共查询到15条相似文献，搜索用时 250 毫秒
1.
采用基于密度泛函理论的第一性原理计算方法,对掺杂Fe和(或)V的金红石型TiO2的电子结构进行了计算。理论模拟的结果表明,纯金红石的禁带宽度为1.98 eV;Fe掺杂金红石型TiO2的禁带宽度为2.18 eV,由Fe3d和O2p轨道杂化在禁带中间形成了两条杂质能级;V掺杂金红石型TiO2的禁带宽度减小为1.80 eV,由V3d和O2p轨道杂化形成的杂质能级位于金红石的导带底,引入了一个浅施主能级;Fe和V共掺杂的金红石禁带中存在一个较宽的杂质能带,禁带宽度减小为1.73 eV。杂质能级的出现以及禁带宽度的减小使得Fe和V掺杂的金红石具有更好的可见光响应能力。同时,Fe和V的类质同像替代使得金红石中MO6八面体具有较大的畸变程度,有助于表面缺陷的增加,从而为光催化反应提供天然活性位。为进一步深入揭示含铁、钒等杂质的天然金红石的可见光催化机制提供了理论支持。 相似文献
2.
本文采集了我国19个产地的天然闪锌矿进行矿物学和光催化性能研究。样品皆为立方Zn S结构,化学成分变化较大,其中Fe对闪锌矿中Zn的替代范围为0.235%~14.826%(质量分数,下同),Cd对闪锌矿中Zn的替代范围为0.133%~1.576%。闪锌矿中Fe含量由低到高,导致颜色由浅变深直至呈黑色,半导体禁带宽度由大变小,估算获得天然闪锌矿的禁带宽度范围为3.18~2.28 e V,明显低于纯Zn S禁带宽度3.68 e V,光催化响应均在可见光范围。验证光催化实验结果表明含Fe较低、含Cd较高的天然闪锌矿可见光催化还原降解甲基橙的效果较佳,如可见光下1 g/L闪锌矿样品(含铁4.262%,含镉1.576%)对30 mg/L甲基橙催化反应4 h后的脱色降解率达到82.11%。天然闪锌矿中Fe含量影响着禁带宽度和光响应范围,Cd含量影响着光催化性能,为高附加值开发利用贱金属资源天然闪锌矿提供了科学依据。 相似文献
3.
本文首次研究了天然半导体矿物——闪锌矿的光催化还原能力。经过9个小时的可见光催化实验,来自于湖南黄沙坪矿的天然闪锌矿样品在可见光下表现出较强的光催化还原能力:91.95%的Cr(Ⅵ)被还原,优于9.5小时后紫外光下70.58%的催化效果。闪锌矿的这种强的光还原能力归因于其导带中的电子具有更负的还原电势。此外,Fe替代Zn的晶格位置在禁带中引入了施主能级,而Fe~(2+)被氧化为Fe~(3+)也有效地捕获了空穴。Cd和Cu替代Zn同样引入了杂质能级,减小了禁带宽度,从而将闪锌矿对光的响应拓展到可见光的波长范围。天然闪锌矿中的这些杂质替代离子不… 相似文献
4.
天然闪锌矿可见光催化还原甲基橙的实验研究 总被引：4，自引：0，他引：4
本文研究了可见光下天然闪锌矿的光催化还原能力,通过可见光下天然闪锌矿对甲基橙的光催化降解实验讨论了天然闪锌矿晶格中的杂质缺陷、导带能级位置、光生空穴捕获剂和溶液pH值对可见光催化降解效率的影响。结果表明,在抗坏血酸做空穴捕获剂的条件下,经2 h的可见光催化实验,甲基橙能被天然闪锌矿完全还原降解。天然闪锌矿晶格中丰富的杂质缺陷在禁带中形成杂质能级,可将闪锌矿对光的响应拓展到可见光的波长范围。与天然金红石相比,闪锌矿对甲基橙的较强光催化还原降解效果与其导带电子更负的氧化还原电势有关。此外,空穴捕获剂和pH值的选择都是影响催化效果的关键因素。天然闪锌矿在可见光催化降解污染物领域颇有应用前景。 相似文献
5.
《吉林大学学报(地球科学版)》2015,(Z1)
闪锌矿是一种重要的宽禁带半导体材料,具有优良的光、电和催化性能,在光学器件和光催化等领域有着广泛的应用前景。天然产出的闪锌矿中存在以类质同像替代Zn的Fe、Cd和Ga等微量元素,对其电子结构产生一定的影响,继而影响天然闪锌矿的半导体性质。同时闪锌矿中微量元素的种类、含量与分布受多种因素的影响,除了与闪锌矿本身的地球化学与晶体化学的性质相关,还受到成矿的地质环境、成矿的物理化学条件和成矿溶液离子浓度的影响。所以通过对不同成因类型的闪锌矿半导体性质的研究,可以得到闪锌矿中微量元素的特征,进而反映闪锌矿的成矿条件。对于寻找生命早期闪锌矿,解释半导体矿物光催化为生命起源提供能量提供可靠的证据。已有理论研究通过第一性原理的计算,得出了闪锌矿存在半导体和绝缘体两种类型。微量元素中,只有铜杂质使闪锌矿由直接带隙变为间接带隙,说明含铜的闪锌矿不宜作为光催化剂,铁、镓、锗、铟、锡和锑元素导致费米能级向高能方向移动且使闪锌矿的半导体类型由p型变成n型,这将增加电子密度且有利于电子跃迁,而锰、钴、铜、镉、汞、银和铅元素没有改变闪锌矿的半导体类型。本研究闪锌矿样品来自不同省份不同成因类型的典型矿床,结合半导体材料电阻率及其导电类型的测量方法、紫外可见光吸收光谱的方法和地球科学微量元素测量方法,通过实验对不同成因类型矿床中代表性闪锌矿的电阻率、吸收光谱、共生矿物组合、组构特征、微量元素的测量,建立闪锌矿矿石电阻率、吸收光谱与微量元素影响的定量关系及理论模型。探讨了闪锌矿电阻率、光谱吸收特征和矿床类型及地质产状的关系。闪锌矿中Fe元素含量越高,电阻率越小,可以形成空穴型导电(p型),因Fe元素进入闪锌矿晶格中要消耗能量,所以其形成温度大于绝缘体闪锌矿形成温度,黑色闪锌矿形成温度高。 相似文献
6.
天然半导体矿物由于成分、缺陷复杂,传统测试方法如紫外可见漫反射等难以准确测定其禁带宽度.本文以针铁矿为例,通过第一性原理计算得到纯针铁矿及掺Al针铁矿的电子结构.计算结果显示,纯针铁矿导带底与价带顶均由Fe3d与O2p轨道组成,而当含杂质Al时,Al2p与O2p发生杂化参与了价带组成.在此基础上,利用同步辐射X射线氧的K边吸收谱与发射谱对纯针铁矿及天然针铁矿的能带结构进行了测定.结果表明,天然含Al的针铁矿禁带宽度为2.30eV,小于纯针铁矿(2.57eV).本研究提供了一种测定天然氧化物矿物禁带宽度的新方法,为深入研究天然半导体可见光催化活性产生机制提供了理论依据. 相似文献
7.
闪锌矿是自然界常见的重要金属矿物,含有很多种杂质元素,其中Fe、Cd是闪锌矿最常见,也是最重要的杂质元素。普遍认为,闪锌矿中的Cd、Fe是类质同象取代了Zn。但是,笔者研究发现闪锌矿的Cd与Zn往往成正相关,与Fe呈负消长。说明闪锌矿的Cd类质同象置换主要不是Zn,而是Fe。而且,闪锌矿Cd与Fe的相关性随其颜色的改变而变化。深色闪锌矿的Cd与Fe呈负相关,褐色闪锌矿Cd与Fe既有负消长关系,又有正消长关系。浅色闪锌矿的Cd与Fe呈正相关的数量大增。暗色闪锌矿多形成于高温,Fe具有强烈置换Zn能力。随着形成温度下降,Fe交代Zn的能力不仅逐渐减弱,而且,闪锌矿晶格的Fe变得不稳定,而被释放出来,主要由Cd替代。浅色闪锌矿形成于低温,矿液结晶的后期。矿液中的Zn可能不能满足闪锌矿结晶对Zn的需求,就由离子参数相似的Cd2+和Fe2+替代。致使闪锌矿的Cd与Fe呈正相关,Cd和Fe与Zn负消长。 相似文献
8.
闪锌矿的吸收光谱和颜色的本质 总被引：1，自引：0，他引：1
本文采用电子吸收光谱和分子轨道（MO）－能带理论模型，系统地研究了不同颜色的闪锌矿呈色的机理和本质。闪锌矿由于其形成条件不同，所含杂质元素各异而颜色变化。黑色闪锌矿含Fe高，其颜色是由于以配位体硫为特征的非键轨道2e到Fe^2 的晶体场型轨道的电子转移在500nm产生吸收所致。只有闪锌矿含Fe低（＜1％）时，它才可具有其他颜色，黄色与受主能级Cu^ 到导带或价带到施主能级Ga^3 的电子跃迁在410nm产生吸收有关；绿色是Co^2 的晶体场跃迁^4A2→^4T2(P)在700nm附近产生的吸收峰所致；红色可能与受主能级Hg^ 到施主能级Ga^3 的电子跃迁在470nm产生宽吸收带有关。当闪锌矿的吸收光谱有其中两个吸收带叠加时，它具有过渡的颜色，如黄绿色或绿黄色、桔黄色或桔红色，主要色调取决于两个吸收带的相对强度。 相似文献
9.
10.
闪锌矿中的Cd主要类质同象置换Fe而不是Zn 总被引：5，自引：1，他引：4
闪锌矿是自然界广泛分布的金属矿物,经常含微量的Fe、Cd等杂质元素,并认为Cd和Fe以类质同象方式取代了Zn。但是作者注意到,闪锌矿中的Cd与Zn基本都呈正相关关系,而与Fe呈很好的负相关关系。依照类质同象的定义,类质同象替换的二个元素应该呈负相关关系。因此,我们认为闪锌矿中的Cd主要不是类质同象替换Zn,而是取代了Fe。闪锌矿中的铁主要是Fe2+。Fe2+与Cd2+地球化学性质相似,FeS与CdS的键长和晶格能相近,因此,Cd完全可以类质同象置换闪锌矿中的Fe2+。 相似文献
11.
Dien Li G. M. Bancroft M. Kasrai M. E. Fleet B. X. Yang X. H. Feng K. Tan Mingsheng Peng 《Physics and Chemistry of Minerals》1994,20(7):489-499
Sulfur K-edge x-ray absorption spectra (XANES and EXAFS) and L-edge XANES of sphalerite (ZnS), chalcopyrite (CuFeS2) and stannite (Cu2FeSnS4) have been recorded using synchrotron radiation. The K- and L-edge XANES features are interpreted using a qualitative MO/energy band structure model. The densities of unoccupied states at the conduction bands of sphalerite, chalcopyrite and stannite are determined using S K- and L-edge XANES features (up to 15 eV above the edge), combined with published metal K-edge XANES. The SK- and L-edge XANES also indicate that, for sphalerite, the Fe2+ 3d band at the fundamental gap has little or no bonding hybridization with S 3p and S 3s orbitals; for chalcopyrite, the Cu+ 3d and Fe3+ 3d bands have strong mixing with S 3p and S 3s states, while for stannite the Cu+ 3d band strongly hybridizes with S 3p and S 3s orbitals, but the Fe2+ 3d band does not. The post-edge XANES features (15–50 eV above the edge) of sphalerite, chalcopyrite and stannite are similar. These features are related to the tetrahedral coordination of sulfur in all these structures, and interpreted by a multiple scattering model. The resonance energies from both the K-edge and L-edge XANES for these minerals are well correlated with reciprocal interatomic distances and lattice spaces. Sulfur K-edge EXAFS analyses using Fourier transform and curve fitting procedures are presented. Comparison of the structural parameters from EXAFS with x-ray structure data shows that the first shell bond distances (BD) from EXAFS are usually accurate to ±0.02 Å, and that coordination numbers (CN) are generally accurate to ±20 percent. For sphalerite, EXAFS analysis yields the structure parameters for the first three neighbour shells around a sulfur atom; the BD and CN even for the third shell are in close agreement with the x-ray structure, and the Debye-Waller term decreases from the first shell to the third shell. It is shown that sphalerite (ZnS) is a good model compound for EXAFS analysis of sulfur in chalcogenide glasses and metalloproteins. 相似文献
12.
Electronic and optical properties of Fe, Zn and Pb sulfides 总被引：1，自引：0，他引：1
Ab initio quantum-chemical calculations of the spatial and electronic structures of sphalerite (ZnS), pyrite (FeS2) and galena (PbS), using the density functional theory (DFT) local density approximation (LDA) and generalized gradient approximation (GGA), the Hartree–Fock (HF) method and the hybrid functional B3LYP, have been carried out. For galena, the DFT LDA and GGA functionals provided the best estimate of the band gap, from within –0.1 eV to +0.4 eV of the measured value. B3LYP and RHF gave rise to errors of +1.3 and +5.4 eV, respectively. The unit cell parameter error varied from between –1.1% and +2.3% for all the functionals examined. For sphalerite the B3LYP functional provided the best estimate of the band gap (error +0.3 eV). The unit cell parameter error varied between –2.1% and +2.0% for the various DFT functionals and B3LYP. RHF gave rise to an error of +3.8%. For FeS2, the DFT-GGA approach provides the best results for both the unit cell and the band gap. This may be due to mutual cancellation of the crystal field splitting and band separation force, which are of equal but opposite magnitudes. The calculated density of states (DOS) for the conduction band is used to interpret the experimental features of the S 1s XANES (X-ray absorption near-edge structure) spectra obtained using synchrotron radiation. Because of the l = ±1 selection rule for electron excitation, the S K-edge XANES spectra represent a transition of the S 1s electron to conduction band S p-like orbitals. The near-edge region, up to 15 eV past the edge is approximated well by the DOS. Individual peaks in the DOS correlate with peaks in the XANES spectra. In addition, the imaginary part of the dielectric function, which reflects the transitions from occupied to unoccupied levels, is used to model the near-edge region of the XANES, using the DFT-GGA formalism. Individual peaks in the XANES spectrum are moderately well resolved using the dielectric function, especially for ZnS and FeS2, while the DOS for the conduction band is more successful in predicting the shape of the XANES spectra for all three minerals. 相似文献
13.
M. Ahadi M. Saber Tehrani P. Aberoomand Azar S. Waqif Husain 《International Journal of Environmental Science and Technology》2016,13(12):2797-2804
Sensitized ZnS nanoparticles were synthesized by chemical precipitation method using anthocyanin as the capping agent and sensitizer. X-ray diffractometer, field-emission scanning electron microscope, transmission electron microscopy, UV visible spectrophotometer, Fourier transform infrared spectroscopy and photoluminescence spectrometry methods were used for the characterization of nanoparticles. The electron microscopy studies of nanoparticles showed that the size of crystallites is in the range of 35–80 nm and optical studies showed a blue shift in the absorption edge by adding capping agent. The effective band gap energy was increased with decrease in the particle size. Photocatalytic activities of sensitized ZnS and pure ZnS were evaluated by degradation of tetracycline in aqueous solution under visible light irradiation, and progress of the reaction was monitored spectrophotometrically. The different parameters affecting degradation such as the pH of solution, amount of semiconductor and reusability of catalyst for three cycles and the photocatalytic degradation kinetics of tetracycline were studied. More than 80% degradation was achieved within 5 h under visible light. 相似文献
14.
LI Yan LU Anhuai WANG Changqiu School of Earth Space Sciences Peking University Beijing 《《地质学报》英文版》2006,80(2)
The photocatalytic reductive capability of a natural semiconducting mineral, sphalerite has been studied for the first time. The sphalerite from the Huangshaping deposit of Hunan Province performed great photoreductive capability that 91.95% of the Cr6+ was reduced under 9 h visible light irradiation, higher than the 70.58% under 9.5 h UV light irradiation. The highly reductive ability results from its super negative potential of electrons in the conduction band. Furthermore, Fe substitution for Zn introduces donor states, and the oxidation process of Fe2+ to Fe3+ makes it an effective hole-scavenger. Cd and Cu substitute for Zn also reduce the bandgap and help broaden the absorbing edge towards the visible light. These substituting metal ions in natural sphalerite make it a hyper-active photocatalyst and very attractive for solar energy utilization. 相似文献
15.
Abstract: Natural sphalerite as a natural cost-effective photocatalyst was characterized and its visible light photocatalytic activity was investigated in terms of substituting ions, impurity phases and surface defects. The substitutions of metal ions for Zn2+ alter the band structure and result in the visible light response. The coexistence of impurity semiconductors and nanosized particles in natural sphalerite samples help to prolong the lifetime of electron-hole pairs. The cleavage planes and fracture surfaces improve the photocatalytic activity of natural sphalerite by providing more active sites than perfect faces. Both the negative charge defects from the non-isoelectronic substitutions and surface elements with variable chemical valence suppressed the recombination of electron-hole pairs by their possible role of capturing photogenerated holes. 相似文献