At present, the world is at the peak of production of traditional fossil fuels. Much of the resources that humanity has been consuming (oil, coal, and natural gas) are coming to an end. The human being faces a future that must necessarily go through a paradigm shift, which includes a progressive movement towards increasingly less polluting and energetically viable resources. In this sense, nanotechnology has a transcendental role in this change. For decades, new materials capable of being used in energy processes have been synthesized, which undoubtedly will be the cornerstone of the future development of the planet. In this review, we report on the current progress in the synthesis and use of one-dimensional (1D) nanostructured materials (specifically nanowires, nanofibers, nanotubes, and nanorods), with compositions based on oxides, nitrides, or metals, for applications related to energy. Due to its extraordinary surface–volume relationship, tunable thermal and transport properties, and its high surface area, these 1D nanostructures have become fundamental elements for the development of energy processes. The most relevant 1D nanomaterials, their different synthesis procedures, and useful methods for assembling 1D nanostructures in functional devices will be presented. Applications in relevant topics such as optoelectronic and photochemical devices, hydrogen production, or energy storage, among others, will be discussed. The present review concludes with a forecast on the directions towards which future research could be directed on this class of nanostructured materials.
The photocatalytic hydrogen evolution reaction (HER) by water splitting has been studied, using catalysts based on crystalline TiO2 nanowires (TiO2NWs), which were synthesized by a hydrothermal procedure. This nanomaterial was subsequently modified by incorporating different loadings (1%, 3% and 5%) of gold nanoparticles (AuNPs) on the surface, previously exfoliated MoS2 nanosheets, and CeO2 nanoparticles (CeO2NPs). These nanomaterials, as well as the different synthesized catalysts, were characterized by electron microscopy (HR-SEM and HR-TEM), XPS, XRD, Raman, Reflectance and BET surface area. HER studies were performed in aqueous solution, under irradiation at different wavelengths (UV-visible), which were selected through the appropriate use of optical filters. The results obtained show that there is a synergistic effect between the different nanomaterials of the catalysts. The specific area of the catalyst, and especially the increased loading of MoS2 and CeO2NPs in the catalyst substantially improved the H2 production, with values of ca. 1114 μm/hg for the catalyst that had the best efficiency. Recyclability studies showed only a decrease in activity of approx. 7% after 15 cycles of use, possibly due to partial leaching of gold nanoparticles during catalyst use cycles. The results obtained in this research are certainly relevant and open many possibilities regarding the potential use and scaling of these heterostructures in the photocatalytic production of H2 from water.
This study aimed to investigate the photocatalytic performance of diverse zinc oxide catalysts containing gold nanoparticles (AuNPs), molybdenum disulfide (MoS2), and reduced graphene oxide (rGO) toward the degradation of the antibiotics levofloxacin (LFX) and ciprofloxacin (CFX) in aqueous solutions. The obtained results demonstrate that LFX is more resistant to degradation when compared with CFX and that the principal route of degradation under visible light is the formation of hydroxyl radicals. Photoluminescence (PL) measurements were employed to verify the inhibitory effect of electron–hole recombination when AuNPs, MoS2, and rGO are integrated into a semiconductor. The catalyst that achieved the highest percentage of CFX degradation was 1%Au@ZnONPs-3%MoS2-1%rGO, exhibiting a degradation efficiency of 96%, while the catalyst that exhibited the highest percentage of LFX degradation was 5%Au@ZnONPs-3%MoS2-1%rGO, displaying a degradation efficiency of 99.8%. A gas chromatography–mass spectrometry (GC-MS) analysis enabled the identification of reaction intermediates, facilitating the determination of a potential degradation pathway for both antibiotics. Additionally, recyclability assessments showed that the synthesized catalysts maintained stable photocatalytic efficiencies after 15 cycles, indicating that the heterostructures have the potential for further usage and may be tested with other organic contaminants as well.
The photocatalytic hydrogen evolution reaction (HER) by water splitting has been studied, using catalysts based on TiO2 nanowires (TiO2NWs), which were synthesized by a hydrothermal procedure. This nanomaterial was subsequently modified by incorporating different loadings of gold nanoparticles (AuNPs) on the surface, previously exfoliated MoS2 nanosheets, and CeO2 nanoparticles (CeO2NPs). These nanomaterials, as well as the different synthesized catalysts, were characterized by electron microscopy (HR-SEM and HR-TEM), XPS, XRD, Raman, Reflectance and BET surface area. HER studies were performed in aqueous solution, under irradiation at different wavelengths, which were selected through the appropriate use of optical filters. The results obtained show that there is a synergistic effect between the different nanomaterials of the catalysts. The specific area of the catalyst, and especially the increased loading of MoS2 and CeO2NPs in the catalyst substantially improved the H2 production. Recyclability studies showed only a decrease in activity of approx. 7% after 15 cycles of use, which opens many possibilities regarding the potential use and scaling of these heterostructures in photocatalytic production of H2 from water.
At present, the world is at the peak of production of traditional fossil fuels. Much of the resources that humanity has been consuming (oil, coal and natural gas) are coming to an end. The human being faces a future that must necessarily go through a paradigm shift, which includes a progressive movement towards increasingly less polluting and energetically viable resources. In this sense, nanotechnology has a transcendental role in this change. For decades, new materials capable of being used in energy processes have been synthesized that undoubtedly will be the cornerstone of the future development of the planet. In this review, we report on the current progress in the synthesis and use of one-dimensional (1D) nanostructured materials (specifically nanowires, nanofibers, nanotubes and nanorods), with compositions based on oxides, nitrides, or metals, for applications related to energy. Due to its extraordinary surface-volume relationship, tunable thermal and transport properties, and its high surface area, these 1D nanostructures have become fundamental elements for the development of energy processes. The most relevant 1D nanomaterials, their different synthesis procedures, and useful methods for assembling 1D nanostructures in functional devices will be presented. Applications in relevant topics such as optoelectronic and photochemical devices, hydrogen production or energy storage, among others, will be discussed. The present review concludes with a forecast on the directions towards which future research could be directed on this class of nanostructured materials.
The production of biodiesel in Brazil is encouraged by the government through the Fuel Stamp, a certification system linked to the National Plan for Production and Use of Biodiesel -PNPB -aimed at promoting economic and sustainable development. It focuses on social inclusion, also intending to reduce dependence on fossil fuels and emission of pollutants and diversify the energetic matrix through the use of different oil sources as raw material. Certification -and with it a number of tax benefits -are granted to industrial processors that are supplied with raw materials coming from small-scale farms. Thus, it facilitates the access of the family farms in this value chain. The objective of this work is to analyze the effects of this system of certification in the transactions between its main agents, farmers and processing industries. For this purpose, the work makes a revision of the studies that national public agencies have elaborated on regional cases and also scientific publications. Results show that this measure allowed the insertion of family farmers in the production chain and enabled the sustainable rural development. However, it presents gaps as the occurrence of failures in the fulfilment of contracts between family farmers and the industry. Moreover, in spite of being crop diversification, one of the objectives of the certification system, the preference of the industry for soy as raw material -because of technological reasons -is displacing traditional regional crops (for example palm and castor oil).
Nowadays we are facing the necessity to find new ways to reduce the use of fossil fuels. This need comes from the excessive use of these sources as energy and the well-known adverse environmental effects than these fuels represents. Currently the fossil fuels represents about the 70% of the world energy sources. This dependency has brought some important problems of contamination such as global warming and climate change, acid rain, alterations of the carbon cycle, among many others. The transportation sector is the largest consumer of petroleum-based fuels in the world, liberating to the atmosphere vast amounts of CO2, NOx, SOx, lead (Pb), mercury (Hg), and many others. These pollutants are not only harmful to the environment but also to the human health, causing lung and heart diseases along with cancer. The increase of price and demand of these fuels and the contamination generated by them makes imperative the search of viable clean technologies looking for the production of clean fuels with high commercial value. Contaminants produced by the combustion of fossil fuels represent a challenging future for the development of new clean fuels. In this regard, an interesting alternative consists in the synthesis of clean diesel fuel thorough the Fischer-Tropsch (FT) reaction. This method produces clean diesel starting from a mixture of H2 and CO obtained from renewable or not renewable energy sources. This synthesis produces high weighted hydrocarbons with high purity. The fuel produced by this process is clean since it does not have aromatic compounds or sulphur or nitrogen-based compounds, preventing the production and release of NOx and SOx during combustion. The FT processes require the use of heterogeneous catalysts. These catalysts are based on active metals (i.e. Co, Ru or Fe) highly dispersed on the surface of appropriate supports. In this research SiO2 nanospheres, synthesized by using the Stӧber procedure, have been used as supports for the deposition of different metals on the surface. The synthesized catalysts were characterized by FE-SEM, HRTEM, XRD and BET, and used for the FT reaction. Preliminary catalytic results are very promising and show that mixtures of low loadings of bimetal nanoparticles dispersed on the surface of SiO2 nanospheres could be efficiently used for the synthesis of paraffin products with different distribution.
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