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Park YH, Kim D, Hiragond CB, Lee J, Jung JW, Cho CH, In I, In SI. Phase-controlled 1T/2H-MoS2 interaction with reduced TiO2 for highly stable photocatalytic CO2 reduction into CO. J CO2 UTIL 2023. [DOI: 10.1016/j.jcou.2022.102324] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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Eid K, Sliem MH, Abdullah AM. Tailoring the defects of sub-100 nm multipodal titanium nitride/oxynitride nanotubes for efficient water splitting performance. NANOSCALE ADVANCES 2021; 3:5016-5026. [PMID: 36132349 PMCID: PMC9419868 DOI: 10.1039/d1na00274k] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/14/2021] [Accepted: 07/09/2021] [Indexed: 05/31/2023]
Abstract
Deciphering the photocatalytic-defect relationship of photoanodes can pave the way towards the rational design for high-performance solar energy conversion. Herein, we rationally designed uniform and aligned ultrathin sub-100 nm multipodal titanium nitride/oxynitride nanotubes (TiON x NTs) (x = 2, 4, and 6 h) via the anodic oxidation of Ti-foil in a formamide-based electrolyte followed by annealing under ammonia gas for different durations. XPS, XPS imaging, Auger electron spectra, and positron annihilation spectroscopy disclosed that the high nitridation rate induced the generation of a mixture of Ti-nitride and oxynitride with various vacancy-type defects, including monovacancies, vacancy clusters, and a few voids inside TiO x NTs. These defects decreased the bandgap energy to 2.4 eV, increased visible-light response, and enhanced the incident photon-to-current collection efficiency (IPCE) and the photocurrent density of TiON x NTs by nearly 8 times compared with TiO2NTs, besides a quick carrier diffusion at the nanotube/electrolyte interface. The water-splitting performance of sub-100 nm TiON6NT multipodal nanotubes was superior to the long compacted TiON x NTs with different lengths and TiO2 nanoparticles. Thus, the optimization of the nitridation rate tailors the defect concentration, thereby achieving the highest solar conversion efficiency.
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Affiliation(s)
- Kamel Eid
- Gas Processing Center, College of Engineering, Qatar University P. O. Box 2713 Doha Qatar
| | - Mostafa H Sliem
- Center for Advanced Materials, Qatar University P. O. Box 2713 Doha Qatar
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Levy M, Chowdhury PP, Nagpal P. Quantum dot therapeutics: a new class of radical therapies. J Biol Eng 2019; 13:48. [PMID: 31160923 PMCID: PMC6542014 DOI: 10.1186/s13036-019-0173-4] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2019] [Accepted: 04/21/2019] [Indexed: 12/12/2022] Open
Abstract
Traditional therapeutics and vaccines represent the bedrock of modern medicine, where isolated biochemical molecules or designed proteins have led to success in treating and preventing diseases. However, several adaptive pathogens, such as multidrug-resistant (MDR) superbugs, and rapidly evolving diseases, such as cancer, can evade such molecules very effectively. This poses an important problem since the rapid emergence of multidrug-resistance among microbes is one of the most pressing public health crises of our time-one that could claim more than 10 million lives and 100 trillion dollars annually by 2050. Several non-traditional antibiotics are now being developed that can survive in the face of adaptive drug resistance. One such versatile strategy is redox perturbation using quantum dot (QD) therapeutics. While redox molecules are nominally used by cells for intracellular signaling and other functions, specific generation of such species exogenously, using an electromagnetic stimulus (light, sound, magnetic field), can specifically kill the cells most vulnerable to such species. For example, recently QD therapeutics have shown tremendous promise by specifically generating superoxide intracellularly (using light as a trigger) to selectively eliminate a wide range of MDR pathogens. While the efficacy of such QD therapeutics was shown using in vitro studies, several apparent contradictions exist regarding QD safety and potential for clinical applications. In this review, we outline the design rules for creating specific QD therapies for redox perturbation; summarize the parameters for choosing appropriate materials, size, and capping ligands to ensure their facile clearance; and highlight a potential path forward towards developing this new class of radical QD therapeutics.
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Affiliation(s)
- Max Levy
- Chemical and Biological Engineering, University of Colorado Boulder, Boulder, CO 80303 USA
- Renewable and Sustainable Energy Institute, University of Colorado Boulder, Boulder, CO 80303 USA
| | - Partha P. Chowdhury
- Chemical and Biological Engineering, University of Colorado Boulder, Boulder, CO 80303 USA
- Renewable and Sustainable Energy Institute, University of Colorado Boulder, Boulder, CO 80303 USA
| | - Prashant Nagpal
- Chemical and Biological Engineering, University of Colorado Boulder, Boulder, CO 80303 USA
- Renewable and Sustainable Energy Institute, University of Colorado Boulder, Boulder, CO 80303 USA
- Materials Science and Engineering, University of Colorado Boulder, Boulder, CO 80303 USA
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Nasrollahzadeh M, Issaabadi Z, Sajjadi M, Sajadi SM, Atarod M. Types of Nanostructures. INTERFACE SCIENCE AND TECHNOLOGY 2019. [DOI: 10.1016/b978-0-12-813586-0.00002-x] [Citation(s) in RCA: 38] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
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Brahmi H, Neupane R, Xie L, Singh S, Yarali M, Katwal G, Chen S, Paulose M, Varghese OK, Mavrokefalos A. Observation of a low temperature n-p transition in individual titania nanotubes. NANOSCALE 2018; 10:3863-3870. [PMID: 29417121 DOI: 10.1039/c7nr07951f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Manipulating the transport properties of titania nanotubes (NTs) is paramount in guaranteeing the material's successful implementation in various solid state applications. Here we present the unique semiconducting properties of individual titania NTs as revealed from thermoelectric and structural studies performed on the same individual NTs. The NTs were in the anatase phase fabricated by anodic oxidation and doped with intrinsic defects created by reducing the lattice thermally. Despite their polycrystalline nature and nanoscale walls, the doped NTs were found to be 4-5 orders of magnitude more electrically conducting than TiO2 nanowires and thin films, with values approaching the bulk single crystal conductivity. The reason for the high conductivity was found to be the high carrier concentration on the order of 1022 cm-3, which counteracted the low mobility values ∼0.006 cm2 V-1 s-1. Furthermore, this high level of carrier concentration transitioned the NTs to a degenerate state, which is the first such example in thermally doped titania NTs. More importantly, our study showed the creation of acceptor states along with donor states in individual nanotubes upon lattice reduction. These acceptor levels were found to be active at low temperatures when donor states were not ionized, shifting the Fermi level (Ef) from the conduction band to the valence band.
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Affiliation(s)
- Hatem Brahmi
- Department of Mechanical Engineering, University of Houston, Houston, TX 77204, USA.
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Ding Y, Nagpal P. Titanium dioxide nanotube membranes for solar energy conversion: effect of deep and shallow dopants. Phys Chem Chem Phys 2017; 19:10042-10050. [DOI: 10.1039/c7cp00774d] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Here we show the effect of shallow and deep dopants on titanium dioxide (TiO2) nanotube membranes, for applications in photocatalytic, photoelectrochemical, photovoltaic, and other photosensitized devices for converting light into chemical feedstocks or electricity.
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Affiliation(s)
- Yuchen Ding
- Chemistry and Biochemistry
- University of Colorado Boulder
- Boulder
- USA
- Renewable and Sustainable Energy Institute (RASEI)
| | - Prashant Nagpal
- Renewable and Sustainable Energy Institute (RASEI)
- University of Colorado Boulder
- Boulder
- USA
- Chemical and Biochemical Engineering
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Ding Y, Nagpal P. Standalone anion- and co-doped titanium dioxide nanotubes for photocatalytic and photoelectrochemical solar-to-fuel conversion. NANOSCALE 2016; 8:17496-17505. [PMID: 27714097 DOI: 10.1039/c6nr05742j] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Several strategies are currently being investigated for conversion of incident sunlight into renewable sources of energy, and photocatalytic or photoelectrochemical production of solar fuels can provide an important alternative. Titanium dioxide (TiO2) has been heavily investigated as a material of choice due to its excellent optoelectronic properties and stability, and anion-doping proposed as a pathway to improve light absorption as well as improving the efficiency of oxygen production. While several studies have used morphological tuning, elemental doping, and surface engineering in TiO2 to extend its absorption, there is a need to optimize simultaneously charge transport and improve interfacial chemical reaction kinetics. Here we show anion-doped (nitrogen, carbon) standalone TiO2 nanotube membranes that absorb visible light for the water-splitting reaction, using both wireless (photocatalysis) and wired (photoelectrochemical) solar-to-fuel conversion (STFC) cells. Using simulated solar radiation, we show generation of hydrogen as a solar fuel using visible light photocatalysis. Furthermore, using a model we elucidate detailed photophysics and photoelectrochemical properties of these nanotubes, and explain the kinetics of photogenerated charge carriers following light absorption. We show that while visible light induces a superlinear photoresponse for catalytic reduction and may benefit from higher incident light intensity, ultraviolet light shows a linear photoresponse and saturation with higher light flux due to trapping of photogenerated charges (mainly electrons). These results can have important implications for design of other metal-oxide membranes for solar fuel generation, and appropriate design of dopants and induced energy levels in these photocatalysts.
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Affiliation(s)
- Yuchen Ding
- Chemistry and Biochemistry, University of Colorado Boulder, USA
| | - Prashant Nagpal
- Chemical and Biochemical Engineering, University of Colorado Boulder, USA. and Materials Science and Engineering, University of Colorado Boulder, USA and Renewable and Sustainable Energy Institute (RASEI), University of Colorado Boulder, Boulder, CO 80303, USA
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Goodman SM, Siu A, Singh V, Nagpal P. Long-range energy transfer in self-assembled quantum dot-DNA cascades. NANOSCALE 2015; 7:18435-18440. [PMID: 26498166 DOI: 10.1039/c5nr04778a] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
The size-dependent energy bandgaps of semiconductor nanocrystals or quantum dots (QDs) can be utilized in converting broadband incident radiation efficiently into electric current by cascade energy transfer (ET) between layers of different sized quantum dots, followed by charge dissociation and transport in the bottom layer. Self-assembling such cascade structures with angstrom-scale spatial precision is important for building realistic devices, and DNA-based QD self-assembly can provide an important alternative. Here we show long-range Dexter energy transfer in QD-DNA self-assembled single constructs and ensemble devices. Using photoluminescence, scanning tunneling spectroscopy, current-sensing AFM measurements in single QD-DNA cascade constructs, and temperature-dependent ensemble devices using TiO2 nanotubes, we show that Dexter energy transfer, likely mediated by the exciton-shelves formed in these QD-DNA self-assembled structures, can be used for efficient transport of energy across QD-DNA thin films.
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Affiliation(s)
- Samuel M Goodman
- Department of Chemical and Biological Engineering, University of Colorado, Boulder, USA.
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Alivov Y, Funke H, Nagpal P. Air-gating and chemical-gating in transistors and sensing devices made from hollow TiO2 semiconductor nanotubes. NANOTECHNOLOGY 2015; 26:295203. [PMID: 26134618 DOI: 10.1088/0957-4484/26/29/295203] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Rapid miniaturization of electronic devices down to the nanoscale, according to Moore's law, has led to some undesirable effects like high leakage current in transistors, which can offset additional benefits from scaling down. Development of three-dimensional transistors, by spatial extension in the third dimension, has allowed higher contact area with a gate electrode and better control over conductivity in the semiconductor channel. However, these devices do not utilize the large surface area and interfaces for new electronic functionality. Here, we demonstrate air gating and chemical gating in hollow semiconductor nanotube devices and highlight the potential for development of novel transistors that can be modulated using channel bias, gate voltage, chemical composition, and concentration. Using chemical gating, we reversibly altered the conductivity of nanoscaled semiconductor nanotubes (10-500 nm TiO2 nanotubes) by six orders of magnitude, with a tunable rectification factor (ON/OFF ratio) ranging from 1-10(6). While demonstrated air- and chemical-gating speeds were slow here (∼seconds) due to the mechanical-evacuation rate and size of our chamber, the small nanoscale volume of these hollow semiconductors can enable much higher switching speeds, limited by the rate of adsorption/desorption of molecules at semiconductor interfaces. These chemical-gating effects are completely reversible, additive between different chemical compositions, and can enable semiconductor nanoelectronic devices for 'chemical transistors', 'chemical diodes', and very high-efficiency sensing applications.
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Affiliation(s)
- Yahya Alivov
- Department of Chemical and Biological Engineering, University of Colorado, Boulder, USA
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Alivov Y, Funke HH, Singh V, Nagpal P. Air-pressure tunable depletion width, rectification behavior, and charge conduction in oxide nanotubes. ACS APPLIED MATERIALS & INTERFACES 2015; 7:2153-2159. [PMID: 25594471 DOI: 10.1021/am5076666] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Metal-oxide nanotubes provide large surface areas and functionalizable surfaces for a variety of optical and electronic applications. Here we report air-tunable rectifying behavior, depletion width modulation, and two-dimensional (2D) charge conduction in hollow titanium-dioxide nanotubes. The metal contact forms a Schottky-diode in the nanotubes, and the rectification factor (on/off ratio) can be varied by more than 3 orders of magnitude (1-2 × 10(3)) as the air pressure is increased from 2 mTorr to atmospheric pressure. This behavior is explained using a change in depletion width of these thin nanotubes by adsorption of water vapor on both surfaces of a hollow nanotube, and the resulting formation of a metal-insulator-semiconductor (MIS) junction, which controls the 2D charge conduction properties in thin oxide nanotubes.
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Affiliation(s)
- Yahya Alivov
- Department of Chemical and Biological Engineering, ‡Materials Science and Engineering, and §Renewable and Sustainable Energy Institute, University of Colorado , Boulder, Colorado, United States
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Samsudin EM, Abd Hamid SB, Juan JC, Basirun WJ, Kandjani AE, Bhargava SK. Controlled nitrogen insertion in titanium dioxide for optimal photocatalytic degradation of atrazine. RSC Adv 2015; 5:44041-44052. [DOI: 10.1039/c5ra00890e] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/02/2023] Open
Abstract
Introducing defects into the intrinsic TiO2structural framework with nitrogen enhanced the photocatalytic response towards the degradation of atrazine as compared to undoped TiO2.
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Affiliation(s)
- Emy Marlina Samsudin
- Nanotechnology and Catalysis Research Center
- University of Malaya
- 50603 Kuala Lumpur
- Malaysia
| | - Sharifah Bee Abd Hamid
- Nanotechnology and Catalysis Research Center
- University of Malaya
- 50603 Kuala Lumpur
- Malaysia
| | - Joon Ching Juan
- Nanotechnology and Catalysis Research Center
- University of Malaya
- 50603 Kuala Lumpur
- Malaysia
| | - Wan Jefrey Basirun
- Nanotechnology and Catalysis Research Center
- University of Malaya
- 50603 Kuala Lumpur
- Malaysia
| | | | - Suresh K. Bhargava
- Centre of Advanced Materials and Industrial Chemistry
- RMIT University
- Melbourne 3001
- Australia
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Ding Y, Singh V, Goodman SM, Nagpal P. Low Exciton-Phonon Coupling, High Charge Carrier Mobilities, and Multiexciton Properties in Two-Dimensional Lead, Silver, Cadmium, and Copper Chalcogenide Nanostructures. J Phys Chem Lett 2014; 5:4291-4297. [PMID: 26273976 DOI: 10.1021/jz5023015] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
The development of two-dimensional (2D) nanomaterials has revealed novel physical properties, like high carrier mobilities and the tunable coupling of charge carriers with phonons, which can enable wide-ranging applications in optoelectronic and thermoelectric devices. While mechanical exfoliation of graphene and some transition metal dichalcogenides (e.g., MoS2, WSe2) has enabled their fabrication as 2D semiconductors and integration into devices, lack of similar syntheses for other 2D semiconductor materials has hindered further progress. Here, we report measurements of fundamental charge carrier interactions and optoelectronic properties of 2D nanomaterials made from two-monolayers-thick PbX, CdX, Cu2X, and Ag2X (X = S, Se) using colloidal syntheses. Extremely low coupling of charge carriers with phonons (2-6-fold lower than bulk and other low-dimensional semiconductors), high carrier mobilities (0.2-1.2 cm(2) V(-1) s(-1), without dielectric screening), observation of infrared surface plasmons in ultrathin 2D semiconductor nanostructures, strong quantum-confinement, and other multiexcitonic properties (different phonon coupling and photon-to-charge collection efficiencies for band-edge and higher-energy excitons) can pave the way for efficient solution-processed devices made from these 2D nanostructured semiconductors.
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Affiliation(s)
- Yuchen Ding
- †Department of Chemistry and Biochemistry, ‡Department of Chemical and Biological Engineering, §Renewable and Sustainable Energy Institute (RASEI), and ∥Materials Science and Engineering, University of Colorado Boulder, Boulder, Colorado 80303, United States
| | - Vivek Singh
- †Department of Chemistry and Biochemistry, ‡Department of Chemical and Biological Engineering, §Renewable and Sustainable Energy Institute (RASEI), and ∥Materials Science and Engineering, University of Colorado Boulder, Boulder, Colorado 80303, United States
| | - Samuel M Goodman
- †Department of Chemistry and Biochemistry, ‡Department of Chemical and Biological Engineering, §Renewable and Sustainable Energy Institute (RASEI), and ∥Materials Science and Engineering, University of Colorado Boulder, Boulder, Colorado 80303, United States
| | - Prashant Nagpal
- †Department of Chemistry and Biochemistry, ‡Department of Chemical and Biological Engineering, §Renewable and Sustainable Energy Institute (RASEI), and ∥Materials Science and Engineering, University of Colorado Boulder, Boulder, Colorado 80303, United States
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