The photocatalytic activity of novel, substituted porphyrin/TiO2-based composites

Article abstract of DOI:10.1016/j.dyepig.2009.08.001

Four novel porphyrins, 5-[3-(3-phenoxy)-propoxy]phenyl porphyrin, 5,15-di-[3-(3-phenoxy)-propoxy]phenyl porphyrin, 5,10,15-tri-[3-(3-phenoxy)-propoxy]phenyl porphyrin, 5,10,15,20-tetra-[3-(3-phenoxy)-propoxy]phenyl porphyrin, and their corresponding Cu(II) porphyrins, were synthesized and characterized spectroscopically. The photodegradation of 4-nitrophenol in aq. suspension was used to determine the photocatalytic activity of polycrystalline TiO₂ samples which had been impregnated with the Cu(II) porphyrins, as sensitizers. The photocatalytic activity of the composite depends mainly on the amount of sensitizer on the TiO₂ surface rather than the nature of the substituted porphyrins.

Full text of DOI:10.1016/j.dyepig.2009.08.001

Dyes and Pigments 84 (2010) 183–189
Contents lists available at ScienceDirect
Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
The photocatalytic activity of novel, substituted porphyrin/TiO2-based composites
,
b
,
a
a
Chen Wang a, Jun Li a , Giuseppe Mele
, Ming-yue Duan , Xiang-fei Lu¨ ,
*
**
Leonardo Palmisano c, Giuseppe Vasapollo b, Feng-xing Zhang a
a Key Laboratory of Synthetic and Natural Functional Molecule Chemistry of Ministry of Education, The College of Chemistry & Materials Science,
Northwest University, Xi’an 710069, PR China
b
`
Dipartimento di Ingegneria dell’Innovazione, Universita del Salento,Via Arnesano, 73100 Lecce, Italy
c
`
‘‘Schiavello-Grillone’’ Photocatalysis-Group, Dipartimento di Ingegneria Chimica dei Processi e dei Materiali, Universita di Palermo, Viale delle Scienze, 90128 Palermo, Italy
a r t i c l e i n f o
a b s t r a c t
Article history:
Four novel porphyrins, 5-[3-(3-phenoxy)-propoxy]phenyl porphyrin, 5,15-di-[3-(3-phenoxy)-propoxy]
phenyl porphyrin, 5,10,15-tri-[3-(3-phenoxy)-propoxy]phenyl porphyrin, 5,10,15,20-tetra-[3-(3-phenoxy)-
propoxy]phenyl porphyrin, and their corresponding Cu(II) porphyrins, were synthesized and characterized
spectroscopically. The photodegradation of 4-nitrophenol in aq. suspension was used to determine the
photocatalytic activity of polycrystalline TiO2 samples which had been impregnated with the Cu(II)
porphyrins, as sensitizers. The photocatalytic activity of the composite depends mainly on the amount of
sensitizer on the TiO2 surface rather than the nature of the substituted porphyrins.
Received 4 May 2009
Received in revised form
18 July 2009
Accepted 6 August 2009
Available online 14 August 2009
Keywords:
Porphyrins
Ó 2009 Elsevier Ltd. All rights reserved.
Cu(II)-porphyrins
Substitutions
Photosensitizer
Photodegradation
Titanium dioxide
1. Introduction
TiO2–porphyrin systems, depending on the position of the
substituent and spacer length [31,32], strength of the polar group
Macrocyclic porphyrins enjoy much attention, as exemplified by
the simulation of proteins in enzyme catalysis [1–3] as well as
molecular recognition [4,5] smart materials [6–12], medical treat-
ment [13–17], photo-sensitization and photocatalyst preparation
[18–22]. In recent years different heterocycles, metal complexes, as
well as porphyrins and their metal derivatives, have been used as
photo-sensitizers for polycrystalline TiO2 in order to enhance the
visible light-sensitivity of the TiO2 matrix and thereby increases its
photocatalytic activity [23–28].
involved (e.g. –OH, –SO3, RCOO–) [33–36] and the electronegativity
of the substituent atoms (e.g. O or Cl) combined with the pyrrole
units [37,38].
However it remains unclear as to whether the number of
peripheral substituents influence the efficiency of TiO2–porphyrins
hybrid systems or whether there exists an optimum ratio of
TiO2:porphyrin. For this reason, this work concerns the synthesis
and characterization of four novel porphyrins (H2Pp; 3a, 3b, 3c, 3d)
each carrying different peripheral substituents, as well as their
corresponding copper(II) derivatives (CuPp; 4a, 4b, 4c, 4d) (Fig. 1).
The photocatalytic activity of polycrystalline TiO2 samples
impregnated with CuPp (4a, 4b, 4c, 4d) was investigated via the
photodegradation of 4-nitrophenol (4-NP) in aqueous suspension.
It was shown that the central coordinated metal in porphyrins
plays
a critical role in the photocatalytic processes of the
porphyrin–TiO2 system. In particular, opportunely designed Cu(II)
porphyrins–TiO2 composites were found to be more effective
sensitizers in the photodegradation of 4-nitrophenol than other
metal–porphyrins (M]Mn, Fe, Zn, Co etc.) [29,30]. The peripherally
substituted group within the porphyrins influences the efficiency of
2. Experimental section
2.1. Materials and measurements
2,3-dichloro-5,6-dicyano-1,4-benzoquinone
(DDQ)
was
* Corresponding author. Tel.: þ86 29 88302604; fax: þ86 29 88303798.
** Corresponding author. Tel.: þ39 0832 297281; fax: þ39 0832 297733.
E-mail addresses: junli@nwu.edu.cn (J. Li), giuseppe.mele@unisalento.it
(G. Mele).
obtained from Aldrich, and other reagents were obtained from
Beijing Chemical Reagents Company. They were used without
further purification with the exception of the pyrrole that was
0143-7208/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.dyepig.2009.08.001

184
C. Wang et al. / Dyes and Pigments 84 (2010) 183–189
O
O
O
O
O
O
O
O
O
O
N
N
N
N
N
N
N
N
N
N
N
N
M
M
M
M
N
N
N
N
O
O
O
O
O
O
O
O
O
O
M=2H: H2Pp (3a)
M=Cu: CuPp (4a)
M=2H: H2Pp (3b)
M=Cu: CuPp (4b)
M=2H: H2Pp (3d)
M=Cu: CuPp (4d)
M=2H: H2Pp (3c)
M=Cu: CuPp (4c)
Fig. 1. Molecular structures of H2Pp(3a, 3b, 3c, 3d), and CuPp(4a, 4b, 4c, 4d).
distilled before use. TiO2 (anatase) was kindly provided by Tioxide
Huntsman. The loaded samples used as the photocatalysts for the
photoreactivity experiments were prepared by impregnating TiO2
(Tioxide, anatase phase, BET specific surface area 8 m2/g).
water. The CH2Cl2 was removed and the remaining oil was
recrystallized from CH3CH2OH to yield colorless crystals of 3-
(3-phenoxy) propoxybenzaldehyde (2). Yield: 35%; Mp: 34–35 ꢀC;
Anal. Calcd. for C19H16O3, %: C, 75.38; H, 6.28. Found C, 74.98; H,
Elemental analyses (C, H and N) were performed by Vario EL-III
CHNOS instrument. Diffuse reflectance (DR) spectra were obtained
at room temperature in the wavelength range 200–800 nm using
a Shimadzu UV-2401PC spectrophotometer with BaSO4 as the
reference material. UV–vis spectra were obtained using a Shimadzu
UV-2550 UV–vis–NIR spectrophotometer. 1H NMR spectra were
recorded on a Varian Inova 400 MHz at room temperature;
chemicals shifts are reported in ppm with respect to the reference
frequency of tetramethylsilane, Me4Si. Mass spectrometry was
carried out on a matrix assisted laser desorption/ionization time of
flight mass spectrometer (MALDI-TOF MS, Krato Analytical
6.29. 1H NMR (CDCl3, 400 MHz):
d, ppm 9.96 (s, 1H), 7.50–7.12 (m,
4H, Ar), 6.93 (t, J ¼ 7.73 Hz, 5H, Ar), 4.26 (t, J ¼ 5.54 Hz, 2H, OCH2),
4.16 (t, J ¼ 5.75 Hz, 2H, OCH2), 2.35–2.21 (m, 2H, CH2).
2.1.3. General procedure for the synthesis of H2Pp(3a), H2Pp(3c),
and H2Pp(3d)
5,10,15,20-tetra-[3-(3-phenoxy)-propoxy]phenyl
porphyrin
H2Pp(3d) was synthesized according to the following steps: 2.13 g
(8.3 mmol) 3-(3-phenoxy)propoxybenzaldehyde (2) and 0.56 mL
(8.3 mmol) pyrrole in 200 mL of chloroform were stirred at room
temperature for 10 min under a nitrogen atmosphere. 0.13 mL
(2.8 mmol) of BF3$OEt2 in 5 mL CHCl3 were added and the reaction
mixture was stirred at room temperature for 40 h and thereafter,
for a further 50 h following the addition of 1.4 g (6.16 mmol) of
dichloro dicyano quinone(DDQ) in CHCl3. The solvent was removed
under vacuum and the crude product purified by chromatography
on a silica gel column using CH2Cl2 and hexane (6/4 v/v) as eluant.
H2Pp(3a) and H2Pp(3c) were obtained by statistic synthesis
starting from a mixture of benzaldehyde: 3-(3-phenoxy)propox-
ybenzaldehyde respectively in 3:1 or 1:3 ratio using a procedure
similar to that described for the preparation of H2Pp(3d). The crude
products were purified using chromatography on a silica gel
column with CH2Cl2 and hexane (6/4 v/v) as eluant.
Company of Shimadzu Biotech, Manchester, Britain). 1 mL of sample
solution and of the matrix mixture were spotted into wells of the
MALDI sample plate and air-dried. The samples were than analyzed
in linear ion mode using CHCA as matrix. External calibration was
achieved using a standard peptide and protein mix obtained from
Sigma.
Specific surface area was measured using the single point BET
method employing a jw-05 apparatus (Beijing China). Total Organic
Carbon (TOC) was measured using USA. O. I Analytical TOC.
2.1.1. General procedure for the synthesis of 3-phenoxypropyl
bromide (1)
Compound (1) was synthesized as described previously [39].
28.0 g (0.3 mol) phenol and 37.7 mL (0.37 mol) 1,3-dibromopropane
in 150 mL H2O were heated with stirring at 100 ꢀC on an oil bath
and 11.3 g (0.28 mol) NaOH dissolved in 40 mL H2O were added to
the reaction system over 30 min. The mixture was refluxed for 4 h
and the water layer was separated and the remaining oil layer
distilled under vacuum. The first distillation yielded unreacted
1,3-dibromopropane, whilst 3-phenoxypropyl bromide (1) was
obtained from the second distillation. Yield: 85%; Mp: 10–11 ꢀC;
Anal. Calcd. for C9H11BrO, %: C, 50.30; H, 5.09. Found C, 50.26; H,
5.15. nD20: 1.5460.
2.1.3.1. 5-[3-(3-phenoxy)-propoxy]phenyl porphyrin H2Pp(3a). Yield:
6%. Mp: >200 ꢀC, Anal. Calcd. for C53H40N4O2, %: C, 83.69; H, 5.30;
N,7.29. Found C, 83.22; H, 5.27; N, 7.32. MS: m/z 765.9 ([M þ H]þ)
amu. 1H NMR (CDCl3, 400 MHz):
d, ppm 8.94–8.77 (m, 8H, b posi-
tion of the pyrrole moiety), 8.21 (d, J ¼ 6.3 Hz, 8H, Ar), 7.84–7.70 (m,
12H, Ar), 7.63 (t, J ¼ 7.4 Hz, 2H, Ar), 6.96–6.87 (m, 4H, Ar), 4.36 (t,
J ¼ 6.0 Hz, 2H, OCH2), 4.23 (t, J ¼ 6.0 Hz, 2H, OCH2), 2.35 (quintuplet,
J ¼ 6.1 Hz, 2H, CH2), ꢁ2.79 (br s, 2H, NH). UV–vis (CHCl3): lmax, nm,
418, (Soret band), 515, 550, 590, 645 (Q bands).
2.1.3.2. 5,10,15-tri-[3-(3-phenoxy)-propoxy]phenyl porphyrin H2Pp(3c).
Yield: 5%, Mp: >200 ꢀC Anal. Calcd. for C71H60N4O6, %: C, 79.84; H,
5.71; N, 5.32. Found C, 80.05; H, 5.68; N, 5.26. MS: m/z 1066.1
2.1.2. General procedure for the synthesis
of 3-(3-phenoxy-propoxy)-benzaldehyde (2)
10.0
g
(0.082 mol) 3-hydroxybenzaldehyde and 12.5 mL
([M þ H]þ) amu. 1H NMR (CDCl3, 400 MHz):
d, ppm 8.93–8.77 (q,
(0.08 mol) 3-phenoxypropyl bromide (1) in 100 mL CH3CH2OH
were heated with stirring at 80 ꢀC on a water bath and 3.2 g
(0.08 mol) of NaOH dissolved in 50 mL CH3CH2OH (5 mL distilled
water was added to CH3CH2OH to completely dissolve the NaOH)
were added dropwise over 1 h and the ensuing mixture was
refluxed for 30 h. The mixture was cooled to room temperature and
filtered to remove NaBr. The filtrate was concentrated under
vacuum and the residual brown oil was dissolved in 20 mL CH2Cl2,
and washed several times with 0.1 M KOH followed by distilled
J ¼ 5.13 Hz, 4.76 Hz, 8H,
b position of the pyrrole moiety), 8.20 (dd,
J ¼ 1.62 Hz, 4H, Ar), 7.86–7.74 (m, 10H, Ar), 7.65–7.60 (t, J ¼ 7.8 Hz, 8H,
Ar), 7.36–7.31 (dd, J ¼ 2.4 Hz, 2H, Ar), 7.27–7.20 (m, 6H, Ar), 6.94–6.85
(m,10H, Ar), 4.35 (t, J ¼ 6.0 Hz, 4H, OCH2), 4.22 (t, J ¼ 6.0 Hz, 4H, OCH2),
2.35 (quintuplet, J ¼ 6.0 Hz, 4H, CH2), ꢁ2.81 (br s, 2H, NH). UV–vis
(CHCl3): lmax, nm, 419, (Soret band), 515, 549, 589, 644 (Q bands).
2.1.3.3. 5,10,15,20-tetra-[3-(3-phenoxy)-propoxy]phenyl porphyrin
H2Pp(3d). Yield: 8%, Mp: >200 ꢀC Anal. Calcd. for C80H70N4O8, %: C,

C. Wang et al. / Dyes and Pigments 84 (2010) 183–189
185
79.10; H, 5.71; N, 4.68. Found C, 79.05; H, 5.80; N, 4.61. MS: m/z
2.1.5.4. Cu(II) 5,10,15,20-tetra-[2-(3-phenoxy)-propoxy]phenyl por-
phyrin CuPp(4d). Yield: 95%. Mp >200 ꢀC, Anal. Calcd. for
CuC80H68N4O8, %: C, 75.13; H, 5.64; N, 4.47. Found C, 75.25; H, 5.37;
N, 4.39. MS: m/z 1277.8 ([M þ H]þ) amu. UV–vis (CHCl3): lmax, nm,
417 (Soret band), 540, 572 (Q bands).
1216.5 ([M þ H]þ) amu. 1H NMR (CDCl3, 400 MHz):
d, ppm 8.87
(s, 8H,
b
position of the pyrrole moiety), 7.80 (d, J ¼ 8.0 Hz, 8H, Ar),
7.62 (t, J ¼ 7.6 Hz, 4H, Ar), 7.36–7.30 (m, 4H, Ar), 7.21 (t, J ¼ 8.0 Hz,
8H, Ar), 6.92–6.86 (m, 12H, Ar), 4.35 (t, J ¼ 6.0 Hz, 8H, OCH2), 4.22
(t, J ¼ 6.0 Hz, 8H, OCH2), 2.34 (quintuplet, J ¼ 6.0 Hz, 8H, CH2), ꢁ2.81
(br s, 2H, NH). UV–vis (CHCl3): lmax, nm, 420, (Soret band), 516, 550,
589, 644 (Q bands).
2.1.6. Preparation of the photocatalysts: CuPp(4a)–TiO2,
CuPp(4b)–TiO2, CuPp(4c)–TiO2 and CuPp(4d)–TiO2
An amount (2,4,6,8,10,12 and 14
mmol) of the sensitizer
2.1.4. General procedure for the synthesis of H2Pp(3b)
(CuPp(4a), CuPp(4b), CuPp(4c) or CuPp(4d)) was dissolved in 30 mL
of CHCl3 and 1 g finely ground TiO2 was added to the solution. The
resulting suspension was stirred for 5 h and the solvent was
removed under vacuum.
0.52 g (2 mmol) 3-(3-phenoxy)propoxybenzaldehyde (2) and
0.45 g (2 mmol) meso-phenyldipyrrole (which was synthesized
using the procedure reported in [41]) in chloroform (250 mL) were
stirred at room temperature for 10 min under a nitrogen atmo-
sphere. 0.03 mL (0.67 mmol) of BF3$OEt2 in 5 mL CHCl3 were added
and the reaction mixture was stirred at room temperature for 20 h;
0.34 g (1.5 mmol) DDQ (in CHCl3) was added slowly to the solution
with vigorous stirring. Subsequently, the reaction mixture was
stirred at room temperature for 24 h and then the solvent was
removed under vacuum. The reaction mixture was purified through
a silica gel-G chromatography column with CH2Cl2 and hexane
(6/4 v/v) as eluant.
2.2. Photoreactivity experiments
The photodegradation setup consisted of a 200 mL beaker
irradiated by a 500 W, 24 V Xenon lamp-house system (instrument:
CHF-XM35-500W. Beijing Trusttech Co. Ltd. China) placed in
a black box. The distance between the lamp and the solution was
110 cm, and the irradiance measured at the distance of 110 cm was
4.061 mW/cm2 (instrument: New Port Dual-Channel Power Meter.
Model 2832-C Irvine, CA, USA). The temperature inside the reactor
was maintained at ca. 25 ꢀC by means of a continuous circulation of
water in a jacket surrounding the reactor.
2.1.4.1. 5,15-di-[3-(3-phenoxy)-propoxy]phenyl porphyrin H2Pp(3b)
. Yield: 12%, Mp: >200 ꢀC Anal. Calcd. for C62H50N4O4, %: C, 81.41;
H, 5.63; N, 6.02. Found C, 81.38; H, 5.51; N, 6.12. MS: m/z 916.6
The reacting suspension consisted of 100 mL 1.0 ꢂ 10ꢁ4 mol/L 4-
NP and 20.0 mg catalyst and it was stirred with a magnetic bar. Air
was bubbled into the suspension for 30 min before switching on the
lamp and the initial pH value of the suspension was 6.40 units. The
photoreactivity runs lasted 400 min and samples of 3 mL were
withdrawn from the suspension every 50 min during the irradia-
tion. The photocatalysts were separated from the solution by
centrifugation and the quantitative determination of 4-NP was
performed by measuring its absorption at 316 nm with a Shimadzu
UV2550 UV–vis–NIR spectrophotometer.
([M þ H]þ) amu. 1H NMR (CDCl3, 400 MHz):
d, ppm 8.92–8.72 (dd,
J ¼ 5.12 Hz, 8H, position of the pyrrole moiety), 8.17 (d, J ¼ 6.44 Hz,
b
4H, Ar), 7.83–7.68 (m, 8H, Ar), 7.62–7.52 (t, J ¼ 7.8 Hz, 4H, Ar), 7.33–
7.27 (m, 4H, Ar), 6.92–6.86 (m, 8H, Ar), 4.30 (t, J ¼ 6.0 Hz, 4H, OCH2),
4.20 (t, J ¼ 6.0 Hz, 4H, OCH2), 2.31 (quintuplet, J ¼ 6.0 Hz, 4H, CH2),
ꢁ2.84 (br s, 2H, NH). UV–vis (CHCl3): lmax, nm, 419, (Soret band),
516, 550, 589, 645 (Q bands).
2.1.5. General procedure for the synthesis of CuPp(4a, 4b, 4c, 4d)
27.0 mg (0.15 mmol) of CuCl2 were added to 60.8 mg
(0.05 mmol) of the H2Pp(3d) dissolved in 20 mL CHCl3 and 3 mL
CH3CH2OH. The mixture was stirred for 24 h at room tempera-
ture and monitored by TLC until the complete disappearance of
the starting material H2Pp(3d). The unreacted solid salt was
filtered and the solvent removed under vacuum. The crude
product was purified by chromatography on a silica gel column
with CH2Cl2 as eluant. CuPp(4d) was obtained in nearly quanti-
tative yield.
3. Results and discussion
3.1. Synthesis of (2), H2Pp(3a, 3b, 3c, 3d), CuPp(4a, 4b, 4c, 4d) and
preparation of the CuPp(4a)–TiO2, CuPp(4b)–TiO2, CuPp(4c)–TiO2
and CuPp(4d)–TiO2 photocatalysts
The synthetic route has been illustrated in Fig. 2. As shown in
Fig. 2, the precursors 3-phenoxypropyl bromide (1) and 3-(3-phe-
noxy) propoxybenzaldehyde (2) were easily prepared and purified.
The four novel porphyrins, H2Pp(3a, 3b, 3c, 3d), were synthesized
by using a procedure inspired the to Lindsey methods [40,41]. 3a
and 3c were obtained through statistic synthesis by controlling the
ratio of benzaldehyde and 3-(3-phenoxy)propoxybenzaldehyde (2)
in 3:1 and 1:3, respectively, and provided rather low yields (6 and
5%, respectively), while 3d was in relative a little high yield (8%). 3b
was synthesized with 12% yield by the reaction of 3-(3-phenox-
y)propoxybenzaldehyde (2) and meso-phenyldipyrrole, that is,
a [2 þ 2] approach. The corresponding copper porphyrins, CuP-
ps(4a, 4b, 4c, 4d) were obtained almost quantitatively.
The UV–vis spectra of 3a, 3b, 3c, 3d, show almost the same Soret
and Q bands. The corresponding copper porphyrin 4a, 4b, 4c, 4d,
leads to a decrease of the number of Q band peaks from four to two
(540 and 572 nm). Moreover, the position of the peaks of the
compounds displayed a weak violet shift (2–3 nm for Soret and 10–
17 nm for Q band, respectively) depending on the porphyrin ligand.
The mass spectra of the porphyrins 3a, 3b, 3c, 3d and the copper(II)
porphyrins 4a, 4b, 4c, 4d showed the positively charged [M þ H]þ
m/z adducts.
The same method was also used to obtain CuPp(4a), CuPp(4b)
and CuPp(4c) in almost quantitative yield by using H2Pp(3a),
H2Pp(3b) or H2Pp(3c) as the starting material respectively.
2.1.5.1. Cu(II) 5-[3-(3-phenoxy)-propoxy]phenyl porphyrin CuPp(4a).
Yield: 95%. Mp: >200 ꢀC, Anal. Calcd. for CuC53H38N4O2, %: C, 77.38;
H, 4.54; N, 6.53. Found C, 77.03; H, 4.63; N, 6.78. MS: m/z 827.4
([M þ H]þ) amu. UV–vis (CHCl3): lmax, nm, 416 (Soret band), 539,
572 (Q bands).
2.1.5.2. Cu(II) 5,10,15,20-tetra-[4-(3-phenoxy)-propoxy]phenyl porphyrin
CuPp(4b). Yield: 96%. Mp >200 ꢀC, Anal. Calcd. for CuC62H48N4O4, %: C,
76.49; H, 4.89; N, 5.52. Found C, 76.25; H, 4.95; N, 5.74. MS: m/z 977.7
([M þ H]þ) amu. UV–vis (CHCl3): lmax, nm, 416 (Soret band), 539, 572
(Q bands).
2.1.5.3. Cu(II) 5,10,15,20-tetra-[4-(3-phenoxy)-propoxy]phenyl por-
phyrin CuPp(4c). Yield: 95%. Mp >200 ꢀC, Anal. Calcd. for
CuC71H58N4O6, %: C, 75.41; H, 5.10; N, 4.58. Found C, 75.68; H, 5.19;
N, 4.97. MS: m/z 1128.1 ([M þ H]þ) amu. UV–vis (CHCl3): lmax, nm,
416 (Soret band), 539, 572 (Q bands).

186
C. Wang et al. / Dyes and Pigments 84 (2010) 183–189
OH
O
O
Br
OH
O
Br
CHO
NaOH
Br
NaOH
CHO
(2)
(1)
CHO
R
H
N
(3:1 with 2)
Cu2+
NH
N
CuPp (4a)
(1) BF3·OEt2
(2) DDQ
N
HN
(3a)
(3b)
R
Cu2+
Cu2+
Cu2+
NH
N
N
N
N
H
CuPp (4b)
CuPp (4c)
H
HN
(1) BF3·OEt2
(2) DDQ
O
O
R
CHO
CHO
R
H
(2)
N
(1:3 with 2)
NH
N
R
(1) BF3·OEt2
(2) DDQ
N
HN
(3c)
R
R
H
N
NH
N
N
CuPp (4d)
R =
R
R
(1) BF3·OEt2
(2) DDQ
HN
O
O
(3d)
R
Fig. 2. Synthesis of the metal-free porphyrins H2Pp(3a, 3b, 3c, 3d) and copper(II) porphyrins CuPp(4a, 4b, 4c, 4d).
The 1H NMR spectra were also consistent with the structure
of the isolated 3a, 3b, 3c, 3d, and one was shown in Fig. 3.
8.82 respectively), and the ratios of two group spin-splitting
peaks area are 2:6 and 6:2 for 3a, 3c, respectively. Similarly, the
Different symmetry of porphyrin molecules 3a, 3b, 3c, 3d, leads
eight
b-H of pyrrole moiety in 3b show the ratio of two groups
to different resonance of the
the different number of substituents as shown in Fig. 4. The
eight -H of pyrrole moiety in 3a and 3c show the unsym-
metrical spin-splitting pattern because two or six -H are close
to the long meso-substituents (which appear in the high field,
8.89 and 8.88 respectively) and the other six or two -H are
close to the phenyls (which appear in the low field, 8.83 and
b-H of the pyrrole moiety due to
symmetrical spin-splitting peaks area is 4:4. 4b shows one
simple peak in 8.87 because its eight
surrounding.
b-H locate in the same
b
b
The DR spectra of CuPp(4a)–TiO2 having impregnation ratio in
the range 6–14 mol/1 g of TiO2 together with the bare TiO2 used as
m
b
photocatalysts are reported in Fig. 5. It is worth noting that no shift
of the band gap edge of TiO2 can be observed in all loaded samples.
Fig. 3. The 1H NMR spectrum of H2Pp(3b).

C. Wang et al. / Dyes and Pigments 84 (2010) 183–189
187
Fig. 4. The spin-splitting patterns of H-pyrrole peaks in 1H NMR spectra of H2Pp(3a, 3b, 3c, 3d).
Nevertheless they reflect light less significantly than the bare
support and their absorption increases by increasing the loading,
showing characteristic strong absorption bands centered at 416–
422 nm (Soret band) and at 540 nm (Q band). The maximum
absorption values of the bands are similar to those observed for
CuPp(4a) in CHCl3 solution (Fig. 5, inset).
aqueous suspension (after 200 min of irradiation) in the presence of
TiO2–porphyrin systems impregnated with different amounts of
sensitizers.
The photoreactivity results indicated that the most effective
amount of sensitizer is 10, 8, 8 and 6 mmol/1 g TiO2 for CuPp(4a)–
CuPp(4d), respectively. This can produce an optimal situation of
monolayer having, presumably, just a minimal extent of aggrega-
tion of the porphyrin molecules impregnated onto TiO2 surface.
DataofCuPp(4a)–TiO2, CuPp(4b)–TiO2, CuPp(4c)–TiO2, CuPp(4d)–
TiO2 samples impregnated with the practical optimal values of
sensitizer and their photocatalytic activities are reported in Table 1.
It can be noticed that the photocatalytic activity decreased in the
following order when using the most efficient photocatalysts:
8-CuPp(4c)–TiO2 > 8-CuPp(4b)–TiO2 > 6-CuPp(4d)–TiO2 > 10-
CuPp(4a)–TiO2 > TiO2 (bare).
3.2. Photoreactivity experiments
The photocatalytic activities for the degradation of 4-nitro-
phenol (4-NP) in water were tested using prepared CuPp(4a)–TiO2–
CuPp(4d)–TiO2 photocatalysts.
The most efficient photocatalysts require an appropriate
amount of sensitizer in order to achieve an optimum coverage of
the TiO2 surface. In fact, a deficient coverage of the TiO2 surface
could not efficiently induce an extension of light absorption in the
visible range, whereas an over coverage could give rise to formation
of multi-layered aggregates with a detrimental effect for the
photocatalytic activity. Consequently different photocatalysts were
prepared by impregnating TiO2 with various amounts (2, 4, 6, 8, 10,
Fig. 7 shows some experiments carried out by using 6-CuPp(4a)–
TiO2–6-CuPp(4d)–TiO2 samplesimpregnatedwith thesameamount
of sensitizer (6
mmol/1 g TiO2) to compare the influence of the
number of the peripheral substitutions on the efficiency of TiO2–
porphyrins systems. All these composites showed a photocatalytic
efficiency for the degradation of 4-NP in aqueous suspension, and
the photocatalytic activity decreased in the following order:
12 and 14 mmol/1 g TiO2) of the sensitizer CuPp(4a, 4b, 4c, 4d) for
the sake of comparison. Fig. 6 shows results of 4-NP degradation in
14-CuPp(4a)-TiO2
12-CuPp(4a)-TiO2
0.75
CuPp(4d)-TiO2
CuPp(4c)-TiO2
CuPp(4b)-TiO2
CuPp(4a)-TiO2
80
10-CuPp(4a)-TiO2
8-CuPp(4a)-TiO2
6-CuPp(4a)-TiO2
TiO2
0.70
70
60
50
40
30
20
10
0
0.65
0.60
0.55
0.50
0.45
0.40
0.35
0.30
8
1.0
0.8
0.6
0.4
0.2
0.0
300
500
600
400 l(nm)
2
4
6
8
10
12
14
200
300
400
500
600
700
800
µmol CuPp /1g TiO2
l
(nm)
Fig. 6. Comparison of the photocatalytic activities in terms of 4-NP concentration
vs. different impregnation ratio CuPp(4a)–TiO2–CuPp(4d)–TiO2 after 200 min of irra-
diation time.
Fig. 5. Diffuse reflectance spectra of bare TiO2 and differently loaded samples obtained
by impregnation of TiO2 with CuPp(4a). Inset: spectrum of CuPp(4a) in CHCl3.

188
C. Wang et al. / Dyes and Pigments 84 (2010) 183–189
Table 1
The different number of substitutions in the porphyrin ring can
affect the efficiency of the photodegradation to a certain extent
with the following decreasing photocatalytic activity order:
6-CuPp(4d)–TiO2 > 6-CuPp(4c)–TiO2 > 6-CuPp(4b)–TiO2 > 6-
CuPp(4a)–TiO2 > TiO2
The photocatalytic activity of the studied composites depends
mainly on the amount of sensitizer impregnated onto the TiO2
surface and only in lesser extent on the peripheral substitutions of
the porphyrins.
Some relative data and comparison of the photocatalytic activities in terms of
degradation of 4-NP vs. optimal impregnation ratio CuPp(4a)–TiO2–CuPp(4d)–TiO2
after 200 min irradiation.
Samples
Size of the
sensitizer
molecule
Calculated
Practical
4-NP (%)
optimal value optimal value converted
(
m
mol/1 g
(m
mol/1 g TiO2) after 200 min
irradiation
(ꢂ10ꢁ18 m2) TiO2)a
CuPp(4a)–TiO2 1.53
CuPp(4b)–TiO2 1.86
CuPp(4c)–TiO2 2.37
CuPp(4d)–TiO2 2.88
8.7
7.1
5.6
4.6
10
8
8
60.76
63.26
64.95
61.59
6
Acknowledgment
a
The calculated optimal value refer to 1 g TiO2 flatly covered by porphyrins onto
the surface.
We are very grateful for the financial support from National
Nature Science funds and The International Cooperation Project of
Shaanxi province (2008KW-33).
1.0
6-CuPp(4d)-TiO2
6-CuPp(4c)-TiO2
6-CuPp(4b)-TiO2
6-CuPp(4a)-TiO2
TiO2
References
0.8
0.6
0.4
0.2
0.0
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