Synthesis of MnO2 Hollow Nanospheres through Selective Etching Method as an Effective Absorbent to Remove Methyl Orange from Aqueous Solution

Xiaohui Hu,Xinyi Zhang,Hong Wang,Linfeng Zhang,Fangsong Zhang

doi:10.1155/2019/7430687

Xiaohui Hu, Xinyi Zhang + Show 3 more

Open Access

https://doi.org/10.1155/2019/7430687

Copy DOI

Abstract

The discharge of dye wastewater has become an unavoidable problem for human health and the environment. Developing an economical and rapid method to prepare effective adsorbents for selective removal of dyes is extremely urgent. In this work, MnO2 hollow nanospheres (MHNSs) were prepared through the selective etching method with the MnCO3 as the sacrificial template. The effect of the pH value, contact time, and initial concentration on the adsorption of methyl orange (MO) onto the MHNSs was systematically investigated. The unique mesoporous hollow structure and large BET surface area (43.74 m2/g) of MHNSs lead to an excellent adsorption capacity (1677.14 mg/g) at the optimal condition. Furthermore, the prepared MHNSs also showed great stability (90% removal rate after four cycles). The adsorption kinetics data fitted well with the pseudo-second-order kinetic model (R2>0.9997). The overall process was jointly controlled by external mass transfer and intraparticle diffusion, and intraparticle diffusion was the dominant factor. The adsorption isotherm results showed that the Freundlich model was more accurate to describe the experimental data than the Langmuir model. The thermodynamic analysis showed that the adsorption of MO on MHNSs was spontaneous and exothermic. Moreover, the calculated ΔG° and the XPS spectra showed that the process was mainly a physical process. It is expected that MHNS has a potential application for purifying dye wastewater due to its great adsorption performance and excellent stability.

Highlights

Water pollution has become a worrying challenge for human health and the ecosystem [1,2,3,4,5,6,7]
Some broken microspheres demonstrated that the spherical hollow structure of prepared MnO2 hollow nanospheres (MHNSs) is derived from the selective etching of the MnCO3 template
The adsorption capacity of methyl orange (MO) onto the MHNSs was systematically investigated by adjusting the pH value, the initial MO concentration, and the contact time

Summary

Introduction

Water pollution has become a worrying challenge for human health and the ecosystem [1,2,3,4,5,6,7]. There is an urgent need to design an efficient method for removing dye molecules from wastewater. Various technologies such as photoelectrocatalysis, membrane filtration, chemical oxidation, and adsorption have been proposed to solve this problem [13,14,15,16,17,18]. It is necessary to design a simple operation and short-reaction-time method for preparing a MnO2 adsorbent with high efficiency. Hollow manganese dioxide adsorbents with high efficiency were prepared by a low-temperature acid etching method [30]. The adsorption capacity of prepared hollow manganese oxide microspheres under different pHs, temperatures, and initial concentrations was evaluated by the adsorption of MO. The possible mechanism of a MO molecule absorbed onto the MHNSs was studied and discussed

Experimental

Results and Discussion

Qm K L

Conclusions