ABSTRACT
Developing innovative technologies for the effective treatment of wastewater containing organic pollutants is of extreme importance across the globe. The organic pollutants such as dyes and nitrophenols are the common hazardous pollutants known for their adverse effects on humans and aquatic organisms. Various methods have been used for the removal of organic pollutants from wastewater but they suffer limitations such as high cost, time consuming removal process and production of sludge or toxic by-products. In recent years, chemical reduction method is becoming popular for removal of organic pollutants using various nanomaterials as catalysts. Nanomaterials show great potential for removal of organic pollutants due to large surface area which provides high catalytic activity. In the present review, current studies on catalytic reduction of organic pollutants (dyes and nitrophenols) using four different types of nanomaterials specifically carbon nanotubes, silica, metal oxide and chitosan polymer based have been explored. The factors affecting the catalytic process and mechanism of catalysis is explained in detail.In addition, a critical discussion about the pros and cons of each nano-catalyst have also been included for developing better understanding of the choice of catalyst.
ABSTRACT
A malária é a endemia tropical mais devastadora do mundo e esse quadro é agravado pela ausência de tratamento eficaz. Entretanto, a resistência dos plasmódios à artemisinina não apresenta relevância clínica e seu mecanismo de ação está associado ao grupo heme, com formação de radicais livres e rompimento da ponte endoperóxido. O comportamento voltamétrico da artemisinina foi estudado por voltametria cíclica e voltametria de onda quadrada. O fármaco é irreversivelmente reduzido em eletrodos de carbono vítreo e os valores de potencial de pico não sofrem influência da acidez do meio, porém observou-se o maior valor de corrente em pH 6,0. O comportamento voltamétrico da artemisinina foi significativamente alterado na presença do grupo heme, provocando uma antecipação de seu pico de redução em cerca de 600 mV. Por voltametria de onda quadrada observou-se que este novo pico foi sensível à adição crescente de concentração de hemina, atingindo valor de corrente cerca de 10 vezes maior em relação ao pico original da artemisinina, numa relação de concentração de 20 mmol/L para o primeiro e 50 mmol/L do segundo. Além disso, resultados indicaram que esse processo eletrocatalítico ocorreu pela formação de Fe(II)-hemina na superfície do eletrodo, com provável processo de eletro-polimerização da hemina sobre o eletrodo de carbono vítreo. Esse efeito adsortivo foi avaliado a partir da estimativa da concentração superficial (G) de hemina sobre o eletrodo de trabalho em pH 6,0. A modificação do eletrodo de carbono vítreo por hemina mostrou que a interação entre artemisinina e o grupo heme ocorre predominantemente sobre a superfície do eletrodo e não em solução. Portanto, esclarecer o mecanismo de ação da artemisinina é importante para o planejamento e desenvolvimento de novos agentes antimaláricos.
Malaria is the tropical disease most devastating of the world and this situation is worsened by the absence of effective treatment. However, the plasmodium resistance to artemisinin does not show clinical relevance. The drug mechanism of action is associated to the heme group, with free radical formation and endoperoxide moiety breakage. The voltammetric behavior of artemisinin was studied by cyclic and square-wave voltametries. This drug was irreversibly reduced on glassy carbon electrode and the peak potential values are pH independent, however the biggest value of current peak was observed at pH 6.0. The voltammetric behavior of artemisinin was significantly changed in the heme group presence, provoking an anticipation of about 600 mV on cathodic peak. By square-wave voltammetry it was observed that this new peak was sensitive to the hemin concentration, reaching a value around 10 times larger regarding the original cathodic peak of artemisinin, being the concentration of 20 mmol/L for the former and 50 mmol/L for the latter. In addition, results indicated that this electro-catalytic process depends on the Fe(II)-hemin formation on the electrode surface, indicating the possible electro-polymerization of hemin on the glassy carbon electrode. This adsorptive effect was evaluated from the superficial concentration (G) estimation of the hemin on the working electrode at pH 6.0. The modification of the glassy carbon electrode using hemin showed that the interaction between artemisinin and the heme group predominantly occurs on the electrode surface and not in solution. Therefore, clarifying artemisinin mechanism of action is important in order to contribute for the design and development of new antimalarial agents.