immersion freezing nucleation were also active for deposition nucleation. Clearly, different properties determine the activity of nucleation sites for each mode, and we use the pore condensation and freezing concept to argue that effective deposition sites have size and/or geometry requirements not of relevance to effective immersion freezing sites. Hence, the ability to nucleate is pathway dependent, and the mode of nucleation has to be explicitly considered when applying experimental data in cloud models.

Mineral dust particles are thought to be an important type of ice-nucleating particle (INP) in the mixed-phase cloud regime around the globe. While K-rich feldspar (K-feldspar) has been identified as being a particularly important component of mineral dust for ice nucleation, it has been shown that quartz is also relatively ice-nucleation active. Given quartz typically makes up a substantial proportion of atmospheric desert dust, it could potentially be important for cloud glaciation. Here, we survey the ice-nucleating ability of 10 α-quartz samples (the most common quartz polymorph) when immersed in microlitre supercooled water droplets. Despite all samples being α-quartz, the temperature at which they induce freezing varies by around 12 ∘C for a constant active site density. We find that some quartz samples are very sensitive to ageing in both aqueous suspension and air, resulting in a loss of ice-nucleating activity, while other samples are insensitive to exposure to air and water over many months. For example, the ice-nucleation temperatures for one quartz sample shift down by ∼2 ∘C in 1 h and 12 ∘C after 16 months in water. The sensitivity to water and air is perhaps surprising, as quartz is thought of as a chemically resistant mineral, but this observation suggests that the active sites responsible for nucleation are less stable than the bulk of the mineral. We find that the quartz group of minerals is generally less active than K-feldspars by roughly 7 ∘C, although the most active quartz samples are of a similar activity to some K-feldspars with an active site density, ns(T), of 1 cm−2 at −9 ∘C. We also find that the freshly milled quartz samples are generally more active by roughly 5 ∘C than the plagioclase feldspar group of minerals and the albite end member has an intermediate activity. Using both the new and literature data, active site density parameterizations have been proposed for freshly milled quartz, K-feldspar, plagioclase and albite. Combining these parameterizations with the typical atmospheric abundance of each mineral supports previous work that suggests that K-feldspar is the most important ice-nucleating mineral in airborne mineral dust.

Acidic macromolecules are traditionally considered key to calcium carbonate biomineralisation and have long been first choice in the bio-inspired synthesis of crystalline materials. Here, we challenge this view and demonstrate that low-charge macromolecules can vastly outperform their acidic counterparts in the synthesis of nanocomposites. Using gold nanoparticles functionalised with low charge, hydroxyl-rich proteins and homopolymers as growth additives, we show that extremely high concentrations of nanoparticles can be incorporated within calcite single crystals, while maintaining the continuity of the lattice and the original rhombohedral morphologies of the crystals. The nanoparticles are perfectly dispersed within the host crystal and at high concentrations are so closely apposed that they exhibit plasmon coupling and induce an unexpected contraction of the crystal lattice. The versatility of this strategy is then demonstrated by extension to alternative host crystals. This simple and scalable occlusion approach opens the door to a novel class of single crystal nanocomposites. Calcium carbonate biomineralisation has long been linked to acidic macromolecules. Here, the authors challenge this view and show that a huge number of gold nanoparticles coated with hydroxyl-rich proteins can be incorporated into a calcium carbonate crystal while maintaining single crystal character.

From biomineralization to synthesis, organic additives provide an effective means of controlling crystallization processes. There is growing evidence that these additives are often occluded within the crystal lattice. This promises an elegant means of creating nanocomposites and tuning physical properties. Here we use the incorporation of sulfonated fluorescent dyes to gain new understanding of additive occlusion in calcite (CaCO 3 ), and to link morphological changes to occlusion mechanisms. We demonstrate that these additives are incorporated within specific zones, as defined by the growth conditions, and show how occlusion can govern changes in crystal shape. Fluorescence spectroscopy and lifetime imaging microscopy also show that the dyes experience unique local environments within different zones. Our strategy is then extended to simultaneously incorporate mixtures of dyes, whose fluorescence cascade creates calcite nanoparticles that fluoresce white. This offers a simple strategy for generating biocompatible and stable fluorescent nanoparticles whose output can be tuned as required. Introducing organic guests to a crystal is a convenient way to tailor its properties. Here, the authors occlude fluorescent dyes within calcite to reveal that additives can occupy distinct zones of a crystal, and strategically embed green, blue, and red dyes to create white fluorescent calcite.

The study focuses on the preparation of electrostatically assembled layer‐by‐layer waterborne nanocoatings comprising negatively charged Nafion and positively charged imidazole modified‐graphene quantum dots (GQD‐Ims). We demonstrate here that Nafion/GQD‐Im nanocoatings can combat the growth of representative Gram‐positive and Gram‐negative bacteria, and their excellent antibacterial performance is preserved after prolonged thermal treatment, indicating that the coatings can withstand dry heat sterilization without any decline in their properties. At the same time, the coatings show remarkable chemical and structural stability, while offering protection against UV‐radiation as manifested by dye decomposition experiments. This novel type of nanocoatings demonstrates a unique combination of highly desirable characteristics, making them ideal candidates for applications related to active packaging for cosmetics and drugs, food processing, and disinfection of medical devices. Electrostatically assembled layer‐by‐layer waterborne nanocoatings comprising negatively charged Nafion and positively charged imidazole modified‐graphene quantum dots can inhibit the growth of bacteria and can withstand dry heat sterilization without any decline in their activity. In addition, the coatings show remarkable chemical and structural stability, while offering protection against UV‐radiation.

Mineral dust particles from wind-blown soils are known to act as effective ice nucleating particles in the atmosphere and are thought to play an important role in the glaciation of mixed phase clouds. Recent work suggests that feldspars are the most efficient nucleators of the minerals commonly present in atmospheric mineral dust. However, the feldspar group of minerals is complex, encompassing a range of chemical compositions and crystal structures. To further investigate the ice-nucleating properties of the feldspar group we measured the ice nucleation activities of 15 characterized feldspar samples. We show that alkali feldspars, in particular the potassium feldspars, generally nucleate ice more efficiently than feldspars in the plagioclase series which contain significant amounts of calcium. We also find that there is variability in ice nucleating ability within these groups. While five out of six potassium-rich feldspars have a similar ice nucleating ability, one potassium rich feldspar sample and one sodium-rich feldspar sample were significantly more active. The hyper-active Na-feldspar was found to lose activity with time suspended in water with a decrease in mean freezing temperature of about 16 °C over 16 months; the mean freezing temperature of the hyper-active K-feldspar decreased by 2 °C over 16 months, whereas the \"standard\" K-feldspar did not change activity within the uncertainty of the experiment. These results, in combination with a review of the available literature data, are consistent with the previous findings that potassium feldspars are important components of arid or fertile soil dusts for ice nucleation. However, we also show that there is the possibility that some alkali feldspars may have enhanced ice nucleating abilities, which could have implications for prediction of ice nucleating particle concentrations in the atmosphere.

Ice-nucleating particles (INPs) facilitate the heterogeneous freezing of cloud droplets and thus modify cloud properties. Hence, it is important to understand the sources of INPs. During the HyICE-2018 campaign, which took place in the boreal forest of Hyytiälä, substantial concentrations of airborne heat-sensitive biological INPs were observed, despite many potential biological sources of INPs being snow-covered. A potential source of INPs that were not covered in snow was lichens that grow on trees; hence, we investigated these lichens as a potential source of biological INPs in this boreal forest environment. INPs derived from lichen sampled during HyICE-2018 are shown to nucleate ice at temperatures as warm as −5 °C with 103 INPs per gram of lichen. Successive filtration to smaller sizes removes some of the most active INPs in suspension, but substantial activity remains, even when filtering to 0.1 µm. The small size of the INPs from lichen means they have the potential to either be emitted directly into the atmosphere or be associated with larger particles, such as lichenous reproductive aerosol types (spores or diaspores). We also show that the INPs from lichens from Hyytiälä are sensitive to heat, which is similar to the INPs sampled from the atmosphere of Hyytiälä and consistent with the presence of ice-active proteins. Adding to previous evidence of lichenous INPs, this study shows that lichens from a European boreal forest in Hyytiälä harbour INPs. This novel finding may be especially important in this snow-covered habitat where few, if any, other biological INP sources are available. The great terrestrial abundance of lichens in Hyytiälä, and around the world, calls for further research to combine their ice-nucleating ability with dispersal studies to evaluate the flux of lichenous INPs into the atmosphere, as well as to what extent these particles reach heights and locations where they might influence cloud properties.

How experienced college and university leaders guide successful institutions—and why they sometimes lose their way. Today's college and university leaders face complex problems that test their political acumen as well as their judgment, intellect, empathy, and ability to plan and improvise. How do they thoughtfully and creatively rise to the challenge? In Leading Colleges and Universities, editors Stephen Joel Trachtenberg, Gerald B. Kauvar, and E. Gordon Gee bring together a host of presidents and other leaders in higher education who describe how they dealt with the issues. Each contributor has been effective as a president or other significant leader in postsecondary education. In this book they share real-life examples and stories that illustrate how they have dealt with the challenges they encountered. Together they answer these and other core questions: • How do you manage college athletics, faculty, a governing board, donors, and a local community? • What do you need to know about crisis management and legal affairs? • When should you be outspoken in the media and when should you be quiet? The book does not shy away from hot contemporary issues, tackling such controversial matters as free speech, Title IX, athletics, fraternities, student and faculty diversity, and board relations. Presidents and would-be presidents—as well as boards, search committees, state boards, legislators, and others involved in higher education—will find much helpful guidance in this timely book.