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H NMR is a common technique for tracking chemical reactions; here it is demonstrated that it can be used effectively to evaluate efficiency of photocatalysts. The photocatalytic degradation of acetylsalicylic acid (Aspirin) by P25 TiO2 and its photolytic degradation by UV light were examined; and they were found to be comparable, suggesting that th...
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... in the evaluation of photocatalysts for breakdown of organic matter. We illustrate this using aspirin as a model PPCP analyte: it is present in wastewater across the globe and its breakdown has been characterized by LC-MS [9]. The first step in the photocatalytic breakdown of aspirin is the deacetylation to salicylic acid and acetic acid ( Fig. 1]) ...
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... 4 aromatic signals corresponding to aspirin slowly decreased over the course of the degradation and are replaced with 3 aromatic peaks corresponding to salicylic acid. The integrated ratio of salicylic acid aromatic protons:acetic acid methyl is slightly lower than the 1:3 ratio that should arise per Fig. 1 suggesting that some of the salicylic acid may be bound to TiO 2 and is removed during centrifugation. The singlet peaks at 2.35 ppm and 2.11 ppm correspond to the CH 3 groups of aspirin and acetic acid, respectively, and their relative integration can serve as a conversion percentage for the ...
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... Before adsorption of SA, the TiO 2 and Sm-TiO 2 samples show two singlet peaks at 3.4 ppm and 2.5 ppm, which are connected to water and DMSO solvent [48]. The NMR spectra of TiO 2 and Sm-TiO 2 modified by SA display the aromatic-H signals between 6.5 ppm and 8 ppm [49]. These signals are particularly strong for Sm-TiO 2 as compared to those of pure TiO 2 . ...
In this work, we provide a new investigation on the effect of Sm³⁺ doping on the sol–gel mixture and stabilization of TiO2 sol. Sm³⁺ dopant was initially dissolved in dilute ethanol solvent to form Sm-ethanol solvation shells. After hydrolysis, the effect of Sm-modified solvent on the growth and aggregation of TiO2 primary particles was put in evidence. ¹H-NMR spectrum of Sm–TiO2 sol shows signals broadening of nBuOH and ethanol molecules without splitting effect, indicating that the two alcohols are located in solvation shells surrounding the Sm³⁺ cations. The stabilization of TiO2 colloidal sol is induced by the bound Sm³⁺-solvate species to Ti-oxo-alkoxy polymers, inhibiting the growth of TiO2 particles. In the absence of Sm³⁺ dopant, the TiO2 colloidal sol shows a high resolution ¹H-NMR spectrum with splitting of ¹H signals of ethanol and free nBuOH. SEM analysis of TiO2 consists of monodisperse spherical particles, whereas Sm–TiO2 shows a massive monolith with small particle size. These effects were correlated with TG/DTA and XRD results showing that Sm³⁺ dopant induces a more complex and prolonged thermal decomposition, decreasing the crystallization degree of TiO2 anatase. The effect of Sm³⁺ doping on UV-absorption region, adsorption capacity, and photocatalytic activity of TiO2 nanoparticles was also investigated.
... MS and NMR coordinate a complementary coupling for PPCPs analysis, where MS identifies the chemical compositions and NMR determines the chemical structures (Simpson et al., 2012). Nevertheless, LC columns or MS instrumentations can get damaged by nanoparticles catalysts, while NMR is resilient to that interference (Croxall et al., 2019). Therefore, when large number of new catalysts need to be screened, NMR would be a more desirable option to avoid instrumental damage. ...
... As NMR is a non-destructive and non-selective technique, the tested samples are available for the subsequent analysis and able to measure multiple PPCPs simultaneously (Malet-Martino and Holzgrabe, 2011). NMR can evaluate the breakdown of PPCPs by catalytic degradation e.g., aspirin (Croxall et al., 2019), the adsorption of target compounds onto the catalysts surface (Nosaka et al., 2014), and confirm the analysis by LCeMS (Richardson and Temes, 2018). Nevertheless, high-purity samples with concentrated parent compounds are required for the NMR measurement due to the low sensitivity (Malet-Martino and Holzgrabe, 2011). ...
... However, the types of samples, the pH value of the solution, the turbidity, and a mixture of different organic target compounds can affect the accuracy of determination (Wolfgong, 2015). Moreover, UV light can be absorbed by most photocatalysts in the system, leading to the failure of measurement by UV-vis spectroscopy (Croxall et al., 2019). Thus, when carbon-/biochar-based photocatalysts are applied, filtration or centrifugation is usually carried out to separate the catalysts before the measurement (Xiao et al., 2013;Yan et al., 2017). ...
Considerable efforts have been made to develop effective and sustainable catalysts, e.g., carbon-/biochar-based catalyst, for the decontamination of organic pollutants in water/wastewater. Most of the published studies evaluated the catalytic performance mainly upon degradation efficiency of parent compounds; however, comprehensive and field-relevant performance assessment is still in need. This review critically analysed the performance indicators for carbon-/biochar-based catalytic degradation from the perspectives of: (1) degradation of parent compounds, i.e., concentrations, kinetics, reactive oxidative species (ROS) analysis, and residual oxidant concentration; (2) formation of intermediates and by-products, i.e., intermediates analysis, evolution of inorganic ions, and total organic carbon (TOC); and (3) impact assessment of treated samples, i.e., toxicity evolution, disinfection effect, and biodegradability test. Five most frequently detected pharmaceuticals and personal care products (PPCPs) (sulfamethoxazole, carbamazepine, ibuprofen, diclofenac, and acetaminophen) were selected as a case study to articulate the performance indicators for a holistic evaluation of carbon-/biochar-based catalytic degradation. This review also encourages the development of alternative performance indicators to facilitate the rational design of catalysts in future studies.
... Spectroscopic methods 16,17 rely on the detection of absorption or emission of specific wavelengths by specific functional groups of the substrates, products and intermediates. NMR 18,19 based methods including newly developed FlowNMR 20 and catalystcoated NMR tubes 21 could provide structural information of samples within a wide detection range. HPLC-MS [22][23][24] is another widely used technique for photocatalytic research providing both qualitative and quantitative information. ...
Probe electrospray ionization mass spectrometry (PESI-MS) has been demonstrated as a useful in situ and online analysis tool for monitoring of various reactions. In this work, PESI-MS with a surface-modified probe was adopted and applied to in situ monitoring of photocatalytic reactions. Typical reactions of semiconductor photocatalysts, namely TiO2, SnO2, WO3, SiC and ZnS, catalyzed methylene blue (MB) and brilliant green (BG) degradation were selected to demonstrate the potential of PESI-MS to heterogeneous photocatalytic reactions occurring in suspensions. Surface modification of the probe ensures increased wettability during the whole monitoring process. PESI-MS could provide continuous sampling and real-time MS results without time-consuming and cumbersome sample pretreatments. This method has other merits including good reproducibility and stability (time scale > 60 min), convenience for operation, low sample consumption, high time resolution and high tolerance to suspended photocatalyst particles. Time-resolved mass spectra and ion chromatograms of every chemical species e.g. the substrate and reactive intermediates could be obtained, which is helpful for a better understanding of the photocatalytic reaction process. Thus, PESI-MS could be a versatile analytical tool for in situ photocatalytic reaction analysis and could be an alternative means for the evaluation of photocatalyst performance.
Global climate change is the most important challenge humankind is facing in the modern era. One of the main scientific concerns is the monitoring of contaminants in the environment, which require the right environmental remediation strategies. In this context, nuclear magnetic resonance (NMR) techniques have a very important role in enabling the discovery of how pollutants are transformed, how they can move and how they can affect human health.
This book discusses the present and the future perspectives of NMR techniques for environmental evaluations. It covers, amongst other topics, the importance of NMR as a contamination discovery tool, how to improve sensitivity in environmental NMR, and multiphase NMR for measurement of samples in their natural state. Samples include lubricant oils, soils and porous media. Due to the direct relationship between the environment and human health, there is information dedicated to the use of magnetic resonance imaging (MRI) to monitor human health as related to environmental pollution. There is also a chapter on how NMR is used in cultural heritage to measure artefacts directly affected by environmental pollution.
Filling a gap in the literature, the book is for researchers explaining how to apply their knowledge of NMR techniques to solve environmental problems, and for students who want to deepen their understanding of this topic.
A series of titanium dioxide-nitrogen doped graphene quantum dot (TiO2-NGQD) composite photocatalysts were synthesized through a simple hydrothermal reaction with varied NGQD content. Through a proposed Z-Scheme heterojunction, the composites were able to achieve increased photocurrent generation and photocatalytic degradation of phenol under both full spectrum and visible only illumination. The prepared composites were able to switch from anodic to cathodic photocurrent by changing the light source from full spectrum to visible wavelengths. The photocatalytic capabilities of the composites were tested by degrading phenol and this was monitored via nuclear magnetic resonance. All composites outperformed the commercial standard P25 TiO2 under both full spectrum and visible irradiation, with the 8 wt% NGQD composite showing a visible improvement of over 600% compared to P25. With the ability to manipulate the generation of majority charge carriers, TiO2-NGQDs have significant potential not only in photocatalysis, but in far reaching applications such as energy harvesting and water splitting.
Comprehensive Multiphase NMR (CMP-NMR) is a recently developed technique capable of simultaneously observing different phases - solutions, gels, and solids - while providing the chemical specificity of traditional NMR. With this new tool, the heterogeneous photocatalysis of phenol by titanium dioxide (P25 TiO2) is re-examined to gain information about the occurrence of reaction at different regions between the catalyst and the solution. It was found that the proportion of phenol in different phases changes over the course of the photodegradation period. The photocatalyst appears to preferentially degrade phenol molecules that are weakly associated with the surface, such that they have restricted mobility in a 'gel-like' state. Diffusion Ordered Spectroscopy (DOSY) corroborates the relative change in phenol signals between freely diffusing solution and diffusion restricted gels as measured using CMP-NMR. The surface of P25 TiO2 was found to foul over the course of the 200-hour photodegradation period that was monitored using the solid-state capabilities of the CMP-NMR. Finally, CMP-NMR showed differences in the photodegradation of phenol by P25 TiO2 to that of a TiO2-nitrogen doped graphene quantum dot (NGQD) composite. With the latter composite, no fouling of the surface was seen over time. This application of CMP-NMR to the field of catalysis demonstrates its potential to better understand and study photocatalytic systems in general.
