ENVIRONMENTAL MONITORING OF TIO 2 BY LIBS

Transcription

1 ENVIRONMENTAL MONITORING OF TIO 2 BY LIBS Jakub WIENER 1, Mária PRŮŠOVÁ 1, Věra MACÍKOVÁ 1, Miloslav POUZAR 2 1 Technical University of Liberec, Liberec, Czech Republic, EU, jakub.wiener@tul.cz 2 University of Pardubice, Pardubice, Czech Republic, EU Abstract Laser induced breakdown spectroscopy (LIBS) is interesting method of elemental analyses with high application potential. In this study we developed a novel method of monitoring of environmental contamination by LIBS. As a model pollutant were used nanoparticles of TiO2 with photocatalytic properties. Proposed method is based on collection of monitored nanoparticles from solid surfaces and following quantitative analysis. Proposed method is suitable for each monitoring of surface contamination. Keywords: TiO2, nanoparticles 1. MAIN TEXT Nanoparticles are now produced in many industrial technologies. More often we can detect stable nanoparticles in our environment as example we can choose silver, carbon or titanium oxide. Quantification of the behaviour of nanoparticles in the human environment or directly in living organisms is aim of many scientific studies, but still is paid attention not enough high in comparison with potential problems in the future. Monitoring of nanoparticles in the environment has many problems. One of the most important problems is example low stability of nanoparticles based on dissolving, aggregation, evaporation or melting. Lot of standard used methods of quantification of nanoparticles in the environment is based on active separation of nanoparticles from the air (usually by filtration). Estimated concentrations are average values estimated in all time of measurement. This kind of method has a long time history and can be easy standardised and compared with the measured values at different measured places. This study is focused on other way haw we can quantify nanoparticles - estimation of particles spontaneously deposed on surfaces by wipe method. The main positive of this methods are: - look into a history of evaluated places (we obtain values connected with the processes before the beginning of sample collection) - collection of samples is easy, quickly and cheap (unqualified persons are acceptable) - we don t need complicated apparatus to collect samples - we can analysed small areas separately (we can estimated concentration at the area 10 cm 2 ) All above described attributes of wipe method show that it is interesting for easy monitoring in industry, ecological disaster, analyses in the working places 2. EXPERIMENTAL PART 2.1 Titanium Oxide P25 Degussa The TiO2 powder (Degussa, P25), which is a standard material in the field of photocatalytic reactions, contains anatase and rutile phases in a ratio of about 3:1. The average sizes of the anatase and rutile elementary particles are 85 and 25 nm, respectively.

2 P25 (Degussa) has been a standard material, which has a relatively large surface area (49 m 2.g -1 ). Interestingly, the P25 powder consists of anatas and rutile phases [2]. Because the P25 powder shows high activity for many kinds of photocatalytic reactions, it has been used in many studies. P25 was used as a model contaminant / pollutant in this study. In selected experiments was TiO2 replaced by orange metal-complex dyestuff to visualise the localisation of the powder on the cellulose collector. Model pollutant TiO2 (Degussa P25) was deposited on smooth glass plate. The areal concentration of the TiO2 powder was from 60 to 600 mg/m2. This TiO2 was deposited at dry conditions to simulate real deposition by sedimentation from the air. 2.2 Wipe method The TiO2 powder was collected by the wipe method from the area 5x10 cm of glass plate. As a collector of powder was used pure cellulose paper (without chemical modification, flexible, 40g/m2) and in the selected cases was used cellulose (cotton) fabric. Dust collector is supported in the wipe method by metal thin plate, which is moved (2,5 cm/s) together with the cellulose collector on the glass plate with the collected particles. All contaminants are after the wipemethod collected on the cellulose collector in shape of line. 2.3 Elemental analyses Elemental analyse of samples prepared by wipe method is realised by Laser Induced Breakdown Spectroscopy (LIBS). This method is optimal for analyses at small place, without any pre-treatment of solid samples, quickly obtained results and high sensitivity comparable with other emission spectroscopy methods. Analyse of Ti (respectively TiO2) on the cellulose collector was realised by the instrument Lea-S500 with the software 2. Set values are visualised on the Fig. 1. Laser irradiation of sample is by used LIBS procedure (Fig. 2) located in two lines (of measured points (green points) in distance 500 micrometers. These two lines of 8 irradiated areas are located perpendicular to collecting line created by wipe-method (Fig. 2). LIBS method is many time used for the elemental analyses of cellulose structures (especially textiles). [1,2,3,4]

3 Fig. 1 Paramethers of LIBS metod Fig. 2 Schematic view on cellulose holder with LIBS measure points (green points) acros the wipe-line (in this case was used a dye)

4 The relationship between the concentration of TiO2 and measured output from LIBS is visualised on Fig. 3. The higher concentration of TiO2 is too high for the LIBS method. LIBS method offered linear dependence of LIBS values till 150 milligrams of TiO2 at 1 m2. Above this value is the LIBS output independent (constant) LIBS values y = 29,927x R 2 = 0, concentration of TiO2 in mg/m2 Fig. 3 Relationship between the concentration of TiO2 and measured output from LIBS 2.4. ANALYSES OF REAL SAMPLES FROM THE ENVIRONMENT Above described analytical method is used for the evaluation of samples collecting real dust at the places with usual (university classroom) and high contamination (lab working with TiO2 nanoparticles) by TiO2. 3. RESULTS AND DISCUSSION The dust particles are collected on the surface of cellulose collector (fig. 5) the sensitivity of LIBS method is high. On the following figures (Fig. 4 and Fig. 5) are real results from the monitoring of TiO2 in buildings. On Fig. 4 we can see, that the contamination of offices and class-room in the Technical University of Liberec is not high maximal measured concentration of TiO2 is smaller then 10 mg/m 2. In laboratory working as main activity with TiO2 is the concentration of TiO2 much higher maximal estimated concentration of TiO2 is around 80 mg/m 2. The nanostructured character of this dust is wisible on the picture from scanning electron microscopy (Fig. 6).

5 Fig. 4 Results from the monitoring of TiO2 in university (red points- laboratory of textile finishing, green points laboratory of physical methods, blue points teachers room) Fig. 5 Results from the monitoring of TiO2 in university lab working with TiO2 nanoparticles (green pointstable in laboratory, blue points shelf in laboratory)

6 Fig. 6 Cellulose paper holder with real dust particles collected by the standard method from the lab working with TiO2 nanoparticles CONCLUSION Proposed wipe - method of dust collection power by LIBS elemental analyses is a high level system if analyses of dust or small particles deposited on solid surfaces. This method was demonstrated on TiO2 nanoparticles, which are used in many applications from sunscreen till white pigments, delustring agent or photocatalytic systems. In lot of these applications is used TiO2 in the form of nanoparticles. Real toxicity of TiO2 nanoparticles is not verified, but is necessary observe the behaviour of this massive environmental contaminant. ACKNOWLEDGMENT This work is supported by grant project: TAČR ALFA, Vodné nanodisperze pro funkční povrchové úpravy TA (NANOCOVER), Czech Republic LITERATURE [1] WIENER, J., SHAHIDI, S., GOBA, M. M.: Laser deposition of TiO2 nanoparticles on glass fabric, Optics and Laser Technology, Volume 45, February 2013, Pages , ISSN [2] PRůŠOVÁ, M., WIENER, J.: APPLICATION OF LIBS METHOD IN ANALYSES OF CARBON AND TITANUM IN TEXTILE STRUCTURE, Textile research journal, Vol. 82, Issue 11, JUL 2012, , ISSN: [3] POUZAR M., PRůŠOVÁ M., ČERNOHOSKY T., WIENER J., KRATOCHVÍL T.: ANALYSIS OF Ti IN TEXTILE STIPPLED BY TiO2 NANOPARTICLE SOL USING DOUBLE-PULSE LIBS AND ED XRF SPECTROMETRY, Journal of Applied Spectroscopy, Vol. 78, No. 5, 2011 [4] POUZAR M., PRůŠOVÁ M., Prokopčáková P., ČERNOHOSKY, T., WIENER J., KREJČOVÁ, A.: LIBS analysis of chromium in samples of dyed wool fabric, Journal of Analytical Atomic Spectrometry, 24, 2009, , ISSN