Soft-Templating of Sulfur and Iron Dual-Doped Mesoporous Carbons: Lead Adsorption in Mixtures

Abstract

Lead pollution in drinking water is one of the most common problems worldwide. In this research, sulfur and iron dual-doped mesoporous carbons are synthesized by soft-templating with sulfur content 4.4-6.1 atom% and iron content 7.8-9 atom%. Sulfur functionalities of the carbons are expected to enhance the affinity of the carbon toward lead whereas iron content is expected to separate the carbon from water owing to its magnetic properties. All the carbons were characterized by pore textural properties, x-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and energy dispersive x-ray (EDX). In order to study the Pb(II) removal efficiently of this carbon in competitive mode and to mimic the real-world use, one additional heavy-metal, including Cr(III), and four other commonly occurring metals-Na(I), K(I), Ca(II) and Fe (III)-are added with lead prior to adsorption experiments. It was observed that Pb(II) adsorption capacity of this carbon was not influenced by the presence of other metals. A highly elevated concentration of Na(I), K(I), Ca(II) and Fe(III) in the eluting solution compared to the initial dose suggested possible leaching of those metals from other salts as impurities, water source or even from the carbon itself, although the XPS analysis of the carbon confirmed negligible adsorption of those metals in carbon. From the equilibrium and kinetic data of adsorption, few parameters have been calculated, including distribution coefficient, diffusive time constant and pseudosecond order rate constant. The overall results suggest that these iron and sulfur dual-doped mesoporous carbons can serve as potential adsorbents for removal of lead from drinking water in the presence of other competing metals.

Keywords: adsorption; doping; lead; mesoporous carbons; water pollution.

Figure 1

Schematic of synthesis of iron and sulfur dual-doped mesoporous carbon.

Figure 2

N₂ adsorption–desorption plots at 77 K (a) and pore size distributions (b) of iron and sulfur dual-doped carbons. obtained by nonlocal density function theory (NLDFT). Inset of Figure 2b shows micropore distribution.

Figure 3

Representative XPS peak fitting of C-1s (a), O-1s (b), S-2p (c) and Fe-2p (d) spectra for MC-Fe-S2.

Figure 4

Scanning electron microscopic (SEM) images of MC-Fe-S2 in different magnifications ((a)–(c); (a) scale bar: 200 $\mathsf{\mu }\mathrm{m}$, (b) scale bar: 10 $\mathsf{\mu }\mathrm{m}$, (c) scale bar 1 $\mathsf{\mu }\mathrm{m}$). Energy dispersive X-ray image of MC-Fe-S2 for C-K (d), S-K (e) and Fe-K (f), all scale bars 200 $\mathsf{\mu }\mathrm{m}$.

Figure 5

Demonstration of magnetic properties of iron and sulfur dual-doped mesoporous carbons by magnetization experiment (a), physical attractions of mesoporous carbons with neodymium magnet for MC-Fe-S1, (b) MC-Fe-S2, and (c) MC-Fe-S3 (d).

Figure 6

Pure Pb (II) adsorption data in pure mesoporous carbon (MC) and iron and sulfur dual-doped mesoporous carbons. All the experiments were performed in batch mode in 25 mL 100 ppb ($\mathsf{\mu }$g/L) Pb(II) and 0.025 g adsorbent (Adsorbent concentration 1 g/L).

Figure 7

Pure Pb (II) adsorbed amount as a function of initial concentration; (a) distribution of coefficient (K_d) of pure Pb(II) as a function of initial concentration (b) and adsorption kinetics of pure Pb(II) (c). The kinetic studies were performed in batch mode with Pb(II) concentration 100 ppb ($\mathsf{\mu }$g/L) and for all experiments, the adsorbent concentration was 1 g/L.

Figure 8

Pb (II) and Cr (III) adsorbed amount as a function of their initial concentration (a) Distribution coefficient (K_d) of Pb(II) and Cr (III) in the mixture (b), Kinetics of Pb(II) and Cr(III) adsorption (c) The kinetic studies were performed in batch mode with Pb(II) and Cr(III) concentration 100 ppb ($\mathsf{\mu }$g/L) and for all experiments, adsorbent concentration was 1 g/L.

Figure 9

Influence of solution pH in the adsorption of Pb(II) and Cr (III) in mixture. The pH studies were performed in batch mode with a Pb(II) concentration of 100 ppb ($\mathsf{\mu }$g/L) and the adsorbent concentration was 1 g/L.