Synergistic Effect of Titanium Dioxide (TiO2) and Ionizing Radiation on Thermal and Mechanical Properties of Carboxymethyl Cellulose (CMC) for Potential Application in Removal of Basic Dye from Wastewater

Carboxymethyl cellulose (CMC)/titanium dioxide (TiO2) was prepared using gamma irradiation at different doses. Carboxymethyl cellulose was used as a matrix and TiO2 in different contents was added (0.25, 0.5, 1, 1.5 wt%) as a filler. The polymer composite films were irradiated at doses of 5, 10 and 15 kGy using 60Co γ-ray to form crosslinked network structure. The prepared composite films were described by different diagnostic procedures including X-ray diffractometer, scanning electron microscope (SEM), FTIR as well as thermal and mechanical properties measurements. CMC/TiO2 composite films were used for removal of basic Violet 7 dye. The adsorption of the dye match with the Langmuir model across chemical monolayer adsorption performance. Adsorption kinetic of dyes was set up to be regular to pseudo second order kinetic model. The results showed that the prepared composite films significantly removed this basic violet 7 dye with maximum absorption capacity (123.6 mg/g).


Introduction
Water contamination happens in various ways, however an enormous quantity of water pollution, as a product of different industrial effluents, happens during the pollution with organic, inorganic and high volume of dyes and this causes the contamination of environment and the orderly health problems for living frameworks [1]. Nevertheless, the pollution of water by dangerous dyes has become a crucial problem, universal because of their persistent bioaccumulation, low degradability and their high harmfulness [2]. There are various methods, for example: biodegradation, catalytic degradation and oxidation, for the elimination of pollutants [3]. Nevertheless, these procedures are more responsive and consistent, anyway additional time-consuming, costly, cumbersome, laborious and tedious. Henceforth, sensitive, a simple, direct analytical and economical process is the adsorbent technique. In the adsorbent technique, hydrophilic polymeric hydrogels can assume a fundamental role in the elimination of pollutant from the waste water [3]. Hydrogels have three-dimensional, tissue like network, crosslinked and insoluble [4,5]. These characteristics are high sorption capacity, important for water safeguarding and the removal of pollutants. In the advancement of such system, polysaccharide polymers are supplementary attractive than the synthetic polymers, on account of their functional properties, for example; great hydrophilicity, biocompatibility and biodegradation [6]. Carboxymethyl cellulose (CMC) has been broadly utilized for the preparation of new designed hydrogels [7,8]. This is for the reason that CMC is a biodegradable natural anionic polysaccharide and biocompatible that can be highly soluble in the water and thus, rising the viscosity of the water [9]. The consolidation of a limited quantity of inorganic particles can improve the exhibition of thermal, mechanical, electrical, optical, antimicrobial and catalytic properties of the polymer structure [10][11][12]. TiO 2 is notable for its numerous favorable circumstances, Titanium dioxide (TiO 2 ) is generally utilized in a variety of medical, food and biological yield [13]. The incorporation of TiO 2 particles into polymeric network is being considered extensively in light of their significant properties, for example, hydrophilic properties, good stability, UV blocking ability, excellent photocatalytic, high oxidation power, liberated from contamination, non-toxic, exhibit antimicrobial activity and chemically inert material [14].
Numerous crosslinkers are generally utilized for polymers crosslinking yet these crosslinkers are either poisonous or costlier and furthermore the crosslinking occur in the presence of organic solvents. Citric acid (CA) is a crosslinker has low toxicity and cost compared with the different crosslinkers. Along these lines, it has been utilized to improve the properties of cellulose in materials applications [15,16]. There are various techniques to improve the surface properties of polymeric materials or to incorporate new useful natural based polymer.
The critical character of plasticizers is to upgrade the processability and flexibility of natural polymer such as starch and CMC by reducing the strong intermolecular interactions between polymer molecules [17]. Consequently, increases the mobility of polymeric chains, which enhances the flexibility, ductility and extensibility of plasticized composite films. Actually, the addition of plasticizers decreases mechanical resistance of the polymer. In addition, plasticization is especially significant on biopolymer composite films, since the dehydration of these structures produces a highly cohesive composite with poor mechanical properties [18]. Since most plasticizers contain hydrophilic groups, these compounds can interface by methods for hydrogen bonds with polymer framework as well as with water particles, increasing the polymer water adsorption [19]. The majority familiar plasticizer utilized for starch based polymers is polyols such as glycerol and sorbitol. The enthusiasm for the utilization of glycerol is because of glycerol properties which lessens the intermolecular forces and increment the mobility of the polymer chains. It can likewise modify the mobility of water because of its ability to decrease the surface energy of aqueous solution [20].
Radiation polymerization has a lot of advantages over other conventional strategies' science it does not involve the utilization of the catalysts or added substances to start the reaction, no compelling reason to include any initiator or crosslinker, disinfection, no waste, more environment friendly and generally low running expense [21,22]. In this manner, in contrast to the chemical initiation technique, the radiation prompted technique leaves no chemical residues, is free of pollution, consequently the purity of the processed yield can be kept up. In the majority cases of polymerization initiated by high energy radiation, easy to control, the processes are homogeneous and the reactions are not temperature dependent [23,24]. Additionally, ionizing radiation has been known as an advantageous tool for improving the polymeric materials through grafting, crosslinking and degradation strategies [25].
In this study, preparing of dyes adsorbent composite films based on CMC and TiO 2 , which are neither harmful nor costly polymer composite film were done utilizing a direct radiation method. The properties of unirradiated and irradiated composite films were evaluated by utilizing different analytical devices, for example, FTIR, XRD, TGA and SEM. The adsorption isotherm model and kinetic studies for adsorption of the basic violet 7 dye onto CMC/1.5 TiO 2 -10 kGy hydrogel composite film has been investigated. The results showed that the prepared composite films significantly removed this dye with maximum adsorption capacity (123.6 mg/g

Preparation of CMC/TiO 2 Composite Films
CMC (3.0 g) was added to 100 ml of deionized water with stirring for about 4 h. until complete miscibility. The desired amount of glycerol (20%) was added as a plasticizer. At that point 5% citric acid (CA) was added to the solution to reduce the solubility of the prepared composite films (just as a crosslinking agent). During the stirring the required amount of TiO 2 was included with various proportions (0.25, 0.5, 1.0, 1.5 wt %) to the solution. Then placed in sonicator for 30 min to get enormous homogeneity. The composite film was removed, the foam was skimmed off and the composite film was poured in leveled polystyrene petri dishes then irradiated at doses of 5, 10 and15 kGy using 60 Co γ-ray to form crosslinked network structure and after that dried for 48 h. at room temperature to form the composite films.

Irradiation Method
Irradiation was completed at a dose rate of 0.33 Gy/s in air using 60 Co gamma cell facility situated at National Center for Radiation Research and Technology (NCRRT), Cairo, Egypt.

Mechanical Testing
Mechanical properties such as elongation at break and tensile strength of the prepared CMC/TiO 2 composite films were carried out utilizing a Mecmesin equipment ( model 10-I, Britain) utilizing a crosshead speed of 5 mm min −1 and load 500 N as per ASTM D-638 standards.

Morphology and Tobograghy Measurement
The fracture surfaces SEM micrographs were taken with a JSM-5400 electron microscope, JEOL, Japan. A sputter coater was utilized to pre-coat conductive gold onto the fracture surfaces before watching the micrographs at 30 kv.

Thermogravimetric Analysis (TGA)
The TGA thermograms were performed by a Shimadzu TGA instrument (Kyoto, Japan).

FTIR Spectroscopy
The infrared spectra were performed utilizing the Thermo scientific Nicolet iS 10, USA.

X-ray Diffraction (XRD)
The XRD of plasticized CMC/TiO 2 composite film before and after irradiation were carried out by a completely automated x-ray diffractometer (Shimadzu type XD-DI). X-ray diffraction pattern was recorded in the range of 2θ on Philips Pw 1730. The diffraction patterns were performed with nickel filter (Cuka) λ = 1.45 °A. The x-ray diffractogram was gotten utilizing the following conditions: filament current = 28 mA, voltage = 40 kv, scanning speed = 20 mm/min.

Application
• Uptake of basic violet 7 dye onto irradiated CMC/ TiO 2 composite film: Basic violet 7 dye is a cationic water soluble dye; it was chosen as a model dye to investigate its uptake using CMC/TiO 2 composite film. The dye stock concentration (500 mg/l) in proper extents to the required concentrations (10-250 mg/l) was set up by dilution of the stock solution. 100 mg of polymeric composite film was included into 59 ml of dye solutions of definite concentration in each test bottle. The bottles were shaken in a thermostatic mechanical shaker at 30 °C with a speed (100 rpm) for time intervals extend (1-28 h.). The effect of the initial pH of dye solution on the adsorption onto the prepared composite films was studied, for a pH range (2-11) at initial dye concentration (100 mg/l) and contact time 4 h to determine the optimum pH. After each experiment, the dye concentration was determined by measuring its absorption at λ max = 544 nm by using UV/Vis double beam Unicam UV2 spectrophotometer. The removal (%) efficiency and the amount of dye adsorbed (q) (mg/g) were determined by the following equations: where C e (mg/l), C o (mg/l), q e (mg/g) and q t (mg/g) are the equilibrium and initial concentrations (mg/l) and the amount adsorbed of the dye at equilibrium and at the time (t), respectively; m (g) is the weight of polymer composite film and V (l) is the volume of the basic violet 7 dye solution.

Results and Discussion
Fourier Transform Infrared Spectroscopy (FTIR) Figure 1 shows the FT-IR spectra of pure CMC, unirradiated CMC/1.5% TiO 2 and irradiated CMC/1.5% TiO 2 -10 kGy. In the CMC spectrum, a tensile vibration beak associated with the OH groups becomes visible at 3270 cm −1 , and the peak at 2881 cm −1 , which is clearly recognized, is correlated to the asymmetric vibration of the CH 2 group (Scheme 1). The familiar vibration of C-OH in CMC is scrutinized at 1059 and 1119 cm −1 . Two weak peaks at 658 and 856 cm −1 are conjugated with stretching vibration [26]. The study of unirradiated and irradiated CMC/1.5% TiO 2 spectra demonstrated that the peaks at 640 and 1320 cm −1 are associated with the Ti-O-Ti tensile vibration, which designated that an inorganic matrix has been created. When TiO 2 was added to CMC, as can be seen in Fig. 1, the FTIR spectra of the prepared composite films were equivalent to the pure CMC composite film with low difference in peaks intensity. This suggests that the added TiO 2 particles have not actuated fundamental changes in the composite film structure. A beak at 918 cm −1 is associated to Ti-O and Ti-O-Ti coupling vibration [27], which designated that an inorganic matrix has been created. The tensile vibration beak for the OH associated with the adorbed water molecules in the TiO 2 particle matrix come out at 3400 cm −1 . Beside, the spectrum of CMC/1.5% TiO 2 composite film shows that by comparing this spectrum with the pure CMC spectrum, the tensile vibration peak related to OH group was moved from 3270 cm −1 to 3275 cm −1 . It must be mentioned that in CMC and CMC/1.5% TiO 2 composite films that include the glycerol, the peaks associated to glycerol overlap with the CMC peaks. These peaks are observed in different regions including 3420 to 3500 cm −1 that are associated with the tensile vibration of the OH group and 1059 and 1119 cm −1 that are associated with the vibration of C-OH. The peaks appeared 452-800 cm −1 due to TiO 2 in CMC/1.5% TiO 2 formed composite films and a [29,30]. Most pure CMC peaks in the composite film transferred to lower or higher wave numbers, which corroborates the manufacture of new interaction between the components of the composite film.

Mechanical Properties
The tensile strength and elongation at break are the mechanical properties that studied in this segment and the effect of irradiation dose and the content of TiO 2 as a filler on this properties were studied. The variation in tensile strength of unirradiated and irradiated CMC samples containing different TiO 2 content are represented in Fig. 2. It is shown that the TS values of irradiated samples CMC/TiO 2 samples were higher than the unirradiated sample. Additionally, it was seen that the TS increases as irradiation dose increase up to 10 kGy and it tends to decrease at higher doses above 10 kGy at a given amount of TiO 2 . This increase in TS values is a result of radiation crosslinking in the prepared composite film up to 10 kGy, through at higher doses degradation occurs. Meanwhile, the higher the content of TiO 2 the higher the TS at a given irradiation dose. The reinforcement of TiO 2 might be credited to the higher surface area of TiO 2 that in contact with CMC causing a decent dispersion of TiO 2 in the polymer network and strong interaction between TiO 2 and CMC. In this manner, high stress between CMC and TiO 2 is relied upon to happen showing the reinforcing effect of TiO 2 [31]. The TS values increases with introducing TiO 2 in CMC is due to compatibility between TiO 2 and CMC matrix of the composite film. From the data we found that an increase in the stress related to TiO 2 content as a result of irradiation. This gives another factor for the improvement in TS. Also, due to irradiation with addition of TiO 2 the function groups of intercalation agent may support extra additional sites for crosslinking. The Ts increase as a result of irradiation CMC of composite film may be due to the formation of free radicals that joined with each other to form crosslinked structure or with TiO 2 through hydrogen bonding.
The change in the elongation at break of the prepared composite film samples relies on the nature polymer and the degree of crosslinking, which limits the movement of polymer chains against the applied force. Figure 3 represent the effect of irradiation dose and TiO 2 % on the elongation at break. It tends to be seen that an orderly decrease in Eb is observed due to the increase of TiO 2 content; this is something contrary to TS. This may be due to reinforcement at low TiO 2 content causes a decrease in the elongation. Additionally, clearly Eb decreases consistently for all CMC/TiO 2 composite film with increasing the irradiation dose. This is ascribed to the formation of crosslinking network structure in the polymer, which limited the mobility of the molecular chains through drawing [31]. At higher doses degradation is predominant, which gives another factor contributes a lot in decreasing the values of elongation at break.

X-ray Diffraction Investigation (XRD)
XRD was done to perceive the change in the morphology of the composite film by means of checking the position and intensity of reflection as appeared in Fig. 4. XRD sample of CMC/TiO 2 showed an intense diffraction peaks characteristic to TiO 2 at 2θ = 25.6º (101), 47.9 (200) and 53.7 (105), which verifies the spinal structure of the Bragg reflections of TiO 2 . While the blank CMC showed a broad peak at 2θ = 20.8º indicating a semicrystalline structure and becomes more comprehensible with addition of TiO 2 . Also, the intensity of the CMC beak of the prepared composite film decreased due to interaction between CMC and TiO 2 particles and the crystallinity of TiO2 particles does not change during the preparation process. Additionally, the decrease of the composite film crystallinity could be the indication of formation of hydrogen bonding between CMC and TiO 2 [30][31][32]. Generally, γ-irradiation at 10 kGy for CMC/1.5% TiO 2 composite film caused a reduce in the crystallinity of the composite films, which may be due to formation of crosslinked composite film. Therefore, TiO 2 not have much effect on the XRD film spectrum.

Surface Morphology (SEM)
The morphology, particle size and porosity of CMC-20% glycerol, unirradiated and gamma irradiated CMC/TiO 2 composite films were scrutinized by scanning electron microscope technique. Figure 5 demonstrates the images of the scanning electron microscopy of the CMC-20% glycerol (Fig. 5 A), unirradiated CMC/TiO 2 composite (Fig. 5B), and gamma irradiated CMC/TiO 2 -10 kGy composite (Fig. 5c). It should be distinguished that glycerol used in these films was 20% and TiO 2 quantity was 1.5%. The results demonstrated that the CMC-20% glycerol film has coherent, non-porous and a smooth surface. Beside, the addition of TiO 2 particles to unirradiated CMC appeared in roughness with aggregated white spots, demonstrating the convenient distribution of TiO 2 particles into the hosting polymer network. In the cellulose film modified with TiO 2 and Gamma irradiation, it is obvious that TiO 2 particles are dispersed within the carboxymethyl cellulose polymer, displayed better interfacial adhesion with the polymer matrix and demonstrate somewhat spherical shape [30].  Figure 6 showed the thermal stability of CMC, unirradiated and irradiated CMC/1.5% TiO 2 composite films. This represented that the irradiated samples is thermally more stable than the corresponding polymer from which it was synthesized. The degradation of blank CMC starts at 225 °C with 20% degradation. In comparison, the degradation of unirradiated CMC/TiO 2 started at 230 °C with just 17% weight loss and the irradiated sample started at 234 °C with 15% loss, which making it more stable than the native material from which it was synthesized. From Table 1 it can be seen that the unirradiated and irradiated CMC/TiO 2 composite films display higher T max than the neat CMC and T max increases with irradiation. This pointed that the thermal stability of irradiated CMC/ TiO 2 composite films is higher than that of the unirradiated ones. The thermograms conclude higher degradation temperature for the irradiated than the blank CMC and the unirradiated samples. That is might be confirming improvement in the thermal stability ascribed to the formation of crosslinked structure.

Uptake of Basic Violet 7 Dye on CMC/TiO 2 Composite Film
The uptake of the dyes from discharge wastewater is a significant issue for the environment. In this study we used the irradiated CMC-20% glycerol, CMC/1.5% TiO 2 and CMC/1.5% TiO 2 -10 kGy hydrogel composite films for the uptake of basic violet 7 dye from wastewater.  Figure 8 represents effect of initial pH on the adsorption of basic violet 7 dye onto CMC/TiO 2 composite film. In this study, 0.2 g of composite film was included into 50 ml of dye solution of definite concentration 100 mg/l in each experimental bottle. The data represented that as the pH increases the dye uptake increases until reaches a maximum value at pH 8, and afterward remained practically consistent over the range (9-11.0). At lower pH values in acidic medium, there will be a competition between the positively charged dye and H + of the aqueous medium toward the carboxylic groups of CMC. As the pH increased (neutral and basic medium), a net negative charge formed on the surface of CMC due the dissociation of carboxylic groups onto CMC, which enhance the attraction between the composite film and the dye. The chosen optimum pH for the adsorption process was pH 8 as shown in Fig. 8. Also, Fig. 8 represents the effect of initial concentration of the basic violet 7 dye (25-250 mg/l) on the adsorption capacity (mg/g) of the dye onto the irradiated  CMC/1.5% TiO 2 composite film. The results represented that the adsorption capacity increases as the initial dye concentration increases. Actually, the adsorption capacity of CMC/TiO 2 toward the basic violet 7 dye is strongly affected by the initial dye concentration. The higher the initial concentration of the basic dye, the stronger the driving forces of the concentration gradient and afterward the higher the adsorption capacity. The adsorption capacity of composite film for the basic violet 7 dye was found to be about 123.8. mg/g at pH 8, initial concentration of dye = 100 mg/l and temperature = 25 °C after 420 min. Figure 9 represent the effect of contact time between the dye solution (initial conc. 100 mg/l) and the prepared CMC/TiO 2 polymer composite film at pH 8 at different temperatures, which indicates that the adsorption process could be considered as quick process since the amount adsorbed reached 123.6 mg/g) after 420 min. From the figure we observed the adsorption increased with time till reaches equilibrium after 420 min this may be due to rapid attachment between the dye and the composite film at the first stage. Then after that, the attachment becomes slow because many of the available external sites of the polymeric composite film were occupied and, slow diffusion of the dye molecules into the pore spaces of the irradiated CMC/TiO 2 composite film. Temperature is an important factor on the adsorption process as shown in Fig. 9. Where amount adsorbed (mg/g) of the dye onto the irradiated CMC/1.5% TiO 2 were studied at 298, 308 and 318 K at pH 8 and adsorbent dosage = 0.2 g. The adsorption capacity (mg/g) increased when the temperature increased from 298 to 308 K, which represented that the adsorption process is an endothermic process. When the temperature reached 318 K a small change in the adsorption process occurred. This may be due to the thermal motion of the dye molecules increased and could run away the interaction and this process reaches balance.

Adsorption Isotherm
The adsorption isotherms of basic violet 7 dye for the irradiated CMC/1.5 TiO 2 at different temperatures are represented in Fig. 10. The data are fitted with the generally used Langmuir and Freundlich models, and the fitted parameters are exposed in Table 2. The Langmuir model is expressed in Eq. 4. What is more, the Freundlich isotherm describes the reversible adsorption and is not confined to the development of the monolayer is expressed in Eq. (5).
(4) C e q e = 1 q m K L + C e q m (5) lnq e = lnK F + 1 n lnC e  where K L and K F are the binding constants in the Langmuir and Freundlich models, respectively and 1/n is empirical parameter in the Freundlich model. The Langmuir model correlation coefficients (R 2 ) for the basic violet 7 dye adsorbed onto the irradiated CMC/1.5% TiO 2 at different temperatures 298, 308 and 318 K were 0.9962, 0.9969 and 0.9972, respectively. These values are higher than those acquire from the Freundlich model, for example, 0.7173, 0.6268 and 0.6878, respectively. Furthermore, the obtained empirical parameters (1/n) from the Freundlich model for the adsorption of the basic violet 7 dye are all under 1.0, which are in general not compatible with the experimentally calculated adsorption values, while the q m values resulted from the Langmuir model are fitted with the experimental data in Table 2. This proposes that the adsorption of the dye follows the Langmuir model as opposed to the Freundlich model, representing a monolayer adsorption behavior of the investigated dye onto the irradiated CMC/1.5% TiO 2 .

Adsorption Kinetics
The kinetics of basic violet 7 dye adsorption are determined to understand the adsorption behaviors for the irradiated CMC/1.5 TiO 2 at different temperatures represented in Fig. 11. As regards, the irradiated CMC/1.5 TiO 2 , the data reveal that, at various temperatures, during the first 420 min, the adsorption plateau showed up the adsorption amounts of 123.6, 138.6 and 142.7 mg/g, respectively. While after 420 min, the adsorbed amounts of the dye didn't change significantly (126.1, 138.7, and 143.2 mg/g, respectively). The kinetic adsorption of the basic violet dye for the irradiated CMC/1.5 TiO 2 was linearly evaluated utilizing the pseudofirst-order (Eq. 6) and pseudo-second-order kinetic (Eq. 7) and the fixed data were shown in Fig. 11. (6) ln q e − q t = lnq e,cal − K 1 t where K 1 (min −1 ) and K 2 (min −1 ) are the pseudo-first-order and pseudo-second-order rate constants.
The kinetic parameters fitted from the experimental data were summarized in Table 2. The linear correlation coefficients (R 2 ) resulted from the pseudo-second-order kinetics for the adsorption of the basic violet 7 dye at various temperatures 298, 308 and 318 K are close to 1.0 (0.9911 or 0.9971 and 0.9909, respectively). These values are higher than those acquired from the pseudo-first-order, for example, 0.5049, 0.9141 and 0.9256, respectively. Moreover, the determined equilibrium adsorption values (q e,cal ) obtained from the pseudo-second-order kinetic model for irradiated CMC/1.5 TiO 2 composite film towards the dye are 129.8, 179.8, and 148.9 mg/g, respectively. Where, (q e,cal ) obtained from the pseudo-first-order kinetic model in general not compatible with the experimentally calculated adsorption values. For that reason, the fitted and the experimental values illustrate considerable consistence here when the pseudo-secondorder kinetic model was used.
It is significant that the prepared Fe 3 O 4 /SiO 2 /GMA/AN (amidoxime) nanocomposite film in this work have superior adsorptivity for the basic red dye than that for other CMC polymeric nanocomposite film as Adsorbents, as listed in Table 3.

Conclusions
CMC/TiO 2 composite film with various content of TiO 2 were prepared using gamma irradiation source which and characterized by FTIR, TGA and SEM. Additionally, Also, the mechanical behavior of the developed composite films was investigated and the dose yielded best values was adopted to use for the application of interest. The possibility (7) t q t = 1 k 2 q e,cal 2 + t q e2,cal Fig. 11 Fitted plots of the pseudo-first-order and pseudo-second-order kinetics of adsorption for basic violet dye onto CMC/1.5% TiO 2 -10 kGy of using the 10 kGy irradiated CMC/1.5% TiO 2 in the removal of basic violet dye from wastewater was examined under the following conditions: optimum irradiation dose 10 kGy, adsorbent CMC/TiO 2 amount: 0.2 g, contact time: 420 min, initial dye concentration: 100 mg/l and pH 8. In this investigation, CMC/1.5% TiO 2 demonstrated excellent adsorption capacity (123.6 mg/g) for uptake of basic violet 7 dye from its solution. The adsorption of the dye follows the Langmuir model a with chemical monolayer adsorption behavior. Adsorption kinetic of dyes was set up to be regular to pseudo second order kinetic model. Hence, the CMC/TiO 2 composite film can be potentially used for the uptake of dye in addition to industrial applications.