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A study was done to evaluate the removal of a cationic dye from simulated waste water onto rice husks (RH). Spectroscopic methods such as FTIR and SEM/EDX were used for adsorbent characterization. Experimental dependency on solution pH, initial dye concentration, agitation speed, adsorbentparticle size, temperature of the solution and contact time was evaluated. The adsorption data was tested using both Langmuir and Freundlich isotherms. The data fitted well into Langmuir isotherm model with a monolayer adsorption capacity of 6.5 mg/g. Further, the separation factor (RL) value was less than unity indicating a favorable adsorption process. Adsorption kinetics was determined using pseudo-first-order, pseudo-second-order and intra-particle diffusion models. The results showed that the adsorption of malachite green onto rice husks followed pseudo-second-order model with a determination coefficient of 0.986. This work has revealed that rice husks have a great potential to sequester cationic dyes from aqueous solutions and therefore it can be utilized to clean contaminated effluents.
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Journal of Environmental Protection, 2017, 8, 215-230
ISSN Online: 2152-2219
ISSN Print: 2152-2197
DOI: 10.4236/jep.2017.83017 March 10, 2017
Adsorption of Malachite Green from Aqueous
Solutions onto Rice Husks: Kinetic and
Equilibrium Studies
V. M. Muinde1*, J. M. Onyari1, B. Wamalwa1, J. Wabomba1, R. M. Nthumbi2
1Department of Chemistry, College of Biological & Physical Sciences, University of Nairobi, Nairobi, Kenya
2Department of Chemistry, University of Johannesburg, Johannesburg, South Africa
A study was done to
evaluate the removal of a cationic dye from simulated
waste water onto rice husks (RH). Spectroscopic methods such as FTIR and
SEM/EDX were used for adsorbent characterization. Experimental depe
dency on solution pH, initial dye concentration, agitation speed, adsorben
particle size, temperature of the soluti
on and contact time was evaluated. The
adsorption data was
tested using both Langmuir and Freundlich isotherms.
The data fitted well into Langmuir isotherm model with a monolayer adsor
tion capacity of 6.5 mg/g. Further, the separation factor (
) value
was less
than unity indicating a favorable adsorption process. Adsorption kinetics was
determined using pseudo-first-order, pseudo-second-order and intra-
diffusion models. The results showed that the adsorption of malachite green
onto rice husks followed pseudo-second-
order model with a determination
coefficient of 0.986. This work has revealed that rice husks have a great pote
tial to sequester
cationic dyes from aqueous solutions and therefore it can be
utilized to clean contaminated effluents.
Adsorption, Malachite Green, Rice Husks, Isotherm, Cationic Dye
1. Introduction
Over the years dyes have been used for coloring industrial products such as food,
textile, paper, plastics, pharmaceuticals, cosmetics and tannery [1]. Currently,
there are over 10,000 dyes which are used globally. They are synthetic and aro-
matic in nature which makes them more stable and difficult to biodegrade [2].
Consequently, these recalcitrant dyes have continued to cause deleterious effects
How to cite this paper:
Muinde, V.M
Onyari, J.M
., Wamalwa, B., Wabomba, J.
Nthumbi, R.M. (2017)
Adsorption of
Malachite Green from Aqueous Solutions
onto Rice Husks: Kinetic and Equilibrium
Journal of Environmental Prote
, 215-230.
December 16, 2016
January 6, 2017
March 10, 2017
Copyright © 201
7 by authors and
Research Publishing Inc.
This work is licensed under the Creative
Commons Attribution
License (CC BY
Open Access
V. M. Muinde et al.
on human health and aquatic ecosystems due to partial or poor treatment me-
thods before disposal. Some dyes like malachite green (MG) and methylene blue
(MB) are carcinogenic and therefore it is important to remove them from efflu-
ents with respect to both environmental and aesthetical reasons [3] [4].
Adsorption is an attractive and useful method for the removal of dyes from
contaminated water samples. Scientists have adopted it as an alternative tech-
nology for eliminating noxious pollutants from water [5]. The process has ad-
vantages such as simple design with low investment in terms of initial cost [6].
Various adsorbents have been investigated for elimination of dyes from water
samples. These adsorbents include activated carbon [7], straw [8] [9], lignocel-
lulosic substrate from agricultural factories [10] and bagasse fly ash [11]. Some
adsorbents used in water purification have some drawbacks. For instance, activated
carbon (AC) requires regeneration for re-use and it is also cost-intensive [12].
Rice husks (RH) is a by-product of rice milling factory and accounts for about
20% of rice products [13]. Utilization of rice husks as a low-cost adsorbent to
eradicate pollutants is attracting attention due to its large quantity in the envi-
ronment. In this work, efficacy of RH for removal of cationic dye from water was
investigated. Dependency of parameters like contact time, dye concentration, pH
and adsorbent dosage on the removal of MG on rice husks was investigated. The
objectives of the study were to evaluate the prospect to use RH to remove mala-
chite green from contaminated water and to characterize the RH using spec-
troscopic methods such as FTIR, SEM/EDS and BET surface area.
2. Materials and Methods
2.1. Preparation of the Adsorbent
The rice husks (RH) was obtained from a milling industry in Kenya. It was
cleaned with double distilled deionized water to get rid of any adhering dirt. It
was air dried and finally dried in the oven (Memmert UM 400, Germany) at
105˚C for three days to remove moisture. The RH was then sieved into three
different particle sizes (<300, >300 <425, and >425 μm) and kept in airtight con-
tainers to be used in the subsequent experiments.
2.2. Preparation of Adsorbate
Malachite green (C52H54N4O12; C.I. 42,000; molecular weight 927.01 g/mol;
nm) was purchased from Kobian Chemicals limited, Nairobi, Kenya and used as
received. A solution of 1000 ppm was prepared using double distilled deionized
water. Serial dilution of the stock solution was done and a calibration curve con-
structed. High purity grade reagents were used. The chemical structure of mala-
chite green is given in Scheme 1.
2.3. Characterization of Rice Husks (RH)
FT-IR studies were carried out on a Perkin Elmer spectrophotometer with a
scanning range of 4000 - 400 cm−1. Pellet technique, which utilizes potassium
bromide (KBr) for analysis was adopted. Functional groups in both raw and
V. M. Muinde et al.
Scheme 1. Chemical structure of malachite green.
reacted RH were identified from the spectra obtained. The surface morphology
of the RH was done using Tescan Vega 3 XMU, (Czech Republic) scanning elec-
tron microscope which was coupled with energy dispersive X-ray spectropho-
tometer for elemental analysis. Surface area and porosity of the RH were deter-
mined using nitrogen adsorption method, (Analyzer (BET) micromeritics ASAP
2020, USA).
2.4. Experimental Design for Batch Adsorption Studies
2.4.1. Effect of Contact Time and Initial Dye Concentration
The above experiments were investigated using 40 mL of the MG dye in 250 mL
Erlenmeyer flasks. A dosage of 0.1 g of the rice husks (RH) with particle size of >
300 < 425 μm was used. The flasks were shaken on a Thermolyne orbital shaker
at a speed of 200 rpm. Varying concentrations of malachite green dye (2.3 - 9.3
mg/L) were prepared for the investigation of influence of initial dye concentra-
tion. Analysis of the supernatant solution of MG was measured using a Shimad-
zu UV-Visible spectrophotometer at a wavelength of 620 nm.
2.4.2. Effect of Solution pH
Malachite green (MG) dye solutions with a pH ranging from 3 to 9 were pre-
pared. The pH was adjusted to the desired value using either 0.1 M NaOH or 0.1
M HCl. 0.1 g of the adsorbent in 40 mL of each adjusted MG solution was agi-
tated at 200 rpm at varying time intervals and then the absorbance was meas-
2.4.3. Effect of Agitation Speed
Effect of agitation speed was investigated by using a range of shaking speeds
(50 - 250 rpm) for different experiments. 0.1 g of rice husks in 40 mL of the dye
solution was agitated on an orbital shaker at a pH of 7. The initial dye concen-
tration was 9.3 mg/L whereas the particle size was > 300 < 425 μm.
V. M. Muinde et al.
2.4.4. Effect of Adsorbent Particle Size
To evaluate the influence of particle size on the adsorption of malachite green,
rice husks (RH) of various meshes (<300, >300 <425, and >425 µm) was utilized.
0.1 g of RH in 40 mL of dye solution was agitated in 250 mL conical flasks at 200
rpm and pH of 7 at different time intervals. The dye concentration was kept
constant at 9.3 mg/L for each experiment. A graph of percentage removal (%)
against time in minutes was plotted.
2.4.5. Effect of Temperature
Adsorption of malachite green onto rice husks was investigated at 296.15,
303.15, 313.15 and 323.15 K with initial dye concentration of 9.3 mg/L and ad-
sorbent dosage of 0.1 g. The solution was shaken at 200 rpm at different time in-
tervals. All experiments were done in triplicates and absorbance measured at a
wavelength of 620 nm.
The percentage dye removal (%) and amount of dye adsorbed on to Rice
(mg/g) was computed using Equations (1) and (2), respectively:
( )
% adsorption 100 oeo
CCC= −
( )
e oe
Q C CVM= −
are initial and equilibrium concentrations (mg/L) of the dye,
is amount of dye adsorbed onto the RH at equilibrium (mg/g),
is the volume
of the dye used (L) and
is the mass of the adsorbent (g).
3. Results and Discussion
3.1. Characterization of Rice Husks
3.1.1. FTIR Analysis
FT-IR studies for rice husks were carried out using potassium bromide (KBr)
pellet technique (Figure 1) with scanning range of 4000 - 400 cm−1. The broad
peak at 3317.41 - 3900.02 cm−1 stretch indicates presence of OH and NH
groups. The peaks observed at 2913.68 and 1364.37 cm−1 were due to stretching
and bending vibration of C-H bond in methyl groups respectively (Kushwaha
. 2014). The peak at 2520.51 cm−1 is characteristic of OH from carboxylic ac-
ids whereas the stretching around 2014.69 - 2162.07 cm−1 is due to
from alkynes. The peaks between 1629.45 - 1732.02 cm−1 are characteristic of
carbonyl group.
The presence of −OH group alongside carbonyl group indicates presence of
carboxylic groups in the rice husks. The peak at 1459.11 - 1508.07 cm−1 is cha-
racteristic of aromatic groups whereas the strong peak at 1031.69 - 1046.79 cm−1
is due to C-O bending. The −OH, −NH, carbonyl and carboxyl groups are vital
sorption sites [14]. Some peaks shifted after adsorption (3317.41 to 3341.91,
3730.52 to 3788.79, 3900.02 to 3911.20, 2520.51 to 2580.85 and 1629.45 to
1635.73) whereas other peaks disappeared after adsorption (3548.75 and
3511.30). This was a clear indication that adsorption of MG onto rice husks
(RH) had taken place and new bonds were formed between MG and RH.
V. M. Muinde et al.
Figure 1. FTIR spectrum before and after adsorption of malachite green.
3.1.2. SEM/EDX Analysis
The surface morphology of rice husks was done using scanning electron micro-
scope (SEM) at 150 × magnification (Figure 2 & Figure 3). Figure 2 is a micro-
graph of rice husks (RH) before adsorption process. It was found that the adsor-
bent has an irregular porous surface which may be responsible for malachite
green adsorption. Figure 3 represents the reacted rice husks with malachite
green after adsorption. It is evident that after removal of the dye, the surface of
the RH was smooth implying that the unfilled adsorption sites of the adsorbent
were covered by the dye and therefore adsorption had taken place. Elemental
analysis of the rice husks (Table 1) indicated substantial amounts of oxygen and
silicon (42.8% and 51.82% respectively). These elements are essential in forma-
tion of bonds during adsorption process.
3.1.3. BET Surface Area and Porosity
The BET (Brunauer, Emmett and Teller) single point (P/Po) analysis for the spe-
cific surface area was 9.8 m2/g whereas the pore volume was 0.068671 cm3/g.
Pore size distribution was 280.3962 Å. These parameters affect the extent in
which adsorption process takes place.
3.2. Batch Experiments
3.2.1. Effect of Contact Time
The effect of contact time was evaluated with dye concentration of 9.3 mg/L,
V. M. Muinde et al.
Figure 2. SEM micrograph of raw rice husks.
Figure 3. SEM micrograph of reacted rice husks.
adsorbent dosage of 0.1 g, a solution volume of 40 mL and agitation speed of 200
rpm. The results revealed that the uptake of the dye was rapid at the initial stages
of adsorption reaction (30 minutes) and thereafter the adsorption was slow as it
approached equilibrium (Figure 4). The above trend of adsorption is ascribed to
substantial amount of vacant surface sites accessible for adsorption at the initial
stage. However, as the reaction approached equilibrium all the sites were already
occupied by the dye hence the adsorption was slow.
V. M. Muinde et al.
Figure 4. Effect of contact time on malachite green removal by RH.
Table 1. Elemental analysis of rice husks.
O 42.80 57.42
Mg 0.22 0.19
Al 0.59 0.47
Si 51.82 39.61
P 0.44 0.31
S 0.31 0.20
Ca 2.08 1.12
Mn 0.45 0.18
Fe 1.28 0.49
Totals 100.00
The curve in Figure 4 indicates probable monolayer coverage of dye on the
surface of rice husks. Rajesh
et al
. [15] recently reported similar results for removal
of malachite green on
Hydrilla Verticilla
biomass. The same trend was also re-
ported by Ahmad and Kumar [16] for the adsorption of malachite green onto
treated ginger waste.
3.2.2. Effect of Initial Dye Concentration
The influence of initial concentration of malachite green (MG) onto rice husks
was investigated with dye concentrations ranging from 2.3 to 9.3 mg/L and ad-
sorbent dosage of 0.1 g. The percentage (%) removal decreased with increase of
initial dye concentration of MG (Figure 5). The % decrease in adsorption is as-
cribed to saturation of the active binding sites of the rice husks at higher con-
centrations of malachite green.
3.2.3. Effect of pH
The pH of the solution affects the surface charge of the adsorbent and degree of
ionization of the dye [17]. In the present study, the pH values were varied from
3 - 9 (Figure 6) while the other parameters were kept constant. 0.1 M HCl and
0.1 M NaOH solutions were used to correct the pH to the desired value. The
percentage (%) adsorption of the dye increased with increase in pH up to an
V. M. Muinde et al.
Figure 5. Effect of initial dye concentration on adsorption of MG onto
rice husks.
Figure 6. Effect of pH on adsorption of malachite green onto rice
optimal value of pH 7.
For pH values greater than 7, the % adsorption of the dye decreased hence the
optimal pH of 7 was selected for subsequent experiments. The low adsorption of
malachite green (MG) onto rice husks at pH 3 - 6 could be attributed to H+ ions
in excess that compete with the dye cations for the adsorption sites [18].
In the pH range of 8 - 9 the adsorption decreases probably due to formation of
soluble hydroxyl complexes.
3.2.4. Effect of Agitation Speed
The study was conducted by varying the speed from 50 to 250 rpm on a Ther-
molyne orbital shaker. Adsorbent dosage was kept constant at 0.1 g, particle size
used was >300 <425 µm, pH of 7 and the volume of the dye solution was 40 mL.
The maximum removal (93.4%) of malachite green onto rice husks was achieved
V. M. Muinde et al.
at 200 rpm and then the adsorption decreased when the agitation speed was in-
creased to 250 rpm (Figure 7). Increasing the agitation speed decreases the
boundary of the transfer of dye molecules from the bulk solution to adsorbent
Figure 7. Effect of agitation speed on adsorption of MG onto rice husks.
3.2.5. Effect of Adsorbent Particle Size on Dye Removal
The influence of adsorbent particle size on adsorption of malachite green (MG)
was tested using three different meshes (<300, >300 <425, and >425 µm). The
adsorbent dosage was 0.1 g; volume of the dye solution was 40 mL, pH of 7 and
shaking speed of 200 rpm. The percentage adsorption of MG decreased from 98
to 95% on increasing the particle size from >300 to >425 µm (Figure 8). The
higher adsorption of MG onto smaller particle size of the adsorbent was attri-
buted to increased accessibility of binding sites due to increased surface area for
bulk adsorption of the dye.
Figure 8. Effect of particle size of RH on malachite green removal.
V. M. Muinde et al.
3.2.6. Effect of Temperature on Dye Adsorption
Experiments were carried out at a temperature range of 296.15 to 323.15 K. The
percentage adsorption of malachite green (MG) decreased (97.3% to 79.0%) with
increasing temperature implying that the process was exothermic, Figure 9. This
could be ascribed to weakening of adsorption forces between the active sites of
the adsorbent and adsorbate. Similar results were reported recently in the re-
moval of malachite green using sugarcane baggasse [19].
Figure 9. Effect of temperature on adsorption of malachite green dye.
4. Equilibrium Isotherms
4.1. Langmuir Adsorption Isotherm
The Langmuir equation is commonly expressed as follows [20]:
e e Lm e m
is monolayer adsorption capacity (mg/g),
is Langmuir isotherm
constant. The values of
can be calculated by plotting
(Figure 10). The essential characteristics of a Langmuir isotherm model can be
expressed in terms of dimensionless constant separation factor,
[17] which is
defined by
( )
L Lo
= +
The value of
indicate the type of bio sorption isotherm to be either unfa-
vorable (
> 1), linear (
= 1), favorable (0 <
< 1) or irreversible (
= 0).
The Langmuir isotherm model gave a good fit to the equilibrium adsorption
data, with
2 of 0.972 compared to Freundlich isotherm which gave determina-
tion coefficient of 0.93. It gave adsorption capacity of 6.5 mg/g which was
slightly higher than 1.484 mg/g value which was reported recently by Chanzu
and coworkers although their
2 was 0.704; a value which is lower than what is
reported in this study, [17]. This suggested that the removal of malachite (MG)
dye followed monolayer coverage onto homogeneous rice husks surface and
therefore interaction between dye molecules was neglible [21]. In the present
work, the
value was found to be 0.61 indicating favorable adsorption (Table
2) whereas the
value was 0.28 L·mg−1.
V. M. Muinde et al.
Figure 10. Langmuir adsorption isotherm for adsorption of MG onto rice husks.
4.2. Freundlich Adsorption Isotherm
The Freundlich equation was applied for the analysis of the initial dye concen-
tration data obtained from equilibrium studies. The equation assumes a hetero-
geneous adsorption surface and active sites with different energy. The equation
is expressed as follows [4]:
e fe
q KC=
The linear form of Equation (5) is given in the following equation
ln ln 1 ln
ef e
q K nC= +
and n are adsorption capacity and intensity respectively and their val-
ues can be obtained from intercept and the slope of the graph of ln
against ln
(Figure 11). Their corresponding values were 0.43 and 27 respectively (Table 2).
The results from Freundlich isotherm model gave a lower adsorption capacity
(0.43 mg·g−1) of malachite green onto rice husks (RH) compared to that of
Langmuir model of 6.5 mg/g. Further, the results demonstrated a better fitting of
Langmuir isotherm model than Freundlich model.
Figure 11. Freundlich adsorption isotherm for removal of MG onto rice husks.
V. M. Muinde et al.
Table 2. Langmuir and Freundlich isotherm parameters for adsorption of MG onto rice
Langmuir isotherm model constants
Freundlich isotherm model constants
n R
6.5 0.28 0.61 0.972 0.43 27 0.93
5. Kinetic Studies
5.1. Pseudo-First-Order Kinetics on Malachite Green Adsorption
The kinetic data was fitted into Lagergren pseudo-first-order rate equation
which is expressed as [22] [23]:
( )
Log log 2.303
et e
qq qkt−= −
are the adsorption capacities at equilibrium and time t whereas
1 (min−1) is the rate constant for the adsorption process. The values of
are given in Table 3. Adsorption of malachite green (MG) onto rice husks bio-
mass did not follow pseudo-first-order kinetics model since there was no agree-
ment between the experimental (Exp
) and calculated (
, cal) adsorption ca-
pacities (Table 3). Furthermore, the coefficient of determination (
2) value was
relatively lower (0.78) compared to pseudo-second-order value of 0.986 (Figure
Figure 12. Pseudo-first-order adsorption kinetics of MG onto rice husks.
5.2. Pseudo-Second-Order Kinetics on Malachite Green
The Lagergren pseudo-second order kinetics equation is expressed in a linear
form as shown below [16] [24] [25]:
t ee
tq kq qt= +
where the equilibrium adsorption capacity (
) and the second order constant
(g·mg−1·min−1) can be determined from the slope and intercept of plot of
(Figure 13). The experimental data from this work fitted well into
V. M. Muinde et al.
pseudo-second-order model with a determination coefficient (
2) of 0.986).
There was good relationship between experimental and calculated value of
(Table 3) indicating that the adsorption experiment followed pseudo-second-
order than the pseudo-first-order kinetics model. Similar results were reported
for removal of methylene blue from aqueous solutions using
Eichhornia Cras-
[24]. The second order constant,
2 was 4.3 g·mg−1·min−1.
Figure 13. Pseudo-second-order adsorption kinetics of MG onto rice husks.
Table 3. Kinetic parameters for adsorption of MG onto rice husks.
order Pseudo-second-order
, cal. (mg·g−1)
1 (min−1)
, cal. (mg·g−1)
2 (g·mg−1·min−1)
0.622 0.05 0.014 0.78 0.625 4.3 0.986
5.3. Mechanism of Adsorption of Malachite Green onto Rice Husks
Weber-Morris Intraparticle Diffusion Model
The above model was applied to illustrate existence of competitive adsorption
processes in the removal of malachite green onto rice husks. The following ex-
pression is used to describe the model [4] [26]:
t id
q kt c= +
is the intra particle diffusion constant (mg·g−1·min0.5) and c represents
the boundary layer thickness. The values of
and c were calculated from the
slope and intercept of the graph (Figure 14) of
against √t in minutes respec-
tively. From the graph,
was found to be 0.057 mg·g−1·min0.5 and c was 0.303
with a determination coefficient (
2) of 0.966. Since the line of the graph (Figure
14) did not pass through the origin, it indicates that intra particle diffusion was
not the only process controlling the adsorption of malachite green dye onto the
rice husks.
V. M. Muinde et al.
Figure 14. Intraparticle diffusion graph for adsorption malachite green.
6. Conclusion
The results obtained from this work indicate that rice husks (RH) can be used as
a low-cost adsorbent for sequestering malachite green from aqueous solutions
such as waste waters. The characterization studies with scanning electron mi-
croscope (SEM) and Fourier transform infra red spectroscopy (FTIR) indicated
presence of sufficient pores and functional groups on RH, which can be used in
the adsorption process. Further, this study revealed that batch adsorption is in-
fluenced by factors such as initial dye concentration, pH of solution, agitation
speed, contact time and temperature. Maximum dye removal of 95.7% was
achieved using initial dye concentration of 2.3 g/L and pH of 7. The Langmuir
adsorption isotherm gave the best fit to the experimental data, suggesting mo-
nolayer adsorption on a homogeneous surface. The adsorption kinetics followed
the pseudo-second-order model with a determination coefficient (
2) of 0.986.
The percentage adsorption of malachite green (MG) decreased from 97.3% to
79.0% with increasing temperature (296.15 - 323.15 K), indicating an exothermic
process. The line of intraparticle diffusion graph did not pass through the origin
and therefore there were other mechanisms controlling the adsorption of MG
onto rice husks.
Deutscher Akademischer Austausch Dienst (DAAD) for the financial support
and also University of Nairobi, Department of Chemistry where most of this re-
search was carried out. Finally, we thank Richard M. Nthumbi of University of
Johannesburg for his assistance in the characterization of the rice husks adsor-
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... FESEM images of GCNP after adsorption showed heterogeneous morphoplgy and disappearance of pores indicating the coverage of surface by dye molecules in the pores (Fig. 8) [53][54][55]. ...
... XRD analysis helps in determining alterations in the crystallinity of adsorbent as well as dye due to adsorption as loading of dye molecules on adsorbent can affect crystallinity due to their diffusion into micro and mesoporous regions of the adsorbent [53]. Comparison of GCNPs diffraction patterns before and after adsorp-tion showed differences in terms of slight decrease n peak intensity, disappearance of the peak which could be due to crystallinity loss [53,54]. Differences in before and after diffractograms can be an thereby possible indication of intercalation of dye molecules on GCNPs surface (Fig. 10) [54,55]. ...
... Comparison of GCNPs diffraction patterns before and after adsorp-tion showed differences in terms of slight decrease n peak intensity, disappearance of the peak which could be due to crystallinity loss [53,54]. Differences in before and after diffractograms can be an thereby possible indication of intercalation of dye molecules on GCNPs surface (Fig. 10) [54,55]. ...
Biowaste based nanoadsorbents have gained much attention in the recent times for wastewater decolourization owing to their low cost, high surface area and high adsorption capacities. In the present research, garlic peel based nanoparticles (GCNP) were synthesized at different temperatures by a one step pyrolytic green approach for the effective removal of cationic dye, malachite green from the aqueous medium. The surface properties of Garlic nanoparticles were elucidated by N2 adsorption- desorption and all the GCNP samples were found to exhibit Type IV(a) isotherm indicating the presence of mesopores in carbon matrix. Using BET calculations, highest surface area (380 m²/g) was obtained for GCNP synthesized at 1000 ◦C. Characterization of nanoparticles was done by XRD, EDAX, SEM and FTIR studies before and after the dye treatment. Adsorption studies conducted using different parameters like contact time, concentration and pH and dosage of adsorbent showed removal efficiency above 90 % for the contact time of 70 minutes. Best adsorption experimental results were obtained for GCNP synthesized at 1000◦C ascribable to its high surface area, higher total pore volume (0.26 cm²/g) and higher carbon content. Four adsorption isotherm models were used to validate batch equillibrium studies and the results showed data in good agreement with Langmuir and Freundlich isotherms with maximum Langmuir adsorbtion capactiy to be 373.7 mg/g. Kinetic modelling of the data showed best fit with the Pseudo second order model with rate constant value of 48.726 g mg⁻¹ min⁻¹. Regenerative studies were conducted conducted upto 6 cycles. Also the GC nanoparticles were tested for their compatibility in membrane form wherein, removal efficiency results were obtained for GCNP anchored in polyvinyl difluoride (PVDF) and polysulfone (PSF) membrane matrix for dye adsorption.
... This denotes that physical attraction and chemical attraction took place between the dye molecules and the PAZ polymer causing effective decolourization of dyes. Hence electrostatic force of attraction and weak vanderwaals force of attraction plays a significant role, causing the dye decolourization [35]. ...
... RT/b, where b symbolizes the adsorption heat (kJ/mol), R is the gas constant (8.314 J/mol.K), T the temperature (K), and A is the adsorption equilibrium binding constant proportional to the maximal binding energy (L/mg)[34][35]. ...
Water is a life-giving and energising substance. People all around the world are struggling due to the deficiency of fresh and hygienic potable water. Clean water is a significant resource for human civilization on Earth and one of the most crucial requirements for all living species to survive. Contamination of water due to synthetic dye is one of the most serious threats to human health. The photocatalystspoly(azomethine), ZnO, TiO2, poly(azomethine)/TiO2 and poly(azomethine)/ZnO were synthesized and used to remove cationic and anionic dyes from contaminated water.The band gap of photocatalysts, reaction kinetics, isotherm studies and thermodynamic studies were assessed and the photocatalytic studies revealed that polyazomethine/ZnO and polyazomethine/TiO2 nanocomposites had significantly higher photocatalytic activity and are more efficient at removing dyes from effluents than PAZ, ZnO, and TiO2 in natural sunlight.
... adsorbent-adsorbate interfaces of both CR and MG dyes. Finally, the values of ΔH° indicate that the adsorption type for both dyes is physisorption[37][38][39]. ...
Full-text available
The fabrication of nanoparticles by green routes is gaining extensive attention owing to their reliability, sustainability, being eco-friendly, cost-effectiveness, high productivity, and purity and biocompatibility. In the current study, zinc oxide nanoparticles (ZnO NPs) were successfully fabricated via green route using leaf extract of Pontederia crassipes. The synthesized sample was characterized by various techniques, such as FT-IR, XRD, BET, FEEM, TEM, and EDS. The characterization results confirmed the success of the synthesis process, with prepared ZnO NPs exhibiting good purity. The synthesized ZnO NPs were employed as an adsorbent for the removal of carcinogenic anionic congo red (CR) and cationic malachite green (MG) dyes from aqueous solutions. All experiments were performed in a batch process where the effects of dye concentration, adsorbent dose, equilibrium time, temperature, pH, and salinity have been investigated. High removal capacity of 96.39% for CR was achieved with pH 2, dye concentration of 40 mg/L, and adsorbent dosage of 1.2 g within 30-min equilibration time. On the other hand, the maximum adsorption efficiency for MG dye was 95.75% with pH 7, dye concentration of 15 mg/L, and ZnO dosage of 1.2 g within 60-min equilibration time. The Temkin and Freundlich isotherm models match the dye adsorption process for CR and MG, respectively. Depending on the thermodynamic functions, it was proven that the adsorption process for both dyes is endothermic and spontaneous. Employing ZnO as anti-breast cancer (MCF7 cancer cell line) was also studied. ZnO NPs exhibit high in vitro cytotoxic efficacy against cancerous MCF7 (IC50 = 39.3 μg/mL.
... In the present paper, batch mode adsorption method was used to remove MG dye from aqueous solution using MLP and MLB adsorbents and the results obtained are given in tables. The adsorption percentage of MG dye onto given adsorbents obtained is almost similar to the adsorbents found in literature like biochar derived from sheep manure (98.94%), rice husk (95.7%), wood apple shell (98.87%), etc. (Muinde et al. 2017;Sartape et al. 2017;Dileko glu 2021). ...
In the present study, the use of low-cost, highly efficient, eco-friendly, and abundantly available (in Kashmir region, J&K India) willow leaves from which adsorbents like willow leaves powder (WLP) and willow leaves biochar (WLB) were prepared, have been found to be efficient for malachite green (MG) dye removal and can be used as an alternative to the current expensive methods of removing the same dye from an aqueous solution. The techniques like Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), and carbon, hydrogen, nitrogen, sulphur (CHNS) analyser were used to characterize the samples without any chemical treatment. SEM of the adsorbents shows the presence of different sized pores, cracks, and crevices. FTIR and CHNS show functional groups and elemental concentration, respectively. The effects of various experimental parameters such as contact time, adsorbent dosage, initial dye concentration, salt treatment, and pH were investigated and optimal experimental conditions were obtained. It has been found that Langmuir, Freundlich, and Temkin isotherms were useful for describing the equilibrium of adsorption system. The equilibrium adsorption data in this research work was found to follow both Langmuir and Freundlich isotherm models and maximum monolayer capacity of WLP and WLB were found to be 10.014 and 21.244 mg/g, respectively. The experimental data for both WLP and WLB followed pseudo-second-order kinetic model with R2= 0.999. Intraparticle diffusion model reveals that more than one mechanism influenced the adsorption process. Thermodynamic study concluded that the adsorption is spontaneous for both adsorbents but exothermic for WLP and is endothermic in nature for WLB. Present exploration and comparison with other reported adsorbents concluded that, WLP and WLB may be useful as low-cost attractive option for the removal of MG dye from aqueous solution and therefore, also from wastewater containing MG dye.
... Besides, the adsorption band of 1,622 cm -1 which is mostly a υCOO (the amide I), suggesting the existence of dipolar interactions between the negative charge of the carboxylate group and MG as a cationic dye, the H-bonding interaction and the dipoledipole H-bonding interaction. The new bands, linked to the band vibrations of the MG molecules, appear at 1,516 cm -1 , 1,447 and 1,320 cm -1 are due to the bending vibration of the C-H bond in the methyl groups, the aromatic part and amide II, respectively [57,58]. These bands indicate that the MG reacted with the clay surface and new bonds were formed between the MG and the clay. ...
Full-text available
This work reports the study of the adsorption of malachite green (MG) dye on Moroccan clay according to different parameters impacting the adsorption phenomenon, such as pH, the temperature of the medium and the MG dye concentration. The clay used as adsorbent was initially characterized by X-ray fluorescence spectrometry, Fourier-transform infrared spectroscopy (FTIR), X-ray diffrac-tion, Brunauer-Emmett-Teller, and thermogravimetric analysis. The results indicate that the equilibrium of MG adsorption is reached in 90 min. The efficiency of dye removal on clay increases with the contact time, initial dye concentration, solution temperature and pH. The experimental data obtained were examined using isothermal and kinetic models based on the errors calculated values of R 2 (correlation coefficient) and χ 2 (chi-square). It was found that the nonlinear forms of the Langmuir isotherm and the pseudo-second-order kinetic model are the best-fitting with experimental data. The thermodynamic study showed that the adsorption was a spontaneous and exo-thermic process. However, FTIR analysis of the adsorbent, before and after MG adsorption, shows that the mechanism of MG adsorption occurs through the phenomenon of chemical interaction between the adsorbate and the adsorbent.
... The rate is also experiment-dependent (adsorbent, contaminant, adsorption method). In general, increasing the rate will increase the biosorption removal rate of adsorbed impurities by minimizing mass transfer resistance, but may damage the physical structure of the biosorbent [147][148][149][150][151][152]. ...
Full-text available
The primary, most obvious parameter indicating water quality is the color of the water. Not only can it be aesthetically disturbing, but it can also be an indicator of contamination. Clean, high-quality water is a valuable, essential asset. Of the available technologies for removing dyes, adsorption is the most used method due to its ease of use, cost-effectiveness, and high efficiency. The adsorption process is influenced by several parameters, which are the basis of all laboratories researching the optimum conditions. The main objective of this review is to provide up-to-date information on the most studied influencing factors. The effects of initial dye concentration, pH, adsorbent dosage, particle size and temperature are illustrated through examples from the last five years (2017–2021) of research. Moreover, general trends are drawn based on these findings. The removal time ranged from 5 min to 36 h (E = 100% was achieved within 5–60 min). In addition, nearly 80% efficiency can be achieved with just 0.05 g of adsorbent. It is important to reduce adsorbent particle size (with Ф decrease E = 8–99%). Among the dyes analyzed in this paper, Methylene Blue, Congo Red, Malachite Green, Crystal Violet were the most frequently studied. Our conclusions are based on previously published literature.
The aim of this research was to pillar the bentonite clay (Bt) with polyhydroxy tin chloride. The synthesized Tin‐pillared interlayer clay (Sn‐PILC) was characterized using X‐ray diffraction (XRD), Fourier Transform Infrared spectra (FT‐IR), Brunauer‐Emmer Teller (BET) analysis, Thermogravimetric analysis (TGA), and Scanning Electron Microscopy (SEM). Adsorption capacity of raw‐Bt and tin pillared interlayer clay (Sn‐PILC) was examined for two dyes, namely, Malachite Green (MG) and Chrysoidine‐Y (CY) from their aqueous solutions. The effects of physicochemical parameters like solution pH, dose, and dye concentration were investigated. The maximum adsorption efficiency at equilibrium dye concentration for Sn‐PILC was 66.229 mg g–1 for MG and 63.792 mg g–1 for CY. Sn‐PILC obeyed Langmuir isotherm for both the dyes whereas raw‐Bt followed Freundlich isotherm. On the other hand, both adsorbents followed PFO as well as PSO kinetic model, indicating physisorption assisted by chemisorption. Thermodynamic studies were performed to determine the adsorption behavior of Sn‐PILC for both the dyes. Regeneration studies revealed 80% efficiency up‐to five adsorption‐desorption cycles.
Full-text available
This research studied the modeling of malachite green (MG) adsorption onto novel polyurethane/SrFe12O19/clinoptilolite (PU/SrM/CLP) nanocomposite from aqueous solutions by the application of biogeography-based optimization (BBO) algorithm-assisted multilayer neural networks (MNN-BBO) as a new evolutionary algorithm in environmental science. The PU/SrM/CLP nanocomposite was successfully fabricated and characterized by some spectroscopic analyses. Four variables influencing the removal efficiency were modeled by MNN-BBO and response surface methodology (RSM). The MNN-BBO model gave higher percentage removal (99.6%) about 7.6% compared to the RSM technique. Under optimal conditions obtained by MNN-BBO, the four independent variables including pH, shaking rate, initial concentration, and adsorbent dosage were 6.5, 255 rpm, 50 mg.L⁻¹, and 0.08 g, respectively. Under these conditions, the results were fitted well to the Langmuir isotherm with a monolayer maximum amount of sorbate uptake (qmax) of 68.49 mg.g⁻¹ and the pseudo-first-order kinetic pattern with the rate constant (K1) of 0.01 min⁻¹ with the R² values of 0.9248 and 0.9980, respectively. The results of thermodynamics demonstrated that the MG uptake was not spontaneous due to the positive value of the adsorption ΔG. In addition, the positive values of ΔS (0.079 kJ/mol K) and ΔH (30.816 kJ/mol) indicated the feasible operation and endothermic approach, respectively. Besides, the wastewater investigations showed that the nanocomposite could be used as a new promising sorbent for efficient removal of MG (R% > 72) and magnetically separable from the real samples. Graphical abstract
Furfural presence in fermentation culture media provokes an inhibition effect in yeast growth. In fact, is a key toxin in lignocellulosic hydrolyzates. This research work attempts to analyze the use of olive endocarp (OE) as adsorbent to remove furfural from aqueous solutions. The adsorption experimental sets studied the effect of particle size, agitation speed, adsorbent load, temperature, and initial furfural concentration. As results, higher adsorption percentages were observed when fragmented OE was smaller than 1.2 mm, agitation speed in the range 80–250 rpm, and the adsorbent load was 90 g OE/300 cm³ of furfural solution (1 g dm⁻³). The equilibrium adsorption capacities, qe, values were varied from 0.270 to 4.750 mg g⁻¹ for initial furfural concentrations of 0.78 g dm⁻³ to 5.89 g dm⁻³. The adsorption data fit to pseudo-second order kinetic model showed good fit values (R² ≥ 0.997, SE ≤ 5%). Dubinin-Radushkevich (DR) model was considered as the best fit (R² = 0.999, SE = 2.95%) for the different studied isotherms. An adsorption free energy value of 896 J mol⁻¹ indicated a physical adsorption mechanism. Remarkable increases in furfural adsorption percentages have been achieved submitting natural olive endocarps to acid treatments.
Full-text available
Malachite Green (MG), a cationic synthetic dye is considered hazardous when discharged into the water bodies without any adequate treatment. It can affect the multiple segments of the environment leading to irreversible persistent changes. So, there is a need for remediation with cost-effective method to remove dyes from effluents. Adsorption is one such technique to remove dyes from wastewater and is effective and economical. The present study describes the removal of MG cationic dye from wastewater using eco-friendly and biodegradable lignin extracted from hydrothermally treated rice straw by adsorption process. Functional group analysis and morphological characterisation was done to the extracted lignin after quantification. The maximum percent removal of MG 92 ± 0.2 % was observed from a series of batch experiments at optimum process parameters of: contact time 80 min, initial dye concentration 50 ppm, lignin dosage 0.25g, pH 7, temperature 30 ⁰ c and with 100 rpm agitation speed. The adsorption kinetics and isotherms were determined for the experimental data using four kinetic models (pseudo-first-order, second order, pseudo-second-order and intra-particle diffusion model) and two isotherm models (Langmuir and Freundlich). The results suggested that the kinetics data fit to the pseudo-second-order kinetic model with the maximum adsorption capacity 36.7 mg/g and the two isotherm models were applicable for the adsorption of MG onto the lignin. Additionally, the thermodynamic parameters ΔS o , ΔH o and ΔG o were evaluated. Therefore, lignin which is an environmental friendly and low cost carbon material that can be used as an adsorbent for dye removal.
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Adsorption kinetics of malachite green onto Algerian activated phosphate rock was studied for better removal of the dye from wastewater. The prepared sorbent displayed à good surface area of 42.2 m²/g. The adsorption process appeared to be of physisorption nature and it took less than 60 min to get equilibrium whereas the kinetics indicated that the adsorption is likely a second order reaction which is further proved with the high R2 value. The intraparticle diffusion model confirms an adsorption mechanism limited on two steps, i.e., (1) surface adsorption, and (2) pore diffusion with a diffusion parameter of Di=10-18 cm2 s-1. Besides, semi-empirical theoretical calculations provide a new insight into adsorption mechanism as a principle of hydrogen bonding and ionic interaction.
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Activated carbon was prepared from Enteromorpha prolifera by zinc chloride activation. The adsorption behaviors of three reactive dyes (Reactive Red 23, Reactive Blue 171 and Reactive Blue 4) onto this biomass activated carbon were investigated in batch systems. The experimental findings showed that the removal efficiencies of three dyes onto activated carbon were maximum at the initial solution pH of 4.5 - 6.0. Thermodynamic studies suggested that adsorption reaction was an endothermic and spontaneous process. Adsorption isotherm of the three dyes obeyed Freundlich isotherm modal. Dye adsorption capacities of activated carbon were 59.88, 71.94 and 131.93 mg·g?1 for RR23, RB171 and RB4 at 27?C, respectively. Second-order kinetic models fitted better to the equilibrium data of three dyes. The adsorption process on activated carbon was mainly controlled by intraparticle diffusion mechanism.
Full-text available
Batch experiments were conducted to study the biosorption of Malachite Green (MG) onto polylactide (PLA)/spent brewery grains (SBGs) films. Films were prepared by solvent-casting method using dichloromethane. Effects of contact time, pH, salt concentration, and optimal experimental condition was evaluated. At pH 6.89 and low salt concentration, Malachite Green was removed effectively. The isotherm data fitted the Freundlich model with 0.969 R2 value and 0.738 slope implying chemisorptions process. The biosorption process followed pseudo-second order kinetics with calculated adsorption capacity at equilibrium (qe) of 0.572 mg/g at 23 °C. The investigation showed that PLA/SBGs films are effective in dye removal from textile, paper and leather industries effluents.
This study investigated the removal of Cobalt ions from aqueous solution using Granular Activated Carbon (GAC) such as Filtrasorb-400 (F-400) in presence of different organic complexing agent, Batch mode experiments were carried out to obtain adsorption kinetics of Co2+ ions onto granular activated carbon F-400 loaded with Salicylic acid, 3,5-Dinitrosalicylic acid and 5-Sulphosalicylic acid one by one at constant temperature 25 ± 0.5 ºC and pH 5. Three different kinetic models namely pseudo first order, pseudo second order and Weber-Morris intra particle diffusion models were applied to experimental results. The experimental study revealed that 300 min of contact time was enough to achieve equilibrium for the adsorption of cobalt. The experimental results indicated a significant potential of the GAC as an adsorbent for cobalt ions removal. © 2015, Journal of Chemical and Pharmaceutical Research. All rights reserved.
In the present study, Hydrilla verticillata biomass was investigated as a novel biosorbent for the uptake of basic dye malachite green from its aqueous solution. Kinetic and equilibrium studies were carried out in batch process. Batch adsorption experiments were conducted to study the effect of pH, temperature, sorbent dosage, initial dye concentration, and contact time for the removal malachite green dye. The dye uptake was maximum for the initial pH of 8, temperature of 30oC, sorbent dosage of 0.55g, initial dye concentration 200mg/l and contact time - 150 min. The kinetic studies were well modeled using pseudo first order and second order with isotherm studies.
This review provides applications of conventional and non-conventional adsorbents for removal of pesticides from wastewaters. The data presented are mainly based on laboratory studies and show potential advantages for treatment of pesticides bearing wastewater by various adsorbents.
In this work, the adsorption potential of agricultural waste material sugarcane baggase to remove malachite green dye from aqueous solution was investigated. The adsorbent was characterized by BET surface area measurement and FTIR analysis. Various parameters such as initial dye concentration, contact time, adsorbent dose and temperature were studied to observe their effects on the dye adsorption process. At optimum values of the above mentioned parameters, more than 95% removal efficiency was obtained within 120 min at adsorbent dose of 1 g/L for initial dye concentration of 50 mg/L. The adsorption of dye was found to follow a pseudo-second-order rate equation. Various thermodynamic parameters (ΔGo, ΔHo, ΔSo) were also estimated. Adsorption mechanisms were investigated with intra-particle diffusion model, Furusawa and Smith model and Boyd's model to get deep insight of adsorption process. Langmuir isotherm model was fitted the best for the adsorption system with an adsorption capacity of 190 mg/g of adsorbent. The present adsorbent may be considered as an alternative adsorbent for the better performance of the malachite green dye removal from its aqueous medium.