Effect of precursor materials and hydrothermal time on the morphology, microstructure and photocatalytic activity of tio2 nanotubes - Thi Ngoc Tu Le

Journal of Science and Technology 54 (4B) (2016) 72-79 EFFECT OF PRECURSOR MATERIALS AND HYDROTHERMAL TIME ON THE MORPHOLOGY, MICROSTRUCTURE AND PHOTOCATALYTIC ACTIVITY OF TiO2 NANOTUBES Thi Ngoc Tu Le1, *, Nu Quynh Trang Ton2, Thi Hanh Thu Vu2 1Dong Thap University, 783 Pham Huu Lau, Ward 6, Dong Thap Province, Vietnam 2University of Science, 227 Nguyen Van Cu, Ho Chi Minh City, Vietnam *Email: ltntu@dthu.edu.vn Received: 15 August 2016 ; Accepted for publication: 10 November 2016 ABSTRACT In this study, effects of precursor materials and hydrothermal reaction time on the morphology, microstructures and photocatalytic activity of TiO2 nanotubes (TNTs) were investigated. Results show that the selection of nanopowder TiO2 precursors and hydrothermal time has significantly affected the morphology, microstructure and photocatalytic property of TiO2 nanotubes. TNTs–Merck was fabricated from TiO2–Merck precursor at 130 °C for 22 h possesses a uniform structure with a range of the diameter of ~ 10 nm and length of ~ 100 nm. Keywords: TiO2, nanotubes, hydrothermal, precursor, photocatalytic 1. INTRODUCTION TiO2 nanotubes have recently attracted a considerable interest of their photocatalytic properties for environmental cleaning and antibacterial activities. So far, many different methods have been used to fabricate the TiO2 nanotubes including: templating [1], sol-gel [2], electrochemical anodization [3], and hydrothermal synthesis methods [4, 5]. A review of these methods was presented in the report of N. Liu et al. [6]. Hydrothermal method is a simple and environmentally friendly approach to fabricate large scale production of nanotubes with simply, cost-effectively experimental facilities [7]. Moreover, TiO2 nanotubes fabricated by this method possess highly uniform morphology. However, there are many factors that affect the formation Effect of precursor materials and hydrothermal time on the morphology, microstructure 73 of nanotube structures: the precursor powder, acid washing steps, calcination temperatures, hydrothermal temperature and time. Vuong et al. [8] investigated the effect of three different precursor materials on the formation of TiO2 nanotubes: (a) the wet gel-TiO2, (b) commercial TiO2 nanopowders (P25-anatase) and (c) the annealed wet gel-TiO2 powders at 500 °C. Results showed that TiO2 nanotubes produced from the third precursor possesses the more uniform morphology than those of the first and second samples with a length of a few hundred nanometers and a diameter of 25 nm. Recently, a study of P. V. Viet et al. [9] on the influence of hydrothermal temperature and the acid pH value on the formation of TiO2 nanotube structure was carried out. Results showed that the morphology of TiO2 nanotubes was uniform at the hydrothermal temperature of 135 °C and pH = 4. Various studies and research groups have focused on the effects of hydrothermal temperature, annealing temperature, the acid pH value or choosing precursor materials on the formation and photocatalytic activities of TNTs. However, to the best of our knowledge, the investigation of effects of precursor materials and hydrothermal time on morphology, microstructure and photocatalytic activity of TiO2 nanotubes has not been studied up to date. In this paper, the fabrication of TiO2 nanotubes (TNTs) by hydrothermal method with various nanopowder precursors was presented. The influence of precursors and hydrothermal time on morphology, microstructure and photocatalytic activity of TiO2 nanotubes were also investigated. 2. EXPERIMENTAL 2.1. Materials Four types of TiO2 nanopowders: TiO2 – P25, TiO2 – Merck, TiO2 – Roha and TiO2 – Rutile were chosen as precursors for the fabrication of TNTs by hydrothermal method. Details of parameters of these precursor materials were presented in Table 1. Table 1. The manufactured parameters of nanopowder TiO2 Precursors. Type of nanopowders Origin Purity External TiO2 – P25 Germany > 99 % White, impalpable TiO2 – Roha India > 96 % White, fine TiO2 – Merck Germany > 99 % White, fine TiO2 – Rutile Russia > 96 % White 74 2.2 M Af wa dis dri inv (TN 2.3 ch (TE ph nm 3.1 3.1 av 70 exh ph . Synthesis o The produ NaOH aque ter carrying ter until pH tilled water ed at 60 °C estigate the Ts – 6), 12 . Character The phas aracterized b M, JEM-1 otoluminesc . . Effect of p .1. Analysis Figure 1 erage particl ÷ 250 nm w Figure 1. T Figure 2 ibits the m ase (101) w f TiO2 nano ction proce ous solution out the filtr ∼9; then 2 boiled at 80 for next 4 h influence of h (TNTs – 12 ization meth es and crys y X-ray dif 400), respec ence (PL) (H recursors o and evaluat shows the d e size of TiO hilst that of EM images shows XRD ain compon ere minor p tubes (TNTs ss of TNTs ; the mixtur ation and ce M HNO3 ac °C until the and then, t hydrotherm ), 22 h (TNT ods tallinity of fraction (Br tively. The oriba iHR3 3. RE n formation ion of precur ifferent rang 2 – P25 is TiO2 – Rutil of various nan c) TiO2 – patterns of ents of sam hases. On Thi Ngoc T ) was followe e was then h ntrifugation, id solution desired pH hese white p al time, the s – 22), 36 h nanopowder uker D8-AD photocatalyt 20) spectra SULTS AND of TNTs sors e of particl 10 ÷ 30 nm; e is 2 ÷ 4 µm opowder TiO Merck and d nanopowder ple were ru the other h u Le, Nu Qu d by TiO2 n eated at 130 the white p was slowly ∼7. The ob owders wer synthesis wit (TNTs – 36 TiO2 precu VANCE), t ic ability o of the terep DISCUSS e sizes of T those of TiO . 2 precursors: ) TiO2 – Ruti precursors. tile phases and, TiO2 – ynh Trang T anopowders °C for 22 h owder was w added into tained produ e annealed a h various hy ) and 48 h (T rsors and T ransmission f TNTs was hthalic acid ION iO2 precurso 2 – Merck a) TiO2 – P25 le. The XRD p (111) while Roha and on, Thi Han were mixed in Teflon a ashed with and final wa cts were filt t 450 °C fo drothermal NTs – 48) at iO2 nanotub electron mi measured u (AT) solutio rs. For inst and TiO2 – , b) TiO2 – Ro attern of Ti those of the TiO2 – Me h Thu Vu with 10 utoclave. distilled shing in ered and r 2 h. To time: 6 h 130 ºC. es were croscopy sing the n at 435 ance, the Roha are ha, O2 – P25 anatase rck were Eff cry XR (11 2 In te ns ity (a .u ) 3.1 tha Ru tha Me Ru wh nan is c Ro the TiO ch ect of precu stallized in D of TiO2 – 0), 36.11 ° ( 0 25 30 35 40 2 Τ Ο Ο Ο Ο Ο R(2 R(111) A(004) R(101) R(110) A(101) Ο Figure 2. XR of nanopow precurs .2. Effect of Figure 3 t TNTs – P2 tile sample w t this sampl rck with th tile showed ich caused b ometer-size onsistent w Figure The cryst ha and TiO2 TNTs – Ro 2 at 2θ = 2 aracteristic p rsor materia anatase phas Rutile sho 101) and 54 45 50 55 60 65 ΟA(211) heta (degree) Ο Ο Ο Ο Ο10) R(220) A(204) R(211) A(105)A(200) TiO2 - R TiO2 - TiO2 TiO R: R A: A D patterns der TiO2 ors. the initial p shows TEM 5, TNTs – R as not form e possesses t e main peak that the hyd y the micro particle of t ith other rep 3. TEM ima a) TNTs – P2 al structure – Merck ex ha, and TN 5.08 °, A ( eaks of 2θ = ls and hydro e with prom wed only pe .35 ° (211). 70 75 utile Merck - Roha 2 - P25 utile natase 20 25 3 Ο Ο In te ns ity (a .u ) R(11 A(101) Figure 4. fabricated fr Ti recursor on images of T oha and TN ed the tube he highest u s of anatase rothermal re meter-size p he precursor orts [10 - 12 ges of TNTs 5, b) TNTs – of TNTs fab ception of T Ts – Merck 101); 37 °, 27.47 °, R thermal time inent peaks aks of rutil 0 35 40 45 50 Ο Ο Ο ΟΟ Ο A(1 A(200) HR(101) A(004) N H 0) 2 Theta (deg XRD patterns om various n O2 precursors the formatio NTs fabric Ts – Merck structure. TE niform struc phase. Bes action of th articles of T s plays an im ]. fabricated fro Roha, c) TNT ricated from iO2 – Rutile possess the A (004); 48 (110); 35.89 on the morp of (101), (0 e phase at d 55 60 65 70 75 Ο Ο ΟN R(311)05) ree) TNTs- P25 TNTs- Roha TNTs- Merck A : Anatase R : Rutile H : H2Ti3O7 N : Na2Ti3O7 of TNTs anopowder . n of TNTs ated by vari samples ex M image o ture, resulti ides, it is no is precursor iO2 – Rutile portant rol m various nan s – Merck an nanopowde ) are shown anatase ph .05 °, A (20 °, R (101) a hology, mic 04), (200), ( iffraction an 20 30 4 R(101) o H A(004R(110) o oo o A(101) In te ns ity (a .u ) 2 Figure 6. Po of TNTs fab hydrot ous precurso hibit tube str f TNTs – Me ng from the ted that TEM does not for (Figure 1d) e in the form opowder TiO d d) TNTs – R r precursors in Figure 4. ases with ch 0); and som nd 41.02 °, rostructure 105), and (2 gles of 2θ = 0 50 60 A(20 N A(211) A(105) o oo o H A(200) o) o Theta (degree) wder XRD pa ricated with v hermal times rs. The resu ucture whil rck sample high purity images o m the tube . It indicate ation of TN 2 precursors: utile. (TiO2 – P2 Results sho aracteristic e rutile pha R (111), resp 75 04). The 27.47 ° 70 80 A : Anatase R : Rutile H : H2Ti3O7 N : Na2Ti3O7 4) TNTs - 6 TNTs - 48 TNTs - 22 tterns arious . lt shows e TNTs – indicates of TiO2 – f TNTs – structure, s that the Ts which 5, TiO2 – wed that peaks of ses with ectively. Thi Ngoc Tu Le, Nu Quynh Trang Ton, Thi Hanh Thu Vu 76 However, only TNTs – P25 does not exhibit characteristic diffraction peak of anatase. A small amount of impurity phases was indexed as H2Ti3O7 and Na2Ti3O7, respectively. In summary, with different nanopowder TiO2 precursors, TiO2 – Merck, is profitable for the fabrication of TNTs by hydrothermal method. 3.2. Effect of the hydrothermal time on TNTs The nanopowder TiO2 – Merck precursor was used for investigating the effect of hydrothermal time on the TNTs formation. Figure 5 shows that the morphology of TNTs in various hydrothermal times is different, indicating that the critical hydrothermal treatment time plays an important role in the formation of tubular structure. For instance, with a short period of treatment time (t = 6 h), TNTs were formed with non-uniform morphology. When increasing reaction time from 12 to 22 h, the crystalline TNTs grows with the more uniform size of 8 ÷ 11 nm in diameter and a few hundred nanometers in length. At 22 h, TNTs has a uniform structure. However, when increasing the hydrothermal time up to 36 ÷ 48 h, the diameter of the tube increases with the un-uniform length of a few tens to a few hundreds of nanometers. This result is entirely consistent with the report of Sheng Jiang et al. [13]. It is suggested that when the hydrothermal reaction time is too long (over 36 h), the stable state of TNTs would be damaged in the boiling NaOH aqueous solution, according to: (i) a portion of TNTs will be dispersed into the solution and acting as nutrients for the growth of nanoribbon structure; (ii) a portion of TNTs would link together to form rafts through a multistep attachment process in order to reduce the surface energy; (iii) or they grow spirally into nanowires along the inner (200) surface. XRD patterns of TNTs – 6, TNTs – 22 and TNTs – 48 were carried out to investigate the process of TNTs formation (Figure 6) The structural analysis indicates that all samples crystallize in anatase phases with prominent peaks at (101) and (200), respectively. When reaction time increases from 6 h to 22 h, the intensity of the peaks significantly increase at A (101), A (200), and A (004) faces and R (110), R (211) faces, whilst the intensity of impurity peaks (H2Ti3O7, Na2Ti3O7) also increase. However, when the hydrothermal reaction time increases to a longer time of 48 h, the characteristic peaks of anatase, rutile, and impurity phases were not observed. It is indicated that in the short term synthesis, the reaction of the hydrothermal process occurs incompletely, which is not enough time for the formation of complete crystallization of materials [14]. On the contrary, with the longer time synthesis, the TNTs would be dispersed in NaOH aqueous solution and formed TiO2 nanosheets arrays instead of tubular structures, which is consistent with TEM results (Figure 5e). This suggests the Eff hy 3.3 of cou ch asc TN acc con tra F TN hy tho inc It ect of precu drothermal t Figure 5 b) TN . Photocata Figure 7a TNTs – Roh ld readily r aracterizing ending orde Ts – Merc ording to t trolled by t ps is reduced igure 7. PL sp Figure 7b Ts. Results drothermal t se of other rease of the suggests tha rsor materia reatment tim . TEM image Ts – 12: 12 h lytic activit shows the P a, TNTs – M eact with •O peak around r: TNTs – M k possesses he better cr he high crys while the r 350 In te ns ity (a .u .) ectra of TNT terephtha shows the e show that ime is chang samples. In hydrotherm t TNTs are f a ls and hydro e is critical s of TNTs fab ; c) TNTs – 2 y of TNTs L spectra of erck and TN H to produc 435 nm). erck, TNTs the higher ystallinity o tallinity of t ecombinatio 400 450 500 c b a Wavelength ( d s fabricated f lic acid aqueo ffect of hyd the intensity ed. TNTs – other words, al time wou abricated fro ) thermal time in the crysta ricated at var 2: 22 h; d) TN terephthalic Ts – P25. t 2-hydroxy The intensi – Roha and photocataly f TNTs – he precurso n of electron 550 600 650 a: TNTs- Merck b: TNTs- Roha c: TNTs- P25 d: terephthalic acid nm) rom a) variou us solution un rothermal tr of fluoresc 22 sample the optimal ld lead to th m high cry on the morp l structure an ious hydrothe Ts – 36: 36 h acid solutio Samples wer l acid tereph ty of this fl TNTs – P25 tic activity Merck. The r material in -hole pairs i 350 400 450 f d e c b In te ns ity (a .u .) Wa a s precursors a der 80 mins eatment time ence peak o shows the h hydrotherm e decrease i stalline prec b) hology, mic d formation rmal times: a and e) TNTs n under 80 m e all lumine thalic, with uorescence p , respectivel than the tho high phot which the f s limited [15 500 550 600 velength (nm) a: TNTs-22 b: TNTs-12 c: TNTs-36 d: TNTs-6 e: TNTs-48 f: terephtha nd b) various UVA irradiati on the phot f TNTs fab igher photoc al time is 22 n photocatal ursor powde rostructure of TNTs [1 ) TNTs – 6: 6 – 48: 48 h. ins UVA ir scent At 435 a fluorescen eak arrang y. This indi se of other ocatalytic a ormation of ]. 650 alic acid hydrotherma on. ocatalytic a ricated with atalytic acti hours, a de ytic ability rs and with 77 5]. h; radiation nm (AT ce signal es in the cates that samples ctivity is electron l time in ctivity of various vity than crease or of TNTs. a critical Thi Ngoc Tu Le, Nu Quynh Trang Ton, Thi Hanh Thu Vu 78 reaction time would obtain the high performance of photocatalytic activities. However, this is only the initial research to find the hydrothermal time points to determine the best tube structure, the time period from 12 to 22 h and 22 to 36 h need to be examined more smooth. This content will be focused on the future of group. 4. CONCLUSIONS The selection of nanopowder precursor and hydrothermal time has significantly affected the morphology, microstructure and photocatalytic property of the hydrothermally synthesized TiO2 nanotubes. The fabricated TNTs from nanopowder precursor with anatase phase (TiO2 – Merck) shows more uniform morphology and better crystallinity of TiO2 TNTs than those of other precursors with rutile phase. In this work, the critical reaction time was at 130 ºC for 22 h with the selection of TiO2 – Merck as the precursor material. The optimized hydrothermal time plays a critical role in the formation and photocatalytic activities of TNTs. Acknowledgment. This research is supported by project the CS2015.01.41. REFERENCES 1. Moonoosawmy K. R., Es-Souni M., Minch R., Dietze M., and Es-Souni, M. – Template- assisted generation of three-dimensionally branched titania nanotubes on asubstrate, CrystEngComm. 14 (2012) 474. 2. Lee C. H., Rhee, S. W., and Choi, H. W. - Preparation of TiO2 nanotube/nanoparticle composite particles and their applications in dye-sensitized solar cells, Nanoscale Res. Lett. 7 (2012) 1. 3. Li S., Yang X., Wei X., Xuan Y., Chen Z. D., and Jiang Y. - Fabrication of high quality TiO2 Nanotubes on Conductive Glasses, ECS Trans. 66 (2015) 229. 4. Sun K. C., Qadir M. B., Jeong, S. H. - Hydrothermal synthesis of TiO2 nanotubes and their application as an over-layer for dye-sensitized solar cells, RSC Advances 4 (2014) 23223. 5. Erjavec B., Kaplan R., Pintar A. - Effects of heat and peroxide treatment on photocatalytic activity of titanate nanotubes, Catal. Today 241 (2015) 15. Effect of precursor materials and hydrothermal time on the morphology, microstructure 79 6. Liu N., Chen X., Zhang J., Schwank J. W. - A review on TiO2-based nanotubes synthesized via hydrothermal method: formation mechanism, structure modification, and photocatalytic applications, Catal. Today 225 (2014) 34. 7. Guo Y., Lee N. H., Oh H. J., Yoon C. R., Park K. S., Lee W. H., Li Y., Lee H. G., Lee K. S., and Kim S. J. - Preparation of titanate nanotube thin film using hydrothermal method, Thin Solid Films 516 (2008) 8363. 8. Vuong, D. D., Tram, D. T. N., Pho, P. Q., and Chien, N. D. - Hydrothermal synthesis and photocatalytic properties of TiO2 nanotubes, In Physics and Engineering of New Materials, Springer Berlin Heidelberg 2009 (2009) 95. 9. Viet P. V., Phan B. T., Hieu L. V., Thi C. M. - The Effect of Acid Treatment and Reactive Temperature on the Formation of TiO2 Nanotubes, J. Nanosci. Nanotechno.15 (2015) 5202. 10. Gribb A. A., Banfield J. F. - Particle size effects on transformation kinetics and phase stability in nanocrystalline TiO2, Am. Mineral. 82 (1997) 717. 11. Chen Q., Zhou W., Du G. H., & Peng L. M. - Trititanate nanotubes made via a single alkali treatment, Adv. Mater. 14 (2002) 1208. 12. Lai C. W., Hamid S. B. A., Tan T. L., and Lee W. H. - Rapid formation of 1D titanate nanotubes using alkaline hydrothermal treatment and its photocatalytic performance, J. Nanomater. 2015 (2015) 1. 13. Sheng J., Hu L., Mo L. E., Li W., Tian H., Dai S. - A multistep attachment process: Transformation of titanate nanotubes into nanoribbons, Science China Chemistry 55 (2012) 368. 14. Razali M. H., Noor A. F. M., Mohamed A. R., Sreekantan S. - Morphological and structural studies of titanate and titania nanostructured materials obtained after heat treatments of hydrothermally produced layered titanate, J. Nanomater. 2012 (2012) 1. 15. Li Q., Liu R., Zou B., Cui T., & Liu B. - Effects of hydrothermal conditions on the morphology and phase composition of synthesized TiO2 nanostructures, Physica B: Condensed Matter. 445 (2014) 42.