Abstract
Herein we first report surface basicity mediated rapid and selective adsorptive removal of organic pollutants over nanocrystalline mesoporous CeO2. The role of surface features in controlling the selectivity and efficiency of adsorption is well known. Nevertheless, the possibility of tuning the adsorption capacity and selectivity of adsorbents through their surface characteristics remains less explored. In this work, the surface basicity of mesoporous CeO2 nanoparticles was improved by Er3+ doping under two different reaction conditions: via sol–gel and sol–hydrothermal methods. The nature and amount of surface basic sites were determined with the help of CO2 temperature programmed desorption (TPD). The adsorption capacity and selectivity of four different CeO2 samples were investigated using Congo red, methyl orange, and methylene blue as the model pollutants. From the adsorption studies, Er3+ doped CeO2 synthesized by the sol–gel method, having the highest amount of surface basic sites, proved to be the most efficient and highly selective adsorbent among the four developed variants of CeO2 towards Congo red. According to the proposed mechanism, surface basicity can be employed as a controlling parameter capable of tuning the adsorption capacity as well as the selectivity of CeO2 towards organic pollutants.
Highlights
CeO2 is one of the most widely employed semiconducting metal oxides in the eld of catalysis and environmental remediation,[1,2,3,4,5] mainly due to (i) its high abundance and low cost,[6] (ii) wide band-gap, non-toxicity and high stability,[7] (iii) tendency for oxygen uptake into the lattice and the possibility of a reversible transition redox system between Ce3+ and Ce4+ and (iv) the chance of formation of solid solutions with other oxides.[6]
A small shi in the peaks towards lower 2q for Er3+ doped samples was observed in the powder X-ray diffraction (PXRD) pattern, and this can be attributed to the increased ionic size of Er3+ compared to that of Ce4+
The selective and rapid adsorption ability of these nanocrystalline mesoporous CeO2 samples towards organic pollutants such as Congo red, methyl orange and methylene blue was investigated in detail
Summary
CeO2 is one of the most widely employed semiconducting metal oxides in the eld of catalysis and environmental remediation,[1,2,3,4,5] mainly due to (i) its high abundance and low cost,[6] (ii) wide band-gap, non-toxicity and high stability,[7] (iii) tendency for oxygen uptake into the lattice and the possibility of a reversible transition redox system between Ce3+ and Ce4+ (ref. 8 and 9) and (iv) the chance of formation of solid solutions with other oxides.[6]. About 10–15% of these dyes are lost during their application and a major share is discharged into water bodies. Many of these dyes have a very complex chemical structure and are found to be non-biodegradable. Depending on pH, Congo red is capable of being present in different ionic forms in water. Such a malign and widely distributed water pollutant should be treated individually by highly efficient means.[40,41,42] Adsorptive removal is one such effective way to remove organic pollutants. While developing the adsorbent material, we have focused on Congo red as our target pollutant
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