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Sorption properties of titanium dioxide. Modern problems of science and education

JOURNAL OF PHYSICAL CHEMISTRY, 2015, volume 89, no. 1, p. 133-136

PHOTOCHEMISTRY AND MAGNETOCHEMISTRY

UDC 544.526.5+549.514.6.352.26

National Academy of Sciences of Ukraine, Institute of Sorption and Endoecology Problems, Kyiv

Email: [email protected] Received by the editor 02/05/2014

Mesoporous samples of titanium dioxide modified with calcium have been synthesized. Their structural, photocatalytic and sorption properties were studied. It has been established that the modified samples differ from titanium dioxide in their characteristics and properties: the specific surface area and average pore volume increase, and the average pore radius decreases; photocatalytic and sorption activity towards dyes and dichromate anion increases.

Key words: titanium dioxide, calcium, photocatalysis, sorption, dyes, dichromate anion. DOI: 10.7868/S0044453715010124

In the photocatalytic method of purifying aqueous solutions from toxic substances, in most cases titanium dioxide is used, which is a cheap and non-toxic catalyst. In addition, after the completion of the reaction, it can be easily separated from the solution by filtration or centrifugation. Currently, photocatalytic removal methods are becoming increasingly important. harmful substances from aqueous solutions using titanium dioxide.

The main disadvantage of this photocatalyst is its insufficient activity. Various methods are known to increase its photoactivity, for example, by increasing the adsorption of the substrate or increasing the kinetic rate constant. Adsorption can be increased by increasing the specific surface area, monolayer capacity and pore volume, and the kinetic rate constant by separating charges and reducing the recombination rate of the electron-hole pair.

The purpose of the work is to obtain and study samples of titanium dioxide modified with calcium citrate method, which are characterized by a high specific surface area, mesoporous structure and increased photocatalytic activity in the reactions of destruction of dyes and photoreduction of the bichromate anion.

EXPERIMENTAL PART

To obtain titanium dioxide samples modified with calcium using the citrate method

initial mixtures were prepared: tetrabutoxy titanium (IV) polymer (Aldrich) (3 g), citric acid (0.06 g), glycerin (2 ml), as well as calcium chloride additives - 0.05 g, 0.1, 0.2, 0.5 and 1 g, respectively, the obtained samples are designated as 1Ca/1O2, 2Ca/1O2, 3Ca/1O2, 4Ca/1O2, 5Ca/1O2. To obtain pure titanium dioxide, we took the same mixture, but without the addition of calcium chloride salt. This synthesis method makes it possible to easily vary the ratios of components in the samples.

The mixtures were calcined at 500 °C for 2 hours in the presence of atmospheric oxygen in a muffle furnace at a heating rate of 2 K/min. After cooling, the resulting powders were thoroughly ground until a homogeneous mass was obtained.

X-ray phase analysis was performed on a DR0N-4-07 diffractometer (Russia) with Cu^ radiation (with a copper anode and a nickel filter) in a reflected beam and registration geometry according to Breguet-Brentano (2© = 10-70°). The average crystallite size was determined by the broadening of the most intense band using the Debye-Scherrer equation: D = 0.9X/(B x cos©), where 0.9 is a constant, X is the wavelength, nm. The crystallite sizes were determined from the most intense peaks characteristic of anatase.

The specific surface area of the samples 05ud), as well as the pore distribution, were determined using a Quantachrom NovaWin2 device. The specific surface area of the samples (Ssp) was determined by the Brunauer-Emmett-Teller (BET) method using nitrogen sorption-desorption isotherms. The pore radius (R) as well as the pore volume (V) were calculated from the desorption branches of the isotherms using the Barret-Joyner-Halenda method.

HALYAVKA, etc.

Rice. 1. Diffraction patterns of the obtained samples: 1 - TiO2, 2 - 3Ca/TiO2, 3 - 5Ca/TiO2. For other designations, see text.

Rice. Fig. 2. Nitrogen sorption-desorption isotherms obtained at 20°C for samples: 1 - 5Ca/TiO2, 2 - 4Ca/TiO2, 3 - 3Ca/TiO2, 4 - TiO2.

Photocatalytic activity was studied using the example of model reactions of destruction of the dyes safranin T and rhodamine, as well as photoreduction of the dichromate anion in aqueous solutions with a photocatalyst content of 2 g/l of solution. Irradiation was carried out with a BUV-30 mercury lamp with a radiation maximum at 254 nm at room temperature in a cylindrical quartz reactor equipped with an electrically driven mechanical stirrer. The change in dye concentration was monitored spectrophotometrically (Lambda 35, PerkinElmer Instruments).

THE DISCUSSION OF THE RESULTS

The crystal structure of the samples was studied using X-ray phase analysis (Fig. 1). The diffraction patterns of all samples contain intense, clearly defined reflections characteristic of crystal lattice anatase (A). Thus, in the diffraction pattern of the dioxide sample

Table 1. Sample characteristics

Sample Bud, m2/g Ksr, cm3/g Gsr, nm

TiO2 43.4 0.13 5.89

1Ca/TiO2 46.7 0.13 5.4

2Ca/TiO2 71.2 0.14 4.8

3Ca/TiO2 75.3 0.15 4.1

4Ca/TiO2 83.9 0.18 4.25

5Ca/TiO2 76.2 0.19 5

Designations: Bud - specific surface area, Usr - average pore volume, gsr - average radius.

Titanium shows the presence of intense peaks 20 = 25.5, 37.8, 54.0, 55.0, which are attributed to the anatase phase (Fig. 1).

The work states that in titanium dioxide powders modified with various alkaline earth metal ions, only the anatase phase is present, which the authors explain by the low content of modifiers in their samples. In contrast to this work, in our case (Fig. 1) peaks 20 = 27.4, 41.2 were also detected, which belong to the rutile (P) phase.

For modified samples, peaks are observed at 20 = 31, which are characteristic of brookite (B). Their intensity increases with increasing calcium content in the powders. The same peaks were found by the authors for TiO2 films modified with calcium ions.

The sizes of crystallites in titanium dioxide agglomerates, calculated using the Debye-Scherrer equation, are 9 nm; in the case of modified samples, their value increases to 12.4 nm, which is consistent with literature data, since the presence of modifiers accelerates the crystallization of titanium dioxide and leads to an increase in size crystallites.

The study of nitrogen sorption-desorption isotherms obtained at 20°C for the synthesized samples showed the presence of a hysteresis loop (Fig. 2), which indicates the mesoporous structure of the powders.

The specific surface area of the modified samples doubles compared to pure titanium dioxide (Table 1). In the series of samples from TiO2 to 5Ca/TiO2 (Table 1), the value of the average pore volume increases from 0.13

PHOTOCATALYTIC ACTIVITY

to 0.19 cm3/g, and the average pore radius, on the contrary, decreases from 5.89 to 5 nm. The pore size distribution area is shown in Fig. 3. As can be seen, for samples 4Ca/TiO2 and 3Ca/TiO2 a narrower pore distribution is observed than for pure titanium dioxide and the sample with the largest amount of calcium - 5Ca/TiO2.

To determine optimal destruction conditions toxic substances in aqueous solutions, it is important to study the kinetics of their sorption on photocatalysts. It was found that the sorption equilibrium in the photocatalyst - safranin T system was established in approximately 1 hour, and for the photocatalyst - rhodamine and photocatalyst - potassium bichromate systems in 2 hours.

The studies carried out showed that for all the studied adsorptive agents and adsorbents, the kinetic adsorption curves have the usual smooth character: a smooth course and small adsorption values (Table 2).

In all studied cases, the photocatalytic reaction is satisfactorily described by a first-order kinetic equation.

To determine the optimal amount of photocatalyst in the studied reactions, their concentration was increased while the substrate concentration remained unchanged. It was found that at a low concentration of photocatalyst (<2 г/л) наблюдается рост констант скорости деструкции красителей и фотовосстановления бихромат-аниона с увеличением содержания фотокатализатора в растворе с последующим выходом на плато при концентрациях фотокатализатора вблизи 2 г/л. Все последующие фотокаталитические реакции проводили при концентрации фотокатализатора 2 г/л.

In the series from 1Ca/TiO2 to 4Ca/TiO2, an increase in photocatalytic activity in dye destruction reactions is observed (Table 2). Thus, the rate constant of photocatalytic destruction of safranin T increases from 3.5 to 5.7 x 10-4 s-1, rhodamine - from 1.7 to 2.5 x 10-4 s-1. Similar data were obtained by the authors for samples

Rice. Fig. 3. Pore size distribution for synthesized samples: 1 - 4Ca/TiO2, 2 - 3Ca/TiO2, 3 - 5Ca/TiO2, 4 - TiO2; r - pore radius, Ktot. - total pore volume.

titanium dioxide doped with calcium ions using the sol-gel method and calcium titanate in the work.

In addition, in the series of samples from 1Ca/TiO2 to 4Ca/TiO2, their sorption capacity towards dyes increases (Table 2), which is associated with their structural characteristics (Table 1). The 5Ca/TiO2 sample, compared to the 3Ca/TiO2 and 4Ca/TiO2 powders, has significantly lower sorption and photocatalytic activity towards dyes.

In the case of photoreduction of the dichromate anion, the 5Ca/TiO2 sample turned out to be the most photocatalytically active (kA = 3.9 x 104, s-1), which is consistent with the work in which it was found that the addition of calcium titanate to titanium dioxide

Table 2. Photocatalytic k x 104, s 1) and sorption (adsorption value A, mg/g) activity of titanium dioxide samples modified with calcium towards dyes and dichromate anion

Sample Safranin T Rhodamine Bichromate anion

ky x 10-4, s"1 A x 10 4, mg/g ky x 10-4, s"1 A x 10 4, mg/g ky x 10-4, s"1 A x 10-6, mg /G

BELIKOV M.L., LOKSHIN E.P., SEDNEVA T.A. - 2012

DEPENDENCE OF THE RATE OF PHOTOCATALYTIC DESTRUCTION OF SAFRANIN ON THE CONCENTRATION OF THE CATALYST

KHALYAVKA T.A., VIKTOROVA T.I., KAPINUS E.I. - 2009

KINETICS OF PHOTOCATALYTIC DESTRUCTION OF ORGANIC COMPOUNDS: INFLUENCE OF SUBSTRATE AND CATALYST CONCENTRATIONS

KAPINUS E.I. - 2012

UDC 677.077.62

M. A. Salyakhova, I. Sh. Abdullin, V. V. Uvaev, E. N. Pukhacheva

STUDY OF ADSORPTION PROPERTIES OF COMPOSITE MATERIALS

WITH IMPROVED TITANIUM DIOXIDE

Key words: composite material with embedded titanium dioxide, titanium dioxide, silicon dioxide, sorption,

adsorption properties.

Keywords: composite material with embedded titanium dioxide, titanium dioxide, silica, sorption, adsorption properties.

Adsorption properties of photocatalytic composite material is evaluated by two parameters: the value of the equilibrium sorption of saturated vapors of benzene and ethyl acetate samples of material and limit the volume of sorption space material samples.

In recent years, research and development of new generation protective materials and products made from them using nanosystems have been intensively developing. Titanium dioxide is most often used in the photocatalytic process as one of the most chemically and thermally stable and non-toxic products. Nano-sized inorganic oxides can be used to disinfect materials contaminated with dangerous toxic substances, including toxic substances, as well as to purify the air from impurities of vapors and gases of toxic chemicals.

The composite material is obtained by sequentially forming an adsorbent layer on a woven cellulose-containing textile base, then a photocatalytic layer. The formation of an adsorbent layer on a woven or non-woven cellulose-containing textile base occurs using sol-gel technology as a result of impregnation of the textile base with an aqueous dispersion containing nano-sized particles of aluminum oxide and drying at a temperature of (100±5) oC. Positively charged alumina particles are attached to the negatively charged surface of the textile base, both due to electrostatic interaction and due to mechanical retention of the alumina particles by the textile base fiber. The formation of a photocatalytic layer on a woven cellulose-containing textile base containing an adsorbent layer occurs using sol-gel technology as a result of impregnation of a material sample with an aqueous dispersion containing a complex of silicon dioxide and titanium dioxide, drying the impregnated sample at a temperature of (80-90) oC for 30 minutes followed by washing with water and drying at a temperature of (100±5) oC. The developed surface of aluminum oxide fixed on the surface of the textile base ensures good adhesion of the silicon dioxide complex with titanium dioxide on the surface of the adsorbent layer.

When forming an adsorbent layer and a photocatalytic layer on a textile basis,

The effective fibers are not damaged and the texture of the textile base does not change.

A photocatalytic composite material containing a woven or cellulose-containing textile base, a photocatalytic layer including a complex of silicon dioxide modified with aluminate ions and titanium dioxide of anatase modification, and an adsorbent layer containing aluminum oxide with a boehmite structure located between the photocatalytic layer and the textile base, characterized by increased adsorption properties in relation to polar and non-polar chemical compounds, exhibits high photocatalytic activity and antibacterial properties when irradiated with UV light. An aqueous dispersion of aluminum oxide is used as a material to form an adsorbent layer. The aqueous dispersion contains nano-sized particles of aluminum oxide with a boehmite structure in an amount of 9.0-9.5 wt.%, solution pH 3.8. Using powder diffractometry, it was established that nano-sized aluminum oxide has the orthorhombic crystal structure of boehmite (y-AОOH) (No. 01-083-1506 in the PDF-2 database). Aluminum oxide with a boehmite structure has a developed surface, a high electropositive charge, has adsorption properties towards polar and non-polar chemical compounds, and the ability to trap microorganisms.

The adsorption properties of a photocatalytic composite material are assessed by two indicators: the equilibrium value of sorption of saturated benzene and ethyl acetate vapors by material samples and the maximum volume of the sorption space of material samples under conditions of static activity at a temperature of 25°C. The adsorption properties of the photocatalytic composite material based on cotton fabric are presented in Tables 1 and 2.

Table 1 - Adsorption properties of photocatalytic composite material based on cotton fabric

photocatalytic benzene

composite material,%

Photo-Connect-Adsor-Equal-Limit-

catalytic SiO2mo bent spring volume

congestion difi- (Y-value we eat sorb-

TiO2, ziro- A1OOH) sorption

anatase bath and boehmite AS, mg/g pro-

A1(OH)4- countries

25 25 50 104 118

The equilibrium value of sorption of saturated vapors of a chemical compound by a sample of a material is determined as the ratio of the amount of vapors of a chemical compound absorbed by this sample to the mass of the sample. The limiting volume of the sorption space of a material sample is calculated based on the equilibrium value of sorption and the density of the chemical compound.

Table 2 - Adsorption properties of photocatalytic composite material based on cotton fabric

As can be seen from the examples given in tables 1 and 2, the composite material with embedded titanium dioxide is characterized by increased adsorption properties in relation to polar and non-polar chemical compounds due to an increase in the available surface area of two adsorbents - nanodisperse oxides of silicon and aluminum.

Literature

1. Filtering and sorbing material with an embedded photocatalyst / M.A. Salyakhova [et al.] // Bulletin of the Kazan Technological University. -2013.t.16. No. 23. - pp. 52-53.

2. Photochemical destruction of textile materials / M.A. Salyakhova [et al.] // Bulletin of the Kazan Technological University. - 2013.t.16. No. 17. - From 92-93.

3. Shabanova, N.A. Chemistry and technology of nanodispersed oxides [Text] / N.A. Shabanova, V.V. Popov, P.D. Sarkisov - M.: ICC "Academkniga", 2007. - 309 p.

Photo-catalyst TiO2, anatase Binder SiO2 modified A1(OH)4- Adsorbent (Y- A1OOH) boehmite Equilibrium sorption value aS, mg/g Limit volume of sorption space WS, cm3/g

25 25 50 134 152

25 30 45 130 148

25 35 40 128 145

30 30 40 126 143

30 35 35 122 139

35 35 30 119 135

© M. A. Salyakhova - asp. department plasmachemical and nanotechnologies of high-molecular materials KNRTU, [email protected]; I. Sh. Abdullin - Doctor of Engineering. Sciences, prof., head. department plasmachemical and nanotechnologies of high-molecular materials KNITU, ab(M1t^@k51i.gi; V.V. Uvaev - Candidate of Chemical Sciences, General Director of JSC KazKhimNII; E.N. Pukhacheva - Candidate of Technical Sciences , senior scientific worker at laboratory No. 5 of OJSC “KazKhimNII”, [email protected].

©M. A. Salyahova - postgraduate of chair of plasmachemical and nanotechnologies of high-molecular materials KNRTU, [email protected]; I. Sh. Abdullin - doctor of technical science, professor of chair of plasmachemical and nanotechnologies of high-molecular materials KNRTU, and [email protected]; V. V. Uvaev - candidate of technical sciences, General Director, of Kazan Chemical Scientific-Research Institute; E. N. Pukhacheva - candidate of technical sciences, Senior researcher of Laboratory of Kazan Chemical Scientific-Research Institute, [email protected].

The sorbent based on titanium dioxide was obtained by ultrasonic treatment of the TiO2 reagent in various electrolytes: distilled water, solutions of NaCl, NaOH, HCl. The microstructure of the resulting sorbents, the elemental composition of the surface, thermal stability, the presence of functional groups on the surface, and the sorption activity of titanium dioxide after ultrasonic treatment were studied. It has been established that the use of ultrasonic treatment of TiO2 increases its sorption activity several times compared to untreated TiO2. In addition, the electrolyte environment in which ultrasonic action occurs changes the thermal stability of the sorbent and affects its behavior in the processes of sorption-desorption of impurities from the surface. The sorbent treated with ultrasound in an alkaline medium had the maximum sorption activity, while the titanium dioxide reagent had the minimum. Titanium dioxide subjected to ultrasonic treatment in a neutral environment (H2O, NaCl) is characterized by the most stable characteristics in the sorption-desorption process.

water purification

titanium dioxide

ultrasonic treatment

impurities of heavy metals

1. Smirnova V.V., Nazarenko O.B. Application of titanium oxides and hydroxides for drinking water purification // Prospects for the development of fundamental sciences: proceedings of the VIII international conference of students and young scientists (Tomsk, April 26-29, 2011). - Tomsk, 2011. - P.383-385.

2. Smirnova V.V., Nazarenko O.B. Development of technology for producing nano-porous sorbent based on titanium dioxide for drinking water purification // Modern equipment and technologies: collection of proceedings of the XVII International Scientific and Practical Conference of Students and Young Scientists (Tomsk, April 9-13, 2012). - Tomsk, 2012. - P.393-394.

3. GOST 4011 - 72. Drinking water. Methods for measuring the mass concentration of total iron.

4. GOST 4974 - 72. Drinking water. Methods for determining manganese content.

5. Smirnova V.V., Nazarenko O.B. The influence of the conditions of preparation and ultrasonic treatment of titanium dioxide on its sorption activity // Prospects for the development of fundamental sciences: proceedings of the IX international conference of students and young scientists (Tomsk, April 24-27, 2012 ). - Tomsk, 2012. - P. 484-486.

Introduction

To achieve European drinking water quality standards in Russia, it is necessary to develop technologies for its purification from various impurities. The most difficult task is to extract soluble impurities of heavy metals and hardness salts from water. To solve this problem, it is necessary to improve the quality of existing sorbents (activated carbon, zeolites, quartz sand, etc.) or develop new ones.

Among inorganic sorbents, titanium dioxide is promising; it has a number of positive properties: it is biologically non-hazardous, it is a sparingly soluble compound, it exhibits multifunctional properties when purifying water from impurities of various natures, and under the influence of radiation it provides bactericidal properties.

The purpose of this work was to increase the sorption activity of titanium dioxide by treating its surface with ultrasound.

Material and research methods

To achieve this goal, a study was carried out of the surface structure and thermal stability of the titanium dioxide (special purity) reagent and its changes during ultrasonic treatment in various electrolytes (distilled water, 0.2 N solutions of sodium chloride, hydrochloric acid and sodium hydroxide).

When carrying out the work, standard methods of physicochemical analysis were used: electron microscopy (EM), differential thermal analysis (DTA), X-ray phase analysis (XRD), infrared spectroscopy (ICS) and others. The physicochemical analysis was carried out using instruments of the Scientific Analytical Center of Tomsk Polytechnic University (thermal analyzer Q 600 STD, IR-Fourier spectrophotometer Nicolet 5700, chromatography-mass spectrometer). The original method was the pre-treatment of sorbents and sorption under the influence of ultrasound (22 kHz, 0.15 W/cm2).

Soluble impurities Fe +2 and Mn +2 that are actually present in the drinking water of the city of Tomsk were chosen as the subject of the study. The content of iron impurities was determined by photometry using standard methods. The method is based on the interaction of iron ions in an alkaline medium with sulfosalicylic acid and the formation of a yellow-colored complex compound. The color intensity, proportional to the mass concentration of iron, was measured at a wavelength of 400-430 nm. The content of manganese impurities was also analyzed by photometry. The method is based on the oxidation of manganese compounds to MnO 4 -. Oxidation occurs in an acidic environment with ammonium or potassium persulfate in the presence of silver ions as a catalyst. In this case, a pink color of the solution appears; the absorption intensity was measured in the wavelength range 530 - 525 nm. Chemical reagents of analytical grade were used to prepare model solutions. Solutions for the study were prepared by dissolving iron (II) sulfate heptahydrate and manganese (II) sulfate pentahydrate. The accuracy of the experiment was increased by constructing a calibration graph and statistical processing of the results obtained with a probability of P = 0.95: for iron - in the concentration range from 0.01 to 2.00 mg/l, for manganese from 0.005 to 0.3 mg/l, with MPC 0.3 and 0.1 mg/l, respectively.

Research results and discussion

According to the results of electron microscopy, the TiO 2 reagent treated with ultrasound in various environments (H 2 O, NaCl, NaOH, HCl) represents porous spheroids with a characteristic size of 5 - 30 μm and agglomerates of smaller particles: 2 - 4 μm with a fraction of micron and submicron (sample S7). At higher magnification (> 3000 times), structural fragments are visible in the structure of the agglomerates, the sizes of which do not exceed 1 μm. Microphotographs of the obtained samples are presented in Figure 1.

Rice. 1. Microphotographs of titanium dioxide treated with ultrasound in an alkaline environment: a - 100 times magnification, b - 3000 times magnification

The surface of ultrasonic-treated TiO 2 was analyzed for impurity content using X-ray photoelectron spectroscopy, the results are presented in Table 1. The sorption activity of titanium dioxide is so high that in some cases, probably from insufficiently purified distilled water, a silicon impurity is detected on the surface (0.95 wt .%) and copper (0.68 wt.%).

Table 1. Elemental composition of titanium dioxide samples treated with ultrasound in various electrolytes

		Elemental composition, wt. %

According to DTA, for all titanium dioxide samples treated with ultrasound, desorption of water is observed when heated to 500 ˚C. A typical thermogram (sample S1) is shown in Figure 2.

Rice. 2. Typical thermogram of titanium dioxide samples treated with ultrasound in H 2 O, NaOH and HCl - a, c NaCl - b

As can be seen from the figure, the thermogram of the TiO 2 sample treated with ultrasound in a sodium chloride solution (sample S4) differs noticeably (Fig. 2.b) from the DTA data of the remaining samples (Fig. 2.a). When heated to 200 ˚C, weakly bound water is removed from sample S4, but its amount is several times less than for other samples. At the same time, with further heating in the range of 650 - 900 ˚C, a more significant decrease in the weight of the sample occurs (6.0 wt.%), which is associated with the thermal decomposition of TiOCl 2 oxochloride and its transition to TiO 2 dioxide.

The infrared transmission spectra of titanium dioxide samples treated with ultrasound are characterized by two intense absorption bands υ (Ti - O) = 650 cm -1 and υ (O - H) = 3000 - 3700 cm -1 .

Rice. 3. Infrared transmission spectrum of a titanium dioxide sample treated with ultrasound

In addition, as can be seen from Figure 3, the IR contains weak intensity absorption bands, characteristic of compounds present on the surface of the sorbent after its processing and drying. Absorption bands υ (Ti - Cl) in the IR are present at lower wave numbers (< 400 см -1), для записи которых требуется иной спектрофотометр.

To study water purification processes, model solutions of iron and manganese were prepared by dissolving an exact weighed portion of the corresponding salts: 3.0 and 1.0 mg/l. Before sorption of impurities, titanium dioxide powder was subjected to ultrasonication in various media: distilled water, 0.2 N. solutions of NaOH, NaCl and HCl. The duration of treatment was 10 minutes at an ultrasonic power of 0.15 W/cm 2 . To the initial solution with a volume of 100 ml and containing 3.0 mg/l of Fe +2 ions, 0.2 g of sorbent was added, mixed and the sample was analyzed for the residual content of iron impurities (Table 2). Similarly, 0.2 g of the same sorbent sample was added to 100 ml of a solution containing 1.0 mg/l Mn +2 ions, stirred, and after a certain time the residual concentration of manganese ions was determined (Table 2). The results are shown in Table 2.

Table 2. Residual content of Fe +2 and Mn +2 impurities after their sorption by TiO 2 samples

Sorbent samples		TiO2 reagent
Entered - found		Added 3.0 mg/l Fe +2	Added 1.0 mg/l Mn +2	Added 3.0 mg/l Fe +2	Added 1.0 mg/l Mn +2	Added 3.0 mg/l Fe +2	Added 1.0 mg/l Mn +2	Added 3.0 mg/l Fe +2	Added 1.0 mg/l Mn +2	Added 3.0 mg/l Fe +2	Added 1.0 mg/l Mn +2
Found, mg/l	In 20 minutes
	In 60 minutes
	After 24 hours

According to the results obtained, the sorption of impurities by titanium dioxide occurred within a relatively short time: the concentration of iron ions from 3.0 mg/l decreases minimally to 1.42 mg/l (reagent) and maximum to 0.53 mg/l (sample S7), at the same time, a decrease in the concentration of manganese ions from 1.0 mg/l was observed for the same sorbent sample as for the iron impurity - minimum to 0.56 mg/l, maximum to 0.24 mg/l. The best results were obtained for a sample of titanium dioxide S7 treated with ultrasound in a NaOH solution, while the initial TiO 2, not treated with ultrasound and not activated with chemical reagents, had the minimum sorption characteristics. Thus, the decrease in the concentration of iron impurities was 5.7 times, manganese - 4.2 times.

With increasing contact time of the sorbent with model solutions, the content of impurities did not change for the sample not treated with TiO 2; for samples obtained in water (S1) and sodium chloride solution (S4), the content of impurities practically did not change within 48 hours. At the same time, the sorbent sample prepared in sodium hydroxide (S7) was characterized by an increase in iron concentration to 0.90 - 1.06 mg/l and an increase in the concentration of manganese ions to 0.47 - 0.74 mg/l. In contrast to the TiO 2 samples discussed above, treated in hydrochloric acid (S10) was characterized by a gradual decrease in the concentration of iron ions in solution from 1.12 to 0.53 mg/l and a decrease in the concentration of manganese ions from 0.31 to 0.25 mg/l l.

conclusions

Ultrasonic treatment of TiO 2 gives a positive result: in comparison with the untreated sorbent, the residual concentration of iron and manganese impurities decreased several times. Treatment of the sorbent, carried out in various media, changes its behavior in the processes of sorption - desorption over time.
The sorbent treated with ultrasound in alkali had the maximum sorption activity, but with prolonged contact, impurities, both iron and manganese, were washed out. At the same time, the sorbent sample obtained in an acidic environment was characterized by a gradual decrease in the concentration of iron and manganese impurities in the solution.
Titanium dioxide samples prepared in distilled water and sodium chloride solution had stable characteristics with respect to the sorption-desorption process: after sorption, the concentration of impurities did not change when the sorbent came into contact with model solutions for 48 hours. The effect of treatment with TiO 2 and pH of the environment on its sorption activity is probably associated with the formation of oxohydroxide structures in alkaline and acidic environments, capable of cation exchange and retention of heavy metal impurities.

Reviewers:

Korobochkin Valery Vasilievich, Doctor of Technical Sciences, Professor, Head of the Department of General Chemical Technology, National Research Tomsk Polytechnic University, Tomsk.
Ilyin Alexander Petrovich, Doctor of Physical and Mathematical Sciences, Professor, Acting Head of the Department of General and Inorganic Chemistry, National Research Tomsk Polytechnic University, Tomsk.

Bibliographic link

Smirnova V.V. INFLUENCE OF STRUCTURE, PROPERTIES AND SURFACE TREATMENT ON THE SORPTION ACTIVITY OF TITANIUM DIOXIDE // Modern problems of science and education. – 2012. – No. 5.;
URL: http://science-education.ru/ru/article/view?id=6958 (access date: 02/01/2020). We bring to your attention magazines published by the publishing house "Academy of Natural Sciences"

Sorption properties of titanium dioxide. Modern problems of science and education

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