The Photodegradation Effect of Metal Oxide-CNT/TiO 2 Composites Bull. Korean Chem. Soc.2011, Vol. 32, No. 3 815 DOI 10.5012 /bkcs.20 11.32.3.815 The Photodegradation Effect of Organic Dye for Metal Oxide (Cr 2 O 3 , MgO and V 2 O 3 ) Treated CNT/TiO 2 Composites Ming-Liang Chen, Jang-Soon Bae, † Hee-Seung Yoon, ‡ Chang-Sung Lim, and Won-Chun Oh * Depart ment of Advanc ed Ma terials Scienc e & Eng ineeri ng, Han seo Un iversity, Chungnam 356-706 , Kore a * E-mail : wc_oh @hanseo.ac.k r† Depart ment of Engine ering a nd Che mical T echnolo gy, Dan kook Un iversi ty, Chu ngnam 330-714, Korea ‡ Depar tment o f Chem ical En gineer ing, C hungnam Nationa l Unive rsity, Yuseu ng, Dae jeon 30 5-764, Korea Recei ved No vember 22, 201 0, Acc epted Decem ber 28, 2010 Three kinds of organometallic compounds (chromium acetylacetonate, magnesium acetate and vanadyl acetylacetonate) were used as transition metal precursor, titanium n-butoxide and multi-walled carbon nanotube as titanium and carbon precursor to prepare metal oxide-CNT/TiO 2 composites. The surface properties and morphology of metal oxide-CNT/TiO 2 composites were by Brauer-Emett-Teller (BET) surface area measurement, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and energy dispersive X-ray (EDX) analysis. The photocatalytic activity of prepared metal oxide-CNT/TiO2 composites was determined by the degradation effect of methylene blue in an aqueous solution under irradiation of visible light. Key Wor ds : MWCNT, Transition metals, TEM, Photocatalytic activity Introduction The degradation of organic pollutants in waste water by photo cata lysis , using the wide optic al band gap mater ial (TiO2), has attracted extensive attentions during recent 20 years. 1,2 However, it has been well known that this type ofphoto -oxid ation h as two ty pica l drawb acks: fi rstly T iO2 is ahigh energy band (Eg≈ 3.2 eV) material that can on ly be excited by high energy ultraviolet irradiation with awavelength of no longer than 385 nm. This practicall y rules out the use of sunlight as an energy source for the photo- reaction. Secondly, a low rate of electron transfer to oxygen and a high rate of recombination between excited electron- hole pairs result in a low quantum yield rate and also alimited photo-oxidation rate. 3 Recently, many studies have been done to improve photocatalytic properties of TiO 2 powde rs by doping using transition metal elements. The prese nce of forei gn metal speci es i s ge neral ly detrimenta l fo r the degradation of organic species in aqueous systems. Cr and V ion implanted TiO2 have showed photocatalytic reactivity higher than TiO2 for the decomposition of NO under solar beam irradiation. 4 Choi et al. 5 found that doping quantum-sized TiO2 with Fe 3+ , Mo 5+ , Ru3+ , Os 3+ , Re 5+ , V 4+ and Rh 3+ enhances the photoreactivity both for the oxidation of CHCl3 and the reduction of CCl 4. The photocatalytic efficiency of TiO2 toward the oxidation of 1,4-dichloro- benzene is improved by the introduction of WO3 andMoO3 6,7 and a beneficial influence of tungsten was foundfor the photodegradation of 4-nitrophenol. 8,9 Also, in order to extend the absorption threshold of TiO2 to visible light, the effects of some transition metal ion dopants such as Fe, V, Mn, Co and Ni have been investigated for the TiO 2 system. 10 Carbon nanotubes (CNTs) attracted worldwide attention in the past decade because of their unique structural, mechanical and electronic conducting properties, corrosion resistance and stability and promising applications in transi- stors, field-emission tips, sensors, supercapacitors, catalyst supports and storage materials for hydrogen. 11-13 Ti O2/carbon nanotube (CNT) composites attracted more attention than others because of the excellent mechanical property, large surface area, and unique electrical and electronic prope rties of CNT . 14 According to our previous works, 15-17 we prepared the CNT/TiO2 composites by a sol-gel methodand obtained enhanced photocatalytic activity because CNT could be act as an electron sensitizer and donator to accept the photo-induced electron (e − ) into the conduction band ofTi O2 particles under UV light irradiation. In this paper, transition metal ion of Cr 3+ , Mg 2+ and V 3+ doped CNT/TiO2 composites were synthesized by sol-gel method. The properties of prepared metal oxide-CNT/TiO 2 composites were characterized by BET surface area mea- surement, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), andenergy dispersive X-ray (EDX) analysis. Also, the photo- catalytic properties of metal oxide-CNT/TiO 2 composites were simply checked by decomposing methylene blue (MB) solution under visible light irradiation. The absorbance ofdecomposed MB solution was determined by an UV/VIS spectrophotometer. Experimental Procedure Materials. Titanium n-butoxide (TNB, Ti{OC(CH3)3}4, 99%) as titanium alkoxide precursor to form TiO 2 was purch ased from Acros Organ ics (USA ). Multi -wal led carbo n
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7/29/2019 The Photodegradation Effect of Organic Dye for Cr2O3 Treated CNT-TiO2
Department of Advanced Materials Science & Engineering, Hanseo University, Chungnam 356-706, Korea* E-mail: [email protected]
† Department of Engineering and Chemical Technology, Dankook University, Chungnam 330-714, Korea‡ Department of Chemical Engineering, Chungnam National University, Yuseung, Daejeon 305-764, Korea
Received November 22, 2010, Accepted December 28, 2010
Three kinds of organometallic compounds (chromium acetylacetonate, magnesium acetate and vanadyl
acetylacetonate) were used as transition metal precursor, titanium n-butoxide and multi-walled carbon
nanotube as titanium and carbon precursor to prepare metal oxide-CNT/TiO2 composites. The surface
properties and morphology of metal oxide-CNT/TiO2 composites were by Brauer-Emett-Teller (BET) surface
area measurement, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-raydiffraction (XRD) and energy dispersive X-ray (EDX) analysis. The photocatalytic activity of prepared metal
oxide-CNT/TiO2 composites was determined by the degradation effect of methylene blue in an aqueous
solution under irradiation of visible light.
Key Words : MWCNT, Transition metals, TEM, Photocatalytic activity
Introduction
The degradation of organic pollutants in waste water by
photocatalysis, using the wide optical band gap material
(TiO2), has attracted extensive attentions during recent 20
years.1,2 However, it has been well known that this type of
photo-oxidation has two typical drawbacks: firstly TiO2 is a
high energy band (Eg ≈ 3.2 eV) material that can only be
excited by high energy ultraviolet irradiation with a
wavelength of no longer than 385 nm. This practically rules
out the use of sunlight as an energy source for the photo-
reaction. Secondly, a low rate of electron transfer to oxygen
and a high rate of recombination between excited electron-
hole pairs result in a low quantum yield rate and also a
limited photo-oxidation rate.3 Recently, many studies have
been done to improve photocatalytic properties of TiO2
powders by doping using transition metal elements. The
presence of foreign metal species is generally detrimental forthe degradation of organic species in aqueous systems. Cr
and V ion implanted TiO2 have showed photocatalytic
reactivity higher than TiO2 for the decomposition of NO
under solar beam irradiation.4 Choi et al .5 found that doping
quantum-sized TiO2 with Fe3+, Mo5+, Ru 3+, Os3+, Re5+, V4+
and Rh3+ enhances the photoreactivity both for the oxidation
of CHCl3 and the reduction of CCl4. The photocatalytic
efficiency of TiO2 toward the oxidation of 1,4-dichloro-
benzene is improved by the introduction of WO3 and
MoO36,7 and a beneficial influence of tungsten was found
for the photodegradation of 4-nitrophenol.8,9 Also, in order
to extend the absorption threshold of TiO2 to visible light,the effects of some transition metal ion dopants such as Fe,
V, Mn, Co and Ni have been investigated for the TiO2
820 Bull. Korean Chem. Soc. 2011, Vol. 32, No. 3 Ming-Liang Chen et al.
addition of a transition metal also had a charge trapping
effect. Charge trapping can be demonstrated by the follow-
ing equations:5
TiO2 + hv →
ecb−
+ hvb
+
(1)
Mn+ + ecb− →M(n−1)+ (2)
Mn+ + hvb+ →M(n+1)+ (3)
The holes could transfer to the TiO2 surface and react with
OH− to produce active OH•. When a transition metal ion
replaced Ti ions in the TiO2 lattice, most of the dopant levels
appeared between the valence band and conduction band of
TiO2. This could increase the surface trapping rate of the
carrier and retard the electron-hole recombination23,28 as
well as enhance the photocatalytic activity of TiO2. Finally,
the MB solution is decomposed to CO2, H2O, NO3, NH4+
and SO42−.
Conclusions
We introduced transition metals into CNT/TiO2 com-
posites to prepare metal oxide-CNT/TiO2 composites by
using three kinds of organometallic compounds (Cr(acac)3,
Mg(CH3COO)2 and VO(acac)2). The BET surface area was
decreased a lot after treatment by organometallic compounds
and titanium for all of metal oxide-CNT/TiO2 composites.
For the sample MCT, the Cr2O3 and TiO2 particles were
homogenously distributed on the surface of MWCNT. For
sample MMT, the TiO2 particles were distributed on thesurface of MWCNT with some partial agglomerations. For
sample MVT, TiO2 particles with some agglomerates dis-
persed on the surface of MWCNT together with V2O3
particles. From the XRD results, Cr2O3, MgO and V2O3
structures were exited in samples MCT, MMT and MVT,
respectively. The anatase type TiO2 structures were also exit-
ed in samples MCT and MMT, and a mixture strcutures of
anatase and rutile type TiO2 were exited in sample MVT.
Three kinds of main elements (C, O and Ti) were exited in
all of metal oxide-CNT/TiO2 composites, and element Cr,
Mg and V was exited in samples MCT, MMT and MVT,
respectively. Comparison with pure TiO2 and CNT/TiO2composites, the prepared metal oxide-CNT/TiO2 composites
showed very high photocatalytic degradation efficiency for
MB solution under visible light irradiation. Because the
transition metal ions could incorporate into the latice of
TiO2, alter the band-gap energy and shift the absorbance
edge of TiO2 to the visible light region.
References
1. Hoffmann, M. R.; Martin, S. T.; Choi, W.; Bahnemann, D. W.Chem. Rev. 1995, 95, 69-96.
2. Lee, D. H.; Choi, S. Y. Met. Mater. Inter. 2004, 10, 357-360.3. Snn, F. Y.; Wu, M.; Li, W. G. Chin. J. Catal. 1998, 19, 229-233.4. Anpo, M.; Ichihashi, Y.; Takeuchi, M.; Yamashita, H. In Science
and Technology in Catalysis 1998; Delmon, B., Yates, J. T., Eds.;Kodansha: Tokyo, 1999; p 305.
5. Choi, W.; Termin, A.; Hoffmann, M. R. J. Phys. Chem. 1994, 98,13669-13679.
6. Do, Y. R.; Lee, W.; Dwight, K.; Wold, A. J. Solid State Chem.1994, 108, 198-201.