Photocatalytic proprieties of zinc oxide thin films synthesized on porous structures by atomic layer deposition

U radu je proučavan utjecaj tankih filmova cinkovog oksida narastanih na poroznim strukturama na fotokatalitičku razgradnju metilenskog modrila kao modelnog zagađivača u otpadnim vodama. S obzirom na to da se kemijske reakcije između fotokatalizatora i vodenih otopina odvijaju upravo na njihovoj međupovršini, fotokatalizatori velikih aktivnih površina pripremani su postupcima elektrokemijske oksidacije aluminija u trajanju od 2 h, 4 h, i 6 h u 0,1 M fosfornoj kiselini (H3PO4) i jetkanja u trajanju od 1 h i 2 h u 85 %-tnoj H3PO4. Na dobivene porozne strukture različitih dubina sintetiziran je tanki film (25 nm) cinkovog oksida tehnikom depozicije atomskih slojeva (ALD). Elementna analiza i detaljna karakterizacija morfologije i poprečnog presjeka uzoraka na mikro i nano-skalama provedene su pretražnim elektronskim mikroskopom (SEM), dok su njihova fotokataliticka svojstva, u cilju određivanja optimalnog fotokatalizatora, promatrana mjerenjem optičke apsorpcije UV-Vis spektrofotometrom u periodu od 200 minuta. Rezultati fotokataliticke razgradnje ukazali su na učinkovito uklanjanje bojila metilenskog modrila pod utjecajem sintetiziranih fotokatalizatora. Pojačana fotokatalitička aktivnost primijećena je kod tankog filma cinkovog oksida sintetiziranog na uzorcima aluminija elektrokemijski oksidiranih 4 sata koji su u 200 minuta razgradili nešto više od 50 % modelnog organskog zagađivača. To možemo pripisati njihovoj pogodnoj morfologiji koja se odlikuje povećanom hidrofilnošću u odnosu na ostala 4 uzorka. Također, analizama je pokazano da uzorci jetkani jedan sat pokazuju bolja fotokatalitička svojstva nego oni jetkani dva sata, što se može objasniti degradacijom poroznosti struktura pri dužem nagrizanju uzorka kiselinom.Photocatalytic degradation of methylene blue, as a model pollutant in wastewaters, was studied using zinc oxide thin films synthesized on porous structures. Given that chemical reactions between photocatalyst and aqueous solutions take place by contact between their surface and fluid, photocatalysts of large specific surfaces were prepared by the processes of electrochemical oxidation of aluminium for 2, 4 and 6 hours in 0,1 M H3PO4 and etching during the period of 1 and 2 hours in 85 % H3PO4. On the obtained porous structures of different depths, a thin film (25 nm) of zinc oxide was synthesized using the atomic layer deposition technique (ALD). Elemental analysis and detailed characterization of morphology and cross-section on the microand nanoscale were performed by scanning electron microscope (SEM), while the photocatalytic properties of the sample were studied by measuring optical absorption by UV-Vis spectrophotometer over a 200 minute time period to determine the optimum photocatalyst. The results of photocatalytic degradation indicated the efficient removal of methylene blue dye under the influence of synthesized photocatalysts. However, remarkable results were achieved with samples of zinc oxide thin films synthesized on aluminium samples electrochemically oxidized of 4 hours. These samples dissipated slightly more than 50 % of the model organic pollutant in 200 minutes, which can be ascribed to their specific morphology with increased hydrophilicity compared to the other 4 samples. Also, analyzes showed that samples of 1 hour of etching showed better photocatalytic properties than those of two hours, which can be explained by the degradation of the porosity of the structures during prolonged etching