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Efficient sunlight driven photocatalytic degradation of organic dyes by CdS/bentonite nanocomposite

IWRA World Water Congress 2017 - Cancun Mexico
2. Water quality, wastewater and reuse
Author(s): Erick C. Neves
Jamiel M. Oliveira
Cristiane C. Nascimento
George Ricardo S. Andrade
Iara F. Gimenez

Erick C. Neves
Federal University os Sergipe
erickcodap@hotmail.com
Jamiel M. Oliveira
Federal University os Sergipe
jamielmenezes@gmail.com
Cristiane C. Nascimento
Federal University os Sergipe
crisnascimentopop@gmail.com
George Ricardo S. Andrade
Federal University os Sergipe
grsandrade@hotmail.com
Iara F. Gimenez
Federal University os Sergipe
iara.gimenez@gmail.com


Keyword(s): Photocatalytic; quantum dots; methyl blue; nanocomposite
Poster:

Abstract

In the past few decades, the significant increase of environmental pollution caused by anthropogenic source has stimulated an intense research effort on optimizing and developing materials, specially in nanoscale, as a fast, economical and environmentally friendly alternatives for the conventional treatment methods. Among these environmental problems, the decontamination of natural water emerges as the most challenging field as it deals with all the biosphere health. In this work, bentonite was thiol-functionalized with 3-mercaptopropyl)trimethoxysilane (BEN-thiol) and used to prepare nanocrystalline cadmium sulfide (CdS) by a simple one-pot method. BEN-thiol/CdS was used as a solar photocatalyst for the degradation of organic dye solutions. Thus, CdS nanocrystals were synthesized using cadmium acetate (9.867 mM) and thiourea (18.759 mM) aqueous solutions as precursors of Cd2+ and S2-, respectively. The reaction was performed at different reaction times and using different amounts of BEN-thiol to evaluate the growth of CdS nanocrystals. For the solar photocatalysis application, methyl blue dye was chosen due to its wide range of application in industry (e.g. textile industry). The optical properties of BEN-thiol/CdS nanocomposites were studied by UV/visible spectroscopy, which showed a systematically shifted towards longer wavelengths as the reaction goes on or decreasing the BEN-thiol amount, as a result of the particle growth. The average diameters of CdS were estimated by TEM and calculated from Brus’s model, showing particles with sizes ranging from 2-5 nm. Furthermore, XRD measurements indicated that CdS presents a cubic structure in all the nanocomposites. The degradation of aqueous methyl blue solutions (20 mL, 20 mg/L) was investigated by solar photocatalysis, being the samples exposed to sunlight from 11 a.m. to 4 p.m. during the springer of 2016 (September-Octuber) under an average radiant exposure around 2900 kJ m−2 at the time of experiments). The temporal evolution of the dye degradation was studied by UV/visible measurement, which showed an efficiency of 70% under only 50 min of solar exposure. Other tests, such as photolysis (performed without the photocatalyst) and adsorption (performed under dark conditions), did showed any contribution to the decolorization process. Measurements of COD (chemical oxygen demand) showed a reduction of approximately 60%, which gives a measure of the degree of mineralization.

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