Graphene-based gas/vapor sensors have attracted much attention in recent years due to their variety of structures, unique sensing performances, room-temperature working conditions, and tremendous application prospects, etc. Herein, we summarize recent advantages in graphene preparation, sensor construction, and sensing properties of various graphene-based gas/vapor sensors, such as NH3, NO2, H2, CO, SO2, H2S, as well as vapor of volatile organic compounds. The detection mechanisms pertaining to various gases are also discussed. In conclusion part, some existing problems which may hinder the sensor applications are presented. Several possible methods to solve these problems are proposed, for example, conceived solutions, hybrid nanostructures, multiple sensor arrays, and new recognition algorithm.

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Cuprous oxide (Cu2O) is an attractive photocatalyst because of its visible-light-driven photocatalytic behavior, abundance, low toxicity, and environmental compatibility. However, its short electron diffusion length and low hole mobility result in low photocatalytic efficiency, which hinders its wider applications. Herein, we report an in situ method to introduce nitrogen-doped carbon dots (N-CDs) into Cu2O frameworks. It is interestingly found that the introduction of N-CDs drives the morphology of N-CDs/Cu2O to evolve from rough cube to sphere, and the most encouraging result is that all of the obtained N-CDs/Cu2O composites exhibit better photocatalytic activities than pure Cu2O cubes. The optimal N-CDs/Cu2O photocatalyst is synthesized with 10 mL of N-CDs solution, which shows the best degradation ability (100%, 70 min), far superior to pure Cu2O cubes (∼5%, 70 min) and P25 (∼10%, 70 min). Beside the photodegradation of methyl orange, N-CDs/Cu2O(10) composites also exhibit excellent photocatalytic activities in the photodegradation of methyl blue and rhodamine B. It is demonstrated that the excellent photocatalytic performance of N-CDs/Cu2O composites can be attributed to the highly roughened structure and the suppression of electron-hole recombination as a result of the introduction of N-CDs. These findings demonstrate that the conjugation of CDs is a promising method to improve the photocatalytic activities for traditional semiconductors.

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