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Over twenty million tons of pineapples have been produced annually worldwide, but their waste is mostly discarded or burnt after harvesting. In this work, the high-value added aerogels from the pineapple leaf waste are developed for the first time by using polyvinyl alcohol (PVA) cross-linkers and a cost-effective freeze drying process. The pineapple fibre (PF) aerogels have highly porous structures with the porosities of 96.98–98.85%, ultra-low densities of 0.013–0.033 g/cm3, and hydrophobicity with water contact angles of approximately 140°, after a surface modification with methyltrimethoxysilane (MTMS). The effects of PF concentrations (0.5–2.0 wt.%) on oil and organic solvent adsorption are investigated comprehensively. Experimental results indicate that the hydrophobic PF aerogels can adsorb motor oil up to 37.9 g/g, approximately two times greater than commercial polypropylene and polyurethane sorbents. The pseudo-second order model can provide a good fit for the oild adsorption kinetics of the developed aerogels. [ABSTRACT FROM AUTHOR]

Pineapple has been known as one of the most popular tropical fruits in Vietnam with a production of over 674,000 t in 2018. However, by-products from pineapple cultivation account for approximately 65 % of the fresh fruit weight and are mostly being dumped, decomposed or burnt now. Therefore, it has recently raised great concern about environmental pollution. For the first time, extracted fibres from pineapple leaves being utilized for developing successfully eco-friendly and cost-effective pineapple fibres (PFs) aerogels by using polyvinyl alcohol as a cross-linker and following a freeze-drying method. The morphology of the PFs aerogels can be controlled well by changing the PFs concentration (0.5 - 2.0 wt%). The PFs aerogels exhibit extremely low densities (12.7 - 32.6 kg/m3) and high porosities (96.9 - 98.8 %). The BET result shows that the surface area of the PFs aerogel has up to 5.6 m2/g and their pore size of 1.3 - 2.2 nm. The developed PFs aerogels show extremely low thermal conductivities ranging from 0.030 to 0.034 W/m.K. Due to the low Young's modulus values ranging from 0.47 - 7.86 kPa, the PFs aerogels are flexible and can be used for heat insulation of the buildings as well as food preservation. [ABSTRACT FROM AUTHOR]

Silica aerogels have attracted great attention owing to their outstanding properties such as ultralow density, high porosity, high surface area, and low thermal conductivities. Their poor mechanical properties and hydrophilicity constrain their practical applications. In this work, phenyltrimethoxysilane (PTMS) and polyvinyl alcohol (PVA) were added into methyltrimethoxysilane (MTMS)-based silica aerogels to enhance their mechanical properties. It was found that PTMS considerably improved the hydrophobicity of MTMS silica aerogels with an increase in water contact angles from 115° to 150°. The addition of PVA considerably increased the hardness, morphology, density, porosity, surface area, and thermal conductivity of MTMS silica aerogels. When PVA concentration was increased from 0 to 2 %, the aerogel hardness, density, and thermal conductivity were also increased from 0 to 14 %, 0.072 to 0.11 g/cm³, and 0.035 to 0.046 W/m.K. In contrast, the aerogel became less porous and the porosity reduced from 97.2 % to 95.72 % and BET surface area decreased from 389 to 43 m²/g. [ABSTRACT FROM AUTHOR]

• Functionalized pineapple aerogel can be used for ethylene gas adsorption. • Functionalized pineapple aerogel can be used for nickel ion removal. • Functionalized pineapple aerogel is a promising candidate for heavy-ions removal. • Functionalized pineapple aerogel is a promising candidate for food preservation. Over 27 million tons of pineapples are produced globally annually, from which approximately 76.4 million tons of pineapple leaf by-product waste are generated. Even though the fibers within the pineapple leaves exhibit excellent properties, several efforts to repurpose pineapple leaf wastes have remained lack luster, with most farmers still disposing the waste to landfills or burning them in open fields. This work sets out to transform pineapple leaf fibers extracted from agricultural pineapple leaf waste into highly porous aerogel for high-value engineering applications to enhance the monetary incentive to repurpose agricultural waste. Pineapple aerogels are developed and functionalized with activated carbon and diethylenetriamine for ethylene adsorption and nickel ions removal applications, respectively. The modified aerogels maintain a porous structure with a porosity of 91.1–96.4% and density of 32.2–92.6 mg/cm3. Activated carbon coated pineapple aerogel exhibits excellent ethylene adsorption capability, with a maximum adsorption capacity of 1.08 mmol/g at atmospheric pressure, surpassing those of commercial ethylene absorbents (0.157 mmol/g). While diethylenetriamine coated pineapple aerogel shows its good nickel ion adsorption with maximum adsorption capacity of 0.835 mmol/g, as predicted by the Langmuir-Freundlich isotherm model. The results suggests modified pineapple aerogels are promising candidates for capturing ethylene in food preservation and nickel ions removal in wastewater. [ABSTRACT FROM AUTHOR]

• Advanced fabrication of rubber aerogel via a cost effective and time saving method. • Rubber aerogel has an ultra-low density and a high porosity properties. • Rubber aerogel has a robust mechanical properties with the Young's modulus. • Rubber aerogel can be a potential material for thermal insulation applications. • Rubber aerogel can be a potential material for sound absorption applications. According to the European Waste Codes EWC 19.12.08, fibers from used tires are known as special wastes that must be burned or buried. However, these activities would pose additional risks including soil pollution, and groundwater contamination. Scientists are continually discovering more new ways to recycle these wastes in order to minimize their ecological consequences. Our effort has been also directed into this direction, and we have been able to convert rubber fibers from tire waste into aerogels, an ideal candidate for a wide range of advanced applications due to their low density, high porosity, low thermal conductivity and high sound absorption coefficient. A novel but simple and time-saving strategy to fabricate rubber aerogel from waste tire fibers, derived from car tire wastes, is reported using a freeze-drying process. The obtained rubber aerogel with a robust mechanical performance, exhibiting a Young's modulus up to 965.6 kPa and density 91 mg cm−3, can withstand a large elastic deformation without fracture. In addition, with a highly porous structure (porosity > 90 %) and an ultralight light density (20−91 mg cm−3), our rubber aerogels have a high sound absorption efficiency (noise reduction coefficient, or NRC of 0.56), and a low thermal conductivity (0.035−0.049 W m-1 K-1). These advanced rubber aerogels can be a promising candidate for thermal and acoustic insulation in cabins, vehicles, buildings, and aerospace. [ABSTRACT FROM AUTHOR]

• Magnesium waste is recycled to aerogel to partially solve the environmental problem. • Obtained magnesium hydroxide aerogels possess porous structure with porosity of 94 %. • Low thermal conductivity of 30–42 mW m−1 K−1; high thermal stability of up to 800 °C. • Competitive acoustic insulation capability to others commercial acoustic insulators. The development of magnesium (Mg) production has led to an ever-increasing volume of magnesium waste, with detrimental effects on the environment. Recycling magnesium waste into magnesium hydroxide (MH) aerogels has been successfully developed to partially solve the problem of magnesium waste. The effects of the Mg concentration on the properties of the MH aerogel have been investigated. The MH aerogel exhibits a porous structure with a low density of 0.081–0.150 g cm−3 and a high porosity of 91.5–94.4 %. Its thermal conductivity and stability are evaluated, showing that the MH aerogel has a good thermal insulation capability with a low thermal conductivity of 30–42 mW m-1 K-1, and it is stable up to 800 °C for about 50 % weight loss. In addition, its acoustic absorption performance is also investigated. The MH aerogel performs a good acoustic absorption capability at low frequency, and its noise reduction coefficient indicates that the MH aerogel is a potential competitor to other acoustic insulators. The results demonstrate that magnesium waste can be recycled into a high-value material for thermal and acoustic insulation applications, enhancing the use of environmental wastes. [ABSTRACT FROM AUTHOR]

• Rubber aerogel has been developed by a time-saving and cost-effective method. • Rubber aerogel has ultra-light density and high porosity. • Rubber aerogel is a promising candidate for oil-spill cleaning applications. • Rubber aerogel has higher oil absorption capacity than conventional absorbents. Petroleum spills have been described as one of the leading aquatic disasters that has resulted in the destruction and degradation of marine ecosystems worldwide, destroying the lives of thousands of organisms within a short period. Parts of the causes of this may be linked to waste products from plastics and rubber tires. This study focuses on fibers from rubber tires, and successfully produces rubber aerogels from them using glutaraldehyde and poly(vinyl alcohol) binders, followed by a freeze-drying process. Our recycled rubber aerogels are extremely pore (92.2–98.3 %) and ultra-low density (0.020−0.091 g/cm3). After a methyltrimethoxysilane (MTMS) coating, rubber aerogels show their super-hydrophobic properties with a water contact angle up to 153°. The effects of rubber fiber and cross-linker contents on the rubber aerogel oil absorption efficiency are thoroughly investigated. Pseudo-first-order and pseudo-second-order kinetics are studied for the absorption of rubber aerogel and the result shows that the pseudo-second-order model could better predict oil absorption performance. A maximum rubber aerogel oil absorption of up to 25.0 g/g is estimated, approximately 1.7 and 2.8 times higher compared to commercial polypropylene mat and nonwoven polypropylene, respectively. Such a material can play an instrumental role towards recycling of car tires and paves the way for maximizing the recycling capacity of waste rubber tires globally. This will in turn reduce the global and environmental impact of waste pollution associated with untreated car tires. [ABSTRACT FROM AUTHOR]

A fully biodegradable hybrid coffee-cotton aerogel has been successfully developed from spent coffee grounds, 100% cotton fiber and polyvinyl alcohol (PVA) flakes via environmental friendly processes. The cotton fibers in coffee aerogel help to maintain the structure and improve the overall properties of the new hybrid coffee-cotton aerogel. The results show that increasing the concentration of fibers, while keeping the concentration of spent coffee grounds constant, the sinking of coffee ground particles in solution and shrinking effect on the aerogels are minimized and the overall mechanical and oil absorption properties are improved. The developed hybrid aerogels possess high porosity of 92–95% and super-hydrophobicity with an average water contact angle of 139°. Oil absorption capacity achieves 16 g/g with 0.50 wt.% of cotton fibers inside the coffee aerogel. Their thermal conductivity is in the range of 0.037–0.045 W/mK and compressive Young's modulus achieves highest at 15.6 kPa. The properties of the hybrid aerogel indicate it as a potential material in several applications such as thermal insulation, oil absorption and filtration. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • rPET-silica aerogels are successfully developed from plastic bottle waste. • Ultra-low thermal conductivity and high thermal stability. • Very low compressive Young’s Modulus and very soft. • Fabrication method can be scaled up for industrial applications. Abstract Recycled polyethylene tetraphalate (rPET) fiber–silica aerogels are successfully developed from rPET fibers obtained from PET plastic bottle waste and tetraethoxysilane (TEOS). The rPET – silica aerogels are prepared through a direct gelation of silica on PET. rPET fibers are treated with dichloromethane to partially dissolve the fibers. The fibers are then dipped and allow to swell in TEOS/ethanol mixture, with the pH controlled to 2.5 using HCl to promote hydrolysis. After the acid hydrolysis, the pH was controlled to 7 with an ammonium hydroxide solution (NH 4 OH) to promote condensation. The surface modification is carried out in a trimethylchlorosilane (TMCS)/n-hexane solution and washed with n-hexane to dry at room temperature to prevent shrinkage. The developed rPET – silica aerogels exhibit super-hydrophobicity with an average water contact angle of 149.9°. Their thermal conductivity is approximately 0.037 W/m K. They have a very low compressive Young’s Modulus (0.95–4.19 kPa) and hence very soft. By utilizing rPET fibers, this work provides an alternative method of recycling PET plastic wastes which ultimately helps in reducing its detrimental impact to the environment. The developed aerogels can be used in several industrial applications such as heat insulation, filtering, sound insulation and absorption. [ABSTRACT FROM AUTHOR]

[Display omitted] • Coal fly ash from thermal power plant is converted into advanced aerogel material. • Developed aerogels possess porosity up to 90% and compressive strength of 150 kPa. • Competitive heat insulation capability to others commercial heat insulators. • Competitive acoustic insulation capability to others commercial acoustic insulators. Massive quantities of fly ash are produced worldwide from thermal power plants, posing a serious environmental threat due to their storage and disposal problems. In this study, for the first time, fly ash is converted into an advanced and novel aerogel through a green and eco-friendly process. The developed aerogel has a low density of 0.10–0.19 g cm−3, a high porosity of up to 90%, a low thermal conductivity of 0.042–0.050 W/mK, and a good sound absorption coefficient (noise reduction coefficient [NRC] value of 0.20–0.30). It also shows a high compressive Young's modulus of up to 150 kPa. Therefore, the newly developed fly ash aerogel is a potential material for thermal and acoustic insulation applications, along with lightweight composites in automotive and aerospace applications. [ABSTRACT FROM AUTHOR]

Given the harmful effects of agricultural waste residues on the environment and the abundance of pineapple byproducts after harvest, converting pineapple waste into a high-engineering value product for practical applications is one of the solutions toward sustainable development in developing countries. For the first time, flexible cellulose aerogels from raw pineapple-leave fibers (PALF) are developed successfully by using an adhesive agent, polyvinyl alcohol (PVA), and deionized (DI) water as a solvent, followed by a freeze-drying process. The effects of the pineapple fiber (PF) concentration on the heat and acoustic insulation properties are also investigated. The PF aerogels show high porosities of nearly 99%, ultra-low densities of (0.013–0.033) g/cm3, and a microporous structure which are determined by FE-SEM, BET and XRD analysis. They have very low thermal conductivities of (0.030–0.034) W/mK, indicating their excellent suitability for heat insulation applications. Indeed, the thermal jacket using a PF aerogel as filler wrapped around a water bottle can maintain the water temperature below 0 °C for 6 h (initial temperature of −3 °C), and above 40 °C for 2.5 h (initial temperature of 90 °C). The heat insulation capacity of the thermal jacket is about three times better than that of a commercially available product. With the same thickness, the noise reduction coefficient of 2.0 wt% PF aerogel samples is greater than that of a commercial absorber Basmel, which demonstrates their potential in acoustic insulation applications. • Ultra-lightweight and highly porous pineapple fiber (PF) aerogels are developed successfully for the first time. • The PF aerogels exhibit great thermal and acoustic insulation properties. • The thermal jacket made of PF aerogels can keep water chilled within 4.5 h. • The flexibility of PF aerogels is demonstrated with low compressive moduli. [ABSTRACT FROM AUTHOR]

• A green and cost-effective method to convert sugarcane bagasse into aerogel has been developed. • Sugarcane bagasse aerogel is a promising candidate for heat insulation applications. • Sugarcane bagasse aerogel is a promising candidate for oil-spill cleaning applications. • Sugarcane bagasse aerogel is highly flexible, and can be bent without breaking. A promising and economic material for various applications, such as thermal insulation in construction building and oil clean-up in marine ecosystems, is successfully developed from the by-product of the sugarcane industry. Biodegradable sugarcane bagasse aerogels are produced using polyvinyl alcohol (PVA) binder, followed by a freeze-drying method. This environmental-friendly recycled aerogel has an ultra-low density ([0.016-0.112] g/cm3), a high porosity ([91.9–98.9]%), and a very low thermal conductivity ([0.031-0.042] W/mK). Its superhydrophobicity properties and its maximum oil absorption capacity (up to 25 g/g) are measured after coating aerogel samples with methyltrimethoxysilane (MTMS). The biodegradable aerogel has a Young's modulus of 88 K Pa and can be bent without breaking, demonstrating its high flexibility. [ABSTRACT FROM AUTHOR]