Investigating the Heavy Metal Adsorption of Mesoporous Silica Materials Prepared by Microwave Synthesis
© The Author(s). 2017
Received: 29 January 2017
Accepted: 11 April 2017
Published: 4 May 2017
Mesoporous silica materials (MSMs) of the MCM-41 type were rapidly synthesized by microwave heating using silica fume as silica source and evaluated as adsorbents for the removal of Cu2+, Pb2+, and Cd2+ from aqueous solutions. The effects of microwave heating times on the pore structure of the resulting MSMs were investigated as well as the effects of different acids which were employed to adjust the solution pH during the synthesis. The obtained MCM-41 samples were characterized by nitrogen adsorption–desorption analyses, X-ray powder diffraction, and transmission electron microscopy. The results indicated that microwave heating method can significantly reduce the synthesis time of MCM-41 to 40 min. The MCM-41 prepared using citric acid (c-MCM-41(40)) possessed more ordered hexagonal mesostructure, higher pore volume, and pore diameter. We also explored the ability of c-MCM-41(40) for removing heavy metal ions (Cu2+, Pb2+, and Cd2+) from aqueous solution and evaluated the influence of pH on its adsorption capacity. In addition, the adsorption isotherms were fitted by Langmuir and Freundlich models, and the adsorption kinetics were assessed using pseudo-first-order and pseudo-second-order models. The intraparticle diffusion model was studied to understand the adsorption process and mechanism. The results confirmed that the as-synthesized adsorbent could efficiently remove the heavy metal ions from aqueous solution at pH range of 5–7. The adsorption isotherms obeyed the Langmuir model, and the maximum adsorption capacities of the adsorbent for Cu2+, Pb2+, and Cd2+ were 36.3, 58.5, and 32.3 mg/g, respectively. The kinetic data were well fitted to the pseudo-second-order model, and the results of intraparticle diffusion model showed complex chemical reaction might be involved during adsorption process.
KeywordsMicrowave synthesis Silica fume MCM-41 Heavy metal adsorption
Heavy metal pollution has become a major environmental problem, threatening the environment and public health. Heavy metals can accumulate in the environment and cause heavy metal poisoning. They are not biodegradable and cannot be metabolized or decomposed. Moreover, they can easily enter the food chain and cause chronic toxic effects with gradual accumulation in living organisms. According to the World Health Organization drinking water guidelines, the acceptable concentration limits for Cu2+, Cd2+, and Pb2+ are 2, 0.003, and 0.01 mg/L, respectively . Several methods have been applied for the effective removal of heavy metal ions such as ion exchange , nano-filtration , solvent extraction , chemical precipitation , adsorption [6, 7], etc. Among the available methods, adsorption technology is the most promising and frequently used technique due to its simplicity, high efficiency, and low cost . Various kinds of adsorption materials have been used to remove heavy metal ions from aqueous solution, such as activated carbon  and clays . However, these materials have low adsorption efficiency for heavy metal ions because of their low pore volume and poor pore structure.
Mesoporous materials have been widely used for the adsorption of heavy metal ions [11–14] due to their exceptionally large specific surface area, regular pore structure, and tunable pore sizes. Since the discovery of M41S silica in 1992 , MCM-41 has become the most popular type of M41S silica materials and one of the most commonly used mesoporous adsorption materials. MCM-41 is characterized by highly uniform pore channels, large pore size, and high surface area . Synthesis of mesoporous MCM-41 materials attracts a lot of interest because of their potential applications in catalysis , ion exchange , biosensors , and drug delivery [20, 21]. Commercial reagents employed in the traditional preparation of MCM-41 are always expensive and toxic, such as tetraethylorthosilicate (TEOS) . Moreover, other silica precursors, such as agricultural waste, have also been used to produce mesoporous silica materials (MCM-41). For instance, using rice husk ash for the synthesis of SBA-15, MCM-41, and MCM-48 has been reported previously [23–25]. The use of mesoporous materials from industrial solid waste, such as coal combustion waste fly ash, as a silica source has also attracted attention due to economic advantages [26, 27]. Silica fume, a very fine amorphous silica powder, is obtained as a by-product during metal production processes. Silica fume mainly contains amorphous SiO2 particles (greater than 85 wt%), and it has been used as an inexpensive silica source in the synthesis of microporous and mesoporous materials . Thus, it further broadens the applications of silica fume which is generally used as an additive in cement and concrete , in bricks and ceramic tiles , as well as a filler in plastics and paints . The use of silica fume as silica source also allows the green synthesis of MCM-41, since it does not require the use of any harmful reagents.
The conventional hydrothermal synthesis process of MCM-41 requires a long crystallization time and a high crystallization temperature. In 1996, thermally stable molecular sieve MCM-41 with hexagonal channels was synthesized in a temperature-controlled microwave oven from aged precursor gels within about 1 h by Wu et al. . At present, microwave irradiation technique is widely applied to the synthesis of mesoporous molecular sieves [33–35]. Compared with the conventional hydrothermal synthesis method, microwave-assisted synthesis method employs microwave dielectric heating, uniform heating, or molecular selective heating. Thus, it offers the advantages of homogeneous heating and fast elevation of the temperature of synthesis system to crystallization temperature, resulting in more homogeneous nucleation, shorter crystallization times [36, 37], and products with uniform size [38, 39].
This work explores the preparation of mesoporous silica materials (of MCM-41 type) using a rapid microwave heating method and their application for Cu2+, Pb2+, and Cd2+ removal from aqueous solutions. The effects of different acids used for pH adjustment and different microwave heating times on the pore structure of MCM-41 were investigated. We also studied the influence of pH on adsorption capacity of the adsorbent. The metal adsorption isotherms were fitted using Langmuir and Freundlich adsorption isotherm models. In addition, kinetics and intraparticle diffusion model were also studied to understand the mechanism of the adsorption process.
Silica fume was used as the silica source and it was obtained from a local metallurgy-grade silicon factory. Its main chemical component (85 wt%) is SiO2. It was dried at 150 °C for 24 h and used after dissolution and purification; more details can be found in Additional file 1: Figure S1 and Table S1. Other reagents, such as sodium hydroxide (NaOH), cetyltrimethylammonium bromide (CTAB), hydrochloric acid (HCl), citric acid, oxalic acid, acetic acid, copper nitrate (Cu(NO3)2), lead nitrate (Pb(NO3)2), and cadmium nitrate (Cd(NO3)2) were purchased from Shanghai Chemical Reagent Company of China and used as received. All of the reagents were analytical grade.
Preparation of MCM-41
The sodium silicate solution was conveniently obtained using dissolution method. Then, the MCM-41 was synthesized by the following procedure: 5 g of CTAB was dissolved in 100 mL of deionized water, and the aqueous solution was continuously stirred for 30 min at room temperature. Then, 50 mL of pretreatment filtrate was slowly introduced into the above CTAB solution under stirring, and then one of several different acids (HCl, citric acid, oxalic acid, or acetic acid) was added dropwise to adjust the pH value of the solution to an optimum range of 10.87–10.88. Subsequently, the solution was stirred for 30 min–1 h and then subjected to microwave heating (SANYO EM-208MS1, China) for different times to allow the hydrothermal reaction to occur. After crystallization of the product, it was then cooled to room temperature, filtered, and washed with deionized water. The obtained solid product was placed in an oven and dried at 110 °C for 12 h. Finally, the synthesized material was calcined at 550 °C for 5 h to remove the template molecules. MCM-41 samples synthesized via this route were designated as x-MCM-41(y), where “x” represents the acid used to adjust reaction solution pH and “y” is the microwave heating time.
The X-ray diffraction (XRD) patterns were recorded on a Rigaku D/MAX-3B diffractometer with Cu–Kα radiation with a voltage of 40 kV. Nitrogen (N2) adsorption–desorption isotherms were measured at 77.5 K by a NOVA 2200e surface area and pore size analyzer (Quantachrome Instruments). The specific surface area of the sample was calculated using BET (Brunauer–Emmett–Teller) method, and pore size distribution was determined using BJH (Berrett–Joyner–Halenda) model. The sample morphology was examined using a JEOL JEM-2100 transmission electron microscope (TEM).
Effect of Initial pH
The effect of pH on Cu2+, Pb2+, and Cd2+ adsorption was investigated over the pH range from 3.0 ± 0.1 to 7.0 ± 0.1. In a typical procedure, the adsorption experiments of Cu2+, Pb2+, and Cd2+ were carried out in a series of conical flasks containing 0.1 g of c-MCM-41(40) and 100 mL of Cu2+, Pb2+, and Cd2+ solutions of 40 mg/L. The pH was adjusted to the desired value by HCl (0.1 M) or NaOH (0.1 M), and the pH values were measured by a pH meter (OHAUS Starter 3C, China). Then, the conical flasks were continuously stirred at 25 °C for 24 h. After reaching adsorption equilibrium, the suspended adsorbent was easily collected from the aqueous solution by centrifugation at a speed of 5000 rpm for 5 min. Then, the supernatant was filtered with a syringe filter of 0.22 μm and analyzed via an AAS spectrophotometer after appropriate dilution.
Adsorption Isotherm Experiment
Kinetic Adsorption Experiment
Results and Discussion
Characterization of MCM-41
Textural properties of the samples prepared with microwave heating
S (m2 g−1)
V (cm3 g−1)
Effect of Solution pH
Comparison of Cu2+, Pb2+, and Cd2+ sorption capacities with other sorbents
J. Hazard. Mater., 184 (2010) 126–134
Water Research, 32(4) (1998) 1314–1322
Desalination, 229 (2008) 170–180
Appl. Water Sci., 3 (2013) 321
J. Environ. Sci. Technol., 12 (2015) 2003–2014
Activated poplar sawdust
J. Hazard. Mater., 137 (2006) 909–914
Sep. Purif. Technol., 54 (2007) 187–197
Proc. 1999 Conference on Hazardous Waste Research, St. Louis, 1999, pp. 121–130
The kinetics of Cu2+, Pb2+, and Cd2+ adsorption on c-MCM-41(40) are shown in Additional file 1: Figure S5. The adsorption of all heavy metals rapidly occurred within 50 min due to the large number of available sites at the initial stage. With the increase in adsorption time, there was a gradual decrease in the concentration of heavy metals in solution as well as the available active sites on adsorbent, due to the accumulation of metal ions on c-MCM-41(40), leading to the decrease in adsorption rate at the later stage.
Kinetic parameters and correlation coefficients of the two kinetic equations on c-MCM-41(40)
q e.exp (mg/g)
First-order kinetic model
Second-order kinetic model
a e,cal (mg/g)
q e,cal (mg/g)
Intraparticle Diffusion Model
In this study, an ordered mesoporous silica material MCM-41 has been conveniently synthesized using silica fume as the silica source under microwave heating. Microwave heating synthesis method significantly reduced the reaction time to 40 min. The sample c-MCM-41(40) prepared with citric acid under microwave heating for 40 min possesses the highest pore volume and pore diameter among all the samples, as well as well-defined crystallinity and regular hexagonal array of mesoporous channels. It also shows good performance for removing Cu2+, Pb2+, and Cd2+ in the pH region of 5.0–7.0. The adsorption data of Cu2+, Pb2+, and Cd2+ showed good fitting with the Langmuir isotherm, suggesting that the adsorption process is a homogeneous process. The maximum adsorption capacities of c-MCM-41(40) for Cu2+, Pb2+, and Cd2+ were 36.3, 58.5, and 32.3 mg/g, respectively. Kinetic data of c-MCM-41(40) were found to fit better with pseudo-second-order kinetic model than pseudo-first-order kinetic model, and the calculated equilibrium adsorption capacities (q e,cal) from the pseudo-second-order adsorption kinetics were very close to the experimental data (q e.exp). In addition, the results of intraparticle diffusion model indicate that the intraparticle diffusion is not the only rate-limiting step, and complex chemical reactions or redox reactions might also be involved.
Financial support from NSFC (21307046, U1137601, and U1402233), Natural Science Foundation of Yunnan Province (2015FB120), and personnel training funds of KMUST (KKZ3201422005) are gratefully acknowledged.
WJZ carried out the whole study, explained and discussed obtained results, and prepared the manuscript. JXW, DW, and XTL, realized the synthetic part. CYH coordinated the analytical part of the study. SFH carried out the physical–chemical measurements of the investigated materials. YML and WHM designed and coordinated the study. All authors read and approved the final manuscript.
The authors declare that they have no competing interests.
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.
- World Health Organization (1998) Guidelines for drinking water quality, addendum to volume 2: Health criteria and other supporting information[M]. WHO PublicationsGoogle Scholar
- Wdjtowicz A, Stokμosa A (2002) Removal of heavy metal ions on smectite ion-exchange column. Pol J Environ Stud 11:97–101Google Scholar
- Al-Rashdi BAM, Johnson DJ, Hilal N (2013) Removal of heavy metal ions by nanofiltration. Desalination 315:2–17View ArticleGoogle Scholar
- Yun HC, Prasad R, Guha AK, Sirkar’a KK (1993) Hollow fiber solvent extraction removal of toxic heavy metals from aqueous waste streams. Ind Eng Chem Res 32:1186–1195View ArticleGoogle Scholar
- Gupta VK, Ali I, Saleh TA, Nayak A, Agarwal S (2012) Chemical treatment technologies for waste-water recycling—an overview. RSC Adv 2:6380–6388View ArticleGoogle Scholar
- Feng Y, Gong JL, Zeng GM, Niu QY, Zhang HY, Niu CG, Deng JH, Yan M (2010) Adsorption of Cd(II) and Zn(II) from aqueous solutions using magnetic hydroxyapatite nanoparticles as adsorbents. Chem Eng J 162:487–494View ArticleGoogle Scholar
- Albadarin AB, Mangwandi C, Al-Muhtaseb AAH, Walker GM, Allen SJ, Ahmad MNM (2012) Kinetic and thermodynamics of chromium ions adsorption onto low-cost dolomite adsorbent. Chem Eng J 179:193–202View ArticleGoogle Scholar
- Yuan Q, Li N, Chi Y, Geng WC, Yan WF, Zhao Y, Li XT, Dong B (2013) Effect of large pore size of multifunctional mesoporous microsphere on removal of heavy metal ions. J Hazard Mater 254–255:157–165View ArticleGoogle Scholar
- Machida M, Amano Y, Aikawa M (2011) Adsorptive removal of heavy metal ions by activated carbons. Carbon 49:3393View ArticleGoogle Scholar
- Beveridge A, Pickering WF (1983) The influence of surfactants on the adsorption of heavy metal ions by clays. Water Res 17:215–225View ArticleGoogle Scholar
- Wu SJ, Li FT, Xu R, Wei SH, Li GT (2010) Synthesis of thiol-functionalized MCM-41 mesoporous silicas and its application in Cu(II), Pb(II), Ag(I), and Cr(III) removal. J Nanopart Res 12:2111–2124View ArticleGoogle Scholar
- Manuel A, Jiménez VM, Enrique R-C, Antonio J-L, José J-J (2005) Heavy metals removal from electroplating wastewater by aminopropyl-Si MCM-41. Chemosphere 59:779–786View ArticleGoogle Scholar
- Wongsakulphasatch S, Kiatkittipong W, Saiswat J, Oonkhanond B, Striolo A, Assabumrungrat S (2014) The adsorption aspect of Cu2+ and Zn2+ on MCM-41 and SDS-modified MCM-41. Inorg Chem Commun 46:301–304View ArticleGoogle Scholar
- Benhamou A, Baudu M, Derriche Z, Basly JP (2009) Aqueous heavy metals removal on amine-functionalized Si-MCM-41 and Si-MCM-48. J Hazard Mater 171:1001–1008View ArticleGoogle Scholar
- Beck JS, Vartuli JC, Roth WJ, Leonowicz ME, Kresge CT, Schmitt KD, Chu CTW, Olson DH, Sheppard EW (1992) A new family of mesoporous molecular sieves prepared with liquid crystal templates. J Am Chem Soc 114:10834–10843View ArticleGoogle Scholar
- Gai LG, Jiang HH, Cui DL, Wang QL (2009) Room temperature blue-green photoluminescence of MCM-41, MCM-48 and SBA-15 mesoporous silicas in different conditions. Micropor Mesopor Mater 120:410–413View ArticleGoogle Scholar
- Wang SP, Shi Y, Ma XB, Gong JL (2011) Tuning porosity of Ti-MCM-41: implication for shape selective catalysis. ACS Appl Mater Inter 3:2154–2160View ArticleGoogle Scholar
- Bruzzoniti MC, Sarzanini C, Torchia AM, Teodoro M, Testa F, Virga A, Onida B (2011) MCM41 functionalized with ethylenediaminetriacetic acid for ion-exchange chromatography. J Mater Chem 21:369–376View ArticleGoogle Scholar
- Asefa T, Duncan CT, Sharma KK (2009) Recent advances in nanostructured chemosensors and biosensors. Analyst 134:1980–1990View ArticleGoogle Scholar
- Botella P, Corma A, Quesada M (2012) Synthesis of ordered mesoporous silica templated with biocompatible surfactants and applications in controlled release of drugs. J Mater Chem 22:6394–6401View ArticleGoogle Scholar
- Guo R, Li LL, Yang H, Zhang MJ, Fang CJ, Zhang TL, Zhang YB, Cui GH, Peng SQ, Feng W, Yan CH (2012) Tuning kinetics of controlled-release in disulfide-linked MSN-folate conjugates with different fabrication procedures. Mater Lett 66:79–82View ArticleGoogle Scholar
- Kumar P, Mal N, Oumi Y, Yamana K, Sano T (2001) Mesoporous materials prepared using coal fly ash as the silicon and aluminium source. J Mater Chem 11:3285–3290View ArticleGoogle Scholar
- Bhagiyalakshmi M, Yun LJ, Anuradha R, Jang HT (2010) Utilization of rice husk ash as silica source for the synthesis of mesoporous silicas and their application to CO2 adsorption through TREN/TEPA grafting. J Hazard Mater 175:928–938View ArticleGoogle Scholar
- Bhagiyalakshmi M, Yun LJ, Anuradha R, Jang HT (2010) Synthesis of chloropropylamine grafted mesoporous MCM-41, MCM-48 and SBA-15 from rice husk ash: their application to CO2 chemisorption. J Porous Mater 17:475–484View ArticleGoogle Scholar
- Seliem MK, Komarneni S, Abu Khadra MR (2016) Phosphate removal from solution by composite of MCM-41 silica with rice husk: kinetic and equilibrium studies. Micropor Mesopor Mater 224:51–57View ArticleGoogle Scholar
- Majchrzak-Kuceba I (2011) Thermogravimetry applied to characterization of fly ash-based MCM-41 mesoporous materials. J Therm Anal Calorim 107:911–921View ArticleGoogle Scholar
- Li DD, Min HY, Jiang X, Ran XQ, Zou LY, Fan JW (2013) One-pot synthesis of aluminum-containing ordered mesoporous silica MCM-41 using coal fly ash for phosphate adsorption. J Colloid Interface Sci 404:42–48View ArticleGoogle Scholar
- Zhu WJ, Zhou Y, Ma WH, Li MM, Yu J, Xie KQ (2013) Using silica fume as silica source for synthesizing spherical ordered mesoporous silica. Mater Lett 92:129–131View ArticleGoogle Scholar
- Gesoğlu M, Güneyisi E, Özbay E (2009) Properties of self-compacting concretes made with binary, ternary, and quaternary cementitious blends of fly ash, blast furnace slag, and silica fume. Constr Build Mater 23:1847–1854View ArticleGoogle Scholar
- Almeida AEFS, Sichieri EP (2005) Study of the adherence between polymer-modified mortars and porcelain stoneware tiles. Mater Res 8(3):245–249View ArticleGoogle Scholar
- Abu-Ayana YM, Yossef EAM, El-Sawy SM (2005) Silica fume—formed during the manufacture of ferrosilicon alloys—as an extender pigment in anticorrosive paints. Anti-Corros Method M 52(6):345–352View ArticleGoogle Scholar
- Wu CG, Bein T (1996) Microwave synthesis of molecular sieve MCM-41. Chem Commun 8:925–926View ArticleGoogle Scholar
- Jiang TS, Shen W, Zhao Q, Li M, Chu JY, Yin HB (2008) Characterization of Co-MCM-41 mesoporous molecular sieves obtained by the microwave irradiation method. J Solid State Chem 181:2298–2305View ArticleGoogle Scholar
- Park SE, Kim DS, Chang JS, Kim WY (1998) Synthesis of MCM-41 using microwave heating with ethylene glycol. Catal Today 44:301–308View ArticleGoogle Scholar
- Fantini MCA, Matos JR, da Silva LC C, Mercuri LP, Chiereci GO, Celer EB, Jaroniec M (2004) Ordered mesoporous silica: microwave synthesis. Mater Sci Eng B 112:106–110View ArticleGoogle Scholar
- Jansen JC, Arafat A, Barakat AK, Bekkum van H, Occelli ML, Robson HE (eds) (1992) Synthesis of 360 microporous materials, vol 2. Van Nostrand Reinhold, New York, p 507Google Scholar
- Tompsett GA, Conner WC, Yngvesson KS (2006) Microwave synthesis of nanoporous materials review. Chem Phys Chem 7:296–319View ArticleGoogle Scholar
- Hwang YK, Chang JS, Kwon YU, Park SE (2004) Microwave synthesis of cubic mesoporous silica SBA-16. Micropor Mesopor Mater 68:21–27View ArticleGoogle Scholar
- Su JD, Prasetyanto EA, Lee SC, Park SE (2009) Microwave synthesis of large pored chloropropyl functionalized mesoporous silica with p6mm, Ia-3d, and Im3m structures. Micropor Mesopor Mater 118:134–142View ArticleGoogle Scholar
- Sing KSW (1985) Reporting physisorption data for gas/solid systems with special reference to the determination of surface area and porosity (Recommendations 1984). Pure & Appl Chem 57(4):603-619Google Scholar
- Rouquerol J, Avnir D, Fairbridge CW, Everett DH, Haynes JH, Pernicone N, Ramsay JDF, Sing KSW, Unger KK (1994) Recommendations for the characterization of porous solids (Technical Report). Pure & Appl Chem 66(8):1739-1758Google Scholar