Sol-gel法制备Y_2O_3∶Eu~(3+)/Yb~(3+)@SiO_2太阳能上转换材料的研究

采用pechini溶胶-凝胶法制备Eu~(3+)/Yb~(3+)共掺Y_2O_3纳米颗粒,采用经典的St?ber方法制备SiO_2包覆上述纳米颗粒的核壳结构。借助X射线衍射仪和傅里叶红外光谱仪等测试手段,研究材料的结构性能。结果表明:SiO_2包覆后,Y_2O_3的晶体结构和粒子的上转换发光机制均未发生改变,Y-O-Si键的形成说明SiO_2成功包覆在Y_2O_3∶Eu~(3+)/Yb~(3+)粒子表面。紫外-可见光分光光度计和光致发光谱测试结果对比表明,SiO_2包覆后的粒子在980 nm处仍有光谱吸收,并且材料的发光强度有较大提高。     

光热化学循环分解CO_2的实验与模拟计算研究

利用未掺杂TiO_2和铁掺杂的Fe-TiO_2样品进行光热化学循环分解CO_2实验,比较两种样品的性能,并利用第一性原理进行模拟计算,对光热化学循环分解CO_2的可行性和反应机理进行了探究。实验观察到FeTiO_2得到CO产量约为TiO_2的1.36倍,且在连续循环反应过程中表现出良好的稳定性。选取锐钛矿TiO_2(101)及掺铁的Fe-TiO_2(101)表面作为简化的模型,通过对两种模型的氧空位形成能、电子结构和光学性质的计算比较,可以得到:掺Fe后的Fe-TiO_2(101)表面带隙有所减小,降低了体系光激发电子迁移所需的能量;FeTiO_2(101)表面的光吸收强度增强,光反应活性提高;Fe-TiO_2(101)表面的氧空位形成能明显低于纯TiO_2(101)表面,表明掺Fe结构不稳定,容易产生更多的氧空位,以促进后续热化学反应的进行。     

复合TiO_2-SiO_2光催化剂的制备及性能研究

以SiO_2气凝胶为载体,采用溶胶凝胶法制备出复合TiO_2-SiO_2光催化剂。通过扫描电子显微镜、傅里叶变换红外光谱、X射线衍射图谱和比表面积测定等分析手段对复合光催化剂进行表征。结果表明,TiO_2微粒均匀搭载在SiO_2气凝胶的表面,复合光催化剂具有丰富的空间孔结构和良好的比表面积。在单因素实验和响应面优化实验基础上得出制备复合光催化剂的最佳工艺条件为:正硅酸乙酯(TEOS)和水的用量比(V/V)为4∶1,悬浮液中TiO_2的浓度为2.21 g/L,溶胶凝胶时间为3.11 d;最优工艺条件下制备的复合光催化剂对10 mg/L的亚甲基蓝溶液进行24 h降解处理,去除率达到99.1%。     

Ho掺杂纳米TiO2光催化性能研究

以钛酸四正丁酯为原料,采用溶胶-凝胶法制备了纯的和Ho掺杂的TiO_2纳米粒子,对样品进行了TG- DTA、XRD和UV-Vis吸收光谱分析,并以甲基橙的光脱色反应考察了样品的光催化性能。发现Ho的掺杂抑制了TiO_2粒径的长大,细化了晶粒;Ho掺入到TiO_2的晶格中,引起了晶格的畸变和膨胀;Ho的掺杂使TiO_2的吸收带边发生微小的蓝移,且在450nm和540nm光区附近产生吸收;适量Ho的掺杂可提高TiO_2的光催化性能,紫外光照下,Ho的掺杂量为0.3%时,光催化性能最佳;可见光下(波长>420nm),Ho掺杂的TiO_2呈现光催化活性,210min内甲基橙的脱色率可达21.6%。     

二次微波法制备纳米TiO_2的实验研究

使用二次微波辅助水热合成法,回避高温煅烧过程,在低温(473K)以下成功制备了锐钛矿型纳米晶体光催化剂TiO_2,样品表征结果证明该粉体样品粒径均匀,晶相单一,具有较大的比表面积和很高的光催化活性。     

纳米粒子和PVA纤维增强水泥基复合材料抗碳化性能研究

为研究纳米粒子掺量和种类、PVA纤维掺量对水泥基复合材料抗碳化性能的影响,通过碳化试验测得各组水泥基复合材料碳化试件的碳化深度。纳米粒子的质量掺量分别为0.5%、1.0%、1.5%、2.0%、2.5%,纳米粒子种类为纳米SiO_2和纳米CaCO_3,PVA纤维的体积掺量分别为0.3%、0.6%、0.9%、1.2%。研究结果表明,纳米SiO_2可以显著提高PVA纤维增强水泥基复合材料抗碳化性能,且在纳米SiO_2掺量低于2.5%时,抗碳化性能随着纳米SiO_2掺量的增加不断增强;PVA纤维可明显提高纳米水泥基复合材料的抗碳化性能,当纤维体积掺量不大于1.2%时,纤维体积掺量较大的纳米水泥基复合材料具有较高的抗碳化性能;纳米CaCO_3与纳米SiO_2均能提高水泥基复合材料的抗碳化性能,纳米SiO_2的提高效果略优于纳米CaCO_3。研究结果为纳米粒子和PVA纤维在水泥基复合材料中的应用提供指导。     

TiO_2/SiO_2双层减反膜在太阳电池上的应用

利用二氧化硅(SiO_2)对太阳电池表面的钝化作用,对传统的二氧化钛(TiO_2)单层减反膜进行了改良.基于理论模拟分析了光反射率随膜层(TiO_2/SiO_2)厚度变化规律,结合实验上SiO_2最佳厚度经验值,制备了晶体硅太阳电池(即TiO_2/SiO_2/Si),并和SiN_x/Si结构的晶体硅太阳电池相比较.分别测试了少子寿命、反射率、电性能参数等,结果表明这种改良后的TiO_2减反膜也可以取得很好的减反效果和钝化效果.镀有TiO_2,SiO_2双层膜与SiN_x减反膜绒面晶体硅片的积分反射率分别为4.9%和3.9%;使用以上两种不同减反膜制备的太阳电池的开路电压均可达到0.62V.可见这种TiO_2双层膜有望在将来的生产中得到具体应用.     

伊红-Y敏化TiO2的制备及其可见光下光催化制氢性能

采用溶胶-凝胶法在不同温度煅烧制得TiO_2,光还原沉积法进行载铂,浸渍法使伊红-Y负载在Pt-TiO_2表面,制得系列染料敏化的Eosin Y-Pt-TiO_2可见光光催化剂。以可见光光催化制氢为探针反应考察了制备的催化剂的活性,发现350℃煅烧的Eosin Y-Pt-TiO_2可见光光催化活性最好。通过XRD、BET、FT-IR、UV-Vis漫反射等手段对样品进行了表征,发现伊红-Y的敏化扩展了TiO_2的可见光响应范围,使其在400～600nm有很强的吸收峰;随着TiO_2煅烧温度的降低,比表面积不断增大,表面羟基的数量也增加,吸附伊红-Y的量也不断增加,因此Eosin Y-Pt- TiO_2可见光光催化活性也相应提高。     

纳米SiO_2和PVA纤维增强地聚合物砂浆抗压强度研究

为研究纳米SiO_2和PVA纤维对地聚合物砂浆工作性和抗压强度的影响,进行了地聚合物砂浆坍落扩展度和抗压性能试验。结果表明,在一定的掺量范围内,随着纳米SiO_2掺量的增加,地聚合物砂浆的坍落扩展度、立方体抗压强度、折后抗压强度和轴心抗压强度均先增大后减小,在纳米SiO_2掺量为1.5%时,抗压强度达到最大值;在试验PVA纤维掺量范围内,随着PVA纤维掺量的增加,地聚合物砂浆坍落扩展度逐渐减小,地聚合物砂浆各试件抗压强度也都呈先增大后减小的趋势,当PVA纤维掺量为0.6%时,抗压强度达到最大值;同时掺加纳米SiO_2和PVA纤维地聚合物砂浆各试件抗压强度比单掺纳米SiO_2或PVA纤维地聚合物砂浆高。     

复合Ce、Ag/TiO2粒子环保涂料制备及其光催化活性研究

用全氟树脂与Ce、Ag／TiO2粒子复合制备有净化大气功能的环保涂料，比较油酸和聚甲基丙烯酸甲酯在改性的Ce、Ag／TiO2表面包覆及在涂料中添加2％、5％、8％、11％（质量％）包覆的改性粒子对光催化活性的影响，表明甲基丙烯酸甲酯包覆比油酸好，包覆的Ce、Ag／TiO2添加量为8％比较合理。     

Photocatalytic H2 production over RuO2@ZnS and RuO2@CuS nanostructures

Photocatalytic hydrogen production is a promising approach of sustainable economy, because a use of sunlight and water to produce a fuel will solve a problem of fossil fuels depletion. Metal sulfides are well known photocatalysts in water splitting process, but in absence of sacrificial electron donor they undergo a photocorrosion. In this paper we studied a possible strategy to protect the sulfide photocatalysts and to improve its photostability by a deposition of small amount of ruthenium oxide at surface of sulfides. Nanocrystalline zinc sulfide and copper sulfide were prepared in a hydrothermal way and have been functionalized by RuO₂. As prepared photocatalysts showed good activity towards hydrogen formation. Modification of sulfides with ruthenium oxide had a few positive effects: it expanded a light absorption range by photocatalysts, enhanced the photocatalytic activity towards H₂ formation, improved a photostability in comparison with neat ZnS and CuS as well as protected from the electronic and structural changes within semiconductors due to irradiation.     

Evaluation of in-situ formed La2O3–TiO2–La2O2CO3 nanocomposite photocatalyst for H2 production

The photocatalytic evolution of H₂ over La₂O₃ decorated TiO₂ catalyst was examined under solar light. It was observed that during the course of the reaction, the transformation of La₂O₃/TiO₂ into La₂O₃–TiO₂–La₂O₂CO₃ occurred and these species effectively suppressed electron-hole pair recombination by forming electron trapping centres on the surface, resulting in an increased visible light absorption and improved H₂ yield. The 2 wt%La₂O₃/TiO₂ nanocomposite demonstrated better H₂ yield (～8.76 mmol (g_cat)^?1) than the bare TiO₂ (～1.1 mmol (g_cat)^?1). The catalyst was stable even after several consecutive recycles with no substantial loss of hydrogen production rate. The H₂ rates were correlated with the physicochemical characteristics of the catalysts examined by BET–SA, H₂-TPR, XRD, UV-DRS, Raman spectroscopy, FTIR, HRTEM, EPR and PL spectroscopy.     

Numerical study of the O2/CO2, O2/CO2/N2, and O2/N2-syngas MILD combustion: Effects of oxidant temperature,O2 mole fraction,and fuel blends

Moderate or Intense Low-oxygen Dilution (MILD) combustion of a syngas fuel under air-fuel, oxygen-enhanced, and oxy-fuel condition are numerically studied with using counterflow diffusion flame. Fuel composition, temperature of oxidant (T_ox), and oxygen mole fraction (X_O2) are selected as the main parameters. Fake species (FCO₂) with the same CO₂ physical properties is used for separation the physical and chemical effects of replacing CO₂ with N₂. According to the results, under the high preheating temperatures, the chemical effect of changing the oxidant composition from N₂ to CO₂ is the main reason of the changes in flame structure, ignition delay time (IDT) and heat release rate (HRR) while physical differences play a more prominent role in the low preheating temperature MILD combustion. In all X_O2, the physical and chemical effects of replacing CO₂ with N₂ have almost the same role on the maximum flame temperature. The results of IDT expressed that chemical discrepancies of CO₂ and N₂ play a key role on IDT enhancement by increasing CO₂ in the oxidant composition. The sensitivity analysis of CH₂O for variations of T_ox and X_O2 shows that reactions R54, R56, R58, and R101 are the main responsible of lower HRR and higher IDT by moving from air-syngas to oxy-fuel MILD combustion.     

保护气氛烧结炉

介绍了HIC封装管壳中玻璃绝缘子网带烧结炉的特殊机械结构、氮氢保护气氛系统和电气保护措施。确立了网带炉低速爬行力学模型及炉内合理的气氛流向。     

New gas chromatographic packing ZIF-67@NH2–SiO2 for separation of hydrogen isotope H2/D2

ZIF-67@NH₂–SiO₂ composites were prepared by loading the metal-organic frameworks ZIF-67 on amino modified SiO₂ gel particles (NH₂–SiO₂, 80–100 mesh) through layer-by-layer self-assembly method. Systematic investigation on the effects of ZIF-67 loading amounts on NH₂–SiO₂ packed stainless steel chromatographic column (specification 1.0 m×2.0 mm I.D.), the flow rate of He as carrier gas and the injection amount of mixed gas (H₂/D₂) on the hydrogen isotope H₂/D₂ separation performance at liquid nitrogen temperature, unraveled the optimal conditions for H₂/D₂ isotope separation. The results showed that the optimal stationary phase materials under the optimized conditions can effectively separate H₂ and D₂ with separation resolution R = 1.52 and the separation time t = 10.15 min. The superior performance of the ZIF-67 is tentatively thought to be due to kinetic quantum sieving (pore size 3.3 Å) effect and chemical affinity sieving effect of Co ion in ZIF-67.     

Photocatalytic reduction of CO2 using TiO2 powders in supercritical fluid CO2

The photocatalytic reduction of CO₂ was investigated using TiO₂ powders in supercritical fluid CO₂. These were irradiated in a stainless steel vessel at 9.0 MPa and 35°C. After reducing the CO₂ pressure to the ordinary state, pure water was added to the vessel while avoiding air contamination. No gaseous reduction products were observed. Formic acid was obtained only in aqueous solution. The optimal irradiation time for the production of formic acid was 5 h. Addition of acidic solutions rather than pure water was preferable for formic acid formation. Formic acid seems to be produced through the protonation of reaction intermediates on TiO₂ powders in solutions. The CO₂-reduction system described here may be of practical value for efficient CO₂-conversion and fixation, storage of solar energy, and production of raw materials for the photochemical industry.     

Photocatalytic reduction of CO2 with H2O on CuO/TiO2 catalysts

Carbon dioxide was photocatalytically reduced to produce methanol and ethanol in the presence of CuO-loaded titania powders suspended in water containing Na₂SO₃ as the hole scavenger. The photocatalysts were synthesized by an impregnation method using P25 (Degussa) as support. At the optimum amount of copper oxide loading (3 wt%), the methanol and ethanol yields were 12.5 and 27.1 μmol/g-catal., respectively, following 6 h of UV illumination. The redistribution of photogenerated charge carriers in CuO/TiO₂ facilitates electron trapping and prohibits the recombination of electrons and holes, which significantly increases photoefficiency. The addition of Na₂SO₃ promotes the formation of ethanol.     

Effects of CO2 addition on flame structure in counterflow diffusion flame of H2/CO2/N2 fuel

Numerical analysis on flame structure in a counterflow diffusion flame has been conducted for understanding the effects of CO₂ addition to fuel, systematically varying initial concentration of CO₂ and axial velocity gradient. The effects of CO₂ addition to fuel side in a counterflow diffusion flame are globally divided into two categories: diluent effects due to the relative reduction in the concentrations of the reactive species, and direct chemical effects caused by the breakdown of CO₂ through the reactions of third‐body collision and thermal dissociation. The deflection of CO₂ mole fraction profile with mixture fraction clarifies that the converted CO quantity from CO₂ is not negligible at low axial velocity gradients. It is also known that the addition of CO₂ does not alter the basic skeleton of the H₂–O₂ reaction mechanism, but contributes to the formation and destruction of hydrocarbon products such as HCO. At high axial velocity gradients the CO converted reaction is suppressed and then CO₂ plays the role of a diluent at these conditions. Copyright © 2001 John Wiley & Sons, Ltd.