Abstract
Biochar has received widespread attention as an eco-friendly and efficient material for immobilization of toxic heavy metals in aqueous environments. In the present study, three types of coconut fiber-derived biochars were obtained by pyrolyzing at three temperatures, i.e., 300, 500, and 700 °C. In addition, nine types of biochars were prepared by chemical modification with ammonia, hydrogen peroxide, and nitric acid, respectively, which were used to investigate changes in physico-chemical properties by inter alia, Fourier transformation infrared spectrophotometry (FTIR), scanning electron microscope (SEM), and BET specific surface area analysis. Batch sorption experiments were carried out to determine the sorption capacity of the biochars for lead (Pb) in aqueous solutions. Results showed that the cation exchange capacity of biochar pyrolyzed at 300 °C and modified with nitric acid increased threefold compared to the control. Loosely corrugated carbon surface and uneven carbon surface of the biochar pyrolyzed at 300 °C were produced during ammonia and nitric acid modifications. Removal rate of Pb by the coconut biochar pyrolyzed at 300 °C and modified with ammonia was increased from 71.8 to 99.6 % compared to the untreated biochar in aqueous solutions containing 100 mg L−1 Pb. However, chemical modification did not enhance adsorption of Pb of the biochars pyrolyzed at higher temperatures (e.g., 500 or 700 °C), indicating that resistance of biochars to chemical treatment increased with pyrolysis temperature.Electronic supplementary materialThe online version of this article (doi:10.1007/s11356-016-7428-0) contains supplementary material, which is available to authorized users.
Highlights
Biochar is a carbon (C)-rich material produced by thermal decomposition of biomass in an oxygen-limited environment (Al-Wabel et al 2013)
This was ascribed to the fact that coconut fiber contains significant amounts of cellulose and hemicelluloses, which is decomposed at high temperatures with small residual ash amounts (Shen et al 2012)
The number of basic functional groups, pH, cation exchange capacity (CEC), and the specific surface area (SSA) of coconut fiber biochars (CFBs) increased with the pyrolysis temperature
Summary
Biochar is a carbon (C)-rich material produced by thermal decomposition of biomass in an oxygen-limited environment (Al-Wabel et al 2013). Biochar typically has a high sorption capacity for contaminants, and on a long-term basis, it may sequester C (Zhang et al 2014; Dong et al 2015). Due to its large specific surface area (SSA), a variety of surface functional groups (hydroxyl, phenolic, carboxyl), microporous structure, high cation exchange capacity (CEC), and high pH, biochar is often regarded as an environmentally friendly and efficient sorbent for immobilizing heavy metals in aqueous environments and/or in pore water of soils and sediments (Zhang et al 2013; Yang et al 2016a, b). Environ Sci Pollut Res (2016) 23:22890–22896 studies have reported high sorption capacities of biochars for different pollutants (Mohan et al 2007; Keiluweit et al 2010). Due to its wide use, Pb has been contaminating many different environments ranging from wastewater to soil
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