磁球连接POSS再通过点击化学接上有机链段
Mesostructured Nanomagnetic Polyhedral Oligomeric Silsesquioxanes(POSS)Incorporated with Dithiol Organic Anchors for Multiple Pollutants Capturing in Wastewater
Hai-Bo He,*,?Bin Li,?Jun-Ping Dong,?Yun-Yi Lei,?Tian-Lin Wang,?Qiong-Wei Yu,?Yu-Qi Feng,*,?and You-Bao Sun§
?Department of Chemistry,Shanghai University,Shanghai,200444,P.R.China
?Key Laboratory of Analytical Chemistry for Biology and Medicine(Ministry of Education),Department of Chemistry,Wuhan University,Wuhan,430072,P.R.China
§Shimadzu(China)Co.,Ltd.,Shanghai Branch,Shanghai,200052,P.R.China
*Supporting Information
wastewater at ambient temperature.The Fe3O4@POSS-SH
within a few seconds under moderate magnetic?eld and exhibit
Contaminants-loaded Fe3O4@POSS-SH can be easily regenerated
hydrochloric acid(for heavy metal ions)under ultrasonication.The
both heavy metal ions and organic dyes,the removal rate for any of
multiple pollutants after repeated use for5cycles.Beyond the
vinyl groups,the Fe3O4@POSS derived materials rationally
and consequently a wide variety of applications may emerge.
thiol-functionalized,nanomagnetic POSS adsorbent
1.INTRODUCTION
Water contamination due to various organic and inorganic pollutants remains a serious environmental and public problem. Heavy metal ions and organic dyes are major environmentally harmful water pollutants commonly associated with industrial and agricultural e?uents.Heavy metal ions,such as mercury, lead,silver are nonbiodegradable and can be accumulated in the environment and living tissues,causing various diseases and disorders of living organisms even at a trace level.1?8The synthetic cationic dyestu?s,such as malachite green(MG)and rhodamine B(RB),can produce adverse health e?ects for both human beings and wildlife because of their carcinogenesis, mutagenesis,teratogenesis,and chronic toxicity.9?14Therefore, separation and remediation technologies are highly needed to reduce the residual pollutants contents below the acceptable threshold values by existing regulations before exposure.Sorption technique is one of the most e?ective and economical way that has been developed for this purpose.2,7,11,15 Recently the silica based mesoporous inorganic/organic hybrid materials are particular attractive as adsorbents for environmental remediation.15?17Indeed,one can expect its high performance for sequestering toxic substances from water samples,due to the large surface areas,well-de?ned pore structures,and tunable surface properties.Unfortunately, mesoporous materials usually exist in super?ne powdered form with microsized particles,which are di?cult to be separated from solution after batch adsorption experiments and easy to cause secondary pollution.As a development in this area,numerous studies have been devoted to the preparation of Received:June3,2013
Accepted:July30,2013
Published:July30,2013
多面体的低聚物
合并丆包含二巯基化物
污染物
八乙烯基
先用POSS修饰
Fe3O4?C
孔结构。
形貌。
离子和有机染料。
可再生丆耐酸碱
污染物
盐酸
乙烯基理性地
novel adsorbing materials by combination of mesoporous silica with magnetic separation.7,18?24Imparting magnetism to adsorbents a?ord a rapid and economic approach to remove the toxic compounds from large-volume samples by applying an appropriate magnetic?eld.Attempts to derive functionalized adsorbents based on magnetic mesoporous silica are undoubtedly of great potential application prospect.More recently,the core/shell-type magnetic mesoporous silica nanocomposites have been the subject of extensive research concerning water treatment as they exhibit high stability and varied functionality.25Typically,such materials can be synthesized by a combination of surfactant-based self-assembly and sol?gel processes,26and the functionality involves highly susceptible silylation or co-condensation routes,thereby su?ering from rather expensive sacri?cial templates(surfactants such as cetyltrimethylammonium bromide,block copolymers, such as F127)to generate mesostructure and tedious procedures(such as the synthesis of silanes with expected functional groups because of the lack of commercially available silanes monomers,and/or drying of the solvents,repeating hydrolysis and silylation cycles)to obtain desirable function-alities.15,18,19Additionally,the previously reported function-alized mesoporous silica adsorbents,whether magnetic or not, prevailed in the accumulation of single pollutants from wastewater.1,7,10,15,19,21These constitute real restrictions in extensive applications for real-world environmental cleanup process.Regarding the industrial and commercial requirements, it is ideal if e?cient mesostructured nanomagnetic materials with multifunctionalities can be achieved by a facile,universal, and economic synthetic approach.
Among the various innovative approaches for building porous materials with speci?c functionality and structure,the stepwise assembly of prede?ned nanoscale building blocks is an intriguing strategy that can be?nely designed and synthesized by tuning the primary building blocks.27,28Polyhedral oligomeric silsesquioxanes(POSS)are recently regarded as ideal building blocks for constructing organic?inorganic hybrid materials.A typical polyhedral oligomeric silsesquioxane (POSS)molecule possesses a cubic rigid(T8)structure represented by the formula R8Si8O12,where the central inorganic core(Si8O12)is functionalized with organic moieties (R)at each of the eight vertices.29,30Microporous/mesoporous materials based on POSS precursors have been prepared by various chemical routes including hydrosilation methods,31 thermolysis,32copper-mediated coupling,33and Schi?base chemistry.34In particular,Nischang35,36pioneered a facile, single-step process by using octavinyl POSS as the sole building blocks in polymerization to construct versatile,high-surface-area,hierarchically structured hybrid materials,therein the nanoporosity of the derived materials could be readily tuned by the use of a relatively inexpensive(in comparison to surfactants and block copolymers)binary porogenic solvent mixture(THF or PEG),and tailorability of the interface properties by functionalization of the residual vinyl groups via thiol?ene addition was also demonstrated.
Inspired by the examples presented above,the fabrication of magnetic mesoporous hybrid materials from POSS building blocks appears indeed desirable.Herein,we proposed a facile route to prepare POSS based magnetic organosilica nano-particles(Fe3O4@POSS)via a radically initiated polymer-ization.Rather than grafting of the methacryloxypropylheptai-sobutyl?POSS/methacrylate based block copolymers from magnetic nanoparticles as recently reported,37the primary rationale for our approach is self-assembling of the sole building blocks of octavinyl POSS to generate mesostructured and functionalizable hybrid layers.Copolymerization occurred on vinyl groups is a versatile synthetic tool for controlling the functionality,and,therefore,tailoring of the chemical,physical, and mechanical properties of materials.Since there are abundant residual vinyl groups resulting from POSS in case of the Fe3O4@POSS,it is adaptable to a wide range of functional monomers to realized derived materials with new properties.For example,it is well-known that numerous vinyl monomers can be employed for polymerization according to the free-radical polymerization principle,the atom-transfer radical polymerization(ATRP)is tolerant toward various halogenated reagents.38Extensive research have been carried out in the?eld of thiol?ene“click”addition,for the advantages such as simple,high e?ciency,and high-yield.39,40It should be emphasized that these synthetic strategies can be carried out under mild reaction conditions.Taking the aforementioned various modi?cation methods into account,it is highly anticipated to derive a wide range of porous structured magnetic materials with controllable functionalities,thereby extensive applications covering environmental remediation, sample pretreatment,drug delivery,catalysis,and magnetic resonance imaging are foreseeable.
As a preliminary exploitation,the modi?cation of Fe3O4@ POSS was implemented by introducing dithiol organic anchors via thiol?ene addition reaction.From the environmental point of view,thiol is a well-known group for the entrapment of heavy metal ions,7,15,21,22,41while the hydrophobicity resulting from self-assembled POSS layer29,35is compatible with the treatment of organic pollutants.Therefore,the removal of multiple pollutants from the wastewater by the Fe3O4@POSS-SH adsorbent was demonstrated in our present work.To the best of our knowledge,this is the?rst work on manufacturing POSS based mesoporous nanomagnetic organosilica,as well as employing it as a single adsorbent to deal with multiple pollutants from wastewater.
2.EXPERIMENTAL SECTION
2.1.Materials.Ferric chloride(FeCl3·6H2O),ferrous chloride (FeCl2·4H2O),aqueous ammonia solution(25%),acrylic acid,lead nitrate(Pb(NO3)2),silver nitrate(AgNO3),and mercuric nitrate (Hg(NO3)2·H2O)were purchased from Sinopharm Chemical Reagent Co.,Ltd.(China).Octavinyloctasilasesquioxane and2,2′-azobisobutyr-onitrile(AIBN)were obtained from Aladdin Chemistry Co.,Ltd.3,6-Dioxa-1,8-octanedithiol,malachite green,and rhodamine B were got from TCI(Shanghai)Development Co.,Ltd.AIBN was recrystallized in ethanol before use.All other reagents were of analytical purity and were used as received without further puri?cation.Double distilled water was used throughout the experiments.
2.2.Preparation of Fe3
O4@POSS-SH.Bare Fe3O4magnetic nanoparticles were prepared by chemical coprecipitation according to the reported procedure.42Acrylic acid(AA)was coated on the surface of Fe3O4to produce AA-Fe3O4.Magnetic nanoparticles(2.00g)were dispersed in100mL of acrylic acid aqueous solution,the pH of which was adjusted to5.50with alkaline solution,followed by stirring at85°C for1h under N2gas protection.The sediment was separated with an external magnet.After it was washed by distilled water and ethanol for several times,the double bond coated composites were dried in vacuum.
The Fe3O4@POSS was synthesized as follows:POSS(400mg)was dissolved in binary solvent mixture of2700μL of THF and535μL of PEG200.Then255mg of AA-Fe3O4was added to the suspension and was ultrasonically mixed for5min.The polymerization was initiated by the addition of96mg of AIBN at60°C.After24h,the as-prepared
沉淀物
Fe 3O 4@POSS composites were subjected to extraction with THF in a Soxhlet apparatus until the eluent was transparent before drying or use.The Fe 3O 4@POSS-SH was fabricated by modi ?cation of Fe 3O
4@
POSS particles with 3,6-dioxa-1,8-octanedithiol through thiol ?ene addition reaction.In a typical batch,100mg of Fe 3O 4@POSS and 350μL of dithiol were mixed adequately in 20mL of ethanol in a ?ask ?tted with a condenser.Thereafter,50mg of AIBN was added into the mixture,and the reaction was carried out at 60°C re ?uxing for 12h with stirring and bubbling with nitrogen stream throughout the procedure.Finally,the resultants were magnetically collected and then puri ?ed by repeating washing,decantation,and resuspension in water and ethanol.The as-prepared adsorbent was dried in a vacuum oven overnight before the adsorption of pollutants.Scheme 1illustrated the synthesis process of Fe 3O 4@POSS-SH.2.3.Characterization.The scanning electron microscopy (SEM)was used to observe the surface morphologies and dimensions of Fe 3O 4,Fe 3O 4@POSS and Fe 3O 4@POSS-SH samples,and the SEM
images were taken with an S-4800?eld emission scanning electron microscope (FE-SEM,Hitachi,Japan)at an accelerating voltage of 20kV with an energy-dispersive X-ray (EDX)spectroscopy.Fourier-
transform infrared (FT-IR)spectra scanned over the range of 400?
4000cm ?1with KBr slice on a Nicolet Avatar 370spectrometer (Nicolet Thermo,U.S.A.)were employed to examine the chemical nature of the synthesized composites.The C,H,and S elemental contents analysis were performed on an EA3000analyzer (Euro Vector,Italy).The nitrogen adsorption/desorption isotherms were measured by using an ASAP 2020N 2adsorption and desorption
analyzer (Micromeritics Co.,Ltd.,U.S.A.).Surface area was calculated using the Brunauer ?Emmett ?Teller (BET)equation from the adsorption isotherms in the relative pressure range of 0.06?0.15.Pore diameters were determined from the desorption branch of the isotherm using the Barrett ?Joyner ?Halenda (BJH)method.The total pore volume was calculated at a relative pressure of P/P 0above 0.99.
The samples were degassed under vacuum at 120°C for 5h prior to
measuring at ?196°C.Wide angle X-ray powder di ?raction patterns (XRD)of the magnetic products were obtained at room temperature on a D-MAX/IIA rotation anode X-ray di ?ractometer (Rigaku Corporation,Japan)equipped with Cu K αradiation (λ=1.5406?)at a scan rate of 4°2θmin ?1from 10°to 70°(2θ).Magnetic properties were analyzed using a vibrating sample magnetometer (VSM,Lakeshore Model-7410,U.S.A.). 2.4.Adsorption Experiments.To assess the adsorption e ?ciency,static adsorption tests were done by taking malachite green,rhodamine B,lead nitrate,silver nitrate,and mercuric nitrate as probes.Water samples were prepared by spiking water with known
amounts of heavy metal salts or organic dyes.The simulated wastewater consisted of malachite green,silver nitrate,mercuric nitrate with an individual concentration of 10mg L ?1.Various aqueous
solutions (10mL)were,respectively,shaken together with desired
amounts of Fe
3O 4@POSS-SH for 1h at room temperarue.After the
adsorbents had been isolated by an external magnet,the supernatant
was transferred to instrumental analysis.
UV ?vis absorption spectra of organic dyes were collected on an SP-2500spectrum instrument (Shanghai Spectrum Co.,Ltd.,China).The concentrations of heavy metal ions were measured by inductively coupled plasma atomic emission spectrometer (ICP-AES)of ICPE-
9000(Shimadzu,Japan).
The initial concentrations of heavy metal ions and organic dyes at diverse levels were selected to yield adsorption isotherms.The speci ?c
amount adsorbed onto
Fe 3O 4@POSS-SH was calculated based on the
following formula:43=?×Q C C V
M ()e 0
e (1)where Q
e (mg g ?1)is the equilibrium adsorption capacities,C
0(mg
L ?1)is the initial concentration,C e (mg L ?1)is the equilibrium
concentration,V (L)is the volume of the aqueous solution and M (g)
is the mass of the adsorbent used.
To optimize the usage of adsorbents,it is important to analyze the adsorption equilibrium data.The well-known Langmuir isotherm and Freundlich isotherm were applied to evaluate the adsorption behavior of probe solutes on Fe 3O 4@POSS-SH adsorbent.
The Langmuir model concerns monolayer adsorption onto a homogeneous surface and can be written as follows:11,17=+C q q K C q 1e
e max L e
max (2)where C e (mg L ?1
)is the equilibrium concentration of solute,q e (mg
g ?1)is the equilibrium adsorption capacity of adsorbent,q max (mg g ?1)
is the saturated adsorption amount of adsorbent,ans K
L is the
Langmuir adsorption constant.Scheme 1.Schematic Representation of the Route for Synthesis of Fe 3O 4
@POSS-SH
The Freundlich model assumes multilayer adsorption occurs on a heterogeneous surface and the linearized equation can be expressed as follows:20,43
=+ q K
n C
log log 1 log
e F e(3) where C e(mg L?1)is the equilibrium concentration o
f solute,q e(mg
g?1)is the equilibrium adsorption capacity of adsorbent,K F(L g?1), and n are Freundlich isotherm constants,which refer to the capacity and intensity of the adsorption,respectively.
3.RESULTS AND DISCUSSION
3.1.Synthesis and Characterization of the Materials. In the present work,iron oxide magnetic nanoparticles(MNPs) were prepared by coprecipitation method,which is simple and yields high production,44thus facilitating the massive applications of such materials among the following approaches. To improve dispersibility and promote functionality of iron oxide particle chunks,acrylic acid(AA)was coated on the nanoparticles via Lewis acid?base and hydrogen bonding interaction between?COOH and iron oxide surface.41,45In the presence of free radicals,the vinyl groups on the surface of AA-Fe3O4may act as spacers to anchor POSS entities and contribute to construct polymeric coated magnetic materials, though polymerization and initation will proceed also anywhere else in this complex mixture.The porosity of polymer can be readily tailored free from surfactants by using binary porogens of THF and PEG200.An inherent consequence of the polymerization of a multifunctional vinyl monomeric species is the existence of numerous residual vinyl groups,35thus3,6-dioxa-1,8-octanedithiol can be incorporated to the surface of Fe3O4@POSS particles by thiol?ene addition reaction.
The typical SEM images of Fe3O4,Fe3O4@POSS and Fe3O4@POSS-SH are shown in Figure1at80000×magni?cation.Figure1a indicates that the pristine Fe3O4 particles are nearly spherical in appearance with an average diameter of10nm.Similar rough polymeric coating with irregular cavities appears on the surface of Fe3O4@POSS and Fe3O4@POSS-SH;however,a growth in the average particle size about20?30nm were observed in Figure1b and1c.Table 1summarized the contents of various elements on the surface of Fe3O4@POSS and Fe3O4@POSS-SH particles obtaining from SEM-EDX spectra(see the Supporting Information, Figure S1).It is apparent that the surface of the two POSS derived MNPs is dominated by Si,indicating an e?ective surface coating on bare Fe3O4.The Fe3O4@POSS-SH is rich in S but rare in Fe,suggesting that the magnetic property is further protected by the self-assembled POSS layer during the “thiol?ene”reaction process.
To gain further insights into the chemical changes associated with the reactions shown in Scheme1,FT-IR spectroscopic measurements were also performed.As expected,in Figure2, all the spectra hold a clearly visible characteristic peak of Fe3O4 at580cm?1.Figure2b displays that after chemical modi?ed
with AA,the adsorption peak of Fe?OH at1635cm?1in Figure2a overlaps with the peak at1639cm?1relating to the stretching vibration of the C C bond in acrylic acid.The load of AA in AA-Fe3O4was determined to be0.21mmol g?1 according to the content of carbon element(0.763wt%,0.64 mmol g?1).Figure2c and Figure2d show strong Si?O?Si stretching vibration bands at1110cm?1,which is the typical absorption peak of the silsesquioxane inorganic framework(Si?O?Si),implying the successful attachment of POSS onto the AA-Fe3O4.In Figure2c,the peaks at3050,1600,1410,and 1275cm?1are characteristic of the residual vinyl groups of POSS.After chemically grafted the3,6-dioxa-1,8-octanedithiol by thiol?ene addition reaction,the intensities of these peaks decrease,while those of alkyl bands around2930(υCH
2
as)and 2850cm?1(υCH
2
s)increase signi?cantly as shown in Figure2d. No obvious peak ofδSH at2580cm?1was found in Figure2d because it is di?cult to detect the stretching vibration due to the weak dipoles.20Nevertheless,the content of sulfur in the Fe3O4@POSS-SH was about10mmol g?1calculating
from Figure1.Representative scanning electron micrographs of(a)Fe3O4, (b)Fe3O4@POSS,and(c)Fe3O4@POSS-SH.
elemental analysis,further evidencing the occurrence of thiol ?ene addition reaction on the surface of Fe 3O 4@POSS.Elemental analyses of C,H,and S are listed in Table S1(see the Supporting Information,Table S1).Figure 3a and 3b display the nitrogen sorption isotherms and the corresponding pore size distribution curves of Fe 3O 4@POSS and Fe 3O 4@POSS-SH,respectively.A type IV isotherm with steep hysteresis loop at relative pressure (P/P 0)of 0.45can be observed,indicating that the two materials have mesoporous structures that originate from the highly cross-linked POSS units.The Fe 3O 4@POSS was proved to have high speci ?c surface area of 653.59m 2g ?1and narrow pore size distribution with an average diameter of 4.56nm.The corresponding data of Fe 3O 4@POSS-SH are 224.20m 2g ?1and 4.45nm,respectively.It is worthwhile to note that after modi ?cation by thiols,there is little variation in pore size but notable shrink in BET surface area and pore volume (from 0.70to 0.28cm 3g ?1),implying the thiol groups would be partially introduced into the interior space of the meso-structrued pores.Although the dimension of “pore window ”was almost una ?ected,the pore “cavity and wall ”may be blocked in a great extent during functionalization.This is similar to what has been observed by Hao et.al as previously reported.46The crystal phases of magnetic products are investigated by XRD analysis.Figure 3c shows the similar XRD di ?raction patterns in which six di ?raction peaks (220,311,400,422,511,and 440)are seen and indexed to the spinal phases for iron oxides.A broad peak with 2θabout centered at 20°was observed in so-called Fe 3O 4@POSS,and Fe 3O 4@POSS-SH (Figure 3c),indicating the formation of amorphous silica polymers on nanocomposites.The results revealed that chemical modi ?cation of the iron oxide nanoparticls did not
make signi ?cant changes in the phase property of Fe
3O 4.Su
?cient magnetic properties are necessary for practical applications of magnetic materials in aqueous solutions.Field dependent magnetization measurements on the samples were
conducted to study their magnetic behaviors.Figure 3d shows
VSM magnetization curves of Fe 3O 4,Fe 3O
4@POSS,and Fe 3O 4@POSS-SH at room temperature.Clearly,the magnetic hysteresis loop curves exhibit neither coercivity nor remanence,indicating that these nanocomposites are superparamagnetic.Maximun saturation magnetizations of Fe 3O 4,Fe 3O 4@POSS,
and Fe 3O 4@POSS-SH are measured at 53.80,29.82,and 14.29emu g ?1,respectively.The decrease in the magnetic strength of nanocomposites results from the POSS coating.As can be observed from Figure S3(see the Supporting Information),the saturation magnetization of Fe 3O 4@POSS-SH is still enough for magnetic separation in a very short time by applying a magnet.3.2.Adsorption Behaviors of the POSS-Based MNPs.
Herein,the octavinyl POSS possesses a cubic rigid (T 8)
structure with the central inorganic core (Si 8O 12)is function-alized with organic vinyl moieties at each of the eight vertices,both the Si ?O core and the vinyl groups provide hydrophobic environment for nonpolar compounds.29,35After a polymer-ization step,the resulted Fe 3O 4@POSS has mesoporous structure coupled with high surface area and subsequently high-density POSS layer with hydrophobic property,which should be an ideal adsorbent for the capture of organic
compounds such as water-soluble organic dyes.Thiol is well-known to have a great a ?nity toward many metal ions,such as Ag +,Hg 2+,Pb 2+,and so on.Accordingly,the as-prepared Fe
3O 4@POSS-SH is highly anticipated to integrate the adsorption functions originated from POSS and thiol,thus enables e ?ective elimination of multiple pollutants in water treatment.In the following study,several environmentally harmful organic dyes and heavy metal ions commonly associated with industrial and agricultural e ?uents were chosen to explore the adsorption performance of Fe
3O 4@POSS-SH.
For comparison,the adsorption performance of Fe 3O 4@POSS was also investigated.
As expected,the Fe
3O 4@POSS exhibits good adsorb ability for the tested organic dyes as demonstrated in Figure 4a and 4b,suggesting the strong binding interactions between the
organic dyes and the high surface area porous hybrid coating stemming from cross-linked POSS.It should be pointed out that the uptake of such organic dyes becomes more e ?cient when the Fe
3O 4@POSS was modi ?ed with dithiol organic chain.Typically,5mg of Fe
3O 4@POSS-SH could remove almost 100%of the malachite green and 96%of the rhodamine B in an individual water sample with the initial concentration of 10mg L ?1(data gathered in Figure 4).As demonstrated by vivid photographs in inset of Figure 4a and Figure 4b,the color in the aqueous solutions of free dyes has markedly faded after adsorption,and the analytes-loaded nanoparticle adsorbent could be fast collected by a magnet within several seconds.Identically,as displayed in Figure 4c in terms of Pb 2+,Hg 2+,and Ag +,although the Fe 3O 4@POSS can remove these heavy metal ions to some extent because of the nanoporous hybrid chemisty from the self-assembled POSS,the material was found to have much better adsorption performance after the introduction of thiol groups,which are principally attributed to the
strong
Table 1.Weight and Atomic Percents of Various Elements on the Surface of Fe 3O 4@POSS and Fe 3O 4@POSS-SH from the Analysis of EDX O 26.7731.0126.7929.51Si 25.3216.7124.3115.26Fe 17.88 5.94 3.47 1.09S 13.67
7.51Figure 2.FT-IR spectra of (a)Fe 3O 4,(b)AA-Fe 3O 4,(c)Fe 3O 4@
POSS,and (d)Fe 3O 4@POSS-SH.
chelating a ?nity of free thiol groups toward heavy metal ions.As a matter of fact,the sulfur and oxygen atoms existing in Fe 3O 4@POSS-SH are also likely to coordinate with metal ions.The Fe 3O 4@POSS-SH as a consequent potential adsorbent was investigated thoroughly in the following study.To investigate the e ?ect of pH on the adsorption performance for dyes and metal ions,the Fe 3O 4@POSS-SH material was mixed with the solution of an individual pollutant at a concentration of 10mg L ?1in the range pH range of 3?9(adjusted by 0.1M NaOH and HNO 3).The results are summarized in Figure 5.Evidently,the adsorption of both dyes and metal ions were pH-dependent.As shown in Figure 5a,at lower pH (3?6)the adsorption capacity of MG and RB both increased as the pH increased,then kept almost constant for MG with further increasing pH,the RB however reached a maximum at pH 6?7.MG and RB are cationic dyes,which have positive charge in general aqueous solution.13,47At lower pH,the strong protonation of the ?SH groups 4,7on the material caused electrostatic repulsion with the positively charged dyes,thus lead to the decreased adsorption capacity as pH decreased.The adsorption capacity of MG changed a little in the pH range of 6?9and the highest adsorption capacity of RB obtained around pH 6?7,implying that the hydrophobic interaction plays a key role between the material and such dyes.When pH is higher than 7,the deprotonation of amine and carboxylic groups in rhodamine B gives rise to a negatively charged molecule,14whose adsorption in turn dropped due to the weakening of the hydrophobic interaction.In Figure 5b,the adsorption capacities of metal ions increased as the pH increased from 4to 7and presented a maximum around pH 7,then decreased with increasing pH in the range of 7?9.The results are mainly attributed to the following reasons:4,7(1)at lower pH,the ?SH groups are pronated,thus diminishing their chelating ability to metal ions and (2)alkaline conditions hinder the adsorption of heavy metals because of formation of stable hydroxyl complexes or hydroxides.It should be emphasized that the pH of natural water is mostly around 7,moreover,in view of the superiority of adsorption performance on both dyes and metal ions at this pH according to the above results,the adsorption tests were conducted without pH adjustment throughout the following adsorption experiment,thereby facilitating the real-life waste-water treatment due to less procedure of sample handling.The adsorption isotherms in Figure S2(see the Supporting Information)demonstrate a positive functional relationship between the adsorption capacity of the Fe 3O 4@POSS-SH and the equilibrium concentration of pollutants.The ?tting isotherm parameters are listed in Table 2.For metal ions,the higher correlation coe ?cients (R L 2)of the linearized Langmuir equation than these of Freundlich equation (R F 2)indicate
that
Figure 3.Nitrogen adsorption ?desorption isotherms of (a)Fe 3O 4@POSS and (b)Fe 3O 4@POSS-SH (the insets are corresponding pore size
distribution curves),(c)XRD patterns,and (d)VSM magnetization curves of Fe 3O 4,Fe 3O 4@POSS,and Fe 3O 4@POSS-SH.
Langmuir model can better ?t to the experimental results.The adsorption behaviors of malachite green and rhodamine B dyes
on the Fe 3O 4@POSS-SH,however,comply with the multilayer type of Freundlich isotherm based on the ?tting results.A detailed comparison with other magnetic mesoporous silica adsorbents that used for the adsorption of metal ions and
organic pollutants (Table S2in Supporting Information)indicates that,the as-prepared Fe 3O 4@POSS-SH has some advantages in terms of surfactant free for mesoporous formation,facile operation in functionalization and comparable
adsorption capacities of metal ions and dye.Moreover,it has
Figure https://www.wendangku.net/doc/8f11599969.html,parative absorption spectra
of (a)malachite green,(b)
rhodamine B,and (c)comparisons between the adsorption of heavy metal ions by di ?erent amounts of Fe 3O 4@POSS and Fe 3O 4@POSS-SH nanoparticles.Curves 1?4stand for the dye solutions treated with
1mg of Fe 3O 4@POSS,1mg of Fe 3O 4@POSS-SH,5mg of Fe 3O 4@POSS,and 5mg of Fe 3O 4@POSS-SH,respectively.The insets are photographs of (i)initial solutions (10mg L ?1of dye)and (ii)dye
solutions after adsorption by the Fe 3O 4@POSS-SH left under the magnet for 10
s.Figure 5.E ?ect of pH on the adsorption amounts of (a)dyes and (b)
heavy metal ions by Fe 3O 4@POSS-SH (initial concentration of each pollutant =10mg L ?1,adsorbent dosage =5mg/10mL for dyes,
adsorbent dosage =20mg/15mL for metal ions,room
temperature).Table 2.Isotherm Parameters for the Adsorption of Pollutants onto Fe 3O 4@POSS-SH
Hg 2+99.800.0510.99623.74 3.570.988
Ag +100.000.0510.99723.47 3.730.959
Malachite green 111.010.230.99137.98 3.940.998
Rhodamine B 142.050.0890.98620.18 2.220.996
孔雀绿
the potential as a single adsorbent for the simultaneou removal of multiple pollutants.3.3.Puri ?cation of Simulated Wastewater and
Regeneration of Fe 3O 4@POSS-SH.The designed Fe
3O 4@
POSS-SH as a single adsorbent for the removal of multi-component pollutants in wastewater is delineated as below.Simulated wastewater was prepared by malachite green,silver nitrate,and mercuric nitrate with the same concentrations of 10mg L ?1.After puri ?cation by 100mg of adsorbent,the residual Hg 2+and Ag +is 0.15and 0.052mg L ?1,respectively,while the solution turns to be completely colorless and no dye is monitored,meaning that the Fe 3O 4@POSS-SH can clear almost all the hazardous materials (98.5%of Hg 2+,99.5%of Ag +,and 100%of dye).These results further throw light on the superior puri ?cation ability of the novel adsorbent for practical wastewater with complicated components.Furthermore,the stability of Fe 3O 4@POSS-SH in aqueous phases was assessed by contacting with various corrosive solutions (Figure S3in the Supporting Information).Naked Fe 3O 4particles were observed easily digested by strong acids as liquids in left bottles in Supporting Information Figure S3c and d present yellow-green color obviously.The Fe 3O 4@POSS-SH,however,was estimated rather resistant to strong acid and basic conditions,as no visible change for transparent liquid with the Fe 3O 4@POSS-SH immersed for 48h (right bottles in Supporting Inforamtion Figure S3c and d).The results are certi ?cations of a complete coating for Fe 3O 4by POSS as proposed.Actually,POSS as a building block for constructing functional molecules and nanometric materials shows signi ?-cantly high thermal and chemical stability.29The “simulated wastewater contaminated ”material was then regenerated according to the literatures 7,10with a little procedure modi ?cation:after treated with 5×2mL of methanol ?acetic acid (95:5,v/v)and 5×2mL of 1mol L ?1HCl in sequence under untrasonic (Note:2.0mL of each elution solution for 10min in every time,eluted 5times in every cycles),the desorption e ?ciency was almost 100%for MG meanwhile over 98%for metal ions when the fresh adsorbent used for the ?rst time.Thus methanol ?acetic acid (95:5,v/v)and 1mol L ?1HCl solutions with the above procedure were chosen for respectively releasing of MG and metal ions from the material in repeated cycles of regeneration.The extent of Fe leaching from Fe 3O 4@POSS-SH during regeneration was also measured quantitatively.The respective eluate from the ?rst 3cycles was collected and used for ICP-AES analysis.As listed in Supporting Information Table S3,only a small proportion of Fe (<1.5wt %)was detected in the eluate even under ultrasonic in strong acid aqueous solution.Such low leaching of Fe from Fe 3O 4@POSS-SH would also result in little sacri ?ce of its magnetism.Therefore,the Fe 3O 4@POSS-SH featured with the rigid silica cube shell is believed to be excellently stable in natural water matrices and wastewater.And its regeneration becomes more feasible by desorption of the pollutants even under extreme conditions.The reusability of the regenerated material was tested by using for removal of pollutants in the simulated wastewater.As depicted in Figure 6,the removal e ?ciency for the simulate wastewater dropped slightly in the subsequent regeneration-reuse cycles.As the renewed one kept desirable removal e ?ciency (at least 92%)after reuse in 5cycles,the as-prepared Fe 3O 4@POSS-SH is believe to have good reusability.This would allow economic and practical operation in relation to wastewater puri ?cation,as well as monitoring analysis,where noxious contaminations are present at (ultra)low concen-tration.The present merits of the material may be ascribe to its nanoporous structure with high BET surface area and tailored functionality via thiol ?ene addition reaction,the inherent unique inorganic/organic hybrid framework of POSS should also not be ignored.
4.CONCLUSIONS
Here,we endowed the functionalizable POSS with magnetism by a facile polymerization step,then mercapto functionalized magnetic porous adsorbent of nanometer size (Fe 3O 4@POSS-SH)was successfully achieved via the thiol ?ene addition
reaction.The obtained thiol tagged magnetic inorganic/organic hybrid material turns out to be an ideal single adsorbent for purifying wastewater coexisting with inorganic heavy metal ions and organic dyes at room temperature.Furthermore,the proposed adsorbent can be easily recovered and the renewed one bears desirable ability to remove the contaminants.In view of the good capture/release e ?ciency,the nanoadsorbent has
the potential for enrichment of such analytes from complex
matrices in trace analysis.More than that,this highly ?exible route concerning POSS,as for well-tailored functionalized magnetic porous materials may emerge for various applications in which anticipated multifunctions,as well as high surface areas are
required.■ASSOCIATED CONTENT *Supporting Information Elemental analysis,EDX spectra of Fe
3O 4@POSS and Fe 3O 4@POSS-SH,adsorption isotherms of metal ions and organic dyes,photos of erosion results for Fe
3O 4and Fe 3O 4@POSS-SH,and leaking of Fe in eluate.This material is available free of charge via the Internet at https://www.wendangku.net/doc/8f11599969.html,.■AUTHOR INFORMATION Corresponding
Author *H.-B.E.:E-mail hbhe2006@https://www.wendangku.net/doc/8f11599969.html,;fax +86-21-66134594;tel +86-21-66132930.Y.-Q.F.:E-mail yqfeng@https://www.wendangku.net/doc/8f11599969.html,;fax +86-27-68755595;tel +86-27-68755595
Figure
6.Removal e ?ciency of Fe 3O 4@POSS-SH for Hg 2+
and Ag +
,
malachite green in simulated wastewater in repeated adsorption ?desorption cycles (in every cycle,initial concentration of each pollutant =10mg L ?1,adsorbent dosage =100mg/10mL,pH =7,temperature =25°C).
赋予丆捐赠含巯基的吸附剂预期的
Notes
The authors declare no competing?nancial interest.■ACKNOWLEDGMENTS
This work was funded by the National Science Foundation of China(Grants20905046and21005057).The authors gratefully thank the Instrumental Analysis&Research Center of Shanghai University for instrumentation.
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