**2. Experimental section**

ZnO is a wide band-gap (∼3.3 eV) semiconductor that has been extensively used because of its catalytic and photochemical properties along with its low cost [1]. There are many reports of ZnO having higher photocatalytic activities than other semiconductors in both air and aqueous media [2,3]. As a photocatalyst, the surface area plays an important role since reactions mainly occur between catalyst surfaces and pollutants. The nanoscale ZnO crystals have shown larger surface areas and higher photocatalyic performances than that of bulk materials [4]. There‐ fore,recent studies have focused on the synthesis of nanostructured ZnO with tunable size and shape [5,6]. However, ZnO nanoparticles are not stable in acidic and alkaline conditions and also show rapid deactivation in bulk due to increased tendency of aggregation [7]. Hence, the development of industrially viable, cost-effective, eco-friendly adsorbents with attractive multiple functions such as adsorption, and decomposition becomes important. Silicate adsorbents engineered with photocatalytic ingredients, for example, tailoring the aluminosili‐ cate layers and their surfaces with nanostructured semiconducting photocatalysts, can make them multifunctional composites and heterogeneous catalysts [8]. ZnO/clay system reveals the potential of this composite for various applications [9–12]. Among clay minerals, the usage of sepiolite as a supportmaterial is rarelyreported[13–18].Natural sepiolite is a verycheap,fibrous and hydrated magnesium silicate with a relatively high surface area. The presence of alkales‐ cent [MgO6] and acidic [SiO4] centers in the sepiolite structure enhances the adsorption of reactant molecules and their degradation possibility. Moreover, silicate layers appear as an attractive support for the assembly of small-sized metals and metal-oxide aggregates (clus‐ ters and nanoparticles) that have been mainly employed for catalytic purposes. The immobili‐ zation of nanoparticles on the inner and outer surfaces of inorganic supports results in the formation of nanocomposite materials. The synergy established among nanoparticles and support systems makes them attractive options for the degradation of pollutants. In the study of Xu et al., quantum-sized ZnO particles supported on sepiolite were prepared using a solgel method with the sepiolite of acid activation as carrier and zinc acetate dihydrate (Zn(CH3COO)2 2H2O) and lithium hydroxide monohydrate (LiOH H2O) as raw materials [13]. Theyfoundthatthenano-ZnOsupportedonsepiolite cannotonlysolve thedispersingproblem but also has a positive synergistic effect on the ZnO photocatalysis. Bautista et al. prepared TiO2-Sep supports of vanadium oxide in order to obtain a new TiO2 support with a high and thermostable surface area [14]. According to this study, vanadium oxides supported on TiO2 coated sepiolite and sepiolite characterization studies indicated that well-dispersed vanadi‐ um in both types of supports was achieved in the systems with vanadia loading below the theoretical monolayer. Above this vanadia loading, the formation of V2O5 nanoparticles with a mainly crystalline character took place as well as the formation of V-Mg mixed metal-oxide phases, especially in systems supported on sepiolite. The hydrophilic character and more open structure ofthe sepiolite was underlined in the study ofArques et al.[15].Accordingly, sepiolite appearedto be a convenient supportforpyryliumsalts to be employed as a heterogeneous solar photocatalyst. Also, promising results have been obtained testing the performance of the new material with ferulic acid as target pollutant, and important percentages of photo-oxidation were achieved. In another study, monolithic catalysts based on Rh/TiO2-sepiolite were developed and tested in the decomposition of N2O traces [16]. The system was found to be extremely sensitive to the amount of rhodium and is an attractive alternative for the elimina‐ tion of N2O traces from stationary sources due to the combination of high catalytic activity with a low pressure drop and optimum textural/mechanical properties. The structural and photoca‐

232 Advanced Catalytic Materials - Photocatalysis and Other Current Trends

The raw SEP used as a support in this study was obtained from the Eskişehir region of Anatolia (Turkey) and characterized by X-ray diffraction and SEM-EDX analyses. The chemical composition was found as SiO2 (69.25%), MgO (28.92%), Al2O3 (1.12%), Na2O (0.55%) and TiO2 (0.16%). The clay was ground to approximately 200-mesh size powder. Zinc nitrate hexahydrate (Zn(NO3)2 6H2O) (99.0%, Merck), sodium carbonate (Na2CO3) (analytical grade, Merck) and (4-[[(4-dimethylamino)phenyl]-azo]benzenesulfonic acid sodium salt] (methyl orange, Merck) were used as provided by the suppliers without further purification. Deionized water, purified with an Elga-Pure Water Purification (UHQ II) system, was used for preparing solutions in the experiments.

The following procedures and techniques were applied for the synthesis and characterization of the photocatalysts:

ZnO catalysts in the absence of SEP were prepared by a coprecipitation method using Zn(NO3)2 6H2O and Na2CO3 precursors [19]. Briefly, the precursors with 0.25 M concentrations were separately dissolved in deionized water. Then, 100 mL of Zn(NO3)2 6H2O were added gradually to 100 mL of Na2CO3 solution under continuous stirring. The resulting white suspension was stirred for 2 h at room temperature followed by several washings and centrifugations at 4000 rpm. Then, the resulting precipitate was dried at 100°C for 12 h and calcined at 500°C with a heating rate of 10°C min-1 for 5 h. Finally, the catalysts were ground into fine powder and named as 0.25 M ZnO.

Depending on the loading of ZnO on the support, precursor concentrations as 0.125 M ZnO, 0.25 M ZnO or 0.5 M ZnO (prepared following the above procedure) were added to the SEP solution. After stirring the mixed suspension for about 12 h at room temperature, several washings and centrifugations (at 4000 rpm) were applied. The resulting catalysts were dried at 100°C for 12 h and then calcined at 500°C with a rate of 10°C min-1 for 5 h. Finally, the catalysts were ground into fine powder and named as 0.125 M ZnO-SEP, 0.25 M ZnO-SEP and 0.5 M ZnO-SEP.

X-ray diffraction was used to monitor the formation of crystal planes and measure the crystalline size of ZnO nanoparticles. The analyses were recorded on a Rigaku-D/MAX-Ultima diffractometer using Cu-Kα radiation (λ=1.54 Å) operating at 40 kV and 40 mA and scanning rate of 2 min-1. Nitrogen sorption analysis was used to measure the surface areas, pore volumes and pore diameters of the catalysts.

The nitrogen adsorption/desorption isotherms were obtained at 77 K using Quantachrome Nova 2200e automated gas adsorption system. The specific surface areas were determined using multi-point BET analysis and the pore sizes were measured by the BJH method of adsorption.

The surface morphologies were determined using scanning electron microscopy (SEM) in combination with energy-dispersive X-ray analysis on an ESEM-FEG/EDAX Philips XL-30 instrument operating at 20 kV. The catalysts were fixed with carbon tape prior to the metalli‐ zation process with gold (Sputter Coater-Balzer SCD050).

In X-ray photoelectron spectroscopy (XPS) tests, Thermo Scientific K-Alpha X-ray photoelec‐ tron spectrometer equipped with electron analyzer and Al-Kα micro-focused monochromator was used. The areas of peaks were estimated by calculating the integral of each peak after subtracting a Shirley background and fitting the experimental curve to a combination of Lorentzian/Gaussian lines. Binding energy shifts were observed in the samples and the instrument was calibrated using the carbon peak (C-1s) at 285 eV as in the other studies [20,21].

The UV-vis diffuse reflectance spectra (UV-vis DRS) of the supports, 0.25 M ZnO and sup‐ ported catalysts were obtained using UV-vis spectrophotometer (UV-2450, Shimadzu) equipped with an integrating sphere reflectance accessory. The baseline correction was done by BaSO4. The spectra were recorded in the range 200–600 nm for the catalysts and the FA using BaSO4 as a reference.

For the photocatalytic experiments, the details of reaction systems were given in our previous studies [22,23]. Briefly, a Pyrex flask reactor was located in an "irradiation box" equipped with eight black light lamps (Philips TL 15W/5BLB) with an emission maximum at λ=365 nm. The lamps were positioned to surround the flask with an incident photon flux of 4.7×1015 photons s-1. Then, 0.2 g of catalysts with 200 mL of 3.27 mg L-1 MO (unless the concentration effect of MO was controlled) was used as reaction solutions. The flask had an inlet for the air circulation and an outlet for the collection of aliquots. Prior to irradiation, suspensions were magnetically stirred in the dark for 30 min. UV-vis spectrophotometer (UV-2450, Shimadzu) was used to monitor the absorbance spectra of MO at 464 nm as a function of irradiation time. All experi‐ ments were performed at room temperature and without concerning the degradation inter‐ mediates. Also, measurements were conducted at least twice and the average value was recorded. MO decolorization percentages were calculated by the following equation:

$$\text{Decolorization }\%=\frac{C\_0 - C}{C\_0} \times 100\%$$

where *C*<sup>0</sup> is the initial concentration of MO and *C* is the concentration of MO after "*t*" minutes irradiation.
