Hummers’ and Brodie’s graphene oxides as photocatalysts for phenol degradation

Undoped metal-free graphene oxide (GO) materials prepared by either a modified Hummers’ (GO-H) or a Brodie’s (GO-B) method were tested as photocatalysts in aqueous solution for the oxidative conversion of phenol. In the dark, the adsorptive capacity of GO-B towards phenol (~35%) was higher than that of GO-H (~15%). Upon near-UV/Vis irradiation, GO-H was able to remove 21% of phenol after 180 min, mostly through adsorption. On the other hand, by using less energetic visible irradiation, GO-B removed as much as 95% in just 90 min. By thorough characterization of the prepared materials (SEM, HRTEM, TGA, TPD, Raman, XRD, XPS and photoluminescence) the observed performances could be explained in terms of their different surface chemistries. The GO-B presents the lower concentration of oxygen functional groups (in particular carbonyl groups as revealed by XPS) and it has a considerably higher photocatalytic activity compared to GO-H. Photoluminescence (PL) of liquid dispersions and XRD analysis of powders showed lower PL intensity and smaller interlayer distance for GO-B relative to GO-H, respectively: this suggests lower electron-hole recombination and enhanced electron transfer in GO-B, in support of its boosted photocatalytic activity. Reusability tests showed no efficiency loss after a second usage cycle and over three runs under visible irradiation, which was in line with the similarity of the XPS spectra of the fresh and used GO-B materials. Moreover, scavenging studies revealed that holes and hydroxyl radicals were the main reactive species in play during the photocatalytic process. The obtained results, establish for the first time, that GO prepared by Brodie’s method is an active and stable undoped metal-free photocatalyst for phenol degradation in aqueous solutions, opening new paths for the application of more sustainable and metal-free materials for water treatment solutions.This work was financially supported by project NORTE-01- 0145-FEDER-031049 (InSpeCt) funded by FEDER funds through NORTE 2020 - Programa Operacional Regional do NORTE and by national funds (PIDDAC) through FCT/MCTES (PTDC/EAMAMB/ 31049/2017). We would also like to thank the scientific collaboration under project ‘‘AIProcMat@N2020 - Advanced Industrial Processes and Materials for a Sustainable Northern Region of Portugal 2020” (NORTE-01-0145-FEDER-000006, NORTE 2020, Portugal 2020 Partnership Agreement, through FEDER), project ‘‘Associate Laboratory LSRE-LCM” (UID/EQU/50020/2019 - FCT/ MCTES – PIDDAC) and project 2DMAT4FUEL (POCI-01-0145- FEDER-029600 - COMPETE2020 – FCT/MCTES - PIDDAC). MP acknowledges the PhD research grant from FCT (Ref. SFRH/ BD/102086/2014). LMPM acknowledges the Spanish Ministry of Economy and Competitiveness (MINECO) and the European Social Fund for a Ramon y Cajal research contract (RYC-2016-19347). GD acknowledges the Slovenian Research Agency (P2-0393). PF acknowledges support from Prince Sultan Bin Abdulaziz International Prize for Water–Alternative Water Resources Prize 201

Nanotubos e grafeno: os primos mais jovens na família do carbono!

O carbono é o sexto elemento mais abundante do universo, encontrando-se presente tanto na forma orgânica, como em materiais inorgânicos. Além das três formas alotrópicas que ocorrem naturalmente (carbono amorfo, grafite e diamante), podem ser também sintetizadas estruturas de carbono com dimensões nanométricas. Nos últimos anos foram descobertas e caracterizadas novas e interessantes nanoestruturas de carbono, incluindo os nanotubos de carbono e o grafeno. Este breve artigo faz uma resenha sobre os métodos de síntese e caracterização destes dois materiais, aludindo a algumas das suas propriedades mais extraordinárias, bem como às suas aplicações mais recentes e de maior impacto em diversos domínios da ciência e da tecnologia, permitindo, de uma forma simples, introduzir os leitores menos familiarizados com o tema no fascinante mundo destas duas nanoestruturas de carbono

Graphene-based materials in catalytic wet peroxide oxidation

In catalytic wet peroxide oxidation (CWPO),an advanced oxidation process, hydrogen peroxide (H2O2) is decomposed catalytically giving rise to hydroxyl radicals (HO•).These radicals, exhibiting high oxidizing potential, serve as effective and non selective species for the degradation of several organic pollutants in liquid phase. Since the report of Lücking et al. [1], carbon materials have been explored as catalysts for CWPO[2]. Recent reports address process intensification issues, broadening the window of industrial applications for this wastewater treatment technology [3]. In this work, graphene-based materials were tested for the first time as catalysts for CWPO

Influence of Electrostatic Interactions During the Resorcinol-Formaldehyde Polymerization on the Characteristics of Mo-Doped Carbon Gels

The resorcinol (R)-formaldehyde (F) polymerization was carried out in different experimental conditions to obtain RF/Mo doped carbon xerogels with different morphology, porosity and nature and dispersion of metal. Attractive or repulsive electrostatic interactions were forced in the starting aqueous solution of RF-monomers using different synthesis conditions, namely, combinations of cationic or anionic surfactants, Mo-precursors and pH values. The results showed that when both cationic surfactant and Mo-precursor were used at neutral pH, attractive interactions with the anionic RF-macromolecules are favored during polymerization and the final carbon xerogel exhibited the most developed porosity and the strongest Mo-organic phase interaction, leading to deeper Mo-phase reduction during carbonization and the formation of highly-dispersed crystalline nanoparticles of Mo2C. On the contrary, the use of both anionic surfactant and Mo-precursor leads to repulsive interactions, which generates less porous carbon gels with a Mo-phase formed by large MoO3 platelet structures and low Mo-surface contents. RF/Mo-doped gels with intermediate properties were obtained by combining cationic and anionic surfactants, metal precursors or both. After carbonization, the obtained materials would be suitable to be used directly as catalysts with different physicochemical properties and active phases.Spanish Project from ERDF/Ministry of Science, Innovation and Universities-State Research Agency RTI2018-099224-B-I0

Nanopartículas magnéticas como catalisadores no tratamento de águas utilizando o processo de foto-Fenton

O interesse nas aplicações de nanopartículas magnéticas tem crescido em quase todos os campos, destacando-se mais recentemente a utilização de nanopartículas de óxidos de ferro para tratamento de águas. De entre os óxidos de ferro existentes na natureza, destacam-se o a-Fe2O3, o g-Fe2O3 e o Fe3O4, que podem ser preparados laboratorialmente por métodos de co-precipitação [1], decomposição térmica [2] e síntese hidrotérmica [3]. As nanopartículas superparamagnéticas de óxido de ferro, também conhecidas como SPIONs - superparamagnetic iron oxide nanoparticles, são um caso particular devido à relação entre a distribuição de tamanhos das partículas e a carga superficial. A implementação destes materiais como catalisadores no tratamento de águas e águas residuais pode revolucionar o conceito das tecnologias catalíticas de tratamento porque quando estas nanopartículas, com propriedades magnéticas, são utilizadas em suspensão (i) proporcionam uma maior área de contacto entre a fase ativa e o meio aquoso e (ii) podem ser rapidamente (e facilmente) separadas do meio líquido por efeito de um campo magnético, ficando retidas no reator catalítico. Desta forma são ultrapassadas, tanto a principal limitação encontrada quando são utilizados catalisadores sem propriedades magnéticas em suspensão (difícil separação por processos de filtração), como a limitação associada à deposição de nanopartículas em substratos fixos (típica diminuição da atividade catalítica). Por outro lado, os compostos farmacêuticos são poluentes de maior relevância devido aos efeitos nefastos que podem causar na saúde pública, nos ecossistemas e no ambiente em geral, onde aparecem como resultado do seu consumo crescente e da sua difícil degradação em estações de tratamento de águas residuais. Estes compostos têm sido encontrados em águas subterrâneas, águas de superfície e inclusivamente em águas utilizadas para consumo, sendo esta última uma situação mais alarmante. Em particular, a difenidramina constituí o princípio ativo de diversos produtos farmacêutico, como o Benadryl®, e é classificada como anti-histamínico de primeira geração para formulações farmacêuticas utilizadas no tratamento de rinite, conjuntivite, insónia, picadas de insetos, enjoos/ansiedade, entre outros. Aparece nas águas devido à sua baixa biodegradabilidade e tem demonstrado efeitos tóxicos, cancerígenos e mutagénicos [4]. Por este motivo, no presente trabalho, foram preparados e caracterizados materiais à base de óxido de ferro com propriedades magnéticas para serem testados na degradação de difenidramina pelo processo de foto-Fenton, onde é utilizada uma mistura catalítica fortemente oxidante de um agente contendo ferro e peróxido de hidrogénio (H2O2)

From Polyethylene to Highly Graphitic and Magnetic Carbon Spheres Nanocomposites: Carbonization under Pressure

Carbon nanocomposites microspheres were synthesized from Low-Density Polyethylene (LDPE) by a facile one-step strategy under solvent-free conditions. The synthesis of these materials was carried out in a closed Hastelloy® reactor at 700 ºC. The treatment, during which autogenic pressure was generated, leads to highly graphitic materials with stunning properties, particularly concerning the oxidation resistance (compared to the graphite stability). The metallic doping triggers the growth of nanostructures with diverse morphologies around the spheres, obtaining samples with magnetic properties.This research is supported by the project P12-RNM-2892 and RMN-172 (Junta de Andalucía, Spain)

Functionalized Graphene Derivatives and TiO2 for High Visible Light Photodegradation of Azo Dyes

Functionalized graphene derivatives including graphene oxide (GO), reduced graphene oxide (rGO), and heteroatom (nitrogen/sulphur (N/S) or boron (B))-doped graphene were used to synthesize composites with TiO2 (T). The photocatalytic performance of composites was assessed for the degradation of Orange G dye (OG) under simulated solar light. All the prepared graphene derivatives—TiO2 composites showed better photocatalytic performance than bare TiO2. A higher photocatalytic activity was found for the composites containing GO and N/S co-doped rGO (kapp = 109.2 × 10−3 and 48.4 × 10−3 min−1 , for GO-T and rGONS-T, respectively). The influence of both initial solution pH and the reactive species involved in the OG degradation pathway were studied. The photocatalytic activity of the samples decreased with the increase of the initial pH (from 3.0 to 10.0) due to the occurrence of electrostatic repulsive forces between the photocatalysts surface and the molecules of OG, both negatively charged. The use of selective scavengers showed that although the photogenerated holes dominate the degradation mechanism, radicals and singlet oxygen also participate in the OG degradation pathway. In addition, reutilization experiments indicated that the samples were stable under the reaction conditions used.ERDF/Ministry of Science, Innovation and Universities-State Research Agency RTI2018-099224-B-I0

Photodegradation of cytostatic drugs by g-C3N4: Synthesis, properties and performance fitted by selecting the appropriate precursor

Graphitic carbon nitride (g-C3N4) was synthetized by a one-step thermal method from different N-rich precursors, namely melamine, dicyandiamide, urea, thiourea and cyanamide. The structure, optical and physicochemical properties of g-C3N4 materials were studied by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy, among others. Both melamine and dicyandiamide provided a less porous structure composed by large flake sheets, whereas urea and thiourea favoured g-C3N4 composed by small flat sheets and wrinkles with a larger porosity. The establishment of more condensed g-C3N4 networks with a reduced band gap was also evidenced for melamine and dicyandiamide precursors, while urea favoured less condensed melem or melon structures. The photoactivity of the different g-C3N4 was assessed for the removal of an aqueous solution containing 5-fluorouracil (5-FU), cyclophosphamide (CP) or a mixture of both cytostatic drugs, under near UV-Vis and solar-LED irradiations. The best performing photocatalysts under near UV-Vis irradiation, were those prepared from melamine (kapp = 14.6 × 10–2 min–1 for 5-FU) and thiourea (kapp = 2.5 × 10–2 min–1 for CP), while urea was the most active under solar-LED irradiation (kapp = 0.183 × 10–2 min–1 for 5-FU). In addition, CP was more resistant to be degraded than 5-FU, and a competitive effect for the generated hydroxyl radicals was evidenced when both pollutant molecules were in the same solution. The photoactivity of g-C3N4 materials was justified by the combination of various effects: (i) surface area, (ii) well-connected and condensed g-C3N4 structures and (iii) high surface C/N ratios with nitrogen vacanciesSpanish Projects from MCIN/AEI/FEDER "Una manera de hacer Europa" RTI2018-099224-B-I00FEDER/Junta de Andalucia-Consejeria de Transformacion Economica, Industria, Conocimiento y Universidades B-RNM-486-UGR20Junta de Andalucia-Consejeria de Universidad, Investigacion e Innovacion -Proyecto P21_00208MICIN/AEIEuropean Social Found (FSE) PRE2019-087946MICIN/AEI RYC-2019-026634-IFSE "El FSE invierte en tu futuro"Universidad de Granada/CBU

Magnetite Nanoparticles as Solar Photo-Fenton Catalysts for the Degradation of the 5-Fluorouracil Cytostatic Drug

Heterogeneous catalysts based on magnetite nanoparticles, Fe3O4, were prepared by the chemical coprecipitation method using iron (III) chloride as a salt precursor. The physicochemical properties of the nanoparticles were determined by different techniques and the efficiency was evaluated for the degradation of the cytostatic drug, 5-fluorouracil (5-FU), in aqueous solution by photo-Fenton process under simulated solar radiation. The most influential parameters, namely pH of the solution, catalyst load, H2O2 dosage, and use of radiation, were studied and optimized in the degradation process. The optimal conditions to achieve a 100% degradation of 5-FU (10 mg L-1) and a high mineralization degree (76%) were established at the acidic pH of 3.0, 100 mg L-1 of catalyst loading, and 58 mM of H2O2 under simulated solar radiation. The contribution of iron leaching to the catalyst deactivation, the role of the dissolved iron ions on homogenous reactions, and the stability of the catalyst were assessed during consecutive reaction cycles.Spanish Project, FEDER/Junta de Andalucia-Consejeria de Transformacion Economica, Industria, Conocimiento y Universidades B-RNM-486-UGR2

Supported Biofilms on Carbon–Oxide Composites for Nitrate Reduction in Agricultural Waste Water

Escherichia coli colonies were grown on different supports for the removal of nitrates from water. A carbon material and different commercial metal oxides, such as SiO2 , TiO2 and Al2O3 , and their corresponding carbon–metal oxide composites were studied. The physicochemical properties were analyzed by different techniques and the results were correlated with their performance in the denitrification process. Developed biofilms effectively adhere to the supports and always reach the complete reduction of nitrates to gaseous products. Nevertheless, faster processes occur when the biofilm is supported on mesoporous and non-acid materials (carbon and silica).Spanish Project ref. RTI 2018-099224-B100 funded by ERDF/Ministry of Science, Innovation and Universities—State Research Agency (Spain