Appendix A. Supporting Text for Chem. Eng. J.

Peroxymonosulfate Activated by Amorphous Particulate MnO2 for

Mineralization of Benzene Gas: Redox Reaction, Weighting Analysis,

and Numerical Modelling.

Text S1

After mixing of MnSO4·5H2O (0.008 M) and (NH4)2S2O8 (0.02 M), the solution

was transferred into a Teflon-lined stainless steel autoclave with the volume of 40 mL

at 140 oC for 12 h. The final products were harvested by centrifugation and washed

with ultrapure water for 3~5 times before drying overnight.

Text S2

As shown in Fig. S1, the suspended particulate MnO2 was a typical amorphous

MnO2 without discernible fringe lattice while a kind of one-dimensional nano-

crystalline α-MnO2 was used for a comparative study. The suspended MnO2

hierarchically presented irregular shapes and a unique sea urchin nanostructure with

diameters 300 nm was observed (Fig. S2.a). Many flakes of individual sea urchin

AMO radiated from its center and aggregated without shaking, gradually forming a

unique nano-microstructure material during the preparation. The SEM photo of the

nano-crystalline α-MnO2 showed a uniform morphology of nanorods with diameters 1

~ 2 μm (Fig. S2.b).

Fig. S1. XRD patterns of suspended AMO and nano-crystalline α-MnO2.

Fig. S2. SEM photos of AMO (a) with sea urchin nanostructure and α-MnO2 (b) with

nanorods crystalline.

Text S3

AMO presented larger BET surface area and pore diameter than α-MnO2, largely

because of its hierarchical sea urchin nanostructure (shown in Table S1). Despite of

many similarities in their mesoporous diameter distributions (median pore size

ranging from 2 to 10 nm), AMO showed a narrow hysteresis loop at a relative

pressure (P/P0) range of 0.6–0.95; while a broad hysteresis loop ascribed to α-MnO2,

appearing at lower relative pressure (0.45 < P/P0 < 0.95); while for, respectively in

Fig. S3 (a) and (b).

Table S1. Summary of surface area, total pore volume and pore diameter of AMO and

α-MnO2.

Sample SBET (m2/g)Total pore volume

(cm3/g)

Average pore

diameter (nm)

AMO 157.71 0.19 37.15

α-MnO2 134.19 0.15 24.57

Fig. S3. N2 adsorption-desorption and pore size distributions of AMO (a) and α-MnO2

(b).

Text S4

Before the concentrations of AMO determined by Uv-vis spectrometry, its

adsorption peak at 418nm was established through Uv-vis spectrophotometric

measurements in the mixing solutions of KMnO4 and Na2S2O3, shown in Figure S4.

As their reactions continued, Mn(IV) ions at 418 nm adsorption peak were gradually

increased and some intermediate species MnOx at 440nm produced whereas KMnO4

at 525 ~ 546 nm was consumed simultaneously. Mn(II) ions were reacted with

KMnO4 and cannot be generated, the reduction products of MnO4- ions were

transformed to manganese dioxide as a result. Then for over the process of benzene

degradation, the residual concentrations of manganese dioxide in the combined

oxidizing system were determined using the molar absorption coefficient (Beer-

Lambert Equation) [1, 2] . It is well known that the UV-vis spectrometry has been

viewed as a highly-efficient and time-saving method in quantitative testing, even

though its precision could be susceptible to light transmittance and monochromatic

fluctuation of samples.

Fig. S4. Determination of maximum absorption wavelength of MnO2 using UV-vis

spectrophotometry.

Text S5

Through the replicate predetermined measurements by a gas chromatography

with flame ionization detector (GC-FID, Agilent HP6890A), the inlet concentration of

benzene gas at ppm-level with 2 orders of magnitude tend to bring along lower

relative standard deviations shown in Table S2.

Table S2. Comparisons in the replicate predetermined measurements of the inlet

concentration of benzene gas.

Std.

Benzen

e [10-6

(V/V)]

Peak area (pA·s) Relativ

e std.

dev.

(%)

1 2 3 4 5 6 mean

1 5028 4967 4960 5068 4984 5032 5007 0.85

15.1 67635 67572 67272 67547 66989 67016 67339 0.43

988.8414593

4

412106

2

413084

1

413694

4

411719

5

410129

8

412554

60.38

Text S6

For benzene removal under the absence of PMS, single MnO2 exhibited the

stronger adsorption ability significantly than its directive oxidation. The benzene

adsorption experiments of as-prepared catalysts were performed in a thermostatic

fixed-bed reactor. 0.15 g test catalysts sieved to 60 ~ 80 mesh were loaded on silica

wool in a stainless steel thermocouple tube (8 mm diameter) of the fixed-bed reactor.

Gaseous benzene was diluted by N2. A flow rate of 1 mL·min-1 and 200 ppm of inlet

benzene were stoichiometrily determined by the mass flow controller (Brooks

5860E). The outlet concentrations of benzene from the reactor were monitored by a

high-resolution benzene gas detector (Tiger Select-0512). The commercial MnO2

(T491 industrial grade, KEMET Inc.) with the particulate size of 1.09 μm was set as

the control group in the adsorption experiments.

Text S7

The samples for ESR were prepared by mixing 0.05 g of AMO particles into a

25 mM 5,5’-dimethyl-1-pirroline-N-oxide (DMPO) solution with a 50 mL aqueous

dispersion for DMPO–•OH. Before each ESR measurement, a nickel foam was

soaked in AMO&PMS solutions for several seconds to collect the particles. For

trapping experiments for the identification of active species, the AMO&PMS

solutions (AMO 2.9 mM and PMS 5.8 mM) containing different trapping agents (0.2

M additive amount) were ultrasonicated for 30 min.

Fig. S5. DMPO spin-trapping ESR spectra of AMO particles collected from

AMO&PMS solutions (a) and active species trapping for benzene degradation with

different scavengers (Ethanol → •OH and SO4-●, TBA → •OH) (b).

In Fig. S5.a, before benzene removal reactions, the four characteristic peaks of

DMPO–•OH with an intensity ratio of 1:2:2:1 were observed in as-prepared AMO,

which suggests the generation of OH radicals [3]. Until to 60 min of reactions, the

intensity of DMPO–•OH signals displayed a slight drop, demonstrating that •OH were

continually regenerated to overcome their great depletion over the PMS activation and

transitional cycles of Mn ions. Once the reactions were terminated after the complete

consumptions of AMO and PMS eventually, few DMPO–•OH signals were be found

and this result can be ascribed to thorough •OH depletion. The observations also

confirm that benzene was predominantly and durably removed with SO4-● radicals.

These observations were also supported via the radical scavenge experiments

(Fig.S5.b) to identify which a kind of active species would more significantly impact

on the degradation conversion. Ethanol scavenger can rapidly react with both •OH

and SO4-●; while tert-butyl alcohol (TBA) can effectively quench •OH and its reaction

rate around 1000-fold faster than SO4-●. As anticipated, when ethanol was added, the

degradation rate of benzene decreased significantly, indicating •OH and SO4-● were

quenched by ethanol [4]. However, minor decrease in degradation was observed, even

though •OH were quickly quenched after the addition of TBA. Therefore, SO4-●

sustained the similar degradation capacity to that without scavenger and became the

major reactive species for benzene degradation.

Text S8

Fig. S6 shows the XPS spectra of Mn 2p3/2 of AMO before and after the reaction.

After the curve-fitting analysis, three components of Mn 2p3/2 peaks with binding

energy (BE) at around 641.2±0.1 eV, 642.5±0.1 eV, and 644.3±0.1 eV attributed to

the surface Mn3+, Mn4+, and the shake-up satellite of Mn3+ species, respectively [5].

The BE of Mn 2p3/2 that showed values larger than 642 eV and the distance E around

5.31 eV of the twin peaks in the spectra Mn 3s indicate the chemical states of Mn

mainly exhibited Mn3+ and Mn4+; while no Mn2+ species appeared because the absence

of a satellite peak at +5 eV from the Mn 2p3/2 peak. When the reaction terminated, the

surface Mn4+/Mn3+ratios which were quantitatively calculated by their XPS peak areas

decreased from 23.7% to 34.6%, implying Mn4+ ions were predominately in AMO

compositions and can be immediately recovered once capturing electrons .

Fig. S6. High-resolution XPS spectra of Mn 2p3/2 of AMO catalysts before and after

reaction.

Text S9

Fig. S7 shows that a highly-efficient benzene mineralization at an optimal

combination of parameters brought about higher porosity and lower pressure drop for

the nanostructure Mn-based catalytic system, much lower k2 would present at the

same. When the additions of 2.9 mM AMO and 5.8 mM PMS, 66.7% of

mineralization rates as well as the lowest k2 = 0.24 Pa/(m/min) presented (Fig. S7.a).

Once k2 increased to 5.59 Pa/(m/min), 1.2 mM AMO and 2.4 mM PMS cannot supply

sufficient consumptions with benzene gas and result in the severe mass resistance on

the AC fibers, thus just 43.1% mineralization rate generated(Fig. S7.c).

Fig. S7. SEM photos of the internal AC layer (fibers) at different k2 after the

ensuing 90-min reactions.

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