REV. CHIM. (Bucharest) ♦ 63 ♦ No. 10 ♦ 2012 http://www.revistadechimie.ro 1013 Colloidal Silica Use As Dyes Removing System MIHAIL SCURTU 1 , ECATERINA ANDRONESCU 1 , CORNELIA GURAN 1 , MARIA SONMEZ 1,2 , ALEXANDRU GRUMEZESCU 1 , LIV PALL 1 , ANTON FICAI 1 , DENISA FICAI 1, * 1 Politehnica University of Bucharest, Faculty of Applied Chemistry and Material Science; 1-7 Polizu Str., 011061 Bucharest, Romania 2 National Research & Development Institute for Textiles and Leather (INCDTP) – Leather and Footwear Research Institute, 93 Ion Minulescu st., 031215 Bucharest, Romania This work was focused on the UV-Vis spectroscopic study of removal of 5 dyes from aqueous solution. The removal of the five dyes is strongly influenced by chemical structure and electrical charge. Best degree of removal was obtained for methylviolet (90.2%) and aniline red (82.8%) while the removal of the other dyes does not exceed 35% (light green - ~35%, indigocarmin 25.5% and tartrazine ~10%). The absorption profile is very similar for all dyes, the first 5h being the most important because after that the degree of removal is maintained relatively constant. Keywords: colloidal silica, dyes removal, environmental protection * Tel.: 0724361569 In the last decade, there has been a constant effort to develop or improve materials which are of fundamental interest to medical or environmental science [1-3]. Silica is an amazing material extensively used for both medical and industrial purposes [4-8]. The properties of silica based materials were continuously improved by different engineering tools which include the rigorous selection of the proper methods [9-11], the use of proper surfactants [12-16], porogens [17], templates [18], surface functionalization [19], and so on. Beside the above mentioned, silica is a common component of many materials, the final results being improved or having new properties [20, 21]. Even if silica is known and used for very long time it still offers new challenges for the researchers, the number of published papers increasing year by year as results from the SCOPUS. Silica and silica related materials have an extraordinary affinity for a wide variety of compounds from heavy metals to fragrances, from simple elements/molecules to large biological active components. The high affinity to such compounds assures to the silica based materials a leading position in many separation techniques [22, 23]. Silica is widely used as adsorbent of various compounds. This application is due to its special morphology, due to its versatility of functionalization or due to the presence of free hydroxyl groups which can form strong hydrogen bonds with different groups of these components [24-28]. Dyes are intensively used in textile industry. Being water- soluble, it is estimated that 10–20% of dye remains in wastewater during the production of these dyes and nearly half of dyes may be lost to the effluents during dyeing of cellulose fibers. Such highly colored wastes not only are aesthetically displeasing but also hinder light penetration and may in consequence disturb biological processes in water. In addition, dyes are toxic to some organisms and hence harmful to aquatic animals [29]. Dye-doped silica has unique applications in bioanalysis and bioseparation. Using appropriate synthetic conditions, a large number of dye molecules (organic or inorganic) can be incorporated inside silica. Dye-doped nanoparticles produce a highly amplified optical signal compared with a single dye molecule. If applied appropriately in bioanalysis, silica nanoparticles can provide a great improvement in analytical sensitivity. Moreover, as the dye is trapped inside the SiO 2 matrix, which provides an effective barrier keeping the dye from the environment, both photobleaching and photodegradation phenomena that affect conventional dyes, can be minimized. The photostability makes these nanoparticles suitable for many applications where high intensity is required. For example, intracellular optical imaging suffers severely from photobleaching [30]. The purpose of this paper is to evaluate the colloidal silica as absorbent materials for different types of organic dyes (tatrazine, methylviolet, aniline red, light green and indigocarmin). Experimental part The dyes removal was tested using commercial, highly dispersed colloidal silica (Merck, 113126). Only commercial available dyes were used: Methylviolet (microscopy grade) and Indigocarmin (min 95%) were purchased from Merck; Tartrazine was purchased from Fluka (microscopy grade); Light green was purchased from Difco Laboratories, UK and Aniline red from May and Baker Ltd, UK. The chemical structures of these dyes are presented in figure 1. UV-Vis measurements were performed using a Thermo Evolution 300 spectrometer operated in transmission mode over the range of 190-1100 nm; the quantification of the dyes was made at that wavelength which assures a maximum absorption. The calibration curve of each dye over a wide range of concentrations (0.0002 – 0.2 mg/mL) was studied and the results are presented in table 1. The equations and the correlation coefficients were determined by using linear and linear to zero fitting relation. As a general rule, the correlation coefficients are higher than 0.999. The removal of dyes was studied as follows: 0.1g silica was suspended in 50 mL solution containing 20μg/mL dye. The absorbance was recorded periodically and plotted versus time for each dye. Before reading, the suspensions were centrifuged 5 min at 10000 rpm. The degree of removal was determined based on the equation 1. (1) where: A 0 – represents the initial absorbance of the dye solution