Surface modification and characterization of carbonaceous adsorbents for the efficient removal of oil pollutants

doi:10.1016/j.jhazmat.2019.05.066

Journal of Hazardous Materials

Volume 379, 5 November 2019, 120673

https://doi.org/10.1016/j.jhazmat.2019.05.066 Get rights and content

Highlights

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The surfaces of activated carbon and multiwall carbon nanotubes were modified with benign oxidizing agents.
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The impact of various different combinations of green oxidizing agents was investigated in detail.
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Both carbonaceous adsorbents responded well to the functionalization and showed encouraging adsorptive removal of BTX.

Abstract

In this study, the impact of different oxidizing agents on the structural integrity of activated carbon (AC) and multiwalled carbon nanotubes (MWCNTs) was studied for the removal of BTX from aqueous solution. Seven different combinations of green oxidizing agents (mild organic acids) in conjugation with NaOCl (basic oxidizing agent) were used. The modified adsorbents were analyzed by Brunauer, Emmett, and Teller (BET) surface area analyzer, Fourier transform infrared spectroscopy (FTIR), Boehm titration, Raman spectroscopy, thermal gravimetric analysis (TGA), x-ray diffraction (XRD), zeta potential, and variable pressure field emission scanning electron microscope (VPFESEM). The results suggested that the carbonaceous sorbents modified with combination of citric acid tartaric acid, malic acid and salicylic acid (CTMS-I) showed increased surface area (O-AC: 871.67 m²/g, O-MWCNTs: 336.37 m²/g) and total pore volume (O-AC: 0.59 cm³/g, O-MWCNTs: 0.04 cm³/g), with the significantly improved thermal stability. Preliminary batch adsorption experiments conducted using the present prepared O-AC and O-MWCNTs, showed an improved performance towards the adsorption of BTX, compared with other available reported adsorbents in the literature.

Graphical abstract

Introduction

Water contamination by oil pollutants (BTX) is a serious environmental issue that is growing with the increased industrialization. There are several remedial technologies namely distillation, extraction, absorption, adsorption, and membrane separation etc. have been used. But adsorption is believed to be the better performing technology for the removal of targeted pollutants even in trivial concentration. The carbon-based nanomaterials are found to be the most promising sorbents because of their large surface areas and well-developed porosity, and unique surface chemistry etc. Among these carbonaceous sorbents bulk (AC) and discrete structures (CNTs) are influential adsorbents for the removal of these aromatic pollutants [1].

Since, the pristine nanomaterials exhibit low sorption capacity due to surface inertness and limited solubility [2], therefore, in order to efficiently remove the active surface species such as benzene, toluene, and xylene (BTX) and improve the interactions between sorbent and sorbate, the surface activity of these carbon-based nanomaterials need to be enhanced by employing covalent and non-covalent modification. In non-covalent approach, the structure of nanotubes is not much affected but the weak interactions between nanotubes and targeted pollutant might be held responsible for low uptake. Oxidation is the most widely accepted and economical way of chemical modification to solve the problems of surface heterogeneity and impurity content [[3], [4], [5]]. Type of oxidizing agents, their concentration, operating temperature, exposure time, and sonication power (specifically for nanotubes) are the governing factors that affect the extent/severity of change in surface chemistry of these nanomaterials. Various strong oxidizing agents such as H₂SO₄, HNO₃, H₂O₂, SOCl₂, KMnO₄, and ozone have been used to carry out wet chemical oxidation and their impact has been well studied and reported. These harsh oxidizing agents severely affected the micropore structure of activated carbon, shorten the length of nanotubes and generate the defects in the graphitic structure [6,7].

Mohammad et al. 2016 treated activated carbon with strong oxidizing agents such as KOH and subsequently with ammonia to introduced basic surface functional groups for the removal of benzene and toluene [8]. Nonetheless, they managed to remove only 50% of these oil pollutants. Similar results have been reported by Li et al. (2011) where NH₃ treated AC yielded only 26.5% removal of o-Xylene [9]. Moreover, Lu et al. (2008) modified carbon nanotubes with different oxidizing agents namely HNO₃, H₂SO₄, HCl, and NaOCl. They substantiated that the NaOCl modified nanotubes out performed harsh oxidizing agents [10]. It is due to the fact that the harsh oxidizing agents contribute in the impairment of structure of the potential sorbents which may lead to low uptake of targeted pollutants, therefore, it is reasonable to propose that the use of mild oxidizing agents can lead to a successful modification without significant structural damage.

Environmental friendly, low molecular weight organic acids as mild oxidizing agents have the ability to modify the surface of the sorbents without causing much structural defects towards their application for the removal of organic contaminants. Easy biodegradability, makes them nontoxic for aquatic life and dispersing ability signifies their role in un-entanglement of ropes of nanotubes [[11], [12], [13]]. Gao et al. suggested that mild oxidizing agents (citric acid, oxalic acid, and malic acid) facilitate the desorption of aromatic compounds and play their role in the degradation of hydrophobic pollutants [14]. Sun et al. modified biochar with mild organic acids namely citric acid and malic acid and proved the enhancement in porosity/surface chemistry and surface interactions with increased sorption of aromatic compound [15]. In the recent study, Alozie et al. (2018) employed citric acid, malic acid, and oxalic acid, individually for the removal of Cr (IV) and reported that the removal of targeted pollutant depends on the reducing capacity of the said mild oxidizing agents [16].

In this work, we performed a systematic study of the chemical oxidation of AC and MWCNTs by various combinations of benign oxidizing agents that possess different degrees of oxidation capacity. These benign oxidizing agents introduce oxygen containing functional groups over the surface of carbonaceous sorbents. These surface functional groups are pertinent in tailoring the surface chemistry of these nanomaterials by increasing the surface area and establishing a porous structure in them. These contributing factors improve the sorption of benzene, toluene, and xylene by electrostatic interactions, π-π interactions, and hydrogen bonding depending upon the pH of background solution [17]. Details pertaining to the literature on the comparative characteristic analysis of activated carbon and MWCNTs with varying mild oxidizing agents are very scarce. Additionally, a little effort has been made to analyze and compare the influence of these surface functional groups on the sorptive behavior towards oil pollutants namely benzene, toluene, and p-xylene etc.

Section snippets

Chemicals

The carbon based nanomaterials namely activated carbon (Purity: ≥ 98%, -100 mesh particle size, vapor pressure: < 0.1 mmHg, autoignition temperature: 850 °C), multiwall carbon nanotubes (Purity: ≥ 98%, Avg. diameter: 9.5 nm ×1 μm, density: 2.1 g/mL), oxidizing agents such as sodium hypochlorite (Purity: ≥ 99.5%), benzoic acid (Purity: ≥ 99.5%), citric acid (Purity: ≥ 99.5%), formic acid (Purity: ≥ 95%), fumaric acid (Purity: ≥ 98%), maleic acid (Purity: ≥ 99.5%), malic acid (Purity: ≥ 99%),

Pore structure characterization

The textural properties of carbon-based nanomaterials play a pertinent role in the sorption of hydrophobic organic compounds. The pristine carbonaceous samples have low physical properties due to the presence of high amount of impurities. These impurities block the surface-active sites and reduce the adsorption capacity of the sorbent. On the other hand, oxidation introduces the porosity in the structure of activated carbon and open the end caps of nanotubes which results in increased surface

Conclusion

In the present work, systematic investigation on the surface modification of activated carbon and multiwall carbon nanotubes for the adsorptive removal of benzene, toluene, and p-xylene was conducted respectively. Seven different combinations of mild oxidizing agents were selected based on the oxygen containing functional groups attached to the surface of carbonaceous adsorbents. Among the investigated combinations, citric acid, tartaric acid, malic acid, and salicylic acid (CTMS-I) modified

Acknowledgment

The authors gratefully acknowledge the financial support by Universiti Teknologi Petronas, Malaysia in the form of URIF project (0153AA-G19).

References (38)

P. Devi et al.
Utilization of sludge based adsorbents for the removal of various pollutants: a review
Sci. Total Environ.
(2017)
H. Zhang et al.
Preparation of rice straw-derived biochar for efficient cadmium removal by modification of oxygen-containing functional groups
Sci. Total Environ.
(2018)
A.A.M. Daifullah et al.
Impact of surface characteristics of activated carbon on adsorption of BTEX
Colloids Surf. A Physicochem. Eng. Asp.
(2003)
H. Anjum et al.
Effect of functionalization condition on characterization of carbonaceous adsorbent
Procedia Eng.
(2016)
J. Mohammed et al.
Adsorption of benzene and toluene onto KOH activated coconut shell based carbon treated with NH₃
Int. Biodeterior. Biodegrad.
(2015)
L. Li et al.
Surface modification of coconut shell based activated carbon for the improvement of hydrophobic VOC removal
J. Hazard. Mater.
(2011)
C. Lu et al.
Surface modification of carbon nanotubes for enhancing BTEX adsorption from aqueous solutions
Appl. Surf. Sci.
(2008)
X.-H. Zhao et al.
Removal of Cu(II) from aqueous solutions by tartaric acid modified multi-walled carbon nanotubes
Colloids Surf. A Physicochem. Eng. Asp.
(2015)
K.E. Kniel et al.
Effect of organic acids and hydrogen peroxide on Cryptosporidium parvum viability in fruit juices
J. Food Protect.
(2003)
A.L. Alpatova et al.
Single-walled carbon nanotubes dispersed in aqueous media via non-covalent functionalization: effect of dispersant on the stability, cytotoxicity, and epigenetic toxicity of nanotube suspensions
Water Res.
(2010)

Y. Gao et al.

Low-molecular-weight organic acids enhance the release of bound PAH residues in soils

Soil Tillage Res.

(2015)

B. Sun et al.

Impact of low molecular weight organic acids (LMWOAs) on biochar micropores and sorption properties for sulfamethoxazole

Environ. Pollut.

(2016)

N. Alozie et al.

Biochar immobilizes soil-borne arsenic but not cationic metals in the presence of low-molecular-weight organic acids

Sci. Total Environ.

(2018)

H. Anjum et al.

A review on adsorptive removal of oil pollutants (BTEX) from wastewater using carbon nanotubes

J. Mol. Liq.

(2019)

F. Rouquerol et al.

Chapter 7 - Assessment of Mesoporosity, in: Adsorption by Powders and Porous Solids

(1999)

Y.-H. Li et al.

Adsorption of cadmium (II) from aqueous solution by surface oxidized carbon nanotubes

Carbon

(2003)

I.I. Salame et al.

Surface chemistry of activated carbons: combining the results of temperature-programmed desorption, Boehm, and potentiometric titrations

J. Colloid Interface Sci.

(2001)

C. Tsai et al.

Characterization of bias-controlled carbon nanotubes

Diam. Relat. Mater.

(2003)

H. Teng et al.

Preparation of activated carbon from bituminous coal with phosphoric acid activation

Carbon

(1998)

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Surface modification and characterization of carbonaceous adsorbents for the efficient removal of oil pollutants

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Chemicals

Pore structure characterization

Conclusion

Acknowledgment

Sci. Total Environ.

Sci. Total Environ.

Colloids Surf. A Physicochem. Eng. Asp.

Procedia Eng.

Int. Biodeterior. Biodegrad.

J. Hazard. Mater.

Appl. Surf. Sci.

Colloids Surf. A Physicochem. Eng. Asp.

J. Food Protect.

Water Res.

Soil Tillage Res.

Environ. Pollut.

Sci. Total Environ.

J. Mol. Liq.

Carbon

J. Colloid Interface Sci.

Diam. Relat. Mater.

Carbon