Effect of the amount and time of addition of a dye template on the adsorption and photocatalytic performance of molecularly imprinted silica
Graphical abstract
Introduction
Synthetic dyes have become an integral component for a variety applications. The majority of these dyes (ca. 70%) belong to the azo group [1]. Approximately 7 × 105 metric tons of dye are produced annually [2] for various applications, such as the plastic, textile, printing and cosmetic. Some estimation suggests that for 1 kg of textile materials the textile finishing industries consume 100 L of water [4]. Such consume is partially a consequence of textile industry, from which it is estimated that each year ca. 2.8 × 105 tons of dyes are discharged [5]
These discharged possibly affect the aquatic life by hindering sunlight penetration in water. Therefore, removing these dyes from wastewater remains a difficult challenge, especially the removal of dyes at a low concentration [6].
Chemical treatment, filtration, oxidation, adsorption, biological treatment and advanced oxidation processing, are among the most commons methods available for remediation of dye wastewaters [3], [7]. However, a condition that is necessary for complete removal is the mineralization of the contaminant [8], which can be achieved by using advanced oxidation processes (AOPs).
Considering emerging contaminants, the heterogeneous photocatalysis is one of more promising strategies among AOPs. The use of TiO2 as catalyst encompasses several advantages, such as low cost and low toxicity [9]. However, the low selectivity to most hazardous compounds is a serious disadvantage of heterogeneous photocatalytic oxidation [10], [11].
To address this drawback, some studies have suggested combining molecularly imprinted (MI) technology with a photocatalytic process. One of its main feature is that MI technology demonstrates high affinity and selectivity for the molecules employed as templates [12], [13]. In this approach, the cavities generated by MI technology could enhance the molecular recognition ability. MI materials have been used in many different applications, such as drug delivery [14], catalysis [15], adsorption [16], [17], [18], chemical sensing [19], preconcentration [20], biological antibodies, and receptor systems [21].
The production of MI as sorbent material is majority based on organic matrix. However, the adsorption sites generated are usually heterogeneous and also possess non-specific interactions between the template and the imprinted sites that compromise the adsorption phenomenon [22]. In order to overcoming these inconveniences, a promising alternative is the use of inorganic matrices, such as silica-based material.
Silica-based imprinted materials can be produced by sol-gel process. Briefly, a percursor (e.g., tetraethylorthosilicate (TEOS)) interacts with a chosen template producing a silica network. After the extraction of the template, specific cavities are created and the produced material can be used as an adsorbent. As shown in the literature [23], [24], the main advantage of silica prepared by sol-gel reactions is that material can be tolerant to a several chemical environments [25], which include exposure to very strong base, very strong acid, and oxidizer species. Silica materials as adsorbents in solid-phase for drug extraction are among the majority of the studies discussing the preparation of silica material containing molecularly imprinting technology [26], [27], [28].
Imprinted photocatalysts based on inorganic matrix have not yet been extensively explored in the literature [29], [30], [31], [32], [33]. In this context, the aim of the current study was to evaluate the effect of the amount and time of addition of a template (RhB) on the characteristics and catalyst activity of a photocatalyst that was prepared via an acid-catalyzed sol-gel route. Different extraction methods were studied and, after selecting the best extraction method, the adsorption kinetics of the MI xerogels (without calcination) were investigated.
Section snippets
Materials and methods
Tetraethoxysilane (Si(OCH2CH3)4, TEOS, Merck,>98%), Rhodamine B (Vetec), and titanium tetrachloride (TiCl4, Merck,>99%) were used as received. Hydrochloric acid (HCl, Nuclear, 38%) was employed as the catalyst.
Preparation of sol-gel materials
The photocatalysts were prepared using a sol-gel process using HCl (0.2 M) as the catalyst. TEOS (45 mmol) was used as the raw material at a 1:2 (HCl:TEOS) volume ratio followed by the addition of TiCl4 (10.4 mmol). The effect of the amount of template was investigated by adding 150, 300 and
Xerogel and Photocatalysts Characterization
Table 1 shows the C and N content, the SBET values and the solvent volume used for the different extraction methods for the 15A0 system (non-calcined). Although a decrease in the C content was observed compared to that in encapsulated silica, the carbon content can be misleading due to the potential presence of residual ethoxide groups in silica that are produced by the sol-gel method [37].
According to Table 1, the highest removal of N was obtained using thermal extraction. However, no increase
Conclusions
In the development of a supported photocatalyst prepared using an acid-catalyzed sol-gel process, the amount of employed template (RhB) and the time of its addition to the reaction medium affect the characteristics and catalyst activity of the resulting photocatalyst. The adsorption kinetic data were well represented by pseudo-second-order kinetics, and the values of kinetic constants are comparable to those of typical silica-based adsorbents. For the systems with a fixed template mass, the
Acknowledgements
This project was partially funded by the CNPq. C. Escobar is grateful for the grant provided by the CAPES. The authors wish to thank the LNLS (Project D11A-SAXS1-8691) for the SAXS beamline measurements.
References (50)
- et al.
Detoxification of azo dyes in the context of environmental processes
Chemosphere
(2016) - et al.
Bacterial decolorization and degradation of azo dyes: A review
J. Taiwan. Inst. Chem. Eng.
(2011) - et al.
Adsorption of dyes onto palygorskite and its composites: A review
J. Environ. Chem. Eng.
(2016) - et al.
Application of low-cost adsorbents for dye removal ?A review
J. Environ. Manage.
(2009) - et al.
A review on advanced oxidation processes for the removal of taste and odor compounds from aqueous media
Water Res.
(2014) - et al.
TiO2 photocatalysis: Design and applications
J. Photochem. Photobiol. C: Photochem. Rev.
(2012) - et al.
Preferential photodegradation of contaminants by molecular imprinting on titanium dioxide
Appl. Catal. B: Environ.
(2010) - et al.
Molecularly imprinted drug delivery systems
Adv. Drug Deliv. Rev.
(2005) - et al.
Microwave-assisted synthesis of selective degradation photocatalyst by surface molecular imprinting method for the degradation of tetracycline onto ClTiO2
Chem. Eng. J.
(2013) - et al.
Synthetic strategies for the generation of molecularly imprinted organic polymers
Adv. Drug. Deliv. Rev.
(2005)
Molecularly imprinted sol gel for ibuprofen: An analytical study of the factors influencing selectivity
Talanta
Sol–el molecular imprinted ormosil for solid-phase extraction of methylxanthines
J. Chromatogr. A
Selective solid-phase extraction using molecular imprinted polymer for the analysis of diethylstilbestrol
Food Chem.
Performance of molecularly imprinted photocatalysts based on fly-ash cenospheres for selective photodegradation of single and ternary antibiotics solution
J. Mol. Catal. A: Chem.
The sol–gel route effect on the preparation of molecularly imprinted silica-based materials for selective and competitive photocatalysis
Colloid Surf. A: Physicochem. Eng. A
Synthesis of molecularly imprinted photocatalysts containing low TiO2 loading: Evaluation for the degradation of pharmaceuticals
J. Hazard. Mat.
Titania–silica as catalysts: molecular structural characteristics and physico-chemical properties
Catal. Today
Effect of Structure and Composition on Epoxidation of HexeneCatalyzed by Microporous and Mesoporous Ti–Si Mixed Oxides
J. Catal.
Selective removal of perfluorooctane sulfonate from aqueous solution using chitosan-based molecularly imprinted polymer adsorbents
Water Res.
Adsorption of reactive dyes on titania–silica mesoporous materials
J. Colloid Interface Sci.
Application of AlMCM-41 for competitive adsorption of methylene blue and rhodamine B: Thermodynamic and kinetic studies
J. Hazard. Mat.
Removal of rhodamine B from aqueous solution by adsorption onto sodium montmorillonite
J. Hazard. Mat.
Removal of dyes using agricultural waste as low-cost adsorbents: a review
Appl. Water Sci.
Microbial Decolorization of Methyl Orange Dye by Pseudomonas spp ETL-M
Int. J. Env. Biorem. Biodegrad.
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