Scientific paper
Kinetics and Thermodynamics of Adsorption of Fuchsin Acid on Nickel Oxide Nanoparticles
Babak Samiey and Saeid Farhadi
Department of Chemistry, Faculty of Science, Lorestan University, 68137-17133, Khoramabad, Iran * Corresponding author: E-mail: babsamiey@yahoo.com
Received: 18-04-2013
Abstract
NiO nanoparticle was used to adsorb fuchsin acid (FA) from aqueous solution. In the used concentration range of FA, its adsorption isotherms on NiO nanoparticles were three-region. NiO nanoparticle was prepared via the thermal decomposition of the tris(ethylenediamine)Ni(II) nitrate complex as a new precursor. In this work, effects of temperature, concentration, particle size, shaking rate, contact time, pH of the solution were investigated. Adsorption process was exothermic in the first and second regions and endothermic in the third region. Adsorption kinetics was studied by a number of equations including the KASRA, pseudo-first-order, pseudo-second-order, Elovich, Avrami and pore-diffusion equations. Adsorption acceleration and adsorption velocity values of this process were obtained by the KASRA equation and it was shown that with increase in FA concentration or temperature or shaking rate, initial adsorption velocity values of process increase.
Keywords: Adsorption; Fuchsin acid; NiO nanoparticle; KASRA model
1. Introduction
Large amount of colored effluent originated from different dye manufacturing units are charged into in the ecosystem and because of their toxicity and mutagenicity1'2 cause environmental danger. Dyes are used in different industries such as paper, plastics, leather, pharmaceutical, food, cosmetics, dyestuffs, textiles, etc. In general, the dyes chosen by industries have good stability and fastness. Once it enters water body as a pollutant, the destruction of these dyes poses a problem. Various chemical, physical and biological treatment methods have developed for the removal of dyes from aqueous solutions, including adsorption,3 membrane filtration,4 oxidation with ozone,5 ozonation,6 photocatalytic degradation,7 and reverse osmosis8 and biodegradation.9 The degradation by-products of organic dyes such as synthetic azo-dyes have dangerous impacts on the environment. Fuchsin acid (FA), an acid dye, is used as a copper corrosion inhibitor,10 biological stains, sometimes as a and for dyeing textiles11 and formation of organic-inorganic hybrid na-nocomposite.12 Chemical structure of FA is shown in Figure 1.
Adsorption, due to its low cost, simplicity of design and ease of operation is a reliable treatment technique.
H2N S03
Figure 1: Molecular structure of fuchsin acid.
Nanoparticle research is an area of intense scientific interest due to a wide variety of potential applications in different fields of science. The interesting and sometimes unexpected properties of nanoparticles are largely due to the large surface area of the material, which dominates the contributions made by the small bulk of the material. In recent years, there has been emphasis on the application of nanoparticles as efficient adsorbents. A number of these materials such as NiO,13 gold,14 chitosan,15 multiwall carbon nanotube/iron oxide magnetic composite,16 mag-hemite,17 MgO,18 TiO2,19 clay,20 Multi-walled carbon na-
notubes,21 hydroxyapatite,22 manganese dioxide,23 alumina24 and magnesium silicate25 nanoparticles have been tested for the adsorption of other compounds. It has been proven that they are effective adsorbents for the removal of dyes and metallic pollutants from aqueous solutions. In this study, we used nickel oxide nanoparticle as adsorbent. Nickel oxide (NiO) is one of the most important transition metal oxides due to its applications in diverse fields, including catalysis,26 fuel cell electrodes,27 gas sensors,28 battery cathodes,29 magnetic materials30 and smart windows.31 NiO nanoparticles show a ferromagnetic behavior and could be a promising photocatalytic material.32
The aim of this work is to estimate adsorption capacity of NiO nanoparticles for FA. These particles showed the highest adsorption capacities of FA compared to many other adsorbents. In order to investigate the mechanism of adsorption process, in addition to conventional kinetic and thermodynamic equations, a new kinetic model was introduced. Furthermore, an optimization of the process was attempted through tuning a series of parameters such as size of NiO nanoparticles, dye concentration, temperature and initial pH values.
250 °C J		J	Ni » Ni jI Nt
100 °c J		Ü	i  A/
600 °C		> , ,-u , JU	
26 (degree)
Figure 2: XRD patterns for [Ni(en)3](NO3)2 decomposed at selected temperatures.
2. Materials and Methods
2. 1. Materials
Ni(NO3)2.6H2O, ethylenediamine, ethanol (99.9%), ether, HCl and fuchsin acid were purchased from Merck. All chemicals were used without further purification.
2. 2. Preparation of NiO nanoparticles
An aqueous solution of Ni(NO3)2.6H2O is treated with a slight stoichiometric excess of ethylenediamine (en) and the resultant deep-purple [Ni(en)3](NO3)2 was precipitated by slow addition of ethanol. After standing for several hours in the cold, the crystals were filtered on a Buchner funnel, washed with ethanol, ether and dried in the open air at 50 °C. The complex was decomposed at 250, 400 and 600 °C. In the XRD spectra of the sample prepared in 250 °C, peaks attributable to metallic nickel are observed, Figure 2. The above protocol was described by Farhadi et al.32
2. 3. Characterization of NiO Nanoparticles
X-ray powder diffraction (XRD) patterns were recorded using a Rigaku D-max C III, X-ray diffractometer using Ni-filtered Cu K a radiation (X = 1.5406 A) to determine the phases present in the decomposed samples. The average sizes of NiO particles were estimated to be about 25.1, 13.1 and 30.3 nm at 250, 400 and 600 °C respectively, by Debye-Scherrer formula:33
D XRD ~
0.9À ßcosff
where Dxrd is the average crystalline size, X is the wavelength of Cu K a, ¡3 is the full width at half maximum (FWHM) of the diffraction peak and 6 is the Bragg's angle. Increasing the calcination temperature up to 600 °C causes conglomeration of NiO nanoparticles which increases their size.34 Infrared spectra were recorded on a Shimadzu system FTIR-8400S spectrophotometer using KBr pellets.
2. 4. Adsorption Experiments
In adsorption experiments, 10 ml of FA solution of different initial concentrations was transferred to a series of 15-ml glass stoppered bottles, each containing 0.0025 g of NiO sample. The solutions were shaken at 80 rpm in a temperature controlled shaking water bath (Fater electronic Co., Persian Gulf model) at 308, 318 and 328 K within ±0.1 K for 20 h to reach equilibrium under experimental conditions. The initial concentrations of FA were in the concentration range of 1.9 x 10-6 -9.3 x 10-5 M. After adsorption, the concentration of FA in the residual solutions was determined by photometry (UV-Vis 160, Shimadzu) at its Xmax value in these solutions (544 nm). The adsorption capacity of FA on the adsorbent, qe (mg g-1), was calculated by a mass balance relation as follows
<h =
1 OOOiv
(2)
(1)
where c0 and ce are the initial and equilibrium concentrations of adsorbate (M) respectively, V is the volume of so-
lution (ml), w is the weight of the used adsorbent (g) and M is the molecular weight of adsórbate (mg mol1). In adsorption kinetic experiments, 10 ml of FA aqueous solution in the concentration range of 2.3 x 10-5 -4.6 x 10-4 M was transferred to a series of glass stoppered bottles, each containing 0.0025 g of NiO nanoparticle sample and solutions were shaken at 40, 80 and 120 rpm and different temperatures. At predetermined times, the contents of FA in the solutions were determined by photometry at its Amax value. In these series of experiments, qe and ce in relation (2) are replaced by qt (adsorption capacity at time t) and ct (concentration of adsorbate at time t), respectively.
In this work, the results are studied by "adsorption isotherm regional analysis model" or abbreviated as ARI-AN model.35 This model is introduced for studying adsorption isotherms up to four regions. In ARIAN model which is explained briefly, it is assumed that region 1 obeys Henry's law:
q. = Kce
(3)
where K is the binding constant of adsorbate on the surface and adsorption increases linearly with concentration. Region 2 starts from the starting second region concentration (abbreviated as ssc) point and when adsorbate is a surfactant, is specially named the hemimicelle concentration (abbreviated as hmc) point. This region includes only monolayer surface aggregate formation and can be studied by an appropriate isotherm such as the Langmuir, Temkin, Dubini-Radushkevich equations, etc. The Langmuir equation36 in linearized form is given as
1

(4)
where K is the Langmuir adsorption constant and qmax is the monolayer capacity. The Temkin equation36 is represented by
9. =c, ln(c2c,)
(5)
where c1 is a constant and c2 is adsorption equilibrium constant.
The Dubinin-Radushkevich equation38,39 is used to estimate the characteristic porosity of the adsorbent and the apparent energy of adsorption. In this work, this equation is used for all regions. The equation is given by
(
4D - bD
RT\n 1+—
I c.
\V
(6)
where BD is related to the free energy of adsorption per mole of adsorbate (mol2 J-2) and qD is the theoretical mo-nolayer saturation capacity. The apparent energy of adsorption from Dubinin-Radushkevich isotherm, E, (J mol-1) can be computed using the relationship
E = ■
(2 Bd)i
(7)
In region 3, new surface aggregates or admicelles and new surface clusters (in the case of surfactants) form. The starting third region concentration (abbreviated as stc) point defines beginning this region. These data are analyzed by the bilayer isotherm equation (Eq. 8) and those derived from it (Eqs. 9 and 10).35 In the third region, assuming adsorption occurs mostly in the first and second layer, we have

(8)
where qmon and qe are the monolayer and equilibrium adsorption capacity, respectively. Ksa and x are the adsorption equilibrium constants of adsorbate molecules in surface aggregates and in all layers above first one, respectively. If adsorbate molecules are adsorbed mostly on the first layer, equation (8) can be written as
I
■vc;
o K
H man Hi
(9)
which is used for low bilayer coverage (abbreviated as LBC) and if the adsorption process is monolayer, equation (8) can be reduced to
I
mon ^ sa
(10)
where equation (10) is a Langmuir-type equation and region 4 starts from maximum adsorption capacity and is as plateau or curve goes down.
3. Results and Discussion
3. 1. Adsorption Isotherm Modeling
Analysis of isotherm data is important for measuring the adsorption capacity of the adsorbent, which is one of the main parameters required for the design of an adsorption system. We used NiO nanoparticles formed at 400 °C as adsorbent because of its small size compared those formed at 250 and 600 °C. The qe uptakes of FA by NiO nanoparticle (formed at 400 °C) in the initial FA concentration range of 2.3 x 10-5 -4.6 x 10-4 M in neutral aqueous solutions at 308, 318 and 328 K are illustrated in Figure 3.
Data were analyzed by ARIAN model and it was shown that adsorption isotherms of FA by NiO nanopartic-le are three-region in the used concentration range of FA. By analysis of data of the first region by Henry's law the binding constant values of adsorption process in this region were obtained, Table 1, and using them AH and AS values are -10.2 kJ mol-1 and 108.2 J mol-1 K-1, respectively.
Table 1. The ssc and qssc values and parameters obtained from the Henry's law and Dubinin-Radushkevich equation for adsorption of FA on NiO nanoparticles (formed at 400 °C) in the first region at 308-328 K.
T	ssc			Henry's law		Dubinin-Radushkevich	
(K)	(M)	(mg g-1)	K	A	R2	ln ^D	E R2
308	8.41 x 10-6	195.3	2.48 x 107	-4.8	0.993	12.3	8.1 0.999
318	1.74 x 10-5	281.7	2.14 x 107	5.7	0.990	9.6	10.5 0.999
328	1.64 x 10-5	284.1	1.94 x 107	6.8	0.987	10.9	10.2 0.990
Dimensions of qD and A are in mg g 1 and those of K and E are in mg g 1 M 1 and kJ mol respectively. Henry's law for experimental data is as qe = Kce + A. Initial FA concentrations corresponding to ssc are 9.2 X 10-5 1.4 X 10-4 and 1.4 X 10-4 M at 308, 318 and 328 K, respectively.
Figure 3: qe versus ce for adsorption of FA on NiO nanoparticles (formed at 400 °C) at different temperatures.
Data of the second region were fitted in the Temkin equation and binding constant values and the related thermodynamic parameters were obtained by this equation, Table 2.
AH and AS values of process in this region are -183.0 kJ mol-1 and -482.2 J mol-1 K-1, respectively. Adsorption of too much FA molecules on the surface of NiO results in formation of new FA surface aggregates on its surface. This results in the formation of the third region.
The third region starts in qe values 465.5, 561.7 and 812.7 mg g-1 and at 308, 318 and 328 K, respectively. In the third region, binding constant values were calculated by the Langmuir-like equation, Table 3, and AH and AS values of process in this region are 46.1 kJ mol-1 and 228.5 J mol-1 K-1, respectively.
As reported before,32 the specific surface area of the NiO nanoparticles is 84.5 m2 g-1 and this results in their high qmon values obtained from the Langmuir-type equation which are 1006.1-1379.3 mg g-1 at different temperatures, Table 3.
Adsorption capacity of NiO nanoparticle for FA is very high and in the FA used concentration range we could not obtain maximum experimental adsorption capacity of NiO nanoparticle for FA molecules and thus we did not observe the fourth region for these experiments. Thus, for comparative purposes, we used qmon values calculated
from Langmuir-like in the third region. The values,
/.v.'."
which are proportional to the relative magnitude of the first region, are about 0.14 at 308, 318 and 328 K, Tables
Table 2. Parameters obtained from the Temkin, Langmuir and Dubinin-Radushkevich isotherms for adsorption of FA on NiO nanoparticles (formed at 400 °C) in the second region at 308-328 K.
T		Temkin			Langmuir		Dubinin-Radushkevich	
(K)	c1	c1	R2	K	qmax	R2	ln qD	E R2
308	123.9	547035	0.993	67742	529.1	0.988	7.8	13.5 0.992
318	4552.9	118550	0.998	714	23474.2	0.992	11.1	8.8 0.992
328	6692.6	94467	0.988	6907	2272.7	0.989	12.4	8.2 0.992
Dimension of c1, qmax and qD is in mg g '. Dimensions of c2, K and E are in M1, M 1 and kJ mol ', respectively.
Table 3. The stc and qstc values and parameters obtained from the Langmuir-like and Dubinin-Radushkevich isotherms for adsorption of FA on NiO nanoparticles (formed at 400 °C) in the third region at 308-328 K.
T	stc	qstc		Langmuir-type		Dubinin-Radushkevich	
(K)	(M)	(mg g-1)	Ksa	qmon	R2	ln qD	E R2
308	7.67 x 10-5	465.5	11094	1006.1	0.983	8.5	11.5 0.989
318	3.56 x 10-5	561.7	31414	1071.8	0.989	8.3	13.9 0.976
328	4.32 x 10-5	812.7	32955	1379.3	0.989	8.9	14.0 0.993
Dimensions qmon and qD are in mg g 1. Dimensions of Ksa and E are in M 1 and kJ mol 1, respectively. Initial FA concentrations corresponding to stc are 2.8 X 10-4, 2.8 X 10-4 and 3.9 X 10-4 M at 308, 318 and 328 K, respectively.
1 and 3. The
values, which are proportional to
the relative magnitude of the second region, are about 0.32, 0.39 and 0.45 at 308, 318 and 328 K, Tables 1, 2 and 3.
As given in Tables 1, 2 and 3, binding constant values of FA to the surface decrease from the first to the third region because the negatively charged surface increases progressively with adsorption of a large number of FA molecules. But, due to hydrophobic interactions between adsorbed FA molecules the process in this region is endothermic and the relative magnitude of this region is 0.54, 0.47 and 0.41 at 308, 318 and 328 K respectively.
NiO nanoparticle shows amphoteric behavior in aqueous media. The point of zero charge (pzc) of NiO na-noparticle, i.e. the point at which the surface charge is neutral, is 10.540 and for lower pH values, surface of NiO nanoparticle is in the protonated form (NiOH+2) This study was carried out in neutral aqueous solutions. As seen in Figure 4, peak of hydroxyl groups at 3558.42 cm1 in FTIR spectrum of NiO shifts to 3504.42 cm1 in FTIR spectrum of FA-adsorbed NiO.
This is due to electrostatic interaction of negatively charged FA molecules with -OH and - OH+ surface groups of NiO surface. This interaction has chemical nature and apparent energy of adsorption from Dubinin-Ra-
dushkevich isotherm, is in the range of 8.2-14.0 kJ mol-1 at different temperatures and regions, Tables 1, 2 and 3. Our tests showed that NiO nanoparticle dissolves in acidic media and thus FA uptake (adsorbed on initially 0.0025 g NiO added as adsorbent in 10-ml samples) decreases, Figure 5, and the NiO used as adsorbent completely dissolves in 1M HCl.
3. 2. Adsorption Kinetic Equations
In this work, a new model and a new equation are introduced for study of adsorption kinetics. The proposed model is named "Kinetics of Adsorption Study in the Regions with Constant Adsorption Acceleration" or abbreviated as KASRA model. KASRA model is based on the following assumptions: (1) each time range that adsorption acceleration in it is constant, is named a "region", (2) there are two regions before attaining plateau region41 and (3) the boundaries between the first and second regions and the second and third (plateau) regions are named starting second region (abbreviated as ssr) and kinetics of adsorption termination (abbreviated as kat) points, respectively and are determined by the KASRA equation, Figure 6.
It is good to say that KASRA is a Persian word meaning king. To derive KASRA equation, a region with constant acceleration of adsorption is considered and we can write:
I,
dt
(11)
Figure 4: FTIR spectra of (a) [Ni(en)3](NO3)2 decomposed at 400 °C and (b) its FA-adsorbed form.
where ai is acceleration of adsorption kinetics in the ith region and i = 1-3. Because of decrease in adsorbent concentration during adsorption process ai values are negative in sign. In these cases, adsorption kinetics profile in the related region is concave downward. But, in some cases, the first region of adsorption kinetics diagram is concave upward or diagram in this region may be linear42 and thus according to KASRA model, the related a1 values are positive or zero, respectively. In such cases, for example
Figure 5: Adsorbed FA versus ce for adsorption of FA on NiO na-noparticles (formed at 400 °C) at 318 K in different concentrations of HCl.
Figure 6: Schematic diagram of adsorption kinetics using KASRA model. Here, aj < 0 and ♦,▲ ■ symbols refer to the first, second and third regions, respectively.
multilayer adsorption of colloidal gold particles on silica,42 or adsorption of some surfactants in concentrations above their cmc,43 initial adsorption of adsorbate molecules facilitates adsorption of other ones and interaction between them acts as a driving force and increases the number of adsorbate molecules and thus a1 for this case is written as
«i = «i, + au.
(12)
where kx is the pseudo-first-order rate constant (min1) that relates to the amount of adsorbed FA and qe x denotes the calculated equilibrium adsorption capacity.
The pseudo-second-order equation48 based on adsorption equilibrium capacity may is expressed in the form
1 t
It k2ll,2 <?,,:
(17)
where a1s and a1a are surface site and adsorbate-induced adsorption accelerations in the first region, respectively. If |a1s| <a1a then a1 > 0 and if |a1s| = a1a then a1 = 0. Similar situation is seen in the isothermal crystallization process in semicrystalline polymers44-46 that is divided to primary and secondary nucleation processes and in the first times of these processes their plots are concave upward or linear. Finally, if |a1s| >>a1a then a1 « a1s <0.
After integration and applying boundary condition vt = v0i at t = t0i, equation (11) becomes
dq, dt
(13)
where v0i and t0i are the velocity and time values in the beginning ith region, respectively and vt is the adsorption velocity in the ith region at time t. By integration form equation (13) and applying boundary condition qt = qti at t = t0i, we have
] 2 , , 1 2 q,=- ar + K; - a,tw )t + q0i-- a/ol
(14)
where q0i is the qt value in the beginning ith region. q02 and t02 are the coordinates of ssr point. Equation (14) is named "Kinetics of_Adsorption Study in the Regions with Constant Adsorption Acceleration" or abbreviated as KASRA equation. This equation can be abbreviated as
q, = At2 +Bt + C
(15)
where k2 is the pseudo-second-order rate constant (g mg1 min1) that relates to the amount of FA adsorbed by the solid phase and qe,2 denotes the calculated equilibrium adsorption capacity. The rate constants obtained from the pseudo-first-order and pseudo-second-order equations change with increase in temperature in a disorder man-ner.49,50 It was tried to derive pseudo-first-order equation51 and was concluded that pseudo-first-order rate constant, k1, increases with increase in initial adsorbate concentration, c0. But, opposite to this conclusion, experimental re-sults52-55 show that k1 values vary irregularly with increase in c0. These two models were compared quantitatively by Aqt, normalized standard deviations, in relation to the experimental and calculated values of qt,
Aq, = lOOx
/.cxp tftxal t. CÎ
(«-1)
(18)
where qt exp and qtcal are experimental and calculated values of qt, respectively.
The Elovich equation56 is expressed as q, --^\n(aß) + ~\r\t
(19)
where a is the initial adsorption rate (mg g1 min1). ¡3 is the adsorption constant (g mg1) related to the surface coverage and is the required mass of adsorbent for adsorption of 1 mg of adsobate. The Avrami equation57 is written as:

(20)
where

hi
n	1 .3
C= i/o, --'Vo,
- (vw - )tal. The KASRA equation and KASRA mo-ciei were miroauced by one of the authors, Babak Samiey. Finally, plateau (third) region begins at the equilibrium time, te and equilibrium adsorption capacity, qe which are coordinates of kat point. In this region, v03 = a3 = 0, q03 = qe and t03 = te and equation (14) reduces to qt = qe.
Also in this study, data were analyzed by a number of equations. The pseudo-first-order equation47 is written as follows

(16)
where kAV is the Avrami rate constant, and nAV the Avrami exponent.
The pore-diffusion equation58 is given as:
<7, =V' +/
(21)
where I is proportional to the boundary layer thickness and kmf is the rate constant for intraparticle diffusion.
3. 3. Effects of Temperature and FA Concentration
The effect of contact time, sizes of NiO particles and initial FA concentration on the adsorption of FA onto NiO
nanoparticles (formed at 400 °C), at 308, 318 and 328 K were studied in the FA concentration range of 6.9 x 10-5 -1.9 x 10-4 M, Figures 7(a)-7(c).
Adsorption experimental data of FA onto NiO was investigated using pseudo-first-order and pseudo-second-order kinetic equations. Data were fitted in the pseudo-second-order better than the pseudo-first-order equation, Table 4. As seen in Table 4, in each certain concentration, k1 and k2 values increase with increase in temperature, but in each temperature their values change irregularly with increase in FA concentration and similarly qe 1 and qe 2 vary irregularly with increase in temperature of FA concentration. It can be explained with respect to the used initial FA concentrations are in the second region (0.069 and 0.184 mM) and third region (0.298 mM FA) of the related adsorption isotherms (from footnotes of Tables 1 and 3) and we know that the process is exothermic in the first and second regions and endothermic in the third region. On the other hand, increase in temperature enhances the rate of transferring FA to surface of adsorbent. Competition of these two effects in 0.069 and 0.184 mM FA and their cooperation in 0.298 mM FA results in the observed trend of changes of k1, k2, qe 1 and qe 2 values.
As given in Table 4, in each certain concentration a values, from Eq. (19), increase with increase in temperature and in each temperature their values increase or keep constant with increase in FA concentration.
As seen in Table 5, the Avrami parameters, kAV and nAV values, change irregularly with increase in both temperature and FA concentration.
Adsorption kinetics may be controlled by film diffusion and intraparticle diffusion steps.59 It is expected that film diffusion (external mass transfer resistance) in the aqueous phase is negligible, which is reasonable in wellshaken adsorption systems. As given in Table 5, the intercepts of adsorption kinetics profiles of qt versus t0.5 from
160 120
I1 ao
40
o
400 300
|> zoo
100 0
(a)			a	a	a	a n	□ □ □ o
a a	a n	□	□	d	•	•	. • • • • •
A □			•				
		*					• 303 K
D	■						
■Â »							□ 313 K
							a 323 K
							
r							
200 400 600 800 t(min)
1000 1200
(*>)	a	a a a û	a ci	£ â a □ •	S . 1
a	a	□		•	
a		□		•	
aa	n			•	
1 A			•		• 303 K
a □		•			
A □		•			□ 318 K
a □ □ •	•				a 328 K
					
					
200
400	600
t (min)
800
1000
Figure 7: qt versus t for adsorption of (a) 0.069, (b) 0.184 and (c) 0.298 mM FA on NiO nanoparticles (formed at 400 °C) at different temperatures.
Table 4. Experimental qe values and coefficients of the pseudo-first-order, pseudo-second-order and Elovich equations for kinetics of FA adsorption on NiO nanoparticles (formed at 400 °C) from solutions at 308-328 K.
[FA ]	9e	Pseudo-first-order				Pseudo-second-order				Elovich	
(mM)	(mg g-1)	ie,1	k1 x 103	H		1e2	k2 x 105	Aq	a	ß	R2
					T=	=308 K					
0.069	127.67	130.96	4.04	20.8		158.98	2.93	11.91	2.495	0.066	0.973
0.184	360.90	644.16	1.12	4.99		1050.42	0.07	4.99	2.427	0.028	0.951
0.298	482.37	456.28	3.37	13.27		578.00	0.59	5.81	6.144	0.013	0.947
					T=	318 K					
0.069	140.43	130.28	9.34	6.19		164.02	5.42	3.93	3.773	0.380	0.959
0.184	371.72	401.72	4.86	15.87		510.99	0.96	8.92	8.657	0.031	0.977
0.298	587.63	592.78	6.14	19.25		726.22	0.97	10.95	16.193	0.012	0.987
					T=	328 K					
0.069	139.30	116.10	18.2	26.22		139.86	16.1	17.80	11.611	0.055	0.985
0.184	354.12	343.87	19.1	2.26		400.80	5.73	2.85	19.921	0.011	0.994
0.298	585.58	550.20	12.9	1.84		724.64	1.56	5.15	19.758	0.009	0.993
Dimension of qe l and qe 2 is in mg-g '. Dimensions of kl and k2 are in min 1 and g mg 1 min respectively. Dimensions of a and ¡i are in mg g-1 min-1 and g mg-1, respectively.
Table 5. Coefficients of the Avrami equation and pore-diffusion equation (the first and second regions) for kinetics of FA adsorption on NiO nanoparticles (formed at 400 °C) at 308-328 K.
[FA ]		Avrami		Pore-diffusion (1st)		Pore-diffusion (2nd)		
(mM)	kAV	nAV	R2	kdif 1	R2	kdif	I	R2
				T = 308 K				
0.069	4.12 x 10-3	0.838	0.989	5.54 -8.73	0.997	5.72	-11.51	0.996
0.184	2.86 x 10-3	1.127	0.989	10.34 -33.36	0.993	18.16	-130.05	0.994
0.298	2.94 x 10-3	0.856	0.992	20.39 -49.41	0.991	12.31	66.49	0.997
				T = 318 K				
0.069	6.90 x10-3	0.840	0.991	10.54 -22.05	0.990	4.31	40.15	0.987
0.184	6.11x 10-3	0.954	0.986	15.66 -20.59	0.999	19.77	-41.96	0.995
0.298	5.95 x 10-3	0.819	0.990	29.75 -28.59	0.995	28.90	-12.46	0.988
				T = 328 K				
0.069	1.03 x 10-2	0.624	0.979	8.18 6.55	0.953	8.82	1.74	0.998
0.184	1.57 x 10-2	0.715	0.994	27.58 11.92	0.990	1.51	163.63	0.992
0.298	9.62 x 10-3	0.862	0.992	52.11 -101.12	0.992	23.36	159.97	0.993
Dimensions of kdi, I and kAV are in mg g 1 min 0'5 , mg g 1 and min 0'5, respectively. nAV is dimensionless. Boundaries of the first and second regions are around t02 and q02 values, given in Table 7.
Table 6. Coefficients of the KASRA equation for kinetics of FA adsorption on NiO nanoparticles (formed at 400 °C) at 308-328 K.
[FA]		First	region			Second	region	
(mM)	A	B	C	R2	A	B	C	R2
				T = 308 K				
0.069	-2.44 x 10-3	0.706	1.267	0.993	-1.97 x 10-4	0.293	18.351	0.998
0.184	-9.95 x 10-4	0.800	1.034	0.996	-4.01 x 10-4	0.771	-9.325	0.996
0.298	-2.69 x 10-3	1.880	-1.740	0.996	-1.88 x 10-4	0.507	137.861	0.998
				T = 318 K				
0.069	-4.37 x 10-3	1.246	-0.886	0.999	-1.56 x 10-4	0.217	65.233	0.996
0.184	-1.30 x 10-2	2.493	2.170	0.995	-1.14 x 10-3	1.237	39.190	0.999
0.298	-4.80 x 10-2	6.180	1.494	0.995	-1.71 x 10-3	1.794	105.568	0.996
				T = 328 K				
0.069	-1.70 x 10-2	2.146	0.357	0.995	-9.82 x 10-4	0.635	36.204	0.993
0.184	-6.30 x 10-2	7.417	4.995	0.988	-1.88 x 10-3	1.154	173.973	0.992
0.298	-3.65 x 10-2	7.132	3.090	0.992	-2.38 x 10-3	1.873	217.290	0.988
Dimensions of A, B and C are in mg g 1 min 2, mg g 1 min 1 and mg g respectively.
Table 7. Experimental te, qe, t02 and q02 values and coefficients of the KASRA equation for kinetics of FA adsorption on NiO nanoparticles (formed at 400 °C) at 308-328 K.
[FA]	te	qe	t02	qo2	First	region	Second	region
(mM)	(min)	(mg g 1)	(min)	(mg g 1)	ai	V01	a2	v02
				T =	308 K			
0.069	720	127.67	120	51.60	-4.88 x 10-3	0.706	-3.94 x 10-4	0.246
0.184	960	360.90	120	82.70	-1.99 x 10-3	0.800	-8.02 x 10-4	0.675
0.298	1300	482.37	120	184.47	-5.38 x 10-3	1.880	-3.76 x 10-4	0.462
				T =	318 K			
0.069	650	140.43	120	87.77	-8.74 x 10-3	1.246	-3.12 x 10-4	0.180
0.184	540	371.72	60	107.58	-2.60 x 10-2	2.493	-2.28 x 10-3	1.100
0.298	540	587.63	60	200.46	-9.60 x 10-2	6.180	-3.42 x 10-3	1.589
				T =	328 K			
0.069	360	139.30	60	69.04	-3.40 x 10-2	2.146	-1.96 x 10-3	0.517
0.184	360	354.12	60	231.70	-0,126	7.417	-3.76 x 10-3	0.928
0.298	360	585.68	60	306.17	-7.30 x 10-2	7.132	-4.76 x 10-3	1.587
Dimensions of a1 and a2 are in mg g 1 min 2 and those of v01 and v02 are in mg g 1 min 1. In the first region, t01 and q01 values are equal to zero. qe values in each FA concentration and each temperature were shown in Table 4.
Eq. (21), for the initial steeper and second regions have negative values which suggests that the boundary-layer effect is close to minimum and diffusion of the FA molecules into the NiO nanoparticles (intraparticle diffusion) is the main rate-controlling step.59,60
Kinetics of FA adsorption on NiO nanoparticles at 308-328 K was studied by the KASRA equation which shows that there are two regions before plateau, Tables 6 and 7.
Results obtained from Table 7 are as follows:
1	- In each kinetic experiment, with increase in time, the number of surface adsorption sites and FA concentration decrease and thus the sign of adsorption acceleration, a, is negative and adsorption velocity, v, value decreases.
2	- In each certain temperature and FA concentration, v0i values decrease and a0i values become less negative from the first region to the second one. This is due to decrease in FA concentration and decrease in the number of unoccupied sites on the surface of NiO nanoparticles.
3	- Similar to a values obtained from the Elovich equation (Table 4), initial velocity values in the first region (v01), increase with increase in temperature in each
certain FA concentration or with increase in FA concentration in each temperature. This is due to similar increase in kdf values (Table 4) under above-mentioned conditions in the first region.
4 - In each region, with increase in temperature in each certain FA concentration, q02 values increase and a01 and a02 values become more negative.
3. 4. Effects of Size of Nanoparticles and Shaking Rate
Adsorption of FA on different sizes of NiO nanoparticles (formed at 250, 400 and 600 °C) in 0.184 mM FA was studied at 318 K and 80 rpm, Figure 8 and Tables 8 and 9. XRD spectra of these samples, Figure 2, showed that with increase in the temperature of NiO nanoparticles formation from 250 to 400 to 600 °C, their sizes change from 25.1 to 13.1 to 30.3 nm, respectively. As shown in Table 9, with increase in size of NiO nanoparticles from the sample formed in 400 °C compared to the sample formed at 600 °C, adsorption acceleration values of the first and second regions of them become less negative, their
Table 8. Coefficients of the KASRA equation for kinetics of adsorption of FA from 0.184 mM FA solution on NiO nanoparticles (formed at different temperatures) at 318 K and various shaking rate.
NiO formed at	A	First B	region C	R2	A	Second B	region C	R2
				At 40 rpm				
400 °C	-1.10 x 10-2	1.917	-1.013	0.996	-6.37 x 10-4	0.991	-8.507	0.994
				At 80 rpm				
250 °C	-1.39 x 10-2	4.058	-1.971	0.994	-6.51 x 10-4	0.740	197.930	0.992
400 °C	-1.30 x 10-2	2.493	2.170	0.995	-1.14 x 10-3	1.237	39.190	0.999
600 °C	-1.41 x 10-3	0.693	0.301	0.999	-1.72 x 10-4	0.332	24.296	0.998
				At 120 rpm				
400 °C	-3.10 x 10-2	3.263	0.439	0.999	-2.87 x 10-3	2.002	6.252	0.995
Dimensions of A, B and C are in mg g 1 min 2, mg g 1 min 1 and mg g 1, respectively.
Table 9. Experimental te, qe, t02 and q02 values and coefficients of the KASRA equation for kinetics of adsorption of FA from 0.184 mM FA solution on NiO nanoparticles (formed at different temperatures) at 318 K and various shaking rate.
NiO formed at	'e (min)	le (mg g 1)	'o2 (min)	qo2 (mg g 1)	First ai	region V01		Second a2	region V02
400 °C	840	372.85	90	At 40 82.70	rpm -2.20 x 10-	2	1.917	-1.27 x 10-3	0.776
250 °C	652	406.29	90	At 80 250.43	rpm -2.78 x 10-	2	4.058	-1.79 x 10-3	0.579
400 °C	540	371.72	60	107.58	-2.60 x 10-	2	2.493	-2.28 x 10-3	1.100
600 °C	871	182.76	120	63.16	-2.82 x 10-	3	0.693	-3.44 x 10-4	0.291
400 °C	360	360.74	45	At 120 84.48	rpm -6.20 x 10-	2	3.263	-5.74 x 10-3	1.744
Dimensions of a1 and a2 are in mg g 1 min 2 and those of v01 and v02 are in mg g 1 min '. In the first region, i0] and q01 are equal to zero.
Figure 8: qt versus t for adsorption of 1.84 mM FA on NiO nanopar-ticles (formed at different temperatures) at various shaking rates.
q02, qe, v01 and v02 values decrease and te values of them increase. On the other hand, q02 and qe values of the nano-structure formed in 250 °C (in spite of its larger size) are higher than those of the sample formed in 400 °C. It seems that this observation is due to the structural change in the sample formed in 250 °C that is because of the presence of metallic nickel in its structure. Also, in a series of experiments, shaking rate of 0.184 mM FA samples at 318 K was increased from 40 to 120 rpm. As shown in Figure 8 and Table 9, in these processes, adsorption acceleration in both regions is negative in sign and initial adsorption velocity of the first and second regions increases with increasing shaking rate. Also, as observed in Table 9, with increase in shaking rate of these samples their te and q02 values decrease and increase, respectively.
4. Conclusions
NiO nanoparticle, prepared by thermal decomposition of the tris(ethylenediamine) Ni(II) nitrate complex, was used as adsorbent to remove negatively charged fuchsine acid (FA) from aqueous solution. In the used concentration range of FA, its adsorption isotherms on NiO nano-particles (formed at 400 °C) according to ARIAN model were three-region. Adsorption process in the first, second and third regions was studied by the Henry's law, Temkin and Langmuir-like equations, respectively and analysis of data showed that the process is exothermic in the first and second regions and endothermic in the third region. IR spectra showed that FA interacts with -OH groups of NiO nanoparticles. With decrease in pH values more amount of NiO nanoparticles dissolve and qe values decrease. Data of adsorption kinetics were analyzed by the pseudo-first-order, pseudo-second-order, Elovich, Avrami, pore-diffusion and KASRA equations. The KASRA equation showed that at 40, 80 and 120 rpm and different temperatures, the sign of adsorption acceleration in the first and second regions of adsorption kinetics of FA on NiO nanoppartic-les was negative and with increase in FA concentration or temperature or shaking rate, initial adsorption velocity values of each region increase.
5. References
1.	S. Tsuda, M. Murakami, N. Matsusaka, K. Kano, K. Tani-guchi, Y. F. Sasaki, Toxicol. Sci. 2001, 61, 92-99.
2.	B. Przybojewska, B. Baranski, E. Spiechowiecz, K. Sitarrek, Toxicol. Lett. 1998, 40, 183-192.
3.	J. Pan, B. Guan, J. Hazard. Mater. 2010, 183, 341-346.
4.	X. Tan, N. N. Kyaw, W. K. Teo, K. Li, Sep. Purif. Technol. 2006, 52, 110-116.
5.	A. Latifoglu, M. D. Gurol, Water Res. 2003, 37, 1879-1889.
6.	F. J. Beltran, J. M. Encinar, M. A. Alonso, Ind. Eng. Chem. Res. 1998, 37, 32-40.
7.	I. K. Konstantinou, T. A. Albanis, Applied Catalysis B: Environmental 2004, 49, 1-14.
8.	K. Ravikumar, S. Krishnan, S. Ramalingam, K. Balu, Dyes and Pigments 2007, 72, 66-74.
9.	W. Liu, Y. Chao, X. Yang, H. Bao, S. Qian, J. Ind. Microbiol. Biotechnol. 2004, 31, 127-132.
10.	J. M. Bastidas, P. Pinilla, E. Cano, J. L.Polo, S. Miguel, Corros. Sci. 2003, 45, 427-449.
11.	http://en.wikipedia.org/wiki/Fuchsine
12.	M. Z. bin Hussein, A. Hj Yahaya, M. Shamsul, H. M. Salleh, T. Yap, J. Kiu, Mater. Lett. 2004, 58, 329-332.
13.	T. , Y., Chem. Eng. J., 123-131.
14.	B. Xu, B. J. Chin. Chem. Soc. 2010, 57, 309-315.
15.	S. Michael Anto, G. Annadurai, Research Journal of Nanos-cience and Nanotechnology 2012, 2, 31-45.
16.	C. L. Chen, X. K. Wang, M. Nagatsu, Environ. Sci. Technol. 2009, 43, 2362-2367.
17.	A. Afkhami, R. Moosavi, J. Hazard. Mater. 2010, 174, 398403.
18.	T. G. Venkatesha, R. Viswanatha, Y. Arthoba Nayaka, B. K. Chethana, Chem. Eng. J. 2012, 198-199, 1-10.
19.	V. Belessi, G. Romanos, N. Boukos, D. Lambropoulou, C. Trapalis, J. Hazard. Mater. 2009, 170, 836-844.
20.	P. Liu, L. Zhang, Sep. Purif. Technol. 2007, 58, 32-39.
21.	F. M. Machado, C. P. Bergmann, T. H. M. Fernandes, E. C. Lima, B. Royer, T. Calvete, S. B. Fagan, J. Hazard. Mater. 2011,192, 1122-113.
22.	E. D. Vega, G. E. Narda, F. H. Ferretti, J. Colloid Interface Sci. 2003, 268, 37-42.
23.	M. Singh, D. Nguyen, T. Ulbrich, N. Strnadova, F. Stepanek, J. Solid State Chem. 2010, 183, 2979-2986.
24.	V. Srivastava, C. H. Weng, V. K. Singh, Y. C. Sharma, Chem. Eng. Data 2011, 56, 1414-1422.
25.	Y. Zhuang, Y. Yang, G. Xiang, X. Wang, J. Phys. Chem. C 2009, 113, 10441-10445.
26.	W. Wei, X. Jiang, L. Lu, X. Yang, X. Wang, J. Hazard. Mater. 2009, 168, 838-842.
27.	F. Li, H. Y. Chen, C. M. Wang, K. A. Hu, J. Electroanal. Chem. 2002, 531, 53-60.
28.	I. Hotovy, J. Huran, L. Spiess, S. Hascik, V. Rehacek, Sens. Actuators B: Chem. 1999, 57, 147-152.
29.	F. B. Zhang, Y. K. Zhou, H. L. Li, Mater. Chem. Phys. 2004, 83, 260-264.
30.	M. Ghosh, K. Biswas, A. Sundaresan, C. N. R. Rao, J. Mater.
Chem. 2006, 16, 106-111.
31.	C. G. Granqvist (Ed.): Handbook of Inorganic Electrochro-mic Materials, Elsevier; Amsterdam, 1995.
32.	S. Farhadi, Z. Roostaei-Zaniyani, Polyhedron 2011, 30, 971-975.
33.	H. P. Klug, L. E. Alexander: X-ray Diffraction Procedures, 2nd Ed., Wiley, New York, 1964.
34.	M. Huang, C. Xu, Z. Wu, Y. Huang, J. Lin, J. Wu, Dyes Pigments, 2008, 276, 327-334.
35.	B. Samiey, S. Golestan, Cent. Eur. J. Chem. 2010, 8, 361369.
36.	I. Langmuir, J. Am. Chem. Soc. 1918, 40, 1361-1403.
37.	M. Boudart, G. Djega-Mariadassou: Kinetics of Heterogeneous Catalytic Reactions, Princeton University Press, 1984, p 132.
38.	M. M. Dubinin, Carbon 1985, 23, 373-380.
39.	J. P. Hobson, J. Phys. Chem. 1969, 73, 2720-2727.
40.	J. A. Lewis, J. Am. Ceram. Soc. 2000, 83, 2341-2359.
41.	S. Paria, C. Manohar, K. C. Khilar, Ind. Eng. Chem. Res. 2005, 44, 3091-3098.
42.	J. D. Fisk, M. Rooth, A. M. Shaw, J. Phys. Chem. C 2007, 111, 2588-2594.
43.	F. Tiberg, B. Jonsson, B. Lindman, Langmuir 1994, 10, 3714-3722.
44.	P. Supaphol, J. E. Spruiell, J. Macromol. Sci. Phys. B 2000, 39, 257-277.
45.	P. Supaphol, Thermochim. Acta 2001, 370, 37-48.
46.	C. Albano, R. Sciamanna, R. Gonzalez, J. Papa, O. Navarro, Eur. Polym. J. 2001, 37, 851-860.
47.	S. Lagergern, Handlinger 1898, 24, 1-39.
48.	Y. S. Ho, G. Mckay, Water Res. 2000, 34, 735-742.
49.	J. M. Borah, S. Mahiuddin, J. Colloid Interface Sci. 2008, 322, 6-12.
50.	S. Karaca, A. Gurses, M. Ejder, M. Afykyyldyz, J. Colloid Interface Sci. 2004, 277, 257-263.
51.	S. Azizian, J. Colloid Interface Sci. 2004, 276, 47-52.
52.	B. H. Hameed, M. I. El-Khaiary, J. Hazard. Mater. 2008, 159, 574-579.
53.	P. Shuchuan, W. Shisheng, C. Tianhu, J. Shaotong, H. Chuanhu, Acta Geologica Sinica 2006, 80, 236-242.
54.	C. F. Chang, C. Y. Chang, K. H. Chen, W. T. Tsai, J. L. Shie, Y. H. Chen, J. Colloid Interface Sci. 2004, 277, 29-34.
55.	X. Yang, B. Al-Duri, J. Colloid Interface Sci. 2005, 287, 25-34.
56.	C. W. Cheung, J. F. Porter, G. McKay, J. Chem. Technol. Biotechnol. 2000, 75, 963-970.
57.	M. Avrami, J. Chem. Phys. 1939, 7, 1103-1112.
58.	G. McKay, V. P. Poots, J. Chem. Technol. Biotechnol. 1980, 30, 279-292.
59.	A. R. Cestari, E. F. S. Vieira, A. A. Pinto, E. C. N. Lopes, J. Colloid Interface Sci. 2005, 292, 363-372.
60.	B. Samiey, M. Rafi Dargahi, Cent. Eur. J. Chem. 2010, 8, 906-912.
Povzetek
Proučevali smo adsorpcijo fuksin žveplove kisline (FA ) iz vodne raztopine na delcih NiO, ki smo jih pripravili s termično dekompozicijo iz tris(etilendiamin)Ni(II) nitratnega kompleksa. Izkazalo se je, da proces adsorpcije lahko razdelimo v tri področja. V prvih dveh je proces eksotermen, v tretjem pa endotermen. Kinetiko adsorpcije smo raziskovali z nekaterimi modeli, kot so KASRA, psevdo prvi red, psevdo drugi red, Elovich, Avrami in enačba za difuzijo v porah. Z uporabo KASRA enačbe smo ugotovili, da se z naraščanjem koncentracije FA v raztopini, temperature ali hitrosti mešanja začetna hitrost adsorpcije poveča.