Abstract
A model HA-type polymer of para-benzoquinone synthetic humic acid (SHA) and its complexes with copper, iron and manganese metal ions were studied using atomic force microscopy (AFM). Natural humic acids (HA) and synthetic humic acids (SHA) were examined by fluorescence spectroscopy, which indicated similarity of SHA and HA spectra. The AFM images of SHA and its complexes revealed variable morphologies, such as small spheres, aggregates and a sponge-like structure. The SHA complexes displayed morphologies similar to those of natural HA. The presence of copper, iron and manganese ions led to the formation of aggregate-type structures in an apparent arrangement of smaller SHA particles.
Highlights
Humic substances (HS) have been the object of numerous studies
It is known that polyhydroxy phenols, as well as hydroquinones and quinones such as para-benzoquinone, are highly sensitive to the action of aqueous alkali solution, yielding polymeric products known as synthetic humic acids (SHA) [21]
This structure can be described by a sequence of phenyl rings having three hydroxyl groups per ring intercalated by monohydroxylated quinone units (Figure 1)
Summary
Humic substances (HS) have been the object of numerous studies. Because of their ability to interact with various components of the environment, HS play an important role in soil and aquatic chemistry. Humic acid (HA, insoluble at acidic pH) and fulvic acid (FA, water soluble at acidic to alkaline pH) are the major fractions in the presence of various chemically reactive functional groups, including carboxyls, phenolic and alcoholic hydroxyls, with pH-dependent properties [1,2]. Their chemical nature and reactivity are still little understood. Recognition studies of the pathway of humic acids formation compare the chemical properties of natural humic acids with those of synthetic humic acidtype polymers These studies have been an important tool to elucidate the overall molecular structure of soil organic matter. To determine the structural similarity of natural humic acid (HA) and synthetic humic acid (SHA), we used fluorescence spectroscopy and atomic force microscopy to study the influence of the aforementioned metallic ions on the structure of a polymer model
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