%0 Journal Article
%A Martín Martinez, María
%A Martín Martínez, María
%A Barreiro, Maria Filomena F.
%A Silva, Adrián M. T. 
%A Figueiredo, José L. 
%A  Faria, Joaquim L.
%A Gomes, Helder T. 
%T Lignin-based activated carbons as metal-free catalysts for the oxidative degradation of 4-nitrophenol in aqueous solution
%D 2017
%@ 0926-3373
%U https://hdl.handle.net/20.500.14352/107220
%X A wheat and hemp lignin, obtained from a soda pulping-precipitation process, was carbonized at 800 ◦C under N2 atmosphere. The resulting carbon material was thermally activated under oxidative atmosphere at four different temperatures (150, 200, 300 and 350 ◦C). The materials prepared at higher activation temperatures (300 and 350 ◦C) have proven their potential in the elimination of 4-nitrophenol (4-NP) from aqueous model solutions (5 g L−1) when using catalytic wet peroxide oxidation (CWPO). In these conditions we were able to remove around 70% of 4-NP after 24 h, with an efficient H2O2 decomposition, in experiments conducted at relatively mild operating conditions (atmospheric pressure, 50 ◦C, pH = 3, catalyst load = 2.5 g L−1 and [H2O2]0 = 17.8 g L−1). By increasing the working temperature to 80 ◦C, complete 4-NP removal was obtained within 48 h (against 93% 4-NP removal at 50 ◦C), with an efficiency of H2O2 consumption of 70% and a significant mineralization (61%). On the other hand, the materials prepared at lower activation temperatures (150 and 200 ◦C), with higher basicity, promote the faster but inefficient H2O2 decomposition, 4-NP removal being lower than 25% after 24 h at 50 ◦C in CWPO. This can be attributed to the formation of species other than HO• radicals during H2O2 decomposition, the recombination of the formed radicals into non-reactive species and a poor adsorption capacity.
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