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Desenvolvimento de xerogéis de carbono magnéticos para o processo de oxidação catalítica com peróxido de hidrogénio

Publication . Ribeiro, Rui; Silva, Adrián; Figueiredo, José; Faria, Joaquim; Gomes, Helder

Neste trabalho é apresentada uma nova metodologia para a preparação de xerogéis de carbono magnéticos. Como demonstrado através da caraterização efetuada, foi possível obter materiais com propriedades bastante distintas apenas por inclusão de precursores de ferro e/ou cobalto durante a reação de policondensação sol-gel entre o resorcinol e o formaldeído, seguida da redução térmica a 800 oC em atmosfera de N2. Tendo em conta o desempenho dos materiais desenvolvidos na oxidação catalítica com peróxido de hidrogénio (CWPO) de soluções concentradas (5 g L-1) de 4-nitrofenol (4-NP) foi demonstrado um importante efeito sinérgico entre as duas fases sólidas decorrente da incorporação dos metais nos xerogéis de carbono. Concretamente, conseguiu-se uma remoção completa de 4-NP em apenas 1 h de reação na presença de xerogel de carbono com ferro e cobalto incorporados na sua estrutura (CX/CoFe), para soluções contendo [4-NP]0 = 5 g L-1, [H2O2]0 = 17.8 g L-1 (estequiométrica), t = 50 oC, pH = 3 e na presença de 2.5 g L–1 de CX/CoFe (correspondendo a uma razão mássica poluente/catalisador de 2). Os resultados apresentados podem abrir caminho ao desenvolvimento de materiais com elevados desempenhos noutras aplicações catalíticas, para além dos processos de CWPO.

2016Conference object

Open access

Enhanced performance of cobalt ferrite encapsulated in graphitic shell by means of AC magnetically activated catalytic wet peroxide oxidation of 4-nitrophenol

Publication . Ribeiro, Rui; Gallo, Juan; Bañobre-López, Manuel; Silva, Adrián; Faria, Joaquim; Gomes, Helder

Here we report preliminary catalytic wet peroxide oxidation (CWPO) experiments performed in the presence of an alternating current (AC) magnetic field. One ferromagnetic graphitic nanocomposite – composed by a cobalt ferrite core and a graphitic shell (CoFe2O4/MGNC), was employed in the process, here named magnetically activated catalytic wet peroxide oxidation (MA-CWPO). An aqueous solution containing 5.0 g L−1 of 4-nitrophenol (4-NP) to simulate a high strength polluted stream was used as model system. The experiments were performed at room temperature and atmospheric pressure, with stoichiometric amount of hydrogen peroxide (H2O2), pH=3 and CoFe2O4/MGNC catalyst load=5.0 g L−1 (corresponding to a 4-NP/CoFe2O4 mass ratio of 6.9, as CoFe2O4 accounts for 14.4 wt% of CoFe2O4/MGNC). It was shown that the performance of CWPO is enhanced upon application of an AC magnetic field (frequency of 533.9 kHz and magnitude of 240 G). As a result, high 4-NP mineralization was obtained by MA-CWPO (as reflected by a total organic carbon abatement of 79% after 4 h of reaction, instead of 39% in the absence of a magnetic field). This positive effect was ascribed to the localised increase of CoFe2O4/MGNC surface temperature resulting from heat release upon exposure of the nanoparticulated catalyst to an AC magnetic field, which accelerates the catalytic decomposition of H2O2 via hydroxyl radicals (HO%) formation.

2018Journal article

Open access

Hybrid magnetic graphitic nanocomposites towards catalytic wet peroxide oxidation of the liquid effluent from a mechanical biological treatment plant for municipal solid waste

Publication . Ribeiro, Rui; Rodrigues, Raquel Oliveira; Silva, Adrián; Tavares, Pedro B.; Carvalho, Ana Maria; Figueiredo, José; Faria, Joaquim; Gomes, Helder

Magnetite, nickel and cobalt ferrites were prepared and encapsulated within graphitic shells, resulting in three hybrid magnetic graphitic nanocomposites. Screening experiments with a 4-nitrophenol aqueous model system (5 g L −1 ) allowed to select the best performing catalyst, which was object of additional studies with the liquid effluent resulting from a mechanical biological treatment plant for municipal solid waste. Due to its high content in bicarbonates (14350 mg L −1 ) and chlorides (2833 mg L −1 ), controlling the initial pH was a crucial step to maximize the performance of the catalytic wet peroxide oxidation (CWPO) treatment. The catalyst load was 0.5 g L −1 , a very low dosage when compared to the high chemical oxygen demand (COD) of the effluent − 9206 mg L −1 . At the optimum operating pH (i.e., pH = 6), ca. 95% of the aromaticity was converted and ca. 55% of COD and total organic carbon (TOC) of the liquid effluent was removed. The biodegradability of the liquid effluent was enhanced during the treatment by CWPO, as reflected by the 2-fold increase of the five-day biochemical oxygen demand (BOD 5 ) to COD ratio (BOD 5 /COD), namely from 0.21 (indicating non-biodegradability) to 0.42 (suggesting biodegradability of the treated wastewater). In addition, the treated water revealed no toxicity against selected bacteria. Lastly, a magnetic separation system was designed for in-situ catalyst recovery after the CWPO reaction stage. The high catalyst stability was demonstrated through five reaction/separation sequential experiments in the same vessel with consecutive catalyst reuse.

2017Journal article

Open access

From nano- to macro-scale: hybrid magnetic carbon nanocomposites as a tool for catalytic wet peroxide oxidation

Publication . Ribeiro, Rui; Silva, Adrián; Faria, Joaquim; Gomes, Helder

There is a need for technological innovation in the water sector worldwide, as a result of the growing demand for water supplies – meeting increasingly restricted quality criteria, while coping with the increasing scarcity of clean water sources1. Under this context, the use of treated wastewater as an alternative water source has emerged as a topic of high priority2. However, meeting current quality requirements for wastewater reuse is a great challenge, in which nanotechnology holds a great potential1. Catalytic wet peroxide oxidation (CWPO) is a promising water/wastewater treatment technology; it enables the formation of highly oxidizing hydroxyl radicals (HO•) under atmospheric pressure and low to moderate temperatures, when a suitable catalyst is employed for the decomposition of hydrogen peroxide (H2O2)3. However, further improvement of catalyst design is still required in order to allow the scale-up of the CWPO technology towards real-scale applications. Bearing this in mind, our work has been focused on the development of highly active and stable hybrid magnetic carbon nanocomposites for CWPO. A detailed catalyst design at the nanoscale, based on the understanding of the surface reactions and interactions involved in the CWPO process, has recently allowed us to move forward towards the treatment of a real industrial wastewater with high pollutant load – collected from a mechanical biological treatment (MBT) plant for municipal solid waste processing. This communication reports the findings obtained in the last four years by our research group in this quest. A particular emphasis is given to the synergistic effects arising from the combination of iron-based catalysts with the easily tuned properties of carbon-based materials.

2018Conference object

Open access

Desenvolvimento de compósitos magnéticos de carbono para oxidação catalítica com peróxido de hidrogénio

Publication . Ribeiro, Rui; Silva, Adrián; Faria, Joaquim; Gomes, Helder

Tendo em vista o desenvolvimento de materiais com elevada performance para oxidação catalítica com peróxido de hidrogénio, foram preparados xerogéis magnéticos de carbono com microesferas de ferro e/ou cobalto embutidas na sua estrutura. Os resultados obtidos revelaram que a incorporação simultânea de espécies de ferro e cobalto na estrutura de carbono permitem uma clara sinergia relativamente aos materiais monometálicos, justificada pela (i) maior acessibilidade às espécies ativas de ferro presentes na superfície do catalisador, (ii) capacidade do Co metálico catalisar a decomposição de H2O2 via formação de radicais hidroxilo (HO•), e (iii) redução eficiente de Fe3+ a Fe2+ promovida pelo Co metálico. Seguidamente, foi preparado um nanocompósito hibrido magnético, com núcleo de magnetite revestido de material grafítico. Verificou-se que (iv) a atividade catalítica da magnetite é melhorada pela sua encapsulação numa estrutura de carbono, ao mesmo tempo que (v) a lixiviação de ferro para a água tratada é fortemente contida. Com base nestes resultados, foi preparado um nanocompósito hibrido magnético com elevada performance, constituído por um núcleo de ferrite de cobalto e revestimento de material grafítico (CoFe2O4/MGNC). Este catalisador de última geração permitiu efetuar o tratamento de uma água residual industrial com elevada carga poluente.

2018Conference object

Open access