Sinteza i karakterizacija elektrolitičkog kupatila za pozlatu na bazi kompleksa zlata sa merkaptotriazolom

Abstract

Elektrolit na bazi kompleksa zlata sa merkaptotriazolom sintetizovan je u širokoj oblasti pH vrednosti od kisele do alkalne (pH=2-12). Nakon sinteze elektrolita urađena je detaljna karakterizacija kompleksa u tečnom i čvrstom stanju u celom opsegu stabilnosti kompleksa. Fizičko-hemijska karakterizacija elektrolita urađena je najpre primenom Ultraljubičaste- Vidljive (UV-vis) spektroskopije i Atomske Emisione Spektrometrije sa indukovano spregnutom plazmom (AAS- ICP). UV-vis spektri elektrolita na pH vrednostima dva i sedam pokazali su pikove na talasnim dužinama koje su vrlo bliske talasnim dužinama pikova za merkaptotriazol, što može ukazati na to da su na ovim pH vrednostima veze Au-MT elektrolitu uspostavljene u najmanjoj meri. UV - vis spektrometrija Au-MT elektrolita na pH 9 pokazala je pik na 272,0 nm što može da ukaže na to da je jedino na ovoj pH vrednosti uspostavljena veza između Au i MT. Pojava pika pri vrednost od 272,0 nm koja je bliska vrednostima koje se mogu naći u literaturi za druge necijanidne elektrolite (sulfiti, tiosulfati i tiousulfati-sulfiti) može da ukaže na to da je veza između Au i MT ostvarena preko atoma sumpora. AAS - ICP analiza je potvrdila predviđene koncentracije zlata u elektrolitu uz maksimalno odstupanje od 0,01 g/dm3. Uporedna toksikološka ispitivanja elektrolita na bazi kompleksa zlata sa merkaptotriazolom (pH=2, 4, 7, 9 i 12) i klasičnog cijanidnog elektrolita (pH=9), urađena metodom "in vitro" na kulturi ćelija humane leukemije K562 su pokazala da je toksičnost organskog kompleksa zlata pri pH vrednostima od: pH=4, 7 i 12 manja u odnosu na alkalni cijanidni elektrolit a nešto veća na pH=2, dok su na pH=9 ove vrednosti približno iste. Elektrohemijska karakterizacija kompleksa zlata sa merkaptotriazolom urađena je merenjem potencijala otvorenog kola, metodom ciklične voltametrije i snimanjem polarizacionih krivih uz praćenje pH vrednosti i provodljivosti elektrolta pre i posle elektrohemijskih eksperimenta. Ova ispitivanja su vršena u periodu od 12 meseci pri različitim pH vrednostima 2, 4, 7, 9 i 12 i optimalnoj koncentraciji zlata u elektrolitu od 2,5 g/dm3 i u periodu od četiri meseca pri optimalnoj pH vrednosti od 9 i koncentracijama zlata u elektrolitu od 1,5; 2,0; 2,5; 3,0 i 3,5 g/dm3. Na elektrolitima čija je pH=4, 7 i 12 prvi vidljivi znakovi raspadanja kompleksa su se pojavili nakon tri meseca od sinteze. Elektrohemijske karakteristike kompleksa zlata sa merkaptotriazolom čija je pH vrednost dva i devet su ostale nepromenjene u periodu od godinu dana. Na ovim elektrolitima nisu zapažene nikakve vizuelne promene u periodu od 12 meseci. Ispitivanje uticaja organskog kompleksa zlata sa merkaptotriazolom na fotoosetljive slojeve koji se koriste pri izradi štampanih ploča urađeno je na prethodno pripremljenim štampanim pločama sa razvijenom mrežom i sa ivicama - linijama na koje je nanešen lak. Fotoosetljivi slojevi na pločicama otporni su na dejstvo elektrolita pri pH vrednostima od 2, 7 i 9. Pri pH=4 prve vizuelne promene se zapažaju nakon 150 s dok se na pH=12 prve promene pojavljuju već nakon 30 s. Sa mikrofotografija površina pločica se takođe može videti da su fotoosetljivi slojevi pločica najotporniji na dejstvo elektrolita na pH=2 i pH=9. Pri pH=9 fotoosetljivi slojevi na pločicama otporni su na dejstvo elektrolita pri svim koncentracijama zlata u opsegu od 1,5 do 3,5 g/dm3. Sintetizovani rastvori kompleksa zlata sa merkaptotriazolom uparavani su na sobnoj temperaturi do suva u cilju dobijanja i karakterizacije nagrađenog jedinjenja u kristalnom obliku. Optička mikroskopija ovih kristala, pokazala je da se kristali dobijeni pri različitim pH vrednostima međusobno razlikuju po boji, krupnoći i homogenosti. Najhomogeniji (po boji i krupnoći) i najsitniji kristali su dobijeni iz elektrolita na pH=9. Najvažnije otkriće IC/Raman spektroskopije je da je Raman spektroskopija obezbedila definitivnu potvrdu o uspostavljenoj vezi jona metala i atoma sumpora. Takođe, ove tehnike su ukazale na to da atom azota u prstenu nagrađenog jedinjenja Au-MT, ostaje protonovan, što ne ide u prilog prvobitnoj pretpostavci proistekloj iz analize UVspektara, da je na pH=9 moguća koordinacija ne samo atoma sumpora, već i atoma azota sa zlatom. Metoda masene spektrometrije ukazala je na prisustvo molekula velikih masa koji mogu da odgovaraju kombinacijama Au-2MT, Au-2MT-Gly, pa se čak ni kombinacija Au- 2MT-2Gly ne može u potpunosti isključiti u konačnoj formulaciji strukture nastalog jedinjenja. Takođe su zapaženi pikovi koji ukazuju na prisustvo trovalentnog zlata. Međutim, maseni spektar čvrstog uzorka otkriva i pojavu pika na m/z koji odgovara masi atoma zlata, to jest može da ukaže na prisustvo jednovalentnog zlata. Ipak, ovaj pik je mnogo slabijeg intenziteta. Jedan od dominantnih pikova kod svih masenih spektara dobijenih za uzorke na pH=2, 4 i 7, je pik na m/z 201, koji može da potiče od dva molekula merkaptotriazola (2MT), što dodatno sugeriše mogućnost formiranja disulfidnog mosta između ova dva molekula. X-ray difraktogram za kristale kompleksa zlata sa merkaptotriazolom dobijene iz elektrolita na pH=9, ne pokazuje poklapanje sa karticama nijednog poznatog jedinjenja zlata, što takođe potvrđuje pretpostavke da je sintetizovano novo jedinjenje. Uporedna karakterizacija elektrohemijski staloženih dekorativnih prevlaka zlata dobijenih iz sveže sintetisnog elektrolita, iz elektrolita nakon stajanja od godinu dana, kao i prevlaka dobijenih iz elektolita dobijenog rastvaranjem kristala zlatomerkaptotriazola (spoljni izgled, debljina, hrapavost, mikrotvrdoća po Knoopu i elektronska mikroskopija - SEM sa EDS-om) pokazala je da su prevlake dobijene iz sva tri elektrolita sjajne sa dobrom adhezijom. Najmanja hrapavost je izmerena za prevlaku dobijenu iz svežeg elektrolita a najveća za prevlaku dobijenu iz elektrolta dobijenog rastvaranjem kristala. U pogledu mikrotvrdoće ne postoje značajne razlike.

An electrolyte based on gold complex with mercaptotriazole was synthesized in a wide pH range from acid to alkaline (pH=2-12). After synthesis of the electrolyte, detailed characterization of the complex in liquid and solid state in the whole range of its stability was performed. Physico-chemical characterization of the electrolyte was performed, firstly by Ultraviolet-visible spectroscopy (UV-vis) and by atomic asorption spectroscopy with inductively coupled plasma (AAS-ICP). UV- spectra of Au-MT electrolyte at pH=2 and 7 show absorbtion peaks at wavelenghts which are very close to the wavelenght of apsorption peak of mercaptotriazole, which may indicate that in these solutions, chemical bonds Au-MT was the weakest. UV- spectra of Au-MT electrolyte at pH=9 shows an absorption peak at 272.0 nm, which may suggest that the bond between MT and Au has only realised in this particular case. The appearance of the peak as the value of 272.0 nm is close to the literature data for the other non-cyanide electrolytes (sulphite, thiosulphate and thiosulphate-sulphite), it may be assumed that the coordination of Au to MT at pH 9 is realized through the sulphur atom. AAS-ICP analysis confirmed the projected gold concentrations in the electrolyte with a maximum deviation of 0.01 g/dm3. For a comparative toxicity study of electrolyte based on the mercaptotriazole gold complex (pH=2, 4, 7, 9 and 12) and the classic alkaline cyanide electrolyte (pH=9), "in vitro" method was applied. For cytotoxicity testing, the culture of K562 cells of human leukemia was used. Results show that the toxicity of organic complex of gold at pH values of 4, 7 and 12 is lower than alkaline cyanide electrolyte but higher at pH=2, while at pH=9 the relative cell viability is almost equal. Electrochemical characterization of gold complex based on mercaptotriazole was performed by: the open circuit potential measurment, cycling voltametry method and recording the polarization curves, with pH values and conductivity of the electrolyte measurment before and after each electrochemical experiment. These tests were performed for a period of 12 months at different pH values: 2, 4, 7, 9 and 12 at optimal concentration of gold in the electrolyte of 2,5 g/dm3 and in the period of four mounths at optimal pH value of 9 and at the concentrations of gold in the electrolyte of 1,5; 2,0; 2,5; 3,0 and 3,5 g/dm3. For electrolytes with pH= 4, 7 and 12 the first visible signs of decomposition of the complex appeared three months after synthesis. Electrochemical characteristics of gold complex with mercaptotriazole at pH value of two and nine remained unchanged for a period of one year. In that period any visual changes on these electrolytes did not appear too these electrolytes. Study of the effect of organic gold complex with mercaptotriazole on photoresist layers used in the manufacture of printed circuit boards, was performed on previously prepared PCB with developed net and lacquered edges - lines. The photoresist layers on the boards are resistant to the effects of electrolyte at pH values of 2, 7 and 9. At pH=4 the first visual changes are observed after 150 s while at pH=12 the first changes appeared after only 30 seconds. From tiles surfaces micrographs it can also be seen that the photoresist layers of tiles most resistant to the effects of electrolyte pH=2 and pH=9. At pH=9 photoresist layers of tiles are resistant to the influence of electrolyte at all concentrations of gold in the range of 1.5 to 3.5 g/dm3. Synthesized solutions of gold complex based on mercaptotriazole are vaporized at room temperature to dry in order to obtain and characterize Au-MT in the crystalline form. Optical microscopy showed that the crystals obtained from solutions of different pH values are different in color, size and homogeneity. The most homogeneous (according to size and color) and the smallest crystals were obtained from the electrolyte with pH=9. The most important finding of IC/Raman spectroscopy analysis is that the Raman spectroscopy has provided a definitive confirmation of bond established between metal ion and sulphur atom. Also, both techniques indicated that the nitrogen atom in the ring of obtained Au-MT compound, remains protonated at pH = 9, which does not support an assumption formulated from the analysis of UV-spectra, that MT molekules at this pH may interact with the metal ion not only through the sulphur, but also through the nitrogen atom. Mass spectrometry indicated the presence of high weight molecule that can match combinations of Au-2MT and 2MT-Au-Gly. Even the combination of 2MT-Au-2Gly could not be completely excluded in the final formulation of the structure of the resulting compound. The peaks indicating the presence of Au (III) were also noticed. Additionally, the mass spectra of solid sample reveal a peak at m/z corresponding to the mass of a gold atom, which may indicate the presence of Au (I). However, this peak is of very weak intensity. One of the major peaks in all mass spectra obtained for the samples at pH = 2, 4 and 7, is the peak at m/z 201, which may originate from a fragment corresponding to the mass of two molecules of mercaptotriazole (2MT); this further suggests the possibility of formation of a disulfide „bridge“ between these two molecules. In available data bases no compound was found that match with the X-ray difractogram of crystals of the gold mercaptotriazole complex obtained from the electrolyte of pH = 9. It confirms the assumption that a new compound was synthesized. Comparative characterization of electrochemically deposited gold decorative coatings obtained from the freshly synthesized electrolyte, then from the electrolyte after a year, and coatings obtained from the electrolyte obtained by dissolving crystals of goldmercaptotriazole (external appearance, thickness, surface roughness, the Knoop microhardness and electron microscopy - SEM with EDS) showed that the coatings obtained from all the three electrolytes are bright and with good adhesion. The smallest roughness was measured for the coatings obtained from fresh electrolyte and the greatest for the coatings obtained from electrolyte obtained by dissolving crystals. In terms of hardness there are no significant differences.