Silica microspheres from rice husk

(1)

Contents lists available atScienceDirect

Industrial Crops & Products

journal homepage:www.elsevier.com/locate/indcrop

Silica microspheres from rice husk: A good opportunity for chromatography stationary phase

Mostafa Shahnani

^a

, Maryam Mohebbi

^a

, Ahmad Mehdi

^b

, Alireza Ghassempour

^a

, Hassan Y. Aboul-Enein

^c,⁎

aMedicinal Plants and Drug Research Institute, Shahid Beheshti University, G.C, Evin, Tehran, Iran

bInstitut Charles Gerhardt de Montpellier, UMR 5253, CNRS-ENSCM-UM, Université de Montpellier, CC 1701, Place Eugène Bataillon, 34095 Montpellier, France

cPharmaceutical and Medicinal Chemistry Department, Pharmaceutical and Drug Industries Research Division, National Research Centre, Dokki, Giza 12622, Egypt

A R T I C L E I N F O Keywords:

Rice husk ash Sodium silicate

Mesoporous silica microsphere HPLC column

Natural compounds analysis

A B S T R A C T

The aim of this research is to produce spherical and porous silica particles from rice husk for chromatographic applications in HPLC columns. After complete combustion of rice husk, white powder of silica was obtained which was dissolved in NaOH and subsequently heated to produce sodium silicate solution. Spherical porous silica gel was synthesized from the prepared sodium silicate in the presence of Pluronic P123 as the surfactant, under acidic solution. Diﬀerent porosities were prepared by applying various factors including diﬀerent va- cuums, temperatures and reaction times in order to obtain the optimum conditions for particle aging. An analytical column was packed with the prepared silica microspheres and evaluated for the separation of 10-deacetylbaccatin III and rutin from taxol and hesperidin, respectively.

1. Introduction

Rice husk (RH) is an agricultural residue which is abundantly produced in rice industry. Silica is the major element of rice husk ash (Chawla et al., 1983). Nowadays, some countries must spend high costs to get rid of RH, due to its disposal and environmental problems (Sun and Gong, 2001). Therefore, extraction of silica from RH would be considered as a new challenge in order to produce a valuable material from a waste product, and the process is cost-eﬀective because of the high amount of RH as waste product and large content of silica in RH ash. There are many reports on extraction of silica from RH (Liou and Wu, 2010;Sun and Gong, 2001;Umeda et al., 2007;Zhang et al., 2010).

After complete combustion of RH, approximately 20 wt% of dry RH is ash; the ash itself is consisted of about 90–98% of silica (Mittal, 1997), but the silica content in RHs could be diﬀerent according to plant growth conditions (Liou and Wu, 2010;Sun and Gong, 2001;Umeda et al., 2007; Zhang et al., 2010). Several approaches to extract silica from RHs have been investigated (Sun and Gong, 2001). Puriﬁcation of the obtained silica is crucial for applications as the HPLC stationary phase, and in this favor various acid leaching procedures have been performed (Hamdan et al., 1997;Kalapathy et al., 2000;Unger, 1979;

Witoon et al., 2008). Kalapathy et al. (Kalapathy et al., 2000) scruti- nized silica construction using RH as the raw material, dissolved in sodium hydroxide solution. They found that assimilating the initial acid

washing of the rice husk ash as well as thefinal water washing of silica, dramatically intensifies the purity of the silica sample. Following an acid pretreatment step results in a highly pure silica which can be used for preparation of sodium silicate solution via treatment with sodium hydroxide. It’s worth noting that the mentioned process does not re- quire very high energy, compared to the production of sodium silicate by liquating the quartz and sodium carbonate at high temperature (1300 °C) (Affandi et al., 2009). Application of extracted silica from RH as a packing for HPLC columns wasfirst introduced by Burns and co- workers, who had prepared C18-modified silica particles (Burns et al., 2006). In another study, Tungkananurak used the extracted silica from RH for preparation of normal-phase HPLC packing (Tungkananurak et al., 2007). They developed a simple method to produce mesoporous silica microspheres using non-ionic surfactants. Mentioned investiga- tions clearly confirm the suitability of the extracted silica from RH for applications as the HPLC stationary phase in different chromatographic modes such as normal and reversed-phase liquid chromatography.

Therefore, we employed this silica for another mode of chromatography, called pre aqueous liquid chromatography (PALC), in which high amount of water as the mobile phase is applied on bare silica stationary phase (Dos Santos Pereira et al., 2009). The aim of the pre- sent work was to prepare silica microspheres with diﬀerent porosities.

The obtained silica was characterized using several analytical techni- ques such as scanning electron microscopy (SEM), energy-dispersive X-

https://doi.org/10.1016/j.indcrop.2018.05.023

Received 15 April 2018; Received in revised form 18 April 2018; Accepted 9 May 2018

⁎Corresponding author.

E-mail address:[email protected](H.Y. Aboul-Enein).

T

(2)

ray spectroscopy, Fourier transform infrared spectroscopy (FTIR), and N2adsorption-desorption measurements.

2. Materials and methods

RH sample used in this study was obtained from Mazandaran lands.

HCl and NaOH were purchased from Merck Chemical Company (Darmshdt, Germany). Pluronic P123 (Maver= 5800), taxol, 10-deacetylbaccatin III, rutin and hesperidin were obtained from Sigma-Aldrich (St. Louis, USA). Silica microsphere 10μm, 100 Å was purchased from YMC Company. Deionized water from Millipore Direct-Q was used throughout the experiments.

2.1. Extraction of silica from RH

RH was gathered from a local rice mill. Undesirableﬁne dust materials were removed over air-blowing separation technique and the rest was washed throughly to remove the physically adhered impurities using tap water. After consecutive washing, RH was dried in an air- circulated oven at 100 ± 2 °C for 10 h. The cleaned RH was burned at 700 °C for 6 h under air to yield a brownish powder. In order to obtain the impurity-free ash, cleaned RH was treated with 1 N aqueous solution of HCl under boiling condition for 1 h, followed by washing with distilled water. The RH was then dried and burned following the same procedure as speciﬁed above. Eventually, the obtained ash was white in color (Fig. 1).

2.2. Preparation of sodium silicate

White ash (5 g) was poured in 500 mL of 1 N NaOH solution and heated at 100 °C for 4 h under eﬃcient stirring to dissolve silica and produce sodium silicate solution. The resulting slurry wasﬁltered and subsequently washed with water to eliminate the residual impurities.

2.3. Preparation of porous spherical silica gel from sodium silicate solution 0.4 g of P123 was dissolved in 50 mL of 2 M HCl solution and 10 mL of sodium silicate solution was added to it under stirring at 250 r.p.m.

The resulting mixture was stirred for about 20 min and then, it was transferred into a polyethylene Erlenmeyer and heated overnight at 75 °C. Obtained particles were thenﬁltered and washed with deionized water and were subsequently dried at 80 °C for 24 h. Next, the powder was calcined at 550 °C for 5 h to remove the surfactant and eventually, porous silica microspheres were obtained. For synthesis of silica gels with diﬀerent pore sizes, various factors including temperature, aging time and vacuum of the oven were controlled (summarized inTable 1).

2.4. Characterization of silica

Chemical compositions and morphologies of the prepared synthetic silica were checked by scanning electron microscope (SEM) (VEGA3- LMU model) manufactured by TESCAN (Czech Republic) coupled to EDS at 15 KV N2adsorption–desorption isotherms were measured at

−196 °C over calcined sample using a Belsorp Mini II instrument (Bel Japan). Surface area and pore size were determined from Nitrogen adsorption branch using Brunauer– Emmett–Teller (BET) method. In order to identify the functional groups of silica and their bonding modes, IR spectra were recorded at 5 cm⁻¹resolution with 60 scans, using Bruker Tensor 27 spectrometer (USA).

2.5. High performance liquid chromatography

Chromatographic experiments were performed using a Knauer HPLC system equipped with the pump of model S 1000 and controller, auto-sampler of model S 3900, and the photodiode array detector of model S 2800. Deacetylbaccatin III and taxol were analyzed using sol- vent mixture of water/methanol as the mobile phase, with the following gradient program: 0–5 min 100% water, 5–15 min 80% water, 15–25 min 70% water, 25–35 min 50% water, 35–45 min 30% water, 45–55 min 20% water. The ﬂow rate was 1 mLmin⁻¹ and injection volume was 20μL.

2.6. Column packing

A stainless-steel column (120 × 4.6 mm) was packed with a column-packing apparatus (Knauer) by means of the slurry technique (2–2.5 g of sample dried at 120 °C and dispersed by ultrasonic stirring in 23 mL of methanol). Methanol was used to push the slurry into the column. The packing pressure was 4500 psig.

Fig. 1.(a) Burned Rice husk at 700 °C for 6 h (b) Cleaned Rice husk after treatment with 1 N aqueous solution of HCl under boiling condition for 1 h.

Table 1

Summary of conditions for production of diﬀerent porosities.

Pore size (nm)

Oven temperature (°C) Oven vacuum (m bar)

Aging time (hour)

2.6 80 800 24

6.1 30 200 24

6.4 60 200 24

11.9 60 200 48

(3)

3. Results and discussion

3.1. Synthesis of silica microsphere

For preparation of silica microspheres, P123 was dissolved in acidic solution and then, sodium silicate solution was slowly added into the mixture under mild stirring at room temperature. After synthesis, three parameters including oven temperature, oven vacuum and aging time were optimized for obtaining silica microspheres with diﬀerent porosities. As it is indicated inTable 1, changing the mentioned parameters can inﬂuence the particle porosity, in a way that high vacuum and two days of heating step at 60 °C led to the formation of particles with larger pore size.

3.2. Physical and chemical properties 3.2.1. FTIR analysis

After preparation of HPLC silica from sodium silicate solution which was extracted from RH, FTeIR spectrum of this synthetic silica was compared with that of YMC silica. FTeIR spectra indicated the ex- istence of siloxane (SieOeSi) bonds at around 1100 cm⁻¹, which is characteristic of the silicate network. Two observed bands at 1090 cm⁻¹ and 801 cm⁻¹ were related to Si-O-Si asymmetric and symmetric bond-stretching vibrations, respectively. The broad band at 3410–3470 cm⁻¹is related to the stretching vibration of the OeH bond from the silanol groups (SieOH), and is also related to the adsorbed water molecules on the silica surface. At 1635 cm⁻¹, there is a small band related to the bending HeOH bond of the adsorbed water molecules. The observed band at 470 cm⁻¹is associated with a network of OeSieO bond-bending modes (Fig. 2a, b).

3.2.2. Silica purity

Generally, purity of the silica is one of the main characters which determines the quality of separation, because in the presence of other metal oxides which can act as Lewis acids, peak tailing for most of the polar compounds may occur (Meyer, 2013). According to the purity and structure, there are three types of silica for chromatographic applications: A, B and C (Kirkland et al., 1993). Energy-dispersive X-ray spectroscopy (EDS) spectrum showed the high presence of silica (SiO2), whereas no peaks for other metal oxide impurities were observed (Fig. 3). It could be concluded that the applied washing process for preparation of silica gel from RH was efficient to remove all metal impurities, and the acid leaching was sufficiently effective to eliminate most of metal oxides from RH ash. The silica gel was produced through

alkali extraction of amorphous silica from white ash, followed by acid neutralization of the silicate solution to form gels.

3.2.3. SEM images

Morphology of the silica gel was studied by scanning electron microscopy (SEM) (VEGA 3 LMU TESCAN). Fig. 4 illustrates the good spherical shape of the silica particles. The spherical form of silica is very crucial, because it results in lower pressure and higher eﬃciency for separation.

Morphology of the silica particles is another important factor that must be considered for HPLC packings, because it plays a main role in separations in terms of resolution. Amorphous particles might cause tailing and hence lower separation eﬃciency (Fekete and Guillarme, 2013;Kirkland and DeStefano, 2006). Therefore, synthesized particles were studied using optical microscopy and scanning electron microscopy (SEM).Fig. 4illustrates SEM images of the silica particles. Ac- cording to the images, on can conclude that the applied method for preparation of silica microspheres could satisfactorily control the nu- cleation, polymerization and growth of silicate under acidic conditions and consequently, SEM images exhibitﬁnely spherical particles.

3.2.4. Analysis of surface area and pore size

In chromatography, porosity causes higher surface area to be ac- cessible for interaction of the analytes with surface of the silica(Urban et al., 2007).Fig. 5shows the nitrogen isotherm of the produced silica particles. The isotherm apparently indicated that the particles are micro- and mesopores, and a multilayer of adsorbate is formed which in turn causes an increase in relative pressure. According to the mean pore diameter at P/P0= 0.4, capillary condensation takes place on the multilayer, which results in a further increase in va. Data from BET plot revealed that the surface area of silica particles is 4.4528E + 02 m²g⁻¹ and total pore volume (P/P0=0.983) is 0.2976 cm³g⁻¹, which make the silica particles appropriate for HPLC applications.

3.3. High performance liquid chromatography

Chemical properties of the synthetic silica were completely similar to those of conventional silica gels used in high performance liquid chromatography. In order to evaluate the synthetic silica gel as the packing material for high performance liquid chromatography, we ex- amined separation of 10-deacethyl baccatin III from taxol, which were isolated using traditional silica column in our previous works (Ghassempour et al., 2009;Rezadoost and Ghassempour, 2012). Also, another mixture consisted of twoﬂavonoids, rutin and hesperidin, was

Fig. 2.FT- IR spectra of (a) synthetic silica gel and (b) YMC company silica gel.

(4)

analyzed using the same method (Fig. 6).

According to the obtained chromatograms, the synthetic silica not only possesses good chemical quality same as that of conventional

silica, but it also demonstrates high resolving power in chromatographic applications.

Fig. 3.EDS spectrum of synthetic silica gel.

Fig. 4.SEM images of synthetic silica gel.

Fig. 5.(a) BET plot and (b) nitrogen isotherm of produced silica gel.

(5)

4. Conclusion and perspectives

A simple method was developed and optimized for preparation of cost-eﬀective silica microspheres, which can be used for HPLC columns.

Application of rice husk as a source of silica, along with the nonionic surfactant, P123, allowed the formation of silica microspheres. HPLC chromatograms of the two mixtures consisted of taxol-taxotear and rutin-hesperidin showed acceptable resolutions between the analytes.

Moreover, this prepared silica can be developed for preparative liquid chromatography stationary phase, based on a cheap and available row material (RH).

Funding

This work was supported by Center for International Scientiﬁc Studies and Collaboration (CISSC). [Grant number: 1462].

Conﬂict of interest

All the authors conﬁrm that they have no conﬂict of interest for this article.

References

Aﬀandi, S., Setyawan, H., Winardi, S., Purwanto, A., Balgis, R., 2009. A facile method for production of high-purity silica xerogels from bagasse ash. Adv. Powder Technol. 20, 468–472.http://dx.doi.org/10.1016/j.apt.2009.03.008.

Burns, D.T., Tungkananurak, K., Jadsadapattarakul, D., 2006. Semi-micro preparation and characterization of bonded phase ODS-silica prepared from rice husk silica.

Microchim. Acta 154, 81–85.http://dx.doi.org/10.1007/s00604-005-0474-9.

Chawla, J., Negi, J., Prabhakar, D., 1983. Utilisation of lignocellulose waste for fuel bricks. Res. Ind (ISSN: 0034-513X).

Dos Santos Pereira, A., David, F., Vanhoenacker, G., Sandra, P., 2009. The acetonitrile shortage: is reversed HILIC with water an alternative for the analysis of highly polar ionizable solutes? J. Sep. Sci. 32, 2001–2007.http://dx.doi.org/10.1002/jssc.

200900272.

Fekete, S., Guillarme, D., 2013. Kinetic evaluation of new generation of column packed with 1.3μm core–shell particles. J. Chromatogr. A 1308, 104–113.http://dx.doi.org/

10.1016/j.chroma.2013.08.008.

Ghassempour, A., Rezadoost, H., Ahmadi, M., Aboul-Enein, H.Y., 2009. Seasons study of four important taxanes and puriﬁcation of 10-deacetylbaccatin III from the needles of

Taxus baccata L. by two-dimensional liquid chromatography. J. Liq. Chromatogr.

Relat. Technol.^®32, 1434–1447.http://dx.doi.org/10.1080/10826070902901184.

Hamdan, H., Muhid, M.N.M., Endud, S., Listiorini, E., Ramli, Z., 1997. 29Si MAS NMR, XRD and FESEM studies of rice husk silica for the synthesis of zeolites. J. Non-Cryst.

Solids 211, 126–131.http://dx.doi.org/10.1016/S0022-3093(96)00611-4.

Kalapathy, U., Proctor, A., Shultz, J., 2000. A simple method for production of pure silica from rice hull ash. Bioresour. Technol. 73, 257–262.http://dx.doi.org/10.1016/

S0960-8524(99)00127-3.

Kirkland, J., DeStefano, J., 2006. The art and science of forming packed analytical high- performance liquid chromatography columns. J. Chromatogr. A 1126, 50–57.http://

dx.doi.org/10.1016/j.chroma.2006.04.027.

Kirkland, J., Dilks, C., DeStefano, J., 1993. Normal-phase high-performance liquid chromatography with highly puriﬁed porous silica microspheres. J. Chromatogr. A 635, 19–30.http://dx.doi.org/10.1016/0021-9673(93)83111-5.

Liou, T.-H., Wu, S.-J., 2010. Kinetics study and characteristics of silica nanoparticles produced from biomass-based material. Ind. Eng. Chem. Res. 49, 8379–8387.http://

dx.doi.org/10.1021/ie100050t.

Meyer, V.R., 2013. Practical High-performance Liquid Chromatography. John Wiley &

Sonshttp://dx.doi.org/10.1002/9780470688427.

Mittal, D., 1997. Silica from ash. Resonance 2, 64–66.http://dx.doi.org/10.1007/

BF02838592.

Rezadoost, H., Ghassempour, A., 2012. Two-dimensional hydrophilic interaction/

Reversed-phase liquid chromatography for the preparative separation of polar and non-polar taxanes. Phytochem. Anal. 23, 164–170.http://dx.doi.org/10.1002/pca.

1338.

Sun, L., Gong, K., 2001. Silicon-based materials from rice husks and their applications.

Ind. Eng. Chem. Res. 40, 5861–5877.http://dx.doi.org/10.1021/ie010284b.

Tungkananurak, K., Kerdsiri, S., Jadsadapattarakul, D., Burns, D.T., 2007. Semi-micro preparation and characterization of mesoporous silica microspheres from rice husk sodium silicate using a non-ionic surfactant as a template: application in normal phase HPLC columns. Microchim. Acta. 159, 217–222.http://dx.doi.org/10.1007/

s00604-007-0743-x.

Umeda, J., Kondoh, K., Michiura, Y., 2007. Process parameters optimization in preparing high-purity amorphous silica originated from rice husks. Materi. Trans. 48, 3095–3100.http://dx.doi.org/10.2320/matertrans.MK200715.

K. Unger, Porous Silica (Journal of Chromatography Library Vol 16) Elsevier, Amsterdam, (1979) 10.1016/S0003-2670(01)95559-X.

Urban, J., Jandera, P., Kučerová, Z., van Straten, M.A., Claessens, H.A., 2007. A study of the eﬀects of column porosity on gradient separations of proteins. J. Chromatogr. A 1167, 63–75.http://dx.doi.org/10.1016/j.chroma.2007.08.027.

Witoon, T., Chareonpanich, M., Limtrakul, J., 2008. Synthesis of bimodal porous silica from rice husk ash via sol–gel process using chitosan as template. Mater. Lett. 62, 1476–1479.http://dx.doi.org/10.1016/j.matlet.2007.09.004.

Zhang, H., Zhao, X., Ding, X., Lei, H., Chen, X., An, D., Li, Y., Wang, Z., 2010. A study on the consecutive preparation of d-xylose and pure superﬁne silica from rice husk.

Bioresour. Technol. 101, 1263–1267.http://dx.doi.org/10.1016/j.biortech.2009.09.

045.

Fig. 6.Chromatograms of mixtures using produced silica gel: (a) Taxol and Taxotear and (b) Rutin and Hesperidinﬂavonoids.