新型氮化碳纳米材料的制备与性能测试

类石墨氮化碳(g-C_3N_4)是一种新型的可见光光催化剂,但类石墨氮化碳g-C_3N_4本身有着的一些缺陷,直接造成其光催化效率低。为了消除这些缺陷的存在,提高其光催化效率。本文是将类石墨氮化碳(g-C_3N_4)进行加工处理得到厚度在50 nm左右的薄片,然后通过XRD、SEM和TEM等多种方法对该催化剂进行表征。并在可见光下对罗丹明B进行降解来判断其催化效率。     

g-C3N4/CQDs光催化材料的制备及性能

采用高温热解法制备了石墨相氮化碳(g-C_3N_4),将其与碳量子点(CQDs)进行水热复合,得到g-C_3N_4/CQDs复合光催化剂。采用SEM、TEM、FTIR、XRD、UV-Vis/DRS、XPS、N2吸附-脱附等温线手段对制备的复合光催化剂进行了表征,以罗丹明B(Rh B)为模拟污染物,考察了g-C_3N_4/CQDs的可见光催化活性及稳定性。结果表明:与g-C_3N_4相比,g-C_3N_4/CQDs对可见光吸收强度增加,同时其吸收波长向可见光区发生红移;当CQDs含量为1.5%(以g-C_3N_4质量为基准)时,所得g-C_3N_4/CQDs光催化材料的催化活性最佳,其对Rh B的光催化降解率是54.5%,是g-C_3N_4光催化降解率的1.38倍,化学反应动力学拟合相关系数R2=0.9982。且g-C_3N_4/CQDs循环使用3次后,其催化降解率仍保持在50%以上。光催化机理研究表明,空穴(h+)、超氧阴离子自由基(·O2–)、过氧化氢分子(H2O2)和羟基自由基(·OH)都是光催化过程中的主要活性物种,四者氧化作用大小依次为:h+·O2– H2O2·OH。     

g-C_3N_4/BiFeO_3复合可见光催化剂的制备及其光催化性能

采用微波溶剂热法和简单的固相热分解反应成功制备了g-C_3N_4/BiFeO_3/BiFeO_3复合可见光催化剂,利用扫描电子显微镜(SEM)、X射线衍射光谱仪(XRD)、傅里叶变换红外光谱仪(FT-IR)和紫外可见漫反射光谱(UV-Vis DRS)等技术对所制备的催化剂进行了表征。结果显示,复合可见光催化剂保持BiFeO_3的钙钛矿结构,g-C_3N_4/BiFeO_3只是复合在BiFeO_3的表面,没有改变BiFeO_3的晶体结构;UV-Vis DRS测试显示,g-C_3N_4/BiFeO_3/BiFeO_3的吸收带边发生了红移,可见光吸收能力得到提升。g-C_3N_4/BiFeO_3和BiFeO_3形成的异质结结构,很好地抑制了光生电子-空穴对的复合率;以罗丹明B为目标降解物,研究了催化剂的可见光催化性能。结果表明,g-C_3N_4/BiFeO_3和BiFeO_3的复合可以显著地提高催化剂的可见光催化活性;在g-C_3N_4/BiFeO_3的掺入量为15%时,g-C_3N_4/BiFeO_3/BiFeO_3对罗丹明B的可见光催化降解率可以达到93.62%。     

CDs/ZnO/g-C3N4三元组份协同作用促进光催化降解染料

采用浸渍-热聚合法制备CDs/ZnO/g-C3N4复合材料，考察其对罗丹明B的光降解效率。利用 XRD、TEM、XPS、UV-Vis DRS、FI-IR等手段对催化剂进行表征和评价。结果表明：CDs/ZnO/g-C3N4仍保持石墨相g-C3N4的晶型结构，三元组份相互协同作用使CDs/ZnO/g-C3N4表现出优异的光催化性能，其降解罗丹明B的效果优于单体g-C3N4、ZnO及ZnO/g-C3N4，脱色率可达到70%左右。     

g-C_3N_4-Ag_3PO_4/Fe_3O_4磁性光催化剂的制备及性能研究

以光催化降解罗丹明B为探针,考察了反应条件对催化剂性能的影响,并通过XRD、FTIR和UV-Vis-DRS对部分催化剂的结构和光吸收性能进行了表征。结果表明,该催化剂中g-C_3N_4呈现出类石墨层状结构,Ag_3PO_4为立方晶相,Fe_3O_4为立方尖晶石型,Ag_3PO_4对g-C_3N_4的复合拓宽了其光谱响应范围,g-C_3N_4、Ag_3PO_4和Fe_3O_4通过分子间作用力复合。光催化降解实验表明,在g-C_3N_4-Ag_3PO_4/Fe_3O_4投加量为0.83 g/L,反应体系pH=7及可见光下反应105 min的条件下,该催化剂对5 mg/L的罗丹明B的降解率高达98.81%。此外,该催化剂还对其它3种染料也表现出良好的光催化降解能力,并且该催化剂可通过磁分离回收,回用稳定性较好。     

g-C_3N_4-Ag_3PO_4/Fe_3O_4磁性光催化剂的制备及性能研究

以光催化降解罗丹明B为探针,考察了反应条件对催化剂性能的影响,并通过XRD、FTIR和UV-Vis-DRS对部分催化剂的结构和光吸收性能进行了表征。结果表明,该催化剂中g-C_3N_4呈现出类石墨层状结构,Ag_3PO_4为立方晶相,Fe_3O_4为立方尖晶石型,Ag_3PO_4对g-C_3N_4的复合拓宽了其光谱响应范围,g-C_3N_4、Ag_3PO_4和Fe_3O_4通过分子间作用力复合。光催化降解实验表明,在g-C_3N_4-Ag_3PO_4/Fe_3O_4投加量为0.83 g/L,反应体系pH=7及可见光下反应105 min的条件下,该催化剂对5 mg/L的罗丹明B的降解率高达98.81%。此外,该催化剂还对其它3种染料也表现出良好的光催化降解能力,并且该催化剂可通过磁分离回收,回用稳定性较好。     

超声协同g-C3N4光催化降解罗丹明B的研究

采用高温热解法制备石墨相氮化碳,采用XRD对制备样品进行表征,并将g-C_3N_4催化剂用于超声协同下光催化降解罗丹明B。探究了超声与光催化对降解罗丹明B的协同作用,以及超声功率、溶液初始pH、光催化剂浓度和罗丹明B初始浓度等对罗丹明B降解效果的影响,对催化剂的循环催化性能进行了测试,并对超声协同光催化降解罗丹明B的主要活性物质和机理进行讨论。结果表明:超声功率为300 W,溶液初始pH=4,g-C_3N_4质量浓度为4 g/L,罗丹明B初始质量浓度为15 mg/L时,对罗丹明B的降解效率最佳,100 min去除率能达到近100%,且主要活性物质为·OH和·O~(2-)。     

超声调控Ag/g-C_3N_4复合材料及光催化性能研究

通过固相加热制备g-C_3N_4,超声调控获得片层状g-C_3N_4,光照Ag NO3与g-C_3N_4成功制备了Ag/gC_3N_4复合光催化材料。利用X射线衍射仪(XRD)以及扫描电子显微镜(SEM)分析产物的物相和形貌,采用紫外-可见吸收光谱表征样品的光学性能。以罗丹明B为模拟污染物,评价超声样品Ag/g-C_3N_4的可见光(λ≥420nm)催化性能。实验结果表明,与纯g-C_3N_4相比,超声的Ag/g-C_3N_4复合光催化材料在可见光下降解罗丹明B的光催化活性最好。分析表明Ag与g-C_3N_4的协同作用抑制光生电子-空穴的复合是可见光催化活性增强的主要原因。     

P掺杂氮化碳催化剂可见光降解亚甲基蓝废水

以磷酸氢二铵和三聚氰胺为原料,采用焙烧法合成P/g-C_3N_4复合光催化剂。使用红外光谱(FT-IR)、荧光光谱(PL)、X射线衍射(XRD)和扫描电子显微镜(SEM)等测试方法对催化剂的结构和光学特性进行表征。结果表明:合成的P/g-C_3N_4复合光催化剂具有类石墨相结构,对可见光的吸收比纯g-C_3N_4有所增加,其荧光发射强度有所降低。可见光照射下降解亚甲基蓝废水结果显示:照射180 min、7 wt%P/g-C_3N_4光催化剂对亚甲基蓝的降解率为15.3%,其反应速率常数为纯g-C_3N_4的1.7倍。P/g-C_3N_4复合光催化剂具有比纯g-C_3N_4更好的可见光催化降解性能。     

g-C_3N_4/ZnO复合材料的制备、表征及可见光催化性能

以一步法原位合成了g-C_3N_4/ZnO异质结复合材料,评价其在可见光下降解亚甲基蓝(MB)的光催化活性,并探讨了g-C_3N_4/ZnO的光催化机制。运用XRD、FTIR、SEM和UV-Vis DRS对所合成的复合材料进行表征。结果表明,经复合后g-C_3N_4和ZnO紧密结合,构建了异质结,提高了光生电子空穴的分离效率,并且在可见光区表现出较强的光响应性;当g-C_3N_4的质量分数为19%时,复合材料g-C_3N_4/ZnO降解MB的反应速率常数为0.020 6 min-1,是纯g-C_3N_4的3.8倍。催化剂重复使用5次,仍保持较高的光催化活性。     

Polymorphism of LiGa5O8 and of LiGa5O8-MgGa2O4Solid Solutions

High-temperature X-ray diffraction and differential thermal analyses showed that LiGa₅O₈ exists in two polymorphs related by the first-order transition at 1138°±3°C of the low-temperature simple-cubic form, space group (probably) O⁷, to the high-temperature spinel (fcc) form, space group O _h ⁷. The transition is rapid, and the high-temperature form in pure LiGa₅O₈ could not be quenched to room temperature under the conditions used. However, the high-temperature polymorph can be quenched under equilibrium conditions when 40 mol% or more MgGa₂O₄ is present. The subsolidus equilibrium relations in the system MgGa₂O₄-LiGa₅O₈ are discussed.     

Magnetoresistance of CuxCo1-xFe2O4 Ferrites

Magnetoresistance measurements (Δ/R) were carried out on Cu _x Co_{1- x} Fe₂O₄ samples with x =1, 0.75, 0.50, 0.25 and cobalt ferrite in the range of magnetic intensity (H) from 1.0 to 4.5 kG. Linear plots were obtained between log (Δ/R) and log H for all compositions except that of cobalt ferrite. The values of n at x =0.5 do not agree with the results of some authors. The discrepancy may be attributed to the value of magnetic field intensity at which such measurements were carried out. The similarity of features of n and μ_D with composition leads us to believe that the magnetoresistance may arise from the scattering of conduction electrons by localized electrons involving the s-d exchange interaction.     

Sintering of Si3N4-Y2O3-Al2O3

Sintering kinetics of the system Si₃N4-Y2O₃-Al₂O3 were determined from measurements of the linear shrinkage of pressed disks sintered isothermally at 1500° to 1700°C. Amorphous and crystalline Si₃N₄ were studied with additions of 4 to 17 wt% Y₂O₃ and 4 wt% A1₂O₃. Sintering occurs by a liquid-phase mechanism in which the kinetics exhibit the three stages predicted by Kingery's model. However, the rates during the second stage of the process are higher for all compositions than predicted by the model. X-ray data show the presence of several transient phases which, with sufficient heating, disappear leaving mixtures of β ' -Si₃N₄ and glass or β '-Si₃N₄, α '-Si₃N₄, and glass. The compositions and amounts of the residual glassy phases are estimated.     

Effects of metal-support interactions on the hydrogenation of CO over PdSiO2 and PdLa2O3

A study of CO hydrogenation over $\text{Pd}\text{SiO}{}_2$ and $\text{Pd}\text{La}{}_2\text{O}{}_3$ has been carried out for the purpose of identifying the effects of Pd dispersion, Pd morphology, and support composition on the catalytic activity of supported Pd. The specific activity of each catalyst for methanol and methane synthesis was determined from microreactor studies carried out at a fixed set of reaction conditions. Palladium dispersion was measured by H₂O₂ titration, and the morphology of the Pd crystallites, as expressed by the distribution of Pd(100) and Pd(111) planes, was determined from in situ infrared spectra of adsorbed CO. The crystallite morphology of the $\text{Pd}\text{SiO}{}_2$ catalysts is the same, independent of Pd weight loading: 90% of the surface is comprised of Pd(100) planes and 10% of the surface is comprised of Pd(111) planes. By contrast, the crystallite morphology of the $\text{Pd}\text{La}{}_2\text{O}{}_3$ catalysts changes with Pd loading. Primarily Pd(100) planes are exposed at low-weight loadings while Pd(111) planes are exposed at high-weight loadings. The Pd dispersion has little effect on the methanol turnover frequency over both $\text{Pd}\text{SiO}{}_2$ and $\text{Pd}\text{La}{}_2\text{O}{}_3$, for dispersions between 10 and 20%. On the other hand, the methane turnover frequency is independent of Pd dispersion over $\text{Pd}\text{SiO}{}_2$, but increases with decreasing dispersion over $\text{Pd}\text{La}{}_2\text{O}{}_3$. It is further observed that the Pd morphology influences the specific activity of $\text{Pd}\text{La}{}_2\text{O}{}_3$ for methanol synthesis: Pd(100) is nearly threefold more active than Pd(111). For a fixed morphology, the specific methanol synthesis activity of $\text{Pd}\text{La}{}_2\text{O}{}_3$ is a factor of 7.5 greater than that of $\text{Pd}\text{SiO}{}_2$.     

Wet Milling of Fe/Al/Al2O3 and Fe2O3/Al/Al2O3 Powder Mixtures

Wet milling of Al₂O₃-aluminide alloy (3A) precursor powders in acetone has been investigated by milling Fe/Al/Al₂O₃ and Fe₂O₃/Al/Al₂O₃ powder mixtures. The influence of the milling process on the physical and chemical properties of the milled powders has been studied. Particle refinement and homogenization were found not to play a dominant role, whereas plastic deformation of the metal particles leads to the formation of dislocations and a highly disarranged polycrystalline structure. Although no chemical reactions among the powder components in Fe₂O₃/Al/Al₂O₃ powder mixtures were observed, the formation of a nanocrystalline, ordered intermetallic FeAl phase in Fe/Al/Al₂O₃ powder mixtures caused by mechanical alloying was detected. Chemical reactions of Fe and Al particle surfaces with the atmosphere and the milling media lead to the formation of highly porous hydroxides on the particle surfaces. Hence the specific surface area of the powders increases, while the powder density decreases during milling. The fraction of Fe oxidized during milling was determined to be 0.13. The fraction of Al oxidized during milling strongly depends on the metal content of the powder mixture. It ranges between 0.4 and 0.8.     

Expansive properties of the mixture C4ASH12 − 2CS III. Effects of temperature and restraint

The effects of temperature and restraint upon the hydration and the expansion of $\text{C}{}_4\text{A}\text{S}\text{H}{}_{12}\text{? 2}\text{C}\text{S}$ mixture compacts in different contact solutions have been investigated. Temperatures above 20°C do apparently hinder the formation of an impervious felt-like layer of ettringite around the $\text{C}{}_4\text{A}\text{S}\text{H}{}_{12}$ particles, thus greatly reducing the retarding effect of the lime. An uniaxial restraint of 1 Kg/cm² is enough to reduce sensibly the expansions which remain however high (about 100%). The results can be satisfactorily interpreted by the reaction and expansion mechanism hypothesized in our previous papers.     

Raman Study of Glasses of Ba2TiSi2O8 and Ba2TiGe2O8

Raman spectra are reported for fresnoite (Ba₂Ti(Si,Ge)₂O₈ glasses, and comparison is made between the Raman spectra of the corresponding crystalline powders and glasses of Ba₂TiSi₂O₈ and Ba₂TiGe₂O₈. The Ba₂TiGe₂O₈ glass spectra show correspondence with the Ba₂TiGe₂O₈ crystalline Raman spectra; the v _s(Ge–O–Ge) mode occurs at 518 cm⁻¹ in the glass and at 521 cm⁻¹ in the crystalline material. Five-fold coordinated titanium is the majority species present in the Ba₂TiGe₂O₈ glass as revealed by a strong band at 824 cm⁻¹ in the I glass spectrum. The Ba₂TiSi₂O₈ glass spectra are similar to the Ba₂TiSi₂O₈ crystalline spectrum; the strongest band is found at 836 cm⁻¹ in the I glass spectrum. Through comparison with the previous Raman data of other titania silicate glasses, we conclude that the Ba₂TiSi₂O₈ glass has a structure similar to the crystalline phase.     

Preparation and properties of poly(Nε,Nε-dicarboxymethyl-l-lysine)

A new ampholytic homopolypeptide, $\text{poly}\text{(N}{}^{\mathrm{\epsilon }}\text{,N}{}^{\mathrm{\epsilon }}\text{-}\text{dicarboxy-methyl-}\text{l}\text{-lysine}\text{)}$, which has one tertiary amino and two carboxyl groups in the side chain has been derived from a hydrochloride salt of poly(L-lysine). The polymer in aqueous solution seems to be in the coil form with locally extended structure (LES) at neutral pH. In both the acidic and alkaline regions, the molar ellipticity of the polymer changes as a result of change in net charge on the side chain. The conformational changes may be from the coil with LES to other coiled forms. 5–7 M NaClO₄ and 80% aqueous methanol induce the α-helix in the polymer at neutral pH. Divalent cations, Cu²⁺ and Ca²⁺, do not induce any remarkably ordered structures such as α-helix or β-structure in the polymer in aqueous solution at any pH. Ultraviolet absorption studies show an absorption peak of the polymer-Cu²⁺ complex near 240 nm. Dependence of the peak intensity on pH at various q values ($\text{q =}\text{[}\text{Cu}{}^{\mathrm{2+}}\text{]}\text{[}\text{residue}\text{]}$) indicates the two steps of the complex formation. At q less than 0.64, the formation is described only with the first step. An average coordination number for Cu²⁺ at the first step was calculated to be about 2 by the method of Mandel and Leyte. The association constant of Cu²⁺ with the residue at the step was determined from the absorption data to be far smaller than that for the Cu²⁺-EDTA complex. The second step of the formation occurs in the case of large q but the absorption data for the second step cannot be obtained exactly due to precipitation.