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Oil spills causes severe degradation to marine ecosystems and poses long term health effects on many animals on the food chain, including humans. A potential viable eco-friendly solution to oil spill clean-ups is the utilization of wool waste fibers as sorbent material, due to is naturally oleophilic nature and abundance as a waste. Repurposing wool waste also allow us to tackle another issue this waste poses: decreasing landfill spaces. This study aims to develop wool aerogels using wool waste fibers and polyvinyl alcohol (PVA) as a cross-linking binder. The synthesized aerogels exhibit high porosity (97.73–99.63%) and low densities (0.004–0.023 g/cm3). After being coated with methyltriethoxysilane (MTEOS), the aerogels exhibit great hydrophobicity with contact angles up to 138°. Using pseudo-first and pseudo-second order models to study the kinetics of the aerogels’ oil absorption performance, it is found that the oil absorption kinetics is better modelled after the pseudo-second order model. The best performing wool-based aerogel recorded an oil absorption capacity of 136.2 g/g, an estimated 9.1 and 15.3 times better than commercial counterparts, polypropylene mat and nonwoven polypropylene respectively. The aerogel fabrication technique (freeze–drying) employed in this study is also 2.5 times faster than the conventional solgel method. The promising results obtained demonstrate that the wool fiber as a great material capable of generating high engineering value and provides a novel alternative in solving environmental impacts plagued by oil spills and landfill-demanding wool waste.

Over 60 million tons of aluminium are produced annually, requiring sustainable and eco-friendly recycling methods of aluminium waste. In this work, aluminium metal waste is utilized in the fabrication of aluminium hydroxide aerogels using a cost-effective and environmental-friendly process. The developed aerogels with varying contents of aluminium and poly(vinyl alcohol) as a binder exhibit a low density (0.060–0.108 g/cm3), a high porosity (92.3–95.5%) and a low electrical conductivity ([1.8–5.2] × 10–8 S/m). The results indicated that aluminium hydroxide aerogels have an ultra-low thermal conductivity of 0.028–0.032 W/m K and are able to withstand high temperature of 800 °C with less than 50% decomposition. It is suggested that the synthesized aerogels can be a promising candidate for high-value engineering applications such as thermal insulation of pipes and buildings to expand the usage of recycled aluminium.

Pineapple leaf and cotton waste fibers known as abundant by-products in the agriculture and textile industry are combined for the first time to produce thermal insulating and flexible cellulose-based aerogel composites via an environmentally friendly and cost-effective freeze-drying process. The effect of total fiber content and the ratio of pineapple leaf fibers (PF) to cotton waste fibers (CF) on the density, porosity, morphology, durability, and thermal properties of aerogel composites are comprehensively investigated. The as-fabricated aerogel composites show an exceedingly low density of 0.019–0.046 g cm−3 with high porosity of more than 96%. Because of the porous structure inside, our aerogel composites exhibit outstanding heat insulation with extraordinarily low thermal conductivity of 0.039–0.043 W m−1 K−1 that is comparable to commercial insulation materials (mineral wool, fiberglass, polystyrene) and previous cellulose-based aerogels from recycled cellulose fibers, sugarcane bagasse, and rice straw. Interestingly, the combination of those fibers has remarkably improved the flexibility of our previous aerogels from pineapple leaf fibers only, in particular, the compressive modulus of aerogel composites (11.33–44.63 kPa) is 6 times higher than that of PF aerogels (5.73 kPa). The sheet of aerogel composite with a dimension of 28 × 28 cm which is rolled up shows no crack on its surface, demonstrating its excellent mechanical strength. The research results increase the possibility of applying the developed aerogel composites from biomass into practical insulation.

Millions of tons of plastic are produced annually, but less than 10% are reported to be recycled. This work sets out to transform environmental plastic (polyethylene terephthalate – PET) waste into aerogels for high-value engineering applications, primarily to enhance the monetary incentive in recycling plastics. Coating techniques, using silicone ceramic (SCC) and (3-aminopropyl)triethoxysilane (APS, or APTES) solutions, are successfully devised to enhance the thermal stability and CO2 adsorption capability of rPET aerogel. The rPET/SCC aerogel exhibits improved thermal stability (up to 600 °C), enhanced thermal insulation (thermal conductivity Kavg = [31.8–34.9] mW/m·K), hydrophobic characteristics (up to 144.7° in contact angle) and enhanced rigidity (Young modulus Eavg = [4.5–124.8] kPa), while maintaining an ultra-low density (ρa = [14–62] g/cm3) and a high porosity (Φavg = [95.6–99.0]%). Moreover, the amine-functionalised rPET aerogel achieves a CO2 adsorption capacity of up to 0.44 mmol CO2/g, superior to several commercial physio-sorbents. These promising results obtained demonstrate that the rPET aerogel is a versatile material suitable for a wide variety of high-value engineering applications, including thermal insulation and direct CO2 capture applications.

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 pin...

For the first time, recycled car tire fibers (RCTF) shredded from car tire waste are developed successfully into a novel material, a rubber aerogel, using polyvinyl alcohol (PVA) and glutaraldehyde (GA) as crosslinkers through a cost-effective freeze-drying method. Its structure and main physical properties are investigated comprehensively for high-value applications, such as heat and sound insulation of buildings and oil spill spilling clean up. The rubber aerogel has ultra-low density (ρa = 0.035 – 0.145 g/cm3) and high porosity (Φavg = 84.31–96.20 %). With a simple but effective coating method with methoxytrimethylsilane (MTMS), both the interior and exterior of the whole rubber aerogel surface can be well coated, and the coated aerogel exhibits a super-hydrophobicity with a water contact angle of up to 134.4°. The rubber aerogel exhibits excellent heat insulation properties (Kavg = 0.035 – 0.047 W/m.K), very good thermal stability up to 500 °C, and significantly-enhanced rigidity up to a Young modulus of Eavg = 458.12 kPa, much larger than that of commercial Styrofoam. The rubber aerogel shows very good durability as it springs back to its original shape after compression tests. The rubber aerogel has a noise reduction coefficient (NRC) of 0.41 and performs approximately 10% better than commercial sound foam absorber at 2000–3000 Hz. The maximum oil absorbtion capacity of the rubber aerogel in this work is 19.3 g/g, very competitive to commercial sorbents. The fabrication method can also be scaled up for several other industrial applications, not limited to sound, heat and sorbent applications.

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.

Carbon-based aerogel is a lightweight porous material with many advanced properties related to its microstructure, such as ultrahigh porosity, large surface area, and low thermal conductivity. With the extreme properties, aerogels are a potential material that can be applied to many applications as insulation and absorption. In this chapter, we briefly review the fabrication and thermal properties of carbon-based aerogels including graphene aerogels, carbon nanotube aerogels, and other aerogels. Several developed methods for fabricating and thermal properties of aerogels have been reported. The chapter is mostly based on our original and review papers dedicated to various aspects of synthesis and applications of aerogels.

A nanoporous rubber aerogel (NRA) is fabricated successfully using recycled textile fibers (RTFs) from car tire wastes, polyvinyl alcohol (PVA) via freeze-drying. The NRA exhibits a low density (down to 0.025 g/cm3), a high porosity (up to 98%), a robust mechanical property with the compressive resistance at 10% deformation above 20 kPa, a high oil-absorption capacity (up to 18 g/g), low thermal conductivity (down to 35 mW/m-K), and a high noise reduction coefficient (NRC value of up to 0.55). In our study, the production time is reduced significantly from 48 h to 17 h compared to previous works. More importantly, the central composite design and response surface methodology are applied to investigate the effect of the RTFs and PVA contents on the volume shrinkage, density, porosity, compressive resistance, oil absorption capacity, and thermal conductivity. As a result, it is found that the contents of RTFs and PVA should be in the range of high-level (4.0–5.0 wt%) and low-level (1.0–1.5 wt%), respectively. In addition, the effect of thicknesses and compositions on the sound absorption property of the NRA is further discussed using the analysis of variance (ANOVA). A higher noise reduction coefficient (NRC) is attained at a large thickness for compositions 1 (5.0 wt% RTFs, 1 wt% PVA). The sound absorption coefficient of the NRA in the high frequencies (1000–6000 Hz) is relatively high, and for the low- and medium frequencies (125–1000 Hz) relatively low. As a result, the NRA can be a potential candidate for oil-spill cleaning, heat-insulating and sound absorbing applications.

Exercising in a tropical climate with constant high temperatures and high humidity increases the risk of heatstroke for active people who frequently train outdoors. For these active persons, a cooling source of water nearby can be essential, and this is usually carried in canteen bottles. However, commercially available water canteen bottles have limited thermal insulation capability to keep the liquid content cooled for the required period. This work proposed an engineering solution to enhance the heat insulation performance of water canteen bottles, using recycled cellulose aerogels made from paper waste for the first time as an insulating layer. Recycled cellulose aerogels wrapped around the water canteen bottle provides excellent thermal insulation performance, while not adding significant weight to the bottle. The temperature of the ice slurry in the canteen bottle was measured periodically over four hours with a mercury thermometer. The effects of the static and dynamic conditions on the temperature rate were also quantified. A 1.5 cm thickness of 1.0 wt.% recycled cellulose aerogel wrapped around the canteen bottle can provide an excellent thermal insulation performance with the lowest rise in temperature, achieving a low final temperature of the ice slurry content of 3.5 &deg, C after 4 h. This result is much better than that provided by available commercial bottles under the same conditions.

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.

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.

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.

For the first time, a versatile, novel and environmentally-friendly aerogel was successfully fabricated from rice straw – one of the most abundant agricultural waste in South-east Asia. The final product is able to be applied in a wide range of applications including oil-spill cleaning, thermal insulation and acoustic absorption. The fabrication process is simple, cost-efficient and totally green without disposal of harmful by-products into the environment. Specifically, rice straw fibers were dispersed along with reinforcers (PVA or cationic starch) followed by freeze-drying to form shaped aerogels. Those samples were then turned into hydrophobic by coating with MTMS using chemical vapor deposition (CVD) method to produce aerogels with exceptional water repellency (WCA exceeding 1500). The morphology, pore structure and physical properties of the aerogels were characterized by scanning electron microscopy (SEM), X-ray powder diffraction (XRD), thermogravimetric analysis (TGA), thermal conductivity, water contact angle (WCA) measurements, oil adsorption and sound absorption measurements. The aerogel samples exhibit extremely low densities (0.05–0.06 g/cm3), high porosities (~97%), excellent heat reduction properties with low thermal conductivities (0.034–0.036 W/m.K), good mechanical properties (Young modulus up to 47 kPa) and oil adsorption efficiency proven with the capacity up to 13 g/g. In addition, huge potential of rice straw aerogels in sound absorption applications is also demonstrated with high noise reduction coefficient (up to 0.6). The samples still retain their thermal insulation, sound insulation capability and hydrophobicity after 2-month exposure in ambient environment.

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.

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.

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.

Recycled polyethylene terephthalate (rPET) aerogels are successfully developed using rPET fibers from plastic bottle wastes for oil spill cleaning applications. The rPET aerogels are formed via a freeze-drying process with polyvinyl alcohol (PVA) and glutaraldehyde (GA) crosslinking agents. After coating with methyltrimethoxysilane (MTMS), the MTMS-coated rPET aerogels exhibit hydrophobicity with a water contact angle of 133°–141° for oil absorption applications. The effects of the rPET fiber concentrations, fiber deniers and cross-linker contents on the oil absorption performance of the rPET aerogels are comprehensively quantified. The 0.5 wt% rPET aerogels show the largest oil absorption capacity of 79.4 g/g, approximately 7.0 and 3.2 times better than commercial sorbents, polypropylene pads and polypyrrole sponges, respectively and slightly larger than 0.5 wt% cellulose-based aerogels from paper waste. From the oil absorption kinetics of the rPET aerogels quantified by the pseudo-first and pseudo–second order models, the 0.5 wt% rPET aerogels can absorb oil up to 3.0 times faster than cellulose-based aerogels. In addition, rPET aerogels are also demonstrated to have a good absorption capacity for different organic solvents. These establish the novelty of the contribution and demonstrate that rPET aerogels can be promising materials for absorption applications due to their high absorption capacities, environmental-friendly and cost-effective fabrication method.