Influence of new templating agent for the synthesis of coral like tio 2 nanoparticles and their photocatalytic activity

Accepted Manuscript Influence of new templating agent for the synthesis of coral-like TiO2 nanoparticles and their photocatalytic activity Satwant Kaur Shahi, Navneet Kaur, Sofia Sandhu, J.S Shahi, Vasundhara Singh PII: S2468-2179(17)30070-9 DOI: 10.1016/j.jsamd.2017.07.006 Reference: JSAMD 110 To appear in: Journal of Science: Advanced Materials and Devices Received Date: 16 May 2017 Revised Date: 12 July 2017 Accepted Date: 19 July 2017 Please cite this article as: S.K Shahi, N Kaur, S Sandhu, J Shahi, V Singh, Influence of new templating agent for the synthesis of coral-like TiO2 nanoparticles and their photocatalytic activity, Journal of Science: Advanced Materials and Devices (2017), doi: 10.1016/j.jsamd.2017.07.006 This is a PDF file of an unedited manuscript that has been accepted for publication As a service to our customers we are providing this early version of the manuscript The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain ACCEPTED MANUSCRIPT Title Page Influence of new templating agent for the synthesis of coral-like TiO2 RI PT nanoparticles and their photocatalytic activity Satwant Kaur Shahia, Navneet Kaura, Sofia Sandhua, J S Shahib, Vasundhara Singha * a Department of Applied Sciences (Chemistry), PEC University of Technology, Chandigarh 160012, INDIA email:vasun7@yahoo.co.in, Tel No.: 91-172-2733263 EP TE D M AN U SC Department of Physics, Panjab University, Chandigarh, 160014, INDIA AC C b ACCEPTED MANUSCRIPT Influence of new templating agent for the synthesis of coral-like TiO2 nanoparticles and their photocatalytic activity Abstract RI PT We report a low cost and environment friendly solvent system to synthesize TiO2 nanoparticles using acidic deep eutectic solvent, choline chloride / p-toluene sulphonic acid as templating and hydrolyzing agent via sol-gel method The effect of varying concentration of deep eutectic solvent has been investigated on the important physicochemical characteristics of as-synthesized TiO2 such as phase, morphology, particle size, surface area and band gap energy A detailed characterization of the obtained nanomaterials has been performed using various techniques, SC including X-ray diffraction (XRD), Scanning electron microscopy (SEM), Brunauer- Emmett- Tellar (BET) surface area, Raman and Ultraviolet-visible absorption spectroscopy The spherical shaped TiO2 nanoparticles was found to M AN U be biphasic having two phases: anatase and rutile with a crystallite size in the range of 5.6-6.8 nm These spherical shaped nanoparticles assembled together to form coral-like morphology The effect of calcination temperature on synthesized products was studied by heating at 750oC The photocatalytic activity of the prepared TiO2 materials has been evaluated by the photo-discoloration of an aqueous methyl orange dye solution (20 ppm) under UV light irradiation The results indicate that photocatalytic efficiency of anatase-rutile mixture in sample DES-3 is higher (98% within 3h) than commercially available Degussa P-25 (87% within 3h) Introduction TE D Titanium dioxide has attracted vast attention because of its widespread technological applications in photocatalysis, photovoltaics, gas sensors, self-cleaning surfaces, white pigments, catalyst supports, lithium ion batteries, memory devices and so on [ 1-5] TiO2 can exist in three distinct phases: anatase, rutile and brookite Thermodynamically, rutile is the most stable phase in bulk material while anatase and brookite are metastable and EP transform to rutile exothermally and irreversibly [6-9] In general, anatase form of TiO2 has been considered to have high photocatalytic activity [10] but there are reports of higher photocatalytic activity of anatase-rutile mixture than pure anatase due to synergistic effect between two phases preventing the recombination of photogenerated electrons AC C and holes [11] It is well known that the performance of TiO2 in various applications and its physico-chemical properties are strongly influenced by its particle size, phase, morphology and surface area [12, 13] It is desirable to develop nanostructures via various synthetic routes that allow for controlling the phase structure, size and morphology of TiO2 in good yield on the nanoscale To date, controllable synthesis of TiO2 has gained much attention and variety of structures have been reported [14-19] Various methods have been explored to synthesize TiO2 nanomaterials such as sol-gel, precipitation, hydrothermal, microwave assisted, chemical vapour deposition and sonochemical method Research in deep eutectic solvents (DES), which is an upcoming media for ionothermal reactions in nanotechnology, is still in its infancy Deep eutectic solvents have now emerged as an attractive alternate to the ACCEPTED MANUSCRIPT conventional ionic liquids showing numerous advantages over the latter due to their ease of preparation in a pure state at low cost, nontoxic nature, more synthetically accessible, biodegradable and can easily be tailored from their inexpensive components to suit certain applications [20] Deep eutectic solvents are obtained by the complexation of a quaternary ammonium salt with various H-bond donors, such as carboxylic acids, amides, and alcohols [21] and fulfil the requirement of highly structured solvents for the synthesis of shape controlled nanomaterials [22, 23] Few RI PT examples are reported in literature, of the use of deep eutectic solvents both as solvent and structure-directing agent to synthesize nanomaterials In a recent study, DESs have been reviewed [24] for their use as designer solvents to produce different kinds of nanomaterials, in which they play an efficient role in determining the shape, size and morphology of nanomaterials such as self-organized TiO2 nanobamboos by using succinic acid and choline chloride [25], gold nanowires [26], spindly bismuth vanadate microtubes [27], nanoflower shaped NiO and NiCl2 nanosheets SC [28] ZnO nanostructures using antisolvent approach [29] and hydrangea-like micro-sized SnO by using choline chloride/urea [30] M AN U In the present work, we have employed low cost acidic deep eutectic solvent, choline chloride (ChCl) / ptoluene sulphonic acid (PTSA) as a templating and as an acidic hydrolyzing agent to synthesize biphasic TiO2 from tetra butyl titanate precursor (TBT) via sol-gel method avoiding the use of corrosive mineral acids The complete characterization and photocatalytic activity of as-prepared samples was studied Further, TiO2 nanoparticles were calcined at 750oC to investigate the effect of heating on the structural properties of TiO2 such as phase change, particle size and based on that photocatalytic activities were determined under UV light illumination 2.1 Reagents and Chemicals TE D Materials and methods All chemicals used in this work, tetra butyl titanate (TBT) ((Ti(OCH2CH2CH2CH3)4, 97%)), choline chloride ((CH3)3N(Cl)CH2CH2OH, 99%)), para toluene sulphonic acid (CH3C6H4SO3H, 98.5%), ethanol, Degussa P-25 (99.5%) and methyl orange were of analytical purity grade, supplied by Sigma-Aldrich and were used as received EP without any further purification 2.2 Preparation of acidic DES AC C The acidic deep eutectic solvent was prepared by using choline chloride (ChCl) and p-toluene sulphonic acid (PTSA) in 1:1 ratio The solvent was heated at 80oC under continuous magnetic stirring till a completely miscible and colourless transparent liquid was obtained 2.3 Synthesis of TiO2 To obtain TiO2 nanoparticles via sol-gel approach, ml of TBT as titania precursor was added drop wise to ml of prepared DES followed by the addition of ml of double distilled water The mixture was magnetically stirred vigorously for 30 minutes at room temperature A clear and transparent homogenous solution was formed The solution was heated and aged at 100oC for 24h in an oven The resultant products were collected, separated by centrifugation, washed thoroughly with distilled water and ethanol, dried in an oven at 70°C overnight to obtain ACCEPTED MANUSCRIPT TiO2 powder To investigate the effect of concentration of acidic DES on phase and morphology of TiO2, experiments were performed under similar conditions with different molar concentration of acidic DES to obtain products, which were labelled as DES-1(3 ml), DES-2 (6 ml), DES-3 (9 ml) and DES-4 (12 ml) respectively To study the effect of calcination temperature on phase structure, as-synthesized products were calcined at temperature 750oC using a multisegment programmable furnace The temperature was increased at a rate of 3.0oC/min, kept for RI PT 3h and then decreased to room temperature The calcined products were labelled as DES-1C, DES-2C, DES-3C and DES-4C 2.3 Characterisation of TiO2 nanoparticles XRD measurements were performed using an X-ray powder diffractometer (XPERT-PRO) operated at 45 SC kV and 40 mA with Cu-Kα radiation (λ=0.15406 nm) and a scan angle (2θ) of 5-80o UV-vis spectra were recorded on spectrometer Lambda 35 (Perkin Elmer) equipped with diffuse reflectance accessory at room temperature BET M AN U surface areas were calculated by using BET (Brunauer Emmett Teller) equation thermally heated at 180oC for h (Quantachrome Nova Win version 10.01) SEM images of samples were obtained using Model SU 8010 (Hitachi) Raman spectra were recorded with Raman spectrometer IHR 550, JY-HORIBA, using 488 nm wavelength of an Argon Laser with Grating-1800 grooves/mm, Detector-Palatier effect cooled ccd (NEW-PORT) 2.4 Photocatalytic experiments The photocatalytic activity of as-synthesized TiO2 samples was investigated by measuring discoloration of methyl orange in an aqueous solution under UV irradiation and compared with commercial Degussa P-25 TE D Discoloration was carried in an immersion well type photochemical reactor made of Pyrex glass with a watercirculating jacket maintained at room temperature, an opening for supply of oxygen and inlet through which the samples were taken from time to time during the experiment with the help of a syringe The photo-reactor was placed on a magnetic stirrer A UV lamp of 150 W was used as a light source to irradiate the solution 60 mg of TiO2 sample powder was mixed in 200 ml of 20 ppm aqueous methyl orange solution (2 g/100 ml) To attain the EP adsorption-desorption equilibrium, solution was stirred in the dark for 30 ml of sample was taken at regular intervals and further separated by centrifugation at 4000 rpm for 20 The obtained upper clear solution was AC C analysed using a UV-vis spectrometer The percentage discoloration was determined according to eqn 1: ஺௢ି஺௧ η = ஺௢ ˟ 100 % (eqn 1) where Ao and At are the absorbances at t=0 and time t respectively assessed by evaluating the absorbance at 463 nm on UV-vis spectrometer Results and discussions 3.1 XRD analysis ACCEPTED MANUSCRIPT X-ray diffraction (XRD) spectra of as-synthesized TiO2 provided the detailed crystalline phase information as given in Fig XRD patterns showed the variation between anatase (101) and rutile (110) phases with change in concentration of acidic DES The crystalline phase, phase composition and particle size of TiO2 and calcined TiO2 was determined and compiled in Table and The relative TiO2 phase percentage was calculated (eqn 2) by calculated by the following equation eqn 2: FR (eqn 2) RI PT analyzing the diffraction peak intensities of anatase (101) and rutile (110) [31] The rutile fraction (FR) was SC where IA and IR are the intensities of anatase peak (101) and rutile peak (110) respectively As shown in Fig 1, Sample DES-1 and DES-2 showed the formation of pure anatase phase of TiO2 (JCPDS-21-1272) Further, increasing the concentration of acidic deep eutectic solvent lead to decrease in the M AN U content of anatase (from 100% in sample DES-1 and DES-2 to 34.7 % in DES-4) with the appearance of rutile phase (28.4% in sample DES-3 and 65.3% in DES-4) (JCPDS-21-1276) The average crystallite size of nanoparticles was estimated by applying Debye-Scherrer equation (eqn 3) on the diffraction peaks of anatase (101) and rutile (110), which showed small variation in size in the range of 5.6 to 6.8 nm ߬ ൌ ௄ ఒ (eqn 3) ఉ ୡ୭ୱఏ TE D Where τ is the mean size of the crystalline domains, λ is the X-ray wavelength (0.154 nm), β is the FWHM of the AC C EP catalyst, K = 0.89 and θ is the diffraction angle The results are presented in Table M AN U SC RI PT ACCEPTED MANUSCRIPT Fig XRD patterns of sample DES-1 (a), DES-2 (b) DES-3 (c) and DES-4 (d) TiO2 Phase Anatase % Rutile % Anatase 100 - 6.8 87.6 3.01 EP Volume of DES added DES-1 ml DES-2 ml Anatase 100 - 6.0 90.7 3.0 DES-3 ml A&R 71.6 28.4 5.9 102.4 3.0 A&R 34.7 65.3 5.6 83.4 3.08 AC C Sample TE D Table Physico-chemical properties of as-synthesized TiO2 DES-4 12 ml XRD crystallite size SBET (nm) (m2g-1) Band gap (Eg) From XRD analysis of calcined samples (Fig 2), it was found that the crystal phase and composition of TiO2 nanoparticles can be entirely changed by calcination With calcination, crystallinity and size of nanoparticles increases and average size of the nanoparticles was in the range of 25 to 35 nm There was a complete transformation of anatase to rutile phase in DES-4 as evident from Fig These results are in good agreement as reported previously in the literature that phase change from anatase to rutile is initiated at temperature higher than 600oC [32] However, complete conversion into rutile phase does not takes place for the synthesized samples DES- ACCEPTED MANUSCRIPT 1, DES-2 and DES-3, instead results into anatase–rutile mixtures with increased rutile content from to 19.4 (DES1 to DES-1C), to 75.2 (DES-2 to DES-2C) and 28.4 to 93.4 % (DES-3 to DES-3C) The average crystallite sizes, M AN U SC RI PT phase and phase composition of various heated samples are listed in Table TE D Fig XRD patterns of calcined TiO2 samples, DES-1C (a), DES-2C (b), DES-3C (c) and DES-4C (d) 3.1.1 Influence of concentration of acidic DES on the phase structure of TiO2 It has been observed from XRD analysis that the concentration of DES has great influence on the phase structure of TiO2 By increasing the volume of acidic DES in sample DES-1 to sample DES-4, acidic concentration EP of the solution increases, which results into change in phase percentage composition of TiO2 The effect of acidic character on the crystal phase of TiO2 was explained by Cheng and co-workers [33], who suggested that Ti (IV) complexes exist as octahedral coordinated complex ions in the solution He proposed that increase in acidity affect AC C the type of bonding between [TiO6] units, which are formed during the hydrolysis of TiO2 precursor in the reaction system The decrease in acidic character of the solution increases the probability of edge shared bonding, which could favour the anatase phase formation of TiO2 as observed in sample DES-1 and DES-2 Increase in the acidity of reaction mixture in DES-4 results into higher rutile phase composition Table Physico-chemical properties of calcined TiO2 Sample Volume of DES added Phase change after calcination Anatase % Rutile % XRD crystallite size (nm) ACCEPTED MANUSCRIPT ml A&R 80.6 19.4 35.6 DES-2C ml A&R 24.8 75.2 36.7 DES-3C ml A&R 6.6 93.4 24.4 DES-4C 12 ml Rutile 100 23.0 SC 3.2 SEM analysis RI PT DES-1C Fig represents the SEM images of the as-synthesized TiO2 nanoparticles in different reaction acidic M AN U concentrations It can be observed that these TiO2 nanoparticles in different DES concentration have variable morphologies When the low concentration of DES was used in DES-1, granular well-ordered nanospheres with grain size of ca nm were observed (Fig a) Further increase in the volume of DES from ml to ml, these nanoparticles combine (Fig b) and appears to be in a process of making coral-like structure Fig c and d shows the morphology of samples DES-3 and DES-4 fabricated at higher concentration of acidic DES, in which TiO2 AC C EP TE D nanospheres form nanoparticle-aggregated coral-like structure SC Fig SEM images of samples DES-1 (a), DES-2 (b) DES-3 (c) and DES-4 (d) RI PT ACCEPTED MANUSCRIPT The mechanism for the growth of TiO2 nanospheres having coral-like morphology can be described as M AN U following During crystallization process, DES is likely act as a capping agent and growth controller, preferring to selectively adsorb on the surface of nanoparticles The crystal growth takes place by the initial formation of tiny nuclei, which grow into small sized primary nanoparticles Further, these particles assemble into bigger spherical aggregates leading to the formation of assembled and thermodynamically favorable coral-like structure (Fig c) 3.3 Raman spectra Fig demonstrate the Raman spectra of the most active as-synthesized TiO2 photocatalyst, sample DES-3 TE D In bulk material, Raman lines at 144 (Eg), 197 (Eg), 639 (Eg), 399 (B1g), 513 (A1g) and 519 (B1g) cm-1 represent the presence of anatase phase [34, 35], signals at 143 (B1g), 447 (Eg), 612 (A1g) and 826 (B2g) shows the presence of rutile [36] and signals at 128, 246, 320 and 366 cm-1 indicate the presence of Brookite phase [37] In Fig of sample DES-3, the presence of Raman signals at around 151 (Eg), 448 (Eg), 514 (A1g) and 615 (A1g) can be EP observed, which characterize the presence of both anatase and rutile phase, confirmed by the XRD results Due to AC C the small size of the nanoparticles, vibrational frequencies are broadened with respect to the bulk material ACCEPTED MANUSCRIPT A1g 300 400 500 600 W aven u m b e r ( c m Fig Raman spectra of sample DES-3 -1 700 800 900 M AN U 200 SC A1g Eg 100 RI PT Intensity (a.u.) Eg ) The surface area of the particles was estimated by Brunauer-Emmett-Teller (BET) method as shown in Table All the prepared samples exhibited high surface area in the range from 102.4 to 83.4 m2/g, which are TE D considerably larger than that reported for the commercial photocatalyst Degussa P-25 having surface area of 50 ± 15 m2/g [38] 3.4 UV-visible absorption spectra The optical properties of TiO2 nanoparticles were characterized by UV-visible absorption spectroscopy EP (Fig.5) The small band gap energy of a semiconductor has an advantage in terms of improving the photocatalytic efficiency of TiO2 and electron-hole recombination rate The band gap values was calculated on the basis of optical AC C absorption spectra by the following equation (eqn 4): (αhν)n = A(hν - Eg) (eqn 4) Where h is Planck's constant, α is absorption coefficient, ν is frequency of vibration, Eg is band gap, A is proportional constant and n is either n = for an indirect allowed transition or n= ½ for the direct forbidden transition By plotting (αhυ)2 as a function of photon energy (hυ) (Fig 5) and extrapolating the linear regions of this curve to (αhυ)n = 0, the band gap energy can be determined The calculated band gap of TiO2 samples range between 3.0 to 3.08 eV, which is slightly smaller than the value for commercial TiO2 Degussa P-25 (3.1eV) AC C EP TE D M AN U SC RI PT ACCEPTED MANUSCRIPT AC C EP TE D M AN U SC RI PT ACCEPTED MANUSCRIPT Fig Optical absorption spectra and band gap of samples (a) DES-1, (b) DES-2, (c) DES-3 and (d) DES-4 ACCEPTED MANUSCRIPT 3.5 Photocatalytic degradation experiments The photocatalytic activity of synthesized anatase and anatase-rutile TiO2 mixture were evaluated by the discoloration of methyl orange solution under UV light irradiation It is obvious from Fig that sample DES-3 with anatase-rutile mixture exhibited higher photocatalytic activity (98% within 3h) than Degussa P-25 (87% within 3h), RI PT DES-1 (82% at 4h), DES-2 (73 % at 4h) and DES-4 (62% at 4h) The phase composition obtained in sample DES-3 (Table 1) is similar to that of Degussa P-25 (70:30 ratio of anatase: rutile) but the particle size is much smaller as compared to Degussa P-25 The smaller size of the particles leads to an increase in the surface area and more surface oxygen vacancies which can be interpreted as an increase in the surface active sites resulting better photocatalytic activity The distinct morphology, smaller particle size and high surface area is probably responsible for higher SC photocatalytic activity of DES-3 sample The photocatalytic activity of anatase/rutile mixture could also be accounted for synergistic effect of coupling of anatase and rutile phase and low electron-hole recombination rate due M AN U to the efficient electron-hole mobility in the junction between dimorphs [39, 40] 80 60 40 20 TE D Degradation (%) 100 30 EP 60 90 120 150 180 DES-1 DES-2 DES-3 DES-4 P-25 210 240 Irradiation time (min) AC C Fig Photocatalytic efficiency of methyl orange solution under UV light with sample DES-1, DES-2, DES-3, DES4 and P-25 The photocatalytic activity of the calcined TiO2 samples (Fig 7) has also been conducted under UV light irradiation as a function of photocatalytic percent degradation versus the irradiation time The data shown in Fig evidently specifies that calcined samples have low photocatalytic activity than non-calcined samples, probably due to larger particle size The sample DES-1C exhibited slightly higher photocatalytic activity (44 % at 4h) than DES2C (38 % at 4h), DES-3C (19 % at 4h) and DES-4C (15 % at 4h) It has been observed that the samples DES-4C and DES-3C, which contain pure rutile phase (100 % in DES-4C) or high rutile content (93.4 % in DES-3C) exhibited low catalytic activity corresponds to as reported earlier that pure rutile phase is much less active photocatalyst [41, 42] ACCEPTED MANUSCRIPT 60 DES-1C DES-2C DES-3C DES-4C RI PT 40 30 20 10 30 60 90 120 150 180 210 240 M AN U SC Degradation (%) 50 Irradiation time (min) Fig Photocatalytic efficiency of methyl orange solution under UV light with sample DES-1C, DES-2C, DES-3C, DES-4C 4.5 4.0 TE D DES-1 DES-2 DES-3 DES-4 P-25 3.5 2.5 2.0 EP Ln (Co/C) 3.0 1.5 AC C 1.0 0.5 0.0 30 60 90 120 150 180 210 240 Time (min) Fig Kinetic studies of as-synthesized samples DES-1, DES-2, DES-3, DES-4 and P-25 The kinetic studies of samples were carried out as shown in Fig 8, in which discoloration profiles have been fitted to a first order kinetics The regression curve of the natural logarithm of normalized methyl orange ACCEPTED MANUSCRIPT concentration versus reaction time (eqn 5) was approximately a straight line, indicating that the photocatalytic reactions followed first-order kinetics: ln C0/C = kt (eqn 5) where C is the concentration of methyl orange (mg/L) at instant time t, C0 is the concentration of MO (mg/L) at t = RI PT (min) and k is the reaction rate constant (minute-1) The rate constant can be determined from the slope of the straight line Discoloration of sample DES-3 shows two stage first order kinetics, which was found to be slow for initial 90 followed by faster rate to 180 The calculated rate constant, k value for DES-3 for both stages was found to be 0.012 (slow rate) and 0.039 (fast rate) with fitting parameters R2 > 0.98 As evident, the k value for SC DES-3 was found to be greater than P-25 (0.012), DES-1 (0.008), DES-2 (0.006) and DES-4 (0.004) min-1 Conclusion M AN U In summary, anatase and anatase-rutile TiO2 have been successfully fabricated with low cost acidic deep eutectic solvent, choline chloride / p-toluene sulphonic acid using a simple sol-gel method avoiding use of corrosive mineral acids The effect of calcination at 750oC on crystal phase structure of TiO2 and concentration variation of DES has also been investigated The as-synthesized samples were found to have two phases, anatase and anataserutile, while on calcination most of the samples were having major rutile phase with a trace of anatase phase or pure rutile phase The spherically shaped nanoparticles with crystallite size in the range of 5.6-6.8 nm aggregated to form coral-like structure The best coral features are obtained for DES-3 when optimum volume of DES (9 ml) was used TE D The photocatalytic activity of the synthesized samples has been evaluated by the photo-discoloration of an aqueous methyl orange dye solution (20 ppm) under UV light irradiation The results indicate that photocatalytic activity of sample DES-3 is higher (98% within 3h) than commercially available Degussa P-25 (87% within 3h) Kinetics of the photocatalytic degradation of dye has been studied and discoloration followed the first order kinetics EP References [1] U Diebold, The surface science of titanium dioxide, Surface Science Reports 48 (2003) 53−229 [2] O Carp, C L Huisman, A Reller, Photoinduced reactivity of titanium dioxide, Progress in Solid State AC C Chemistry 32 (2004) 33−177 [3] X B Chen, S S Mao, Titanium dioxide nanomaterials: Synthesis, properties, modification and applications, Chemical Reviews 107 (2007) 2891−2959 [4] A Hagfeldt, M Gratzel, Light-induced redox reactions in nanocrystalline systems, Chemical Reviews 95 (1995) 49−68 [5] A Fujishima, K Honda, Electrochemical photolysis of water at a semiconductor electrode, Nature 238 (1972) 37−38 [6] O Legrini, E Oliveros, A Braun, Photochemical processes for water treatment, Chemical Reviews 93 (1993) 671-698 ACCEPTED MANUSCRIPT [7] H Y Zhu, Y Lan, X P Gao, S P Ringer, Z F Zheng, D Y Song, J C Zhao, Phase transition between nanostructures of titanate and titanium dioxides via simple wet-chemical reactions, Journal of American Chemical Society 127 (2005) 6730 [8] T Mitsuhashi, O J Kleppa, Transformation enthalpies of the TiO2 polymorphs, Journal of American Ceramic Society 62 (1979) 356-357 Material Science Engineering A 403 (2003) 87-93 RI PT [9] K R Zhu, M S Zhang, J M Hong, Z Yin, Size effect on phase transition sequence of TiO2 nanocrystal, [10] D Wang, L Xiao, Q Luo, X Li, J An, Y Duan, Highly efficient visible light TiO2 photocatalyst prepared by sol-gel method at temperatures lower than 300oC, Journal of Hazardous materials 192 (2011) 150-159 SC [11] M C Yan, F Chen, J Zhang, M Anpo, Preparation of controllable crystalline titania and study on the photocatalytic properties, Journal of Physical Chemistry B 109 (2005) 8673-8678 [12] H Liu, Y Liang, H Hu, M Wang, Hydrothermal synthesis of mesostructured nanocrystalline TiO2 in an ionic M AN U liquid-water mixture and its photocatalytic performance, Solid State Science 11 (2009) 1655-1660 [13] X.Y Ma, Z.G Chen, H B Jiang, J Zou, S Z Qiao, Fabrication of uniform anatase TiO2 particles exposed by {001} facets, Chemical Communication 46 (2010) 6608-6610 [14] S K Shahi, N Kaur, V Singh, Fabrication of Phase and morphology controlled Pure Rutile and Rutile/Anatase TiO2 nanostructures in functional ionic liquid/water, Applied Surface Science 360 (2016) 953–960 TE D [15] S K Shahi, N Kaur, V Singh, Green synthesis of photoactive nanocrystalline anatase TiO2 in recyclable and recoverable acidic ionic liquid [bmim] HSO4 Journal of Material Science 50 (2015) 2443–2450 [16] K L Ding, Z J Miao, B J Hu, G M An, Z Y Sun, B X Han, Z M Liu, Shape and size controlled synthesis of anatase nanocrystals with the assistance of ionic liquid, Langmuir 16 (2010) 5129−5134 EP [17] X W Zhao, W Z Jin, J G Cai, J F Ye, Z H Li, Y R Ma, J L Xie, L M Qi, Shape and Size-controlled synthesis of uniform anatase TiO2 nanocuboids enclosed by active {100} and {001} facets, Advance Functional AC C Materials 21 (2011) 3554−3563 [18] R G Thomas, C Matteo, P Taejong, M Filippo, T W Ralph, F Paolo, B M Christopher, Nonaqueous synthesis of TiO2 nanocrystals using TiF4 to engineer morphology, oxygen vacancy concentration and photocatalytic activity, Journal of American Chemical Society 134 (2012) 6751−6761 [19] J S Chen, J Liu, S Z Qiao, R Xu, X W Lou, Formation of large 2D nanosheets via PVP assisted assembly of anatase TiO2 nanomosaics, Chemical Communication 47 (2011) 10443−10445 [20] E L Smith, A P Abbott, K S Ryder, Deep eutectic solvents (DESs) and their applications, Chemical reviews 114 (2014) 11060-11082 ACCEPTED MANUSCRIPT [21] A Abo-Hamad, M Hayyan, M A AlSaadi, M A Hashim, Potential applications of deep eutectic solvents in nanotechnology, Chemical Engineering Journal 273 (2015) 551-567 [22] Q Zhang, K D O Vigier, S Royer, F Jérôme, Deep eutectic solvents: synthesis, properties and applications, Chemical Society Reviews 41 (2012) 7108-7146 [23] F S Mjalli, J Naser, B Jibril, V Alizadeh, Z Gano, Tetrabutylammonium chloride based ionic liquid RI PT analogues and their physical properties, Journal of Chemical & Engineering Data 59 (2014) 2242-2251 [24] D V Wagle, H Zhao, G A Baker, Deep eutectic solvents: sustainable media for nanoscale and functional materials, Accounts of Chemical Research 47 (2014) 2299-2308 [25] C Y Chen, K Ozasa, F Kitamura, K I Katsumata, M Maeda, K Okada, N Matsushita, Self –organization of TiO2 nanobamboos by anodization with deep eutectic solvent, Electrochimica Acta 153 (2015) 409-415 SC [26] M Chirea, A Freitas, B S Vasile, C Ghitulica, C M Pereira, F Silva, Gold nanowire networks: synthesis, characterization, and catalytic activity, Langmuir 27 (2011) 3906-3913 [27] W Liu, Y Yu, L Cao, G Su, X Liu, L Zhang, Y Wang, Synthesis of monoclinic structured BiVO4 spindly M AN U microtubes in deep eutectic solvent and their application for dye degradation, Journal of Hazardous Material 181 (2010) 1102-1108 [28] X Ge, C Gu, Y Lu, X Wang, J Tu, A versatile protocol for the ionothermal synthesis of nanostructured nickel compounds as energy storage materials from a choline chloride-based ionic liquid, Journal of Materials Chemistry A (2013) 13454-13461 [29] J Y Dong, W H Lin, Y J Hsu, D S H Wong, S Y Lu, Ultrafast formation of ZnO mesocrystals with excellent photocatalytic activities by a facile Tris-assisted antisolvent process, Crystal Engneering TE D Communication 13 (2011) 6218-6222 [30] H Zheng, C D Gu, X L Wang, J P Tu, Fast synthesis and optical property of SnO nanoparticles from choline chloride-based ionic liquid, Journal of nanoparticle research 16 (2014) 1-9 [31] R A Spurr, H Myers, Quantitative analysis of anatase-rutile mixtures with an X-ray diffractometer, Analytical EP Chemistry 29 (1957) 760-762 [32] D A H Hanaor, C C Sorrell, Review of the anatase to rutile phase transformation, Journal of Materials AC C Science, 46 (2011) 855-874 [33] H Cheng, J Ma, Z Zhao, L Qi, Hydrothermal preparation of uniform nanosize rutile and anatase particles, Chemistry of Materials (1995) 663-671 [34] X Chen, S S Mao, Titanium dioxide nanomaterials: synthesis, properties, modifications, and applications, Chemical reviews 107 (2007) 2891-2959 [35] T Ohsaka, F Izumi, Y Fujiki, Raman spectrum of anatase, TiO2, Journal of Raman spectroscopy (1978) 321-324 ACCEPTED MANUSCRIPT [36] S P S Porto, P.A Fleury, T C Damen, Raman Spectra of TiO2, MgF2, ZnF2, FeF2, and MnF2, Physical Reviews, 154 (1967) 522-526 [37] G A Tompsett, G A Bowmaker, R P Cooney, J B Metson, K A Rodgers, J M Seakins, Journal of Raman Spectroscopy 26 (1995) 57-62 of methylene blue, Bull Korean Chemical Society 30 (2009) 193–196 RI PT [38] E W Kim, D S Kim, B T Ahn, Synthesis of mesoporous TiO2 and its application to photocatalytic activation [39] Z Jinghuan, X Xin, N Junmin, Hydrothermal hydrolysis synthesis and photocatalytic properties of nanoTiO2 with an adjustable crystalline structure, Journal of Hazardous Material 176 (2010) 617−622 SC [40] D C Hurum, K A Gray, T Rajh, M C Thurnauer, Recombination pathways in the Degussa P-25 formulation of TiO2: surface versus lattice mechanisms, Journal of Physical Chemistry B 109 (2005) 977–980 M AN U [41] T Alammar, H Noei, Y Wang, A.V Mudring, Mild yet phase-selective preparation of TiO2 nanoparticles from ionic liquids, Nanoscale (2013) 8045–8055 [42] T.A Kandiel, R Dillert, A Feldhoff, D.W Bahnemann, Direct synthesis of photocatalytically active rutile AC C EP TE D TiO2 nanorods partly decorated with anatase nanoparticles, J Phys Chem 114 (2010) 4909–4915 ACCEPTED MANUSCRIPT Highlights We report a synthesis of TiO2 nanospheres in deep eutectic solvents DESs were used as an efficient hydrolyzing, templating and structure directing agent Avoided the use of mostly used corrosive mineral acids, making it a green process TiO2 nanospheres aggregated coral-like structure was successfully synthesized Excellent photocatalytic activity of samples was observed AC C EP TE D M AN U SC RI PT  ... Title Page Influence of new templating agent for the synthesis of coral- like TiO2 RI PT nanoparticles and their photocatalytic activity Satwant Kaur Shahia, Navneet Kaura, Sofia Sandhua, J S... Panjab University, Chandigarh, 160014, INDIA AC C b ACCEPTED MANUSCRIPT Influence of new templating agent for the synthesis of coral- like TiO2 nanoparticles and their photocatalytic activity Abstract... Ahn, Synthesis of mesoporous TiO2 and its application to photocatalytic activation [39] Z Jinghuan, X Xin, N Junmin, Hydrothermal hydrolysis synthesis and photocatalytic properties of nanoTiO2 with