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Understanding the effect of additive on the interfacial charge‐carrier transfer dynamics is very crucial to obtaining highly efficient perovskite solar cells (PSCs). Herein, we designed a simple additive, dimethyl oxalate (DO), functioning as an effective defect passivator of perovskite grain boundaries via the coordination interaction between the carbonyl (C=O) and the exposed Pb2+. The modification with DO produces pinhole‐free and compact perovskite films, enhancing the transportation capability of carriers. As a consequence, the DO‐treated PSCs exhibited a power conversion efficiency (PCE) of 22.19%, which is significantly higher than that of the control device without additive (19.58%). More importantly, detailed transient absorption characterization reveals that the use of additive can decrease the hot‐carrier cooling dynamics, improve the carrier transfer, and eliminate nonradiative recombination in PSCs. This present work provides a profound understanding the additives effect on the carrier dynamics in PSCs toward the Shockley−Queisser limit. [ABSTRACT FROM AUTHOR]

This paper reports the synthesis of ZnO-SnO2 nanocomposites modified by PdO nanoparticles named PdO-ZSO which are prepared by the one-step hydrothermal method at 160 °C for 12 h and gas sensing test to H2 and C4H10 inflammable gas. Meanwhile, PdO-ZSO nanoparticles are XRD, SEM, TEM, EDS, XPS and other characterization methods to further explain its morphological formation process. As the sensing materials, PdO-ZSO exhibits extraordinary gas sensing behaviors for hydrogen (H2) and butane (C4H10) and the response reaches 98 and 58 to H2 and C4H10 at operating temperature of 370 °C, respectively. And the response time and recovery time are both less than 2 s and 4 s respectively, with good repeatability and outstanding long-term stability. The existence of PdO is able to increase the resistance modulation range of heterostructure. And the enhanced gas sensing performances can be ascribed to the catalysis of noble metal doping and the formation of ternary heterostructure between PdO and ZnO-SnO2 nanocomposites. [ABSTRACT FROM AUTHOR]

It is highly desirable to develop sensors with high response and selectivity at room temperature of operating temperature. Besides, efficient and low-cost sensors are also required for future social development. In this paper, it is developed a detector with two-dimensional (2D) material of Ti3C2Tx MXene sensing material by a chemical etchant for ammonia sensing, which shows high response and excellent selectivity to ammonia (NH3) at room temperature of operating temperature. A key point of this work is the thermal treatment temperature of the sensing ceramic tube at 280 °C, which removes the adsorbed water and partially oxidized the material. In ambient condition, Ti3C2Tx MXene-280 shows the response to 500 ppm NH3 with 147 %, and the counterpart response and recovery time are 67 and 157 s at room temperature of operating temperature, respectively. In the environment of different relative humidity, its sensing performance is maintained at around 50 % of the initial performance, which shows great moisture resistance. The higher response and good selectivity of Ti3C2Tx MXene-280 sensor to NH3 at room temperature are ascribed to the powerful hydrogen bond formed between the OH−, O2− functional groups on Ti3C2Tx MXene-280 and NH3, as well as the synergistic effect of TiO2 and Ti3C2Tx MXene, generated after heating treatment, which increases the electron transport efficiency. The results demonstrated that the facilely designed Ti3C2Tx MXene-280 sensor is believed to contribute to developing future portable and selective sensing electronics at room temperature. [ABSTRACT FROM AUTHOR]

Different ratios (0, 1 and 3 mol%) of Ag decorated ZnO nanocrystallines are prepared via a simple low-temperature solvothermal method. The characterization results show that the as-prepared products are composed of numerous small nanocrystallines with irregular shapes. XPS analysis reveals the adsorbed oxygen on the surface of ZnO, which can react with the detected gas molecules and improve the sensor response. The gas-sensing properties of the sensors made from the Ag-decorated ZnO nanocrystallines are tested for hydrogen detection at 260 °C. The results show that the sensor made from 1 mol% Ag-decorated ZnO nanocrystallines exhibits excellent gas-sensing properties, demonstrating a high gas response of 59.35 toward 3000 ppm hydrogen, a fast response time (5 s) and recovery time (6 s) (with 1000 ppm hydrogen), good repeatability and stability. The improved hydrogen sensing properties can be attributed to the catalytic effect of Ag nanoparticles, which offer more active sites for the reaction and facilitate the adsorption and desorption of hydrogen on the surface of ZnO nanocrystallines. [ABSTRACT FROM AUTHOR]

Monitoring the concentration of methane (CH4) can effectively protect the environment from the damage of methane emission. The high sensing performances of methane gas sensor still remain a considerable challenge. Herein, to solve problems mentioned above, nanoporous network SnO2 (NN-SnO2) construct with ultra-small nanoparticles, which exhibits excellent gas-sensing performances for methane, are successfully synthesized via a weak acid glucose-assisted hydrothermal synthesis. The NN-SnO2 displays three particular particle morphologies: roundness, oval and polygon, with an average particle size of ~ 9 nm. When evaluated as a sensing material for methane, the NN-SnO2 sensor exhibits ultra-high response (Ra/Rg = 9.80), fast response/recovery times (τres/τrecov= 1 s/3 s) toward 3000 ppm methane at a operating temperature of 420 °C, which are far superior to the vast majority methane semiconducting sensors, and more importantly, it has barely been reported that the sensor based on NN-SnO2 presented such excellent gas-sensing performances for methane. The outstanding response of the NN-SnO2 for methane gas is derived from the unique mesopores nature and small particles sizes of the as-synthesized NN-SnO2, and the charge transfer between the surface of SnO2 nanoparticles and methane gas molecules. [ABSTRACT FROM AUTHOR]

One-dimensional fiber-like SnO2 nanomaterials (SnO2 nanofibers) were prepared by 'green' preparation approach that using shaddock peels as bio-templates via a facile hydrothermal method for the first time. The microstructure, morphology, chemical states and specific surface areas were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and N2 adsorption-desorption, respectively. Results indicating the as-synthesized SnO2 are fiber-like structures and composed of numerous nanoparticles, and with large specific surface areas (36.50 m2 g−1). The XPS spectra confirms that the existence of adsorbed oxygen (Oads) on the surface of product, which may lead to the response of gas sensor. The gas-sensing properties of the sensor based on SnO2 nanofibers for volatile organic compounds (VOCs) were investigated, such as methanol, ethanol, isopropanol, acetone, formaldehyde and n-butanol. The sensor showed high gas response, low detection limit and fast response towards various VOCs gases at the optimal operating temperature of 260 °C. These results demonstrated the potential of using as-synthesized SnO2 nanofibers for VOCs gases detection. In addition, the possible formation mechanism and the gas-sensing mechanism were also discussed. [ABSTRACT FROM AUTHOR]

Knowledge of the dynamic changes in the water absorption process of heat-treated wood is important for providing a scientific basis for the reasonable application of heat-treated wood, especially for outdoor applications. Nuclear magnetic resonance (NMR) techniques provide detailed information about the moisture components and moisture transport processes in wood, which are not available with other methods. In this work, water absorption of untreated and heat treated Chinese fir (Cunninghamia lanceolata [Lamb.] Hook.) heartwood was investigated using various NMR methods. The heat treatment temperatures were varied between 160 °C and 220 °C. According to the spin-spin relaxation time (T2), there were two components of water in the samples heat-treated at 160 °C and 180 °C as well as the untreated sample, while three components of water were found in the samples heat-treated at 200 °C and 220 °C, and the mass of each component was calculated by the integral peak areas of the T2 curve. The amount of bound water and free water in heat-treated samples were less compared to the untreated ones, and the water absorption decreased correspondingly, due to the increasing heat-treated temperature. The results obtained by one dimensional frequency coding indicated that the heat treatment made wood difficult to be accessed by moisture. Besides, NMR images revealed that the free water absorption in latewood was faster than in earlywood, but earlywood could absorb more water than latewood. [ABSTRACT FROM AUTHOR]

The mesoporous ZnCo2O4 nanosheets were synthesized via a facile hydrothermal method and subsequent thermal annealing treatment. The sample was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transition electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and N2 adsorption/desorption isotherms (BET) to obtain information about its crystal structure, morphology, and BET surface area, respectively. The nanosheets present hexagonal shape with mesoporous structure in nature. The obtained mesoporous ZnCo2O4 nanosheets exhibit a high specific surface area of 191.64 m2/g. The electrochemical properties of the mesoporous ZnCo2O4 nanosheets were investigated by cyclic voltammetry (CV), galvanostatic charge/discharge (GCD) in 6 mol/L KOH aqueous electrolyte. The ZnCo2O4 nanosheets show a high specific capacity of 835.26 F/g at the current density of 1.0 A/g, as well as good cycle stability with specific capacitance remaining 73.28% of the initial value after 1000 continuous charge-discharge cycles under the current density of 8 A/g. These superior electrochemical features demonstrate that the mesoporous ZnCo2O4 nanosheet is a promising electroactive material for supercapacitor. [ABSTRACT FROM AUTHOR]

Pd-functionalized one-dimensional (1D) SnO2 nanostructures were synthesized via a facile hydrothermal method and shaddock peels were used as bio-templates to induce a 1D-fiber-like morphology into the gas sensing materials. The gas-sensing performances of sensors based on different ratios of Pd-functionalized SnO2 composites were measured. All results indicate that the sensor based on 5 mol % Pd-functionalized SnO2 composites exhibited significantly enhanced gas-sensing performances toward butane. With regard to pure SnO2, enhanced levels of gas response and selectivity were observed. With 5 mol % Pd-functionalized SnO2 composites, detection limits as low as 10 ppm with responses of 1.38 ± 0.26 were attained. Additionally, the sensor exhibited rapid response/recovery times (3.20/6.28 s) at 3000 ppm butane, good repeatability and long-term stability, demonstrating their potential in practical applications. The excellent gas-sensing performances are attributed to the unique one-dimensional morphology and the large internal surface area of sensing materials afforded using bio-templates, which provide more active sites for the reaction between butane molecules and adsorbed oxygen ions. The catalysis and "spillover effect" of Pd nanoparticles also play an important role in the sensing of butane gas as further discussed in the paper. [ABSTRACT FROM AUTHOR]

Citric acid capped CdS quantum dots (CA-CdS QDs), a new assembled fluorescent probe for copper ions (Cu2+), was synthesized successfully by a simple hydrothermal method. In this work, the fluorescence sensor for the detection of heavy and transition metal (HTM) ions has been extensively studied in aqueous solution. The results of the present study indicate that the obtained CA-CdS QDs could detect Cu2+ with high sensitivity and selectivity. It found that the existence of Cu2+ has a significant fluorescence quenching with a large red shifted (from greenish-yellow to yellowish-orange), but not in the presence of 17 other HTM ions. As a result, Cu2S, the energy level below the CdS conduction band, could be formed at the surface of the CA-CdS QDs and leads to the quenching of fluorescence of CA-CdS QDs. Under optimal conditions, the copper ions detection range using the synthesized fluorescence sensor was 1.0 × 10‒8 M to 5.0 × 10‒5 M and the limit of detection (LOD) is 9.2 × 10‒9 M. Besides, the as-synthesized CA-CdS QDs sensor exhibited good selectivity toward Cu2+ relative to other common metal ions. Thus, the CA-CdS QDs has potential applications for detecting Cu2+ in real water samples. [ABSTRACT FROM AUTHOR]

The fluorescence intensity of N, S co-doped graphene quantum dots (N, S-GQDs) can be quenched by Fe 3+ and Hg 2+ . Density functional theory (DFT) simulation and experimental studies indicate that the fluorescence quenching mechanisms for Fe 3+ and Hg 2+ detection are mainly attributed to the inner filter effect (IFE) and dynamic quenching process, respectively. The electronegativity difference between C and doped atoms (N, S) in favor to introduce negative charge sites on the surface of N, S-GQDs leads to charge redistribution. Those negative charge sites facilitate the adsorption of cations on the N, S-GQDs' surface. Atomic population analysis results show that some charge transfer from Fe 3+ and Hg 2+ to N, S-GQDs, which relate to the fluorescent quenching of N, S-GQDs. In addition, negative adsorption energy indicates the adsorption of Hg 2+ and Fe 2+ is energetically favorable, which also contributes to the adsorption of quencher ions. Blue fluorescent N, S-GQDs were synthesized by a facile one-pot hydrothermal treatment. Fluorescent lifetime and UV-vis measurements further validate the fluorescent quenching mechanism is related to the electron transfer dynamic quenching and IFE quenching. The as-synthesized N, S-GQDs were applied as a fluorescent probe for Fe 3+ and Hg 2+ detection. Results indicate that N, S-GQDs have good sensitivity and selectivity on Fe 3+ and Hg 2+ with a detection limit as low as 2.88 and 0.27 nM, respectively.