Composite Xerogel Research Articles

Efficient Stabilization and Directional‐Controlled Release of Vitamin C in Disaccharide/Megasaccharide Composite Xerogels

Efficient Stabilization and Directional‐Controlled Release of Vitamin C in Disaccharide/Megasaccharide Composite Xerogels

Efficient Stabilization and Directional‐Controlled Release of Vitamin C in Disaccharide/Megasaccharide Composite Xerogels

AbstractComposite xerogel films with structural orientation, controlled swelling degree, and drug‐release ability are prepared using biocompatible megamolecular liquid crystalline polysaccharide (sacran) secreted by a cyanobacterium Aphanothece sacrum. The sacran xerogel films (Sac‐XFs) are formed by drying sacran aqueous solution including vitamin C (L‐ascorbic acid, AA) and trehalose under various conditions. In X‐ray diffraction and differential scanning calorimetry of Sac‐XFs, diffractions or melting points of either AA or trehalose are not detected, indicating no crystal formation. Additionally, the stability of entrapped AA in Sac‐XFs is evaluated through changes in film color and percentage loss, to indicate that AA stability is enhanced by entrapment in Sac‐XFs in the presence of trehalose. Scanning electron microscopy of Sac‐XFs reveals the morphological orientation, and number of striped lines along the longitudinal axis of film edges on side views while no visible textures in top views. When Sac‐XFs are immersed in water, anisotropic swelling is observed, and anisotropy decreases with an increase in the drying temperature of the films. AA is released preferentially from the hydrogel sheet edges, indicating the direction‐controlled release. Thus, the trehalose/sacran composite xerogels offer an alternative platform for preserving and controlled‐releasing sensitive substances for fields of foods, pharmaceutics, and cosmetics.

Design of Phytic Acid Crosslinked Xerogels as Organic Photocatalysts for Visible Light‐Assisted Degradation of Dyes

AbstractExtensive research is being carried out on the degradation of water pollutants using various strategies to overcome the global water crisis. In the present study, xerogels as a better alternative is utilized to metal oxides for the photocatalytic degradation of toxic water pollutants such as dyes. Xerogels of polyaniline (PANI) and polypyrrole (PPy) are synthesized using phytic acid as a dopant as well as cross‐linker in the weight ratios of 1:1, 1:2, and 2:1 via simple chemical oxidative polymerization. The synthesized xerogels are analyzed for their spectral, morphological, thermal, and optical properties using FTIR, UV–vis, XRD, SEM, and TGA techniques. The xerogels are also tested for their photocatalytic activity against textile dyes – Methylene Blue (MB), Alizarin Red S, (ARS), Rhodamine B (RhB), and Methyl Orange (MO). Among all the composite xerogels, PANI/PPy‐2/1 showed excellent degradation efficiency of 91% for MB dye, 88% for RhB dye, 96% for ARS dye, and 92% for MO dye respectively. The composite PANI/PPy xerogels showed better degradation efficiency than their pristine counterparts. The fragments of the degraded dyes are examined using the LCMS technique and a tentative dye degradation mechanism is proposed.

Investigation of platelet activation and calcium store release by a topical hemostatic xerogel dressing for improved blood clotting

AbstractAdequate topical hemostatic dressings are required as first‐line approach for reduction of uncontrolled hemorrhage, a leading cause of mortalities. Platelets play a major role during blood clotting to prevent hemorrhage during injuries. Here, we demonstrate the mechanisms activated through protease activating receptor 1 (PAR1), a platelet membrane protein in response to a porous composite xerogel dressing incorporating SiNPs (size 122 ± 10 nm) and calcium (2.5 mM), characterized by scanning electron microscopy–energy dispersive x‐ray spectroscopy and Fourier transform infrared spectroscopy. The composite displayed 13.9‐fold improved blood clotting index in comparison to commercial dressing. The composite displayed increased platelet aggregation due to development of well‐formed pseudopodia as compared to bare xerogel, SFLLRN (a thrombin mimic), adenosine di‐phosphate (a platelet activator), and heparin (a thrombin inhibitor). Further, PAR1 gene was significantly upregulated in model A549 epithelial cell line (1.2‐fold) and human platelets (1.4‐fold). The composite enhanced calcium release and its extrusion in A549 cells. Upregulation of PAR1 on the platelet surface and calcium release are crucial for platelet shape change and aggregation. The data indicate that xerogel composite containing SiNPs and calcium enhanced blood clotting through activation of PAR1. Such dressings can provide a potential hemostatic solution to reduce blood loss, disability, and mortality during surgery and trauma care.

Biopolymer-Mushroom Nanofiber Composite Xerogel Film: Bio-Base-Mediated Green, Chemically Resistant, Edible, and Printable Films

Biopolymer-Mushroom Nanofiber Composite Xerogel Film: Bio-Base-Mediated Green, Chemically Resistant, Edible, and Printable Films

Poly(methylphenylsiloxane)-modified resorcinol-terephthalaldehyde phenolic xerogel monoliths

Fabrication of polymer porous xerogel with environment-friendly and simplified procedure is important target for reducing pollution and production cost. In this research, a sustainable method to prepare thermal insulator of polysiloxane-phenolic composite porous xerogel monoliths was studied by replacing hazardous and volatile formaldehyde with terephthalaldehyde in phenolic component and applying facile ambient drying process. The homogeneous dispersion of poly(methylphenylsiloxane) and resorcinol-terephthalaldehyde in xerogels was achieved by adjusting catalysis condition, water-ethanol content and prepolymer component. Typical poly(methylphenylsiloxane) and resorcinol-terephthalaldehyde composite xerogel monolith had density of about 0.3 g/cm3, 65.4% mass retention rate at 800 °C under nitrogen atmosphere, and thermal conductivity 0.063 W/(m·K) at room temperature. According to Thermogravity analysis coupled with Fourier Transform Infrared Spectra (TG-FTIR), pyrolysis mechanism and structure transformation were revealed. The typical pyrolyzed derivatives at 600 °C and 800 °C well preserved the integrated structure, low density, thermal insulation property, and thermal oxidation stability.

Efficient removal of perfluorobutanesulfonic acid from water through a chitosan/polyethyleneimine xerogel

Due to the recently ratified legislations, the use of long-chain poly- and perfluoroalkyl substances (PFASs) must be reduced and in the absence of a safe alternative, short-chain PFASs are currently used in their place. The continuously growing utilization of the short-chain PFASs, results in their abrupt introduction in the environment, and highlights the importance of adopting efficient remediation strategies. This study addresses an appropriate solution to remove perfluorobutanesulfonic acid (PFBS) from aqueous media through a static adsorption process. Specifically, a chitosan/polyethyleneimine based composite xerogel was prepared and its ability to remove PFBS from water was studied in detail. Behavioral patterns of the PFBS adsorption process were perused over a broad range of concentrations from ppb to ppm, and the adsorption studies reveal that the maximum PFBS adsorption capacity reaches up to 305 mg/g within 24 h from the beginning of the process. In addition to the electrostatic interaction between the amine groups of the xerogels and the negatively charged PFBS molecules, the formation of hydrogen bonds were also revealed by the chemical characterization and confirmed by molecular dynamics simulation studies.

Synthesis of bagasse nanocellulose-filled composite polyurethane xerogel for the efficient adsorption of Rhodamine-B dye from aqueous solution: investigation of adsorption parameters.

In this study, polyurethane (PU)-based xerogels were synthesized by using the biobased polyol derived from chaulmoogra seed oil. These polyol was used for the preparation of PU xerogels using methylene diphenyl diisocyanate hard segment and polyethylene glycol (PEG6000) as soft segment with 1,4-diazabicyclo[2, 2, 2]octane as catalyst. Tetrahydrofuran, acetonitrile and dimethyl sulfoxide were used as the solvents. Nanocellulose (5wt %) prepared from bagasse were added as filler, and the obtained composite xerogels were evaluated for chemical stability. The prepared samples were also characterized by using SEM and FTIR. Waste sugarcane bagasse nanocellulose proved as a cheap reinforcer in the xerogel synthesis and for the adsorption of Rhodamine-B dye from the aqueous solution. The factors that affect the adsorption process have been studied including the quantity of the adsorbent (0.02-0.06g), pH (6-12), temperature (30-50) and time (30-90). Central composite design for four variables and three levels with response surface methodology has been used to get second-order polynomial equation for the percentage dye removal. RSM was confirmed by the measurement of analysis of variance. Increase in the pH and quantity of the adsorbent was found to increase the sorption capacities of the xerogel (NC-PUXe) towards rhodamine B, maximum adsorption.

The Effects of rGO Content and Drying Method on the Textural, Mechanical, and Thermal Properties of rGO/Polymer Composites

Composite hydrogels samples consisting of poly(methyl methacrylate/butyl acrylate/2-hydroxyethylmethacrylate) (poly-OH) and up to 60% reduced graphene oxide (rGO) containing rGO were synthesized. The method of coupled thermally induced self-assembly of graphene oxide (GO) platelets within a polymer matrix and in situ chemical reduction of GO was applied. The synthesized hydrogels were dried using the ambient pressure drying (APD) and freeze-drying (FD) methods. The effects of the weight fraction of rGO in the composites and the drying method on the textural, morphological, thermal, and rheological properties were examined for the dried samples. The obtained results indicate that APD leads to the formation of non-porous xerogels (X) of high bulk density (D), while FD results in the formation of highly porous aerogels (A) with low D. An increase in the weight fraction of rGO in the composite xerogels leads to an increase in D, specific surface area (SA), pore volume (Vp), average pore diameter (dp), and porosity (P). With an increase in the weight fraction of rGO in A-composites, the D values increase while the values of SP, Vp, dp, and P decrease. Thermo-degradation (TD) of both X and A composites takes place through three distinct steps: dehydration, decomposition of residual oxygen functional group, and polymer chain degradation. The thermal stabilities (TS) of the X-composites and X-rGO are higher than those of the A-composites and A-rGO. The values of the storage modulus (E') and the loss modulus (E") of the A-composites increase with the increase in their weight fraction of rGO.

Construction of titanium-aluminum xerogel composite coagulant for removal of tetracycline in water: synergy effects and improvement mechanisms insight.

Titanium xerogel coagulant (TXC) is a new type of coagulant that has attracted much attention in recent years. However, the tetracycline removal performance of TXC was not satisfactory because low isoelectric point (pHiep) inhibited the electrical neutralization efficiency of TXC in an alkaline environment. To overcome this shortcoming, a composite xerogel coagulant (titanium-aluminum xerogel composite coagulant) was prepared. The removal of tetracycline and turbidity was used as evaluation indexes. It was proved that the combination of aluminum (III) and titanium (IV) enhanced the resistance of TXC to pH. The synthesized titanium-aluminum xerogel composite coagulant (TXAC) has an excellent removal ability of tetracycline in a wide pH range (pH = 5-10). At pH 8.8, the dosage required to remove 80% tetracycline from water decreased from 93 (TXC) to 35mg/L (TXAC). The reason for this improvement could be attributed to (i) aluminum (III) enhanced the electric neutralization of TXC to negatively charged pollutants in an alkaline environment; (ii) the complexing ability of organic matter and aluminum (III) was enhanced. This work provides a feasible scheme for the pretreatment of tetracycline in water to meet the pretreatment requirements of special water.

Effect of cotton fiber addition and carbonization temperature to the structural-and-surface-property change of C/C composite xerogels as electrodes for electric double layer capacitors

Carbon/carbon (C/C) composites containing micropores, mesopores and macropores as trimodal structure are a class of promising electrode materials for electric double layer capacitors. The existence of cotton fibers can change pore structure, electrical resistance and surface properties of C/C composites by the increase of carbonization temperature. In this work, C/C composite xerogel electrodes possessing trimodal structure were prepared from resorcinol, formaldehyde, and cotton fibers. Sufficiently high carbonization temperatures had to be reached to obtain electrodes possessing high electrical double layer capacitance. The addition of cotton fibers lowered effective carbonization temperatures and created macropores, which facilitated transport of carbonization gases and heat transfer in pores located deep in the samples. Cotton fibers also prevented collapse of mesopores during vacuum drying. Samples with cotton fibers added had 27–40% more mesopore volume. The highest specific capacitance obtained was 175 F g−1 during discharge at 0.5 A g−1.

Polyimide hybrid membranes with graphene oxide for lithium–sulfur battery separator applications

Novel polyimide composite films containing graphene oxide are prepared for use in the lithium-sulfur (Li–S) battery. Poly(amic acid)s of biphenyl tetracarboxylic dianhydride (BPDA) and 4,4′-oxydianiline (ODA) are synthesized and mixed with graphene oxide, followed by chemical imidization and freeze-drying. The samples are in the form of xerogels, which have excellent thermal and chemical stability with negligible thermal shrinkage. They also adsorb polysulfide reversibly and allow lithium ions to pass through, thereby improving battery performance. The Li–S batteries are fabricated by inserting the PI composite xerogel films as the separator between electrodes. They show a high coulombic efficiency of above 99% and exhibit an initial discharge capacity of 1306.5 mAh/g at 0.2C, and are maintained at 730 mAh/g even after 100 cycles. In the repeated charge/discharge experiment, the electrolyte uptake and interfacial compatibility of the PI hybrid xerogel separator are improved significantly compared to those measured from the PI separator. • Preparation of polymer hybrid membrane for lithium-sulfur battery separator applications. • Separators with excellent electrochemical and thermal stability. • Prevention of diffusion of polysulfides by electrostatic interaction with hybrid membrane. • Batteries with high coulomb efficiency, cycling stability, and capacity recovery after high-speed charging and discharging.

Imidazolium Ionic Liquids as Designer Solvents Confined in Silica Nanopores.

Composite silica xerogels were prepared via acid catalysed sol–gel route using tetraethoxysilan (TEOS) as silica precursor, and 1-butyl-3-methylimidazolium tetrafluoroborate [BMIM][BF4] or 1-butyl-3-methylimidazolium chloride [BMIM][Cl] ionic liquids, used simultaneously as co-solvents, catalysts and pore templates, at various IL-to-silica ratios. Morphology of the xerogels prepared using the different IL templating agents were investigated using scanning electron microscopy (SEM), nitrogen sorption and small angle neutron scattering (SANS). The thermal behavior of the composites was analyzed by thermal gravimetry, whereas the compositions were checked by infrared spectroscopy and EDX. The differences in the morphology and thermal behavior of the composites due to the different IL additives were revealed.

Ultrablack Poly(vinyl alcohol)‐Graphite Composite Xerogel with Vertically Arranged Pores for Highly Efficient Solar Steam Generation and Desalination

Ultrablack materials have attracted wide attention due to their high light absorbance and efficient photothermal conversion used in the field of solar steam generation to alleviate the drinking water crisis. Herein, ultrablack and low‐cost poly(vinyl alcohol)‐graphite composite xerogels (PGCXs) that have vertically arranged pores and high thermal conductivities are fabricated. The PGCX‐50% shows high light absorbance (95.44%), good wettability, and a water evaporation rate of 1.24 kg m−2 h−1 under 1 sun illumination when coupled in a two dimensional (2D) evaporator. To further improve the solar steam generation performance, the PGCX‐50% is switched to a three dimensional (3D) evaporator by rotating it. Under 1 sun illumination, the 3D evaporator has a highest water evaporation rate of 3.80 kg m−2 h−1, which is 3.07 times that of the 2D evaporator, due to its larger evaporation area and higher surface area at subambient temperature. Finally, a heatsink‐like 3D evaporator is designed and a water evaporation rate of up to 9.54 kg m−2 h−1 is achieved when coupled with wind energy. The high water evaporation rates of the PGCX even in concentrated brines ensure its great potential for drinking water production and seawater desalination.

Influence of Evaporation Drying on the Porous Properties of Carbon/Carbon Composite Xerogels.

Carbon/carbon (C/C) composite xerogels dried by evaporation were prepared in this study to observe the change of their porous properties and their morphology by nitrogen sorption apparatus and a scanning electron microscope. Resorcinol and formaldehyde (RF) sols as a matrix phase and cotton fibers (CF) as a dispersed phase were mixed and gelated to be CF/RF composite hydrogels. The composite hydrogels were exchanged by t-butanol (TBA), dried by evaporation at 50 °C, and carbonized at 1000 °C to become the C/C composite xerogels. The results show that the CF addition does not decrease the mesoporous properties of the C/C composite xerogels. Moreover, the CF addition can alleviate the pore shrinkage, and it can maintain the mesopore structure. The mesopore size and the micropore size of C/C composites are insignificantly changed because the CF addition and the solvent exchange using TBA may suppress the pore shrinkage despite the gas-liquid interface existing during the evaporation drying.

Photothermal polymethylsilsesquioxane-vinyltrimethoxysilane-polypyrrole xerogel for efficient solar-driven viscous oil/water separation through one-pot synthesis route

Increasing oil spill accidents and oil industrial wastewater have led to the frequent occurrence of oily contaminants. To remedy these environmental risks, separating oil/water mixtures by absorbent materials has shown great potential. However, viscous oils are difficult to clean up with conventional materials because of their high viscosity with respect to practical applications. A photothermal (PMSQ)-vinyltrimethoxysilane (VTMS)-polypyrrole (PPy) xerogel was fabricated to heat the viscous oil by utilizing the photothermal property of PPy. The chemical structure and micronano morphology of the obtained composite xerogel were confirmed by Fourier transform infrared spectroscopy, scanning electron microscopy, and contact angle goniometry. Experiments of oil adsorption show that the PMSQ-VTMS-PPy xerogel could be applied for viscous oil/water mixture separation, exhibiting excellent properties such as water-repellency, high oil/water separation capacity, adequate buoyancy, good reusability, and easy fabrication. Such a remarkable performance of the PMSQ-VTMS-PPy photothermal xerogel is caused by the fact that crude oil could be heated by harvesting sunlight to reduce the viscosity of oil and achieve the goal of rapidly separating the oil/water mixture. Because of the facile and scalable merits, the one-pot sol–gel method presented is very suitable for industrial uses.

Hydrophobic and heat-resistant poly(methylphenylsiloxane)-modified resorcinol–formaldehyde composite xerogel monoliths and the carbonized derivatives

Resorcinol–formaldehyde (RF) aerogels are widely used as thermal insulation materials. The present investigation of RF aerogels emphases on improving hydrophobic property and high-temperature residual yields. In this study, polysiloxane-modified RF composite xerogel monoliths were prepared by gelation of poly(methylphenylsiloxane) prepolymer with RF in cosolvent and ambient pressure drying. The influence of phenyl content on structure and thermal property of xerogels was investigated. The as-prepared RF composite monoliths were lightweight and hydrophobic with density lower than 0.300 g/cm3 and water contact angles approaching 130°. Morphology analyses indicated that polysiloxane grew and formed a continuous layer on RF porous skeleton with controlled reaction parameter. Thermogravimetry analyses (TGA) certified that the controlled incorporation of polysiloxane in composite xerogels enhanced the thermal degradation temperature at which the weight loss of RF xerogels reaches 5% (T5%) and increased the residual yields at 1000 °C. The carbonized derivatives were obtained for further enhancing the thermal stability by removal of small molecules during carbonization. Xerogel monoliths preserved hydrophobic property till 500 °C carbonization due to the thermal stability of poly(methylphenylsiloxane). The heat-resistant composite xerogels remained monolith structure after 800 °C treatment under nitrogen condition.

Ultrafast, Highly Sensitive, and Selective Detection of p-Xylene at Room Temperature by Peptide-Hydrogel-Based Composite Material

A peptide/carbon dot (CD) composite xerogel is used as a selective p-xylene VOC (volatile organic compound) sensor. The fiber formation by the peptide allows us to attain a semiconducting property,...

Characterization and thermal conductivity of cellulose based composite xerogels

This article is based on the elaboration of different combinations of cellulose based xerogel, derived from orange trees, while incorporating mineral and organic fillers such as cellulose nanocrystals (CNC) or olive pomace for a potential use in the field of thermal insulation. The main objective of this study is the creation of an insulating material with developed thermal properties and low thermal conductivity λ by referring to the evaporation technic, while using the technic of the hot plate evolving in a non-stationary regime, which allow developing a simple and inexpensive method with fillers (organic and inorganic) leading to xerogels with higher thermal properties. In addition, a characterization system incorporated in analytical technics such as X-ray diffraction (XRD), scanning electron microscopy (SEM) or optical microscope can highlight the morphological and structural properties, which allow showing a certain alliance between the morphological and geometrical characteristics of the fillers and the control of physical, thermal properties of the xerogels.

Thermal activation of charge carriers in ionic and electronic semiconductor β-AgIVVO3 and β-AgIVVO3@VV 1.6VIV 0.4O4.8 composite xerogels.

Silver vanadium oxide (SVO) and Silver Vanadium Oxide/Vanadium Oxide (SVO@VO) composite hydrogels are formed from the self-entanglement of β-AgVO3 nanoribbons and slightly reduced vanadium oxide (VO) (VV1.6VIV0.4O4.8) nanoribbons; respectively. Starting from randomly distributed nanoribbons within hydrogels, and after a controlled drying process, a homogeneous xerogel system containing tuneable SVO : VO ratios from 1 : 0 to 1 : 1 can be obtained. The precise nanoribbons compositional control of these composite system can serve as a tool to tune the electrical properties of the xerogels, as it has been demonstrated in this work by impedance spectroscopy (IS) experiments. Indeed, depending on the composition and temperature conditions, composite xerogels can behave as electronic, protonic or high temperature ionic conductors. In addition, the electric and protonic conductivity of the composite xerogels can be enhanced (until a critical irreversible point), through the temperature triggered charge carrier creation. As concluded from thermogravimetry, IR, UV-Vis and EPR spectroscopy studies, besides the SVO : VO ratio, the thermal induced oxidation/reduction of V5+ to V4+, and thermally triggered release of strongly bonded water molecules at the nanoribbon surface are the two key variables that control the electric and ionic conduction processes within the SVO and composite SVO/VO xerogels.