Abstract
Vernadite has excellent oxidation and adsorption performance, suggesting that it has good application prospects for the removal of phenolic substances and heavy metals from wastewater. In this study, after vernadite was synthesized by two different methods, the removal performance difference between the samples synthesized by the new and traditional methods (Ver-H and Ver-OH, respectively) was explored by sample characterization, phenol degradation, and Pb2+ adsorption experiments. The results show that, compared with Ver-OH, Ver-H has a larger particle size, specific surface areas, and total organic carbon (TOC) degradation capacity; the equilibrium degradation capacity of TOC of Ver-H was increased by 31.3%. The difference in the amount of TOC degradation may be attributed to more Mn(IV) oxygen vacancies in Ver-H, which facilitate the removal of intermediate products formed during phenol degradation. In addition, the larger specific surface areas provide the mineral surface with a larger number of active sites; Ver-H can therefore adsorb more intermediate products to promote their mineralization into CO2. The adsorptions of Pb2+ by Ver-H and Ver-OH are both consistent with Langmuir isothermal adsorption, and the maximum adsorption capacities are 569.79 g/kg and 623.10 g/kg, respectively. The lack of significant difference indicates that both vernadites have strong adsorption capacities for Pb2+.
Highlights
Manganese oxides are widely distributed in the environment as important components of soil and sediments, with additional prevalence in oceans, rivers, and lakes
As shown in the figure, the diffraction peaks of the synthesized minerals are low in intensity with broad halfpeak widths, indicating that the minerals synthesized by the new method are structurally consistent with those synthesized by the traditional method, both of which are pure and slightly crystallized vernadite
Compared to the traditional method, the new method consumes a small amount of concentrated sulfuric acid instead of a large amount of sodium hydroxide; this method is simpler, economical, and environmentally friendly
Summary
Manganese oxides are widely distributed in the environment as important components of soil and sediments, with additional prevalence in oceans, rivers, and lakes. Owing to their high activity, catalytic efficiency, low toxicity, and abundance, they are widely used in the fields of adsorption and oxidative degradation, as well as in capacitors [1,2,3,4,5,6]. Vernadite is a layered manganese oxide commonly found in nature; it is formed by the close hexagonal accumulation of oxygen ions and water molecules [7] It has a high specific surface area, structural defects, and a mixed valence state of Mn [8, 9] and plays a pivotal role in the biogeochemical cycle of metals and carbon. When the pH was lower than 4, oxidation dominated; at pH exceeding 4, the removal of phenol was mainly due to vernadite adsorption
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