Length-controlled cellulose nanofibrils produced using enzyme pretreatment and grinding

The length of cellulose nanofibrils (CNFs) is a significant parameter for various applications. The goal of this research was to employ a fabrication method to produce length-controlled CNFs; the chosen technique was enzy-grinding (enzyme pretreatment followed by mechanical grinding). Here, we presented the results of the optimization of the diameter and length, the characterization of the properties of CNFs and nanofilms prepared using these fibrils. The cellulose morphology, crystallinity index (CrI), chemical structure, and thermal stability were investigated as functions of the enzyme loading and hydrolysis time. The results showed that enzy-grinding could effectively reduce the diameter and length of cellulose fibrils. The average diameter was about 8.6 ± 3.6 nm, and the length could be controlled over the range from 0.76 ± 0.38 μm to ≥ 4 μm (i.e. aspect ratios from 43 to ≥ 328). After the grinding process, the CNFs maintained high thermal stability and no change in the chemical structure compared to the original pulp. The transmittance and mechanical properties of the CNF films were strongly dependent on the fibril length. The fabrication of length-controlled CNFs using the enzy-grinding process is meaningful and significant research which could be relevant to the optimization of such materials for various applications.     

Cobalt oxide and carbon modified hematite nanorod arrays for improved photoelectrochemical water splitting

Given the proper band gap, low cost and good stability, hematite(α-Fe_2O_3) has been considered as a promising candidate for photoelectrochemical(PEC) water splitting, however suffers from the sluggish surface water oxidation reaction kinetics. In this study, a simple dip-coating process was used to modify the surface of α-Fe_2O_3 nanorod arrays with cobalt oxide(CoO_x) and carbon(C) for the improved PEC performance, with a photocurrent density at 1.6 V(vs. reversible hydrogen electrode, RHE) increased from 0.10 mA/cm~2 for the pristine α-Fe_2O_3 to 0.37 mA/cm~2 for the CoO_x/C modified α-Fe_2O_3 nanorods. As revealed by electrochemical analysis, thanks to the synergistic effect of CoO_x and C, the PEC enhancement could be attributed to the enhanced charge transfer ability, decreased surface charge recombination, and accelerated water oxidation reaction kinetics. This study serves as a good example for improving PEC water splitting performance via a simple method.     

Enhanced open-circuit voltage in methoxyl substituted benzodithiophene-based polymer solar cells

The open-circuit voltage (V _oc) is one of the important parameters that influence the power conversion efficiency (PCE) of polymer solar cells. Its value is mainly determined by the energy level offset between the highest occupied molecular orbital (HOMO) of the donor and the lowest unoccupied molecular orbital (LUMO) of the acceptor. Therefore, decreasing the HOMO value of the polymer could lead to a high V _oc and thus increasing the cell efficiency. Here we report a facile way to lower the polymer HOMO energy level by using methoxyl substituted-benzodithiophene (BDT) unit. The polymer with the methoxyl functionl group (POBDT(S)-T1) exhibited a HOMO value of–5.65 eV, which is deeper than that (–5.52 eV) of polymer without methoxyl unit (PBDT(S)-T1). As a result, POBDT(S)-T1-based solar cells show a high V _oc of 0.98 V and PCE of 9.2%. In contrast, PBDT(S)-T1-based devices show a relatively lower V _oc of 0.89 V and a moderate PCE of 7.4%. The results suggest that the involvement of methoxyl group into conjugated copolymers can efficiencly lower their HOMO energy levels.     

Modeling Time-Varying Effects With Large-Scale Survival Data: An Efficient Quasi-Newton Approach

Nonproportional hazards models often arise in biomedical studies, as evidenced by a recent national kidney transplant study. During the follow-up, the effects of baseline risk factors, such as patients’ comorbidity conditions collected at transplantation, may vary over time. To model such dynamic changes of covariate effects, time-varying survival models have emerged as powerful tools. However, traditional methods of fitting time-varying effects survival model rely on an expansion of the original dataset in a repeated measurement format, which, even with a moderate sample size, leads to an extremely large working dataset. Consequently, the computational burden increases quickly as the sample size grows, and analyses of a large dataset such as our motivating example defy any existing statistical methods and software. We propose a novel application of quasi-Newton iteration method to model time-varying effects in survival analysis. We show that the algorithm converges superlinearly and is computationally efficient for large-scale datasets. We apply the proposed methods, via a stratified procedure, to analyze the national kidney transplant data and study the impact of potential risk factors on post-transplant survival. Supplementary materials for this article are available online.     

Synthesis and extremely high gas permeability of polyacetylenes containing polymethylated indan/tetrahydronaphthalene moieties

Polymethylated poly(diphenylacetylene) derivatives, a new category of substituted polyacetylenes, were successfully synthesized, and proved to show extremely high gas permeability.     

胶体晶体剪切模量的影响因素

利用自行搭建的扭转共振谱仪,研究了不同粒子体系胶体晶体在不同体积分数下的剪切模量,利用反射光谱测量了相应的晶体结构及内部孔洞等参数.结果表明,同一粒子体系的剪切模量均随体积分数的增加而增大;而对于同样的粒子数密度,不同粒子体系的剪切模量随体系内部孔洞所占比例增加呈增大趋势.对实验结果的分析及与理论分析的对比表明,决定胶体晶体剪切模量大小的主要因素是胶体晶体中粒子的最近邻间距,从而统一解释了体积分数和内部孔洞对胶体晶体剪切模量的影响.     

吡唑亚胺镍配合物的合成、表征及催化1, 3-丁二烯聚合

合成了一系列吡唑亚胺二齿Ni(Ⅱ)配合物(4a~4e), 并通过红外光谱、元素分析及单晶衍射等对配合物进行了表征。 配合物4b属于单斜晶系, 以Ni原子为中心形成扭曲的三角双锥构型。 该系列配合物在倍半乙基氯化铝(EASC)的活化下, 对1, 3-丁二烯聚合表现出较高的顺-1, 4选择性, 得到了相对分子质量为4500~9000、顺-1, 4含量在91%左右的液体聚丁二烯。 随着取代基空间位阻的增大, 催化活性逐渐减低。 进一步详细研究了Al/Ni摩尔比和温度对聚合的影响。 在20~60 ℃范围内, 催化活性随着聚合温度的升高而提高, 聚合温度为80 ℃时, 聚合物收率仅略有降低, 表明该系列催化剂产生的活性中心具有良好的高温稳定性。     

锚定基团对HKUST-1/TEMPO共催化体系催化性能的影响

用异烟酸(Iso-NTA)为桥接分子, 将有机小分子自由基4-氨基-2,2,6,6-四甲基哌啶-1-氧自由基(4-NH₂-TEMPO)与异烟酸缩合, 合成出含吡啶官能团的TEMPO自由基(Iso-NTA-TEMPO). 与TEMPO相比, Iso-NTA-TEMPO具有较高的氧化电位, 在无Cu(Ⅱ)辅助时, Iso-NTA-TEMPO对苯甲醇的氧化效率高于TEMPO. 在与HKUST-1组成的复合催化体系中, Iso-NTA-TEMPO可通过吡啶基团与HKUST-1孔道中的Cu(Ⅱ)相互作用, 从而在催化过程中(部分)锚定在HKUST-1孔道内部. 与TEMPO/HKUST-1体系相比, Iso-NTA-TEMPO/HKUST-1体系表现出对芳香醇更加高效的催化活性. 采用模板辅助溶剂诱导结晶法合成的HKUST-1晶体表面具有较多缺陷, 更有利于Iso-NTA-TEMPO自由基分子扩散进入HKUST-1孔道内部, 也有助于提高Iso-NTA-TEMPO/HKUST-1体系的催化效率. Iso-NTA-TEMPO/HKUST-1体系可将各种取代基(苄醇、 杂环醇以及二级脂肪醇)高效、 高选择性地氧化成相应的醛或酮.     

Effects of supply air temperature and inlet location on particle dispersion in displacement ventilation rooms

The effects of supply temperature and vertical location of inlet air on particle dispersion in a displacement ventilated (DV) room were numerically modeled with validation by experimental data from the literature. The results indicate that the temperature and vertical location of inlet supply air did not greatly affect the air distribution in the upper parts of a DV room, but could significantly influence the airflow pattern in the lower parts of the room, thus affecting the indoor air quality with contaminant sources located at the lower level, such as particles from working activities in an office. The numerical results also show that the inlet location would slightly influence the relative ventilation efficiency for the same air supply volume, but particle concentration in the breathing zone would be slightly lower with a low horizontal wall slot than a rectangular diffuser. Comparison of the results for two different supply temperatures in a DV room shows that, although lower supply temperature means less incoming air volume, since the indoor flow is mainly driven by buoyancy, lower supply temperature air could more efficiently remove passive sources (such as particles released from work activities in an office). However, in the breathing zone it gives higher concentration as compared to higher supply air temperature. To obtain good indoor air quality, low supply air temperature should be avoided because concentration in the breathing zone has a stronger and more direct impact on human health.     

强激光远场光束质量参数的测试

 提出漫射红外成像-多点标校测量方法,用于测量强激光远场光束质量参数。在激光远场距离处设置漫反射靶板,用成像探测器摄取经靶面漫射的脉冲强激光光斑图像;在靶面中心处挖小孔,孔后放置能量探测器实时测量激光脉宽和峰值功率。同时对整个激光光斑图像进行能量定标,进而得出远场脉冲强激光的实际空间能量/功率分布、总能量,以及相应的光束质量参数。应用该测量方法,对高能TEA CO₂激光进行测量研究,测得其远场光束截面半径为80.2 mm,发散角为1.55 mrad。