污水净化过程中二氧化钛的使用

The Use of Titanium Dioxide in the Process of WaterPurificationValentina Smirnova, Olga Nazarenko and Alexander IlyinTomsk Polytechnic University,30 Lenin Ave, Tomsk, 634050, Russia.vv_smirnova@Abstract – This paper relates to the problem of drinking water contaminants from soluble heavy metals. Proposed for sorption purification of water using titanium dioxide, which was synthesized by chemical and electrochemical methods. The synthesized products are nanostructured compounds x-ray amorphous and crystalline titanium dioxide. Adsorbed and crystallization water is removed by heating from sorbent to 110 °C in air. To stabilize the amorphous structure of the sorbent calcined at 600 °C. At the same time formed titanium dioxide, containing two crystalline phases: anatase and rutile. Sorption properties with respect to the soluble ions of Fe+2/Fe+3 and Mn+2 was investigated in static mode, using titanium dioxide powders synthesized in acidic, neutral and alkaline media. Pre-sorbents were subjected to activation by the action of ultrasound (22 kHz, 0.15 W/cm2). The best results were obtained using a titanium dioxide powder, which was synthesized in an alkaline environment. For practical use of sorbent needed to achieve two objectives: to transfer the sorbent powder into pellets with preservation of the active surface, resistant to water and to develop a system of regeneration of used sorbent. In this paper we studied the water resistance of granular titanium dioxide and how it can regenerate after purification.Keywords: water purification, titanium dioxide, ultrasound treatment, cavitation, IR spectroscopy, thermal analysis, the heavy metal impuritiesI.I NTRODUCTIONInitial purification of drinking water is primarily from the use of mechanical methods in which the sorption loading are: quartz sand, charcoal, activated carbon and some of minerals. This gives rise to secondary contamination, related to the leaching them from the sorbent. Water treatment with chemical sorbents is a new promising direction in obtaining large amounts of clean drinking water. In this regard, chemically inert to leaching and promising sorbent is titanium dioxide, which has recently seen an increased interest, as on the surface except for the sorption process is possible and the process of disinfecting water. In addition, titanium dioxide under certain conditions can act as cation and anion both. This versatility in the water treatment increases the interest in the study of the sorbent. At the same time, the properties and characteristics of titanium dioxide, and how it is received not been studied for practical use. One method of modifying the surface of the sorbents is their ultrasonic treatment in various media with the formation of sorption sites in cavitation. When the ultrasonic cavitation bubbles effects occur within which pressure fluctuations (± P) reaches 105 kPa. Under the action of ultrasound is the change of solid surfaces and thereby increases the sorption capacity.The aim of this study was to establish the nature of the functional groups formed under the conditions of cavitation, and their influence on the sorption activity of soluble impurities of iron and manganese cations.II.EXPERIMENTAL METHODSTitanium dioxide was synthesized by hydrolysis of titanium tetrachloride [1, 2], followed drying (110 °C) and calcination in air (600 °C). To determine the nature of the functional groups on the surface of the synthesized titanium dioxide recorded infrared spectra (IR) absorption of the sample in the range 4000 - 400 cm-1 (FT-IR spectrometer, Nicolet 5700 Research and Analytical Center TPU). Recording of samples the spectra were carried out in the form of compressed tablets of potassium bromide. Thermal properties of the synthesized titanium dioxide were investigated by means thermoanalyzer Q 600 STD when heated to 800 °C at 10 °C per minute in the air. The accuracy of temperature measurement was 0.01 °C. Soluble impurities Fe+2 and Mn+2, really present in the drinking water of Tomsk city, were used as objects of study. The content of iron impurities were determined by photometry of the standard method [3]. The method is based on the interaction of iron ions with sulfosalicylic acid in an alkaline medium and the formation of yellow colored complex compound. The color intensity is proportional to the weight concentration of iron was measured at a wavelength of 400 - 430 nm. The content of manganese impurities were analyzed by photometry [4]. The method is based on the oxidation of manganese compounds to MnO4-. Oxidation occurs in the acidic environment of ammonium or potassium persulfate in the presence of silver ions as a catalyst. Thus there is a pink color of the solution, the absorption intensity was measured at the wavelength range 530 - 525 nm. To prepare the model solutions used analytical grade purity chemicals. Solutions for the study was prepared by dissolving geptahydrate iron sulfate (II) and pentahydrate manganese sulfate (II). The accuracy of the experiment provided the construction of calibration function and statistical processing of the data with a probability P = 0.95: for iron - in the range of concentrations from 0.01 to 2.00 mg/l, for manganese – from 0.005 to 0.3 mg/l. For the experiments were prepared model solutions of iron and manganese, 3 and 1 mg/l, respectively, by dissolving accurately weighed portion of salts. Previously, before the sorption experiments, the synthesized978-1-4673-1773-3/12/$31.00 ©2013 IEEE(base) of titanium dioxide powder was subjected to repeated ultrasound exposure in various media: distilled water, 0.2 N solutions of NaOH and HCl. Duration of treatment was 10 minutes at a power of 0.15 W/cm 2 ultrasound exposure.III. RESULTS OF EXPERIMENTSFor the initial solution, a volume of 100 ml containing 3.00 mg/l ions Fe +2, added 0.20 g of sorbent (base and activated in various media), mixed and analyzed on a sample of the residual content of impurities of iron (Table 1, 2). Similarly, in 100 ml of a solution containing 1 mg/l of ions Mn +2, added 0.20 g of the same samples of the sorbent was stirred and after a certain time determined by the residual concentration of manganese ions (Table 1, 2). The results of extraction of contaminants through the base and titanium dioxide treated with ultrasound in different media (H 2O, NaOH, HCl), are presented in tables. Preliminary results at a conference of the Russian were discussed [5].TABLE I. THE RESIDUAL CONTENT OF IMPURITIES Fe +2 and Mn +2 AFTER SORPTION SPECIMEN ACTIVATED IN ALKALINE ANDACIDIC MEDIA Samples of sorbentTiO 2 in NaOHTiO 2 in HClPermission - foundP e r m i s s i o n o f 3.00 m g /l F e +2P e r m i s s i o n o r 1.00 m g /l M n +2P e r m i s s i o n o f 3.00 m g /l F e +2P e r m i s s i o n o f 1.00 m g /l M n +2F o u n d , m g /lAfter 20 min 0.53 0.24 1.12 0.31After 60 min 0.90 0.64 1.10 0.27After 24 h 1.06 0.74 0.73 0.26 After 48 h 0.96 0.47 0.53 0.25According to the results of sorption of impurities in titanium dioxide takes place within a relatively short time: the concentration of iron ions with 3.00 mg/l minimum is reduced to 1.42 mg/l and a maximum of 0.53 mg/l, while at the same time reducing the concentration of manganese ions with 1.00 mg/l was observed for the same sample of the sorbent, and that traces of iron - the minimum concentration of 0.24 mg/l, maximum 0.56 mg/l. The best results were obtained for a sample of titanium dioxide treated by ultrasound in a solution of NaOH, and the sorption characteristics had minimal base TiO 2, not treated by ultrasound and is not activated by chemical reagents. Thus, reducing the concentration of iron impurity is on the average 5.7 times, manganese – 4.2 times.TABLE II. THE RESIDUAL CONTENT OF IMPURITIES Fe +2 and Mn +2 AFTER SORPTION BASE SAMPLE AND SIRBENT ACTIVATED INDISTILLED WATERSamples of sorbent TiO 2base TiO 2 in H 2OPermission - foundP er m i s s i o n o f 3.00 m g /l F e +2P e r m i s s i o n o f 1.00 m g /l M n +2P e r m i s s i o n o f 3.00 m g /l F e +2P e r m i s s i o n o f 1.00 m g /l M n +2F o u n d , m g /lAfter 20 min 1.42 0.56 0.90 0.31After 60 min 1.25 0.53 0.69 0.27After 24 h 1.25 0.53 0.86 0.19 After 48 h 1.25 0.53 1.06 0.28By increasing the contact time of sorbent with model solutions of the impurity content did not change for the sampleTiO 2 not treated, for the sample prepared in distilled water and impurity content remained practically unchanged for 48 hours. At the same time a sample of the sorbent prepared in sodium hydroxide, was characterized by increased iron concentrations up to 0.90 – 1.06 mg/l and higher concentrations of manganese ions to 0.47 – 0.74 mg/l. In contrast to the above samples TiO 2, treated in hydrochloric acid, was characterized by a smooth decrease in the concentration of iron ions in solution from 1.12 to 0.53 mg/l and lower concentrations of manganese ions from 0.31 to 0.25 mg/l.Figure 1. The IR transmission spectrum of activated ultrasonic sample aftertreatment in an alkaline mediaIR spectrum of the precipitate obtained in an alkaline medium (Fig. 1) is characterized by a relatively narrow absorption band ( = 550 - 560 cm -1). In the IR spectrum, there are also weak absorption bands corresponding to ( Ti - O = 912, 1020, 1147 cm -1). In the range from 1400 to 1600 cm -1 are weak absorption bands corresponding to deformation vibrations of water molecules that have a different relationship with the energy of titanium dioxide. In a broad band is represented by the absorption in the IR spectrum associated with the stretching vibrations of O - H: 2900 - 3700 cm -1.Figure 2. The IR transmission spectrum of activated ultrasonic sample aftertreatment in acid mediaIn acidic medium (Fig. 2) formed on the surface of the sorbent structural fragments, which absorb in the infrared spectrum of light of different ranges. The absorption band corresponding Ti - O = 517 - 707 cm -1, which is wider than the previous model. However, this absorption band, there is another unresolved absorption band in the 1040 - 1160 cm -1,which reflects the presence of two types of bonds Ti - O. In the IR spectrum of the sample contains weak absorption bands in the range 1400 - 1550 cm-1 are associated with deformation vibrations of water molecules (δ = H - O - H). He absorption band associated with vibrations of υ O - H is a broad isotropic band, containing virtually no peaks that could be due to the homogeneity of the structure of the sorbent and the higher its stability. When the sorption of impurities, according to the results, this sorbent retains impurity cations more strongly, while the sorbent is activated in an alkaline solution, tends to reconstruct the structure and desorption of contaminants (Table 1).From the analysis of the IR spectra shows that the samples activated in acidic and alkaline media have similar absorption bands, except for the absorption bands of υ = 1040 - 1160 cm-1, which is associated with an additional structure of the sorbent and the greater the binding energy of Ti - O in compared with the structure, which absorbs in the range 517 - 707 cm-1.The thermal stability of the synthesized samples of hydrated titanium dioxide was studied by heating in air to a temperature of 1200 °C. A typical thermogram is shown in Figure 3. Upon heating the sample from the removal of adsorbed water was observed at 20 - 180 °C and was accompanied by endoeffect (with a maximum of 100 °C). With a further increase in temperature was observed with respect to a smooth decrease in weight of the sample to 590 °C and then a more rapid decrease in its accompanied exothermally that are most likely associated with the process of phase transition from the amorphous structure in the crystal structure of anatase and rutile.Figure 3. A typical thermogram of hydrated titanium dioxide a sampleThus, adjusting the processing temperature of the synthesized sorbent is possible to obtain single-phase (anatase or rutile) and polyphase (anatase - rutile) samples of sorbents.IV.DISCUSSIONIn heterogeneous systems, cavitation processes in the action of ultrasonic vibrations usually occur at solid-liquid interface. The energy released during the collapse of the bubble, is sufficient to implement the processes of dissociation and ionization, as a solid (titanium dioxide) and solvent (water). The dissociation of water takes place by the ionic mechanism with the formation of a large number of protons (greater than Кw) and a radical mechanism with the formation of hydrogen atoms and hydroxyl groups. The hydrogen atoms rapidly recombine with each other to form molecules of hydrogen and hydroxyl groups are transformed into hydrogen peroxide. Hydrogen molecule by collision with the surface of titanium dioxide and water molecules are removed from the solution by diffusion. Hydrogen peroxide is characterized by a significant time of life after cavitation, but eventually decomposes to atomic oxygen, which effectively oxidizes iron (II) to iron (III) and manganese (II) to manganese (IV).One of the characteristics of ultrasonic cavitation is that it is a very effective mechanism for the local concentration of the relatively low average energy of the acoustic field in very small volumes, which leads to the creation of extremely high energy density and giving the system a high reactivity, related to additional with the peculiarities of the structure and properties titanium dioxide.Direct confirmation of the existence of a high power density can serve as luminescence, observed during ultrasonic treatment.Measuring the sign of the potential (ζ) shows how the charged surface of titanium dioxide (positive or negative), and then, by what mechanism, the dissociation of water flowing under the action of ultrasound. Thus the sign of ζ can be determined cation-anion or treated sorbent. At high energy densities (in the cavitation bubble) dissociation of water can proceed as follows:H2O → H2O+ + ē,H2O → 1/2H2+ + OH-.Positively charged ions of substances with a high reactivity are oxidants whose lifetime is very small.Part of the energy shock waves, thermal energy emissions in cavitation bubbles and the energy ripple of cavitation bubbles are consumed in the formation of free radicals, which interact with the impurity ions can occur with small or no activation energy. In the cavitation process involving vesicles filled with water vapor. The water molecules in the gaseous state, trapped in rising microbubbles are destroyed, forming a highly active as ions and radicals, including hydroxyl radicals: H2O → HO· + H·,2OH· → H2O2.The standard enthalpy of electrolytic dissociation expended (at 20 °C) is 57.15 kJ/mol [6], which can be significantly reduced on the surface of titanium dioxide because of its polarizing effect.Hydroxyl radicals are involved in the reactions in the gas phase in the bubbles, or at the gas - water or in the bulk solution and at the interface between a solid (titanium dioxide) - the liquid. Saturation of oxygen gas heterogeneous systems, except for the formation of radicals OH·, initiates the formation of peroxide radicals and overperoxides. Then the recombination of radicals at the interface or in the bulk solution to the hydrogen peroxide:O2 + H· → HO2·,O2 → O + O,O + H2O → HO· + HO·,HO2· + HO2· → H2O2 + O2.If we compare the lifetimes of the formed radicals and ions, then after a short period of time, the main oxidant is hydrogen peroxide, which can generate oxygen atoms:H2O2→ H2O + O.Thus, the effects of ultrasound in the cavitation mode provides the operating time of free radicals and oxidants which in some cases contribute to the precipitation of water-soluble heavy metal impurities. For example, under the action of oxidizing iron (II) is oxidized to iron (III) and falls as a precipitate Fe(OH)3 and Mn (II) is oxidized to MnO2. Strong oxidants formed in cavitation are radicals HO2·, OH· and atomic oxygen.CONCLUSION1. The process of hydrolysis and precipitation of hydrated sorbent is based on titanium dioxide and its thermal stability when heated in air.2. It is established that the primary precipitated product formed by hydrolysis of TiCl4 is х-ray amorphous substance. When heated, it is dehydration, crystallization of anatase in the first, and then to rutile.3. Pre-and post-treatment with ultrasound at the time of the sorption step up the process of sorption of impurities of iron and manganese: the concentration of iron impurities is reduced by 5.7 times, and manganese -4.2 times.4. The sorption capacity of titanium dioxide depends on the pre-sonication in solutions with different pH: the maximum effect was achieved in 0.2 N solution of NaOH.5. According to the IR absorption spectra under sonication in alkaline medium formed by oxo- (υ = 517 - 707 cm-1) and hydroxide (υ = 1400 - 1550 cm-1) group with a high sorption activity.6. Found that the sorption activity of the sorbent, activated in the alkaline (Table 1) decreases with time, resulting in leaching of adsorbed impurities is observed. At the same time, the sorption activity of the sorbent, activated in an acidic medium, remained unchanged.7. Ultrasonic treatment of sorbents based on titanium dioxide leads to its modification and improvement of its sorption capacity.R EFERENCES[1] A.P. Ilyin, V.M. Milushkin, O.B. Nazarenko, V.V. Smirnova,“Development of new methods of water purification from soluble impurities of heavy metals” (Razrabotka novykh metodov ochistki vody ot rastvorimykh primesej tyazhelykh metallov), Bulletin of the Tomsk Polytechnic University (Izvestiya Tomskogo Politekhnicheskogo Universiteta), Tomsk, 2010, vol. 317, № 3, pp. 40-44 (in Russian).[2]V.V. Smirnova, O.B. Nazarenko, “The use of titanium oxides andhydroxides for water purification” (Primenenie oksidov i gidroksidov titana dlya ochistki pit'evoj vody), Prospects of Fundamental Sciences Development VIII Int. Conf. (Perspektivy razvitiya fundamental'nykh nauk trudy VIII mezhdunarodnoj konferentsii), Tomsk, 2011, pp. 383-385 (in Russian).[3]GOST (Gosudarstvennyj standart) 4011 – 72, Russian Federation.Drinking water. Methods for measuring the mass concentration of total iron (in Russian).[4]GOST (Gosudarstvennyj standart) 4974 – 72, Russian Federation.Drinking water. Methods for determination of manganese (in Russian). [5]V.V. Smirnova, O.B. Nazarenko. “Effect of preparation conditions andthe ultrasonic treatment of titanium dioxide on its sorption activity”(Vliyanie uslovij prigotovleniya i ul'trazvukovoj obrabotki dioksida titana na ego sorbtsionnuyu aktivnost'), Prospects of Fundamental Sciences Development IX Int. Conf. (Perspektivy razvitiya fundamental'nykh nauk trudy IX mezhdunarodnoj konferentsii), Tomsk, 2012, pp. 484-486 (in Russian).[6]V.V. Goncharuk, V.V. Malyarenko, V.A. Yaremenko. “The use ofultrasound in water purification” (Ispol'zovanie ul'trazvuka pri ochistke vody), Water Chemistry and Technology (Khimiya i tekhnologiya vody), 2008, vol. 30, № 3, pp. 196 – 199 (in Russian).。