Selective Optical Sensing of Hg(II) in Aqueous Media by H‑ Acid/SBA-15: A Combined Experimental and Theoretical Study Pezhman Zarabadi-Poor, † Alireza Badiei,* ,† Ali Akbar Yousefi, ‡ and Joaquín Barroso-Flores § † School of Chemistry, College of Science, University of Tehran, Tehran, Iran ‡ Department of Plastic Materials Processing and Engineering, Iran Polymer and Petrochemical Institute, Tehran, Iran § Centro Conjunto de Investigació n en Química Sustentable UAEM-UNAM, Car. Toluca-Atlacomulco, Km 14.5 Unidad San Cayetano, Personal de la UNAM, Toluca 50200, Estado de Mé xico, Me ́ xico * S Supporting Information ABSTRACT: The H-acid dye intermediate was successfully attached to the SBA-15 mesoporous silica surface in a two-step modification process. Synthesized materials were characterized using several techniques including Fourier transform infrared spectroscopy, N2 adsorption-desorption measurements, small-angle X-ray scattering, transmission electron microscopy, and thermogravimetric analysis. The fluorescent sensing properties were examined in the final product toward several metal ions and showed high selectivity for Hg 2+ . Computa- tional studies were performed in order to obtain a detailed electronic description of the quenching mechanism of H-acid fluorescence by Hg 2+ as well as studying the structure and bonding in the [H-acid]Hg 2+ complex. 1. INTRODUCTION The SBA-15 1,2 mesoporous silica has proven to be an excellent support for lots of applications due to its high surface area, uniform open pores, thick walls, high hydrothermal and thermal stability, optical transparency in visible region, and biocompat- ibility. 3 In order to make these kinds of materials usable in applications such as catalysis, 4-6 solid phase microextraction, 7 optical sensors, 8 etc., the surface modification procedure is vastly employed to introduce different functional groups into the mesoporous silicas via grafting or co-condensation approaches. 9 Fluorescence spectroscopy is one of the most popular techniques in sensing applications; functionalization of SBA-15 and other mesoporous silicas by organic fluorophores has attracted a great deal of attention because it provides selective, sensitive, low cost, and rapid response optical sensors. 10-12 Because of the toxicity of heavy metal ions for living organisms and the human body, synthesis of new fluorescent sensors for optical detection of metal ions such as Cu 2+ , Zn 2+ , and Hg 2+ , among others, has become a broad field of research. 10,13-18 Among the heavy metal ions, mercury in its different forms such as metallic, inorganic, and organometallic is very hazardous and can cause serious problems, 19 i.e., acrodynia (pink disease), Hunter-Russell syndrome, and Minamata disease. Therefore, detection and elimination of mercury compounds is still an interesting and undergoing research field. Up to now, several SBA-15-based optical sensors have been reported for the fluorimetric detection of Hg 2+ ions. These optical sensors consist of a fluorescent molecule, i.e., pyrene, 8 rhoda- mine, 20,21 naphthalimide, 22 and others, attached to the SBA-15. Although reported sensors exhibited satisfying results on selective and sensitive detection of Hg 2+ ions in water, production cost of sensors and availability of the sensing probe remain a challenge; further research in design and synthesis of new sensors is required. Young reported the selective detection of Hg 2+ in aqueous solution using a dye intermediate, H-acid, and obtained satisfying results. 23 Then, Sun et al. incorporated the H-acid into a layered double hydroxide and examined the applicability of synthesized composite for Hg 2+ selective detection on a thin film. 24 Herein, we report the synthesis of H-acid modified SBA-15 (SBA-15-HA) to enable the usage of this optical Hg 2+ sensor in a wider practical field. The synthesized materials were fully characterized and the recognition ability of SBA-15-HA as a chemosensor was investigated using fluorescence spectroscopy. According to our knowledge, the mechanism of mercury sensing by H-acid as well as their bonding nature remains an open question. Therefore, quantum- mechanical calculations were performed in order to provide more detailed information on the aforementioned issues. 2. EXPERIMENTAL AND COMPUTATIONAL PROCEDURES 2.1. Materials. Tetraethyl orthosilicate (TEOS, Merck) was employed as a silica source; poly(ethylene glycol)-block-poly- (propylene glycol)-block-poly(ethylene glycol) (P123, Aldrich) was used as a structure-directing agent; and 3-(chloropropyl)- trimethoxysilane (CPTMS, Merck), 1-amino-8-naphthol-3,6-disul- fonic acid monosodium salt (H-acid or ANDS, Merck), Received: February 10, 2013 Revised: April 8, 2013 Published: April 15, 2013 Article pubs.acs.org/JPCC © 2013 American Chemical Society 9281 dx.doi.org/10.1021/jp401479z | J. Phys. Chem. C 2013, 117, 9281-9289