Nanomaterials

Editorial

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4 pages, 143 KiB

Open AccessEditorial

ZnO- and TiO₂-Based Nanostructures

by Andrea Lamberti

Nanomaterials 2018, 8(5), 325; https://doi.org/10.3390/nano8050325 - 14 May 2018

Cited by 6 | Viewed by 3814

Abstract

Transition-metal oxide (TMO) nanostructures are the focus of current research efforts in nanotechnology since they are the most common minerals on Earth, and also thanks to their special shapes, compositions, and chemical and physical properties.[...] Full article

(This article belongs to the Special Issue ZnO and TiO₂ Based Nanostructures)

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Research

Jump to: Editorial, Review

15 pages, 4245 KiB

Open AccessFeature PaperArticle

Lipid-Coated Zinc Oxide Nanoparticles as Innovative ROS-Generators for Photodynamic Therapy in Cancer Cells

by Andrea Ancona, Bianca Dumontel, Nadia Garino, Benjamin Demarco, Dimitra Chatzitheodoridou, Walter Fazzini, Hanna Engelke and Valentina Cauda

Nanomaterials 2018, 8(3), 143; https://doi.org/10.3390/nano8030143 - 2 Mar 2018

Cited by 106 | Viewed by 10200

Abstract

In the present paper, we use zinc oxide nanoparticles under the excitation of ultraviolet (UV) light for the generation of Reactive Oxygen Species (ROS), with the aim of further using these species for fighting cancer cells in vitro. Owing to the difficulties in [...] Read more.

In the present paper, we use zinc oxide nanoparticles under the excitation of ultraviolet (UV) light for the generation of Reactive Oxygen Species (ROS), with the aim of further using these species for fighting cancer cells in vitro. Owing to the difficulties in obtaining highly dispersed nanoparticles (NPs) in biological media, we propose their coating with a double-lipidic layer and we evaluate their colloidal stability in comparison to the pristine zinc oxide NPs. Then, using Electron Paramagnetic Resonance (EPR) coupled with the spin-trapping technique, we demonstrate and characterize the ability of bare and lipid-coated ZnO NPs to generate ROS in water only when remotely actuated via UV light irradiation. Interestingly, our results reveal that the surface chemistry of the NPs greatly influences the type of photo-generated ROS. Finally, we show that lipid-coated ZnO NPs are effectively internalized inside human epithelial carcinoma cells (HeLa) via a lysosomal pathway and that they can generate ROS inside cancer cells, leading to enhanced cell death. The results are promising for the development of ZnO-based therapeutic systems. Full article

(This article belongs to the Special Issue ZnO and TiO₂ Based Nanostructures)

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15 pages, 2457 KiB

Open AccessArticle

The Critical Role of Thioacetamide Concentration in the Formation of ZnO/ZnS Heterostructures by Sol-Gel Process

by Eloísa Berbel Manaia, Renata Cristina Kiatkoski Kaminski, Bruno Leonardo Caetano, Marina Magnani, Florian Meneau, Amélie Rochet, Celso Valentim Santilli, Valérie Briois, Claudie Bourgaux and Leila Aparecida Chiavacci

Nanomaterials 2018, 8(2), 55; https://doi.org/10.3390/nano8020055 - 23 Jan 2018

Cited by 12 | Viewed by 5851

Abstract

ZnO/ZnS heterostructures have emerged as an attractive approach for tailoring the properties of particles comprising these semiconductors. They can be synthesized using low temperature sol-gel routes. The present work yields insight into the mechanisms involved in the formation of ZnO/ZnS nanostructures. ZnO colloidal [...] Read more.

ZnO/ZnS heterostructures have emerged as an attractive approach for tailoring the properties of particles comprising these semiconductors. They can be synthesized using low temperature sol-gel routes. The present work yields insight into the mechanisms involved in the formation of ZnO/ZnS nanostructures. ZnO colloidal suspensions, prepared by hydrolysis and condensation of a Zn acetate precursor solution, were allowed to react with an ethanolic thioacetamide solution (TAA) as sulfur source. The reactions were monitored in situ by Small Angle X-ray Scattering (SAXS) and UV-vis spectroscopy, and the final colloidal suspensions were characterized by High Resolution Transmission Electron Microscopy (HRTEM). The powders extracted at the end of the reactions were analyzed by X-ray Absorption spectroscopy (XAS) and X-ray diffraction (XRD). Depending on TAA concentration, different nanostructures were revealed. ZnO and ZnS phases were mainly obtained at low and high TAA concentrations, respectively. At intermediate TAA concentrations, we evidenced the formation of ZnO/ZnS heterostructures. ZnS formation could take place via direct crystal growth involving Zn ions remaining in solution and S ions provided by TAA and/or chemical conversion of ZnO to ZnS. The combination of all the characterization techniques was crucial to elucidate the reaction steps and the nature of the final products. Full article

(This article belongs to the Special Issue ZnO and TiO₂ Based Nanostructures)

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12 pages, 8422 KiB

Open AccessArticle

Crystallization of TiO₂ Nanotubes by In Situ Heating TEM

by Alberto Casu, Andrea Lamberti, Stefano Stassi and Andrea Falqui

Nanomaterials 2018, 8(1), 40; https://doi.org/10.3390/nano8010040 - 14 Jan 2018

Cited by 24 | Viewed by 7312

Abstract

The thermally-induced crystallization of anodically grown TiO₂ amorphous nanotubes has been studied so far under ambient pressure conditions by techniques such as differential scanning calorimetry and in situ X-ray diffraction, then looking at the overall response of several thousands of nanotubes in [...] Read more.

The thermally-induced crystallization of anodically grown TiO₂ amorphous nanotubes has been studied so far under ambient pressure conditions by techniques such as differential scanning calorimetry and in situ X-ray diffraction, then looking at the overall response of several thousands of nanotubes in a carpet arrangement. Here we report a study of this phenomenon based on an in situ transmission electron microscopy approach that uses a twofold strategy. First, a group of some tens of TiO₂ amorphous nanotubes was heated looking at their electron diffraction pattern change versus temperature, in order to determine both the initial temperature of crystallization and the corresponding crystalline phases. Second, the experiment was repeated on groups of few nanotubes, imaging their structural evolution in the direct space by spherical aberration-corrected high resolution transmission electron microscopy. These studies showed that, differently from what happens under ambient pressure conditions, under the microscope’s high vacuum (p < 10⁻⁵ Pa) the crystallization of TiO₂ amorphous nanotubes starts from local small seeds of rutile and brookite, which then grow up with the increasing temperature. Besides, the crystallization started at different temperatures, namely 450 and 380 °C, when the in situ heating was performed irradiating the sample with electron beam energy of 120 or 300 keV, respectively. This difference is due to atomic knock-on effects induced by the electron beam with diverse energy. Full article

(This article belongs to the Special Issue ZnO and TiO₂ Based Nanostructures)

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19 pages, 4232 KiB

Open AccessArticle

Thermally Stimulated Currents in Nanocrystalline Titania

by Mara Bruzzi, Riccardo Mori, Andrea Baldi, Ennio Antonio Carnevale, Alessandro Cavallaro and Monica Scaringella

Nanomaterials 2018, 8(1), 13; https://doi.org/10.3390/nano8010013 - 5 Jan 2018

Cited by 7 | Viewed by 5352

Abstract

A thorough study on the distribution of defect-related active energy levels has been performed on nanocrystalline TiO₂. Films have been deposited on thick-alumina printed circuit boards equipped with electrical contacts, heater and temperature sensors, to carry out a detailed thermally stimulated [...] Read more.

A thorough study on the distribution of defect-related active energy levels has been performed on nanocrystalline TiO₂. Films have been deposited on thick-alumina printed circuit boards equipped with electrical contacts, heater and temperature sensors, to carry out a detailed thermally stimulated currents analysis on a wide temperature range (5–630 K), in view to evidence contributions from shallow to deep energy levels within the gap. Data have been processed by numerically modelling electrical transport. The model considers both free and hopping contribution to conduction, a density of states characterized by an exponential tail of localized states below the conduction band and the convolution of standard Thermally Stimulated Currents (TSC) emissions with gaussian distributions to take into account the variability in energy due to local perturbations in the highly disordered network. Results show that in the low temperature range, up to 200 K, hopping within the exponential band tail represents the main contribution to electrical conduction. Above room temperature, electrical conduction is dominated by free carriers contribution and by emissions from deep energy levels, with a defect density ranging within 10¹⁴–10¹⁸ cm⁻³, associated with physio- and chemi-sorbed water vapour, OH groups and to oxygen vacancies. Full article

(This article belongs to the Special Issue ZnO and TiO₂ Based Nanostructures)

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23 pages, 12185 KiB

Open AccessArticle

Organozinc Precursor-Derived Crystalline ZnO Nanoparticles: Synthesis, Characterization and Their Spectroscopic Properties

by Yucang Liang, Susanne Wicker, Xiao Wang, Egil Severin Erichsen and Feng Fu

Nanomaterials 2018, 8(1), 22; https://doi.org/10.3390/nano8010022 - 4 Jan 2018

Cited by 23 | Viewed by 7976

Abstract

Crystalline ZnO_-ROH and ZnO_-OR (R = Me, Et, iPr, nBu) nanoparticles (NPs) have been successfully synthesized by the thermal decomposition of in-situ-formed organozinc complexes Zn(OR)₂ deriving from the reaction of Zn[N(SiMe₃)₂]₂ with ROH [...] Read more.

Crystalline ZnO_-ROH and ZnO_-OR (R = Me, Et, iPr, nBu) nanoparticles (NPs) have been successfully synthesized by the thermal decomposition of in-situ-formed organozinc complexes Zn(OR)₂ deriving from the reaction of Zn[N(SiMe₃)₂]₂ with ROH and of the freshly prepared Zn(OR)₂ under an identical condition, respectively. With increasing carbon chain length of alkyl alcohol, the thermal decomposition temperature and dispersibility of in-situ-formed intermediate zinc alkoxides in oleylamine markedly influenced the particle sizes of ZnO_-ROH and its shape (sphere, plate-like aggregations), while a strong diffraction peak-broadening effect is observed with decreasing particle size. For ZnO_-OR NPs, different particle sizes and various morphologies (hollow sphere or cuboid-like rod, solid sphere) are also observed. As a comparison, the calcination of the fresh-prepared Zn(OR)₂ generated ZnO_-R NPs possessing the particle sizes of 5.4~34.1 nm. All crystalline ZnO nanoparticles are characterized using X-ray diffraction analysis, electron microscopy and solid-state ¹H and ¹³C nuclear magnetic resonance (NMR) spectroscopy. The size effect caused by confinement of electrons’ movement and the defect centres caused by unpaired electrons on oxygen vacancies or ionized impurity heteroatoms in the crystal lattices are monitored by UV-visible spectroscopy, electron paramagnetic resonance (EPR) and photoluminescent (PL) spectroscopy, respectively. Based on the types of defects determined by EPR signals and correspondingly defect-induced probably appeared PL peak position compared to actual obtained PL spectra, we find that it is difficult to establish a direct relationship between defect types and PL peak position, revealing the complication of the formation of defect types and photoluminescence properties. Full article

(This article belongs to the Special Issue ZnO and TiO₂ Based Nanostructures)

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1155 KiB

Open AccessArticle

Piezoelectric Potential in Single-Crystalline ZnO Nanohelices Based on Finite Element Analysis

by Huimin Hao, Kory Jenkins, Xiaowen Huang, Yiqian Xu, Jiahai Huang and Rusen Yang

Nanomaterials 2017, 7(12), 430; https://doi.org/10.3390/nano7120430 - 7 Dec 2017

Cited by 17 | Viewed by 4603

Abstract

Electric potential produced in deformed piezoelectric nanostructures is of significance for both fundamental study and practical applications. To reveal the piezoelectric property of ZnO nanohelices, the piezoelectric potential in single-crystal nanohelices was simulated by finite element method calculations. For a nanohelix with a [...] Read more.

Electric potential produced in deformed piezoelectric nanostructures is of significance for both fundamental study and practical applications. To reveal the piezoelectric property of ZnO nanohelices, the piezoelectric potential in single-crystal nanohelices was simulated by finite element method calculations. For a nanohelix with a length of 1200 nm, a mean coil radius of 150 nm, five active coils, and a hexagonal coiled wire with a side length 100 nm, a compressing force of 100 nN results in a potential of 1.85 V. This potential is significantly higher than the potential produced in a straight nanowire with the same length and applied force. Maintaining the length and increasing the number of coils or mean coil radius leads to higher piezoelectric potential in the nanohelix. Appling a force along the axial direction produces higher piezoelectric potential than in other directions. Adding lateral forces to an existing axial force can change the piezoelectric potential distribution in the nanohelix, while the maximum piezoelectric potential remains largely unchanged in some cases. This research demonstrates the promising potential of ZnO nanohelices for applications in sensors, micro-electromechanical systems (MEMS) devices, nanorobotics, and energy sciences. Full article

(This article belongs to the Special Issue ZnO and TiO₂ Based Nanostructures)

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1624 KiB

Open AccessArticle

ZnO Nanoparticles Protect RNA from Degradation Better than DNA

by Jayden McCall, Joshua J. Smith, Kelsey N. Marquardt, Katelin R. Knight, Hunter Bane, Alice Barber and Robert K. DeLong

Nanomaterials 2017, 7(11), 378; https://doi.org/10.3390/nano7110378 - 8 Nov 2017

Cited by 19 | Viewed by 6311

Abstract

Gene therapy and RNA delivery require a nanoparticle (NP) to stabilize these nucleic acids when administered in vivo. The presence of degradative hydrolytic enzymes within these environments limits the nucleic acids’ pharmacologic activity. This study compared the effects of nanoscale ZnO and MgO [...] Read more.

Gene therapy and RNA delivery require a nanoparticle (NP) to stabilize these nucleic acids when administered in vivo. The presence of degradative hydrolytic enzymes within these environments limits the nucleic acids’ pharmacologic activity. This study compared the effects of nanoscale ZnO and MgO in the protection afforded to DNA and RNA from degradation by DNase, serum or tumor homogenate. For double-stranded plasmid DNA degradation by DNase, our results suggest that the presence of MgO NP can protect DNA from DNase digestion at an elevated temperature (65 °C), a biochemical activity not present in ZnO NP-containing samples at any temperature. In this case, intact DNA was remarkably present for MgO NP after ethidium bromide staining and agarose gel electrophoresis where these same stained DNA bands were notably absent for ZnO NP. Anticancer RNA, polyinosinic-polycytidylic acid (poly I:C) is now considered an anti-metastatic RNA targeting agent and as such there is great interest in its delivery by NP. For it to function, the NP must protect it from degradation in serum and the tumor environment. Surprisingly, ZnO NP protected the RNA from degradation in either serum-containing media or melanoma tumor homogenate after gel electrophoretic analysis, whereas the band was much more diminished in the presence of MgO. For both MgO and ZnO NP, buffer-dependent rescue from degradation occurred. These data suggest a fundamental difference in the ability of MgO and ZnO NP to stabilize nucleic acids with implications for DNA and RNA delivery and therapy. Full article

(This article belongs to the Special Issue ZnO and TiO₂ Based Nanostructures)

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2467 KiB

Open AccessArticle

ZnO Interactions with Biomatrices: Effect of Particle Size on ZnO-Protein Corona

by Jin Yu, Hyeon-Jin Kim, Mi-Ran Go, Song-Hwa Bae and Soo-Jin Choi

Nanomaterials 2017, 7(11), 377; https://doi.org/10.3390/nano7110377 - 6 Nov 2017

Cited by 48 | Viewed by 5357

Abstract

Zinc oxide (ZnO) nanoparticles (NPs) have been widely used for food fortification, because zinc is essential for many enzyme and hormone activities and cellular functions, but public concern about their potential toxicity is increasing. Interactions between ZnO and biomatrices might affect the oral [...] Read more.

Zinc oxide (ZnO) nanoparticles (NPs) have been widely used for food fortification, because zinc is essential for many enzyme and hormone activities and cellular functions, but public concern about their potential toxicity is increasing. Interactions between ZnO and biomatrices might affect the oral absorption, distribution, and toxicity of ZnO, which may be influenced by particle size. In this study, ZnO interactions with biomatrices were investigated by examining the physicochemical properties, solubility, protein fluorescence quenching, particle–protein corona, and intestinal transport with respect to the particle size (bulk vs. nano) in simulated gastrointestinal (GI) and plasma fluids and in rat-extracted fluids. The results demonstrate that the hydrodynamic radii and zeta potentials of bulk ZnO and nano ZnO in biofluids changed in different ways, and that nano ZnO induced higher protein fluorescence quenching than bulk ZnO. However, ZnO solubility and its intestinal transport mechanism were unaffected by particle size. Proteomic analysis revealed that albumin, fibrinogen, and fibronectin play roles in particle–plasma protein corona, regardless of particle size. Furthermore, nano ZnO was found to interact more strongly with plasma proteins. These observations show that bulk ZnO and nano ZnO interact with biomatrices in different ways and highlight the need for further study of their long-term toxicity. Full article

(This article belongs to the Special Issue ZnO and TiO₂ Based Nanostructures)

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5796 KiB

Open AccessArticle

Resistive Switching of Sub-10 nm TiO₂ Nanoparticle Self-Assembled Monolayers

by Dirk Oliver Schmidt, Nicolas Raab, Michael Noyong, Venugopal Santhanam, Regina Dittmann and Ulrich Simon

Nanomaterials 2017, 7(11), 370; https://doi.org/10.3390/nano7110370 - 4 Nov 2017

Cited by 15 | Viewed by 5284

Abstract

Resistively switching devices are promising candidates for the next generation of non-volatile data memories. Such devices are up to now fabricated mainly by means of top-down approaches that apply thin films sandwiched between electrodes. Recent works have demonstrated that resistive switching (RS) is [...] Read more.

Resistively switching devices are promising candidates for the next generation of non-volatile data memories. Such devices are up to now fabricated mainly by means of top-down approaches that apply thin films sandwiched between electrodes. Recent works have demonstrated that resistive switching (RS) is also feasible on chemically synthesized nanoparticles (NPs) in the 50 nm range. Following this concept, we developed this approach further to the sub-10 nm range. In this work, we report RS of sub-10 nm TiO₂ NPs that were self-assembled into monolayers and transferred onto metallic substrates. We electrically characterized these monolayers in regard to their RS properties by means of a nanorobotics system in a scanning electron microscope, and found features typical of bipolar resistive switching. Full article

(This article belongs to the Special Issue ZnO and TiO₂ Based Nanostructures)

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7019 KiB

Open AccessArticle

Preparation of Nano-TiO₂-Coated SiO₂ Microsphere Composite Material and Evaluation of Its Self-Cleaning Property

by Sijia Sun, Tongrong Deng, Hao Ding, Ying Chen and Wanting Chen

Nanomaterials 2017, 7(11), 367; https://doi.org/10.3390/nano7110367 - 3 Nov 2017

Cited by 35 | Viewed by 6887

Abstract

In order to improve the dispersion of nano-TiO₂ particles and enhance its self-cleaning properties, including photocatalytic degradation of pollutants and surface hydrophilicity, we prepared nano-TiO₂-coated SiO₂ microsphere composite self-cleaning materials (SiO₂–TiO₂) by co-grinding SiO₂ [...] Read more.

In order to improve the dispersion of nano-TiO₂ particles and enhance its self-cleaning properties, including photocatalytic degradation of pollutants and surface hydrophilicity, we prepared nano-TiO₂-coated SiO₂ microsphere composite self-cleaning materials (SiO₂–TiO₂) by co-grinding SiO₂ microspheres and TiO₂ soliquid and calcining the ground product. The structure, morphology, and self-cleaning properties of the SiO₂–TiO₂ were characterized. The characterization results showed that the degradation efficiency of methyl orange by SiO₂–TiO₂ was 97%, which was significantly higher than that obtained by pure nano-TiO₂. The minimum water contact angle of SiO₂–TiO₂ was 8°, indicating strong hydrophilicity and the good self-cleaning effect. The as-prepared SiO₂–TiO₂ was characterized by the nano-TiO₂ particles uniformly coated on the SiO₂ microspheres and distributed in the gap among the microspheres. The nano-TiO₂ particles were in an anatase phase with the particle size of 15–20 nm. The nano-TiO₂ particles were combined with SiO₂ microspheres via the dehydroxylation of hydroxyl groups on their surfaces. Full article

(This article belongs to the Special Issue ZnO and TiO₂ Based Nanostructures)

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5931 KiB

Open AccessArticle

Photoelectrochemical Water Splitting Properties of Ti-Ni-Si-O Nanostructures on Ti-Ni-Si Alloy

by Ting Li, Dongyan Ding, Zhenbiao Dong and Congqin Ning

Nanomaterials 2017, 7(11), 359; https://doi.org/10.3390/nano7110359 - 31 Oct 2017

Cited by 7 | Viewed by 3975

Abstract

Ti-Ni-Si-O nanostructures were successfully prepared on Ti-1Ni-5Si alloy foils via electrochemical anodization in ethylene glycol/glycerol solutions containing a small amount of water. The Ti-Ni-Si-O nanostructures were characterized by field-emission scanning electron microscopy (FE-SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and diffuse reflectance [...] Read more.

Ti-Ni-Si-O nanostructures were successfully prepared on Ti-1Ni-5Si alloy foils via electrochemical anodization in ethylene glycol/glycerol solutions containing a small amount of water. The Ti-Ni-Si-O nanostructures were characterized by field-emission scanning electron microscopy (FE-SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and diffuse reflectance absorption spectra. Furthermore, the photoelectrochemical water splitting properties of the Ti-Ni-Si-O nanostructure films were investigated. It was found that, after anodization, three different kinds of Ti-Ni-Si-O nanostructures formed in the α-Ti phase region, Ti₂Ni phase region, and Ti₅Si₃ phase region of the alloy surface. Both the anatase and rutile phases of Ti-Ni-Si-O oxide appeared after annealing at 500 °C for 2 h. The photocurrent density obtained from the Ti-Ni-Si-O nanostructure photoanodes was 0.45 mA/cm² at 0 V (vs. Ag/AgCl) in 1 M KOH solution. The above findings make it feasible to further explore excellent photoelectrochemical properties of the nanostructure-modified surface of Ti-Ni-Si ternary alloys. Full article

(This article belongs to the Special Issue ZnO and TiO₂ Based Nanostructures)

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7125 KiB

Open AccessArticle

Ti-Based Biomedical Material Modified with TiO_x/TiN_x Duplex Bioactivity Film via Micro-Arc Oxidation and Nitrogen Ion Implantation

by Peng Zhang, Xiaojian Wang, Zhidan Lin, Huaijun Lin, Zhiguo Zhang, Wei Li, Xianfeng Yang and Jie Cui

Nanomaterials 2017, 7(10), 343; https://doi.org/10.3390/nano7100343 - 23 Oct 2017

Cited by 18 | Viewed by 4194

Abstract

Titanium (Ti) and Ti-based alloy are widely used in the biomedical field owing to their excellent mechanical compatibility and biocompatibility. However, the bioinert bioactivity and biotribological properties of titanium limit its clinical application in implants. In order to improve the biocompatibility of titanium, [...] Read more.

Titanium (Ti) and Ti-based alloy are widely used in the biomedical field owing to their excellent mechanical compatibility and biocompatibility. However, the bioinert bioactivity and biotribological properties of titanium limit its clinical application in implants. In order to improve the biocompatibility of titanium, we modified its surface with TiO_x/TiN_x duplex composite films using a new method via micro-arc oxidation (MAO) and nitrogen ion implantation (NII) treatment. The structural characterization results revealed that the modified film was constructed by nanoarrays composed of TiO_x/TiN_x composite nanostitches with a size of 20~40 nm. Meanwhile, comparing this with pure Ti, the friction property, wear resistance, and bioactivity were significantly improved based on biotribological results and in vitro bioactivity tests. Full article

(This article belongs to the Special Issue ZnO and TiO₂ Based Nanostructures)

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1376 KiB

Open AccessArticle

Study of the Photodynamic Activity of N-Doped TiO₂ Nanoparticles Conjugated with Aluminum Phthalocyanine

by Xiaobo Pan, Xinyue Liang, Longfang Yao, Xinyi Wang, Yueyue Jing, Jiong Ma, Yiyan Fei, Li Chen and Lan Mi

Nanomaterials 2017, 7(10), 338; https://doi.org/10.3390/nano7100338 - 20 Oct 2017

Cited by 26 | Viewed by 4735

Abstract

TiO₂ nanoparticles modified with phthalocyanines (Pc) have been proven to be a potential photosensitizer in the application of photodynamic therapy (PDT). However, the generation of reactive oxygen species (ROS) by TiO₂ nanoparticles modified with Pc has not been demonstrated clearly. In [...] Read more.

TiO₂ nanoparticles modified with phthalocyanines (Pc) have been proven to be a potential photosensitizer in the application of photodynamic therapy (PDT). However, the generation of reactive oxygen species (ROS) by TiO₂ nanoparticles modified with Pc has not been demonstrated clearly. In this study, nitrogen-doped TiO₂ conjugated with Pc (N-TiO₂-Pc) were studied by means of monitoring the generation of ROS. The absorbance and photokilling effect on HeLa cells upon visible light of different regions were also studied and compared with non-doped TiO₂-Pc and Pc. Both N-TiO₂-Pc and TiO₂-Pc can be activated by visible light and exhibited much higher photokilling effect on HeLa cells than Pc. In addition, nitrogen-doping can greatly enhance the formation of ¹O₂ and •O₂⁻, while it suppresses the generation of OH•. This resulted in significant photodynamic activity. Therefore, N-TiO₂-Pc can be an excellent candidate for a photosensitizer in PDT with wide-spectrum visible irradiation. Full article

(This article belongs to the Special Issue ZnO and TiO₂ Based Nanostructures)

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6809 KiB

Open AccessArticle

Enhanced UV-Visible Light Photocatalytic Activity by Constructing Appropriate Heterostructures between Mesopore TiO₂ Nanospheres and Sn₃O₄ Nanoparticles

by Jianling Hu, Jianhai Tu, Xingyang Li, Ziya Wang, Yan Li, Quanshui Li and Fengping Wang

Nanomaterials 2017, 7(10), 336; https://doi.org/10.3390/nano7100336 - 19 Oct 2017

Cited by 26 | Viewed by 5100

Abstract

Novel TiO₂/Sn₃O₄ heterostructure photocatalysts were ingeniously synthesized via a scalable two-step method. The impressive photocatalytic abilities of the TiO₂/Sn₃O₄ sphere nanocomposites were validated by the degradation test of methyl orange and •OH trapping [...] Read more.

Novel TiO₂/Sn₃O₄ heterostructure photocatalysts were ingeniously synthesized via a scalable two-step method. The impressive photocatalytic abilities of the TiO₂/Sn₃O₄ sphere nanocomposites were validated by the degradation test of methyl orange and •OH trapping photoluminescence experiments under ultraviolet (UV) and visible light irradiation, respectively. Especially under the visible light, the TiO₂/Sn₃O₄ nanocomposites demonstrated a superb photocatalytic activity, with 81.2% of methyl orange (MO) decomposed at 30 min after irradiation, which greatly exceeded that of the P25 (13.4%), TiO₂ (0.5%) and pure Sn₃O₄ (59.1%) nanostructures. This enhanced photocatalytic performance could be attributed to the mesopore induced by the monodispersed TiO₂ cores that supply sufficient surface areas and accessibility to reactant molecules. This exquisite hetero-architecture facilitates extended UV-visible absorption and efficient photoexcited charge carrier separation. Full article

(This article belongs to the Special Issue ZnO and TiO₂ Based Nanostructures)

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2298 KiB

Open AccessArticle

Microstructuring of Mesoporous Titania Films Loaded with Silver Salts to Enhance the Photocatalytic Degradation of Methyl Blue under Visible Light

by Nicolas Crespo-Monteiro, Anthony Cazier, Francis Vocanson, Yaya Lefkir, Stéphanie Reynaud, Jean-Yves Michalon, Thomas Kämpfe, Nathalie Destouches and Yves Jourlin

Nanomaterials 2017, 7(10), 334; https://doi.org/10.3390/nano7100334 - 17 Oct 2017

Cited by 8 | Viewed by 3976

Abstract

The microstructuring of the distribution of silver nanoparticles (NPs) in mesoporous titania films loaded with silver salts, using two-beam interference lithography leading to 1 Dimension (1D) grating, induces variations in the photocatalytic efficiency. The influence of the structuration was tested on the degradation [...] Read more.

The microstructuring of the distribution of silver nanoparticles (NPs) in mesoporous titania films loaded with silver salts, using two-beam interference lithography leading to 1 Dimension (1D) grating, induces variations in the photocatalytic efficiency. The influence of the structuration was tested on the degradation of methyl blue (MB) under ultraviolet (UV) and visible illumination, giving rise to a significant improvement of the photocatalytic efficiency. The periodic distribution of the NPs was characterized by transmission electron microscopy (TEM), high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) and scanning electron microscopy (SEM). Full article

(This article belongs to the Special Issue ZnO and TiO₂ Based Nanostructures)

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4988 KiB

Open AccessArticle

Periodic TiO₂ Nanostructures with Improved Aspect and Line/Space Ratio Realized by Colloidal Photolithography Technique

by Loïc Berthod, Olga Shavdina, Isabelle Verrier, Thomas Kämpfe, Olivier Dellea, Francis Vocanson, Maxime Bichotte, Damien Jamon and Yves Jourlin

Nanomaterials 2017, 7(10), 316; https://doi.org/10.3390/nano7100316 - 12 Oct 2017

Cited by 5 | Viewed by 3800

Abstract

This paper presents substantial improvements of the colloidal photolithography technique (also called microsphere lithography) with the goal of better controlling the geometry of the fabricated nano-scale structures—in this case, hexagonally arranged nanopillars—printed in a layer of directly photopatternable sol-gel TiO₂. Firstly, [...] Read more.

This paper presents substantial improvements of the colloidal photolithography technique (also called microsphere lithography) with the goal of better controlling the geometry of the fabricated nano-scale structures—in this case, hexagonally arranged nanopillars—printed in a layer of directly photopatternable sol-gel TiO₂. Firstly, to increase the achievable structure height the photosensitive layer underneath the microspheres is deposited on a reflective layer instead of the usual transparent substrate. Secondly, an increased width of the pillars is achieved by tilting the incident wave and using multiple exposures or substrate rotation, additionally allowing to better control the shape of the pillar’s cross section. The theoretical analysis is carried out by rigorous modelling of the photonics nanojet underneath the microspheres and by optimizing the experimental conditions. Aspect ratios (structure height/lateral structure size) greater than 2 are predicted and demonstrated experimentally for structure dimensions in the sub micrometer range, as well as line/space ratios (lateral pillar size/distance between pillars) greater than 1. These nanostructures could lead for example to materials exhibiting efficient light trapping in the visible and near-infrared range, as well as improved hydrophobic or photocatalytic properties for numerous applications in environmental and photovoltaic systems. Full article

(This article belongs to the Special Issue ZnO and TiO₂ Based Nanostructures)

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3746 KiB

Open AccessArticle

TiO₂ Nanowire Networks Prepared by Titanium Corrosion and Their Application to Bendable Dye-Sensitized Solar Cells

by Saera Jin, Eunhye Shin and Jongin Hong

Nanomaterials 2017, 7(10), 315; https://doi.org/10.3390/nano7100315 - 12 Oct 2017

Cited by 12 | Viewed by 4448

Abstract

TiO₂ nanowire networks were prepared, using the corrosion of Ti foils in alkaline (potassium hydroxide, KOH) solution at different temperatures, and then a further ion-exchange process. The prepared nanostructures were characterized by field emission scanning electron microscopy, Raman spectroscopy, and X-ray photoelectron [...] Read more.

TiO₂ nanowire networks were prepared, using the corrosion of Ti foils in alkaline (potassium hydroxide, KOH) solution at different temperatures, and then a further ion-exchange process. The prepared nanostructures were characterized by field emission scanning electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. The wet corroded foils were utilized as the photoanodes of bendable dye-sensitized solar cells (DSSCs), which exhibited a power conversion efficiency of 1.11% under back illumination. Full article

(This article belongs to the Special Issue ZnO and TiO₂ Based Nanostructures)

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2693 KiB

Open AccessArticle

Tuning the Electronic Conductivity in Hydrothermally Grown Rutile TiO₂ Nanowires: Effect of Heat Treatment in Different Environments

by Alena Folger, Julian Kalb, Lukas Schmidt-Mende and Christina Scheu

Nanomaterials 2017, 7(10), 289; https://doi.org/10.3390/nano7100289 - 23 Sep 2017

Cited by 16 | Viewed by 5169

Abstract

Hydrothermally grown rutile TiO₂ nanowires are intrinsically full of lattice defects, especially oxygen vacancies. These vacancies have a significant influence on the structural and electronic properties of the nanowires. In this study, we report a post-growth heat treatment in different environments that [...] Read more.

Hydrothermally grown rutile TiO₂ nanowires are intrinsically full of lattice defects, especially oxygen vacancies. These vacancies have a significant influence on the structural and electronic properties of the nanowires. In this study, we report a post-growth heat treatment in different environments that allows control of the distribution of these defects inside the nanowire, and thus gives direct access to tuning of the properties of rutile TiO₂ nanowires. A detailed transmission electron microscopy study is used to analyze the structural changes inside the nanowires which are correlated to the measured optical and electrical properties. The highly defective as-grown nanowire arrays have a white appearance and show typical semiconducting properties with n-type conductivity, which is related to the high density of oxygen vacancies. Heat treatment in air atmosphere leads to a vacancy condensation and results in nanowires which possess insulating properties, whereas heat treatment in N₂ atmosphere leads to nanowire arrays that appear black and show almost metal-like conductivity. We link this high conductivity to a TiO_2−x shell which forms during the annealing process due to the slightly reducing N₂ environment. Full article

(This article belongs to the Special Issue ZnO and TiO₂ Based Nanostructures)

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1967 KiB

Open AccessArticle

In Vitro Sonodynamic Therapeutic Effect of Polyion Complex Micelles Incorporating Titanium Dioxide Nanoparticles

by Satoshi Yamamoto, Masafumi Ono, Eiji Yuba and Atsushi Harada

Nanomaterials 2017, 7(9), 268; https://doi.org/10.3390/nano7090268 - 11 Sep 2017

Cited by 15 | Viewed by 4585

Abstract

Titanium dioxide nanoparticles (TiO₂ NPs) can act as sonosensitizers, generating reactive oxygen species under ultrasound irradiation, for use in sonodynamic therapy. For TiO₂ NPs delivery, we prepared polyion complex micelles incorporating TiO₂ NPs (TiO₂ NPs-PIC micelles) by mixing TiO [...] Read more.

Titanium dioxide nanoparticles (TiO₂ NPs) can act as sonosensitizers, generating reactive oxygen species under ultrasound irradiation, for use in sonodynamic therapy. For TiO₂ NPs delivery, we prepared polyion complex micelles incorporating TiO₂ NPs (TiO₂ NPs-PIC micelles) by mixing TiO₂ NPs with polyallylamine bearing poly(ethylene glycol) grafts. In this study, the effects of polymer composition and ultrasound irradiation conditions on the sonodynamic therapeutic effect toward HeLa cells were evaluated experimentally using cell viability evaluation, intracellular distribution observation, and a cell staining assay. TiO₂ NPs-PIC micelles with widely distributed features induced a significant decrease in cell viability under ultrasound irradiation. Furthermore, prolonging the irradiation time killed cells more effectively than did increasing the ultrasound power. The combination of TiO₂ NP-PIC micelles and ultrasound irradiation was confirmed to induce apoptotic cell death. Full article

(This article belongs to the Special Issue ZnO and TiO₂ Based Nanostructures)

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3362 KiB

Open AccessArticle

Growth Method-Dependent and Defect Density-Oriented Structural, Optical, Conductive, and Physical Properties of Solution-Grown ZnO Nanostructures

by Abu Ul Hassan Sarwar Rana, Ji Young Lee, Areej Shahid and Hyun-Seok Kim

Nanomaterials 2017, 7(9), 266; https://doi.org/10.3390/nano7090266 - 10 Sep 2017

Cited by 15 | Viewed by 5209

Abstract

It is time for industry to pay a serious heed to the application and quality-dependent research on the most important solution growth methods for ZnO, namely, aqueous chemical growth (ACG) and microwave-assisted growth (MAG) methods. This study proffers a critical analysis on how [...] Read more.

It is time for industry to pay a serious heed to the application and quality-dependent research on the most important solution growth methods for ZnO, namely, aqueous chemical growth (ACG) and microwave-assisted growth (MAG) methods. This study proffers a critical analysis on how the defect density and formation behavior of ZnO nanostructures (ZNSs) are growth method-dependent. Both antithetical and facile methods are exploited to control the ZnO defect density and the growth mechanism. In this context, the growth of ZnO nanorods (ZNRs), nanoflowers, and nanotubes (ZNTs) are considered. The aforementioned growth methods directly stimulate the nanostructure crystal growth and, depending upon the defect density, ZNSs show different trends in structural, optical, etching, and conductive properties. The defect density of MAG ZNRs is the least because of an ample amount of thermal energy catered by high-power microwaves to the atoms to grow on appropriate crystallographic planes, which is not the case in faulty convective ACG ZNSs. Defect-centric etching of ZNRs into ZNTs is also probed and methodological constraints are proposed. ZNS optical properties are different in the visible region, which are quite peculiar, but outstanding for ZNRs. Hall effect measurements illustrate incongruent conductive trends in both samples. Full article

(This article belongs to the Special Issue ZnO and TiO₂ Based Nanostructures)

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6097 KiB

Open AccessArticle

Preparation and Characterization of ZnO Nanoparticles Supported on Amorphous SiO₂

by Ying Chen, Hao Ding and Sijia Sun

Nanomaterials 2017, 7(8), 217; https://doi.org/10.3390/nano7080217 - 10 Aug 2017

Cited by 67 | Viewed by 7580

Abstract

In order to reduce the primary particle size of zinc oxide (ZnO) and eliminate the agglomeration phenomenon to form a monodisperse state, Zn²⁺ was loaded on the surface of amorphous silica (SiO₂) by the hydrogen bond association between hydroxyl groups [...] Read more.

In order to reduce the primary particle size of zinc oxide (ZnO) and eliminate the agglomeration phenomenon to form a monodisperse state, Zn²⁺ was loaded on the surface of amorphous silica (SiO₂) by the hydrogen bond association between hydroxyl groups in the hydrothermal process. After calcining the precursors, dehydration condensation among hydroxyl groups occurred and ZnO nanoparticles supported on amorphous SiO₂ (ZnO–SiO₂) were prepared. Furthermore, the SEM and TEM observations showed that ZnO nanoparticles with a particle size of 3–8 nm were uniformly and dispersedly loaded on the surface of amorphous SiO₂. Compared with pure ZnO, ZnO–SiO₂ showed a much better antibacterial performance in the minimum inhibitory concentration (MIC) test and the antibacterial properties of the paint adding ZnO–SiO₂ composite. Full article

(This article belongs to the Special Issue ZnO and TiO₂ Based Nanostructures)

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4041 KiB

Open AccessArticle

Growth Mechanism Studies of ZnO Nanowires: Experimental Observations and Short-Circuit Diffusion Analysis

by Po-Hsun Shih and Sheng Yun Wu

Nanomaterials 2017, 7(7), 188; https://doi.org/10.3390/nano7070188 - 21 Jul 2017

Cited by 23 | Viewed by 6854

Abstract

Plenty of studies have been performed to probe the diverse properties of ZnO nanowires, but only a few have focused on the physical properties of a single nanowire since analyzing the growth mechanism along a single nanowire is difficult. In this study, a [...] Read more.

Plenty of studies have been performed to probe the diverse properties of ZnO nanowires, but only a few have focused on the physical properties of a single nanowire since analyzing the growth mechanism along a single nanowire is difficult. In this study, a single ZnO nanowire was synthesized using a Ti-assisted chemical vapor deposition (CVD) method to avoid the appearance of catalytic contamination. Two-dimensional energy dispersive spectroscopy (EDS) mapping with a diffusion model was used to obtain the diffusion length and the activation energy ratio. The ratio value is close to 0.3, revealing that the growth of ZnO nanowires was attributed to the short-circuit diffusion. Full article

(This article belongs to the Special Issue ZnO and TiO₂ Based Nanostructures)

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2185 KiB

Open AccessArticle

Oxygen Partial Pressure Impact on Characteristics of Indium Titanium Zinc Oxide Thin Film Transistor Fabricated via RF Sputtering

by Ming-Hung Hsu, Sheng-Po Chang, Shoou-Jinn Chang, Wei-Ting Wu and Jyun-Yi Li

Nanomaterials 2017, 7(7), 156; https://doi.org/10.3390/nano7070156 - 26 Jun 2017

Cited by 16 | Viewed by 5214

Abstract

Indium titanium zinc oxide (InTiZnO) as the channel layer in thin film transistor (TFT) grown by RF sputtering system is proposed in this work. Optical and electrical properties were investigated. By changing the oxygen flow ratio, we can suppress excess and undesirable oxygen-related [...] Read more.

Indium titanium zinc oxide (InTiZnO) as the channel layer in thin film transistor (TFT) grown by RF sputtering system is proposed in this work. Optical and electrical properties were investigated. By changing the oxygen flow ratio, we can suppress excess and undesirable oxygen-related defects to some extent, making it possible to fabricate the optimized device. XPS patterns for O 1s of InTiZnO thin films indicated that the amount of oxygen vacancy was apparently declined with the increasing oxygen flow ratio. The fabricated TFTs showed a threshold voltage of −0.9 V, mobility of 0.884 cm²/Vs, on-off ratio of 5.5 × 10⁵, and subthreshold swing of 0.41 V/dec. Full article

(This article belongs to the Special Issue ZnO and TiO₂ Based Nanostructures)

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Review

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7171 KiB

Open AccessReview

Fabrication of Semiconductor ZnO Nanostructures for Versatile SERS Application

by Lili Yang, Yong Yang, Yunfeng Ma, Shuai Li, Yuquan Wei, Zhengren Huang and Nguyen Viet Long

Nanomaterials 2017, 7(11), 398; https://doi.org/10.3390/nano7110398 - 19 Nov 2017

Cited by 71 | Viewed by 11158

Abstract

Since the initial discovery of surface-enhanced Raman scattering (SERS) in the 1970s, it has exhibited a huge potential application in many fields due to its outstanding advantages. Since the ultra-sensitive noble metallic nanostructures have increasingly exposed themselves as having some problems during application, [...] Read more.

Since the initial discovery of surface-enhanced Raman scattering (SERS) in the 1970s, it has exhibited a huge potential application in many fields due to its outstanding advantages. Since the ultra-sensitive noble metallic nanostructures have increasingly exposed themselves as having some problems during application, semiconductors have been gradually exploited as one of the critical SERS substrate materials due to their distinctive advantages when compared with noble metals. ZnO is one of the most representative metallic oxide semiconductors with an abundant reserve, various and cost-effective fabrication techniques, as well as special physical and chemical properties. Thanks to the varied morphologies, size-dependent exciton, good chemical stability, a tunable band gap, carrier concentration, and stoichiometry, ZnO nanostructures have the potential to be exploited as SERS substrates. Moreover, other distinctive properties possessed by ZnO such as biocompatibility, photocatcalysis and self-cleaning, and gas- and chemo-sensitivity can be synergistically integrated and exerted with SERS activity to realize the multifunctional potential of ZnO substrates. In this review, we discuss the inevitable development trend of exploiting the potential semiconductor ZnO as a SERS substrate. After clarifying the root cause of the great disparity between the enhancement factor (EF) of noble metals and that of ZnO nanostructures, two specific methods are put forward to improve the SERS activity of ZnO, namely: elemental doping and combination of ZnO with noble metals. Then, we introduce a distinctive advantage of ZnO as SERS substrate and illustrate the necessity of reporting a meaningful average EF. We also summarize some fabrication methods for ZnO nanostructures with varied dimensions (0–3 dimensions). Finally, we present an overview of ZnO nanostructures for the versatile SERS application. Full article

(This article belongs to the Special Issue ZnO and TiO₂ Based Nanostructures)

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7306 KiB

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Engineering the Surface/Interface Structures of Titanium Dioxide Micro and Nano Architectures towards Environmental and Electrochemical Applications

by Xiaoliang Wang, Yanyan Zhao, Kristian Mølhave and Hongyu Sun

Nanomaterials 2017, 7(11), 382; https://doi.org/10.3390/nano7110382 - 9 Nov 2017

Cited by 37 | Viewed by 8239

Abstract

Titanium dioxide (TiO₂) materials have been intensively studied in the past years because of many varied applications. This mini review article focuses on TiO₂ micro and nano architectures with the prevalent crystal structures (anatase, rutile, brookite, and TiO₂(B)), [...] Read more.

Titanium dioxide (TiO₂) materials have been intensively studied in the past years because of many varied applications. This mini review article focuses on TiO₂ micro and nano architectures with the prevalent crystal structures (anatase, rutile, brookite, and TiO₂(B)), and summarizes the major advances in the surface and interface engineering and applications in environmental and electrochemical applications. We analyze the advantages of surface/interface engineered TiO₂ micro and nano structures, and present the principles and growth mechanisms of TiO₂ nanostructures via different strategies, with an emphasis on rational control of the surface and interface structures. We further discuss the applications of TiO₂ micro and nano architectures in photocatalysis, lithium/sodium ion batteries, and Li–S batteries. Throughout the discussion, the relationship between the device performance and the surface/interface structures of TiO₂ micro and nano structures will be highlighted. Then, we discuss the phase transitions of TiO₂ nanostructures and possible strategies of improving the phase stability. The review concludes with a perspective on the current challenges and future research directions. Full article

(This article belongs to the Special Issue ZnO and TiO₂ Based Nanostructures)

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2346 KiB

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ZnO Nanowire Application in Chemoresistive Sensing: A Review

by Simas Rackauskas, Nadia Barbero, Claudia Barolo and Guido Viscardi

Nanomaterials 2017, 7(11), 381; https://doi.org/10.3390/nano7110381 - 9 Nov 2017

Cited by 67 | Viewed by 7326

Abstract

This article provides an overview of the recent development of ZnO nanowires (NWs) for chemoresistive sensing. Working mechanisms of chemoresistive sensors are unified for gas, ultraviolet (UV) and bio sensor types: single nanowire and nanowire junction sensors are described, giving the overview for [...] Read more.

This article provides an overview of the recent development of ZnO nanowires (NWs) for chemoresistive sensing. Working mechanisms of chemoresistive sensors are unified for gas, ultraviolet (UV) and bio sensor types: single nanowire and nanowire junction sensors are described, giving the overview for a simple sensor manufacture by multiple nanowire junctions. ZnO NW surface functionalization is discussed, and how this effects the sensing is explained. Further, novel approaches for sensing, using ZnO NW functionalization with other materials such as metal nanoparticles or heterojunctions, are explained, and limiting factors and possible improvements are discussed. The review concludes with the insights and recommendations for the future improvement of the ZnO NW chemoresistive sensing. Full article

(This article belongs to the Special Issue ZnO and TiO₂ Based Nanostructures)

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13874 KiB

Open AccessReview

Wet-Chemical Preparation of TiO₂-Based Composites with Different Morphologies and Photocatalytic Properties

by Liqin Xiang and Xiaopeng Zhao

Nanomaterials 2017, 7(10), 310; https://doi.org/10.3390/nano7100310 - 9 Oct 2017

Cited by 54 | Viewed by 6851

Abstract

TiO₂-based composites have been paid significant attention in the photocatalysis field. The size, crystallinity and nanomorphology of TiO₂ materials have an important effect on the photocatalytic efficiency. The synthesis and photocatalytic activity of TiO₂-based materials have been widely [...] Read more.

TiO₂-based composites have been paid significant attention in the photocatalysis field. The size, crystallinity and nanomorphology of TiO₂ materials have an important effect on the photocatalytic efficiency. The synthesis and photocatalytic activity of TiO₂-based materials have been widely investigated in past decades. Based on our group’s research works on TiO₂ materials, this review introduces several methods for the fabrication of TiO₂, rare-earth-doped TiO₂ and noble-metal-decorated TiO₂ particles with different morphologies. We focused on the preparation and the formation mechanism of TiO₂-based materials with unique structures including spheres, hollow spheres, porous spheres, hollow porous spheres and urchin-like spheres. The photocatalytical activity of urchin-like TiO₂, noble metal nanoparticle-decorated 3D (three-dimensional) urchin-like TiO₂ and bimetallic core/shell nanoparticle-decorated urchin-like hierarchical TiO₂ are briefly discussed. Full article

(This article belongs to the Special Issue ZnO and TiO₂ Based Nanostructures)

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