One-pot synthesis of green-emitting nitrogen-doped carbon dots from xylose

Carbon dots (CDs) are interesting carbon nanomaterials that exhibit great photoluminescent features, low cytotoxicity, and excellent water stability and solubility. For these reasons, many fields are starting to integrate their use for a variety of purposes. The catalytic performance of VOPO4 has been evaluated in the synthesis of nitrogen-doped carbon dots (N-CDs). The synthesis reaction was carried out at 180 °C using VOPO4 as a heterogeneous catalyst for 2 to 4 h of reaction time. After reaction, the N-CDs were purified using a novel method for the protection of the functional groups over the surfaces of the N-CDs. The morphological, superficial, and photoelectronic properties of the N-CDs were thoroughly studied by means of TEM, HRTEM, XPS, and photoluminescence measurements. The conversion of the carbon precursor was followed by HPLC. After three catalytic runs, the catalyst was still active while ensuring the quality of the N-CDs obtained. After the third cycle, the catalyst was regenerated, and it recovered its full activity. The obtained N-CDs showed a great degree of oxidized groups in their surfaces that translated into high photoluminescence when irradiated under different lasers. Due to the observed photoelectronic properties, they were then assayed in the photocatalytic degradation of methyl orange.This research was funded by the Spanish Ministry of Science and Innovation (PID2021-122736OB-C42, PID2021-122613OB-I00) and FEDER (European Union) funds (PID2021-122736OB-C42, P20-00375, UMA20-FEDERJA88)

CDs and N-CDs preparation from xylose and xylose-enriched biomass liquors for methyl orange photocatalytic degradation.

CDs are newly discovered carbon nanoparticles that present unique properties. Each nanoparticle consists of a graphitic lattice core covered by a functionalized surface composed by several polar functional groups attached1,2. Due to this functionalization, CDs exhibit photoinduced electronic transference, fluorescence and up-conversion photoluminescence3. CDs have raised increasing attention for their undemanding synthesis procedure combined with the fact that they have been proved to be non-toxic and can be modified to reach satisfactory quantum yield values. A current tendency in the obtention of CDs is the pursuit of a synthesis method that fulfils the requirements of green chemistry but keeps production costs low. Therefore, CDs obtained from green precursors coming from biomass is an emergent research topic4,3,5,6,7. The most frequent and best-known method for CDs production is hydrothermal or solvothermal method7,3,2.The acidic conditions required by this method are commonly achieved using mineral acids such as HCl; nonetheless, the hydrothermal method is compatible with heterogeneous catalysis, which have been proved in this work. As a consequence of their photoluminescence and electron transfer properties, CDs can work as electron mediators, photosensitizers, as well as photocatalysts by themselves 10. It has been proved that CDs when photo excited are outstandingly good electron donors and electron acceptors, since either electron acceptors or electron donors are able to quench the photoluminescence emitted by CDs effectively 9.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Influence of Lewis and Brønsted acid catalysts in the transformation of hexoses into 5-ethoxymethylfurfural

Several sulfonated polymers, which are typical Brønsted acid catalysts, have been employed in the production of two biofuels: 5-ethoxymethylfurfural (EMF) and ethyl levulinate (EL) as main byproduct, and the catalytic results have been attributed to their different chemical and morphological properties. The Purolite CT275DR attained the best results from 5-hydroxymethylfurfural (HMF) with a 63% EMF yield after 16 h at 100 ◦C thanks to their more abundant superficial acid sites. Moreover, Purolite CT275DR was able to efficiently dehydrate and etherify fructose, with a total EMF plus EL yield of 65% after 24 h at 100 ◦C. When glucose or galactose were used as feedstock, alumina was utilized to provide Lewis acid sites, necessary for the transformation of aldoses in so- lution enabling a combined biofuel yield (EMF plus EL) of 40% from glucose after 24 h at 140 ◦C. With the study of the role of each catalyst, both Brønsted and Lewis acid catalysts (resin and alumina, respectively) were required to obtain considerable EMF yields from aldoses. The reutilization of the catalysts employed for 5 cat- alytic runs demonstrated that Purolite CT275DR suffers no appreciable loss of activity, but alumina showed progressive losses in activity in each cycle due to carbonaceous deposits and catalyst loss.Funding for open access charge: Universidad de Málaga / CBUA This research was funded by the Spanish Ministry of Innovation, Science and Universities (RTI2018-094918-B-C44), FEDER (European Union) funds (RTI2018-094918-B-C44 and UMA18-FEDERJA-171) and Malaga University. Authors thank to Universidad de M ́alaga/CBUA for funding for open access charge. C.G.S. acknowledges FEDER funds for her postdoctoral contract (UMA18-FEDERJA-171). B.T.O. acknowledges the Ministerio de Universidades for his predoctoral contract (FPU20/ 02334

Si-Al nanospheres for the valorization of galactose and agarose into 5-hydroxymethylfurfural.

5-hydroxymethylfurfural (HMF) is a compound that has gained attention to potentially substitute fossil resources in areas such as the polymer industry or the production of energy vectors. HMF is produced from the acid treatment of hexoses, such as glucose or galactose. In this sense, algae biomass has gained interest as it can be grown in both, sweet and salt water and their growth rate and CO2 fixation are several times higher than those of terrestrial plants. Red algae, which are rich in agarose, a galactose and 1,6-dehydrogalactose heteropolymer, can potentially be used as feedstock to produce HMF [1]. Hence, in this work, alumina supported nanospheres have been synthetised and employed as acid catalysts due to their high acidity and porosity that allows the selective conversion of these biomass derived compounds into valuable HMF.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Valorisation of glucose into biofuels and high value-added chemicals using zeolites as catalysts.

Hexose sugars can be valorised under acidic conditions to produce the platform chemical 5-hydroxymethylfurfural (HMF), which can be transformed in a broad spectrum of chemicals with applications as biofuels or monomers for polymers [1]. 5-ethoxymethylfurfural (EMF) is one of the derivatives of HMF useful as biofuel or fuel additive, produced usually from the etherification of HMF with ethanol. However, the high price of HMF is an important drawback for its use as feedstock for the production of EMF, which, together with the low yields and selectivity that are often attained by treating biomass or biomass derived compounds, are limiting its industrial application. In this work, several zeolites with different morphologies and chemical compositions have been employed as acid catalysts for the etherification reaction of HMF and ethanol to produce EMF, as well as the direct conversion of glucose into EMF.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tec

Influence of Structure-modifying Agents in the Synthesis of Zr-doped SBA-15 Silica and Their Use as Catalysts in the Furfural Hydrogenation to Obtain High Value-added Products through the Meerwein-Ponndorf-Verley Reduction

Zr-doped mesoporous silicas with different textural parameters have been synthesized in the presence of structure-modifying agents, and then characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), N2 adsorption-desorption at -196 ºC, NH3 thermoprogrammed desorption (NH3–TPD), CO2 thermoprogrammed desorption (CO2–TPD), and X-ray photoelectron spectroscopy (XPS). These porous materials were evaluated in the furfural hydrogenation through the Meerwein-Ponndorf-Verley (MPV) reaction. The catalytic results indicate that the catalyst synthesized under hydrothermal conditions and adding a pore expander agent is more active and selective to furfuryl alcohol. However, the Zr-doped porous silica catalysts that were synthesized at room temperature, which possess narrow pore sizes, tend to form i-propyl furfuryland difurfuryl ethers, coming from etherification between furfuryl alcohol (FOL) and isopropanol molecules (used as H-donor) by a SN2 mechanism.This research was funded by the Ministry of Economy and Competitiveness (Spain) (grant numbers: CTQ2015-64226-C3-3-R, IEDI-2016-00743), Junta de Andalucía (Spain) (P12-RNM-1565), and FEDER (European Union) funds

Application of zeolites for the production of biofuels and furans from hexose sugars in ethanol.

The use of zeolites as catalysts in the transformation of glucose and 5-hydroxymethylfurfural (HMF) into 5-ethoxymethylfurfural (EMF) was evaluated. The behaviour of the catalysts could be explained by their morphology, composition, acid properties and chemical coordination of the active sites. The progress of the reaction was followed by High Performance Liquid Chromatography (HPLC) and 13C Nuclear Magnetic Resonance (NMR). Several intermediates were identified, and a reaction path is proposed. Different cosolvents were also employed in this study to enhance the selectivity towards different possible valuable compounds, and they were found to have a positive influence for the production of EMF and furfural.Funding for open access charge: Universidad de Málaga / CBU

Hidrocalumita: preparación por el método mecanoquímico y su aplicacion en la isomerización de glucosa a fructosa.

La fructosa es la llave para la formación de diversas moléculas plataformas tales como, furfural, 5-hidroximetilfurfural (HMF), acido levulinico, ácido fórmico y acido láctico. Actualmente en la industria se utilizan mayormente enzimas debido a los mejores resultados de selectividad y rendimiento del proceso de glucosa a fructosa. Es por este motivo que la búsqueda de catalizadores heterogéneos, que no necesiten condiciones de reacción tan singulares, hace que sea un amplio campo de investigación dentro de la catálisis.DEASYL SA Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Tailoring basic and acidic properties of MgAl hydrotalcite by fluoride anions: Effect on glycerol oligomerisation

In this work, two families of catalysts based on mixed metal oxides derived from MgAl hydrotalcites were synthesized with a Mg/Al molar ratio of 3. On the one hand, in the first family, the fluoride anion was incorporated in the interlayer space by using ammonium fluoride, exploiting the “memory effect” characteristic of hydrotalcites. In the second family, fluoride anions substituted oxides anions in the layer, incorporating directly them during the precipitation of hydroxides, by using cryolite as a precursor for both fluorine and aluminium. The hydrotalcites were transformed into mixed metal oxides by thermal treatment and tested in the glycerol etherification reaction at 230 ºC, in a batch reactor at atmospheric pressure. The hydrotalcites and the corresponding mixed metal oxides were characterized by different experimental techniques, such as X-ray diffraction (XRD), elemental analysis (CHF), N2 sorption at -196ºC, thermogravimetric analysis (ATD-TG), X-ray photoelectron spectroscopy (XPS), temperature-programmed desorption of CO2 and NH3 (CO2-TPD and NH3-DTP) and solid state nuclear magnetic resonace (ssNMR) of 19F. It was found that the mixed metal oxides prepared from hydrotalcites, where fluorine was incorporated in the synthesis step using cryolite, achieved the maximum conversion values and complete selectivity towards diglycerol. Diglycerols were the unique detected products and, in some cases, the formation of triglycerols was also detected.Funding for open access charge: Universidad de Málaga / CBU