Diffusion-driven and size-dependent phase changes of gallium oxide nanocrystals in a glassy host

Defect-assisted photocatalytic activity of glass-embedded gallium oxide nanocrystals

The use of glassceramics in photocatalysis is an attractive option for the realization of smart optical fibers and self-cleaning windows. Here we present the photocatalytic activity of germanosilicate glasses embedding Ga₂O₃ nanocrystals prepared by batch melting and glass heat treatment. The powdered material is used for UV-assisted degradation of rhodamine in water. The kinetics show changes after repeated experiments. In the first cycle, the apparent rate is governed by a second-order reaction with a Gaussian-like shape, whereas the second cycle follows a first-order reaction. The modification appears to be correlated with perturbations in the defect population. Photoluminescence has been used to monitor the evolution of such defects. Kinetic data on photoreactions and defect formation have been modelled in a combined frame in which the defect concentration determines the photocatalytic activity. The results prove the photocatalytic ability of the studied glassceramics. Moreover, the general validity of the kinetic model can be of interest for other systems in which the photocatalytic response depends on photoreactive species concentration.

Ethylene Dehydroaromatization over Ga-ZSM-5 Catalysts: Nature and Role of Gallium Speciation

Bifunctional catalysis in zeolites possessing both Brønsted and Lewis acid sites offers unique opportunities to tailor shape selectivity and enhance catalyst performance. Here, we examine the impact of framework and extra-framework gallium species on enriched aromatics production in zeolite ZSM-5. We compare three distinct methods of preparing Ga-ZSM-5 and reveal direct (single step) synthesis leads to optimal catalysts compared to post-synthesis methods. Using a combination of state-of-the-art characterization, catalyst testing, and density functional theory calculations, we show that Ga Lewis acid sites strongly favor aromatization. Our findings also suggest Ga(framework)-Ga(extra-framework) pairings, which can only be achieved in materials prepared by direct synthesis, are the most energetically favorable sites for reaction pathways leading to aromatics. Calculated acid site exchange energies between extra-framework Ga at framework sites comprised of either Al or Ga reveal a site-specific preference for stabilizing Lewis acids, which is qualitatively consistent with experimental measurements. These findings indicate the possibility of tailoring Lewis acid siting by the placement of Ga heteroatoms at distinct tetrahedral sites in the zeolite framework, which can have a marked impact on catalyst performance relative to conventional H-ZSM-5.

LiGa5O8:Cr-based theranostic nanoparticles for imaging-guided X-ray induced photodynamic therapy of deep-seated tumors

Using X-ray as the irradiation source, a photodynamic therapy process can be initiated from under deep tissues. This technology, referred to as X-ray induced PDT, or X-PDT, holds great potential to treat tumors at internal organs. To this end, one question is how to navigate the treatment to tumors with accuracy with external irradiation. Herein we address the issue with a novel, LiGa₅O₈: Cr (LGO:Cr)-based nanoscintillator, which emits persistent, near-infrared X-ray luminescence. This permits deep-tissue optical imaging that can be employed to guide irradiation. Specifically, we encapsulated LGO:Cr nanoparticles and a photosensitizer, 2,3-naphthalocyanine, into mesoporous silica nanoparticles. The nanoparticles were conjugated with cetuximab and systemically injected into H1299 orthotopic non-small cell lung cancer tumor models. The nanoconjugates can efficiently home to tumors in the lung, confirmed by monitoring X-ray luminescence from LGO:Cr. Guided by the imaging, external irradiation was applied, leading to efficient tumor suppression while minimally affecting normal tissues. To the best of our knowledge, the present study is the first to demonstrate, with systematically injected nanoparticles, that X-PDT can suppress growth of deep-seated tumors. The imaging guidance is also new to X-PDT, and is significant to the further transformation of the technology.

Donor-Acceptor Control in Grown-in-Glass Gallium Oxide Nanocrystals by Crystallization-driven Heterovalent Doping

Incorporation of doping ions in nanocrystals is a strategy for providing nanophases with functions directly related to ion features. At the nanoscale, however, doping can also activate more complex effects mediated by perturbation of the nanophase size and structure. Here, we report a paradigmatic case in which we modify grown-in-glass γ-Ga₂ O₃ nanophases by nickel or titanium doping of the starting glass, so as to control the concentration of oxygen and gallium vacancies responsible for the light emission. Optical absorption and luminescence show that Ni²⁺ and Ti⁴⁺ ions enter into the nanophase, but differential scanning calorimetry and X-ray diffraction indicate that Ni and Ti also work as modifiers of nanocrystal growth. As a result, doping influences nanocrystal size and concentration, which in turn dictate the number of donors and acceptors per nanocrystal. Finally, the chain of effects turns out to control both the intensity and spectral distribution of the light emission.