Browsing by Subject "Photocatalyst"

Now showing 1 - 5 of 5

Open Access
First-principles study of binary group IV-V polymorphs in 2D tetrahex structure
(2021-08) Ershadrad, Soheil
Tetrahex materials are a novel family of 2D materials, made of an ordered se-quence of tetragons and hexagons, with exotic electronic, optical and mechanical properties. Motivated by the promising photocatalytic and auxetic properties found in the Tetrahex-carbon, we investigate the behavior of binary group IV-V polymorphs in this structure (denoted by th-XY2 where X = C and Si, and Y = N, P, As, and Sb), through ﬁrst-principles methods. We demonstrate that these compounds exhibit robust energetic, dynamical, thermal, and mechanical stabilities. Our calculations show that the intrinsic structural anisotropy within this family induces strongly anisotropic mechanical, electronic, and optical behav-ior. These materials oﬀer high ultimate strain, comparable to that of graphene. The majority are semiconductors in nature, where th-CAs2 and th-CP2 possess direct and quasi-direct band gaps, respectively, and the rest have indirect band gaps. Besides, an indirect-to-direct band gap transition can be induced in th-CSb2 through strain engineering. Studied compounds have good optical absorption in the visible and ultraviolet regions of the light spectrum, suitable for optoelectron-ics applications. Their band gaps are wide enough to provide the photogenerated energy required for the splitting of water. In th-CAs2 and th-CP2, the positions of band edges are perfectly compatible with the water oxidation and reduction potentials. Besides, they oﬀer anisotropic high charge carrier mobilities, which prolongs the average lifetime of charge carrier drift. Having all these features in one package, these compounds, especially th-CAs2 and th-CP2, can be consid-ered promising candidates for high-performance photocatalytic water splitting. Moreover, we found auxetic behavior in th-CN2 and th-SiN2 around their equilib-rium structure. Having this rare feature endows these compounds with potential applicability in numerous areas, from biotechnology to defense.
Open Access
Hierarchical synthesis of corrugated photocatalytic TiO2 microsphere architectures on natural pollen surfaces
(Elsevier BV, 2017) Erdogan, D. A.; Ozensoy, E.
Biomaterials are challenging, yet vastly promising templates for engineering unusual inorganic materials with unprecedented surface and structural properties. In the current work, a novel biotemplate-based photocatalytic material was synthesized in the form of corrugated TiO2 microspheres by utilizing a sol-gel methodology where Ambrosia trifida (Ab, Giant ragweed) pollen was exploited as the initial biological support surface. Hierarchically synthesized TiO2 microspheres were structurally characterized in detail via SEM-EDX, Raman spectroscopy, XRD and BET techniques in order to shed light on the surface chemistry, crystal structure, chemical composition and morphology of these novel material architectures. Photocatalytic functionality of the synthesized materials was demonstrated both in gas phase as well as in liquid phase. Along these lines, air and water purification capabilities of the synthesized TiO2 microspheres were established by performing photocatalytic oxidative NOx(g) storage and Rhodamine B(aq) degradation experiments; respectively. The synthetic approach presented herein offers new opportunities to design and create sophisticated functional materials that can be used in micro reactor systems, adsorbents, drug delivery systems, catalytic processes, and sensor technologies.
Open Access
Morphology-tailored synthesis of tungsten trioxide (Hydrate) thin films and their photocatalytic properties
(ACS Publications, 2011-01-10) Jiao, Z. H.; Wang, J. M.; Ke, L.; Sun, X. W.; Demir, Hilmi Volkan
Tungsten trioxide hydrate (3WO(3)center dot H(2)O) films with different morphologies were directly grown on fluorine doped tin oxide (FTO) subsi:rate via a facile crystal-seed-assisted hydrothermal method. Scanning electron microscopy (SEM) analysis showed that 3WO(3)center dot H(2)O thin films composed of platelike, wedgelike, and sheetlike nanostructures could be selectively synthesized by adding Na(2)SO(4), (NH(4))(2)SO(4), and CH(3)COONH(4) as capping agents, respectively. X-ray diffraction (XRD) studies indicated that these films were of orthorhombic structure. The as-prepared thin films after dehydration showed obvious photcicatalytic activities. The best film grown using CH(3)COONH(4) as a capping agent generated anodic photocurrents of 1.16 mA/cm(2) fork oxidization of methanol and 0.5 mA/cm(2) for water splitting with the highest photoconversion efficiency of about 0.3% under simulated solar illumination.
Open Access
Synthesis and characterization of silver phosphate from lyotropic liquid crystalline mesophase template as a photocatalyst
(2018-07) Canbolat, Nüveyre
Increasing energy demands and environmental problems are the driving forces of the current literature. Over the years, many new compounds have been synthesized and also morphological control of the well-known compounds have been the major topics to improve/contribute to the solutions of energy demand and environmental issues. One of these issues is finding an efficient and stable photocatalyst for some of the environmental problems. Ag3PO4 has been a target material for dye degradation and water splitting processes. Silver phosphate has a suitable band gap for photo-oxidation process under visible light irradiation. However, it has stability and reusability problems that needs to be resolved to effectively use as an efficient photo-catalyst. Because of that, many research worked on the synthesis and stability issues of this material. In this thesis, the work focuses on surfactant:Ag(I):H3PO4 lyotropic liquid crystalline mesophase to synthesize mesoporous Ag3PO4. Two different surfactants (small, 10-lauryl ether, C12EO10 and large pluronic, triblock copolymer, P123, HO(CH2CH2O)20-(CH(CH3)CH2O)70-(CH2CH2O)20H), two different silver salts (AgNO3, SN and AgCF3SO3, AgOTf) and two different phosphate precursors (H3PO4 and LiH2PO4) have been used throughout this investigation. Solutions were prepared in water or ethanol by first dissolving surfactant, then adding stoichiometric ratio of AgNO3, and H3PO4. To achieve clear and homogenous solution, a small amount of HNO3 is added to the above solution. Without HNO3, some yellow precipitation occurs that needs to be filtrated out. According to XRD patterns, SEM images, and N2 adsorption-desorption isotherms, the yellow precipitate is bulk Ag3PO4. Decanted solution and normal acidified solution compares well with each other and the results are similar in further steps of the synthesis. Therefore, adding small amount of HNO3 to the solution overcomes the precipitation of bulk Ag3PO4 and used in further steps of the synthesis. Then, the solutions can be spin or drop-cast coated over glass slides to form the mesophases and thin/thick films. The films diffract at small angles, indicating the formation of the mesophase. However, the mesophases are not stable and gradually transform into soft mesocrystals that diffract at small and high angles. Later step is to determine a desired calcination temperature for mesoporosity. Therefore, first a high temperature (over 300˚C) treatments have been applied to burn all surfactant in the films. This ensures mesoporosity, but it also results some bulk formations; silver metal forms at high temperatures. Therefore, the calcination or heat treatment temperature has been gradually reduced down to room temperature (RT). At RT, soft mesocrystal forms that can be heat treated at various low temperatures (70-150˚C) to form Ag3PO4 in many different morphologies; these samples have no silver metal. All Ag3PO4 samples, obtained under different conditions, were tested in Rhodamine-B (Rh-B) dye degradation by visible light irradiation with a good activity. But the catalyst is not stable under catalytic conditions. To solve this problem, some samples were prepared under vacuum to convert surfactants carbons to coat the surface of the catalyst by carbon that stabilized the catalyst. In the last section of the thesis, cation exchange method has been developed to convert pre-formed mesoporous LiMPO4 (M = Mn, Co, and Ni) to Ag3PO4. Mesoporous Ag3PO4 has been obtained from all precursors but the ones obtained from LiCoPO4 performed the best in photo-degradation of dye under visible light and the ones obtained from LiMnPO4 is almost inactive. Therefore, this part needs further studies to understand details of these observations. Introducing carbon and cation exchange methods seem to be effective solutions for the stability problem of this photocatalyst. All synthesis products are tested in the photodegradation experiment and compared with each other. This thesis is partially clarified; how to synthesize mesoporous Ag3PO4, what the behavior of silver in system is, and how to stabilize the catalyst. Furthermore, the cation exchange process opens a new horizon for the Ag3PO4 synthesis.
Open Access
Thermal evolution of structure and photocatalytic activity in polymer microsphere templated TiO2 microbowls
(Elsevier, 2014) Erdogan, D. A.; Polat, M.; Garifullin, R.; Güler, Mustafa O.; Ozensoy, E.
Polystyrene cross-linked divinyl benzene (PS-co-DVB) microspheres were used as an organic template in order to synthesize photocatalytic TiO2 microspheres and microbowls. Photocatalytic activity of the microbowl surfaces were demonstrated both in the gas phase via photocatalytic NO(g) oxidation by O2(g) as well as in the liquid phase via Rhodamine B degradation. Thermal degradation mechanism of the polymer template and its direct influence on the TiO2 crystal structure, surface morphology, composition, specific surface area and the gas/liquid phase photocatalytic activity data were discussed in detail. With increasing calcination temperatures, spherical polymer template first undergoes a glass transition, covering the TiO 2 film, followed by the complete decomposition of the organic template to yield TiO2 exposed microbowl structures. TiO2 microbowl systems calcined at 600 °C yielded the highest per-site basis photocatalytic activity. Crystallographic and electronic properties of the TiO2 microsphere surfaces as well as their surface area play a crucial role in their ultimate photocatalytic activity. It was demonstrated that the polymer microsphere templated TiO2 photocatalysts presented in the current work offer a promising and a versatile synthetic platform for photocatalytic DeNOx applications for air purification technologies.