ABSTRACT Water contamination by heavy metals represents a high risk of environmental pollution and a precursor of several human diseases. The presence of these metals at high levels in wastewater treatment plants and industrial effluents motivated the search for remediating these pollutants. Among remediation methods, adsorption is extensively used to decontaminate waters containing these metals. Thus, this study prepared, characterized, optimized, and applied two types of adsorbents to a prepared metal ion solution (PMS): a bioadsorbent based on banana peel flour (BPF) and a synthetic adsorbent based on magnetite encapsulated by chitosan (MEC). A systematic study was performed with PMS containing Al (III), Ba (II), Pb (II), Cu (II), Cr (III), Fe (II), Mn (II), and Zn (II) to determine the best conditions for simultaneous metal ion adsorption Adsorption studies evaluated the experimental adsorption isotherms according to the variation in pH values, the mass of adsorbents, and contact time, and the kinetic study applied pseudo-first- and pseudo-second-order models. The best parameters were the pH of 6, a mass of adsorbents of 25 mg, and fast saturation time of around 10 minutes. The kinetic model that best fitted the process was the pseudo-second-order for all metals in both adsorbents. The PMS adsorption capacity achieved by MEC was higher than BPF. The removal by MEC was Al=Fe=Pb=Cu=Cr> Zn>Mn>Ba, in the percentages of 100, 100, 100, 100, 100, 98, 88, and 76%, respectively. The BPF showed Pb>Fe>Cr>Cu>Al>Zn>Ba>Mn, in the percentages of 97, 67, 63, 50, 46, 45, 44, and 5%, respectively. The results suggest that the affinity between adsorbents with certain metal ions is due to the characteristics of the adsorbent surface and the number of chemical species available in the solution, which may interfere with the adsorptive process. Above all, the percentage of simultaneous removal of metal ions by both adsorbents was relevant, making them promising for remediating heavy metal ions in sanitary sewage after conventional treatment and industrial effluents containing mixed metal ions.

RESUMO A contaminação de água por metais pesados ainda é um grande risco de poluição. Diante deste cenário, processos adsortivos e diversos materiais adsorventes têm sido empregados para descontaminação. Dentre os materiais sintéticos e bioadsorventes empregados, os sintéticos são eficientes na remoção de metais em solução aquosa, contudo agregam alto custo comparados aos bioadsorventes. Os bioadsorventes são em geral provenientes de biomassa agroindustrial e vêm se destacando por serem abundantes, renováveis e com custo acessível para remediação de efluentes com metais pesados na forma ionizada. Dentre os bioadsorventes, a casca da banana reúne grupos funcionais capazes de adsorver íons de metais pesados em meio aquoso. Dessa forma, este trabalho descreve o método de preparação e caraterização da farinha da casca de banana (FCB) através das técnicas de Microscopia Eletrônica de Varredura (MEV), Espectroscopia Dispersiva em Energia de Raios X e Espectroscopia na Região do Infravermelho bem como estudos da capacidade adsortiva desse bioadsorvente para o íon Cu (II) em soluções aquosas. Os estudos de adsorção foram realizados através da avaliação das isotermas experimentais de adsorção em função do tempo de contato, variações do pH, temperatura e concentração de íon Cu (II) na solução pela técnica de batelada. As isotermas experimentais foram submetidas aos modelos matemáticos de isotermas de Langmuir e Freundlich. A capacidade máxima de adsorção alcançada pela FCB foi 15,1 mg de Cu (II) por grama de FCB, pH ajustado em 5 e tempo de saturação bastante rápido, em torno de 10 minutos. A isoterma de Langmuir foi o modelo que melhor se ajustou ao processo adsortivo de cobre (II) pela FCB e o preenchimento dos sítios ativos foi na faixa de 98,7%.

ABSTRACT Contamination of water by heavy metals is still a major risk of pollution. Considering this scenario, adsorptive processes and various adsorbent materials have been used for decontamination. Among the synthetic materials and bioadsorbents used, the synthetics are efficient in the removal of metals in aqueous solution, however they add a high cost compared to bioadsorbents. The bioadsorbents are generally derived from agroindustrial biomass and have been noted for being abundant, renewable and cost-effective for the remediation of effluents with heavy metals in the ionized form. Among the bioadsorbents, the banana peel contains functional groups capable of adsorbing heavy metal ions in aqueous medium. Thus, this work describes the method of preparation and characterization of the banana peel flour through the techniques of Scanning Electron Microscopy (SEM), Dispersive Energy of x-ray (EDX) and Fourier Transform Infrared Spectroscopy (FT-IR), as well as studies of the adsorptive capacity of this bioadsorbent for the Cu (II) ion in aqueous solutions. The adsorption studies were carried out by evaluating experimental adsorption isotherms as a function of contact time, pH, temperature and Cu (II) ion concentration in the solution by batch technique. The experimental isotherms were submitted to the mathematical models of Langmuir and Freundlich isotherms. The maximum adsorption capacity achieved by the FCB was 15.1 mg of Cu (II) per gram of FCB, adjusted pH at 5 and very fast saturation time, around 10 minutes. The Langmuir isotherm was the model that best fitted the copper (II) adsorptive process by FCB and the filling of the active sites was around 98.7%.

This work concerns the preparation a nitrogen-doped TiO2 by ionothermal synthesis methods and the photocatalytic studies. In this procedure, alkoxide was used as a titanium source, and a deep eutectic mixture of choline chloride and urea (molar ratio 1:2) served as a solvent and source of nitrogen. Different samples were synthesized varying the percentages of the eutectic mixture, titanium butoxide, and water, as well as temperature and reaction time. The catalysts were characterized by X-ray diffraction, Raman spectrometry, scanning electron microscopy, and diffuse reflectance spectroscopy. N-doping was confirmed by X-ray photoelectron spectroscopy. The photocatalytic activity of the N-TiO2 nanoparticles was evaluated in the oxidation of N,N-dimethyl-4-nitrosoaniline (RNO) dye. The best photocatalytic activity under illumination by UV and visible light was found for the catalysts prepared under reflux in the presence of water, and for the catalysts prepared hydrothermally using intermediate percentages of the nitrogen source (the eutectic mixture).

Este trabalho apresenta um estudo da degradação do herbicida diuron utilizando os anodos Ti/Ru xTi(1-x)O2 e Ti/Ir xTi(1-x)O2 (x = 0,3, 0,5 e 0,7). A investigação da degradação foi conduzida na presença e na ausência de cloreto. O estudo da remoção do herbicida em função da densidade de corrente na ausência de cloreto rendeu remoções de 41 e 49% de demanda química de oxigênio (COD) e remoções de 10 e 14% de carbono orgânico total (TOC) a 100 mA cm-2, respectivamente. Mantendo-se o tempo de eletrólise constante (4 h), a composição do anodo Ti/Ru0,7Ti0,3O2 foi determinada como a mais ativa para remoção do diuron e seu subproduto. O valor de remoção máximo atingido após 4 h foi 58%. A adição de cloreto dobrou a taxa de remoção, e obteve-se 100% de remoção de COD para Ti/Ru0,3Ti0,7O2. A análise por cromatografia líquida de alto rendimento (HPLC) confirmou a remoção total do herbicida em meio de cloreto e indicou a formação de subprodutos de degradação. Os subprodutos gerados são apresentados em função da densidade de corrente aplicada e da composição do anodo. Os anodos baseados em Ir promoveram a oxidação de maneira mais branda e forneceram mais subprodutos em meio aquoso.

This work presents a study of the electrochemical degradation of the herbicide diuron using Ti/Ru xTi(1-x)O2 and Ti/Ir xTi(1-x)O2 (x = 0.3, 0.5 and 0.7) anodes. The investigation of the degradation was conducted in the presence and in the absence of chloride. The study of the herbicide removal as a function of the current density in the absence of chloride yielded 41 and 49% COD (chemical oxygen demand) removals and 10 and 14% TOC (total organic carbon) removal at 100 mA cm-2, respectively. By keeping the electrolysis time constant (4 h), Ti/Ru0.7Ti0.3O2 anode composition was determined as the most active for removal of diuron and its byproduct. The maximum removal value achieved after 4 h was 58%. Addition of chloride doubled the removal ratio, and 100% COD removal was obtained for Ti/Ru0.3Ti0.7O2. High-performance liquid chromatography (HPLC) analysis confirmed the total removal of the herbicide in chloride medium and indicated the formation of byproducts. The generated byproducts presented as function of the applied current density and the anode composition. Ir-based anodes promoted milder oxidation and furnished more byproducts in aqueous medium.