ZnO半导体气体传感器

气体传感器从其材料与结构来说是多种多样的,但简单而又实用的气敏元件多采用金属氧化物半导体作为原料,其中ZnO、SnO_2和γ—Fe_2O_3是常用的检测还原性气体的敏感材料。这三种金属氧化物是一种N型半导体,当其表面吸附了电子给予性气体分子(例如H_2、CO等气体)时,由于半导体与气体分子之间费米能级的差异,会使电子从吸附于表面的气体分子向半导体方向运动,因此N型半导体的载流子密度加大,导电率增     

木犀草素清除自由基活性的密度泛函理论研究

采用密度泛函理论(DFT)的方法,分别从静态和动态两大方面分析了黄酮类化合物木犀草素分子不同酚羟基清除自由基活性的大小。分别从该化合物的结构参数、酚羟基(O-H)解离能、半醌式自由基电子的自旋密度分布、前线轨道相关性质分析了其性质与分子活性位的关系,深入解析了木犀草素分子上不同酚羟基清除·OH的反应历程,在UB3LYP/6-311G(d,p)水平下,优化得到了该分子C5、C7位酚羟基与·OH发生抽氢反应的过渡态结构。结果表明,C4’位O-H BDE最小,自旋密度分布最为均匀,·OH可以无需克服能垒直接夺取该位酚羟基H生成自由基和水,该位酚羟基最易失去H,抗氧化活性最大,C5位酚羟基与·OH发生抽氢反应所需要克服的能垒最大,该位酚羟基活性最小。     

基于MWCNTs的气敏测试纸

介绍了一种简单、可直接在纸上制作的气体传感测试纸.由多壁碳纳米管(MWCNTs)在纸上摩擦,粘附的MWCNTs即为传感器的敏感层.采用相同方法分别在不同的纸张上制作传感器,并对气敏性能进行了比较,结果表明:滤纸的多孔性和粗糙的表面,可以促使其上的敏感层吸附和释放气体分子,使气体传感器在室温条件下完全恢复.传感器具有良好的重复性和稳定性.气体传感测试纸可以进一步用于挥发性有机气体(VOCs)的检测开发.     

分子动力学模拟聚乙烯在碳纳米管表面的扩散

通过采用分子动力学方法模拟不同链长的聚乙烯分子在单壁碳纳米管表面的扩散,探究了聚乙烯的动力学性质。研究表明随着链长的增加聚乙烯在碳纳米管表面的扩散系数减小,且二者间存在明显的标度关系。聚乙烯在碳纳米管表面扩散的扩散系数和聚乙烯吸附在碳纳米管表面的构象有关,有序结构的聚乙烯比无序结构的聚乙烯在碳纳米管表面扩散的快。此外,由于受到碳纳米管吸附作用的影响,聚乙烯分子在平行于管轴和垂直于管轴2个方向上的扩散系数不同,扩散表现各向异性。     

煤表面对多种气体分子混合吸附的微观机理

应用量子化学密度泛函理论,在6-311 g水平上对建立的吸附模型进行全优化.结果表明,煤的表面能够与多组分气体发生混合吸附.煤表面吸附氧、氮和二氧化碳分子组成的吸附态中,氧分子和氮分子在煤表面的侧链吸附,CO2则在苯环的上方.煤表面氨基上的C原子和N原子的电子向氧分子中的氧原子转移.煤表面吸附了二氧化碳和氮分子,氧分子所得的电子减少,表明如果煤表面吸附其它种类分子,则削弱了吸附氧的作用.吸附后O2的频率变化较大,N2和CO2的频率变化很小.煤表面与矿井采空区各种气体发生吸附时的亲和顺序为:氧气>水>二氧化碳>氮气>一氧化碳>甲烷.     

碳纳米管修饰电极研究鸟嘌呤及其核苷的电化学行为及测定

利用微波辅助功能化的单壁碳纳米管可以均匀分散于二次水中,并可以在玻碳电极表面形成稳定的薄膜,利用该修饰电极研究了鸟嘌呤与鸟嘌呤核苷的电化学行为及其测定,并对鸟嘌呤和鸟嘌呤核苷的分别或同时测定条件进行了优化.结果表明,与裸玻碳电极相比,鸟嘌呤及其核苷在该单壁碳纳米管修饰电极上的氧化峰电流和检测灵敏度大大提高,该方法检出限低、分析速度快.酸降解的DNA在该修饰电极上可以得到对应鸟嘌呤的灵敏溶出峰,峰电流与DNA浓度在一定范围内成线性关系.     

甲烷气体对煤吸附二氧化碳气体的影响研究

煤炭自燃是煤矿的主要灾害之一。不仅烧毁宝贵资源,还严重危害井下工作人员的安全与健康。CO₂气体灭火可以应用于矿井的防灭火工作。煤矿井下的气体是多种气体的混合物,煤对很多种气体具有吸附特性。运用量子化学理论高斯03软件包对二氧化碳气体在煤表面吸附时,甲烷气体对其吸附能力的影响进行研究。结果表明,当煤表面分别吸附1个和2个CO₂分子时,有1个CH₄分子存在会促进煤表面吸附CO₂分子。但当CO₂分子的个数大于2个时,有1个CH₄分子存在就会抑制煤表面吸附CO₂分子。因此,CH₄分子对煤表面吸附CO₂分子是有影响的。甲烷气体的含量能够影响煤对二氧化碳气体的吸附。     

掺杂CNT的Fe2O3气体传感器对乙醇气敏特性的研究

采用酸化后的碳纳米管（CNT）对Fe2O3进行不同比例的掺杂,利用扫描电镜（SEM）对气敏材料进行表征,制作成旁热式气体传感器后在乙醇气氛中与Fe2O3气体传感器进行对比。重点分析了掺杂量,工作温度及气体浓度对传感器灵敏度及响应恢复时间的影响,并对气敏机理进行了详细研究。结果表明碳纳米管的适量掺杂有效的提高了传感器的灵敏度并缩短了响应恢复时间,其中在216℃时对50×10-6的乙醇气体灵敏度达3.4。     

石墨烯气体传感解吸附特性研究

分析探讨了石墨烯气体解吸附特性与解吸附方法。通过实验分析石墨烯对NO2气体分子的响应时间、气体分子解吸附时间,分析探讨石墨烯的气敏特性。实验表明,石墨烯对NO2气体传感灵敏度高,响应快,但恢复过程缓慢,气体解吸附时间长。分析表明,通过加热的方法、光照的方法可有效减少石墨烯气体解吸附时间,改善解吸附特性。     

一维纳米材料在气体传感器中的应用

评述了目前一维纳米材料在气体传感器中的应用进展.包括单壁碳纳米管、多壁碳纳米管、单根金属及金属氧化物纳米带或纳米线制作的传感器,这些传感器能在室温下检测,具有灵敏度高、漂移小的优点,但由于制作成本高昂、检测条件苛刻,离实用还很远.将氧化物一维纳米材料用于制作旁热式气敏元件,在保持其高灵敏度的同时提高稳定性,有助于解决旁热式气敏元件实用中存在的稳定性差的问题,将成为目前实用化研究的一个热点.     

柔性高灵敏单壁碳纳米管气体传感器研究

在柔性聚对二甲苯C基底上制作了基于单壁碳纳米管的小型化、高灵敏、反应快速的气体传感器。使用介质电泳集成碳管束,并利用单链脱氧核糖核酸修饰增强器件灵敏度。当传感器暴露在甲醇蒸气中时,会出现明显可重复的反应,它可以检测含量低至4.3×10-6的甲醇,并且在相当宽的体积分数范围有清晰的分辨能力。对于4.3×10-6的含量,未修饰的传感器对应电阻变化率是4.8%;经过脱氧核糖核酸修饰,电阻变化率增加到了12.3%。此外,该传感器还显示了很快的响应速度和很好的测试复验性。研究表明:这种柔性气体传感器在未来环境监测应用中有很好的前景。     

Development of an ozone gas sensor using single-walled carbon nanotubes

This study deals with the fabrication of an ozone gas sensor using single-walled carbon nanotubes (SWCNTs) as sensing material. The SWCNTs are dispersed by N,N-dimethylformamide (DMF). The CNT-DMF solution was dropped between interdigitated electrodes’ fingers to fabricate ozone gas sensor. For ozone environment, a commercial ozone generator was introduced. To improve sensor response, the deposited carbon nanotubes network was thermally treated at high temperature in a furnace. The sensor exhibits high sensitivity to ozone gas at concentration as low as 50 ppb, and fast response time, which is promising for future commercialization of carbon nanotubes based ozone gas sensor.     

Molecular dynamics simulation of non-covalent single-walled carbon nanotube functionalization with surfactant peptides

Non-covalent functionalized single-walled carbon nanotubes (SWCNTs) with improved solubility and biocompatibility can successfully transfer drugs, DNA, RNA, and proteins into the target cells. Theoretical studies such as molecular docking and molecular dynamics simulations in fully atomistic scale were used to investigate the hydrophobic and aromatic π–π-stacking interaction of designing four novel surfactant peptides for non-covalent functionalization of SWCNTs. The results indicated that the designed peptides have binding affinity towards SWCNT with constant interactions during MD simulation times, and it can even be improved by increasing the number of tryptophan residues. The aromatic content of the peptides plays a significant role in their adsorption in SWCNT wall. The data suggest that π–π stacking interaction between the aromatic rings of tryptophan and π electrons of SWCNTs is more important than hydrophobic effects for dispersing carbon nanotubes; nevertheless SWCNTs are strongly hydrophobic in front of smooth surfaces. The usage of aromatic content of peptides for forming SWCNT/peptide complex was proved successfully, providing new insight into peptide design strategies for future nano-biomedical applications.     

Structure and electronic properties of "DNA-gold-nanotube" systems: a quantum chemical analysis

The development of novel DNA sensors is a crucial issue in the diagnosis of pathogenic and genetic diseases. We have used density functional theory (DFT) to investigate the performance of hybrid DNA sensors consisting of a gold atom (Au) deposited on two types of single-walled carbon nanotubes: armchair SWCNT(8,0)/Au and zigzag SWCNT(5,5)/Au and compared these with bare Au. We also chose adenine:thymine (A:T) as a Watson-Crick base pair of the DNA double helix. In the recognition probe, SWCNT/Au/A, adenine is immobilized on the SWCNT/Au supporter via its active N7 anchor point. After thymine hybridization (SWCNT/Au/A:T), the overall modulations compared with the original systems. Due to the complimentary functions of gold, which acts as a powerful electron withdrawing and transmitting group and of the SWNCTs, which act as electron collecting centers, respectively, the hybrid systems, "SWNCTs/Au", were found to exhibit more stability and sensitivity than the Au center alone. The changes in the HOMO-LUMO band gaps and in the atomic partial charges upon binding of thymine were rather small, but the change of the overall dipole moment was considerably larger in SWCNT/Au/A than it was in Au/A alone. The overall results suggest that the "SWCNTs/gold" system is a potential candidate for a nanostructure-based DNA sensor.     

Effect of NH3 gas on the electrical properties of single-walled carbon nanotube bundles

This study deals with the fabrication of sensors from single-walled carbon nanotubes (SWNTs) of 1.2 nm in diameters by a screen-printing method. These sensors have been exposed to ammonia (NH₃) gas at room temperature with nitrogen as the carrier gas.It was found that the electrical properties of SWNTs alter with temperature or the adsorption of ammonia gas. The SWNT is very sensitive to NH₃ gas. It can detect NH₃ in as low as concentration of 5 ppm. The sensitivity increases with increasing concentration. A saturation state is established at a concentration of ∼40 ppm, and the sensitivity of the sensor continues to increase in conjunction with an increase in concentration levels. Both the heating and increasing flux rates of carrier gas are used to improve gas desorption. The adsorption mechanism of gaseous molecules on SWNT bundle is discussed.     

Electronic properties and gas adsorption behaviour of pristine,silicon-, and boron-doped (8, 0) single-walled carbon nanotube: A first principles study

Carbon nanotubes (CNTs) have received enormous attention due to their fascinating properties to be used in various applications including electronics, sensing, energy storage and conversion. The first principles calculations within density functional theory (DFT) have been carried out in order to investigate the structural, electronic and optical properties of un-doped and doped CNT nanostructures. O₂, CO₂, and CH₃OH have been chosen as gas molecules to study the adsorption properties based on zigzag (8,0) SWCNTs. The results demonstrate that the adsorption of O₂, CO_2, and CH₃OH gas molecules on pristine, Si-doped and B-doped SWCNTs are either physisorption or chemisorption. Moreover, the electronic properties indicating SWCNT shows significant improvement toward gas adsorption which provides the impact of selecting the best gas sensor materials towards detecting gas molecule. Therefore, these pristine, Si-, and B-doped SWCNTs can be considered to be very good potential candidates for sensing application.     

Adsorption of plasma proteins onto PEGylated single-walled carbon nanotubes: The effects of protein shape,PEG size and grafting density

Single-walled carbon nanotubes (SWCNTs) covalently functionalized or noncovalently coated with polyethylene glycol (PEG) of different sizes (M_w = 2000 and 5000) and grafting densities (5–16 PEGs per SWCNT) are simulated with human fibrinogen (HFG) and serum albumin (HSA). Proteins migrate toward the SWCNT, but their adsorption extents differ. The extent of the HFG-SWCNT binding decreases with increasing PEG size and grafting density because PEGs more completely cover SWCNTs and thus block hydrophobic interactions between HFGs and SWCNTs, which occurs on PEG-functionalized SWCNTs but not on PEG-coated ones. In particular, the HFG-SWCNT binding significantly decreases in the transition region of PEG conformation from mushroom to brush, where PEGs extend like brushes as described in the Alexander-de Gennes theory. While the HFG adsorption is modulated by PEG conformation, the HSA adsorption is much weaker and less influenced by PEG, because spherical HSAs can bind to the restricted area of the SWCNT and thus cannot bind to the SWCNT as tightly as do linear HFGs. These findings agree with experiments showing less adsorption of proteins on the SWCNT functionalized with larger and more PEGs, and support experimental suggestions regarding the dependence of protein adsorption on protein shape and the mushroom-brush transition of PEG conformation.     

Metal (Pd, Pt)-decorated carbon nanotubes for CO and NO sensing

Using the first-principles calculations, we investigated adsorption of CO and NO gas molecules on the Pd- and Pt-decorated single-walled carbon nanotube (SWNT). The metal-decorated SWNTs exhibit strong affinity toward the gas molecules. Our results reveal that the CO and NO gas molecules can be chemisorbed on the Pd or Pt atom, accompanying with the large binding energy and significant charge transfer. Adsorption of these gases would affect the electronic conductance of the materials, which can serve as a signal of gas sensor. In particular, adsorption of NO generates the magnetic properties to the metal-decorated SWNT, which can also serve as a sensitive signal for chemical sensors. After adsorption of CO and NO, the changes in binding energy, charge transfer and conductance may lead to the different response in the metal-doped CNT-based sensors. It is expected that these results could provide helpful information for the design and fabrication of the CO and NO sensing devices.     

Free and forced vibration analysis of viscoelastic damped FG-CNT reinforced micro composite beams

In this paper, free and forced vibration analysis of viscoelastic microcomposite beam reinforced by functionally graded single-walled carbon nanotubes (FG-SWCNTs) is studied using the modified couple stress theory (MCST). The material properties of micro composite beam by generalized rule of mixtures carbon nanotubes are estimated. In addition, these properties are stated as uniform, and functionally graded (FG) distributions in the thickness direction. Energy method and Hamilton’s principle are employed to establish the governing equations of motion for the vibration of viscoelastic damped micro composite beam reinforced by SWCNTs based on the Kelvin–Voigt model. The influences of material length scale parameter, structural damping coefficient and different distributions of SWCNTs on non-dimensional complex natural frequency and amplitude vibration of the viscoelastic micro composite beam are investigated. The results reveal that the lowest vibration amplitude of FG microcomposite beam by the FG-X and the highest occurs by FG-◊. Moreover, in the presence of external periodic load and the absence of structural damping coefficient, the vibration amplitude increases and FG microcomposite beam becomes unstable, even though the amplitude of vibration decreases with increasing structural damping coefficient. It is shown that the natural frequency of SWCNT reinforced composite is more than the frequency of multi-walled carbon nanotubes because SWCNT have more stiffness. In addition, the results illustrate that the experimental data by Lei et al. agree well with those predicted by the MCST in the present work.