PHOTOCATALYTIC DEGRADATION OF RO16 DYE USING HYDROTHERMALLY SYNTHESIZED CeO2/ZnO COMPOSITES

Cink-oksid je poznati fotokatalizator koji se uglavnom koristi za razgradnju organskih zagađujućih suspstanci u vodi uz pomoć veštačke ili sunčeve svetlosti [1, 2]. S druge strane, modifikovanje poluprovodnog fotokatalizatora drugim oksidima može poboljšati fotokatalitičku aktivnost usled sinergijskog efekta pojedinačnih oksida u smislu povećanja adsorpcije i širenja oblasti mogućih talasnih dužina za apsorpciju svetlosti. Da bi se odredio optimalan sadržaj CeO2 za najbolju fotokatalitičku aktivnost ZnO, vodeni rastvor Zn(NO3)2 sa različitim sadržajem Ce(NO3)3 (0; 2,5; 5 i 10 mol.%) tretiran je hidrotermalnim postupkom na 180 °C tokom 18 h u prisustvu NH3(aq). Dobijeni uzorci ispirani su destilovanom vodom i etanolom, centrifugirani i sušeni na 105 °C tokom 3 h. Strukturna, mikrostrukturna, optička i fotokatalitička svojstva dobijenih prahova ispitana su rendgenskom difrakcijom praha (XRPD), skenirajućom elektronskom mikroskopijom (FESEM), transmisionom elektronskom mikroskopijom (TEM) i UV-Vis spektroskopijom. Fotokatalitička aktivnost dobijenih kompozita ispitana je na tekstilnoj azo-boji reaktivno narandžasta 16 (RO16, od engl. Reactive Orange 16) i upoređena je sa jednofaznim ZnO. XRPD rezultati su pokazali da je jednofazni ZnO (heksagonalna struktura vircita, prostorna grupa P63mc) dobijen u sintezi bez Ce(NO3)3. Ako je sadržaj Ce(NO3)3 bio 2,5; 5 ili 10 mol.%, dobijeni uzorci sadržali su smešu ZnO i CeO2 (struktura fluorita, prostorna grupa Fm m). Izračunati fazni sastavi proizvoda dobro odgovaraju polaznim sastavima, čime je potvrđeno nastajanje kompozita CeO2/ZnO sa različitim molarnim odnosima. Kako se sadržaj CeO2 povećavao primećeno je blago smanjenje zapremine jedinične ćelije ZnO, sa 47,950(4) Å3 za jednofazni ZnO na 47,726(4) Å3 za 10% CeO2/ZnO, zbog blagog smanjenja parametara jedinične ćelije: a od 3,2566(1) do 3,2519(1) Å i c od 5,2206(4) do 5,2114(4) Å, redom. Krajnji fazni sastav, kao i nenarušena vircitna struktura ZnO ukazali su da je CeO2 raspoređen po površini ZnO, što su potvrdili FESEM i TEM. Mikroskopski rezultati su pokazali da je veličina sfernih kristalita CeO2 bila 5 ± 1 nm, dok je ZnO imao bimodalnu raspodelu veličine kristalita od 5 nm do 4 µm. Stoga morfologija ZnO praha varira od izduženih nanozrna do mikroštapića koji dalje grade 3-D morfologiju nalik mašnama. Kompozit 5%CeO2/ZnO je pokazao najbolju fotokatalitičku aktivnost razgradivši RO16 za 180 minuta. Nanokompoziti CeO2/ZnO sa 2,5 i 10 mol.% CeO2 pokazali su sličnu fotoaktivnost kao nemodifikovani ZnO. Može se zaključiti da optimalan sadržaj CeO2 iznosi 5 mol.%. [1] B. Simović, A. Golubović, I. Veljković, D. Poleti, J. Zdravković, D. Mijin, A. Bjelajac, Journal of the Serbian Chemical Society, 79 (2014) 1433–1443. [2] B. Simović, D. Poleti, A. Golubović, A. Matković, M. Šćepanović, B. Babić, G. Branković, Processing and Application of Ceramics, 11 (2017) 27–38.Zinc oxide is a well-known photocatalyst mainly used to degrade organic water pollutants using artificial or sunlight [1, 2]. On the other hand, the modification of semiconductor photocatalysts by other oxides can improve their photocatalytic activity regarding synergistic effect of single oxides in the sense of increasing the adsorption and broadening region of possible wavelengths for light absorption. In order to find the optimal CeO2 content for the best photocatalytic activity of ZnO, the aqueous solution of Zn(NO3)2 with different Ce(NO3)3 content (0, 2.5, 5 and 10 mole%) was hydrothermally treated at 180 °C for 18 h in the presence of NH3(aq). The obtained samples were rinsed out with distilled water and ethanol, centrifuged and dried at 105 °C for 3h. The structural, microstructural, optical and photocatalytic properties of resulting powders have been investigated by the XRPD, FESEM, TEM and UV-vis techniques. The photocatalytic activity of obtained composites was tested on the Reactive Orange 16 (RO16) textile azo dye and compared to the single-phase ZnO. Based on XRPD results, the single-phase ZnO (hexagonal wurtzite structure, space group P63mc) was obtained without addition of Ce(NO3)3. If Ce(NO3)3 content was 2.5, 5 or 10 mole.%, the obtained samples consisted of ZnO and CeO2 (fluorite structure, space group Fm m) mixed phases. The calculated final phase compositions corresponded well with starting compositions, which confirmed the formation of CeO2/ZnO composites with different molar ratios. As CeO2 content increased, the slight decrease in ZnO unit cell volume, from 47.950(4) Å3 for single-phase ZnO to 47.726(4) Å3 for 10% CeO2/ZnO, was noticed due to negligible decrease in unit cell parameters: a from 3.2566(1) to 3.2519(1) Å and c from 5.2206(4) to 5.2114(4) Å, respectively. The final phase compositions as well as preserved ZnO wurzite structure indicated that CeO2 was distributed onto ZnO surface, which was confirmed by FESEM and TEM. The microscopic results showed that the size of spherical CeO2 crystallites was 5 ± 1 nm, while ZnO had a bimodal distribution of the crystallite size from 5 nm to 4 µm. Hence the morphology of ZnO varies from elongated nanograins to microrods that further build a 3-D tie-like morphology. The 5% CeO2/ZnO composite demonstrated the best photocatalytic activity by degrading RO16 for 180 minutes. CeO2/ZnO composites with 2.5 and 10 mole.% CeO2 showed similar photoactivity as unmodified ZnO. It could be concluded that the optimal CeO2 content is 5 mole.%. [1] B. Simović, A. Golubović, I. Veljković, D. Poleti, J. Zdravković, D. Mijin, A. Bjelajac, Journal of the Serbian Chemical Society, 79 (2014) 1433–1443. [2] B. Simović, D. Poleti, A. Golubović, A. Matković, M. Šćepanović, B. Babić, G. Branković, Processing and Application of Ceramics, 11 (2017) 27–38

Phase transition from nanostructured titania to layered titanаte

The environmental friendly titanium-based nanomaterials such as titania and titanates are often used in industry regarding to their extraordinary properties: biological and chemical stability, photocatalytic activity, cost-effectiveness. Among other procedures, the hydrothermal process became a very important way to synthesize the titania and titanate nanostructures. In this work, nine products were obtained by modifying the experimental conditions (6, 12 and 18 h at 110, 135 and 160 °C) of hydrothermal treatment of starting nanoanatase in alkaline medium (5 mol dm–3 NaOH solution). The possibility to obtain the single titanate phase was investigated as well as the influence of different experimental conditions on structural and microstructural properties of obtained products. As shown by XRPD and TEM, when commercial nanoanatase is hydrothermally treated, the single titanate phase was obtained after energetically the most intensive treatment i.e. 18 h at 160 °C. Among all other eight products, a certain amount of anatase remained, with the decreasing content as the temperature and time of hydrothermal treatment increases. This intensification of hydrothermal treatment significantly increases the solubility of TiO2 promoting the changes in morphology from nearly spherical anatase particles to elongated titanate nanosheets. This is the consequence of Ti−O−Ti bonds breaking and formation of Ti–O–Na or Ti–OH bonds and thus the growth of lamellar structures giving the complete transformation of anatase nanoparticles into titanate nanosheets after 18 h at 160 °C. The calculated unit cell parameters of this titanate phase, a = 18.188(6), b = 3.7669(3), c = 2.9812(6) Å, show the slight elongation along a-axis comparing to H2Ti2O5·H2O (PDF #47-0124). This could be explained by partial Na+ –H+ ion exchange. Based on EDS and TG of obtained pure titanate, the Na0.4H1.6Ti2O5·H2O formula could be assigned to the titanate phase. The FTIR and TG analyses showed the hygroscopic nature of Na0.4H1.6Ti2O5·H2O nanosheets and the consequential surface adsorption of water. However, the HRTEM/SAED revealed the shortening of interplanar distances along a because of the dehydratation due to vacuum and electron radiation during the TEM analysis additionally confirming the layered structure of obtained titanate. This work describes a simple synthetic procedure for production of titanate nanosheets useful for diverse applications but also finally distinguish the titanates from titania in terms of structure and microstructure.Ekološki nanomaterijali kao što su titan-dioksid i titanati često se koriste u industriji zbog njihovih izvanrednih svojstava: biološke i hemijske stabilnosti, fotokatalitičke aktivnosti, ekonomičnosti. Pored drugih postupaka, hidrotermalni proces postao je veoma važan metod za sintezu nanostrukturnih titan-dioksida i titanata. U ovom radu, devet proizvoda dobijeno je variranjem eksperimentalnih uslova (6, 12 i 18 h na 110, 135 i 160 °C) hidrotermalnog tretmana polaznog nanoanatasa u alkalnoj sredini (5 mol dm–3 rastvora NaOH). Ispitana je mogućnost za dobijanje titanatne faze kao i uticaj različitih eksperimentalnih uslova na strukturna i mikrostrukturna svojstva dobijenih proizvoda. Kao što je pokazano XRPD-om i TEM-om, čista titanatna faza nastaje nakon najintenzivnijeg hidrotermalnog tretmana, tačnije nakon 18 h na 160 °C. Kod ostalih osam proizvoda zaostaje određena količina anatasa, pri čemu se ona smanjuje sa porastom temperature i dužine trajanja hidrotermalnog tretmana. Naime, intenziviranje hidrotermalnog tretmana znatno povećava rastvorljivost TiO2 dovodeći do promena u morfologiji od približno sfernih čestica anatasa do izduženih titanatnih nanopločica. Ovo je posledica raskidanja veza Ti−O−Ti i stvaranja novih veza Ti–O–Na ili Ti–OH pa samim tim i rast lamelarnih struktura, čime dolazi do transformacije nanočestica anatasa u titanatne nanopločice.Transformacija je potpuna nakon 18 h na 160 °C. Izračunati parametri jedinične ćelije ove titanatne faze a = 18,188(6), b = 3,7669(3) i c = 2,9812(6) Å pokazuju blago izduženje duž a-ose u poređenju sa H2Ti2O5·H2O (PDF #47-0124). Ovo bi se moglo objasniti delimičnom jonskomizmenom Na+ –H+ . EDS i TG analizama dobijenog čistog titanata utvrđeno je da je njegova najverovatnija formula Na0,4H1,6Ti2O5·H2O. FTIR i TG analize pokazale su da nanopločice Na0,4H1,6Ti2O5·H2O apsorbuju vodu po površini te su potvrdile higroskopnu priroduovog titanata. Međutim, HRTEM/SAED je pokazao smanjenje međuslojnog rastojanja duž a-osezbog dehidratacije usled vakuuma i elektronskog zračenja tokom TEM analize dodatno potvrđujući slojevitu strukturu dobijenog titanata. Ovaj rad opisuje jednostavan sintetski postupak za dobijanje titanatnih nanopločica korisnih za razne primene, a takođe konačno objašnjava razliku između titanata i titandioksida sa stanovišta strukure i mikrostrukture

Effect of dopants on anatase structure

It is well known that TiO2-based Degussa P-25 is the mostly used comer-cial photocatalyst and that TiO2 exists in three crystalline modifications: tetragonal anatase (I41/amd) and rutile (P42/mnm) and orthorhombic brookite (Pbca). On heating, anatase and brookite, as metastable phases, can be transformed to rutile. The aim of this work was to investigate the effect of different dopants on anatase-rutile phase transition and thus on their photocatalytic behavior. For that matter, samples TiO2 M (M = Cu, Mn and V) having 5 at.% of dopants were prepared by 30 minutes hand-mixing of anatase and corresponding oxide (CuO, MnO2 and V2O5) powders in an agate mortar following by heat treatment at 700 °C for 3 h. The powder of pure anatase phase was also treated at same conditions. TG/DTA was used to define thermal treatment, and the obtained samples were characterized by powder XRD method in order to reach phase compositions, unit cell parameters and crystallite sizes. Since in the case of undoped anatase only 3 wt.% of rutile was formed, the presence of dopants accelerated phase transition: 26 and 76 wt.% of rutile was obtained beside anatase in TiO2 Mn and TiO2 V, respectively, while complete anatase to rutile phase transition occured in TiO2-Cu. The least rutile quantity in TiO2-Mn is related to the isovalency of Ti4+ and Мn4+ meaning that the incorporation of Мn4+ in TiO2 is not followed by the formation of new defects, which are driving force for phase transition, as in the case of TiO2 Cu. About 5 wt.% of the unreacted CuO was found in TiO2 Cu, which is almost all introduced quantity of CuO. This can be related to the fact that the ionic radius of Cu2+ for octahedral environment (0.870 Å) is larger than that of Ti4+ (0.745 Å). As a result, Cu2+ ions can hardly be incorporated in TiO2 comparing to smaller Мn4+ (0.670 Å) and V5+ (0.680 Å) although a small amount of Cu2+ surely was necessary to cause phase transition. Since no residues of initial oxides were found in TiO2 Mn and TiO2 V, it can be concluded that these metal ions were incorporated into anatase lattice. By comparing the calculated unit cell parameters of anatase mutually, the shrinkage along c-axis was revealed meaning the shortening of bond distances between М–Оapical. The photocatalytic activity of all synthesized samples will be tested since nanocrystalline samples were obtained according to determined crystallite sizes (55–90 nm).Degussa P-25 је фотокатализатор на бази титан(IV)-оксида, који се најчешће користи у индустрији. TiO2 се јавља у три полиморфне модификације: тетрагоналним анатасу (I41/amd) и рутилу (P42/mnm) и ромбичном брукиту (Pbca). Анатас и брукит, као метастабилне фазе, приликом загревања прелазе у рутил. Циљ овог истраживања је испитивање утицаја различитих допаната на фазни прелаз анатаса у рутил као и на фотокаталитичка својства. Узорци TiO2-M (M = Cu, Mn и V), који садрже 5 at.% допанта, припремљени су термохемијском реакцијом на 700 °C током 3 h између хомогенизованих прахова анатаса и одговарајућих оксида (CuO, MnO2 и V2O5). Ради поређења, прах чистог анатаса је термички третиран под истим условима. Помоћу ТГ/ДТ анализе дефинисани су услови термичког третмана, док су добијени узорци окарактерисани рендгенском дифракцијом на поликристалном материјалу да би се одредио фазни састав, параметри јединичних ћелија и величина кристалита. У случају недопираног анатаса настало је свега 3 mas.% рутила, 26 и 76 mas.% рутила добијено је у TiO2 Mn и TiO2 V, редом, док се потпуни фазни прелаз анатас–рутил одиграо у TiO2 Cu. Ово значи да присуство допанта убрзава фазну трансформацију. Најмања количина рутила у TiO2 Mn може се објаснити изовалентним Ti4+ и Мn4+, тј. да уградња Мn4+ у TiO2 није праћена настанком нових дефеката који представљају вучну силу за одигравање фазног прелаза, као што је то случај код TiO2 Cu. Око 5 mas.% непрореаговалог CuO (готово почетна количина) заостало је у TiO2 Cu, зато што се Cu2+-јони теже уграђују у решетку TiO2 због већег радијуса Cu2+ у октаедарском окружењу (0,870 Å) од радијуса Ti4+ (0,745 Å), за разлику од мањих Мn4+ (0,670 Å) и V5+ (0,680 Å). Ипак, сигурно је мала количина Cu2+-јона била неопходна како би иницирала фазни прелаз. Како у TiO2 Mn и TiO2 V нису присутни остаци полазних оксида, може се закључити да су се ови јони метала уградили у решетку анатаса. Међусобним поређењем параметара јединичне ћелије анатаса, уочено је скраћење дуж c-осе, што указује на скраћење дужина веза М–Оапикални. Израчуната величина кристалита (55–90 nm) показала је да су сви добијени узорци нанокристални, па ће њихова фотокаталитичка својства бити испитана

Ag/ZnO NANOCOMPOSITES FOR PHOTOCATALYTIC APPLICATION

In this work, the decoration of noble metal nanoparticles on a semiconductor surface was used as a strategy to reach strong visible light absorption and efficient electron-hole separation to enhance the photocatalytic activity of ZnO. The Ag-modified ZnO nanopowders were obtained by the green synthesis. Zinc acetate dihydrate with different silver nitrate content (0, 0.75, 1.5 and 3 mol%) was dissolved in ethylene glycol in the presence of chitosan. The obtained mixtures in the form of gel were heated at 150 °C for 2 h and subsequently calcined at 400 °C for 1 h. The obtained samples were characterized by XRPD, FESEM, HRTEM, and UV-vis techniques while the photocatalytic efficiency was tested by monitoring the degradation of textile dyes Reactive Orange 16 (RO16), Acid Green 25 (AG25), Mordant Blue 9 (MB9), and Ethyl Violet (EV) then compared with the commercial ZnO nanopowder. The results showed that the Ag/ZnO samples consisted of ZnO nanoparticles with an average crystallite size of about 25 nm and Ag (20–30 nm) distributed on the surface of ZnO. The uniformity in size and nearly spherical shape of ZnO nanoparticles, forming various forms of agglomerates, were observed. Compared to both, the unmodified and commercial ZnO, all the prepared Ag/ZnO composites showed a broad band in the visible region at 500 nm, resulting in a narrowing of the band gap. This band confirms the surface plasmon resonance of the metallic Ag nanoparticles, since they can absorb visible light and activate the photocatalyst in the visible spectrum. All the obtained nanopowders showed higher adsorption power and photocatalytic activity in the degradation of RO16 dye than the commercial ZnO. The powder with 1.5 mol% of Ag had the highest photocatalytic efficiency as a consequence of smaller Ag particles and their good distribution, as well as the narrowest band gap. This means that the photocatalytic activity does not depend on the Ag content only and that the size and distribution of the metal particles play an important role. Since the ZnO with 1.5 mol% of Ag demonstrated the best photocatalytic activity, the same sample was tested for diverse dyes and the high photocatalytic efficiency was also confirmed by testing on AG25, MB9 and EV dyes

HIGHLY CONDUCTIVE V-DOPED d-Bi2O3 WITH 3×3×3 SUPERSTRUCTURE

Due to the increasing demands for new highly efficient and environmentally friendly energy conversion technologies, the oxide ion conductors applicable in solid oxide fuel cells (SOFCs) have widely been investigated. The high temperatureδ-Bi2O3 phase has been proposed as a good candidate for electrolyte in SOFCs because it is the fastest known ionic conductor. In this study, the possibility to stabilize O 2– ion conductors related to the -Bi2O3 polymorph in Bi12VxO18+5x/2 (x = 0.5–1) system was investigated. Six starting mixtures of α-Bi2O3 and V2O5 were dry homogenized in an agate mortar, heat treated at 1000 °C for 1 h and then slowly furnace cooled. The samples were characterized by XRD, TEM/SAED, optical microscopy, DTA and EIS techniques. Based on XRD and TEM/SAED, if x ≥ 0.6 the high-temperature reaction between α-Bi2O3 and V2O5 resulted in formation of microcrystalline single-phase specimens containing the phase based on δ-Bi2O3. The obtained phases showed main diffraction peaks corresponding to the cubic -Bi2O3 (space group Fm-3m and a ≈ 5.6 Å). However, the detected weak reflections indicate that the true unit cell is the 3×3×3 supercell with a ≈ 16.6 Å. An expected decrease of the unit cell parameters with the dopant amount was found as the consequence of smaller dopant ionic radius {ri(V5+) = 0.54 Ǻ and ri(Bi3+) = 1.03 Ǻ in the six-coordinated environment [1]}. In the case of Bi12V0.5O19.25, traces of α-Bi2O3 were also found. The XRD data of Bi12V0.7O19.75 were used for the Rietveld refinement giving Bi102V6O168 as the composition of the 3×3×3 supercell. The octahedrally coordinated V 5+ ions fully occupy 4a Wyckoff position, i.e. the corners and face centers of cubic supercell, and partially occupy 32f. The Bi3+ ions are placed at the rest of 32f and at 24e and 48h with full occupation. At the 32f site, the cations are surrounded by five oxide ions making a square pyramid. At the 24e site, the Bi3+ ions with four oxide ions form a square pyramid with the cation at the apex. The coordination of Bi3+ at the 48h is square planar. Cyclic DTA curves showed that the following 3×3×3 → -Bi2O3 → -Bi2O3 → Bi2O3(l) consecutive phase transitions occur on heating. On cooling, -Bi2O3 crystallizes from the melts and remains stable to about 530 °C. At this temperature, an order-disorder transition takes place, i.e. -Bi2O3 → 3×3×3. The sintered disk-shaped pellets were characterized by EIS at temperatures between 760 and 820 °C. The sample with x = 0.6 demonstrates one of the highest known conductivity among the published O2– ion conductors, i.e. 0.66 S cm–1 at 760 °C with the lowest activation energy of 0.21(1) eV. 1. R. D. Shannon, Acta Cryst. A 32 (1976) 75

The influence of dopants on anatase-rutile phase transition

Titanium dioxide exists in three different crystalline forms: anatase, rutile, and brookite. It is well known that on heating, anatase and brookite can be easily transformed to rutile which is considered as the most stable phase [1]. The aim of this study was to investigate the influence of different dopants on anatase-rutile phase transition. Doped TiO2 samples (TiO2-M, M = V, Mn, and Cu) containing 5 at% of the dopant were prepared by mixing anatase and appropriate oxide (V2O5, MnO2, and CuO) in agate mortar for 30 min. In order to determine the heat treatment conditions, TG/DTA analysis of the samples was performed. Finally, mixed powders as well as the pure anatase phase (TiO2) were heat treated at 700 °C for 3 h. XRD analysis was performed to estimate the phase composition, unit cell parameters, and crystallite sizes. Rutile was formed in all samples: 2.8 wt% in TiO2, 25.5 wt% in TiO2-Mn, 75.8 wt% in TiO2-V, and 95.2 wt% in TiO2-Cu. In TiO2- Mn, TiO2-V, and TiO2, anatase was present beside rutile, while in the case of TiO2-Cu 4.8 wt% of the unreacted CuO was found. Obtained results revealed that all the dopants accelerated anatase-rutile phase transition in the following order: Cu2+ > V5+ > Mn4+. It is well known that defects are the driving force for the anatase-rutile phase transition and since Ti4+ and Mn4+ are isovalent, no new defects were formed by incorporating Mn4+ ions into TiO2 lattice. This resulted in the least amount of rutile in TiO2-Mn comparing to TiO2-V and TiO2-Cu where new defects were probably formed. As no initial oxides were found in TiO2-Mn and TiO2-V, it can be concluded that Mn4+ and V5+ ions were incorporated into the anatase lattice. On the other hand, in the case of TiO2-Cu, even 4.8 wt% of initial CuO was found. The detected residue of CuO can be explained by the fact that the ionic radius of Cu2+ for an octahedral environment (0.870 Å) is much larger than that of Ti4+ (0.745 Å), unlike those for Mn4+ (0.670 Å) and V5+ (0.680 Å). Although almost all introduced quantity of CuO, i.e. 96 %, was found in TiO2-Cu, a small amount was surely necessary to cause the anatase-rutile phase transition. According to calculated crystallite sizes which were in the range of 55 – 90 nm, nanocrystalline samples were prepared. 1. P. I. Gouma, M. J. Mills J. Am. Ceram. Soc. 2001, 84 (3) 619–622

Nanokompoziti TiO2/PANI za primenu u fotokatalizi

Poznato je da je titan-dioksid, kao netoksičan, stabilan i ekonomičan materijal, jedan od najčešće korišćenih fotokatalizatora. S druge strane, elektroprovodni polianilin (PANI) je takođe pogodan kandidat za primenu u fotokatalizi. Cilj ovog rada bio je dobijanje nanokompozita TiO2/PANI sa boljom fotokatalitičkom aktivnošću u odnosu na TiO2. U cilju optimizacije sadržaja polimera sintetisano je 4 uzorka TiO2/x%PANI (x = 0, 1, 3 i 5 mas.%), koji su okarakterisani XRD i TG/DTA metodama, dok je fotokatalitička aktivnost ispitana kroz razgradnju toksične tekstilne boje RO16. Pokazano je da su svi kompoziti fotokatalitički aktivniji od TiO2, i da optimalan sadržaj polianilina iznosi 3 mas.%. Naime, uzorak TiO2/3%PANI je, nakon 60 minuta, razgradio 95 % boje, što je za 17 % više u odnosu na TiO2, dok je nakon 120 minuta fotorazgradnja boje potpuna. Pored toga, ovaj uzorak je pokazao čak 14 puta izraženiju adsorpciju od TiO2. Efikasnost TiO2/5%PANI je slična TiO2/3%PANI, ali sa slabije izraženim adsorpcionim svojstvima, dok je efikasnost TiO2/1%PANI bliska TiO2.It is well known that the non-toxic, stable and economical titanium dioxide is one of the most commonly used photocatalysts. On the other hand, the conductive polyaniline (PANI) is also suitable candidate for photocatalytic application. The aim of this work was to obtain the TiO2/PANI nanocomposites with increased photocatalytic activity comparing to TiO2. In order to determine the optimal PANI content, four TiO2/x%PANI samples (x = 0, 1, 3 and 5 wt.%) were synthesized and characterized by XRD and TG/DTA analysis. The photocatalytic activity was tested on the toxic textile RO16 dye. It is shown that all the composites exhibited better photocatalytic performances than TiO2 and that the optimal PANI content amounted 3 wt.%. Namely, the TiO2/3%PANI degraded 95 % of the dye within 60 minutes, which is for 17 % better comparing to TiO2. The full photodegradation was reached in 120 min. This sample showed even 14 times better adsorption than TiO2. The efficiency of TiO2/5%PANI was similar to TiO2/3%PANI, but with poorer adsorption, while the efficiency of TiO2/1%PANI was close to TiO2

Highly efficient TiO2/Ppy photocatalysts

Titanium dioxide is the most suitable semiconductor for photocatalytic application due to its high efficiency, increased stability, low-cost, and non-toxicity. However, it is possible to enhance the photocatalytic activity of TiO2 by homogenizing it with conductive polymers. One of the most attractive conductive polymers is polypyrrole (PPy) owing to its stability, low-cost, and special redox properties. The aim of this work was to obtain the TiO2/PPy nanocomposites with a higher photocatalytic activity compared to TiO2. In order to determine the optimal content of PPy, four TiO2/x%PPy samples (x = 0, 1, 3, and 5 wt.%) were synthesized and characterized by XRD and TG/DSC analyses. The photocatalytic activity was examined towards the degradation of toxic textile azo dye Reactive Orange 16. It was observed that an increase in PPy content led to better adsorption capacity of the synthesized nanocomposites. Samples TiO2/1%PPy and TiO2/5%PPy demonstrated better photocatalytic activity than TiO2, while TiO2/3%PPy showed very similar photocatalytic activity to TiO2. Near complete degradation of the dye (98 %) was reached in 75 min by using TiO2/1%PPy, comparing to pure TiO2, which degraded the same amount of the dye in 120 min. Considering all the obtained results, the optimal content of PPy in the composite for degradation of Reactive Orange 16 is 1 wt.%

Structural transformation from titania nanoparticles to sodium titanate nanosheet exhibiting sensing properties

TiO2-based nanomaterials, such as titanium dioxide and layered titanates, are increasingly used in nanotechnology due to biological and photochemical stability, catalytic activity, non-toxicity and cost-effectiveness. In addition, it is known that some titanates can be used for humidity sensors regarding hydrophilic nature of their surface [1]. Nine TiO2-based products were obtained by the hydrothermal treatment of starting nanoanatase using NaOH solution (c = 5 mol cm–3) under different conditions (from 6 h at 110 °C to 18 h at 160 °C). Such optimization was necessary in order to obtain single sodium titanate phase allowing the testing of sensing properties but also long time waited distinction between titania and titanates in terms of structural and microstructural properties. The intensification of hydrothermal treatment notably increased the solubility of nanoanatase causing the phase and morphology transition from nearly spherical titania nanoparticles into elongated titanate nanosheets. According to XRPD and HRTEM/SAED, the single titanate phase was prepared after the most energy-intensive treatment, i.e. at 160 °C for 18 h. The Na0.4H1.6Ti2O5·H2O could be ascribed as its formula, based on EDS and TG. The phase composition and crystallite size were calculated in Jade software for all nine samples while unit cell parameters of single-phased sodium titanate were obtained by Rietveld refinement using FullProf software in Winplotr environment. The calculated unit cell parameters of sodium titanate, a = 18.16(7) Å, b = 3.754(7) Å, c = 2.99(1) Å, show the slight elongation along a‑axis comparing to H2Ti2O5·H2O (PDF card No. 47-0124) probably due to partial Na+–H+ ion exchange. The TG and FTIR analyses showed the hygroscopic nature of Na0.4H1.6Ti2O5·H2O nanosheets revealing the water adsorption on surface. Hence, the obtained Na0.4H1.6Ti2O5·H2O was for the first time used to produce a humidity sensor, which displayed remarkably rapid response and very fast recovery time

From Titania to Titanates: Phase and Morphological Transition

Regarding their extraordinary properties, such as biological and chemical sta-bility, photocatalytic activity, cost-effectiveness, the titanium-based nanoma-terials are the subject of an intense research. Although titania is well knownas a photocatalyst, the titanates are promising candidates for the wide rangeof applications including ion exchange, high adsorption capacity toward or-ganic molecules and radioactive toxic metal ions[2], in photovoltaics, H- andLi-storage, gas sensors, etc. The hydrothermal process became a very import-ant way to obtain these materials in nanostructural form since the discovery ofanatase-based alkaline hydrothermal treatment reported by Kasuga et al. [1].In this work, nine products were obtained by modifying the experimental conditions(6, 12 and 18 h at 110, 135 and 160 °C) of hydrothermal treatment of starting nano-anatase in less alkaline medium (5 mol dm–3 NaOH solution) than usual. Specimensare labeled as TT–t, where T is temperature of the treatment and t is duration of thetreatment. The step-by-step optimization of this simple and costless procedure wasnecessary in order to obtain a pure titanate phase and to finally distinguish the ti-tanates from titania in terms of structure and microstructure. The nanocrystallinesamples were characterized by HRTEM/SAED, XRPD, EDS, TG, UV-VIS and BETtechniques.According to XRPD and HRTEM, the complete conversion of anatase to puretitanate phase was achieved after energetically the most intensive treatment, i.e.18 h at 160 °C. Among other products, a certain amount of anatase remained,with its decreasing content as the temperature and time of hydrothermal treatmentincreases. This increment significantly improves the solubility of TiO2 promoting thechanges in morphology from the approximately spherical anatase nanoparticles intoelongated titanate nanosheets (Fig. 1). Based on EDS and TG, the Na0.4H1.6Ti2O5·H2Oformula could be assigned to T160_18. The HRTEM/SAED revealed the shortening ofinterplanar distances along aaxis because of the dehydratation due to the high vacuumof the TEM chamber and high energy of the electron beam irradiation confirming thelayered structure of Na0.4H1.6Ti2O5·H2O (Fig. 2). Because of the poor characterizationof titanate nanosheets found in literature, the optical and textural properties ofproducts were also investigated. A blue shift toward lower wavelength is observedwith the temperature increasing being the most pronounced for the T160_18 (Fig. 3).This is the consequence of full transformation of TiO2 into Na0.4H1.6Ti2O5·H2O. Forthe same reason, the values of specific surface areas decreased with the temperatureincreasing.As shown in this work, the structure, morphology and texture of samples stronglydepend of the conditions of hydrothermal treatment. The production of single phasetitanate and its detailed microscopic characterization finally allowed the clarificationof long-standing confusion between titania and titanates.References:[1] T Kasuga et al, Langmuir 14 (1998), p. 3160.[2] Y Zhang et al, RSC Advances 5 (2015), p. 79479.[3] The authors acknowledge funding from the Ministry of Education, Science andTechnological Development of the Republic of Serbia, Grant Numbers III45007and III45019. The support of the bilateral cooperation with Slovenia is alsogratefully acknowledged (Project No. 451-03-3095/2014-09/32)