Nitrogen
dioxide (NO2) detection is of great importance
because the emission of NO2 gas profoundly endangers the
natural environment and human health. However, a few challenges, including
lowering detection limit, improving response/recovery kinetics, and
reducing working temperature, should be further addressed before practical
applications. Herein, a series of N-doped graphene quantum dot (N-GQD)-modified
three-dimensional ordered macroporous (3DOM) In2O3 composites are constructed and their NO2 response properties
are studied. The results show that compared to pure 3DOM In2O3, reduced graphene oxide (rGO)/3DOM In2O3, and N-doped graphene sheets (NS)/3DOM In2O3, the N-GQDs/3DOM In2O3 sensing materials
exhibit higher NO2 responses with fast response and recovery
speed and low working temperature (100 °C). In addition, the
detection limit of NO2 response for the optimal N-GQDs/In2O3 sensor
is as low as 100 ppb. Upon exposure to CO, CH4, NH3, acetone, ethanol, toluene, and formaldehyde, only very weak
responses could be observed, indicating good selectivity for the synthesized
material. More attractively, the responses of the optimized N-GQDs/In2O3 sensor exhibit no obviously big fluctuation
over 60 days, implying good long-term stability. We suggest that the
formation of heterojunctions between 3DOM In2O3 and N-GQDs and the doping N atoms in N-GQDs play crucial roles in
improving the NO2 sensing properties.
Step-scheme (S-scheme) photocatalysts have received much attention owing to the enhanced photocatalytic redox ability. However, the carrier transport driven only by the interfacial electric field of the S-scheme heterojunction is not efficient enough to satisfy the highly active CO 2 reduction. In this study, we realize the coupling of multiple electric fields and the accelerating of charge transfer in the CdS/BiOCl heterojunction by regulating the contact interface of CdS and BiOCl. The photoreduction CO 2 test results show that all composites exhibit a higher photocatalytic activity than pure CdS and BiOCl, indicating the inherent advantages of the S-scheme heterojunction. More importantly, the CdS/BiOCl composites (Cx-B001) assembled by the {001}facet-exposed BiOCl nanosheets show significantly boosted photocatalytic activity compared to the counterpart (Cx-B010) constructed by the {010}-facet-exposed BiOCl nanosheets. The enhanced CO 2 reduction activity of Cx-B001 is attributed to the more effective charge transport, which is synergistically driven by the electric field at the heterojunction interface and the polarization electric field in the BiOCl phase. This work may provide some useful insights into the design of highly efficient S-scheme photocatalysts.
Scheme 1. Graphical description of the method of dispersing Ru ions in solid carriers. a) Conventional impregnation method. b) Ionic liquids homogeneous dispersion and in situ confined polymerization method.
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