Nano mesocellular foam silica (MCFs):An effective adsorbent for removing Ni2+ from aqueous solution

Xiao-dong Li , Qing-zhou Zhai

a Department of Basic Science, Jilin Jianzhu University, Changchun 130118, China

b Research Center for Nanotechnology, Changchun University of Science and Technology, Changchun 130022, China

Abstract Nano mesocellular foam silica (MCFs)was synthesized through the hydrothermal method in this study.Powder X-ray diffraction and scanning electron microscopy were used to characterize the MCFs sample.The sample presented spherical particles and regular morphology.The results of transmission electron microscopy showed that synthesized MCFs has a three-dimensional honeycomb pore structure,which aids in the adsorption of nickel ion (Ni2+).The results of low-temperature nitrogen gas adsorption-desorption showed that the pore diameter of the synthesized MCFs was 19.6 nm.The impacts of pH, temperature, amount of adsorbent, initial concentration of Ni2+, and contact time on the adsorption effect of Ni2+ by MCFs were studied.Under the optimized adsorption conditions, the adsorption rate reached 96.10% and the adsorption capacity was 7.69 mg/g.It has been determined through the study of kinetics and adsorption isotherms that the adsorption of Ni2+by MCFs follows the pattern of the pseudo-second-order kinetic model, simultaneously belonging to the Freundlich adsorption type.The thermodynamic results of adsorption showed that, when the temperature is between 25°C and 45°C, the adsorption is a spontaneous exothermic reaction.

Keywords:Nickel ion; Adsorption; MCFs; Kinetics; Thermodynamics; Hydrothermal method; Wastewater treatment

1.Introduction

In 1992, researchers from the Mobil company synthesized MCM-41 series mesoporous materials for the first time (Beck et al.,1992;Kresge et al.,1992).As nanomaterials have a high level of chemical stability, biocompatibility, and simple synthesis ability, as well as low-cost characteristics, they have been used in adsorption(Chen et al.,2017),catalysis(Li et al.,2017), biomedicine, and electrochemistry, attracting the attention and extensive research interest of scientists (Che et al., 2004; Zhai, 2013; Fang et al., 2017).Mesoporous materials have the characteristics of high specific surface area,low relative density, high porosity, continuously adjustable pore size within a certain range, and hydrothermal stability,overcoming the limitation of pore size deficiency of microporous zeolite.They can adsorb pollutants more effectively, and can be used in environmental purification,adsorption catalysis, and other fields (Zhao et al., 1998).Unlike MCM-41 materials, mesocellular foam silica (MCFs)(Schmidt et al.,1999)has a three-dimensional(3D)connected pore structure, with larger pore size and specific surface area.Larger spherical pores are connected through windows,which are more favorable to adsorption of substances.During industrial wastewater treatment, the one-dimensional pores of MCM-41 are easily plugged in the adsorption process,but the 3D pore of MCFs can overcome this shortcoming to a large extent.

Nickel is an abundant element in the crust and one of 14 trace elements necessary for human body.It participates in the metabolism and composition of some enzymes of the human body, stimulates hematopoietic function, promotes erythrocyte regeneration, and can treat anemia and cirrhosis.It has a cushioning effect on asthma, cardiopulmonary insufficiency, and cor pulmonale, and plays a role in maintaining human physiological function.However, the human body internally adsorbs too much nickel, which can damage the cardiac muscle, lung, liver, and kidneys, and can even cause cancer (Ahmed et al., 2019; Gupta et al.,2019; Pei, 2001; Wei et al., 2008).Nickel can be adsorbed by human beings through drinking water and through the food chain.As a global pollution problem,heavy metal pollutants, such as nickel, have received a lot of attention from scientists (Guo and Song, 2010).Domestic and foreign nickel wastewater treatment technologies mainly include ion exchange, chemical reduction,membrane separation, electrochemical treatment, reverse osmosis,and distillation electrodialysis methods.To some extent,these technologies have achieved good results in removing nickel.However, the problem of secondary pollution exists (Guo and Song, 2010), especially when the concentration of heavy metal ions in water is low, the removal rate is low, and the operation cost is high.Of the numerous methods for removing heavy metal pollutants, the adsorption method is simplest and most effective.The performance of adsorbent determines the effect of the adsorption method on removing heavy metal ions from polluted water.In recent years, nano-mesoporous molecular sieve materials have been used to adsorb heavy metal ions(Walcarius and Mercier, 2010), and MCM-41 has been used to study the adsorption of Cu2+,Zn2+,and other heavy metal ions (Ballesteros et al., 2010; Lin et al., 2014;Wongsakulphasatch et al., 2014).

The traditional way to adsorb heavy metals such as Ni(II)is through activated carbon(Clifford et al.,1986),but the cost is high and regeneration is difficult.Rice husk and natural bentonite have been studied for the removal of heavy metal ions, but their disadvantages include poor mechanical and thermal stability, low selectivity, low removal ability, and long adsorption equilibrium time (Guo and Song, 2010).Some adsorbents for Ni(II)have been discussed, but their adsorption abilities are still not ideal (Ewecharoen et al.,2008; Gupta et al., 2019; Hasar, 2003; Khan et al., 2011;Nityanandi et al., 2006; Zenasni et al., 2013).It is still important to investigate new adsorbents for Ni(II).In this study, nano-mesoporous MCFs material was synthesized under acidic conditions using poly(ethylene glycol)-blockpoly(propylene glycol)-block-poly(ethylene glycol)(P123)as a template and tetraethylorthosilicate (TEOS)as a silica source.The adsorption of Ni(II)by MCFs was studied, the conditions of adsorption equilibrium were probed, and adsorption kinetic and thermodynamic properties were examined.The adsorption properties of nano-mesoporous MCFs materials are significant as they constitute a potential green treatment method.

2.Experimental setup

2.1.Reagent

The reagents for MCFs synthesis were the following:triblock copolymer template, P123 (average molecular weight 5800,Aldrich Inc.),tetraethyl orthosilicate(TEOS,First Plant of Shanghai Reagent, China), 1,3,5-trimethylbenzene (TMB,Beijing Chemical Plant,China)as a pore expansion agent,and hydrochloric acid (Beijing Chemical Plant, China).

The Ni(II)standard solution (1 mg/mL)was made as follows:0.4784 g of NiSO4·7H2O were dissolved in a proper amount of water containing 2 mL of H2SO4(with a volume ratio of 1:1), then transferred into a 100-mL volumetric flask and diluted to the standard value.Nickel sulfate and sodium hydroxide were produced by the Beijing Chemical Plant,China.

The buffer solution (pH = 2.0)was made as follows:5.0 mL of 0.20 mol/L NaOH solution were added to a 100-mL tri-acid (all phosphoric acid, acetic acid, and boric acid concentrations were 0.04 mol/L)mixed solution.Phosphoric acid,acetic acid, and boric acid were produced by the Beijing Chemical Plant, China.

All the reagents used in the experiment were analytically pure, and the water was deionized water.

2.2.Experimental method

2.2.1.Preparation of MCFs

MCFs was synthesized with the hydrothermal method.2 g of P123 were dissolved in 15 g of deionized water and 60 g of hydrochloric acid solution with a concentration of 2 mol/L.The mixed solution was magnetically stirred until it completely dissolved.4.25 g of TEOS were slowly added and magnetic stirring was used to form a homogeneous solution.Afterwards,1.5 g of TMB(with a mass ratio of TMB to P123 of 0.75)were slowly dripped and stirred continuously at 40°C for 24 h.The stirred solution was transferred to an autoclave and crystallized at 100°C for 48 h.After crystallization, the autoclave was taken out and cooled at room temperature.The product was filtered and washed with deionized water several times, then dried at room temperature.White mesoporous MCFs molecular sieve powder was obtained by placing the drying products in a ceramic crucible and calcined at 550°C for 24 h, removing the tri-block copolymer template.

2.2.2.Adsorption of Ni2+by nano-mesoporous MCFs

A working solution with a volume of 5.0 mL (the values used in the other conditional experiments are shown in parentheses:1.0, 2.5, 7.5, and 10.0 mL)at the Ni2+standard concentration of 4.0 mg/mL were taken and placed into a 100-mL beaker.2.0 mL of the tri-acid(phosphoric acid,acetic acid, and boric acid)-sodium hydroxide buffer solution with pH=2.0(1.0, 3.0,4.0,5.0,and 6.0)were added to adjust the pH value.13.0 mL(17.0,15.5,10.5,and 8.0 mL)of deionized water were added to keep the total volume at 20 mL.0.0050 g(0.010, 0.020, 0.080, 0.10, 0.15, and 0.20 g)of MCFs were accurately weighed, added to the sample, and stirred for 30 min (5, 10, 15, 20, 25, 35, 40, 45, and 50 min)at a room temperature of 25°C (4, 30, 35, 40, 45, 50, and 55°C).Filtration was carried out and the filtrate was retained.The appropriate amount of filtrate was taken and the content of nickel in the filtrate was determined through arsenazo-III spectrophotometry (Geng and Zhai, 2014).The adsorption rate and adsorption capacity were calculated.

The adsorption rate is calculated by Eq.(1):

whereRadsis the adsorption rate (%),C0is the initial concentration (mg/mL), andCtis the concentration at timet(mg/mL).

The equilibrium adsorption capacity is calculated by Eq.(2):

whereqeis the equilibrium adsorption capacity (mg/g),Ceis the equilibrium concentration (mg/mL),Vis the volume of Ni2+solution (mL), andmis the amount of adsorbent (g).

2.3.Principle

2.3.1.Adsorption isotherm

The adsorption mechanism of metal ions in solution was studied through Langmuir and Freundlich isotherms.

The Langmuir isothermal equation is (Langmuir, 1918).

The Freundlich isothermal equation is (Freundlich, 1906).

whereqmis the metal ion saturation adsorption capacity(mg/g),KLis the Langmuir constant, andKFand 1/nare empirical constants.

The Langmuir isotherm is drawn with 1/Ceas the horizontal coordinate and 1/qeas the vertical coordinate,while the Freundlich isotherm is drawn with lgCeas the horizontal coordinate and lgqeas the vertical coordinate.

2.3.2.Adsorption kinetics

In this study,the mechanism of adsorption of the metal ion by MCFs was studied using the adsorption kinetic models commonly used at present, namely, the pseudo-first-order and pseudo-second-order kinetic adsorption models.

The pseudo-first-order kinetic model is (Lagergren, 1898)

The pseudo-second-order kinetic model is(Ho and McKay,1999)

whereqtis the adsorption capacity of adsorbate at timet(mg/g),k1is the first-order adsorption rate constant(min-1), andk2is the second-order adsorption rate constant(g/(mg?min)).

The first-order dynamic curve was fitted withtas the horizontal coordinate and lg（qe-qt） as the vertical coordinate,and the second-order curve was fitted withtas the horizontal coordinate andt/qtas the vertical coordinate.

2.3.3.Adsorption thermodynamics

The thermodynamic parameters of the adsorption process may be calculated by the following formulas (Gerel et al.,2007):

whereKcis the equilibrium constant; ΔG0is the Gibbs free energy change of the adsorption process(kJ/mol);R′is the gas constant, andR′=8.314 J/(mol?K);Tis the thermodynamic absolute temperature (K); ΔH0is the enthalpy change of the adsorption process(kJ/mol);and ΔS0is the entropy change of the adsorption process (J/(mol?K)).The adsorption thermodynamics curve was obtained with 1/Tas the horizontal coordinate and lnKcas the vertical coordinate.

2.4.Instruments and characterization

The D5005 X-ray diffractometer (Germany Siemens Company)was used to carry out a powder X-ray diffraction(XRD)experiment.Through the XRD spectrum of the sample,the crystal phase structure and periodic arrangement characteristics of the sample were determined.The Cu-Kα target and λ = 1.540560 ? (where λ is the wavelength)were used.The operating voltage (tube voltage)was 50 kV, the operating current (tube current)was 150 mA, the scanning range was 0.4°-10°,and the step length was 0.02°.A Philips XL30 field emission scanning electron microscope (SEM, the Netherlands)was used to measure the SEM photographs to observe the particle size and morphology of the sample with an operating voltage of 20 kV.The high-resolution transmission electron microscope(TEM)picture was obtained with an FEI Tecnai G2 F20 field emission TEM to observe the structure and morphology of the sample with a working voltage of 200 kV.The specific surface area,pore volume,and pore size distribution of the sample were determined through low-temperature nitrogen adsorption-desorption experiments.The sample was determined with an ASAP 2020 V3.01 H adsorption analyzer of the American Micromerities Company under liquid-nitrogen conditions at 77 K.The sample was activated in a vacuum at 363 K for 12 h.The data were calculated with the Broekhoff and de Boer (BdB)method(Broekhoff and de Boer, 1968a, 1968b), and the specific surface area was analyzed and calculated with the Brunauer-Emmett-Teller (BET)method (Brunauer et al., 1938).The pore size distribution was analyzed and calculated with the Barrett-Joyner-Halenda (BJH)method (Barrett et al., 1951).Characteristic groups of the sample were analyzed through infrared spectroscopy,and recorded with a Nicolet 5DX-FTIR spectrometer (Mike Company, USA).With the KBr tablet compressing technique, the mass ratio of the sample to KBr was 99:1 and the measurement range of the wavenumber was 400-4000 cm-1.A 722S spectrophotometer (Shanghai Lengguang Technology Co., Ltd., China)was used for the determination of nickel content through arsenazo-III spectrophotometry (Geng and Zhai, 2014).

3.Results and discussion

3.1.Influence of adsorption conditions on adsorption efficiency

3.1.1.Effect of pH value of initial solution on adsorption of Ni(II)

Solution pH is one of the most important factors affecting the adsorption rate and capacity.The adsorption efficiency is dependent on the solution pH value, because variation in pH results in variation in the degree of ionization of the adsorptive molecule and the surface properties of the adsorbent.Fig.1 shows the relationship between the pH value of the initial solution and the adsorption rate and adsorption capacity of nickel.It can be seen that with the increase of the pH value, the adsorption rate and adsorption capacity of nickel present the same trend.The adsorption rate and capacity of nickel adsorbed by MCFs are larger and the adsorption effect is stronger, with a pH value of 1.0-3.0 than with other pH values.When the pH value is 2.0, the adsorption rate and adsorption capacity reach the maximum values and the effect of the adsorption of Ni2+by the nanomesoporous MCFs molecular sieve is the best.When the pH value ranges from 3.0 to 6.0, the hydrolysis of Ni2+is significant and Na+and Ni2+compete for the adsorption site of the MCFs surface.As a result,the adsorption amount of Ni2+is reduced.

Fig.1.Effect of pH on adsorption of Ni(II)(m = 0.050 g,C0 = 1.0 mg/mL, t = 40 min, and T = 25°C).

3.1.2.Effect of adsorbent amount on adsorption of Ni(II)

Fig.2 shows that, for the Ni(II)solution with an initial concentration of 1.0 mg/mL, the nickel adsorption efficiency increases gradually with the increase in the adsorbent amount.When the MCFs amount reached 0.050 g, the adsorption rate reached its maximum.The adsorption capacity of nickel gradually decreased within the MCFs amount range of 0.01-0.20 g.This is because, with the increase of the adsorbent amount, the adsorption sites provided by MCFs increased.This decreased the level of competition of Ni2+on the adsorbent surface as well as the adsorption capacity.Based on the curves of adsorption rate and adsorption capacity, the optimum amount of adsorbent in the experiment was 0.050 g.

3.1.3.Effect of temperature on adsorption of Ni(II)

Fig.2.Effect of adsorbent amount on adsorption of Ni(II)(pH=2.0,C0 = 1.0 mg/mL, t = 40 min, and T = 25°C).

Fig.3.Effect of adsorption temperature on adsorption of Ni(II)(pH = 2.0, C0 = 1.0 mg/mL, m = 0.050 g, and t = 40 min).

It can be determined from the relationship between the temperature and adsorption rate as well as the temperature and adsorption capacity of Ni(II)(Fig.3)that,with the increase of temperature, both the adsorption rate and adsorption capacity increase first and then decrease.At a room temperature of 25°C ± 1°C, the adsorption efficiency is greatest.This can be attributed to the fact that the adsorption of Ni2+by MCFs is physical adsorption at 4-25°C and chemisorption at 25-55°C.

3.1.4.Effect of initial concentration of Ni2+on adsorption of Ni(II)

From the curves of the relationship between the initial concentration of Ni2+and the adsorption rate,as well as the adsorption capacity (Fig.4), it can be seen that the adsorption rate of nickel increases with the increase of the initial concentration of Ni2+when the value is less than 1.0 mg/L.The maximum value was reached at an initial concentration of 1.0 mg/mL and then decreased gradually.As the initial concentration of Ni2+increases, the concentration gradient increases, and this can increase the interaction between MCFs and Ni2+.The adsorption capacity increased with the increase of the initial concentration of Ni2+.According to the curves of the adsorption rate and adsorption capacity, the optimum initial concentration was 1.0 mg/mL.

3.1.5.Effect of contact time on adsorption of Ni(II)

From the curves of the nickel adsorption rate and adsorption capacity versus time (Fig.5), it can be seen that the adsorption rate and adsorption capacity of Ni2+by nanomesoporous MCFs present the same trend with the increase of time.The maximum adsorption rate and adsorption capacity were reached at 30 min, and then the adsorption equilibrium was observed.These changes in adsorption rates can be explained by the concentration gradient.In the initial stage,the high concentration gradient contributes to the production of the driving force.With the increase of time, the concentration gradient decreases until the equilibrium is reached.This is the reason why the adsorption rate remains stable after a specific time interval.

Fig.4.Effect of initial concentration of Ni2+ on adsorption of Ni(II)(pH = 2.0, m = 0.050 g, t = 40 min, and T = 25°C).

Fig.5.Effect of contact time on adsorption of Ni(II)(pH = 2.0,C0 = 1.0 mg/mL, m = 0.050 g, and T = 25°C).

In summary,under the optimized parameters,the maximum adsorption rate of Ni2+was 96.10% and the adsorption capacity was 7.69 mg/g.We summarized the adsorption abilities of some adsorbents in the removal of Ni(II)and listed the corresponding parameters in Table 1.It can be seen that MCFs has definite adsorption capacity for Ni(II).In addition,MCFs as an adsorbent cannot produce secondary pollution of the environment.

3.2.Adsorption kinetics

The experimental results of adsorption kinetics were fitted linearly with the pseudo-first-order kinetic equation and pseudo-second-order kinetic equation.The results are shown in Fig.6, and the related kinetic parameters obtained are shown in Table 2.It can be seen that, when the adsorption kinetic data are fitted with the pseudo-first-order kinetic equation, the correlation coefficient (R)is smaller, and the adsorption equilibrium capacity of different calculated concentrations is quite different from the experimental measurement value.However, when the pseudo-second-order kinetic equation is used for fitting, the correlation coefficients are all greater than 0.99, and the calculated values of equilibrium adsorption capacity of each concentration are in agreement with the experimental values.Therefore, the kinetics of the Ni2+adsorption system by MCFs accords with the pseudosecond-order kinetic equation.

Table 1 Comparison of adsorption capacity of Ni(II)from aqueous medium by various adsorbents.

Fig.6.Pseudo-first-order and pseudo-second-order adsorption kinetic curves.

Table 2 Corresponding parameters of adsorption kinetic equations.

3.3.Adsorption isotherm

The linear fitting results of the Langmuir adsorption isotherm equation and Freundlich adsorption isotherm equation of Ni(II)adsorbed by MCFs are shown in Fig.7.The specific results of linear fitting of the corresponding adsorption isotherm equation and the corresponding parameters are shown in Tables 3 and 4.The correlation of the Freundlich adsorption isotherm equation fitting effect is better and has a higher correlation coefficient.However, the maximum saturated adsorption capacity of the fitting result of the Langmuir isotherm equation is negative,which does not accord with the experimental results.The process of MCFs adsorption of Ni(II)conforms to the Freundlich adsorption model and is heterogeneous adsorption.

3.4.Adsorption thermodynamics

Fig.7.Fitting curves of Langmuir and Freundlich adsorption isotherm equations.

Table 3 Langmuir isothermal equation data.

Table 4 Freundlich isothermal equation data.

Fig.8.Adsorption thermodynamic curve.

The adsorption thermodynamic curve drawn from the experimental data is shown in Fig.8.The calculated results for the Gibbs free energy change ΔG0, the adsorption enthalpy change ΔH0, and the adsorption entropy change ΔS0of the adsorption process are shown in Table 5.The adsorption thermodynamic equation of nano-mesoporous MCFs for the adsorption of Ni(II)is ln（qe/Ce） = 5332/T-13.11,and the correlation coefficientR=0.9966.The linear effect is good.It can be seen from Table 5 that the ΔG0value of the Ni(II)adsorption process by MCFs is negative,the adsorption reaction is spontaneous,and ΔG0is within a range of 0 and-20 kJ/mol,indicating that the adsorption of Ni(II)by MCFs is physical adsorption(Gerel et al.,2007).The adsorption enthalpy change ΔH0=-41.856 kJ/mol(ΔH0＜0),indicating that the reaction is an exothermic reaction.The adsorption entropy change is a negative value(ΔS0=-65.092 J/(mol?K)),indicating that the adsorption process is a process of entropy decreasing.

3.5.Characterization of adsorbent sample

Fig.9 shows XRD images of MCFs samples before and after the adsorption of Ni(II)(referred to as MCFs and MCFs-Ni(II), respectively; a.u.means arbitrary units, and 2θ is the diffraction angle).The results show that MCFs has three characteristic diffraction peaks and has significant(100), (110), and (200)crystal plane diffraction peaks(Schmidt et al., 1999),which indicates that the material has long-term order.It is proven that the synthesized material is a mesoporous MCFs molecular sieve.The powder XRD images after the adsorption of Ni(II)display (100)and(110)crystal plane diffraction peaks, but the diffraction intensity decreases,showing that MCFs-Ni(II)remained the framework characteristics of MCFs mesoporous structurematerial, but the ordered degree of the material decreased.Fig.10(a)shows the TEM image of MCFs, in which ordered honeycomb pore channels can be seen,indicating that MCFs with homogeneous and ordered channels have been prepared.From the diagram, it can be seen that the pore size of MCFs is about 12 nm.The two-dimensional hexagonal ordered mesoporous channel arrangement is presented and the pore stripes are clearly ordered.Fig.10(b)shows the SEM image of MCFs,allowing for observation of the morphology, size, and structure of the MCFs sample.It can be clearly seen that, as a whole, MCFs molecules are spherical and granular with an average diameter of 2.2 μm.The regular foam structure can be observed.According to the results of a low-temperature nitrogen gas adsorptiondesorption experiment on MCFs (Fig.11; STP represents standard temperature and pressure), the adsorption and desorption isotherm curves of the samples are typical type II adsorption isotherms.The adsorption at low pressure is the same as that of microporous material.There is no obvious boundary between monolayer adsorption and multilayer adsorption.The biggest difference from a type IV adsorption isotherm is that there is no capillary condensation and no breakthrough at medium pressure, but there is an obvious jump at high pressure.There is a very large hysteresis ring in the relative pressure range of 0.70-0.98, which indicates that the sample has a mesoporous structure and the relative pressure at the bottom of the hysteresis ring is greater (Schmidt et al., 1999).These results indicate that the MCFs mesoporous molecular sieve has a macroporous structure.The parameters of physical chemical properties of the sample are shown in Table 6.Fig.12 is a Fourier transform infrared spectrum of MCFs.The adsorption peak at 3446 cm-1is attributed to the -OH stretching vibration of adsorbed water and the free hydroxyl group,and the adsorption peak at 1733 cm-1is attributed to the stretching vibration of free hydroxyl -OH.The adsorption peak at 1500 cm-1is attributed to the bending vibration of adsorbed water, the adsorption peak at l103 cm-1is attributed to the asymmetric stretching vibration of Si-O of siloxane, the adsorption peak at 815 cm-1is attributed to the bending vibration of Si-OH,and the adsorption peak at 457 cm-1is attributed to the flexural vibration of the planar-associating silanol group.

Table 5 Adsorption thermodynamic data.

Fig.9.XRD pattern of MCFs and MCFs-Ni(II)samples.

Fig.10.TEM and SEM images of MCFs sample.

Fig.11.Nitrogen gas adsorption-desorption pattern of MCFs sample.

Table 6 Parameter list of MCFs properties.

Fig.12.Fourier transform infrared spectrum of MCFs sample.

4.Conclusions

(1)Under the conditions of 25°C ± 1°C at room temperature, pH 2.0, adsorbent MCFs dosage 0.050 g, and an initial concentration of Ni2+1.0 mg/mL system, the nickel adsorption rate can reach 96.10% and the adsorption capacity is 7.69 mg/g when the contact time is 30 min.

(2)The adsorption kinetic results showed that the adsorption process of Ni(II)by MCFs follows the pattern of the pseudo-second-order kinetic model.

(3)Through the linear fitting of the Langmuir isotherm adsorption equation and Freundlich isotherm adsorption equation for nickel adsorption by MCFs, it was found that the adsorption process accords with the Freundlich adsorption model, being physical adsorption over the range of 25-45°C.

(4)Over a temperature range of 25-45°C, the Gibbs free energy change of the adsorption process of Ni(II)by MCFs ΔG0＜0,indicating that the adsorption reaction is spontaneous.The adsorption enthalpy change ΔH0=-41.856 kJ/mol, and the adsorption entropy change ΔS0=-65.092 J/(mol?K),indicating that the adsorption reaction is an exothermic reaction and a process of entropy decreases.