Water-alcohol-TiO2 dispersions as sustainable ink.

Nanocrystalline titanium dioxide (TiO2) is a widespread multifunctional and environmentally friendly material that has numerous applications requiring micro-/nanofabrication or thin film deposition. In most cases, the fabrication of titania films can be achieved using cost-efficient solution chemistry combined with various coating or printing techniques. The practical implementation of these methods requires the preparation of a suitable ink with properly adjusted rheological properties. Conventionally, such adjustments are achieved based on TiO2 hydrosols containing various organic surfactants and stabilizing agents. However, the use of such additives may affect the properties of the deposited functional layer, which can be crucial for electronic and optical applications. In this work, we address a comprehensive study of simple surfactant-free TiO2 dispersion systems based on various water-alcohol solvents and demonstrate the possibility of controlling the rheological properties of the titania ink in a wide range that is suitable for several printing applications. As a particular example, we demonstrate the application of a water-i-propanol-TiO2 dispersion as a functional ink for the offset printing of interference images.

Inkjet Printing Humidity Sensing Pattern Based on Self-Organizing Polystyrene Spheres.

This study is devoted to the development of photonic patterns based on polystyrene spheres (PSS) incorporated in chitosan hydrogels by inkjet printing. Using this method, high-resolution encrypted images that became visible only in high humidity were obtained. Inks based on PSS with carboxylic groups on the surface were made, and their rheological parameters (viscosity, surface tension, and ζ-potential) were optimized according to the Ohnesorge theory. The obtained value of the ζ-potential indicated the stability of the synthesized colloidal inks. The dependences of the printing parameters on the concentration of ethylene glycol in PSS dispersion, the drop spacing, the shape of the printed pattern, waveform, the temperature of the printing process, and the degree of ordering of the PSS-based photonic crystal were investigated. The scanning electronic microscope (SEM) images confirmed that the optimal self-organization of PSS was achieved at the following values of 0.4% weight fraction (wt%) carboxylic groups, the drop spacing of 50 µm, and the temperature of the printing table of 25 °C. High-resolution microstructures were obtained by drop-on-demand printing with a deposited drophead diameter of 21 µm and an accuracy of ±2 µm on silicon and glass substrates. The deposition of chitosan-based hydrogels on the obtained polystyrene photonic crystals allowed reversibly changing the order of the diffraction lattice of the photonic crystal during the swelling of the hydrogel matrix, which led to a quick optical response in the daylight. The kinetics of the appearance of the optical response of the obtained coating were discussed. The simplicity of production, the speed of image appearance, and the ability to create high-resolution patterns determine the potential applications of the proposed systems as humidity sensors or anticounterfeiting coatings.

Correction: Inkjet assisted fabrication of planar biocompatible memristors.

[This corrects the article DOI: 10.1039/C9RA08114C.].

Light-controllable systems based on TiO2-ZIF-8 composites for targeted drug release: communicating with tumour cells.

Drug delivery systems based on the zeolitic imidazolate framework ZIF-8 have recently attracted viable research interest owing to their capability of decomposing in acidic media and thus performing targeted drug delivery. In vivo realization of this mechanism faces a challenge of relatively slow decomposition rates, even at elevated acidic conditions that are barely achievable in diseased tissues. In this study we propose to combine drug delivery nanocomposites with a semiconductor photocatalytic agent that would be capable of inducing a local pH gradient in response to external electromagnetic radiation. In order to test this principle, a model drug-releasing nanocomposite comprising photocatalytic titania nanotubes, ZIF-8, and the antitumor drug doxorubicin has been investigated. This system was demonstrated to release the drug in a quantity sufficient for effectively suppressing IMR-32 neuroblastoma cells that were used as a model diseased tissue. With locally applied UV irradiation, this result was achieved within 40 minutes, which is a relatively short time compared to the release duration in systems without photocatalyst, typically taking from several hours to several days.

Optical interference-based sensors for the visual detection of nano-scale objects.

In this study, we present a new concept for the simple visual detection of nano-scale objects in solutions. To achieve this goal, we developed chromogen-free interference-based sensors that provided a color visible reaction directly after the interaction of the analyte with the substrate. The effect is based on the strong optical interference occurring at the interface between the inkjet printed sol-gel titania film (a layer with high refractive index) and the adsorbed nano-sized objects (layer with low refractive index), which can be detected even with the naked eye. Herein, we have developed a synthetic strategy for the inkjet printing of interference sensors with controllable color change through thickness adjustment.

Inkjet assisted fabrication of planar biocompatible memristors.

In this study we address a novel design of a planar memristor and investigate its biocompatibility. An experimental prototype of the proposed memristor assembly has been manufactured using a hybrid nanofabrication method, combining sputtering of electrodes, patterning the insulating trenches, and filling them with a memristive substance. To pattern the insulating trenches, we have examined two nanofabrication techniques employing either a focused ion beam or a cantilever tip of an atomic force microscope. Inkjet printing has been used to fill the trenches with the functional titania ink. The experimental prototypes have qualitatively demonstrated memristive current-voltage behavior, as well as high biocompatibility.

Photocatalytic and adsorption properties of TiO2-pillared montmorillonite obtained by hydrothermally activated intercalation of titanium polyhydroxo complexes.

We report on a new approach for the synthesis of TiO2-pillared montmorillonite, where the pillars exhibit a high degree of crystallinity (nanocrystals) representing a mixture of anatase and rutile phases. The structures exhibit improved adsorption and photocatalytic activity as a result of hydrothermally activated intercalation of titanium polyhydroxo complexes (i.e., TiCl4 hydrolysis products) in a solution with a concentration close to the sol formation limit. The materials, produced at various annealing temperatures from the intercalated samples, were characterized by infrared spectroscopy, differential scanning calorimetry (DSC)/thermogravimetric analysis (TGA), X-ray diffraction, dynamic light scattering (DLS) measurements, and liquefied nitrogen adsorption/desorption. The photocatalytic activity of the TiO2-pillared materials was studied using the degradation of anionic (methyl orange, MO) and cationic (rhodamine B, RhB) dyes in water under UV irradiation. The combined effect of adsorption and photocatalysis resulted in removal of 100% MO and 97.5% RhB (with an initial concentration of 40 mg/L and a photocatalyst-sorbent concentration of 1 g/L) in about 100 minutes. The produced TiO2-pillared montmorillonite showed increased photocatalytic activity as compared to the commercially available photocatalyst Degussa P25.

Composites based on heparin and MIL-101(Fe): the drug releasing depot for anticoagulant therapy and advanced medical nanofabrication.

We describe the synthesis and properties of a new composite material based on heparin and MIL-101(Fe) metal-organic framework. The intrinsic instability of MIL-101(Fe) towards hydrolysis enables binding of heparin molecules to the framework structure as is evidenced by DFT calculations and adsorption experiments. The de novo formed heparin-MOF composites showed good biocompatibility in in vitro and demonstrated pronounced anticoagulant activity. The specific interaction between the bioactive molecule and the carrier is critical for the selective degradation of the complex in the body fluids and for the enhanced activity. Hep_MIL-101(Fe) composite could serve as a drug-releasing depot for nanofabrication and to introduce anticoagulant activity to medical devices and biocoatings. Addition of Hep_MIL-101(Fe) to a sol-gel derived thrombolytic matrix allowed the combination of anticoagulant and thrombolytic activities in a single hybrid nanomaterial that could be applied as a bioactive nanocoating for PTFE vein implants.

Stimuli-Responsive Mechanoluminescence in Different Matrices.

Here, for the first time, we investigated the effects of matrixes with different nature on the stimuli-responsive mechanoluminescence (ML) of incorporated nanoparticles. It turned out that the contraction forces initiated by polymerization process can have compressive effects that differ by orders. This effect was achieved owing to the introduction of ML crystals in an alumina sol-gel system, which has large surface of coagulation contact. As one particle of boehmite results in a tension of 10-17-10-16 N per one particle of matrix, compared to 10-19 N of PDMS matrix, the threshold of mechanoluminescence was reached at 0.04 Pa, whereas the most active materials to date did not exceed this value. Thus, this material can be a perspective for the production of impact detectors, photonic displays of the next generation, and other advanced devices.

Inkjet fabrication of highly efficient luminescent Eu-doped ZrO2 nanostructures.

We have demonstrated for the first time an inkjet fabrication of highly efficient luminescent structures based on Eu-doped ZrO2 nanocrystals (3.4 ± 0.3 nm), with a refractive index close to the one of the bulk materials. The nanoparticles were synthesised using a nonhydrolytic method in benzyl alcohol where the particles were post treated using acetic acid, leading to the formation of a stable colloid. It was shown that the non-polar methyl group of the acetic acid is responsible for its penetration through the hydrophobic layer all the way through to the surface of the ZrO2, leading to the cleavage of the Zr-OCH2C6H5 bond and the formation of surface acetate species and a concomitant decomposition of the zirconia superlattice. Hereby we show a new and efficient universal ink production through a multi-step process - starting from solvothermal synthesis, dispersion of nanocrystals in water, and adaptation of the rheological parameters of the resulting sols. Eventually, we were able to obtain inks that we used for the production of optical coatings, monolayer luminescent-protected holography and anti-counterfeiting printing. These structures, obtained at room temperature through inkjet printing, present dense xerogel structures with high optical transparency, a high refractive index and more efficient luminescence compared with the non-homogeneous structures produced as a mixture of rare-earth elements and nanocrystals.

van der Waals Metal-Organic Framework as an Excitonic Material for Advanced Photonics.

Synergistic combination of organic and inorganic nature in van der Waals metal-organic frameworks supports different types of robust excitons that can be effectively and independently manipulated by light at room temperature, and opens new concepts for all-optical data processing and storage.

Reversible sol-gel-sol medium for enzymatic optical biosensors.

In this paper we for the first time report a reversible sol-gel-sol approach to obtain optical enzymatic biosensors with improved enzyme stability and good sensitivity by using desktop inkjet printing. The developed technique is based on the bio-inorganic inks allowing for a sol-gel-sol transition of the inorganic matrix: from liquid ink to a solid alumina matrix with entrapped enzymes and a subsequent color response due to the enzymatic reaction upon the resuspension of the matrix. This approach improves the stability of the enzymes entrapped in the porous inorganic matrix, and at the same time maintains a high sensitivity of the biomolecules, whose facile release is ensured by the gel-sol transition. Rheological parameters of the developed bio-inorganic ink are highly adjustable making it suitable for the deposition on different surfaces by inkjet printing. The potential and utility of this approach is demonstrated by a successful production of optical biosensors for glucose and uric acid.

Inkjet printing of TiO2/AlOOH heterostructures for the formation of interference color images with high optical visibility.

This paper describes a practical approach for the fabrication of highly visible interference color images using sol-gel ink technique and a common desktop inkjet printer. We show the potential of titania-boehmite inks for the production of optical heterostructures on various surfaces, which after drying on air produce optical solid layers with low and high refractive index. The optical properties of the surface heterostructures were adjusted following the principles of antireflection coating resulting in the enhancement of the interference color optical visibility of the prints by as much as 32%. Finally, the presented technique was optimized following the insights into the mechanisms of the drop-surface interactions and the drop-on-surface coalescence to make it suitable for the production of even thickness coatings suitable for printing at a large scale. We propose that the technology described herein is a promising new green and sustainable approach for color printing.

Inkjet Color Printing by Interference Nanostructures.

Color printing technology is developing rapidly; in less than 40 years, it moved from dot matrix printers with an ink-soaked cloth ribbon to 3D printers used to make three-dimensional color objects. Nevertheless, what remained unchanged over this time is the fact that in each case, dye inks (CMYK or RGB color schemes) were exclusively used for coloring, which inevitably limits the technological possibilities and color reproduction. As a next step in printing color images and storing information, we propose the technology of producing optical nanostructures. In this paper, we report use of inkjet technology to create colored interference layers with high accuracy without the need for high-temperature fixing. This was made possible due to using titania-based colloidal ink yielding monolithic coatings with a high refractive index (2.00 ± 0.08 over the entire visible range) when naturally dried. By controlling the film thickness by using inkjet deposition, we produced images based on controlled interference and implementing color printing with one ink. The lack of dyes in the proposed method has good environmental prospects, because applied systems based on a crystalline anatase sol are nontoxic and biologically inert. The paper explains in detail the principle of producing interference images by the classical inkjet method and shows the advantages of this technique in depositing coatings with uniform thickness, which are required for large-scale interference color imaging even on unprepared polymer films. This article demonstrates the possibility of inkjet printing of nanostructures with a precision in thickness of up to 50 nm, we believe that the proposed approach will be the groundwork for developing interference color printing approach and allow to implement new methods of forming optical nano-objects by widely available techniques.

Anomalous adsorption of biomolecules on a Zn-based metal-organic framework obtained via a facile room-temperature route.

Herein, we report a new method for the crystal growth of two Zn-based MOFs at room temperature (known MOF-5 and a new modification of [{Zn2(TBAPy)(H2O)2}·3.5DEF]n (1)) by employing slow diffusion conditions. Employing both Zn-based MOFs with different pore morphology made it possible to discover an anomalous adsorption of L-histidine in of up to 24.3 × 10(15) molecules cm(-2) at 25 °C. This is one of the first reports aimed not only at describing a new method for the targeted formation of crystalline MOFs and coordination polymers, but also at demonstrating the use of Zn-based MOFs as potential drug delivery materials, with highly effective adsorption of l-histidine given herein as an example.

The first depleted heterojunction TiO2-MOF-based solar cell.

A single-step hydrothermal synthesis of a TiO2-Mil-125 composite was applied for the first time to produce a depleted perovskite/TiO2-MOF heterojunction solar cell with 6.4% power conversion efficiency (PCE), characterized by durable stability in air.

A facile sol-gel synthesis of impurity-free nanocrystalline titania.

This paper reports an original technique that provides a highly pure crystalline sol of titania with controllable particle size by ultrasonic activation of the hydrolysis products of titanium isopropoxide in an aqueous medium at a near-neutral pH, which is potentially promising in impurity-sensitive electronics and biochemical engineering. Optimal conditions (H2O/TIP ratio, sonication time, etc.) for preparation of stable nanocrystalline titania sol were adopted. A new mechanism of regulation of aggregation and polycondensation under ultrasonic irradiation is proposed. Entrapment of human serum albumin (HSA) in the formed porous titania matrix results in high thermal stability of the protein dopants: the denaturation temperature of HSA is shifted by 31 °C.