Preparation and characterization of rice husk based carbons

Journal of Environmental Treatment Techniques

2019, Volume 7, Issue 1, Pages: 150-157

J. Environ. Treat. Tech.

ISSN: 2309-1185

Journal web link: http://www.jett.dormaj.com

Preparation and Characterization of Husk Based

Carbons: Effect of the Temperature

2, 3

Yacouba Sanou , Mande Seyf-Laye Alfa-Sika , Ephraim Vunain , Samuel Pare

- Laboratory of Analytical, Environmental and Bio-Organic Chemistry, UFR/SEA, University Ouaga 1 Prof. Joseph KI-

ZERBO, 03 BP 7021, Burkina Faso.

- Water Chemistry Laboratory, FAST, University of Lome, BP. 1515, Togo

- Beijing Key Laboratory of Water Resources and Environmental Engineering, China University of Geosciences, Beijing

00083, P.R. China

- Chancellor College, University of Malawi, Department of Chemistry, Malawi

Received: 05/12/2018

Accepted: 29/03/2019

Published: 30/03/2019

Abstract

This study on the production of activated carbons (AC) prepared through chemical activation using sodium hydroxide

solution consisted to evaluate the effect of temperature using two values (500°C and 650°C). The characterization of the AC were

carried out using Brunauer-Emmett-Teller (BET) experiments, Scanning Electron Microscopy (SEM), Energy Dispersive

Spectroscopy (EDS) and Fourier Transform- Infrared (FT-IR). A comparison of pore characteristics with UIPAC’s norms

showed that all the produced carbons were mesoporous and both carbons had low surface areas of 12.13 and 29.45 m /g for AC1

and AC2, respectively; AC1 and AC2 being AC prepared at 500°C and 650°C, respectively. Low surface areas were due to the

activation solution and the temperature of pyrolysis of biomass which affect strongly the characteristics of carbon. At Zero Point

Charge, pH of both carbons is too closed and basic indicating their ability to fix cationic species on their surface.

Keywords: Activated carbon, Chemical activation, Rice husk, Temperature, Surface area.

adsorbates. Activated charcoals are well known as an

Introduction

alternative to biological and physical-chemical methods in

wastewater treatment due to its good adsorptive ability [5].

Studies have been focused on the preparation of new

composite adsorbents with low-cost materials that have the

additional virtue of possessing improved adsorptive

properties compared to other conventional adsorbents [6-8].

Activated carbons can be used for the treatment of water,

purification of petrol and adsorption of gas [9]. The use of

activated carbons requires a knowledge of parameters such

as microstructure, surface functional groups and elemental

composition which will allow to explain the efficiency and

sustainability of the carbons [10].

Rice husk is of the interest as it is an agricultural by-

product, non-toxic, bio-degradable, abundant and

renewable resource [11, 12]. Rice husk yields a high ash

content (19%) mainly consists of silica and carbon [13].

Rice straw is one of the most abundant natural sources in

the world. Its annual production is about 731 million

tonnes, which is distributed in Asia (667.6 million tonnes),

America (37.2 million tonnes), Africa (20.9 million

tonnes), Europe (3.9 million tonnes), and Oceania (1.7

million tonnes) [14, 15]. It is a kind of lignocellulosic

biomass which contains about 32–47% cellulose, 19–27%

hemicellulose, and 5–24% lignin [16, 17]. This material is

one of the most agricultural wastes listed in Burkina Faso.

Agriculture is one of the largest area of the economy of

Burkina Faso. Agricultural by/products and wastes are

discharged in the environment and can become a threat for

the environment and human health. In the context of

sustainable development, the protection of environment

became a socio-economic challenge. Therefore, researches

are looking for technical solutions to reduce or valuate solid

wastes coming from human activities. Wastes from

agricultural by products can be used for composting, biogas

production and carbon preparation. In general, commercial

adsorbents including carbons, granular ferric hydroxide,

and others are described as limited in their use due to high

operational cost for developing countries. For this reason,

other economic and eco-friendly materials are looked for.

Activated carbons (AC) can be produced from many

lignocellulosic biomasses such as coconut shell [1], maize

cob [2], Jatropha wood [3], apricot stone [4], etc. Many

researches were focused on modifying AC surfaces that

have the ability to interact with both organic and inorganic

Corresonding author: Yacouba Sanou, Laboratory of

Analytical, Environmental and Bio-Organic Chemistry,

UFR/SEA, University Ouaga 1 Prof. Joseph KI-ZERBO,

BP E-mail:

7021,

Burkina

Faso.

prosperyacson@gmail.com. Mobile: (+226) 72191530.

Journal of Environmental Treatment Techniques

2019, Volume 7, Issue 1, Pages: 150-157

In this study, rice husk is catalyzed through a chemical

activation in order to increase surface area and pores of the

adsorbent. The general objective of this work is to prepare

activated carbons based on rice husk using chemical

activation. The effect of temperature on the prepared

carbons will be studied.

3.1.2. Porosity

Pore dimensions of both carbons are listed in Table 1.

As highlighted, the pore radius of two carbons are ranging

between 10 and 250 Å indicating a mesoporous structure of

both AC [21]. According to this classification, mesoporous

materials have a smaller pore volume. Although being

mesoporous, GAC2 has the higher pore volume due to the

enhancement of pores by the high temperature. With the

higher temperature of pyrolysis, the more the interaction

between the rice husk and NaOH solution is high causing

an increase of pore dimensions. At a higher temperature,

the chemical activation affects significantly the

development of surface area and the evolution of pore

structure [20]. So, mesopores are predominant in both AC

with some micropores.

Material and Methods

.1 Preparation of activated carbons

Rice Husk (RH) of TS2 type was obtained from rice

production fields at Koubri Village (12°10'3" N, 1°21'20"

W) in Burkina Faso. RH was washed thoroughly to remove

any dirt and then dried in a stove at 105°C during 2 h.

Chemical activation of the dried RH was done using 0.16 N

NaOH. Each activated RH was filtered and dried in an oven

at 120°C for 4 h. The carbonization of dried activated RH

was carried in an oven at 500°C (denoted as AC1 hereafter)

or 650°C (denoted as AC2 hereafter) for 2 h using a heating

speed of 30°C/min. This protocol is similar to the one

described by Thajeel et al. [18] where the activated RH was

washed before the pyrolysis step.

Table 1: Pore dimensions of the AC

Carbons

Pore volume (cm /g) Pore radius (Å)

AC1

AC2

0.016

0.035

10.5

Norm of UIPAC 0.1-0.4

10-250

.2. Characterization of prepared carbons

The surface area and pore dimensions of carbons were

Figure 1 shows the distribution of pore volume of AC2

as obtaining by Barrett-Joyner-Halenda (BJH) method. The

cumulative distribution of AC2 indicates a decrease of pore

volume with pore radius increasing. The concentration of

determined

experiments with Quantachrome NovaWin

010 (Quantachrome Instruments, Version 11.0) at liquid

using Brunauer-Emmett-Teller (BET)

Data

pore volume between

2 and 15 nm indicates the

predominance of mesopores. However, the presence of pore

volume with a radius less than 2 nm indicates that there are

some micropores on AC2 surface. The pore volume

distribution of AC1 using Dubinin-Astakhov (DA) method

is given in Figure 2 where the maximum pore volume is

concentrated between 10 and 11 Å (fig. 2).

nitrogen temperature. Elemental composition of carbons

was analyzed with Energy Dispersive Spectroscopy (EDS)

using a dimensional analyzer 7401F (JOEL, JED-2300

analysis Station). While Scanning Electron Microscopy

(SEM) was used to determine the surface morphology and

microstructure of carbon particles using a microscope ICT-

VAST. Fourier Transform-Infrared spectra of charcoal

material were recorded to detect the surface functional

groups with an infrared spectrophotometer (TENSOR 27-

BRUKER GERMANY) operating in the range of 4000-

0.04

.035

0.03

.025

EPV

CPV

00 cm using the potassium bromate pellet (KBr) method.

The point of Zero Charge (pH_P_Z_Cwas determined

according to the method described by Noh et al. [19].

)

.02

.015

.01

Results and Discussion

.1. Microstructural characteristics

.1.1. Surface area

Prepared carbons have a granular form and BET

surfaces obtained from multipoint plots showed a surface

.005

areas of 12.13 and 29.45 m /g for AC1 and AC2,

respectively. The increase of temperature caused an

increase of the surface area of the AC. Indeed, the increase

of temperature during the carbonization of rice husk

involves the development of many pores causing an

increasing of surface area. The more the temperature of

pyrolysis is high, the more the surface area is likely to be

high. The chemical activation affects significantly the

development of surface area and the evolution of pore

structure [20].

100 200 300 400 500 600

Pore radius(Å)

Figure 1: Distribution of pore volume for BJH adsorption of AC2

(EPV: Excremental Pore Volume; CPV: Cumulative Pore Volume)

To analyze the pores distribution of both AC, BJH

desorption is applied in order to study the correlation

between adsorption and desorption plots. The distribution

of pores size from 20 to 150 Å is concentrated in the area of

ultramesopores indicating the mesoporosity of both AC

Journal of Environmental Treatment Techniques

2019, Volume 7, Issue 1, Pages: 150-157

(

figure 3). Maximum cumulative pores volume of AC1

found between 10 and 100 Å indicates the mesoporous

predominance (Figure 4).

were developed from the decomposition of raw RH

structure by heating and converted it to small particles with

large surface area [23].

.14

.12

Desorption

Adsorption

.08

.06

.04

.02

Figure 2: Distribution of pore volume for DA method of AC1

.1.3. Surface morphology

Figures 5 and 6 show the micrographs from scanning

electron microscopy magnified at 2000 times of AC1 and

AC2, respectively. At 50 magnifications (figure 5), a

similar grain sizes are observed. When SEM images were

magnified 2000 times, AC1 presents a fin structure and

smaller pores indicating a low pore radius, while AC2 has a

coarse structure with lager pores indicating a larger pore

volume (figure 6). SEM micrographs of activated carbons

show that they have averagely porous structures with

regular mesopores. Similar structure of AC based on rice

husk was found by Salame et al. [22]. All AC samples have

a mesoporous structure with cracks and crevices. The pores

200

400

600

Pore radius (Å)

Figure 3: Plot of distribution of pores size for BJH adsorption-

desorption of AC2

Figure 4: Plot of distribution of pores size for BJH adsorption-desorption of AC1

Journal of Environmental Treatment Techniques

2019, Volume 7, Issue 1, Pages: 150-157

.2. Physical-chemical characteristics

.2.1. Chemical composition

Dimensional analysis showed

elements as highlighted in EDS spectra (figure 7). At

00°C, all oxides in raw rice husk couldn’t be destroyed

a lot of chemical

and transformed to the carbon element. The presence of

calcium and magnesium in the composition of AC1 can be

due to a low interaction at low temperature between NaOH

solution and rice husk with the inorganic matter of raw RH

containing 5.5% of the following mixture oxides: CaO,

Fe O , MgO, Al O , Na O, K O, MnO [24].

(a)AC1

(b) AC2

Figure 6: SEM images at 2000 magnifications

The elemental composition (%, wt/wt) is determined by

dimensional analysis (Table 2). Both ACs contain mostly

carbon and silicon. High silicon content in AC2 could be

due to the conversion of carbon content to quartz. The

decrease of oxygen content in AC2 compared to AC1 is

attributable to the breaking of oxygen bond in cellulose,

hemicellulose and lignin structures at high temperature

during the carbonization.

(b) AC2

Figure 5: SEM micrographs at 50 magnifications

Journal of Environmental Treatment Techniques

2019, Volume 7, Issue 1, Pages: 150-157

.2.2. Chemical surface functions

Analysis of both TF-IR spectra (Figures 8 to 9)

showed that the band around 3419.68 cm would be

the hydroxyl group of cellulose or hemicellulose. The

band at 1589 cm can be attributed to the vibration of

the aromatic C = C double bond of lignin [25]. The

band at 1376.5 cm is attributed to the vibration of

calcium or magnesium while the band at 1095 cm

corresponds to of the C-O or Si-O bond [18]. The

band around 795 cm was attributable to the Al-O

bond and the one around 464 cm corresponds to the

vibration of the Si-O-Si bond. The band around 693

cm is the vibration of the Na-O bond. The existence

of the hydroxyl group, the C-O bond and the aromatic

C = C double bond suggest the presence of phenols

and ether oxides indicating that the sites active on AC

are mainly acid sites [23]. In addition, the correlation

between IR spectra and elemental composition

concludes that quartz is the main oxide in both ACs.

(a)AC1

.2.3. pH of zero point charge

At the point of zero charge, pH of both AC was 7.97

and 7.95 for AC1 and AC2, respectively. A higher

temperature reduced traces of activation agent in the AC

causing a slow decrease of pH. The closed pH of both AC

could be due the low difference of temperature (500 and

50°C). In addition, the use of the same chemical for the

activation of rice husk contributed to reduce the difference

between pH of both AC. The basic pH of both AC

indicates their availability to fix dyes from water.

Notwithstanding, the reactivity of adsorbent surface always

depends on the pH of the operating environment.

.3. Effect of the activation temperature on properties of

Two values of temperature (500 and 650°C) are used to

study the influence of the activation temperature on AC

properties. When activation temperature was low (500°C),

(

b) AC2

Figure 7: Energy Dispersive Spectroscopy spectra of both AC

the reaction between activated RH and CO was slow and

the surface area, total volume and micro pore volume were

relatively small. With increasing activation temperature

Table 2: Elemental composition of the AC

(650°C), the surface area, total volume and micro pore

Carbons

C (%)

AC1

46.13

8.59

2.36

39.95

0.85

0.53

1.59

AC2

40.35

7.61

1.94

49.55

0.55

volume were increased because of the higher reaction rate

between carbon and CO , and higher rate of releasing of

volatile matter. At highest activation temperature, the

O (%)

reaction between carbon and CO was very faster. So, the

Al (%)

Si (%)

speed of widening pores was faster than that of developing

pores, resulting an increase of pore diameters and formation

of mesopores. As such, the surface area, micropore volume

and micropore percentage were decreased [26].

Na (%)

Mg (%)

Ca (%)

Table 3: Surface area and pore dimensions of ACs

Surface area

Pore volume Pore radius

(

-): not detected

Name of AC

(

m /g)

(cm /g)

(Å)

10.5

AC1

AC2

12.13

29.45

0.016

0.035

Journal of Environmental Treatment Techniques

2019, Volume 7, Issue 1, Pages: 150-157

Figure 8: FT-IR spectrum of AC1

Figure 9: FT-IR spectrum of AC2

Journal of Environmental Treatment Techniques

2019, Volume 7, Issue 1, Pages: 150-157

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In this present study, both ACs are the mesoporous type

with regular pores. Elemental analysis showed that both AC

had a carbonaceous structure as highlighted by the high

carbon content. Infrared spectra highlighted that prepared

ACs have phenols and oxide ethers as chemical functions

on their surface. These chemical functions show that both

produced carbons could be used as potential adsorbents for

the removal of dyes, heavy metals and other toxic

pollutants in water / wastewater treatment. Most of active

sites available on the surface of carbons are acid sites.

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This work was carried out in the Laboratory of

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University Ouaga 1 Prof. Joseph KI-ZERBO (Burkina

Faso). The authors would like to thank Exceed / Swindon

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Vietnamese Academy of Sciences and Technology is

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with SEM micrographs and BET experiments.

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Ethical issue

Authors are aware of, and comply with, best practice in

publication ethics specifically with regard to authorship

4. P. Binod, R. Sindhu, R. R. Singhania, S. Vikram, L.

Devi, S. Nagalakshmi, N. Kurien, R. K. Sukumaran, A.

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(avoidance of guest authorship), dual submission,

manipulation of figures, competing interests and

compliance with policies on research ethics. Authors

adhere to publication requirements that submitted work is

original and has not been published elsewhere in any

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