Design and fabrication of continuous flow photoreactor using semiconductor oxides for degradation of organic pollutants

Journal of Water Process Engineering 32 (2019) 100922

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Design and fabrication of continuous flow photoreactor using semiconductor oxides for degradation of organic pollutants

T

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Abdel-hameed M. El-Aassar, Heba Isawi , Mostafa El-Noss, Rasha A. El-Kholy, Moustafa M. Said, Hosam A. Shawky Egyptian Desalithenation Research Center (EDRC), Desert Research Center (DRC), El-Mataryia, Cairo, Egypt

A R T I C LE I N FO

A B S T R A C T

Keywords: Photocatalysis PS modified membrane Continuous flow photoreactor (TiO2/SiO2) nanocomposites and (TiO2/ZnO) nanocomposites

The goal of this research was to design and fabricate the continuous flow photoreactor (PR) to degrade organic contaminants in wastewater using heterogeneous photocatalytic process. Different nanomaterials such as ZnO and SiO2 were produced via a hydrothermal procedure and mixed with TiO2 (Degussa) to act as a catalyst. The nanomaterials were doped with polysulfone (PS) to prepare modified flat sheet membranes via the phase inversion process. The characterization of the synthesized nanomaterials and membranes were carried out via Fourier transforms infrared spectroscopy (FTIR), X-ray diffraction (XRD), particle size analyzer (PSA), scanning electron microscope (SEM) and contact angle (CA) measurement. Also, the efficiency of the synthesized polymeric nanocomposites (NCs) membranes and the PR were evaluated by revising the outcome of different parameters. These parameters included feed water pH, flow rate, the presence of an oxidizing agent (H2O2), pollutant types, and pollutant concentrations. Phenol compound and methyl orange (MO) were utilized as examples of organic pollutants. The obtained results using the (PS/TiO2/ZnO) (NCs) membrane (I) showed the degradation of 72% and 16.5% in the case of Phenol and MO respectively, under ultraviolet light. Conversely, the degradation was 30% and 11% using Phenol and MO respectively, under visible light. Furthermore, the (PS/ TiO2/SiO2) (NCs) membrane (II) was able to degrade 18.1% and 40.3% in the case of Phenol under UV radiation and visible light, respectively. The performance was improved by increasing the oxygen content, through the addition of H2O2 and the degradation attained 97% and 95% under visible light in case of MO and Phenol, respectively using membrane (II).

• Highlights • Synthesis and characterization of ZnO and SiO • •

2 nanoparticles via hydrothermal process and mixed with TiO2 (Degussa) to form (TiO2/SiO2) and (TiO2/ZnO) nanocomposites. Use heterogeneous photocatalytic process for treatment of organic pollutants in waste water Doping these nanomaterials with polysulfone (PS) to prepared modified flat sheet membrane using phase inversion method.

1. Introduction Nowadays, water contamination has become a widespread issue. The aspect of global water insufficiency is a vital need to prevent pollution of water resources from numerous impurities type [1,2]. The aromatics, fabric dyes, pesticide, and other industrial organic ⁎

contaminants are not only visually disagreeable, however, are excessively toxic to some creatures. Consequently, a procedure to clean the organic pollutants from the wastewater is a crucial requirement. Newly, numerous techniques have been used to remove organic impurities from wastewater, for instance, physical procedures, chemical oxidation, photocatalytic methods, electrochemical oxidation, and biological usage [3]. The former procedure is one of the greatest and favorable expertises for removing organic impurities due to its great proficiency with sunlight [4,5]. The photocatalytic reaction show practical to environmental cleaning by using the oxidation of organic complexes via semiconductor materials, for instance, TiO2, CdS, Fe2O3, SiO2 and ZnO [6]. ZnO and TiO2 are renowned catalysts in various photocatalytic reactions [7]. Between these numerous semiconductors, the titanium dioxide (TiO2), have a higher photocatalytic activity, nontoxic, showing suitable regular potential band (Vbp) and chemically stable. Conversely, these oxides absorb only a small portion of solar light and are little-applied use [8]. The photocatalytic activity of TiO2

Corresponding author. E-mail address: [email protected] (H. Isawi).

https://doi.org/10.1016/j.jwpe.2019.100922 Received 10 January 2019; Received in revised form 10 August 2019; Accepted 18 August 2019 2214-7144/ © 2019 Elsevier Ltd. All rights reserved.

Journal of Water Process Engineering 32 (2019) 100922

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performances have been enhanced via doping of NCs such as ZnO-TiO2 [7], SiO2-GO [27], Al–ZnO [28], Ag–ZnO [29], Co–ZnO [30], and graphene oxide-silver NCs [31]. This incorporation is mainly attributed to the growth of the visible area of the photocatalyst. Briefly the nanomaterials concentration embedded into the membrane surface is limited; it is significant to consider the catalytic effect of the nanomaterials, which are inserted inside the membrane. The objective of this study is to fabricate and design the continuous flow PR for treatment of organic contaminants in wastewater using heterogeneous photocatalytic process. The greatest advantage of this technique is lower maintenance, costs, and construction as well as it presented favorable results in degradation of organic contaminations from wastewaters. Preparation of ZnO and SiO2 via a hydrothermal process and mixed with TiO2 (Degussa) aims to enhance the photocatalytic activity in sunlight. These nanomaterials were incorporated with PS to synthesize the modified flat sheet membrane through the phase inversion process. The characterization of the synthesized nanomaterials and membranes were carried out using particle size analyzer, scanning electron microscope (SEM), ATR-FTIR spectroscopy and contact angle measurement. Also, the efficiency of both synthetized polymeric NCs membranes and the PR were evaluated by studying the effect of different parameters. These parameters included feed water pH, flow rate, oxygen content, pollutant types, and pollutant concentrations. The pollutants such as phenolic compound and methyl orange were used as examples of organic pollutants. This technique develops the photocatalytic activity and solving the problem of high concentration of organic contaminants in surface and/or groundwater.

differs reliant on its crystallinity, surface area, particle size, and the method of preparation [9]. There are various methods for nanomaterials preparation such as sol-gel [10], micro emulsion [11] and a hydrothermal method [12]. Among these processes, the hydrothermal techniques is the most effective techniques for adjusting size and surface characteristics of nanomaterial's to create uniform nanoparticles with a high surface area. Further, the hydrothermal technique does not require the use of organic solvents and considered an ecological friendly procedure, wherever the preparation is achieved in a closed system [13]. ZnO NPs is a proper photo catalyst as it is non-toxic and lower cost however its wide band gap (Eg) necessitates an excitation in the UV expanse. Conversely, a substantial excitation is delivered via sunlight which covers about 60 W of UV light irradiation [14]. Conversely, abundant effort has been completed to enhance the photocatalytic efficacy of ZnO NPs via reducing the band gap through doping with nonmetal [15] and noble metal [16]. The photocatylitic activity of TiO2 can be enhanced via the adding of SiO2 which advances the obtainable surface area of the catalyst, letting an increase adsorption of pollutant composites. The enhanced adsorption of contaminant particles on the surface of SiO2 consecutively developed the photocatalytic activity of TiO2/SiO2 doped oxides compared to pure TiO2. Moreover, the adding of SiO2 growths the quantity of surface adsorbed H2O and OH groups, which affects the photocatalytic activity of TiO2/SiO2 doped oxides [17]. Furthermore, the SiO2 NPs is added to the combination as a support substantial to improve the thermal strength of the photocatalyst and to enhance its surface acidity, which is an effectual means of rising photocatalytic activity. Recently, foremost challenge is to rearrange the ecb/hvb recombination level to develop the TiO2 photocatalyst proficiency and spread the absorption spectra to the visible region [18]. This process generates a modification in the concentration of the electron or hole, thus growing the charge carrier concentration and enhancing the conductivity of these materials. An additional technique is to couple TiO2 with a slight band gap semiconductors (SiO2 and/or ZnO) owning a higher conveyance band than that of TiO2. The extensive band gap of TiO2 is 3.2 eV, which means that it can only be produced by UV light (l ≤ 387.5 nm) [19]. Consequently, to decrease the energy gap of TiO2 NPs it should be doped with other metal oxides (ZnO, CdS, Fe2O3, SiO2 and SiO2) to increase photocatalytic efficiency [20]. The enhancement of observable light photocatalysis has come to be the greatest substantial topics in photocatalysis today and in the future research. The photocatalytic activity of TiO2 can be enhanced by doping with metal and non-metal ions such as SiO2/TiO2 and ZrO2/ TiO2. TiO2, ZnO, and SiO2 are the most oxides used in photocatalytic applications. These oxides are considered as semi-conductors with wide band gab [4]. The SiO2/TiO2 NCs have much consideration [21] due to higher photocatalytic activity, surface area, surface acidity, and thermal stability than pure TiO2 [22,23]. The photocatalytic activity can be enhanced via growing the number of active places where the electron donor and acceptor are promoted and adsorbed in the photocatalytic reaction. The effects of SiO2 and ZnO NPs contents on the photocatalytic activity of TiO2 were also considered. The photocatalytic activities of the prepared (ZnO/TiO2) and (SiO2/TiO2) NCs were compared with pure TiO2 as a reference catalyst under the same conditions. Membrane separation technologies have been approximately beneficial for water cleaning, [24]. The greatest appropriate supportive membrane used in photocatalytic degradation is prepared from PS due to its thermal stability, high mechanical and chemical properties. By presenting these nanomaterials into the membrane structure, several progressive properties can be achieved. The former examination exhibited the improvement of the antifouling efficiencies and photocatalytic, hydrophilicity and permeability of the PS membrane after the combination of TiO2 NPs [3,25]. The TiO2/PS NCs membrane was used for the elimination of Cr(VI) as well as the subtraction of its toxicity via photocatalytic degradation, [26]. Furthermore, the membrane

2. Experimental 2.1. Materials The membrane substrate was synthesized from PS (Udel P 3500 LCD MP7, MW = 77000, Mn = 22,000) using N,N’-dimethylacetamide (DMAc) as a solvent via the phase inversion method, these chemicals were purchased from Sigma–Aldrich. Methyl orange (MO) and phenol were used as an example of organic pollutants in the photocatalytic processes and purchased from May and Baker LTD Dagenham England and Egyptian Co. for Chemicals & Pharmaceuticals. Titanium dioxide was supplied from Degussa Company; it is characterized by average particles size (APS): 25 nm and > 99.9% of the TiO2 content. The Titania particles are a mixture of both Anatase (80%) & Rutile (20%), (Evonik), 65 Challenger RD, Ridgefield NJ, U.S. Solvents and inorganic salts were reagent grade and used without further purification. Tetraethylorthosilicate (TEOS), (Sigma–Aldrich; 98%) were used to prepare silica nanoparticles (NPs). H2O2 30% Solution, was used as an oxidizer agent and antiseptic additives and purchased from Gamma Laboratory Chemicals. Sodium hydroxide (ethanol; NaOH; 98%; HCl; 30% were purchased from El Motaheda Company) and used for pH adjustments. The deionized water (DI) was used as the solvent for the reactive dye. Zinc chloride was used to synthesize the ZnO NPs and Sodium lauryl sulphate (SLS) was used as a surfactant. The total organic carbon (TOC) was estimated titrimetrically using the ferrous sulphate (FeSO4.7H2O), Orthophenanthroline as indicator and the Potassium dichromate (K2Cr2O7), these materials were supplied by Sigma Aldrich. 2.2. Design of the continuous flow photoreactor There is an inspiration for generating, designing and fabrication of the continuous flow photoreactor prototype for wastewater purification of organic pollutants using heterogeneous photocatalytic process to protect the health, the environs, and collective pleasure. This photoreactor is composed of four units connected together. The continuous flow photoreactor is presented in Fig. 1a. This continuous flow photoreactor carries is fabricated by El-Safwa Industrial Company and the quartz tubes are created by El-Fatah Industrial Company. The system 2

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Fig. 1. (a) Sketch diagrams of the single unit of the continuous flow photoreactor and (b) The proposed photocatalytic mechanism.

3

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membrane under UV light irradiation. TiO2 is a nontoxic material with high photocatalytic activity. In visible light, TiO2 absorbs onto the surface of the membrane, leading to in situ generation of hydrogen peroxide (H2O2) which acts as activating agent. The incorporation of TiO2 with PS membrane can improve the negative surface charge of the PS membrane which improves the degradation capabilities of the membrane surface, due to the presence of reactive oxygen species such as O2% −, H2O2, and HO% radicals generated by TiO2, or the direct UV illumination [35]. In the presence of TiO2 NPs, photocatalytic reactions take place at the coating surface with oxygen and water. These radicals have photocatalytic activities that destroy various toxic organic pollutants and oxidize organs [36]. The photocatalytic activities of the PS/ TiO2 NCs membrane under UV light irradiation take place based on the following mechanism [37]:

includes a pre-purification unit, a contaminant injection tank, main electrical panel, variable speed driven feed pump, monitoring panel (flow meters, temperature gauge, and pressure gauge), ABS plastic coated steel pipes, a combination of connected bolts, 6 connected quartz tubes, 7 UV lamps and trolley carries all the previous components. The assemblage is energetic via a frequency generator. The continuous flow photoreactor consists of six connected quartz tubes with inner and outer diameters equal to 18 and 20 mm, respectively and the length of each tube is 52 cm.The quartz tubes are fixed into stainless steel plates which is capable of resisting corrosion prompted via the most corrosive chemical composites, 50 mm thickness, and are organized parallel to the length of the photoreactor. The PS membrane is fixed onto the inside wall of the quartz tubes of the continuous flow photoreactor. The continuous flow photoreactor support surface consists of a square cross-section with surface area equal to 84.64 m2. The assemblage of the skeletons was fixed onto the carrier trolley which consists of plastic coated steel pipes and its dimensions are 92, 88, and 76 cm. The feed flows directly over the PS membrane surface with flow rates ranging from 10 to 80m3/h. The continuous flow photoreactor is fabricated with seven UV lamps to make sure good radiation dispersion, Fig. 1a. A sylvania UVA lamp (F40W/2FT/T12/BL368) with a tube length of 55 cm and was fixed onto the carrier trolley. The fabricated system was illuminated with a 365 nm UV lamps. The flow rate is organized via a flow meter (ITTU Integrated Technology Transfer Unit). The photocatalytic degradation efficiency of MO and/or phenol through each test is measured when steady-state values are touched (after 30 min). The output samples are collected every 15–30 min. The particulars regarding the continuous flow photoreactor structure of model unit are presented in Fig. 1a.

H+ + (MO) Dye → Dye•+ → oxidation of substrate (MO dye)

(1)

Organic pollu tan ts (Dye•+) + OH• Semiconductor + UV light

⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯→ degradation products (CO2 + H2 O) + Mineral acid

(2)

2.4. Synthesis of the nanomaterials and nanocomposites membranes 2.4.1. Synthesis of ZnO, SiO2 nanomaterials and (TiO2/ZnO) and (TiO2/ SiO2) nanocomposites ZnO and SiO2 nanoparticles were prepared via the hydrothermal method, which does not need the use of organic solvents and can be considered an ecologically friendly procedure. Three grams of zinc chloride was dissolved in 20 mL of deionized water. 16 mL of a 5 M NaOH solution was added dropwise to the zinc chloride solution while gently stirring for a period of 60 min at 50 °C. During this period, 1.5 g of SLS was dissolved in 15 mL of distilled water (DI) and was added to the zinc chloride mixture [13]. SLS shows a vital role in the adjustment of the ZnO particles, and doings as an insulator between the nanoparticles, letting them overcome the interacting forces between them to create a uniform distribution. A white precipitate performs directly upon mixing the zinc chloride solution. The mixture was moved into a Teflon stainless steel autoclave (volume 80 mL) and filled with deionized water up to 80% of the reactor volume for hydrothermal treatment at 120 °C for 5 h. Then, stainless steel autoclave was permissible to cool down naturally. The suspended ZnO NPs were centrifuged at 4000 rpm for 15 min and collected as a white precipitate. The precipitates were washed 2–3 times with deionized water and then ethanol to eliminate contaminations. They were then dried at 50 °C for 5 h and stored. The SiO2 NPs were produced by mixing of HCl/alcohol, n-propanolTEOS, and water/alcohol blends were added at the same fall rate. The mixture was stirred at ambient temperature for 10 min. The sol-solutions were then transferred into a stainless Teflon-lined autoclave. The powders obtained by the hydrothermal process were separated via centrifugation and dehydrated in a vacuum oven at 30 °C for 4 h. Thus, nanosized SiO2 were obtained [38,39]. The (TiO2/ZnO) and (TiO2/SiO2) NCs were prepared by grinding the (ZnO/TiO2) and (TiO2/SiO2) NCs powder and placed in a crucible then heated at 300 °C for 3 h. The mixtures were kept to cool at room temperature (25 °C). The (TiO2/ZnO) and (TiO2/SiO2) NCs were prepared with different ratios (1:1, 1:2, and 2:1).

2.3. Anticipated photocatalytic mechanism of the continuous flow photoreactor According to photocatalytic theory, we have advanced an anticipated reaction mechanism for the TiO2/SiO2 and TiO2/ZnO catalyzed photo-degradation of aqueous MO and Phenol Fig. 1b. Under UV and/ or sun light the TiO2 can decompose the organic compounds and generate substitutional carbon deficiencies [17]. Alike procedures of metal oxides doping have been displayed to decrease the band gap of catalysts such as SiO2 and ZnO [7,32]. The UV/Vis absorption spectrum of the TiO2 doped SiO2 and TiO2 doped ZnO shows a red shift as compared with the spectrum of pure TiO2 [33]. The TiO2/SiO2 and TiO2/ZnO NCs are used as a photocatalysts, they are capable of concurrent adsorption/ absorption of both the reactants (the organic compounds and dissolved dioxygen) and the required light energy. Fig. 1b displays the represent the simple photocatalytic procedure, in which excited electrons created via absorption of nearby the UV light are first shifted to the deficiency level, at that time they absorb extra energy lower than that of the first excitation to relocation toward the transmission band, using the creation of the excited-state species TiO2/SiO2* and TiO2/ZnO*. This excitedstate species is an additional significant redox reactant than usual TiO2 because of the creation of electron–hole pairs, in addition to the holes and electrons in the TiO2/SiO2* and TiO2/ZnO* consequently react with O2 and OH¯ molecules on the catalyst surface to form superoxide anion radicals (%O¯) and%OH radicals, respectively. The %O2¯ radicals at that time interact with adsorbed H2O to create more %OH radicals, which are identified to be an influential oxidizing species, which formerly interact with the methyl orange and/or phenol compounds to decompose them. By way of the dissociation of the organic compounds improvements, the adsorption balance is shifted and more methyl orange and/or phenol compounds can passage from aqueous solution to the catalyst boundary where it is consequently dissociated. This anticipated mechanism is partially depend on various published studies regarding the creation of % OH radicals throughout photocatalytic procedure [34]. In this work, operational photocatalytic removal of MO and/or Phenol from aqueous solutions was reported using PS/TiO2 NCs

2.4.2. Synthesis of nanocomposite membranes The freshly microporous PS substrate was prepared just before use through the phase inversion method. The PS membrane was cast from a homogeneous polymer solution containing 18wt% PS and 82wt% DMAc [40], TiO2 NPs or mixtures of TiO2 with different metal oxide (0.16 wt %) were doped with 20 ml of DMAc. The mixture was sonicated for 3 h at 25 °C in sonication cell to confirm a homogeneous 4

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Fig. 2. The ATR-FTIR spectra of (a): (ZnO-TiO2) and (b and c) (TiO2/SiO2) with a different ratio (1:1) and (1:2), respectively.

2.4.4. Photocatalytic experiments The photocatalytic activities of samples were estimated by evaluating the degradation rate of MO solution (as a dye model) after a regular interval UV light irradiation as well as under sun lights. The stages were as follow, the experiments were done in a continuous PR with appropriate concentration (5 mg/L MO and /or phenol) using DI water. MO and /or phenol were passing through the synthesized membranes with TiO2 NPs or mixtures of TiO2 with different metal oxide with 5-hertzflow rate and 320 ml/min. The percentage of the degradation rate of the MO solution was measured using the following equation [41].

spread of the nanoparticles. Then the mixture was stirred with the rest amount of the solvent containing18wt% PS for 8 h at 60–80 °C to have best dispersions of the nanoparticles in the polymer matrix. These membranes will be used as support layers. PS will be stirred and heated till the polymer mixture was totally dissolved, and then degassing was achieved in an ultrasonic water bath. The resulting polymer solution was reserved in the atmosphere until the temperature of the polymer solution reached room temperature and cast to the desired thicknesses onto the polyester non-woven sheet using a casting machine. The PS membrane sheet was immersed into the coagulation water bath and kept in it for 24 h until most of the solvent and nonreactant polymer be removed. These conditions included; polymer concentration (18 wt.%), thickness (30 μm), the motor speed of the casting machine (400 RPM).

D=

Stress Stress/ strain Strain

(4)

where D is the degradation rate, C0, A0 and C, A are the concentration and absorbance of MO and/or phenol solution at the absorption peak, 464 nm and 500 nm in adsorption equilibrium before and after UV irradiation, respectively. The light transmissions of organic dye and phenol were characterized by a UV–vis spectrometer (Perkin-Elmer Lambda 750 spectrometer).

2.4.3. Nanomaterials and nanocomposites membranes characterizations and performance assessment The prepared nanomaterials were characterized via Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and X-ray diffraction (XRD). The synthesized nanoparticles and nanocomposite membranes were characterized via Infrared spectroscopy (FTIR) by a Genesis Unicam spectrophotometer. The X-ray diffraction designs of the improved films were determined by a Philips Model PW 3710 X-ray diffraction instrument. The SEM Quanta FEG was used to describe the membrane surface and cross-section characteristics. The contact angle was used to determine the membrane surface hydrophobicity and hydrophilicity using a (VCA Video Contact Angle System, KrÜss DSA25B, Germany) contact angle meter. A water drop was located onto the membrane surface after air-dried at 25 °C using deionized water with a digital micro syringe, at minimum six measurements at different sites were acquired for every membrane. The mechanical measurements of the prepared membranes were carried out by Universal Testing Instruments, UTI, V4.5 A. The elongation and tensile strength were carried out. Tensile tests were used to estimate Young’s modulus and strain at fracture of samples at the rate of 10 mm/min. Young’s modulus (Mega pascal, Mpa) was calculated using the following equation:

Young’s modulus (Mpa) =

CO-C AO-A × 100 = × 100 CO AO

2.4.5. The membrane reusability The reusability of PS(TiO2/SiO2) and PS(TiO2/ZnO) NCs membranes was reached by 0.1MHCl as a desorbing agent. The photo-degradation performance was achieved using phenol at room temperature, with interval time ranged from 0 to 180 min under UV light radiation and /or visible light, the flow rate of motor speed (5hrtz) and pH = 7. The membrane samples were washed with a deionized water and 0.1MHCl several times and subjected again to photo-degradation performance process for six cycles. The circulating multi-turns washing series were repeated to device the effect of membrane reusability as exposed via the photo-degradation performance decline. 3. Result and discussion 3.1. Characterizations of the nanomaterials and nanocomposite membranes 3.1.1. Characterizations of the nanomaterials The ATR-FTIR spectrum of (TiO2/ZnO) and (TiO2/SiO2) NCs are presented in Fig. 2. The peaks at 3420 cm−1 and 1620 cm−1 are due to the stretching vibration and twisting vibration of the OH group, respectively, these beaks is related to Si−OH or Ti −OH. This peaks still prevails even though the sample was calcined at high temperature due to Si−OH presence is the physically absorbed water molecules from the

(3)

UV/visible spectrophotometer, Unicam, model 300, England was used to attain the suitable wave length for measuring the absorption of the MO and /or phenol solution. 5

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Fig. 3. SEM micrographs of (a) TiO2; (b, c) (TiO2/ZnO); (d, e, and f) (TiO2/SiO2) NCs with different ratios (1:1) and (2:1), respectively.

spheres in shapes Fig. 3a. Moreover, the chemical reactivity of the nanoparticles has a tendency to be developed through reducing particle size owing to improve in the surface to volume ratio [7]. Fig. 3b and c of the SEM images of (TiO2/ZnO) NCs and the SEM images of (TiO2/ SiO2) NCs are also showed with the different ratio in Fig. 3d–f. It can be seen that the (TiO2/SiO2) NCs have a diameter of around 58 nm and it shows a spherical and rougher surface if compared to (TiO2/ZnO). Meanwhile, as can be seen in Fig. 3e–f, SiO2 layers have a porous structure onto the surface of TiO2 NPs. The XRD diffraction patterns of TiO2, TiO2/SiO2, and TiO2/ZnO NCs are shown in Fig. 4. The degree of crystallinity of TiO2, TiO2/SiO2, and TiO2/ZnO NCs was evaluated qualitatively via X-ray diffraction by determination of the area of the scattering peaks presented in. It was observed that all of the XRD configurations of the nanoparticles are

environs via silica [42,43]. The presence of SiO2 is verified by absorption bands at 958 cm−1 Si−OH stretching vibrations and symmetric Si–O–Si stretching vibrations at 796 cm−1 [44]. The absorption peak at 1058 cm−1 is ascribed to the asymmetric Si–O–Ti stretching vibration [45]. Furthermore, the peak at 672 cm−1 can be owed to stretching vibrations of TieO. The peak at 440 cm−1 is the stretching vibration of SieOeSi and TieOeTi [46]; Mendez-Vivar et al., 2001]. These outcomes point to Ti element have been effectively incorporated into the matrix of the SiO2 shell, thus enhancing a hydrophilic property of SiO2 shell. The surface morphology of the TiO2 NPs, (TiO2/ZnO) and (TiO2/ SiO2) NCs were characterized by scanning electron microscopy (SEM), Fig. 3. The SEM image of TiO2 NPs shows it in the form of spots with the size ranges from 10 to 30 nm with an average 16.5 nm and appears as 6

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Fig. 4. X-ray diffraction patterns of TiO2, TiO2/SiO2, and TiO2/ZnO.

due to O]S]O groups of Neat PS [50]. The detected band around 1595 cm−1 is mainly due to the rotation of the C]C of the benzene ring. Furthermore, the absorption peaks at434 and 505cm−1 confirm the presence of the stretching vibration band of TieOeTi [51] for the PS/TiO2; PS/(TiO2/ZnO) and PS/(TiO2/SiO2) NCs membranes. The incorporation of (TiO2/SiO2) NCs is confirmed by absorption bands at 970 and 792 cm−1 due to the stretching vibrations band of SieOH and SieOeSi, respectively [52] onto the PS/(TiO2/SiO2) NCs membrane. Moreover, the absorption peaks of the synthesized PS/(TiO2/ZnO) NCs membrane at 439, 635, 691 and 716 cm−1 can be assigned to significant absorption peaks of ZnO and Ti–O [53] onto the PS/(TiO2/ ZnO) NCs membrane. The detected band around ˜556 cm−1 is corresponding to stretching vibration of ZnO NPs. The appearance of the stretching band around ˜ 1584 cm−1 which confirms the HeOeH bending vibration comes from the atmospheric moisture [7]. In conclusion, these peaks confirmed the successful combination of TiO2, (TiO2/ZnO) and (TiO2/SiO2) NCs onto the PS membranes.

Table 1 The crystallinity of TiO2, (TiO2/SiO2), and (TiO2/ ZnO). Sample

Crystallinity (%)

TiO2 TiO2/SiO2 TiO2/ZnO

79.42 31.73 41.47

relatively similar. The peaks corresponding to the anatase TiO2 phase were appeared at 2θ = 25.2, 37.8, 48.0, 54.5 and 62.6°, a weak peak at 2θ = 27.5 represent the rutile form, [47]. There are sharp and strong peaks of anatase phase 2θ = 25.2°in the XRD patterns of all samples [48]. Also, the peaks corresponding to ZnO NPs are indexed as 31.82°, 34.54°, 36.42°, 47.46°, 56.74°, 62.92°, 66.06°, 68.42°, 69.06° and 78.82°, respectively. All diffusion peaks of the sample are corresponding to the typical hexagonal wurtzite configuration of ZnO NPs. Similarly, X-ray diffraction pattern was described by [49]. The peak at 11.52 for SLS surfactant indicates that some impurities of SLS found in ZnO NPs.Table 1, showing that the crystallinity of the TiO2 NPs decreases after doping with SiO2 and ZnO NPs, [38,39]. Fig. 5 shows a histogram of the outcomes gotten from the measurements of the particle size distribution (PSD) of TiO2, TiO2/ZnO, and TiO2/SiO2 NCs. It is obvious that the mean diameter and standard deviation values of the TiO2 NPs size were 42.8 nm and 30 nm (69.8%), Fig. 5a. The mean diameter and standard deviation values of the TiO2/ ZnO NCs size were 109.9 nm and 65.5 nm (59.9%), Fig. 5b. The mean diameter and standard deviation values of the TiO2/SiO2 NCs size were 91.5 nm and 56.2 nm (61.4%), Fig. 5c which are in contract with the preceding magnitudes attained from the SEM results.

3.1.3. Morphology analysis of membranes SEM was used to detect the membrane surface morphology of each membrane, including neat PS, PS/TiO2, PS/(TiO2/ZnO) and PS/TiO2/ SiO2) NCs membranes with a different magnification, respectively. Fig. 7a–c display the PS support layer is porous; with a nano metric pore size, and a smooth surface. It can be shown from Fig. 7d-l that the membranes surfaces have a nano metric pore size, and a smooth surface and with higher magnification there are several white spots on the NCs membrane surfaces. This demonstrates that TiO2, (TiO2/ZnO) and (TiO2/SiO2) NCs particles are uniformly dispersed in the membranes surfaces. Moreover, from Figs. 7d-l, it can be detected that TiO2, (TiO2/ZnO) and (TiO2/SiO2) NCs are inserted in the membranes tissue. Nonetheless, the TiO2, (TiO2/ ZnO) and (TiO2/SiO2) NCs have a propensity of agglomeration onto the membrane surfaces. Furthermore, PS/TiO2, PS/(TiO2/ZnO) and PS/TiO2/SiO2) NCs membranes have several networks, confirming contaminants diffuse and pass through the networks. These networks of PS/TiO2, PS/(TiO2/ ZnO) and PS/TiO2/SiO2) NCs membranes can improve the mass removal of organic impurities, confirming the restriction of the NCs membranes with better photocatalytic properties as well as, they have positively prepared. The water contact angle (WCA; θ) is the greatest shared factor used to describe the hydrophilicity of membrane surfaces. Hydrophilic

3.1.2. Characterizations of the nanocomposite membranes The FT-IR spectra of neat PS, PS/TiO2; PS/(TiO2/ZnO) and PS/ (TiO2/SiO2) NCs membranes are existing in Fig. 6. The FT-IR curves show a peak band seeming at 721 cm−1 due to the CeH bond in the aromatic group. The presences of hydrogen bending of para-substituted aromatic groups are shown at the absorption band at 871 cm−1. The spectrum band was observed at 1241 cm−1 which can be attributed to the stretching vibration of the CeOeC in the aryl ether group. The appearance of asymmetric stretching vibration band∼ 1340 cm−1 is 7

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Fig. 5. The histogram of (a) TiO2; (b) TiO2/ZnO; (c) TiO2/SiO2 Particle size distributions.

Fig. 6. The FT-IR spectra of neat PS, PS/TiO2, PS/(TiO2/SiO2), and PS/(TiO2/ZnO) nanocomposite membranes. All the experiments were done at room temperature (25°C). 8

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Fig. 7. SEM images of the top surface for Neat PS (a,b,c), PS/TiO2 (d,e,f), PS/(TiO2/ZnO) (g,h,i) and PS/TiO2/SiO2) (j,k,l) NCs membranes with different magnification. All the experiments were done at room temperature (25°C).

membranes have a WCA of 0° < θ < 90°, while hydrophobic membranes have a CA of 90° < θ < 180°. In Fig. 8, the mean WCA for the neat PS, PS/TiO2, (PS/TiO2/SiO2) and PS/(TiO2/ZnO) NCs membranes were 71 ± 2.2°, 44.7 ± 2°, 41.4 ± 2.3°, and 57.32 ± 1.8°, respectively, demonstrating they have a hydrophilic surface which could reflect the antifouling competency of the membranes. Fig. 8, shows the lower WCA of neat PS/TiO2 membrane (44.7 ± 2°) due to the hydroxyl group of the TiO2 NPs which improves the membrane surface hydrophilicity. The decreasing in the WCA of (PS/TiO2/SiO2) NCs membrane with incorporation of TiO2/SiO2 NCs materials leads to the higher surface hydrophilicity. The enhancement of WAC may be attributed to the combination of SiO2 NPs which responsible for the hydrogen bonds with hydroxyl groups and adsorb water molecules on the TiO2/SiO2 surface [54]. This consideration approves that hydrophilicity and wettability of the (PS/TiO2/SiO2) NCs membrane could be enhanced by the incorporation of hydrophilic inorganic TiO2/SiO2 NCs into the

polymer structure during membrane fabrication. The improved hydrophilicity of the (PS/TiO2/SiO2) NCs membrane may be due to a greater attraction of water molecules by the nanomaterials and to the presence of energetic hydrophilic efficient groups on the membranes surfaces. On the other hand, the membrane hydrophilicity decreased upon doping of the ZnO NPs to the NCs membrane when compared to the neat PS/TiO2 membrane. The mechanical properties of neat PS, PS/TiO2; PS/(TiO2/ZnO) and PS/(TiO2/SiO2) NCs membranes are revealed in Table 2, and the stressstrain curves are shown in Fig. 9. The PS/(TiO2/ZnO) and PS/(TiO2/ SiO2) NCs membranes show enhanced stress (Mpa) and strain (%) when compared to the neat PS and PS/TiO2 NCs membrane. The membranes have stress (Mpa) and strain (%) values in the following order: PS/(TiO2/ZnO) > PS/(TiO2/SiO2) > PS/TiO2 > neat PS NCs membranes. The membranes have Young’s modulus (Mpa) values in the following order: neat PS/TiO2 > Neat PS > PS/(TiO2/ SiO2) > PS/(TiO2/ZnO) NCs membranes. The enhancement in the

9

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Fig. 8. The contact angle of neat PS, PS/TiO2, PS/(TiO2/ZnO) and PS/(TiO2/SiO2) nanocomposite membranes. All the experiments were done at room temperature (25°C).

bonds structure which reinforced the network structure due to the more porous silicon oxide [56].

Table 2 Mechanical properties of neat PS, PS/TiO2, PS/(TiO2/ZnO) and PS/(TiO2/SiO2) nanocomposite membranes. Name

Strain (%)

Stress (Mpa)

Young’s modulus (Mpa)

Neat PS PS/TiO2 PS/(TiO2/SiO2) PS/(TiO2/ZnO)

1.2 1.3 1.3 1.32

11.6 14 19 20

739.8 1082 624 573

3.2. Performance evaluation of photocatalytic process 3.2.1. Factors affecting photocatalytic nanocomposite membranes After the system reaches equilibrium (depending upon the nature, concentration of the organic compound and the flow rate), as specified via identical inlet-outlet MO and/or Phenol concentration, the UV light is turned on. The outlet sample is then collected manually at regular intervals time the steady state is achieved around 30 min. After finishing the experimentations, the photoreactor is flushed under UV light for 1 h using DI water. The photocatalytic removal of MO and/or Phenol is take place at a built-up scale by means of prototype unit, with sample flow rate changing from 20 to 80 m3/ h. In photocatalytic degradation of MO and/or Phenol as a wastewaters model, using different synthesized PS/TiO2 membrane was considered to examine the activity of synthesized NCs membranes for degradation of an organic impurity below UV radiation. The outcomes were achieved using different parameters such as the solution pH was ranged from 4 to 10, flow rate of motor speed ranged from 20 to 80 m3/ h at 5 to 20 Hz, respectively, MO and/or Phenol concentrations of 1 to 7 mg/L, different concentrations of TiO2 extended from 0.2 to 0.4 wt% and various concentration of H2O2 extended from 0.1 to 2%, see Fig. 10. The experiments were prepared at room temperature (25 °C) with interval time ranged from 0 to 180 min because the time of the degradation efficiency is an imperative factor in the photocatalytic procedure in UV light radiation. The pH is a considerable factor in the assessment of photocatalytic activity in an aqueous solution. The effect of pH was deliberate via keeping all other experimental circumstances constant and changing the initial pH value. The initial pH plays an essential role in photocatalytic activity; it is responsible for the separation of active functional sites on the catalyst and adsorbent. To evaluate the influence of pH on the charge possessions of the semiconductor and photocatlytic degradation of phenol using PS/TiO2 NCs membrane to conclude the optimum pH for the degradation of phenol. The effect of pH was considered in the range (4–10) keeping all other factors constant, the phenol removal increases with raising pH to reach the higher degradation at pH 7, Fig. 10a. The consequences show that the degradation efficiency of PS/TiO2 membrane increased at pH 7. The difference of the pollutants pH effects on the changes of the external charge of TiO2 NPs and shifts the potentials of catalytic reactions. Under alkaline or acidic circumstance the TiO2 NPs surfaces can be deprotonated or protonated, respectively according to the following equations; [5 and 6]. TiO2 is described to possess a greater oxidizing activity at lower pH

Fig. 9. The mechanical properties of neat PS, PS/TiO2, PS/(TiO2/ZnO) and PS/ (TiO2/SiO2) nanocomposite membranes.

mechanical properties of PS/(TiO2/ZnO) NCs membranes is mostly owing to the cross-linked polymeric structure in the rigid aromatic structure in the membrane backbone and the incorporation of inorganic NCs onto the polymeric membrane, causing increased flexibility and strength in addition to the incorporation of ZnO NPs addicted to the membrane creates it more crystalline, and the crystalline membrane is more solid than the amorphous ones as well as, improves the rigidity of the membrane chain [13]. The mechanical properties of the NCs membrane are contingent mostly on the membrane inter-molecular forces functional along the membrane backbone [55]. The development of the PS/(TiO2/SiO2) NCs membrane may be due to the titania-silica bond structure through TieO and SieO bonds which improve the membrane mechanical properties and enhanced the polymeric backbone [54]. The embedding of (TiO2/SiO2) NCs to the polymeric membrane improved the tensile strength due to the Ti― O― Si 10

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Fig. 10. Factors affecting on photocatalytic degradation of MO and/or Phenol using PS/TiO2 membranes; (a) Effect of pH of phenol (5 mg/L) and flow rate of motor speed (5hrtz, 20 m3/h); (b) Effect of flow rate of motor speed (hertz) of phenol (5 mg/L) and pH = 7; (c) The effect of methyl orange concentration at pH = 7 and flow rate = 5hrtz; (d) The effect of phenol concentration at pH = 7 and flow rate = 5hrtz; (e) Effect of TiO2 concentration (wt.%) at pH = 7, flow rate = 5hrtz and phenol conc. was 5 mg/L; (f) Effect of adding H2O2 of phenol (5 mg/L), pH = 7 and flow rate 5hrtz; (g) TOC as organic matter % estimation using 7 mg/L Methyl Orange at pH = 7 and flow rate 5hrtz (20 m3/h). All the experiments were done at room temperature (25°C) and with interval time ranged from 0 to 180 min under UV light radiation. 11

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nevertheless additional H+ at very low pH can reduce the reaction rate. However in alkaline pH under columbic force aims revulsion among OH– ions and the negatively charged surface of the catalyst, thus preventing the formation of OH• radicals and reducing the degradation. Hence, the optimization of pH is essential for better degradation results [57]. Furthermore, the PS/TiO2 membrane surface becomes negatively charged at pH ˜ 7, while the phenolic compound and MO have static positive charge, therefore the degradation efficiency of PS/TiO2 membrane increased at pH 7 Fig. 10a, this is mainly due to the formation of OH• radicals by photoholes, OH• is a strong oxidizing specie in Advanced Oxidation Processes (AOPs), while at pH > 7 both PS/TiO2 membrane surface and the organic pollutants become negatively charged and repulsive forces appeared, therefore reducing the photocatalytic activity and degradation efficiency of PS/TiO2 membrane [14]. The degradation efficiency of PS/TiO2 membrane decreased at pH < 7 due to the presence of H+ ions on the membrane and catalyst surfaces, which declined the photocatalytic activity and degradation efficiency of PS/TiO2 membrane. The adsorption of PS/TiO2 membrane was estimated via exposure the membrane to MO dyes for a certain time ranged from 0 to 90 min without UV light irradiation and calculates the adsorption of the dye onto the PS/TiO2 membrane surface. It is found that the adsorption reached the steady state at 30 min. TiOH + H+ TiOH2+

(5)

TiOH + OH– TiO– + H2O

(6)

ranging from 1 to 7 mg/L on degradation efficiency (%) was considered using PS/TiO2 membrane at flow rate 5hrtz (20 m3/h) and pH 7, as shown in Fig. 10c. The consequences exhibited that with increasing the MO concentration from 1 mg/L to 7 mg/L the degradation efficiency increased in Fig. 10c. It is found that as the MO concentration and the time exposure increase the degradation efficiency increases. This result may be due to that the OH• radicals should be mainly formed from the adsorbed HO– and H2O molecules by electron donation to the photogenerated holes. The rate of the determination step of the reaction could be the formation of OH• radicals since they react very rapidly with aromatic ring compound, [59]. The influence of initial phenol concentration ranging from 1 to7 mg/L on the rate of degradation efficiency (%) was deliberate by means of PS/TiO2 NCs membrane at flow rate 5hrtz (20 m3/h) and pH 7, as shown in Fig. 10d. It is clear that with increasing the initial concentration of phenol from 1 mg/L to 7 mg/L the degradation efficiency increase. Fig. 10e shows the photo-degradation results using PS membrane doped with diverse concentrations of TiO2 NPs. The operation conditions included dye concentration equal to 20 mg/L, reaction time ranged from 0 to 180 min., pH value equals 5. It was believed that as the quantity of catalyst improves the number of dye molecules engrosses and the numbers of photons absorbed were increased due to an increase in the number of catalyst particles. The rate of photo-degradation reaction improves via increasing the quantity of TiO2 NPs and reaches its exciting at 0.4 wt.%. This indicates that the increase in catalyst amount actually increases the number of active spots on the photocatalyst surface thus casing an increase in the number of •OH radicals is responsible for the organic pollutant degradations [60]. The examination searcher shows that •OH radicals are the highest active species in the photocatalytic procedure. To improve the quantity of active species, we added hydrogen peroxide (H2O2) as oxidant agents. Hydrogen peroxide is a chemical compound with the formula H2O2. It is a clear liquid, slightly more viscous than water. Hydrogen peroxide is the simplest peroxide (a compound with an oxygen-oxygen single bond). It is used as an oxidizer agent and antiseptic. With the adding of H2O2 and the adsorption-desorption equilibrium was reached; the photocatalytic degradation procedure was rapidly increasing. This mainly owing to the added H2O2 was first adsorbed on the PS/TiO2 membrane surface, which contributed to the amount of organic compound (MO and/or Phenol) desorption, thus the observed MO and/or Phenol concentration declined much more rapidly because of the existence of H2O2. Fig. 10f showed that 2 wt.% H2O2 was the optimal concentration in the PS/TiO2/UV/H2O2 system, which was enhanced than the other concentration. The photocatalytic efficiency was increased by the addition of H2O2 with a small amount which accelerates the reaction rate of the PS/TiO2 membranes and reaches its maximum degradation at 2 wt.%, Fig. 10f. The PS/TiO2/H2O2/UV procedure is more effective than the PS/TiO2/UV radiation procedure for organic compound (MO and/or Phenol) degradation due to influence of •OH and •O−. The results highlighted that with adding H2O2 shows an improvement of organic compound (MO and/or Phenol) degradation rate. The mineralization of organic compound (i.e. elimination of TOC from an aqueous solution) is presented in Fig. 10g. The degradation of MO dye was monitored via TOC estimation where the TOC calculated as organic matter %. It is found that the Organic matter % increased with increasing the degradation efficiency as in Fig. 10g. Compared to the degradation efficiency, mineralization is dawdling which is also confirmed via [61]: 0.043% of the organic matter of MO was estimated after 30 min of the reaction time, while the removal efficiency reached 12.5%. Observably, the degradation produces of the MO dyes definitely still exist in the aqueous solution. The Organic matter % reached 0.0725% with efficiency 13.5% after 180 mints using 7 mg/L methyl orange as a pollutant model under UV light and at flow rate 20 m3/h (5 Hz). The results gotten in this study matched with [61]. For their

To examine the influence of residence time on the removal efficiency of Phenol, three flow rates (20, 40, and 80 m3/h at 5, 10 and 20 hrtz respectively) are estimated at different time intervals from 0 to 180 min. The photocatalytic efficiency depends mainly on the electrical panel with a variable speed drive for the feed pump motor speed flow rate Fig. 10b. The photocatalytic efficiency increases at a low motor speed equal 5hrtz (20 m3/h) in PS/TiO2 membrane. Conversely, the photocatalytic degradation decreases with the speed flow rate increase due to the acceleration of the photocatalytic reaction with increasing the fed solution flow rate. It is concluded that the degradation efficiency decreased when the flow rate increased. The feed flow rate is inversely proportional to the photocatylitic efficiency. This is mainly attributed to at lower flow rate various photoactive sites continue available for the reaction [36]. At higher flow rate, the photoactive sites tend to a limit which can be described via the rise of unavailable sites. The procedure at higher flow rate becomes a systematized chemical stage. Consequently, it is showed that residence time is an important factor for the application of PS/TiO2 photocatalytic expertise for wastewater treatment. Fig. 10b showed that the removal efficiency of pollutants increases with decreasing flow rate. The flow rate of the feed solution depends mainly on its viscosity and concentrations. The photocatalytic reaction rates may be dependent on the bulk feed solution to the catalyst mass diffusion [58]. There are two evident aspects get up from affecting feed flow rate on the photocatalytic degradation process; firstly is the availability of the PS/TiO2 surface to the Phenol and the photons, and secondly is a significant effect of the exterior mass diffusion resistance mostly at low feed flow rates, owing to the increasing dispersion size of the reactant (the MO and/or Phenol) from the solution to the PS/TiO2 surface. Therefore, its observable that flow rate plays an essential role in the degradation procedure. For low flow rates, the feed water flow is little; the oxygen species is greatly more capable of getting into interaction with a PS/TiO2 membrane surface. Additionally, a feed water flow contributes to satisfactory UV light intensity. However for higher flow rates, the feed water flow increases; which has the difficulty of photon in going into the PS/TiO2 membrane surface. Conversely, increasing the feed flow rate also indicates to a higher mass diffusion. Especially, with higher mass diffusion and electron/hole recombination there was an improve of contaminant degradation. The effect of initial concentration of methyl orange (MO) dye are 12

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Fig. 11. Photo-degradation performance of (a) PS/(TiO2/ZnO, 1:1 wt.%) NCs membrane (I); (b) PS/(TiO2/SiO2, 2:1 wt.%) NCs membrane (II); and (c)The effect of H2O2 (1 wt. %) additive with NCs membrane (I); (d)The effect of H2O2 (1 wt. %) additive with NCs membrane (II), using MO 5 mg/L and phenol 5 mg/L: All the experiments were done at room temperature, with interval time ranged from 0 to 180 min under UV light radiation and /or visible light, the flow rate of motor speed (5hrtz, 20 m3/h) and pH = 7.

Fig. 11d shows the effect of the addition of H2O2 1 wt.% concentration on the photo-degradation performance of NCs membrane (II) under visible light for both phenol and MO. The Fig. 11d indicates that the degradation efficiency improved in the case of MO (97% after 180 min.) than in the case of phenol (95% after 180 min.).

total removal, the period of UV light exposure should be elongated. A lower elimination of TOC content (as organic matter %) was expected as the advanced intermediates contend with the initial MO dye molecules throughout the degradation procedure. Furthermore, the slow kinetics of MO dye degradation afterward a certain time may be clarified via the exertion in changing the nitrogen atoms of the dyes into oxidized nitrogen complexes, as anticipated in Sakthivel et al. [62], as well as the presence of the higher number of azo-groups in MO dyes molecules delay the degradation procedure.

4. Conclusions The innovation of this work is to fabricate and design the continuous flow PR for treatment of organic impurities in wastewater using heterogeneous photocatalytic process. Different nano-metal oxides such as ZnO and SiO2 were synthesized by the hydrothermal method and mixed with TiO2 (Degussa) to act as a catalyst to improve the photodegradation procedure under visible light. These different nanomaterials were doped with PS support membrane to prepare modified flat sheet membrane using the phase inversion procedure. The synthesized nanoparticles and membranes were described via ATR-FTIR spectroscopy, contact angle measurement, particle size analyzer and scanning electron microscope (SEM). Also, the efficiency of both synthetized polymeric NCs membranes and the continuous PR were evaluated by studying the influence of various parameters. These parameters included feed water pH, motor speed flow rate, oxygen content, pollutant types, and pollutant concentrations. The impurities as methyl orange and phenol compound were used as a model of organic pollutants. The achieved results indicated that the (PS/TiO2/ZnO) NCs membrane (I) showed a degradation of 72% and 16.5% in the case of phenol and MO under ultraviolet light respectively. Conversely, the degradation was 30% and 11% in the case of phenol and MO under visible light respectively. Moreover, the (PS/ TiO2/ SiO2) NCs membrane (II) was able to degrade 18.1% and 40.3% in the case of phenol under UV radiation and visible light, respectively. The performance was enhanced by increase the oxygen content, i.e., the addition of H2O2 and the degradation was 97% and 95% under visible light in case of MO and Phenol, respectively using (PS/TiO2/SiO2) NCs membrane (II). It was also

3.2.2. The enhancement of photocatalytic activity of PS/TiO2 nanocomposite membranes In this study PS mixed with (TiO2/ZnO) and (TiO2/SiO2) NCs with different ratios (1:1, 1:2, and 2:1). The best ratios are (TiO2 doped ZnO, 1:1 wt.%) gives (PS/TiO2/ZnO) NCs membrane (I), and PS mixed with (TiO2 doped SiO2, 2:1 wt.%) resulting (PS/TiO2/SiO2) NCs membrane (II). Fig. 11a, shows that the performance of photo-degradation increases in case of NCs membrane (I) under UV light, in case of Phenol and MO than in case of visible light for both phenol and MO, respectively. This is due to that, the band boundaries of these semiconductor materials is lying in the UV area which creates them inactive below visible light irradiation. Fig. 11b shows that the photo-degradation performance improved in case of NCs membrane (II) under UV light, in case of phenol and MO than in case of visible light for both phenol and MO, respectively. This is owing to that, the band boundaries of these semiconductor materials lie in the UV area which creates them less active in visible light irradiation. Fig. 11c shows the effect of the addition of H2O2 1 wt.% concentration on the photo-degradation performance of NCs membrane (I) under visible light for both phenol and MO. The Fig. 11c indicates that the degradation efficiency improved in the case of phenol (52.3% after 180 min) than in the case of MO dye (42.9% after 180 min). 13

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