CASTEU6:--: (SI'AI:>;) iI QUALI 98 DEVELOPMENT OF CERAMIC GLAZES WITH OPTICAL ABSORPTION AND EMISSION PROPERTIES: APPLICATION AS WALL TILE GLAZES WITH SANITARY (BACTERICIDAL) PROPERTIES M. T. Tichell"', A. Pascual'", J. Bakali"', V. Kozukharov'''', E. Cordrmcillo'"", P. Escribano"?', J. Ca rda'"'' " ESMA LTES, S. A., 12110, Alcorn (Spain) ''''University of Chem ical Technology and Metallurgy (Sofia (Bu lgaria) '''''Department of Organic and Inorganic Che m istry, Un ivers idad [aurne L 12080, Ca stellon . ABSTRACT TIl<' pn'sellt stlldy describes the derclopmcnt of a ceramic s la:e (frit), u-h ich 011 applicatioll exhibit» opticel propcrtics with a bactericidal tffect. The material obtained, compared to sim ilar <'XistillS products, present» intprorcd It'mr resistance ill st'rl'ice, hiS'1gloss and potential lise ill sanitari; products and ceramic tral! tiles. The materiai tms dnvloped "y selecting rare-earth oxides, 11'hose compatibility lms studied ill differC1lt frit formuunions, sl/"seqllellfly mcasurins; their absorption and etnission properties ill the ultmriolct to infrared radiation rallge. The properties ofthe materials obtained were clutmctcriscd and mntsured by UV and uisiblr absorption spectrophotometric techniques, emission (pltotolumincsccnt spectm m), alld infrared as trcll as nuclcur magnetic resOll/mce spectroscopic techniques ('"H IUvlN ). Structural, microstructurni nnd microannivticai studic» ll'en' also conducted 0 11 the prepared samples by X-my diffruction (X RO) and scanni ng electron microscopy (SEA'1) ill all instrument eql/ipped u-ith ellerSI! dispcrsir« X-ray inicroanalvsis (EOX). Finallu, the properties ll'en' assessed which the materials dt'l'eloped exhibited as finished products. These inrolrcd refractive properties (gloss) ami bactericidal capability, selectillS for tile latter case certain strains of bacteria (Scherichia coli, PSl'l/dOIll Olltl aeruginosa alld Stnfilococcus uureus ). and mlOlysillg the degrc«of growth or a/Isellce ofsrowtll of these colonies by optiCilI microscopy and image analusi«. p.Gr - 17 ill QUALI ~_ 98 CASTELLO:" (SPAI:" ) 1. INTRODUCTION At present a new field known as photochemistry is being developed in Solid State Chemistry. The research results not only have fundamental implications but also open up a vast potential of real technological applications. Recently "Progress in Inorgani c Chemistry" published a monograph entitled: "Molecular Level Artificial Photosynthetic Materials", dealing with aspects of the molecular nature of Chemistry and Materials Science in the field of artificial photosynthetic materials design, which can convert solar energy into other products that yield energy or directly in electricity. This requires integrating a variety of factors in the material that is developed. Such factors include light absorption, electron and I or energy transfer processes, and fina lly the obtainment of useful products with interesting properties"! The lite rature has traditi onall y described sensitised w ide-bandgap semicond uc tors'". Typical wi de-bandgap semicond uc tors are the n-types suc h as TiO" ZnO and SrTiO" which exhibit high stability, easy processibil ity, and do not decompose under radiati on . The se nsitisation process of a se micond uctor material involves an absorption capacity in a range of wavelengths exceed ing the ga p. Thi s phen omenon became known in 1873 following Vogel's!" invest igations into organic inks deposited on semicond uc tor halogen mineral gra ins, whe n he man aged to ra ise the photosynthet ic se nsitivity of these particles in low energy regions of the spectrum (visible region ). This system simply consists of an optically active molecule that can be exc ited electro nically, and on be ing ads orbe d onto the semicond uc tor surface allows introducing the excited electron into the conduction band, thus gene rating photoelectrochemi cal and photocatalyt ic processes. Vogel's work led to extensive research that has continued up to the present decadel'll5l l' l. These studies have produced important advances in the degree of understanding of the fundamental processes involved, such as degree of sensitisation, light absorption efficiency and development of single-layer manufacturing techniques. In recent years research has focused on TiO, production with nanoparticle sizes to raise speci fic surface area and increase the gap. Progress ha s also been made in developing new synthes is methods (sol-gel method s), and transparent film applications. This has allowed deveioping photoanodes and thin layer solar cells combine d with an appropriate photosen sitive pigment, thus achieving sunlight-electric ity conversion efficiencies of the order of 7 to 10 %. The literature!" reports numerous examples of molecul ar photosensitisers designed using TiO, with transition metal complexes, together with chlorophyll derivatives and natural porphyrins. These studies have led to a ne w line of research focused on synthesising [I }. " Prog ress ill Inorganic Chemistry" . Vol. 44 . Pu bli shed by : G. J. .MEYER, J OI L~ \ 'v'[LEY :\ :\ D S() \lS, Nue va York, 199 7. [Z]. c. A . B IG,\;OZZ I, K . R. Sc.:H()(Y\'OVER AND F. SCA.""HXJLA, "A <upramotecular approach 1£1 lig/II Iwn'e;; tillg an d: -eneitization of toide­ bandgap semiconductor» A l ltt' llllfl efft!cts and d targe separation" in Progress in Inorganic Chemistry Vol. 4-1. Published by: G. J. Meyer; John Wiley and Sons, Nueva York, 1997. (3). H . w. VOCEL , BER. Detscn. Chem. Ces. 6, 1302. (l873 ). HI· B. O 'RE:\GA:'-J Yrv1. G J<...\ TZH., Natu re (London), 353 , 73 7 (1991). [5). T. A .H EI\l FR, C A. BIG:\Olll YG. J. I\:lnER, J. PHYS. Quem., 97, 11987, (199 3 ). [6 ). R. ARGAllI, C A. BICr-..:0 77 I, T. A. H EJ ~l E R , E. x . C \SI EL L\\;O .-\~ D G. J. M r vre. l/lorg. Ofem, 33, 5741 , (199..1). [i ). A. K AY y :vt GR.\ TZEL, J. PH'fS. C hern., 97, 62n (1993). P. GI- 18 CASTELL6:-J (SPAI:'>: ) iii QUALI 98 semicond uctor pairs tha t exhibit different electronic gaps such as CdS-ZnO, CdSe-TiO" which exhibit non-linear optical properties"!"! A new method was developed by the Toto company, based on superhydrophilic photocatalytic tech nology (Honda-Fujishima effect invented by professor Honda and professor Fujishima of Tokyo University in the 70s, and patented by Toto). It has a bactericidal effect by capturing charge bearers. The optical excitation of electrons is produced by means of colloidal semiconductor particles having a high faul t density. The free bea rers are tra pped in the faults in which they undergo radiative and non-radiative recombination, as set out in the scheme: TiO, hv - TiO (ec• whe re ec• and h,. are free charge bea rers in the valence and conduction bands, and e, and h, are respectively the trapped electro ns and holes. In this fashion, the re arises a grea t charge accumulation in the minute stru cture of a semicond uctor colloid, which produces increased efficiency in interface red ox reactions on the colloid surface. This fact, cons isting of simultaneous ly trapping photogenerated holes and electrons ha s recen tly been demonstrated in colloidal TiO, sus pensions. Moreover, these trapped cha rge bearers exhibit characteristic absorption bands in the infrared and ultraviolet reg ions. Studies ha ve also been performed by trapping electrons in ZnO, WO, and SnO, colloids, investigating the photolysis phenom en on by laser tlashes. These expe riments have led to technology applications such as the development of photochromic matenals'''"! "! As an example, the photocatalysis ph enom enon consists of a semiconductor that breaks down organic compounds in wa ter or those in the air by oxidation through exposu re to light. On the other hand, the rare-earth oxides present electron transfer ba nds at f-f level transitions of levels. Fig. 1 schematically depicts interaction between photons (light) and matter. There are certain properties of electro n activity, which are desirable such as energy-level promotion of electrons, usually between the fundamental atomic state and a higher level. Such charge tra nsfer generally produces optical absorpti on phenomena in the visible and near UV spectrum, as well as emission phenom ena. This has allowed developing all the laser technology (ruby, Cr', RE" rare earths ). In rare ea rth and transition metals compo unds, the absorption bands can be attributed to electron transitions centred on individua l atoms having incom plete "d" or " f" leve ls. Thus the rare-earth oxides exhibit broad absorption ba nds in the visible spectrum, which indicate electron transfer un der low ene rgy conditions. (8]. D. LJL ~ r. v K \\ I.\ I, ]. Pit h . Che rn" 97, 10769 (199 3) , (91. E. Cor~Ol")" C I L tO. J. B. C .I, RO.-", x t . A : T F. '\ A, G. \-10 '-,-1<:1,) :-. .\ '<0 P. ESCRlfI" ",O, J. Sill-Cd Science ami Tcd llloh'S,u.S, to·B, (1997). [lOJ. C. S. T U:CHI " -,0 D. F. OLLI S, "Piw tocatalyf ic dt'gradatitlll {)f M-gmrh" '/'fi rer conm minaut-: lIIecllfllli"m" illi '(lllliIlS " .lIdro.\".1I1 radical attock", Jou rnal o f Catalvsis. 122, 178- 192 (1990). [111. .\1. R. H O FF\ IA .... <; S. T. ;.:' .... en-,,\\'. C HOJ A''0 D. W. B.\lIl B I:\:'\'\, "E nrirownen tat aFplicatio"" ~f-..cmiconductor ph (lll l (f1ta l y ~i ~ " . Chern. Rev, 95, 69-96, (1995) , P. GI · 19 iii QUALI ..L/f 98 CA5TELL6N (SPAI:',J) In thi s way, sensitised luminescence involves enabling the absorbed energy of an ion (sensitiser) in an absorp tion band to be em itted in the emission band of another ion (activator). Ene rgy transfer from the sensitiser to th e activator occu rs through the following types of transfer: emission-reabsorption, non-radiative resonant, and non­ radi ative non- resonant tra nsfer'!", CONDUCTION t Promotio n to the BANDGAP conduction band ~ f " ~ ! f~ iir;,:f, r .,,:;~y'1iiiI t Exciting \Promotion '0 ' he transfers valence band d-d t f-f ~ transfer "A "8 Figure 1.