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The slow kinetics of the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) in air cathodes severely limit the development of reversible zinc–air batteries. Thus, bifunctional oxygen catalysts with excellent electrocatalytic activity and durability for both the oxygen reduction and oxygen evolution reactions (ORR/OER) are keys to achieving long-term rechargeable zinc–air batteries. However, it remains challenging to further improve the performance by adding more active sites. To address this, a series of nitrogen-doped carbon (CN) with NiCo alloys has been synthesized by pyrolyzing a simple bimetal zeolitic-imidazolate framework (ZIF) and then evenly loaded with metallic Ru nanoparticles, resulting in Ru–NiCo/NC samples. Benefiting from the large pore volume and high activities, the Ru–NiCo/NC electrocatalysts exhibit higher ORR (E1/2 = 0.84 V) and OER performance with an overpotential of 342 mV at 10 mA cm−2, along with superior cycle stability. More significantly, when employed in rechargeable zinc–air batteries, Ru–NiCo/NC catalysts demonstrate a high power density of 132.3 mW cm−2, significantly outperforming Pt and Ru-based zinc–air batteries. Additionally, DFT (density functional theory) results indicate that the addition of Ru leads to a downshift of the d-band center from the Fermi level, which benefits the reduction of energy barriers and enhances the desorption of O-containing intermediates. This work provides a feasible strategy for developing efficient and high-performance bifunctional electrocatalysts. [ABSTRACT FROM AUTHOR]

The development and optimization of electrocatalysts is one of the key points to reduce the energy barrier of electrocatalytic water splitting and improve the kinetics of electrocatalytic reactions. It is necessary to develop low-cost, high-performance electrocatalysts with large-scale application prospects. In order to solve this problem, hybrid structured ZnCo2O4@Co3O4 nanowires are successfully synthesized through hydrothermal synthesis and electrodeposition. As electrocatalysts for water splitting, ZnCo2O4@Co3O4 can reach a current density of 50 mA cm−2 at an overpotential of 278 mV for the OER and 166 mV@−10 mA cm−2 for the HER, which could be higher than that of single ZnCo2O4 and Co3O4. At the same time, ZnCo2O4@Co3O4 samples also exhibit a cell voltage of 1.67 V at a high current density of 50 mA cm−2 and superior durability for 50 h. The fabricated product also showcases a specific capacitance of 1316 F g−1 at 1 A g−1. Additionally, the assembled device attains a maximum energy density of 47.3 W h kg−1 at a power density of 1126 W kg−1. Furthermore, density functional theory (DFT) calculation further confirms that the heterostructure can significantly promote Gibbs free energy for hydrogen adsorption. And the significant increase in the density of total states (DOS) also enhances the catalytic activity for the HER. [ABSTRACT FROM AUTHOR]

Fine-particle pollution associated with winter haze threatens the health of more than 400 million people in the North China Plain. The Multiphase chemistry experiment in Fogs and Aerosols in the North China Plain (McFAN) investigated the physicochemical mechanisms leading to haze formation with a focus on the contributions of multiphase processes in aerosols and fogs. We integrated observations on multiple platforms with regional and box model simulations to identify and characterize the key oxidation processes producing sulfate, nitrate and secondary organic aerosols. An outdoor twin-chamber system was deployed to conduct kinetic experiments under real atmospheric conditions in comparison to literature kinetic data from laboratory studies. The experiments were spanning multiple years since 2017 and an intensive field campaign was performed in the winter of 2018. The location of the site minimizes fast transition between clean and polluted air masses, and regimes representative for the North China Plain were observed at the measurement location in Gucheng near Beijing. The consecutive multi-year experiments document recent trends of PM2.5 pollution and corresponding changes of aerosol physical and chemical properties, enabling in-depth investigations of established and newly proposed chemical mechanisms of haze formation. This study is mainly focusing on the data obtained from the winter campaign 2018. To investigate multiphase chemistry, the results are presented and discussed by means of three characteristic cases: low humidity, high humidity and fog. We find a strong relative humidity dependence of aerosol chemical compositions, suggesting an important role of multiphase chemistry. Compared with the low humidity period, both PM1 and PM2.5 show higher mass fraction of secondary inorganic aerosols (SIA, mainly as nitrate, sulfate and ammonium) and secondary organic aerosols (SOA) during high humidity and fog episodes. The changes in aerosol composition further influence aerosol physical properties, e.g., with higher aerosol hygroscopicity parameter κ and single scattering albedo SSA under high humidity and fog cases. The campaign-averaged aerosol pH is 5.1 ± 0.9, of which the variation is mainly driven by the aerosol water content (AWC) concentrations. Overall, the McFAN experiment provides new evidence of the key role of multiphase reactions in regulating aerosol chemical composition and physical properties in polluted regions. [ABSTRACT FROM AUTHOR]

The efficiency of photodynamic therapy (PDT) is severely constrained due to the innate hypoxic environment, besides the elevated level of glutathione (GSH). To get rid of the hypoxic environment and higher concentrations of GSH in the solid tumors, we propose an approach of oxygen self-sufficient multimodal imaging-guided nanocomposite CaO2–MnO2–UCNPs–Ce6/DOX (abbreviated as CaMn–NUC), in which CaO2 nanoparticles in the hydrophobic layer were seated on the hydrophilic MnO2 sheet and conjugated with chlorin e6 (Ce6) loaded upconversion nanoparticles (UCNPs–Ce6) via the click chemistry approach. CaMn–NUC was presented to overcome hypoxia and GSH-associated photodynamic resistance due to in situ oxygen generation and GSH reduction of MnO2 upon endocytosis, and a bulk amount of Mn2+ ions generated in the process under acidic tumor environment acts as the MRI contrast agent. Moreover, the MnO2 sheet protects Ce6 from self-degradation under irradiation; thus, it can be used to switch control of cellular imaging. Afterwards, in a regulated and targeted manner, the chemotherapeutic drug (doxorubicin hydrochloride, DOX) can be released with the degradation of CaMn–NUC in the acidic tumor microenvironment (TME). Thus, we testify a competent nanoplatform employing 808 nm-excited UCNPs–Ce6 for concurrent imaging and PDT in consideration of the large anti-Stokes shifts, deep penetration into biological tissues, narrow emission bands, and high spatial-temporal resolution of the UCNPs. Thus, our proposed nanoplatform postulates a strategy to efficiently kill cancer cells in a concentration- and time-dependent manner via the in situ oxygenation of solid tumor hypoxia to enhance the efficiency of multimodal imaging-guided chemo-photodynamic therapy. [ABSTRACT FROM AUTHOR]

Ongoing efforts have contributed to the exploration of peroxidase-like nanozymes while preserving their benefits in bioassays. Unfortunately, many peroxidase-like nanozymes still exhibit a low catalytic activity accompanied by oxidase-like activity with interferences of O2 and color which limit their applicability. Herein, we carried out a "green" approach to synthesize citrate-coated osmium nanozyme with a high peroxidase-like performance. Comprehensive experiments were validated in which the Os nanozyme could achieve excellent steady-state kinetic parameters and a high specific activity (393 000 Unit per g), which was better than those of most reported nanozymes. More significantly, the Os nanozyme possesses a higher peroxidase-like activity and negligible oxidase-like activity compared with those of common noble metal-based nanozymes (Pt and Au), freeing the corresponding assay system from the interference of O2 and color. In addition, the Os nanozyme presents robustness against complex environments and some metal ions that usually act as noble metal-based nanozymes. As a proof-of-concept, the Os nanozyme has been successfully employed to fabricate colorimetric assays for glucose and pyruvic acid detections with the associated color gradients. These findings collectively prove that the Os nanozyme could be a novel and promising peroxidase mimic candidate for bioassays and beyond. [ABSTRACT FROM AUTHOR]

Photodynamic therapy (PDT) and photothermal therapy (PTT) are well-developed light therapy methods for cancer; however, both have a few areas that need improvement. A sustained PDT effect depends on the sustained generation of reactive oxygen species (ROS); therefore, adjusting the type of photosensitizer or the reaction mechanism to prolong the duration of the oxidation–reduction reaction is a possible solution for the continuation of the PDT effect. Further, if PTT could be combined with other treatments, it would bring about a more satisfactory therapeutic effect. To increase the treatment effect of the above two therapeutic methods, a collaborative treatment model of photo/chemodynamic therapy (PCDT) and PTT is needed and is the focus of this study. On the one hand, PCDT is a therapy that integrates PDT with Fenton-like reactions, and Fenton-like reactions can help PDT to produce more ROS by making better use of H2O2 in the tumor microenvironment. On the other hand, the PTT effect can also promote PCDT effects to some extent because rising temperature can elevate the redox reaction rate. Therefore, a copper oxide semiconductor photosensitizer was selected in this research to realize the abovementioned therapeutic purposes and experimental concepts. A porous silica carrier can facilitate the uniform attachment of the copper oxide photosensitizer to the SiO2 surface to form a relatively uniform nanostructure, and the nanoporous structure can increase the performance of the whole material to a certain extent. Based on these perspectives, SiO2@CuO nanotube (NT), an agent of both Fenton-like photosensitization and photothermal reagent, is synthesized by the hydrothermal co-precipitation template approach to shrink the tumor through the combined effect of PCDT and PTT. In this system, copper ions can participate in the Fenton-like reactions and make better use of H2O2 to generate more ROS. Herein, 808 nm light was chosen for irradiation because of its suitable excitation ability, applicable penetration and low intrinsic damage. The experimental results show that SiO2@CuO NT is a promising agent that combines PCDT and PTT for cancer treatment. This work provides guidance for the synthesis of Fenton-like photosensitizers for the PCDT effect. [ABSTRACT FROM AUTHOR]

Improving luminescence intensities of rare-earth (RE)-doped upconversion nanoparticles (UCNPs) have aroused great attention recently. In this study, NaGdF4: Yb3+, Ce3+, and Ho3+ UCNPs doped with varying concentrations of Zn2+ were synthesized in one step by high temperature pyrolysis using oleate chemicals. X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), ICP-MS (inductively coupled plasma-mass spectrometry), upconversion emission spectra and luminescence lifetimes were used to study the samples. It was found that as the concentration of Zn2+ increased from 0 to 15 mol%, the luminescence intensities of both red and green emissions first increased and then decreased, with the maximum value of Zn2+ doping at 10 mol%. We concluded that Zn2+ dopant and F− vacancies accounted for the intensity changes. Our research can be beneficial for the structural design and applications of RE-doped UCNPs. [ABSTRACT FROM AUTHOR]

Improving luminescence intensities of rare-earth (RE)-doped upconversion nanoparticles (UCNPs) have aroused great attention recently. In this study, NaGdF4: Yb3+, Ce3+, and Ho3+ UCNPs doped with varying concentrations of Zn2+ were synthesized in one step by high temperature pyrolysis using oleate chemicals. X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), ICP-MS (inductively coupled plasma-mass spectrometry), upconversion emission spectra and luminescence lifetimes were used to study the samples. It was found that as the concentration of Zn2+ increased from 0 to 15 mol%, the luminescence intensities of both red and green emissions first increased and then decreased, with the maximum value of Zn2+ doping at 10 mol%. We concluded that Zn2+ dopant and F− vacancies accounted for the intensity changes. Our research can be beneficial for the structural design and applications of RE-doped UCNPs. [ABSTRACT FROM AUTHOR]

Gadolinium-based macromolecular contrast agents (CAs) with favorable biocompatibility, targeting specificity, and high relaxivity properties are desired for magnetic resonance imaging (MRI) of tumors. Herein, a novel triblock polymeric micelle based on poly(glycerol) (PG) and poly(ε-caprolactone) (PCL) was designed as a nanocarrier to fabricate a tumor targeted contrast agent (CA). Through conjugating gadolinium chelates and folic acid (FA) molecules to the PG block, a triblock-micelle contrast agent (T-micelle) formed from self-assembly demonstrated a low critical micelle concentration (CMC) of 6 mg L−1 and a hydrodynamic diameter of about 250 nm. Compared with small-molecule CAs, the T-micelle exhibited a higher longitudinal relaxivity (r1) of 14.71 mM−1 s−1. Moreover, the cellular viability assay revealed negligible cytotoxicity, and estimation of targeting capacity showed significant targeting specificity to tumor cells. In addition, MRI on tumor-bearing mice confirmed that the T-micelle could efficiently accumulate at the tumor region through targeting specificity and provide obvious contrast enhancement. Consequently, the T-micelle is a promising gadolinium-based macromolecular CA for tumor diagnosis. [ABSTRACT FROM AUTHOR]

Macromolecular contrast agents labeled with targeting ligands are now receiving growing interest in tumor-targeted magnetic resonance imaging. In this study, a macromolecular contrast agent based on PEGylated chitosan was synthesized and characterized, and its application as an MRI contrast agent was then demonstrated both in vitro and in vivo. First, the chitosan backbone was partially grafted with poly(ethylene glycol), which was used to improve the in vivo stability, followed by modifying with azide groups. Second, alkynyl-terminated PAMAM dendron modified with gadolinium diethylenetriaminepentaacetic acid (Gd-DTPA) was synthesized and conjugated onto the chitosan backbone through click chemistry. Finally, the obtained mCA was further functionalized with folic acid to improve the target specificity. The obtained FA labeled mCA exhibited higher relaxivity (9.53 mM−1 s−1) relative to Gd-DTPA (4.25 mM−1 s−1) and showed negligible toxicity as determined by the WST assay. In vivo MRI results suggested that a relatively high signal enhancement was observed in the tumor region, which made it a promising candidate for tumor-targeted MRI CA. [ABSTRACT FROM AUTHOR]

Contrast agents with high efficiency and safety are excellent candidates as magnetic resonance imaging probes. Herein, a multi-arm star-branched polymer was prepared by conjugating oligolysine onto a rigid hyperbranched poly(amido amine) core via click chemistry, followed by covalent modification with Gd chelate and folic acid (FA-OLL-g-HBPAMAM-DTPA-Gd). This multi-arm star-branched polymer contrast agent exhibited much higher longitudinal relaxivity (r1 = 13.34 mM−1 s−1) as compared to a commercial contrast agent (Gd-DTPA, r1 = 4.2 mM−1 s−1). No obvious histological toxicity was observed from histological assessment, which illustrated that FA-OLL-g-HBPAMAM-DTPA-Gd exhibited excellent biocompatibility. Both in vitro and in vivo MRI studies showed that the macromolecular contrast agent provided better signal contrast enhancement and presented obvious target specificity to KB xenografts with a sufficient time window for MRI scanning; moreover, this multi-arm star-branched mCA has great potential for developing sensitive and biocompatible MRI CA with targeting ability. [ABSTRACT FROM AUTHOR]

Gadolinium-based nanoscale magnetic resonance imaging (MRI) contrast agents (CAs) have gained significant momentum as a promising nanoplatform for detecting tumor tissue in medical diagnosis, due to their favorable capability of enhancing the longitudinal relaxivity (r1) of individual gadolinium ions, delivering to the region of interest a large number of gadolinium ions, and incorporating different functionalities. This mini-review highlights the latest developments and applications, and simultaneously gives some perspectives for their future development. [ABSTRACT FROM AUTHOR]

Rare-earth-doped up-conversion nanoparticles (UCNPs), which are capable of converting infrared light to shorter-wavelength photons, have attracted worldwide attention due to their unique characteristics. However, the emission brightness of UCNPs is greatly limited by the unsatisfactory absorptivity of lanthanide ions. Herein, we adopted a novel strategy to enhance the up-conversion intensity using NIR dye IR-808 as an antenna to sensitize the core–shell–shell structured NaGdF4:Yb,Er@NaGdF4:Yb@NaNdF4:Yb UCNPs. When excited with 808 nm light, the IR-808 emitted a broadband peak, which perfectly overlapped with the absorption of Nd3+ and Yb3+ ions. Thus, the active shell of NaNdF4:Yb can efficiently capture the emitted NIR photons and transfer them to the transition layer of NaGdF4:Yb. The transition layer acted as an energy bridge to connect the active shell and up-converting zone, avoiding the energy back-transfer from the activators to Nd3+ ions. The optimized dye sensitization combined with the well-designed core–shell–shell structure tremendously enhances the NIR photon absorptivity of UCNPs and eliminates the deleterious cross-relaxation between the activators and sensitizers, eventually leading to dramatic enhancement of the up-conversion intensity. This study provides a new insight into the dye-sensitized up-conversion luminescence of rare earth-based nanoparticles and facilitates their practical applications. [ABSTRACT FROM AUTHOR]

Rare-earth-doped up-conversion nanoparticles (UCNPs), which are capable of converting infrared light to shorter-wavelength photons, have attracted worldwide attention due to their unique characteristics. However, the emission brightness of UCNPs is greatly limited by the unsatisfactory absorptivity of lanthanide ions. Herein, we adopted a novel strategy to enhance the up-conversion intensity using NIR dye IR-808 as an antenna to sensitize the core-shell-shell structured NaGdF 4 :Yb,Er@NaGdF 4 :Yb@NaNdF 4 :Yb UCNPs. When excited with 808 nm light, the IR-808 emitted a broadband peak, which perfectly overlapped with the absorption of Nd 3+ and Yb 3+ ions. Thus, the active shell of NaNdF 4 :Yb can efficiently capture the emitted NIR photons and transfer them to the transition layer of NaGdF 4 :Yb. The transition layer acted as an energy bridge to connect the active shell and up-converting zone, avoiding the energy back-transfer from the activators to Nd 3+ ions. The optimized dye sensitization combined with the well-designed core-shell-shell structure tremendously enhances the NIR photon absorptivity of UCNPs and eliminates the deleterious cross-relaxation between the activators and sensitizers, eventually leading to dramatic enhancement of the up-conversion intensity. This study provides a new insight into the dye-sensitized up-conversion luminescence of rare earth-based nanoparticles and facilitates their practical applications.

Herein, we fabricated efficient MR imaging probes by incorporating gadolinium oxide nanoparticles (Gd 2 O 3 ) and gadolinium hybrid nanoparticles (GH) within RBCs. The Gd 2 O 3 and GH encapsulated in the RBCs exhibited high relaxation rates and revealed high sensitivity for T 1 MR imaging.