2.1. Sulfonic acid-functionalized silica X-G for the selective adsorption of trace gaseous ammonia from air
Inherently toxic and gaseous corrosive ammonia (NH3) exhibit critical health and environmental challenges. Nevertheless, elimination of low level of NH3 from air is still a daunting task. Thus, in a work, a SO3H-functionalized silica X-G herein referred as MPTS-X with outstanding porous architectural stability and plentiful Bronsted acid sites was constructed, whereas its physicochemical attributes and adsorption behavior for NH3 were examined systematically [6]. Experiments involving static adsorption revealed that the MPTS-1.0 exhibited elevated NH3 adsorption capacity of 4.02 mmol⋅g−1 at 0.1 bar and 7.00 mmol⋅g−1 at 1.0 bar, much more elevated in comparison with MPTS-0 (3.19 and 1.95 mmol⋅g−1). Summarily garnered results as depicted in Figure 2, revealed that MPTS-1.0 has remarkable adsorption selectivity, as dynamic adsorption and field test revealed that MPTS-1.0 could rapidly capture trace NH3. Hence, this appraisal potentially offers a feasible route of fabricating adsorbents for the elimination of gaseous ammonia from air [6].
2.2. Influence of pH on bio-induced fabrication of L-Lysine bioactive glass (LBG) hybrid xerogels (X-Gs) for customized textural and rheological properties
The influence of pH on bio-induced fabrication of hybrid LBG X-Gs for bespoke textural and rheological properties has been investigated [7]. Herein, customized mesoporous hybrid LBG X-Gs has been synthesized via bioinspired strategy at ambient environment. L-lysine molecular entities were inculcated within bioactive glass (BG) architecture via physiochemically affiliated interaction. Nitrogen sorption examination affirmed the mesoporous stature of all four LBG X-Gs with differing pore size, volume as well as surface area as depicted in Figure 3 [7].
These new genre of material is anticipated as potential for service nutrients for cell development and also is constituted of customized textural and rheological behaviors for specific bone engineering applications.
2.3. Fabrication of corn starch@Hemp X-Gs for phyto-pharmaceutical applications
In a work, supercritical CO2 was utilized as an ecobenign medium for differing procedure vis-a-viz starch gel drying, supercritical extraction from hemp seed flour (SCE process), hemp seed oil (HSO) impregnation (SCI process), as well as integrated procedure for hemp seed flour (HSF) extraction as well as starch gels impregnation (SCE-SCI process) for development of added-value materials capable of being utilized as phyto-pharmaceuticals. Starch A-Gs optimization was conducted by temperature variation (35 and 45 °C) and pressure (8, 10, and 20 MPa), so as to garner materials with elevated porosity, capable of facilitating maximal inclusion capacity for hemp seed extracts. It was displayed that parameters of starch gel drying remarkably affected material morphology as function of A-G inclusion level as depicted in Figure 4 [8].
These critical fatty acids have advantageous health benefits like cardiovascular protection against neurodegenerative as well as inflammatory infections [8].
2.4. Fabrication and characterization of CaF2@Tb3+@silicon-oxygen X-G
In an investigation, Tb3+@CaF2 (CaF2: Tb3+) nanoparticulates underwent synthesization with the silylant entity synthesized from meta-aminobenzoic acid and 3-isocyanatopropyltriethoxysilane as the surface modifying entity. The prepared nanoparticulates underwent covalent bonding to silicon-oxygen architecture through sol-gel procedure with tetraethyl orthosilicate (TEOS) as the precursoral entity, resulting in chemically bonded hybrid X-G. Chemically doping these nanoparticulates facilitates the even dispersion with the stabilized hybrid structure [9].
2.5. Carbon X-G microporous architecture
The atomic model of carbon X-G microporous architecture underwent reconstruction using a modified virtual porous carbon (VPC) model as presented in Figure 5.
Here, the physical factors of the reconstructed model, specifically the forecasted nitrogen adsorption isotherm, aligns properly with the experimental data. Furthermore, the gas adsorption as well as diffusion within the carbon X-G microporous architectures are studied at the pore-level. Garnered results depict that the reduction of isos-teric adsorption heat as well as the excessive adsorption within the carbon X-G microporous architecture are mainly contributed by adsorbates desorption within the ultra-micropores with incremental temperature. The microporous architecture appears sensitive selective for oxygen within air, as a result of the influence of molecular sieving as well as the elevated solid-fluid interactivity within the pore wall along with oxygen. Thus, as desorption of oxygen within the ultra-micropores as a result of inherently escalating steric repulsion with increasing temperature from 298 K to 573 K, the selectivity of microporous architecture for oxygen minimizes, hence the gap within isosteric adsorption heat for nitrogen and oxygen is minimized [10].
2.6. Resorcinol-oriented carbon X-G@ZnO nanoarchitecture for solar-light propelled sulfamerazine photo-degradation
In recent times, antibiotics releasing, such as sulfonamides within the surroundings has propelled remarkable interests because of the prospect of forming antibiotic-inhibitive bacteria. Hence, the fabrication of remediation strategies for effluents constituting of this entities is of paramount imperativeness. Thus, in a work, a resorcinol-premised carbon X-G@zinc oxide photocatalyst (XC@ZnO) was constructed for the efficient promotion of the photo-degradation of the antibiotic referred to as sulfamerazine in aqueous media [11]. Results garnered from photocatalytic examination under simulated solar radiation reveal that the fabricated composites are superiorly to pristine oxide in sulfamerazine photo degradation, as all fabricated XC@ZnO attained elevated reaction rate constants (kapp) in comparison with pristine ZnO. Hence, postulated modification was good in successfully enhancing aqueous media photo-degradation of sulfamerazine, thereby proving viability of fabricated composites for photocatalytic uses [11].
2.7. Fabrication of zirconium-organic X-G
There prevails a daunting tasks of developing some solid-state proton conductive entities exhibiting elevated conductivity not only at elevated operating temperatures (>353 K) but at commencement temperature and also in cold climates sub-zero temperature (<273 K) or at elevated-altitude drones. Thus, in a work, a set of zirconium-organic xerogels (Zr@Fum-X-G) exhibiting porosity along with defectivity, facilitated by N2 sorption, thermogravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS), displaying elevated anhydrous proton conductivity across temperature range of 233 to 433 K as depicted in Figure 6 [12].
Garnered results further reveal that zirconium-organic X-Gs exhibiting remarkable conductivity is further utilize as impedance sensor for formic acid [12].
2.8. Zirconium oxy-chloride@ammonium phosphate X-G
The kinetics of Cd (II) ions adsorption along with adsorption of Cd (II) ions relative to pH on the hydrothermally modified Zr-phosphate specimens have been examined [13]. Zr-phosphate was prepared utilizing Zr-oxy-chloride and ammonium phosphate as elucidated in Figure 7 [13].
The hydrothermally inclined functionalization was conducted utilizing dried X-G of Zr-phosphate at temperatures of 150, 200 and 250 °C respectively. Here, the hydrothermal functionalization escalated the specific surface area, the mesoporous composition as well as facilitation of greater acidic sites at the surface. Studies of Cadmium ions adsorption upon these adsorbents revealed complete elimination of Cd (II) from the aqueous solutions with an initial concentration of ≤0.0001 mol dm−3 and a pH> 3 in a short duration [13].
2.9. Development of Xerogel pill with outstanding swallowing behavior
A new dosage formed with dose-control as well as swallow-facilitating functions, referred as “Xerogel pills,” underwent fabrication for pediatric or geriatric patients. X-G pills is a versatile dosage form where one dose is pieced into multiple pills which are double-architectured miniature spheres possessed of interior and an exterior dried-gel layer (X-G shell) [14]. Here, the fabrication strategy (formulation and procedure) of the X-G pills was initiated through utilization of a synergy of wet-milling as well as drop freeze-drying (DFD) approaches as depicted in Figure 8 [14].
However, it was opined that further enhancements of physical strength as well as drug composition evenness is essential to inculcate the XG pills for practical application [14].
2.10. Magnetic sensitive mesoporous alginate@β-cyclodextrin polymeric X-G
In a study, mesoporous (~7–8 nm) biopolymeric HDG beads referred as HNTs-FeNPs@Alg/β-CD underwent synthesization through ionic polymerization pathway to differentiate heavy metallic ions as depicted in Figure 9 [15].
HNTs-FeNPs@Alg/β-CD nanocomposites adsorption capacity was more elevated in comparison with pristine halloysite nanotubes (HNTs), iron nanoparticles (FeNPs), and virgin alginate beads. Here, it was shown that not only chemo-sorption but also physisorption acted as the sorption mechanism. Miniaturization of the porosity, surface area, as well as pore volume of expended adsorbent, in addition, results garnered from sorption examination, affirmed that pore filling as well as hyper-particulate diffusion functioned significantly in elimination of heavy metals [15].
2.10. Construction of Polyaniline (PANI)@Carbon Xerogel (C-X) nanocomposite as supercapacitor electrode
In a novel work, PANI@C-X nanocomposites having varying mass ratios was constructed [16]. Here, influence of PANI concentration on porosity as well as electrochemical behavior of the nanocomposites were examined. Surface examination of specimens revealed that PANI inclusion within CX architecture minimized its specific surface area with a concurrent expansion of the average pore diameter from the microporous to the mesoporous range as depicted in Figure 10 [16].
Supercapacitor electrodes usage, and their electro-capacitive behavior examination reveal that PANI inclusion within CX architecture enhanced the gravimetric capacitance from 156 to 612 F∙g−1 at current density of 0.1 A∙g−1 with satisfactory stability whereby, nanocomposite of PANI:CX = 5:1 w/w exhibited a retention percentage of 87.6% post 1500 repetitive cycles. Generally, the synergy between PANI and CX is ascribed to fabrication of meso-porosity as well as the decrement in electrode resistance [16].
2.11. Silica@epoxy@corn stalk ash nanocomposite X-G for thermal and acoustic insulation
Synthesization of silica@epoxy@corn stalk ash nanocomposite X-G in ambient pressure drying was conducted via sol-gel strategy as depicted in Figure 11 [17].
The even distribution of silica X-G in pristine ER was reported excepting nanocomposite including 1.5 wt. % silica X-G. The low density nanocomposites exhibited elevated heat stability as well as low heat conductivity [17]. The nanocomposites acoustic velocity minimized with escalating inclusion of silica X-G. The nanocomposites water sorption was slightly elevated in comparison with pristine ER. This research offered a novel heat and acoustic insulation material as alternative to the health risking conventional materials [17].
2.12. Fabrication and properties of Cork@silica X-G nanocomposites
Ecobenign nanocomposites underwent synthesization from a silica precursoral entity and cork under mild situations and dried at atmospheric pressure as presented in Figure 12 [18].
As a result of covalent bonding between the component entities, these CorSil nanocomposites were uniform, light with machinability disposition, exhibiting Shore D hardness of about 67 with compressive strength of about 22.6 MPa thereby positioning them as good alternatives for wood, as well as other naturally occurring products, and other thermoplastic polymeric matrices, with fire inhibitive behavior [18].
2.13. PANI@layered vanadium oxide X-G hybrid nanocomposites
PANI@layered vanadium oxide X-G hybrid nanocomposites referred as PV@X-G hybrid nanocomposites have undergone successful synthesization through a simplified hydrothermal strategy as depicted structurally in Figure 13 [19].
FESEM images showcase that the fiber and rod shaped PV@X-G hybrid nanocomposites surface morphology were tailored through control of the relative concentration between PANI and peroxovanadic acid solution resulting in the formation of a V2O5·nH2O X-G. Results garnered from FTIR and XPS spectra affirm the creation of PV@X-G hybrid nanocomposites, with prevalence of PANI and water molecular entities within the nanocomposites and partial minimization of V5+ to V4+., which agree well with XRD results. XPS spectra analysis also reveals the relative contents of V5+ and V4+ in both composites. UV-Vis spectra further affirms these nanocomposites formation. Results garnered from HRTEM image affirms the growth direction of formed nanorods along 〈00l〉 [19].
2.14. Fe(acac)3@SiO2 @PVA hybrid X-G superparamagnetic nanocomposites
In previous decades, nanotechnologies had attained high success in fabrication and characterizing of magnetic nanocomposites with customized properties, capable of being utilized in versatily in as drug/gene delivery, bioseparation, magnetic resonance imaging, hyperthermia and as catalysts in chemical synthesization [20-23].
Thus, in a study, Fe(acac)3@silica@PVA hybrid X-G nanocomposites were garnered acid catalysed sol-gel strategy using uniform mixture of iron(III) acetylacetonate (Fe(acac)3), tetraethylorthosilicate (TEOS), and polyvinyl alcohol (PVA). Premised on thermal examination, the thermal disposition of both X-G specimens were unveiled and facilitated the selection of optimal calcination temperatures so as to garner iron oxide silica magnetic nanocomposite specimen [24]. The TEM images of specimen N-0 devoid of PVA heated at varying temperatures are presented in Figure 14 [24].
2.15. Characterization and fabrication of silica@chitosan@TCP X-G nanocomposites for bone regeneration
Silica@biopolymeric X-G nanocomposites are very enchanting platforms for varying emerging biomedical uses, especially for bone mending. The inclusion of calcium phosphates within the hybrid architecture facilitates development of implants with enchanting biological properties. Hence, in a work, silica@CS@tricalcium phosphate (TCP) X-G, where garnered from the sol-gel procedure facilitated by ultra-sound probe [25]. Advanced technique of osteoblasts to biomaterial is seen with time, whereas the X-G surface is barricaded with cells close together and to the material surface. Post one week, mature focal adhesions, well-fashioned stress fibers, and cell-to-cell contacts were prevalent (Figures 15 a–c). Post 72 h, the actin stress fiber pattern turns to periphery, and post 1 week, cells appeared to barricade the surface though devoid of the significant prevalence of mature focal adhesions (Figure 16) [25].
2.16. Fabrication of 3-D hollow cellulose X-G nanocrystals
Cellulose nanocrystals (CNCs), have been investigated as nanofillers for nanocomposites because of their inherent enchanting behaviors, including elevated aspect ratio, superior mechanical attributes, low density and low coefficient of thermal expansion [26]. Thus, in a work, complex 3-D architectures as pseudo-catenoid hollow X-G with well-arranged CNCs were fabricated from dynamic hydrogels (HDG) through mechanical stretching as well as air-drying procedure [26]. Garnered results offer a novel perspective for development and construction of advanced materials with enhanced mechanical properties and multifunctionalities [26]. A common instance of catenoid in our daily life is the soap bubble between two open rings (Figure 17a). On elimination of gravity and in comparison with surface tension, this geometry can be perceived as ideal catenoid, which is mainly propelled by the liquid system surface tension [26].
During the dynamic HDG stretching procedure, the tensile stress sharply escalated up to λ = 3 while slowly increasing with elevated λ (Figure 18 a, b) [26]. Furthermore, the subsequent air-drying procedure further enhanced the CNCs orientation within the polymeric matrix. From Figure 17c, the HDG tube of PC1/10 post mechanical stretching presented light yellow interference color between the crossed polarizers. From Figure 18 (d, e), the PC architectures displayed elevated angle dependence within the diffraction patterns through escalating the elongation ratios from 1 to 10 [26].
From Figure 19 (a, b) the ultimate fracture forces of the PC X-G devoid of CNCs or with 2 wt. % CNCs sharply decremented with incremental λ. When λ = 1 and 2, the ultimate fracture force of the PC X-G was not remarkably influenced by the CNCs composition (Figure 19 a, b, d), revealing the function of geometry within X-G tubes garnered with low elongation ratios thereby reinforcing the mechanical attributes of the X-G, while switching the plastic rupture to brittle rupturing mode, as presented in Figure 19 b. Specifically, CNCs effectively enhanced the ultimate fracture force in the stretched PC X-G with λ = 5 or 10 (Figure 19 d), but small improvement in the short X-G tubes (λ = 1, 2) [26].
Herein, finite element analysis was utilized for elucidation of the stress distribution and deformation of varying specimens. From Figure 19 b-c, the catenoid specimens could eliminate the stress concentration in local zone in comparison with cylindrical specimens, endowing the catenoid samples with higher elongation at break and better energy dissipation ability. This result also can be demonstrated by mechanical test. As shown in Figure 19 d, the cylindrical X-G with/without CNCs displayed elevated ultimate fracture forces in comparison with PC. Besides, the cylindrical X-G devoid of CNCs presented the typical yield point prior its complete breakage, as presented in Figure 19e [26].
These results are guideline for designing and construction materials with targeted architectures and functions, like construction, shock absorption, and so on [26].
2.17. Fmoc-FF and cationic peptides multicomponent X-G matrices for tissue engineering
In region of supramolecular chemistry, peptide-oriented materials represent progressive multifunctional biotechnological tool, with enchanting applications in healthcare, optoelectronics, diagnostics, green chemistry and energy harvesting [27]. Peptide-oriented HDG (P-HGs) are amongst the versatile set of peptide-oriented materials, which are specially recognized. P-HGs exhibit a 3-D architecture similar to polymeric HDG. However, such final conformation is achieved as a consequence of a peculiar multiscale aggregating process, which involves supramolecular interactions between nano-helices or nanofibers, generated by self-assembly of the peptide sequences. Most importantly, the formation of these matrices does not require the employment of biologically toxic cross-linking agents. Further benefits of P-HGs include reproducibility, transparency, injectability, and easy cellular harvesting [27].
Thus, in previous decades, peptide-oriented HDG are incrementally being utilized as appropriate matrices for biomedically and pharmaceutically affiliated uses like drug conveyance and tissue engineering. Hence, recently, synthesization and gelation attributes of a miniaturized collection of cationic peptides, composed of a Lys residue at the C-terminus and attained with an Fmoc entities or with the fluorenyl methoxycarbonyl-diphenylalanine (FmocFF) at the N-terminus were garnered. Here, it is shown that the synergy of these peptides with hydro-gelator FmocFF, in differing weight/weight ratios, facilitates the garnering of seven novel self-sorted HDG, sharing similar peptide arrangements of their supramolecular matrices [27]. Selected immunofluorescence images and micrographic images of all the seven matrices are presented in Figure 21 [27].
Micrographic images reveal that the mixed HGs are composed of long fibrils, involved in a mutually physically aligned entanglement. Nevertheless, it is essential to recognize that, for Fmoc-K1, Fmoc-K2, and Fmoc-K3, fibers appeared highly apparent and defined in mixed HDG relative to the corresponding virgin ones [27]. CR birefringence microscopic examination was conducted so as to understand the nature of the fibrillary agglomerates. Selected images of CR stained X-G are reported in second (bright field) and third (polarized light) rows of Figure 21 [27].
Amongst all the multi-part peptide@HGs, CR display birefringence showing that the layered matrices display two refractive indices based on their orientation under polarized light. The 2-D WAXS data for Fmoc-K and FmocFF-K series and their corresponding 1-D profiles are displayed in Figures 22 and 23, respectively. The 2-D data of the FmocFF@Fmoc-K1 fiber (Figure 22a) display varying continual diffraction rings, revealing the absence of distinctly preferred alignment within the illuminated fibrous volume. Contrarily, the 2-D WAXS data of other fibers composed of Fmoc-K2 (Figure 23b) and Fmoc-K3 (Figure 23c) display a developing part fibrous disposition [27].
2.18. Carrageenan@gelatin HDG with multi-walled carbon nanotubes molecular architectural modulation and mechanical properties
HDG, 3-D hydrophilically inclined water-insoluble polymeric networks exhibiting mechanical attributes typical of solids, have garnered continual interests over a long period of time. Hence, in a work, the architecture and properties of HDG premised on gelatin@carrageenan@CNTs nanaocomposites have been studied [28]. Here, it was reported that the inculcation of polysaccharides and proteins within the composite HDG resulted in the repression of their single architectural features as well as homogenization of two macromolecular entities within a singular architectural formation.
In accordance with powder X-ray diffraction data (PXRD), two main parts, CNTs and gelatin, are the weakly ordered structures; the third one, carrageenan, forming a stabilized crystalline phase (Figure 24a). Both specimens in the gel phase are elucidated by similar type of diffraction pattern in form of two strongly broadened amorphous halos (Figure 24b), equivalent to the average interatomic proximity. Regarding to sample drying, the peaks align to a single small wide peak within interval of diffraction angles 10–15 degrees. [29].
Inherently morphological behavior of –carrageenan@gelatin HDG was SEM examined. The SEM images reveal that the specimen is in an even state with a smooth surface (Figure 24c), which is in line with the XRD data (Figure 24a). Here, the images display satisfactory distribution of CNTs within the HDG matrix devoid of any apparent visible aggregation. Additionally, a highly regularized polymeric network with mildly thinner polymeric bundles in the presence of CNTs (Figure 24b) in comparison with virgin carrageenan@gelatin HDG is observed (Figure 24d) [29].
AFM experiments [29] offer direct architectural visualization of polysaccharide protein HDG at the nanometric and elucidated the disposition of the examined architecture in the presence of CNT. Figure 25 (a, c) present the AFM surface images of X-G (dried HDG) films devoid and with CNTs, correspondingly. On drying of –carrageenan@gelatin HDG, essential for the AFM experiment, from (Figure 25 a) the formation of the biopolymeric architecture is observed, referred as the biopolymeric scaffold [29]. For this composite HDG, the fiberous substrate initiating the gel formation are short when compared with those of pristine carrageenan solution (Figure 25 b) with a thickness of about 30 nm. Hence, inculcation of CNTs within the carrageenan-gelatin HDG did not influence the surface morphology of the film surface. The AFM image (Figure 25 c) is comprised of a network architecture of miniaturized aggregates within range of 70–100 nm in size. The AFM revealed that the nanotubes are evenly dispersed, being packed and in wrapping with biopolymeric matrices [29].