The Synthesis and Characterization of Nano Composites of CdO and Its Applications for the Treatment of Simulated Dye Wastewater

The current study emphasizes the fabrications of Cadmium Oxide by extremity up approach adopting co-precipitation procedure. The surface morphology of fabricated Nano composites cadmium oxide was analyzed by Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microcopy (SEM) techniques. The treatment of simulated dyes wastewater was carried out by adsorption method using CdO Nano composites. In addition Malachite Green Oxalate (MGO) was selected as a model replicated system of dye wastewater, to explore the potential practicability for the elimination of the toxic dye. The adsorption experiments were heralded under the optimized conditions like adsorbent dosage, dye concentration and temperature. The acceptability of adsorption progression was estimated by proceeding adsorption models like Freundlich, Langmuir and D-R (Dubinin–Radushkevich). The values of R 2 show that Freundlich model is the best fitted model. The thermodynamic study was conducted to determine the values of free energy (∆G°), entropy (∆S°) and enthalpy (∆H°) change of the system. Adsorption Kinetic was also studied by Boyd’s model. The results demonstrated that adsorption efficiency was found to be 93% for Cadmium Oxidedye-Nano composites systems. The present model system can be employed on industrial scale as a single step process for the removal of dye pollutants and thus it could provide a new raised area for waste minimization. Original Research Article Atiya Firdous and Hameed; ACSJ, 13(1): 1-10, 2016; Article no.ACSJ.23799 2


INTRODUCTION
Nanotechnology, is the statistics and sculpture of deploying matter at the Nano scale (1-100 nm), offers the potential of unique nanomaterial's for the comportment of surface water, groundwater and wastewater tainted by toxic metal ions, organic and inorganic solutes and microorganisms [1]. Due to their inimitable activity toward contaminants many Nano materials are under active research and advancement for use in the treatment of water [2]. Environmental pollution is one of the scorching issues of the today's world [3]. Pollution not only causes environmental vagaries but also causes dissimilar illnesses. Textile seepage is a major contributor of water pollution [4]. The dumping of dyes into getting water reasons reimbursements to the atmosphere and effect bionetwork [5].
Dyes are festooned, ionizing and aromatic organic composites which spectacle and attraction towards the substrate to which it is being pragmatic. Their erections have aryl rings which delocalized electron system. These arrangements are said to be accountable for the absorption of electromagnetic radiation that has unsettled wavelengths, based upon the energy of the electron clouds [6]. The amputations of dyes have been conceded out by different methods: coagulation, chemical oxidation, membrane separation, electrochemical, biological and adsorption processes [7]. In the present studies adsorption was implemented by using Nano particles which are interim as active adsorbent [8].
In the contemporaneous study CdO was synthesized by cadmium chloride by implementing sol gel method. They have high surface reactivity and adsorption capacity to remove dyes from the simulated waste water system [9]. The exclusion of Malachite green dye (MGO) dyes was carried out using CdO nanoparticles by implementing adsorption method. Adsorption experiments were heralded at the optimized amount of adsorbent, contact time, concentration of adsorbate and temperature. Experimental data showed that CdO nanoparticles can effectively remove more than 93% of the dye from the aqueous solution. The adsorption isotherms like Langmiur, Freundich and Dubinin-Radushkevich were employed and the values of respective constants were calculated to estimate the adsorption characteristics [10]. Various thermodynamic parameters such as the Gibbs free energy (ΔG°), enthalpy (ΔH°), and entropy (ΔS°) change were also studied. Pseudo-second order models were used to describe the kinetics of dyes adsorption [11].
The surface morphology of adsorbent and adsorbate was determined by Fourier Transform Spectroscopy (FTIR) and Scanning Electron Microscope (SEM) techniques. The measurement was studied to explore the potential achievability for the removal of (MGO) dye [12].

MATERIALS AND METHODS
The removal of dye was carried out by developing simulated dye system for this purpose MGO was used for the removal studies. The cadmium chloride [CdCl 2 .6H 2 O] and sodium hydroxide were selected to prepare their Nano particles and utilized for the removal of respective dyes. All chemicals were analytical grade and customs without further purification. The solutions were prepared with deionize distilled water. Malachite green oxalate (MGO) (C.I. # 42000) was used with molecular weight 927.02gm/mol and molar extinction coefficient is found to be 148900 M -1 cm -1 [13].

Preparation of Dye Solutions
The 500 mg/L solution of MGO dye was prepared and its λ max was recorded by UV-visible spectrophotometer (T80 UV/VIS Spectrophotometer). The working standards were prepared by diluting stock solution to the desired concentrations [14].

Preparation of Nanoparticles
CdO nanoparticles were prepared by dissolving 100 gm of CdCl 2 .5H 2 O in 500 ml distilled water. The prepared solution was added to 1 M NaOH. Both solutions were mixed and the mixture was stirred for 8 hours on shaking incubator at 200 rpm at temperature 30°C then suspended slurry was primed. The resulting solution was evaporated to parchedness by adopting evaporation method after that the content were oven dried at 500°C and CdO particles were prepared and they stored in desiccators for further use.

SURFACE MORPHOLOGY OF CADMIUM OXIDE NANO PARTICLES
The surface morphology of synthesized Nano composite was inspected by FTIR and SEM techniques.

FTIR Analysis
The presence of strong FTIR interactions are confirmed by the FTIR spectrum in the wavelength region of 389-390 nm cm

Scanning Electron Microscopy (SEM) Analysis
The surface morphology of synthesized CdO Nano composites was studied by SEM technique. It was observed that the sizes were about 500 nm range.
The empty sites present on the surface of CdO provide active sites for the adsorption of dye molecules. After adsorption empty spaces were filled by dye molecules that were adsorbed on the surface of CdO which appears as shown in the Fig. 2 [16].

Batch Adsorption Experiments
Adsorption studies were accompanied by the batch technique. Batch experiments were carried out to determine the adsorption isotherms. The flasks were traumatized at a perpetual rate, permitting sufficient time for adsorption equilibrium. It was expected that the functional shaking speed allows all the surface area to come in contact with the dye over the progression of the tests. All experiments were approved out in duplicate and the average value was used for additional calculation. The possessions of various parameters on the rate of adsorption process were perceived by varying contact time, adsorbent concentration and temperature of the solution. The solution volume was kept constant.

Effect of Amount of Adsorbent
The % removal of dye onto the adsorbent as a function of adsorbent dosage is shown in Fig. 3. It was observed that the adsorption efficiency increased from 35 -93% for CdO. As the adsorbent dose increases from 0.1 to 0.8 g the amount of adsorbent was increase due to the availability of active sites. Hence percentage removal was also upturns [17].

Effect of Contact Time
Adsorption equilibrium was achieved after certain time interlude. The process adsorption of dye on the surface of adsorbent was increased by the intensification in contact time and removal effectiveness reached to an optimum value when the equilibrium between both adsorbate and adsorbent was achieved [18]. The maximum adsorption capacity of MGO for CdO was found to be 91.40% at 80min as shown in Fig. 4.

Adsorption Isotherms
The study of equilibrium parameters between adsorbate and adsorbent is identified as adsorption isotherm. These isotherms express us about the effectiveness of adsorbent as well adsorption mechanism. Hence, enable to make a correlate the equilibrium data by using theoretical or empirical equation which was helpful for the prediction and interpretation of adsorption mechanism [19]. There are several isotherm equations available for analyzing experimental adsorption mechanism, the most common being Langmuir, Freundlich and Dubini Radushkevich (D-R) models. These models were thus commissioned to fit our investigational data [20].

Freundlich Adsorption Isotherms
The empirical equation used to describe heterogeneous system is given by the Freundlich isotherm. It is articulated as: Where X/m is the amount adsorbed per unit mass of the adsorbent, Ce is the equilibrium concentration and 1/n and K are Freundlich constants. These parameters give a measure of adsorption capacity of the adsorbent and intensity of adsorption, respectively [21]. It is observed that the process of adsorption is less favorable at high temperatures because the decreasing value of K with the rise in temperature indicates that adsorption affinity of dye decreases with the rise in temperature.

Langmuir Adsorption Isotherm
A finite number of active sites which are homogeneously distributed over the surface of the adsorbent were the basis of the Langmuir isotherm model. This model also states that, there is no interaction between adsorbed molecules and have the same affinity for adsorption of a mono layer adsorption process [22]. The Langmuir isotherm is expressed as Ce X/m = 1 KVm + Ce Vm

D-R adsorption Isotherm
The adsorption data were applied on Dubinin-Radushkevich (D-R) isotherm equation, which is represented in the linear form as:

= ln −
Where, X m is the monolayer capacity of adsorbent, K is a constant related to adsorption energy; ε is adsorption potential, which can be calculated as: Where R is a gas constant, T is absolute temperature; X/m and C e have usual meaning as described in the above mentioned equation. The D-R plots of ln (X m ) Vs ε 2 were obtained at various temperatures and the values of K and X m are given in Table 1

Thermodynamic Parameter
The values of thermodynamic parameters ∆G°, ∆H° and ∆S° were calculated from the distribution constant K D . They were calculated from the plot of ln K D with the reciprocal of temperature (1/T) by using the following equations

Adsorption Kinetics
The study of adsorption kinetics provides the information regarding the rate of adsorption and feasibility of adsorption process. The experimental data were applied to examine the kinetics by Lagergren's pseudo first order and Ho-Mckay's pseudo-second order models [28] as represented: The values of rate constant and R 2 for the MGO sorption on CdO systems are represented in above table. The results show that the system follows the pseudo second order kinetics.
Where k id is the intra-particle diffusion rate constant which was obtained from the slope of the linearized plot of qt verses t 1/2 . The intercept gives an idea of the thickness of the boundary layer i.e. the larger the intercept; the greater will be the boundary layer effect .
The positive values of slope shows controlled adsorption process [29].

RESULTS AND DISCUSSION
In the contemporaneous study, CdO was used as an easily prepared and most nominal adsorbent for the removal of reactive dye including Malachite green oxalate dye (MGO) dye. CdO nanoparticles was synthesized by adopting sol-gel method, CdO nps have high surface area, hygroscopic in nature, porous and amorphous powder. Adsorption, thermodynamic and kinetics studies were proceeded to determine the validity of progression. The adsorption experiments were run under the optimized conditions of amount of adsorbent, stay time, initial concentration and at different temperatures. The adsorption models like: Freundlich, D-R and Langmuir adsorption isotherm models were applied for the mathematical description of the adsorption equilibrium data. Adsorption of (MGO) dye on CdO nps follows Freundlich isotherm mode. Thermodynamic parameters, Gibbs free energy, enthalpy and entropy changes shows that the adsorption of Malachite green Oxalate (MGO) dye onto CdO was spontaneous and exothermic process. The kinetic data showed that the adsorption of (MGO) dye onto CdO nps followed the pseudo second order.

CONCLUSION
It was estimated that inexpensive, easily prepared and effective CdO nps could be used in place of commercial adsorbents for the elimination of dyes from aqueous solution. Minute amount of CdO nps obligatory for the removal of dyes, Unquestionably CdO adsorbents offer a lot of promising benefits in the prospect.