Degradation of the Reactive Blue 4 Dye in Aqueous Solution Using Zero-Valent Copper Nanoparticles

The degradation of the Reactive Blue 4 (RB4) dye by zero-valent copper nanoparticles (nZVC) was investigated. Degradation rates of approximately 90% were reached within 10 minutes of reaction. Total Organic Carbon (TOC) analysis shows that the dye molecules undergo mineralization, therefore indicating the degradation process is oxidative. Experimental tests, held in the presence of tertiary butyl alcohol, acting as a hydroxyl radicals (∙OH) captor, and copper (I) oxide, demonstrated that the reaction mechanism is governed by the concentration of Cu (I) instead of ∙OH. The second-order kinetics model was the most appropriate one to explain the experimental data. Higher values of the reaction rate constant were obtained in higher temperatures and higher nZVC doses and in lower RB4 initial concentrations. The initial pH in more acidic conditions (3 and 4) was kinetically more favorable to the degradation reaction; the activation energy was estimated to be 42 kJ mol−1 based on calculations using the experimental data. Finally, the recovered nanoparticles were utilized on a new reaction cycle, showing a small loss of their efficiency and catalytic activity

Degradation of textile dye by Fe/Ni bimetallic nanoparticles supported chitosan beads using fluidized bed reactor

Neste trabalho, estudou-se a degradação do corante Vermelho Direto 80 (VD-80) por nanopartículas à base de ferro e níquel (NP Fe/Ni) em suporte utilizando reator de leito fluidizado (FBR). Inicialmente, o suporte das NP Fe/Ni em sílica, em bentonita e em esferas de quitosana (EQ) foi avaliado. O material gerado pelo suporte em EQ (EQ-Fe/Ni) apresentou características mais vantajosas para utilização em FBR, como distribuição de tamanho estreita e maior resistência mecânica que os demais. No entanto, devido à elevada lixiviação de material por parte das EQ-Fe/Ni no sistema em condições de aplicação e a sua instabilidade química, foram propostas três metodologias para otimização do seu preparo, nomeadas “Vias A, B e C”. As principais diferenças entre as metodologias foram: (i) o emprego ou não de uma etapa prévia de secagem das EQ, (ii) o tempo de contato das EQ com os metais antes da redução química e (iii) a forma de separação dos materiais do meio líquido pós suporte. As EQ-Fe/Ni produzidas pela “Via C”, por apresentarem baixa lixiviação de Fe e Ni para o meio, alta estabilidade química e comportamento hidrodinâmico estável, foram utilizadas nos estudos de degradação do VD-80. O efeito das variáveis pH inicial (4, 7 e 10) e dose de EQ-Fe/Ni (20, 35 e 50 g L -1 ) na remoção do VD-80, em ensaios em batelada, foi estudado por meio de um planejamento fatorial 22, com repetições no ponto central. A remoção foi monitorada por espectrofotometria de absorção molecular UV/Vis, sendo as amostras analisadas sem e com ajuste prévio de pH (7,6). Foram observadas remoções da ordem de 45,6-98,9% (pH 7,6), e, 32,9-71,4% (pH sem ajuste) após 22 h de reação. Foi verificado que a remoção ocorreu tanto por adsorção como degradação. Pela análise de variância do planejamento fatorial, foi determinado que a dose foi a única variável que afetou significativamente a remoção. Portanto, não se ajustou o pH inicial no ensaio de degradação utilizando o FBR. Os valores de velocidade mínima de fluidização calculados teoricamente apresentaram desvios relativos da ordem de 5,58-41,86% em relação ao experimental. A remoção do VD-80 no FBR atingiu aproximadamente 38% após 2,5 h de reação e foi superior a 60% ao final de 22h, resultando em baixa geração de lodo residual e baixa lixiviação de Fe e Ni para o meio.In this work, the Red Direct 80 dye (DR-80) degradation by iron and nickel bimetallic nanoparticles (Fe/Ni-NP) supported chitosan beads using fluidized bed reactor (FBR) was studied. Initially, the Fe/Ni-NP support on silica, bentonite and chitosan beads (CB) was evaluated. The material generated by the Fe/Ni-NP support on CB (Fe/Ni-CB) presented more advantageous characteristics for use in FBRs, such as narrow size distribution and greater mechanical resistance than the others did. However, due to its high leaching of material in the system under application conditions and its chemical instability, three methodologies were proposed to optimize the Fe/Ni-CB preparation, named "Pathways A, B and C". The main differences between the methodologies were: (i) the use or not of a previous drying stage of the CB, (ii) the contact time of the CB with the metals before the chemical reduction and (iii) the separation of the material from the liquid medium after the support. The Fe/Ni-CB produced by "Pathway C", due to its low leaching of Fe and Ni to the medium, high chemical stability and stable hydrodynamic behavior, were used in the DR-80 degradation studies. The study of the initial pH (4, 7 and 10) and Fe/Ni-CB dose (20, 35 and 50 g L -1 ) effects on DR-80 removal was performed in batch assays, part of a 22 factorial design with repetitions in the central point. The DR-80 removal was monitored by UV/Vis molecular absorption spectrophotometry, and the samples were analyzed without and with pH adjustment (7.6). Removal values of the order of 45.6-98.9% (pH 7.6), and, 32.9-71.4% (without pH adjustment) were observed after 22 h of reaction. It was found that the removal occurred by both adsorption and degradation. The analysis of variance of the factorial design determined the Fe/Ni-CB dose was the only variable that significantly affected the DR-80 removal. Therefore, the initial pH was not adjusted in the degradation assay using the FBR. The minimum fluidization velocity values theoretically calculated presented relative deviations of the order of 5,58-41,86% in relation to the value determined experimentally. The DR-80 removal in the FBR reached approximately 38% after 2.5 h of reaction and was higher than 60% at the end of 22h, resulting in low residual sludge generation and low Fe and Ni leaching into the medium.Coordenação de Aperfeiçoamento de Pessoal de Nível Superio

EVALUATION OF DIRECT RED 80 DYE ADSORPTION BY CHITOSAN MICROSPHERES

The damage caused to the environment by the textile industry, creates a demand for simple and inexpensive methods that remove waste water dyes. In this sense, this work had as objective to evaluate and optimize the adsorptive capacity of the chitosan microspheres, of the direct red azo dye 80. The materials were characterized by SEM and FTIR techniques. The results confirmed the adsorption phenomenon through bands and changes in the surface of the adsorbent, caused by the fixing of the dye. A Multivariate Planning with Response Surface was performed, finding a saddle point, evidencing that the optimal point of the parameters is in another experimental domain. The adsorption was studied through isotherms, presenting a better regression adjustment (r> 0.98) for the Freundlich model. The results showed effectiveness of color removal (97% in 24h) and operational ease with the adsorbent

Efeito da etapa de centrifugação no tamanho de nanocristais de celulose

Investigou-se, utilizando a técnica de espalhamento dinâmico de luz depolarizado, a relação das propriedades dinâmicas de suspensões de nanocristais de celulose (NCC) com a força G de centrifugação aplicada no processo de purificação das mesmas. Amostras contendo NCC foram preparadas por meio de hidrólise com ácido sulfúrico e centrifugadas nas intensidades de 1840, 4140, 7370, 11510 e 16580 de força G. Determinou-se os coeficientes de difusão translacionais e rotacionais e, a partir destes, calculou-se as larguras (d) e os comprimentos (L) dos NCC. Os valores de L e de d encontraram-se nas faixas de 213 ± 10 a 294 ± 14nm e de 4,4 ± 1,2 a 9,5 ± 2,0nm, respectivamente. Os resultados concordaram com os disponíveis na literatura, confirmando a aplicabilidade da técnica no estudo da dinâmica dos NCC em suspensões aquosas. Não observou-se variação significativa de L com o aumento da força G na faixa estudada. Por outro lado, houve redução de d para valores de força G acima de 7370

THE EFFECT OF CENTRIFUGATION STAGE ON CELLULOSE NANOCRYSTALS’ SIZE

The relation between the cellulose nanocrystals (CNC) dynamic properties and the centrifugation G force applied on their purification process was investigated using the depolarized dynamic light scattering technic. Samples containing CNC were prepared using sulfuric acid hydrolysis and centrifugated on the following G forces: 1840, 4140, 7370, 11510 e 16580. The translational and rotational diffusion coefficients were determined for the different samples, from these values, the CNC widths (d) and lengths (L) were calculated. The values for the d and L lied from 213 ± 10 nm to 294 ± 14 nm and 4,4 ± 1,2 nm to 9,5 ± 2,0nm, respectively. The results agree with the the literature, confirming the applicability of the technic on the study of NCC dynamic properties in aqueous suspensions. There was no significant variation on the values of L by the increment on the G force within the studied interval. On the other hand, d reduced with the G force increase for values above 7370