Selective Formation of Metastable Ferrihydrite in the Chiton Tooth

Metastable precursors are thought to play a major role in the ability of organisms to create mineralized tissues. Of particular interest are the hard and abrasion‐resistant teeth formed by chitons, a class of rock‐grazing mollusks. The formation of chiton teeth relies on the precipitation of metastable ferrihydrite (Fh) in an organic scaffold as a precursor to magnetite. In vitro synthesis of Fh under physiological conditions has been challenging. Using a combination of X‐ray absorption and electron paramagnetic resonance spectroscopy, we show that, prior to Fh formation in the chiton tooth, iron ions are complexed by the organic matrix. In vitro experiments demonstrate that such complexes facilitate the formation of Fh under physiological conditions. These results indicate that acidic molecules may be integral to controlling Fh formation in the chiton tooth. This biological approach to polymorph selection is not limited to specialized proteins and can be expropriated using simple chemistry.     

Theoretical analysis of the local orientation effect and the lift‐hyperlayer mode of rodlike particles in field‐flow fractionation

We investigated theoretically the effects of the cross‐stream migration and the local average orientation of rodlike particles on the shape‐based separation using field‐flow fractionation. The separation behavior was analyzed by comparing the retention ratios of spheres and rods. The retention ratio of a rod was evaluated through the derivation of its cross‐sectional concentration profile by considering the rod migration and the local average orientation. Our study in various flow conditions showed that the rod migration, caused by the hydrodynamic interaction with a wall, can affect the separation behavior as a lift‐hyperlayer mode. We also demonstrated that the local average orientation, which is a function of a local shear rate and a rotational diffusivity, results in the transverse diffusivity that is different from its perpendicular diffusivity. These results suggest that the experimental separation behaviors of rods in field‐flow fractionation may not be fully explained by the current theory based on the normal mode and the steric mode. We also characterized each condition where one of the normal mode, the steric mode of spheres, and the lift‐hyperlayer mode of rods is dominant.     

光催化合成金属Ag纳米颗粒的生长机制——晶核密度控制的生长模式转换

利用AgNO3水溶液,通过严格控制TiO2薄膜的化学活性,系统研究了在TiO2表面光催化合成金属Ag纳米颗粒的生长行为。研究发现,光催化合成金属Ag纳米颗粒存在着两个完全不同的生长机制,分别对应着金属Ag纳米颗粒的各向同性和各向异性生长。当溶液浓度较低时,Ostwald熟化(OR)机制主导着金属Ag纳米颗粒的长大过程;当溶液浓度较高时,取向附生(OA)机制决定着金属Ag纳米颗粒长大成纳米片。原位消光光谱分析表明,OR机制和OA机制生长的前期具有相近消光特征,决定金属Ag纳米颗粒生长模式的关键是AgNO3溶液的浓度,更准确地说是金属Ag初级晶核的局域密度。在此基础上提出了有关光催化合成金属Ag纳米颗粒的生长模型。     

NMR波谱仪集中优化管理模式

论述了核磁中心采用的相对集中管理模式.集中管理模式主要体现在上样辅助、中央供气、数据集中上传与下载3个方面.另外,还提出了未来可以从集中供高纯N2和LN22个方面进一步改善中心的集中管理模式,从而能够更好的优化测试效率和工作环境.     

泡沫塑料富集–石墨炉原子吸收光谱法测定贝类水产品中痕量铊

采取微波消解的前处理手段消解样品,经泡沫塑料分离富集后,用石墨炉原子吸收光谱法测定贝类水产品中痕量铊。以1.5 mL Fe3+,2 mL H2O2和5%王水介质作为吸附体系将样品中铊分离富集,再以硝酸钯、抗坏血酸作为基体改进剂进行测定。铊的质量浓度在0～50μg/L范围内线性良好,相关系数为0.999 7,方法的检出限可达0.07μg/g。测定结果的相对别准偏差为1.53%～4.01%(n=7),加标回收率为87.1%～98.3%。泡沫塑料富集–石墨炉子吸收光谱法测定贝类水产品中痕量铊是一种准确、安全、便捷的检测方法。     

UPLC-QTOF-MS法研究甘油三酯作为水生环境中农药污染的潜在生物标志物

以鲫鱼为代表性研究对象, 采用超高效液相色谱-四极杆飞行时间质谱(UPLC-QTOF-MS)技术, 分别研究了3种农药(敌百虫、 高效氯氰菊酯和吡虫啉)对其体内代谢的影响. 通过Masslynx软件在MS ^E模式下采集数据, 使用UNIFI软件进行自动检测和数据过滤, 并将差异性物质与在线代谢组数据库进行比较, 鉴定出甘油三酯类(TGs)物质具有明显差异. 其中, 吡虫啉对TGs代谢的影响最大, 且肝脏的代谢差异比大脑更显著, 低浓度的急性暴露诱导肝脏中的TGs积累, 其含量与暴露浓度之间的关系符合Michaelis-Menten方程的增长趋势. 结果表明, TGs可在短时间内(≤2 h)灵敏地反映农药吡虫啉的低浓度(≤20 ng/mL)暴露, 可作为考察吡虫啉对水生生物毒性的潜在生物标记物, 有助于建立一种快速、 灵敏的预警方法.     

SO_4~(2-)功能化处理对Fe_2O_3催化剂上氨选择性催化还原NO_x性能的促进机理研究

采用沉淀法制备了Fe(OH)_3和Fe_2O_3。通过硫酸化处理得到SO_4~(2-)/Fe(OH)_3和SO_4~(2-)/Fe_2O_3两种催化剂,并将其应用于氨选择性催化还原NO_x(NH_3-SCR)反应,研究了SO_4~(2-)功能化处理对Fe_2O_3催化剂上NH_3-SCR脱硝性能的促进机理。结果表明,与纯的Fe_2O_3相比,硫酸化处理得到的催化剂上SCR活性得到显著提升;其中,SO_4~(2-)/Fe(OH)_3表现出更加优异的催化性能,在250-450℃时NO_x转化率高于80%,且具有优异的稳定性和抗H_2O+SO_2性能。XRD、Raman、TG、FT-IR、H_2-TPR、NH_3-TPD和in situ DRIFTS等表征结果显示,硫酸功能化处理能抑制Fe_2O_3的晶粒生长,同时SO_4~(2-)与Fe~(3+)结合形成硫酸盐复合物,提高了催化剂表面酸性位点的数量和酸强度,抑制了Fe_2O_3上的氨氧化反应,从而提高了其脱硝催化性能。     

La0.7Sr0.3CoO3-δ钙钛矿催化剂表征及其催化氧化碳黑性能研究

为了研究La_(0.7)Sr_(0.3)CoO_(3-δ)钙钛矿催化剂对碳黑的催化氧化过程,本研究通过研究催化剂和碳黑的两种不同接触方式,即紧密接触与松散接触,讨论了其对碳黑催化氧化过程的影响。结果表明,与松散接触和无催化剂接触条件相比,紧密接触条件下碳黑的tig(起燃温度)分别下降了89.5和157.4℃,同时随着催化剂/碳黑的比例增加,碳黑氧化的tig、tm(最大转化温度)、tf(燃净温度)均向低温区域移动,表明该催化剂对碳黑有着良好的催化氧化性能。     

Filling a Gap: The Coordinatively Saturated Group 4 Carbonyl Complexes TM(CO)8 (TM=Zr,Hf) and Ti(CO)7

Homoleptic Group 4 metal carbonyl cation and neutral complexes were prepared in the gas phase and/or in solid neon matrix. Infrared spectroscopy studies reveal that both zirconium and hafnium form eight-coordinate carbonyl neutral and cation complexes. In contrast, titanium forms only the six-coordinate Ti(CO)₆⁺ and seven-coordinate Ti(CO)₇. Titanium octacarbonyl Ti(CO)₈ is unstable as a result of steric repulsion between the CO ligands. The 20-electron Zr(CO)₈ and Hf(CO)₈ complexes represent the first experimentally observed homoleptic octacarbonyl neutral complexes of transition metals. The molecules still fulfill the 18-electron rule, because one doubly occupied valence orbital does not mix with any of the metal valence atomic orbitals. Zr(CO)₈ and Hf(CO)₈ are stable against the loss of one CO because the CO ligands encounter less steric repulsion than Zr(CO)₇ and Hf(CO)₇. The heptacarbonyl complexes have shorter metal−CO bonds than that of the octacarbonyl complexes due to stronger electrostatic and covalent bonding, but the significantly smaller repulsive Pauli term makes the octacarbonyl complexes stable.     

“三三制”人才培养模式下化学实验教学改革的探索与实践

南京大学国家级化学实验教学示范中心基于"三三制"本科人才培养理念,对化学实验教学进行了改革,完善了"专业学术类"人才培养的实验课程,加强了"交叉复合类"实验课程建设,探索了"就业创业类"人才培养的实验课程及平台建设,取得了显著的建设成效。