Treatment of oily wastewater by oxidation with amphiphilic carbon-based catalysts

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Lignin-based activated carbons as metal-free catalysts for the oxidative degradation of 4-nitrophenol in aqueous solution

Publication . Martin-Martinez, Maria; Barreiro, M.F.; Silva, Adrián; Figueiredo, José; Faria, Joaquim; Gomes, Helder

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.

2017Journal article

Restricted access

Exploring the activity of chemical-activated carbons synthesized from peach stones as metal-free catalysts for wet peroxide oxidation

Publication . Martin-Martinez, Maria; Álvarez-Torrellas, Silvia; García, Juan; Silva, Adrián; Faria, Joaquim; Gomes, Helder

Peach stones were used as raw material for the synthesis of activated carbons with different properties. Firstly, peach stones were chemically activated using a 12M H3PO4 solution and carbonized under flowing air (400 °C). The obtained activated carbon, named as PS, is characterized by a high surface development (SBET=1262m2 g−1) and acidic character (pHPZC=4.2). A fraction of PS was further carbonized under N2 atmosphere at 800 °C to remove surface functionalities and to increase its basicity (PS-800). In addition, a Pt catalyst supported on PS (3% w/w Pt/PS) was synthesized by incipient wetness impregnation, resulting in a considerable hydrophilicity increasing. The synthesized materials were tested in the catalytic wet peroxide oxidation (CWPO) of highly concentrated solutions of 4-nitrophenol (4-NP, 5 g L−1) during 24 h experiments, conducted at relatively mild operating conditions (T=50–110 °C, pH=3, catalyst load=2.5 g L−1 and [H2O2]0=17.8 g L−1, corresponding to the stoichiometric amount of H2O2 needed for the complete mineralization of 4-NP). It was observed that the increase of electron-donating functionalities in PS-800 promotes the generation of reactive HO% radicals, being the activity towards CWPO twice higher than that obtained with the pristine PS. Besides, increasing operating temperature substantially enhances CWPO, finding a 80% of 4-NP removal at 110 °C. On the other hand, despite the sharp increment in H2O2 decomposition due to the presence of Pt particles in Pt/PS catalyst, this decomposition is inefficient in all cases, with a consequent poor pollutant removal. This can be attributed to the recombination of HO% radicals into non-reactive species −scavenging effects, promoted by the hydrophilicity of the catalyst.

2018Journal article

Open access

Enhancement of p-nitrophenol adsorption capacity throughN2-thermal-based treatment of activated carbons

Publication . Álvarez-Torrellas, Silvia; Martin-Martinez, Maria; Gomes, Helder; Ovejero, Gabriel; García, Juan

In this work several activated carbons showing different textural and chemical properties were obtained by chemical and physical activation methods, using a lignocellulosic material (peach stones) as precursor. The activated carbon resulting from the chemical activation, namely as CAC, revealed the best textural properties (S BET = 1521 m 2 g −1 , pore volume = 0.90 cm 3 g −1 ) and an acidic character. It was found that the activated carbon obtained at 300 °C (under air atmosphere, PAC_air), and those synthesized at 750 °C in presence of N 2 flow with bubbling of water/12 M H 3 PO 4 solution (PAC_N 2 (H 2 O)/PAC_N 2 (H 3 PO 4 )), respectively, revealed worse textural properties, compared to CAC. Two functionalization treatments, by using sulphuric acid at boiling temperature (PACS) and nitric acid-urea-N 2 heating at 800 °C (PAC-NUT), were applied to PAC_air, in order to enhance the adsorption ability of the carbon material. Several techniques were carried out to characterize the physical and chemical properties of the obtained carbon materials. The modification treatments had influence on the carbon surface properties, since the nitric acid-urea-N 2 heating treatment led to a carbon material with highly-improved properties (S BET = 679 m 2 g −1 , pH IEP = 5.3). Accordingly, the original and modified-carbon materials were tested as adsorbents to remove 4-nitrophenol (4-NP), assessing batch and fixed-bed column adsorption tests. PAC-NUT carbon offered the best adsorption behavior (q e = 234 mg g −1 ), showing a high ability for the removal of 4-NP from water.

2017Journal article

Open access

Lignin-derived carbon materials as catalysts for wet peroxide oxidation

Publication . Martin-Martinez, Maria; Barreiro, M.F.; Silva, Adrián; Figueiredo, José; Faria, Joaquim; Gomes, Helder

Lignin is one of the most abundant organic polymers in the nature, and is obtained in large amounts as a residue in paper and cellulosic bio-ethanol production industries (5-36x108 T/year) [1,2]. A major part of this industrial lignin is incinerated for energy production [3]. Nevertheless, the utilization of lignin as a fuel is not economically rational [3], and the development of alternative uses for lignin has been increasing in interest over the recent years. Due to its high carbon content and to a structure similar to that of bituminous carbon [2], it seems to be an adequate precursor for the production of activated carbon materials. Several examples can be found in the scientific literature regarding the preparation of activated carbons from lignin, using different procedures [4-6]. Highly porous materials have been developed, with specific surface areas (SSA) ca. 2000 m2 g-1 and adsorbent capacities comparable to those reported for a number of commercial activated carbons [7]. Advanced oxidation processes, primarily based on the action of hydroxyl radicals (HO) to oxidize organic pollutants, are regarded as promising solutions for the treatment of aqueous effluents containing recalcitrant and non-biodegradable compounds [8,9], typically found in wastewaters of several industries (pharmaceutical, petrochemical, dyes, paper…). These type of compounds are particularly difficult to remove by conventional biological processes, mainly when present at high concentrations (1-10 g L-1) [10]. Among advanced oxidation processes, catalytic wet peroxide oxidation (CWPO) uses hydrogen peroxide (H2O2) and a suitable catalyst to promote the formation of the HO, for the degradation of the organic species, under relatively mild operation conditions (0.1-0.2 MPa, 20-130º C).

2016Conference paper

Open access