Activated Carbon-Fly Ash-Nanometal Oxide Composite Materials : Preparation , Characterization , and Tributyltin Removal Efficiency

e physicochemical properties, nature, and morphology of composite materials involving activated carbon, �y ash, nFe3O4, nSiO2, and nZnO were investigated and compared. Nature and morphology characterizations were carried out by means of scanning electron and transmission electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy. Other physicochemical characterizations undertaken were CNH analysis, ash content, pH, point of zero charge, and surface area and porosity determination by BET. Experimental results obtained revealed that activated carbon, nSiO2, activated carbon-�y ash, activated carbon-�y ash-nFe3O4, activated carbon-�y ash-nSiO2, and activated carbon-�y ash-nZnO compositematerials exhibited net negative charge on their surfaces while �y ash, nFe3O4, and nZnO possessed net positive charge on their surfaces. Relatively higher removal efficiency (>99%) of TBT was obtained for all the composite materials compared to their respective precursors except for activated carbon. ese composite materials therefore offer great potential for the remediation of TBT in wastewaters.


Introduction
Fly ash, generated during the combustion of coal for energy production consists of �ne, powdery particles predominantly spherical in shape, either solid or hollow, and mostly glassy (amorphous) in nature [1].Fly ash has been proposed as a good adsorbent for NOx, SOx, and mercury removal from �ue gases as well as adsorption of organic gas [1,2].Fly ash has a potential application in wastewater treatment because of its major chemical components, which are alumina, silica, ferric oxide, calcium oxide, magnesium oxide, and carbon, and its physical properties such as porosity, particle size distribution, and surface area.Hence, it has been used as a low-cost adsorbent for the removal of heavy metals [3][4][5][6], dyes [7], phenolic compounds [8], and humic acids [9] in wastewaters.Activated carbon, on the other hand, is also widely used in a variety of areas, namely, as an adsorbent in air and water pollution control, a catalyst in the chemical and petrochemical industries, and a puri�er in the food and pharmaceutical industries [10].In the water treatment �eld, activated carbon is o�en used as an adsorbent for the removal of various synthetic and naturally occurring organic chemicals in drinking water [11].In wastewater treatment, activated carbon is a powerful adsorbent because of its large surface area and pore volume, which allows the removal of liquid-phase contaminants, including organic compounds, heavy metal ions, and colors.Adsorption on activated carbons has been investigated extensively due to their use in many applications including the removal of toxic volatile organic compounds (VOCs) and pollutants in water and air [12][13][14][15].
Within the last few years, intensive wide spread contamination of the atmosphere and surface water related to adverse industrial operations has been of great concern and call for the development of better adsorbents.Many researchers have therefore focused on the search for better adsorbents with very high adsorption capacities, use of nanometal oxides as adsorbents, and the surface modi�cation of existing adsorbents.Limited work was thus reported on the use of composite materials for wastewater treatments.Some of the reported works in this area is by Zhang et al. [10] who reported the preparation of CuFe 2 O 4 /activated carbon magnetic adsorbents with mass ratio of 1 : 1, 1 : 1.5, and 1 : 2 for the adsorption of acid orange II (AO7) in water and subsequent separation of adsorbent from the medium by a magnetic technique.eir results suggest that the composite has much higher catalytic activity than that of activated carbon, and this is attributed to the presence of CuFe 2 O 4 .Shukla et al. [14] studied the synthesis of composites of carbon and natural zeolite with varying amounts of carbon as prospective adsorbents to adsorb organic contaminants from waste water such as phenol.ey reported that the adsorption isotherm indicated an enhanced adsorption of phenol on the composites as compared with the natural zeolite, and that adsorption increased with increase in carbon content of the composite materials.e adsorption and degradation of trichloroethylene (TCE) through dechlorination using synthetic granular activated carbon and zerovalent iron (GAC-ZVI) composites was reported by Tseng et al. [16].ey reported that the usage of granular activated carbonzerovalent iron composites liberated a greater amount of Cl than when zerovalent iron was used alone.Jha et al. [17] also investigated the preparation of composite materials of activated carbon, and zeolite by activating coal �y ash by fusion and reported that the composites of activated carbon and zeolite proved to be suitable for the uptake of toxic metal ions.
Researches have therefore focused on the enhancement of the effectiveness of activated carbon and �y ash by modifying their speci�c properties by chemical modi�cation (treatment with acids or bases), thermal activation, impregnation, and/or surfactant modi�cation [18][19][20][21] in order to enable the carbon to develop affinity for certain contaminants.No work has been reported on the preparation of composite materials involving activated carbon, �y ash, nFe 3 O 4 , nSiO 2 , and nZnO as precursors, except for Fatoki et al. [22] who reported the preparation and characterization of activated carbon-nFe 3 O 4 , activated carbon-nSiO 2 , and activated carbon-nZnO hybrid materials.Composite materials involving activated carbon, �y ash, and nanometal oxides are expected to have high adsorption capacity due to their nature, morphology, and properties, and due to the presence of nanooxides in the composite materials; it is also expected that the remediation mechanism by these materials will combine the synergistic effect of adsorption and oxidation during the adsorption processes and not adsorption alone.
e aim of this study is, therefore, to prepare activated carbon, �y ash, and nanometal oxide composite materials capable of enhancing the adsorption of pollutants from wastewaters and to carry out a detailed characterization of these materials in order to understand the properties that will be of great importance to environmental management.

Preparation of Composite Materials.
Activated carbon, �y ash, and nanometal oxides in the ratio 1 : 1 : 1 were dispersed in 0.5 M HCl to form slurries. e slurries were stirred by means of a stirrer and evaporated to dryness in an oven.e composite materials obtained were washed with Milli-Q water, �ltered, further dried in an oven at 100 ∘ C for 24 hours, and ground to �ne powder using agate mortar and pestle [22,24].

Instrumentation. FEI scanning electron microscope
(Nova Nano SEM 230) and transmission electron microscope (TECNAI G 2 20) were used for the SEM and TEM analyses of the precursors and composite materials.Fourier transmission infrared (FTIR) absorption spectra of the precursors and composite materials were obtained by using the potassium bromide (KBr) pellet method of sample preparation and Perkin Elmer Spectrum 1000 instrument for analysis.Euro Ea elemental analyzer was use for carbon, nitrogen, and hydrogen (CNH) analyses.Phase identi�cation of the precursors and activated carbon-�y ash-nanometal oxide composite materials were determined by X-ray diffractometry using a PANalytical PW 3830 diffractometer, while TriStar 3000 analyser (Micromeritics Instrument Corporation) was used for surface area and porosity determination.

pH and Point of Zero Charge (PZC) Determination
. e pH was determined by gently boiling 50 mL of Milli-Q water in a �ask containing 0.1 g of the samples for 5 mins.e pH was measured using a Mettler Toledo pH meter aer the solution was cooled to room temperature.Mass titration technique was used to determine the PZC [22,25].Increasing amounts of sample from 0 to 2 g were added to 10 mL of 0.01 M NaNO 3 solution.e resulting pH of each suspension was measured aer 24 hours.e pH plateau for the highest concentrations of solid in a successive series of mass titrations is taken as the PZC.
2.5.Ash Content Determination.Approximately ±0.1 g of the precursors and composite materials were measured into crucibles and heated in a muffle furnace at a temperature of about 500-600 ∘ C for 4 hours.e samples were withdrawn from the furnace aer ashing, allowed to cool in a desiccator, and then reweighed.e ash content of the precursors and composite materials was calculated by difference, and this process was carried out in triplicate.2.6.TBT Removal Efficiency and Analysis.e removal efficiency of TBT by these materials was tested by applying overall optimal conditions for the adsorption of TBT from TBT-contaminated arti�cial seawater.e removal efficiency () is de�ned as where   is the initial concentration of TBT (100 mg/L) in arti�cial seawater placed in a conical �ask and shaken at 200 rpm for 60 min with 0.5 g of the adsorbents, and   is the equilibrium solution concentration.e concentration of TBT was determined aer derivatization by the addition of 2 mL of acetate buffer (pH = 4.5) and 1.0 mL of 1% NaBEt 4 and extraction into hexane by horizontal shaking in a separation funnel.e extracts were reduced to 1 mL and analyzed by the use of GC-FPD (Shimadzu GC-2010 Plus) with a capillary column HP 5 (5% phenyl methyl siloxane, 30 m × 0.25 mm, i.d., �lm thickness 0.25 m), and the temperature was programmed as follows: initially at 60 ∘ C hold for 1 min, then heated to 280 ∘ C at 10 ∘ C/min, and hold for 4 min.e injection and detector temperatures were 270 ∘ C and 300 ∘ C, respectively, and the carrier gas was high purity helium.
A plot of the percent removal of TBT by the various adsorbents was obtained, and the results were compared.1(a) and 1(b)) showed that activated carbon exhibit aggregated irregular surfaces with a large number of micropores and crevices of various sizes at the surface.e SEM and TEM of activated carbon con�rmed that the activated carbon is a better adsorbent for the adsorption of pollutants from wastewaters.

SEM and TEM. e scanning electron micrograph (SEM) and transmission electron micrograph (TEM) of activated carbon (Figures
Figure 2(a) showed that the particles of Matla �y ash are spherical with smooth and regular surfaces.e TEM of �y ash (Figure 2(b)) presents agglomeration of different particle sizes.e �y ash particles showed different size distributions with spherical shapes.Figure 6(a) showed that activated carbon-�y ash composite material is made up of smooth surface materials (activated carbon) and spherical materials (�y ash) deposited at various position throughout the surfaces of the activated carbon.e TEM (Figure 6(b)) showed that the activated carbon (irregular surfaces) was aggregated with the spherical particle of �y ash.e SEM and TEM (Figures 6(a) and 6(b)) showed that the �y ash particles maintained their spherical morphology a�er the preparation of activated carbon-�y ash composite material.
e SEM and TEM of activated carbon-�y ash-nFe 3 O 4 composite material (Figures 7(a) and 7(b)) showed that the composite material exhibit aggregated irregular surfaces with large number of micropores and crevices at the surface.Fly ash and nFe 3 O 4 were found at the surface of the activated carbon.
e SEM and TEM of activated carbon-�y ash-nSiO 2 composite material (Figures 8(a) and 8(b)) showed that the composite material also exhibited aggregated irregular surfaces with large number of micropores and crevices at the surface.e nSiO 2 and �y ash were distributed at the surface of the activated carbon.
e SEM of activated carbon-�y ash-nZnO composite material (Figure 9(a)) showed that the activated carbon, �y ash, and nZnO particles were fused together.�arge intergranular voids and crevices were associated with the activated carbon-�y ash-nZnO composite material with �y ash still maintaining its spherical regular shape.�e TEM of activated carbon-�y ash-nZnO composite material (Figure 9(b)) thus showed a clustered activated carbon, �y ash, and nZnO composite material with large intergranular voids and crevices.

FTIR Absorption Spectra.
In the FTIR spectrum of activated carbon, �y ash, and activated carbon-�y ash composite material (Figure 10), the absorption at 1616 cm −1 (curve (a)) is assigned to the C=C stretching of activated carbon that a new bond was formed during the preparation of the activated carbon-�y ash-nFe 3 O 4 composite material.Activated carbon-y ash-nSiO 2 composite F 12: F�I� spectrum of precursors and activated carbon-�y ash-nSiO 2 composite material.
In the F�I� spectrum of activated carbon, �y ash, nSiO 2 , and activated carbon-�y ash-nSiO 2 composite material (Figure 12), the absorption at 1616 cm −1 (curve (a)) is assigned to the C=C stretching of activated carbon, and the absorption at 1097 cm −1 (curve (b)) is assigned to the C-C stretching of �y ash, while the absorption at 1101 cm −1 (curve (d)) is assigned to the asymmetric vibration of Si-O.e absorption at 809 cm −1 (curve (d)) is assigned to the symmetric vibration of Si-O [28].It was found that the wavenumber of the symmetric vibration of Si-O changed from 809 cm −1 of nSiO 2 to 805 cm −1 (curve (h)) of the activated carbon-�y ash-nSiO 2 composite material.e wavenumber of the absorption peak decreased by 4 cm −1 .A decrease in the wavenumber suggests that a new bond was formed during the preparation of the activated carbon-�y ash-nSiO 2 composite material.In the F�I� spectrum of activated carbon, �y ash, nZnO, and activated carbon-�y ash-nZnO composite material (Figure 13), the absorption at 1616 cm −1 (curve (a)) is assigned to the C=C stretching of activated carbon, and the absorption at 1097 cm −1 (curve (b)) is assigned to the C-C stretching of �y ash, while the absorption at 1110 cm −1 (curve (e)) is assigned to the asymmetry vibration of Zn-O, and the absorption at 808 cm −1 (curve (e)) is assigned to the Zn-O stretching of nZnO.It was found that the wavenumber of Zn-O vibration changed from 1110 cm −1 of nZnO to 1094 cm −1 (curve (i)) of the activated carbon-�y ash-nZnO composite material.e wavenumber of the absorption peak decreased by 16 cm −1 .Decrease in the wavenumber suggests that a new bond was formed during the preparation of the activated carbon-�y ash-nZnO composite material.
e result obtained thus shows that the shi in the band is a function of the metal ions present in the composite materials.e F�I� data also con�rm the absence of impurity in both the precursors and the prepared composite materials.

pH and Point of Zero Charge (PZC) Measurement.
From Figure 15, the preparation of activated carbon-�y ash composite material using activated carbon (pH 3.3) and �y ash (pH 10.70) as precursors resulted in activated carbon-�y ash composite material of pH 3.51.e pH was higher than the pH of activated carbon by 59.8% and lower than the pH of �y ash by 67.2%.e preparation of activated carbon-�y ash-nFe 3 O 4 composite material using activated carbon (pH 3.3), �y ash (pH 10.70), and nFe 3 O 4 (pH 5.95) as precursors resulted to activated carbon-�y ash-nFe 3 O 4 composite material of pH 3.41.e pH was higher than pH of activated carbon by 32.3%, lower than pH of �y ash by 68.1%, and lower than pH of nFe 3 O 4 by 42.7%.
e preparation of activated carbon-�y ash-nSiO 2 composite material using activated carbon (pH 3.3), �y ash (pH 10.70), and nSiO 2 (pH 5.53) as precursors resulted in F 21: Ash content (%� �ersus acti�ate� car�on� �y ash� nano�articles� an� com�osite materials� activated carbon-�y ash-nSiO 2 composite material of pH 3.34.e pH was higher than pH of activated carbon by 1.2%, lower than pH of �y ash by 68.8%, and lower than pH of nSiO 2 by 39.6%.e preparation of activated carbon-�y ash-nZnO composite material using activated carbon (pH 3.3), �y ash (pH 10.70), and nZnO (6.71) as precursors resulted to activated carbon-�y ash-nZnO composite material of pH 6.42.e pH was higher than pH of activated carbon by 48.6%, lower than pH of �y ash by 40.0%, and lower than pH of nZnO by 4.3%.e result obtained shows that the pH values of the composite materials were determined by the pH value of each of the precursors that made up the composite materials.
Figure 16 showed that the point of zero charge (PZC) of activated carbon, �y ash, and activated carbon-�y ash composite material are 2.06, 12.17, and 3.19, respectively.e PZC of activated carbon-�y ash composite material was higher than PZC of activated carbon by 35.42%, but lower than the PZC of �y ash by 73.79%.e graph showed that the presence of �y ash (high PZC value and basic) in the activated carbon (acidic) raised the PZC of activated carbon to form activated carbon-�y ash composite material of PZC of 3.19.
Figure 17 showed that the PZC of activated carbon, �y ash, nFe 3 O 4 , and activated carbon-�y ash-nFe 3 O 4 composite material are 2.06, 12.17, 6.58, and 2.84, respectively.e PZC of activated carbon-�y ash-nFe 3 O 4 composite material was higher than the PZC of activated carbon by 27.46%, lower than PZC of �y ash by 76.66%, and also lower than the PZC of nFe 3 O 4 by 56.84%.
From Figure 18, the PZC of activated carbon, �y ash, nSiO 2 , and activated carbon-�y ash-nSiO 2 composite material are 2.06, 12.17, 4.25, and 3.60, respectively.e PZC of activated carbon-�y ash-nSiO 2 composite material was therefore higher than the PZC of activated carbon by 42.78%, lower than PZC of �y ash by 70.42%, and also lower than the PZC of nSiO 2 by 15.29%.
From Figure 19, the PZC of activated carbon, �y ash, nZnO, and activated carbon-�y ash-nZnO composite material are 2.06, 12.17, 6.80, and 6.14, respectively.e PZC of activated carbon-�y ash-nZnO composite material was therefore higher than the PZC of activated carbon by 66.45%, lower than PZC of �y ash by 49.55%, and also lower than the PZC of nZnO by 9.71%.
Comparing the PZC values of the precursors and the composite materials, it could be concluded that it is not the presence of the nanoparticles alone that determines the PZC changes, but the PZC of each of the component precursors that made up the composite materials.
3.6.X-Ray Diffraction.e diffractogram of activated carbon shows the absence of crystalline substances, while the �y ash is dominated mainly by crystalline minerals mullite and quartz with large characteristic peaks of quartz (SiO 2 ) as reported by Fatoki et al. [22] and Ayanda et al. [23], respectively.e x-ray diffractograms of nFe 3 O 4 , nSiO 2 , and nZnO have also been reported by Fatoki et al. [22].Figures 22 to 25 thus show the X-ray diffractograms of activated-�y ash, activated carbon-�y ash-nFe 3 O 4 , activated carbon-�y ash-nSiO 2 , and activated carbon-�y ash-nZnO composite materials.
All the diffractograms obtained showed de�ned characteristic peaks corresponding to the mineral constituents of the precursors and the composite materials.is showed that the precursors and all the prepared composite materials are pure.

Surface Area and Porosity Determination.
Results obtained on the Brunauer, Emmett, and Teller (BET) surface area and porosity determinations of activated carbon-�y ash-nanometal oxide composite materials as well as their precursors are shown in Table 1 and Figure 26.
It is therefore evident from the results presented in Figure 27 that apart from activated carbon which showed comparable result with the composite materials, all the composite materials exhibited higher (>99%) TBT removal efficiency than their respective precursors.ese composite materials  are therefore potentially good materials for remediation application of TBT laden wastewater.

Conclusion
Experimental results showed that the pH values of activated carbon, nSiO 2 , activated carbon-�y ash, activated carbon-�y ash-nFe 3 O 4 , activated carbon-�y ash-nSiO 2 , and activated carbon-�y ash-nZnO are negatively charged and will therefore be suitable for the sorption of cationic complexes, while the pH values of �y ash, nFe 3 O 4 , and nZnO are slightly lower than their corresponding PZC values which suggest that their surfaces are positively charged and will therefore be favourable to the sorption of anionic complexes and heavy metals.e ash content determination also showed that the level of inorganic materials present in the adsorbent composite materials is a function of the precursors that make up the composite materials.e XRD and FTIR analyses con�rmed the absence of impurity in the precursors and the prepared composite materials.e results of BET surface area and porosity determination also supported the higher sorption of TBT by the composite materials.e compositing of activated carbon, nanometal oxides, and �y ash increased the surface area and micropore area of �y ash and nano metal oxides which resulted in higher sorption capacity of the composite materials than their precursors.

F 3 :F 4 :
(a) SEM of �y nFe 3 O 4 .(b) TEM of nFe 3 O 4 .(a) SEM of nSiO 2 .(b) TEM of nSiO 2 .e SEM of nFe 3 O 4 (Figure 3(a)) showed that nFe 3 O 4 consists of agglomerated globules with irregular and rough surfaces.e TEM of nFe 3 O 4 (Figure 3(b)) presents agglomeration of particles.e TEM thus showed that nFe 3 O 4 is made up of different shapes including square, spherical, and hexagonal shapes.e SEM of nSiO 2 (Figure 4(a)) showed that nSiO 2 exhibit agglomerated irregular surfaces with a large number of micropores and a few voids and crevices, while the TEM of nSiO 2 (Figure 4(b)) showed a bimodal distribution of particles size.e SEM and TEM of nZnO (Figures 5(a) and 5(b)) showed that nZnO particles consist of nonuniform granules and more regular surfaces.e TEM of nZnO (Figure 5(b)) con�rmed the various shapes and sizes of nZnO particles.

F 8 :F 10 :
(a) ��� of activated carbon-�y ash-n�iO 2 composite material.(b) ��� of activated carbon-�y ash-n�iO 2 composite material.(a) (b) F 9: (a) ��� of activated carbon-�y ash-n�nO composite material.(b) ��� of activated carbon-�y ash-n�nO composite material.[26, 27], while the absorption at 1097 cm −1 (curve (b)) is assigned to the C-C stretching of �y ash.It was found that the wavenumber of C-C stretching of �y ash changed slightly from 1097 cm −1 of �y ash to 109� cm −1 (curve (f)) of the activated carbon-�y ash composite material.e wavenumber of the absorption peak decreased by 4 cm −1 .e slight change in the wavenumber suggests that a new bond was formed during the preparation of the activated carbon-�y ash composite material.In the F�I� spectrum of activated carbon, �y ash, nFe 3 O 4 , and activated carbon-�y ash-nFe 3 O 4 composite material (Figure 11), the absorption at 1616 cm −1 (curve (a)) is assigned to the C=C stretching of activated carbon, and the absorption at 1097 cm −1 (curve (b)) is assigned to the C-C stretching of �y ash, while the absorption at 586 cm −1 (curve (c)) is assigned to the Fe-O stretching of nFe 3 O 4 .It was found that the wavenumber of Fe-O stretching changed from 586 cm −1 of nFe 3 O 4 to 560 cm −1 (curve (g)) of the activated carbon-�y ash-nFe 3 O 4 composite material.e wavenumber of the absorption peak decreased by 26 cm −1 .Decrease in the wavenumber suggests F�I� spectrum of precursors and activated carbon-�y ash composite material.

F 13 :
F�I� spectrum of precursors and activated carbon-�y ash-nZnO composite material.

F 14 :
A plot of element (%) against the precursors and composite materials.

F 15 :
p� of acti�ated car�on� �y ash� nano metal o�ides� and composite materials.

3 F 16 : 3 F 17 :
Result of mass titration experiments with activated carbon, �y ash, and activated carbon-�y ash composite material.Variation of pH versus mass of solid in 0.01 M NaNO 3 .Result of mass titration experiments with activated carbon, �y ash, nFe 3 O 4 , and activated carbon-�y ash-nFe 3 O 4 composite material.Variation of pH versus mass of solid in 0.01 M NaNO 3 .

3 F 18 : 3 F 19 :
Result of mass titration experiments with activated carbon, �y ash, nSiO 2 and activated carbon-�y ash-nSiO 2 composite material.Variation of pH versus mass of solid in 0.01 M NaNO 3 .Result of mass titration experiments with activated carbon, �y ash, n�nO, and activated carbon-�y ash-n�nO composite material.Variation of pH versus mass of solid in 0.01 M NaNO 3 .
T 1: BET result of activated carbon-�y ash-nano metal oxide composite materials.