Journal of Colloid and Interface Science 432 (2014) 229–235

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Journal of Colloid and Interface Science

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Facile synthesis and characterizations of copper–zinc-10,15,20-tetra(4-pyridyl) porphyrin (Cu–ZnTPyP)coordination polymer with hexagonal micro-lump andmicro-prism morphologies

http://dx.doi.org/10.1016/j.jcis.2014.07.0050021-9797/� 2014 Elsevier Inc. All rights reserved.

⇑ Corresponding author at: Key Laboratory of Industrial Ecology and Environ-mental Engineering, School of Environmental Science & Technology, DalianUniversity of Technology, Dalian 116024, China.

E-mail address: xyli@dlut.edu.cn (X. Li).

Zhiguang Zhang a,b,c, Xinyong Li a,b,d,⇑, Qidong Zhao a,b, Jun Ke a,b, Yong Shi a,b,Pancras Ndokoye a,b, Lianzhou Wang d

a Key Laboratory of Industrial Ecology and Environmental Engineering, School of Environmental Science & Technology, Dalian University of Technology, Dalian 116024, Chinab State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian 116024, Chinac School of Chemistry and Chemical Engineering, Liaoning Normal University, Dalian, Liaoning 116029, Chinad ARC Centre of Excellence for Functional Nanomaterials, School of Chemical Engineering, The University of Queensland, St Lucia, Brisbane, Queensland 4072, Australia

a r t i c l e i n f o

Article history:Received 29 April 2014Accepted 7 July 2014Available online 11 July 2014

Keywords:PorphyrinSurfactantInfinite coordination polymerGrowth mechanismLight absorption property

a b s t r a c t

Cu–ZnTPyP coordination polymer with hexagonal micro-lump and micro-prism morphologies has beensuccessfully synthesized through a facile surfactant assisted self-assembly method based on Cu(OAc)2-

�2H2O and Zinc-5,10,15,20-tetra(4-pyridyl) porphyrin (ZnTPyP) in DMF/H2O solvent. The morphologiesof three-dimensional micro-prisms and micro-lumps obtained at different concentrations of cetyltri-methylammonium bromide (CTAB) were investigated by scanning electronic microscopy. The composi-tions of the micro-prisms were studied by energy-dispersive spectra and inductively coupled plasma-atomic emission. X-ray diffraction analysis revealed a circular hexametric cage structure cross-linkedby the main Zn–N axial coordination of the pyridyl ligands inside the micro-scale coordination polymers.The UV–Vis diffuse reflection spectroscopy revealed the formation of J-type aggregates in the both micro-structures. The formation mechanism of Cu–ZnTPyP coordination polymer structure was investigated byvarying CTAB concentration. Their surface photovoltage spectra indicated that the novel hexagonalmicro-prism morphology of the coordination polymer displayed enhanced photo response under visiblelight, which is beneficial for exploiting the practical application of Cu–ZnTPyP compound.

� 2014 Elsevier Inc. All rights reserved.

1. Introduction

Functional nanomaterials by means of self-assembly havebecome a cutting-edge research of material fabrication [1]. Infinitecoordination polymers (ICPs) are considered as a unique class ofinorganic–organic hybrid materials with metal centers and organiclinkers [2], which is one of the important hybrid functional nanom-aterials. Researchers have shown considerable interest in thosehybrids due to their chemically adjustable porosities and highinternal surface areas. As their microstructures can be deliberatelyand easily modified, the ICPs have gained growing attention inpotential applications such as gas storage [3] and separation [4],drug delivery [5], and catalysis [6]. The formation of various ICPs

morphologies mainly depends on the intra-molecules non-cova-lent interactions such as metal–ligand interactions [7], hydrogenbonding [8] and p–p stacking [9]. In comparison with metalorganic frameworks (MOFs), these ICPs exhibit a higher level ofstructural tailorability, including size and morphology-dependentproperties.

Recently, some groups demonstrated that nano- and micro-scaled particles based on ICPs could be synthesized by using vari-ous processes, including solvothermal [10] and self-assembly [11].For example, Mirkin and coworkers took advantage of bis-metallo-tridentate Schiff base ligands and metal acetates to prepare nano-sized ICPs. However, the nano-scale ICPs of transition metalsappear to be still limited to small molecular ligands, namely 1,4-benzenedicarboxylate (BDC) and 2,6-bis[(4-carboxyanilino)car-bonyl] pyridine.

Porphyrin and its derivative compounds, as a kind of largep-conjugated compounds, have become the class of promisingorganic building blocks due to their diversity functional groups

230 Z. Zhang et al. / Journal of Colloid and Interface Science 432 (2014) 229–235

and unique optoelectronic properties. To the best of our knowledge,the fabrication of novel ICPs using porphyrins as macrocyclic molec-ular ligands is of fundamental significance. Meso-pyridyl attachedporphyrins, such as the 5,10,15,20-tetra(4-pyridyl) porphyrin andZinc-5,10,15,20-tetra(4-pyridyl) porphyrin derivatives, have beenutilized in the construction of metal organic frameworks andmulti-porphyrin arrays [12–15], because of the central metal–Naxial coordination bonding interaction. In recent years, the designand synthesis of well-defined ICPs with porphyrin building blockshas become a very attractive topic in scientific research. Huangand coworkers [16] have reported the synthesis of nano-plates andmicro-spindles nanostructures by using copper-tetrapyridylporph-yrin coordination polymers (CuTPyP). The suggested growth mech-anism reveals that the formation of micro-spindles could beachieved from the interaction between the central coordinationand peripheral pyridyl functional groups in porphyrin molecules.Li and coworkers [17] reported the adjustment of reaction tempera-tures as a key factor for Zn(OAc)2 reaction with 5,10,15,20-tetra(4-pyridyl) porphyrin (H2TPyP) in DMF in order to form micro-prismsand micro-octahedral ICPs through Zn–N axial coordination of thepyridyl ligand. However, the synthesis of micro-prisms and micro-lamps ICPs using the Cu–Zn tetrapyridylporphyrin remains a greatchallenge and the formation mechanism is still unclear.

In this work, porphyrin ICP structures are fabricated based oncopper–zinc tetrapyridylporphyrin (Cu–ZnTPyP) with the assis-tance of cetyltrimethylammonium bromide (CTAB), a cationic sur-factant, in DMF/H2O solvent. The effect of CTAB concentration ongrowth and morphology control of three-dimensional (3D)micro-prisms and micro-lamps of the ICPs is systematically inves-tigated. Chemical compositions, crystal structures, and morpholo-gies of these samples are characterized by means of EDX, ICP,ESR, XRD and SEM. Meanwhile, the photo response properties ofthese ICPs are studied by UV–Vis absorption and surface photovolt-age spectroscopies.

2. Experimental section

2.1. Materials and methods

2.1.1. MaterialsZinc-10,15,20-Tetra(4-pyridyl) porphyrin (ZnTPyP, >99.9%) was

purchased from Aldrich. Copper(II) acetate monohydrate, N,N-Dimethylformamide (DMF) and CTAB were purchased from Sinop-harm Chemical Reagent Co. Ltd. (Shanghai, China). All reagentswere analytical grade and used without further purification.

Scheme 1. A reaction scheme for the preparation procedures of micro-lump andmicro-prism coordination polymer particles.

2.1.2. MethodsThe structures of the Cu–ZnTPyP hexagonal micro-lumps and

micro-prisms were determined by X-ray diffraction (XRD, RIGAKU,Dmax22000) with Cu Ka radiation (k = 0.15418 nm) over the 2hrange of 5–30�. The morphologies were observed by scanning elec-tronic microscopy (SEM, JEOLJSM-6360 LV electron microscopeoperating) with an accelerating voltage of 30.0 kV, and the compo-sitions were examined by energy-dispersive spectroscopy (EDS).The determination of elements in the samples was performed onan inductively coupled plasma-atomic emission spectrometer(PerkinElmer, Optima 2000DV). The light absorption propertieswere measured using a UV–Vis diffuse reflectance spectrophotom-eter (JASCO, UV-550) with a wavelength range of 200–800 nm. Theseparation and transfer behaviors of the photo-generated chargecarriers in the samples were investigated using a lock-in-basedsurface photovoltage (SPV) measurement system, which consistsof a monochromator (model Omni-k 3005) and a lock-in amplifier(model SR830-DSP) with an optical chopper (model SR540) run-ning at a frequency of 20 Hz. All of the SPV measurements were

performed at room temperature. Electron paramagnetic resonance(ESR) spectra were taken on a Bruker ECS106 X-Band spectrometerusing the modified operation procedure. Typical experimental con-ditions were frequency 9.865 GHz, temperature 298 K, modulationamplitude 1.00 G, microwave power 20 mW, conversion time5.12 ms, time constant 1.28 ms, resolution 5000 pts, and averageof 10 scans. The pore structure of obtained samples was character-ized by N2 adsorption using an adsorption apparatus (Quanta-chrome NOVA Instruments V 2.2 gas sorption analyzer). Specificsurface area of the samples was determined from the Brunauer–Emmett–Teller (BET) equation, and pore volume was determinedfrom the total amount adsorbed at relative pressures near unity.

2.2. Preparation of Cu–ZnTPyP hexagonal micro-lumpsand micro-prisms

Cu–ZnTPyP hexagonal micro-lumps were obtained via a facilesurfactant assisted self-assembly (SAS) method [18]. 5 mM, 2 mLof acetic solution of zinc meso-tetra (4-pyridyl) porphyrin(ZnTPyP) was added into 16 mM 60 mL of copper acetate solutiondrop by drop in the presence of CTAB (10 mM) under vigorous stir-ring at room temperature. The color of the mixture became brownred and then turbid under stirring for few seconds at room temper-ature. After stirring for 15 min, the product was kept overnight.The as-obtained purple precipitate was centrifuged and washedby using deionized water for several times to remove the remain-ing and unreacted surfactants. The final product was dried in a vac-uum box at 60 �C for 6 h. Cu–ZnTPyP hexagonal micro-prisms werefabricated through the same procedures but with a different CTABconcentration (40 mM) (see Scheme 1).

3. Results and discussion

3.1. SEM and EDX characterizations

The morphologies of the as-obtained Cu–ZnTPyP micro-lumpsand micro-prisms are shown in Fig. 1a and c. The micro-lumpssample with 850 nm in side length and about 900 nm in height(the inset in Fig. 1a) was fabricated under low concentration ofCTAB (10 nM). We could observe that the smoothness of sidesand bottoms of the hexagonal lumps are apparently different,which could be caused by the surfactant coordination interactions.Apart from the concentration of CTAB, the micro-prism samples

Fig. 1. SEM and EDX images of Cu–ZnTPyP micro-lumps (a and b) and Cu–ZnTPyP micro-prisms (c and d).

Z. Zhang et al. / Journal of Colloid and Interface Science 432 (2014) 229–235 231

were synthesized under the same conditions. When the concentra-tion of CTAB was increased from 10 mM to 40 mM, we observeduniform and regular hexagonal micro-prisms with a typical sidelength of about 400 nm and a typical edge length of about4.5 lm as shown in Fig. 1c. Meanwhile, it could be observed thatthe hexagonal base of micro-prism sample is smoother than thatof micro-lumps at the surface, which indicates CTAB could adjustthe coordination reaction rate and facilitate the formation ofsmooth surface. Furthermore, the micro-sized samples could pos-sess large surface area and small pore sizes (Fig. S1 and Table S1,in supporting information), which is beneficial for their applica-tions in catalysis, separation, and storage.

The chemical compositions of these two samples were mea-sured by using EDX. As shown in Fig. 1b and d, both samples con-tain C, N, Zn, Cu elements. The ratio of N to Zn corresponding tomicro-lumps and micro-prisms is 35.8 and 36, which are as higheras 4.48 times and 4.5 times than that in the initial reagents (N:Zn = 8). It is clear that, the increase in ratio is ascribed to the intro-duction of CTAB, which indicates that CTAB took part in the forma-tion of the samples. The observed ratios of Zn to Cu in thecorresponding samples are 13 and 5.14, respectively. Althoughthe ratio of Zn to Cu is 0.01 at the initial stage, it dramaticallyincreased in the final samples, suggesting the majority of copperions did not react with ZnTPyP. When the concentration of CTABwas increased from 10 mM to 40 mM, the ratio of Zn to Cudecreased from 13 to 5.14, which demonstrates CTAB could pro-mote the coordination reaction between Cu2+ and ZnTPyP. Besides,oxygen element shown in EDX may be attributed to the residualacetate and solvent. The characterization by the inductively cou-pled plasma-atomic emission spectrometer further showed thatthe ratios of Zn to Cu in Cu–ZnTPyP hexagonal micro-lumps andmicro-prisms are 11.8 and 6.1, respectively, which is consistentwith the results of EDX.

3.2. XRD patterns

The internal structures of the Cu–ZnTPyP micro-ICPs, hexagonalmicro-lumps and micro-prisms were investigated by using XRDcharacterization. As shown in Fig. 2, the Cu–ZnTPyP hexagonal

micro-lumps and micro-prisms exhibit similar XRD patterns (curvea), which are different from the previously reported CuTPyP micro-spindles (curve d) [16]. By comparing with previous reports, wefind that the XRD patterns for the two synthesized micro-struc-tures match the simulated XRD patterns on the basis of the crystalstructure of ZnTPyP obtained by Goldberg et al. (CCDC ref. codeYOVTOS), which indicates the similar internal structures of thetwo microstructures correspond to the single crystals with thespace group R3 and unit cell dimensions of a = b = 33.110 Å,c = 9.374 Å, a = b = 90� and c = 120� [19]. In these microstructures,the zinc atom at the center of ZnTPyP should be six-coordinatedto four pyrrole nitrogens of the porphyrin core and two pyridylN-atoms of the other porphyrin molecules, which approach fromboth sides of the molecular framework [20].

The characteristic peak attributed to (220), which is designatedfrom the ZnTPyP simulated pattern, is remarkably intense for theCu–ZnTPyP hexagonal micro-lumps and micro-prisms. This featureindicates that ZnTPyP molecules in the Cu–ZnTPyP hexagonalmicro-lumps and micro-prisms are favorably grown along thecrystallographic c axis [21]. Meanwhile, the XRD patterns of theCu–ZnTPyP hexagonal micro-lumps and micro-prisms are differentfrom that of Cu–TPyP, indicating that Cu is not a predominant coor-dinating atom because the reaction is dominated by the coordina-tion between pyridyl group and Zn ion.

3.3. ESR spectra

According to the electrons layout of copper atom, there is a sin-gle unpaired electron existing in Cu(II). The chemical states of cop-per ions in the as-prepared solid samples could be measured byusing ESR tool [22–24]. Fig. 3 shows ESR spectra of Cu–ZnTPyPmicro-lumps and micro-prisms taken at room temperature. Theapparent peaks observed in the two coordination polymers areattributed to Cu(II) ions. However, compared with the previousstudies on the ESR of copper in solid samples, hyperfine splittingpeaks of Cu(II) ions are not observed, which might be due to thehigh concentration of Cu(II) ions in coordination polymer samples.When Cu(II) ion is located in crystal field as a highly dispersionform, the hyperfine splitting peaks could be measured. High

Fig. 2. The XRD patterns of the simulated pattern (a) based on the published crystal structure data of ZnTPyP (CCDC ref. code: YOVTOS) [17], the Cu–ZnTPyP micro-lumps (b),the Cu–ZnTPyP micro-prisms (c) and the Cu-TPyP micro-spindles (d) [14].

Fig. 3. The ESR Spectra of Cu–ZnTPyP micro-lumps and micro-prisms at roomtemperature.

232 Z. Zhang et al. / Journal of Colloid and Interface Science 432 (2014) 229–235

concentration of Cu ions in solid samples results in the broad peakand the disappearance of hyperfine splitting peaks due to thesevere interference among Cu(II) ions. It reveals the significant roleof these two different coordination polymers with high concentra-tions of Cu(II) ions in the formation of the unique morphologies,which is consistent with the results of EDX.

3.4. Morphology modulation

It was found that, the absence of copper ions led to transparentsolution of ZnTPyP or ZnTPyP–CTAB and complete failure of ICPstructures formation overnight. When adding copper ions intothe solution, apparent precipitations formed even without CTAB.A large quantity of suspending precipitate was observed immedi-ately when ZnTPyP was rapidly added into the aqueous solutionof CuAc2 under stirring during the feed-in process. As shown inFig. 4a, some of the obtained samples have a morphology of imper-fect hexagonal micro-prisms, which further reveals the drivingforce of coordination between Cu ions and porphyrin moleculesin micro-prisms formation. Moreover, some defect sites existingon the surface of the as-prepared particles and their morphologiesare not uniform. The result shows that the reaction was finished ina short time due to the fast coordination rate between ZnTPyP andCu2+ ions.

As it is known, the morphology and size parameters can beinfluenced by many factors, among which the surfactant could pro-vide a soft template, which plays an important role in modifying

the size and morphology [25]. The surfactant is a surface-activeagent that can adjust the growth speed of nanostructures, andmay induce the assembly by decreasing the surface energy [26].Thus, in this work, we also investigated and discussed the effectsof CTAB surfactant on the formation of Cu–ZnTPyP ICP structures.

The FE-SEM images in Fig. 4b and c show that the porphyrin ICPstructures prepared with 10 mM CTAB are hexagonal micro-lumpswith about 850 nm in average side length and about 900 nm in theaverage edge length. In order to control the coordination ratebetween porphyrin molecules and Cu ions, different concentra-tions of CTAB were added. As shown in Fig. 4d and e, when the con-centration of CTAB is increased to 20 mM, the morphology ofparticles becomes smooth on the surface of hexagonal micro-lumps. This result establishes the conclusion that the increase inCTAB concentration could reduce the defects on the surface of hex-agonal micro-prisms and suppress the growth of section. As isknown, the surfactant is an effective active agent that can reducethe growth speed of nanostructures, and may induce a more mod-erate assembly by decreasing the surface energy [27], presumablydue to a growth process of Cu–ZnTPyP ICPs prompted by surfac-tant-assisted self-assembly of ZnTPyP intermolecular and ZnTPyPmolecules with ions Cu2+.

When the concentration of CTAB is increased to 40 mM, regularhexagonal micro-prisms with a typical side length of about 400 nmand a typical edge length of about 4.5 lm are obtained (Fig. 4f). Theresults indicate that with the increase in CTAB concentration, par-ticle morphology evolves from imperfect hexagonal micro-lumpsto regular hexagonal micro-prisms. Therefore, it suggests that theincrease in CTAB concentration to a certain high level could sup-press the growth of section cross, promote the prolongation ofthe micro-prism in the axial direction and thus retard the fastaggregation and coordination process of ZnTPyP molecules withCu2+. With the addition of an appropriate amount of CTAB, regularand ordered 3D Cu–ZnTPyP ICP microstructures can be formed inDMF/H2O due to the cross-linking ability originating from the lin-ear structure of CTAB. On the other hand, CTAB can be employed asa potential crystal face inhibitor in the reaction, which promotesthe occurrence of oriented nucleation resulting in the anisotropicgrowth of the micro-ICPs [28].

3.5. Formation mechanism

Understanding the effect of the concentration of CTAB on theICP structure and morphology is very beneficial for adjusting themorphology of the Cu–ZnTPyP ICP structure. Based on the above

Fig. 4. SEM images of the Cu–ZnTPyP hexagonal micro-lumps and micro-prisms obtained under different concentrations of CTAB: (a) without addition of CTAB; (b) and (c)[CTAB] = 10 mM; (d and e) [CTAB] = 20 mM; (f) [CTAB] = 40 mM.

Fig. 5. (a) Illustration of crystal cell of Cu–ZnTPyP hexagonal micro-lump and micro-prism: Zn, bright yellow; N, blue; C, gray; (b) Scheme of formation mechanism of Cu–ZnTPyP hexagonal micro-lump and micro-prism. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

Z. Zhang et al. / Journal of Colloid and Interface Science 432 (2014) 229–235 233

results, a schematic diagram for the growth mechanism of the Cu–ZnTPyP ICP structure is suggested in Fig. 5. The ZnTPyP moleculesbehave as tetratopic square panels with D4h symmetry, which canlead to different topologies depending upon the characteristics offoreign species connected to the donor sites of N atoms on thepanel. Formation of uniform crystal morphologies mainly resultsfrom coordinating the zinc atom at the center with the four pyrid-yls in TPyP molecule nearby. On the basis of the significance of theabove-mentioned coordination, the structure can be described asthe one consisting of a circular hexametric cage cross-linked byaxial coordination of pyridyl ligands and zinc atoms, which propa-gates in three different directions of the trigonal lattice in Fig. 5a[21]. By means of XRD analysis, it is demonstrated that copper ionscan only promote the formation of crystal morphologies, but notmodifying the unit cell. We suggest that Cu atoms primarily coor-dinate with the pyridyls outside the unit cell. In addition, Cu atomsmay participate in connecting the elemental layer-like crystal cellfor axial growth of the samples.

As observed, some hexagonal prisms with many surface defectscould be directly generated in the absence of CTAB molecules. Thesurface defects of the hexagonal prisms as shown in Fig. 1a are dueto the rapid reaction rate. It has been reported that the surfactant

micelles can dissolve porphyrin and reduce the aggregation of theporphyrin molecules [29]. Thus, additional CTAB molecules couldinhibit the fast aggregation of the pristine porphyrin moleculesand support a more moderate coordination process. During thegrowth of the Cu–ZnTPyP hexagonal micro-lumps and micro-prisms, the nucleation of the assembled layered structure of hexag-onal micro-lumps and micro-prisms is mainly driven by two kindsof nucleation process, namely the coordination with Cu ions, andthe aggregation of porphyrin molecules.

According to the previous reports, CTAB molecules could aggre-gate surrounding ZnTPyP tetratopic square panels due to thehydrophobic interaction, which hinders coordinating between Zn,Cu and N atoms in porphyrin molecules and the aggregation of por-phyrin molecules. When the concentration of CTAB in the pristinesolution is as low as 10 mM or 20 mM, the growth rates along theradial and axis directions are close, because the amounts ofadsorbed CTAB onto the micro-lumps in the two directions aresimilar.

According to previous reported papers, the increase in surfac-tant concentration in reaction mixture could efficiently lowernucleation rate and enlarge crystal sizes [30]. In the solutioncontaining both porphyrin and CTAB molecules of considerable

Fig. 6. (a) The UV–Vis absorption spectra of ZnTPyP in DMF (curve I), the UV–Vis DRS of Cu–ZnTPyP micro-lumps (curve II) and Cu–ZnTPyP micro-prisms (curve III). (b) TheSPV spectra of the Cu–ZnTPyP hexagonal micro-lumps and micro-prisms.

234 Z. Zhang et al. / Journal of Colloid and Interface Science 432 (2014) 229–235

concentration, the hydrophobic interaction between CTAB and por-phyrin is more probable and stronger from the two sides of por-phyrin plane than from the edge of porphyrin plane. As a result,due to the difference in the spatial distribution of CTAB on themicro-lumps at axis and radial surfaces, the growth along the axisdirection of the prism is more favorable than the radial direction.Thus, with the increase in CTAB concentration, the aspect ratio ofthe obtained micro-lumps will be changed. The CTAB moleculeswith enough high concentration (40 mM), could effectivelyenhance the axis coordination via inhibiting the aggregation ofpristine porphyrin in the radial direction by the solubilizationeffect. Therefore, CTAB plays an important role in the control ofmorphology as long as some difference in the surface polarity ofthe structure exists between the axis and radial directions, whichis useful to obtain ICP structures with large aspect ratio. Besides,high concentration of CTAB could be beneficial to formation ofstructures with smooth surface.

3.6. UV–Vis diffuse reflectance spectra (DRS)

UV–Vis DRS of the Cu–ZnTPyP hexagonal micro-lumps and hex-agonal micro-prisms are shown in Fig. 6a, The absorption peakaround 422 nm for ZnTPyP can be attributed to the porphyrin Soretband, while the two weak absorption peaks at 557 and 596 nm canbe assigned to the Q bands. Meanwhile, the single Soret band at422 nm for ZnTPyP in DMF splits into two bands at 433 and471 nm for the micro-lumps of Cu–ZnTPyP. Nevertheless, the twoQ bands for ZnTPyP in DMF shift to a lower energy (561 and608 nm) for the Cu–ZnTPyP micro-lumps in solution. These resultssuggest the formation of J-type aggregates with an edge-to-edgemolecular arrangement in the micro-lumps of ZnTPyP [31]. Simi-larly, the self-assembled Cu–ZnTPyP micro-prisms were observedwith a relatively weaker Soret band at 435 nm and a stronger Soretband at 470 nm as well as the red-shifted Q bands at 561 and608 nm. A broader and stronger absorption band was found forCu–ZnTPyP hexagonal micro-lumps and micro-prisms, whichcould absorb much more visible light than ZnTPyP in DMF. There-fore, a better optical absorption capability of visible light isobtained with Cu–ZnTPyP hexagonal micro-lumps and micro-prisms.

3.7. SPV property

The SPV technique can provide a rapid, nondestructive survey ofthe photo-induced change in surface potential of semiconductors[32]. Fig. 6b shows the SPV spectra of the Cu–ZnTPyP hexagonalmicro-lumps and micro-prisms. The apparent photovoltage

response under visible light demonstrates that electrons insideICPs organics semiconductor could be excited by wide-energy-range photons and become free charge carriers. Furthermore, invisible light region, the SPV value of hexagonal micro-prisms ishigher than that of micro-lumps, which may be due to the sizeeffect, thus, the larger size is beneficial for the transport of chargecarriers and decreasing the charges recombination possibility [33].The enhanced SPV response may be attributed to the expandedstructure of Cu–ZnTPyP micro-prisms, which provides much moreavailable space for the effective separation of photo-inducedcharges. The photo response properties of the obtained micro-crys-tals exhibit interesting potential applications in solar cell and sens-ing devices.

4. Conclusions

In summary, ICP structures of Cu–ZnTPyP hexagonal micro-lumps and micro-prisms were successfully synthesized. The for-mation of ICP uniform morphologies is mainly driven by the coor-dination of polymerization between ZnTPyP and Cu2+ ions. Thesolubility enhancement of CTAB suppresses aggregation of TPyPmolecules which decreases the nucleation rate and promotes thegrowth of axial length and its coordination as well. The increasein CTAB concentration provides a good template for hexagonalmicro-prism formation by hindering the coordination and aggrega-tion between porphyrin molecules. The aspect ratio of micro-prisms could be modulated through variation of CTAB as struc-ture-directing agent. Furthermore, distinguishable bands of SPVresponse generated by the Cu–ZnTPyP samples could also beobserved in the visible region. These materials might be potentiallyapplied in optoelectronic micro devices, sensors, and photocataly-sis areas.

Acknowledgments

This work was supported financially by the National NatureScience Foundation of China (Nos. 21377015, 21207015 and51178076), the Key Laboratory of Industrial Ecology and Environ-mental Engineering, China Ministry of Education and the Funda-mental Research Funds for the Central Universities.

Appendix A. Supplementary material

Supplementary data associated with this article can be found, inthe online version, at http://dx.doi.org/10.1016/j.jcis.2014.07.005.

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