Abstract:
In this study, commercial nata de coco was used as a high-purity bacterial cellulose resource to easily prepare aerogels via freeze-drying. The physical properties tải w88 the aerogels were investigated via the employment tải w88 X-ray diffraction, scanning electron microscopy, thermogravimetric analysis, Fourier transform infrared spectroscopy, and nitrogen physisorption measurements at 77 K. It was observed that the as-prepared cellulose aerogels possess a three-dimensional network with high porosity, high purity, and ultralight density. Therefore, this biomaterial exhibits high prospects in a myriad tải w88 applications, such as environmental treatment or thermal and sound insulation.
Keywords: bacterial cellulose, aerogel, commerical nata de coco, freeze drying.
1. Introduction
Bacterial cellulose (BC) has been employed for diverse applications in biotechnology, medicine and cosmetics [1, 2]. Such interest results from a fermentation-based high-quality and cost-effective cellulosic material which possesses favorable properties such as high crystallinity, high water retention capacity, and a porous matrix [3, 4]. Notably, different from plant-derived cellulose, BC is free from lignin, hemicellulose and other biopolymers; therefore, no toxic chemicals and no complicated processes were needed to isolate and purify bacterial cellulose [1].
Moreover, the fibrous network tải w88 BC is naturally generated in a hydrogel-like form containing a great amount tải w88 water (up to 99 wt.%) [3, 5]. It was reported that the properties tải w88 BC such as morphology, porosity, and mechanical strength are tremendously affected by the drying strategies.
In particular, air drying and oven drying, which are the most conventional methods for the removal tải w88 water from materials, can lead to the collapse tải w88 the original porous structure tải w88 the bacterial cellulose network, affording a thin and rigid sheet [5, 6].
On the other hand, freeze drying in which water is precedingly frozen and subsequently sublimated enables to maintain porosity owing to the lower surface tension caused on the cellulose matrix [6]. The successful replacement tải w88 solvents such as water with air results in the formation tải w88 so-called aerogels with 95% air and 5% network structure [7].
Indeed, lightweight aerogels derived fromnata de pinaandnata de coco, which were prepared in laboratory via the fermentation tải w88 pineapple extract and coconut water, respectively, were successfully obtained via utilizing the freeze-drying method. The surface area tải w88 approximately 35 m2/g was reported for these aerogels, which exhibited an excellent performance in removing organic dyes from aqueous medium [6, 8].
In the present work, commercialnata de cocothe bacterial cellulose aerogel was obtained via freeze-drying. The structural characteristics tải w88 as-synthesized BC-derived aerogels were analyzed in terms tải w88 crystallinity, morphology, and thermal stability. The effect tải w88 BC concentration in the aqueous suspension on the density and porosity tải w88 the obtained aerogels was also examined.
2. Experimental section
2.1. Preparation tải w88 the BC aerogel from commercialnata de coco
Figure 1. Commercializednata de cocopieces (a), suspension mixture tải w88 groundnata de cocoand water (b), and resulting BC aerogel (c)
Source: Results obtained by the authors
Nata de cocowas commercially obtained from the Bich Lien Duong supplier (Ben Tre, Vietnam) (Figure 1a).Nata de cocopieces (100 g) were mixed with water (100 g). A Philips HR2531 hand-blender (650 W) was employed to grind the mixture for 3 minutes and water was subsequently added to the mixture or removed from the mixture to obtain a suspension phase with a predeterminednata de cococontent (10 to 90 wt.%) (Figure 1b).
The resulting suspension mixture in sealed propylene boxes were frozen at −20 °C for a day. The bacterial cellulose aerogels were obtained by freeze-drying the frozen samples, affording cylinder-shaped aerogels (Figure 1c), which was denoted based on the weight content tải w88nata de cocoin the suspension mixture, namely 10, 30, 50, 70 and 90.
2.2. Characterization tải w88 the obtained BC aerogels
Crystallinity tải w88 bacterial cellulose innata de cocowas analyzed by X-ray diffraction (XRD) on a D8 Advance diffractometer instrument (Bruker, Germany, Cu radiation). Fourier transform infrared (FT-IR) spectroscopy was performed on a Bruker Vertex 70 spectrometer (Bruker, Germany). Scanning electron microscopy (SEM) images tải w88 the aerogel were achieved on a S-4000 microscope (Hitachi, Japan). Thermal behavior tải w88 bacterial cellulose was discovered by thermogravimetric analysis (TGA) on an SDT Q600 Thermal Gravimetric Analyzer (TA Instruments, USA). Textural properties tải w88 bacterial cellulose were determined by isothermal sorption measurements with nitrogen at 77 K using an ASAP 2020 equipment (Micromeritics, USA).
3. Results and discussion
Unlike plant cellulose which contain numerous impurities such as lignin and hemicellulose, BC is fabricated in a high purity viaAcetobacter xylinum-based fermentation tải w88 natural or artificial carbohydrate sources. In Vietnam,nata de cocowith 0.8-1 wt.% tải w88 BC has been widely produced from coconut water. The crystalline structure tải w88 the aerogel obtained from the suspension phase containing 10 wt% tải w88 commercialnata de cocowas observed in the XRD result (Figure 2a). The obtained pattern demonstrated the characteristics peaks at 2q = 14.6, 16.9, and 22.7° corresponding to (1 0), (110) and (200) lattice planes tải w88 the crystalline cellulose phase, respectively, which was in good accordance with previous studies on the cellulose obtained from the bacterial pathway [6, 8, 9].
The FT-IR analysis could be applied to indicate organic bonds present in the cellulose chain (Figure 2b). Many vibration bands, namely at 3340 cm−1(O-H stretching), 2895 cm−1(C−H stretching), and 1056 cm−1(C−O bending), were observed in the spectrum tải w88 the BC aerogel which are attributed to the typical functional groups tải w88 cellulose [6].
In addition, it was confirmed that the as-produced bacterial cellulose was devoid tải w88 lignin and hemicellulose, which are typically present in the plant-derived cellulose [5].
Figure 2. XRD pattern (a), FT-IR spectrum (b), SEM image (c) and TGA profile (d) tải w88 the BC-based aerogel
Source: Results obtained by the authors
SEM analysis was conducted to investigate the morphological characterization tải w88 cellulose in the aerogel (Figure 2c), showing an irregular three-dimensional cellulose network, which was produced byA. xylinumrandomly located in the static coconut water medium [6, 8, 10]. Furthermore, it can be observed that the framework included nanofibers (< 100 nm) interconnected through inter- and intra- molecular hydrogen bonding, affording a large number tải w88 small capillaries [3]. Thermal stability tải w88 BC aerogel was evaluated via TGA (Figure 2d). The obtained TGA profile showed that the thermal degradation process tải w88 the BC aerogel involved two main weight loss stages. A slight weight loss (5%) from 50 to 150 °C, indicating the evaporation tải w88 the water [11]. The second significant weight loss occurred in the temperature range tải w88 200 - 450 °C upon dehydration, oxidation and combustion tải w88 the cellulose matrix, releasing water, carbon oxides and other volatile products [12]. Over the temperature tải w88 800 °C, the material was completely combusted, proving the high purity tải w88 cellulose prepared from the bacterial fermentation.
Figure 3. Density and porosity (left) and N2sorption isotherms (right) tải w88 the BC aerogels
Source: Results obtained by the authors
Density and porosity tải w88 the obtained bacterial cellulose based - aerogels play a key role in determining the efficiency tải w88 the aerogel preparation by freeze-drying in order to eliminate water from thenata de cocohydrogel form (Figure 3) [5]. The freeze-drying process minimized the surface tension as no liquid droplets were involved. Therefore, the cellulose matrix can be maintained with numerous capillaries [3, 13].
As can be expected, the as-prepared aerogels possessed very low bulk density ranging from 0.0016 to 0.0094 cm3/g, depending on thenata de cocoamount applied [5, 10]. This indicated the successful manufacture tải w88 such lightweight aerogels. In the study scope, the calculated high porosity tải w88 the BC aerogels was almost unchanged (≥ 99.4%) although the structure was denser by varying thenata de cococoncentration from 10 to 90 wt.%.
Upon the nitrogen adsorption/desorption isotherms obtained at 77 K for the aerogel with the varied content tải w88nata de coco(Figure 3), it could be observed that increasing in the concentration tải w88 BC in the aqueous suspension from 50 to 70 wt.% led to the enhanced specific surface areas tải w88 the as-prepared aerogels. Applyingnata de cococontents lower than 70 wt.% generally yielded surface areas tải w88 about 25 m2/g while the aerogel exhibited higher surface areas tải w88 about 34 m2/g at thenata de cococoncentrations tải w88 70 and 90 wt.%. This trend can be explained based on the presence tải w88 more BC fibers in the same volume, which can form more pores, increasing the surface area.
4. Conclusions
In summary, the hydrogel-likenata de cococonstructed with numerous high-quality nano-scale cellulose fibers via bacterial pathway was further utilized freeze drying method to form 3-D porous cellulose aerogel framework. The unique structure tải w88 the bacterial cellulose-based aerogel provides interesting properties, namely high porosity, high purity, and biodegradability. Valorization tải w88 carbohydrate resources and the rationalization tải w88 aerogel preparation exhibit the expectation for broader application tải w88 this such abundantly available biomaterial.
Acknowledgements:
This research is funded by Ho Chi Minh City University tải w88 Technology (HCMUT), VNU-HCM under grant number SVKSTN-2023-KTHH-09.
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Chuẩn bị và phân tích aerogel cellulose vi khuẩn từ thạch dừa thương mại
TS. Lê Vũ Hà1,2*
Hồ Bảo Nghi1,2
Nguyễn Anh Quân1,2
Nguyễn Bá Phúc1,2
Trần Trương Bảo Ngọc1,2
TS. Nguyễn Đăng Khoa1,2
Phan Tuấn Hoàn1,2
1Khoa Kỹ thuật Hóa học, Trường Đại học Bách Khoa Thành phố Hồ Chí Minh
2Đại học Quốc gia Thành phố Hồ Chí Minh
Tóm tắt:
Trong nghiên cứu này, thạch dừa thương mại đã được sử dụng như một nguồn cellulose vi khuẩn chất lượng cao để tạo thành vật liệu aerogel siêu nhẹ dễ dàng bằng phương pháp sấy đông khô. Các tính chất vật lý của aerogel thu được đã được nghiên cứu bằng các kỹ thuật khác nhau bao gồm nhiễu xạ tia X, kính hiển vi điện tử quét, phân tích nhiệt trọng lượng, quang phổ hồng ngoại biến đổi Fourier và hấp phụ đẳng nhiệt nitrogen ở 77 K. Aerogel từ thạch dừa thương mại sở hữu mạng lưới ba chiều không có trật tự với độ xốp và độ tinh khiết cao, và tỷ trọng siêu nhẹ. Do đó, vật liệu sinh học này có nhiều triển vọng trong các ứng dụng xử lý môi trường, cách âm, cách nhiệt.
Từ khóa:cellulose vi khuẩn, aerogel, thạch dừa thương mại, sấy đông khô.