JOURNALor SCll'.NCi;OI'HNl)l-.
ChL-nuL'iil and Hinlogical Sci . 2012, Vol, *i7. No, 8. pp. 22-27 This papiT IS ;ivail.ihle (inline ;il hllp7/sklb,liiiLic alii.vn
S T l i n ON T I N : R K M O N A L O K I M I K N O L I K O M A Q U E O I S SOLUTION BY I'KROXIDK OXIDATION 0 \ KK PILLAR ( LA^ S L c M i n h C a m , Vu T h i T h i c i . N g u y e n M i n h T u a n a n d L e Van K h u
l-'iiciillv ol Chemistry. Ha Noi Nalional Univcrsitv of Etliicalitm Abslrati. In this work, from Bcnl-CD. refined bcntonik- (Bcnl-TC) was prepared using Ihc wc; mctluKi and the pillared benloniles Bcnt-Al, Bcnt-Al/Fc and Bcnl-Al/Cu WCIC synthcsi/cd by the intercalation of Al. Al/Fc and Al/Cu polycalion pillars inlo the mtcrlaycr channels of bcntonile solid, respectively. The catalytic aclivily of llicsc pillared hcnlonites was studied in oxid;ilion reaction of phenol wilh hydrogen peroxide (HjO^) in aqueous solulion al 40 C and atmospheric pressure. The obtained experimental results revealed that Benl-Al/Cu was the best catalyst. It can be interpreted Ihal Benl-.AI/Cu possesses large basal spacing (dooi) and Cu likely ts a good catalyst promoter for Al in order lo generate more OH radials in lliat oxidation reaction
Keywfjrds: AI(Fe)-pi!lar clay, peroxide, phenol oxidation.
1. Introduction
Water pollution is truly an urgently global problem Among the numerous pollutants, phenols are a parlicularly serious problem because lhc\ arc so widespread in the environmenl and because in an aqueous media ihcy ore highly toxicity to most organisms. Several technologies have been developed lo remove organic contaminating compounds from waste-waler, making use of adsiirption, biological treatment and wet oxidation (WO). However, of these methods, only the WO processes show sufficient viability and efficiency for ircaling organic conlaminanls in dilute aqueous solution.
Unfortunately, the cost of trealmenl in industrial applications is relatively high due to the need for high processing temperature and pressure. The use of an appropriate catalyst for WO (catalytic wet oxidation CWO) allows improvement of the oxidation ability of WO processes [ 1 , 2 ] . In CWO, hydrogen peroxide is commonly used as the oxidizing agent because it can generate OH radicals which have the best oxidation power in the liquid oxidation reactions. Among the solid catalysts used for CWO reaction pillared clays seem
Received June 4, 2012. Accepted September 25. 2012.
Contact Le Minh Cam, e-mail address: Ieminhcamsp@yahoo,com
Sludy on the removal of phenol Irom at/lieoiis saliila/n hy peroxide oxidation over pillai i lays
to stand out due lo their versatility in the synthesis to oblain solids having adequate pore size and appropriate polycation pillars, i e, lo generate active and stable hclciogeneous catalysts in aqueous media [3].
In this work, catalysts were synthesized from bcntonile clays inlercalatcd by Al, Al-Fe and Al-Cu polycation pillars. Over these catalysts the modified Fentoii |iroccss can be performed lo completely oxitlizc organic molecules under iiiikl conditions and without considerable leaching of catalytically active cations. The remarkable performance of catalysts investigated in this work would highlight the importance of Al (He, Cu) pillared benlonitcs as efficient catalysts in oxidation reactions of organic pollutant,
2. Content
2 . 1 . E x p e r i m e n t
2.1.L Pillared bentonitc synthesis
Refined benionilc (Bcnl-TC) was prepared from natural Co Dmh bcntonile (Bent-CD) obtained in the Co Dinh region (Thanh Hoa Province, Viclnam) using the wet method [4]. Pillared benlonitcs were prepared as follows:
* Bent-Al (Bentonite pillared by Al polycationsj
Bent-Al was prepared by the slow addition of 0.4M NaOH solution to 0.4M AlCl.j solution undergoing vigorous stirring until the molar ratio of OH-/AP"'" reached 2.0, followed by aging for 10 days al room temperature, Al polyoxocations were formed in the .solution according lo the equation:
I3AICI3 + 32NaOH -> Ali304(OH):,.,Cl7 +32NaCl -^ 4H2O
Four grams of Na-benlonile was placed in suspension in 100 ml of distilled water.
The Al polyoxocation solulion was added slowly to the Na-bentonite suspension, and the mixture was stirred for 2 hours al 70°C in a water bath. The solid was filtered out of the suspension and thoroughly washed wilh distilled water. After drying al 50 - 60°C for 12 hours, the resultant sample was calcined al 400°C for 3 hours wilh a heal lamp al 3°C /min to obtain the Bent-AI.
* Bent-Al/Fe and Benl-Al/Cu (Bcntonile pillared by Al-Fe and Al-Cu polycalions respectively)
Bent-Al/Fe and Benl-Al/Cu were prepared by adding the Fe (or Cu) polyoxocation solution to the Al-polyoxocation solulion and stirring for 2 hours al room temperature to obtain a Fe (Cu)/Al ratio of 0.33. The resultant solution was aged in the same way as for the Al-pillaring solution. The bentonite pillared by Al-Fe polycations (Bent-Al/Fe) and Al-Cu polycations (Bent-Al/Cu) were subsequently prepared in the way similar to that of Bent-Al.
* Bent-Al-Cu-imp ( Bent-Al impregnated with Cu^^ cation solution)
Bent-Al-Cu-imp was separated using the impregnated method as follows: an 23
't.iit' iiiii Vu Ihl'fhici, Nguyen Minh Tuan and Le Van Khu
.ip|ti,ipii,iic .inioiiiii nl CIKNO,!),. was di.ssolvcd in 10 mL of distilled water. The
\l-pilhiKd IKIIUHIIIC was impiegnaicd with (leslily prepared .solution. The resulting paste was ihcii sitiwlv c\,ii)oiatcd till il was complclcly dried. The dried sample was powdered and i<ilun..tl iii npcii an loi (^ hours al -lOO'C Io yield final catalyst: Bcnl-ALCu-imp.
2.1.2. Ciilahsl characlti'i/iiHon
kcfiiK-d .iiul pillaicd bcnioiuic samples were characterized by the XRD technique.
usiny a Philips DitliaLUimctcr. cquip|K-(l wilh fillcicd Cu K„ radiation. The dala were collccicd ill llic 211 i.iMgc ol 2 ^ - S,5 . wiili a sic[i si/e of 0.02' and scan rale of 27min 2.1.3. Cal:il> tic lesl
Phenol t)\idalinn in an at.|Lieous solution was ctiiricd out in a 250 mL glass reactor, stiriini; al 40 C and almosjiliL-rK piessiirc. In cach lest, the reactor was filled with 200 mL of 1 mii/l phenol solution and stirred lor 30 min before adding 0.5 g of catalyst.
Then, stirring continuous foi anolhcr 5 nun. a certain volume of hydrogen peroxide 30 % IwO solution was uMiiinually added to tiic reactor uilh a flow rate of appropriately 0.6 mL/min. During Ihc reaction process, alter a certain period of time, liquid samples from the icactoi were taken to determine phenol concentration. Con\ersion of phenol during reaction is calculated as follows
n ( ' / ) - C x l O O / C „ where a (%): conversion of phenol.
CQ: initial concentration of phenol (mg/L);
C' concentration of phenol al lime l (mg/L).
Phenol concentration was determined using a LILV-310S UV-Vis Spectrophotometer at A = 270 nm. At the end of cach reaction run. the amount of iron, copper and aluminium cations that leached from solid catalysts was also measured using the AAS method,
2.2. Result a n d discussion 2.2.1. Pillared bentonites
Figure 1 picsenls the XRD patterns of the study samples Bcnt-TC. Bent-Al, Benl-Al/Cu and Bent-Al/Fe.
It IS weU-known [3] thai an XRD peak with 26 < 10" is characteristic of a mesopore presence in solid layered materials and values of dooi indicate the dimension of channels (pores) between the aluminosilicate 2:1 layers in bentonite structure.
From Figure 1, it is noted that due to pillaring Al, Al-Cu, and Cu-Fe polycations, the distance between interlayered channels of pillared bentonite clays increases from 13.97 A (Bent- TC) to 20.17 A (Bent-Al/Fe). This increase may provide favorable conditions for the mass-transfer of reactants in a heterogeneously catalytic reaction system.
Study on the removal of phenol from ttiiiiecnis .wlution b\ peroxide tnuhiiion over /nltai clay'
Figure 1. XRD pattern of (a) Betit-TC, (h) BeiU-Al, (c) Bent-Al/Cu and (c) Bent-Al/Fe
1.1.1. Phenol oxidation
The catalytic acti\it> of pillared bentonites was investigated in the phenol oxidation reaction with hydrogen peroxide (HjOj).
The reaction occurs through the following equation C„Hr,0H-H 14Hj0j >COo- I7H2O The obtained results are shown in Table i.
Table 1. Conversion (%) of phenol oxidation over different catalysts
Samples Bent-TC Bent-AI Bem-AI/Fe Bent-Al/Cu Bent-Al-Cu imp
Time (minute) 30
13.38 16.83
2.17 60 7.80 18.38 17.94 14.00 8 . 2 0 -
75 7 88
19.44 .14 18
IOO 23.10
87 00 130 22.66 22 12 21.18
150 25.56
91.72"
.54.13*
200 23.37
2t 77
90.16 260
23.86
92 34 300 21 14
1400 83 54 97.10 96 87 97 15 96.26 Note ': dala at 160 min and ": dala al 45 min.
Table 1 shows that the phenol oxidation reaction with H2O2 under given conditions reached equilibrmm at 1400 minutes ( ~ 23 hours). In equilibrium, phenol conversion over all pillared bentonite catalysts is practically the same and equal to '^ 97 % (Figure 2),
It is demonstrated that Al, Al-Fe and Al-Cu polycation pillars dispersed on the internal or external surface of bentonite may catalyze phenol oxidation reaction. But, from data of Table 1 and Figure 3, it may be seen that the reaction rate of phenol oxidations over these catalysts in rather different.
25
[.c Minh Cam, Vu Thi Thiet, Nguyen Minh Iban and Le Van Khu
Figure 2a. Catalytic activity of modified clays ill the phenol oxidation reaction
Figure 2b. Phenol conversion (%) at 1400 minutes
( o n < * n « « ( % )
moo
(ODO
"" •*IS
,>» / ?
•rr' /
\ / A ——
7 ^
• » M < - * M U
» r M - « K u
— •<««
too n o »•>
r * n e | m n i i > n |
Figure 3. Phenol conversion over catalysts from 0 to 300 minutes
Figure 4. The effect of Cu in catalytic activity of modified clays Figure 4 indicates that after about 200 minutes, phenol conversion over a Berit-Al/Cu sample can reach 97% and over Bent-AI-Cu-imp it is up to 90%. This means that Bent-Al/Cu and Bent-Al-Cu-imp samples possess more active sites for reaction.
H2O2 -)• OH
Clearly, the more OH radicals are formed, the more phenol conversion occurs. Thus, in this case Cu is probably a good catalytic promoter for Al to improve catalytic activity of Al pillared bentonite catalysts.
Based on phenol conversion (%) at 200 minutes (Figures 3 and 4), we can predict propensity for catalytic activity as follows;
Bent-Al/Cu > Bent-Al-Cu-Imp > Bent-Al Bent-Al/Fe > Bent-Tc
Note that Bent-Al/Fe has the largest dooi (20.10 A, from Figure 1). However, the catalytic activity of the Bent-Al/Fe sample is not higher than that of the Bent-Al sample.
So, in this reaction the role and the nature of catalytic sites seem to be more important than the dimension of the pores (channels) of the material. Indeed, the phenol molecule (~6 A) is smaller than dooi (14-20 A), that of pillared bentonites, and consequently the transfer of H2O2 and CeHsOH molecules within catalyst micropore is not difficult.
26
Sludy on the removal of phenol from tujuetms solution hy peroxide oxidation over pillar t lays
From Table 1 and Figures 2a and 2b wc can sec that the Bent-TC sample also catalyzes phenol oxidation by H2O2 although the amount of conversion is insignificant.
This can be interpreted as an influence of metal (Cu. Fc. Ti) impurities in Bent-TC and a possible role that they play regarding catalytic sites for that reaction.
From Figures 3 and 4, il is noted ihal the catalytic aclivily of the Bcnt-Al-Cu-imp sample is lower than that of Bcnt-Al/Cu. The reas(Mi for this is that with the impregnation method, Cu^""" ions do nol make contact wilh A l ' ' ions as well as they do wilh the pillaring method. Indeed, the impregnation mclhod can disperse some CLI^+ ions at the external surface of bentonite causing there to be fewer catalytic sites (Al-Cu) than there would be with the pillaring method.
3. Conclusion
This work has been a preliminary investigation into the catalytic behavior of pillared bentonite clays when acted upon by Al, Al-Fe and Al-Cu polycatuins (polyoxides) causing a phenol oxidation reaction by hydrogen peroxide. Some conclusions obtained from Ihis work are as follows:
1-Refined bcnlonite (Beni-TC) from Co Dinh (Thanh Hoa Province, Vietnam) was used in synthesizing four pillared bentonite catalysts by the inlercalalalion of single and mixed oxide pillars of aluminium and iron (or copper): Benl-Al, Bcnt-Al/Fe , Benl-Al/Cu and Bent-Al-Cu-imp. The basal spacing dimention of pillared beutoniles was increased revealing the success of catalyst synthesis as intended.
2-Phenol oxidation by H2O2 at low temperature was performed in five samples:
Bent-TC, Bent-Al, Bent-Al/Fe, Bent-Al/Cu and Benl-Al-Cu-imp. The results showed that Cu is a good promoter for Al as a Bent-Al catalyst, Bent-Al/Cu is the best catalyst lo effect the oxidation of phenol by H2O2 under the conditions given in this work. The relative strength of catalytic activity ofthe samples is as follows:
Benl-Al/Cu > Bent-Al/Cu-imp > Bent-Al - Bent-Al/Fe > Bent -TC
3-From the obtained results it can be suggested thai pillared bentonite catalysis containing AI-Cu pillars could be promising catalysis for phenol oxidation by H2O2.
REFERENCES [1] R. M. Lion, S. H. Chen, J. Hazar., 2009. Mater. 172, 498.
[2] M. E. S. Ojeda, A. Fabregat, F Stuber, 2007. Chem. Eng. J. 132. 105.
[3] J. Carriazo, E. Guelou, J. Barrault, J. M. Tatibouel, R. Molina, S. Moreno,. 2005.
WaterRes. 39, 3981.
[4] JamesO.Ocf a/., 2008. Journal of North Carolina Academy of Science 124(4), 154.
