VIETNAM JOURNAL OF CHEMISTRY VOL. 51(3) 363-367
APPLICATION OF PHOTOCATALYST Fe-C-TiOj COATED ON ACTIVATED CARBON IN THE DEGRADATION OF RHODAMINE B
Le Thi Thanh Thuy', Phung Thi Nguyen^ Phi Thi Huong^ Nguyen Minh Phuong^
Nguyen Dinh Bang^ Nguyen Van Noi*
' Faculty of Chemistry, Qui Nhon University
^Faculty ofChemistry, Hanoi University of Science Received 14 September 2013
Abstract
Carbon and iron co-doped titanium dioxide catalyst carried on activated carbon (Fe-C-TiOj/AC) was successfully synthesized using the sol-gel method and then treated by hydrothermal treatment. Activated carbon (AC) was modified by HNOj and poly(sodium styrene sulfonate) (PSS) before being carried on the caulyst. The composite was characterized by XRD, UV-VIS spectrophotometry, IR, SEM and BET. The performances of the supported catalysts have been evaluated for the degradation of Rhodamine B (RhB) solution under visiblC'-Iight irradiation. Results show that, with the appropnate amount of activated carbon, prepared catalysts Fe-C-Ti02/xAC showed the high catalytic activities and Fe-C-Ti02/12AC sample showed the best performance. Catalysts carried on AC and modified by HNO3 and PSS have better efficiency than non-modified one.
Keywords: Activated carbon, photocatalyst, Rhodamine B, poIy(sodium styrene sulfonate), HNO3.
1. INTRODUCTION
TiO: photocatalyst has been used widespreadly in the treatment of wastewater and environmental pollutants on account of its high efficiency, non- foxicity, propitious recycle ability and low cost.
Besides, the final products of the photocatalysis in the advance oxidahon process are CO2. H3O, inorganic ions, minerals... [1. 2]. However, the application of Ti02 is limited because the catalyst is only activated under UV radiation and it is difficult to recycle. Therefore, catalyst modification is crucial to enhance the activity of catalyst. There are a number of papers pertaining to the modification of the catalyst by doping with metals as V, Cr, W, Fe so that the catalyst can perform its function under the visible light. Among these metals. Ti02 doped with Fe is in progress because Fe can replace the positions of Ti** in the crystalline, reducing the band gap energy, which is conducive to the activation in the visible light [3]. Moreover, Fe ions function as traps to incarcerate electrons and hinder the recombination of elecfron/hole pairs, resulting in the increase of catalyst's performance. In addition, the introduction of some non-metal elements as N, C, S, P and halogens into TiO; structure also reinforces the activity of the catalyst. Ti02 doped by carbon has a great potential for degradation of organic
waste. To recycle the catalyst and lower the cost, materials are designed to provide a high surface area to support the catalyst. They are activated carbon, glass, silicagens, polymers, zeolites, cottons, celluloses...[6, 7], These materials share some common characteristics: (1) binding to the catalyst;
(2) non-desfroying catalyst, (3) high surface area, (4) high affinity to the adsorption of pollutant molecules [7]. For ages, activated carbon has unarguably been the most preferred material since it has high surface area and porous sizes, adsorbing effectively organic compounds and it is relatively stable. Additionally, activated carbon facilitates the photo-catalysis not only by clutching the photo-agents and free radicals OH but also by adsorbing pollutant molecules on the photochemical centers of the catalyst [7]. There are types of techniques to coat catalyst on the material surface including sol-gel, thermal treatment, chemical vapor deposition, electrodeposition, hydro- thermal, low temperature impregnance [7-9]. In this paper, Ti02 co-doped by iron and carbon coated on activated carbon was prepared by sol-gel followed by solvothermal method. The activated carbon was treated by HNOj and PSS before carrying catalyst.
Characterization of the catalyst was conducted by XRD, IR, XPS, SEM, UV-Vis and BET. The catalytic activity of the catalyst was examined by the degradation of RhB dye.
VJC, Vol. 51(3), 2013 2. EXPERIMENTAL 2.1. Catalyst preparation Chemicals
TIOT (tetraisopropyl orthotitanate 98%), nitric acid (HNO3 68%), ancol ethylic (C2HSOH 99.7%) and iron (III) nitrate (Fe(N03)3.9H20 pure), Rhodamine B (CjjjHaiClNzOj).
Activated carbon Tra Bac (AC - particle sizes from 0,075 mm to 4.75 mm, surface area BET 928.15 mVg).
The preparation of Fe-C-TiOi coated on activated carbon pretreated by HNO3 (Fe-C-TiO/AC-N)
Treatment of carbon with HNO3: The coal is ground to a fine powder 0.16 mm before being washed with water and boiled in 2 hours to eliminate gases such as O2, CO2, SO2. Next, extracted carbon was immersed into HNO3 I2M and stirred for 3 hours at room temperature, then soaked in 24 hours.
Finally, activated carbon was washed several times with distilled water, then dried in 3 hours at lOO^C.
The preparation of (Fe-C-TiOj/AC-N): Pour 6ml of TIOT into 34 ml of ethylic alcohol (solution A), solution B contained 17 ml of ethanol, 0.4 ml of nitric acid (68%), 1.6 ml distilled water, 48.2 mg of Fe(N03)3.9H20 and 0.2 g AC-N. Drop solution A into solution B under slowly stirring in 14 hours at room temperature and left for gelation in 2 days before being autoclaved in Teflon vessel in 10 hours at 1 ZO°C. The resulted powder was washed and dried at lOOT in 24 hours to obtain the Fe-C-Ti02/AC-N catalyst.
The preparation Fe-C-TiOs coaled on activated carbon pretreated by PSS (Fe-C-TiO/AC-P)
Treatment of carbon with PSS: the procedure of grinding and washing coal was the similar to the previous one. Next, 0.2 g of carbon powder was immersed into 40 ml of 0.5% PSS solution before being ultrasonicated in 1 hour and stirred in the next 3 hours. The final product was filtered, washed and dried at room temperature.
The preparation of (Fe-C-TiOz/AC-P): Pour 6ml of TIOT into 34 ml of ethylic alcohol (solution A), solution B contained 17ml of ethanol, 0.4ml of nitric acid (68%), 1.6 ml distilled water, 48.2 mg of Fe(N03)3.9H2O. Drop solution A into solution B under slowly stirring in 24 hours at room temperature. Then put 0.2 g AC-P into the solution, continue stirred slowly in 14 hours at room temperature and left for gelation in 12 hours before being autoclaved in Teflon vessel in 10 hours at ISO^C. The resulted powder was washed and dried at lOO^C in 24 hours to obtain the Fe-C-Ti02/AC-P catalyst.
Le Thi Thanh Thuy, etal 2.2. Characterization of catalyst
The crystal phase composition of catalyst was determined by XRD (D8-Advance 5005). Surface characterization was specified by SEM (Hitachi S4800). Wavelength absorption was conducted by UV-Vis (Tasco-V670 photospecfrometer).
Functional groups were identified by IR spectroscopy (IR prestige 21). Nitrogen isothermal adsorption (Brunauer-Emmett-Teller-BET) was done by TriStar 3000 V6.07 A. RhB concentrations were determined by UV-Vis at 553nm (the absorption maximum wavelength of RhB).
2.3. Examination of catalytic activity experiment The catalytic acfivity of prepared material was examined by the degradation of RhB solution (2 Omg/I) under visible irradiation. The compact light (36 W) was used instead of solar light with a range of wavelengths from 400 to 700 nm. 100 ml of RhB solution in 250ml beaker was added with an appropriate amount of catalyst (I-3g/l). The solution was then mixed at a constant rate in the dark for 30 minutes to ensure a desorption/adsorption equilibrhtm before being Irradiated. After certain periods of time, the RhB concentrations were determined by the UV-Vis spectroscopy.
3. RESULTS AND DISCUSSION 3.1. Catalyst characteristics
The XRD patterns (Fig. I) show that Fe-C-Ti02 after being coated on activated carbon by two ways exhibits the typical peaks referring to the anatase form. The phase composition, nano-scale particles are preserved compared with the original materials though the lafter is a litter bit larger. The catalyst coated on AC-P is more surmounted and smaller in the particle sizes regarding to the one coated on AC- N (Fig. 2).
Fe-C-TiOi/AC-N Fe-C-TiOj/AC-P Fe-C-TiOj TiOj
ahatan Fig 1: XRD pattern of Fe-C-TiOz/AC-N;
Fe-C-TiOj/AC-P; Fe-C-TiOj; TiOi
VJC, Vol. 51(3), 2 0 1 3 Application of photocatalyst Fe-C-TiO;...
hydroxyl a n d acid groups o n t h e surface which bond to O I F , H* ions o f catalyst, enhancing the adhesiveness (Fig. 4 ) . Therefore, less amount of the catalyst w a s carried on t h e supporting material of AC-N and the particle sizes may increase (Fig. 3 ) .
Table I s h o w s that the surface areas B E T of A C virgin and A C after carrying catalyst are different.
T h e reason is that during the treatment of activated carbon, HNO3 is a strong oxidant leading to change the porous structure, which decreases the number of small capillaries and increases the number of large ones, and therefore reduces the surface area.
Fig. 2- ( S E M ) images o f A C virgin (2a);
Fe-C-TiOj/AC-P (2b); F e - C - T i O j / A C - N (2c)
The reason m a y b e t h e different m e c h a n i s m s o f coating materials. A C - P functions a s negative charge centers and the catalyst d o e s as positive centers, resulting in the unchanged particle sizes after coating (Fig. 3). T h e best coating corresponds t o an appropriate concentration o f P S S which accumulates the charge density on catalyst. In t h e case o f A C pretreated with HNO3, carbon is supplied more
Fig. 3: Aschematic charge-driven self- assembly process of T i 0 2 / A C composites
H H OH- H* OII,'H*Y OH- H* OH H* OH-
- T i ^ - t f - - T i ' M ) - ' - T i * ^
c5
Fig 4: Ti02 coated on AC-N
This consequence causes a decline of the physical adsorption of activated carbon. In the case of AC-P, PSS molecules adhering catalyst go into the porous structure of activated carbon, resulting in the decrease of surface area and pore sizes.
Table 1: Some physical properties of AC, Fe-C-Ti02, Fe-C-TiOi/AC-N, Fe-C-Ti02/AC-P composites
Sample Fe-C-TiOj/AC-P Fe-C-Ti02/AC-N Fe-C-Ti02
AC
Mean size (nm) from the XRD results
4.33 5.13 4.23
-
BET surface area, m^ g"' 285.55 264.75 237.25 928.16
Vp, cm' g"' 0.41 0.30 0.23
-
VJC, Vol. 51(3), 2013
IR spectrum (Fig. 5a) gives the distinction between activated carbon treated with PSS and HNO3. To specify, there are peaks at 1069 cm'' and 1111 c m ' In AC-P sample corresponding to the stretching vibration of S=0, and peak at 1400 cm"' corresponding to vibration of -C=C- group in the styrene ring, which confirms the appearance of PSS on the surface of AC [8]. In the case of treatment with HNO3, the appearances of - C = 0 , -C-O- and -OH groups on the surface of AC were confirmed by peaks of 1646 cm"', 1071 cm"'vi 1538 cm"' [10].
This verifies that more OH'. H*...ions were accumulated on the activated carbon after being treated with HNO3, which is conducive to carrying catalyst on the AC-N and can be identified by IR spectroscopy. Regard to Fe-C-Ti02/AC-N. peak at 1436 cm"' refers to the -COO-Ti and peak at 502 cm"' refers to Ti-O-C bonds while for Fe-C- TiOj/AC-P, longer wave number at 142 cm"' compared with 1400 cm"' proves the Ti-PSS bonds (-CfiHi-O-Ti). Besides, peaks at 551 cm"' and 505 cm"' correspond to the bonds of Ti-0 and Ti-O-C in catalyst. As a result, the catalyst was coated successfully with HNO3 and PSS by the verification of IR spectroscopy.
Fig. 5. IR pattern of (5a) AC virgin; AC-P, AC-N and (5b)Fe-C-Ti02/AC-N;
Fe-C-TiOj/AC-P; Fe-C-TiOz; TiO;
UV-VIS spectrum (Fig. 6) shows that after carrying catalyst on activated carbon, there is a
Le Thi Thanh Thi/y, et al combination between the spectrum of Fe-C-Ti02 and that of AC. The longer wavelength of absorption of modified catalyst interprets that the catalyst is activated under visible lighL
Wavelength (nm) Fig 6: UV-Vis pattern of AC virgin; Fe-C- TiOj/AC-N; Fe-C-TiOi/AC-P; Fe-C-TiOj; Ti02 3.2. Examination of the catalytic activity of the catalyst in the degradation of RhB under visible light
Figure 7 shows that catalyst carried on the AC exhibits the great efficiency in RhB degradation under the visible irradiation. After 90 minutes of irradiation, 99% of RhB was decomposed. This explains that AC assists considerably in the catalysts performance. The large surface area of AC adsorpted more organic molecules, increasing the rate of decomposition process. Interestingly, Fe-C- TiOj/AC-P degraded RhB faster than Fe-C- Ti02/AC-N, which may be account of the better adhesion of Fe-C-Ti02/AC-P on AC (Fig.2). To optimize the amount of catalyst in RhB degradation, 1-2.5 g/l of catalyst was investigated for both types.
The optimum amount of catalyst is 1.6 mg/l as shown in Fig. 7. The higher quantity of amount may cause the light absorption hindrance, decreasing the efficiency of degradation.
Fig. 8 compares the degradation of RhB of AC virgin and AC carrying catalyst with the same amount of catalyst (1.6 g/l). The resuU points out that if only AC virgin was used, the degradation of RhB is purely adsorption. AC adsorpted RhB until saturation after 60 minutes, which can be proved by unchanged of RhB concentration over time. This illustrates the function of catalyst on AC.
4. CONCLUSIONS
The results show that the catalyst was successful carried on the AC by either PSS or HNO3. The nature of catalyst remained to be unchanged
VJC, Vol. 51(3), 2 0 1 3
regarding to p h a s e c o m p o s i t i o n , particle sizes as well as structure. F u r t h e r m o r e , t h e large surface area of AC adsorbs m o r e organic m o l e c u l e s , a n d that enhances R h B degradation. T h e catalyst with its larger size favors t h e catalyst separation from solution and recycle. T h i s p a p e r illusfrates that F e - C-Ti02 carried on A C is a great potential catalyst in degradation of toxic organic c o m p o u n d s under solar light irradiation.
£ - ^
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—*—i.4a/i
— * ^ 1 E B 1
| - o - 2 S 9 f l
time (min) Fig. 7." Optimize the a m o u n t of catalyst in the
degradationof R h B b y F e - C - T i O j / A C - N (7a) and F e - C - T i O j / A C - P (7b) catalysts
100 3C
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Figure 8: C o m p a r i s o n of activity of b^o catalysts F e - C - T i O i / A C - N and F e - C - T i O i / A C - P w i t h A C virgin Acknowledgements: This research was financially supported by the KC.02.TN08/11-15 Project, Program for Potential Science and Technology
Application of photocatalyst Fe-C-Ti02...
Projects (KC02/11-15) from the Ministry of Science and Technology, Vietnam; and QG 11-13 Project, Vietnam National University.
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