Synthesis of Polymeric Phthalocyanine Sulfonate Photosensitizer and ...

Macromolecular Research, Vol. 18, No. 5, pp 496-503 (2010) DOI 10.1007/s13233-010-0502-4

www.springer.com/13233

Synthesis of Polymeric Phthalocyanine Sulfonate Photosensitizer and Its Photodegradation on Rhodamine B in Aqueous Medium Peng Zhao*, Je-wan Woo, and Yong-sung Park Department of Industrial Chemistry, College of Natural Science, Sangmyung University, Seoul 110-743, Korea

Yenan Song Department of Applied Chemistry, School of Science, Harbin Institute of Technology, Harbin 150001, P.R. China

Fushi Zhang The Key Lab of Organic Photoelectrons and Molecular Engineering of Ministry of Education, Department of Chemistry, Tsinghua University, Beijing 100084, P.R. China Received October 1, 2009; Revised December 14, 2009; Accepted December 14, 2009 Abstract: Novel phthalocyanine sulfonate (H2PPcSx) was synthesized from the sulfonation of a steric polymeric phthalocyanine and investigated as a photocatalyst in a homogenous system. The molecular weight of H2PPcSx was characterized as 9213-11692 by MALDI-TOF MS, classified as an oligomer with a 14-18 degree of polymerization. The electronic spectrum indicated a less aggregative tendency of H2PPCSx than the usual monomeric phthalocyanine photocatalyst. Efficient photodegradation of butyl Rhodamine B (bu Rh B) catalyzed by H2PPcSx was achieved in a homogenous solution; the spectral character indicated that decomposition occurred on the benzene ring in the Rh B molecular. For a 50 mg L-1 bu Rh B solution, the percentage degradation reached 95% in 4 h using 100 mg H2PPcSx as a photocatalyst. A mechanism involving the participation of both singlet oxygen and radicals was established for the photodegradation. Keywords: polyphthalocyanine, photocatalysis, homogenous catalysis, Rhodamine, singlet oxygen.

dimers and aggregates can reduce the lifetime and the quantum yield of excited states since the non-radiative dissipation route is enhanced.8 Subsequently, the quantum yield of singlet oxygen (Φ∆) reduces, which directly abates the catalytic efficient of monomeric phthalocyanine. Previous studies indicated that the complexity of sulfonation and the isomerization of phthalocyanine can decrease their aggregative tendency.9,10 Similarly, the polymerization of phthalocyanine supports them with steric structure and various compositions, which are desired to reduce their aggregation and elevate the Φ∆ as well. The doping and copolymerization of phthalocyanine with existing polymer is a common method to prepare polymeric phthalocyanine photocatalyst:11 the condensation of phthalocyanine precursor can directly form pure phthalocyanine polymer. The multi-nuclear polymeric phthalocyanines were synthesized and investigated on the photooxidation of phenol by Iliev.12,13 Furthermore, the investigation of polymeric phthalocyanine as photocatalyst is still in lack since the polymerization makes the phthalocyanines insoluble in common solvents. We recently reported a polymeric phthalocyanine with steric structure,14 but the bad solubility restricted its applica-

Introduction Phthalocyanines (Pcs) are of the most important photosensitive compounds, which are widely used in photocatalyst, photo-electric conversion, and photo dynamic therapy (PDT).1-3 These compounds have a strong absorption to visible lights and a high yield of active oxygen species, which facilitate its photosensitive process via type II (singlet oxygen (eq. 2)) or type I (radical, (eq. 3)) mechanisms.4 The active oxygen species (singlet oxygen and radical) are strong oxidants in photocatalyst or biological system. In homogenous catalyst system, Type II mechanism via singlet oxygen catalyzed by Pcs was predominant in photocatalyst as reported.5-7 Pc(S0) hν Pc(S1) isc Pc(T1) Pc(S0)+1O2 Pc(T1)+3O2 3 Pc(S0)+O−2 · Pc(T1)+ O2

(1) (2) (3)

However, in aqueous medium the aggregation and dimerization of monomeric phthalocyanine, especially at high concentration, restrict their applications as photocatalyst. Fabricated *Corresponding Author. E-mail: [email protected] The Polymer Society of Korea

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Photodegradation of Butyl Rhodamine B by a Low Aggregative Phthalocyanine Oligomer in Homogenous System

tion. In this study, we improved the polymeric phthalocyanine to good solubility in aqueous medium; the target polymer was synthesized from cyclization of tetra-phthalonitriles14 and the subsequent sulfonation. Additionally, we noticed that Rhodamine is more sensitive to radical species than singlet oxygen, and its degradation is achieved in heterogeneous photocatalytic system.15 Thereby, we try to investigate the photocatalytic property of our synthesized photosensitizer using butyl Rhodamine B as the target compound in the homogenous aqueous medium.

Experimental Materials and Methods. NaN3, fuming sulfuric acid (15% SO3), butyl Rhodamine B (bu Rh B), cetyltrimehtyl ammonium bromide (CTAB), PBS buffer solution (pH 7.4), p-nitroso-N,N'-dimethylaniline (RNO), 5,5-dimethyl-1-pyrroline-N-oxide (DMPO), and imidiazole, were purchased commercial reagents and in analytical or chemical grade. The disulfonate zinc phthalocyanine (ZnPcS2) and the sulfonate metal free phthalocyanine (H2PcSx) were synthesized and characterized in our lab.16 The electronic spectra were obtained from a HP8452 Spectrometer. Both samples were in aqueous medium. FTIR was obtained from an Avatar 360A Spectrometer using solid KBr pellet. NMR was performed on a JOEL JNM-ECA300 Spectrometer. MALDI-TOF MS test was on a BIFLEX III Spectrometer. The elemental analysis was carried out on a Vario EL III Element Analyzer. The total organic carbon (TOC) in the system was detected by a TOC-V-CSH analyzer. The average viseosimetric molecular weight (Mη) was calculated by comparative method using PVP-K15 (Mη 8,000-12,000) as the standard. The relative viscosity (ηr) of 0.1 g/L H2PPcSx and 0.1 g/L PVP-K15 DMF solution was measured separately at 298 K using dilution method on an Ubbelohde viscometer. Then the intrinsic viscosity [η] of the H2PPcSx and standard PVP-K15 was resolved using extrapolation method. The Mη of H2PPCSx was calculated by the known values of PVP-K15 based on the [η] value. The detail of this method was described in elsewhere.17 Synthesis and Characterization of Polymeric Phthalocyanine Sulfonate. The metal free polymeric phthalocyanine (H2PPc) was synthesized and characterized from a tetrahedral tetra-phthalonitriles (Pn4)15,18 (shown in Scheme I). 5 g H2PPc was mixed with 15 mL fuming sulfuric acid under argon atmosphere, and then the mixture was stirred at 353 K for 6 h in inert ambient. The sulfonate product was precipitated in iced water saturated with NaCl at 268 K during 12 h. The salt-out product was extracted with 1,000 mL methanol in Soxhlet Extractor for 48 h to remove the excessive NaCl. Then the solid was purified on silica gel chromatography with H2O: HAc (10:1) as eluent. The firstly eluotropic yellow and aqua component was impurity particles produced by the sulfonation. The successive dark green soluMacromol. Res., Vol. 18, No. 5, 2010

Scheme I. A schematic of homogeneous photodegradation system.

tion was the main products. Collect and evaporate it under vacuum resulting in green solid H2PPcSx (2.5 g, approximate 45%). The H2PPcSx only dissolves in water, ethane glycol, DMSO and DMF. Pn4: FTIR(KBr pellet): νmax/cm-1, 3070s (C-H), 2300s (-CN), 1585s, 1480s, 1277s, 1150w (Ph), 1080s (C-O), δH (300 MHz; DMSO-d6; Me4Si): 7.92 (1H, t, J 3Hz, Ph), 7.80 (1 H, d, J 2.6 Hz, Ph), 7.25 (1H, d, J 2.5 Hz, Ph), 4.65 (2 H, s, CH2). δC (300 MHz; DMF): 56.3(s), 67.4(s). MALDI-TOF MS (matrix:dithranol): calcd C37H20N8O4 [M+H]+:641, found: 640. Elemental Analysis: Found: C 69.30; H 3.21; N 17.53; O 10.07. Calc. for (C37H20N8O4): C 69.3; H 3.2; N 17.5; O 10.0%. H2PPc: FTIR(KBr pellet): νmax/cm-1, 3250-3650 br (N-H), 2282(w, -CN)1654s, 1549s, 1310s, 1142s (Ph), 1083s (C-O), Uv-vis( DMF): νmax/nm, 705, 690 (Q bands), 330 (B band). Element analysis: calc. for (H2PPc, (C37H22N8O4)n, found ((C37H21N8O4)n): C 69.3, N 17.4, O 9.9, H 3.4%. Mη:8,00016,000. H2PPcSx: FTIR(KBr pellet): νmax/cm-1, 3200- 3600 br (N-H), s, 2312w (-CN) 1688s, 1539s, 1304s (Ph) 1090s (C-O), δH (300 MHz; DMSO-d6; Me4Si): 7.9-9.8 (m, Ph), 4.2-4.6 (m, CH2) 1.8-2.2 (br, N-H); δC (300 MHz; DMF) 102.7, 116.8, 118.8, 119.3, 146.5, 146.8 (Ph) 169.7 (Ph, C-SO3Na), 51.5 (CH2), 68.6 (quaternary C); calc.for (H2PPcSx) (C37N8OxHy (SO3Na)z)n; Found (C37N8O10H20S3)n: C 53.4, N 13.5, O 19. 2, H 2.4, S 11.5%. MALDI-TOF-MS (no matrix, in methanol-H2O solution): found: 9213, 9833, 10443, 11093, 11692. Mη: 9,00012,000. The ratio of C: N of Pn4 (3.96), H2PPc (3.98), and H2PPcSx (3.95) is in consistent with each other in the elemental analysis. It indicated no carbon or nitrogen atom drops during the condensation and sulfonation process. The chemical shifts (13C NMR) for CH2 and quaternary C of Pn4 is similar with that of H2PPcSx, which also indicated the basic tetrahedral skeleton effective preserves during the polymerization 497

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Scheme II. Molecular structure of phthalocyanine oligomer sulphonate (H2PPcSx).

and sulfonation reaction from Pn4 to H2PPcSx. The FTIR showed similar stretching of C-O bond with all the Pn4, H2PPc and H2PPcSx, which indicated the ester bonds are stable during the sulfonation. The above evidences prove the molecular structure is expected as in Scheme II. The method of Ubbelohde viscosity gives an Mη of 9,00012,000 in ten parallel experiments. The Mη of unsulfonated H2PPc is 8,000-16,000, which proved the polymeric structure is not broken during the sulfonation from H2PPc to H2PPcSx. The accurate molecular weight detected by MALDI-TOF (in Figure 1) shows molecular peaks from 9213-11692 with

Figure 1. Molecular weight peaks of H2PPcSx by MALDI-TOF MS. 498

the interval about 630. The interval between each peak is consistence with the molecular weight of monomer Pn4 (Mw 640). The degree of polymerization (n) of the synthesized H2PPcSx is about 14-18, which can be classified as oligomer. The smaller oligomer with lower polymeric degree has already separated through the silica gel chromatogram. Photodegradation Experiment of Butyl Rhodamine B. The concentration of bu RH B was 40 mg/L in distilled water. The light source was a halogen lamp (Philips Halogen A, 75 W) with a glass jacket in the reaction flask cooled with circulating water (seen Scheme II). In each test, 200 mL bu Rh B solution was put into the flask. The amount of catalyst H2PPcSx was increased from 25, 50, 75, 100 to 200 mg. The reactive mixture was stirred for 30 min in dark before the test. Air was bubbled into the flask by Scorpion I Pump once the irradiation started. The sampling time was selected as 5, 20, 40, 80, 120, 180 and 240 min after experiments starts. Several blank and reference experiments were performed to evaluate the consistency of light, air bubble and catalyst concentration. The decomposition of bu Rh B was monitored by the absorbance of the reactant samples at 554 nm wavelength, which was the absorption maximum of bu Rh B. A standard linear work curve of bu Rh B was previously obtained by collecting absorbance at 554 nm from concentration 1 to 50 mg/L. The mineralization of Rh B in the photodegradation was reflected by measuring the TOC after 240 min. The variation of TOC without the bu Rh B in the same condition was also detected for differentiating the influence of H2PPcSx. The recycle test was used to investigate the catalytic durance of H2PPcSx on bu Rh B. In a 200 mL Macromol. Res., Vol. 18, No. 5, 2010


bu Rh B solution, the initial dosage of H2PPcSx (100 mg) did not change throughout the test, only the bu Rh B was adjusted to the initial concentration (40 mg/L) after one cycle. Photochemical Characterization and Quantum Yield of Photodegradation. The photobleaching of synthesized H2PPcSx was investigated in pH 7.4 buffer solution under the same light source irradiation. The quantum yield of photobleaching (Φp) was calculated by: V ( Cpc, 0 – Cpc, t )NA Φp = ---------------------------------------JhνAt

(4)

Quantum yield of bu Rh B (ΦRhB) of H2PPcSx was calculated from the equations shown below:19,20 VCRhb, 0 k ΦRhB = ------------------Jhν A

(5)

Where V is the reaction volume (m3), Cpc,0 and Cpc,t were the initial and measured concentration of H2PPcSx during the photobleaching test, respectively. NA is Avogadro number, CRhb,0 is the initial concentration of bu Rh B, Jhν is the overlap integral of the irradiation light source intensity and the absorption of the Pc in the region of the interference filter transmittance,20 the intensity of light source is 8.2×1015 photons.s-1.cm-1 measured by a Hamamatsu S1337 BQ Silicon Photodiode, A is the illuminated area (m2), t is the irradiation time, k is the rate constant of photodegradation (s-1). k was determined by the slope of kinetics fitting curves. The first order kinetics was assumed in this homogeneously aqueous medium.19 Active Oxygen Species Studies. To investigate the active oxygen species, H2PPcSx was dissolved in a pH 7.4 phosphate buffer at the concentration of 1 g/L. The singlet oxygen quantum yield (Φ∆) was determined by using RNO and imidazole as the radical scavenger.21 The bi sulfonate zinc phthalocyanine (ZnPcS2) (singlet oxygen quantum yield 0.4920) was used as the standard to calculate singlet oxygen quantum yield of H2PPcSx. To probe the radical species, the experiments were carried out on a BRUKER 300 ESR spectrometer with DMPO as radical scavenger. The experimental details and data treatment were same as reported elsewhere.22

Results and Discussion Electronic Spectrum and Aggregation Behavior. From the electronic spectrum, the Q band of H2PPcSx (shown in Figure 2(a), compared with monomeric H2PcSx) only exhibits a single peak at 698 nm. The peak shows bathochromic shift comparing with H2PcSx (double peaks at 627 nm and 666 nm). The bathochromic shift of Q band is the character of polymeric phthalocyanine compounds,23 while the sulfonation of phthalocyanine usually caused hypsochromic shift of Q band for the electronic attraction effect3,19 of sulfonate group. Here the Q band at 698 nm is a synthetical effect of above influences. It also indicates a lower degree of polyMacromol. Res., Vol. 18, No. 5, 2010

Figure 2. (a) Electronic spectrum of H2PPcSx in water compared with H2PcSx (embedded, the spectra affected by CTAB, initial concentration 1 g L-1); (b) the fitness to Beer’s Law and of H2PPcSx in pH 7.4 buffer (embedded, corresponded spectra).

merization, because Woehrle24 ever concluded that larger polymerization degree resulted in larger bathochromic. A wide shoulder peak is found at 610-650 nm without obvious aggregative peak. The absorption peak of H2PPcSx at 350 nm correlates with the -CN residue in the polymer.14 For polymeric H2PPcSx, the fitness to Beer’s Law indicates the low aggregative tendency of H2PPcSx. It only deviates from Beer’s law weakly at high concentration (2 g/ L, in Figure 2(b)). The addition of CTAB does not change the Q band’s shape of H2PPcSx in the solution which gives the same conclusion of the low aggregation. For the addition of CTAB in aggregative phthalocyanine solution usually induces sharper and stronger Q band for the disaggregating effect.9 While the strong adsorption peak at 627 nm for H2PcSx is the characterized aggregative peak for monomeric pthhalocyanine. The aggregation level of phthalocyanine can be estimated quantitatively by measuring the increment of Q band intensity after adding CTAB.9 The aggregative degree is about 10% for H2PPcSx in this approach. This 499

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value is lower than other sulfonate Pc (AlPcSx and SiPcSx 8). The steric structure of H2PPcSx oligomer inhibits the planar π-π stacking between each molecule and reduces the aggregation. The low aggregation of Pcs is important for its application in aqueous medium as photosensitizer. The quantum yield of photobleaching (Φp) of H2PPcSx is 2.35×10-6, which equals to the stable unsubstituted zinc phthalocyanine25 (ZnPc, 2.0×10-6). The spectra recording during the photobleaching test indicated no decomposition of the oligomeric structure occurs. Above results show the H2PPcSx is a stable sensitizer under the self-sensitive active oxygen species in the photocatalytic process. Degradation of bu Rh B under Visible Light Irradiation. Figure 3 showed the absorption spectra with different irradiation times in the photocatalytic system in presence of 100 mg of H2PPcSx. The characteristic absorption peak of bu Rh B at 554 nm decays with the proceeding of light irradiation, indicating the decomposition of bu Rh B in the system. The peak position of bu Rh B does not shift and no new adsorption peak appears at any other wavelength on the spectra during the reaction process, which indicated the mechanism is the broking of benzene ring oxidized by the active oxygen species.26,27 Because of another decomposed route in the heterogeneous system, the dispatch of the alkyl groups of Rh B usually results in hypsochromic shift of the adsorption peak. The final degradation percent of bu Rh B is 89% within 3 h and 95% within 4 h, respectively. A recent publication of phthalocyanine analogue (ferrous tetra porphyrazine) showed about 78% degradation within 27 h.28 However, it should be noted that the comparison only presents referenced meaning due to the different experimental conditions. After 4 h degradation, the peak of bu Rh B shows little absorption which indicated there is little chromophore (organic-cyclic compound) in the solution. The TOC content of initial reactant

Figure 3. Electronic spectra of bu Rh B collected at different interval during the photodegradation catalyzed by H2PPcSx (embedded, the spectra at 0 min and 240 min). 500

Figure 4. (a) Photodegradation of t-bu Rh B catalyzed by H2PPcSx under varied experimental conditions; (b) Effect of H2PPcSx dosage on photodegradation of bu Rh B.

and after 240 min reaction is 264.3 and 252.4 mg/L, respectively. The TOC of blank test without bu Rh B in the same condition is 250.3 and 249.9 mg/L, respectively. The calculated mineralized ratio is 82% in this case. It indicated the bu Rh B well decomposed into inorganic with few organic compounds residue. The strength and position of Q bands of H2PPcSx did not change in the whole reaction process (Figure 3 embedded), it indicated the H2PPcSx oligomer is stable and no co-degradation with bu Rh B occurs. Figure 4(a) shows a contrast experiment at controlled conditions. The decreasing of bu Rh B concentration shows that the effective degradation occurs only when all the necessary conditions are satisfied. It includes the existing of light irradiation, H2PPcSx and bubbled air. The decomposition ratio of bu Rh B by the self-sensitive process in the absence of H2PPcSx is only about 8%, while it was 10%29 in heterogeneous system. The inhibition of reaction without air bubbling and photosensitizer indicated the active oxygen species predominates in the degradation. And the electron inject degradation30 of absorbed bu Rh B in heterogeneous Macromol. Res., Vol. 18, No. 5, 2010


system did not take place in this homogeneous system. All results prove a clear mechanism of a photo-oxidation through active oxygen species under the visible light irradiation, with H2PPcSx as the photosensitive catalyst. The amount of catalyst influences the degradation degree of bu Rh B as well (shown in Figure 4(b)). As the catalyst amount increasing from 25 to 100 mg, the bu Rh B concentration decreases fast, this means the increasing of degraded rate of bu Rh B. However, when the amount of photosensitizer increases to 200 mg, the excessive catalyst no longer enhances the degradation. It indicated that the light scattering and self-quenching of excited state may decrease the reaction rate19 although the increasing amount of catalyst leads to a higher active oxygen generation rate. Meanwhile, the increasing tendency of aggregation at high concentration also decreased the photosensitive capacity of H2PPcSx in the solution. The first order kinetics of bu Rh B decomposition in homogeneous solution is investigated (Figure 5, data listed in Table I). The linear correlations are valid within the initial 120 min reaction and for H2PPcSx dosage ranging from 25 to 100 mg. The rate constant k was calculated to be 1.3×10-2 and 9.9×10-3 min-1 for 100 and 50 mg H2PPcSx, respectively. It is equivalent to the photodegradation catalyzed by nanoparticle in heterogeneous system26,27,31(shown in Table I). The ΦRhB are 0.43 and 0.55 calculated from 50 and 100 mg dosages, respectively. The above results give high irradiated efficiency of light and prove the rapid actualization of this photodegradation thorough its mechanism were different from that in heterogeneous system. The high solubility and low aggregation of H2PPcSx attributes to the fast reaction rate. Oppositely, the aggregation of monomeric phthalocyanine sensitizers inhibits their capacity to produce active oxygen species and thus reduces their sensitive efficiency in photodegradation. The photocatalytic durance of H2PPcSx was investigated

Figure 5. Photodegradation kinetics curves of bu Rh B with varied dosages of H2PPcSx. Macromol. Res., Vol. 18, No. 5, 2010

Table I. Experimental Data of the bu Rh B Photodegradation in Homogeneous (catalyzed by H2PPcSx) and the Comparison to Some Heterogeneous Systems k min-1 H2PPcSx (100mg )

9.9×10

Fe(II)Pz(Me-dtn)4[26]

-

Fe-Co- TiO2 [24] SiO2-TiO2 [25] k /CuPcS2. TiO2 [31]

Degradation Degree % ΦRhB

-3

95%, 4 h

0.43

78%, 27 h -3

4.12×10

-

4.65×10-3 > 99%, 3h, 220 nm Uv

-

1.08×10-2

Figure 6. Durance photodegradation effect of H2PPcSx on bu Rh B in recycle test (up curve: degradation degree; down curve: TOC elimination).

by a recycled test; the result (in Figure 6) shows, the degradation degree of bu Rh B in 4 h still reaches 75% in presence of initial catalyst dosage (100 mg) after 6 recycles. The spectrum of H2PPcSx after six recycles is similar to the initial ones indicating without any changing of oligomer structure. It ascribes to the low photobleaching of H2PPcSx (Φ p, 2.35×10-6). The correlated TOC elimination efficiency decreases from 81% to 70% after six recycles simultaneously. The above result shows H2PPcSx is a stable photosensitizer with durative catalytic capacity on degradation of bu Rh B and the TOC. Degradation Mechanism on Photochemistry. To fully understand the mechanism of the photodegradation, a water soluble singlet oxygen quencher NaN39,19 was added in the comparison experiment. The decomposition rate of bu Rh B dropped just 5 min after the quencher put into the system. It proved that type II (through singlet oxygen) is the main mechanism for the oxidation and the decomposition of bu Rh B. The data shows about 60% descend in the photodegradation rate by quencher NaN3. Increasing NaN3 concentration to 5×10-3 mol/L does not further change the decomposition rate of bu Rh B, which shows that 10-3 mol/L NaN3 already completely quenched the singlet oxygen in the experiment. The Φ∆ is 0.31 for H2PPcSx in the system. No distinct descend 501

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tive photodegradation of bu Rh B is achieved in homogenous system sensitized by H2PPcSx. The decomposition degree of bu Rh B is 95% within 4 h under visible light irradiation. The type II photosensitive mechanism (though singlet oxygen) is the primary process in the photodegradation. The hydroxyl radical probed by ESR suggests the participation of type I mechanism as well. As a low aggregation phthalocyanine polymer with well water solubility, besides the photocatalyst, the H2PPcSx is also expected to be applied in photodynamic therapy, photochromism, photovoltaic, and other areas.

References Figure 7. ESR signals of OH·: DMPO adduct in PBS buffer (pH 7.4) in presence of H2PPcSx under irradiation.

of Φ∆ is measured after 1 h light irradiation. The value is larger than that of monomeric metal free phthalocyanine sulfonate, and similar to ZnPcS2 and SiPcSx.8 Here, the efficiency of the singlet oxygen producing profits from the low aggregation of H2PPcSx. Photosensitization with radical species in type I mechanism usually exists simultaneously for Pcs as previously discussed.4 As shown in Figure 7, the signal of ESR shows no radical species signals without irradiation. When using irradiation for 8 min, the characteristic peak of OH·: DMPO adducts with an intensity ratio of 1:2:2:132 appearing. The signal still exists after 48 min exposure without obvious decreasing in intensity, which indicates a continuous production of hydroxyl radical in the system. The hydroxyl radical (OH·) is a strong and non-selective oxidant (E0 = +3.06 V), which usually existed in the system using nano-material catalyst.33 We suggested the hydroxyl radical transfers from the super oxygen ion radical (O2− ·, producing from phthalocyanine triplet excited state with molecular oxygen (in eq. 3)) in our photocatalytic system.32 H2PPcSx with oligomer structure is more stable than the monomeric phthalocyanine and helpful to reduce the self-dissipation of the produced radical, especially in the case of hydroxyl radical. Thus, the successful photodegradation of bu Rh B becomes available in homogeneous system with the continuous generation of both singlet oxygen and hydroxyl radical. However, the homogeneous system has a problem in separation of catalyst from the degradation product.6,9,12 The further work, such as enclosing the H2PPcSx with the nano fiber,34 proceeds to resolve this problem in our lab.

Conclusions The novel polymeric phthalocyanine sulfonate oligomer (H2PPcSx) shows a lower aggregative tendency than monomeric phthalocyanine sulfonate in aqueous medium. A effec502

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