TiO2 ceramic ultrafiltration membrane for ciprofloxacin removal

Materials Chemistry and Physics 229 (2019) 106–116

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Materials Chemistry and Physics journal homepage: www.elsevier.com/locate/matchemphys

Development and performance evaluation of a novel CuO/TiO2 ceramic ultrafiltration membrane for ciprofloxacin removal

T

Priyankari Bhattacharyaa, Debarati Mukherjeeb,c, Surajit Deyc, Sourja Ghoshb,c, Sathi Banerjeea,∗ a

Metallurgical and Materials Engineering Department, Jadavpur University, Kolkata, 700032, India Academy of Scientific and Innovative Research (AcSIR), CSIR-Central Glass and Ceramic Research Institute, India c Ceramic Membrane Division, CSIR-Central Glass and Ceramic Research Institute, Kolkata, 700032, India b

HIGHLIGHTS

GRAPHICAL ABSTRACT

ceramic UF membrane was de• Novel veloped using green synthesized CuO NP and TiO2 NP.

scan of membrane showed pre• Line sence of Cu and Ti on inner side of support.

study of ciprofloxacin re• Rejection sulted in 99% removal within 60 min. effect on algae revealed • Toxicity minimized effect on exposure to permeate.

ARTICLE INFO

ABSTRACT

Keywords: CuO TiO2 Ceramic ultrafiltration membrane Ciprofloxacin Algal toxicity

Pharmaceutical and Personal Care Products (PPCPs) consists of diverse group of organic chemicals, which becomes a source of emerging concern, if their concentration in aqueous solution exceeds a certain limit. Ciprofloxacin, a frequently used antibiotic, gets excreted from body and its residues are found in water bodies. It is known to inhibit growth of microflora of ecosystem thereby posing great threat to environment. The present work focusses on novel approach of one step removal of ciprofloxacin from synthetic solution using nanocomposite ceramic ultrafiltration membrane based separation process. Copper oxide nanoparticles (CuO NP) synthesized by green route were used along with TiO2 nanoparticles (TiO2 NP) as composite to develop high flux ceramic ultrafiltration (UF) membrane over indigenously developed clay-alumina based macroporous support. The membrane was characterized in terms of X Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR) to confirm about the membrane composition, field emission scanning electron microscopy (FESEM), Atomic Fluorescence Microscopy (AFM) was done to get an insight into the morphological properties, the permeation of the membrane was analyzed in terms of BET, clean water permeability, molecular weight cut-off (MWCO). FTIR analysis of membrane post filtration, suggested surface adsorption of ciprofloxacin on membrane and involvement of C]O, COOe, TieOeTi and CuO groups in the process. Effect of various process parameters viz., transmembrane pressure (TMP), cross-flow velocity (CFV), operating time and feed concentration was observed on rejection efficiency of ciprofloxacin using the UF membrane. About 99.5% removal of ciprofloxacin was achieved within 60 min of operating time at 2.0 bar TMP and 2 Lmin-1 of CFV using a feed concentration of 500 μgL−1. Toxicity evaluation of membrane treated permeate was carried out in algae and impact on cellular components and stress enzymes were quantified, showing reduced effect on membrane treated permeate than

∗

Corresponding author. E-mail address: [email protected] (S. Banerjee).

https://doi.org/10.1016/j.matchemphys.2019.02.094 Received 30 November 2018; Received in revised form 18 February 2019; Accepted 28 February 2019 Available online 28 February 2019 0254-0584/ © 2019 Elsevier B.V. All rights reserved.

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untreated solution. The process thus targets in remediation of such emerging organic contaminants in a costeffective, environmental-friendly way for production of clean permeate that can be safely disposed off in the environment.

1. Introduction

98% efficiency. TiO2 nano powder was studied for removal of norfloxacin and levofloxacin whereas TiO2 coupled with ZSM-5 was observed for removal of acetaminophen [22,23]. Copper oxide nanoparticles (CuO NPs) on the other hand is used for removal of Cd2+ and Fe3+ from wastewater [4], and has wide application in the field of gas sensors, catalysis as well as show antibacterial activity. CuO NPs was impregnated on surface of activated carbon for removal of multipollutant like atrazine, caffeine, diclofenac respectively from drinking water. Application of Cu2+ and TiO2 for removal of PPCP has been studied alone and in conjugation with other nanoparticles [23]. Zeolite modified by Cu2+ was studied for removal of salicylic acid, carbamazepine, while CueZneFe-LDH composite was used for removal of acetaminophen [23,24]. Nanocomposite membranes are prepared by incorporation of nanomaterials into ceramic matrix by either coating on surface or by membrane casting. These membranes have high permeability, more stable flux and high rejection rate. Studies have shown that by incorporation of titania –based active layer into porous ceramic membranes results in enhanced separation including MF, UF and NF. TiO2 is used in combination with other metal oxide nanoparticles as it forms heterojunction when reacted with another material [25]. In the present study nanocomposite ultrafiltration membrane was developed by surface coating with CuO NPs and TiO2 NPs over clayalumina based support. Slurry was prepared using Dolapix CE64 as dispersant, which is carbonic acid-based polyelectrolyte and used for uniform dispersion of nanoparticles [26] along with polyethylene glycol (PEG) as binder and hydroxyethyl cellulose (HEC) as plasticizer. CuO NPs used in this study was synthesized through green route using algal extract. Conventional method for synthesis of CuO NPs has certain limitations like high energy need and associated toxicity by use of chemicals which can be reduced by synthesis of nanoparticles by green route. Using different plant and biomass extract is eco-friendly and lesstoxic way of synthesizing nanoparticles using different biomass extract has thus been proposed [27]. To observe any probable toxicity of membrane treated permeate on microbiota if discharged in environment, toxicity effect of untreated ciprofloxacin and membrane treated permeate was observed on microalgal community. Effect on growth rate, chlorophyll content, enzyme activity, nitrogen content was discussed in detail.

Release of antibiotics in the environment by human activities and pharmaceutical effluents are considered to be of great concern because of the persistent nature of antibiotics as well as their inhibiting character of certain ecological processes [1]. Most of the antibiotics widely used as antibacterial agents were proved to be genotoxic in nature [1,2]. Moreover, antibiotic resistant bacteria are increasing in environment due to these discharges which causes serious consequences in terms of gene resistance enhancement [3,4]. Ciprofloxacin is an antibiotic belonging to the group of drugs commonly known as fluoroquinolone and is used to treat bacterial infections like anthrax, plague etc. in humans. Ciprofloxacin causes disruption of normal soil microflora thereby disturbing ecological balance. Fluoroquinolone is already known to cause serious side effects including swelling or tearing of tendons. Research have shown that 45–62% of unmetabolized administered dose gets excreted through urine or feces and enters the environment via sewage, leaching of landfills, pharmaceutical wastes, utilization of sewage sludge as manure or in agriculture etc. [1]. Concentration of ciprofloxacin in environment can range from ngL−1 to mgL−1. Concentration upto 31 mgL−1 in pharmaceutical effluent was reported [5]. Attempts have been undertaken to biodegrade ciprofloxacin but because of its recalcitrant nature some level of mineralization was observed. Different treatment approaches were undertaken for effective removal of pharmaceutical and personal care products (PPCPs) like adsorption, biological treatment, chemical methods, separation etc. [6–8]. Pharmaceutical wastewater treatment was done using conventional activated sludge process in combination with chemical treatment [9]. Tetracycline, sulfamethoxazole, and tylosin were efficiently adsorbed on micro and mesoporous carbons [10]. Ozonation efficiently removed about 90–99% removal of diclofenac and sulfamethoxazole [11,12]. Membrane based separation process is highly being used for removal of personal care products, pesticides as they remove wide range of pharmaceuticals compared to conventional treatment processes [13]. Wang et al. (2018) reported more than 95% removal of PPCPs was obtained by the combination membrane bioreactor and reverse osmosis or nanofiltration [14]. Application of membrane bioreactors or membranes in combination with advanced oxidation process or in alone has been studied [15]. Use of ultra/nano filtration membrane as separation techniques for wastewater treatment are being extensively used and is currently is employed for pretreatment [16]. Ceramic membrane-based process is more advantageous than polymeric membranes because of their higher mechanical, thermal and chemical stability. Ceramic membranes were successfully applied for treatment of various wastewaters including those from domestic and industrial sectors [17,18]. One of the limiting factors for industrial applications of membranes includes biofouling. These could be overcome by use of nanocomposite membrane which results in low biofouling due to presence of inorganic nanomaterial, thus increasing membrane productivity. Metal oxide nanoparticles are widely used for removal of harmful contaminants and heavy metals from water. Nanocomposites are formed by combining one or two nanomaterials having unique properties resulting in desirable properties. TiO2 and CuO are widely used as nanocomposites due to their properties such as narrow band gap energy, stability, nontoxicity etc. [19,20]. Titanium dioxide (TiO2) has high chemical stability and excellent biocompatibility along with photocatalytic and other optical and electrical properties. Use of TiO2 in separation process arises from its anti fouling and antimicrobial characteristics [21]. TiO2 as photocatalyst is known to remove estrogens, bisphenols etc. with

2. Material and methods 2.1. Chemicals For preparation of CuO NP, copper sulphate solution (CuSO4. 5H2O, Sigma-Aldrich, Germany) was used. The nanocomposite membrane was prepared using the slurry consisting of as-prepared CuO NP, TiO2 NP (Sigma-Aldrich, Germany), hydroxyethyl cellulose (HEC, Sigma –Aldrich, Germany), Dolapix CE64 (Zschimmer and Schwarz GmbH, Germany) and Polyethylene glycol (PEG, Merck, India). 2.2. Synthesis of CuO NPs Cyanobacterial strain (Anabaena sp.) was collected and dried. Extract was prepared by boiling dried algae taking 1 gm algae in 50 mL distilled water. For synthesis of nanoparticles, 1 mM CuSO4.5H2O was taken and algal extract was added slowly with constant stirring. Nanoparticle formation was observed when there was a change in solution colour from blue to brown and reaction was stopped. Nanoparticle formation was commenced at pH-8. Nanoparticles were 107

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then cooled, dried and sieved for further use [28].

spectroscopy (FTIR, PerkinElmer, USA) was carried out within the wavenumber range of 400 cm−1 to 4500 cm−1for determining the functional groups present in UF membrane before and after application. Surface topology and surface roughness of the UF membrane was determined from Atomic force microscopy (AFM, Nanonics, Israel, NSOM) in ambient air contact mode appropriate for ceramics. The results obtained were then analyzed using WSxM 5.0 Develop 8.3 software. Surface area and pore diameter of membrane was determined from BET (Braunauer-Emmett-Teller, Quantachrome Autosorb Automated Gas Sorption System, USA) surface area analyzer. X-ray photoelectron spectroscopy of unsupported membrane (XPS, 5000 XPS-analyzer, Versaprobe-II, USA) was carried out to understand the chemical state of the composite. Samples were scanned within 0–1100 electron volts (eV) of binding energy. Pore diameter of the macroporous support was determined by mercury intrusion porosimetry analysis (Pore Master, Quantachrome, USA). Surface morphology as well as coating thickness of membrane was analyzed from field emission scanning electron microscopy (FESEM, Zeiss, Germany). The molecular weight cut off (MWCO) of the membrane was calculated by finding the rejection of Poly Ethylene Glycol (PEG, Merck, Germany) of various molecular weights viz., 6000, 10000, 20000, 35000 Da by UF membrane filtration using 5 L of feed. The permeate was analyzed by solid weight measurement using digital refractometer (Anton Paar, Germany). Developed UF membrane was also characterized in terms of clean water permeability and compared with support using deionized water. Permeability study was carried out at different transmembrane pressure (TMP), for 60 min of operation time and 2 Lmin-1 crossflow velocity (CFV).

2.3. Preparation of CuO − TiO2 composite ultrafiltration membrane 2.3.1. Preparation of slurry Titanium dioxide (TiO2) and copper oxide nanoparticle (CuO NP) composite were used for preparation of ultrafiltration membrane over clay/alumina support. Green synthesized CuO NPs was used. Optimized concentration of TiO2eCuO nanopowders was evenly dispersed using suitable binder (HEC), dispersant (Dolapix) and plasticizer (PEG). CuO concentration was successively increased and mixed with TiO2 nanoparticles in different proportions (Table 1) and was dispersed in Dolapix CE64 (2 wt%) and stirred for 1 h at 100 rpm for uniform dispersion. It was followed by addition of hydroxyethyl cellulose (2 wt%) and PEG (4 wt%) under stirring condition of 100 rpm and ambient temperature. Stirring was continued for 24 h until a stable, bubble free suspension having uniform solid loading is produced. Based on the sedimentation rate and viscosity and experiments, optimized ratio of CuO and TiO2 NP was selected for coating on support. Sedimentation height was noted by observing the drop in solid-liquid interface height at regular time interval for about 60 min. Sedimentation rate attenuation curve is obtained from sedimentation height and time and calculated from equation (1) [29,30].

vi =

h = t

hi ti

hi ti

1 1

(1)

where vi is the sedimentation rate at time ti, Δh is difference of sedimentation height with time, Δt is time, and hi is sedimentation height at time ti. Viscosity of slurry was measured by using cone and plate method of ultra DVLV-III Rheometer (M/s Brookfield, UK). Effective viscosity of nanofluid as a function of volume fraction was determined by equation (2) proposed by Einstein (1956).

µnf = (1 + 2.5 + 6.2 2) µbf

2.5. Application of developed nanocomposite UF membrane The developed UF membrane was used for removal of ciprofloxacin from synthetic solution in cross flow filtration mode. The membrane was conditioned by immersing in clean water overnight for obtaining stable flux. The membrane was then housed in stainless steel module of dimensions 10mm/7 mm (O.D/I.D) and 150 mm length. Recirculation pump of 0.55 KW power and 50 Hz frequency was used. Feed solution was recirculated for 15 min at zero pressure to obtain stable flux. Effect of time (0–180 min), TMP (0–5.5 bar), CFV (1.5–3.0), feed concentration (50–1000 ppb) was observed on removal efficiency. Permeate collected at various intervals from bottom port of module was analyzed for presence of ciprofloxacin. Remaining permeate was recirculated back to feed tank. At the end of experiment, permeate was collected for toxicity study on algae. Membrane and set-up was then cleaned with liquid detergent and dilute acid for removal of contaminants. The effects of various operating parameters viz., TMP, CFV, filtration time upon permeate flux and ciprofloxacin removal was statistically analyzed using ANOVA employing R3.4.3 software. The coefficient of determination (R2) was estimated to find the fitting behavior between the experimental and model predicted response.

(2)

where μnf is the effective viscosity of nanofluid, μbf is the base fluid viscosity, and μbf is the volume fraction of the suspended particles [31]. 2.3.2. Preparation of UF membrane UF membrane was developed using optimized CuO and TiO2 composition over clay-alumina support. The support was developed indigenously at CSIR-Central Glass and Ceramic Research Institute. The support used had a porosity of 37% and pore size of 1.14 μm [32]. It is hollow, tubular, single-channeled having 10mm/7 mm (outer diameter/inner diameter) and 150 mm length, developed by extrusion method from cost effective composition of clay and alumina. Tubes were subjected to ultrasonication with acetone followed by oven drying at 100 °C to remove any surface impurities. It was dip coated using the prepared slurry for contact time of 5 min. Care was taken to avoid any bubble formation in slurry as well as during coating to avoid any defects like crack formation in the membrane surface. Coated tubes were then left for curing at room temperature with ∼35% humidity followed by sintering at 550 °C at slow heating rate. Balance slurry was used for characterization of unsupported membrane.

2.6. Environmental effect of ciprofloxacin Toxicity effect of ciprofloxacin before and after membrane filtration was observed on microalgae Anabaena cylindrica. Pure strain of algae was obtained from a Biotechnology Institute, at Kolkata and culture was

2.4. Membrane characterization Thermal gravimetric analysis (TGA) and differential thermal analysis (DTA) was conducted by Thermogravimetric Analyzer [NETZSCH, Germany]. This analysis is required for identifying temperature regimes where probable material or mass loss may take place and also to understand the thermal stability of the prepared membrane. X-ray diffraction study was carried out to understand the crystalline nature of developed ultrafiltration membrane (UF). Experiments were carried out from 5°- 80°, 2θ using Cu as anode material (λ = 1.541Å) at 25 °C in Philips 1710 diffractometer (Netherlands). Fourier transform infrared

Table 1 Slurry composition of ceramic UF membrane.

108

Sl No.

CuO concentration (g)

TiO2 concentration (g)

1. 2. 3. 4. 5.

0.0625 0.125 0.25 0.5 1.0

1.6875 1.625 1.5 1.25 0.75

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maintained in laboratory under aseptic conditions. Algal biomass was transferred aseptically to sterile conical flasks containing untreated ciprofloxacin (500 ppb) and membrane permeates in triplicates along with one set of control. The flasks with algae were weighed and plugged with cotton to restrict entry of other aerial microflora and kept in laminar airflow under proper illumination and temperature of 25 ± 2 °C was maintained. Growth rate, chlorophyll content, nitrogen content, protein, carbohydrate and catalase enzyme assay were performed on algal biomass. Growth rate was measured by weighing algal biomass under sterile conditions at a particular time keeping 24 h time interval considering the evaporation loss caused from media. Chlorophyll a content was measured spectrophotometrically at 664 nm [33]. Nitrogen content was measured in TC-600 oxygen Nitrogen Analyzer, USA. Protein content was measured as per method described Lowry et al. and carbohydrate content was measured by anthrone method and both measured spectrophotometrically [34,35]. Catalase enzyme activity was measured by reduction of H2O2 on addition of enzyme and measured spectrophotometrically at 240 nm [36]. Microscopic image of algae exposed to control, untreated and membrane permeate of ciprofloxacin after 72 h was obtained (Olympus, STM6).

viscosity for slurry composition 3 calculated from equation (2) was about 3.5 mPa s which was closer to that of experimental viscosity which was 4.5 mPa s. From the above results, slurry composition 3 consisting of 1:3 (w/w) of CuO: TiO2 i.e., 0.25 CuO NP and 1.25 g TiO2 NP was selected for further coating studies. 1.6

(1) (2) (3) (4) (5)

1.4

Sedimentation rate

1.2 1.0 0.8 0.6 0.4

3. Results and discussions

0.2

3.1. Preparation of coating slurry

0.0 0

Sedimentation rate determines the stability of slurry as stable suspension is an indicator for good quality coating. From Fig. 1a it can be observed that CuOeTiO2 slurry no. 3 was most stable with lowest sedimentation rate which reached stability within 25 min and was stable for 48 h. Slurry composition 1 and 2 showed a lower sedimentation rate compared to slurry 4 and 5 which showed higher sedimentation rate. Sedimentation rate increased with increasing CuO concentration resulting in unstable suspension. It might be noted that particle size of CuO NP is about 3.4 nm whereas that of TiO2 is around 20 nm. As a result, increasing CuO content is causing particle agglomeration thereby initiating increase in effective particle size and thus particle gravity sets in triggering faster sedimentation rate [37]. Zeta potential experiments of slurry (Figure not shown) further shows agreement with the sedimentation experiments. Zeta potential value of slurry composition 3 was positive resulting in stable suspension due to electrostatic repulsion. Zeta potential values of slurry composition 1 and 2 were negatively charged with value around −2.53 mV and −2.7 mV suggesting unstable suspension. Slurry composition 4 and 5 also showed negative zeta potential with about −8.7 mV and −8.9 mV respectively again showing unstable suspension. From Fig. 1 (b) it is observed that, viscosity decreased with increasing shear rate for slurry composition 4 and 5. Increase in shear rate increases flowability of suspension. When suspension contains aggregated particles, shear rate increases whereas viscosity decreases suggesting unstable suspension with agglomerated particles. CuO content in slurry composition 4 and 5 was increased than that of slurry composition 1, 2 and 3 causing molecular aggregation. As a result, shear thinning behavior was observed for 4 and 5 slurries. Nanoparticles are known to interact well with base fluid at lower concentrations but with increasing particle concentration, particle-particle interaction becomes dominant rather than particle-fluid interaction causing aggregates. Slurry composition 3 was the most stable among all five compositions as evident from sedimentation study and zeta potential values and it showed Newtonian behavior. It was reported that there was an increase in the viscosity for 13 nm particle nanofluid than that of 50 nm particle [38]. In another study, conducted on ZnO-EG nanofluid displayed a transition from Newtonian to non-Newtonian behavior by increasing ZnO content [39]. This suggests that nanofluids behaves as Newtonian for lower particle volume concentrations (slurry composition 1,2, and 3 in this case) but increase with increasing particle volume concentration (slurry composition 4 and 5). Effective

10

20

30

40

50

60

Time (min)

Fig 1(a)

17 16

(1) (2) (3) (4) (5)

15 14

-1

Viscosity (mPas )

13 12 11 10 9 8 7 6 5 4 0

10

20

30

40

50

60

70

80

90

100

110

-1

Shear rate (s )

Fig. 1 (b) Fig. 1. (a) Sedimentation behavior of different slurry compositions for UF membrane preparation (b) change of viscosity with shear rate for different slurry compositions for UF membrane preparation. 109

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3.2. UF membrane characterization

crystallite size by incorporation of CuO in form of CueOeTi bond. Crystallite size of CuO was calculated as 16.4 nm and that of TiO2 as 23 nm, whereas the crystallite size of unsupported was 7.02 nm. Moreover, incorporation of CuO also reduced the transition temperature of anatase to rutile. Similar results were observed by Ilkhechi and Kaleji, where they doped 5% mol of Cu in TiO2 and found no characteristic peak of Cu due to incorporation of Cu in TiO2 lattice. The authors suggested that since the ionic radius of Cu2+ ion (CN: 4, 0.58A⁰) approaches that of Ti4+ ions (CN: 6, 0.66A⁰) in TiO2, Cu2+ ions will replace lattice Ti4+ ions and occupy its place [41]. Surface area of unsupported membrane as determined from BET was around 37 m2/g. Pore diameter was derived from mercury intrusion porosimetry and found to be around 35 nm whereas that of support was 1.1 μm. FTIR spectrum of membrane before and after ciprofloxacin study revealed major shift in peaks (Fig. 2c). The typical peaks of TieOeTi

From TGA curve of unsupported UF membrane (Fig. 2a) it was observed that there was a weight loss around 150 to 200 °C due to removal of surface water. After that no major weight loss was observed upto 500 °C. There was a negligible weight loss around 530–540 °C due to decomposition of HEC and other organic polymers. From DTA curve (Fig. 2a), exothermic peak at around 180 °C was due to removal of surface water. XRD pattern exhibited strong diffraction pattern at 26.78° and 54.8° indicating TiO2 in rutile phase (JCPDS no.: 88–1175) as observed in Fig. 2b [40]. Peaks of CuO was not observed in XRD pattern suggesting incorporation of Cu2+ in TiO2 lattice. Calculating the crystallite size from Scherrer formula of pure CuO and TiO2 and that of CuOeTiO2 nanocomposite unsupported membrane resulted in decrease of 105

TGA DTA

3

103

1

101

endo exo ( V/mg)

100

0

99

-1

98

-2

97

(020)

Wt. loss (%)

(b)

2

(a)

102

Intensity

104

(110)

4

-3

96 95

-4 0

100

200

300

400

500

600

700

800

10

900 1000

20

30

40

50

60

70

80

2

Temperature ( C)

120

After ciprofloxacin adsorption As such membrane

110 100

50

830 912

60

3413 3451

(c)

598 660

40

2923 2930

1626 1617 1760

70

1179

696

80

455

Transmittance (%)

90

30 0

500

1000

1500

2000

2500

3000

3500

4000

4500

-1

Wavenumbers (cm ) Fig. 2. (a) TG/DTA behavior of unsupported UF membrane (b) XRD analysis of unsupported UF membrane (c) FTIR analysis of membrane before and after permeation with ciprofloxacin. 110

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bond were observed at 455cm-1, 660 cm-1 and 830cm-1, respectively were observed before membrane study. Peaks at 598 cm−1 is due to CuO bond vibrations. Bands at 1626 cm−1 corresponds to C]O stretching of amides and 3451 cm−1 is due to the stretching vibration of eOH group of TiO2 surface adsorbed water. Bands at 1179 cm-1 and 2923 cm-1 were ascribed to the symmetric stretching of COO− group and asymmetric stretching vibration of carbonyl group, respectively. Peak at 1760 cm−1 corresponded to carboxyl group whereas peak at 912 cm−1 was due to phenolic CeO group. After membrane study with ciprofloxacin, prominent bands at 696, 1617, 2930 and 3413 cm−1 was observed suggesting surface adsorption and involvement of C]O, COOe, TieOeTi and CuO groups [41,42]. Fig. 3 (a) portrays electron microscope image of ceramic support tube with porous structure. FESEM analysis of developed UF membrane showed reduced pores as compared to support with increase in number of surface grains due to coating with nanoparticles (Fig. 3b). This membrane after filtration experiments with ciprofloxacin shows further reduction in some pores which might be due to some particle deposition although not very significant (Fig. 3c). Further confirmation of coating on ceramic support was obtained from elemental composition of bulk sample through line scan FESEM analysis (Fig. 3 d, e) where intensity of Si, Al and O2 decreased in coated area where signals of Ti, Cu and O2 were found. Intensity of Al was highest as the support was composed of 80% alumina. Intensity of Ti was more than Cu which also conform the slurry composition ratio. EDX analysis (Fig. 3f) shows presence of a strong intensity peak of Al followed by Ti, Si, Cu and O2. Absence of any other elemental peaks proves that the coated membrane is devoid of any impurities. From Fig. 4 (a) it was observed that binding energy at 282.8 ev was that of C1s. Binding energy at 464.8 and 458.3 ev of Ti existed as 2p1/2 and 2p3/2 in high resolution spectra indicating Ti4+ the only chemical state of Ti element (Fig. 4 b) [43]. Peak at 528.8 ev corresponded to O1s

of TiO2 and CuO (Fig. 4c). Cu 2p spectra existed as binding energies of Cu 2p3/2 at 932.9 along with some shake-up satellite peaks (Fig. 4d). Lower binding energies of Cu 2p1/2 and 2p3/2 at 952.9 ev and 940 ev ruled out possibility of existence of reduced copper species like Cu 2+ or Cu [44,45]. Gap between Cu 2p1/2 and Cu 2p3/2 is about 20 ev which agrees the standard CuO spectrum [46,47]. The N1s peak at 401.4 ev after adsorption of ciprofloxacin ruled out amino group involved in adsorption process. About 29% increase in N+ peak was observed. Shift in O1s peak after adsorption to 11% indicated involvement of oxygen containing groups of composite in adsorption of ciprofloxacin [48]. The molecular weight of PEG at which 90% rejection was obtained by UF membrane filtration was found to be 31 KDa as shown in Fig. 4 (a). The UF membrane was further characterized in terms of clean water permeability and compared to uncoated support. Clean water permeability of support was 216 Lm−2h−1bar−1 whereas that of UF membrane was 150 Lm−2h−1bar−1 (Fig. 4 b). AFM analysis (Fig. 4c) provided insight into surface morphology and surface roughness of coated membrane. The area in view represents 3.1 μm × 3.1 μm square with relatively uniform features of the sample. Surface roughness analysis of ∼100 nm was obtained which was far greater than the particles size of CuO and TiO2 (3.4 nm and 20 nm respectively) which might be due to interparticle sintering between the nanoparticles and clay-alumina support [49]. 3.3. Effect of transmembrane pressure, time and crossflow velocity on membrane flux Effect of transmembrane pressure (TMP), time and cross flow velocity (CFV) upon permeates flux has been represented in Fig. 5(a–c) respectively. Permeate flux was found to increase with TMP, maximizing at 5 bar, as it is the principal driving force responsible for membrane filtration. CFV was found to have synergistic effect on

(b)

(a)

(c)

(d)

(e)

(f)

(f)

Fig. 3. FESEM micrographs of (a) ceramic clay-alumina support (b) CuOeTiO2 nanoparticles coated UF membrane (c) membrane after application with ciprofloxacin (d) surface scan of UF membrane (e) line scan of the membrane (f) EDX analysis of the membrane. 111

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O1s

Before ciprofloxacin adsorption After ciprofloxacin adsorption

2p3/2

Ti 2p

800

700

600

500

400

300

200

Intensity/a.u

Cu 3p

2p1/2

Ti 3s Ti 3p

C 1s

Cu 3s

Ti 2s

N 1s

1100 1000 900

(b)

Ti 2p

O KLL Cu 2p1 Cu2p3

Intensity/a.u

(a)

100

470

0

468

466

O1s

540

Intensity/a.u 538

536

534

532

530

528

526

524

522

460

458

456

2p3/2

(d)

Intensity/a.u

1s

462

454

Binding energy/ev

Binding energy/ev

(c)

464

520

965

Cu 2p

2p1/2

960

955

950

945

940

935

930

925

Binding energy/ev

Binding energy/ev

Fig. 4. XPS wide scan spectra of unsupported membrane (CuOeTiO2) (a) before and after ciprofloxacin adsorption; high resolution spectra of (b) Ti 2p (c) O 1s (d) Cu 2p.

permeate flux. Fig. 5a suggested that with increasing TMP, permeate flux increased steadily with 145 Lm−2h−1 flux at 0.5 bar and reaching the highest flux of 645 Lm−2h−1 at 5.0 bar pressure (5 L of 500 ppb feed concentration). Flux profile of membrane using ciprofloxacin as feed (5 L, 500 ppb feed concentration) at 2.0 bar pressure and 2 Lmin-1 CFV, resulted in almost constant flow of about 220–216 Lm−2h−1 upto 180 min of operation time. The flux decline was very negligible suggesting no pore blocking due to removal (Fig. 5 b). Effect of CFV on permeate flux was shown in Fig. 5c where it was observed that CFV did not have much effect on permeate flux with increase in flux from 205 Lm−2h−1 at 1 Lmin-1 CFV to 229 Lm−2h−1 at CFV 4 Lmin-1. ANOVA analysis was done to determine the effect of filtration parameters viz., TMP, time and CFV on permeate flux. From Table 2 (a) it was observed that time played significant effect on flux (p < 0.05). The regression equation as developed shows an antagonistic effect of time on flux. The R2 value being 0.94 suggests a good model fit. The values of permeate flux as obtained during the entire span of filtration by model fitting in R. A good fit between the experimental and predicted values was found, which is clear from the plot of predicted versus experimental response. From Table 2 (b) it was observed that TMP had significant effect on flux (p < 0.05) with R2 value being 0.96. The regression equation suggest synergistic effect of TMP on flux.

From Table 2 (c) it was observed that CFV did not exhibit any significant effect on permeate flux (p > 0.05). From F value as obtained through ANOVA, it was observed that TMP played the most significant role on permeate flux. 3.4. Removal of ciprofloxacin Ciprofloxacin removal efficiency of developed UF membrane with TMP, time, and CFV was reported in Fig. 6(a–c). Constant increase of ciprofloxacin removal with increasing pressure is obtained with maximum removal of 99% at 2.5 bar pressure. Later removal became almost constant at 98.7% with negligible increase (Fig. 6a). No significant effect of CFV on removal was observed with slight increase of 98.9% at 2 Lmin-1 CFV from 96.7% at 1 Lmin-1 CFV followed by 97% and 97.2% for 3 Lmin-1 and 4 Lmin-1 CFV respectively (Fig. 6c). Time on the other hand had positive effect on removal where percent removal increased with time reaching to 99% within 60 min of operation but later reduced to 90% at 90 min and reached only 92.1% upto 180 min of operation. This might be due to the fact that the membrane acted as adsorptive membrane which was supported from FTIR results. After 60 min, surface desorption might have set in causing reduction in removal efficiency which again regained after certain time becoming constant at 92% when the equilibrium of adsorption and desorption reached 112

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1600

Ceramic support UF membrane

MWCO - 31 KDa

100

1400 1200 -2 -1

Flux (Lm h )

Rejection (%)

80

60

(a) 40

(b)

1000 800 600 400

20

200 0

0 5000

10000

15000

20000

25000

30000

0

35000

1

2

3

4

5

6

2

Transmembrane pressure (kg/cm )

Molecular weight (Da)

(c)

Fig. 5. (a) Molecular weight cutoff of the UF membrane (b) clean water permeability of support and coated membrane (c) AFM analysis of nanoparticles coated UF membrane. Table 2a ANNOVA analysis of effect of time. Sl. No

Source

DF

Sum of Squares

Mean Square

F Value

Probability > F

Effect of time on flux

Model Residual Model Residual

1 11 11 7

17.8985 3.3522 25.9780 2.2909

17.8985 0.3047 25.9780 2.2909

58.732 70.21 79.378 –

< 0.05

Significant

< 0.05

Significant

Effect of time on removal

Table 2b ANNOVA analysis of effect of TMP. Sl. No

Source

DF

Sum of Squares

Mean Square

F Value

Probability > F

Effect of transmembrane pressure on flux

Model Residual Model Residual

1 8 1 8

277495 9078 7.5455 9.1635

277495 1135 7.5455 1.1454

244.54 – 6.5874 –

< 0.05

Significant

> 0.05

Insignificant

Effect of transmembrane pressure on removal

(Fig. 6b). ANOVA analysis was done to determine the effect of filtration parameters viz., TMP, CFV, time on rejection of ciprofloxacin. Data in Table 2 (a) suggested that time had significant influence on removal of ciprofloxacin where p value was < 0.05. The regression equation shows

synergistic effect of time on removal upto 60 min of filtration at a stretch after which the dependency becomes insignificant, which is clear from the p value being 0.06 (> 0.05). A good fit between experimental and predicted values were obtained as evident from R2 value of 0.96. 113

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Table 2c ANNOVA analysis of effect of CFV. Sl. No

Source

DF

Sum of Squares

Mean Square

F Value

Probability > F

Effect of CFV flux

Model Residual Model Residual

1 2 1 2

328.8605 18.067 0.008 2.922

328.8605 9.0335 0.008 1.461

36.40455 – 0.00548 –

> 0.05

Insignificant

> 0.05

Insignificant

Effect of CFV on removal

(Values are Mean ± S.D; p < 0.05). 700

600

94 300 Effect of transmembrane pressure on flux

% rejection

200

100

92

1

2

3

4

140

94

120

2 -1

92 100 80

90 0

96

160

-1

400

(b)

180

Flux (L m h )

(a)

96

98

Effect of time on flux % rejection

90 0

5

% rejection of Ciprofloxacin

200

% rejection of Ciprofloxacin

-2 -1

220

98

500

Flux (Lm h )

100

100

20

40

60

80

100

120

140

160

180

Time (mins)

2

Transmembrane pressure (kg/cm ) 100 230 98

% rejection of Ciprofloxacin

-2 -1

Flux (Lm h )

225

(c)

220

96

215

94

210

92

205 90 1.0

1.5

2.0

2.5

3.0

Crossflow velocity (L/min)

3.5

4.0

Fig. 6. Effect of different filtration parameters on flux behavior and rejection of ciprofloxacin as feed (a) TMP (b) time (c) CFV (feed conc-500 ppb; TMP-2.5 bar; CFV2ml min−1; time- 180min). (a)

(b)

3.5. Toxicity study on microalgae

(c)

Microscopic images (Fig. 7) of algae exposed to untreated and membrane treated depicted toxic effect of ciprofloxacin algae. Algal cells were found to be disrupted with yellowish tinge i.e. loss of photosynthetic pigments, whereas algae growing in membrane permeate had intact cells similar to algal cells in control. Growth rate of algae in three growing media is shown in Table 3. It can be observed that the growth rate of algae in control and membrane permeate is comparable i.e. 0.75 and 0.68 g dry weight/L/day respectively but that of algae in untreated ciprofloxacin was very less i.e. 0.3 g dry weight/L/day respectively. Similar trend was observed in chlorophyll content, nitrogen content and protein content where the concentrations was found to decrease in algae exposed to untreated ciprofloxacin. Biomass production was affected due to effect of stress on algal cells resulting in reduced chlorophyll content. Reduction in protein content might be attributed to hydrolysis of algal cells due to stress created under ciprofloxacin environment. Interestingly, an increase in carbohydrate

Fig. 7. Microscopic images of algae exposed to (a) media as control (b) ciprofloxacin 500 ppb (c) membrane permeate (after 72 h of exposure).

Table 2 (b) showed that effect of TMP on removal was insignificant (p > 0.05). CFV also did not have any significant effect on removal as evident from Table 2 (c) (p > 0.05). The F value showed maximum effect on ciprofloxacin removal was played by time followed by TMP and CFV respectively.

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Table 3 Effect of ciprofloxacin (untreated and membrane permeate) on algal growth, biochemical parameters and enzyme in compared to control. Parameter

Algae (control)

Algae (untreated ciprofloxacin)

Algae (membrane permeate)

Growth rate (g dry weight/L/day) Chlorophyll (mg/g) Nitrogen content (%) Protein (mg/g) Carbohydrate (mg/g) CAT (U/mg protein/min)

0.75 ± 0.05 4.8 ± 0.05 5.66 345 ± 15 320 ± 18 2.4 ± 0.08

0.3 ± 0.05 2.7 ± 0.04 4.68 148 ± 8 335 ± 11 3.8 ± 0.05

0.68 ± 0.05 4.3 ± 0.05 5.46 338.8 ± 12 314 ± 15 2.1 ± 0.05

content was observed which might be due to reduction in nitrogen content in algae exposed to untreated ciprofloxacin solution. Under nitrogen limiting condition, microalgae are known to accumulate lipid in their cells and increase production of carbohydrate i.e. glycogen in this case [50]. Increase in catalase enzyme activity in algae exposed to untreated ciprofloxacin further supported the fact that algal cells were under stress which resulted in generation of reactive oxygen species and increased the production of hydrogen peroxide. Catalase is one of the cells defense mechanism which increases or decreases depending upon the type of stress the cell get exposed [50,51].

Technology (SERB, Govt. Of India) vide. PDF/2016/003273 for providing financial support to carry out the experimental work under their funding project. References [1] C. Girardi, J. Greve, M. Lamshöft, I. Fetzer, A. Miltner, A. Schäffer, M. Kastner, Biodegradation of ciprofloxacin in water and soil and its effects on the microbial communities, J. Hazard Mater. 198 (2011) 22–30, https://doi.org/10.1016/j. jhazmat.2011.10.004. [2] E.M. Golet, I. Xifra, H. Siegrist, A.C. Alder, W. Giger, Environmental exposure assessment of fluoroquinolone antibacterial agents from sewage to soil, Environ. Sci. Technol. 37 (2003) 3243–3249, https://doi.org/10.1021/es0264448. [3] K. Xia, A. Bhandari, K. Das, G. Pillar, Occurrence and fate of pharmaceuticals and personal care products (PPCPs) in biosolids, J. Environ. Qual. 34 (2005) 91–104, https://doi.org/10.2134/jeq2005.0091.·. [4] R. Taman, M.E. Ossman, M.S. Mansour, H.A. Farag, Metal oxide nano-particles as an adsorbent for removal of heavy metals, J. Adv. Chem. Eng. 5 (2015) 1–8, https:// doi.org/10.4172/2090-4568.1000125. [5] J. Peternela, M.F. Silva, M.F. Vieira, R. Bergamasco, A.M.S. Vieira, Synthesis and impregnation of copper oxide nanoparticles on activated carbon through green synthesis for water pollutant removal, Mater. Res. (2017) 1–11 https://doi.org/10. 1590/1980-5373-MR-2016-0460. [6] J. Park, N. Yamashita, C. Park, T. Shimono, D.M. Takeuchi, H. Tanaka, Removal characteristics of pharmaceuticals and personal care products: comparison between membrane bioreactor and various biological treatment processes, Chemosphere 179 (2017) 347–358. [7] H.B. Quesada, A.T.A. Baptista, L.F. Cusioli, D. Seibert, C.O. Bezerra, R. Bergamasc, Surface water pollution by pharmaceuticals and an alternative of removal by lowcost adsorbents: a review, Chemosphere 22 (2019) 766–780. [8] B. Czech, K.T. Rotko, Visible-light-driven photocatalytic removal of acetaminophen from water using a novel MWCNT-TiO2-SiO2 photocatalysts, Separ. Purif. Technol. 206 (2018) 343–355. [9] D. Suman Raj, Y. Anjaneyulu, Evaluation of biokinetic parameters for pharmaceutical wastewaters using aerobic oxidation integrated with chemical treatment, Process Biochem. 40 (2005) 165–175. [10] L. Ji, F. Liu, Z. Xu, S. Zheng, D. Zhu, Adsorption of pharmaceutical antibiotics on template-synthesized ordered micro and mesoporous carbons, Environ. Sci. Technol. 44 (2010) 3116–3122, https://doi.org/10.1021/es903716s. [11] M. Huber, S. Canonica, G. Park, U. von Gunten, Oxidation of pharmaceuticals during ozonation and advanced oxidation processes, Environ. Sci. Technol. 37 (2003) 1016–1024. [12] L. Perez-Estrada, S. Malato, W. Gernjak, A. Aguera, E. Thurman, I. Ferrer, A. Fernandez-Alba, Photo-fenton degradation of diclofenac: identification of main intermediates and degradation pathway, Environ. Sci. Technol. 39 (2005) 8300–8306. [13] J. Radjenovic, M. Petrovic, D. Barceló, Analysis of pharmaceuticals in wastewater and removal using a membrane bioreactor, Anal. Bioanal. Chem. 387 (2007) 1365–1377. [14] Y. Wang, X. Wang, M. Li, J. Dong, C. Sun, G. Chen, Removal of pharmaceutical and personal care products (PPCPs) from municipal waste water with integrated membrane systems, MBR-RO/NF, Int. J. Environ. Res. Public Health 15 (2018) 269, https://doi.org/10.3390/ijerph15020269. [15] S.P. Dharupaneedi, S.K. Nataraj, M. Nadagouda, K.R. Reddy, S.S. Shukla, T.M. Aminabhavi, Membrane-based separation of potential emerging pollutants, Separ. Purif. Technol. 210 (2019) 850–866. [16] Y. Yoon, P. Westerhoff, S.A. Snyder, E.C. Wert, Nanofiltration and ultrafiltration of endocrine disrupting compounds, pharmaceuticals and personal care products, J. Membr. Sci. 270 (2006) 88–100 https://doi.org/10.1016/j.memsci.2005.06.045. [17] P. Bhattacharya, S. Ghosh, S. Swarnakar, A. Mukhopadhyay, Tannery effluent treatment by microfiltration through ceramic membrane for water reuse: assessment of environmental impacts, Clean. - Soil, Air, Water 43 (2015) 633–644 https://doi.org/10.1002/clen.201300199. [18] P. Bhattacharya, S. Majumdar, S. Bandyopadhyay, S. Ghosh, Recycling of tannery effluent from common effluent treatment plant using ceramic membrane based filtration process: a closed loop approach using pilot scale study, Environ. Prog. Sustain. Energy 35 (2016) 60–69 https://doi.org/10.1002/clen.201300199. [19] E.P. Etape, L.J. Ngolui, J. Foba-Tendo, D.M. Yufanyi, B.V. Namondo, Synthesis and characterization of CuO, TiO2, and CuO-TiO2, mixed oxide by a modified oxalate route, J. Appl. Chem. (2017) 1–10 https://doi.org/10.1155/2017/4518654.

4. Conclusion The present work focuses on one step removal of ciprofloxacin from synthetic solution using nanocomposite ceramic UF membrane based process. The membrane was developed using TiO2 NPs and green synthesized CuO NPs. Coating was conducted over indigenously developed clay-alumina based ceramic support. Membrane characterization showed incorporation of Cu and Ti on inner side of membrane which was further confirmed by XPS analysis suggesting presence of Ti and Cu elements existing as oxides. It also indicted involvement of oxide containing groups of nanocomposites in adsorption of ciprofloxacin. AFM analysis showed relatively uniform coating surface. Significant observation was made from FTIR analysis where presence of 696, 1617, 2930 and 3413 cm−1 bands suggested surface adsorption of ciprofloxacin and involvement of C]O, COOe, TieOeTi and CuO groups in adsorption process. This became evident when observing rejection behavior of the membrane where maximum adsorption of 99% was attained within 60 min of operation. Simultaneous desorption was also predominant which was evident from reduction in adsorption efficiency after 60 min of operation. Almost constant flux of 218 Lm−2h−1 was observed suggesting negligible fouling and longer application of membrane without need of frequent cleaning. Toxicity study of ciprofloxacin on microalgae revealed cellular damage of cells exposed to untreated ciprofloxacin as compared to cells in control system or membrane permeate. Maximum algal growth was observed in control (0.75 g dry weight/L/day) which was closer to algae exposed to membrane permeate (0.68 g dry weight/L/day) with least growth in untreated feed (0.3 g dry weight/L/day). Interestingly, there was an increase in catalase enzyme activity in algae exposed to untreated ciprofloxacin as compared to algae in membrane permeate and control, which supported the fact that algal cells were under stress as increased CAT activity suggests generation of reactive oxygen species. Therefore, it might be concluded that the novel approach of coating ceramic support with CuO and TiO2 nanoparticles resulted in 99% removal of ciprofloxacin within 60 min of operation with 218 Lm−2h−1bar−1 flux and minimizing damage to environment. The generation of retentate concentrates containing ciprofloxacin is a setback for the study which will be addressed in the next part of the experiment using methods like advanced oxidation process. Acknowledgement The authors would like to thank Department of Science and 115

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