Environmentally superior cleaning of diatom frustules using sono-Fenton process: Facile fabrication of nanoporous silica with homogeneous morphology and controlled size

https://doi.org/10.1016/j.ultsonch.2020.105044Get rights and content

Highlights

  • Removal of organic materials from diatom frustules using sono-Fenton process.

  • Characterization of the obtained nanoporous silica by SEM, XRD, FT-IR, BET and TGA.

  • Study of the effect of operational parameters on the cleaning of diatom frustules.

  • Identification of the organic compounds released from diatom cells to the solution.

Abstract

Existing techniques for the preparation of silica structures from diatom cells include cleaning of frustules through baking at high temperature and oxidant cleaning using concentrated sulfuric acid, hydrogen peroxide, nitric acid, or sodium dodecyl sulfate (SDS)/ethylenediaminetetraacetic acid (EDTA). In this study, sono-Fenton (SF) process was examined to prepare nanoporous silica through cleaning diatom frustules, while preserving their structural features. Single colonies of Cyclotella sp. were cultivated in batch mode f/2-enriched seawater. Combination of Fenton process with ultrasonication was found to be more efficient than the sum of individual processes in the removal of organic compounds from Cyclotella sp. structure. The optimized amounts of operational parameters were determined as suspension pH of 3, diatom cell density of 4.8 × 105 cell mL−1, H2O2 concentration of 60 mM, Fe2+ concentration of 15 mM, ultrasound irradiation power of 400 W and the temperature of 45 °C. The results of energy-dispersive X-ray spectroscopy (EDX) and thermal gravimetry (TG) analyses proved that organic materials covering the cell wall were significantly removed from the frustules through SF process. Scanning electron microscopy (SEM) images showed that after SF treatment, silica nanostructures were produced having uniform pores less than 15 nm in diameter. N2 adsorption–desorption isotherms demonstrated that almost non-porous structure of diatom frustules became mesoporous during removing the organic matrix. Lipids, amino acids, carbohydrates and organic acids or their oxidized products were identified using GC–MS analysis as the main organic compounds released from diatom cells to the solution after SF treatment. Treated frustules exhibited adsorption capability of 91.2 mg/g for Methylene Blue, which was almost 2.5 times higher than that of untreated frustules (34.8 mg/g).

Introduction

Nature shows extraordinary complex architecture in different microorganisms and this is why material scientists derive innovation in designing novel biomaterials using these structures [1]. Diatoms, as one of the examples of such microorganisms, has attracted considerable attention owing to their unique architecture of cell walls (frustules), which is related to their excellent photosynthesis performance [2]. They are found in the waterways, oceans, soils and produce approximately 20% of the oxygen generated on the earth annually [3]. Diatoms are generally known as fast-growing and dominant species (about 50%) of phytoplankton community under unlimited condition, given enough silicate and nutrients content higher than approximately 2 μmol L−1 silicate [4], [5]. Based on differences in morphology and structure of the frustules, more than 100,000 various diatoms species are classified [5]. Gordon and Drum, for the first time, proposed the potential application of diatom frustules in nanotechnology in 1994 [6]. Since then, considerable attention has been paid to the capability of unicellular diatoms to synthesize three-dimensional silica with a specific structure [5], [7]. According to the literature, the diatoms frustules have been characterized by their biocompatibility, multiple pore surfaces, excellently ordered micro/nanostructures, unique optical characteristics, mechanical and thermal stability and have been considered as potential candidates for different applications [8], [9]. Particularly, frustules can act as photonic crystals owing to the shape and size of pore morphology bodies, which leads to unique optical characteristics [10]. Incorporation of some biomolecules such as antibodies, enzymes and proteins into the individual structure of frustule can result in the development of hybrid bioreactor and biosensor that provides new opportunities in nanomedicine and biotechnology fields [11], [12]. Several research works have been conducted to study the application of frustules in solar cells, instead of the high-cost sensitized TiO2 [13]. Because of biological compatibility, chemical inertness and porous structure, the frustules possesses the promising potential to be applied as a drug delivery carrier [14]. The other interesting applications of diatoms include catalysis, adsorption, efficient filtration, immunoprecipitation and nanofabrication without altering the 3D structure which can provide the novel strategies in nanotechnology [8], [9], [15], [16]. The cell wall of the diatom is covered by an organic matrix that protects the frustule from dissolution in the aqueous medium. For most applications, the organic materials embedding the cell wall should be eliminated [17], [18]. Sulfuric acid, hydrogen peroxide, nitric acid, or sodium dodecyl sulfate (SDS)/ethylenediaminetetraacetic acid (EDTA) oxidants are most frequently proposed for removal of the organic components [19], [20], [21]. In the conventional cleaning processes using above-mentioned reagents, the concentrated and hot acidic solution is used for a certain period of time. However, the obtained acidic solution could not be removed using filter cloths due to its corrosive and oxidizing behavior. On the other hand, the subsequent dilution or centrifugation may take several hours to remove acidic solution. For instance, collection of frustules from 1000 mL diatom suspension (cultivated for 14–21 days) requires almost 600 mL of 98% sulfuric acid and produces 2–4 L of waste liquid [21]. Moreover, the organic compounds are not completely eliminated due to agglomeration of the cells and insufficient contact between the organic matrix and oxidant [21]. High temperature (500–900 °C) baking is also conducted to eliminate the organic matrix from diatom frustules, but may damage the cribellum [22]. Therefore, the conventional frustule cleaning processes need to be improved to produce large quantities of high-quality frustules for different applications.

Fenton process as one of the advanced oxidation processes (AOPs) uses the reaction between ferrous ions and hydrogen peroxide to produce OH radicals (Eq. (1)), which can non-selectively oxidize most organic compounds [23]. Sonolysis is another AOP method which can produce OH radicals through water dissociation as a result of generation of local fields, known as hot spots, with the high temperature and pressure (Eq. (2)) [24]. Recently, great attentions have been paid on the combination of Fenton process and ultrasonic irradiation as a new AOP, which is known as sono-Fenton (SF) process. Promising studies have been performed in the removal of different organic contaminants including dyes, pharmaceutical compounds and pesticides using SF process [25], [26].Fe2+ + H2O2 + H+ → Fe3  + radical dotOH + H2OH2O + ))) → radical dotOH + Hradical dot

SF process can provide sufficient potential for the removal of organic compounds from diatom cells through additional production of reactive radical species. Moreover, utilization of ultrasonic irradiation during the cleaning process can remarkably inhibit the agglomeration of the cells, which can lead to the production of high-quality frustules. To the best of our knowledge, this is the first study that reports the removal of organic materials covering diatom cells using SF process. The aims of this study are: (a) to examine the ability of sono-Fenton process in cleaning of diatom frustules, (b) to investigate the effect of operational parameters such as concentration of Fe2+ and H2O2, suspension pH, the ultrasound power, the cell density of diatom and temperature on removal of total organic carbon (TOC) and total nitrogen (TN) from diatom cells, (c) and to characterize the properties and structure of diatom frustules before and after performing sono-Fenton process using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), Fourier transform infrared spectroscopy (FT-IR), N2 adsorption–desorption process and thermal gravimetry (TG) analyses. Finally, the organic materials released from the diatom cells were identified using gas chromatography-mass spectroscopy (GC–MS).

Section snippets

Materials and methods

Cyclotella sp. cells were obtained from the Iranian Biological Resource Center. H2O2 (30%), FeSO4·4H2O (99%), NaOH (≥98%), H2SO4 (≥98%), HCl (37%), diethyl ether (C4H10O, ≥99.7%), ammonium formate (HCO2NH4, 99.9%), N,O-bis-(trimethylsilyl)-acetamide (C8H21NOSi2, ≥95%), and Methylene Blue (C16H18N3SCl) were purchased from Merck (Germany).

Cultivation of Cyclotella sp.

Cultivation of single colonies of Cyclotella sp. was carried out in batch mode f/2-enriched seawater at 18 ± 1 °C and pH 7, under a light intensity of 70 µmol m

Comparison of different processes for the removal of organic materials from diatom frustules

Fig. 1(a) shows a comparative investigation on the cleaning of diatom frustules by means of total organic carbon (TOC) and total nitrogen (TN) removal efficiencies (RE%) using different processes. Low TOC (6.9%) and TN (4.3%) removal efficiencies were observed when diatom suspension was subjected to H2O2 oxidant. To investigate the cleaning ability of mechanical stirring, the diatom suspension was vigorously stirred (2000 rpm) without adding H2O2 and Fe2+. The observations demonstrated that the

Conclusions

A comparative investigation on the cleaning of diatom frustules using different processes including Fenton, ultrasound and sono-Fenton systems has been conducted by means of determination of total organic carbon and total nitrogen removal efficiencies. Combining Fenton process with ultrasonication exhibited a positive synergy, in terms of TOC and TN removal efficiencies, while the addition of hydrogen peroxide alone to the diatom suspension had no remarkable beneficial influence. The results

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

The authors acknowledge the support provided by the University of Tabriz. P. Gholami would like to thank Centre for International Mobility (CIMO), Finland for providing EDUFI fellowship (decision number TM-18-10895).

References (52)

  • A. Khataee et al.

    Heterogeneous sono-Fenton process using pyrite nanorods prepared by non-thermal plasma for degradation of an anthraquinone dye

    Ultrason. Sonochem.

    (2016)
  • N.S.M. Yusof et al.

    Physical and chemical effects of acoustic cavitation in selected ultrasonic cleaning applications

    Ultrason. Sonochem.

    (2016)
  • N. Jaafarzadeh et al.

    The performance study on ultrasonic/Fe3O4/H2O2 for degradation of azo dye and real textile wastewater treatment

    J. Mol. Liq.

    (2018)
  • X. Li et al.

    Ultrasonic-enhanced Fenton-like degradation of bisphenol A using a bio-synthesized schwertmannite catalyst

    J. Hazard. Mater.

    (2018)
  • N.P. Tantak et al.

    Degradation of azo dyes by sequential Fenton's oxidation and aerobic biological treatment

    J. Hazard. Mater.

    (2006)
  • A.H. Ltaïef et al.

    Electrochemical treatment of aqueous solutions of organic pollutants by electro-Fenton with natural heterogeneous catalysts under pressure using Ti/IrO2-Ta2O5 or BDD anodes

    Chemosphere

    (2018)
  • S.G. Babu et al.

    Ultrasound-assisted mineralization of organic contaminants using a recyclable LaFeO3 and Fe3+/persulfate Fenton-like system

    Ultrason. Sonochem.

    (2017)
  • Y. Shen et al.

    Facile synthesis of porous carbons from silica-rich rice husk char for volatile organic compounds (VOCs) sorption

    Bioresour. Technol.

    (2019)
  • V.I. Popkov et al.

    Enhancement of acidic-basic properties of silica by modification with CeO2-Fe2O3 nanoparticles via successive ionic layer deposition

    Appl. Surf. Sci.

    (2019)
  • Z. Sun et al.

    Precipitation and subsequent preservation of hydrothermal Fe-Mn oxides in distal plume sediments on Juan de Fuca Ridge

    J. Mar. Syst.

    (2018)
  • A.P. Nowak et al.

    Electrochemical behavior of a composite material containing 3D-structured diatom biosilica

    Algal Res.

    (2019)
  • Y. Qi et al.

    Selective adsorption of Pb(II) from aqueous solution using porous biosilica extracted from marine diatom biomass: Properties and mechanism

    Appl. Surf. Sci.

    (2017)
  • B. Talluri et al.

    Physicochemical properties of chimie douce derived, digestively ripened, ultra-small (r<2 nm) ZnO QDs

    Colloids Surf., A

    (2019)
  • L. Wang et al.

    Insight into the synergistic effect between nickel and tungsten carbide for catalyzing urea electrooxidation in alkaline electrolyte

    Appl. Catal. B

    (2018)
  • U. Tyagi et al.

    Simultaneous pretreatment and hydrolysis of hardwood biomass species catalyzed by combination of modified activated carbon and ionic liquid in biphasic system

    Bioresour. Technol.

    (2019)
  • T. Yoshioka et al.

    AC electrophoretic deposition of organic–inorganic composite coatings

    J. Colloid Interface Sci.

    (2013)
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