The aim of this paper synthesis a novel and inexpensive sorbent with good stability in acidic and alkaline solutions. Schiff’s base vanillin thiourea [email protected] oxide nanoparticle composite ([email protected]) was characterized by Fourier transform infrared (FT-IR), Brunauer-Emmett-Teller (BET), X-ray diffraction (X-ray), scanning electron microscopy (SEM) and thermal gravimetric analysis (TGA). A Many surface active groups, e.g. OH, NH, C=O, N=C=S and C=N were detected in the matrix of [email protected] The surface area and pore volume of [email protected] were 10.6 m2/g and 0.017 cm3/g. The XRD pattern illustrates that the material of [email protected] has an amorphous structure with embedded by crystalline phase has diffraction peaks at 31.84?, 34.52?, 36.33?, 47.63?, 56.71?, 62.96?, 68.13?, and 69.18?. [email protected] was successfully used for sensitive detection and efficient removal of toxic dyes from wastewater. The operating variables studied were concentration, pH, time and temperature for removal of brilliant green (Br.G), toluidine blue (To.B) and trypan blue (Tr.B). The removal percentages of Br.G, To.B and Tr.B (95%-100%) were in pH 8-10, 3-11 and 3-11at 3, 3 and 15 min for Br.G, To.B for Tr.B. Langmuir model was best described for equilibrium process and maximum monolayer adsorption capacities were found to be 474, 381 and 337 mg/g for Br.G, To.B and Tr.B. Removal process was spontaneous, ?G° values were -7.3, -8.6 and -2.9 KJ/mol. As this result shown the [email protected] was a suitable adsorbent for dye removal.
Keywords: Vanillin; Polyurethane; Zinc oxide NPs; Brilliant green, Toluidine blue; Trypan blue
Nile river water is the most important element for vital activities of living beings that used for drinking (Ali, 2012). Dyes are the one of that contamination which comes from many industries manufacturing textile is effect on these living beings. There is about 10-20% dyes used is lost in residual liquors through washing operations, so we have to get rid of these dyes (Wong et el., 2008). Cationic dyes can cause an increase in heart rate, shock, vomiting, cyanosis, jaundice, quadriplegia, Heinz body formation and tissue necrosis in humans (Ahmad and Kumar, 2010) as brilliant green and toluidine blue. Brilliant green (Br.G) is a golden crystal dye with a triphenylmethane family (Allen, 2013) which widely used in a different purpose, such as dermatological agent, veterinary medicine, besides as poultry feed to inhibit spreading of mold (Nandi et el., 2009), but toluidine blue (To.B) is phenothiazine dye which uses in medicine science, textile industry and biotechnology (Weis et el., 1999; Wainwright, 2003; O’Riordan, 2005; Wainwright, 2005). For trypan blue (Tr.B), it is a carcinogenic azo dye which is used for the preparation of color staining solutions, staining histological sample materials of human origin (Nadaroglu et el., 2017). It also extensively used in the textile, food and paint industries for dyeing silk, cotton, wool, nylon and also for coloring oil, waxes, varnish and plastics (Lade et el., 2015).
Removal of brilliant green, toluidine blue and trypan blue dyes from wastewaters before their release into natural streams and Nile River is very essential for environmental safety. Different methods used for this as coagulation and flocculation (Han et el., 2005), adsorption (Gupta et el., 2003), Biosorption (Sari et el., 2008), electrochemical techniques (Kumar, 2006), but adsorption is the most effective technique because it is very easy, inexpensive and it can treat with concentrated dyes and we can make regeneration for the spent sorbent (Gupta and Ali, 2013). Many adsorbent used for removing dyes from wastewater, e.g. orange peel (Sivaraj et el., 2001), fly ash (Mohan et el., 2002), zeolites (Arma?an and Turan, 2004; Ozdemir et el., 2004) and polyurethane foam.
Polyurethane foam (PUF) sorbent has highly surface area due to existence of open porous structures, low cost, stable in acid / base solutions and stable up to 180 ºC (Moawed, 2006; El-Shahat et el., 2008). PUF has polar and nonpolar groups in their structure (Baldez et el., 2008; Lee et el., 2009; Moawed and Radwan, 2017), so it can extract different substances. Metal oxide nanoparticles have a great attention lately, especially zinc oxide nanoparticles. ZnONPs get involved in various applications such as gas sensors (Gao et el., 2005), solar cells (Hames et el., 2010) and photcatalysts (Kamat et el., 2002). Because of non-toxicity, low cost and high adsorptive properties (Sharma et el., 2017), it is a good choice for removal of dyes.
The aim of this paper, polyurethane foam sorbent was modified using thiourea (NH2CSNH2), vanillin (C8H8O3) to form Schiff’s base vanillin thiourea polyurethane foam (SVT-PUF). The stable powder of [email protected] composite was prepared by condensation of SVT-PUF with ZnO NPs in ethanol. [email protected] was characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), thermal analysis (TGA), Brunauer-Emmett-Teller (BET) and FT-IR. Applications of [email protected] for removing of brilliant green, trypan blue and toluidine blue dyes from wastewater at different time, initial concentration, pH and temperature were tested.
All spectrophotometric measurements were performed using a JASCO (V-630 UV-VIS Spectrophotometer, Japan). The pH measurements were carried out with a Jenway 3510, UK pH-meter. SEM analysis was carried out using JEOL model JSM-6510LV, USA. FT-IR spectra were recorded using KBr disc by a JASCO FTIR-410 spectrometer in the 4000-400 cm-1 spectral range. The XRD patterns were recorded by X-ray diffractometer (D8-Brucker Model) using anode Material Cu K? radiation (?=1.5406 Å) at a generator voltage and current of 40 kV and 40 mA, respectively. The sample was scanned using Bragg’s configuration in the 2? range of 4.01-79.99° and step size (2?) was 0.02° with a scan step time of 0.7 s. BET surface area of [email protected] was characterized by N2 adsorption/desorption isotherms at -196 ? C using a NOVA 3200, USA apparatus. Thermal gravimetric analysis (TGA), differential thermal analysis (DTA) and differential scanning coulomtry analysis (DSC) were carried out using simultaneous DSC-TGA device model (SDTQ 600, USA) under N2 atmosphere with a heating rate of 10 °C/min from 29 to 1000 °C. The bulk conductivity was measured using Keithley, 6517B electrometer-high resistance Meter.
2.2. Reagents and Materials
Schiff’s base vanillin thiourea polyurethane foam (PUF) was prepared using open cell flexible polyurethane foam polyether type which supply from an Egyptian company for foam production. 5 g of PUF cubes was soaked in 1 mol/L HCl leaving it whole night soaked then squeezed it very well to get over all HCl remain and then washed it with distilled water. A 25 ml concentrated HCl was added to 5 g PUF-NH2 cubes until this mixture was warmed. A 60 ml of saturated solution of ammonium thiocyanate (1:2) was added slowly to PUF-NH2 cubes and the solution was warmed until the solution got turbid. The turbid mixture was poured into cold water, filtered and dried at room temperature (Mathapati et el., 2012). The next step is adding vanillin to PUF (1:1) to reflux with 200 ml ethanol for 2h .The [email protected] composite was prepared by refluxing the SVT-PUF with ZnONPs at 6 h then filtered, washed with ethanol and air dried.
Stock solutions of brilliant green (Br.G; C27H34N2O4S, 482.65 g/mol), toluidine blue (To.B; C15H16ClN3S, 305.83g/mol) and trypan blue (Tr.B; C34H24N6O14S4Na4, 960.81 g/mol) were prepared by dissolving 0.1 g of each dye in 100 ml distilled water.
2.3. Recommended procedures
A series of 100 ml conical flasks containing 25 ml of Br.G, To.B or Tr.B dye solutions of known pH and concentration were shaken with 0.1 g of [email protected] After 1 h, the solution samples were filtered and the concentration of the remaining and the recovered dye from [email protected] were estimated spectrophotometrically. The percentage of dye removal (%E) and capacity of [email protected] (Q, mmol/g) were calculated by the following equation:
Where C? and Ce are the initial and remaining dye concentrations of Br.G, To.B and Tr.B dyes in solution, respectively. V is the volume of Br.G, To.B and Tr.B dyes and m is the mass of [email protected]
3. Results and discussion
3.1. Characterization of [email protected]
FT-IR spectra of PUF, SVT-PUF and [email protected] are shown in figure 1A. The characteristic absorptions peaks of PUF were observed at 3733-3131 cm-1 (NH, OH), 2977;2877 cm-1 (CH aromatic and aliphatic), 1712 cm-1 (CO) and 1646 cm-1 (C=C). The broadband of NH and OH groups were shifted from 3733-3131 cm-1 to 3800-2740 and 3421-3112 cm-1 for SVT-PUF and [email protected] spectra, respectively. While the CH, CO and C=C groups were shifted to 2740 ; 2964/2859, 1750;1702 and 1630;1641 cm-1. In SVT-PUF spectrum, the new bands for N=C=S, C=N and C-S groups were observed at 2070, 1510 and 640 cm-1. While the new bands for N=C=S, N=C and Zn-O were developed at 2075, 1540 and 433 cm-1 in [email protected] spectrum.
The broadband of NH/OH was shifted to 3559-3170, 3567-3139 and 3475-3124 cm-1 in spectra of [email protected]:Br.G, [email protected]:To.B and [email protected]:Tr.B (Fig. 1B). Also, the band of N=C=S was shifted to 2086, 2078 and 2086 cm-1 and the Zn-O was shifted to 420, 416 and 455 cm-1. The CH aromatic, CH aliphatic, CO and C=C were observed at 2969, 2877, 1720 and 1650 cm-1 for [email protected]:Br.G, [email protected]:To.B and [email protected]:Tr.B.
The electronic spectra of PUF, SVT-PUF and [email protected] were tested using Nujol mulls method (Emara et el., 2011). The characteristics of absorption band of PUF was observed at 213-361 nm due to the ? ? ?* and n ? ?* transition (Fig. 2). This band was shifted from 213-361 nm to 212-398 nm (red shift) after coupling with vanillin then was shifted to 224-335 nm (blue shift) after coupling with zinc oxide nanoparticles. It indicates the formation of SVT-PUF and [email protected], respectively. The characteristic band of [email protected] spectrum was shifted in the spectra of [email protected]ONPs:Br.G, [email protected]:To.B and [email protected]:Tr.B from 224-335 to 224-363, 224-363 and 224-363 nm (red shift) after sorption of Br.G, To.B and Tr.B dyes.
Reactive surface functional groups of the [email protected] are strongly important factor for removing of dyes from wastewater; the Boehm titration method provides evidence for the existence of acidic and basic sites (Boehm, 1994). The acidic and basic sites of [email protected] were 0.87 and 0.47 mmol/g, this result show that the [email protected] has mainly acidic character.
The DC electrical conductivity (?DC) values of SVT-PUF, [email protected] and ZnONPs were measured at room temperature and found to be 1.23×10-8, 7.1×10-8 and 5.8×10-6 ?1 m-1, respectively. The conductivity of [email protected] is greater than PUF. This can be attributed to additional new groups due to the interaction between PUF and ZnONPs. Also, the higher conductivity could be due to the uniform distribution of zinc oxide on PUF, as the ZnONPs have excellent electric conductivity.
The surface charge of [email protected] was zero at pHZPC 7.3 (Fig, 3A). The surface charge become positive at pH 7.3.The maximum values of ?pH for [email protected] are +3.43 and -1.64 at pH 3.3 and 9.3, respectively. Figure 3B shows that the pHf of [email protected] is little change from pH 3 to pH 9. Due to the buffering effect of water on the [email protected] surface, the pH measurements would only be considered in a pH range of 3-9. Figure 3C shows that the maximum of removal percentages of Br.G, To.B and Tr.B dyes are achieved at pH 8-10, 3-11 and 3-11, respectively. Although the surface of [email protected] was positive charge at pH 85%. Due to illustrate this result, the figure 3b shows that the surface [email protected] has buffering effect from pH 3-11 therefore not repulsion occurs between the dyes and [email protected]
The surface area for [email protected] was calculated by N2 adsorption/desorption isotherms using Brunauer/Emmett/Teller (BET). Figure 4A shows that the isotherm for sorption and desorption of N2 onto [email protected] is nearly similar to ? type of IUPAC classification (Lowell et el., 2011), proving mesopores dominated property. Amount adsorbed increases gradually as a relative pressure increases. The lower line was the nitrogen adsorption isotherm and the upper line was the nitrogen desorption isotherm. The hysteresis loop is explained as type H3 representing aggregates of plate-like particles giving a slit-shaped pore. The surface area of [email protected] (10.6 m2/g) is higher than the surface area of polyurethane foam (2.8 m2/g) (Han et el., 2015). Barrett/Joyner/ Halenda (BJH) methods were used to find pore volume and pore radiuses are 0.017 cm3/g and 4.124 nm (Fig. 4B). The ratio of mesopores to micropores volumes (1.7× 10-2 cm3/g: 1.5×10-3 cm3/g) is 11:1; such a ratio indicates that the [email protected] would be a good candidate for the removal of dyes.
Iodine number (IN) is the way to know the micro-pore content of surface. The iodine molecule is relatively small with an area of 0.4 nm2 and can enter in the smaller micro pores (Alaya et el., 2000; Baçaoui et el., 2001). The iodine number can use for approach determination of surface area and microporosity (? 2 nm) of the sorbent (Nunes and Guerreiro, 2011; Saka, 2012). The iodine number of [email protected] is 3.62 mmol/g (459.05 mg/g). The specific surface area of [email protected] was also estimated using iodine number () (Wu, 2007; Mianowski, 2007) where S is the area occupied by adsorbed iodine molecules at the maximum mono-layer surface coverage (m2/g), N is the Avogadro number (6.02 ×1023), A is the iodine surface area (0.2096 ×10?18 m2) and M is the iodine molar mass (126.92 g/mol). So, the specific surface area obtained is 456.4 m2/g. The BET surface area of [email protected] is very small compared with calculated surface area by iodine number method. It indicates that the iodine number method is incorrect for determination of [email protected] surface area (Tran, 2017). Thus it can be concluded that the adsorption process of iodine molecules occurred not only by the pores of the surface of [email protected] but also through its functional groups e.g. ether groups.
The methylene blue number is defined as the maximum amount of dye adsorbed by 1 g of adsorbent (Nunes and Guerreiro, 2011). Methylene blue can measure mesporsity (2-50 nm) of the sorbent and evaluate its cation exchange (Tounsadi et el., 2016). The surface area of MB is 2.08 nm2 and can enter in micropores and mesopores (Nunes and Guerreiro, 2011). The methylene blue number for [email protected] is 0.84 mmol/g (270.25 mg/g). This value indicates that the surface of [email protected] contains mesopores and also has better cation-exchange capacity compared to other sorbents (Table 1)
Different concentration of Br.G, To.B and Tr.B dyes (2-12 mg/L) was plotted against capacity of [email protected] The R2 values for the sorption of Br.G, To.B and Tr.B dyes [email protected] onto were 0.962, 0.990 and 0.994. Also, the intercept values of these plots were 0.013, 0.019 and 0.011, respectively as shown in table 2. In addition the estimated capacity (Q) of [email protected] for Br.G, To.B and Tr.B were 0.47, 0.30 and 0.19 mmol/g (227, 91.7 and 182.5 mg/g), respectively. The results indicate that the [email protected] has a good sorption capacity compared to other sorbents (Table 1, 2).
Thermal properties of PUF, ZnONPs and [email protected] were investigated by TGA, DTA and DSC measurements. TGA curves of [email protected] showed a smooth stepwise manner containing five steps of thermal decomposition (Fig. 5A), the first step decomposition begins at 229 °C and the weight loss are 1.6, 31.1, 44.6, 11.1 and 13.2 % in the ranges 27-229, 230-312, 313-421, 421-824 and ;824 °C, respectively. In first step, the weight loss of [email protected] (1.6%) at 27-229 °C is due to evaporation of adsorbed water molecules. The major weight losses (75.7%) occur between 230 and 421°C is due to the decomposition of SVTPUP matrix. The decomposition occurs (11.1%) at 421-824 °C is due to the crystallinity of ZnO. At T ; 421 ºC, the remained of [email protected] (24.3 wt %) represents the percentage of ZnO NPs that content in [email protected] TGA curve of PUF showed that the thermal decomposition begins at 207.1 ?C to 400 ?C and the weight loss are 34.1, 55.7 and 10.0% in the ranges 207–302 and 302–400 ?C, respectively (Moawed and El-Shahat, 2013). That indicates thermal stability of [email protected]
The DTA and DSC curves of PUF showed two endothermic peaks at 288.5 and 356.8 ?C (Moawed and El-Shahat, 2013). DTA curve for ZnONPs has exothermic peak between 370 and 520 °C illustrates the maxima at 435 °C (Mashrai et el., 2017). While, the [email protected] has four endothermic peaks at 305, 377, 805 and 880°C and two exothermic peaks one at 62 and 943°C as shown in (Fig.5B), this result support the chemical interaction between SVTPUF and ZnONPs.
The XRD pattern of [email protected] is shown in figure 6A. The Figure shows a hump at 2? around 25o and some diffraction peaks at 2 theta higher than 30o. The XRD pattern illustrates that the material has amorphous structure which is the PUF polymer with crystalline phase embedded in it. The diffraction peaks at 31.84?, 34.52?, 36.33?, 47.63?, 56.71?, 62.96?, 68.13?, and 69.18? are attributed to zinc oxide nanoparticles (inset graph Fig.6B). These diffraction peaks are similar to other results reported in (Zhou et el., 2007; Khoshhesab et el., 2011) and are reported to be hexagonal wurtzite phase of ZnO. Also, those diffraction peaks are the same reported in Joint Committee on Powder Diffraction Standards (JCPDS file PDF NO. 36-1451) (Li et el., 2010). However, there is one diffraction peak observed at 2theta around 77.21°. This peak can be attributed to the coupling between PUF and ZnO NPs. The average crystallite size of [email protected] can be calculated from the diffraction peaks using Debye-Scherrer formula (Klug and Alexander, 1974):
Where ? is the wavelength of X-rays (0.15418 nm), ? is the Bragg diffraction angle, and ? is the full width at half-maximum (FWHM) of the diffraction peak. The average particles size was calculated and was found to be 18.36 nm. The value found for the crystallite size is in good agreement with the value reported in (Mashrai et el., 2017).
The surface morphology of [email protected] was investigated using SEM at different magnifications as shown in Fig. 7. SEM images of the surface of [email protected] at low magnification show that it has a rough surface, containing many spaces and pores indicating good sorption characteristics (Fig.7A). At higher magnification as in Fig. 7B we can see that ZnONPs are aggregated on the surface of the PUF. The ZnONPs are also absorbed inside the polymer through the pores as we can see in Figs. 7c and 7d. All of that prove that the coupling between the polymer and ZnONPs was successful.
3.2. Kinetic studies
The effect of contact time on the removal of Br.G, To.B and Tr.B onto [email protected] was tested by shaking dye solutions at different time (3-60 min). Fig.1AS showed that the time need for complete removal of Br.G, To.B and Tr.B were 60, 60 and 15 min, respectively. It was indicated that at first time the removal was very fast, then slow gradually as the active sites being saturated with time and adsorption process become slower.
The diffusion rates of Br.G, To.B and Tr.B onto [email protected] were estimated using Weber-Morris (4), Bangham (5) and Reichenberg (6) equations.
Where ki (mg/g min1/2) is the intraparticle diffusion rate coefficient, the ?t value is a mathematical function of F = Qt/Qe. Di is the effective diffusion coefficient, and ? and k? are constants. Qe (mg/g) and Qt (mg/g) are the sorption capacity at equilibrium and after time t (min). Particle diffusion mechanism for sorption of Br.G, To.B and Tr.B onto [email protected] was studied with Morris–Weber model (Weber and Morris, 1963). Plotting Qt vs. t1/2 give straight line did not pass through the origin with Ki=0.74, 0.85 and 0.57 mg/g min1/2, (R2 = 0.53, 0.59, 0.73) as shown in fig.1b. The intercept values (film thickness) were 1.01, 0.71 and 1.03 for the sorption of Br.G, To.B and Tr.B. The intercepted values are due to streaming fluid for sorption of Br.G, To.B and Tr.B dyes onto [email protected] and the higher the value of it, the greater the boundary layer effect (Salem et el., 2016). The deviation of the linear plot consist of two steps (Moawed et el., 2014). The first step, the diffusion rate is high then, decreased with the time pass in the second step. The values of ki(1) , ki(2) of these steps are (2.74 , 0.089 mg g-1 min1/2) for Br.G , (2.65 , 0.032 mg/g min1/2) for To.B and (1.35 , 0.2 mg/g min1/2) for Tr.B. ki(2) decrease as the active centers were blocked by sorbed dye molecules. The first step is a transport step after transfer the adsorbed solution into adsorbent, it is too fast step. The second step is equilibrium step which represents diffusion of adsorbate molecules from the external of the adsorbent into the pores of adsorbent molecules (Tran et el., 2017). Rate of diffusion of To.B ; Br.G ;Tr.B which mean ki dependent on the molecular size of dyes. The lighter molecule’s weight as To.B will diffuse faster in contract Tr.B which has heavier molecule’s weight. Larger ki, better adsorption mechanism which related to improved bonding between adsorbate molecules with adsorbent particles.
The kinetic data used further to know the slowness of adsorption step according to Bangham model (Nowak and Bangham, 1996). The double logarithmic plots against time doesn’t give perfect line with a correlation coefficient (R2= 0.69, 0.74 and 0.77) for sorption of Br.G, To.B and Tr.B dyes onto [email protected], respectively (Fig.1CS). This means that the film diffusion is not the sole rate-controlling step. The values of ? (Table 3) are 0.47, 0.55 and 0.40 for Br.G, To.B and Tr.B dyes which means ? value independent of the dye size.
The plot of Bt versus t is straight line do not pass through the origin (Fig.1DS) proving that mass transfer is involved the values of the effective diffusion coefficient (Di) by plot F VS. t0.5 1/2.The results show that Di values are 8.74 ×10-7, 1.15 ×10-7 and 1.36 ×10-7 cm/min for Br.G, To.B and Tr.B dyes, respectively and it is independent of the size of the dyes
Table 4 shows the kinetic parameters of pseudo first order (7) and pseudo second order (8) studies for the sorption of Br.G, To.B and Tr.B onto [email protected]
By checking R2 for three dyes (Fig.1ES and 1FS), we found that sorption of three dyes followed a pseudo second model (0.956, 0.933 and 0.991) rather than pseudo first order (0.369, 0.434 and 0.669) (Table 4) that means the pseudo second order is dominated which prove that rate limiting step may be chemical adsorption means chemisorption reaction which involves valence forces by sharing or electron exchange between the adsorbate and the adsorbent (Wang and Aiqin, 2008). The values of the rate constant of the sorption (k2), calculated from the slopes, are 0.28, 0.16 and 0.17 g/ mg/ min. The Half-life time (t1/2) of sorption for second order which it depends on the concentration and this time used to characterize how fast the reaction occurs, calculated by the following equations: (t1/2 = 1/ (k2 C?), t1/2 = 0.30 , 0.50 and 0.48 min for Br.G , To.B and Tr.B dyes. The initial rate constant (h = K2 Qe2) of Br.G, To.B and Tr.B dyes are 2.99, 2.09 and 1.94 min g/mg.
3.3. Equilibrium studies
The equilibrium data estimated from the sorption isotherms are required to understand the mechanism of sorption. The experimental data were analyzed using models of Freundlich (9), Langmuir (10) and Dubinin-Radushkevich (11).
Where Qe (mg/g) is the adsorbed amount of dyes at equilibrium, Ce (mg/L) is the equilibrium concentration of dyes, Qm (mg/g) and Kl (L/mg) are Langmuir constants, and n are Freundlich constants, is the maximum amount of dyes conserved in the [email protected], ? is a constant related to the energy of transfer of dyes from the bulk aqueous solution onto the [email protected] and ? is Polanyi potential.
The relation between log Qe versus log Ce was linear with R2 values of 0.919, 0.722 and 0.991 for Br.G, To.B and Tr.B dyes, respectively (Fig.2a). The Freundlich constants (1/n) are 0.53, 0.64 and 0.49 for Br.G, To.B and Tr.B dyes which reveal a higher probability of multilayer adsorption (Nassar et el.,2012; Auta and Hameed, 2012, 2013) of Br.G, To.B and Tr.B on the active heterogeneous sites of [email protected] gives n values more than one indicates the desirable adsorption process (Table 5).
Plots of Ce/Qe vs. Ce of the experimental data according to the Langmuir model were linear with R2 values of 0.941, 0.935 and 0.908 for Br.G, Tr.B and To.B, respectively (Fig.2b). The separation factor RL was calculated according to equation (Hall, 1966) where C? is the highest initial concentration of dye, to explain the favorability of the adsorption process. The values of RL were found to be 0.016, 0.023 and 0.053 for Br.G, To.B and Tr.B. The values of RL between 0 and 1 which indicate the adsorption of Br.G, To.B and Tr.B dyes on [email protected] is a favorable process.
The D–R isotherm represents a single uniform pore adsorption. The D–R isotherm is a general form of the Langmuir type because it does not suppose a surface was homogeneous or adsorption potential was constant (Kilislioglu and Bilgin, 2003; Ünlü and Ersoz, 2006). Plot the relation ln Q vs. ?2 (), where R is the universal gas constant (8.314×10?3 KJ./K/mol) and T is the absolute temperature in K give a straight line (R2 = 0.963, 0.936 and 0.874) for Br.G, To.B and Tr.B dyes (Fig.2c). E (KJ/mol) is the mean free energy of adsorption of one mole of the adsorbate when transferred to the surface of adsorbent (Ergene et el., 2009) was calculated with the help of equation (Hobson, 1969): . The values of E were 2.78, 2.96 and 2.39 KJ/mol, proving that adsorption was not dominated by the chemical ion exchange mechanism as E is not in the range of 8–16 KJ/mol and E smaller than 8 KJ/mol, the physical forces dominate (Rafatullah et el., 2009).
3.4. Thermodynamic studies
The removal percentages of Br.G, To.B and Tr.B were plotted against the solution temperature (Fig. 3a). It is very obvious that temperature has little effect on the adsorption of Br.G except at temperature 59°C there is a slight decrease from 100% to 99% at 76°C, on the contrary for Tr.B and To.B by increasing temperature, the removal percentage of those dyes decrease. The [email protected] will be more efficient for removal of Br.G from hot wastewater industries. For Br.G, elevation of temperature makes increasing for the mobility of the large dye ions. Furthermore, increasing the temperature may produce a swelling effect within the internal structure of [email protected] enabling the large dyes to penetrate further (Mckay et el., 1982), so it makes a change for pore-geometry of the sorbent. In Tr.B which has a higher molecular weight than others, so it cannot enter the pores of the sorbent.
Thermodynamic behavior of sorption of Br.G, Tr.B and To.B dyes on [email protected] was studied and thermodynamic parameters were calculated using the following equations:
Where Kc is the equilibrium constant of adsorption, T is the temperature (K) and R is the gas constant. Plots of ln K versus 1/T were linear (R2 = 0.753, 0.929 and 0.953) and the numerical values of enthalpy (?H°) and entropy (?S°) were obtained from the slope and the intercept (Fig.3b). For extraction of Br.G, Tr.B and To.B dyes, respectively. The values of thermodynamic parameters are presented in Table 6. The change in free energy (?G) can be calculated from the relation:. Negative values of ?G° represent spontaneous adsorption process and exothermic in nature. Decreasing negativity of (?G°) values indicate that movement of molecules is less freedom and adsorption process is less spontaneous (Dahri et el., 2017) with increase temperature as in adsorption of To.B and Tr.B. also having ?G° between ( means adsorption of Br.G, To.B and Tr.B onto [email protected] is a physisorption process (Chieng et el., 2015) . Positive value of ?H° (56.06 KJ/mol) indicate that the reaction is endothermic for Br.G only, besides its values higher than 8 KJ/mol means adsorption of Br.G is a physisorption type (Nandi et el., 2009; Rehman et el., 2013).This theory supported by increasing of amount of dye adsorbed by increasing temperature and this totally different from To.B and Tr.B which have (?H°=-0.077 and -14.84 KJ/mol) means that the reaction is exothermic as with increasing temperature amount of dyes adsorbed decrease. ?S° values were negative in To.B and Tr.B (?S°=-0.04,-31.8 KJ/mol K) means To.B more restricted to the surface than Tr.B (decrease randomness) compared to a positive value in Br.G (?S°= 0.21KJ/mol K) means the increasing of randomness at the interface between solid and solution (increase freedom of adsorbed species) (Purkait et el., 2007; Selvam et el., 2008).
We collected different sample of water as laundry water, tap water, Nile water and waste water. A 25 ml aliquot of water sample was spiked with different amounts of tests dyes. The solutions were shacked for 30 min at pH 7, the remaining concentration of dyes in the supernatant solution was determined. The average removal percentage of dyes from the samples was in the range of 82-95%.this results prove that [email protected] has a good efficiency for sorption of Br.G, To.B and Tr.B from Nile water. The average value of RSD% was found to be 1.7-4.1% (n = 6). Which is considered as a relevant value (less than 10%) for real samples. The obtained data conferred susceptible accuracy of the developed method based on the satisfactory values of RSD%.
Schiff’s base vanillin thiourea [email protected] was used as an adsorbent for removal of Br.G, To.B and Tr.B dyes. Batch mode was carried out at different concentration, different pH, different temperature and different time. The mount of dye adsorbed increase with increase concentration at pH 3-11 at equilibrium time 60 min for Br.G and To.B and 15 min for Tr.B. for kinetic adsorption of dyes, the pseudo second order was dominated with half-life time (t1/2) 0.30-.050 min for 3dyes. In isothermal studies, the adsorption data found the best fit for models as follows: Langmuir ? Freundlich ? Dubinin–Radushkevich. [email protected] has a dual nature, it can be endothermic for Br.G or exothermic for To.B and Tr.B, also there is a decrease in randomness for Br.G and increase in randomness for To.B and Tr.B at the interface between solid and solution. There is a favorable spontaneous reaction for Br.G, To.B and Tr.B, all of this based on the ?H°, ?S°and ?G° values.