Elaboration and characterization of a new activated carbon obtained from oregano residue : Application in environmental field

This study focuses on the valorization of extraction residues of medicinal plants which represent approximately 80% of the gross weight of the plant. In this context we proceeded to the transformation of “marc oregano” to a material adsorbent type activated carbon. The oregano marc, obtained after extraction of essential oils and organic compounds, has undergone a chemical activation using the phosphoric acid 85% (H3PO4). It is well known as precursors of lignocellulosic activating agent, allows the development of a large porosity in the activated material. The activated product has subsequently underwent heat treatment in the temperature range from 200 to 350 ◦C. The optimum temperature for development was set at 300 ◦C. The results obtained showed that the adsorbent material O300 has developed the interesting textural properties. It is an adsorbent material like activated carbon, which presents, according to the BET method, a specific surface of 1200 m2 · g−1 (specific surface area of commercial activated carbon is of about 905 m2 · g−1). The application of adsorbent material developed O300 in microbial decontamination of urban waste water, has revealed its effectiveness and its important adsorptive properties against pathogens pollutants from


INTRODUCTION
Morocco has very significant potentials in the field of medicinal and aromatic plants (MAP).Currently, it perfoms the important productions of the MAP and their derivatives, which gives it a significant place in the international market.Among these we distinguish the plant of oregano which is widely used in cosmetic, pharmaceutical and food industries thanks to the flavoring, antimicrobial and antioxidant properties [1][2][3].
However, the extraction residues obtained from the MAP, which represent over 80% of the weight of the plant are not yet exploited.Which requires a valorization of these residues by opening a new way of exploiting these natural resources, and the transformation of these residues at activated carbon and applying it in the environmental field.It is within this context that fits the present work which has set its objectives itself: The valuation of oregano extract residues and its transformation into adsorbent material, and application of the material developed in the field of microbial decontamination of liquid effluents urban.
Activated carbons can be produced from a number of lignocellulosic precursor materials including: nuts olive, palm, peach and apricot [4,5], sawdust [6] and nut shells [7].They are exposed to different activation methods in order to achieve a material with better adsorbent properties.The chemical activation using phosphoric acid (H 3 PO 4 ) is widely used for lignocellulosic precursors [8,9].By its acid action it intervenes as catalyst of the dehydration, it can also be promoter of separation between cellulose and lignin degradation agent and units of cellulose [10].In addition to its role as inhibitor of carbon oxidation, phosphoric acid plays a catalytic role in the dehydration reaction.By its curing agent, it also promotes the development of a three-dimensional structure with a high porosity and with a very high specific surface.

CHEMICAL ACTIVATION PROCESS OF OREGANO MARC
The chemical activation process was conducted in the following experimental conditions: A mass of marc oregano (O) was mixed with phosphoric acid at different proportions.Kneading the mixture is performed at room temperature.The resulting mixture is heat-treated under air at different temperatures: 200, 250, 300 and 350  (numbers 200, 250, 300 and 350 indicate the temperature of treatment).The samples were then washed with water and then dried at 110 • C. The products obtained were ground and stored until used.The optimization of operating conditions showed that the mass ratio marc oregano/H 3 PO 4 is equal to 1 and the temperature 300 • C are optimal conditions for preparation of activated carbon.

(DTA/TGA) analyses of the oregano marc
In order to study the thermal behavior of studied precursor and to determine the temperature range of MATEC Web of Conferences According to the thermogram of Figure 1, relative to oregano marc we observe three weight losses: The first, between 25 • C and 140 • C, corresponds to the dehydration of oregano marc between 25 and 140 • C. The second loss, which has a peak at around 300 • C, is due to the departure of volatile molecules (CO, CO 2 and CH 4 . ..) during reorganizations and transformations of organic molecules.The third loss corresponds to the pyrolysis of residual carbon.

Elemental analysis
Elemental analysis was performed to determine the contents of carbon, hydrogen and oxygen, that are the main constituents of activated carbon.This analysis was conducted for oregano marc named "O" and the adsorbent materials prepared at different temperatures.The results obtained are reported in Table 1.
The results mentioned in the Table 1 show that oregano marc is relatively rich in organic carbon, which allows being a good precursor for the preparation of activated carbon.The results also show the effect of temperature treatment on the levels of hydrogen and oxygen, which decreases with increasing temperature.
The atomic percentage of carbon increases in the material elaborated until the temperature of 300 • C, then decreases beyond this temperature because of pyrolysis reactions that take place in the material subject to a higher temperature and which allow a rearrangement of carbon skeleton during the heat treatment.

Specific surface area
The specific surface area of O 300 material was determined based on the BET method.The measurements of adsorption and desorption were performed in an apparatus type Micromeritics ASAP 2010.
The highly developed specific surface area obtained by chemical activation of oregano marc and mainly that of elaborated material at 300 • C, shows the effectiveness of phosphoric acid and heat treatment in the opening of the porosity and improvement of the specific surface area of this product.
The sample obtained at 300 • C (O 300 ) present a large surface area which is of about 1200 m 2 g −1 .This value is higher than that of commercial activated carbon which has a surface of about 905 m 2 g −1 .

Determination of porosity and morphology of the obtained materials
The porosity and distribution of the pore size of each material were determined by mercury intrusion porosimetry.The apparatus used was of type IV 9500 Micrometrics Autopore.
The results obtained from the material studied, are reported in Table 2.The internal porosity of the material is estimated at O 300 53.29%.This material is characterized by the presence of mesopores.The texture of the adsorbent material is represented by scanning electron microscopy (SEM) shown in the Figure 2.
The Scanning Electron Micrograph shows that the activation of the cellulosic precursor in the presence of phosphoric acid followed by heat treatment has a 04005-p.2REMCES XII significant influence on the morphology of the obtained materials.The result showed a surface with rough morphological structure.The sample sintered at 300 • C show highly porous structure.

APPLICATION OF ADSORBENT MATERIAL O 300 IN THE MICROBIAL DECONTAMINATION OF WASTEWATER
Previous studies [11] showed that the bacteria adhere to solid supports prepared from carbon materials.In this context, we tested the effect of the material adsorbent O 300 against fecal coliform content in the wastewater of urban discharges.We proceeded to a filtration through a column charged with the material adsorbent O 300 .The number of bacteria in the polluted wastewater tested was estimated at 10 11 (CFU/ml).The filtered waters were then analyzed and compared with the starting samples and also with filtered samples through a column charged with commercial activated carbon.The results show that treated wastewater by the material O 300 contain no bacteria (0 CFU/ml) contrary to those treated with Commercial Activated Carbon (CAC) that are still rich in bacteria pollutants (6.4.10 4 CFU/ml).These interesting results show the effectiveness of the material O 300 against water microbial pollutants.

CONCLUSIONS
This study provides a new way of valorization of medicinal plants extraction residues by their transformation to adsorbent materials.The activated carbon obtained at 300 • C is characterized by a developed textural properties and an important specific area (about 1200 m 2 g −1 ), which gives it a high adsorption capacity.The results obtained in the treatment of wastewater tested, showed that O 300 could be used as effective depolluting of wastewater thanks to these important adsorptive properties.

200 , O 250 , O 350 and O 300
• C. Materials elaborated from oregano are called: O

Table 1 .
Elemental analysis of the the oregano marc (O) and elaborated materials.
activation, we performed a thermogravimetric analysis (DTA/TGA).The thermal and thermogravimetric analyses were carried out under argon flow with a Netzsch STA 409 apparatus.Samples of about 15 mg were heated from room temperature to 1000 • C at a heating rate of 10

Table 2 .
Porosity of sample sintered at 300 • C.