Tetracycline Removal through the Synergy of Catalysis and Photocatalysis by Novel NaYF4:Yb,Tm@TiO2-Acetylacetone Hybrid Core-Shell Structures

Novel hybrid core-shell structures, in which up-converting (UC) NaYF₄:Yb,Tm core converts near-infrared (NIR) to visible (Vis) light via multiphoton up-conversion processes, while anatase TiO₂-acetylacetonate (TiO₂-Acac) shell ensures absorption of the Vis light through direct injection of excited electrons from the highest-occupied-molecular-orbital (HOMO) of Acac into the TiO₂ conduction band (CB), were successfully synthesized by a two-step wet chemical route. Synthesized NaYF₄:Yb,Tm@TiO₂-Acac powders were characterized by X-ray powder diffraction, thermogravimetric analysis, scanning and transmission electron microscopy, diffuse-reflectance spectroscopy, Fourier transform infrared spectroscopy, and photoluminescence emission measurement. Tetracycline, as a model drug, was used to investigate the photocatalytic efficiencies of the core-shell structures under irradiation of reduced power Vis and NIR spectra. It was shown that the removal of tetracycline is accompanied by the formation of intermediates, which formed immediately after bringing the drug into contact with the novel hybrid core-shell structures. As a result, ~80% of tetracycline is removed from the solution after 6 h.

Direct Electron Transfer from Upconversion Graphene Quantum Dots to TiO2 Enabling Infrared Light-Driven Overall Water Splitting

Utilization of infrared light in photocatalytic water splitting is highly important yet challenging given its large proportion in sunlight. Although upconversion material may photogenerate electrons with sufficient energy, the electron transfer between upconversion material and semiconductor is inefficient limiting overall photocatalytic performance. In this work, a TiO₂/graphene quantum dot (GQD) hybrid system has been designed with intimate interface, which enables highly efficient transfer of photogenerated electrons from GQDs to TiO₂. The designed hybrid material with high photogenerated electron density displays photocatalytic activity under infrared light (20 mW cm⁻²) for overall water splitting (H₂: 60.4 μmol g_cat.⁻¹ h⁻¹ and O₂: 30.0 μmol g_cat.⁻¹ h⁻¹). With infrared light well harnessed, the system offers a solar-to-hydrogen (STH) efficiency of 0.80% in full solar spectrum. This work provides new insight into harnessing charge transfer between upconversion materials and semiconductor photocatalysts and opens a new avenue for designing photocatalysts toward working under infrared light.

Rare-Earth Doping in Nanostructured Inorganic Materials

Impurity doping is a promising method to impart new properties to various materials. Due to their unique optical, magnetic, and electrical properties, rare-earth ions have been extensively explored as active dopants in inorganic crystal lattices since the 18th century. Rare-earth doping can alter the crystallographic phase, morphology, and size, leading to tunable optical responses of doped nanomaterials. Moreover, rare-earth doping can control the ultimate electronic and catalytic performance of doped nanomaterials in a tunable and scalable manner, enabling significant improvements in energy harvesting and conversion. A better understanding of the critical role of rare-earth doping is a prerequisite for the development of an extensive repertoire of functional nanomaterials for practical applications. In this review, we highlight recent advances in rare-earth doping in inorganic nanomaterials and the associated applications in many fields. This review covers the key criteria for rare-earth doping, including basic electronic structures, lattice environments, and doping strategies, as well as fundamental design principles that enhance the electrical, optical, catalytic, and magnetic properties of the material. We also discuss future research directions and challenges in controlling rare-earth doping for new applications.

Upconversion luminescence detection of ascorbic acid based on NaGdF4:Yb,Er@NaYF4 nanoparticles and oxidase-like CoOOH nanoflakes

In this work, we developed a simple and selective luminescence sensing system for detecting ascorbic acid (AA) based on NaGdF₄:Yb,Er@NaYF₄ upconversion nanoparticles (UCNPs) and oxidase-like CoOOH nanoflakes. When p-phenylenediamine (PPD) and oxidase-like CoOOH nanoflakes were added to the UCNPs solutions, PPD, as a typical substrate of oxidase, could be oxidized to PPDox. The luminescence intensity of UCNPs was quenched because PPDox could play a role as an energy acceptor. When AA was added to the above solution mixture, the CoOOH nanoflakes were destroyed, and then, the luminescence intensity was recovered. Under the best experimental conditions, the linear range for detection of AA was 0.8 to 280 μM, and the detection limit was 0.25 μM. Furthermore, the system could be applied to real sample analysis with satisfactory results.

980 nm NIR light driven overall water splitting over a combined CdS–RGO–NaYF4–Yb3+/Er3+ photocatalyst

Infrared light (NIR) accounts for more than 50% of the energy donated by the Sun to the Earth, but most of this type of energy is not utilized in photocatalytic reactions.

Detoxification of DON by photocatalytic degradation and quality evaluation of wheat

Deoxynivalenol (DON) is regarded as the most common contaminant of cereal grains. Therefore, finding an efficient and safe detoxification technology is of great significance in the field of food. In this study, upconversion nanoparticles@TiO2 composites were used for the photocatalytic degradation of DON in wheat. The effect of photocatalytic oxidation on wheat quality was also evaluated by studying the basic physical and chemical indexes of wheat. The results showed that the removal rate of DON in wheat could reach 72.8% within 90 min when the dosage of photocatalyst UCNP@TiO2 was 8 mg mL-1 and the ratio of wheat to liquid was 1 : 2. In addition, the composites can be easily removed by washing, thus ensuring the low exposure dose of the nanomaterials in wheat. Studies on the nutritional quality of wheat showed that photocatalytic technology had little effect on the starch, protein, amino acid content of wheat (p > 0.05). The whiteness of wheat flour decreased and the yellowness increased. The scanning electron microscopy (SEM) images of wheat starch showed that the surfaces of starch granules were damaged to varying degrees with the prolongation of illumination time. Meanwhile, the fatty acid value and wet gluten content and pasting properties of wheat decreased significantly during photocatalysis (p < 0.05). This study demonstrates that photocatalytic degradation will have a promising prospect in toxin removal.

Recent Advances in Magnetic Upconversion Nanocomposites for Bioapplications

The combination of magnetism and upconversion luminescent property into one single nanostructure is fascinating for biological fields, such as multimodal bioimaging, targeted drug delivery, and imaging-guided therapy. In this review, we will provide the state-of-the-art advances on magnetic upconversion nanocomposites towards their bioapplications. Their structure design, synthesis methods, surface engineering and applications in bioimaging, drug delivery, therapy as well as biodetection will be covered.

Core-Shell NaHoF4@TiO2 NPs: A Labeling Method to Trace Engineered Nanomaterials of Ubiquitous Elements in the Environment

Understanding the fate and behavior of nanoparticles (NPs) in the natural environment is important to assess their potential risk. Single particle inductively coupled plasma mass spectrometry (spICP-MS) allows for the detection of NPs at extremely low concentrations, but the high natural background of the constituents of many of the most widely utilized nanoscale materials makes accurate quantification of engineered particles challenging. Chemical doping, with a less naturally abundant element, is one approach to address this; however, certain materials with high natural abundance, such as TiO₂ NPs, are notoriously difficult to label and differentiate from natural NPs. Using the low abundance rare earth element Ho as a marker, Ho-bearing core -TiO₂ shell (NaHoF₄@TiO₂) NPs were designed to enable the quantification of engineered TiO₂ NPs in real environmental samples. The NaHoF₄@TiO₂ NPs were synthesized on a large scale (gram), at relatively low temperatures, using a sacrificial Al(OH)₃ template that confines the hydrolysis of TiF₄ within the space surrounding the NaHoF₄ NPs. The resulting NPs consist of a 60 nm NaHoF₄ core and a 5 nm anatase TiO₂ shell, as determined by TEM, STEM-EDX mapping, and spICP-MS. The NPs exhibit excellent detectability by spICP-MS at extremely low concentrations (down to 1 × 10^-3 ng/L) even in complex natural environments with high Ti background.

Decorating Ag3PO4 nanodots on mesoporous silica-functionalized NaYF4:Yb,Tm@NaLuF4 for efficient sunlight-driven photocatalysis: synergy of broad spectrum absorption and pollutant adsorption-enrichment

A broad-spectrum photocatalyst with pollutant-adsorption capability was synthesized by decorating silver orthophosphate nanodots on mesoporous silica-functionalized upconversion nanoparticles for efficient natural sunlight-driven photocatalysis.

Visible-to-NIR Photon Harvesting: Progressive Engineering of Catalysts for Solar-Powered Environmental Purification and Fuel Production

Utilization of diffusive solar energy through photocatalytic processes for environmental purification and fuel production has long been pursued. However, efficient capture of visible-near-infrared (NIR) photons, especially for those with wavelengths longer than 600 nm, is a demanding quest in photocatalysis owing to their relatively low energy. In recent years, benefiting from the advances in photoactive material design, photocatalytic reaction system optimization, and new emerging mechanisms for long-wavelength photon activation, increasing numbers of studies on the harnessing of visible-NIR light for solar-to-chemical energy conversion have been reported. Here, the aim is to comprehensively summarize the progress in this area. The main strategies of the long-wavelength visible-NIR photon capture and the explicitly engineered material systems, i.e., narrow optical gap, photosensitizers, upconversion, and photothermal materials, are elaborated. In addition, the advances in long-wavelength light-driven photo- and photothermal-catalytic environmental remediation and fuel production are discussed. It is anticipated that this review presents the forefront achievements in visible-NIR photon capture and at the same time promotes the development of novel visible-NIR photon harnessing catalysts toward efficient solar energy utilization.