Alexandr V. Vinogradov

Metal–organic frameworks as competitive materials for non-linear optics

The last five years have witnessed a huge breakthrough in the creation and the study of the properties of a new class of compounds - metamaterials. The next stage of this technological revolution will be the development of active, controllable, and non-linear metamaterials, surpassing natural media as platforms for optical data processing and quantum information applications. However, scientists are constantly faced with the need to find new methods that can ensure the formation of quantum and non-linear metamaterials with higher resolution. One such method of producing metamaterials in the future, which will provide scalability and availability, is chemical synthesis. Meanwhile, the chemical synthesis of organized 3D structures with a period of a few nanometers and a size of up to a few millimeters is not an easy task and is yet to be resolved. The most promising avenue seems to be the use of highly porous structures based on metal-organic frameworks that have demonstrated their unique properties in the field of non-linear optics (NLO) over the past three years. Thus, the aim of this review is to examine current progress and the possibilities of using metal-organic frameworks in the field of non-linear optics as chemically obtained metamaterials of the future. The review begins by presenting the theoretical principles of physical phenomena represented by mathematical descriptions for clarity. Major attention is paid to the second harmonic generation (SHG) effect. In this section we compare inorganic single crystals, which are most commonly used to study the effect in question, to organic materials, which also possess the required properties. Based on these data, we present a rationale for the possibility of studying the non-linear optical properties of metal-organic structures as well as describing the use of synthetic approaches and the difficulties associated with them. The second part of the review explicitly acquaints the reader with a new class of materials which successfully combines the positive properties of organic and inorganic materials. Using recently synthesized metal-organic frameworks and coordination polymers in the field of non-linear optics as an example, we consider synthetic approaches used for obtaining materials with desired properties and the factors to be considered in this case. Finally, probable trends towards improving the quality of the synthesized materials with regards to their further use in the field of non-linear optical effects are described.

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.

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.

Low-temperature sol–gel synthesis of crystalline materials

Sol–gel chemistry has opened a new era of modern materials science by enabling the production of ceramic materials at near-room temperature. Thousands of papers have been published since its inception, and new hybrid materials and composites widely used in our everyday life have been obtained. From a chemical point of view, these materials actually have compositions identical to their high-temperature ceramic analogs, but there is a drastic difference in structure and phase composition. In the majority of cases, oxide systems produced using the sol–gel method possess an amorphous structure and huge surface area with narrow micro/mesopore size distribution. At the same time, there are a great variety of oxides and mixed-oxide systems with quite a number of polymorphic modifications and, consequently, certain properties can only be produced by high-temperature treatment. Investigation of the mechanisms and methods of crystallization for such systems in the colloidal state at temperatures less than 100 °C would significantly contribute to the development of new materials obtained by low-temperature sol–gel synthesis. Taking into account the millions of different thermosensitive organic, inorganic, and bio-organic substances that could be used in producing hybrids and composites, the potential of low-temperature sol–gel technology is immense. In fact, it is a ‘second wind’ for developing classical sol–gel technology, with its more than a hundred-year history. The present review describes the fundamental principles of crystallization of oxide sol–gel systems in solution and gives examples of the applications of composites produced by low-temperature sol–gel synthesis.

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.

UV-curable hybrid organic–inorganic composite inks with a high refractive index for printing interference images and holograms

Herein we report a new, facile and inexpensive methodology for obtaining highly refractive polymers suitable for inkjet printing using hexacoordinated titanium complexes (THC) and a UV-curable lacquer based on triethylene glycol dimethacrylate (TGD) that is a cheap and non-toxic monomer that can be rapidly polymerized under UV irradiation under ambient conditions. The resulting polymeric materials are characterized by a refractive index (RI) of about 1.85 in the solid state and have rheological properties suitable for inkjet printing applications. The polymeric materials can be printed onto solid supports resulting in surface structures giving rise to interference images and masking of rainbow holograms illustrating thus the prospective practical applications of the described approach.

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 printing of transparent sol-gel computer generated holograms

In this paper we report for the first time a method for the production of transparent computer generated holograms by desktop inkjet printing. Here we demonstrate a methodology suitable for the development of a practical approach towards fabrication of diffraction patterns using a desktop inkjet printer and nonocrystalline sol-gel ink. In particular, the reported inkjet printing method can be used to generate transparent diffraction structures on supports such as those widely applied in security technologies. Transparent highly refractive layers were deposited with a high precision via a wet-to-dry printing method based on the sol-gel transition phenomenon. With this approach we were able to print a diffraction pattern by TiO2 xerogel, with which a transparent computer generated hologram was created. We argue that this new technology can form the foundation for a new generation of commercial protective coating technologies applied by industrial inkjet printing.

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.

Preparation and physicochemical properties of Nicotinamide@AlOOH biocompatible composite based on sol-gel materials

This paper is devoted to studying the properties of the functional nanocomposite nicotinamide@boehmite. Nicotinamide is introduced directly into a sol of boehmite with the subsequent aging and drying. The results of obtaining high-purity boehmite sol prepared with the use of ultrasonic machining as a physical method of peptization are presented. The structure of the composite is studied with the help of a complex of methods: X-ray-phase analysis, IR-spectroscopy, electron microscopy, and the low-temperature adsorption-desorption of nitrogen. The release of nicotinamide is studied in a histidine buffer at pH = 7.4. Forty-eight percent of the introduced nicotinamide is released in the first 2 h with subsequent sharp retardation resulting in a complete release for a long time.