Surface modification may lead activated carbon (AC) to take on different properties. This study aimed to promote surface modification of activated carbons using corona treatment (electrical discharge). In this study, powdered commercial activated carbon was used. Activated carbons were subjected to corona treatment at different exposure times (2, 5, 8 and 10 min) at 4.5 cm height from the source. To observe differences promoted by treatment, activated carbons were analyzed by acidity, surface functional groups, Fourier Transform Infrared Spectroscopy (FTIR), elemental analysis (ChN), proximate analysis and thermogravimetry. Corona treatment impacted surface chemistry of activated carbons. There was a trend of increasing surface acidity according to exposure time. There were changes in functional groups, increasing carboxyl acid and decreasing lactone and phenol groups. FTIR analysis showed peaks in the bands at 3500, 1650 and 1300 cm-1. Increase of oxygen content and decrease of carbon content were also found. Immediate analysis followed similar tendency for volatile and fixed carbon content. There were also differences in thermogravimetry analysis. Treated activated carbons were different compared to virgin activated carbon. This difference was performed by surface oxidation. Thus, this study showed that corona treatment caused surface modifications and might impact adsorption process.

The main and new surface modification methods of activated carbon (AC) and their influence on application (adsorption capacity) were reviewed. Adsorption capacity is an important issue, contributing to hazardous substances environment management. According to literature, it is true that surface chemistry strongly affects adsorption capacity. Surface chemistry can be modified by several methods that lead to different activated carbon properties. Furthermore, adsorbate properties, and their relationships with surface structure, can impact adsorption properties. Surface modifications can be conducted by adding some atoms to the surface structure, making the surface more acidic or basic. Introduction of oxygen and ammonia atoms (chemical modification) are the main processes to make the surface more acidic and basic, respectively, although may bring chemical wastes to environment. Surface modification is done by chemical and physical modifications that lead activated carbons to present different properties. The main and new methods of chemical and physical modifications are compared and presented in this paper. Some new physical methods, like corona treatment, plasma discharge and microwave radiation, can be applied to cause surface modifications. Corona treatment can be a practical and new way to cause surface modification on an activated carbon surface.

Dye degradation is a significant topic in environmental science, since dyes can bring several problems to the environment. Activated carbon (AC) is an important material used as adsorbent of these hazardous substances, but need to be improved especially into specific substances. This paper aimed to evaluate the impact of activated carbon surface modified by corona treatment (electric discharge) on adsorption of different dyes. Activated carbons were treated by corona treatment to cause surface modification, modifying exposure time to treatment (2, 5, 8 and 10 minutes). Evaluation of adsorption was performed by adsorption isotherms and kinetic adsorption. Dyes differed in their charge (anionic or cationic) and molecular weight. Dyes used were Methylene Blue (cationic) and Congo Red (anionic). Surface area and Scanning Electron Microscopy (SEM) were also conducted. Surface chemistry was impacted by corona treatment and interfered in dye adsorption. There was decrease of dye adsorption for both dyes according to time exposure. However, the decrease of Methylene Blue (25%) was higher than Congo Red (14%), suggesting that either charge or molecule weight interfere in the adsorption isotherms. In kinetic adsorption, there was no difference between treatments, although there was a difference in adsorption equilibrium. SEM showed that surface was impacted (pore destruction) by corona treatment. Furthermore, estimated surface area was strongly impacted by the treatment, reducing with the increase of time exposure. Thus, textural properties might have contributed to reduce adsorption capacity of both dyes and play a higher role than chemical properties. IMPACTO DE CARVÕES ATIVADOS TRATADOS COM DESCARGA CORONA NA ADSORÇÃO DE CORANTES CATIÔNICOS E ANIÔNICOSRESUMO: A degradação de corantes é um importante tópico nas ciências ambientais, já que os corantes podem trazer diversos problemas para o meio ambiente. O carvão ativado é um importante material usado como adsorvente dessas substâncias causadoras dos mais diversos danos, mas precisam ser melhoradas especialmente quando envolve substâncias específicas. Este manuscrito tem como objetivo avaliar o impacto da superfície de carvões ativados modificados pelo tratamento corona (descarga elétrica) na adsorção de diferentes corantes. Os carvões ativados foram tratados pelo tratamento corona para promover a modificação na superfície, modificando os tempos de exposição ao tratamento (2, 5, 8 e 10 minutos). A avaliação da adsorção foi realizada pelas isotermas de adsorção e velocidade de adsorção. Os corantes diferiram pelas suas cargas (aniônico e catiônico) e massa molecular. Os corantes utilizados foram o Azul de Metileno (catiônico) e o Vermelho Congo (aniônico).A área superficial e a microscopia eletrônica de varredura (MEV) também foram realizadas. A superfície química foi impactada pelo tratamento corona e interferiu na adsorção dos corantes. Houve decréscimo na adsorção dos corantes para ambos de acordo com o tempo de exposição. No entanto, o decréscimo de Azul de ...

Lignocellulosic materials have a complex polymeric structure, so, to obtain a high yield of glucose by hydrolysis reactions is necessary a pretreatment of the material. In this work, the effect of pretreatment corona (electric discharge) on different properties in three lignocellulosic materials (microcrystalline cellulose, cellulose pulp and bagasse) was evaluated. corona treatment was applied in three different exposure times (2, 6 and 10 minutes). Crystallinity, obtained by X-ray diffraction, showed a significant increase in samples of bagasse after pretreatment. No changes in acidity of materials was observed. Cationic and anionic tests indicate that the surface of bagasse is negatively charged after pretreatment. Amount of methylene blue adsorbed in the materials decreased with increasing of exposure time. Acid hydrolysis of materials with and without pretreatment were evaluated in amount of total reducing sugars (%TRS). A small decrease in %TRS occurred after pretreatment corona mainly in bagasse samples. HPLC analysis of hydrolysis products of pretreated bagasse showed higher yields in glucose, a raw material of interest for second generation ethanol.

RESUMOProcessos de pré-tratamento em biomassa lignocelulósica são essenciais a fim de tornar o material mais disponível a reações. Modificar a cristalinidade, a porosidade ou a acidez superficial dos materiais pode aumentar o rendimento em reações. Dessa forma, estudos direcionados a novos pré-tratamentos são importantes para analisar seu efeito no rendimento em uma reação específica e tornar mais viável a utilização dessa matéria-prima. Este trabalho utilizou o equipamento de tratamento Corona, em bagaço de cana-de-açúcar, analisando o efeito causado em diferentes tempos de exposição. Foram realizadas reações de hidrólise ácida, e os resultados analisados com % de ART (açúcares redutores totais) apresentaram uma diminuição na disponibilidade de açúcares. Em relação à cristalinidade, houve aumento considerável das amostras tratadas em comparação às amostras in natura. Na adsorção, foi observado que a superfície do bagaço é tendenciosamente negativa, pois maiores valores foram encontrados com o corante catiônico, no qual o tratamento corona prejudicou a adsorção em função do tempo de exposição. Pôde-se observar que o tratamento corona proporcionou modificações na estrutura das fibras do bagaço, tendo efeito sobre as análises e reações. Palavras-chave: