Photoelectrophoresis of colloidal iron oxides 1. Hematite (α-Fe2O3)

Zhang, Z.; Boxall, Colin; Kelsall, G. H.

doi:10.1016/0927-7757(93)80013-5

Cited by 45 publications

(29 citation statements)

References 26 publications

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“…The conduction band electrons could be removed from the particles via two competing photochemical mechanisms in acidic solution. One is the reductive dissolution of iron oxides ( R 1 ), the other is the formation of hydrogen from the reduction of hydrogen ions ( R 2 ) [ Zhang et al , 1993]. …”

Section: Resultsmentioning

confidence: 99%

Photoreductive dissolution of Fe‐containing mineral dust particles in acidic media

Cwiertny

Carmichael³

et al. 2010

J. Geophys. Res.

111

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[1] In this study, the photoreductive dissolution of Fe-containing mineral dust particles in acidic media is investigated. Photolysis experiments were performed using a solar simulator to irradiate acidic mineral dust suspensions prepared from source materials of Inland Saudi sand (IS), Saharan sand (SS) and one commercial sample, Arizona test dust (AZTD). The results show that Fe dissolution is a pH-dependent process, and total Fe solubility decreases with the solution pH increasing. Comparing iron dissolution from different source materials, Fe(II)-containing AZTD is more soluble than IS and SS samples, irrespective of the presence or absence of light. Experiments performed at three different temperatures of 278, 293, and 308 K show that both total dissolved Fe and dissolved Fe(II) increase with temperature and upon light exposure. Results of dissolution studies with AZTD performed at low pH also illustrate that the nature of the acid strongly influences iron solubilization. Fe solubility decreases in the suspensions of H 2 SO 4 and HNO 3 in the presence of light, whereas Fe solubility increases in the HCl solution under the irradiation compared to the dark reaction. Finally, our results confirm earlier work showing that photoreductive dissolution of Fe is very sensitive to dissolved oxygen. Results from this laboratory study show that mineralogy and speciation of iron, as well as environmentally relevant factors including pH, light, O 2 , and nature of the inorganic anion, NO 3 − , SO 4 2− , and Cl − , must be considered when modeling the input of iron to the oceans.

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Section: Resultsmentioning

confidence: 99%

Photoreductive dissolution of Fe‐containing mineral dust particles in acidic media

Cwiertny

Carmichael³

et al. 2010

J. Geophys. Res.

111

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“…These impurities and defects likely serve as non-radiative recombination or trapping centers to compete with the radiative recombination. While the exact role of carboxylate impurities is not clear, the hydroxide defects are good hole scavengers, as reported in studies of ZnO [4] and other metal-oxides [13].…”

Section: Pl Spectramentioning

confidence: 91%

Photoluminesence and FTIR study of ZnO nanoparticles: the impurity and defect perspective

Xiong

Pal

Serrano

et al. 2006

Phys. Status Solidi (c)

450

163

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We studied the possible correlations between defects and photoluminescence spectra in ZnO nanoparticles of sizes ranging from 43 nm to 73 nm in diameter. The defects and impurity contents were characterized by Fourier-transform infrared (FTIR) spectroscopy. The results show fewer carboxylate and hydroxyl impurities for particles of larger sizes. No significant variation in oxygen vacancy content was found among samples. Annealing in vacuum at 300 °C significantly reduces the carboxylate and hydroxyl impurities in the samples. The total luminescence intensity (UV + visible) increases as the particle size grows for both the unannealed and annealed samples. This suggests that both types of luminescence are subject to nonradiative quenching by near surface defect centers, possibly carboxylate and hydroxyl impurities. There may be quenching due to intrinsic lattice defects too. It is found that annealing in vacuum enhances the visible luminescence both absolutely and relative to the UV exciton luminescence. In addition to the 2.5 eV green luminescence peak, a peak centered at 2.8 eV can also be resolved, espeically for the 43 nm sample. . Understanding the roles of defects and especially surface defects are important for these applications utilizing nano-structured ZnO. During or after nanostructure synthesis, the surfaces can often be easily contaminated by impurities and other defects. These surface defects usually reduce the performance for such applications. For example, surface defects such as hydroxyl are known to quench the exciton luminescence in ZnO [4]. It can also prevent efficient charge transfer between ZnO and adsorbed molecules at the interfaces. The most obvious trend versus particle size is that the surface-to-volume ratio increases for smaller particles, and the transport distance from any interior point to surface traps and recombination sites decreases in the same trend. Examining nanoparticle ZnO photoluminescence (PL) spectra provides us a way to understand the roles of defects in the above photon-excited processes. In this paper, we report our study of ZnO nanoparticles ranging from 43 to 73 nm. The defect and impurity content in these materials were characterized by Fourier transfer infrared spectroscopy (FTIR). We correlate the particle size and defects/impurities to the measured PL spectra. It is found that annealing treatment significantly reduces the surface impurities.

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“…4͒ as well as in other metal-oxide semiconductors. 31 Presently, the most recognized hypothesis on the origin of the green luminescence in ZnO involves the radiative recombination of electrons captured at oxygen vacancy sites with trapped holes. 32 In our study, both the exciton and defect PL intensity increases versus the particle size.…”

Section: -3mentioning

confidence: 99%

Correlations among size, defects, and photoluminescence in ZnO nanoparticles

Xiong

Pal

Serrano

2007

Journal of Applied Physics

189

102

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We studied the correlations among size, defects, and photoluminescence emissions in ZnO nanoparticles of sizes ranging from 25 to 73 nm. The impurities and defects were characterized by Fourier-transform infrared spectroscopy and Raman spectroscopy. Particles of larger size revealed fewer surface impurities and enhanced E 2 mode of hexagonal ZnO crystals, while the oxygen vacancy centers did not vary significantly with particle size. A simultaneous increase of excitonic luminescence and defect luminescence intensities with the increase of particle size is shown, indicating both emissions are subjected to nonradiative quenching by near surface defects. The study on the size-dependent green luminescence in our samples suggests that the emission might be a bulk property instead of having a surface origin in nanostructured ZnO. Two different radiative recombination processes are involved in the excitonic emission of ZnO. While the slow decay component ͑370 ps͒ did not depend on particle size, the fast component varied from 56 to 96 ps. We attribute the slow component to free exciton recombination, while the fast component is attributed to near surface exciton recombination.

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Photoelectrophoresis of colloidal iron oxides 1. Hematite (α-Fe2O3)

Cited by 45 publications

References 26 publications

Photoreductive dissolution of Fe‐containing mineral dust particles in acidic media

Photoreductive dissolution of Fe‐containing mineral dust particles in acidic media

Photoluminesence and FTIR study of ZnO nanoparticles: the impurity and defect perspective

Correlations among size, defects, and photoluminescence in ZnO nanoparticles

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