Superb adsorption capacity of hydrothermally synthesized copper oxide and nickel oxide nanoflakes towards anionic and cationic dyes

Fakhri, Study of the adsorption of methyl orange from aqueous solution using nickel oxide nanoparticles: equilibrium and kinetics studies, J. Chang, Adsorption kinetics and isotherms for[r]

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Original Article

Superb adsorption capacity of hydrothermally synthesized copper

oxide and nickel oxide nanoﬂakes towards anionic and cationic dyes

K Yogesh Kumara, S Archanaa, T.N Vinuth Rajb, B.P Prasanab, M.S Raghuc,

H.B Muralidharad,*

aDepartment of Chemistry, School of Engineering and Technology, Jain University, Jakkasandra Post, Kanakapura Taluk, Ramanagara District 562112, India bDepartment of Physics, School of Engineering and Technology, Jain University, Jakkasandra Post, Kanakapura Taluk, Ramanagara District 562112, India cDepartment of Chemistry, Nitte Meenakshi Institute of Technology, Yelahanka, Bangalore 560 064, India

dCentre for Incubation, Innovation, Research&Consultancy, Jyothy Institute of Technology, Bangalore 560082, India

a r t i c l e i n f o Article history:

Received 17 March 2017 Received in revised form 11 May 2017

Accepted 17 May 2017 Available online 25 May 2017

Keywords:

CuO NiO Adsorption MGO MO

a b s t r a c t

The CuO and NiO nanoflakes were synthesized by a hydrothermal reaction The secondary nucleation and growth of hydroxides resulted in the formation offlake like architectures as the prepared nanoparticles were used as an adsorbent for malachite green oxalate (MGO) and methyl orange (MO) The structure, morphology and surface properties of the nanoparticles were characterized by XRD, SEM and TEM Effects of the experimental conditions on the adsorption behavior were studied by varying the contact time, initial concentration, initial pH and temperature The adsorption of MGO increased with increase in the pH, while the MO adsorption showed an opposite trend The adsorption kinetics was studied in terms of pseudo-first and second-order kinetics, the Langmuir and Freundlich models were also applied to the equilibrium adsorption data The adsorption process was spontaneous and exothermic in nature and followed the pseudo-second-order kinetic model Our study indicates that the CuO and NiO nanoflakes can be used as alternative adsorbents for the efficient removal of dyes from an aqueous solution

©2017 The Authors Publishing services by Elsevier B.V on behalf of Vietnam National University, Hanoi This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/)

1 Introduction

Water pollution is an important environmental issue that has received major worldwide attention Many industries such as textile, leather, food processing, and dyeing cosmetics generate massive amounts of wastewater Dye chemicals represent one of the most prominent contaminants contained in the wastewater effluents[1] Thefirst contaminants that are recognized in water are dyes, which must be removed before discharging them into water bodies Introduction of dyes into aquatic systems is hazard-ous as they can cause distinct limitations such as the hindrance of light penetration and the mutagenic change increases in chemical oxygen demand (COD) and biological oxygen demand (BOD) of a water system reflecting its low quality

Malachite green oxalate (MGO) and methyl orange (MO) are two typical examples of industrially relevant toxic cationic and anionic dyes with known harmful effects on humans Therefore, treatment

of effluents containing dyes becomes increasingly important from both toxicological and ecological perspectives Many conventional methods such as precipitation, ion exchange, solvent extraction, biosorption, filtration, and electrochemical treatment have been employed for removal of contaminants from industrial wastewaters [2e4] These methods are either expensive or inefficient for

treat-ing effluents with high concentration of contaminants They also have significant disadvantages such as incomplete removal, re-quirements and production of toxic sludge or other waste products that require further disposal The adsorption technique emerges as a competitive method for treatment of dyestuff wastewater due to its easy handling, high efficiency and economic feasibility[5e7]

The introduction of nanoparticles comprising a variety of shapes, sizes and compositions have led to changes in waste-water treatment approaches Preparation and characterization of novel nanomaterials are important in materials science Nano-particle based adsorbents possess high surface area in addition to various non-saturated reactive surface atoms, which enable selective and reversible binding of dye molecules[8] There are various candidate nano-materials, including carbon nanotubes, nano-wires and nano-particles Adsorbents containing metallic

*Corresponding author

E-mail addresses:yogeshkk3@gmail.com(K Yogesh Kumar),hb.murali@gmail

com(H.B Muralidhara)

Peer review under responsibility of Vietnam National University, Hanoi

Contents lists available atScienceDirect

Journal of Science: Advanced Materials and Devices j o u r n a l h o m e p a g e : w w w e l s e v i e r c o m / l o c a t e / j s a m d

http://dx.doi.org/10.1016/j.jsamd.2017.05.006

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nanoparticles or multi-walled carbon nanotubes have been widely applied to bind and coordinate biological materials, organic pollutants, and various metal ions[9]

Copper oxide (CuO) and nickel oxide (NiO) nanoparticles have been extensively studied for many years due to their important roles in catalysis, metallurgy, and high-temperature superconduc-tors Several preparation methods of CuO and NiO nanoparticles have been reported[10e14] Chemical and physical properties of

these materials depend on its composition, structure, phase, shape and size distribution Current efforts are being undertaken to explore the possible utilization of these metal oxide nanoparticles for socio-economic development

In this context, we report a cost-effective removal of cationic (MGO) and anionic (MO) dyes from an aqueous solution using low cost, recyclable, and easily available metal oxides (CuO, NiO) To the best of our knowledge, such metal oxides have not been much employed, especially in the dye removal process through adsorp-tion A systematic investigation of the effects of initial dye con-centration, initial pH, adsorbent dose, temperature of the solution on dye uptake and plausible dye-adsorbent interaction during adsorption is carried out in this study This particular approach has signiﬁcant advantages such as cost effective, simplicity in equip-ment, ease in preparation, short reaction time and better repeat-ability More importantly, the as-prepared CuO and NiO nanoﬂakes exhibit an excellent dye removal ability in wastewater treatment

2 Experimental

2.1 Materials and stock solution preparation

All reagents including copper(II) nitrate trihydrate (CuNO3$3H2O), nickel nitrate hexahydrate (Ni(NO)3$6H2O), sodium hydroxide (NaOH), Triton X-100 (C14H22O(C2H4O)n), cationic dye (MGO) and anionic dye (MO) were used as absorbates for the adsorption studies All the chemicals used in the experiments were of AR grade and used without any puriﬁcation

Standard solutions (100 mg L1) of MGO (C52H54N4O12) and MO (C14H14N3NaO3S) were prepared by adding appropriate amounts in the deionized water and further diluted to the required concen-trations for adsorption experiments The structures of the above mentioned dyes are given inFig 1a and b

2.2 Adsorbent preparation and characterization

In a typical procedure, 20 ml of 0.2 mol L1NaOH solution was slowly added into a 20 ml of 0.1 mol L1copper(II) nitrate trihy-drate and nickel(II) nitrate solution containing 0.004 mol L1 of Triton X-100, with constant stirring After vigorous stirring for h, the mixture was autoclaved at 200 C for h After the reaction system was naturally cooled to room temperature, the precipitate was separated from solution and thoroughly washed several times,

ﬁrst with deionized water then with absolute ethanol and subse-quently dried in an oven at 50C for h

Eqs (1) and (2) show the possible formation mechanism of metal oxide nanoparticles from metal ion solution In a supersat-urated solution when the nuclei form at the same time, subsequent growth of these nuclei results in the formation of particles with a very narrow size distribution

M2ỵ ỵ X H2O/MOHịX (1)

MOHịX/MOx=2 ỵ X=2 H2O (2)

2.3 Characterization techniques

X-ray diffraction (XRD) patterns were obtained on a Bruker D2 Phaser XRD system Surface morphology (SEM) was studied using scanning electron microscope (JEOL JSM 840A) and Transmission electron microscope (TEM) Philips CM-200 instrument Finally, the BET surface area, total pore volume and average pore size were measured using ASAP 2010 Micrometrics instrument by Bru-nauereEmmetteTeller (BET) method

2.4 Batch method

Batch mode of experiments for the adsorption of dyes was done by using a sequence of 100 mL conicalﬂasksﬁlled with 50 mL of dyes 25 mg of adsorbent was added into solutions containing various concentrations of dyes (10, 20, 30, 40 mg L1) which were stirred at a constant temperature in an incubator shaker until the steady state was attained Furthermore, the solutions obtained were centrifuged and the supernatant liquids were subjected for the determination of residual concentrations The amount of adsorbate adsorbed at an equilibrium condition, Qe(mg g1) was calculated by the following equation:

QeẳC0WCeịV (3)

where‘C0’and‘Ce’are the initial and equilibrium concentrations (mg L1), respectively.‘V’is the volume of solution (L) and W is the mass of adsorbent used (g)

Effect of pH on the adsorption capacity of dyes was evaluated by agitating 20 mg L1dye solution with 250 mg L1of metal oxides for predetermined equilibrium time at pH ranging from 2.0 to 8.0 The pH of the solution was adjusted by using 0.5 M HCl or 0.5 M NaOH Similarly the rate of MGO and MO adsorption onto metal oxides was investigated by kinetics and isotherm study Duplicate experiments were carried out for all operating variables studied and only average values were taken into consideration

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3 Results and discussion

3.1 Characterization of adsorbent

Fig 2a shows the XRD pattern of CuO nanoparticles The peaks at 2q¼32.62, 35.61, 38.80, 48.75, 53.68and 58.42can be assigned to (110), (002), (111), (202), (020) and (113) of CuO (JCPDS 80-1916) [12] Fig 2b shows the main peaks at 37.26, 43.32, 62.84, 75.18, and 79.23, which correspond to the (111), (200), (220), (311) and (222) planes of NiO nanoparticles (JCPDS 78-0643) [15], the crystallite size has been estimated from the XRD pattern using the Scherrer's equation There are no peaks observed for any impurity, indicating the high purity of the sample

The surface morphology of the CuO and NiO nanoflakes was studied by SEM.Fig 3a and b show a uniform growth of the metal oxide nanostructures SEM images with higher magnification show that the grown nanostructures are in the form of nanoflakes which were interconnected with each other and created pores and crevices, yielding large surface areas for easy diffusion of the dyes onto the surface of metal oxides

TEM was used to further investigate the microstructure of the as-synthesized CuO and NiO nanoflakes It revealed the formation of nanoflakes with a cubic crystal structure as shown inFig 4a and b The color contrast of both oxides is homogeneous, indicating a uniform dense structure and a smooth surface[16] This observa-tion is in accordance with the corresponding SEM image Using the BET method, the surface areas of the CuO and NiO nanoflakes were determined to be 69.27 m2 g1and 9.72 m2/g respectively, and their total pore volume was 0.023 cm3g1

4 Adsorption studies

4.1 Effect of initial concentration

Fig 5shows the time profile of MGO and MO adsorptions at different initial concentrations in a range from 10 to 40 mg L1at pH 7.0 for 90 The dye adsorption capacities onto CuO and NiO increased with increase in the concentration of dye solutions The adsorption rates were extraordinarily fast in thefirst for all the concentrations The adsorption nearly finished within 60 min, indicating the fast adsorption rate The removal

efficiencies for dyes initially increased and then decreased, which might be due to the fact that large numbers of vacant active sites were available for the adsorption at a lower initial concentration, and once the sites became saturated, it was difficult to capture the dye molecules because of repulsive forces exerted by the adsor-bate molecules In the case of MGO, the removal efficiency was higher than that of MO at low initial concentrations, probably due to smaller spatial prohibition in the molecular structure of MGO and its positive feature, making it more accessible to the adsorption sites of CuO and NiO It is seen that the adsorption capacity (Qt) of both dyes increased with the initial dye concen-tration This suggests that dye concentration is a major factor in overcoming the mass transfer resistance of the dye between the aqueous and solid phases

4.2 Effect of pH

Fig 6demonstrates that a maximum percentage of dye removal was observed at pH for MGO (83.4 and 86%) and at pH for MO (93.2, 84.6%) for CuO and NiO respectively, beyond which it was constant To determine the adsorption mechanism, measurements of zero point charge (pzc) of the adsorbent are crucial, since it is well known that adsorption of a cationic dye is favorable at pH>pzc By contrast, for an anionic dye the favorable adsorption condition is pH<pzc Here we observed that the pzc of CuO and NiO was in the range of 9e10 Therefore, in an acidic environment

(pH<pzc), a lower adsorption efﬁciency is expected because of the repulsive forces between the adsorbent and adsorbate Further-more, in acidic pH, the increased surface excess of Hỵions on the adsorbent implied competition of the Hỵ ions with cationic dye molecules, which reduced the adsorption of dye molecules How-ever, under alkaline conditions, the electrostatic attraction force increased resulting in a higher % of adsorption of the cationic dye This is attributed to an increase in the number of negatively charged sites, because of deprotonation

4.3 Adsorption isotherm

In this study, Langmuir and Freundlich models were used to determine the adsorption equilibrium between the adsorbent and dye molecules The Langmuir equation is based on the assumption that the adsorption site is homogeneous in which each site

30 40 50 60 70

(a)

(311) (220) (112)

(202)

(112) (020)

(021) (113) (111) (200)

(110)

Intensity

(a.u.)

2θ (degree)

30 40 50 60 70 80

(b)

(104) (311) (220)

(200)

(111)

Intensity

(a.u.)

2θ (degree)

(4)

accommodates one adsorbate molecule or ion; adsorption is a monolayer coverage phenomenon and there is no interaction be-tween adsorbed molecules or ions[17] The Freundlich equation is an empirical equation explored for heterogeneous systems and is not restricted to the formation of a monolayer[18]

Qe¼

KLCe

1ỵaLCe

(4)

QeẳKfCe1=n (5)

where ‘Ce’ is equilibrium (residual) concentration of solute (mg L1),‘Qe’is the amount of adsorbed at equilibrium (mg g1),

‘Qm’is the maximum adsorption capacity andKLis the Langmuir adsorption model constant (L mg1) For the Freundlich equation,

KFis the adsorption model constant (L g1) and n is Freundlich adsorption model exponent

Fig 3.Low and high magniﬁcation SEM micrographs of (a) CuO and (b) NiO nanoﬂakes

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The Langmuir and Freundlich isotherms for the two dyes are shown inFigs and 8respectively The related parameters and correlation coefﬁcients were calculated via a process of linear regression for both isotherm models The corresponding results are presented inTable It is seen that the correlation coefﬁcient values

for both Langmuir and Freundlich isotherm models are closer to The maximum adsorption capacity determined from the Langmuir isotherm model for MGO and MO dyes on CuO is 178 and 158 mg g1respectively; similarly for NiO it is found to be 189 and 165 mg g1 The values of KL obtained are in the range of 0e1,

0 20 40 60 80 100 120

0 20 40 60 80 100

MGO (a)

10 PPM 20 PPM 30 PPM 40 PPM

Remov

al efficiency

in %

Time in Minutes 20 40 60 80 100 120

0 20 40 60 80 100

MO

(a)

Remov

al efficiency

in %

Time in Minutes

10 ppm 20 ppm 30 ppm 40 ppm

0 20 40 60 80 100 120

0 20 40 60 80

MGO

(b)

Remov

al efficiency

in %

Time in Minutes

0 20 40 60 80 100 120

0 20 40 60 80

MO

(b)

Remov

al efficiency

in %

Time in Minutes

Fig 5.Effect of different initial concentrations on adsorption of MGO and MO on CuO (a) and NiO (b)

2

40 45 50 55 60 65 70 75 80 85 90 95

(a)

Remov

al efficiency

in %

pH of solution

MGO on CuO MGO on NiO

2

60 65 70 75 80 85 90 95

(b)

Remov

a

l efficiency

in %

pH of solution MO on CuO MO on NiO

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indicating that the adsorption of both dyes on the CuO and NiO is favorable in an adsorption process Moreover, the values of n are greater than 1, conﬁrming that the metal oxides are good adsor-bents with high adsorption intensity for both dyes

Table 2compares the maximum adsorption capacities of both CuO and NiO nanoﬂakes for dyes with those of other metal oxide nano-particles It is seen that the maximum adsorption capacities of our oxides are notably higher as compared to other candiate adsorbents

4.4 Kinetic studies

The kinetics of MGO and MO removal on CuO and NiO was further investigated The pseudo-ﬁrst-order kinetic models Eq.(6)

and pseudo-second-order kinetic models Eq.(7)were applied to describe this adsorption process, respectively:

logQeQtị ẳlogQe

k1

2:303 t

(6)

t

Qt ẳ

1

k2Qe2

ỵ

Qet (7)

where‘Qe’and‘Qt’(mg g1) are the adsorption capacities at equi-librium and at any time t (min), respectively k1(min1) and k2 (g mg1 min1) are the pseudo-ﬁrst-order and pseudo-second-order rate constants, respectively The kinetic parameters and the correlation coefﬁcients (R2) of both the oxides with MGO and MO are given inTable 3a and3b, respectively

Thefirst-order-rate constant k1can be obtained from the slope of the plot ln(qe qt) vs t (Fig S1) The results obtained from applying thefirst order kinetic model indicated that the correlation coefficient (R2) values of thefirst-order rate model were not high for the different concentrations of MGO and MO; furthermore, the value of ‘Qe’ was smaller than the value of Qt, suggesting the inapplicability of the pseudo-first-order model to describe the adsorption process.Fig S2revealed that all the experimental data could fit well to the pseudo-second-order model with high

0 10 12 14

0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.10 0.11 0.12

MGO on CuO MO on CuO (a)

Ce

C e /Q e

0 10 12 14 16 18 0.03

0.04 0.05 0.06 0.07 0.08 0.09 0.10 0.11 0.12 0.13 0.14 0.15

(b)

MGO on NiO MO on NiO

C e /Q e

Ce

Fig 7.Fits of the Langmuir adsorption isotherms of MGO and MO on CuO (a) and NiO (b)

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.5

1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3

log Q

e

log Ce (a)

MGO on CuO MO on CuO

0.2 0.4 0.6 0.8 1.0 1.2 1.5

1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3

(b)

log Q

e

log Ce

Fig 8.Fits of the Freundlich adsorption isotherms for MGO and MO on CuO (a) and NiO (b)

Table

Adsorption isotherm model parameters of adsorption of MGO and MO on CuO and NiO

Adsorbent Adsorbate Langmuir Parameters Freundlich Parameters

Q0(mg g1) KL R2 KF(mg g1) nF R2

CuO MGO 178.89 0.20 0.99 36.6 1.98 0.99

MO 158.73 0.27 0.99 42.65 2.27 0.99

NiO MGO 189.03 0.14 0.96 29.16 1.78 0.99

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correlation coefficients (R2>0.999) The values of‘Qe'cal was also very close to the values of ‘Qe'exp, which indicates that the adsorption process of MGO and MO on CuO and NiO obeyed the pseudo-second-order model Also, the adsorption data notfit the pseudo-first-order model

4.5 Thermodynamic studies

It can be perceived fromFig 9that the temperature adversely affects the removal efﬁcacy of both the dyes on CuO and NiO The adsorption capacity of dyes diminishes as the temperature rises from 303 to 323 K This may be due to the fact that, at higher temperature the solute molecules show an inclination to escape from the solid phase and re-enter the liquid phase as a result of increased mobility[19]

Thermodynamic parameters were calculated to evaluate the thermodynamic feasibility of the process using the following equations[20]:

lnkC¼DS

0

R

DH0

RT (8)

DG0¼ RTlnk

C (9)

wherekCis the distribution coefﬁcient for the adsorption,DH0is the enthalpy change,DS0is the entropy change,DG0is the Gibb's free energy change, R is the gas constant, T is the absolute tem-perature.DH0andDS0were calculated from the slope and intercept of the linear plot of lnKCversus 1/T Once these two parameters were obtained, DG0 was determined The negative value of DH0 conﬁrmed the exothermic nature of MGO and MO adsorption by CuO and NiO The values ofDG0were negative at all temperatures, demonstrating the thermodynamic feasibility and the spontaneity of the adsorption process The adsorption was associated with a negative value ofDS0(Table 4)

4.6 Mechanism of adsorption

It is worthy elucidating why CuO and NiO have such a high adsorption performance toward MGO and MO It has been previ-ously suggested that the adsorption of ionic dyes or organic pol-lutants may be associated with the electrostatic attraction and surface complexation[21,22] In the present study, the adsorption of

Table

Comparison of monolayer maximum capacities of some adsorbents for MGO and MO from aqueous solutions

Adsorbents Adsorbate Adsorption capacity (mg g1) References

Zeolite-Iron Oxide MGO 21.05 [24]

Peanut shell MGO 33.85 [25]

Sawdust MGO 62.71 [26]

TiO2nanoparticles MGO 63.08 [27]

Wood apple MGO 80.64 [28]

CuO MGO 178.8 Present Study

NiO MGO 189.0 Present Study

NiO nanoparticles MO 11.21 [29]

CuO MO 12.8 [30]

Chitosan MO 30.86 [31]

Cross linked Chitosan MO 81.3 [32]

NiO microsphere MO 113.6 [33]

CuO MO 158.73 Present Study

NiO MO 165.83 Present Study

Table 3(a)

Kinetic parameters for the adsorption of MGO and MO on CuO

Kinetic models Parameters MGO MO

10 20 30 40 10 20 30 40

First order kinetic model qe, Cal (mg g1) 19.28 40.36 75.33 104.7 36.55 72.44 102.3 144.5

K1(min1) 0.034 0.034 0.036 0.035 0.037 0.035 0.039 0.041

R2 0.79 0.94 0.94 0.93 0.81 0.95 0.90 0.88

qe, Exp (mg g1) 42.9 78.9 109.2 132.1 44.1 82.9 111 130.6

Second order kinetic model qe, Cal (mg g1) 47.61 90.9 119.04 147.05 49.75 100 123.4 149.2

K2(min1) 0.11 0.1 0.1 0.07 0.06 0.05 0.07 0.061

R2 0.99 0.99 0.99 0.99 0.99 0.99 0.99 0.99

qe, Exp (mg g1) 42.9 78.9 109.2 132.1 44.1 82.9 111 130.6

Table 3(b)

Kinetic parameters for the adsorption of MGO and MO on NiO

Kinetic models Parameters MGO MO

10 20 30 40 10 20 30 40

First order kinetic model Qe., Cal(mg g1) 35.07 79.95 115.19 133.57 21.1 56.41 92.1 121.4

K1(min1) 0.039 0.046 0.044 0.041 0.027 0.035 0.04 0.039

R2 0.987 0.902 0.923 0.826 0.900 0.913 0.839 0.835

Qe, exp(mg g1) 40.9 72.7 105.75 126.45 40.8 71.3 99.6 120.1

Second order kinetic model Qe, Cal(mg g1) 47.05 81.1 120.48 142.45 43.7 78.6 109.8 137.9

K2(min1) 0.06 0.077 0.068 0.067 0.092 0.077 0.078 0.064

R2 0.997 0.998 0.998 0.997 0.997 0.997 0.996 0.982

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MGO and MO on CuO and NiO can be attributed to electrostatic attraction It is well known that, if the pH of the solution is below the isoelectric point of an adsorbent, the adsorbent will possess a better adsorption capacity The natural pH value (z7.0) of the dye solution is much lower than the isoelectric point of both CuO and NiO (9e11)

Therefore, CuO and NiO are expected to become promising materials for rapid and deep treatment of high concentration dye-containing wastewater because of their fast adsorption rate and high capacity desorption of dye molecules at a natural pH[23]

5 Conclusion

In this study, the low-cost, environmentally friendly, greater adsorption capacity CuO and NiO nanoflakes were prepared by the hydrothermal method and utilized for the removal of dyes from an aqueous solution by the adsorption process with a removal effi -ciency >90% The removal efficiency is dependent on the initial concentration, pH and temperature of the solution Based on this study, the optimum conditions for an effective removal of dyes by adsorption onto metal oxide nanoflakes can befine-tuned Addi-tionally, the adsorption thermodynamics analysis revealed that the adsorbent processes were spontaneous The adsorption of both the dyesfit the pseudo second-order kinetic model Furthermore, an in-depth study on selective interaction phenomena of these dyes with nanoparticles is currently under process, which could be an important tool in remediation technology and nanotechnology as well Excavation of the full potential of CuO and NiO for removing MGO and MO from real industry wastewater samples will also demand further studies

Acknowledgements

This work is supported by the Visvesvaraya Technological Uni-versity under research grant scheme (Project No VTU/Aca/2010-11/

a-9/11353) The authors are also grateful to K.S Institute of Tech-nology, Bangalore for their support and IIT Kanpur, IIT Bombay and PPRI Bangalore for providing instrumental facilities The authors are thankful to Ms Sangeetha, Assistant Professor in English for assistance in improving the language

Appendix A Supplementary data

Supplementary data related to this article can be found athttp:// dx.doi.org/10.1016/j.jsamd.2017.05.006

References

[1] H Ali, Biodegradation of synthetic dyesda review, Water Air Soil Pollut 213

(2010) 251e273

[2] A Dabrowski, Z Hubicki, P Podkoscielny, E Robens, Selective removal of the heavy metal ions from waters and industrial wastewaters by ion-exchange method, Chemosphere 56 (2004) 91e106

[3] F Fu, Q Wang, Removal of heavy metal ions from wastewaters: a review, J Environ Manag 92 (2011) 407e418

[4] T.A Kurniawan, G.Y.S Chan, W.H Lo, S Babel, Physico-chemical treatment techniques for wastewater laden with heavy metals, Chem Eng J 118 (2006) 83e98

[5] B Li, Y.C Dong, C Zou, Y.M Xu, Iron(III)eAlginateﬁber complex as a highly

effective and stable heterogeneous fenton photocatalyst for mineralization of organic dye, Ind Eng Chem Res 53 (2014) 4199e4206

[6] A Yadav, S.A Mukherji, Removal of chemical oxygen demand and color from simulated textile wastewater using a combination of chemical/physico-chemical processes, Ind Eng Chem Res 52 (2013) 10063e10071

[7] C.S.D Rodrigues, L.M Madeira, R.A Boaventura, Decontamination of an in-dustrial cotton dyeing wastewater by chemical and biological processes, Ind Eng Chem Res 53 (2014) 2412e2421

[8] J.M Chern, S.N Huang, Study of nonlinear wave propagation theory Dye adsorption by activated carbon, Ind Eng Chem Res 37 (1998) 253e257

[9] M Tuzen, M Soylak, Multiwalled carbon nanotubes for speciation of chro-mium in environmental samples, J Hazard Mater 147 (2007) 219e225

[10] P Larsson, A Andersson, Complete oxidation of CO, ethanol, and ethyl acetate over copper oxide supported on titania and ceria modiﬁed titania, J Catal 179 (1998) 72e89

0.00300 0.00305 0.00310 0.00315 0.00320 3.0

3.1 3.2 3.3 3.4 3.5 3.6 3.7

MGO on CuO MO on CuO

(a)

lnK

C

1/T (K-1)

0.00300 0.00305 0.00310 0.00315 0.00320 2.4

2.5 2.6 2.7 2.8 2.9 3.0

(b)

1/T (K-1)

ln K

c

Fig 9.Effect of temperature on absorption of MGO and MO on CuO (a) and NiO (b)

Table

Thermodynamics parameters for the adsorption of MGO and MO on CuO and NiO

Parameters Temperature MGO on CuO MO on CuO MGO on NiO MO on NiO

DG0(kJ mol1) 30C 7.43 8.01 6.52 6.35

40C 9.03 8.85 7.57 6.92

50C 10.5 9.61 8.00 7.41

DH0(kJ mol1) 4.11 16.62 16.21 9.97

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[11] V Chikan, A Molnar, K Balazsik, One-step synthesis of methyl isobutyl ketone from acetone and hydrogen over Cu-on-MgO catalysts, J Catal 184 (1999) 134e143

[12] J.T Richardson, Surface properties of nickel oxide, J Catal (1966) 328e332

[13] F Fievet, M Figlarz, Preparation and study by electron microscopy of the development of texture with temperature of a porous exhydroxide nickel oxide, J Catal 39 (1975) 350e356

[14] N.B Hannay, Semiconductors, Reinhold Publishing Corp., New York, 1959 [15] A.L Patterson, The Scherrer formula for X-ray particle size determination,

Phys Rev 56 (1939) 978

[16] P.P Zhang, X.M Ma, Y.M Guo, Q.Q Cheng, L Yang, Size-controlled synthesis of hierarchical NiO hollow microspheres and the adsorption for Congo red in water, Chem Eng J 189 (2012) 188e195

[17] Y.Y Liu, J Tang, X.Q Chen, J.H Xin, Decoration of carbon nanotubes with chitosan, Carbon 43 (2005) 3178e3180

[18] I.A.W Tan, B.H Hameed, A.L Ahmad, Equilibrium and kinetic studies on basic dye adsorption by oil palmﬁbre activated carbon, Chem Eng J 127 (2007) 111e119

[19] H Demir, A Top, D Balkose, S Ulku, Dye adsorption behavior of Luffa cylin-dricaﬁbers, J Hazard Mater 153 (2008) 389e394

[20] M Arshadi, M.J Amiri, S Mousavi, Kinetic, equilibrium and thermodynamic investigations of Ni(II), Cd(II), Cu(II) and Co(II) adsorption on barley straw ash, Water Resour Ind (2014) 1e17

[21] B Cheng, Y Le, W.Q Cai, J.G Yu, Synthesis of hierarchical Ni(OH)2and NiO

nanosheets and their adsorption kinetics and isotherms to Congo red in wa-ter, J Hazard Mater 185 (2011) 889e897

[22] F Yu, J Ma, Y.Q Wu, Adsorption of toluene, ethylbenzene and m-xylene on multi-walled carbon nanotubes with different oxygen contents from aqueous solution, J Hazard Mater 192 (2011) 1370e1379

[23] F Yu, Y.Q Wu, J Ma, Inﬂuence of the pore structure and surface chemistry on adsorption of ethylbenzene and xylene isomers by KOH-activated multi-walled carbon nanotubes, J Hazard Mater 237 (2012) 102e109

[24] N Jain, M.K Dwivedi, R Agarwal, P Sharma, Removal of malachite green from aqueous solution by ZeoliteIron oxide magnetic nanocomposite, J Environ Sci Toxicol Food Technol (2015) 42e50

[25] J Li, W Zhang, Adsorptive removal of malachite green from aqueous solution using modiﬁed peanut shell, Desalination Water Treat 51 (2013) 5831e5839

[26] K.S Bharathi, S.T Ramesh, Removal of dyes using agricultural waste as low-cost adsorbents: a review, Appl Water Sci (2013) 773e790

[27] Z.M Abou-Gamra, M.A Ahmed, TiO2nanoparticles for removal of malachite

green dye from waste water, Adv Chem Eng Sci (2015) 373e388

[28] A.S Sartape, A.M Mandhare, V.V Jadhav, P.D Raut, M.A Anuse, S.S Kolekar, Removal of malachite green dye from aqueous solution with adsorption technique using Limonia acidissima (wood apple) shell as low cost adsorbent,

Arab J Chem (2013),http://dx.doi.org/10.1016/j.arabjc.2013.12.019

[29] F Falaki, A Fakhri, Study of the adsorption of methyl orange from aqueous solution using nickel oxide nanoparticles: equilibrium and kinetics studies, J Phys Theor Chem 10 (2013) 117e124

[30] A Shiue, C.M Ma, R.T Ruan, C.T Chang, Adsorption kinetics and isotherms for the removal methyl orange from wastewaters using copper oxide catalyst prepared by the waste printed circuit boards, Sustain Environ Res 22 (2012) 209e215

[31] T.K Saha, N.C Bhoumik, S Karmaker, M.G Ahmed, H Ichikawa, Y Fukumori, Adsorption of methyl orange onto chitosan from aqueous solution, J Water Res Prot (2010) 898e906

[32] R Huang, Q Liu, J Huo, B Yang, Adsorption of methyl orange onto protonated cross-linked chitosan, Arab J Chem 10 (2017) 24e32