In this work, water-soluble Yb3+/Er3+ codoped Bi2O3 upconversion (UC) nanospheres with uniform morphology have been successfully synthesized via a solid-state-chemistry thermal decomposition process. With 980 nm near-infrared irradiation, the Bi2O3:Yb3+/Er3+ nanospheres have bright UC luminescence (UCL). Moreover, multicolor UC emissions (from green to red) can be tuned by simply changing the Yb3+ ions doping concentration. After citric acid molecules were grafted on the surface of Bi2O3:20% Yb3+/2% Er3+ nanospheres, the MTT assay on HeLa cells and CCK-8 assay on osteoblasts show that the UC nanospheres exhibit excellent stability and biocompatibility. The possibility of using these nanoprobes with red UCL for optical imaging in vivo has been demonstrated. Furthermore, Bi3+ and Yb3+ containing nanospheres as binary contrast agent also exhibited significant enhancement of contrast efficacy than iodine-based contrast agent via X-ray computed tomography (CT) imaging at different voltage setting (80–140 kVp), indicating they have potential as CT imaging contrast agent. Thus, Yb3+/Er3+ codoped Bi2O3 nanospheres could be used as dual modality probe for optical and CT imagings.
Bi 2 O 3 nanospheres co-doped with Yb 3+ /Er 3+ upconverting ions pair have been successfully synthesized via a facile hydrothermal method followed by a heat treatment. The resulting Bi 2 O 3 :Yb 3+ ,Er 3+ nanospheres show a monodisperse spherical morphology with narrow size distribution (~180 nm) and display intense upconversion luminescence under 980 nm laser excitation. It is found that the crystal structure, morphology and upconversion luminescence properties of nanospheres have a direct relationship with the doping concentration of Yb 3+ and the subsequent calcination temperature. These Bi 2 O 3 :Yb 3+ ,Er 3+ nanospheres can be prepared in large quantities and can be easily modified with a layer of biocompatible polyethyleneimine (PEI) molecules. The yielded nanospheres could not only maintain uniform size and morphological characteristics, but also show good water dispersibility and biocompatibility. Remarkably, these Bi 2 O 3 :Yb 3+ ,Er 3+ upconversion nanophosphors could also act as an effective contrast agent for X-ray computed tomography (CT) imaging, which show higher contrast efficacy than commercial iodine-based contrast agent. The proposed facile synthetic route and inexpensive matrix materials pave the way for broad use of these Bi 2 O 3 :Yb 3+ ,Er 3+ nanospheres as ideal dual-mode bioimaging probes in biomedical field.
Coupling a semimetal with a semiconductor on nitrogen-doped carbon for photocatalytic reforming of biomass-derived feedstocks into high value-added chemicals is of great significance; however, no success has been achieved to date. Here, uniformly dispersed Bi/Bi2O3 nanospheres with a Mott–Schottky heterojunction embedded on the nitrogen-doped biochar nanosheets (Bi/Bi2O3@N-BC) were developed and successfully used in photocatalytic biomass-reforming to lactic acid. A built-in electric field between the interfaces of Bi and Bi2O3 was constructed via the Schottky effect of the Bi/Bi2O3 heterojunction, resulting in the rapid separation/migration of electrons–holes; whereas the N-BC facilitates the adsorption of reactants and the mass transfer of products or by-products. The highest yield of lactic acid reached was 91.21%, and Bi/Bi2O3@N-BC displayed excellent stability, reusability and universality. The experimental results indicated that the contents of photoinduced h+, ˙O2−, ˙OH and 1O2 increased with prolonging the visible-light irradiation time, and trapping tests suggested that ˙O2−, 1O2 and h+ promoted the lactic acid production in turn, whereas ˙OH inhibited the reaction. A 1000-fold scale-up experiment showed that the economically and environmentally viable system has potential for application in the industrial production of lactic acid, and this work also provides an efficient strategy for the development of functional photocatalysts and photocatalytic biorefinery.
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