Browsing by Author "Ranjith, K. S."
Now showing 1 - 10 of 10
Results Per Page
Sort Options
Item Open Access Conscientious design of Zn-S/Ti-N layer by transformation of ZnTiO3 on electrospun ZnTiO3@TiO2 nanofibers: stability and reusable photocatalytic performance under visible irradiation(American Chemical Society, 2018) Ranjith, K. S.; Uyar, TamerHerein, we report the rational design of Zn-S/Ti-N on TiO2 as a hierarchical nanoarchitecture from the ZnTiO3@TiO2 nanofibers (NFs) through electrospinning followed by a hydrothermal process using l-cysteine as an S/N source. Controlling the hydrothermal temperature, the hierarchical form of NFs exhibited highly efficient visible catalytic behavior for organic dye (i.e., Rhodamine B) degradation since S and N based surface function on the oxide surface resulted in unique interlayer induced strain coupled surface defects. The surface functionalization of the ZnTiO3 surface with S and N was solidly confirmed by X-ray photo-electrospectroscopy (XPS) and energy-dispersive X-ray (EDX) with elemental mapping results. Inducing the S/N functionality at higher hydrothermal temperature reverses the structural arrangement of ZnTiO3 favoring the interaction of S preferably with Zn and Ti with N for the formation of ZnS/TiN@TiO2 NFs. The tunable band function through the Zn-S/Ti-N cofunctionalization exhibited effective long-term catalytic performance under UV and visible irradiation with a degradation rate of 0.0362 and 0.0313 min-1, which is nearly 3.1 and 1.3 times higher than that of the ZnTiO3@TiO2 and ZnTiO3-S/N@TiO2 NFs, respectively. The catalysts are highly photoactive after multiple photocatalytic cycles with stable surface and structural features under visible irradiation. The study could provide new opportunities for designing hierarchical structures in ternary form of nanoscale architectures for effective visible photocatalytic activity. CopyrightItem Open Access Electrospinning combined with atomic layer deposition to generate applied nanomaterials: A review(American Chemical Society, 2020) Vempati, S.; Ranjith, K. S.; Topuz, Fuat; Bıyıklı, Necmi; Uyar, TamerCombining different material processing techniques is one of the keys to obtain materials that depict synergistic properties. In this review, we have reviewed a combination of two highly potential techniques, namely, electrospinning and atomic layer deposition (ALD), in the view of various applications. Over the past 10 years, our research groups are involved in the exploration of employing this combination for a range of applications. We also include some basic information on both the processes and diversity of nanostructures as a result of their combination. Nonwoven nanofiber membranes are excellent candidates for a wide range of applications. Also, they can act as templates to produce various other kinds of nanostructures when combined with ALD in small/large scale production. These nanostructures could be used as such or further subjected to other processing techniques yielding hierarchical structures. In this review, we exclusively survey and highlight the unique capabilities of combined electrospinning and ALD for applications in catalysis, photocatalysis, solar cells, batteries and gas sensors.Item Open Access Hierarchical electrospun PIM nanofibers decorated with ZnO nanorods for effective pollutant adsorption and photocatalytic degradation(Elsevier B.V., 2018) Ranjith, K. S.; Satilmis, B.; Uyar, TamerItem Open Access Immobilized Pd-Ag bimetallic nanoparticles on polymeric nanofibers as an effective catalyst: Effective loading of Ag with bimetallic functionality through Pd nucleated nanofibers(Institute of Physics Publishing, 2018) Ranjith, K. S.; Celebioglu A.; Uyar, TamerHere, we present a precise process for synthesizing Pd-Ag bimetallic nanoparticles (NPs) onto polymeric nanofibers by decorating Pd-NPs through atomic layer deposition followed by a chemical reduction process for tagging Ag nanostructures with bimetallic functionality. The results show that Pd-NPs act as a nucleation platform for tagging Ag and form Pd-Ag bimetallic NPs with a monodisperse nature with significant catalytic enhancement to the reaction rate over the bimetallic nature of the Pd-Ag ratio. A Pd-NP decorated polymeric nanofibrous web acts as an excellent platform for the encapsulation or interaction of Ag, which prevents agglomeration and promotes the interaction of Ag ions only on the surface of the Pd-NPs. We observed an effective reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) by sodium borohydride (NaBH4) to access the catalytic activity of Pd-Ag bimetallic NPs on a free-standing flexible polymeric nanofibrous web as a support. The captive formation of the polymeric nanofibrous web with Pd-Ag bimetallic functionality exhibited superior and stable catalytic performance with reduction rates of 0.0719, 0.1520, and 0.0871 min-1 for different loadings of Ag on Pd decorated nanofibrous webs such as Pd/Ag(0.01), Pd/Ag(0.03), and Pd/Ag(0.05), respectively. The highly faceted Pd-Ag NPs with an immobilized nature improves the catalytic functionality by enhancing the binding energy of the 4-NP adsorbate to the surface of the NPs. With the aid of bimetallic functionality, the nanofibrous web was demonstrated as a hybrid heterogeneous photocatalyst with a 3.16-fold enhancement in the reaction rate as compared with the monometallic decorative nature of NaBH4 as a reducing agent. The effective role of the monodisperse nature of Pd ions with an ultralow content as low as 3 wt% and the tunable ratio of Ag on the nanofibrous web induced effective catalytic activity over multiple cycles.Item Open Access Monodispersed, highly interactive facet (111)-oriented Pd nanograins by ALD onto free-standing and flexible electrospun polymeric nanofibrous webs for catalytic application(Wiley-VCH Verlag, 2017-10) Ranjith, K. S.; Celebioglu A.; Eren, H.; Bıyıklı, Necmi; Uyar, TamerAn atomic layer deposition (ALD) of monodispersed palladium (Pd) nanograins (≈2 nm) onto electrospun polymeric nanofibers (NF) is presented. By ALD, monodispersed Pd nanograins with (111) exposed facets are decorated on the surface of the free-standing flexible nanofibrous webs (NW). The Pd nanograin-decorated free-standing NW exhibit catalytic reduction of 4-nitrophenol to 4-aminophenol. Even under low loading capacity (≈20 µg mg−1), Pd nanograins manifest effective catalytic performance which can be referred to direct exposure of Pd single crystalline highly interactive (111) plains with high surface area on the NW. The Pd nanograins and the interactive sites along with the high surface area NW yield effective catalytic reduction of 4-nitrophenol to 4-aminophenol with the catalytic reduction rate of 0.0531 min−1. Pd nanograins display thermally tunable effective catalytic reduction properties with activation energy (Ea) of 1.705 J mol−1 on varying the reaction temperature from 12 to 42 °C. Moreover, Pd nanograin-decorated NW are exhibited the effective reusable behavior with stable structural integrity even after repeated catalytic reactions. The approach of this study opens up synthesis and surface decoration of metal nanostructures onto NF through ALD with controlled size and facet orientation for designing reusable and free-standing flexible catalytic nanofibrous materials.Item Open Access Multifunctional ZnO nanorod-reduced graphene oxide hybrids nanocomposites for effective water remediation: effective sunlight driven degradation of organic dyes and rapid heavy metal adsorption(Elsevier, 2017-10) Ranjith, K. S.; Manivel, P.; Rajendrakumar, R. T.; Uyar, TamerWe demonstrate the multi-functionality engineering on nanocomposite by combining one dimensional (1D) ZnO nanorod (NR) and two dimensional (2D) reduced graphene oxide (rGO) for efficient water remediation. Nano-engineered ZnO NR-rGO nanocomposites show efficient water remediation in terms of degradation of organic dyes and removal of heavy metal ions. Herein, we report on the fabrication of ZnO NR-rGO nanocomposite via a facile template-free hydrothermal route with an aim to improve the visible photocatalytic efficiency of the ZnO NR based nanocomposites. The structural and morphological features reveal that the rGO sheets are attached on the ZnO NRs and form a hybrid composite assembly. The surface enabled ZnO NR-rGO nanocomposites were used to degrade organic dye molecules (methylene blue (MB), methyl orange (MO) and rhodamine B (RhB)) under visible irradiation and adsorb Cu (II) and Co (II) ions from water through an adsorption process. The nanocomposite containing 7.5 wt% rGO and ZnO NRs shows a 4-fold enhancement in the visible photocatalytic activity and effective removal of Cu (II) and Co (II) ions from aqueous solution respectively. The photocatalytic performance is discussed in detail with respect to interaction between ZnO NRs and rGO sheets, light-harvesting properties of the nanocomposites. The effective experimental adsorption data also fit very well with the pseudo-second-order model which reveals the surface adsorption of metal ions. The results provide insight into a new method utilize for both visible photo degradation and adsorption for the removal of various wastewater pollutants. Construction of hybrid form of nanostructures delivers the effective catalytic properties with tunable functionalities for the water remediation.Item Open Access Nanograined surface shell wall controlled ZnO–ZnS core–shell nanofibers and their shell wall thickness dependent visible photocatalytic properties(Royal Society of Chemistry, 2017) Ranjith, K. S.; Senthamizhan A.; Balusamy, B.; Uyar, TamerThe core-shell form of ZnO-ZnS based heterostructural nanofibers (NF) has received increased attention for use as a photocatalyst owing to its potential for outstanding performance under visible irradiation. One viable strategy to realize the efficient separation of photoinduced charge carriers in order to improve catalytic efficiency is to design core-shell nanostructures. But the shell wall thickness plays a vital role in effective carrier separation and lowering the recombination rate. A one dimensional (1D) form of shell wall controlled ZnO-ZnS core-shell nanofibers has been successfully prepared via electrospinning followed by a sulfidation process. The ZnS shell wall thickness can be adjusted from 5 to 50 nm with a variation in the sulfidation reaction time between 30 min and 540 min. The results indicate that the surfaces of the ZnO nanofibers were converted to a ZnS shell layer via the sulfidation process, inducing visible absorption behavior. Photoluminescence (PL) spectral analysis indicated that the introduction of a ZnS shell layer improved electron and hole separation efficiency. A strong correlation between effective charge separation and the shell wall thickness aids the catalytic behavior of the nanofiber network and improves its visible responsive nature. The comparative degradation efficiency toward methylene blue (MB) has been studied and the results showed that the ZnO-ZnS nanofibers with a shell wall thickness of ∼20 nm have 9 times higher efficiency than pristine ZnO nanofibers, which was attributed to effective charge separation and the visible response of the heterostructural nanofibers. In addition, they have been shown to have a strong effect on the degradation of Rhodamine B (Rh B) and 4-nitrophenol (4-NP), with promising reusable catalytic efficiency. The shell layer upgraded the nanofiber by acting as a protective layer, thus avoiding the photo-corrosion of ZnO during the catalytic process. A credible mechanism for the charge transfer process and a mechanism for photocatalysis supported by trapping experiments in the ZnO-ZnS heterostructural system for the degradation of an aqueous solution of MB are also explicated. Trapping experiments indicate that h+ and OH are the main active species in the ZnO-ZnS heterostructural catalyst, which do not effectively contribute in a bare ZnO catalytic system. Our work also highlights the stability and recyclability of the core-shell nanostructure photocatalyst and supports its potential for environmental applications. We thus anticipate that our results show broad potential in the photocatalysis domain for the design of a visible light functional and reusable core-shell nanostructured photocatalyst.Item Open Access Polymeric nanofibers decorated with reduced graphene oxide nanoflakes(Elsevier, 2017) Ranjith, K. S.; Uyar, TamerResearch into graphene-polymeric based membranes by tuning its structural and functional properties will facilitate new opportunities on these hierarchical platforms. The objective is to play a role on the external skin of the polymeric nanofibers to enhance it structural and functional properties by introducing thin layered graphene oxide flakes to improve the absorption behavior, and to modulate the mechanical and electronic properties and more. By modifying the polymers and including some metal nanostructures within the graphene functionality may lead to the development of complex hybrid system for advanced applicability in fields such as catalyst, electronics, sensing, storage based devices, etc. Constructing the graphenebased systems with polymeric membranes having unique architecture and functionality will provide innovation in materials science in related fields. The hierarchical arrangement of reduced graphene oxide-polymeric membrane can play a key role in multifunctional application in the fields of electronics, catalysts, and sensors.Item Open Access Rational synthesis of Na and S co-catalyst TiO2-based nanofibers: presence of surface-layered TiS3 shell grains and sulfur-induced defects for efficient visible-light driven photocatalysis(Royal Society of Chemistry, 2017) Ranjith, K. S.; Uyar, TamerSurface-modified TiO2 nanofibers (NFs) with tunable visible-light photoactive catalysts were synthesised through electrospinning, followed by a sulfidation process. The utilization of sodium-based sulfidation precursors effectively led to the diffusion and integration of sulfur impurities into TiO2, modifying its band function. The optical band function of the sulfur-modified TiO2 NFs can be easily manipulated from 3.17 eV to 2.28 eV through surface modification, due to the creation of oxygen vacancies through the sulfidation process. Sulfidating TiO2 NFs introduces Ti-S-based nanograins and oxygen vacancies on the surface that favor the TiO2-TiS3 core-shell interface. These defect states extend the photocatalytic activity of the TiO2 NFs under visible irradiation and improve effective carrier separation and the production of reactive oxygen species. The surface oxygen vacancies and the Ti-S-based surface nanograins serve as charge traps and act as adsorption sites, improving the carrier mobility and avoiding charge recombination. The diffused S-modified TiO2 NFs exhibit a degradation rate of 0.0365 cm-1 for RhB dye solution, which is 4.8 times higher than that of pristine TiO2 NFs under visible irradiation. By benefiting from the sulfur states and oxygen vacancies, with a narrowed band gap of 2.3 eV, these nanofibers serve as suitable localized states for effective carrier separation.Item Open Access Surface decoration of Pt nanoparticles via ALD with TiO2 protective layer on polymeric nanofibers as flexible and reusable heterogeneous nanocatalysts(Nature Publishing Group, 2017) Celebioglu, A.; Ranjith, K. S.; Eren, H.; Bıyıklı, Necmi; Uyar, T.Coupling the functional nanoheterostructures over the flexible polymeric nanofibrous membranes through electrospinning followed by the atomic layer deposition (ALD), here we presented a high surface area platform as flexible and reusable heterogeneous nanocatalysts. Here, we show the ALD of titanium dioxide (TiO2) protective nanolayer onto the electrospun polyacrylonitrile (PAN) nanofibrous web and then platinum nanoparticles (Pt-NP) decoration was performed by ALD onto TiO2 coated PAN nanofibers. The free-standing and flexible Pt-NP/TiO2-PAN nanofibrous web showed the enhancive reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) within 45 seconds though the hydrogenation process with the degradation rate of 0.1102 s-1. The TiO2 protective layer on the PAN polymeric nanofibers was presented as an effective route to enhance the attachment of Pt-NP and to improve the structure stability of polymeric nanofibrous substrate. Commendable enhancement in the catalytic activity with the catalytic dosage and the durability after the reusing cycles were investigated over the reduction of 4-NP. Even after multiple usage, the Pt-NP/TiO2-PAN nanofibrous webs were stable with the flexible nature with the presence of Pt and TiO2 on its surface.