Metal-Organic Frameworks as Photocatalysts for Solar-Driven Overall Water Splitting.

Metal-organic frameworks (MOFs) have been frequently used as photocatalysts for the hydrogen evolution reaction (HER) using sacrificial agents with UV-vis or visible light irradiation. The aim of the present review is to summarize the use of MOFs as solar-driven photocatalysts targeting to overcome the current efficiency limitations in overall water splitting (OWS). Initially, the fundamentals of the photocatalytic OWS under solar irradiation are presented. Then, the different strategies that can be implemented on MOFs to adapt them for solar photocatalysis for OWS are discussed in detail. Later, the most active MOFs reported until now for the solar-driven HER and/or oxygen evolution reaction (OER) are critically commented. These studies are taken as precedents for the discussion of the existing studies on the use of MOFs as photocatalysts for the OWS under visible or sunlight irradiation. The requirements to be met to use MOFs at large scale for the solar-driven OWS are also discussed. The last section of this review provides a summary of the current state of the field and comments on future prospects that could bring MOFs closer to commercial application.

Metal Nodes of Metal-Organic Frameworks can Activate Molecular Hydrogen.

Hydrogenation of multiple bonds are among the most general and important organic reactions. Typical heterogeneous catalysts are based on transition metal nanoparticles, including noble metals. Data are presented here showing that metal nodes of MIL-101(Cr) and UiO-66 in the absence of occluded metal nanoparticles can promote hydrogenation of polarized X=Y double bonds of nitro and carbonyl groups. The catalytic activity is a function of the composition of the metal node and the organic linker. It is proposed that the reaction mechanism is based on the operation of frustrated Lewis acid/base pairs.

Enhanced Catalytic Performance of Quasi-HKUST-1 for the Tandem Imine Formation.

Copper-based metal-organic framework (Cu3 (BTC)2 (H2 O)3 ]n ⋅nH2 OMeOH (HKUST-1) has been subjected to thermolysis under air atmosphere at different temperatures ranging from 100 to 300 °C. This treatment produces the partial removal of ligands, the generation of structural defects and additional porosity in a controlled way. The resulting defective materials denoted according to the literature as quasi-MOFs, were subsequently employed as heterogeneous catalysts in the one pot synthesis of N-benzylideneaniline from aniline and benzyl alcohol in open air as terminal oxidant at 70 °C under base- and dehydrating agent-free conditions. The Q-HKUST catalysts calcined at 240 °C (QH-240) was the most efficient in the series, promoting imine synthesis. Data from Knoevenagel condensation of malononitrile shows that in QH-240 the distances of Cu ions in HKUST-1 cavities are preserved, increasing the Knoevenagel activity, but a strong rearrangement takes place at 300 °C or above. The unsaturated copper active sites with simultaneous presence of micro- and mesopores in QH-240 are responsible for this excellent catalytic performance. The effective parameters on catalytic activity of QH-240 including deligandation temperature, the amount of catalyst, the ratio of reactants, and reaction temperature as well as the stability and recyclability of the catalyst were also investigated. The possible mechanism used by QH-240 follows alcohol aerobic oxidation and subsequent anaerobic condensation of aldehyde intermediate with aniline.

Photoactive Zr and Ti Metal-Organic-Frameworks for Solid-State Solar Cells.

Solid-state photovoltaic cells based on robust metal-organic frameworks (MOFs), MIL-125(Ti), MIL-125(Ti)-NH2 , UiO-67, Ru(bpy)2 -UiO-67, (bpy 2,2'-bipyridine) as active components and spiro-MeOTAD (MeOTAD 2,2',7,7'-tetrakis[N,N-di(p-methoxyphenyl)amino]-9,9'-spirobifluorene) as hole transporting layer have been prepared., The photovoltaic response of this material increases in the presence of bathochromic -NH2 groups on the linker or Ru (II) polypyridyl complexes light harvester. These results show that the strategies typically employed in photocatalysis to enhance the photocatalytic activity of MOFs can also be applied in the field of photovoltaic devices.

Bifunctional metal-organic frameworks for the hydrogenation of nitrophenol using methanol as the hydrogen source.

This work reports the reduction of 4-nitrophenol to 4-aminophenol using UiO-66(Zr) as a bifunctional photocatalyst and hydrogenation catalyst using methanol as the hydrogen source. In particular, a series of UiO-66(Zr)-X (X: NH2, NO2 and H) and MIL-125(Ti)-NH2 catalysts have been screened as bifunctional catalysts for this process. UiO-66(Zr)-NH2 was found to be the most active material to promote light-assisted nitro hydrogenation under both UV-Vis and simulated sunlight irradiation. The tandem reaction occurs via hydrogen generation from a water/methanol mixture in the first step and, then, reduction of 4-nitrophenol to 4-aminophenol. UiO-66(Zr)-NH2 acts as a truly heterogeneous catalyst and can be reused several times without significant loss of activity, maintaining its crystallinity. This work shows the possibility of using MOFs as solar-driven bifunctional catalysts to promote the hydrogenation of organic compounds using methanol as the hydrogen source.

Influence of Neighborhood Size and Cross-Correlation Peak-Fitting Method on Location Accuracy.

A known technique to obtain subpixel resolution by using object tracking through cross-correlation consists of interpolating the obtained correlation function and then refining peak location. Although the technique provides accurate results, peak location is usually biased toward the closest integer coordinate. This effect is known as the peak-locking error and it strongly limits this calculation technique's experimental accuracy. This error may differ depending on the scene and algorithm used to fit and interpolate the correlation peak, but in general, it may be attributed to a sampling problem and the presence of aliasing. Many studies in the literature analyze this effect in the Fourier domain. Here, we propose an alternative analysis on the spatial domain. According to our interpretation, the peak-locking error may be produced by a non-symmetrical sample distribution, thus provoking a bias in the result. According to this, the peak interpolant function, the size of the local domain and low-pass filters play a relevant role in diminishing the error. Our study explores these effects on different samples taken from the DIC Challenge database, and the results show that, in general, peak fitting with a Gaussian function on a relatively large domain provides the most accurate results.

Parametric Evaluation of Errors Using Isolated Dots for Movement Measurement by Image Cross-Correlation.

Digital Image Correlation (DIC) is a common tool for assessing the movement of objects in a scene. Among others, one of the most popular techniques consists of tracking a dotted texture imitating speckle patterns. In this work, we analyzed the individual dots that form this pattern in order to propose an optimum size, shape, and dynamic range that allows minimizing the tracking error. Tracking was accomplished by using normalized cross-correlation with peak interpolation in order to obtain subpixel accuracy. For the models here used, we show that dot radii of 30-40 px with 150 gray levels are enough to obtain an accurate subpixel tracking resolution. Also, we show that 0.002 px is the performance limit of this technique, being this limit in accordance with the experimentally achievable subpixel limit.

Non-Contact Smartphone-Based Monitoring of Thermally Stressed Structures.

The in-situ measurement of thermal stress in beams or continuous welded rails may prevent structural anomalies such as buckling. This study proposed a non-contact monitoring/inspection approach based on the use of a smartphone and a computer vision algorithm to estimate the vibrating characteristics of beams subjected to thermal stress. It is hypothesized that the vibration of a beam can be captured using a smartphone operating at frame rates higher than conventional 30 Hz, and the first few natural frequencies of the beam can be extracted using a computer vision algorithm. In this study, the first mode of vibration was considered and compared to the information obtained with a conventional accelerometer attached to the two structures investigated, namely a thin beam and a thick beam. The results show excellent agreement between the conventional contact method and the non-contact sensing approach proposed here. In the future, these findings may be used to develop a monitoring/inspection smartphone application to assess the axial stress of slender structures, to predict the neutral temperature of continuous welded rails, or to prevent thermal buckling.

Photoinduced Charge Separation on the Microsecond Timescale in Graphene Oxide and Reduced Graphene Oxide Suspensions.

Transient absorption spectroscopy of graphene oxide (GO) and reduced graphene oxide (rGO) suspensions provides evidence for the photochemical generation of a charge-separated state on the microsecond timescale upon laser excitation. The lifetime and quantum yield of charge separation in suspended rGO were found to be higher than for GO. This could be advantageous for optoelectronic and photocatalytic applications, where graphene-based materials act as charge (electron) carriers. The electron-transfer quenching of the rGO charge-separated state by different amines is more efficient when the amine is a better electron donor and more easily oxidized.

Realistic limits for subpixel movement detection.

Object tracking with subpixel accuracy is of fundamental importance in many fields since it provides optimal performance at relatively low cost. Although there are many theoretical proposals that lead to resolution increments of several orders of magnitude, in practice this resolution is limited by the imaging systems. In this paper we propose and demonstrate through simple numerical models a realistic limit for subpixel accuracy. The final result is that maximum achievable resolution enhancement is connected with the dynamic range of the image, i.e., the detection limit is 1/2∧(nr.bits). The results here presented may aid in proper design of superresolution experiments in microscopy, surveillance, defense, and other fields.

[Satisfaction with life, victimization, and perception of insecurity in Morelos]. / Satisfacción con la vida, victimización y percepción de inseguridad en Morelos, México.

OBJECTIVE: To examines the influence of victimization, perceived insecurity and restrictions on daily routines in life satisfaction. MATERIALS AND METHODS: Participants were 7535 (50.2% men) aged between 12 and 60, selected from a proportional stratified sampling. MANOVA and polytomous logistic regression model were calculated. RESULTS: We found significant differences in victimization, perceived insecurity and restrictions on daily routines in relation with life satisfaction levels. Also, physical protective measures, control of personal information, perception of insecurity in public areas and restrictions on daily routines were related to lower levels of satisfaction with life. CONCLUSIONS: Lowest levels of satisfaction with life were associated with victimization, perception of insecurity in public areas, and restrictions on daily routines.

Influence of Dopant Loading on the Photo- and Electrochemical Properties of (N, O)-Co-doped Graphene.

A series of (N, O)-co-doped graphenes with different N and O loadings are prepared by the pyrolysis of natural chitosan. When the percentage of dopant increases, the conduction-band potential and charge-separation quantum yield increase, whereas the charge-separation lifetime decreases.

Visible-light photoresponse of gold nanoparticles supported on TiO2 : a combined photocatalytic, photoelectrochemical, and transient spectroscopy study.

In the context of gaining understanding on the origin of the visible-light photoresponse of TiO2 containing gold nanoparticles, the photocurrent spectra and photocatalytic H2 evolution of titania (P25) and Au-P25 were compared. Whereas no photocurrent was detected upon visible-light irradiation for either of the two photocatalysts, Au-P25 exhibited photocatalytic H2 evolution for wavelengths between 400 and 575 nm. This contradictory behavior under visible-light irradiation of Au-P25 was rationalized by transient absorption spectroscopy. It was suggested that photocatalytic H2 generation results from methanol quenching of the charge-separation state in each semiconductor nanoparticle, but the lack of photocurrent is due to the short lifetime of the charge separation, which makes interparticle charge migration for micrometric distances unlikely.

Method for targetless tracking subpixel in-plane movements.

We present a targetless motion tracking method for detecting planar movements with subpixel accuracy. This method is based on the computation and tracking of the intersection of two nonparallel straight-line segments in the image of a moving object in a scene. The method is simple and easy to implement because no complex structures have to be detected. It has been tested and validated using a lab experiment consisting of a vibrating object that was recorded with a high-speed camera working at 1000 fps. We managed to track displacements with an accuracy of hundredths of pixel or even of thousandths of pixel in the case of tracking harmonic vibrations. The method is widely applicable because it can be used for distance measuring amplitude and frequency of vibrations with a vision system.

Photophysical evidence of charge-transfer-complex pairs in mixed-linker 5-amino/5-nitroisophthalate CAU-10.

The photochemistry of two isostructural metal-organic frameworks based on 5-amino/5-formamidoisophthalate (CAU-10-NH2 /NHCHO) or mixed-linker 5-amino/5-formamido- and 5-nitroisophthalate (CAU-10-NO2 /NH2 /NHCHO) has been studied using laser flash photolysis. 355 nm excitation of CAU-10-NH2 /NHCHO leads to a transient absorption spectrum characterized by a broad continuous absorption from 380 to 800 nm that was attributed to the presence of holes (440 nm) and electrons (600 nm) based on iPrOH and N2 O quenching, respectively. In contrast, no transients were observed for the isostructural mixed-linker CAU-10-NO2 /NH2 /NHCHO, data that is compatible with the uniform distribution of linkers 5-amino/5-formamido/5-nitroisophthalate as charge-transfer complex pairs. The same effect of quenching of 5-aminoisophthalate transients by 5-nitroisophthalate was also observed in aqueous solution (pH 9) but with much lower strength. Using a simple Stern-Volmer formalism allowed the estimation of the interaction of 5-aminoisophthalate with 5-nitroisophthalate in MOF to be 5.2×10(4) times stronger than in the aqueous phase.

Valorization of Field-Spent Granular Activated Carbon as Heterogeneous Ozonation Catalyst for Water Treatment.

Developing sustainable cost-effective strategies for valorization of field-spent granular activated carbon (s-GAC) from industrial water treatment has gained much interest. Here, we report a cost-effective strategy for the regeneration of s-GAC as an adsorbent in a large-scale drinking water treatment plant and used as an efficient and durable ozonation catalyst in water. To achieve this, a series of samples is prepared by subjecting s-GAC to thermally controlled combustion treatments with and without pyrolysis. The catalytic performance of the optimized sample is evaluated for oxalic acid degradation as the model pollutant under batch (>15 h) and continuous flow operations (>200 h). The partially deactivated catalyst upon reuse is restored by thermal treatment. Electron paramagnetic resonance and selective quenching experiments show the formation of singlet oxygen (1O2) during catalytic ozonation. The GAC-ozonation catalyst is efficient to minimize the formation of chlorinated disinfection by-products like trihalomethanes and haloacetic acids in an urban wastewater effluent.

Solar Gas-Phase CO2 Hydrogenation by Multifunctional UiO-66 Photocatalysts.

Solar-assisted CO2 conversion into fuels and chemical products involves a range of technologies aimed at driving industrial decarbonization methods. In this work, we report on the development of a series of multifunctional metal-organic frameworks (MOFs) based on nitro- or amino-functionalized UiO-66(M) (M: Zr or Zr/Ti) supported RuOx NPs as photocatalysts, having different energy band level diagrams, for CO2 hydrogenation under simulated concentrated sunlight irradiation. RuOx(1 wt %; 2.2 ± 0.9 nm)@UiO-66(Zr/Ti)-NO2 was found to be a reusable photocatalyst, to be selective for CO2 methanation (5.03 mmol g-1 after 22 h;, apparent quantum yield at 350, 400, and 600 nm of 1.67, 0.25, and 0.01%, respectively), and to show about 3-6 times activity compared with previous investigations. The photocatalysts were characterized by advanced spectroscopic techniques like femto- and nanosecond transient absorption, spin electron resonance, and photoluminescence spectroscopies together with (photo)electrochemical measurements. The photocatalytic CO2 methanation mechanism was assessed by operando FTIR spectroscopy. The results indicate that the most active photocatalyst operates under a dual photochemical and photothermal mechanism. This investigation shows the potential of multifunctional MOFs as photocatalysts for solar-driven CO2 recycling.

Vibration frequency measurement using a local multithreshold technique.

In this paper, we demonstrate the use of a video camera for measuring the frequency of small-amplitude vibration movements. The method is based on image acquisition and multilevel thresholding and it only requires a video camera with high enough acquisition rate, not being necessary the use of targets or auxiliary laser beams. Our proposal is accurate and robust. We demonstrate the technique with a pocket camera recording low-resolution videos with AVI-JPEG compression and measuring different objects that vibrate in parallel or perpendicular direction to the optical sensor. Despite the low resolution and the noise, we are able to measure the main vibration modes of a tuning fork, a loudspeaker and a bridge. Results are successfully compared with design parameters and measurements with alternative devices.

Image processing for safety assessment in civil engineering.

Behavior analysis of construction safety systems is of fundamental importance to avoid accidental injuries. Traditionally, measurements of dynamic actions in civil engineering have been done through accelerometers, but high-speed cameras and image processing techniques can play an important role in this area. Here, we propose using morphological image filtering and Hough transform on high-speed video sequence as tools for dynamic measurements on that field. The presented method is applied to obtain the trajectory and acceleration of a cylindrical ballast falling from a building and trapped by a thread net. Results show that safety recommendations given in construction codes can be potentially dangerous for workers.