Supporting Information for

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Supporting Information for

Degradation Kinetics of Isoproturon and its Subsequent Products in Contact with TiO

2

Functionalized Silica Nanofibers

Eva Loccufierâ, Koen Deventer^b, Dave Manhaeghe^c, Stijn W.H. Van Hulle^c, Dagmar R. D’hoogeâ, Klaartje De Buysser^d, Karen De Clerckâ

a Department of Materials, Textiles and Chemical Engineering, Faculty of Engineering and Architecture, Ghent University, Technologiepark 70A, 9052 Ghent, Belgium

b Doping Control Laboratory, Ghent University, Technologiepark 30, 9052 Ghent, Belgium

c Laboratory of Industrial Water and Ecotechnology (LIWET), Department of Green Chemistry and Technology, Ghent University Campus Kortrijk, Graaf Karel de Goedelaan 5, 8500 Kortrijk, Belgium

d Sol-gel Centre for Research on Inorganic Powders and Thin Films Synthesis (SCRiPTS), Department of Chemistry, Faculty of Sciences, Ghent University, Krijgslaan 281 S3, 9000 Ghent, Belgium

Corresponding authors: [email protected], [email protected]

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S1. Details on materials and experimental methods

Fig S1. Schematic representation of the photocatalytic test set-up. (a: UV lamp, b: tempering beaker with cooled water at 15°C, c: isoproturon solution, d: nanofibrous membrane sample holder, e: stirring bar, f: magnetic stirrer)

Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) was carried out to quantify the amount of titanium present on the silica nanofibrous membranes. To ± 20 mg of TiO2 functionalized silica nanofibers, 1 mL of concentrated HF was added in a closed Teflon Savillex beaker for digestion overnight on a hotplate at 110°C. Afterwards, evaporation to dryness at 90°C was performed and the samples were re-dissolved in 2 mL of 12 mol L^-1 hydrochloric acid (HCl). The samples were properly diluted with 0.12 mol L^-1 HCl, according with their Ti content. Yttrium was admixed to the samples and calibration standards were used as internal standard. Analysis was carried out with Spectra Arcos ICP-OES equipment.

An average of three measurements was used.

Quantitative phase analysis by Rietveld refinement (TopasAcademic) with addition of an internal standard gives details about the mass percentages of the crystalline phases and the amount of amorphous phase (the membrane) can be calculated by use of the internal standard.

X-ray powder diffraction (XRD) analysis on precipitated nanopowders was collected on a Thermo Scientic ARL X'tra Diffractometer (CuKα, 1.5405 Å ) with solid state Si-Li detector. The measurements were performed in a θ - 2 θ geometry over an angular

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range of 5-70° using a 0.02° step size and 1 s step counting time. The internal standard approach was selected for the determination of the amorphous content by XRD analysis and Rietveld refinement. The method is based on the use of model structures that are refined using a least-squares procedure to improve the agreement between the experimental diffraction pattern and the pattern calculated from the model structures. Background function, scale factor, size broadening and cell parameters were refined. Rietveld refinement was also used for the determination of the percentage crystallinity of the sample. For this purpose, a known crystalline powder of another crystalline phase (10 wt% of zincite (ZnO)) that serves as an internal standard was mixed with the powder samples.

S2. Additional information on the characterization of TiO2 functionalized membranes

Fig S2. SEM images superhydrophilic silica nanofibrous membranes dip-coated with TiO2 solution (a) 0.05 mol L^-1 at 160 mm.min^-1, (b) 0.34 mol L^-1 at 80 mm.min^-1, (c) 0.34 mol L^-1 at 160 mm.min^-1, (d) 0.50 mol L^-1 at 80 mm.min^-1 and (e) 0.50 mol L^-1 at 160 mm.min^-1. after washing off the unfixed TiO2 nanoparticles; main text see zoomed versions.

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S3. Extra information on kinetic modeling methods

Part A: quasi-steady-state approximations with 3 generations

I. Reference case: single reactions A k₁

→

B k₂

→

C

Ignoring volume effects, the continuity equations and corresponding solutions for the concentration of A and B are ( k₂ not equal to k₁ ; only A at the start) [1]:

d[A]

dt =−k₁

[

A

]

❑^⇒

[

A

]

=[A]₀e^−k¹^t (S1) d[B]

dt =k₁

[

A

]

−k₂

[

B

]

❑

⇒

[

B

]

=

[

A

]

₀ ^k¹

k2−k1

(e^−k¹^t−e^−k²^t) (S2)

A

¿¿ d[C]

dt =k₂

[

B

]

=¿

(S3)

For ^k2 equal to ^k1 the solutions are:

[

A

]

_❑=[A]₀e^−k¹^t (S4)

[

B

]

_❑=

[

A

]

0k₁t e^−k¹^t (S5)

[

C

]

_❑=

[

A

]

₀(1−e^−k¹^t−k₁t e^−k¹^t) (S6)

If we apply the quasi-steady-state approximation (QSSA) for the calculation of the intermediate concentration, hence, formally the derivative for the concentration change of B is taken equal to zero in the set of differential equations it holds that:

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d[A]

dt =−k₁

[

A

]

❑^⇒

[

A

]

=[A]₀e^−k¹^t (S7)

k₁

[

A

]

−k₂

[

B

]

=0❑^⇒

[

B

]

=k₁ k2

[

A

]

(S8)

d[C]

dt =[A]₀k₁e^−k¹^t❑^⇒

[

C

]

=

[

A

]

₀(1−e^−k¹^t) (S9) These approximate solutions are in good agreement with the exact solution in case k₂≫k₁ (Eq. (S1)-(S3)).

II. Extended case: triple reactions

Focusing on one overall degradation pathway (A to B1 to C11), the continuity equations (again ignoring volume effects) are given by:

k

(¿¿1+k₂+k₃)

[

A

]

d[A]

dt =−¿

(S10)

d

[

^B1

]

dt =k₁

[

A

]

−

(

^k11+k₁₂+k₁₃

) [

^B1

]

^(S11)

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d[C₁₁]

dt =k₁₁

[

^B1

]

^(S12)

Applying the QSSA for the calculation of the concentration of the intermediate one obtains:

k

(¿¿1+k₂+k₃)

[

A

]

❑^⇒

[

A

]

=[A]₀e^−(k¹⁺^k²^+k³^)t d[A]

dt =−¿

(S13)

d[B₁]

dt =k₁

[

A

]

−

(

^k11+k₁₂+k₁₃

) [

^B1

]

⁼⁰

❑

⇒

[

^B1

]

⁼

^[

^A

^]

⁰_k ^k¹

12+k₁₂+k₁₃e^−(k¹^+k²^+k³^)t (S14) d

[

^C11

]

dt =

[

A

]

₀ ^k¹^k¹¹

k₁₂+k₁₂+k₁₃e⁻⁽^k¹^+k²^+k³⁾^t❑

⇒

[

^C11

]

⁼

^[

^A

^]

0( k₁

k₁+k₂+k₃)( k₁₁

k₁₁+k₁₂+k₁₃)(1−e⁻⁽^k¹^+k²⁺^k³⁾^t) (S15) which is in line with the reference case (again only A at the start), and requires for a reasonable reliability that ^k11+k₁₂+k₁₃≫k₁ .

Similar equations can be written down for the other degradation pathways so that:

k_u

∑

u=1 3

¿t

¿

−¿

[

A

]

=[A]₀e^¿

(S16)

[

^Bi

]

⁼

^[

^A

^]

⁰⁽ ^kⁱ

∑

v=1 3

k_iv )e⁻

(

^∑u=1

3

k_u

)

^t

(S17)

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[

^Cij

]

⁼

^[

^A

^]

⁰ ^kⁱ

∑

u=1 3

k_u k_ij

∑

v=1 3

k_iv

(1−e⁻

(

^∑u

ku

)

^t

) (S18)

III General case: nmax,1 reactions followed by nmax,2 reactions The following equations result::

[

A

]

=[A]₀e⁻⁽ ^∑^u=1

u=nmax ,1

ku)t (S19)

[

^Bi

]

⁼

^[

^A

^]

0

k_i

∑

v=1 v=nmax ,2

k_iv e⁻^∑^u⁼¹

u=nmax,1

kut

(S20)

[

^Dij

]

⁼

^[

^A

^]

0

ki

∑

u=1 u=nmax,1

k_u kij

∑

v=1 v=nmax,2

k_iv

(1−e⁻

(

^∑u=1 u=nmax,1

k_u

)

^t

) (S21)

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Part B: Quasi-steady-state approximations with 4 generations

I. Reference case: single reactions A k₁

→

B k₂

→

C k₃

→

D

The associated continuity equations (ignoring volume effects) are:

d[A]

dt =−k₁

[

A

]

(S22)

d[B]

dt =k₁

[

A

]

−k₂

[

B

]

(S23)

d[C]

dt =k₂

[

B

]

−k₃

[

C

]

(S24)

d[D]

dt =k₃

[

C

]

(S25)

Upon application of the QSSA for the calculation of the concentration of two intermediates (B and C) follows that:

d[A]

dt =−k₁

[

A

]

_❑^⇒

[

A

]

=[A]₀e^−k¹^t (S26) d[B]

dt =0=k₁

[

A

]

−k₂

[

B

]

❑

⇒

[

B

]

=k₁

k₂

[

A

]

_(S27)

d[C]

dt =0=k₂

[

B

]

−k₃

[

C

]

❑

⇒

[

C

]

=k₂

k₃

[

B

]

(S28)

d[D]

dt =k₃

[

C

]

=k₁

[

A

]

=k₁[A]₀e^−k¹^t❑

⇒

[

D

]

=

[

A

]

₀(1−e^−k¹^t) (S29)

For a good approximation, it is required that ^k3≫k₂≫k₁

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II. Extended case: triple reactions (cf. Figure 2 in the main text)

Focusing on the top degradation pathway (A to B1 to C11 to D111) the continuity equations are:

k

(¿¿1+k₂+k₃)

[

A

]

d[A]

dt =−¿

(S30)

d

[

^B1

]

dt =k₁

[

A

]

−

(

^k11+k₁₂+k₁₃

) [

^B1

]

^(S31)

d[C₁₁]

dt =k₁₁

[

^B1

]

^−(k111+k₁₁₂+k₁₁₃)[C₁₁] (S32) d[D₁₁₁]

dt =k₁₁₁

[

^C11

]

^(S33)

Upon application of the QSSA for the calculation of the concentrations of the intermediates (here B1 and C111), it follows that:

d[A]

dt =−(k₁+k₂+k₃)

[

A

]

_❑^⇒

[

A

]

=[A]₀e^−(k¹⁺^k²^+k³^)t (S34)

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d[B₁]

dt =0=k₁

[

A

]

−

(

k₁₁+k₁₂+k₁₃

) [

^B1

]

❑

⇒

[

^B1

]

⁼_k ^k¹

11+k₁₂+k₁₃[A]₀e⁻⁽^k¹^+k²⁺^k³⁾^t (S35)

k

(¿¿111+k112+k113)

[

^C11

]

d[C11]

dt =0=k₁₁

[

^B1

]

^−¿

❑

⇒

[

^C11

]

⁼_k ^k¹¹

111+k₁₁₂+k₁₁₃

[

^B1

]

^(S36)

d[D₁₁₁]

dt =k₁₁₁

[

^C11

]

^=k111( k₁₁ k111+k112+k113

)( k₁ k11+k12+k13

)[A]₀e^−(k¹⁺^k²^+k³^)t (S37) In agreement with the structural form of Equation (S21) [D₁₁₁] becomes equal to

[

^D111

]

⁼

^[

^A

^]

0( k₁

k₁+k₂+k₃)( k₁₁

k₁₁+k₁₂+k₁₃)( k₁₁₁

k₁₁₁+k₁₁₂+k₁₁₃)(1−e⁻⁽^k¹^+k²^+k³⁾^t) (S38) III. General case: nmax,1/2/3 reactions

The following equations result by extrapolation:

[

A

]

=[A]₀e⁻⁽ ^∑^u=1

u=nmax ,1

k_u)t (S39)

[

^Bi

]

⁼

^[

^A

^]

0

k_i

∑

v=1 v=nmax ,2

k_iv e⁻^∑^u⁼¹

u=nmax,1

kut

(S40)

[

^Cij

]

⁼

^[

^A

^]

0

k_i

∑

u=1 u=nmax ,1

k_u k_ij

∑

v=1 v=nmax ,2

k_iv (S41)

[

^Dijk

]

⁼

^[

^A

^]

0

ki

∑

u=1 u=nmax,1

k_u kij

∑

v=1 v=nmax ,2

k_iv kijk

∑

w=1 3

k_ijw

(1−e⁻

(

^∑u=1 u=nmax,1

k_u

)

^t

)¿ (S42)

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S6. Literature based degradation pathways of isoproturon

Fig S3. Proposed intermediate products of the TiO2 catalyzed photocatalytic degradation of isproturon (IPU) of several generations, based on proposed reaction schemes in literature. Fig. S4 for chemical formulas.

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Fig S4. Examples of chemical structures of the proposed intermediates for the TiO2 catalyzed photocatalytic degradation of of IPU. Four main reaction pathways have been proposed in literature, namely (i)hydroxylation (e.g. on the isopropyl group, the dimethylamine group and the aromatic ring), (ii) N-demethylation or oxidation of amino groups linked to the benzene ring; (ii) methyl substation; (iv) ispropyl substitution; in the present work (i) is put forward as being a dominant contributor through several generations. Note that other similar products can be drawn.

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S7. Additional information recorded data LC-MS

Fig S5. Recorded LC-MS values in time of the reaction intermediates from generation two in the reaction scheme of Fig S4. In order to detect the intermediates with m/z 193 and 209, an injected volume of 600 µL compered to 30 µL for m/z 223 and 1 µL for IPU (m/z 207). Even than, isopropyl substitution has not been detected in the global MS spectrum.

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S8. Additional information oncatalyst reusibility and quantification of the toxicity

Fig S6. SEM images of a hydrophilic silica nanofibrous membrane dipcoated with a 0.34 mol L^-1 TiO2

solution at 160 mm min^-1 after cyclic testing for 5 times for 8 hours using different IPU solutions. This shows that the TiO2 nanoparticles remain on the membrane, eventhough no extra chemical fixation step is used after dip-coating of the silica nanofibers.

Fig S7. Oxygen uptake rate of the activated sludge in an open reactor for a blank and 5 mg L^-1 untreated IPU solution when varying the KL,a value of the reactor. The black line indicates the determined value of KL,a of the used reactor as depicted in Fig 9a (namely 0.68 h^-1). Slight deviation results in a change in absolute value of the oxygen uptake rate of the activated sludge, but the relative trend between the solutions remains unaltered.

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Fig S8. Oxygen uptake rate of the activated sludge determined by respirometric tests of all the tested IPU solutions (5 and 10 mg.L^-1, UV irradiation time of 4, 6, 8 and 16 hours) compared to a blank (tab water). The UV light treatment increases the OUR, resulting in less inhibition of the activated sludge.

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References

[1] P. Atkins, J. De Paula, Physical Chemistry, 9th Editio, W.H. Freeman and Company, 2010. https://books.google.be/books?id=DkZmDwAAQBAJ.

[2] D.T. Gillespie, A general method for numerically simulating the stochastic time evolution of coupled chemical reactions, J. Comput. Phys. 22 (1976) 403–434.

doi:10.1016/0021-9991(76)90041-3.

[3] D.T. Gillespie, Exact stochastic simulation of coupled chemical reactions, J. Phys.

Chem. 81 (1977) 2340–2361. doi:10.1021/j100540a008.

[4] P.H.M. Van Steenberge, D.R. D’Hooge, Y. Wang, M. Zhong, M.F. Reyniers, D.

Konkolewicz, K. Matyjaszewski, G.B. Marin, Linear gradient quality of ATRP copolymers, Macromolecules. 45 (2012) 8519–8531. doi:10.1021/ma3017597.

[5] S.K. Fierens, D.R. D’hooge, P.H.M. Van Steenberge, M.F. Reyniers, G.B. Marin, MAMA-SG1 initiated nitroxide mediated polymerization of styrene: From Arrhenius parameters to model-based design, Chem. Eng. J. 278 (2015) 407–420.

doi:10.1016/j.cej.2014.09.024.