In situ imaging of three dimensional freeze printing process using rapid x-ray synchrotron radiography

Three dimensional freeze printing (3DFP) combines the advantages of freeze casting and additive manufacturing to fabricate multifunctional aerogels. Freeze casting is a cost-effective, efficient, and versatile method capable of fabricating micro-scale porous structures inside the aerogels for many different applications. The 3DFP provided the capability of fabricating highly customized geometries with controlled microporous structures as well. However, there are still many unexplained phenomena and features because of the complexity of post-processes and indirect observation methods. This study demonstrates the design and construction of the in situ imaging systems, which use the x-ray synchrotron radiography to observe freeze casting and 3DFP processes. With the advantages provided by the in situ x-ray imaging techniques, the ice crystal growth with its unique lamellar structures can be observed during the freeze casting process. The movement of freeze front, material deposition, and growth of ice crystals can also be visualized during the inkjet-based 3DFP process.

Composite Zn(II) Ferrocyanide/Polyethylenimine Cryogels for Point-of-Use Selective Removal of Cs-137 Radionuclides

The feasibility of several approaches to the fabrication of monolith composite cryogels containing transition-metal ferrocyanides for Cs⁺ ion uptake has been evaluated. Although in the series of investigated metal ion precursors (Cu(II), Zn(II), Ni(II), and Co(II)), in situ formation of the sorption active phase in polyethyleneimine (PEI) cryogel was feasible only in the case of Zn(II) ferrocyanide, this approach has shown significant advantages over the immobilization of ex situ synthesized ferrocyanide nanoparticles. Nanoparticles of the mixed ferrocyanide Zn_1.85K_0.33[Fe(CN)₆] formed in situ had an average size of 516 ± 146 nm and were homogeneously distributed in the monolith located at the polymer surface rather than embedded in the matrix. The Young modulus of the PEI cryogel increased after modification from 25 to 57 kPa, but composites maintained high permeability to the flow. Sorption of Cs⁺ ions has been investigated at superficial velocity up to 8 m/h. Steep breakthrough profiles and uptake efficiency of >99.5% until breakthrough point confirmed that a supermacroporous structure of the monolith composite assured good mass transfer, so that intraparticle diffusion was not the limiting stage of sorption kinetics. Application of the rate-constant distribution model (RCD model) to analyze the breakthrough curves of Cs⁺ sorption allowed the identification of two types of sorption sites with a difference in sorption rate constants of ~1 log unit. Most likely, sorption on “fast” sorption sites was governed by ion exchange between Cs⁺ ions in solution and K⁺ ions in the ferrocyanide lattice. Cs-137 radionuclide removal was investigated using the monolith composite columns of various geometries at superficial velocity up to the 6.6 m/h; specific gamma activity was reduced from 265 kBq/L to the background level, showing high potential of these materials for POU application.

3D printed chitosan scaffolds: A new TiO2 support for the photocatalytic degradation of amoxicillin in water

TiO₂-supported chitosan scaffolds (TiO₂/CS) are here proposed as promising material for wastewater treatment, in particular for the removal of pharmaceutical compounds. TiO₂/CS are tested for the amoxicillin photodegradation under UV/Vis irradiation. Amoxicillin (AMX) is an antibiotic of the beta-lactam family. Due to the release of antibiotics in wastewater and their persistence in the environment, harmful effects can develop on the aquatic and terrestrial organisms. TiO₂ chitosan scaffolds with photocatalytic activity for wastewater remediation have been prepared by 3D printing using commercial P25-TiO₂. The formulation for the 3D printer was prepared by dispersion of chitosan and TiO₂ in powder form at the concentration 6% w/v and 1% w/v, respectively. The TiO₂ particles (crystalline anatase and rutile phases) embedded in the chitosan have a size of about 20 nm, like in the starting material, as verified by X-ray diffraction and Raman spectroscopy and are homogeneously distributed in the scaffold, also after repeated photocatalytic tests, as revealed by SEM-EDS. The mechanical properties of the 3D structures are suitable for the targeted application as they can be easily handled without breakage. The AMX photodegradation efficiency under light irradiation by TiO₂/CS made with scaffolds of different thicknesses (3, 5, 15 layers), was assessed in water by means of UV-Vis absorption and HPLC/UV measurements, at two different AMX:TiO₂ molar ratios: 1/100 and 1/10. The 3D printed TiO₂/CS system, even after repeated cycles, shows a high photodegradation efficiency, compared to the direct AMX photolysis. A zero-order kinetics for TiO₂ supported photodegradation was found, whereas a pseudo-first order was observed for water dispersed TiO₂. Mass spectrometry analysis revealed the presence of AMX degradates such as penilloic and penicilloic acids and diketopiperazine. The proposed 3D printed chitosan scaffolds may be used as reusable substrate for the TiO₂ photocatalytic degradation of antibiotic pollutants in wastewater.

Highly Efficient and Recyclable Carbon-Nanofiber-Based Aerogels for Ionic Liquid-Water Separation and Ionic Liquid Dehydration in Flow-Through Conditions

Ionic liquids (ILs) are being widely used in many diverse areas of social interest, including catalysis, electrochemistry, etc. However, issues related to hygroscopicity of many ILs and the toxic and/or nonbiodegradable features of some of them limit their practical use. Developing materials capable of IL recovery from aqueous media and dehydration, thus allowing their recycling and subsequent reutilization, in a single and efficient process still poses a major challenge. Herein, electrically conductive aerogels composed of carbon nanofibers (CNFs) with remarkable superhydrophobic features are prepared. CNF-based 3D aerogels are prepared through a cryogenic process, so called ice-segregation-induced self-assembly (ISISA) consisting of the unidirectional immersion of an aqueous chitosan (CHI) solution also containing CNFs in suspension into a liquid nitrogen bath, and subsequent freeze-drying. The CNF-based 3D aerogels prove effective for absorption of ILs from aqueous biphasic systems and recovery with quite low water contents just through a single process of filtration. Moreover, the electrical conductivity of CNF-based 3D aerogels is particularly interesting to treat highly viscous ILs because the Joule effect allows not only shortening of the absorption process but also enhancement of the flux rate when operating in flow-through conditions.

Enhanced photovoltaic properties of perovskite solar cells by TiO2 homogeneous hybrid structure

In this paper, we fabricated a TiO₂ homogeneous hybrid structure for application in perovskite solar cells (PSCs) under ambient conditions. Under the standard air mass 1.5 global (AM 1.5G) illumination, PSCs based on homogeneous hybrid structure present a maximum power conversion efficiency of 5.39% which is higher than that of pure TiO₂ nanosheets. The enhanced properties can be explained by the better contact of TiO₂ nanosheets/nanoparticles with CH₃NH₃PbI₃ and fewer pinholes in electron transport materials. The advent of such unique structure opens up new avenues for the future development of high-efficiency photovoltaic cells.

Photocatalytic and antimicrobial activities of chitosan-TiO2 nanocomposite

Chitosan, a natural polysaccharide widely used for various biological applications due to their potential benefits. Incorporation of biomaterials with semiconductor has been exploited for waste water treatment and biological applications due to their nanometric sizes and biocompatibility of chitosan. Chitosan-Titanium dioxide (CS-TiO₂) nanocomposite was synthesized and their optical, structural, spectral, thermal, morphological and elemental analyses were carried out by several techniques. The particle size of the synthesized CS-TiO₂ nanocomposite was around 90nm and has a crystalline structure with anatase phase of TiO₂. The prepared nanocomposite acts as a photocatalyst for the removal of rhodamine B (RhB) and congo red (CR) dyes under visible light irradiation. The pseudo first order kinetics was derived according to Langmuir-Hinshelwood (L-H) model. The nanocomposite also proved to be an excellent antimicrobial agent against Gram-positive and Gram-negative bacteria; and also show activity against fungus. The antimicrobial activity of the CS-TiO₂ nanocomposites exhibits a zone of inhibition ranged between 10.333±0.5773 and 25.667±1.5275 (mm).

Preparation and characterization of crosslinked chitosan/gelatin scaffolds by ice segregation induced self-assembly

Chitosan and gelatin are biodegradable and biocompatible polymers which may be used in the preparation of 3D scaffolds with applications in biomedicine. Chitosan/gelatin scaffolds crosslinked with glutaraldehyde were prepared by ice segregation induced self-assembly (ISISA); a unidirectional freezing at -196°C followed freeze-drying to produce macroporous materials with a well-patterned structure. This process may be included within the green chemistry by the preparation of the porous structures without using organic solvents, moreover is a versatile, non-difficult and cheap process. The scaffolds prepared by ISISA were characterized by scanning electron microscopy, attenuated total reflectance Fourier transform infrared spectroscopy, thermal gravimetric analysis, differential scanning calorimetry, and their stability was evaluated by degree swelling and degradation tests. The scaffolds present properties as high porosity, high degree swelling and good stability which make them suitable of applications as biomaterials.

Chitin-Prussian blue sponges for Cs(I) recovery: from synthesis to application in the treatment of accidental dumping of metal-bearing solutions

Prussian blue (i.e., iron[III] hexacyanoferrate[II], PB) has been synthesized by reaction of iron(III) chloride with potassium hexacyanoferrate and further immobilized in chitosan sponge (cellulose fibers were added in some samples to evaluate their impact on mechanical resistance). The composite was finally re-acetylated to produce a chitin-PB sponge. Experimental conditions such as the freezing temperature, the content of PB, the concentration of the biopolymer and the presence of cellulose fibers have been varied in order to evaluate their effect on the porous structure of the sponge, its water absorption properties and finally its use for cesium(I) recovery. The concept developed with this system consists in the absorption of contaminated water by the composite sponge, the in situ binding of target metal on Prussian blue load and the centrifugation of the material to remove treated water from soaked sponge. This material is supposed to be useful for the fast treatment of accidental dumping of Cs-contaminated water.

Effect of synthesis routes on the properties and bactericidal activity of cryogels incorporated with silver nanoparticles

AgNPs-incorporated cryogels prepared via three synthesis routes were explored as antibacterial sorbents for water disinfection.

Fabrication of polymeric biomaterials: a strategy for tissue engineering and medical devices

Fabrication of biomaterials scaffolds using various methods and techniques is discussed, utilising biocompatible, biodegradable and stimuli-responsive polymers and their composites. This review covers the lithography and printing techniques, self-organisation and self-assembly methods for 3D structural scaffolds generation, and smart hydrogels, for tissue regeneration and medical devices.

Rational synthesis of chiral layered magnets by functionalization of metal simple hydroxides with chiral and non-chiral Ni(II) Schiff base complexes

Synthesis of new heterometallic layered magnets with controlled chirality have been achieved by insertion of chiral and non-chiral salen-type Ni(II) complexes into copper and cobalt layered simple hydroxides.