Modelos de ácidos húmicos do tipo poliméricos tem mostrado semelhanças químicas com os ácidos húmicos naturais (AH). Devido à complexidade das substâncias húmicas (SH), esses modelos de ácidos húmicos do tipo poliméricos, no qual os sítios ligantes podem ser melhores definidos, podem ser usados no estudo de metais e outras aplicações. Neste estudo, obteve-se um polímero com características análogas às dos AH coletados em área de cultivo com sistema plantio direto por 9 anos, por meio de reações de síntese, através da polimerização oxidativa em meio alcalino utilizando como precursor a para-benzoquinona. Foi realizado um estudo do ácido húmico (AH) e do ácido húmico sintético (AHS) utilizando espectroscopia de ressonância paramagnética eletrônica (RPE Humic acid-type polymer models have been shown to be similar to natural humic acids (HA) in terms of chemical properties. Due to the complexity of humic substances (HS), this humic acid-type polymer models, in which the ligand sites are better defined, can be used in the study of metals and for other applications. In this study, a polymer with characteristics analogous to those of humic acids isolated from soil surface cultivated using a no-tillage system for nine years, was obtained by means of synthesis reactions, through oxidative polymerization in an alkaline medium using para-benzoquinone as precursor. An EPR spectroscopy study was made of natural humic acids (HA) and synthetic humic acids (SHA). A semiquinone-type free radical signal was detected in the SHA. The spectra showed similar signals for HA from soil and synthetic HA complexed with Fe 3+ , Cu 2+ and Mn 2+ ions.
The adsorption kinetics and equilibrium of methylene blue (MB) onto reticulated formic lignin (RFL) from sugar cane bagasse was studied. The adsorption process is pH, temperature and ionic strength (µ) dependent and obeys the Langmuir model. Conditions for higher adsorption rate and capacity were determined. The faster adsorption (12 hours) and higher adsorption capacity (34.20 mg.g-1) were observed at pH = 5.8 (acetic acid-sodium acetate aqueous buffer), 50 ºC and 0.1 ionic strength. Under temperature (50 ºC) control and occasional mechanical stirring it took from 1 to 10 days to reach the equilibrium.
A polymer with characteristics similar to those of humic acids was obtained by synthesis reactions from oxidative polymerization in an alkaline medium using para-benzoquinone, hydroquinone and 4-aminobenzoic acid as precursors. Samples of natural and synthetic humic acid were used to examine the adsorption behavior of Cu 2? ions on these substrates. The mathematical models described by Langmuir and Freundlich equations were applied, yielding the maximum adsorption intensity values K 0 (Langmuir), maximum adsorption capacity, b (Langmuir) and the adsorbent adsorption capacity, m (Freundlich). Based on solubility studies, pH 3 was selected for the development of the adsorption experiment. The Cu 2? ion presented a favorable adsorption, with RL (equilibrium parameter) responses in Langmuir isotherms falling within the desirable ranges.
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
<p><em>Brazil has a very large surface area and therefore is not always possible the people to have access to all varieties of fruit. Considering this fact, the consumption of frozen fruit pulp has been increase. The aim of this study was to evaluate the content of total phenolics, flavonoids and antioxidant activity of nine commercial frozen fruit pulps. The antioxidant activity was evaluated by the ability to scavenging the 2.2-diphenyl-1-picryl-hydrazil (DPPH) radical, while the phenolic analysis was performed by spectrophotometry. The pulps showed levels of total phenolic compounds ranged from 14.97 mgEAG.100g<sup>-1</sup> (lemon) to 112.40 mgEAG.100g<sup>-1</sup> (orange). The highest content of flavonoids was observed for the raspberry pulp (35.09 mgEQ.100g<sup>-1</sup>). The orange pulp showed higher antioxidant capacity, with sequestration percentage of 108.79%, followed by kiwi, peach and tamarind. The results of this study demonstrated that the frozen fruits pulp are good sources of antioxidant compounds and their use should be encouraged among the population.</em></p><p>DOI: 10.14685/rebrapa.v5i3.143</p><p> </p><p><em><br /></em></p>
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