Unconventional Strategy to Anatase TiO2 Nanocrystals with Tunable

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Unconventional Strategy to Anatase TiO Nanocrystals with Tunable Surface Chemistry via Liquid Crystalline Polyamides as Functional Matrix Chenxi Zhang, Lingli Zhang, Ning You, Zhe Cui, Peng Fu, Minying Liu, Xinchang Pang, and Qingxiang Zhao J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.7b08542 • Publication Date (Web): 13 Nov 2017 Downloaded from http://pubs.acs.org on November 14, 2017

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The Journal of Physical Chemistry

Unconventional Strategy to Anatase TiO2 Nanocrystals with Tunable Surface Chemistry via Liquid Crystalline Polyamides as Functional Matrix Chenxi Zhang,§1, Lingli Zhang,§1,2 Ning You, §1 Zhe Cui,*1 Peng Fu,*1 Minying Liu,*1 Xinchang Pang,*1 and Qingxiang Zhao*1 1

School of Materials Science and Engineering, Zhengzhou University, Zhengzhou

450001, China 2

Department of Biological Engineering, Zhengzhou Technical College, Zhengzhou

450121, China *To whom correspondence should be addressed. §These authors contributed equally to this work. E-mail: [email protected]; [email protected]; [email protected]; [email protected]; [email protected]

1

ACS Paragon Plus Environment


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ABSTRACT: An unconventional but robust route to synthesize anatase TiO2 colloidal nanocrystals with tunable surface chemistry and dimensions was developed via liquid crystalline polyamides (LCPA) with pyridine rings as functional matrix. Titanium(IV) tetraisopropoxide (TTIP), as the precursor of TiO2 nanocrystals, was selectively incorporated into the compartment containing pyridine ring units via coordination interaction between pyridine rings and precursors, following by in situ direct polycondensation reaction of two monomers with TTIP into amorphous TiO2 nanoparticles encapsulated into LCPA matrix. The functional polyamide chains capping on the surface of TiO2 nanoparticles can be readily carbonized at 500 °C in inert atmosphere (argon), subsequently the formed carbon as protecting coating on the surface of TiO2 nanocrystals to prevent nanocrystals from aggregation. In addition, the amorphous TiO2 was simultaneously transformed into anatase TiO2 after 500 °C calcination. The carbon shell on the surface of anatase TiO2 nanocrystals can be readily removed by calcination at relative low temperature (400 °C) in air. At last, the carboxyl-terminated polymers, such as PMMA-COOH or PEG-COOH, were chosen as functional ligands for the surface modification of anatase TiO2 nanocrystals to fabricate core@shell anatase TiO2@polymer colloidal nanocrystals. The sizes of anatase TiO2 nanocrystals can be also tuned by adjusting the molar ratio of TTIP precursors to pyridine units.

2


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INTRODUCTION Attributable to their unique properties, such as electrical,1 optical,2 magnetic,3,4 catalytic,5 etc., the design and preparation of functional colloidal nanocrystals with tunable dimensions and surface chemistry have received broad attention in applications of nanomaterials,6 such as in preparing biosensors,7 solar cells,2,8 light-emitting diodes,9,10 catalysts,11 etc.12 The numerous advantages of functional nanocrystals can be achieved by reducing bulk materials into nanostructures.13 Titanium dioxide (TiO2),12 as one of the materials most widely studied in the field of materials science, owing to its broad applications, such as used in gas sensors,14 energy storage,15 biocompatible materials,16 photovoltaics,17,18 photocatalysis,18,19 to name but a few. The TiO2 exists in three crystalline phases: rutile, anatase and brookite.20 Among them, the anatase TiO2 was widely investigated because of its strong catalytic and photocatalytic activity.21 So anatase TiO2 nanocrystals have been broadly

utilized

in

solar

cells,22

lithium-ion

batteries,23,24

gas

sensors,14

photocatalysis25 and so on. Due to the physical and chemical properties of TiO2 nanocrystals depending heavily on the structure, particle sizes, crystalline phase, surface chemistry, specific surface area and morphology, a facile synthesis of size-tunable anatase TiO2 colloidal nanocrystals with tunable surface chemical properties is of great interest for numerous applications mentioned above. Different synthesis strategies have been utilized for the preparation of anatase TiO2 nanocrystals including functional nanoreactor method,26,27 sol-gel processes,28 hydrothermal reactions,29 organic solution-phase synthesis,30 template-assisted techniques,31 3



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thermolysis of organometallic precursors,12 combustion synthesis32 and so on. However, these conventional methods have different disadvantages including composition inhomogeneities, uncontrollable surface chemical structures, nonuniform nanocrystal dimensions, uncontrollability of crystalline phase, etc. In this regard, the convenient and facile approaches to fabricate pure anatase TiO2 nanocrystals with uniform dimensions and tunable surface chemical properties are necessary.2 Polyamide, especially thermotropic liquid crystalline polyamides (LCPA) containing heterocyclic repeating units have received considerable attention due to their outstanding thermal stability, chemical resistance and electrical and mechanical properties.33,34 Furthermore, it is worth noting that the pyridine ring is typically heterocyclic structure, as one of the most stable architectures, and it is broadly used in the preparation of LCPA owing to its stiffness, asymmetric structure and metal ions complexing abilities.35,36 Owing to unique chemical structures and preparation conditions, LCPA containing pyridine units are the outstanding choice to be utilized as functional polymeric matrix for the fabrication of anatase TiO2 nanocrystals. Herein, we report an unconventional but robust route to fabricate anatase TiO2 colloidal nanocrystals with tunable surface chemistry and dimensions via liquid crystalline polyamides (LCPA) with pyridine rings as functional matrix. Titanium(IV) tetraisopropoxide (TTIP), as the precursor of TiO2 nanocrystals, was selectively incorporated into the compartment containing pyridine ring units via coordination interaction between pyridine rings and precursors, following by in situ direct polycondensation reaction of two monomers with TTIP into amorphous TiO2 nanoparticles encapsulated into LCPA matrix. The 4


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functional polyamide chains capping on the surface of TiO2 nanoparticles can be readily carbonized at 500 °C in inert atmosphere (argon), subsequently the formed carbon as protecting coating on the surface of TiO2 nanocrystals to prevent nanocrystals from aggregation. In addition, the amorphous TiO2 was simultaneously transformed into anatase TiO2 after 500 °C calcination. The carbon shell on the surface of anatase TiO2 nanocrystals can be readily removed by calcination at relative low temperature (400 °C) in air. At last the carboxyl-terminated polymers, such as PMMA-COOH or PEG-COOH, were chosen as functional ligands for the surface modification of anatase TiO2 nanocrystals

to

fabricate

core@shell

anatase

TiO2@polymer

colloidal

nanocrystals. The sizes of anatase TiO2 nanocrystals can be also tuned by adjusting the molar ratio of TTIP precursors to pyridine units.

EXPERIMENTAL SECTION Materials.

All chemicals for the synthesis of liquid crystalline polyamides

(LCPA) were procured from Aladdin Co. (China). N-methyl-2-pyrrolidone (NMP), tetrahydrofuran (THF) and pyridine (Py) were purified by distilling with calcium hydride under reduced pressure. Titanium(IV) isopropoxide (TTIP, ≥ 97.0%) were purchased from Sigma-Aldrich without further purification. Carboxyl-terminated poly(methyl methacrylate) (PMMA-COOH, Mn=5600 g/mol; PDI=1.05) and carboxyl-terminated poly(ethylene glycol (PEG-COOH, Mn=4600 g/mol; PDI=1.12) were purchased from Polymer Source Inc. All other reagents were purified by common purification procedures. Characterizations.

Thin KBr pellets of monomer and polymers were employed

to record their FTIR spectra at room temperature, using Protégé 460 FTIR 5



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Spectrometer manufactured by Nicolet. NMR spectra were recorded at room temperature using BRUKER Spectrometer operating at 300.13 MHz for 1H and at 75.47 MHz for

13

C NMR spectra. The used solvent were deuterated trifluoroacetic

acid (TFA-d), dimethyl sulfoxide (DMSO-d6) and CDCl3. The crystalline architectures of all the samples were characterized by X-ray diffraction (XRD; SCINTAG XDS-2000, Cu Kα radiation). The polymeric shell weight fraction of core@shell anatase TiO2@polymer colloidal nanocrystals was determined by thermogravimetric analysis (TGA; TA Instrument TGA Q 50). Morphology of amorphous

TiO2/polyamides

nanocomposites,

carbon-coated

anatase

TiO2

nanocrystals, and core@shell anatase TiO2@polymer colloidal nanocrystals were measured by transmission electron microscope (JEOL 1200EX TEM; operated at 80 kV). The preparation method of TEM samples: (a) amorphous TiO2/polyamides composites was firstly hot-pressed into the bulk, and then TEM samples were prepared by using microtome (ULTRACUT E, Reichert-Jung) and the prepared TEM samples are below 100 nm thickness; (b) TEM samples of carbon-coated anatase TiO2 nanocrystals were prepared by using a drop of nanocrystals ethanol solution that was prepared by ultrasonically dispersing onto a carbon coated copper TEM grid, and then allowed ethanol to evaporate at room temperature; (3) TEM samples of core@shell anatase TiO2@polymer colloidal nanocrystals were prepared by utilizing a drop of anatase TiO2@polymer colloidal nanocrystals toluene (PMMA) or dichloromethane (PEG) solution (∼10 µL at c=1 mg/mL) onto a carbon coated copper TEM grid, and then allowed solvent to evaporate at room temperature. In order to characterize polymeric shell of anatase TiO2@polymer colloidal nanocrystals, the polymeric shell (PMMA or PEG) were stained with ruthenium tetraoxide (RuO4) by exposing to the TEM grids to RuO4. In addition, the energy dispersive spectroscopy (EDS) 6


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microanalysis of all the samples was measured by field emission scanning electron microscopy (FE-SEM; FEI Quanta 250). Monomer Preparation. The novel dicarboxylic acid with pyridine rings was synthesized via a two-step reaction.37 3,5-pyridinedicarboxylic acid chloride was firstly prepared via 3,5-pyridinedicarboxylic acid and bis(trichloromethyl) carbonate as reactants, DMF as catalyst in THF in an ice-bath for 1.5h under magnetic stirring. Secondly, the 3,5-pyridinedicarboxylic acid chloride was slowly added into a solution of para aminobenzoic acid in NMP in an ice-bath, and the mixture was reacted for 3h. After that, the reaction mixture was poured into methanol to precipitate the final product. The precipitate was separated by filtration, washed well successively with methanol and water and dried at 80 °C for 12 h under vacuum. The whole synthesis process was shown in Scheme S1. Preparation amorphous

of

Amorphous

TiO2/polyamides

TiO2/Polyamides

nanocomposites

were

Nanocomposites. prepared

via

The direct

polycondensation reaction (Scheme S2) of 3,5-bis[(4-carboxyanilino) carbonyl] pyridine and undecanedioic amide.38 3,5-bis[(4-carboxyanilino) carbonyl] pyridine, undecanedioic amide, triphenyl phosphite, NMP and TTIP precursors were added into a dry 250 mL three-necked round bottom flask which was equipped with a magnetic stirrer and a condenser pipe (the molar ratio of TTIP as precursor to pyridine ring= 1:1). The reaction mixture was heated under reflux in an oil bath at 100 °C for 6 h. Finally, the composite solution was slowly poured into cold methanol under vigorous stirring upon which precipitates of amorphous TiO2/polyamides nanocomposites immediately formed. The crude precipitates were washed by methanol and water successively, and then dried in a vacuum oven at 80 °C to constant weight (yield: 93.2%). 7



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Preparation of Carbon-Coated Anatase TiO2 Nanocrystals.

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The amorphous

TiO2 nanoparticles embedded into LCPA with pyridine units as functional matrix can be transferred into anatase TiO2 nanocrystals under calcinations at 500 °C in argon (2h), at the same time, and the outer polyamide capping on the surface of amorphous TiO2 nanoparticles was calcinated into carbon as protecting shell (yield: 89.6%). During the calcination, carbon coating as shell on the surface of anatase TiO2 nanocrystals can prevent nanocrystals aggregation. Fabrication of Anatase TiO2 Nanocrystals without Carbon Coating. After core@shell anatase TiO2@carbon nanocrystals were prepared, the carbon coating of these nanocrystals can be removed by calcinations at 400 °C in air (5h). Due to the thermodynamically stable crystalline architecture, the shapes of anatase TiO2 nanocrystals are stable after calcination at 400 °C in air. After removing carbon coating, the color of nanocrystals is changed to gray (yield: 95.2%). Fabrication of Core@Shell Anatase TiO2 @Polymer Colloidal Nanocrystals. After the carbon coating on the surface of anatase TiO2 nanocrystals was removed by calcinations at 400 °C in air, anatase TiO2 nanocrystals (100mg) were dispersed into 100 mL of toluene by ultrasonic instrument for 3h, and then end-carboxyl polymers as ligands (e.g., PMMA-COOH, 400mg) were added into the toluene solution for other 3h ultrasonic dispersion. After ultrasonic dispersion, the surface of anatase TiO2 nanocrystals can be capped by functionalized polymers as polymeric ligands, and then the final anatase TiO2 nanocrystals capped by PMMA as polymeric shell (e.g., anatase TiO2@PMMA colloidal nanocrystals) can be obtained. The centrifuging can be used to remove the excess polymeric ligands (12000 rpm, 10min). Attributed to the PMMA shell on the surface of anatase TiO2 nanocrystals, they can be uniformly dispersed into organic solvent (e.g., toluene) (yield: 84.5%). With polymeric ligands as shell 8


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changing from PMMA-COOH to PEG-COOH, the solvent can be changed to dichloromethane, and the other conditions are kept fixed.

RESULTS AND DISCUSSION

Scheme 1. Schematic stepwise representation of the fabrication process to core@shell polymeric ligand-capped anatase TiO2 nanocrystals (anatase TiO2@polymer colloidal nanocrystals) via using liquid crystalline polyamides (LCPA) with pyridine rings as functional matrix.

As shown in Scheme S1, 3,5-bis[(4-carboxyanilino) carbonyl] pyridine (BCACP) as new monomers were synthesized by using a two-step reaction of one equivalent of 3,5-pyridinedicarboxylic acid with two equivalent of para aminobenzoic acid. The chemical structures of 3,5-bis[(4-carboxyanilino) carbonyl] pyridine were characterized and confirmed by FT-IR, 1H and

13

C

NMR analyses (Figure S1, Figure S2 and Figure S3). The new liquid crystalline polyamides (LCPA) containing pyridine rings were synthesized by 9



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the direct polycondensation reaction of an equimolar mixture of diacids BCACP and undecanedioic amide in a medium consisting of NMP and triphenyl phosphite (TPP) (Scheme 1 and Scheme S2). The entire polycondensation reaction readily proceeded in a homogeneous solution. In addition, it is worth noting that the polymerization reaction solvent can dissolve TTIP (precursor of TiO2 nanoparticles). The reaction mixture was heated under reflux in an oil bath at 100 °C for 6 h. The chemical structures of LCPA were also characterized and confirmed by FT-IR, 1H and

13

C NMR analyses shown

in Figure S4, Figure S5 and Figure S6, respectively. During the synthesis process of LCPA, TTIP precursors can be absorbed into LCPA matrix by coordination bonds between pyridine rings and precursors, and LCPA can provide the frameworks and matrix to uniformly disperse precursors of TiO2 to prevent from aggregation of precursors, because of its rigid and crystalline polymer chain structures.33,34 After that, the TTIP as precursor of TiO2 was in situ reacted to amorphous TiO2 nanoparticles that were encapsulated into LCPA functional matrix. TEM measurements were conducted to investigate and confirm the structures of amorphous TiO2/polyamides nanocomposites. The dark dots in the TEM images correspond to TiO2 nanoparticles dispersed into polyamide matrix (Figure 1), and the average diameter is 10.9 ± 1.4 nm. In addition, in order to confirm the crystalline phase structure, X-ray diffraction (XRD)

measurement

was

used

to

characterize

TiO2/polyamides

nanocomposites, and the diffraction pattern was illustrated in Figure 2(D-a). According to XRD pattern, no obvious diffraction peak can be located, 2θ from 20° to 100°, signifying the amorphous structure of the TiO2 nanoparticles.

10


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Figure 1. Representative TEM images of TiO2 nanoparticles encapsulated into LCPA functional matrix (A: scale bar=200 nm; B: scale bar=100 nm). The digital image of amorphous TiO2/polyamides nanocomposites as the inset in B.

In Scheme 1, the outer matrix polyamide coating on the surface of amorphous TiO2 nanoparticles can be readily carbonized at 500 °C in an argon atmosphere, and the formed carbon coating on the surface of TiO2 nanocrystals can be acted as a protecting layer to prevent TiO2 nanocrystals from aggregation to merge into larger particles.39 At the same time, the crystalline architecture of TiO2 nanoparticles was transformed into anatase TiO2 nanocrystals after 500 °C calcination. TEM measurements were used to characterize the morphology of anatase TiO2 nanocrystals coated with carbon, as illustrated in the TEM image in Figure 2(A). Based on the representative image, comparing with TiO2 nanoparticles before and after high temperature calcinations, nonuniform dimension distribution of particles is attributed to irregular carbon coating on the surface of TiO2 nanocrystals. The architecture of anatase TiO2 nanocrystals with carbon coating can be further characterized more clearly by high resolution TEM (HR-TEM), the crystal lattices of anatase TiO2 nanocrystals were clearly demonstrated in Figure 2(B). The average lattice spacing of 11



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0.35 nm (marked in the Figure 2(B)) corresponds to the (101) plane of anatase TiO2.40 According to TEM image, the average diameter of anatase TiO2 nanocrystals coated with carbon is about 10 nm. X-ray diffraction (XRD) characterization is also used to confirms the crystalline structure of anatase TiO2 nanocrystals, and the result was shown in Figure 2(D-b). Based on the result of XRD characterization, strong diffraction peaks can be clearly observed. The different peaks at scattering angles (25.31°, 37.91°, 48.10°, 53.96°, 55.11°, and 62.72°) can be assigned to the different diffraction (101), (004), (200), (105), (211) and (204) crystal planes of anatase TiO2, respectively.25 These peaks are characteristic as the anatase crystalline phase structure of TiO2 (JCPDS card no. 21-1272), and the XRD pattern shows almost 100% crystallinity (98.5%) of anatase phase.17,41 Besides XRD, energy dispersive spectroscopy (EDS) microanalysis is also utilized to confirm the composition of anatase TiO2 nanocrystals with carbon coating, as shown in Figure S7(A).

12


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Figure 2. Representative TEM images and XRD patterns of TiO2 nanoparticles. (A) TEM image of anatase TiO2 nanocrystals coated with carbon layer (scale bar=100 nm). (B) HR-TEM image of anatase TiO2 nanocrystals coated with carbon layer (scale bar=5 nm). (C) TEM image of anatase TiO2 nanocrystals after removing carbon coating (scale bar=100 nm). (D) XRD patterns of amorphous TiO2/polyamides nanocomposites (a) and the anatase TiO2 nanocrystals coated with carbon layer (b).

For preparing final core@shell anatase TiO2@polymer colloidal nanocrystals, the removing of carbon coating of anatase TiO2 nanocrystals is necessary. The removal of carbon coating can be carried out by calcination at relative low temperature (400 °C) in air. Due to the thermodynamically stable crystalline phase, the anatase TiO2 nanocrystals can almost keep the same shapes after calcination at 400 °C in air.12 With the removing of carbon coating, the color of anatase TiO2 nanocrystals powder changed from black to gray as shown in insets of Figure 2 (Figure 2(A) and Figure 2(C)). In order to compare with the morphologies, TEM characterization of anatase TiO2 nanocrystals was also conducted after the removing of carbon coating (Figure 2(C)). Based on the TEM image, comparing with the anatase TiO2 nanocrystals coated with carbon, the nanocrystals are uniform, and the average diameter is about 9 nm. In order to further confirm the composition of nanocrystals, energy dispersive spectroscopy (EDS) microanalysis was also applied to characterize anatase TiO2 nanocrystals before and after removing of carbon coating (Figure S7). According to the EDS spectra, the carbon coating was almost completely removed after calcining at 400 °C in air for 5h. These anatase TiO2 nanocrystals after removing of carbon coating can be used to further fabricate core@shell anatase TiO2@polymer colloidal nanocrystals by the 13



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surface modification, the end-functionalized polymers (e.g., carboxyl-terminated PMMA (PMMA-COOH) or PEG (PEG-COOH)) as functional macromolecular ligands.42 As a kind of strong ligand, carboxylic acid-functionalized ligands can be absorbed on the surface of inorganic nanocrystals by coordination bond between carboxyl group and surface metal atom of inorganic nanocrystals to form compact comb-like structure, especially for transition metal oxides.43-46 First, the fabrication of the core@shell anatase TiO2@PMMA colloidal nanocrystals is used as an example to show the strategy depicted in Scheme 1, the PMMA-COOH as macromolecular ligands. The toluene was used as solvent to disperse anatase TiO2 nanocrystals by ultrasonic instrument. After that, PMMA-COOH as polymeric ligands was added in the toluene solution. After ultrasonic dispersion, the surface of anatase TiO2 nanocrystals can be absorbed by end-functionalized polymers to form the final core@shell anatase TiO2@PMMA colloidal nanocrystals. Owing to PMMA polymeric ligands capping on the surface anatase TiO2 nanocrystals, comparing with the immediate precipitation of anatase TiO2 nanocrystals without any macromolecular ligands from toluene solution, the core@shell anatase TiO2@PMMA colloidal nanocrystals could be readily dispersed into toluene solvent (Figure 3(B)). TEM measurements were used to characterize the morphology of core@shell anatase TiO2@PMMA colloidal nanocrystals, and the representative TEM image was shown in Figure 3(A). On the basis of TEM image, the average size of anatase TiO2 nanocrystals is 9.1±1.1 nm (Figure 3(A)), and the size distribution of anatase TiO2 nanocrystals is shown in Figure S8. Comparing with amorphous TiO2 nanoparticles, the average diameter is smaller due to the crystalline formation of from amorphous structure to anatase phase.12 In addition, for further confirming the structures of the core@shell anatase TiO2@PMMA colloidal nanocrystals by TEM measurement, 14


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PMMA ligands as organic shell is stained by ruthenium tetraoxide (RuO4).47-49 The clear PMMA domain can be observed in Figure 3(B), the average size of the thickness is 8.2 ± 1.2 nm based on TEM result. The existence of PMMA shell on the surface of anatase TiO2 nanocrystals were further characterized by 1H-NMR and TGA, shown in Figure S9 and Figure S10. In addition, with macromolecular ligands changed from PMMA to PEG, water-dispersed anatase TiO2 colloidal nanocrystals (i.e., core@shell anatase TiO2@PEG colloidal nanocrystals) can be obtained by the same method (Figure S11 and Figure S12). It is worth noting that the sizes of anatase TiO2 nanocrystals can be also adjusted by changing the molar ratio of precursors to pyridine units during the preparation of LCPA. For example, with the molar ratio of TTIP to pyridine unit changed from 1:1 to 10:1, the average diameter of anatase TiO2 can be adjusted to 19.5 ± 2.3 nm when other conditions fixed (Figure S13 and Figure S14).

Figure 3. Representative TEM images of core@shell anatase TiO2@PMMA colloidal nanocrystals (A: scale bar=100 nm; B: scale bar=200 nm). (A) Inset: digital image of core@shell TiO2@PMMA colloidal nanocrystals. (B) TEM image after PMMA macromolecular shell was stained by RuO4 (scale bar=200 nm); Insets: digital images of toluene solution of anatase TiO2 nanocrystals after removal of carbon coating (a) 15



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and core@shell anatase TiO2@PMMA colloidal nanocrystals (b). CONCLUSION In conclusion, an unconventional but robust route to synthesize anatase TiO2 colloidal nanocrystals with tunable surface chemistry and dimensions via liquid crystalline polyamides (LCPA) with pyridine rings as functional matrix is reported. Titanium(IV) tetraisopropoxide (TTIP), as the precursor of TiO2 nanocrystals, was selectively incorporated into the compartment containing pyridine ring units via coordination interaction between pyridine rings and precursors, following by in situ direct polycondensation reaction of two monomers with TTIP into amorphous TiO2 nanoparticles encapsulated into LCPA matrix. The functional polyamide chains capping on the surface of TiO2 nanoparticles can be readily carbonized at 500 °C in argon atmosphere. After that, the formed carbon can be acted as protecting coating on the surface of TiO2 nanocrystals to prevent nanocrystals from aggregation. In addition, the amorphous TiO2 was simultaneously transformed into anatase TiO2 after 500 °C calcination. The carbon shell on the surface of anatase TiO2 nanocrystals can be readily removed by calcination at relative low temperature (400 °C) in air. Finally, the carboxyl-terminated polymers, such as PMMA-COOH or PEG-COOH, were chosen as functional ligands for the surface modification of anatase TiO2 nanocrystals to fabricate core@shell anatase TiO2@polymer colloidal nanocrystals. The sizes of anatase TiO2 nanocrystals can be also tuned by adjusting the molar ratio of TTIP precursors to pyridine units. Hence, we envision that other functional inorganic@organic core@shell colloidal nanocrystals with novel and desirable properties can be also fabricated by

16


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LCPA with pyridine units as functional matrix approach for use in electronics, sensors, catalysts, magnetic devices and other areas.

Acknowledgements The work was financially supported by the National Key Research and Development

Program

Foundation

for

of

China

Excellent

(2017YFB0307605), Youth

University (1421320045, to Peng Fu),

Scholars

Special of

Science

Zhengzhou

the National Science Foundation for

Young Scientists of China (Grant No.51703206, to Zhe Cui), Postdoctoral Fund of Henan Province (Grant No.2014004, to Zhe Cui), Key scientific and technological project of Henan province (Grant No.152102310070, to Zhe Cui) and 1000 Young Talent (to Xinchang Pang). Supporting Information. Summary of characterization data for the final core@shell anatase TiO2@polymer colloidal nanocrystals and intermediates: 1H-NMR, 13C-NMR FT-IR, TGA, EDS, TEM and digital images. This information is available free of charge via the Internet at http://pubs.acs.org.

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Unconventional Strategy to Anatase TiO2 Nanocrystals with Tunable

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