preparation of novel spherical pva/atp composites with macroreticular structure and their adsorption...
TRANSCRIPT
Pa
La
Lb
a
ARRA
KPACDH
1
dWsaaa
mhsaic
aip
1d
Chemical Engineering Journal 173 (2011) 446– 455
Contents lists available at ScienceDirect
Chemical Engineering Journal
jo u r n al hom epage: www.elsev ier .com/ locate /ce j
reparation of novel spherical PVA/ATP composites with macroreticular structurend their adsorption behavior for methylene blue and lead in aqueous solution
iuqing Yanga, Yanfeng Lia,∗, Huaiyuan Hua, Xinliang Jina, Zhengfang Yeb,∗∗, Yingxia Maa, Sidi Zhanga
State Key Laboratory of Applied Organic Chemistry, College of Chemistry and Chemical Engineering, Institute of Biochemical Engineering & Environmental Technology,anzhou University, Lanzhou 730000, PR ChinaDepartment of Environmental Engineering, Institute of Environmental Sciences & Technology, Peking University, Beijing 100871, PR China
r t i c l e i n f o
rticle history:eceived 8 June 2011eceived in revised form 31 July 2011ccepted 2 August 2011
eywords:VA
a b s t r a c t
A novel spherical composite of polyvinyl alcohol (PVA) and attapulgite (ATP) with macroreticular struc-ture, i.e. MR-PVA/ATP composites, was prepared as an adsorbent for some contaminations from aqueousenvironment, which would hold the advantages of PVA and ATP in the same time. The resulting adsorbentshold uniform and rich aperture with good mass transfer property, processing properties and stability.It has been proved with easy separation and excellent adsorption for methylene blue and lead in aque-ous solution, and the adsorption rate will be accelerated when increasing porogen in its preparation.
ttapulgiteompositeyes adsorptioneavy metal removal
The adsorption process of methylene blue and lead on it includes both chemo-adsorption and physicaladsorption. The adsorption process all fits the pseudo second order kinetics very well with rapid initialadsorption rate. The addition of attapulgite increased the adsorption capacity of lead ions significantly.By further graft functional groups on the ATP, it has potential to prepare various adsorbents to satisfyspecific requirements. Such kind of adsorption material will perform a wide application prospect in thepurification treatment for wastewater.
© 2011 Elsevier B.V. All rights reserved.
. Introduction
In recent years, with the accelerated process of industrializationevelopment, environmental pollution is getting worse and worse.ith the development of the living standard, people require a more
ustainable environment, thus, environment issues cause for morend more concern [1,2]. To improve the surrounding environment,ppropriate materials and methods to improve the environmentlso become a research hotspot [3,4].
Adsorption process has been proven one of the best water treat-ents around the world because of its high efficiency, ease of
andling, and availability of different adsorbents [5,6]. Here areome of the important low-cost adsorbents: silica gel, activatedlumina, zeolites, activated carbon, etc. Additionally, more researchs necessary to find the practical utility of low-cost adsorbents onommercial scale [7–10].
Compared to other materials, functional polymer spherical
dsorbent’s particle size and pore size can be controlled, makingt an easy access to uniform size sphere. The reticular structure,roducing a relatively large surface area, also prepares this kind∗ Corresponding author. Fax: +86 931 8912113.∗∗ Corresponding author. Fax: +86 010 62756526.
E-mail addresses: [email protected] (Y. Li), [email protected] (Z. Ye).
385-8947/$ – see front matter © 2011 Elsevier B.V. All rights reserved.oi:10.1016/j.cej.2011.08.003
of adsorbent with good mass transfer property. Polyvinyl alco-hol (PVA) has regular linear structure with a large number of sidehydroxyls on the molecular chain indicating excellent hydrophilic-ity and reactivity. Through the functional modification, it can bemade into a variety of adsorbents, such as ion-exchange film[11], hydrogel [12], and metal-complexion membrane [13] and soon. The mechanical strength, chemical stability and resistance tobiodegradation will be enhanced through chemical and physicalcrosslinking, hardening modification and other processing tech-nologies [14].
Palygorskite with many pores is of good adsorption, ionexchange and catalytic properties. It can be prepared as activenano-attapulgite (ATP) through functional modification [15–18].The same as PVA, ATP, abundant in nature, is cheap and easilyavailable. ATP also has excellent hydrothermal stability, indicat-ing a complement to PVA’s thermal instability. In recent years, theresearch of ATP focused on the nano-size graft [19], though theproducts after graft always show excellent absorption properties,they are difficult to separate from the aqueous solution, which seri-ously weaken their competitive strength to other adsorbents interms of the convenience.
In the field of aquatic environment, toxic metals, like As, Hgand Cd, has been notoriously known to cause severe health prob-lems to animals and human beings [20,21,7]. Discharging even asmall amount of dye into water can affect aquatic life and food
eering
wditsoc
ampc[
cpstamitablm
2
2
aLtMtCCru
2
Qdm3e
L. Yang et al. / Chemical Engin
ebs due to the carcinogenic and mutagenic effects of syntheticyes [22,23]. Therefore, their removal from contaminated water
s required strongly. Different from the traditional way to removehese two kinds of pollutants by different adsorbents designedeparately, to design and prepare adsorbents that could simultane-usly adsorb these two types of pollutants will reduce the energyonsumption and cost both in preparation and application.
Composite PVA with ATP will prepare the adsorbent with thedvantages of both them. Macroreticular adsorbent has betterass transfer performance, larger load capacity, indicating a bright
rospect for application. Further grafting functional groups on ATPan also prepare various adsorbents with specific requirements19,7].
In this work, we prepared a spherical PVA/ATP (MR-PVA/ATP)omposite with rich macroreticular structure, good processingroperties and physical–chemical stability which are of excellentimultaneously adsorption ability to dye and heavy metal. By simul-aneously sorption for them, it will reduce the energy consumptionnd cost both in preparation and application. Different from theajor studies of ATP focusing on grafting modification, the compos-
te PVA/ATP beads are easy to separate. Through further introducinghe macroreticular, the resulting products hold uniform and richperture with good mass transfer property. The composite can evene used for drinking water treatment because of non-toxic for bio-
ogical active substances. We also studied the sorption behavior ofethylene blue and lead on it systematically and comprehensively.
. Experimental
.1. Materials
Polyvinyl alcohol (PVA) with a degree of polymerization of 1750nd an alcoholysis degree higher than 99% was obtained fromanzhou Vinylon Factory, which was directly used without fur-her purification. Nano-attapulgite (ATP) was supplied from Anhui
ingmei Co., Ltd., which was ultrasound dispersed for 0.5 h, andhen treated with 2 M HCl with continuous stirring at 80 ◦C for 2 h.alcium carbonate (CaCO3) was obtained from Tianjing guangfuo., Ltd., which was further fine grinded with a ball mill. All othereagents used were of analytical-reagent grade. Deionized watersed to prepare all the solutions in sorption studies.
.2. Preparation of adsorbents
The main synthetic schematic drawing is shown in Fig. 1.uantitative PVA floccules, sodium alginate, ATP and CaCO3 were
issolved in distilled water at reflux temperature until uniformlyixed (about 1 h). The mixture was trickled into a gently stirred% CaCl2-saturated boric acid solution by an injector with diam-ter approximately 3 mm and immersed for 24 h to form stable
Fig. 1. The preparation sche
Journal 173 (2011) 446– 455 447
crosslinked composite sphere (Fig. 2). For forming macroreticular,the HCl solution (1 M) was used until no bubbles. After HCl reactedwith CaCO3 in the beads they became porous. The macroreticularbeads were washed to neutral with distilled water to remove resid-ual hydrochloric acid. The resulting product, showing regularlyspherical beads, has excellent mechanical strength with an aver-age diameter of 5 mm. MR-PVA with none ATP addition, PVA/ATPwith none porogen addition and MR-PVA/ATP with ATP and poro-gen ratio of 4:1 were used in the sorption section to compare theiradsorption property.
2.3. Sorption process
The sorption process was performed in a batch experiments.For batch tests, a given amount of adsorbent (0.5 g) was addedinto aqueous solution (100 mL) at a known concentration, constanttemperature of 30 ◦C and constant rate 140 rpm in a thermostatoscillator under dark environment. After a desired period of sorp-tion, the solution was removed out and the concentration wasmeasured.
The sorption capacity and efficiency of adsorbate onto the beadswere calculated according to the equations.
Q = (C0 − C)Vw
(1)
E = (C0 − C)C0
× 100% (2)
where Q is the adsorption capacity in mg/g, E is the adsorptionefficiency, C0 and C is the initial and outlet concentration in mg/L, Vis the volume of solution in L and w is the total amount of adsorbentin g.
2.4. Measurements
The size and morphology of the beads were observed by aJEOC JSM-6701F scanning electron microscope (SEM) at acceler-ating voltages of 5 kV. The thermal stability of the adsorbentswas studied with a Metler Toledo Star thermo gravimetric ana-lyzer. The pore volume (0.1548 mL/g), pore diameter (11.67 nm)and BET surface area (53.06 m2/g) were determined by a Quan-tachrome NovaWin2 Instrument. A thermostat oscillators (HaiSheng Da HQD 150L) was used for shaking all of the solutions.The concentrations of lead ions in solution were determinedusing a GBC Avanta A 5450 atomic adsorption spectrophotome-ter (AAS). The concentrations of methylene blue in solution weredetermined using a PERSEE TU-1810 UV–vis spectrophotome-
ter. The pH of solutions was determined using a HANNA pHmeter.The chemical stability was determined as followed approach.Acid solutions were prepared with pH 0–6 using nitric acid
matic of hybrid beads.
448 L. Yang et al. / Chemical Engineering Journal 173 (2011) 446– 455
king
whwdd
3
3
bspPatsttwp
ftCsctc
ot
Fig. 2. Cross-lin
hile alkali solutions were prepared with pH 8–14 using sodiumydroxide. The carriers were soaked in these solutions for oneeek at 50 ◦C, thoroughly rinsed with deionized water, andried in desiccators until no further change in weight wasetected [24].
. Results and discussion
.1. Prepare of MR-PVA and MR-PVA/ATP
ATP could adsorb many adsorbates very well for a large num-er of functional groups on its surface. However, it cannot beeparated easily. PVA has excellent processing properties andhysical–chemical stability. Considering the defaults of ATP andVA, we designed and prepared composite PVA with ATP owningll the advantages of both. In order to study the effect of ATP addi-ion on the properties, we added acid activated ATP in PVA sol with aeries of designed content to prepare the hybrid beads. Experimen-al results show that the addition of ATP has an optimal range. Whenhe ATP added little, there is little improvement on the adsorption,hen the addition of ATP is too much, the shape and mechanicalroperties will deteriorate.
To further improve the PVA/ATP composite’s mass transfer per-ormance, the calcium carbonate was added as a porogen, andhen removed by the use of dilute hydrochloric acid. The effect ofaCO3 content on adsorption performance for methylene blue wastudied. We can see from the result that the addition of calciumarbonate significantly reduced the adsorption time, this is due tohe introduction of large porous after the addition of the calcium
arbonate.In addition, we also studied the effect of porogen and ATP ration adsorption property for methylene blue. The results indicatedhat porogen and ATP also has an optimum dosage ratio range.
type in hybrid.
3.2. Adsorbent characterization
3.2.1. Structure of MR-PVA/ATPFig. 3 shows the shape and surface morphologies of PVA-ATP
beads by digital camera and the surface and inner of beads by scan-ning electron microscope. It is seen from Fig. 3 that the beads exhibitperfect ball (left of Fig. 3a) with an average diameter of 5 mm. TheATP crystal rod can be seen clearly in the macropores (Fig. 3b). Thereare a number of macropores in the beads with average aperture of300 um (Fig. 3c). There are still many smaller macropores embed-ded in the hollow wall with average aperture of 10 �m (Fig. 3d).There still micropore with average diameter of 11.67 nm. This struc-ture indicates that the composite of PVA/ATP has a large surfacearea (53.06 m2/g) and excellent mass transfer performance. Theseproperties are favorable for producing good adsorption capacity.
The aperture morphology of PVA/ATP with different porogencontent is obviously different. Fig. 3e and f shows the pore structureof the composite with porogen added excessively and added none,respectively. It is seen from the figure that when the porogen addedexcessively there are many defects in the pore structure and thepore size is larger and when added too few, there are only a smallquality of uneven pores found on the surface. Structures mentionedabove could explain the following adsorption results.
3.2.2. Stability of MR-PVA and MR-PVA/ATPThe chemical stability of MR-PVA and MR-PVA/ATP is shown in
Fig. 4. It can be seen clearly that the addition of ATP into the hybridbeads greatly improved the chemical stability from the less massloss. At low acid/base concentration, the chemical stability is sig-nificantly improved and it changes little when at high acid/base
concentration. Both of them are more stable in alkaline environ-ment compared to acidic environment. This is probably due to theexistence of abundant hydrogen bond in the hybrid beads and theinherent properties (more stable in alkaline environment) of PVA.
L. Yang et al. / Chemical Engineering Journal 173 (2011) 446– 455 449
F he mam
aMsoPaaTsrT
ig. 3. (a) The shape of hybrid beads by digital camera, (b) The ATP crystal rod in ticroscope.
The hybrid beads also exhibit well improved thermal stabilityfter adding the ATP. The thermogravimetry (TG) curves of ATP,R-PVA and MR-PVA/ATP are shown in Fig. 5. The TG curve of ATP
hows a slow downward trend. There is total 7.05% lost as a resultf several functional groups’ breaking down. The TG curve of MR-VA shows two consequent stages: the first comes between 274.3nd 320.4 ◦C followed by the second stage from 396.8 to 464.5 ◦Cnd then a slow downward trend. There is total 44.88% lost at last.
his might be caused by the decomposition of PVA, boric acid andodium alginate in the beads. Finally, various inorganic substancesemain. The TG curve of MR-PVA/ATP shows two different stages:he first stage starts from 296.8 ◦C and followed by the second frompH14121086420
Mas
s los
s (%
)
0
10
20
30
40
50
MR-PVAMR-PVA/ATPMR-PVAMR-PVA/ATP
Fig. 4. Chemical stability tests for MR-PVA and MR-PVA/ATP.
croreticular and (c)–(f) porous morphologies of hybrid beads by scanning electron
413.3 to 421.5 ◦C. Eventually, the total lost is 30.92%, which may dueto the decomposition of the PVA, boric acid, sodium alginate andfunctional groups on the ATP in the beads. Finally, various inorganicsubstances and added ATP remain.
3.3. Sorption studies
3.3.1. Sorption and its mechanism of methylene blue and lead
onto MR-PVA/ATPTo know the adsorption effect and clarify the sorption mech-anism, the adsorption of adsorbents to methylene blue and leadwas studied respectively. Two sorption mechanisms, chemosorp-
600400200
TG (%
)
50
60
70
80
90
100
ATPMR-PVAMR-PVA/ATP
a
b
c
Temperature (ºC)
Fig. 5. The thermogravimetry (TG) curves for (a) ATP, (b) MR-PVA and (c) MR-PVA/ATP.
450 L. Yang et al. / Chemical Engineering Journal 173 (2011) 446– 455
9876543210
14
16
18
20
Sor
ptio
n ca
paci
ty (m
g/g)
tsoms
3
smtiAAbAddd
3
toomtw
ATP dosage (g)
Fig. 6. Effect of ATP dosage on.
ion and physical sorption, were disclosed in the research. Theorption force may come from the existence of hydrogen bondsf a number of hydroxyl in adsorbents between N and S atomic inethylene blue and abundant hydroxyl in the hybrid for lead. The
orption mechanism can be further explained by sorption models.
.3.2. Effect of ATP dosageTheoretically, with the increase of ATP in the composite, the
orption capacity would increase because of better adsorption ofethylene blue onto ATP. The effect of the ATP dosage on adsorp-
ion of methylene blue onto the MR-PVA/ATP is shown in Fig. 6. Its clearly seen that the sorption capacity rises significantly whenTP increase in low dosage and then tend to slow. However, moreTP would not always be better. Fig. 3a shows the shape of hybrideads. The left one is ATP appropriately added (MR-PVA/ATP withTP dosage of 5 g) and the right one is excessively added (with ATPosage of 10 g). That is to say, the addition of ATP has an optimumosage range. Taking this situation into account, we selected theosage of 4 g ATP (MR-PVA/ATP) for sorption section.
.3.3. Effect of ATP and porogen (CaCO3) ratioFig. 7 shows the effect of ATP and porogen ratio on the adsorp-
ion of methylene blue onto the hybrid beads. It is seen that, the usef high content of CaCO3 in the low ATP dosage and low content
f CaCO3 in the high ATP dosage are the two optimum compositeethods. This can be explained as follows: the ATP is embedded inhe PVA when the ATP content is low and then could not contactith the solution easily, the increase of porogen content increase
Fig. 8. Effect of common ions on sorption (a) met
Fig. 7. Effect of ATP and CaCO3 ratio on sorption methylene blue onto hybrid beads.
the transfer properties and also increase the contact probability ofATP and solution, which resulting in increased sorption capacity.When adding ATP at a high content, the opportunity of adsorbatecontacting with ATP is greater. At this point, the surface area is thedominant factor. When porogen content is excessive, the spheremainly occupied by the oversized apertures which lead to relativelysmall surface area. The small amount of porogen addition makesthe aperture in the appropriate range this is to say in these rangesthe composite achieved the optimum adsorption without affectingthe transfer properties under the premise of increased surface area.Overall comparison, the ratio 4:1 of ATP and CaCO3 is optimum.
3.3.4. Effect of common ions and regenerate of compositeThe solution contain 10 mmol K+, Ca2+, Na+, Mg2+ and H+ was
prepared to study the effect of common ions, respectively. It canbe seen from Fig. 8 that the addition of K+, Ca2+, Na+ and Mg2+ hasnot affected the sorption capacity of lead markedly, but acceleratedthe sorption of methylene blue differently on the composite. Theexistence of H+ depressed the sorption capacity of lead. These mightdue to the change of surface charge when added the types of ions.
Hence, the acid solution can be used to regenerate composite.To do this, the composite adsorbed lead in 100 mL 100 mg/L of leadsolution for 24 h was filtrated and cast into 50 mL 10 mmol/L ofH2SO4, HNO3, HCl, NaOH and NaCl for 6 h. The desorption efficiency
was 2.5, 92.62, 95.24, 27.98 and 1.19%, respectively. Obviously, theHNO3 and HCl can be used to regenerate composite. The desorptionresults of NaOH and NaCl were beared out the effect of common ionsabove.hylene blue and (b) lead onto MR-PVA/ATP.
L. Yang et al. / Chemical Engineering Journal 173 (2011) 446– 455 451
hylen
l1twtodbdfas
3
lfbls
ifiMtmtis
Fig. 9. Effect of pH on sorption (a) met
To clarify how H+ effect on sorption of methylene blue andead, the pH 1.0–7.0 was investigate under initial concentration of00 mg/L as shown in Fig. 9. The curves both show two differentrends. The sorption capacity of Pb(II) ions increased significantlyith a pH rise from 1.0 to 5.0 but decreased slightly with a fur-
her pH rise from 6.0 to 7.0. On the contrary, the sorption capacityf methylene blue decreased with a pH rise from 1.0 to 6.0 butecreased slightly with a further pH rise from 6.0 to 7.0. This coulde attributable to a competitive sorption between Pb(II) and H+ ionsue to deprotonation of functional groups on the composite. There-ore, the solution pH up to 5.0 could be optimal for the composites efficient Pb(II) sorbent. The existence of H+ could promote theorption of methylene blue on the composite.
.3.5. Effect of initial methylene blue concentrationThe effect of the initial concentration on adsorption of methy-
ene blue onto the PVA/ATP was investigated under pH 5 at 30 ◦Cor 24 h as shown in Fig. 10a. In our investigation, the methylenelue sorption capacity rises significantly with an increase of methy-
ene blue concentration. It is due to abundant active groups on theurface of ATP and the large surface area of the hybrid beads.
In these concentrations, the sorption capacity of MR-PVA/ATPs higher than MR-PVA and PVA/ATP. It might be due to moreunctional groups in MR-PAV/ATP and larger surface area. It isndicated that the sorption performance of MR-PVA is worse than
R-PVA/ATP, so the addition of ATP is indeed necessary. The sorp-ion capacity of methylene blue onto PVA/ATP is lowest, which
ight caused by both the smaller surface area and lower massransfer properties, indicating that the mass transfer propertiess another important factor in this type of adsorption. Relativelyeamless surface hinders the transfer of adsorbate.
Fig. 10. Effect of initial concentration on sorption (a)
e blue and (b) lead onto MR-PVA/ATP.
In this study, the highest sorption efficiency is achieved 98.57%at the initial methylene blue concentration around 100 mg/L forMR-PVA/ATP, 96.07% at the initial methylene blue concentrationaround 40 mg/L for PVA/ATP, and 92.86% at the initial methyleneblue concentration around 20 mg/L for MR-PVA.
3.3.6. Effect of initial lead concentrationThe effect of the initial concentration on adsorption of lead onto
the PVA/ATP was investigated under pH of 5 at 30 ◦C for 6 h asshown in Fig. 10b. The lead sorption capacity rises significantlywith an increase in lead concentration, whereas the sorption effi-ciency declines. At a lower initial concentration, especially in therange of 0–200 mg/L, abundant active groups on the surface ofbeads can react with lead ions, resulting in a significantly increasedsorption capacity of lead. Then the adsorption process graduallybecomes slow when increasing the initial concentration. Both thesorption capacity and efficiency reach a high level at the optimalinitial concentration of around 200 mg/L. The highest sorption effi-ciency achieved in this study is 99.64% at the initial concentration ofaround 20 mg/L. That is to say, almost all lead ions will be adsorbedonto the beads if the initial concentration is lower than 20 mg/L.
3.3.7. Sorption isothermsThe concentration range from 20 to 200 mg/L for methylene blue
and 50–500 mg/L for lead were selected to be modeled for the sakeof time used to reach equilibrium. The adsorption of methyleneblue and lead onto the hybrid beads basically reaches equilibrium
in 120 h and 24 h respectively in this concentration range.The modeled quantitative relationship between methylene blueconcentration and the sorption process, the calculated correlationcoefficients and standard deviations are listed in Table 1, and the
methylene blue and (b) lead onto hybrid beads.
452 L. Yang et al. / Chemical Engineering Journal 173 (2011) 446– 455
Table 1The calculated correlation coefficients and standard deviations of sorption isotherm for sorption of methylene blue onto the hybrid beads.
Models Langmuir Freundlich Tempkin
R2 SD R2 SD R2 SD
0.90.90.9
ca
owcibfclp
tidibtmae
d
att
wmart
o
TI
MR-PVA 0.0089 0.1541
MR-PVA/ATP 0.0559 0.0873
PVA/ATP 0.9675 0.0774
omparison of sorption isotherm through the calculated constantsnd isotherm equations are listed in Table 2.
It can be seen that the sorption isotherm of methylene bluento the beads all fit the Freundlich model well, which has beenidely applied to many sorption processes, with the correlation
oefficients more than 0.90. They also fit the Tempkin model, whichndicates the chemisorption, might due to the existence of hydroxylond between the methylene blue and the beads, make the mainunction. The PVA/ATP also fit the Langmuir model which indi-ates the mono-layer adsorption. It might be for few pores andow surface area of it, which determined the bad mass transfererformance and sorption capacity.
The modeled quantitative relationship between lead concen-ration and the sorption process and the comparison of sorptionsotherm through the calculated correlation coefficients, standardeviations, isotherm equations and calculated constants are listed
n Table 3. It can be seen that the sorption isotherm of lead onto theeads fit the Langmuir model well, which has been widely appliedo monolayer sorption processes, with the correlation coefficients
ore than 0.90, which might due to the porous structure in it. Itlso fit the D-R model, which is applied to estimate the mean freenergy of adsorption.
The following is the classic description of these four models inetail.
The basic assumption of the Langmuir theory is that uptake ofdsorbate occurs on a homogenous surface by monolayer adsorp-ion without any interaction between adsorbed substances, andakes the following linear form:
Ce
Qe= 1
bQm+ Ce
Qm(3)
here Qm is the quantity of adsorbate required to form a singleonolayer on unit mass of adsorbent (mg/g) and Qe is the amount
dsorbed on unit mass of the adsorbent (mg/g) when the equilib-
ium concentration is Ce (mg/L) and b (L/mg) is Langmuir constanthat is related to the apparent energy of adsorption.The Freundlich isotherm theory says that the ratio of the amountf solute adsorbed onto a given mass of adsorbent to the concen-
able 2sotherm constants and equations for sorption of methylene blue onto the hybrid beads.
Models Adsorbents Constants
kf × 10−4 ((L/mg)1/n)
MR-PVA 1.903
Freundlich MR-PVA/ATP 1.853
PVA/ATP 2.448
Models Adsorbents Constants
Qm (mg/g)
Langmuir PVA/ATP 169.5
Models Adsorbents Constants
AT × 10−4 (L/min)
MR-PVA 7.674
Tempkin MR-PVA/ATP 7.744
PVA/ATP 8.609
981 0.0155 0.8534 4.989998 0.0061 0.8787 4.801981 0.0153 0.9098 3.301
tration of the solute in the solution is not constant at differentconcentrations. The heat of adsorption decreases in magnitude withincreasing the extent of adsorption. The linear Freundlich isothermis commonly expressed as follow:
log Qe = log Kf + 1n
log Ce (4)
where Kf (mg1−1/n L1/n g−1) and n (g/L) are the Freundlich constantscharacteristics of the system, indicating the relative adsorptioncapacity of the adsorbent related to the bonding energy and theadsorption intensity, respectively.
Tempkin model assumes that the heat of adsorption of allthe molecules in the layer decreases linearly with the coverageof molecules due to the adsorbate–adsorbate repulsions and theadsorption of adsorbate is uniformly distributed and that the fallin the heat of adsorption is linear rather than logarithmic. The lin-earized Tempkin equation is given by Eq. (5)
Qe = BT ln AT + BT ln Ce (5)
where BT = (RT)/bT, T is the absolute temperature in K and R is theuniversal gas constant (8.314 J/mol K). The constant bT is relatedto the heat of adsorption, AT is the equilibrium binding constant(L/min) corresponding to the maximum binding energy.
Dubinin have proposed another isotherm which is not basedon the assumption of homogeneous surface or constant adsorp-tion potential, but is applied to estimate the mean free energy ofadsorption (E). D–R equation is represented in a linear form by Eq.(6):
ln Qe = ln Qm − Kε2 (6)
where K (mol2/J2) is a constant related to mean adsorption energy,
and ε is the Polanyi potential, which can be calculated from Eq. (7).ε = RT ln(
1 + 1Ce
)(7)
Equation
n (mg/L)
1.0136 log Qe = 0.9866 log Ce − 0.72060.989 log Qe = 1.0111 log Ce − 0.73221.0798 log Qe = 0.9261 log Ce − 0.6111
Equation
b (L/mg)
0.001162 Ce/Qe = 0.0059 Ce + 5.079
Equation
BT (J/mol) bT
13.62 185.0 Qe = 13.62 ln Ce − 41.9414.63 172.3 Qe = 14.63 ln Ce − 44.8911.86 212.5 Qe = 11.86 ln Ce − 35.15
L. Yang et al. / Chemical Engineering Journal 173 (2011) 446– 455 453
Fig. 11. Effect of sorption time on sorption of (a) methylene blue and (b) lead ions onto the beads.
Table 3The calculated isotherm constants, correlation coefficients, standard deviations and equations for sorption of Lead onto MR-PVA/ATP.
Models Constants R2 SD Equations
Langmuir Qm (mg/g) 45.870.9577 0.8959
CeQe
=0.0218 Ce + 1.493B (L/mg) 0.01461
Freundlich kf × 10−3 ((L/mg)1/n) 3.9480.8621 0.0719 log Qe = 0.395 log Ce + 0.596
N (mg/L) 2.532
TempkinAT × 10−3 (L/min) 1.891
0.8819 4.109 Qe = 10.72 ln Ce − 23.34BT (J/mol) 10.72bT 235.1Qm (mg/g) 38.47
7
ln Qe = 3.65 −
Tr
E
3
rpsess
dM
TT
D-R 0.940K × 10−4 ((mol/J)2) 3.593E (J/mol) 37.30
he sorption energy can also be worked out using the followingelationship
= 1√2K
(8)
.3.8. Effect of sorption timeSorption kinetics is studied to determine the time required to
each the ions sorption equilibrium. Fig. 11 shows representativelots of the methylene blue and lead ions sorption capacity versusorption time under initial concentration of 100 mg/L. The sorptionfficiency on the beads rises nonlinearly with the increase of theorption time. The sorption process can clearly be divided into two
teps: an initial rapid step and a subsequent slow step.The adsorption of methylene blue onto the beads is very rapiduring the initial 48 h, in which the sorption capacity of MR-PVA,R-PVA/ATP and PVA/ATP reach to 93.28, 93.91 and 77.19 mg/g,
able 4he calculated kinetic parameters, correlation coefficients and standard deviations for so
Models Constants
Pseudo first-order
kad × 10−4 (L/min)
Qe (Cal) (mg/g) a
R2
SD
Pseudo second-order
k2 × 103 (g/mgmin)
h × 10−2 (mg/gmin)
Qe (Cal) (mg/g)
R2
SD
Elovich
˛ (mg/gmin)
ˇ (g/mg)
R2
SD
a Experimental Qe of MR-PVA, MA-PVA/ATP, PVA/ATP is 17.56, 19.50 and 18.14 mg/g, r
0.1086 2280[
ln(
1 + 1Ce
)]2
respectively. From 48 to 144 h, the sorption rate becomes quiteslow. When it comes to lead ions, the sorption of lead ions onto thebeads is very rapid during the initial 6 h. From 6 to 24 h, the sorptionrate becomes quite slow. Thus we can conclude that the sorptioncapacity in the secondary long-term step only contributes little tothe total sorption. The initial rapid step sorption may attribute tothe physical and surface reactive sorption from a facilely immedi-ate interaction between methylene blue (lead ions) and the activegroups bared on the surface of the hybrid beads. However, the sub-sequent slow step is caused by the reactive sorption inside thebeads. The diffusion of methylene blue and lead ions into the innerof the beads need a long period, resulting in a rather long time toreach the equilibrium sorption. It can be predicted from Fig. 11 that
an even higher adsorption capacity might be achieved if the sorp-tion time were longer, indicating a great potential of the sorption ofmethylene blue and lead ions. It also can be seen from Fig. 11a thatsorption of methylene blue onto the PVA/ATP is much slower thanrption of methylene blue onto the beads.
MR-PVA MR-PVA/ATP PVA/ATP
3.762 7.254 6.21815.05 13.60 13.960.9986 0.9949 0.99400.0287 0.0636 0.035713.23 6.062 8.1412.652 6.704 4.13618.73 20.16 18.350.9963 0.9987 0.98320.1935 0.1036 0.40850.1207 0.3148 0.16630.3546 0.3402 0.35270.9568 0.9291 0.95071.8024 2.4633 0.8476
espectively.
454 L. Yang et al. / Chemical Engineering Journal 173 (2011) 446– 455
Table 5The calculated kinetic parameters, correlation coefficients and standard deviations for sorption of Lead onto MR-PVA and MR-PVA/ATP.
Models Constants MR-PVA MR-PVA/ATP
Pseudo first-order
kad × 10−3 (L/min) 1.869 1.439Qe (Cal) (mg/g)a 12.37 17.02R2 0.8667 0.9895SD 0.07076 0.03527
Pseudo second-order
k2 × 10−5 (g/mgmin) 8.661 17.44h × 10−2 (mg/gmin) 3.451 13.99Qe (Cal) (mg/g) 19.96 28.33R2 0.9752 0.9929SD 0.05435 0.04315
Elovich
˛ (mg/gmin) 0.1205 0.6160ˇ (g/mg) 0.3068 0.2208R2 0.9449 0.9104SD 1.641 1.587
.
taMo
3
em
mcc(
l
w(ts
tg
wa
cbt
Q
wda
oIciidodf
a Experimental Qe of MR-PVA, MA-PVA/ATP is 14.00 and 26.01 mg/g, respectively
he others. It might be due to the smaller and less porous structurend it also indicates slower mass transfer properties compared toR-PVA and MR-PVA/ATP. Finally, Fig. 11b shows that the addition
f attapulgite increases the sorption capacity significantly.
.3.9. Sorption kineticsThe pseudo first order, pseudo second order and Elovich kinetic
quations were employed to analyze the sorption kinetics ofethylene blue and lead ions onto the beads.The pseudo first-order equation which is often used for esti-
ating kad considered as mass transfer coefficient in the designalculations. The integrated rate law after application of the initialondition of Qt = 0 at t = 0, becomes a linear equation as given by Eq.9)
og(Qe − Qt) = log Qe − kadt
2.303(9)
here Qe and Qt are the amounts of methylene blue adsorbedmg/g) at equilibrium time and at any instant of time, t, respec-ively, and kad (L/min) is the rate constant of the pseudo first orderorption.
The pseudo-second-order kinetic has since been widely appliedo a number of sorption systems can be written in a linear form, asiven by Eq. (10).
t
Qt= t
Qe+ 1
h(10)
here h = k2Q 2e that can be regarded as the initial sorption rate as t
pproaches 0. The k2 (g/mg min) is the second-order rate constant.Elovich equation is a rate equation based on the adsorption
apacity describing adsorption on highly heterogeneous adsor-ents. Eq. (11) is simplified by assuming ˛ ̌ � t and by applyinghe boundary conditions Qt = 0 at t = 0 and Qt = Qt at t = t.
t = 1ˇ
ln(˛ˇ) + 1ˇ
ln t (11)
here ̨ (mg/g min) is the initial adsorption rate and ̌ (g/mg) is theesorption constant related to the extent of the surface coveragend activation energy for chemisorption.
The calculated kinetic parameters for pseudo first order, sec-nd order and Elovich kinetic models are listed in Tables 4 and 5.t can be seen that the calculated Qe by second order was morelose to the experiment Qe. From the corresponding parameters, its observed that the kinetic behavior of methylene blue and leadons sorption onto the MR-PVA/ATP is both more appropriately
escribed by the pseudo second order model. The pseudo sec-nd order model was developed based on the assumption that theetermining rate step may be chemisorption promoted by covalentorces through the electron exchange, or valency forces throughelectrons sharing between adsorbent and adsorbate, indicating thatthe sorption of methylene blue and lead ions on these adsorbents isboth mainly the chemically reactive sorption. The correlation coef-ficient of these three adsorbents all above 0.99 indicated that thephysical adsorption is the other sorption pattern of methylene blueon these adsorbents.
The sorption process also fit Elovich kinetic with correlationcoefficient more than 0.90 and standard diversion not very high.It means that sorption of methylene blue and lead ions on theseadsorbents there is not only one pattern. This is the same with theresult described above.
4. Conclusions
In this work, we prepared a kind of spherical macro-reticularinorganic/polymer hybrid containing a number of functionalgroups by composite method and this method has been provedefficacious. Composite PVA with ATP, the MR-PVA/ATP is easy toseparate and of excellent adsorption ability for dyes and heavymetals. The resulting products, holding uniform and rich aper-ture, is of good mass transfer property, processing properties andphysical–chemical stability. Further grafting functional groups onATP; we can prepare various adsorbents to satisfy specific require-ments.
The sorption process of methylene blue and lead ions on it con-tains two parts, chemosorption and physical sorption. The sorptionprocess all fits the pseudo second order kinetics very well withrapid initial sorption rate. The addition of attapulgite increased thesorption capacity of lead ions significantly. The addition of porogenaccelerated the sorption rate. The adsorption ability can be furtheroptimized by regulating the initial concentration, sorption time,and solution pH. Such resin that can adsorb heavy metal ions anddyes concurrently can be used widely in the purification treatmentfor wastewater.
Acknowledgements
The authors gratefully acknowledge financial supports from theNational Major Specific Program of Science and Technology onControlling and Administering of Water’s pollution (2009ZX07212-001-04), and National Training Fund for Talented Person of BasicSubjects (J0730425, J1010067).
Appendix A. Supplementary data
Supplementary data associated with this article can be found, inthe online version, at doi:10.1016/j.cej.2011.08.003.
eering
R
[
[
[
[
[
[
[
[
[
[
[
[
[
L. Yang et al. / Chemical Engin
eferences
[1] M. Wang, M. Webber, B. Finlayson, J. Barnett, Rural industries and water pol-lution in China, J. Environ. Manage. 86 (2008) 648–659.
[2] A. Azizullah, M.N.K. Khattak, P. Richter, D.P. Häder, Water pollution in Pakistanand its impact on public health: a review, Environ. Int. 37 (2011) 479–497.
[3] I.D. James, Modeling pollution dispersion, the ecosystem and water quality incoastal waters: a review, Environ. Modell. Softw. 17 (2002) 363–385.
[4] F. Huang, X. Wang, L. Lou, Z. Zhou, J. Wu, Spatial variation and source apportion-ment of water pollution in Qiantang River (China) using statistical techniques,Water Res. 44 (2010) 1562–1572.
[5] E.A. Deliyanni, E.N. Peleka, K.A. Matis, Removal of zinc ion from water byadsorption onto iron-based nanoadsorbent, J. Hazard. Mater. 141 (2007)176–184.
[6] L.Q. Yang, Y.F. Li, L.Y. Wang, Y. Zhang, X.J. Ma, Z.F. Ye, Preparation and adsorp-tion performance of a novel bipolar PS-EDTA resin in aqueous phase, J. Hazard.Mater. 180 (2010) 98–105.
[7] K. Sharma, S. Mittal, M. Koel, Analysis of trace amounts of metal ions usingsilica-based chelating resins: a green analytical method, Crit. Rev. Anal. Chem.33 (2003) 183–198.
[8] Y.J. Jiang, Q.M. Gao, H.G. Yu, Y.R. Chen, F. Deng, Intensively competitiveadsorption for heavy metal ions by PAMAM-SBA-15 and EDTA-PAMAM-SBA-15 inorganic–organic hybrid materials, Microporous Mesoporous Mater. 103(2007) 316–324.
[9] M.N.V. Ravi Kumar, A review of chitin and chitosan applications, React. Funct.Polym. 46 (2000) 1–27.
10] A. Bhatnaga, M. Sillanpaa, Utilization of agro-industrial and municipal wastermaterials as potential adsorbents for water treatment: a review, Chem. Eng. J.
157 (2010) 277–296.11] K.W. Street, C.M. Hill, W.H. Philipp, Properties of a novel ion-exchange film, Ind.Eng. Chem. Res. 43 (2004) 7600–7607.
12] L. Jin, R. Bai, Mechanisms of lead adsorption on Chitosan/PVA hydrogen beads,Langmuir 18 (2002) 9765–9770.
[
[
Journal 173 (2011) 446– 455 455
13] H. Bessbousse, T. Rhlalou, J.F. ois Verche‘re, L. Lebrun, Novel metal-complexingmembrane containing poly(4-vinylpyridine) for removal of Hg(II) from aque-ous solution, J. Phys. Chem. B 113 (2009) 8588–8598.
14] J.F. Ge, Biodegradable Polymer Materials and Applications, Chemical IndustryPress, Beijing, 2002.
15] R.L. Frost a, Y. Xi, H. He, Synthesis, characterization of palygorskite supportedzero-valent iron and its application for methylene blue adsorption, J. ColloidInterface Sci. 341 (2010) 153–161.
16] Y. Liu, Y. Zheng, A. Wang, Enhanced adsorption of methylene blue from aqueoussolution by chitosan-g-poly (acrylic acid)/vermiculite hydrogel composites, J.Environ. Sci. 22 (2010) 486–493.
17] P. Cerezo, C. Viseras Iborra, A. Lopez-Galindo, F. Ferrari, C. Caramella, Use ofwater uptake and capillary suction time measures for evaluation of the anti-diarrheic properties of fibrous clays, Appl. Clay Sci. 20 (2001) 81–86.
18] C. Viseras, A. Lopez-Galindo, Pharmaceutical applications of some Spanish clay(sepiolite, palygorskite, bentonite): some preformulation studies, Appl. ClaySci. 14 (1999) 69–82.
19] P. Liu, J.S. Guo, Polyacrylamide grafted attapulgite (PAM-ATP) via surface-initiated atom transfer radical polymerization (SI-ATRP) for removal of Hg (II)ion and dyes, Colloids Surf. A 282–283 (2006) 498–503.
20] J.L. Valverde, A. de Lucas, M. Gonzalez, J.F. Rodriguez, Ion-exchange equilibriaof Cu2+, Cd2+, Zn2+, and Na+ ions on the cationic exchanger amberlite IR-120, J.Chem. Eng. Data 46 (2001) 1404–1409.
21] L.R. Bernabe, C. Alejandro, Preparation and adsorption properties of resins con-taining amine, sulfonic acid, and carboxylic acid moieties, J. Appl. Polym. Sci.90 (2003) 700–705.
22] T. Robinson, G. McMullan, R. Marchant, P. Nigam, Remediation of dyes in textileeffluent: a critical review on current treatment technologies with a proposed
alternative, Bioresour. Technol. 77 (2001) 247–255.23] A. Al-Futaisi, A. Jamrah, R. Al-Hanai, Aspects of cationic dye molecule adsorptionto palygorskite, Desalination 214 (2007) 327–342.
24] K.M. Khoo, Y.P. Ting, Biosorption of gold by immobilized fungal biomass,Biochem. Eng. J. 8 (2001) 51–59.