Application of tio2–p25 in the photodegradation of n–lauryl diethanolamine and cinnamic acid in presence of oxygen

Journal of Science and Technology 55 (xx) (2017) 249–256 APPLICATION OF TiO2–P25 IN THE PHOTODEGRADATION OF n–LAURYL DIETHANOLAMINE AND CINNAMIC ACID IN PRESENCE OF OXYGEN Loc L. C. 1, 2, *, Anh H. C. 2, Anh N. P. 2, Tot N. T. N. 2, Quy N. N. 2, Tri N. 1, Cuong H. T. 1, Van N. T. T. 1 1Institute of Chemical Technology, Vietnam Academy of Science and Technology 1 Mac Dinh Chi Street, Ward 1, District 1, Ho Chi Minh City, Vietnam 2Faculty of Chemical Engineering, University of Technology–VNUHCM 268 Ly Thuong Kiet Street, Ward 14, District 10, Ho Chi Minh City, Vietnam *Email: camloc.luu@gmail.com Received: 30 December 2017; Accepted for publication: 9 March 2017 ABSTRACT In this paper, the activity of TiO2–P25 in the photodecomposition of recalcitrant organic compounds such as n–lauryl diethanolamine (n–LDA) and cinnamic acid (CA) solution in UV + BLED light in presence of oxygen was investigated and the optimum conditions of reaction were determined. With physicochemical characteristics such as anatase/rutile ratio of 80/20, the crystallite size of 23 nm, BET surface area of 43.6, the light absorption wavelength of 390 nm, band gap energy of 3.17 eV, and point of zero charge of 6.3, TiO2–P25 catalyst is able to photodecompose more than 95 % of LDA and CA after 90 minutes in presence of oxygen under irradiation of UV–B light. Keywords: cinnamic acid, n–lauryl diethanolamine, oxygen, TiO2–P25. 1. INTRODUCTION Pollution of persistent organic compounds (POCs) is one of the primary concerns. In wastewater, POCs are usually aromatic hydrocarbons, condensed polycyclic compounds, organochlorines. These matters are highly toxic to organisms and humans and derived from various sources [1]. Until now, photocatalysis is considered as a capable method to degrade thoroughly POCs [2], reusable treated wastewater [3]. Currently, TiO2 – Degussa P25 (TiO2– P25) is one of the commercial photocatalysts that is highly active and commonly used. TiO2– P25 is used in treatment of phenolic compounds and pesticides in wastewater [4–6] such as phosphamidon [7], dephenamid [8], indole–3–acetic and indole–3–butyric acid [9], dimethoate [10], propham, propachlor and tebuthiron [11], 4–chlorophenol and 2,6–dicholorophenol [12]; substances in urban wastewater (acetaminophen, antipyrine, atrazine, carbamazepine, diclofenac, flumequine, hydroxybiphenyl, ibuprofen, isoproturon, ketorolac, ofloxacin, progesterone, Application of TiO2–P25 in the photodegradation of n–lauryl diethanolamine and cinnamic acid 250 sulfamethoxazole and triclosan) [13, 14], textile wastewater (reactive red 4, methylene blue [15– 17], reactive red 222 [18], crystal violet [19], remazol black [16], methyl orange and congo red [20]), herbicide (picloram [21] and imazethapyr [22]),... Cinnamic acid (C9H8O2) of phenolic acids is a very persistent unsaturated carboxylic. It usually presents in wastewater of processing plant of vegetables and vegetable oils, mostly in wastewater of processing plant of palm oil and olive oil (105.3 mg/L) [23]. Cinnamic acid (CA) is processed by advanced oxidation processes by H2O2 [24], Fenton reaction Cu2+/H2O2 [24] Fe2+/H2O2 [24, 25] or Fe2+/H2O2 combining UV [25]. However, the photocatalytic reaction of TiO2 using various oxidizing agents to degrade CA wasn’t studied. Our survey is carried out within 7 Framework Programme of the European Council “Photocatalytic materials for treatment of persistent organic industrial waste”, it showed that the wastewater of some seafood processing plants in Ho Chi Minh City contained persistent organic compounds in which n–lauryl diethanolamine (C16H35NO2) had the highest concentration from 50 to 100 μg/L. n–Lauryl diethanolamine (n–LDA) is a surfactant discharged from the cleaning stage of processing tools as well as floor after every workday. By conventional biological treatment used in all plants, it is impossible to decompose this surfactant. Up to now, no study about treating of this substance has been announced. Therefore, the scope of this work is to apply TiO2–P25 catalyst in the photodegradation of n–lauryl diethanolamine and cinnamic acid under UV light (λ = 365 nm) using oxygen as oxidizing agents and propose the optimum reaction conditions. 2. MATERIALS AND METHODS Before reaction, catalyst TiO2–P25 (Degussa, Merck) was activated at 450 °C for 2 hours in the air flow of 3 L/h. Photoactivity of catalyst in the decomposition of n–LDA or CA (concentration ~ 50 mg/L) was surveyed under the light of 365 nm in wavelength. n–LDA and CA were purchased from Sigma–Aldrich. All chemicals were used without further purification. The reaction was conducted in batch, reaction volume of 250 mL and stirrer speed of 250 rpm. To determine optimum conditions, the influence of initial pH, solution temperature, concentration of oxygen and catalyst was studied. n–LDA concentration in solution was determined by high–performance liquid chromatography HPLC (Scharlau – Spain) in Faculty of Chemistry, University of Science – VNUHCM. Stationary phase: ACE3–C1 column (diameter of 4.6 mm, length of 150 mm, the particle size of 3.5 µm) was stabilized at 40 °C. The mobile phase has ratio phase A: phase B of 20:80 (v/v) with the flow speed of 0.5 mL/min. In which, phase A is deionized aqueous solution containing 0.1% formic acid and phase B is a MeOH solution containing 0.1 % formic acid. CA concentration was analyzed by a spectrum analyzer UV–1800 (Shimadzu, Japan) in Institute of Chemical Technology – VAST at a wavelength of 272 nm [26]. 3. RESULTS AND DISCUSSION TiO2–P25 catalyst used in this study has anatase/rutile ratio of 80/20, crystal size of 23 nm, pore diameter of 3.3 nm, pore volume of 0.037 cm3/g, specific surface area of 43.6 m2/g, absorbable light wavelength λ = 390 nm, band gap energy Eg = 3.17 eV, and point of zero charge PZC of 6.3. 3.1 lig no con am sub Fi 3.2 wa n– to con inc con be lig gen So sol of lim (1. ab to an Loc L. . Adsorptio Survey re hts) (Figure more than ducting pho ount of n– stances are gure 1. Conc . Photodegr Influence s presented Figure 2a LDA conver 0.1 g/L, t centration w reased, and centration w cause when ht adsorptio erate light s the optimum Figure 2b ution was in OH* and H iting electr 0 L/min) n– sorption of t the surface d leading to C., Anh H. C n and photo sults of ads 1) showed t 20 mg/g an tocatalytic LDA and C difficult to d entration vari (UV–LED, adation of n of reaction in Figure 2. showed th sion reached he time of as increase the stable co as increase the concentr n coefficien hielding eff concentrat showed tha creased from OO* radica ons–holes LDA degra he solution. of liquid and decrease in t ., Anh N. P. lysis orption (wi hat CA was d adsorption reaction, the A metaboli ecompose u ation of n–LD λ = 365 nm) C –lauryl die conditions at with low stable valu reaching s d from 0.025 nversion w d to 0.1 g/L ation of TiO t would be ect that redu ion of 0.05 g t n–LDA co 0.5 to 0.7 L ls, oxygen a recombinatio dation was On the othe air bubbles he treatment (a) , Tot N. T. N th catalyst, adsorbed ve reached sa adsorption zed in pho nder UV rad A (a) and CA at T = 25 °C; n–LDA or CA ~ 5 thanolamin on photodeg concentrati e after 60 mi tabilization to 0.05 g/L as increased , the n–LD 2 was too h decreased. ced the surfa /L was chos nversion wa /min. This lso played a n. Howeve decreased d r hand, with , reducing t efficiency. ., Quy N. N., no lights) a ry little on T turation afte should be i tolysis is v iation. (b) in adsor pHinitial = 7,0; 0 mg/L. e radation of ons of TiO2 nutes. If cat reduced to , treatment e from 74 to A degradati igh, reaction Besides tha ce area of th en. s increased w was because n important r, when ai ue to foam strong distu he catalyst a Tri N., Cuon nd photolys iO2–P25 wh r 40 minute mplemented ery low. Th ption (Ccat = 0 Vstirrer = 250 n–LDA ove –P25 (0.025 alyst concen 30 minute fficiency of ~ 100%. Ho on was redu solution ha t, residual e TiO2 expo hen airflow oxygen sup role in the rflow was appearance rbance, cata mount direc g H. T., Van is (no catal ile n–LDA s. Therefor for 40 minu is proved b .5 g/L) and p v/ph; r catalyst T and 0.05 tration was i s. When T n–LDA sign wever, when ced to 71% d high turb TiO2 particl sed to light supplied to ported the g capture of e increased t , this preve lyst particle tly involved ( N. T. T. 251 yst, with adsorbed e, before tes. The oth two hotolysis iO2–P25 g/L), the ncreased iO2–P25 ificantly catalyst . This is idity and es could [27, 28]. reaction eneration lectrons, oo high nted UV s moved reaction b) Ap 25 spe 60 99 of ne tha ph con app ab plication of T 2 Figure 2c ed of reacti and 20 min −100 %. Ac catalyst surf gatively cha n PZC of ca According otodecompo Figure 2. Inf Figure 2d version inc roximately out 25 °C − a) Effe (Qair = 0. c) Ef (Ccat = 0.05 g iO2–P25 in showed tha on was incre utes, respec cording to th ace. When s rged, adsorb talyst, cataly to analysi sition of n–L luence of vari showed w reased not the same a common tem ct of catalyst 7 L/min; pH = fect of initial /L; Qair = 0,7 the photode t when initia ased, the tim tively. How e authors [2 olution pH w ed cationic c st adsorbed pH < PZ pH > PZC: s, PZC of T DA occurre ous factor on oxyg hen reactio much and nd reached perature of concentration 7; T = 25 °C pH solution L/min; T = 2 gradation of l pH solutio e of reachin ever, the co 9], solution as greater t ompounds anionic com C: TiOH + TiOH + OH iO2–P25 w d favorably n–LDA conv en on TiO2–P n temperat after 60 m ~ 99.8 %. water sampl ) 5 °C) n–lauryl die n was increa g stabilizati nversion in pH had an han PZC of and convers pounds acco H+  TiOH ⁻  TiO⁻ + as 6.3 and at pH = 9 w ersion (X) ov 25 catalyst. ure increase inutes, the Therefore, r e at weather (Ccat = 0 d) Effe (Ccat = 0.05 thanolamine sed from 5 on was redu three cases impact on th catalyst, cat ely, when so rding to the 2 + H2O n–LDA had as suitable. er photodecom d from 20 degradatio eaction tem condition in b) Effect of a .05 g/L; pH = ct of reaction g/L; Qair = 0. and cinnam to 7 and 9, t ced from 90 was the sam e electrical alyst surface lution pH w reactions: pKa = 8.7 position tim to 30 °C, ns of n–LD perature wa Vietnam. irflow 7; T = 25 °C temperature 7 L/min; pH ic acid he initial down to e about property became as lower (1) (2) [30] so e with n–LDA A were s chosen ) = 9) 3.3 cat inc con low con con inc con of F 0.3 82 Loc L. . Photodegr Influence alyst TiO2–P Similarly reased over version cou er than tha taining arom centration reased from version wa catalyst. igure 3. Influe CA degra L/min (Fig %. Howev a) Effe (Qair = 0 c) Ef (Ccat = 0.25 C., Anh H. C adation of of reaction 25 was pres to n–LDA time (Figur ld not reac t of n–LDA atic ring th from 0.125 68 to 86 % s not increas nce of reactio dation incre ure 3b). Aft er, if airflow ct of catalyst .3 L/min; pH fect of initial p g/L; Qair = 0.3 ., Anh N. P. cinnamic ac conditions ented in Fig photodegrad e 3a) but it h a stable v despite usin at was more to 0.5 g/L . If conten ed substanti n factors on p ased when er 90–minut was incre concentration = 7; T = 25 °C H solution L/ph; T = 25 , Tot N. T. N id on photooxi ure 3. ation, in CA was slower alue. In the g higher cat persistent th , efficiency t of catalyst ally, follow hotodecomp increasing a e reaction, th ased to 0.5 ) °C) ., Quy N. N., dation of CA photooxid than the n– other word alyst amoun an acyclic n of CA de was contin ed by a decr osition of CA irflow supp e conversio L/min, tre (Ccat = 0 d) Eff (Ccat = 0.25 Tri N., Cuon with oxyg ation the co LDA case, s, the metab t. This can b –LDA. Whe gradation af uously incre ease (down with oxygen lied to the n of CA inc atment effic b) Effect of a .25 g/L; pH = ect of reaction g/L; Qair = 0. g H. T., Van en as an ox nversion of after 90 mi olic rate of e explained n increasing ter 90 min ased to 0.5 to 78 %) at on TiO2–P25 solution fro reased from iency was i irflow 7; T = 25 °C temperature 3 L/ph; pH = N. T. T. 253 idant on CA was nutes the CA was that CA catalyst utes was g/L, the 0.75 g/L catalyst. m 0.1 to 72 up to ncreased ) 3.8) Application of TiO2–P25 in the photodegradation of n–lauryl diethanolamine and cinnamic acid 254 slowly, and CA conversion was slowly increased from 82 to 85% after 90–minute reaction. So the efficiency is highest with airflow of 0.3 L/min. Compared to n–LDA photooxidation, in CA photoreaction the airflow supplied to the reactor was low (0.3 compared to 0.7 L/min) as the complete oxidation of a n–LDA molecule (C16H35NO2) needed 25 O2 molecules, while a CA molecule (C9H8O2) was fully oxidized with 10 O2 molecules. When increasing initial pH solution from 3.8 to 5 and 7, the initial rate of reaction decreased. At pH = 3.8 and pH = 5 the conversion was reached stable value (X ~ 100%) respectively after 40 and 80 minutes, while at pH = 7 the conversion could not reach stable even after 90 minutes (X ~ 80 %). This was explained that pKa of CA was 4.4, so low pH was appropriate for reaction. When temperature was increased from 25 to 35 °C, CA conversion was increased not much and after 90–minute reaction, the conversion of CA reached approximately the same about 96 % (Figure 3d). Thence, reaction temperature was chosen to be the natural temperature of water environment 25 °C. The optimum conditions to degrade n–LDA and CA is summarized in the following Table 1. Table 1. The optimal conditions for photocatalytic degradation of n–LDA and CA on TiO2– P25 catalyst. Reactant Oxidizing agent Temperature (°C) Catalyst concentration (g/L) Oxidizing flow Initial pH Stable time (min) Conversion after 90 minutes (%) n–LDA O2 25 0.25 0.7 L/min 9 20 100 CA O2 25 0.25 0.3 L/min 3.8 40 96 4. CONCLUSIONS The adsorption and photolysis of n–LDA and CA with TiO2–P25 catalyst were not substantial. The nature of reactant played a decisive role in determining the optimal reaction condition. Photodecomposition of CA occurred more hardly than n–LDA and higher catalyst concentration was needed. n–LDA with pKa = 8.7 should be photodecomposed favorably at pH = 9, when CA with pKa = 4.4 so it’s photodegradation occurred favorably at pH = 3.8. 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