熱剝離法制備石墨烯納米片對Pb2+和Cd2+的吸附

李保慶　袁文輝　李　莉(廣東環(huán)境保護工程職業(yè)學(xué)院，重金屬污染防治與土壤修復(fù)重點實驗室，廣東佛山586；華南理工大學(xué)化學(xué)與化工學(xué)院，廣州50640；華南理工大學(xué)環(huán)境科學(xué)與工程學(xué)院，廣州50640)

熱剝離法制備石墨烯納米片對Pb2+和Cd2+的吸附

李保慶1袁文輝2,*李莉3
(1廣東環(huán)境保護工程職業(yè)學(xué)院，重金屬污染防治與土壤修復(fù)重點實驗室，廣東佛山528216；2華南理工大學(xué)化學(xué)與化工學(xué)院，廣州510640；3華南理工大學(xué)環(huán)境科學(xué)與工程學(xué)院，廣州510640)

石墨粉氧化后，在氮氣氣氛下，快速高溫剝離制得石墨烯納米片。采用X射線衍射(XRD)、掃描電子顯微鏡(SEM)、透射電子顯微鏡(HRTEM)、拉曼(Raman)光譜、傅里葉變換紅外(FT-IR)光譜和氮氣吸附-脫附等分析手段對石墨烯樣品進行了表征。這些分析測試結(jié)果顯示：石墨烯樣品主要由很薄的1－4層石墨組成，呈褶皺狀態(tài)，比表面積為628.5 m2?g－1。研究了石墨烯吸附水溶液中的Pb2+和Cd2+的pH值、吸附時間、吸附溫度和金屬離子初始濃度等影響因素，Pb2+和Cd2+的最大吸附量分別為460.20和72.39 mg?g－1。結(jié)果表明，熱剝離法制得的高質(zhì)量石墨烯納米片可以作為一種高效的從水中去除Pb2+和Cd2+的吸附材料。

石墨烯；熱剝離；表征；吸附；重金屬離子

[Article]

www.whxb.pku.edu.cn

1　Introduction

Heavy metal ions present in water pose a severe threat to human health and ecosystem.They are found in industrial and domestic waste waters1,and acidic leachate2from landfills.Accordingly, these heavy metal ions must be removed prior to discharge into surface waters.Many different adsorbents,such as activated carbon,ash,zeolites,metal oxides,chitosan,and agricultural byproducts3－8,have been used to remove heavy metal ions from water.In recent years,carbon-based materials have served as the major adsorbents of heavy metal ions in practice because of their superior pore distribution structure and large specific surface area9－11.For example,Shim et al.12studied metal ions adsorption on modified carbon fibers and Machida et al.13examined the simultaneous adsorption of Cu2+and Pb2+.Mohan et al.14studied the adsorption properties of cadmium and zinc using activated carbon derived from bagasse.Leyva-Ramos et al.15researched the adsorption of Cd2+from aqueous solution on natural and oxidized corncob.Li et al.16conducted the competitive adsorption of Pb2+, Cu2+and Cd2+ions from aqueous solutions by multiwalled carbon nanotubes(CNTs).As one member of the carbon family,graphene has been confirmed to be a possible candidate for metal ions adsorption fields.

Graphene is a one-atomic-thick planar sheet of sp2-bonded carbon atoms that are densely packed in a honeycomb crystal lattice.Its extended honeycomb network is the basic structural element of some allotropes:it can be stacked to form three-dimensional(3D)graphite,rolled to form one-dimensional(1D) nanotubes,and wrapped to form zero-dimensional(0D)fullerenes17.Because of the splanar structure of graphene,it is attracting great interest for producing field-effect transistors,lithium ion batteries,hydrogen storage,molecular sensors,artificial muscle actuators,and reinforcing fillers in high performance polymer composites18.The upper and lower surface of single layer graphene gives it a theoretical specific surface area 2600 m2?g－1,9but it is still a challenge to prepare a single layer graphene in practice. Freestanding graphene was discovered experimentally by Novoselov et al.19,but its chemical and physical characteristic are still not fully understood20.As the researches showed above,the properties of graphene materials depend on the number of graphene layers.For adsorption applications,various graphene structures with few layers are desirable because this gives the largest surface area per gram.Recently,graphene materials have attracted a lot of attention for heavy metal ions removal from aqueous solution.Hou et al.21successfully linked chelating groups to graphene oxide(GO)surface to form ethylene diamine tetraacetic acid-graphene oxide(EDTA-GO),which was found to be an ideal adsorbent for Pb2+removal with a high capacity of (479±46)mg?g－1.Pei et al.22investigated the effect of humic acid (HA)on Cu2+adsorption onto reduced GO and graphene.When HAwas added at pH 4.0 and 6.0,more Cu2+was adsorbed.Hu et al.23studied the adsorption of Cu2+,Cd2+,and Ni2+from aqueous single metal solutions on GO membranes.The maximum adsorption capacities of the GO membranes for Cu2+,Cd2+,and Ni2+were obtained,respectively.

There are many methods24－29to prepare graphene nanosheets (GNSs)up to now.Among them,the thermal exfoliation method is fast and efficient.Thus,it is interesting to adsorb heavy metal ions from aqueous solution by GNSs prepared through thermal exfoliation.

In the present study,high-quality GNSs with fewer layers(~4 layers)and large specific surface area(628.5 m2?g－1)were successfully prepared by thermal exfoliation.The ability of the graphene to adsorb Pb2+and Cd2+from aqueous solution was evaluated and the effect of pH,adsorption time,adsorption temperature,and equilibrium concentration of metal ions were also evaluated in detail.

2　Experimental

2.1Preparation of graphene sheets

GNSs were prepared in two steps:graphite powder(99.8%, ~325 mesh,Alfa Aesar)was oxidized using a modified Hummers′method25,27,28and then rapidly exfoliated at high temperature under nitrogen atmosphere24,26.In the oxidation process,a reaction flask containing magnetic stir bar was charged with 200 mL concentrated sulfuric acid(98.0%,AR,Tianjin Rui Jin Te Chemical Reagent Factory,China)and 5 g sodium nitrate(98.0%,AR, Tianjin Rui Jin Te Chemical Reagent Factory,China),cooled by immersion in an ice bath.The mixture was stirred for 15 min and 5 g graphite from the procedure described above was added into the mixture.After the graphite was well dispersed,25 g potassium perchlorate(98.0%,AR,Tianjin Rui Jin Te Chemical Reagent Factory,China)and 15 g potassium permanganate(98.0%,AR, Tianjin Rui Jin Te Chemical Reagent Factory,China)were added slowly over a period of 15 min to avoid a sudden increase in temperature.The ice bath was removed after the suspension had been continuously stirred for 30 min.Then the reaction flask was loosely capped and was stirred for 48 h at room temperature. Subsequently,the suspension was diluted with 250 mL warm deionized water and 40 mL H2O2(30%,AR,Guangdong Guanghua Chemical Factory,China)to reduce residual permanganate and manganese dioxide to colorless soluble manganese sulfate. The suspension was centrifuged at 10000 r?min－1and washed with a mixed aqueous solution of 6%(w)HCl/3%(w)H2O2,then washed with water until the pH was 7 and dried in a vacuum oven at 60°C for 16 h to obtain GO.For thermal exfoliation,0.2 g GO was first loaded in a quartz boat of 100 mm in length and 20 mm in diameter and inserted into a 1.5 m-long quartz tube with an inner diameter of 22 mm and outer diameter of 25 mm.The sample was flushed with N2for 1 h,and then the quartz tube was quickly inserted into a Lindberg tube furnace preheated to 1050°C and held in the furnace for 30 seconds and this produced the GNSs for these experiments.

2.2Characterization

X-ray diffraction(XRD)patterns were obtained at room temperature from a Bruker-D8 Advance(German)power diffractometer using Cu Kαradiation(λ=0.1541 nm)operating at 40 kVand 40 mA.The morphology and structure of the prepared GNSs were observed by scanning electron microscope(SEM,S-3700N, Japan)and high-resolution transmission electron microscope (HRTEM)(FEI,Tecnai C2F30 S-Twin).Fourier transform infrared (FT-IR)spectra were recorded with a Bruker Vector 33 FT-IR spectrometer.Raman spectra were measured using a Horiba Jobin Yvon LabRam Aramis Raman spectrometer with a laser focal length of 632.8 nm.BET specific surface area and pore distribution were determined from nitrogen adsorption,using a MicromeriticsASAP 2010(USA)analyzer.

2.3Reagents and measurements of adsorption tests

The Pb2+and Cd2+stock solution of 100 mL(1 mg?mL－1)was prepared by dissolving reagent grade PbCl2and CdCl2.To prepare differing concentration metal ions solution,0.1 mol?L－1NaCl and 5 mL hexamethylene tetramine buffer solution were added into appropriate stock solution,then diluted to 100 mL with distilled water in a 100 mL flask.Initial pH of each solution was adjusted by 0.1 mol?L－1HCl or NaOH,and was measured with a pH meter (Ecoscan-pH6,Singapore)

2.4Determination of the point of zero charge

The point of zero charge was determined using the following method:100 mL of distilled water was added into an Erlenmeyer flask,and then was heated until boiling for 30 min to eliminate CO2dissolved in water.Once boiling ceased,the flask was immediately capped.Subsequently,0.03 g of GNSs and 10 mLof the pretreated water were placed in a 50 mL Erlenmeyer flask,which was sealed with a rubber stopper and left on a shaker table for 48 h at room temperature.Then pH value of filtrate was measured and was taken to be the point of zero charge30.

2.5Adsorption measurements

A series of adsorption isotherm experiments were carried out using a bottle point method,in order to investigate the effects of various parameters on the adsorption of Pb2+and Cd2+onto GNSs. Each bottle was a 100 mL Erlenmeyer flask containing 20 mL of metal ions solution and 15 mg of GNSs that was outgassed at 150°C.Once the bottles were filled they were placed on a thermostatically controlled shaking table at a set temperature for 3 days,which allowed them to reach equilibrium.The initial concentrations of Pb2+and Cd2+in the solution ranged from 100 to 500 mg?L－1.Then the equilibrium solution was piped out and diluted with 0.1 mol?L－1HCl to allow for their measurement and to convert all metal species to ion form.The pH of the solutions was always<6.5 throughout the experiments to prevent precipitation of metal hydroxides.The metal solution was vacuum filtered and the concentration of the residual metal ions was analyzed using atomic adsorption spectroscopy(AAS,Varian AA 240FS).The quantities of adsorbed Pb2+and Cd2+were calculated the difference between the initial and the final amounts in the metal solution8,12.

Fig.1　XRD patterns of(a)graphite powder,(b)GO,and(c)GNSs

3　Results and discussion

3.1Results of characterization

XRD patterns of graphite powder,GO and GNSs were displayed in Fig.1.The characteristic peak of graphite powder presented at 2θ=26.58°.After oxidation,a new peak of GO could be seen at 2θ=11.36°,indicating the successful transformation from graphite to GO.The variation of d-spacing from 0.34 nm of graphite powder to 0.78 nm of GO could be calculated by Scherrer′s equation31,owing to the oxide-induced O-containing functional groups and inserted H2O molecules32that could be confirmed by FT-IR.After rapid thermal exfoliation,the diffraction peak of GO disappeared,and a new weak peak of GNSs in the inset was observed(see inset),indicating the O-containing functional groups were removed and GO was successfully exfoliated to GNSs which consist of fewer layers(1－4 layers)of graphene.

Fig.2 shows FT-IR spectra of GO and GNSs.For GO,the strongest peak at 3413 cm－1exhibits O―H stretching vibrations of adsorbed water molecules and structural OH groups,and the peak at 1626 cm－1presents O―H bending vibration33.The peaks at around 1735 and 1053 cm－1are attributed to the presence of carboxyl and epoxy functional groups32－34.The peaks of O-containing groups indicate that during the oxidation process of graphite flake, the original extended conjugated π-orbital system of the graphite was destroyed and the O-containing groups were inserted among the interspace.After rapid thermal treatment of GO,these O-containing groups were eliminated,as is shown by the weakening of the peaks at 1735,1626,1225,and 1053 cm－1(see Fig.2b).The presence of a new peak at 1565 cm－1reflects the skeletal vibration of GNSs35.These results reveal the successful conversion from GO to GNSs through rapid thermal exfoliation.

Fig.2　FT-IR spectra of(a)GO and(b)GNSs

The Nitrogen adsorption-desorption isotherms and pore size distribution of GNSs are shown in Fig.3.BET specific surface area and the total pore volume of GNSs prepared by thermal exfoliation are~628.5 m2?g－1and~2.28 cm3?g－1,respectively,which are much larger than those of graphite powder(~8.5 m2?g－1)and indicate that the average particle size of graphite has been decreased during the process of oxidation and exfoliation.Although the specific surface area of GNSs is much smaller than the theoretical specific surface area(2600 m2?g－1),the specific surface area of our samples is still larger than those reported previously (184 m2?g－1)35.A hysteresis loop in the Nitrogen adsorption-desorption isotherms of GNSs was observed,which demonstrated that the samples are porous structure formed between parallel layers36.

Fig.4a displays the low-magnification SEM image of GNSs. The morphology of evident agglomeration and worm appearance can be observed.Fig.4b shows the high-magnifaction SEM image of GNSs.The GNSs intrinsically possess37a curled morphology, which consist of thin wrinkled paper-like structure.It is obvious that the stacking of GNSs is fluffy and disordered and the appearance is agglomerated and overlapped.Thus,it is easy to form a porous structure,which is in agreement with the Nitrogen adsorption-desorption measurement.

The morphology of GNSs was further analyzed using TEM and HRTEM as shown in Fig.4(c,d).Fig.4c shows that GNSs are composed of thin wrinkled graphene,indicating that GNSs were prepared successfully.Fig.4d shows the smooth and homogeneous appearance for most surface of GNSs,which demonstrated the high-quality of the prepared GNSs34.However,it still can be observed that the GNSs have multi-layered graphene on some sites due to the little agglomeration among graphene layers.Concluded from the scale in Fig.4(c,d),the thickness of GNSs is approximately 1.3 nm and the GNSs are composed of approximately 1－4 layers of graphene，which can be proved by the conclusions of Stankovich38and Cheng26.Stankovich reported that the thickness of a chemically derived single-layer graphene was~1.1 nm.Cheng also discovered that the thicknesses of single-,double-,and triplelayer graphenes are approximately 0.57,1.25,and 1.83 nm,respectively.The agglomerated and overlapped individual monatomic graphene layers make the sample stack together,leading to the smaller specific surface area than the theoretical one(2600 m2?g－1)9.

Fig.3　Nitrogen adsorption-desorption isotherms(a)and pore size distribution(b)of GNSs

Fig.4　SEM(a,b)and TEM(c,d)images of GNSs

The significant structural changes during the process of GO to GNSs can also be characterized by Raman spectroscopy,as shown in Fig.5.For graphite powder,the Raman spectra at 1567 cm－1displays a G band corresponding to the first-order scattering of the E2gmode observed for sp2domains and D band,which represents edge planes and disordered structures39.In the Raman spectra of GO,the G band is broadened and shifted to 1578 cm－1and a broad D band at 1335 cm－1also appears.These changes of Raman spectra indicated that the original extended conjugated π-orbital system of graphite were destroyed and oxygen-containing functional groups were inserted into carbon skeleton.The Raman spectra of graphene showed a G band at 1577 cm－1and D band at 1334 cm－1. Comparing the D/G band intensity ratio(ID/IG)of GNSs with that of GO,we found that the ratio(ID/IG=1.17)of GNSs is larger than that in GO(ID/IG=1.04).Although the graphitization degree is in inverse ratio to the ID/IGvalue40,41,the process of oxidation and thermal exfoliation results in the significant decrease in average size of the in-plane sp2domains.Even if new graphitic domainswere created,they are smaller in size to the ones present in GO before reduction.The variation of data indicates the decrease of size of the in-plane sp2domains,as well as the increase of edge planes and of the degree of disorder to the as-synthesized GNSs34,42.In addition,there is a 10 cm－1blue shift in G band position when compared with bulk graphite(1567 cm－1)and this shift is attributed to the transformation of bulk graphite crystal to GNSs34.These evidences demonstrated the significant changes of structure from graphite powder to GO and then to GNSs.

Fig.5　Raman spectra of(a)graphite powder,(b)GO,and(c)GNSs

3.2Adsorption performance

In the adsorption experiments,four effect factors including pH, adsorption time,temperature and initial concentration were investigated and the maximum adsorption capacities of Pb2+and Cd2+on GNSs were determined at optimum pH,adsorption time and temperature.

3.2.1Effect of pH on the adsorption

A series of metal solutions by dissolving corresponding metal salts at the same initial concentration were adjusted to a pH range of 1.0－6.5 with 0.1 mol?L－1HCl or NaOH,then the adsorption experiments were conducted.According to the solubility-product constant(Ksp)of Pb(OH)2(1.43×10－15)or Cd(OH)2(7.20×10－15), and the initial concentration of metal ions of 0.001 mol?L－1,the pH value for the onset of precipitation is 8.08 or 8.42,respectively, which indicates no precipitation will occur in the pH range that we used.The removal efficiency(E)is calculated based on the Eq.(1),

where C0and Ceare initial and equilibrium concentrations(mg?L－1)of metal ions in aqueous phase,respectively.

Effect of pH on the adsorption of Pb2+and Cd2+by GNSs is shown in Fig.6.It can be observed that the uptake of Pb2+and Cd2+is tiny at pH 1.0－3.1.The reason for this phenomenon is that there are no any O-containing groups covering the surface active sites of GNSs and the surface active sites are occupied by plenty of H+in the liquid phase.Thus,the H+restrained the binding between the surface active sites of GNSs and metal ions at pHrange of 1.0－3.1.With the increase of pH,the charge of GNSs surface became more negative,43which caused electrostatic interactions and resulted in higher adsorption of metal ions.The graphed effect of pH also demonstrated the success of exfoliation of GO by rapid thermal treatment at high temperature.Most of the O-containing groups were eliminated successfully in the form of H2O or CO2. The plots demonstrated that the adsorption percentages of Pb2+and Cd2+onto GNSs are 96.27%at pH 5.80 and 76.75%at pH 6.30, respectively.

Fig.6　Effect of pH on the adsorption of Pb2+and Cd2+by GNSs

Fig.7　Effect of adsorption time on the adsorption of Pb2+and Cd2+by GNSs

3.2.2Effect of adsorption time

The experiment to explore the effects of adsorption time of Pb2+and Cd2+onto GNSs was examined using initial metal ion concentration of 0.001 mol?L－1at pH 5.5 for Pb2+and at pH 6.1 for Cd2+.Fig.7 shows the kinetic curves of Pb2+and Cd2+adsorbed onto GNSs.It can be observed that the uptake capacities of Pb2+and Cd2+increase sharply in the initial 20 min,and then rise slowly and reaches equilibrium at 30 min.The adsorption process achieved equilibrium in a short time,indicating that the GNSs are prospectively an excellent adsorptive material.

3.2.3Effect of equilibrium concentration of metal ions

Equilibrium concentration of metal ions plays an important role in the adsorption of metal ions onto adsorbent.The appropriate concentration is advantageous to the interaction between metal ions and graphene.Aseries of solutions with Pb2+and Cd2+initial concentration ranges from 100 to 500 mg?L－1at pH 5.5 for Pb2+and at pH 6.1 for Cd2+were used to investigate the effect of initial concentration.From Fig.8,it is obvious that the adsorption ca-pacity increases with increasing equilibrium concentration of metal ions,and reaches saturation progressively.In addition,the adsorption capacity of Pb2+increased sharply with the equilibrium concentration of Pb2+,comparing with that of Cd2+,which demonstrated that Pb2+has easier adsorptive property onto GNSs.

Fig.8　Effect of equilibrium concentration on the adsorption of Pb2+and Cd2+by GNSs

3.2.4Adsorption isotherms

The adsorption isotherms of Pb2+and Cd2+onto GNSs were measured to estimate the performance of graphene for metal ion removal.Adsorption experiments were conducted in optimal conditions from above adsorption results.The adsorption isotherms of Pb2+and Cd2+at the temperature range of 20－40°C are shown in Fig.9.It can be found that the adsorption capacities of metal ions increase with the increase of the equilibrium ions concentration.As shown in Fig.9,the adsorption capacity for Pb2+increases sharply until to about 500 mg?L－1of the equilibrium concentration,while that for Cd2+increases slowly.In addition,a reciprocal relationship between temperature and the uptake capacity of the metal ions can be observed from the curves.This indicates that the adsorption of metal ions onto GNSs is an exothermic reaction and room temperature is favorable to the adsorption experiments.For the same equilibrium concentration,the adsorption capacities of Pb2+and Cd2+reached up to 460.20 and 72.39 mg?g－1at 20°C,respectively,which are much higher or no less than that of functionalized GNSs(406.6 mg?g－1for Pb2+and 73.42 mg?g－1for Cd2+)44and the references listed in Table 1,and the adsorption capacities of Pb2+and Cd2+onto GNSs are higher than that of CNTs and modified GNSs.Therefore,it can be concluded that graphene has more superior adsorptive properties for removing Pb2+and Cd2+than CNTs and modified GNSs.

Finally,we explain the origin of these high adsorption capacities of Pb2+and Cd2+onto GNSs.Sanchez-Polo and Rivera-Utrilla50,51had estimated the adsorption sites of Cπ electrons on graphene layer as well as the aromatics adsorption.Consequently, the Pb2+and Cd2+adsorption sites can be also expected to be involved in Cπ electrons.The high-quality of GNSs prepared in this paper provided more abundant Cπ electrons,increasing the stronger adsorptive power among graphene and metal ions.In addition,Yushin and colleagues52demonstrated that as pore size decreased,uptake capacity on materials increased.As mentioned above,the pore size distribution of as-prepared GNSs revealed the highcontentofmicro-andmeso-porositytothestructure.Therefore, it can be considered that GNSs are superior in removal of Pb2+and Cd2+.

Fig.9　Adsorption isotherms of Pb2+and Cd2+at different temperatures

Table 1　Comparison of adsorption capacity of Pb2+and Cd2+by different adsorbents

4　Conclusions

High-quality GNSs with fewer layers were successfully fabricated by a rapid thermal exfoliation method.XRD results confirmed the successful exfoliation of GO to GNS.FT-IR and Raman spectra demonstrated the difference of groups introduced into GO and the structure between GO and GNSs.SEM and HRTEM analyses showed that the resultant GNS sample consisted of 1－4 layers of individual monatomic graphene and possessed a large surface area.For the same equilibrium concentration of metal ions, the adsorption capacities(Qe)of Pb2+and Cd2+onto GNSs were 460.20 and 72.39 mg?g－1,respectively,which are much larger or no less than CNTs and modified GNSs.Moreover,the adsorption process achieved equilibrium in only 30 min.Also,the adsorption mechanism was preliminarily explained by Cπ－cation interactionand the micropore structure of graphene.The outstanding properties of GNSs prepared by the rapid thermal exfoliation route make it an attractive adsorptive material for removing Pb2+and Cd2+in future.

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Adsorption of Pb2+and Cd2+on Graphene Nanosheets Prepared Using Thermal Exfoliation

LI Bao-Qing1YUAN Wen-Hui2,*LI Li3
(1The Key Laboratory of Heavy Metal Pollution Prevention and Soil Remediation,Guangdong Vocational College of Environmental Protection Engineering,Foshan 528216,Guangdong Province,P.R.China;2School of Chemistry and Chemical Engineering, South China University of Technology,Guangzhou 510640,P.R.China;3College of Environmental Science and Engineering, South China University of Technology,Guangzhou 510640,P.R.China)

Graphene nanosheets(GNSs)were prepared using oxidation of graphite powder followed by rapid thermal exfoliation under a nitrogen atmosphere.The as-prepared samples were characterized using X-ray diffraction(XRD),scanning electron microscopy(SEM),high-resolution transmission electron microscopy (HRTEM),Raman spectroscopy,and Fourier transform infrared(FT-IR)spectroscopy.The specific surface area was determined using the nitrogen adsorption and desorption method.These analytic techniques revealed that the samples possessed a curled morphology consisting of a thin paper-like structure,which was made of a few graphite layers(approximately four layers)and a large specific surface area(628.5 m2?g－1).The effects of pH, adsorption time,temperature and initial concentration of Pb2+and Cd2+on adsorption onto the GNSs were investigated.The maximum adsorption capacities of GNSs for Pb2+and Cd2+ions were approximately 460.20 and 72.39 mg?g－1,respectively.These results indicate that the resulting high-quality GNSs can be used as an attractive adsorptive material for removing Pb2+and Cd2+from water.

Graphene;Thermal exfoliation;Characterization;Adsorption;Heavy metal ion

December 22,2015;Revised:February 17,2016;Published on Web:February 18,2016.*Corresponding author.Email:cewhyuan@scut.edu.cn;Tel:+86-20-87111887. The project was supported by the Presidential Foundation of Guangdong Vocational College of Environmental Protection Engineering in 2013,China (KY201303001)and National Natural Science Foundation of China(20976057).

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10.3866/PKU.WHXB201602182

廣東環(huán)境保護工程職業(yè)學(xué)院2013年院長基金及國家自然科學(xué)基金(20976057)資助項目