Synthesis of sustainable silica xerogels/aerogels using inexpensive steel slag and bean pod ash: A comparison study

Research on the Properties of Steel Slag with Different Preparation Processes

To promote the resource utilization of steel slag and improve the production process of steel slag in steelmaking plants, this research studied the characteristics of three different processed steel slags from four steelmaking plants. The physical and mechanical characteristics and volume stability of steel slags were analyzed through density, water absorption, and expansion tests. The main mineral phases, morphological characteristics, and thermal stability of the original steel slag and the steel slag after the expansion test are analyzed with X-ray diffractometer (XRD), scanning electron microscope (SEM), and thermogravimetric analysis (TG) tests. The results show that the composition of steel slag produced by different processes is similar. The main active substances of other processed steel slags are dicalcium silicate (C2S), tricalcium silicate (C3S), CaO, and MgO. After the expansion test, the main chemical products of steel slag are CaCO3, MgCO3, and calcium silicate hydrate (C-S-H). Noticeable mineral crystals appeared on the surface of the steel slag after the expansion test, presenting tetrahedral or cigar-like protrusions. The drum slag had the highest density and water stability. The drum slag had the lowest porosity and the densest microstructure surface, compared with steel slags that other methods produce. The thermal stability of steel slag treated by the hot splashing method was relatively higher than that of steel slag treated by the other two methods.

Amino-terminated SiO2-Al2O3 composite aerogels from fly ash for improved removal of Cu2+ and Pb2+ ions in wastewater: one-pot synthesis, excellent adsorption capacity and mechanism

In this study, by using a sol-gel grafting-atmospheric drying method, amino-terminated SiO₂-Al₂O₃ composite aerogels, namely 3-aminopropyltriethoxysilane (APTES) or 3-(2-amino-ethoxy) propylmethyldimethoxysilane (AEAPMDS) modified SiO₂-Al₂O₃ aerogels (AMSAAs), were synthesized from the fly ash and characterized by field-emission scanning electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy etc.. And the AMSAAs were verified as excellent adsorbents for removing heavy metal ions (Cu²⁺ and Pb²⁺ ions) from wastewater. The effects of modification conditions and testing parameters including pH value, adsorbent dose, initial ions concentration, adsorption time and temperature were systematically investigated. Results demonstrated that 0.2 mol/L APTES modified aerogels (0.2APTES-SAAs) possessed the best adsorption properties. Under the optimal pH value of 4.0-6.0 and the adsorbent dose of 0.4-0.6 g/L, the equilibrium adsorption capacities of Cu²⁺ and Pb²⁺ ions were as high as 195 mg/g and 500 mg/g within 20-30 min, respectively. The adsorption processes were agreed fairly well with Freundlich isotherm adsorption model and the pseudo-second-order kinetic model, which indicated that the adsorption processes were heterogeneous multilayer adsorption and controlled by the chemical reaction between AMSAAs and heavy metal ions. The obtained adsorption thermodynamic parameters (ΔH°, ΔS° and ΔG°) revealed that the adsorption processes were exothermic and spontaneous with decreased randomness at the solid-liquid interface. The excellent recyclability of as-prepared AMSAAs proved as economically promising adsorbents for practical applications.

Immobilization of Lipase from Candida antarctica B (CALB) by Sol-Gel Technique Using Rice Husk Ash as Silic Source and Ionic Liquid as Additive

This work presents the immobilization in situ of commercial lipase from Candida antarctica B (CALB) by the sol-gel technique (xerogel) using silica from rice husk ash (RHA) as a source of silicon. It was used the Ionic Liquid (IL) 1-octyl-3-methylimidazolium bromide (C8MI.Br) as additive. The immobilized derivatives were characterized per SEM, XRD, and per method BET. The enzymatic activity of xerogels was evaluated with different tests, these being the reactional thermal analysis, immobilization yield, and operational and storage stability. The XDR showed that the obtained xerogels have halos in the region between 15 and 35° (2θ) what characterizes it as amorphous materials. The SEM analysis of xerogel shows irregular particles with dimensions less than 20 μm. The immobilized presented an esterification activity (EA) with 263.2 and 213.8 U/g, with and without IL, respectively, higher than the free enzyme (169.6 U/g). The immobilized, with and without IL, presented a significant improvement in the activity performance in relation to free enzyme for the three reactional temperatures (40, 60, and 80 °C) evaluated. The operational stability demonstrated that is possible to use xerogel without ionic liquid for 17 recycles and 21 recycles in IL presence. This methodology allows the preparation of new highly active and selective enzyme catalysts using the rice husk ash as a source of silicon, and the ionic liquid [C8MI]Br as additive. Furthermore, the new materials can provide greater viability in the processes, ensuring longer catalyst life.

Insights into the Role of Biopolymer-Based Xerogels in Biomedical Applications

Xerogels are advanced, functional, porous materials consisting of ambient, dried, cross-linked polymeric networks. They possess characteristics such as high porosity, great surface area, and an affordable preparation route; they can be prepared from several organic and inorganic precursors for numerous applications. Owing to their desired properties, these materials were found to be suitable for several medical and biomedical applications; the high drug-loading capacity of xerogels and their ability to maintain sustained drug release make them highly desirable for drug delivery applications. As biopolymers and chemical-free materials, they have been also utilized in tissue engineering and regenerative medicine due to their high biocompatibility, non-immunogenicity, and non-cytotoxicity. Biopolymers have the ability to interact, cross-link, and/or trap several active agents, such as antibiotic or natural antimicrobial substances, which is useful in wound dressing and healing applications, and they can also be used to trap antibodies, enzymes, and cells for biosensing and monitoring applications. This review presents, for the first time, an introduction to biopolymeric xerogels, their fabrication approach, and their properties. We present the biological properties that make these materials suitable for many biomedical applications and discuss the most recent works regarding their applications, including drug delivery, wound healing and dressing, tissue scaffolding, and biosensing.

Modeling and Optimization of β-Galactosidase Entrapping in Polydimethylsiloxane-Modified Silica Composites

Protein entrapment has multiple applications in enzymatic hydrolysis, drug delivery, etc. Here, we report the studies that successfully utilized the Box–Behnken design to model and optimize the parameters of β-galactosidase entrapment in sol–gel-derived silica composites. We have also demonstrated the influence of polymer–polydimethylsiloxane as a composite modifying agent on the activity of entrapped enzymes. We have determined how different sol-gel process parameters influence the activity of entrapped enzymes. The highest impact on β-galactosidase activity was exerted by the water:tetramethoxysilane ratio, followed by polydimethylsiloxane content. Optimized synthesis parameters have been utilized to obtain a composite with maximum β-galactosidase activity. Performed porosity studies have shown that the addition of polydimethylsiloxane increased the pore diameter. Microscopy studies demonstrated that polydimethylsiloxane-modified composites are softer and less rough. Studies of β-galactosidase activity using the o-NPG test showed statistically significant shifts in the enzyme temperature and pH profiles compared to the soluble form. An improvement in the reusability of the enzyme and a significant increase in the thermal stability was also observed. When lactose was used, a strong correlation was observed between the substrate concentration and the type of the catalyzed reaction. Moreover, we have demonstrated that the yields and rates of both lactose hydrolysis and galactooligosaccharides formation were correlated with reaction temperature and with the presence of polydimethylsiloxane. All these findings provide the opportunity for industrial use of optimized PDMS-modified silica composites in lactose elimination from dairy products, e.g., milk or whey.

Research progress and applications of silica-based aerogels - a bibliometric analysis

Silica aerogels are three-dimensional porous materials that were initially produced in 1931. During the past nearly 90 years, silica aerogels have been applied extensively in many fields. In order to grasp the progress of silica-based aerogels, we utilize bibliometrics and visualization methods to analyze the research hotspots and the application of this important field. Firstly, we collect all the publications on silica-based aerogels and then analyze their research trends and performances by a bibliometric method regarding publication year/citation, country/institute, journals, and keywords. Following this, the major research hotspots of this area with a focus on synthesis, mechanical property regulation, and the applications for thermal insulation, adsorption, and Cherenkov detector radiators are identified and reviewed. Finally, current challenges and directions in the future regarding silica-based aerogels are also proposed.

Silica aerogels are three-dimensional porous materials that were initially produced in 1931. During the past nearly 90 years, silica aerogels have been applied extensively in many fields.

A Comprehensive Review of Synthesis, Applications and Future Prospects for Silica Nanoparticles (SNPs)

Silica nanoparticles (SNPs) have shown great applicability potential in a number of fields like chemical, biomedical, biotechnology, agriculture, environmental remediation and even wastewater purification. With remarkably instinctive properties like mesoporous structure, high surface area, tunable pore size/diameter, biocompatibility, modifiability and polymeric hybridizability, the SNPs are growing in their applicable potential even further. These particles are shown to be non-toxic in nature, hence safe to be used in biomedical research. Moreover, the molecular mobilizability onto the internal and external surface of the particles makes them excellent carriers for biotic and non-biotic compounds. In this respect, the present study comprehensively reviews the most important and recent applications of SNPs in a number of fields along with synthetic approaches. Moreover, despite versatile contributions, the applicable potential of SNPs is still a tip of the iceberg waiting to be exploited more, hence, the last section of the review presents the future prospects containing only few of the many gaps/research extensions regarding SNPs that need to be addressed in future work.

Aerogels as promising materials for antibacterial applications: a mini-review

The increasing cases of bacterial infections originating from resistant bacteria are a serious problem globally and many approaches have been developed for different purposes to treat bacterial infections. Aerogels are a novel class of smart porous materials composed of three-dimensional networks. Recently, aerogels with the advantages of ultra-low density, high porosity, tunable particle and pore sizes, and biocompatibility have been regarded as promising carriers for the design of delivery systems. Recently, aerogels have also been provided with antibacterial activity through loading of antibacterial agents, incorporation of metal/metal oxides and via surface functionalization and coating with various functional groups. In this mini-review, the synthesis of aerogels from both conventional and low-cost precursors is reported and examples of aerogels displaying antibacterial properties are summarized. As a result, it is clear that the encouraging antibacterial performance of aerogels promotes their use in many antibacterial applications, especially in the food industry, pharmaceutics and medicine.