Decoupling the Conflicting Roles of Photoactivation and Boosting Chemiresistor Response by Pulsed UV Light Modulation.

UV photoactivation has been widely employed to trigger the response of semiconductor chemiresistors at room temperature (RT). Generally, continuous UV (CU) irradiation is applied, and an apparent maximal response could be obtained via optimizing UV intensity. However, owing to the conflicting roles of (UV) photoactivation in the gas response process, we do not think the potential of photoactivation has been fully explored. Herein, a pulsed UV light modulation (PULM) photoactivation protocol has been proposed. Pulsed UV-on facilitates the generation of surface reactive oxygen species and refreshes the surface of chemiresistors, while pulsed UV-off avoids the side effects of UV-induced desorption of the target gas and the decline of base resistance. PULM enables decoupling those conflicting roles of CU photoactivation, resulting in a drastic boost of response to trace (20 ppb) NO2 from 1.9 (CU) to 131.1 (PULM UV-off), and a decline of limit of detection from 2.6 ppb (CU) to 0.8 ppb (PULM) for a ZnO chemiresistor. This work highlights that PULM allows full exploitation of the potential of nanomaterials for sensitively detecting trace (ppb-level) toxic gas molecules and opens a new opportunity for designing highly sensitive, low-power consumed RT chemiresistors for ambient air quality monitoring.

Modified optical properties via induced cation disorder in self-activated NaMg2V3O10.

Cation disorder in the phosphor lattice could be one of the effective approaches to modify the luminescence efficiency. In this work, cation substitutions of (Mo6+→ V5+) and (Na+→ Mg2+) were conducted in the self-activated NaMg2V3O10. All the samples of Na1+xMg2-xV3-xMoxO10 (x = 0, 0.01, 0.05, 0.1, 0.2, 0.3) were prepared via solid-state reaction. The morphological properties were measured via SEM and EDS analyses. Structural Rietveld refinement was performed to investigate the microstructure in the lattices. The cation substitution brings about structural disorder in the phosphor, which exerts great modifications in the luminescence properties. NaMg2V3O10 presents an intrinsic indirect transition with a band gap of 3.22 eV. The incorporation of Mo6+ and Na+ in the lattices moves the optical absorption to a longer wavelength bringing about a narrower band gap. The luminescence intensity, thermal stability and corresponding lifetime were modified by the cation disorder in the self-activated phosphor.

A new silver metaniobate semiconductor of Ag0.5La0.5Nb2O6 with defect-perovskite structure.

Silver-containing lanthanum metaniobate Ag0.5La0.5Nb2O6 nanoparticles were synthesized by sol-gel polymerized complex method. A typical defect-perovskite structure was confirmed by XRD Rietveld refinements. The surface characteristics of the sample were tested by SEM, TEM and EDS measurements. SEM and TEM show that the sample presents ball-like particles with the diameters of 100nm to 400nm. The sample shows both self-activated luminescence and photocatalytic activities. Ag0.5La0.5Nb2O6 has a direct transition with band energy of 2.85eV. The Ag4d-O2p hybridization in the valence band contributes to the narrowed band gap. The luminescence properties of Ag0.5La0.5Nb2O6 have been investigated for the first time. The luminescence is characterized by two emission centers with maximum wavelength near 460 and 530nm. The emission and excitation spectra, decay curves and the thermal quenching mechanism were discussed. Ag0.5La0.5Nb2O6 shows the efficient photocatalytic activities and the photodegradation rate for methylene blue dye (MB) can reach about 95% under visible light (>420nm) irradiation in 5h. The trapped experiments for the active species were tested and discussed, which verified that OH radicals could be the major active species in photocatalysis.