Tunable optical and fluorescent properties of graphene quantum dots (GQDs) by heteroatom doping and surface functionalization provide tremendous advantages for practical applications. One of these notable issues is the construction of stimuli-responsive GQDs which can be used as smart green nonmetal materials in the field of sensor and biotechnology. In this work, N-doped graphene quantum dots (NGQDs) encapsulated by organic species were obtained through hydrothermal method, of which the quantum yield achieved 22.9%, much higher than that of bare NGQDs (1%). Interestingly, it was found that the functionalized NGQDs exhibited a color oscillation in open air and its fluorescence emission can be reversibly switched "on−off" via redox reactions. Meanwhile, the PL emission would be transformed from excitation-independent to excitation-dependent through modifying the surface states of NGQDs. The origin of PL is then studied, emphatically distinguishing the role of different C−N configurations and surface functional groups. The NGQDs of distinct optical and luminescent characteristic can serve as fluorescent sensors for detection of CH 2 O and probes for bioimaging.

Nitrogen doped graphene quantum dots (NGQDs) were successfully prepared via a hydrothermal method using citric acid and urea as the carbon and nitrogen precursors, respectively. Due to different post-treatment processes, the obtained NGQDs with different surface modifications exhibited blue light emission, while their visible-light absorption was obviously different. To further understand the roles of nitrogen dopants and N-containing surface groups of NGQDs in the photocatalytic performance, their corresponding composites with TiO2 were utilized to degrade RhB solutions under visible-light irradiation. A series of characterization and photocatalytic performance tests were carried out, which demonstrated that NGQDs play a significant role in enhancing visible-light driven photocatalytic activity and the carrier separation process. The enhanced photocatalytic activity of the NGQDs/TiO2 composites can possibly be attributed to an enhanced visible light absorption ability, and an improved separation and transfer rate of photogenerated carriers.

In this study, we demonstrate that a large potential can be generated when one end of 1D and/or 2D semiconducting nanostructures such as zinc oxide (ZnO) and molybdenum disulfide (MoS 2 ) is exposed to a wide species of chemical molecules. In particular, single-crystalline semiconductor ZnO NW arrays are chosen as the functional media to generate electricity from various molecules including gaseous species from human breath, and to drive a single CNT field-effect transistor (FET). They are biocompatible and have fast electron transfer kinetics, [12] and the crystal facets of ZnO including the top polar (0001) or (0001 ) and side nonpolar (1010) surfaces can actively interact with various molecules. [13] The magnitude of the voltage generated by ZnO NWs is about one order of magnitude larger than the typical streaming or piezoelectric potentials. The notion of voltage generation through moleculesurface interactions has the advantages of simplicity, costeffectiveness, fast response to a wide range of molecules, and high power output, making our approach a promising tool in energy conversion and sensing applications. Nanoenergy Generators www.advancedsciencenews.com

Interfacial charge transfer is crucial in the efficient conversion of solar energy into fuels and electricity. In this paper, heterojunction composites were fabricated, comprised of anatase TiO2 with different percentages of exposed {101} and {001} facets and nitrogen-doped quantum dots (NGQDs) to enhance the transfer efficiency of photo-excited charge carriers. The photocatalytic performances of all samples were evaluated for RhB degradation under visible light irradiation, and the hybrid containing TiO2 with 56% {001} facets demonstrated the best photocatalytic activity. The excellent photoactivity of TiO2/NGQDs was owed to the synergistic effects of the following factors: (i) The unique chemical features of NGQDs endowed NGQDs with high electronic conductivities and provided its direct contact with the TiO2 surface via forming Ti–O–C chemical bonds. (ii) The co-exposed {101} and {001} facets were beneficial for the separation and transfer of charge carriers in anatase TiO2. (iii) The donor-acceptor interaction between NGQDs and electron-rich {101} facets of TiO2 could remarkably enhance the photocurrent, thus hindering the charge carriers recombination rate. Extensive characterization of their physiochemical properties further showed the synergistic effect of facet-manipulated electron-hole separation in TiO2 and donor-acceptor interaction in graphene quantum dots (GQDs)/TiO2 on photocatalytic activity.

In order to obtain acetone sensor with excellent sensitivity, selectivity, and rapid response/recovery speed, graphene-like ZnO/graphene oxide (GO) nanosheets were synthesized using the wet-chemical method with an additional calcining treatment. The GO was utilized as both the template to form the two-dimensional (2-D) nanosheets and the sensitizer to enhance the sensing properties. Sensing performances of ZnO/GO nanocomposites were studied with acetone as a target gas. The response value could reach 94 to 100 ppm acetone vapor and the recovery time could reach 4 s. The excellent sensing properties were ascribed to the synergistic effects between ZnO nanosheets and GO, which included a unique 2-D structure, large specific surface area, suitable particle size, and abundant in-plane mesopores, which contributed to the advance of novel acetone vapor sensors and could provide some references to the synthesis of 2-D graphene-like metals oxide nanosheets.