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Biomass conversions to chemicals via various conventional technologies require high energy consumption, high temperature, high pressure, or high system cost. Alternatively, photocatalysis is one of the greener technologies because it utilizes the energy from lamps or natural sunlight with catalysts to synthesize chemicals under mild conditions and room temperature. In this work, zinc oxide (ZnO) particles were successfully synthesized using polyvinylpyrrolidone as an additive in coprecipitation to control the size and protect the aggregation. The crystal structure of hexagonal wurtzite was found in the obtained nanoparticles. The photocatalytic activities of the obtained samples were evaluated for the production of high-value chemicals (gluconic acid, xylitol, arabinose, and formic acid) via the photocatalytic conversion of glucose under UV-A irradiation. The photocatalytic results indicated the relationship of defects (i.e., oxygen vacancies and zinc vacancies) with glucose conversions. From the ZnO nanoparticles calcined at various temperatures from 400 to 700 °C, the one calcined at 700 °C showed the highest glucose conversion of 21.5% with a high yield of carboxylic acid products (gluconic acid and formic acid). The gluconic acid showed the highest yield of 15% for 180 min, while the formic acid, arabinose, and xylitol presented the highest yields of 7, 1, and 0.5% for 180 min, respectively. Pure ZnO nanoparticles can convert glucose into value-added products without adding an acid or base in the reaction.
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Coffee ground waste from the coffee beverage preparation is mainly discarded and consequently ends up in landfill, which cause the contamination of caffeine in various environmental compartments. This study focuses on the upcycling of coffee-ground waste to carbon quantum dots (CQDs) for use as a modifying material to improve the visible light activity of titanium dioxide (TiO2). The CQD solution was synthesized by hydrothermal method, which has an average size of 2.80 ± 0.63 nm. The CQDs/TiO2 photocatalysts were prepared by combining CQD solutions at various amounts with sol-gel TiO2 and then coated on the fiberglass cloths (FGCs). The photocatalytic application mainly focuses on the removal of caffeine from the water. The photocatalytic experiment was preliminary run in a simple batch reactor under visible light. The 5CQDs/TiO2 coated FGC (5 mL of CQD solution/g of Ti-based on sol-gel) showed the best performance, and it was selected for the removal of caffeine and other pharmaceuticals (i.e., carbamazepine and ibuprofen) in the recirculating reactor. The removals of caffeine, carbamazepine, and ibuprofen after irradiation for 9 h were 82%, 88%, and 84%, respectively. The residual concentrations were significantly lower than the reported toxicity levels based on specific species. The changes in total organic carbon were observed, indicating the mineralization of pharmaceuticals in water. The 5CQDs/TiO2 coated FGC showed good flexible performance. No obvious loss of activity was observed for five runs. The actual wastewater from the coffee pot cleaning process was also tested. The removal was 80% for caffeine and 86% for color in the unit of the American Dye Manufacturers Institute (ADMI).
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Hydrothermal synthesis has been extensively utilized for fabricating carbon quantum dots (CQDs). Generally, the average sizes of the CQDs are controlled by using specific precursor concentrations, processing temperatures, and reaction times. In our study, the average size of CQDs can simply be controlled by using a different filling volume of sucrose solution in the hydrothermal reactor while keeping the other experimental parameters constant. If homogeneous nucleation plays a major role in the hydrothermal synthesis, the CQDs synthesized by using different filling volumes should have relatively the same size. Nonetheless, we found that the average size of CQDs is inversely correlated with the filling volumes. Particularly, for the hydrothermal syntheses with the filling volumes of 20%, 50%, and 80%, the average size of the CQDs is 15, 13, and 4 nm, respectively. Therefore, the hydrothermal synthesis of CQDs with size-tunability can be achieved by the heterogeneous process associated with the total surface areas between the precursor and reactor.
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The remarkable optoelectronic capabilities of perovskite structures enable the achievement of astonishingly high-power conversion efficiencies on the laboratory scale. However, a critical bottleneck of perovskite solar cells is their sensitivity to the surrounding humid environment affecting drastically their long-term stability. Internal additive materials together with surface passivation, polymer-mixed perovskite, and quantum dots, have been investigated as possible strategies to enhance device stability even in unfavorable conditions. Quantum dots (QDs) in perovskite solar cells enable power conversion efficiencies to approach 20%, making such solar cells competitive to silicon-based ones. This mini-review summarized the role of such QDs in the perovskite layer, hole-transporting layer (HTL), and electron-transporting layer (ETL), demonstrating the continuous improvement of device efficiencies.
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High-performance lab-scale perovskite solar cells often have a precious metal as the top electrode. However, there are drawbacks to using metal top electrodes on a large scale, such as inducing degradation processes, requiring a high-temperature deposition process under vacuum, and having low scalability. Recently many studies have shown the potentials of using a carbon electrode because of its conductivity, flexibility, low cost, and ease of fabrication. This review article presents an overview of using carbon materials to replace the top electrode in perovskite photovoltaics. We discuss various fabrication techniques, various carbon-based device structures, and the advantages of using carbon materials. A collection of research works on device performance, large-scale fabrication, and device stability is presented. As a result, this review offers insight into the future of large-scale flexible solar cells.
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Development of conversion of biomass derivatives in combination with utilization of solar energy by photocatalysts is a promising alternative strategy for biorefineries. The photocatalytic reaction could convert glucose to a mixture of value-added chemicals under UV irradiation. Modifications of titanium dioxide (TiO2) nanoparticles by metal or metalloid (i.e., B and Ag) and nonmetal (i.e., N) dopants were carried out. The effects of co-doping (i.e., B/N and Ag/N) on physicochemical characteristics of the modified photocatalysts, photocatalytic glucose conversion, and the yields of the target chemical products (i.e., gluconic acid, xylitol, arabinose, and formic acid) were studied. The doping of the photocatalysts by different single dopants could improve the performance in terms of productivity and was further enhanced by the synergism from co-doping. The improvement in catalytic performances of the photocatalysts corresponded with the alterations in physicochemical characteristics of the catalysts resulting from the dopants.
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TiO2 nanofibers were fabricated by combination of sol-gel and electrospinning techniques. Ag-doped TiO2 nanofibers with different Ag contents were prepared by two different methods (in situ electrospinning or wetness impregnation of Ag on TiO2 nanofibers) and heat treated at 500 °C for 2 h under an air or N2 atmosphere. The obtained catalysts were characterized by field emission scanning electron microscopy, X-ray diffraction, photoluminescence, and N2 adsorption analyzed by the Brunauer-Emmett-Teller (BET) method. Photocatalytic glucose conversions with electrospun TiO2 and Ag-doped TiO2 nanofibers for production of high-value products were carried out. From different doping methods, the results indicated that 1 wt % Ag-TiO2 nanofibers prepared by an in situ method with calcination under N2 achieved the highest glucose conversion (85.49%). From several Ag loading contents (i.e., 0, 1, 2, and 4 wt %) in Ag-doped TiO2 nanofibers, the nanofibers exhibited different glucose conversions [in order of 2 wt % (99.65%) > 1 wt % (85.49%) > 4 wt % (77.72%) > 0 wt % (29.64%)]. Arabinose, xylitol, gluconic acid, and formic acid were found as the high-value chemicals with the photocatalytic reaction of TiO2 and Ag-doped TiO2 nanofibers under UVA irradiation. Product yields of each converted chemicals from different photocatalysts from different Ag loading contents showed relatively same trends with the glucose conversion. From all results, it can be concluded that the good characteristics of 2 wt % Ag-TiO2 nanofibers such as the smallest anatase crystallite size (8.25 nm) and the highest specific surface area (S BET = 53.69 m2/g) promoted the highest photocatalytic activity. Additionally, TiO2 and Ag-doped TiO2 nanofibers exhibited higher photocatalytic performance for glucose conversion than commercial TiO2 (P25) and synthesized TiO2 nanoparticles. Finally, Ag-doped TiO2 nanofibers showed recycling ability with high photocatalytic glucose conversion after four-time use.
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Nanocomposite materials were prepared by compounding polypropylene (PP) with zinc oxide (ZnO) nanoparticles, using a twin-screw extruder. The compound was molded by injection molding to form dumbbell-shaped specimens. The influence of ZnO nanoparticle content on the morphology, mechanical properties, chemical structure, photocatalytic activity, and antibacterial properties of the obtained nanocomposites was investigated. The morphological images showed that the ZnO nanoparticles were well distributed in the PP matrix. Characterizations of the mechanical properties and chemical structures before and after sunlight exposure found that at the shortest exposure time, crosslinks could occur in the nanocomposites, which resulted in improved mechanical properties. However, sunlight exposure with the time period longer than 18 weeks caused the reduction of the mechanical properties, due to degradation of the PP matrix. It was found that PP with 2% ZnO could achieve the photocatalytic degradation of methylene blue up to 59%. Moreover, the result of antibacterial tests indicated that the nanocomposites had better antibacterial properties than neat PP.
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The photocatalytic treatment of gaseous benzene under visible light irradiation was developed using electrospun carbon nanotube/titanium dioxide (CNT/TiO2) nanofibers as visible light active photocatalysts. The CNT/TiO2 nanofibers were fabricated by electrospinning CNT/poly(vinyl pyrrolidone) (PVP) solution followed by the removal of PVP by calcination at 450 °C. The molar ratio of CNT/TiO2 was fixed at 0.05:1 by weight, and the quantity of CNT/TiO2 loaded in PVP solution varied between 30 and 60 % wt. CNT/TiO2 nanofibers have high specific surface area (116 m2/g), significantly higher than that of TiO2 nanofibers (44 m2/g). The photocatalytic performance of the CNT/TiO2 nanofibers was investigated by decolorization of 1 × 10-5 M methylene blue (MB) dye (in water solution) and degradation of 100 ppm gaseous benzene under visible light irradiation. The 50-CNT/TiO2 nanofibers (calcined CNT/TiO2 nanofibers fabricated from a spinning solution of 50 % wt CNT/TiO2 based on PVP) had higher MB degradation efficiency (58 %) than did other CNT/TiO2 nanofibers and pristine TiO2 nanofibers (15 %) under visible light irradiation. The photocatalytic degradation of gaseous benzene under visible light irradiation on filters made of 50-CNT/TiO2 nanofibers was carried out in a simulated air purifier system. Similar to MB results, the degradation efficiency of gaseous benzene by 50-CNT/TiO2 nanofibers (52 %) was higher than by other CNT/TiO2 nanofibers and pristine TiO2 nanofibers (18 %). The synergistic effects of the larger surface area and lower band gap energy of CNT/TiO2 nanofibers were presented as strong adsorption ability and greater visible light adsorption. The CNT/TiO2 nanofiber prepared in this study has potential for use in air purifiers to improve air treatment efficiency with less energy.
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Contaminantes Atmosféricos/análisis , Benceno/análisis , Luz , Nanofibras/química , Nanotubos de Carbono/química , Titanio/química , Adsorción , Filtros de Aire , Catálisis , Azul de Metileno/análisis , Nanofibras/efectos de la radiación , Nanotubos de Carbono/efectos de la radiación , Propiedades de Superficie , Titanio/efectos de la radiaciónRESUMEN
Hollow carbon nanofibers (HCNFs) were prepared by electrospinning method with several coaxial nozzles, in which the level of the inner nozzle-end is adjustable. Core/shell nanofibers were prepared from poly(methyl methacrylate) (PMMA) as a pyrolytic core and polyacrylonitrile (PAN) as a carbon shell with three types of normal (viz. inner and outer nozzle-ends are balanced in the same level), inward, and outward coaxial nozzles. The influence of the applied voltage on these three types of coaxial nozzles was studied. Specific surface area, pore size diameter, crystallinity, and degree of graphitization of the hollow and mesoporous structures of carbon nanofibers obtained after carbonization of the as spun PMMA/PAN nanofibers were characterized by BET analyses, X-ray diffraction, and Raman spectroscopy in addition to the conductivity measurements. It was found that specific surface area, crystallinity, and graphitization degree of the HCNFs affect the electrical conductivity of the carbon nanofibers.
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Phosphorus (P) recovery was carried out through struvite precipitation from urines. Human urine, however, contains not only high nutrients for plants, such as P and nitrogen, but also pharmaceuticals and hormones. In this work, effects of magnesium (Mg) dose (in terms of Mg:P ratio) on P recovery efficiency and pharmaceutical amounts contained in struvite were investigated. Batch-scale experiments of synthetic and human urines revealed that struvite precipitation formed more X-shaped crystals with an increased molar ratio of Mg:P, while the amount of pharmaceuticals (tetracycline, demeclocycline, and oxytetracycline) in struvite decreased with an increased molar ratio of Mg:P. The lowest pharmaceutical amounts in struvite were found at the Mg:P ratio of 2:1 from both samples. Moreover, the maximum P recovery efficiency, quantity and purity of struvite were found in the range of 1.21 to 2:1. It indicated that the molar ratio of Mg:P has a significant impact on struvite precipitation in terms of pharmaceutical amounts in struvite; morphology, quantity and purity of struvite; and P recovery.
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Compuestos de Magnesio/aislamiento & purificación , Preparaciones Farmacéuticas/aislamiento & purificación , Fosfatos/aislamiento & purificación , Fósforo/aislamiento & purificación , Humanos , Compuestos de Magnesio/orina , Microscopía Electrónica de Rastreo , Modelos Teóricos , Nitrógeno/química , Preparaciones Farmacéuticas/orina , Fosfatos/orina , Fósforo/orina , Estruvita , Propiedades de SuperficieRESUMEN
Struvite (MgNH4PO4·6H2O) is normally used as a fertilizer in agriculture, where struvite crystallization from hydrolysed human urine is a simple and reliable method for phosphorus (P) recovery. Human urine, however, contains high amount of pharmaceuticals, which may cause health risk for applications. This research investigates the possibility of decreasing the amount of pharmaceuticals (tetracycline, demeclocycline and oxytetracycline) in struvite crystals recovered from synthetic and human urines by focusing on storage time, and of increasing the quality of struvite production. Urines were stored for different times up to 15 days prior to recovery of phosphorus by two steps, spontaneous precipitation and struvite crystallization. The morphology of spontaneous precipitates and struvite crystals was observed. Spontaneous precipitation removed around 17-24% of phosphate from synthetic and human urines, while pharmaceuticals were removed with a quite high amount at a short storage time (5 days) and this amount decreased with increasing the storage time (10 and 15 days). Urines with>70% remaining phosphates were re-used for struvite crystallization by adding extra magnesium. It was found that maximum P-recovery efficiency could be achieved from struvite crystallization at 5-day storage time, 70% and 68% of remaining P in the separated supernatant from synthetic and human urines, respectively, whereas less than 1% pharmaceuticals remained in the struvite crystals from both samples. This indicates that the procedure in this work is a good method for phosphorus recovery, in which high struvite purity (>99%) is obtained with low amount of pharmaceuticals.
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Compuestos de Magnesio/química , Fosfatos/química , Fósforo/aislamiento & purificación , Tetraciclinas/análisis , Cristalización , Humanos , Concentración de Iones de Hidrógeno , Hidrólisis , Compuestos de Magnesio/orina , Fosfatos/orina , Fósforo/química , Fósforo/orina , Manejo de Especímenes/métodos , Estruvita , Factores de TiempoRESUMEN
Neuronal activities play critical roles in both neurogenesis and neural regeneration. In that sense, electrically conductive and biocompatible biomaterial scaffolds can be applied in various applications of neural tissue engineering. In this study, we fabricated a novel biomaterial for neural tissue engineering applications by coating electrospun poly(lactic acid) (PLA) nanofibers with a conducting polymer, polypyrole (PPy), via admicellar polymerization. Optimal conditions for polymerization and preparation of PPy-coated electrospun PLA nanofibers were obtained by comparing results from scanning electron microscopy, X-ray photoelectron spectrometer, and surface conductivity tests. In vitro cell culture experiments showed that PPy-coated electrospun PLA fibrous scaffold is not toxic. The scaffold could support attachment and migration of neural progenitor cells. Neurons derived from progenitor exhibited long neurite outgrowth under electrical stimulation. Our study concluded that PPy-coated electrospun PLA fibers had a good biocompatibility with neural progenitor cells and may serve as a promising material for controlling progenitor cell behaviors and enhancing neural repair.
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Materiales Biocompatibles/farmacología , Conductividad Eléctrica , Ácido Láctico/química , Neuronas/citología , Neuronas/efectos de los fármacos , Polímeros/química , Pirroles/química , Andamios del Tejido/química , Animales , Materiales Biocompatibles/química , Proliferación Celular/efectos de los fármacos , Supervivencia Celular/efectos de los fármacos , Hipocampo/citología , Nanofibras/química , Nanotecnología/métodos , Células-Madre Neurales/citología , Células-Madre Neurales/efectos de los fármacos , Poliésteres , Ratas , Propiedades de Superficie , Ingeniería de TejidosRESUMEN
We propose new strategy to facilitate the fabrication of conjugated polymer fiber with higher oriented structures, which focused on electrospinning of a blend solution of regioregular poly(3-hexylthiophene) (rr-P3HT) and poly(vinyl pyrrolidone) (PVP). SEM observation revealed that the blend system forms homogeneous composite nanofibers. This system exhibits the specific feature of strong interchain contribution of P3HT from UV-vis absorption, fluorescence spectroscopic, XRD, and photoelectron spectrometric (for HOMO levels) investigations. We also demonstrate the removal of the PVP component from the P3HT/PVP composite fibers through the selective extraction and such strong interchain stacking of pristine P3HT fiber mat can be remarkably maintained.
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We report herein a simple procedure for the fabrication of TiO2 nanofibers by the combination of electrospinning and sol-gel techniques by using poly(vinylpyrrolidone) (PVP), titanium(IV) butoxide, and acetylacetone in methanol as a spinning solution. TiO2 nanofibers (260-355 nm in diameter), with a bundle of nanofibrils (20-25 nm in diameters) aligned in the fiber direction, or particle-linked structures were obtained from the calcination of as-spun TiO2/PVP composite fibers at temperatures ranging from 300 to 700 degrees C. These nanofibers were utilized as photocatalysts for hydrogen evolution. The nanofiber photocatalyst calcined at 450 degrees C showed the highest activity among the TiO2 nanofibers tested such as ones prepared by the hydrothermal method and anatase nanoparticles (Ishihara ST-01). These results indicate that one-dimensional electrospun nanofibers with highly aligned bundled nanofibrils are beneficial for enhancement of the crystallinity, large surface area, and higher photocatalytic activity.
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Hidrógeno/química , Metanol/química , Nanotubos/química , Nanotubos/ultraestructura , Titanio/química , Catálisis , Cristalización/métodos , Electroquímica/métodos , Luz , Ensayo de Materiales , Nanotubos/efectos de la radiación , Tamaño de la Partícula , Fotoquímica/métodos , Rotación , Titanio/efectos de la radiaciónRESUMEN
Electrospinning has become a versatile tool for fabricating nanofibers from materials of diverse origins. Normally, mats of randomly-aligned fibers were obtained. A number of techniques have been proposed to arrive at uniaxially-aligned fibers. This work reports a new technique, i.e., dual vertical wire technique, for fabrication of uniaxially-aligned fibers. This technique utilized two stainless steel wires that were vertically set in a parallel manner between a charged needle and a grounded collector plate. This technique allowed simultaneous collection of aligned fibers (between the parallel vertical wires) and a randomly-aligned fiber mat (on the collector plate). Application of the technique on poly(vinyl alcohol) (PVA) to prepare uniaxially-aligned fibers was found to be successful at short collection times. Unexpected formation of a large fiber tow consisting of individual as-spun nanofibers that were bound into a bundle was observed at long collection times. Morphological appearance and size of the fiber tow was affected by the change in the distance between the two vertical wire electrodes, while the average diameter of the individual fibers was not (i.e., about 340 to 350 nm). Lastly, mechanical properties and thermal behavior of the fiber tow were also investigated.