Aplicación de ZnO/TiO2/g-C3N4 para la degradación de naranja de metilo bajo la exposición de luz UV y visible

A novel photocatalyst ZnO/TiO2/g-C3N4 was synthesized successfully to operate under UV and visible light for application in methyl orange degradation in water. The optimized photocatalysts were characterized by X-ray diffraction, and UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS). The photocatalytic activity of the ZnO/TiO2/g-C3N4 heterojunction under visible light for methyl orange degradation is higher than commercial TiO2, which can be attributed to a decrease in the bandgap energy and a good separation of the photogenerated electron-hole pairs, which reduces the recombination and improves the production of hydroxyl radicals.Se sintetizó con éxito un nuevo fotocatalizador de ZnO/TiO2/g-C3N4 para operar bajo luz UV y visible en la degradación de naranja de metilo en agua. Los fotocatalizadores optimizados se caracterizaron por difracción de rayos X y espectroscopía de reflectancia difusa UV-vis (UV-Vis DRS). La actividad fotocatalítica bajo luz visible de la heterounión de ZnO/TiO2/g-C3N4 para la degradación de naranja de metilo es mucho mayor que la del TiO2 comercial, lo que podría atribuirse a una disminución de la energía de banda prohibida y una buena separación de los pares electrón-hueco fotogenerados, lo cual disminuye la recombinación y mejora la producción de radicales hidroxilo

Síntesis de los fotocatalizadores binarios SnO2/TiO2y ternarios SnO2/TiO2/nanohojas de g-C3N4 para la degradación de naranja de metilo y ciprofloxacino en presencia de luz ultravioleta

When emergent pollutantsare in wastewater they need oxidation advanced processes for their degradation, such Heterogeneous Photocatalysis. Nowadays more efficient photocatalysts than titanium dioxide (TiO2) are being sought to degrade complex molecules. Nanoparticles and Quantum Dots (QDs) of Tin Oxide (SnO2) were synthesized by different methods, binary SnO2/TiO2and ternary SnO2/TiO2/g-C3N4nanosheets heterojunctions were synthetized by wet impregnation method to Methyl Orange (MO) as model pollutant and Ciprofloxacin (CIP) degradation. The most efficient photocatalysts for MO degradation were SnO2-SG300/P25 andP25. The SnO2-QDs/P25 junction showed a great MO adsorption capacity. The binary heterojunctions SnO2-npAldrich/P25 and SnO2-SG300/P25 showed higher degradation percentages than TiO2and P25.Los contaminantes emergentes,al encontrarse en aguas residuales, requieren procesos avanzados de oxidación para su degradación, como la fotocatálisis heterogénea. Actualmente se buscan fotocatalizadores más eficientes que el dióxido de titanio (TiO2) para degradar moléculas complejas. Se sintetizó dióxido de estaño (SnO2) nanométrico y puntos cuánticos (QDs) por distintos métodos;se sintetizaron juntas binarias de SnO2/TiO2y juntas ternarias de SnO2/TiO2/nanohojas de g-C3N4por impregnación húmeda, para la degradación de Naranja de Metilo (NM) como contaminante modelo y Ciprofloxacino (CIP). Los fotocatalizadores más eficientes para la degradación de NM fueron SnO2-SG300/P25 y P25. La junta SnO2-QDs/P25 mostró una gran capacidad de adsorción del NM. Para la degradación de CIP las juntas SnO2-npA/P25 y SnO2-SG300/P25 mostraron porcentajes de degradación superiores al TiO2y P2

Heterojunctions for Photocatalytic Wastewater Treatment: Positive Holes, Hydroxyl Radicals and Activation Mechanism under UV and Visible Light

Forming heterojunctions by coupling two or more semiconductors is an important strategy to develop stable and efficient photocatalysts able to operate both under near-UV and visible light. Five novel heterojunction sys-tems were synthesized in the present study, using a modified sol-gel method: Bi2Mo3O12/TiO2, ZnFe2O4/TiO2, FeTiO3/TiO2, WO3(US)/TiO2 and WO3/TiO2. These heterojunction semiconductors were characterized by us-ing XRD, SEM and EDX, UV–Vis diffuse reflectance spectroscopy and BET. Their photocatalytic activities were evaluated using methyl orange (MO) degradation under both near-UV and visible light. From the various het-erojunctions developed, the WO3(US)/TiO2 photocatalyst was the one that showed the highest photocatalyticefficiency with this being assigned to the formation of a double heterojunction involving anatase, rutile and monoclinic WO3 phases. On this basis, a photocatalyst activation mechanism applicable to near-UV and visible light irradiation was proposed. This mechanism explains how the photogenerated electrons (e–) and positive holes (h+) can be transferred to the various phases. As a result, and given the reduced holes and electron recom-bination surface, hydroxyl radicals found were more abundant. To confirm this assumption, hole formation in the valence band was studied, using hole-scavenging reactions involving ion iodine (I–), while hydroxyl radical production used fluorescence spectroscopy

Water quality for agricultural irrigation in the Calera aquifer region in Zacatecas, Mexico

In the region that includes the Calera, Zacatecas aquifer, the intensive production of chili (Capsicum ssp.) is of great economic importance, and depends entirely on groundwater. Being an overexploited aquifer in a karst and semi-arid zone, water availability becomes more limited and water quality is relevant. The objective of the research was to evaluate the impact on the chemical quality of the water and determine its aptitude for agricultural use through the criteria of salinity, sodicity and toxicity. For two consecutive cycles, a sampling was performed according to NOM-014-SSA1-1993 to wells that are frequently used for irrigation of chili. Five strata were designed whose depth ranges from 50 to 280 m above the static level. For the three criteria the water quality parameters were determined, their classification was shown on a Richards diagram and their hydrogeochemistry using a Piper diagram. A statistical analysis of main components, a randomized complete block analysis and a cluster analysis were performed to identify the parameters that have a significant impact on water quality. The results showed that the cultivation of chili has not impacted the quality of the aquifer water and that the depth of the wells does not influence it, rather it depends on the region where each well is located, recharge processes, geology of the region , speed of underground currents and infiltration by the action of faults and geological fractures.En la región que comprende el acuífero Calera, Zacatecas, la producción intensiva del cultivo de chile (Capsicum ssp.) es de suma importancia económica, y depende por completo del agua subterránea de un acuífero sobreexplotado en una zona cárstica y semiárida, donde la disponibilidad de agua se torna más limitada y la calidad del líquido es de relevancia. El objetivo de la investigación fue evaluar el impacto a la calidad química del agua y determinar su aptitud para uso agrícola mediante los criterios de salinidad, sodicidad y toxicidad. Durante dos ciclos consecutivos se llevó a cabo un muestreo, según la norma NOM-014-SSA1-1993, a los pozos que con más frecuencia se usan para irrigación de chile. De acuerdo con la profundidad resultaron cinco estratos, que van de 50 a 280 m sobre el nivel estático. Para los tres criterios se determinaron los parámetros de calidad de agua; su clasificación se mostró en un diagrama de Richards y su hidrogeoquímica mediante un diagrama de Piper. Se analizaron bloques completos al azar, así como los componentes principales y un clúster, a fin de identificar los parámetros que inciden de modo considerable en la calidad del agua. Los resultados evidenciaron que el cultivo de chile no ha impactado la calidad del agua de acuífero y que la profundidad de los pozos no influye en ésta; más bien depende de la región en donde se ubica cada pozo, procesos de recarga, geología de la región, velocidad de las corrientes subterráneas, y la infiltración por la acción de fallas y fracturas geológicas

Nanoparticulate Double-Heterojunction Photocatalysts Comprising TiO2(Anatase)/WO3/TiO2(Rutile) with Enhanced Photocatalytic Activity toward the Degradation of Methyl Orange under Near-Ultraviolet and Visible Light

Nanoparticulate double-heterojunction photocatalysts comprising TiO2(Anatase)/WO3/TiO2(Rutile) were produced by a sol–gel method. The resulting photocatalysts exhibit clear synergistic effects when tested toward the degradation of methyl orange under both UV and visible light. Kinetic studies indicate that the degradation rate on the best double-heterojunction photocatalyst (10 wt % WO3-TiO2) depends mainly on the amount of dye concentration, contrary to pure oxides in which the degradation rate is limited by diffusion-controlled processes. The synergistic effects were confirmed through systematic and careful studies including holes and OH radical formation, X-ray diffraction, electron microscopy, elemental analysis, UV–vis diffuse reflectance spectroscopy, and surface area analysis. Our results indicate that the successful formation of a double heterojunction in the TiO2(Anatase)/WO3/TiO2(Rutile) system leads to enhanced photoactivity when compared to individual oxides and commercial TiO2 P25

Enhancing the hydrogen generation of TiO2nanoparticles by decorating its surface with BiI3and PbI2quantum dots

This work reports the performance of TiO2/BiI3and TiO2/PbI2nanocomposites for hydrogengeneration. BiI3and PbI2quantum dots (QDs) were grown on TiO2(P25 Degussa) using a fastinjection method. According to the analysis by X-ray diffraction, the nanocomposites have a mixture of anatase, rutile and cubic phases from TiO2, BiI3and PbI2. The images obtainedfrom transmission electron microscopy revealed that the TiO2support have sizes in therange of 70e220 nm while the QDs of BiI3and PbI2(co-catalysts) grown on TiO2have sizesin the range of 12e17 nm. The presence of these iodides on TiO2created oxygen vacanciesdefects (confirmed by photoluminescence measurements) that extended the light ab-sorption of TiO2from the UV to the VIS range. According to the results from the photo-catalytic experiments for hydrogen generation (achieved using pure water and UV-VISlight), the hydrogen generation rates produced by the TiO2/BiI3and TiO2/PbI2nano-composites were 437e580 times, 81e108 times and 21e30 times, higher than these for pureTiO2, PbI2and BiI3, respectively. The maximum hydrogen generation rates of the TiO2/BiI3and TiO2/PbI2nanocomposites were 290.7 and 219.2mmol h 1g 1, respectively. In addition,the TiO2/BiI3and TiO2/PbI2nanocomposites contained defects that acted as electrontrapping centers, which in turn, delayed the electron-hole recombination and this favoredthe photocatalytic generation of H2. Moreover, the heterojunction formed between the TiO2and the iodides allowed the transfer of electrons from the conduction band of TiO2towardthe conduction band of the iodides, creating a“sink”for the electrons which delayed theelectron hole recombination. The results presented here demonstrated that the depositionof iodide co-catalyst on TiO2is a feasible option to enhance the hydrogen generation

Photocatalytic degradation of metoprolol in aqueous medium using a TiO2/ natural zeolite composite

Photodegradation of metoprolol using a TiO2 and Mexican natural zeolite composite (T/MZ) was studied. The photocatalyst was successfully synthesized by physical mixing method where commercial TiO2 Degusa P25 was supported on thermochemical modified clinoptilolite. X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy and Fourier transform infrared spectroscopy confirmed the TiO2 incorporation over the clinoptilolite surface without structural changes of the zeolite. Point of zero charge of 6.2 was found for the T/MZ, while the bandgap energy of 3.15 eV was obtained by UV–Vis diffuse reflectance spectroscopy. Photodegradation tests of metoprolol as a model emerging pollutant were carried out, finding that the T/MZ composite to have superior degradation percentages thant the commercial TiO2 P25 for all the pH values tested (3–9), which demonstrates a synergistic effect between the semiconductor material and the zeolitic support. Finally, it was found that the kinetics degradation of metoprolol follows the Langmuir, Hinshelwood, Hougen and Watson (LHHW) model

The impact of surgical delay on resectability of colorectal cancer: An international prospective cohort study

AimThe SARS-CoV-2 pandemic has provided a unique opportunity to explore the impact of surgical delays on cancer resectability. This study aimed to compare resectability for colorectal cancer patients undergoing delayed versus non-delayed surgery.MethodsThis was an international prospective cohort study of consecutive colorectal cancer patients with a decision for curative surgery (January-April 2020). Surgical delay was defined as an operation taking place more than 4 weeks after treatment decision, in a patient who did not receive neoadjuvant therapy. A subgroup analysis explored the effects of delay in elective patients only. The impact of longer delays was explored in a sensitivity analysis. The primary outcome was complete resection, defined as curative resection with an R0 margin.ResultsOverall, 5453 patients from 304 hospitals in 47 countries were included, of whom 6.6% (358/5453) did not receive their planned operation. Of the 4304 operated patients without neoadjuvant therapy, 40.5% (1744/4304) were delayed beyond 4 weeks. Delayed patients were more likely to be older, men, more comorbid, have higher body mass index and have rectal cancer and early stage disease. Delayed patients had higher unadjusted rates of complete resection (93.7% vs. 91.9%, P = 0.032) and lower rates of emergency surgery (4.5% vs. 22.5%, P ConclusionOne in 15 colorectal cancer patients did not receive their planned operation during the first wave of COVID-19. Surgical delay did not appear to compromise resectability, raising the hypothesis that any reduction in long-term survival attributable to delays is likely to be due to micro-metastatic disease