Search

Colloidal quantum dots (CQDs) are promising materials candidates for next-generation semiconductor gas sensors, due to their high surface activity and solution-processability. Despite the improved sensitivity demonstrated by PbS CQDs, their long-term stability remains a challenge for practical applications. In this paper, we propose a stabilization strategy for PbS CQD gas sensors by using atomic-ligand engineering. The oleic acid ligands surrounding PbS CQDs are replaced by halide ligands (Cl–, Br– and I–, respectively) via a phase-transfer ligand exchange method. The sensitivity and long-term stability of the PbS CQD gas sensor towards nitrogen dioxide (NO 2) at room temperature are impressively improved. The excellent humidity stability of the iodine ligand exchanged PbS CQD gas sensor is also demonstrated. The mechanism is investigated by real-time electrical measurement, combined with operando diffuse reflection Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analysis. The results indicate that the large atomic radius and high binding energy of iodide ligands enhance surface passivation and provide favorable conditions for NO 2 adsorption and charge transfer. This study highlights the importance of surface ligand engineering in the development of practical CQD gas sensors. • Atomic-ligand engineering is proposed to stabilize PbS CQD for NO 2 detection. • Iodine ligands improve detection limit to 0.78 ppb with stability in 0–90% RH range. • Iodide ligands enhance passivation and facilitate NO 2 adsorption & charge transfer. [ABSTRACT FROM AUTHOR]

Colloidal quantum dots (CQDs) are considered as one of the ideal materials candidates for next-generation electronics and optoelectronics. Their large surface-to-volume ratio with exchangeable surface ligands offers a versatile freedom for the regulation of the semiconductor gas sensors. Here we demonstrated an atomic-ligand exchange strategy to construct highly sensitive and selective SnO 2 quantum dot gas sensors. Both the cations and anions of the atomic ligands were engineered to enhance the gas adsorption and carrier transport via a film-level atomic ligand exchange treatment, among which the CuCl 2 -treated SnO 2 CQD gas sensors exhibiting highest response of 1755 toward 50 ppm H 2 S with a fast response and recovery time (48 s/35 s) at 70 °C. The Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS) and UV–vis absorption spectra suggest that the long-chain organic ligands capping on the SnO 2 CQDs were successfully exchanged by the atomic ligands and the quantum confinement of the CQDs were well conserved, which is favorable to preserve the catalytic activities of QD materials in real gas-sensing devices. Simultaneously, the copper (II) introduced on the surface of SnO 2 CQD films can also act as a catalytic promoter by forming p-CuO/n-SnO 2 heterojunctions, thereby enhancing the H 2 S-sensing performance at relatively low temperatures. [ABSTRACT FROM AUTHOR]

Colloidal quantum dots (CQDs) are promising building blocks for low-cost and high-performance gas sensors due to their excellent solution processability and extremely small size. Among chalcogenide CQDs, PbSe has a large exciton Bohr radius and exhibits strong confinement energies, facilitating the fast charge-carrier transport. However, CQDs-based devices are susceptible to degrade due to the poor stability of CQDs. Here, in order to obtain air-stable PbSe CQDs for gas sensing application, we synthesized PbSe CQDs using a cation exchange method with in situ chloride and cadmium passivation. The sharp absorption peak in UV–vis absorption spectra confirmed strong quantum confinement in the PbSe CQDs and their average diameter was estimated to be 2.87 ± 0.23 nm. To construct gas sensors, PbSe CQDs were spin-coated onto ceramic substrates and then Pb(NO 3 ) 2 treatment was carried out to remove the long-chain ligands surrounding PbSe CQDs. At 25 °C, the sensor was highly sensitive and selective to NO 2 with a response of 22.3 at 50 ppm and a fast response time of 7 s. Moreover, the sensor response showed a 85.2% stability as the time increased up to 20 days, suggesting the potential applications of PbSe CQDs for NO 2 monitoring at room temperature. [ABSTRACT FROM AUTHOR]

Human health and environmental safety are imperceptibly disturbed by illegally used plasticizers. A fluorescence sensor array based on B-doped graphene quantum dots was designed to detect six plasticizers. Specifically, the dexterous design is the first to disperse B-doped graphene quantum dots in two solvents of different polarities (N,N-Dimethylformamide and Cyclohexane), select three characteristic fluorescence peaks of B-doped graphene quantum dots in the above two solvents, and construct a 3 × 2 array, with a total of 6 array points. The basis of the detection is that the plasticizers affect the dispersion of B-doped graphene quantum dots in different solutions, which are accompanied by the change of its fluorescence signals. Or the plasticizers affect the electron transfer process of B-doped graphene quantum dots in different solvents, resulting in fluorescence quenching. Fluorescence information output by the sensor array showed a good linear relationship with the concentrations of the six plasticizers. The quantitative detection capability can be specified as: the detection range is 100 ng/mL-195 mg/mL, and the detection limit is 1.05–11.58 ng/mL. The fluorescence sensor array also showed good analytical performance in real samples, with recoveries ranging from 95% to 106%. This method has satisfactory specificity, reproducibility, stability and practicality, making it potential for application. • B-GQDs fluorescence sensor array for detecting plasticizers. • B-GQDs have diverse fluorescence properties in different polar solvents. • The plasticizer affects the polarity of the solvent as the detection principle. • The highly sensitive and ultra-rapid detection of six plasticizers was completed. [ABSTRACT FROM AUTHOR]

Human health and environmental safety are imperceptibly disturbed by illegally used plasticizers. A fluorescence sensor array based on B-doped graphene quantum dots was designed to detect six plasticizers. Specifically, the dexterous design is the first to disperse B-doped graphene quantum dots in two solvents of different polarities (N,N-Dimethylformamide and Cyclohexane), select three characteristic fluorescence peaks of B-doped graphene quantum dots in the above two solvents, and construct a 3 × 2 array, with a total of 6 array points. The basis of the detection is that the plasticizers affect the dispersion of B-doped graphene quantum dots in different solutions, which are accompanied by the change of its fluorescence signals. Or the plasticizers affect the electron transfer process of B-doped graphene quantum dots in different solvents, resulting in fluorescence quenching. Fluorescence information output by the sensor array showed a good linear relationship with the concentrations of the six plasticizers. The quantitative detection capability can be specified as: the detection range is 100 ng/mL-195 mg/mL, and the detection limit is 1.05–11.58 ng/mL. The fluorescence sensor array also showed good analytical performance in real samples, with recoveries ranging from 95% to 106%. This method has satisfactory specificity, reproducibility, stability and practicality, making it potential for application. • B-GQDs fluorescence sensor array for detecting plasticizers. • B-GQDs have diverse fluorescence properties in different polar solvents. • The plasticizer affects the polarity of the solvent as the detection principle. • The highly sensitive and ultra-rapid detection of six plasticizers was completed. [ABSTRACT FROM AUTHOR]

The discovery of odorant receptors inspiring researchers to refine the artificial olfactory system with the better design of receptor function and transducer function. Colloidal quantum dots (CQDs) offer an abundance of available surface area for chemical and electronic interactions, making them ideal receptors for gas molecules. In this paper, we propose optical fiber antenna (OFA) that mimic the structure and function of biological antenna by using CQDs as the artificial receptors for gas molecules. The charge transfer between the gas molecules and quantum dots is designed to modulate the interaction between the quantum dot solids and light through the variation of refractive index (RI) of quantum receptors. Specifically, lead sulfide (PbS) CQDs serving as NO 2 receptors were deposited on the optical structure for comparison. The solution-processability of CQDs enable their uniform and conformal coating on the fiber. The OFA exhibited a sensitivity of 35 pm ppm−1 for NO 2 sensing at room temperature with the detection limit estimated to be 1 ppb. The proof of OFA concept may pave the way to artificial olfactory networking and will benefit for the development of high precise, large scale, real time distributed gas monitoring application beyond human olfaction. • Optical fiber antenna that mimics the structure and function of biological antenna for gas molecules detection was proposed. • The charge transfer will modulate the interaction between the QD solids and light through the variation of RI of receptors. • OFA exhibited a sensitivity of 35 pm ppm-1 for NO 2 sensing with the detection limit estimated to be 1 ppb. [ABSTRACT FROM AUTHOR]

Colloidal quantum dot (CQD) is emerging as new substitution gas sensing materials due to the excellent accessibility of gas molecules to CQD surfaces realized via surface ligand removal. Here we demonstrated highly sensitive and selective H 2 S gas sensors based on PbS CQD solids. The sensor resistance decreases upon H 2 S gas exposure and the response is defined as the ratio of the sensor resistance in clean air to that in H 2 S gas. As the operating temperature increased within the range 50–135 °C, the sensor response increased while the response and the recovery time decreased. The sensor was fully recoverable toward 50 ppm of H 2 S at 108 °C and the highest response was 2389 at 135 °C with the response and recovery time being 54 s and 237 s, respectively. The dependence of sensor response on the H 2 S gas concentration in the range of 10–50 ppm is linear, suggesting a theoretical detection limit of 17 ppb toward H 2 S at 135 °C. Meanwhile, the sensor showed superb response selectivity toward H 2 S against SO 2 , NO 2 and NH 3 . We propose that the PbS CQDs film where the surface states determine the conduction type via remote doping may undergo a p-to-n transition due to H 2 S exposure at elevated temperatures. [ABSTRACT FROM AUTHOR]