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. 2016 Nov 23;3(11):160524.
doi: 10.1098/rsos.160524. eCollection 2016 Nov.

A facile, versatile approach to hydroxyl-anchored metal oxides with high Cr(VI) adsorption performance in water treatment

Ji Ma  1 , SiZhi Zuo-Jiang  1 , Yunhao He  1 , Qinglei Sun  1 , Yunguo Wang  1 , Wei Liu  1 , Shuangshuang Sun  1 , Kezheng Chen  1
Affiliations

A facile, versatile approach to hydroxyl-anchored metal oxides with high Cr(VI) adsorption performance in water treatment

Ji Ma et al. R Soc Open Sci. .

Abstract

In this study, a facile and versatile urea-assisted approach was proposed to synthesize Chinese rose-like NiO, pinecone-like ZnO and sponge-like CoO adsorbents. The presence of urea during syntheses endowed these adsorbents with high concentration of surface hydroxyl groups, which was estimated as 1.83, 1.32 and 4.19 mmol [OH-] g-1 for NiO, ZnO and CoO adsorbents, respectively. These surface hydroxyl groups would facilitate the adsorption of Cr(vi) species (e.g. HCrO4-, Cr2O72- and CrO42-) from wastewater by exchanging with hydroxyl protons or hydroxide ions, and hence result in extremely high maximum adsorbed amounts of Cr(vi), being 2974, 14 256 and 408 mg g-1 for NiO, ZnO and CoO adsorbents in the pH range of 5.02-5.66 at 298 K, respectively. More strikingly, the maximum adsorbed amounts of Cr(vi) would be greatly enhanced as the adsorbing temperature is increased, and even amount to 23 411 mg g-1 for ZnO adsorbents at 323 K. Based on the kinetics and equilibrium studies of adsorptive removal of Cr(vi) from wastewater, our synthetic route will greatly improve the adsorptivity of the as-synthesized metal-oxide adsorbents, and hence it will shed new light on the development of high-performance adsorbents.

Keywords: adsorption; chromium; metal oxides; water treatment.

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Figures

Figure 1.
Figure 1.
SEM images and XRD patterns of (a) NiO, (b) ZnO and (c) CoO adsorbents. A magnified SEM image is shown as an inset in panel b1, and digital photographs of Chinese rose, pinecone and sponge are shown as insets in panel a1, b1 and c1, respectively.
Figure 2.
Figure 2.
Conductometric titration of (a) NiO, (b) ZnO and (c) CoO adsorbents. (d) Surface charge density [OH−] of these adsorbents.
Figure 3.
Figure 3.
(a) The kinetics of Cr(VI) adsorption onto NiO, ZnO and CoO adsorbents with an initial concentration of 25 mg l−1 at 298 K. (b) Linear plots of the data in panel a based on the pseudo-second-order model.
Figure 4.
Figure 4.
Adsorption isotherms of Cr(VI) on (a) NiO, (b) ZnO and (c) CoO adsorbents at different temperatures.
Figure 5.
Figure 5.
(a) pH-dependent zeta potential values of NiO, ZnO and CoO adsorbents in aqueous solution at 298 K. (b) Effect of pH values on the equilibrium adsorption capacity for these adsorbents with initial Cr(VI) concentration of 100 mg l−1 at 298 K.
Figure 6.
Figure 6.
SEM images of (a,b) NiO, (c,d) ZnO, and TEM images of (e,f) CoO adsorbents after Cr(VI) adsorption (panels a,c,e) and desorption (panels b,d,f).
Figure 7.
Figure 7.
XRD patterns of (a) NiO, (b) ZnO and (c) CoO adsorbents after Cr(VI) adsorption and desorption. (d) Cr(VI) equilibrium adsorption on these adsorbents with initial Cr(VI) concentration of 100 mg l−1 in six successive adsorption–desorption cycles at 298 K.
Figure 8.
Figure 8.
The kinetics and equilibrium (inset) of Cr(VI) adsorption on NiO, ZnO and CoO adsorbents with an initial Cr(VI) concentration of 50 µg l−1 at 298 K.
See this image and copyright information in PMC

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