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Abstract

Phenol and its derivatives constitute widespread water pollutants. They have been found to accelerate tumor formation, cancer, and mutation. In this paper, walnut shell residue has been used as a raw material in preparation of powder activated carbon by the method of chemical activation with zinc chloride for the adsorption of phenol from dilute aqueous solutions. The influence of the mass impregnation ratio (R = ZnCl2 /walnut shell) and physical activation by the CO2 stream on the physical and chemical properties of the prepared carbons was examined. The effects of main parameters such as contact time (t), initial phenol concentration (Co), and solution’s pH were studied on phenol adsorption. The maximum uptake of phenol at 25°C was 214 mg g–1 at pH near phenol pKa and Co = 1,000 mg L–1. All data were fitted well with Langmuir isotherm, but after CO2 modification, deviation from Langmuir shows that both physical and chemical adsorption occurred during adsorption. The kinetic data were fitted to different models such as pseudo-first-order, pseudo-second-order, and diffusion model. Pseudo-second-order model has been chosen as the best model. In overall, walnut shell shows excellent adaptive characteristics for the removal of phenol and appears as a very promising sorbent due to its high uptake capacity and to its low cost.
* Corresponding author.
1944-3994/1944-3986 © 2018 Desalination Publications. All rights reserved.
Desalination and Water Treatment
www.deswater.com
doi: 10.5004/dwt.2018.22642
130 (2018) 63–70
October
Preparation of controlled porosity activated carbon from walnut shell for
phenol adsorption
Abbas Akbarzadeha, Mohsen Arbabib,*, Sara Hematib,c
aWater Research Institute (WRI), The Institute for Energy and Hydro Technology (IEHT), Ministry of Energy, Tehran, Iran,
email: abbasakbarzadeh@yahoo.com
bDepartments of Environmental Health Engineering,School of Health, Social Determinants of Health Research Center,
Shahrekord University of Medical Sciences, Shahrekord, Iran, Tel. +98 38 33333710; Fax:+98 38 33334678;
email: m.arbabi @skums.ac.ir (M. Arbabi)
cEnvironmental Health Engineering, School of Health, Shahrekord University of Medical Sciences, Shahrekord, Iran,
email: hemati.sara88@yahoo.com
Received 2 October 2017; Accepted 18 June 2018
abstract
Phenol and its derivatives constitute widespread water pollutants. They have been found to accel-
erate tumor formation, cancer, and mutation. In this paper, walnut shell residue has been used as
a raw material in preparation of powder activated carbon by the method of chemical activation
with zinc chloride for the adsorption of phenol from dilute aqueous solutions. The influence of the
mass impregnation ratio (R = ZnCl2/walnut shell) and physical activation by the CO2 stream on the
physical and chemical properties of the prepared carbons was examined. The effects of main param-
eters such as contact time (t), initial phenol concentration (Co), and solution’s pH were studied on
phenol adsorption. The maximum uptake of phenol at 25°C was 214 mg g–1 at pH near phenol pKa
and Co = 1,000 mg L–1. All data were fitted well with Langmuir isotherm, but after CO2 modifica-
tion, deviation from Langmuir shows that both physical and chemical adsorption occurred during
adsorption. The kinetic data were fitted to different models such as pseudo-first-order, pseudo-sec-
ond-order, and diffusion model. Pseudo-second-order model has been chosen as the best model. In
overall, walnut shell shows excellent adaptive characteristics for the removal of phenol and appears
as a very promising sorbent due to its high uptake capacity and to its low cost.
Keywords: Adsorption; Activated carbon; Walnut shell; Phenol
Article
Agricultural-based adsorbents have received an upsurge of interest in the water treatment industry especially in the area of adsorption. They have been widely investigated as the next generation adsorbents due to their unique physio-chemical properties and high affinity towards a wide variety of constituents ranging from organic compounds to heavy metal ions. In addition, agricultural-based adsorbents are now a cheaper and sustainable option as opposed to non-renewable and expensive adsorbents originating from coal, polymers, and petroleum residues. Among different agriculture wastes available, walnut shells exhibit great potential as activated carbon precursor. They have outstanding chemical stability, high surface area and low ash content. In this review, walnut shell-based adsorbents have been assessed in terms of their activation methods and preparation. Furthermore, adsorbents' resulting characteristics and factors influencing the adsorption capacity have been summarized and thoroughly analyzed. It has been determined that the adsorption efficiency is heavily associated with the characteristics of the adsorbent including pore diameter, surface area, surface functional groups and the nature of the background solution including pH, temperature and ionic strength. This review identifies different activation methods reported in the literature including chemical and physical activation and chemical impregnation and functionalization. The literature survey also entails a comprehensive discussion involving types of mechanisms and factors controlling adsorption behaviors towards targeted contaminants. Moreover, a detailed analysis of adsorption isotherms and kinetics involved in the adsorption process is also included. Finally, this review mentions future research needs and challenges of adsorption by walnut shell-based adsorbents.
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