Browsing by Author "Zhang, Lei"
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Item Beat frequency quartz-enhanced photoacoustic spectroscopy for fast and calibration-free continuous trace-gas monitoring(Springer Nature, 2017) Wu, Hongpeng; Dong, Lei; Zheng, Huadan; Yu, Yajun; Ma, Weiguang; Zhang, Lei; Yin, Wangbao; Xiao, Liantuan; Jia, Suotang; Tittel, Frank K.Quartz-enhanced photoacoustic spectroscopy (QEPAS) is a sensitive gas detection technique which requires frequent calibration and has a long response time. Here we report beat frequency (BF) QEPAS that can be used for ultra-sensitive calibration-free trace-gas detection and fast spectral scan applications. The resonance frequency and Q-factor of the quartz tuning fork (QTF) as well as the trace-gas concentration can be obtained simultaneously by detecting the beat frequency signal generated when the transient response signal of the QTF is demodulated at its non-resonance frequency. Hence, BF-QEPAS avoids a calibration process and permits continuous monitoring of a targeted trace gas. Three semiconductor lasers were selected as the excitation source to verify the performance of the BF-QEPAS technique. The BF-QEPAS method is capable of measuring lower trace-gas concentration levels with shorter averaging times as compared to conventional PAS and QEPAS techniques and determines the electrical QTF parameters precisely.Item Cavity-enhanced photoacoustic sensor based on a whispering-gallery-mode diode laser(Copernicus Publications, 2019) Pan, Yufeng; Dong, Lei; Wu, Hongpeng; Ma, Weiguang; Zhang, Lei; Yin, Wangbao; Xiao, Liantuan; Jia, Suotang; Tittel, Frank K.A cavity-enhanced photoacoustic (CEPA) sensor was developed based on an ultra-narrow linewidth whispering-gallery-mode (WGM) diode laser. A cavity-enhanced photoacoustic module (CEPAM) was designed to match the output beam from the WGM-diode laser, resulting in an increase in the excitation light power, which, in turn, significantly enhanced the photoacoustic signal amplitude. The results show that a signal gain factor of 166 was achieved, which is in excellent agreement with the power enhancement factor of 175 after considering the power transmissivity. The performance of the sensor was evaluated in terms of the detection sensitivity and linearity. A 1σ detection limit of 0.45 ppmV for C2H2 detection was obtained at atmospheric pressure with a 1 s averaging time.Item Functionalization of single walled carbon nanotubes(2006) Zhang, Lei; Barron, Andrew R.Single walled carbon nanotubes (SWNTs) exhibit unique mechanical and physical properties and immediately after their discovery they were regarded as novel materials for future technologies. SWNTs are widely thought of as one of the basic building blocks to nanotechnology. However, they are very hard to disperse and dissolve in either water or organic solvent. The insolubility of nanotubes makes it very difficult to make composites of nanotubes with other materials. This limits nanotubes from the application for future technology. A feasible functionalization of nanotubes, i.e., the attachment of "chemical functional groups" provides a strategy for overcoming these barriers and has thus attracted synthetic chemists and materials scientists to contribute their efforts to making breakthrough. Functionalization can improve solubility and processibility, and will be able to link the unique properties of nanotubes to those of other types of materials. Through the chemical functional groups, nanotube may show improved solubility and compatibility with solvents, polymers, nanoparticles and other nanotubes. A functionalized SWNT may have mechanical or electrical properties that are different from those of the pristine SWNT, and thus may be used for fine-tuning the chemistry and physical properties of SWNTs. Fluorination of side walls of the SWNTs has been performed by using the technology developed for the fluorination of graphite, and then subsequent nucleophilic substitutions have been explored. It has been ascertained that in fluorination at the optimal temperature, C:F ratios of up to 2:1 can be achieved without disruption of the tubular structure. The fluorinated SWNTs proved to be much more soluble than pristine SWNTs in alcohols, N,N-dimethylformamide and some other selected organic solvents. This improved solubility and the high fluorine addition allow much more efficient solution-phase chemistry on the fluorinated SWNTs. The goals of this work were to examine novel type of reactions that one can do with fluorinated SWNTs and study the basic aspects of functionalization of SWNTs, i.e. the mechanism of functionalization, the structure of fluorinated SWNTs, and the distribution of functional groups in the functionalized SWNTs. In this thesis, an extensive NMR study of fluorinated SWNTs has been explored (Chapter 1) and this study gives us a deeper insight to the structure of fluorinated SWNTs and the mechanism of fluorination. A series of "hydroxyl nanotube" have been simply prepared by two types of one-step methods (Chapter 2). Amino-acid functionalized nanotubes with high water solubility and sensitive pH value dependence have been achieved, and the influence of different chain length of amino acid on the water solubility was detailed (Chapter 3). The nanotube-nanoparticle heterostructures have been prepared and used to investigate the distribution of functional groups along the axis of nanotubes (Chapter 4). Finally, a novel type of reaction, Diels-Alder cycloaddition to fluorinated nanotubes was successfully performed under a mild reaction conditions (Chapter 5).Item Highly sensitive and selective CO sensor using a 2.33 μm diode laser and wavelength modulation spectroscopy(Optical Society of America, 2018) Cui, Ruyue; Dong, Lei; Wu, Hongpeng; Li, Shangzhi; Zhang, Lei; Ma, Weiguang; Yin, Wangbao; Xiao, Liantuan; Jia, Suotang; Tittel, Frank K.A ppm-level CO sensor based on a 2f wavelength modulation spectroscopy (2f-WMS) technique was developed for the application of SF6 decomposition analysis in an electric power system. A detailed investigation of the optimum target line selection was carried out to avoid spectral interference from high purity SF6 in a wide wavelength range. A diode laser emitting at 2.33 μm and a 14.5-m multipass gas cell (MGC) was employed to target the R(6) line of the CO first overtone band and increase the optical path, respectively, thus resulting in a minimum detection sensitivity of 1 ppm. A Levenberg-Marquardt nonlinear least-squares fit algorithm makes full use of the information from all data points of the 2f spectrum and as a result, a measurement precision of ~40 ppb was achieved with a data update rate of 0.6 s. The sensor performance was also evaluated in terms of the gas flow rate, stability, and linearity. The results showed that the best operating condition with a precision of 6 ppb can be achieved by increasing the gas flow rate to the value that matches the optimum averaging time of 48 s.Item Highly sensitive photoacoustic multicomponent gas sensor for SF6 decomposition online monitoring(Optical Society of America, 2019) Yin, Xukun; Dong, Lei; Wu, Hongpeng; Zhang, Lei; Ma, Weiguang; Yin, Wangbao; Xiao, Liantuan; Jia, Suotang; Tittel, Frank K.A ppb-level photoacoustic multicomponent gas sensor system for sulfur hexafluoride (SF6) decomposition detection was developed by the use of two near-infrared (NIR) diode lasers and an ultraviolet (UV) solid-state laser. A telecommunication fiber amplifier module was used to boost up the excitation optical power from the two NIR lasers. A dual-channel high-Q photoacoustic cell (PAC) was designed for the simultaneous detection of CO, H2S, and SO2 in SF6 buffer gas by means of a time division multiplexing (TDM) method. Feasibility and performance of the multicomponent sensor was evaluated, resulting in minimum detection limits of 435 ppbv, 89 ppbv, and 115 ppbv for CO, H2S, and SO2 detection at atmospheric pressure.Item Highly sensitive SO2 photoacoustic sensor for SF6decomposition detection using a compact mW-level diode-pumped solid-state laser emitting at 303 nm(The Optical Society, 2017) Yin, Xukun; Dong, Lei; Wu, Hongpeng; Zheng, Huadan; Ma, Weiguang; Zhang, Lei; Yin, Wangbao; Xiao, Liantuan; Jia, Suotang; Tittel, Frank K.A compact ppb-level SO2 photoacoustic sensor was developed for the application of SF6decomposition detection in electric power systems. The selection of the SO2 target spectrum is discussed in detail in the infrared (IR) and ultraviolet (UV) spectral regions. Based on the result of the spectrum selection, a small-sized UV-band diode-pumped solid-state laser (DPSSL) emitting at 303.6 nm with an output power of 5 mW was developed. A differential photoacoustic cell (PAC) was designed to match the output optical beam, obtain a high Q-factor and reduce the system flow noise in the SF6 buffer gas. The performance of the sensor system was assessed in terms of gas flow rate, linearity and detection sensitivity. A SO2 detection limit (1σ) of 74 ppbv was achieved with a 1-s integration time, which corresponds to a normalized noise equivalent absorption (NNEA) coefficient of 1.15 × 10−9 cm−1WHz-1/2.Item Overtone resonance enhanced single-tube on-beam quartz enhanced photoacoustic spectrophone(AIP Publishing LLC, 2016) Zheng, Huadan; Dong, Lei; Sampaolo, Angelo; Patimisco, Pietro; Ma, Weiguang; Zhang, Lei; Yin, Wangbao; Xiao, Liantuan; Spagnolo, Vincenzo; Jia, Suotang; Tittel, Frank K.A single-tube on-beam quartz enhanced photoacoustic spectroscopy (SO-QEPAS) spectrophone, which employs a custom-made quartz tuning fork (QTF) having a prong spacing of 700 μm and operating at the 1st overtone flexural mode, is reported. The design of QTF prong geometry allows the bare QTF to possess twice higher Q-factor values for the 1st overtone resonance mode falling at ∼17.7 kHz than in the fundamental resonance mode at ∼2.8 kHz, resulting in an 8 times higher QEPAS signal amplitude when operating in the 1st overtone resonance mode. Both the vertical position and length of the single-tube acoustic micro-resonator (AmR) were optimized to attain optimal spectrophone performance. Benefiting from the high overtone resonance frequency and the quasi 1st harmonic acoustic standing waves generated in the SO-QEPAS configuration, the AmR length is reduced to 14.5 mm. This allows the realization of compact spectrophone and facilitates the laser beam alignment through the QTF + AmR system. The signal enhancement in the overtone resonance mode and the high acoustic coupling efficiency between the AmR and QTF in the SO-QEPAS configuration yields an overall sensitivity enhancement factor of ∼380 with respect to the bare custom QTF operating in the fundamental resonance mode.Item Ppb-level H2S detection for SF6 decomposition based on a fiber-amplified telecommunication diode laser and a background-gas-induced high-Q photoacoustic cell(AIP Publishing, 2017) Yin, Xukun; Dong, Lei; Wu, Hongpeng; Ma, Weiguang; Zhang, Lei; Yin, Wangbao; Xiao, Liantuan; Jia, Suotang; Tittel, Frank K.A ppb-level hydrogen sulfide (H2S) gas sensor for sulfur hexafluoride (SF6) decomposition analysis was developed by means of a background-gas-induced high-Q differential photoacoustic cell (PAC) and a fiber-amplified telecommunication diode laser. The watt-level excitation laser power compensates the sensitivity loss as a result of using a low cost, near-IR laser source. The differential design with a large cylindrical resonator diameter allows the PAC to accommodate the high power beam and maintain a low noise level output. The theory of background-gas-induced high-Q PAC is provided and was verified experimentally. A H2S detection limit (1σ) of 109 ppb in a SF6 buffer gas was achieved for an averaging time of 1 s, which corresponds to a normalized noise equivalent absorption coefficient of 2.9 × 10−9 cm−1 W Hz−1/2.Item Quartz enhanced photoacoustic H2S gas sensor based on a fiber-amplifier source and a custom tuning fork with large prong spacing(AIP Publishing LLC, 2015) Wu, Hongpeng; Sampaolo, Angelo; Dong, Lei; Patimisco, Pietro; Liu, Xiaoli; Zheng, Huadan; Yin, Xukun; Ma, Weiguang; Zhang, Lei; Yin, Wangbao; Spagnolo, Vincenzo; Jia, Suotang; Tittel, Frank K.A quartz enhanced photoacoustic spectroscopy (QEPAS) sensor, employing an erbium-doped fiber amplified laser source and a custom quartz tuning fork (QTF) with its two prongs spaced ∼800 μm apart, is reported. The sensor employs an acoustic micro-resonator (AmR) which is assembled in an “on-beam” QEPAS configuration. Both length and vertical position of the AmR are optimized in terms of signal-to-noise ratio, significantly improving the QEPAS detection sensitivity by a factor of ∼40, compared to the case of a sensor using a bare custom QTF. The fiber-amplifier-enhanced QEPAS sensor is applied to H2S trace gas detection, reaching a sensitivity of ∼890 ppb at 1 s integration time, similar to those obtained with a power-enhanced QEPAS sensor equipped with a standard QTF, but with the advantages of easy optical alignment, simple installation, and long-term stability.Item Quartz-enhanced conductance spectroscopy for nanomechanical analysis of polymer wire(AIP Publishing LLC, 2015) Zheng, Huadan; Yin, Xukun; Zhang, Guofeng; Dong, Lei; Wu, Hongpeng; Liu, Xiaoli; Ma, Weiguang; Zhang, Lei; Yin, Wangbao; Xiao, Liantuan; Jia, Suotang; Tittel, Frank K.Quartz-enhanced conductance spectroscopy is developed as an analytical tool to investigate dynamic nanomechanical behaviors of polymer wires, in order to determine the glass transition temperature (Tg). A polymethyl methacrylate (PMMA) microwire with a diameter of 10 μm was bridged across the prongs of a quartz tuning fork (QTF). With the advantage of QTF self-sensing as compared with micro-cantilevers or other resonators, the resonance frequency and Q factor can be directly determined by means of its electrical conductance spectra with respect to the frequency of the external excitation source (dI/dV vs f), and therefore, no optical beam is required. The Tg of the PMMA microwire was determined by the maximum loss modulus of the QTF, calculated from the resonance frequency and the Q factor as a function of temperature. The measured Tg of the PMMA is 103 °C with an error of ±2 °C. Both heating/cooling and physical aging experiments were carried out, demonstrating that the technique is both reversible and reproducible.Item Sidewall functionalization of carbon nanotubes with organosilanes for polymer composites(2013-09-24) Barrera, Enrique V.; Zhu, Jiang; Zhang, Lei; Khabashesku, Valery N.; Margrave, John L.; Kim, Jong Dae; Rice University; United States Patent and Trademark OfficeThe present invention is directed to methods of functionalizing carbon nanotubes (CNTs), particularly single-wall carbon nanotubes (SWNTs), with organosilane species, wherein such functionalization enables fabrication of advanced polymer composites. The present invention is also directed toward the functionalized CNTs, advanced CNT-polymer composites made with such functionalized CNTs, and methods of making such advanced CNT-polymer composites.Item Sidewall functionalization of nanotubes with hydroxyl terminated moieties(2009-12-15) Khabashesku, Valery N.; Zhang, Lei; Margrave, John L.; Margrave, Mary Lou; Rice University; United States Patent and Trademark OfficeThe present invention is directed to methods of forming sidewall-functionalized carbon nanotubes, wherein such functionalized carbon nanotubes have hydroxyl-terminated moieties covalently attached to their sidewalls. Generally, such methods involve chemistry on carbon nanotubes that have first been fluorinated. In some embodiments, fluorinated carbon nanotubes (“fluoronanotubes”) are reacted with mono-metal salts of a dialcohol, MO—R—OH, where M is a metal and R is hydrocarbon or other organic chain and/or ring structural unit. In such embodiments, —O—R—OH displaces —F on the nanotube, the fluorine leaving as MF. Generally, such mono-metal salts are formed in situ by the addition of MOH to one or more dialcohols in which the fluoronanotubes have been dispersed. In some embodiments, fluoronanotubes are reacted with amino alcohols, such as being of the type H2N—R—OH, wherein —N(H)—R—OH displaces —F on the nanotube, the fluorine leaving as HF.Item Simultaneous dual-gas QEPAS detection based on a fundamental and overtone combined vibration of quartz tuning fork(AIP Publishing LLC, 2017) Wu, Hongpeng; Yin, Xukun; Dong, Lei; Pei, Kailong; Sampaolo, Angelo; Patimisco, Pietro; Zheng, Huadan; Ma, Weiguang; Zhang, Lei; Yin, Wangbao; Xiao, Liantuan; Spagnolo, Vincenzo; Jia, Suotang; Tittel, Frank K.A dual-gas quartz-enhanced photoacoustic spectroscopy (QEPAS) sensor system based on a frequency division multiplexing technique of a quartz tuning fork (QTF) was developed and experimentally demonstrated. Two beams from two independently modulated lasers are focused at two different positions between the QTF prongs to excite both the QTF fundamental and 1st overtone flexural modes simultaneously. The 2f-wavelength modulation technique is employed by applying two sinusoidal dithers, whose frequencies are equal to a half of the QTF fundamental and 1st overtone frequencies, respectively, to the currents of two excitation lasers. The resonance frequency difference between two flexural modes ensures that the correlated photoacoustic signals generated by different target gases do not interfere with each other. The proposed QEPAS methodology realizes a continuous real-time dual-gas monitoring with a simple setup and small sensor size compared with previous multi-gas QEPAS sensors.