Diffuse Reflectance Infrared Spectroscopy Research Articles

H2 generation from aqueous ethanol over ZnO nanowires, the photo-transformation of surface species

ZnO nanowires (NWs) with wurzite structure and a very high [0001] preferred orientation were grown on a ZnO thin film, from a gas-solid process, in the absence of catalyst. ZnO NWs were characterized by FESEM, XRD, HRTEM, XPS, PL and Raman spectroscopy and used as photocatalysts for the photo-transformation of ethanol(aq) in the gas phase. The existence of different defects such as oxygen vacancies was evidenced. The photocatalytic process was followed by in-situ diffuse reflectance infrared spectroscopy (DRIFTS) coupled to on-line mass spectrometry (MS) analysis. The surface species determined during the irradiation (λ = 365 nm) of ZnO NWs under ethanol/water vapor flow at room temperature are related with the hydrogen production and carbon-containing products evolved.

Significant Roles of Surface Hydrides in Enhancing the Performance of Cu/BaTiO2.8H0.2 Catalyst for CO2 Hydrogenation to Methanol

AbstractTuning the anionic site of catalyst supports can impact reaction pathways by creating active sites on the support or influencing metal‐support interactions when using supported metal nanoparticles. This study focuses on CO2 hydrogenation over supported Cu nanoparticles, revealing a 3‐fold increase in methanol yield when replacing oxygen anions with hydrides in the perovskite support (Cu/BaTiO2.8H0.2 yields ~146 mg/h/gCu vs. Cu/BaTiO3 yields ~50 mg/h/gCu). The contrast suggests that significant roles are played by the support hydrides in the reaction. Temperature programmed reaction and isotopic labelling studies indicate that BaTiO2.8H0.2 surface hydride species follow a Mars van Krevelen mechanism in CO2 hydrogenation, promoting methanol production. High‐pressure steady‐state isotopic transient kinetic analysis (SSITKA) studies suggest that Cu/BaTiO2.8H0.2 possesses both a higher density and more active and selective sites for methanol production compared to Cu/BaTiO3. An operando high‐pressure diffuse reflectance infrared spectroscopy (DRIFTS)‐SSITKA study shows that formate species are the major surface intermediates over both catalysts, and the subsequent hydrogenation steps of formate are likely rate‐limiting. However, the catalytic reactivity of Cu/BaTiO2.8H0.2 towards the formate species is much higher than Cu/BaTiO3, likely due to the altered electronic structure of interface Cu sites by the hydrides in the support as validated by density functional theory (DFT) calculations.

Significant Roles of Surface Hydrides in Enhancing the Performance of Cu/BaTiO2.8 H0.2 Catalyst for CO2 Hydrogenation to Methanol.

Tuning the anionic site of catalyst supports can impact reaction pathways by creating active sites on the support or influencing metal-support interactions when using supported metal nanoparticles. This study focuses on CO2 hydrogenation over supported Cu nanoparticles, revealing a 3-fold increase in methanol yield when replacing oxygen anions with hydrides in the perovskite support (Cu/BaTiO2.8 H0.2 yields ~146 mg/h/gCu vs. Cu/BaTiO3 yields ~50 mg/h/gCu). The contrast suggests that significant roles are played by the support hydrides in the reaction. Temperature programmed reaction and isotopic labelling studies indicate that BaTiO2.8 H0.2 surface hydride species follow a Mars van Krevelen mechanism in CO2 hydrogenation, promoting methanol production. High-pressure steady-state isotopic transient kinetic analysis (SSITKA) studies suggest that Cu/BaTiO2.8 H0.2 possesses both a higher density and more active and selective sites for methanol production compared to Cu/BaTiO3 . An operando high-pressure diffuse reflectance infrared spectroscopy (DRIFTS)-SSITKA study shows that formate species are the major surface intermediates over both catalysts, and the subsequent hydrogenation steps of formate are likely rate-limiting. However, the catalytic reactivity of Cu/BaTiO2.8 H0.2 towards the formate species is much higher than Cu/BaTiO3 , likely due to the altered electronic structure of interface Cu sites by the hydrides in the support as validated by density functional theory (DFT) calculations.

Facilitating methane conversion and hydrogen evolution on platinized gallium oxide photocatalyst through liquid-like water nanofilm formation

The dehydrogenative coupling of methane, an approach aimed at converting methane into valuable chemicals like ethane and hydrogen, can be facilitated under ambient thermal conditions using semiconductor photocatalysts. Herein, we present an efficient continuous-flow photocatalytic system for methane conversion by inducing the formation of physically adsorbed water nanofilms on the surface of a Pt-loaded Ga2O3 photocatalyst. The microscopic properties of the adsorbed water were examined by diffuse reflectance infrared (IR) spectroscopy and ab initio molecular dynamics (AIMD) calculations. In comparison to the photocatalytic non-oxidative coupling of methane operated in the absence of water vapor, the presence of the interfacial water resulted in a 90-fold and 500-fold enhancement in the production rate of hydrogen and ethane, respectively. The rate of ethane formation significantly increased with increasing water vapor pressure (PH2O) under a high methane pressure (PCH4) of 200 kPa. The selectivity for ethane reached 65 % based on carbon content at PH2O = 3 kPa and PCH4 = 200 kPa. Through diffuse reflectance IR spectroscopy, volumetric water vapor adsorption analysis, and AIMD calculations conducted under the reaction conditions, we observed the formation of a liquid-like water nanolayer on the Ga2O3 surface at 300 K. Thus, this strategy of inducing water nanofilms affords a highly efficient photocatalytic system for hydrogen and ethane production.

Prediction of the distribution of soil properties in deep Colluvisols in different pedogeographic regions (Czech Republic) using diffuse reflectance infrared spectroscopy

Colluvisols form a significant part of the erosion–deposition soil catena mainly in undulating, agriculturally managed landscapes. Due to their sedimentary origin, they are soils with highly variable properties. For such diverse and often extremely deep soils, it is essential to capture the vertical distribution of properties in as much detail as possible. This study demonstrates the potential of the diffuse reflectance infrared spectroscopy (DRIFT) to derive accurate information on the stratigraphy and selected soil properties (soil organic carbon and calcium carbonate contents and aluminium and iron concentrations) of deep colluvial profiles in three regions in the Czech Republic with different dominant soil types (Chernozem, Luvisol, and Cambisol). The normalization of the spectrum using the quartz spectral band was found to be suitable for assessing the carbonate content in Chernozems and Luvisols (coefficients of determination (R2) were 0.89 and 0.88, respectively). The amount of organic carbon can be predicted from such normalized spectra with less confidence (R2 = 0.64). Organic matter quality as an indicator of their stability and maturity was computed from aliphatic compounds spectral bands (2930 cm–1) and aromatics and CO groups band around 1640 cm–1. The highest values of this indicator were found in Colluvisols in the Chernozem region (> 6, while, e.g., in the Cambisol region it is < 1), especially in the layers corresponding to the oldest sediments or buried in-situ horizons. In the Cambisol region, the buried B horizon was identified based on normalized (i) clays and Fe oxides bands and (ii) wider band of OH groups, which in this case is related to the content of iron oxyhydroxides. The study proved that the applied set of spectral parameters is an effective tool for the description of diverse soil parameters and for identification of the boundaries of individual soil layers. It is equally suitable for carbonate-free soils as well as for soils with higher carbonate contents, which usually cause difficulties in the interpretation of soil organic matter spectral parameters. It provides a comprehensive view of the soil and its mineral and organic components and can provide information that is difficult to measure by other methods.

Development of Hungarian spectral library: Prediction of soil properties and applications

Updating soil information systems (SIS) requires advanced technologies to support the time and cost-effective and environment-friendly soil data. The use of mid- infrared (MIR) Spectroscopy as alternative to wet chemistry has been tested. The MIR spectral library is a useful technique for predicting soil attributes with high accuracy, efficiency, and low cost. The Hungarian MIR spectral library contained data on 2200 soil samples from 10 counties representing the first Soil Information and Mentoring System (SIMS) survey. Archived soil samples were prepared and scanned based on Diffuse Reflectance Infrared spectroscopy (DRIFT) technique and spectra data were saved in the fourier transform infrared (FTIR) spectrometer OPUS software. Preprocessed filtering methods, outlier detection methods and calibration sample selection methods were applied for spectral library. MIR calibration models were built for soil attributes using Partial Least Square Regression (PLSR) method. Coefficient determination (R2), The Root Mean Squared Error (RMSE) and Ratio of Performance to Deviation (RPD) were used to assess the goodness of calibration and validation models. MIR spectral library had the ability to significantly estimate soil properties such as SOC, CaCO3, sand, clay and silt through various scale models (national, county and soil type). The findings showed that our spectral library soil estimations are precise enough to provide information on national, county and soil type levels enabling a wide range of soil applications that demand huge amounts of data such as soil survey, precision agriculture and digital soil mapping.

Chemical looping reforming characteristics of methane and toluene from biomass pyrolysis volatiles based on decoupling strategy: Embedding NiFe2O4 in SBA-15 as an oxygen carrier

To realize the directional conversion of biomass to produce hydrogen-rich syngas, biomass gasification with a complex reaction system was decoupled into two sub-processes. NiFe2O4@SBA-15 was prepared by an embedding strategy via the impregnation method to achieve high reactivity during the volatile chemical looping reforming process. The chemical looping reforming of methane and toluene was investigated based on a fixed-bed reactor and on-line mass spectrometry and gas chromatography. It was found that the selectivity and conversion were improved after embedding, and the conversion of toluene reached 97.5 % at 750 °C. The NiFe2O4@SBA-15 maintained good stability after 15 cycles, and the reaction performance had not obviously decreased. Real-time reaction performance showed that the conversion of lattice oxygen could reach 100% above 750 °C. The reaction system belonged to the phase boundary-controlled mechanism based on the conversion of lattice oxygen, and the activation energy was 43.10 kJ·mol−1. In addition, in-situ diffuse reflectance infrared spectroscopy(DRIFTS) study had shown that the dissociation of methane and toluene and the further conversion of formate might be the reaction rate-limiting steps. Although methane and toluene competed in adsorption, the reaction processes were independent.

Establishing the Baltic origins of archaeological amber beads from Dura-Europos (Syria) using non-destructive DRIFTS

Sourcing archaeological amber has hitherto been limited by a reliance on chemical techniques that require some degree of destructive sampling. The majority of amber artifacts are friable, weakened after millennia spent unprotected from environmental stressors, and as such are especially vulnerable during analysis or even sampling. Here, we assess the capability of an entirely nondestructive analytical technique — Diffuse Reflectance Infrared Spectroscopy (DRIFTS) — to scientifically identify archaeological Baltic amber. Using a reference collection of geological amber specimens, our direct comparison of DRIFTS spectra to those collected via conventional transmission FTIR, which necessitates destructive sampling, demonstrates the validity of the new technique. Thirteen beads from the archaeological site of Dura-Europos in Syria were subsequently analyzed using DRIFTS alone. Five of the beads showed spectral features indicative of Baltic amber, whereas the others were too degraded to yield diagnostically measurable spectra. Our study thus confirms the capability of the DRIFTS technique to analyze whole, untreated amber artifacts when their integrity is of high concern. Furthermore, our results indicate a previously unestablished connection between Dura-Europos and northern Europe during the first two centuries CE through long-distance exchange networks stemming from the Mediterranean basin.

A potential application for life-related organics detection on Mars by diffuse reflectance infrared spectroscopy

Life information searching is a hot point for Mars exploration. Ancient Mars was very likely to reach a habitable environment, and there was a real possibility of arising life on Mars. However, the current Mars has a harsh environment. Under such conditions, life materials on Mars are supposed to have taken the form of relatively primitive microbial or organic residues, which might be preserved in some mineral matrices. Detection of these remnants is of great significance for understanding the origin and evolution of life on Mars. The best detection method is in-situ detection or sample return. Herein, diffuse reflectance infrared spectroscopy (DRIFTS) was used to detect characteristic spectra and the limit of detection (LOD) of potential representative organic compounds with associated minerals. In view of high oxidation due to the electrostatic discharge (ESD) during dust actives on Martian surface. The degradation of organic matter by ESD process was studied under simulated Mars conditions. Our results show that the spectral characteristics of organic matter are significantly different from that of associated minerals. The different organic samples have different mass loss and color change after ESD reaction. And the signal intensity of infrared diffuse reflection spectrum can also reflect the changes of organic molecules after ESD reaction. Our results indicated that the degradation products of organics rather than organic itself are most likely to be founded on current Martian surface.

Prediction of the soil organic carbon in the LUCAS soil database based on spectral clustering

The estimation of the level of the soil organic carbon (SOC) content plays an important role in assessing the soil health state. Visible and Near Infrared Diffuse Reflectance Spectroscopy (Vis-NIR DRS) is a fast and cheap tool for measuring the SOC. However, when this technology is applied on a larger area, the soil prediction accuracy decreases due to the heterogeneity of the samples. In this paper, we first investigate the global model performance in the LUCAS EU-wide topsoil database. Then, different clustering strategies were tested, including the k-means clustering based on the principal component analysis (PCA) and hierarchical clustering, combined with the partial least squares regression (PLSR) models, and a clustering based on a local PLSR approach. The best validation results were obtained for the local PLSR approach with R2 = 0.75, root mean squared error of prediction (RMSEP) = 13.38 g/kg and ratio of performance to interquartile range (RPIQ) = 2.846, but the algorithm running time was 30.05 s. Similar results were obtained for the k-means clustering method with R2 = 0.75, RMSEP = 14.61 g/kg and RPIQ = 2.844, at only 4.52 s. This study demonstrates that the PLSR approach based on k-means clustering is able to achieve similar prediction accuracy as the local PLSR approach, while significantly improving the algorithm speed. This provides the theoretical basis for adapting the spectral soil model to the needs of real-time SOC quantification.

In search of the bottlenecks of ammonia synthesis over Ru/Vulcan under ambient conditions.

Hydrogenation of the N-N bond under ambient conditions over 1 wt% Ru/Vulcan was monitored through operando Diffuse Reflectance Infrared Spectroscopy (DRIFTS) and DFT. IR signals centered at 3017 cm-1 and 1302 cm-1 were visible with attributes similar to the asymmetric stretching and bending vibrations of gas phase ammonia at 3381 cm-1 and 1650 cm-1. The intensities of the signals increased with consecutive H2 : Ar and N2 flow cycles at room temperature and atmospheric pressure due to accumulation of the formed NHX on the catalyst surface. DFT estimations revealed that a compound with a molecular stoichiometry of N-NH3 can give rise to an IR signal centered at 3051.9 cm-1. The results of this study, combined with the known vapor liquid phase behavior of ammonia, suggest that under subcritical conditions, the bottlenecks of ammonia synthesis are both N-N bond dissociation and ammonia desorption from the pores of the catalyst.

Pt-Modified Nano-Sized Mn2O3 Oxide Prepared from the Mn3O4 Phase with Tetragonal Symmetry for CO Oxidation

One of the current problems in the environmental catalysis is the design of an effective and less costly catalytic system for the oxidation of CO. The nano-sized α-Mn2O3 oxide has been prepared and modified with 0.5 wt.% Pt. The catalysts have been characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), temperature-programmed reduction (TPR) and diffuse-reflectance infrared spectroscopy (DRIFTS). Finely divided PtO and Pt(OH)2 are being formed on the Mn2O3 surface as a result of the strong interaction between platinum and the nano-oxide. Based on DRIFTS investigations and the model calculations, a Langmuir–Hinshelwood type of mechanism is supposed for CO oxidation on Pt/Mn2O3. The CO and oxygen are adsorbed on different types of sites. The Mars–van Krevelen mechanism is the most probable one over pure Mn2O3, thus suggesting that CO2 is adsorbed on the oxidized sites. The CO adsorption in the mixture CO + N2 or in the presence of oxygen (CO + N2 + O2) leads to a partial reduction in the Pt+ surface species and the formation of linear Pt1+−CO and Pt0−CO carbonyls. Both of them take part in the CO oxidation reaction.

(Invited) Selective CO2 Conversion in Protonic Ceramic Electrochemical Cells

Protonic ceramic electrochemical cells (PCECs) are solid-state electrochemical devices that employ proton-conducting oxides as electrolytes, which offer a promising approach for electrification of chemical manufacturing, including CO2 reduction to produce value-added chemicals. The primary advantage of PCECs is their intermediate operating temperatures (300-600 °C), which thermodynamically and kinetically favor the CO2 reduction chemistry at the negative electrode. Unfortunately, the conventional negative electrode of PCECs, such as BaZr0.8-xCexY0.2O3- \U0001d6ff-Ni or BaZr0.8-xCexY0.1Yb0.1O3- \U0001d6ff-Ni, cannot reduce CO2 to either CH4 or CO with a selectivity of >99%, leading to the production of a mixture of CO and CH4. In this talk, we will present the rationally designed negative electrodes for CO2 conversion PCECs. The PCECs equipped with the new negative electrodes selectively favor the CO2-to-CO conversion. A selectivity of ~100% toward CO has been demonstrated over a wide range of operating temperatures (400-600 °C) and applied potential/current density. The negative electrode demonstrated in this work fully suppresses the CH4 production. In situ diffuse reflectance infrared spectroscopy (DRIFTS) was performed to probe the CO2 reduction mechanisms over the negative electrodes. This work validates that PCECs equipped with the rationally designed negative electrode can selectively manufacture chemicals.

Enhancing the oxidation efficiency of elemental mercury in the presence of NO and SO2 by using Cu(II)O doped TiO2 photothermal catalysts: Kinetics and mechanisms

This study aimed to apply sol–gel synthesized Cu(II)O doped TiO2 to enhance the oxidation of gaseous elemental mercury (Hg0) in the flue gases containing NO and SO2 at the temperatures of 120-180℃ under the irradiation of near-ultraviolet (near-UV). The influences of SO2 and NO on the oxidation efficiency of Hg0 were investigated by in-situ diffuse reflection infrared spectroscopy (DRIFT) and density functional theory (DFT). Experimental results showed that an optimal 5 %Cu(II)O/TiO2 had the oxidation efficiencies of Hg0 from 40 to 100 % at 120-180℃. The oxidation efficiencies of Hg0 were 85 and 70 % at 120℃, and 40 and 5 % at 180 °C, in the presence of solely SO2 and NO, respectively. Surface characterization showed that Cu(II)O was evenly dispersed over the surface of TiO2 catalysts. NO could inhibit the oxidation of Hg0 since it consumed the chemisorbed oxygen (Oα) and compete with Hg0 at the surface active sites. In contrast, SO2 could promote the oxidation efficiency of Hg0 due to the formation of HgSO4 on the surface of Cu(II)O/TiO2 catalysts. In the exposure of NO/SO2, NO and SO2 can be adsorbed on the catalyst surface reacting with ̇OH. The photothermal oxidation reactivity of Hg0 was inhibited due to the competitive adsorption between NO/SO2 and Hg0. The Langmuir-Hinshelwood (L-H) kinetic model successfully simulated the oxidation rate of Hg0. Moreover, DFT was further applied to estimate the binding energies of different gas molecules confirming the competence for active sites on the surface of Cu(II)O/TiO2 between NO/SO2 and Hg0.

Nanosheet-state cobalt-manganese oxide with multifarious active regions derived from oxidation-etching of metal organic framework precursor for catalytic combustion of toluene

For the first time, a nanosheet-state CoMnx mixed oxide with multifarious active regions was synthesized by oxidation-etching assembly of metal organic framework (MOF) precursor and applied for catalytic combustion of toluene at low temperatures. The obtained optimum catalyst denoted as CoMn6 showed excellent performance, which achieved 90% conversion of 1,000 ppm toluene under a weight hourly space velocity (WHSV) of 60,000 mL/(g·h) at 219 °C. While, it also exhibited long-term stability with strong water resistance property. The characterizations of physicochemical properties indicated that the oxidation-etching assembly process built an abundant mesoporous structure in the CoMnx catalyst, which greatly increased the specific surface area (SSA). Especially, potassium permanganate as oxidant and manganese source led to uniform dispersion and assembling of cobalt atoms, which caused the generation of low-crystallinity CoMnx mixed oxide with abundant dislocations, vacancies, phase interfaces and amorphous structures, resulting in excellent low-temperature reducibility, outstanding lattice oxygen mobility and abundant active species such as Mn3+, Co3+ and adsorbed oxygen species. Density functional theory (DFT) calculations demonstrated that gaseous oxygen with the longer bond length (1.406 Å) and stronger adsorption energy (−4.443 eV) could be adsorbed and activated well on the MnCo2O4.5 (311) plane, which is beneficial for the toluene oxidation. In situ diffuse reflectance infrared spectroscopy (DRIFTS) technique was applied to track the intermediates of toluene combustion under different atmospheres, which further deduced the contributions of different active regions and oxidation mechanism over the CoMnx catalyst. The present facile strategy of oxidation-etching assembly of the MOF precursor for the creating of novel catalyst with high performance could be applied in a wide variety of materials besides VOC combustion catalysts.

Rationally designed negative electrode for selective CO2-to-CO conversion in protonic ceramic electrochemical cells

Protonic ceramic electrochemical cells (PCECs) are solid-state electrochemical devices that employ proton-conducting oxides as electrolytes, which offer a promising approach for electrification of chemical manufacturing, including CO2 reduction to produce value-added chemicals (e.g., CO). The primary advantage of PCECs is their intermediate operating temperatures (300–600 °C), which thermodynamically and kinetically favor the CO2 reduction chemistry at the negative electrode. However, the conventional negative electrodes of PCECs, such as BaZr0.8−xCexY0.2O3-δ-Ni or BaZr0.8−xCexY0.1Yb0.1O3-δ-Ni, cannot reduce CO2 to either CH4 or CO with a selectivity of >99 %, leading to the production of a CO and CH4 mixture. Herein, an oxide-supported in-situ exsolved Ni-Fe alloyed nanoparticle electrocatalyst, Sr2Fe1.4Mo0.5O6-δ-Ni0.175 (SFM-Ni0.175), is first employed as the negative electrode of PCECs. The PCECs equipped with this new negative electrode selectively favor the CO2-to-CO conversion. A selectivity of ~100 % toward CO has been demonstrated over a wide range of operating temperatures (400–600 °C) and applied potentials/current densities. The negative electrode demonstrated in this work fully suppresses the CH4 production. In situ diffuse reflectance infrared spectroscopy (DRIFTS) was performed to probe the CO2 reduction mechanisms over both SFM-Ni0.175 and the traditional negative electrode (BCZYYb7111 +Ni), which indicates SFM-Ni0.175 inhibits the formation of formate species, leading to selective production of CO. This work validates that PCECs equipped with the rationally designed negative electrode can selectively manufacture chemicals.

Chemical Composition, Optical Properties and Sources of PM2.5 From a Highly Urbanized Region in Northeastern Mexico

Here, we report the chemical composition and optical properties of the fine particles (PM2.5) and water-soluble organic carbon (WSOC) of these particles. Additionally, the potential sources of WSOC emission were determined through the study on fluorescence excitation–emission matrix spectra and parallel factor analysis (EEM-PARAFAC). Samples were collected in an urban site of the Monterrey Metropolitan Area in Mexico during summer and winter and characterized using attenuated total reflectance-Fourier-transform infrared spectroscopy (ATR-FTIR), ultraviolet-visible-near infrared-diffuse reflectance spectroscopy (UV–Vis-NIR-DRS), fluorescence spectroscopy, X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) techniques. The ATR-FTIR analyses allowed the identification of inorganic ions (e.g., CO32−, SO42−, and NO3−), organic functional groups [e.g., carbonyls (C=O), organic hydroxyl (C-OH), carboxylic acid (COOH)], and aromatic and unsaturated aliphatic hydrocarbons. The results obtained by XRD and XPS revealed the presence of organic and inorganic chemical species in PM2.5. The diffuse reflectance spectra of PM2.5 provided the absorption bands in the UV region for CaSO4, CaCO3, and aluminosilicates. The absorption coefficient at 365 nm (Abs365) and Ångström absorption exponent (AAE) values obtained for the aqueous extracts suggest that many of the water-soluble organic compounds corresponded to brown carbon (BrC) chromophores. The mass absorption efficiency values at 365 nm (MAE365) were higher in the winter than summer samples, suggesting the presence of more BrC compounds in the winter samples. The fluorescence indices combined with EEM-PARAFAC analysis showed that the WSOC fraction was mainly composed of humic-like substances (HULIS) which are both of terrestrial and microbial origin.

Surface-Terminated Hydroxyl Groups for Deciphering the Facet-Dependent Photocatalysis of Anatase TiO2.

Understanding the relation between a crystal facet and photocatalytic performance is of great importance for the development of effective catalysts. In this work, we focus on anatase TiO2 with controllable exposed facets toward photocatalytic hydrogen evolution by water splitting. By combining temperature-programmed desorption (TPD) and diffuse reflectance infrared spectroscopy (DRIFTS), we obtain that the adsorption of hydroxyl groups and the photo-driven breaking of hydroxyl groups depend strongly on the exposed facets. As a result, the higher catalytic hydrogen evolution activity of TiO2 enclosed with (101) facets than that of (001) facets should be ascribed to the more favorable depletion of hydroxyl groups. Moreover, graphene quantum dots (GQDs) with rich surface functional groups are deliberately deposited on the TiO2 surface. The determination of the states and dynamics of surface hydroxyl groups suggests that GQDs facilitate the reaction of hydroxyl groups on (001)TiO2, thus leading to the activity enhancement. By contrast, the already active (101)TiO2 become apparently less efficient after GQD deposition due to the restricted reaction of hydroxyl groups. Overall, our findings not only provide a unique guidance for understanding the crystal-plane-dependent photocatalysis but also present a powerful approach by which to tailor the photocatalytic performance.

Prediction of soil carbon and nitrogen contents using visible and near infrared diffuse reflectance spectroscopy in varying salt-affected soils in Sine Saloum (Senegal)

Soil organic carbon (C) and nitrogen (N) contents have an essential role in soil fertility, but they may be affected by salinity, which is especially responsible for land degradation in arid and semiarid regions. The objective of this work was to study the ability of visible and near infrared diffuse reflectance spectroscopy (VNIRS) to predict soil C and N contents and electrical conductivity (EC, a proxy for soil salinity) in variably salt-affected topsoils of the Sine Saloum region (Senegal). Different calibration procedures and spectral pretreatments were compared, and variable log-transformation usefulness was evaluated for prediction optimization.Predictions involved three calibration procedures: global partial least squares regression (PLSR), which used all calibration samples similarly; locally weighted (local) PLSR, with target samples predicted individually by giving higher weight to closest calibration spectra; and global PLSR per salinity class, after spectral discrimination of these classes. Predictions were performed with possible spectrum pretreatments (e.g., derivatization) and variable decimal log-transformation.The study was performed on 311topsoil samples (0–25 cm depth), either unsalted to slightly salty (Salt-, EC ≤ 2mScm−1; 262samples) or medium to highly salty (Salt+, EC > 2mScm−1; 49samples). Soil salinity was accurately discriminated using spectra: in validation, 100% and 95% of Salt- and Salt+ samples were correctly assigned on average, respectively. Best C and N content predictions were achieved after log-transformation using calibration by class (R2VAL = 0.87) and local calibration (R2VAL = 0.77), respectively; best EC prediction was achieved without log-transformation using global calibration (R2VAL = 0.90). This suggested C and N content predictions were affected by salinity; logC and logN distributions were almost symmetrical, hence log-transformation usefulness, while logEC distribution was very asymmetrical. No pretreatment yielded systematically good predictions; nevertheless, first-order derivative using 31-point gap often yielded good predictions, and second-order derivatives poor results.

An investigation on the promoting effect of Pr modification on SO2 resistance over MnOx catalysts for selective reduction of NO with NH3.

Pr-modified MnOx catalyst was synthesized through a facile co-precipitation process, and the results showed that MnPrOx catalyst exhibited much better selective catalytic reduction (SCR) activity and SO2 resistance performance than pristine MnOx catalyst. The addition of Pr in MnOx catalyst led to a complete NO conversion efficiency in 120-220°C. Moreover, Pr-modified MnOx catalyst exhibited a superior resistance to H2O and SO2 compared with MnOx catalyst. After exposing to SO2 and H2O for 4h, the NO conversion efficiency of MnPrOx catalyst could remain to 87.6%. The characterization techniques of XRD, BET, hydrogen-temperature programmed reduction (H2-TPR), ammonia-temperatureprogrammed desorption (NH3-TPD), XPS, TG and in situ diffuse reflectance infrared spectroscopy (DRIFTS) were adopted to further explore the promoting effect of Pr doping in MnOx catalyst on SO2 resistance performance. The results showed that MnPrOx catalyst had larger specific surface area, stronger reducibility, and more L acid sites compared with MnOx catalyst. The relative percentage of Mn4+/Mnn+ on the MnPrOx-S catalyst surface was also much higher than those of MnOx catalyst. Importantly, when SO2 exists in feed gas, PrOx species in MnPrOx catalyst would preferentially react with SO2, thus protecting the Mn active sites. In addition, the introduction of Pr might promote the reaction between SO2 and NH3 rather than between SO2 and Mn active sites, which was also conductive to protect the Mn active sites to a great extent. Since the presence of SO2 in feed gas had little effect on NH3 adsorption on the MnPrOx catalyst surface, and the inhibiting effect of SO2 on NO adsorption was alleviated, SCR reactions could still proceed in a near-normal way through the Eley-Rideal (E-R) mechanism on Pr-modified MnOx catalyst, while SCR reactions through the Langmuir-Hinshelwood (L-H) mechanism were suppressed slightly.