Preparation and adsorption properties of cotton linters and coal-gangue-based cellulose/SiO 2 composite aerogels

: High-value comprehensive utilization of coal gangue solid waste, reducing synthesis cost and environmental hazards has become an important research direction for green development. In this study, acid-alkali treated coal gangue was used as the silica source, and abundant cotton short staple in Xinjiang was used as the raw material of aerogel. Cellulose/SiO 2 composite aerogels were prepared by sol-gel method using N-N methylenebisacrylamide (MBA) as cross-linking agent and hydrochloric acid (HCl) as catalyst. The samples were characterized and analyzed by XRD, SEM, FT-IR, XPS, EDS, BET, and mechanical property tests. The results show that the composites exhibit low density and high porosity. The density ranges from 0.177-0.371 g/cm -3 with a high porosity of 88.7 %. SEM and BET results showed that the composites showed a three-dimensional mesh structure, and the specific surface area was as high as 325.742 m 2 /g, with a pore size of 21.997nm, which is a mesoporous material. The adsorption performance of the composite aerogel was tested by choosing the dye methylene blue (MB) to simulate wastewater, and the results showed that the


1.Introduction
Coal resources are the main fossil energy source in China, and the coal resource reserves in Xinjiang are 2.19 million tons, accounting for 40.5 % of the national proportion [1][2] .Its development and utilization is of great significance in promoting China's national economy and social development.Coal gangue is a kind of solid waste with low carbon content produced in the process of coal mining and washing, accounting for about 10 % to 15 % of the original coal [3] .It is one of the solid wastes with a large amount of emissions at present.At present, the main treatment method of coal gangue for the accumulation of landfill, not only the utilization rate is low, and easy soil, the atmosphere caused serious pollution [4][5] .Therefore, the high value utilization of coal gangue has a long and far-reaching significance.Coal gangue is rich in large amounts of SiO2 and Al2O3 [3,6] , from which SiO2 can be extracted as aerogel material after acid-base treatment.SiO2 aerogel not only has the characteristics of traditional aerogel, can withstand high temperature of about 1000 ℃ [7][8] .It is a threedimensional skeletal structure made of stacked silica nanoparticles with proven and farreaching applications in adsorbents, insulation and carrier materials.In addition SiO2 has both quantum orbital effect and volume effect dual effect [9][10][11][12] , which is easy to fill in other materials to realize material composite, and in this way expand the functionality of materials [13][14][15][16] .Wei et al [17] , successfully prepared silica aerogel powder using onepot method with gangue as raw material.The specific surface area of the resulting material is as high as 700 m 2 /g, with a porosity of more than 90 %, which can effectively adsorb pollutants in air and water, but the related adsorption experiments were not continued to be explored.
Cellulose-based aerogels, as the third generation aerogels [18][19][20] , possess high specific surface, high porosity and are widely available, easy to obtain, and inexpensive, and are often used as carriers for composite materials [21] .Cellulose is internally a chained polysaccharide macromolecule polymer consisting of glucose as a small unit [22]   , which is highly susceptible to modification due to the strongly reactive hydroxyl groups in its molecular chain.However, cellulose has poor thermal stability and degradation occurs near 300 °C, which greatly limits its industrial application [23] .
Simeng Liu [24] modified cellulose oxidized by TEMPO and prepared cellulose/SiO2 composite aerogel spheres by using sol-gel technique with sodium nine-hexosilicate as silicon source.Its specific surface area was as high as 229.44 m 2 /g and the average pore size was at 3.32 nm, and the dye methylene blue (MB) was chosen to simulate the dye adsorption experiments, and the removal rate was as high as 99.23 %.Nia et al [25] selected 3-aminopropyltriethoxysilane to modify cellulose and prepared dendritic cellulose/SiO2 nanocomposites by hydrothermal technique.After BET characterization, the specific surface area reached 350 m 2 /g and the pore diameter was about 3.9 nm, and the adsorption test was carried out on two dyes, methylene blue and methyl orange, and the results showed that the adsorption amount of the material for the two dyes was 270 mg/g and 300 mg/g, respectively.At present, the research on cellulose and silica composites has been more mature, but the selection of raw materials are similar, most of the finished material for the preparation of the gangue as raw material for the preparation of cellulose/SiO2 composites rarely reported [26] .In this study, cellulose/SiO2 composite aerogel materials were prepared by choosing the abundant cotton short-staple cellulose from Xinjiang as the raw material, NaOH/urea/H2O [27] as the cellulose dissolution system, acid-alkali treated coal gangue as the silica source, by adjusting the content of SiO2, and by using the sol-gel method.Through the dye adsorption test, the adsorption effect on the dye methylene blue under different conditions was investigated, and the application prospect of linters and coal-ganguebased composites in wastewater treatment was elucidated.In addition to effectively reduce the pollution of gangue to the environment and improve the comprehensive utilization of waste, with a view to providing basic data in the high-value utilization of waste and sewage treatment.

Preparation of cellulose/SiO2 composite aerogel
In this experiment, the gangue treated with acid and alkali was chosen as the silica source, configured with 10%, 20%, 30%, 40% (relative to the cellulose content, ω/ω) and strong alkali in an aqueous solution to be fully dissolved, and HCl was added as a catalyst and stirred for 10 min at room temperature.Then mix the cellulose solution with SiO2 aqueous solution, add the crosslinking agent MBA, fully stirred in a 40 ℃ water bath, making the mixture dispersed uniformly, when the solution is viscous, quickly poured into the polytetrafluoroethylene molds, and left to stand for a number of hours at room temperature to make it gel.After gelation, the samples were washed to neutrality with deionized water, after which the samples were aged in Na2SiO3 mother liquor for a number of times, and then freeze-dried after solvent replacement with anhydrous ethanol and tert-butanol to obtain cellulose-SiO2 composite aerogels.and named samples CATS1, CATS2, CATS3, and CATS4.

Infrared spectroscopy tests (FT-IR)
In this experiment, VEETEX-70 infrared spectrometer (BRUKE, Germany) was chosen to analyze the samples in infrared.During sample preparation, the aerogel was pulverized, dried and then tested by KBr compression method, which was scanned in the wavelength range of 4000-500 cm -1 with a resolution of 4 cm -1 and a wave number accuracy of 0.01 cm -1 . [28]

X-ray diffraction tests (XRD)
A D/max2500 X-ray diffractometer (Bruker, Germany) was used for the determination of the fibrin aerogel samples.The scanning range was 2θ=10°~80°, the scanning frequency was 10 min-1, the tube voltage was 40 kV, and the tube current was 40 mA.

Scanning Electron Microscope (SEM)
In this experiment, SU8000 scanning electron microscope (Hitachi, Japan) was chosen to observe the morphology of the samples.The samples were made by cutting a small thin slice of aerogel, fixing it with silica gel, ensuring that the samples were dry and gold spraying them before starting, and testing them at a current of 10 μA and an accelerating voltage of 5 kV. [29]

X-ray photoelectron spectroscopy (XPS)
An ESCALAB 250Xi X-ray photoelectron spectrometer (Thermo Fisher Scientific, USA) was used to test the elemental composition and valence states of the sample surface.Where the incident X-ray source emits 1486.6 eV of monochromatic light, the Binding Energy (BE) is calibrated to 284.6 eV of C1s, with a flux energy of 15 eV and a scanning energy step of 0.05 eV, and the data obtained from the characterization are fitted to peaks by the XPSSPEAK41 analysis software [30] .

Specific surface area and pore size testing
In this experiment, ASAP2050 automatic high-pressure physical adsorption instrument (Mac Instruments, USA) was used to test the specific surface area and pore size of the samples.The prepared samples were weighed 0.2 g and degassed for 24 h.N2 adsorption and desorption experiments were carried out and the specific surface area was calculated using BET and the pore size distribution was calculated using BJH [31] .

Mechanical property tests
In this experiment, H5KT-0633 static mechanical tester (TInius Osien, UK) was chosen to test the static mechanical properties of the samples.The compression test was in cylindrical compression mode with a compression rate of 10 mm/min [32] .

Methylene Blue Adsorption Test
The cationic dye MB was selected as the pollutant for the experiment, and a certain concentration of MB solution was prepared with deionized water [33] .As shown in  Take 30 mg of adsorbent and 50 mL of adsorbent solution, stir under a magnetic stirrer, and when the adsorption reaches equilibrium, take a sample and measure it.The adsorbent was separated from the MB solution by a 25×0.45μmorganic filter membrane during sampling, and the absorbance of the solution before and after adsorption was recorded using a UV-visible spectrophotometer, and the amount of adsorbent adsorbed to the MB and the removal rate of the adsorbent were calculated according to Eq. (2-1),(2-2) [34][35] .
Where qe denotes the adsorption capacity in mg/g; C0 denotes the initial concentration of MB solution, Ce denotes the concentration of MB solution at the moment of t in mg/L; V denotes the volume of MB solution in L; m denotes the mass of adsorbent in g; Q denotes the adsorption rate in %.

Density and porosity analysis
The diameter (d) and height (h) of the sample were measured with vernier calipers and the corresponding volume (V) was calculated, then the mass (m) of the sample was weighed using an electronic balance and the density (ρs) of the sample was calculated from the following equation (3-1) [36] , and the measurements were repeated several times, and finally the average value was sought.The skeleton density (ρT) of the composite is a key factor in measuring the structure of the composite, which can more accurately reflect the structural characteristics of the material after loading of the new substance, and is calculated from the following equation (3-2) [37] .Porosity (ps) is an important parameter to characterize the aerogel structure, reflecting the cross-linking state inside the aerogel structure.Its calculation formula is shown in (3-3) [37][38] .
where V is the volume of the composite, V = 3.14 × (d/2) 2 × h, and ωc and ωs are the mass percentages of cellulose and SiO2 in the CATS composite aerogel; ρq is the density of cellulose-SiO2 composite aerogel; ρT is the cellulose-SiO2 composite aerogel backbone density; ρc is the cellulose backbone density, noted as 1.528 g/cm 3 and ρS is the backbone density of SiO2, noted as 2.2 g/cm 3 [21] .Note: where CA aerogel has ρT = ρc = 1.528 g/cm 3[39-40] Figure 3.1 shows the relationship between the density of cellulose/SiO2 composite aerogel and SiO2 content, from the figure it can be seen that the density of composite aerogel in the range of 0.177~0.371g/cm 3 , has a low density, and with the increase of SiO2 content, the density is increasing trend.The porosity, on the other hand, shows the opposite trend, with the increase in density the porosity gradually decreases, which is mainly due to the particle filling effect, with the increase in the content of SiO2, silica particles will be filled in the voids of the aerogel, the arrangement is more dense, resulting in the rise of its density, which also results in the reduction of pore space and the decrease of porosity.

Morphology
In this experiment, the cellulose-SiO2 composite aerogel with a diameter of about 4.8 cm, white, cylindrical and lighter was prepared by sol-gel, freeze-drying technique using a small round beaker as a mold.The lightest mass of the prepared aerogel reaches 0.347 g.It also has some compressive properties.As can be seen from the figure, when the loading of silica reaches 30%, the maximum compressive strength that can be withstood is 1.53 MPa, which improves the compressive capacity by about 5 times compared with cellulose aerogel.In addition, according to the change of the slope of the curve in the figure, it can be seen that there is a certain elastic recovery of the material under 40% of the deformation of the force.
It can also be seen from the figure that compared with the cellulose aerogel, the doping of SiO2 improves the mechanical properties of the aerogel, which is due to the small particle size of SiO2 particles on the surface of the aerogel, large specific surface area, a large proportion of the atoms accounted for within the surface layer, and insufficient apparent coordination, and therefore it can increase the contact area with the aerogel, so that both of them can be combined more adequately, which contributes to the stress transfer.When continuously increasing the SiO2 content will make the particles close to each other, which not only makes the aerogel easy to be brittle, but also the particles are easy to be agglomerated with each other, resulting in the strength of composite aerogel becoming low.These SEM images show that SiO2 was successfully modified without destroying the original structure of CA.In addition, as the content of SiO2 increased, the deposition phenomenon became more and more obvious, which blocked the pore channels to some extent, and the space became more and more dense, which corresponded to the adsorption results, and the excessive loading of SiO2 reduced the adsorption performance of their materials.that there are obvious absorption peaks at 3437 cm -1 , 2903 cm -1 , 1647 cm -1 and 1083 cm -1 , and these peaks are typical of cellulose type II.The peak near 3437 cm -1 is a typical characteristic peak of hydrogen bonding in cellulose, the peak near 2903 cm -1 is a symmetric stretching vibration peak of methylene C-H in cellulose, and the peak near 1647 cm -1 is a bending vibration peak of O-H bonding, the peak out near 1083 cm - 1 is the stretching vibration peak of the C-C backbone in cellulose.After complexation with SiO2, the spectra of the CATS series were roughly similar to the CA spectra, but new peaks appeared at 960 cm -1 , 800 cm -1 , and 459 cm -1 , with the peaks at 960 cm -1 being the stretching vibration of Si-OH, 800 cm -1 being the stretching vibration of Si-O-Si, and 459 cm -1 being the bending vibrational peak of the Si-O bond.This indicates that SiO2 was successfully compounded with cellulose and the functional group structure of CA was not destroyed during the compounding process.And with the increase of SiO2 content, the silicon content in the samples gradually increased, indicating the successful composite modification of SiO2.
Table 3-2 shows the EDS analysis of cellulose/SiO2 composite aerogels.The table presents the elemental composition of the samples and the percentage content of each element.As can be seen from the table, the increase in the amount of SiO2 was followed by an increase in the silica content of the aerogel, from 5.40 % to 33.41 %.Note: Pore size is the average pore size (including micropores + mesopores)

Effect of different silica content on adsorption performance
Figure 3. 10 shows the effect of different SiO2 loadings on the adsorption of the materials, which were prepared with SiO2 mass fractions of 10%, 20%, 30%, and 40% (relative to the content of cellulose), ground and pulverized, and then 30 mg of the adsorbent was taken and added to 50 ml of a 50 mg/L solution of MB at room temperature and adsorbed to equilibrium.The figure shows that the addition of SiO2 makes the adsorption effect of the material significantly improved, without the addition of SiO2, its adsorption amount of 50.192 mg/g , after the addition of SiO2 adsorption effect shows a trend of increasing and then decreasing, when the content of SiO2 increased to 20 %, the adsorption amount reaches a maximum value of 75.336 mg/g .
Continuing to increase the SiO2 content, the adsorption began to decrease, down to 58.385 mg/L .This is mainly due to the fact that at low SiO2 content, the material increases the porous structure and specific surface area of the cellulose due to the addition of SiO2.At the same time, cellulose and SiO2 synergize with each other, the adsorption sites increase, the adsorption amount increases, as we continue to increase the content of SiO2, SiO2 excessive deposition on the surface of cellulose, the spatial structure of the cellulose is more dense, the pore is reduced, the adsorption sites are subsequently reduced.The addition of SiO2 increases the surface area, which can lead to mutual repulsion of water molecules and molecules of pollutants, thus reducing their adsorption capacity.This is in accordance with the SEM results., the adsorption amount began to decrease, showing a negative correlation, but the adsorption amount was higher compared to that under acidic conditions.This is mainly due to the fact that MB is a cationic dye, which is more easily ionized under alkaline conditions, while the adsorbent carries a negative charge on its surface under alkaline conditions, and the two produce electrostatic adsorption.Meanwhile, the structure of methylene blue molecule under and alkaline conditions undergoes an alkalicatalyzed cleavage reaction, resulting in a change in its molecular structure, in which the methyl portion of its molecular structure is cleaved, generating methylene radicals and negative ions.These methylene radicals and negative ions can react chemically with some active sites on the surface of the cellulose silica composite, thus causing the methylene blue molecules to be firmly adsorbed on the surface of the composite, which enhances the interaction force of adsorption, facilitates the occurrence of adsorption, and improves the adsorption efficiency.However, too high alkalinity makes the adsorbent surface carry more negative charge, and at this time, the positive charge of methylene blue is weakened, and the interaction force between the two is weakened, which in turn reduces the adsorption effect of methylene blue, leading to a decrease in adsorption effect.

Adsorption kinetics modeling investigations
In order to explore the process of adsorption more deeply, quasi-primary kinetic model and quasi-secondary kinetic model were developed, which are important parameters to explore the rate of reactive adsorption and the adsorption process [10] .
Figure 3.12 (a) shows the effect of CA and CATS2 on MB adsorption at different times.
From the figure, it can be seen that the adsorption rate is faster in the first 60 min, and in the late stage of adsorption, the adsorption rate gradually decreases and the adsorption time is slow.This is mainly due to the adsorption effect in the pre-adsorption period, there are a large number of active sites on the surface of the adsorbent, making the adsorption rate grow faster, as the adsorption time gradually becomes longer, the number of active sites decreases, and it takes longer to make the adsorbent diffuse to the inside of the adsorbent.Therefore, the adsorption process became slow.When the adsorption time reached about 7 h, the adsorption rate gradually stabilized and the adsorption amount reached saturation, i.e., the adsorption equilibrium was reached, and the adsorption amounts of CA and CATS2 were 50.124 mg/g and 82.311 mg/g at this time.This indicates that ion exchange occurs between the cationic dye and the aerogel, and the adsorption process is chemisorption, the rate of which is mainly determined by the interaction force of chemisorption.
In addition, a Weber-Morris internal diffusion model was developed to explore more precisely the factors affecting the adsorption rate and the control steps during the adsorption process.

Adsorption isotherm modeling explorations
The adsorption isotherm describes the relationship between the concentrations of solute molecules in the two phases at adsorption equilibrium [41] .The most typical of these models are the Langmuir isothermal adsorption and Freundlich isothermal adsorption models.Langmuir isothermal adsorption model means that the molecules on the surface of the adsorbent have no interaction force and the adsorption is monomolecular layer adsorption; Langmuir isothermal adsorption model describes the non-homogeneous phase adsorption process, which is an empirical formula.
In this study, the adsorption properties of the two materials were first tested at different initial concentrations.MB solutions with initial concentrations of 10 mg/L, 20 mg/L, 30 mg/L, 40 mg/L, 50 mg/L, 60 mg/L, and 80 mg/L were selected for the experiments.As shown in Figure 3.13, throughout the adsorption proceeding, the initial concentration of the dye varies, which has a great influence on the surface mass transfer and diffusion of the material, which in turn leads to a difference in its adsorption capacity.It can be seen from the figure that there is a positive correlation between concentration and adsorption as the concentration of dye increases.The initial concentration increased from 10 mg/L to 80 mg/L, and the adsorption amount of CA increased from 15.033 mg/g to 51.637 mg/g.The adsorption of CATS2 increased from 16.422 mg/g to 78.185 mg/g.This is due to the fact that as the concentration of the dye increases, there are more dye molecules in solution, This leads to an increase in the driving force between the dye molecules and the adsorbent, making it easier for mass transfer and diffusion to the surface of the adsorbent, and therefore an increase in adsorption.In addition, a negative correlation between the adsorption rate and concentration can be observed in the figure, as the adsorption rates of CA and CATS2 decreased from 90.14 % and 99.66 % to 61.27 % and 58.48 %, respectively, with an increase in dye concentration from 10 mg/L to 80 mg/L.This is due to the fact that at lower concentrations, the dye molecules can make full use of the adsorbent's voids, the mass transfer and diffusion resistance is low, and the active sites of the adsorbent itself are not fully utilized, At high concentrations, the adsorption gradually reaches saturation, and the active sites of the adsorbent itself are basically occupied, resulting in a portion of the dye molecules still existing within the solution, so the adsorption rate decreases.

Adsorption thermodynamic modeling investigations
Thermodynamic modeling of adsorption is an important criterion for responding to whether adsorption is spontaneous or not and the degree of adsorption, as well as one of the most important aspects of the study of adsorption performance.Figure 3.15 shows the lnKd vs. 1/T for CA and CATS2 with correlation coefficients of 0.996 and 0.981.△S 0 and △H 0 were obtained by the slope and intercept of the relationship curves, respectively, and the results are shown in

4.Conclusion
In this paper, the abundant cotton shorts in Xinjiang are used as the substrate, and the acid-alkali treated gangue is used as the silica source, which provides a fast and easy preparation of cellulose-silica composite aerogel by sol-gel method.Composite aerogel materials with different silica contents were successfully prepared.And the following conclusions were drawn: (1) As can be seen by the pair of by SEM images, the cellulose-SiO2 composite aerogel retains a loose and porous three-dimensional mesh structure and a continuous sheet-like silica gel thin layer is flattened on its surface; From the density and porosity analysis, it can be seen that the composite aerogel has low density and large porosity, With the addition of SiO2, the density of the material shows a positive correlation with the addition of SiO2, which fluctuates between 0.177 and 0.371 g/cm 3 .Porosity up to 88.7 % and decreases with increasing material density; From the FT-IR and XRD diagrams, it can be seen that the composite aerogel has both type I and type II cellulose structures, and some of the cellulose underwent a phase transition during the preparation process; It can be seen from the BET data that the incorporation of SiO2 increases both the specific surface area and the pore size of the material relative to the pure cellulose aerogel, The specific surface area is as high as 325.742 m 2 /g and the pore size is 21.997 nm, which belongs to mesoporous materials.
(2) Adsorption experiments were conducted using MB dye simulating factory wastewater.The results showed that CATS2 could realize the adsorption of CR dye under alkaline and room temperature conditions.The maximum adsorption amount reached 82.311 mg/g, the adsorption model was consistent with the Langmuir isotherm model, and the adsorption equation was consistent with the proposed secondary kinetic equation, The intraparticle diffusion model suggests that the adsorption process is controlled by multiple steps, and the adsorption thermodynamics indicates that the adsorption is exothermic, with low temperatures favoring adsorption.After cycling test, the adsorption rate was still above 80 % after 5 cycles.

Figure 2 . 1
Figure 2.1 Schematic diagram of the preparation process 2.3 Characterization methods

Figure 2 . 2 ,
Figure 2.2, By plotting the standard curve of mass concentration and absorbance of MB

Figure 3 . 2
Figure 3.2 CATS2 Appearance and Topography3.2.2 Compression analysisFigure 3.3 demonstrates the relationship between the variation of the material at

Figure 3 . 3
Figure 3.3 Stress-strain diagrams of cellulose/SiO2 composite aerogels with different SiO2 contents and their compressive strength versus SiO2 content

Figure 3 . 5
Figure 3.5 Comparison between CA and CATS series FT-IR 3.3.3X-ray diffraction (XRD) analysis Figure 3.6 shows the XRD comparison between CA and CATS series, from which

Figure 3 . 6
Figure 3.6 Comparison of XRD of CA and CATS series 3.3.4EDS analysis Figure 3.7 shows the EDS diagram of cellulose/SiO2 composite aerogel, from

Figure 3 .
Figure 3.8 shows the XPS analysis spectrum of cellulose/SiO2 composite aerogel.

Figure 3 .
Figure 3.8 (b) shows the two main peaks of C 1s at 284.7 eV and 286.58 eV,

Figure 3 . 8 (
C) shows the outgoing peaks of O 1s at 533.48 eV and 532.58 eV, corresponding to C-O and C=O bonds, respectively.Figure 3.8 (d) shows the outgoing peaks of Si 2p at 103.38 eV and 103.98 eV, which both correspond to Si-O-Si bonds.In summary, Si was successfully loaded on cellulose aerogel.

Figure 3 . 9
Figure 3.9 BET test plot of CA with CATS2

Fig. 3 .
Fig. 3.10 Effect of different SiO2 content on the adsorption effect of MB 3.4.2Effect of different pH values on adsorption performance Figure 3.11 shows the effect of materials on MB adsorption performance at

Figure 3 . 11
Figure 3.11 Effect of different pH values on the adsorption performance of MB

Figures 3 .
Figures 3.12(b) and (c) show the quasi-primary and quasi-secondary kinetic

Figure 3 .
12(d), shows the fitted curves of the Weber-Morris internal diffusion model for CA and CATS2.From the figure, it can be seen that the adsorption process is mainly divided into three stages: (1) external diffusion stage, which has many active sites on the surface of the aerogel, and the adsorption driving force is large, making the adsorption rate faster; (2) The internal diffusion stage, in which MB molecules diffuse from the aerogel surface into the internal pores, the adsorption rate of this process is relatively slow compared to the external diffusion stage; (3) The adsorption equilibrium stage is reached, in which the MB adsorption and desorption rates are the same and the adsorption rate is basically unchanged.These three stages illustrate that internal diffusion is not the only control step, but is jointly determined by the simultaneous control of multiple steps.

Figure 3 . 12
Figure 3.12 Graphical representation of adsorption kinetic correlations (a: comparison of adsorption at different times, b: proposed primary kinetic model, c: proposed secondary kinetic model, d: internal diffusion model)

Figure 3 . 13
Figure 3.13 Effect of different initial concentrations on the adsorption performance of MB Then, Langmuir and Freundlich isothermal adsorption models were developed to

3. 5 RecyclabilityFigure 3 .
Figure 3.16 reflects the effect of the number of cyclic adsorption cycles on the

Figure 3 . 16
Figure 3.16 Effect of number of cycles on adsorption performance of CATS2

Table 3 -
1 Density and porosity data of cellulose-SiO2 composite aerogels with different SiO2 contents

Table 3 -
2 EDS analysis of CATS composite aerogels

Table 3 - 3
Pore structure parameters for CA and CATS2

Table 3 - 5
Parameters ;of the Weber-Morris internal diffusion model forCA and CATS2

Table 3 -
7. △G° are less than 0, indicating that the adsorption process is a spontaneous reaction.The thermodynamic temperature increased from 293.15 K to 323.15 K, and the Gibbs free energy ΔG° of CA and CATS2 increased from -4935.792 kJ/mol and -5709.036kJ/mol to -4613.774kJ/mol and -5373.338kJ/mol, which suggests that low-temperature environments are more favorable for the adsorption of MB.The table also shows that the enthalpy changes of CA and CATS2 are negative in the temperature range of 293.15-323.15K, which further indicates that the reaction is exothermic and the low temperature environment is more favorable for adsorption.

Table 3 -
7 CA andCATS2 as a function of lnKd and 1/T

Table 3 - 7
Thermodynamic parameters of CA and CATS2 at different temperatures