Chapter 4 
Removal of Phenol from Wastewater Using Fenton-Like Reaction over Iron Oxide–Modified Silicates 

Additional information is available at the end of the chapter 
http://dx.doi.org/10.5772/65097 
Abstract
Iron-containingactivephasewasdepositedonnaturallayeredsilicate(vermiculite)usingseveraltechniquessuchasionexchange,precipitation,andforcedhydrolysisduringhydrothermaldigestion.Tuningofthesynthesisconditionsresultedinpreparationofthecatalystswithdifferentloadingofactivephaseandphysicochemicalproperties.Thecompositematerialswerecharacterizedwithrespecttotheirstructure(X-raydiffraction),agglomerationstateofFe(diffusereflectanceUV-visspectroscopy),andchemicalcomposition.Catalytictestswereperformedinsemi-batchreactorunderatmosphericpressure.Aqueoussolutionofphenolwasusedasamodelindustrialeffluent,andhydrogenperoxidewasaddedasanoxidant.Spectraltechniqueswereusedforidentificationofintermediateoxidationproducts.Spentcatalystswerealsocharacterized,andstructuralandchemicalchangesweredetermined,e.g.,leachingdegreeofactivephase.
Keywords: Fenton-like process, advanced oxidation processes, catalysis, silicate, ver

Refractoryorganiccompounds,suchasdyes,phenols,orendocrinedisruptingcompounds(EDC),arecharacterizedwithhightoxicity,carcinogenicproperties,andthisposesaserioushazardtoaquaticlivingorganisms.Difficultyofcontaminations’removaliscausedbytheirresistancetoaerobicdigestion,stabilitytolight,heat,andoxidizingagents.Technologiesusedcurrentlyforwastewatertreatment,however,usedwidely,sufferfromdesignshortcomingsorareveryexpensive.Emergingtechnologies,so-calledadvancedoxidationprocesses(AOP),is
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alargegroupofmethodsbasedonoxidationusingstrongoxidants,suchasozoneorhydrogenperoxide.InAOPmethods,higherconversionlevelsmaybeobtainedatatmosphericpressureandtemperatureslowercomparedtootheroxidationprocesses[1–6].Moreover,chemicaloxidantsmaybeaccompaniedbycatalystsorphysicalagentssuchassunlight,UVorγradiation,ultrasounds,microwave,orcavitation,increasingefficiencyofthereaction[7,8].
The catalysts used in the Fenton-like system are, among others, natural iron-bearing earthmaterials, such as goethite, hematite, magnetite, or ferrihydrite [9–11]. Modificationof ironoxides to improve their performance in organic pollutant degradation can be achieved bysubstitution with other transition metals [12]; however, introduction of heavy metals may bequestionable from the point of view of the secondary contamination with catalytic leachates.It is also known that nanoscale materials are characterized with differentproperties comparedto their bulk phase [8, 13, 14]. Nanocatalysts offer higher specificsurface areas and few or nomass-transfer limitations. It is expected that reaction rate will be higher for nanomaterials.Also, diffusionof large organic molecules (organic dyes, pharmaceuticals) will be no longerproblematic as it is observed in microporous materials. On the other hand, the separation andrecycling of nanocatalysts at a technical scale still present a challenge.
To circumvent the costly catalyst separation process, magnetic properties of some iron oxidesmay be exploited [15, 16]. The other possibility is the immobilization on solid support. Themost popular materials in this group are activated carbon, silica, and aluminum oxide [17–21]; however, more advanced technologies are also studied employing graphene oxide [22].The encapsulation of iron oxide nanoparticles in polymer matrix or carbonized sewer sludgewas reported as another possibility to stabilize oxide nanoparticles [23, 24].
Facing much more stringent environmental regulations, new waste-free technologies must bedeveloped, based on cheaper, non-toxic materials. Clays proposed as starting materials fulfillall requirements for low-cost, ecological precursors for industrial technologies or large-scaleapplications. Such materials could be used as catalysts in a large group of emerging technologies consisting on oxidation processes, such as wet oxidation, catalytic wet air oxidation, andadvanced oxidation processes. Natural clay minerals provide with excellent support for Fe-containing nanocrystalline active phase of the Fenton-like reaction. Vermiculite, which was

2. Materials and methods
Commercial expanded vermiculite (South Africa), fraction size 0.5–2 mm, was provided byRomico Polska Sp. z o.o. The silicate was pulverized in electrical blender, and fraction below180 μm was separated (sample S0). Such prepared vermiculite was used as a support fordeposition of nanocrystalline iron oxides.
Two standard procedures [27, 28] were applied to obtain well-definedoxide structures. Pure2-line ferrihydrite was prepared by precipitation from 0.1 M Fe(NO3)3·9H2O (p.a., POCh)solution using 1 M KOH (p.a., POCh). Potassium hydroxide solution was added dropwise atRT and constant stirring until pH was equal to 7. Product was centrifuged, washed with water,and freeze dried. Similar procedure was used to obtain vermiculite-supported ferrihydrite.Suspension of 5 g of vermiculite (S0) was prepared in 150 mL of distilled water, then 100 mLof Fe(NO3)3·9H2O solution was added dropwise. Suspension was stirred for the next 2 h toallow ion exchange. In the next step, 1 M KOH solution was added to raise pH up to 7.

S2 HS2 33.6 
S3 HS3 67.2 
S4 – 134.4 

Table 1. Intended Fe/vermiculite ratio in vermiculite-supported Fe oxide catalysts.
Pure hematite with crystal size of 4 nm was prepared by forced hydrolysis. 3.32 g ofFe(NO3)3·9H2O was dissolved in preheated HCl (p.a., POCh) solution (0.002 M, 400 mL) toobtain Fe concentration of 0.02 M.. Solution was transferred into polypropylene bottlefittedin autoclave and heated at 98°C for 7 days. Product was centrifuged, washed with water, andfreeze dried. Synthesis of vermiculite-supported nano-hematite was performed using acidifiediron nitrate solutions with the addition of 20 g of vermiculite. Sample codes, depending on Fe/vermiculite ratio, were HS0 (no Fe salt was added), HS1, HS2, and HS3 (Table 1).
Phenol removal was studied as a test reaction, and semi-batch reactor was used to minimizeformation of side products [26]. Round-bottomflaskequipped with refluxcondenser washeated to 70°C on magnetic stirrer. Each time reactor was charged with 340 mL of phenolsolution (pH = 5.4) and 600 mg of catalyst. Hydrogen peroxide (30%, p.a., POCh) was added

Reaction codePhenol concentration (g/L)H2O2 volume added in one injection (mL)
Catalyst R112Catalyst R010.12Catalyst R01m0.10.2
Table 2. Reaction conditions of phenol removal over vermiculite-supported iron oxide catalysts.
The conversion, X (%), of model pollutant (phenol) was calculated according to Eq. (1):
C -C
X = 0 ×100% (1)
C
0 
where C0 is the starting concentration and C is the concentration at a given reaction time.
Fresh and spent catalysts were characterized by X-ray diffractionmethod (XRD) using apowder diffractometer(Bruker, D2 PHASER) equipped with CuKα radiation source. TheSherrer equation (2) was used for determination of nano-hematite crystal size:

0.89l
D = (2)
bcos q 
where λ is the X-ray wavelength, β is the line broadening at half the maximum intensity, andθ is the Bragg angle.
The coordination and aggregation of iron present in the catalysts were studied by diffusereflectance-UV-visspectroscopy (DRS-UV-vis). The measurements were performed in therange of 190–900 nm with a resolution of 2 nm using an Evolution 600 (Thermo) spectrophotometer. Content of iron was measured using spectrophotometric technique at wavelength λ = 510 nm (Thermo SCIENTIFIC EVOLUTION 220) as a complex with 1,10-phenanthroline afterleaching of metal cations in 6 M HCl.

3. Results and discussion
3.1. Catalytic tests
Three types of catalytic tests were carried out in semi-batch reactor: concentrated (R1—1 g/L)and diluted (R01—0.1 g/L) phenol solutions with the addition of significant excess of oxidant(six times 2 mL) and diluted phenol solution with the minimum amount of oxidant added (sixtimes 0.2 mL). In each series of catalytic tests, it was observed that initiation phase is the firststep, as in the case of free-radical reactions, especially for experiments carried out in concentrated phenol solution (Figure 1A). Initial 10–20 min are characterized with slow increase inpollutant conversion. After 30–50 min of the reaction over iron oxide-containing catalysts,conversion rapidly increased reaching values above 95%. Non-modifiedsilicates, on the otherhand, presented very low activity. Sample submittedto hydrothermal treatment (HS0) slightlyincreased phenol oxidation compared to non-catalytic process; however, in the lattercase,conversion was not higher than 8% after 75 min. On the contrary, the addition of startingvermiculite (S0) to reaction mixture resulted in slow increase in phenol conversion up to 42%.Reduction in particle size was the only preparation step in this case; therefore, contaminationspresent in the starting materials, such as interlayer and adsorbed transition metal cations aswell as naturally occurring iron oxides and carbonates, may be responsible for the observedcatalytic effect.

Figure 1. Conversion of phenol in oxidation reaction over vermiculite-supported iron oxide catalysts; A—initial con-centration of phenol 1 g/L, volume of H2O2injection = 2 mL; B—initial concentration of phenol 0.1 g/L, volume of H2O2injection = 2 or 0.2 mL.
When diluted solution of phenol was used (Figure 1B) and accompanied by small excess ofoxidant (R01m—0.2 mL), almost no effectwas observed within assigned experimental time.Only one sample, doped with nano-hematite, HS2, showed catalytical properties after 50 minof reaction. The non-catalytical reaction performed with large excess of oxidant (R01—2 mL)resulted in quite significantconversion equal to 48% within 75 min. Slightly higher activitywas observed when ferrihydrite-doped samples, S2 and S3, and non-modifiedsilicates wereadded as catalysts. After constant gradual increase of conversion, it reached 60–75% within 75minutes. Only one sample with the highest loading of ferrihydrite and samples doped withnano-hematite allowed to reach the conversion level above 95%. Nevertheless, it should bestressed that after initial increase in conversion, it was inhibited and much slower at longerreaction times in the case of removal of concentrated pollutant. Similar effectof the reactionstagnation, due to accumulation of the reaction products, was also observed in homogeneous

nano-hematite.
According to results of the catalytic tests described above, 2-line ferrihydrite supported onvermiculite is less active than analogous materials containing hematite. Additional experiment, performed in concentrated phenol solution (1 g/L) and using active sample HS3 ascatalyst, provided information about reaction path and intermediate products. UV-vis spectrafor samples withdrawn during experiment, quenched with methanol or mixed additionallywith VO3−/H2SO4solution, allowed to distinguish between transition products formed in thecourse of the reaction. After 29 min of the reaction, which corresponds to 43% of phenolconversion, colored products were formed. In the UV-vis spectrum recorded in methanol(Figure 2A) bands assigned to phenol (278 and 284 nm), hydroquinone (300 nm) and benzoquinone/quinhydrone (245, 255, and 300 nm) were identified.However, bands assigned tocatechin were strongly overlapped by other strong peaks, and it cannot be excluded that thisproduct was also formed. After 62 min of the experiment phenol conversion reached 97%, nocolored products were recorded, and reaction was completed.

Figure 2. Identificationof transition products of phenol oxidation over HS3 catalyst (reaction conditions: PhOH = 1g/L, volume of H2O2injection = 2 mL): A—derivative UV-vis spectra recorded in MeOH, B—derivative UV-vis spectrarecorded in VO3−/H2SO4; P—phenol; Q—qiunhydrone; B—benzoquinone; H—hydroquinone; C—catechin.
However, in the spectra measured after the reaction of the sample of effluentwith VO3−/H2SO4mixture (Figure 2B), peaks below 230 nm, assigned to unidentifiedorganic compounds,were recorded at the end of the test. Evolution of pH followed opposite trend as phenolconversion, and at 29 and 62 min, it was equal to 2.87 and 2.48, respectively. Those observationsconfirm that final products are not only H2O and CO2 but also organic acids.

3.2. Characterization of as received and spent catalysts
Iron oxide-bearing catalysts were obtained by direct deposition of formed oxide on the silicatesupport. Vermiculite was selected due to its mechanical and thermal stability. On the contraryto montmorillonite, it is not exfoliating rapidly in contact with water, and swelling is limitedto changes of number of water molecules in the interlayer space. Moreover, mineral itselfcontains significant amount of iron.As it was shown in Figure 3, both expected oxide structures were formed [27, 28]. XRD patternof 2-line ferrihydrite consists of two broad reflections,while nano-hematite is characterized bythe presence of several sharp but not intense peaks. Ferrihydrite structure was not observedafter deposition on the support due to inherent poor ordering of the structure and low contentin the composite material. On the other hand, using the Sherrer equation, it was confirmedthatcrystal size of pure nano-hematite phase was 4 nm. Only traces of nano-hematite could beidentifiedin two vermiculite-supported samples with the highest loading of deposited phase—HS2 (3.36 Fe wt.%) and HS3 (6.72 Fe wt.%). Therefore, it was not possible to determine precisecrystal parameters for oxide phase.

Figure 3. Structure of vermiculite-supported ferrihydrite- (A) and nano-hematite-containing (B) catalysts; F—ferrihydrite; H—nano-hematite; 0, 1, 2—basal reflectionsof vermiculite corresponding to 0, 1, and 2 layers of interlayer water;i—interstratified vermiculite phases.
Changes in vermiculite structure reflected chemical modifications performed in each synthesis. Starting material (S0) was characterized with complex patterntypical for vermiculites bothcontaining in the interlayer divalent cations and collapsed structure (0 layers of water).Moreover, the interlayer cations are accompanied with 1 or 2 layers of water. Additional peaksbelow 8° 2θ were assigned to interstratified contracting and non-contracting phases [30].
and formation of so-called HIV—hydroxy-interlayered vermiculites [31, 32]. Similar shift wasobserved also for the sample with the highest nano-hematite content: HS3—1.39 nm.
Application of potassium hydroxide, however, resulted in a deeper rearrangement of inter-layer space. Both peaks assigned to interstratificationand one water layer almost disappeared.On the other hand, intercalation of K+resulted in a large increase in peak intensity at 1 nm [33].On the contrary, in the samples doped with nano-hematite in hydrothermal conditions(Figure 3B), peak assigned to 0 layers of interlayer water decreased with increasing amount ofoxide.

In the structure of spent catalysts, traces of hematite were still possible to identify; however,other changes concerning catalyst properties were noticed. Vermiculite support upon reactionin concentrated solution was transformed into Mg2+/Fe3+intercalated structure containing 2layers in water molecules (Figure 4A). In the samples doped with ferrihydrite, only traces ofinterlayer potassium were preserved, and interlayer spaces were occupied with di- andtrivalent cations released from silicate matrix. Hydration state and the number of watermolecules strongly depended on the initial amount of iron oxide—the lower doping level theeasier rehydration proceeded. Similar dependence was observed also for nano-hematitedeposited samples. Such phenomenon should be explained as a result of blocking of interlayerspaces with iron hydroxides. Moreover, iron oxide particles, which were grown near the edgesof vermiculite layers, may act as cementing agent, preventing structure swelling. It was alsoobserved that rehydration of the structure depends on the reaction conditions (Figure 4B): thehigher concentration of phenol and hydrogen peroxide, the easier intercalation of watermolecules. As it was shown in Figure 4C/D, swelling intensity, which may be expressed aspeaks 1.42 (2 layers of water) and 1.20 nm (1 layer of water) intensity ratio, increased at higherconcentration of substrates. It cannot be excluded that acidic reaction products also enhancedstructural changes of vermiculite support.

Figure 4. Structure of spent catalysts: A—vermiculite-supported iron oxide catalysts after reaction with phenol concentration 1 g/L; B and C—evolution of basal spacings of HS1 sample at differentreaction conditions; D—evolution ofbasal spacings of nano-hematite-containing catalysts after reaction with phenol concentration 1 g/L;H—nano-hematite; 0, 1, 2—basal reflectionsof vermiculite corresponding to 0, 1, and 2 layers of interlayer water; i—interstratifiedvermiculite phases.
Sample named (nm)d (nm)d (nm)d (nm)d (nm)
Fresh catalysts (precipitated)S02.401.401.211.171.00S21.431.01S31.391.01S41.371.01

HS1 2.60 1.43 1.24 1.19 1.01 
HS2 2.55 1.42 1.24 1.20 
HS3 2.53 1.39 1.22 1.18 
Spent catalysts (hydrothermal) 
HS0 R1 * 1.42 1.24 1.20 
HS1 R01m * 1.42 1.24 1.19 
HS1 R01 * 1.43 1.25 1.20 
HS1 R1 * 1.43 1.25 1.20 
HS2 R01m * 1.40 1.23 1.19 
HS2 R1 * 1.43 1.25 1.21 
HS3 R01 * 1.39 1.23 1.19 
HS3 R1 * 1.42 1.25 1.20 
Interstratification 2 layers of water Inter-stratification 1 layer of water 0 layers of water K+ 
Mg2+/Fe3+ in interlayers Mg2+/Fe3+ in in interlayers 
interlayers 
*2.4-2.6 nm (low-intensity peak). 

Table 3. Interlayer distances of iron oxide-modified vermiculite-based catalysts before and after reaction.
The basal spacings calculated for modifiedvermiculites (Table 3) show that synthesis consist
phenol oxidation, first peak (~2.5 nm) became less noticeable.

It may be concluded that deposited iron oxide phases changed properties of the support;however, alteration was reversible in reaction conditions. Although XRD patternsdo not allowto follow degradation of active phase directly, some indications of that process may beobserved through properties of vermiculite.
More data considering properties of the deposited iron oxides were provided by DRS-UV-visspectroscopy. As it was mentioned before, vermiculite itself contains iron [25] and UV-visspectrum recorded for solid-state samples consisted of several characteristic bands. IsolatedFe3+cations in the tetrahedral coordination give rise to peaks at 224 nm in both silicate materials(S0 and HS0), and cations in the octahedral coordination may be identifiedby the presence ofband at 260 nm [34, 35]. The bands at 319 and 358 nm are characteristic for small oligonuclearFexOy clusters. Formation of bulk Fe2O3particles gave characteristic bands above 400 nm [34].
Ferrihydrite and hematite were characterized by multiple bands, revealed by the second
assigned to 6A1→ 4T1 transitions at 310 and 840 nm and 6A1→ 


Figure 5. Agglomeration state of iron species in vermiculite-supported ferrihydrite- (A) and nano-hematite-containing
(B) catalysts (DRS-UV-vis spectra).
Due to possible release of the cations from vermiculite and the contamination of depositediron oxides during synthesis, the octahedra may be distorted, and consequently, ligand field

ure 6A). It is possible that adsorbed on the surface and interlayer Fe3+cations present in originalmaterial were released and redeposited in the form of larger clusters. Catalysts modified withferrihydrite after reaction with diluted phenol solution (R01) were depleted with active phase,and DRS-UV-vis spectra have shown minimum at 300 and 480 nm. Much larger minimum wasregistered in the differentialspectrum of sample S3 after reaction with concentrated phenolsolution. The shape and positions of minima (390, 453, and 524–550 nm) reflected distributionof absorption peaks in fresh catalyst. It may be expected that degradation of the catalyst issignificant, although it is mechanical rather than chemical in nature.

Figure 6. Leaching of iron species from vermiculite-supported iron oxide-containing catalysts upon phenol oxidationreaction (DRS-UV-vis spectra).
In nano-hematite-containing catalysts, degradation proceeded differentlyfor each sample. Atthe lowest loading of active phase (Figure 6B, HS1), leaching was the most noticeable comparedto the other samples, which were used in the reaction with concentrated substrates (R1).Moreover, the largest minimum was observed at 360–400 nm, while at 454 and 530 nm, twosmaller features were observed. When the amount of hematite was increasing, minimarecorded in DRS-UV-vis spectra were smaller and shifted to higher wavelengths (Figure 6C/D).Therefore, it may be concluded that optimization of the active phase loading is more importantfor hematite-containing composites, both in terms of catalyst stability and its activity. Surprisingly, although degradation of the catalysts is less noticeable in the reaction using lowerconcentration of phenol, the addition of lower excess of oxidant may also increase leaching ofactive components (e.g., Figure 6B). This feature may result in olation-oxolation processes,proceeding differently in the presence of H2O2.
On the basis of catalyst characterization, the following model was proposed for more activesilicate-based nano-hematite-modifiedmaterials (Figure 7). In optimum conditions of about
3.36 wt.% of iron, which corresponds to 4.8 wt.% of deposited iron oxide, interlayer spaces ofvermiculite are not blocked by hydroxides and are free to accommodate Fe3+cations. On thesurface of the layered support, patches of nanocrystalline phase are formed. Below theoptimum hematite loading, besides well-definednanocrystals, also oligomeric clusters of ironoxide are deposited, which may be easily dissolved by the reaction substrates and products inthe course of the reaction. The interlayer space of vermiculite is still available for an ionexchange process. Above the optimum loading of the active phase, interlayer spaces ofvermiculite are blocked by hydroxy-compounds, which may be removed during the reaction.Deposited nano-hematite phase remains almost intact during the reaction.

Figure 7. Simplified structure of nano-hematite-containing vermiculite-supported catalysts.


3.3. Catalytic activity vs. catalyst degradation
Changes in the catalyst chemical composition were followed during the reaction and correlatedwith catalytical results. In Table 4, it was presented that ferrihydrite-containing catalysts weremore susceptible to Fe leaching. Surprisingly, the lower was oxide doping, the higherpercentage of active phase was dissolved. No such straight relationship was observed for nanohematite-containing catalysts. Apparently, small oligoclusters and interlayered hydroxyspecies described in model in Section 3.2, indeed, contributed significantlyto dissolved species.It was also observed that catalytic activity should not be attributedcompletely to homogeneousreaction. Reaction mixtures over ferrihydrite-doped catalysts were characterized with higherconcentration of Fe available for homogeneous reaction. Times, required to obtain phenolconversion equal 40 and 50%, were longer for ferrihydrite-containing catalysts in comparisonto hematite-doped materials. Moreover, in the lattercase Fe concentrations in the reactionmixtures were relatively low. As it was described in Section 3.1, when diluted phenol solutionwas used for the reaction activity stagnated due to product accumulation. Another explanationcould be recombination of radicals formed over the catalysts. Therefore, time for 50% phenolconversion is more or less 10 min delayed compared to 40% conversion. On the other hand,time differencefor the reactions performed in concentrated phenol solution is closer to 1–3min. Another conclusion may be formed on the basis of the analysis of residual phenolconcentrations. Within 75 min of the reaction, phenol concentration is reduced to 3–31 and 2–6 mg/L for ferrihydrite- and hematite-containing catalysts, respectively, in reactions usingstarting solution equal to 100 mg/L. When 1 g/L phenol solution was used, finalconcentrationswere equal to 8–11 and 15–30 mg/L for both iron containing series of catalysts. In this way, itwas confirmedthat dispersed pollutants are more difficultto remove efficientlythenconcentrated.
Sample name Fe content inFe available (mg/Fe leached fromPhOH residualt40% (min) t50% (min)catalystL)* catalyst (%)**(mg/L)*

S2 89.1 
S2 R01 5.7 3.6 26 32 44 
S2 R1 n.d. n.d. 11 52 54 
S3 109.2 
S3 R01 4.6 2.4 31 34 46 
S3 R1 27.1 14.0 21 29 32 
S4 154.2 
S4 R01 2.8 1.0 3 40 50 
S4 R1 n.d. n.d. 8 28 29 
HS0 59.0 
HS0 R01m 0.9 0.9 92 – – 
HS0 R01 0.5 0.4 35 32 49 
HS0 R1 1.3 1.2 863 – – 
HS1 76.7 
HS1 R01m 3.2 2.3 89 – 62 
HS1 R01 2.5 1.8 4 29 33 
HS1 R1 26.0 19.2 19 41 43 
HS2 86.8 
HS2 R01m 3.2 2.1 4 – – 
HS2 R01 1.0 0.7 2 24 26 
HS2 R1 13.4 8.7 15 22 25 
HS3 119.1 
HS3 R01 5.1 2.4 6 33 41 
HS3 R1 23.9 11.4 30 30 33 
n.d., not determined. 
*In solution after 75 min of reaction. 
**Percentage of initial content. 

Table 4. Comparison of Fe content in catalysts and reaction solutions, residual concentration of phenol and time of 40and 50% phenol conversion.


4. Conclusions
Depending on the experimental conditions, a nanocrystalline phase of hematite was formedin the hydrothermal synthesis. On the other hand, precipitation resulted in the formation offerrihydrite phase. It was demonstrated that the latterphase is less active than nano-hematite;moreover, it was shown that optimum loading of the active phase is required to obtain thehighest reaction efficiency:fast and high phenol conversion with minimum amount of sideproducts as well as limited catalyst degradation. Among the transition products, formation ofquinones was confirmedusing derivative UV-vis spectroscopy. Physicochemical techniquesalso confirmedthat nano-hematite-containing catalysts were more stable in studied reaction—only limited changes were observed in agglomeration state of Fe-containing materials, andleaching of iron was reduced. It was also shown that each group of catalysts is in differentextents susceptible to degradation. However, the observed catalytic effectcannot be attributedonly to homogeneous reaction. It was confirmedthat dispersed pollutants are more resistantto degradation.

Author details
Agnieszka Węgrzyn
Addressallcorrespondenceto:a.m.wegrzyn@uj.edu.pl;a.m.wegrzyn@gmail.com
FacultyofChemistry,JagiellonianUniversityinKrakow,Kraków,Poland

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