ZnO Aerogel with Uniform and Tunable

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A facile synthesis of cellulose/ZnO aerogel with uniform and tunable nanoparticles based on ionic liquid and polyhydric alcohol Xiaoqian Li, Jie Zhang, Zhaoyang Ju, Yao Li, Junli Xu, Jiayu Xin, Xingmei Lu, and Suojiang Zhang ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.8b03106 • Publication Date (Web): 22 Oct 2018 Downloaded from http://pubs.acs.org on October 27, 2018

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ACS Sustainable Chemistry & Engineering

A facile synthesis of cellulose/ZnO aerogel with uniform and tunable nanoparticles based on ionic liquid and polyhydric alcohol Xiaoqian Li

a,b,

Jie Zhang a, Zhaoyang Ju a, Yao Li a, Junli Xu a, Jiayu Xin a,

Xingmei Lu

*,a,b,c,

and Suojiang Zhang*,a,b

a. CAS Key Laboratory of Green Process and Engineering, Institute of Process Engineering, Chinese Academy of Sciences, 1 North Second Street, Zhongguancun, Beijing, 100190, China. b. College of Chemistry and Chemical Engineering, University of Chinese Academy of Sciences, 19 A Yuquan Road, Beijing 100049, China. c. Dalian National Laboratory for Clean Energy, 457 Zhongshan Road, Dalian 116023, China

ACS Paragon Plus Environment

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KEYWORDS: Cellulose Aerogel, Zinc Oxide, In situ, Ionic Liquid, Tunable, Recycling

*

Corresponding author, E-mail: [email protected];

[email protected]

ABSTRACT: Cellulose/zinc oxide (ZnO) aerogels are traditionally produced using methods that harmful to the environment because of the acids and alkalis that are involved in the production process. This study reported a facile approach for synthesizing cellulose aerogels with uniform and tunable ZnO nanoparticles that are based on ionic liquid 1-Allyl-3-methylimidazolium chloride ([Amim]Cl)

and

polyhydric

alcohol.

The

entire

preparation

process

is

environmental friendly and controllable. The hybrid aerogels are lightweight (0.0463 g/cm3) with a high surface area (267 ± 4 m²/g) and possess great compressive strength (51.53 N/cm2). Furthermore, the morphology and size of


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the ZnO nanoparticles are observed to be tunable; the ZnO nanoparticles can be uniformly synthesized in situ on the cellulose fibers by adjusting the concentration of Zn(Ac)2 precursor and the hydrolytic time. The cellulose/ZnO aerogel exhibits good catalytic efficiency during the degradation of polyethylene terephthalate (PET) and can be directly taken out without separation for recycling.

INTRODUCTION Aerogels, are excellent three-dimensional carrier candidates because they are light solid materials that possess relatively high porosity and large inner surface area.1-3 Aerogels exhibit unique characteristics and they are produced by replacing the liquid solvent in the gel with air without substantially altering the network structure or the volume of the gel body. Remarkably, aerogels can be synthesized with a unique porous structure, displaying a porosity up to 99%,4 which results in several outstanding performances, including low thermal conductivity, high optical transparency and low sound velocity.5 Due to the excellent properties, an extensive range of thermal, acoustic, electrical, catalytic and medical applications have been suggested. Nevertheless, traditional representative aerogels, such as silica, carbon and resorcinol/formaldehyde aerogels, are short of biodegradability and sustainability. Cellulose aerogels, which is one of the promising


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aerogels, overcomes the aforementioned problems. As one of the oldest materials on the earth, cellulose is abundant and nontoxic natural polymers; further, it is biodegradable, biocompatible and renewable. Thus, cellulose aerogels exhibit low density and high surface area, along with exceptional strength, and ductility.

Recently, hybrid cellulose materials have drawn significant attention. Cellulose aerogels can be manufactured by dissolving the native cellulose in a solvent and by subsequently regenerating using an anti-solvent.6-9 The regenerated cellulose aerogels possess isotropic and homogeneous structures that make them possible to load the metal particles, the exploitation of hybrid cellulose/ZnO materials should be meaningfully considered and evaluated. Initially, cellulose fibres have numerous hydroxyl groups, showing a hydrophilic property which is easy to combine nanoparticles.10-12 In addition, because of the higher porosity and larger inner specific surface area, cellulose aerogels provide porous scaffolds for loading more nanoparticles compared with cellulose membranes.1,1315

The biodegradability and quantum confinement effect of the cellulose/ZnO hybrids

result in a number of potential applications in sensors, solar cells,16-17 anti-microbial materials,18 and catalytic process.19-20 To realize a highly efficient catalytic processes, ZnO should possess a high specific surface area as a catalyst. However, two issues that are associated with the application of cellulose/ZnO hybrids remain, including 1) the agglomerated growth of the ZnO particles and 2) the environmentally harmful effect that is typically associated with the synthesis process. Therefore, we aim to discover a facile methodology by which cellulose/ZnO aerogel can be synthesized using ionic liquids and diethylene glycol. Room temperature ionic liquids, which are desirable green solvents,21-


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can dissolve cellulose instead of the traditional solvent systems,23-24 for instance, N-

methyl-2-pyrrolidinone/lithium

chloride

(NMP/LiCl),25

Dimethylacetamide

(DMAc)/LiCl,26 dimethyl sulfoxide-paraformaldehyde/paraformaldehyde (DMSO/PF),27 N-methyl-morpholine-N-oxide (NMMO).28 Diethylene glycol may replace NaOH which and provide –OH to react with Zn2+.

Here, a facile preparation of cellulose/ZnO aerogel with uniform, tunable and spherical ZnO nanoparticles was reported based on ionic liquid and diethylene glycol. During the process, the reagents, including ionic liquid 1-Allyl-3-methylimidazolium chloride ([Amim]Cl) and diethylene glycol, were observed to display hypotoxicity and low corrosivity. By adjusting to appropriate size, the nanoparticles can be trapped in porous materials without aggregation. The cellulose/ZnO aerogels are highly porous (267 ± 4 m²/g) the ZnO nanoparticles are observed to be homogeneously synthesized in situ. In this study, the cellulose/ZnO aerogels are used as recyclable catalysts to effectively degrade Polyethylene terephthalate (PET). After degradation, aerogels display little deformation and shrinkage; further, as compared to the traditional catalysts, aerogels can be directly taken out without a necessity to be separated. This makes it possible to easily reuse the aerogels in subsequent experiments.

EXPERIMENTAL SECTION Materials and reagents


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Microcrystalline cellulose (MCC) was purchased from Sigma-Aldrich and zinc acetate dehydrate (Zn(CH3COO)2) was obtained from Xilong Chemical Co., Ltd. Ethanol (CH3CH2OH) and ethyl acetate (C4H8O2) were obtained from Beijing Chemical Works; tert-Butanol (C4H10O), ethylene glycol ((CH2OH)2) and diethylene glycol (C4H10O3) was purchased from Sinopharm Chemical Reagent Co., Ltd. Polyethylene terephthalate (PET) was kindly provided by Beijing Yingchuang Renewable Resources Co.,Ltd. 1-Allyl-3-methylimidazolium chloride ([Amim]Cl) was purchased from Linzhou Keneng Materials Technology Co. Ltd.. All other chemicals utilized in this study were analytical grade and used as received.

Preparation of regenerated cellulose aerogel [Amim]Cl was used in this work. It has lower viscosity compared to the ionic liquids which exhibit excellent capability to dissolve cellulose.29 Furthermore, [Amim]Cl is liquid at room temperature which is easier to remove. [Amim]Cl was washed with ethyl acetate thrice. To ensure the accuracy of the experimental results, the ionic liquid was dried until the water content below 1%. According to the certain proportions, the MCC and [Amim]Cl were mixed in a round bottom flask and stirred at 70 °C until the solution is clear and transparent. The viscous solution was defoamed by vacuum drying oven and ultrasonic machine. By adding distilled water gently to the solution, the cellulose hydrogel was regenerated. Then the hydrogel was washed and soaked by distilled water, ethanol and C4H10O, successively. Ultimately, after pre-freezing the regenerated cellulose sample for 12 h, the sample was lyophilized for at least 24 h.

Recovery of ionic liquid


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After the hydrogel was regenerated and formed, the ionic liquid in the hydrogel was washes by water several times until the ionic liquid was removed completely. During this process, the ionic liquid aqueous solution was collected. Then, the solution was centrifuged to at 11000 rpm to remove a small amount of cellulose flotsam. The supernatant was pour into a round bottom flask and using rotary evaporator to remove water at 70 ℃ for 5 hours. Finally, the ionic liquid was dried in the oven for further use.

Preparation of cellulose/ZnO aerogels The lyophilized aerogels were dipped in zinc acetate aqueous solution with different concentration (0.25 wt%, 0.50 wt%, 1.00 wt%, 2.00 wt% and 5.00 wt%) at room temperature. The aerogels were dipped in solution for 3 h for adsorption equilibrium, and were soaked and washed by water several times. Subsequently, the aerogels, 10 ml zinc acetate aqueous solution (0.25 wt%, 0.50 wt%, 1.00 wt%, 2.00 wt% and 5.00 wt%), 100 ml diethylene glycol were mixed together in the round bottom flask at 170 °C. After taking out the aerogels for 1h, they were dialysed in the order given: distilled water, ethanol (CH3CH2OH) and tert-butanol (C4H10O). Ultimately, after pre-freezing the regenerated cellulose sample for 12 h, the sample was lyophilized for at least 24 h. The aerogels samples were numbered by Zn2+ concentration and hydrolytic time.

PET degradation The provided Polyethylene terephthalate (PET) were PET sheets which should be smashed prior to use. Ethylene glycol is the solvent which could not dissolve PET powders. PET can only be degraded in ethylene glycol if a catalyst is added. In brief, 20 g


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ethylene glycol and 5 g PET powders were mixed in a round bottom flask at 180 °C. The aerogels were added into the flask when the temperature is stable for 25-30min. After degradation, aerogels were taken out for the subsequent experiments, and the solution was poured into a beaker with distilled water. The diluted solution was stirred at 70 °C for 30 min and pumping filtrated after cooling. The pumping filtrated solution should be cooled at 4 °C for 12 h and be pumping filtrated again before dried. The residue in this step is the bis(2-hydroxyethyl) terephthalate (BHET) monomer. Before the measurement of NMR, tiny residual was dissolved in deuterated dimethylsulfoxide (DMSO). As for GPC, the residual was dissolved in the mixed solution of trichloromethane and O-Chlorophenol of which the volume ratio was 7:3 of a concentration of 2 mg/ml.

Analytical instruments and methods The phase composition and crystallinity of the cellulose/ZnO aerogels were characterized by XRD (SmartLab 9KW, Rigaku, Japan) in which the 2θ angle ranges from 5° to 90°. The thermal stability was tested by Thermogravimetric Analysis (DTG-60H, Shimadzu, Japan) under a nitrogen atmosphere from 30 °C to 700 °C. The nitrogen gas adsorption (ASAP2020HD88, Micromeritics instrument, America) was used to characterize the Brunauer-Emmett-Teller surface area, pore volume and pore size of aerogels. And the samples were dried in vacuum dry oven and degassed at 160 °C for 12 h before use. The morphology of aerogels was characterized by X-ray microtomography (Xradia 410 Versa, Carl Zeiss, America) and Field emission scanning electron microscope (SU8020, Hitachi High-Technologies, Japan). The specimens were treated by spray-gold before SEM measurements. In the PET degradation experiments, Gel permeation chromatography


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(PL-GPC 50, Agilent Technologies, America) and Nuclear magnetic resonance(Avance Ⅲ 600 MHz, Bruker, Switzerland) was used to characterize BHET monomer. Mechanical properties were tested by Universal testing machine (M5-50, Mark-10 Corporation, America) with a descending rate of 10 mm/min and the calculation method was described in supporting information. The degree of polymerization of regenerated cellulose was determined according to method FZ/T 01131-2016 in textile industry standard by using the ulsteria viscometer. The viscosity of the regenerated cellulose solution was measured and the degree of polymerization was calculated. The functions are as follows: 𝜂0 = h × t

(eq.1)

DP = 0.75𝜂

(eq.2)

M = 162 × DP

(eq.3)

Where 𝜂0 is relative viscosity, h is the viscometer constant (s-1) used for the determination when calibrated, t is the time when the solution flows through the viscometer(s), M is molecular weight of cellulose. According to the corresponding relationship between the characteristic viscosity of 𝜂0 and 𝜂* C in the data provided by the method, 𝜂0 is calculated, where C is the concentration of cellulose solution and 𝜂 is the characteristic viscosity.

RESULTS AND DISCUSSION A schematic illustration of the entire reaction is presented in Figure 1. When the cellulose aerogel was immersed in a zinc acetate (Zn(Ac)2) solution, the three-dimensional network structure sucks Zn2+ guest molecules into the pores until the absorption equilibrium was reached. Theoretically, Zn2+ could interact with –OH of cellulose through electrostatic


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binding. To eliminate the excess and unstably anchored Zn2+, the aerogel was washed by water, which was a basic and significant step. Thereafter, it was possible to synthesize uniformly-distributed ZnO in situ. First, Zn(Ac)2 is hydrolysed to form an intermediate Zn(OH)(CH3COO) by inducing H2O (which can be expressed in eq. 4). Zn(CH3COO)2 + H2O → Zn(OH)(CH3COO) + CH3COOH

(eq.4)

Then condensation occurs between the intermediate species to yield Zn-O-Zn bonds as expressed in eq.5 and 6. Finally, the ZnO nucleation centre is formed via successive hydrolysis and condensation reactions and growth at the absorbed site. Zn(CH3COO)2 + Zn(OH)(CH3COO) → Zn2(O)(CH3COO)2 + CH3COOH

(eq.5)

Zn(OH)(CH3COO) + Zn(OH)(CH3COO) → Zn2(O)(CH3COO)2 + H2O )

(eq.6

To verify that ZnO can be synthesized in situ on cellulose, a calculation based on Density Functional Theory (DFT) was performed on glucose with zinc ion. As depicted in Figure 2, Zn2+ tended to disperse near the hydroxyl in glucose and interact with the two adjacent hydroxyl oxygens. The bond energy was approximately 16-20 kcal/mol, which was considered to be relatively stable. The electrostatic potential surface exhibited low bond energy in the red region, and the bond energy iswas the lowest between Zn2+, O5 and O6, which was indicative of the strongest bond. The calculation results shown ZnO can be synthesized on cellulose in situ. To support the observation and reveal the reactive site further, the interaction between Zn2+ and cellulose aerogel was characterized by FTIR. After immersing cellulose aerogel into the Zn(Ac)2 solution, the FTIR results were given in Figure 3. The peaks at around 3400 cm-1 shows the characteristic hydrogen bonded –


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OH peak. The peaks at 2892 and 1432 cm-1 of cellulose aerogel are the –CH stretching and HCH bending vibration respectively, which change slightly after immersing in Zn(Ac)2 solution. However, the peaks at 1636 cm-1 change to lower wavenumbers at 1573 cm-1 which corresponded to the in-plane stretching vibrations of hydroxyl groups of in glucose. It illustrates that the –OH of glucose have some interactions with Zn2+ which was consistent with the calculation results.

In Figure S1, the prepared aerogel shows an intact skeleton structure. The molecular weight of cellulose was measured thrice. The degree of polymerization was 340, 346 and 328 respectively, and the calculated molecular weight of cellulose was approximately 55000. The bulk densities were determined as the ratio of mass to volume. And the bulk density of aerogels with different Zn2+ concentration was between 0.0415 to 0.0593 g/cm3. The results were provided in Table S1. It can be seen that the densities of aerogels increased with the increase of different Zn2+ concentration. Further, the steric morphology of cellulose aerogels was determined using X-ray microtomography. The regenerated cellulose aerogel can be obtained by dissolving microcrystalline cellulose (MCC) in the ionic liquids and can be subsequently regenerated using non-solvents.30 In Figure 4, the aerogel was observed to be homogeneous in every direction along the XY, YZ and XZ axes even though the cellulose fibers were randomly oriented. The Figure 4(d) depicts a highly porous and interconnected three-dimensional network, indicating the ability to be act as excellent carrier, and the homogeneous structure also provides a possibility of uniformly loading the ZnO nanoparticles.


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ZnO nanoparticles were synthesized on cellulose using a facile polyol method. The aerogels were characterized by X-ray diffraction analysis (XRD) and Scanning Electron Microscopy (SEM). In Figure S2 a, the broad and obtuse diffraction peaks belong to the regenerated cellulose fibres. In Figure S2 b, the peaks at 31.72 °, 34.38 °, 36.20 °, 47.54 ° and 56.54 °correspond with (100), (002), (101), (102), (110) faces, which is in good agreement with hexagonal wurtzite structure of zinc oxide according to Joint Committee on Powder Diffraction Standards (JCPDS) card 036-1451.31 The ZnO displayed high purity and no peaks of impurities were observed such as zinc hydroxide. And it was observed in Figure 5 that with the increase of Zn2+ concentration, the intensity of peaks increases. Based on the X-ray diffraction patterns, the mean crystal size of ZnO in the aerogels was analysed using Jade software based on the Debye-Scherer equation (eq.7) that can be given as follows:

D

(

  180

) cos 

(eq.7)

where D is the crystalline size, and κ represents a constant coefficient ranging from 0.8 to 1.4 and a value of 0.9 was used in the equation. λ denotes the X-ray wavelength of 0.154 nm, β is the width at half of the maximum wave, and θ is the diffraction angle.32 The mean crystal size of ZnO in the aerogel with (a) different Zn2+ concentrations and (b) hydrolytic time are summarized in Table S2. The particle sizes are in close agreements with the SEM results. Under these conditions, the ZnO nanoparticles were observed to be uniformly distributed, size-congruent and non-aggregated, which conformed to the catalytic groove.


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It can be seen from Figure 6 the morphology and structures of the cellulose aerogels were maintained in all the cases. The pore sizes were approximately 10-15 nm, and cellulose fibres with a diameter of approximately 10 nm were highly interlaced with numerous junctions (Figure S3). The synthesized particles were hexagonal wurtzite ZnO, which exhibited the most stable structure.33 As can be observed in eq.1-3, H2O acts as the reactant and the product; therefore, the hydration ratio influences the hydrolysis and condensation rate during the overall reaction. By controlling this parameter, ZnO can nucleate and grow with different particle morphologies.34 As depicted in Figures 6 and S4, ZnO nanoparticles nucleated and grew with an increase in the concentration of Zn2+ or hydrolytic time even though excessive Zn2+ caused aggregation. According to the XRD patterns, the mean crystal sizes of ZnO were analysed using Jade software based on Debye-Scherer equation (see supporting information). The crystal size ranged from 5.9 to 383.6 nm (Table. S2), which was consistent with the particle size that was observed in the SEM images. Thus, the ZnO nanoparticles can be tuned by changing Zn2+ concentration and hydrolytic time. The uniformly-distributed and suitable-size ZnO nanoparticles can be synthesized in the optimum conditions of 1.00 wt% Zn2+ with 15 min hydrolytic time.

To estimate the specific surface area (SBET), the aerogels were analysed based on the desorption branch of nitrogen adsorption-desorption using Brunauer-Emmett-Teller (BET) method. All the cellulose/ZnO aerogels isotherms performed typical type IV (Figure S5), which were the characteristic features of the multilayer adsorption on mesoporous materials with strong adsorbent-adsorbate interactions.35 Figure 7 depicts the SBET of cellulose/ZnO aerogels with different Zn2+ concentrations. With the increase in


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the concentration of Zn2+, the specific surface area ascent firstly and descend afterwards. Initially, the composite aerogel surface area went up due to the increase of particles surface area. However, the overloaded ZnO nanoparticles grew and blocked the aerogel pores, which caused a drastic decrease in surface area. CA - 1.00 wt%ZnO simultaneously exhibited both the highest specific surface area (267±4 m²/g) which were higher than those observed in current cellulose/ZnO materials.36 Because of the unique size range of pores of cellulose aerogels, the BJH method may under-evaluate the pore size and volume.37 So the pore volume of the aerogel was evaluated by a more reliable method using the equation 8 blow38:

(

𝑉𝑝 = 1 ―

𝜌𝑏 𝜌𝑠

)

×𝑉

(𝑒𝑞. 8)

Where Vp is the pore volume of aerogel, ρb and ρs is the bulk density and skeleton density of aerogel, respectively. And V is the volume of aerogel. The pore volume was approximately 1.93 cm3/g.

Figure 8 illustrates the thermal gravimetric diagram of cellulose/ZnO aerogels with different Zn2+ concentrations. Here, the concentrations of Zn2+ were 0.25, 0.50, 1.00, 2.00 and 5.00 wt% with a common hydrolytic time of 15 min. As depicted in the graph, all the curves exhibited an analogous weight loss trend in their thermograms. There were three apparent weight loss platforms. First, the broad platform occurred from room temperature to 100 °C, which can explain the dehydrolysis of cellulose. Because of the elimination of water molecules in relation to physical adsorption and hydrogen bonding, the weight loss was observed to become approximately 10%. Further, the major amount of weight loss was observed between 280 °C and


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360 °C which is the pyrolysis of cellulose. 39 And the thermal decomposition temperatures of aerogels were approximately 340°C. With the increase in temperature, the decarboxylation and decarbonylation reactions occurred and produced CO and CO2. Overall, the ZnO has a relatively limited influence on the thermal stability of the hybrid aerogels.

PET could be effectively depolymerized into bis(hydroxyalkyl) terephthalate (BHET) monomers or oligomers with zinc salts such as zinc acetate and zinc chloride. 40-41 Thus, cellulose/ZnO aerogels are expected to be useful as recyclable catalysts to degrade PET. First, they exhibited a good thermal stability and mechanical property (51.53 N/cm2) (the mechanical property method was described in supporting information). Second, the uniformly-distributed ZnO nanoparticles exhibited a high specific surface area and effective active sites. Additionally, as compared to the traditional ZnO composite catalysts, aerogels can be taken out directly without filtration and can be further reused to degrade PET. During the degradation experiments, the cellulose/ZnO aerogels were recycled thrice. The degradation process is described in detail in PET degradation of experimental section. The second-step residuals in every catalytic process were individually characterized by Gel permeation chromatography (GPC) and Nuclear magnetic resonance (NMR). The NMR charts presented in Figure S6 (a), (c) and (e) demonstrated that the residuals were pure BHET monomers that did not contain any impurities. With respect to the graphs in Figure S6 (b), (d) and (f), prominent peaks were observed to appear at 18.75, 18.72 and 18.80 respectively, which corresponded to the peaks of BHET, while the high and broad peaks belong to the solvent. The percentage conversion and yield of the monomer reached 100% and 78%, respectively, indicating an


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efficient catalytic effect. After the completion of three degradation cycles, the percentage conversions were all observed to become 100%; further, almost no shrinkage was observed on aerogels.

CONCLUSION In closing, the cellulose/ZnO aerogels were successfully prepared using a facile method based on ionic liquid and diethylene glycol. During the processes, the spent reagents displayed hypotoxicity; further, the aerogels were observed to be both sustainable and recyclable. The homogeneous aerogels were highly porous and the ZnO nanoparticles were uniformly synthesized in situ. Additionally, the tunable spherical ZnO nanoparticles were trapped in the aerogels without excessive aggregation. Finally, we observed that aerogels can be used as recyclable catalysts to efficiently degrade PET. The percentage conversion and yield of BHET reached 100% and 78% respectively, and the catalysts were directly taken out without separation and were further reused during the subsequent PET degradation.


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ASSOCIATED CONTENT Supporting Information Aerogel basic properties, ZnO crystal size, Zn2+ concentration in aerogel and characterizations of PET degradation experiment

AUTHOR INFORMATION Corresponding Author * Corresponding author, E-mail: [email protected]. Tel/Fax: +86-10-82544800. Corresponding author, E-mail: [email protected].


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Funding Sources ACKNOWLEDGMENT This work was financially supported by the National Natural Scientific Fund of China (No. 21476234, No. 21336002),

International Cooperation and Exchange

of the National Natural Science Foundation of China (51561145020) and the Strategic Priority Research Program of Chinese Academy of Science, Grant No. XDA21060300, and CAS Key Laboratory of Green Process and Engineering, Institute of Process Engineering, Chinese Academy of Sciences.


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FIGURES

Figure 1. The whole schematic illustration of reactions


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Figure 2. (a)-(e): Configurations of Zn2+ at different positions of glucose derived from DFT calculation. (f): Electrostatic potential surface of a single glucose molecule


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Figure 3. The FTIR diagram of cellulose aerogel and cellulose aerogel dipped in Zn(Ac)2 solution


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Figure 4. Three-dimensional structure of the cellulose-ZnO aerogel derived from X-ray microtomography: the images of (a) XY axis, (b) YZ , (c) XZ , (d) the three-dimensional structure of aerogel


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Figure 5.

The influences of ZnO peak intensity on (a) different Zn2+

concentration (0.25, 0.50, 1.00, 2.00 and 5.00 wt%) and (b) hydrolytic time (5, 10, 15 and 20 min)


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Figure 6. The FE-SEM images of ZnO nanoparticles synthetic process with different Zn2+ concentration: 0.00 (a), 0.25 (b), 0.50 (c), 1.00 (d), 2.00 (e) and 5.00 wt% (f)


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Figure 7. The specific surface area of cellulose/ZnO aerogels


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Figure 8. The thermo gravimetric of cellulose/ZnO aerogels with different Zn2+ concentration


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For Table of Contents Use Only


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Cellulose/ZnO aerogel was prepared using a facile method and can be used as recyclable catalysts to efficiently degrade PET without separation.


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ZnO Aerogel with Uniform and Tunable

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