Rapid and efficient removal of Pb(II) from aqueous solutions using biomass-derived activated carbon with humic acid in-situ modification

https://doi.org/10.1016/j.ecoenv.2017.07.061Get rights and content

Highlights

  • Humic acid (HA) was used as a modifying agent for activated carbon preparation.

  • Oxygen-containing functional groups on the surfaces of the prepared activated carbon was enhanced.

  • The prepared activated carbon was exhibited rapid and efficient performance of Pb(II) removal from aqueous solutions.

  • The adsorption mechanisms of Pb(II) were investigated by XPS study.

Abstract

This study developed an humic acid (HA) in-situ modified activated carbon adsorbent (AC-HA) for the rapid and efficient removal of Pb(II) from aqueous media, and adsorption mechanisms are discussed. The physicochemical characteristics of activated carbons (AC) were investigated via N2 adsorption/desorption, scanning electron microscopy (SEM), Boehm's titration method and Fourier transform infrared spectroscopy (FTIR). AC-HA exhibited richer oxygen-containing functional groups than the original AC. In addition, the removal performance of AC-HA (250.0 mg/g) toward Pb(II) was greatly improved compared with the original AC (166.7 mg/g). The batch adsorption study results revealed that the Pb(II) adsorption data were best fit by the pseudo-second-order model of kinetics and Langmuir isotherm of isothermals, and therefore, the effect of the solution pH was studied. The superior performance of AC-HA was attributed to the HA modification, which contains numbers of groups and has a strong π-π interaction binding energy with AC and Pb(II) species. The adsorption mechanisms were confirmed via the XPS study. More importantly, the modified method is simple and has a low cost of production.

Introduction

The rapid development of industry is leading to significant heavy metals pollution in developing countries (Chi et al., 2017; Soylak et al., 1996). Heavy metal lead (Pb) is stored in the formations (Lu et al., 2009). Metal Pb in the human body will be oxidized into divalent lead ions, Pb(II). It will replace the body's calcium and zinc ions, thereby, causing significant harm to human body (Pan et al., 2010, Wu et al., 2014). Among many methods for dealing with Pb(II) contamination in water, adsorption by activated carbon (AC) is a rapid and convenient method and has been proven by previous studies (Kadirvelu et al., 2000; Gundogdu et al., 2012; Liu et al., 2013; Qiu et al., 2016; Sreejalekshmi et al., 2009; Yu et al., 2015).

For improving the Pb(II) removal performance by AC from aqueous solutions, chemical treatment methods were used for AC modification such as metallic oxide loading (Reed et al., 2000), surface sulfuration (Macıas-Garcıa et al., 2004), and surface oxidation (Mesquita et al., 2006). In this work, humic acid (HA) was used as a modifying agent for in-situ modification of AC to enhance the Pb(II) removal performance from wastewaters. The reasons for using HA are as follows: (1) many groups, such as carboxylic, phenol, hydroxyl, amine and quinone groups, are included in the HA result in a number of different potential sites for metal ions binding, thereby effectively improving the removal capacity of Pb(II); (2) the enhanced stability and transport, through strong π-π interactions, of HA binds ACs (Yang et al., 2011). The metal ions will be adsorbed by HA, which also forms strong complexes on the AC surfaces. The information on the Pb(II) removal on ACs modified with HA is, therefore, crucial for understanding the modification of ACs and for the removal of heavy metal pollutants. However, the HA in-situ modified AC for Pb(II) removal has not been fully investigated.

Phragmites australis (PA) is widely cultivated due to the extensive construction of constructed wetlands in China (Wu et al., 2011). PA withers in the winter and causes problems for the constructed wetland operation such as poor water quality, matrix obstruction and destruction of landscape. A reasonable harvest of withered PA can be effective to solve these problems (Wang et al., 2015a). The abundant biomass waste of withered PA as a precursor for producing activated carbon is a promising strategy (Gundogdu et al., 2013; Guo et al., 2016a; Guo et al., 2017). This approach results in a high-value use of waste, and the prepared AC contains excellent physical and chemical properties.

The objectives of this work were (1) to study the physicochemical characteristics of the HA-modified AC and compare their removal performance of Pb(II) with the original AC; (2) to investigate the adsorption mechanisms of Pb(II) using the HA-modified ACs according to different adsorption studies (the effect of contact time, initial Pb(II) concentration and solution pH) and instrumental analyses (XPS).

Section snippets

Preparation of AC-HA

Phragmites australis (PA) is the biomass precursor used for the preparation of ACs. The pretreatment of PA was described in previous studies (Guo et al., 2014, Guo et al., 2016b). The powder of PA (10 g) was impregnated in an 85 wt% H3PO4 solution with a mass ratio of 2:1 and a given amount (1 and 2 g) of humic acid (HA). After stirring for 10 h at 25 °C, the mixture of precursors was put in a muffle furnace and heated up to 450 °C and then maintained at that temperature for one hour under the N2

Characterizations

The SEM images of ACs clearly reveal the porous morphology (Fig. 1), which is attributed to the typical structure of AC (Yuan et al., 2015, Zhang et al., 2016). During the HA in-situ doping preparation process, the surfaces of the prepared AC exhibits a pore collapse phenomenon due to the correction of HA. This phenomenon is also illustrated in Fig. 2, N2 adsorption and desorption isotherms of ACs. The isotherms of modified ACs (AC-HA-1 and AC-HA-2) are lower than that of AC, which indicates

Conclusion

In this work, humic acid (HA) was doped into activated carbon (AC), which is derived from biomass wastes (Phragmites australis) via the phosphoric acid activation, resulting in modified activated carbon (AC-HAs) that is used for highly efficient removal of heavy metals from contaminated aqueous media. Compared with AC, AC-HAs exhibited higher surface acidity (2.677 mmol/g) and rich oxygen-containing functional groups as well as more preferable adsorption capacity (250 mg/g) of Pb(II). This was

Acknowledgments

This work was supported by the National Natural Science Foundation of China (51578321). Zizhang Guo (201606220157) would like to acknowledge the fellowship from the China Scholarship Council (CSC).

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