Dry Gel Research Articles

Removal of Organic Acids from Indoor Air in Museum Storage Rooms by Active and Passive Sorption Techniques

ABSTRACT Adsorbent materials can be used for the removal of organic acids from air in storage rooms with heritage collections. The organic acid removal efficiency of two commercially available activated carbon air-filters were tested in situ in two unoccupied stores with densely packed collections. One filter was designed for outdoor type pollutants (Filter A), while the other was designed for organic acids in indoor air (Filter B). Furthermore, the acetic acid removal efficiency of a desiccant silica gel rotor used for dehumidification was measured in a laboratory at different relative humidity levels. Finally, passive removal of acetic acid by silica gel and unfired clay brick were tested in a chamber, and for clay brick at room level as well. Filter B had the highest removal efficiency. The removal efficiency of both filter types depended on the airflow and the filter performance varied considerably in situ from the values reported from standard laboratory tests. Increasing the filter airflow reduced the removal efficiency from 77% and down to 7% for Filter A, and from 92% to 24% for Filter B. There was almost no effect of active air filtration on the concentration of organic acids when this was measured in the middle and in the corner of the storage rooms away from the ventilation inlets. The desiccant dehumidifier removed 98–100% of the acetic acid from the air, independently of the relative humidity. The desiccant rotor will, however, only be running when there is a need for dehumidification and as a result will only periodically remove pollutants. The high acid removal efficiency by dry silica gel was furthermore demonstrated in a chamber test. A clay brick wall in a test room established a concentration gradient across the room and reduced the concentration of organic acids by 56% compared to close to the emission source.

Specific Loss Power of Co/Li/Zn-Mixed Ferrite Powders for Magnetic Hyperthermia.

An important research effort on the design of the magnetic particles is increasingly required to optimize the heat generation in biomedical applications, such as magnetic hyperthermia and heat-assisted drug release, considering the severe restrictions for the human body’s exposure to an alternating magnetic field. Magnetic nanoparticles, considered in a broad sense as passive sensors, show the ability to detect an alternating magnetic field and to transduce it into a localized increase of temperature. In this context, the high biocompatibility, easy synthesis procedure and easily tunable magnetic properties of ferrite powders make them ideal candidates. In particular, the tailoring of their chemical composition and cation distribution allows the control of their magnetic properties, tuning them towards the strict demands of these heat-assisted biomedical applications. In this work, Co0.76Zn0.24Fe2O4, Li0.375Zn0.25Fe2.375O4 and ZnFe2O4 mixed-structure ferrite powders were synthesized in a ‘dry gel’ form by a sol-gel auto-combustion method. Their microstructural properties and cation distribution were obtained by X-ray diffraction characterization. Static and dynamic magnetic measurements were performed revealing the connection between the cation distribution and magnetic behavior. Particular attention was focused on the effect of Co2+ and Li+ ions on the magnetic properties at a magnetic field amplitude and the frequency values according to the practical demands of heat-assisted biomedical applications. In this context, the specific loss power (SLP) values were evaluated by ac-hysteresis losses and thermometric measurements at selected values of the dynamic magnetic fields.

Aloe vera: A tropical desert plant to harness the mechanical energy by triboelectric and piezoelectric approaches

The tropical desert plant (aloe-vera, AV) derived natural bio-organic material used to convert the waste mechanical energy into electrical energy. The piezoelectric force microscopy measurement of AV film shows the amplitude resembles the butterfly-like shaped, and the phase loop depicts the 180° switching of domains confirming the ferroelectricity of AV. The obtained converse piezoelectric coefficient (d33) is 6.5 pm V−1, and remnant polarization is 1.02 μC/cm2 for poled AV film due to the development of long-range order of acemannan (A) chains and their interaction between them A-A or A-uronic acids through the newly formed hydrogen bonds. The piezoelectric AV film-energy harvester (AV film-EH) generates a peak-to-peak output response of (1.2 V, 200 nA), and the instantaneous peak power is ≈ 0.42 μW at 10 MΩ upon 4 N force. The non-contact surface potential measurement and KPFM results confirm the AV is a moderate positive triboelectric material having a surface potential of +1.14 V, respectively. The triboelectricity of AV explored in two approaches, such as dry film (F) and gel (G) type interacting with the different materials. The AV film-PDMS, AV gel-PDMS TENG, delivers an instantaneous power density of 0.19 μW/cm2 upon 2 m/s2 acceleration of shaft load and 0.22 μW/cm2 upon biomechanical hand force. Next, successfully demonstrated the AV film-EH could work as a self-powered finger monitoring sensor to monitor human finger bending angles. It also explored that the electrical output of AV film-PDMS TENG is used to power the smartwatch successfully. Here, the generated electric energy from the desert plant is clean, cost-effective, and plentiful to develop the self-powered biosensor/implantable devices.

Supercritical drying of thermoresponsive gels based on N-isopropylacrylamide

Thermoresponsive materials are of great interest for medicine, pharmacy and food industry. During the production of these materials they are often taken into their dry state, requiring gentle processes with minimum effect over their properties. In this study, supercritical drying process was used to obtain dry products from thermoresponsive N-Isopropylacrylamide based gels and compared to other typical drying processes like hot air- and freeze- drying. Depending on the method, different degrees of modification of the structure were observed, which have a significant influence on the final properties of the materials and on their rehydration. Results show that supercritical technology can be used to produce dry porous materials with less collapsed structure or modified properties than conventional or freeze drying techniques while keeping the thermoresponsive nature, which is translated into materials with higher porosity and surface area, and slightly improved swelling degree. Swelling kinetics results showed that materials dried by conventional drying displayed sigmoidal anomalous behavior, those dried by freeze-drying exhibited a two-stage anomalous behavior, and materials obtained by supercritical drying presented behaviors close to Fickian which is of great interest for further drug release applications.

Catalytic isomerization of n-hexane over beta (BEA) zeolite by dry-gel convention (DGC) and hydrothermal (HTS) methods

Catalytic Isomerization of n-hexane over Beta (BEA) zeolite synthesized by dry gel conversion (DGC) and hydrothermal (HTS) methods were studied. The isomerization was influenced by types of synthesized methods, and combined selectivity for branched alkanes (2- and 3-methylpentanes, 2,2-dimethylbutane, 2-, and 3-methylbutanes, 2,2-dimethylpropane, and 2-methylpropane) decreased in the order: BEA (DGC) > BEA (HTS). BEA synthesized by DGC had the highest activity and selectivity for the isomerization, and BEA Synthesized by HTS has the highest activity for cracking to lower alkanes and alkenes. These differences are ascribed to the difference of surface area, pore volume, acid properties, and reaction parameters.

Pectin–glycerol gel beads: Preparation, characterization and swelling behaviour

Low methyl-esterified pectin (AU701) was found to form gel beads with glycerol. Wet AU701-glycerol gel beads exhibited similar diameter and hardness compared to the AU701-Ca gel beads, prepared by ionotropic gelation with Ca2+ and used for comparison. The morphology of dry pectin gel beads determined by scanning electron microscopy revealed that the beads exhibited rough and grooved surface. The AU701-glycerol gel beads absorbed more grams of water than AU701-Ca gel beads (12.2 g vs 3.9 g per 1 g of the beads). Rheological properties and hardness of the AU701-glycerol gel beads improved with the increase of the pectin/glycerol ratio. Swelling behavior of the AU701-glycerol gel beads was determined after sequential incubation in simulated gastric (SGF) and intestinal (SIF) fluids. The AU701-glycerol gel beads swelled in SGF to a greater extent and revealed higher stability in SIF than the gel beads cross-linked by Ca2+.

Synthesis of Hierarchical Chabazite Zeolite via Interzeolite Transformation of Coke-containing Spent MFI

Nowadays, it’s highly desirable to develop a sustainable strategy for utilizing the wasted zeolite catalysts to selectively produce value-added and useful zeolites in industry. Herein, using the coke-containing spent MFI zeolite as the raw materials, a robust interzeolite transformation by a steam-assisted dry gel conversion method was reported to synthesize the hierarchical SSZ-13 zeolites (CHA type) with high crystallinity and well-developed mesoporosity (mesopore volume = 0.38 m3/g). The obtained hierarchical SSZ-13 exhibited a marked improvement of catalytic lifetime in methanol to olefins (MTO) reaction, showing about 2.5 times longer than that of the conventional SSZ-13 in bulk single-crystal structure. The catalyst also presented long-term stability after 3 consecutive cycles of reaction and regeneration. It was found that the coke in the spent MFI could function not only as a qualified hard template for mesoporosity formation but also as a restrictor to hinder the zeolite grain growth. The ordered aluminosilicate fragments decomposed from MFI zeolites at the initial period may act as nutrients, which were then rearranged to form CHA zeolites at a high crystallization rate. Besides, the enhanced diffusion rate and adsorption capacity arising from the hierarchical pores in SSZ-13 greatly decreased the coking rate and improved its coke tolerance by lowering the probability of secondary reaction inside zeolite channels. This work will provide a general and efficient way to transform waste zeolite catalysts into more valuable hierarchical zeolites.

Green synthesis of submicron-sized Ti-rich MWW zeolite powders via a novel mechanochemical dry gel conversion in mixed steam environment

In this research, a novel green mechanochemical dry gel conversion method (MDGC) is reported to obtain submicron-sized Ti-rich MWW zeolite. First, titanium and silica sources were milled under milder conditions in a planetary ball mill to construct the uniform SiO2-TiO2 composite powders with higher Ti contents. Subsequently, submicron-sized Ti-rich MWW zeolite powder was prepared via dry gel conversion (DGC) route using the obtained composite under mixed steam environment consisting of water and piperidine. The physicochemical properties of the SiO2-TiO2 composites before and after calcination and corresponding Ti-MWW-MDGC were investigated by XRD, UV–Vis, FT-IR, SEM, XRF, and N2 absorption-desorption. Moreover, Ti-MWW (30)-MDGC exhibited a superior catalytic activity during epoxidation with H2O2 compared with the traditional DGC method, and the conversion of 1-hexene increased from 4.2% to 26.3%. The MDGC method is a promising approach for the green production of various zeolites with higher heteroatom contents, such as TS-1, Ti-Beta and Sn-MWW, etc.

Experimental study of the silica gel drying in a fluidized bed apparatus

In this paper, the design and principle of operation of the dryer with a centrifugal fluidized bed is considered. It is a batch apparatus with a vertical drying agent supply and is intended for drying dispersed materials with a particle diameter from 1 to 5 mm, having a high initial moisture content and a strong moisture and solid dry frame bond. Silica gel with a particle diameter from 2.2 to 2.5 mm, used for drying air and industrial gases, was used as a drying object. The scheme of the test bench is given and described. The results of an experimental study of the process of low-temperature drying of silica gel (the temperature of the drying agent ranged from 35 to 65 °C) are presented. The obtained experimental data is presented as a dependence of the thermophysical parameters of the material and the drying agent on the drying time. The comparison of drying efficiency at different modes is given. On the basis of the obtained data, a positive conclusion about the possibility of using this apparatus for low-temperature drying of capillary-porous bodies is made.

In Situ Encapsulation of Pt Nanoparticles within Pure Silica TON Zeolites for Space-Confined Selective Hydrogenation.

Straightforward encapsulation of Pt clusters (∼2 nm) into the pure silica TON-type zeolite (ZSM-22) was reached in a dry gel conversion route, where the ionic liquid template was removed via the hydrocracking-calcination-reduction approach. The obtained Pt@ZSM-22 series possessed high crystallinity, large surface area, and ultrafine Pt clusters inside the zeolite crystals. They exhibited remarkable activity in the semi-hydrogenation of phenylacetylene into styrene; the lead sample with 0.2 wt % Pt loading afforded a large turnover number up to 117,787. The preferential high affinity of the pure silica ZSM-22-encapsulated Pt clusters toward the substrate phenylacetylene rather than the hydrogenated product was derived from the unique space-confinement effect of zeolite microchannels, which is responsible for such excellent performance.

Synthesis of titanium silicalite-1 (TS-1) zeolite with high content of Ti by a dry gel conversion method using amorphous TiO2–SiO2 composite with highly dispersed Ti species

In this study, we have developed a new method to synthesize mesoporous titanium silicalite-1 (TS-1) with a higher content of active titanium in the framework (more than 5%) than that obtained from the conventional hydrothermal synthesis. The new method combines two methods as follows: (1) a sol-gel method in tetrahydrofuran for the synthesis of TiO2–SiO2 composite with highly dispersed Ti species and (2) a dry gel conversion method for the crystallization to TS-1. This investigation revealed that the dispersion of Ti in the starting materials was quite important to synthesize mesoporous TS-1 with high content of Ti besides dry conversion method. The obtained mesoporous TS-1 with a high content of titanium showed higher catalytic activity in 1-hexene epoxidation than conventional TS-1. This high activity is likely to originate from the high content of titanium in the framework.

Jet Cutting Technique for the Production of Chitosan Aerogel Microparticles Loaded with Vancomycin.

Biopolymer-based aerogels can be obtained by supercritical drying of wet gels and endowed with outstanding properties for biomedical applications. Namely, polysaccharide-based aerogels in the form of microparticles are of special interest for wound treatment and can also be loaded with bioactive agents to improve the healing process. However, the production of the precursor gel may be limited by the viscosity of the polysaccharide initial solution. The jet cutting technique is regarded as a suitable processing technique to overcome this problem. In this work, the technological combination of jet cutting and supercritical drying of gels was assessed to produce chitosan aerogel microparticles loaded with vancomycin HCl (antimicrobial agent) for wound healing purposes. The resulting aerogel formulation was evaluated in terms of morphology, textural properties, drug loading, and release profile. Aerogels were also tested for wound application in terms of exudate sorption capacity, antimicrobial activity, hemocompatibility, and cytocompatibility. Overall, the microparticles had excellent textural properties, absorbed high amounts of exudate, and controlled the release of vancomycin HCl, providing sustained antimicrobial activity.

Dry gel conversion synthesis and performance of glass-fiber MIL-100(Fe) composite desiccant material for dehumidification

Abstract Metal organic frameworks (MOFs) MIL-100(Fe) is considered to be a promising porous adsorbent for dehumidification due to its good hydrophilicity and hydrothermal stability. However, the powdery MIL-100(Fe) prepared by the conventional hydrothermal method is not suitable for industrial rotary desiccant dehumidifier. In order to produce a high-performance rotor core component, a new dry gel conversion in situ synthesis strategy for glass-fiber MIL-100(Fe) monolithic adsorbent was proposed in this paper. The effects of the reaction sol concentration on the crystalline phase, morphology, pore structure, adsorption/desorption performance and the cycling stability of the monolith were discussed in detail. The results showed that MIL-100(Fe) crystals which evenly dispersed in the surface and voids of glass fiber, could be conveniently synthesized in the reaction sols with molar ratios of 1Fe (III)/0.67BTC/xH2O (x = 93–185). Among them, the MIL-100(Fe) monolith obtained at x = 93 exhibited a high loading (85.7%), large BET specific surface area (1441 m2/g), S-shaped water vapor adsorption isotherm and high saturated adsorption ratio (0.496 g/g) at 298 K and 60% RH, low desorption activation energy (48.28 kJ/mol) as well as a reliable cycling stability. Favorable adsorption/desorption performance of MIL-100(Fe) monolith and convenient dry gel preparation process provide a guidance for the manufacture of high-performance dehumidification rotary wheel.

Effect of graphene oxide on morphological and structural properties of graphene reinforced novolac-derived carbon aerogels: A modified Quasi-Percolation Model

Graphene reinforced polymer derived carbon (carbon/graphene) aerogels were synthesized by carbonization of novolac/graphene oxide aerogels. Novolac/graphene oxide aerogels were synthesized using solvent-saturated-vapor-atmosphere technique. To this aim, 20 wt% solution of novolac resin with 0, 2, and 5 wt% graphene oxide in 2-propanol were made and were cured in an autoclave. Wet aerogels were dried in air and were carbonized at 800 °C in nitrogen atmosphere. Eliminating the time-consuming methods of drying like supercritical and freeze drying is one of the advantages of this method of synthesis of organic aerogles. Fourier transform infrared spectroscopy, field emission scanning electron microscopy, X-ray diffraction, nitrogen adsorption/desorption, and small angle X-ray scattering measurements were used to characterize the samples. It was shown that the density, the average pore size, and the pore size distribution were affected by addition of graphene oxide nanosheets. Total pore volumes of carbon/graphene aerogels were increased and the apparent density of the samples were decreased by addition of graphene oxide nanosheets. The effect of addition of graphene oxide on pore structure was mainly on mesopore and macropore region and there was fewer changes in micropore volume. Carbon/graphene aerogels with 5 wt% graphene oxide revealed the lowest density (0.167 g cm−3) with the largest BET surface area of 580.6 m2 g−1. The surface area of the carbon aerogels in this research (>500 m2 g−1) is the largest surface area achieved by ambient drying of the wet gel. It was shown that the crystallite sizes were increased by addition of graphene oxide. Graphene oxide nanosheets acted as templates for crystallization of carbon atoms which resulted in formation of bigger crystallites during carbonization. A model has been proposed based on Quasi-Percolation Model to explain the formation of bigger crystallites in presence of graphene nanosheets.

A Mini Review of Microneedle Array Electrode for Bio-Signal Recording: A Review

Bio-signal recording is vital for human condition monitoring and early disease diagnosis. An electrode is a biosensor for bio-signal collection. The conventional wet electrode is not suitable for long-term bio-signal recording owing to the gradual drying of the electrolytic gel and increase in the electrode-skin interface impedance. Microneedle array electrode is a dry electrode that can painlessly pierce skin, form a contact interface between the microneedles and skin tissue, eliminate the high impedance of stratum corneum, weaken the motion artifact, and accurately record bio-signals without skin preparation and application of electrolytic gel. This review focuses on the recently developed fabrication techniques, the mechanical performance, and bio-signal recording performance of microneedle array electrode. The microneedle array electrode is a potential electrode for long-term bio-signal recording, although progress is required in terms of safety and scaled-up manufacture.

Structuring oil-in-water emulsion by forming egg yolk/alginate complexes: Their potential application in fabricating low-fat mayonnaise-like emulsion gels and redispersible solid emulsions

Overconsumption of fat-rich foods has caused increasing incidences of human chronic diseases. Thus, it is promising to fabricate reduced-fat foods, but the reduction in fat content often causes undesired textural changes in foods. In this study, we showed a facile method to structure oil-in-water emulsions via the electrostatic complexation between alginate (Alg) and egg yolk proteins at acid pHs (lower than pH 5.0), and the resulting emulsion gels displayed significant viscoelasticity, thixotropy and plasticity, which are comparable to a full-fat mayonnaise product with 75% oil content. Besides, the textural attributes of the structured emulsion gels can be tailored by simply altering the addition amount of vinegar, a commonly used ingredient in fabricating mayonnaise-like products to confer good sensory profile. After lyophilization, we obtained dry emulsion gels with a high oil content (~75%), and it was found that the dried gel prepared at pH 5.8 showed better dispersibility than at other pHs, highlighting the potential application prospect of the gels to be developed as a carrier for loading functional oil soluble compounds.

Washable and flexible screen printed graphene electrode on textiles for wearable healthcare monitoring

Electrocardiogram (ECG) is an essential route to monitor and prevent cardiovascular related disease. Conventional silver/silver chloride (Ag/AgCl) electrodes are not able to be used for long-term monitoring due to the drying of gel and skin irritation. Graphene has been investigated as a promising material for wearable health-monitoring electronics. Here, a graphene-coated textile electrode was developed for ECG monitoring. The graphene electrode was prepared by screen printing graphene ink on a pre-modified textile substrate. The electrical resistance of the graphene textile electrode can be controlled by increasing the printing passes. The ECG signals obtained by the graphene textile electrode showed comparable performance to the conventional Ag/AgCl electrode. The graphene textile electrode shows satisfactory washability, high flexibility and good tortuosity. The performance of the ECG signal shows negligible change over nine washing cycles and 2000 bending cycles. Overall, the screen-printed graphene textile electrode in this work presents an inexpensive fabrication platform solution for long-term healthcare monitoring in wearable electronics.

Versatile composite hydrogels for drug delivery and beyond.

Hydrogels have extended applications across multiple fields. A novel hydrogel material is often evaluated for its properties and applications in either a wet or dry state, but not both. In this study, we investigated a protein-based, composite hydrogel system in both its wet and dry states. Bovine serum albumin (BSA) was used as the hydrogel base. With the assistance of organosilanes, BSA solutions became hydrogels under facile reaction conditions. In the first part, the wet gel was prepared in situ in a syringe; upon injecting through a needle, the gel retained its structure. The use of the nascent gel system as an injectable drug-delivery vehicle is of particular interest. We therefore developed a microplate platform that allows a "one-plate" study-i.e. gel preparation, payload loading and release-all being performed in a single plate. This one-plate method further enables a systematic study of various controlling parameters for drug release. For example, we can tune the release rate by simply adjusting the phosphate content in the hydrogel formulation. Besides, for low-releasing compounds, the release profile was also tunable while using the one-plate method. In the second part, we further demonstrate the versatility of our composite hydrogels. By simply varying the feed ratio of two organosilanes, (3-mercaptopropyl)methyldimethoxysilane and (3-mercaptopropyl)trimethoxysilane, and phosphate concentrations, dry gels exhibiting various absorption capacities towards water, organic solvents, and oil can be prepared. Further characterizations using SEM and 29Si NMR spectroscopy revealed porous structures and hybrid siloxane bridges within the composite material.

Aerogels for the separation of asphalt-containing oil-water mixtures and the effect of asphalt stabilizer.

In order to separate the asphalt-containing oil–water mixture, an aerogel film was produced through supercritical drying of a polymer gel synthesized using the ring opening metathesis polymerization of dicyclopentadiene (DCPD). The polydicyclopentadiene (PDCPD)-based aerogels have a porous structure, super-lipophilicity and super-hydrophobicity which resulted in successful separation of the simple oil–water mixture, oil–water emulsion and asphalt-containing toluene–water mixture. However, the presence of asphalt decreases the separation efficiency by blocking the pores and acting as an emulsifier. An asphalt stabilizer was then employed to reduce the asphalt particle size and weaken the flow passage blockage, consequently improving the filtration speed and the asphalt content in the filtrate. The combination of PDCPD aerogel film with an asphalt stabilizer has great application prospects for separating asphalt-containing oil–water mixtures.

压花明胶凝胶覆膜技术与花材干燥技术优化

压花明胶凝胶覆膜技术与花材干燥技术优化