Solvothermal growth of {0 0 1} exposed anatase nanosheets and their ability to mineralize organic pollutants. The effect of alcohol type and content on the nucleation and growth of TiO2 nanostructures
Szymon DudziakMarta KowalkińskaJakub KarczewskiMarcin PisarekKatarzyna SiuzdakAdam KubiakKatarzyna Siwińska‐StefańskaAnna Zielińska‐Jurek
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Herein, the series of {0 0 1} exposed anatase nanosheets from HF-assisted solvothermal growth synthesis were obtained. The two-dimensional TiO2 were characterized, including both bulk (XRD, DR-UV–Vis, Mott-Schottky) and surface characteristics (N2 sorption, XPS, SEM) with experimental results compiled with Density Functional Theory (DFT) calculations. The effect of alcohol amount and type was studied, demonstrating the crucial role of nucleation rate on the final material properties, which was connected with the possible ligand exchange between F− and ROH in the [TiF6]2− octahedra, leading to further TiO2 condensation through an ether elimination reaction. Highly active 2D nanoparticles were easily obtained for different reaction times when a moderate amount of n-butanol or n-hexanol was introduced to the synthesis. The photoactivity of 2D TiO2 with exposed {0 0 1} facet strongly depended on the photocatalytic available surface area with an increased amount of ortho–hydroxyphenol (catechol) formed as a by-product. Meanwhile, the rise of n-butanol or n-hexanol content during solvothermal reaction or changing it to ethanol allowed to form smaller and more crystalline anatase particles, but their activity was hindered. For these samples, the slow phenol disappearance and no catechol formation occurred due to (i) a lower amount of adsorbed fluorine, (ii) band position shifting towards lower values, and (iii) the surface presence of Ti3+, which prevented the generation of OH radicals. It was also found that changing the nucleation rate by modifying the reaction environment influences the fluorine ions distribution, determining the final properties of 2D structure photocatalyst.The properties and mechanisms for repetitious sorption of phenol to organobentonites from water were studied. Results showed that organobentonites could be used to sorb phenol from water many times with high removal rates. The sorption capacities of three single-cation organobentonites were 120 CTMAB-bentonites > 120 CPC-bentonites > 120 DTMAB-bentonites, when the original concentration of phenol was 1000 mg/L. The sorption mechanisms changed from adsorption to partition in the process of repetitious sorption. Sorption of phenol to CPC-bentonites could bring synergic sorption. The distribution coefficience (Kp) were related to the quantities of phenol on CPC-bentonites, while the distribution coefficience of phenol on CTMAB-bentonites and DTMAB-bentonite were constant.
Bentonite
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The sorption kinetic and isothermal behaviors of BDE-47 on three natural soils with different soil organic matter fractions(fOC) were studied. The results demonstrated that a two(fast and slow)-compartment first-order model was more appropriate for describing the sorption kinetic data, compared to a one-compartment first-order model, especially in the initial sorption stage within 49 h. The fast sorption was dominant during the whole sorption process from beginning to the apparent sorption equilibrium; while the contribution of the slow sorption to the total sorption amount gradually increased over time and then attained to a plateau at 97 h. The achieving time to the individual sorption capacity for the fast sorption was much shorter than that for the slow sorption. The contribution of the fast sorption to the increase in the total sorption amount of BDE-47 was prevailing at the start of sorption process from 3 h to 5 h; while the fraction of the slow sorption became principal in the subsequent stage of sorption process. Within the narrow equilibrium concentration range due to the fairly low aqueous solubility of BDE-47, the fitting results by the linear partitioning model were comparable with the linear portion by the nonlinear Freundlich model in this study. As for the Freundlich model, the nonlinear exponent(n) values of BDE-47 for the two samples with lower fOC(0.72%) or higher fOC(7.90%) were obviously lower than 1.0(0.75±0.03 and 0.74±0.02, respectively), suggesting somewhat nonlinear sorption characteristics in the studied range of apparent equilibrium concentrations of BDE-47; whereas the linear behavior of BDE-47 for the left sample with medium fOC(2.86%) was indicated by its n value much closed to 1.0(1.03±0.03).
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In this paper,the container wall sorption percentage and the sorption ratio of Am betweensolution and such sorption materials as bentonite are studied with the HPGe detector connected-with S-85 multichannel system,the influence of container wall sorption on sorption ratio also isdiscussed.The results show that the container wall sorption with solid sorptive materials is lowerthan that without solid sorptive materials. The container wall sorption should be considered forthe sorptive materials with low sorption ratio values and can be neglected for those with highsorption ratio values.
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Redistribution
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Underlayer exposed ZnO:Al-TiO2 coupled films are prepared by different means.Surface morphology by SEM,microstructure by XRD,film thickness by surface profiler and photocatalysis are investigated.In order to explain the enhanced photocatalysis,reaction Ag++→Ag↓ is adopted to clarify the mechanism.It turns out that during the process of photocatalysis the exposed part of the underlayer releases e-and this suppresses recombination of light-induced charges,thus enhanced photocatalysis.
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The sorption kinetics and isotherms of BDE-28 on three natural soils with different soil organic matter fractions (f(oc)) were investigated. The results indicated that a two (fast and slow)-compartment first-order model was more appropriate for describing the sorption kinetic data, compared to a one-compartment first-order model, especially in the initial sorption stage within 25 h. The fast sorption was predominant during the whole sorption process from beginning to the apparent sorption equilibrium; while the contribution of the slow sorption to the total sorption amount gradually increased and then achieved a plateau at 49 h or 55 h. The approaching time to the individual sorption capacity for the fast sorption was much shorter than that for the slow sorption. The contribution of the fast sorption to the increase in the total sorption amount of BDE-28 was prevailing at the beginning of sorption process from 2.5 h to 4.5 h; whereas the fraction of the slow sorption became primary at the subsequent stage of sorption process. The fitting results by the Dubinin-Ashtakhov (DA) model were comparable with those by the Freundlich model in the range of apparent equilibrium concentration studied. As for the Freundlich model, the nonlinear exponent (n) values of BDE-28 for the two samples with lower f(oc) (0.72%) or higher f(oc) (7.90%) approached to 1.0 (1.03 +/- 0.05 and 1.00 +/- 0.05, respectively), suggesting the linear sorption characteristics in the studied range of apparent equilibrium concentrations of BDE-28; while the nonlinear behavior of BDE-28 for the left sample with medium f(oc) (4.42%) was indicated by its n value less than 1.0 (0.89 +/- 0.04).
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TiO2 is as promising photocatalyst for environmental degradation of organic compounds and solar energy conversion. Commercial titania is a mixture of rutile and anatase phases, and, for as of yet unknown reasons, anatase is the photocatalytically more active form. In contrast to rutile, atomic-scale information on well-characterized anatase surfaces and their chemical properties was virtually absent at the beginning of this project. We have performed surface science investigations of anatase with the goal to understand, and ultimately control, the surface chemistry underlying its diverse applications. We have of (1) characterized all main crystallographic surface orientations of anatase, namely the (101), (100), (001), and (103) surfaces (2) have investigated the influence of surface imperfections such as defects and steps; (3) have investigated the influence of dopants on epitaxial (001) anatase films; and (3) have investigated the chemical and adsorption and reaction processes of simple molecules (water and methanol) on anatase surfaces. The experiments were performed in collaboration with Pacific Northwest National Laboratory (PNNL) using a variety of complementary surface science techniques. They have lead to a thorough characterization of this model system and have provided a more complete understanding of TiO2, which could possibly lead to improved efficiency in of photocatalytic applications.
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