Diffuse Reflectance Infrared Fourier Transform Research Articles

Construction of biochar assisted S-scheme of CeO2/g-C3N4 with enhanced photoreduction CO2 to CO activity and selectivity

The multi-interface contacted S-scheme photocatalyst was used for CO2 reduction in this research. A hybrid nanostructures catalyst was constructed using g-C3N4 nanosheet, oxidized CeO2 nanoparticles, and biochar (BIO, cattail-derived). The g-C3N4-BIO/CeO2 catalyst exhibited high selectivity (> 95 %) in converting CO2 to CO in a gas-solid-liquid phase CO2 reduction system. Theoretical and experimental evidence suggests that the multi-interface and interfacial internal electric field (IEF) play a crucial role in enhancing electron transfer and redox ability in CO2 reduction processes. Ce4+ species in CeO2 have the capability to donate two electrons, facilitating the two-electron reduction process involved in the transformation of CO2 to CO. Additionally, Ce4+ in CeO2 acted as an electron trapping agent and could be reduced to Ce3+ ion after trapping electrons, which facilitated the separation process of photogenerated carriers inside CeO2. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) demonstrated that COOH* intermediate played a key role as the rate determining step in the overall CO2 photoreduction to CO. This investigation will contribute to the development and application of new and environmentally friendly BIO-based S-scheme photocatalysts.

Combining ACE, PLS-R, and SVM-R for rapid detection of adulteration in saffron samples by diffuse reflectance infrared fourier transform spectroscopy

Accurate estimation of saffron purity is essential for ensuring product integrity, particularly in the presence of common chemical adulterants such as tartrazine, sunset yellow, and quinoline yellow. This study introduces the alternating conditional expectations (ACE) algorithm, coupled with diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), as an innovative chemometric approach to address this challenge. The ACE algorithm utilizes optimal transformations for both independent and dependent variables, revealing non-linear relationships and maximizing linear effects between transformed variables. To prepare the spectral data for ACE modeling, we will perform moving average smoothing and Standard Normal Variate (SNV) transformation for preprocessing. Subsequently, we will employ the duplex algorithm to select both calibration and prediction sets from the preprocessed data matrix. The effectiveness of the ACE model was evaluated using several metrics, including the coefficient of determination (R2), adjusted R-squared (R2adj), sum of squared errors (SSE), Regression Sum of Squares (SSR) and mean squared error (MSE). ACE model exhibited excellent performance in determining saffron content even in the presence of adulterants like tartrazine, sunset yellow, and quinoline yellow, on both calibration and prediction sets. Our model achieved excellent performance on both datasets. On the calibration set, a high R2 value (0.9951) indicates a strong correlation between predicted and observed saffron content in the model. The R2adj (0.9950) further strengthens this conclusion by accounting for model complexity, suggesting the model avoids overfitting. These findings are complemented by robustness measures. The statistical parameters of the ACE model, such as total sum of squares (SST) (1.103∗104), SSR (1.098∗104), SSE (54.414), and MSE (0.878), were calculated to compare the performance of the developed methods for determining Saffron's concentration in each mixed sample.

Controlling charge migration and CO2 conversion through surface decoration of 2D-hydrotalcite on bismuth oxybromide for enhanced artificial photosynthesis

Photocatalytic reduction of CO2 in pure H2O media to produce chemicals presents an appealing avenue for simultaneously alleviating energy and environmental crises. However, the rapid recombination of photogenerated charge carriers presents a significant challenge in this promising field. Heterojunction engineering has emerged as an effective approach to address this dilemma. Here, by decorating 2D NiAl-layered double hydroxides (NAL) onto bismuth oxybromide (BOB), we have created a S-scheme heterojunction (N1B1 composite). This catalyst affords CO2-to-CO yields of 102.30 μmol g−1 with a selectivity of 100 %. Ultraviolet photoelectron spectroscopy (UPS) and in-situ irradiated X-ray photoelectron spectroscopy (ISI-XPS) reveal that charge transfer occurs efficiently from BOB to 2D-NAL upon light irradiation. The designed N1B1 heterojunction achieves 7.3-fold and 2.1-fold increase in the internal electric field strength compared to bare 2D-NAL and BOB, respectively, which should be accountable for the improved charge migration. Additionally, pulsed chemisorption and in-situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) show the presence of multiple carbonate intermediates with activated OCO bonds upon N1B1 composite, with *CO2− being identified as the most crucial species for CO production.

Adsorption of CO2/CH4 on the aromatic rings and oxygen groups of coal based on in-situ diffuse reflectance FTIR

The adsorption mechanisms of CH4 and CO2 on the coal surface is the theoretical basis for CO2 sequestration with enhanced coalbed methane recovery (CO2-ECBM). Molecular simulation is the main method to study the adsorption mechanism at present, but the model used in the process of molecular simulation could not accurately characterize the coal macromolecular structure. Therefore, we used in-situ diffuse reflectance Fourier-transform infrared spectroscopy (FTIR) to study the adsorption of CO2/CH4 on the aromatic rings and oxygen groups of coal. The results showed that CO2 and CH4 were physisorbed on the aromatic rings, and the aromatic rings represented the primary competitive adsorption sites for CO2 and CH4, CO2 was preferentially adsorbed at the top of the aromatic ring compared to CH4. Both carboxyl and carbonyl groups were beneficial for CO2 adsorption but not for CH4 adsorption. Compared to aromatic rings, the adsorption affinity of carboxyl groups for CO2 were stronger. The results of this study revealed the adsorption mechanisms of CO2 and CH4 on the aromatic rings and oxygen groups, as well as the impact of oxygen groups on the gas adsorption capacity, providing a theoretical basis for applying CO2-ECBM in the medium-volatile bituminous coal reservoirs.

Photocatalytic CO2 reduction and destruction of rhodamine B on Bi0/BiOCl with tunable oxygen vacancies induced by 60 CO γ-rays irradiation

In this work, Bi0/OVs-BiOCl photocatalysts were in-situ constructed by irradiating BiOCl with 60Co γ-rays. The powerful penetrating ability of γ-rays induce the Bi-O bonds in BiOCl to break, thereby leading to the deoxygenation (OVs) and the formation of metal Bi0. The presence of Bi0 and OVs endows the photocatalysts with enhanced separation of photogenerated charges and enriched active sites. Under the excitation of simulated sunlight, the BOC-5 sample with an irradiation dosage of 5 KGy demonstrates the best photocatalytic performance, and the yield of CO on the sample is 2.19 μmol·g−1·h−1, which is 2.27 times higher than that on the reference sample. In-situ diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) reveals the formation of intermediates during the conversion of CO2 to CO. Under irradiation of a 300 W xenon lamp, the degradation rate of rhodamine B (RhB) on the BOC-5 sample is 0.05843 min−1, which is 3.42 times of that on the reference sample (0.01708 min−1). The main active species in the degradation process were explored using electron paramagnetic resonance (EPR) and free radical capture experiments at room temperature. This study provides a novel strategy for the preparation of BiOCl-based photocatalysts with high photocatalytic activity through 60Co γ-rays irradiation.

Strong water-resistant Co-Mn solid solution derived from bimetallic metal–organic frameworks for catalytic destruction of toluene

The construction of Co-Mn mixed metal oxides catalysts derived from bimetallic MOFs has great significance for catalytic destruction of toluene. Hence, a series of CoaMnbOx-MOFs with different physicochemical properties were successfully synthesized via pyrolysis of Co-Mn bimetallic MOFs. Attributing to the higher specific surface area, more active sites (Co3+ and Mn3+), stronger reducibility and abundant defect sites, the as-prepared Co1Mn1Ox-MOFs dispalyed an optimal catalytic performance, especially the excellent water vapor resistance. The result of the In Situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy demonstrated that toluene can be degraded at relatively low temperatures (＜100 °C). Benzyl alcohol, benzaldehyde, benzoic acid and maleic anhydride were the main intermediate products in toluene degradation process. This work reveals the value of bimetallic MOFs derived Co-Mn oxides for toluene oxidation and presents a novel avenue for designing mixed metal oxide catalysts with potential applications in VOCs catalytic oxidation.

Ligand-Coordinated Pt Single-Atom catalyst facilitates Support-Assisted Water-Gas shift reaction

The water–gas shift (WGS) reaction (CO+H2O→CO2+H2,ΔH=-41.1kJ/mol) is an essential process in the production of hydrogen and has grown significantly in usage over time. In this study, we further explore a novel strategy that can create single-atom catalysts (SACs) from metal-ligand single-sites on high surface area oxide supports for catalyzing the WGS reaction. The metal–ligand approach results in high metal loading, exhibits an ultimate dispersion of metal species and maximizes atom efficiency. 1,10-phenanthroline-5,6-dione (PDO) was chosen as the ligand for its oxidative potential for stabilizing Pt metal cations via two different binding pockets. The single-atom nature of the Pt-ligand is characterized with extended X-ray absorption fine structure (EXAFS), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and transmission electron microscopy (TEM) techniques. The catalytic activity is evaluated for the WGS reaction, revealing that Pt-ligand SACs supported on defective TiO2 show higher inherent catalytic activity than Pt NPs and a significantly lower activation energy. This characteristic is generally desirable for the redox mechanism. Density functional theory (DFT) calculations reveal that metal–ligand SACs allow CO interaction with oxygen atoms from the TiO2 surface. The redox mechanism of the WGS reaction demonstrates a lower effective activation barrier than the associative mechanism for Pt-ligand SAC. Moreover, the metal–ligand strategy, according to DFT results, facilitates the reaction redox mechanism by reducing the CO binding energy and promoting CO2 and H2 formation process.

Ethanol synthesis via catalytic CO2 hydrogenation over multi-elemental KFeCuZn/ZrO2 catalyst.

Technological enablers that use CO2 as a feedstock to create value-added chemicals, including ethanol, have gained widespread appeal. They offer a potential solution to climate change and promote the development of a circular economy. However, the conversion of CO2 to ethanol poses significant challenges, not only because CO2 is a thermodynamically stable and chemically inert molecule but also because of the complexity of the reaction routes and uncontrollability of C-C coupling. In this study, we developed an efficient catalyst, K-Fe-Cu-Zn/ZrO2 (KFeCuZn/ZrO2), which enhances the EtOH space time yield (STYEtOH) to 5.4 mmol gcat -1 h-1, under optimized conditions (360 °C, 4 MPa, and 12 L gcat -1 h-1). Furthermore, we investigated the roles of each constituent element using in situ/operando spectroscopy such as X-ray absorption spectroscopy (XAS) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). These results demonstrate that all components are necessary for efficient ethanol synthesis.

Photocatalytic degradation of low-concentration gaseous benzene in air via bifunctional tin-doped titanium dioxide catalyst

Benzene, a common volatile organic compound (VOC) detected in indoor environments, poses challenges for its removal because of its stable molecular structure and low-concentration. In this study, we successfully synthesized tin-doped titanium dioxide (Sn-TiO2) using a simple hydrothermal method. Various characterization techniques including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunner–Emmet–Teller (BET) and molecular probes were employed to analyze the phase composition, structure and morphology, as well as photocatalytic properties of TiO2 and Sn-TiO2. The characterization results showed that moderate addition of tin doping not only effectively enhanced the capture ability of benzene molecules but also promoted hydroxyl radicals (·OH) generation, which was further validated by in-situ diffuse reflectance infrared Fourier transform (DRIFT) spectra and density function theory (DFT) calculations. Degradation experiments on gaseous benzene revealed that under 15 W ultraviolet (UV) light irradiation in humid and closed conditions for 60 min, 1 % Sn-TiO2 achieved a benzene degradation efficiency of 93.14 %, with almost complete mineralization. Furthermore, flow system experiments demonstrated efficient decomposition of trace amounts of benzene (∼10 mg/m3) in the air to satisfy emission standards when employing 1 % Sn-TiO2 at a flow rate of 100 L/min.

Photocatalytic CO2‐to‐CH4 Conversion with Ultrahigh Selectivity of 95.93% on S‐Vacancy Modulated Spatial In2S3/In2O3 Heterojunction

AbstractPhotocatalytic conversion of CO2 to methane faces challenges due to the stability of CO2, unpredictable intermediates, and complex electron transfer steps. Herein, a spatial In2S3/In2O3 heterojunction with abundant S vacancies (ISIO(VS)) is obtained through facile Polyvinylpyrrolidone (PVP) treatment to reach a methane yield of 16.52 µmol·g−1·h−1 with a selectivity of 95.93%, which is the highest among reported In2S3 and In2O3 based catalysts. The work function (Wf), differential charge density, and Kelvin Probe Force Microscopy (KPFM) results confirm that S vacancies strengthen the built‐in electric field (BEF) of In2S3/In2O3 (ISIO) heterojunctions, improving carrier separation. Density functional theory (DFT) calculations reveal that S vacancies induce electron redistribution, facilitating adsorption and activation of CO2 and *CO intermediate, thus promoting hydrogenation to yield *CHO. The reaction pathway of photocatalytic CO2 reduction is revealed by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and Gibbs free energy (ΔG). The S vacancies modify electronic orbitals and the highest occupied molecular orbital (HOMO) of In atom, resulting in a stronger interaction between the catalyst and *CHO, which reduces ΔG*CHO and regulates the selectivity of CH4. This study paves a new avenue for the design of photocatalysts with highly selective reduction of CO2 to CH4 through defect engineering.

Design Strategies for High-Performance NH3-SCO Catalysts: Identifying and Modulating Direct Anchoring Sites for Ag on TiO2.

Ammonia (NH3) slip from diesel vehicle aftertreatment systems and internal combustion engines fueled by NH3 or NH3/H2 poses serious environmental problems. Ag-based catalysts are widely used for the selective catalytic oxidation of NH3 to N2 (NH3-SCO), and their performance is greatly dependent on the state of Ag, which is influenced by the anchoring sites on the support. Despite efforts to identify the direct anchoring sites of metal atoms on TiO2, conflicting views persist. Here, we compared the correlation between Ag dispersion and the content of hydroxyl (OH) groups or defects on TiO2 and conducted density functional theory (DFT) calculations, and the results confirmed that the surface OH groups of TiO2 serve as the direct anchoring sites for Ag. By modulating the OH group content through thermal induction, the optimal OH group content on TiO2-800 resulted in more metallic Ag nanoparticles (Ag0 NPs) in larger sizes, leading to the development of an excellent NH3-SCO catalyst. Moreover, in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), kinetic studies, and DFT calculations suggested that more Ag0 NPs in larger sizes on 10Ag/TiO2-800 were conducive to O2 activation and NH3 dissociation. Our findings provide new insights for designing efficient NH3-SCO catalysts, and OH groups as direct anchoring sites could be extended to other metals and supports for the rational design of catalysts.

Electrons redistribution of palladium-copper nanoclusters boosting the direct oxidation of methane to methanol

The direct oxidation of methane to methanol (DOMM) at mild conditions is an enormous attractive yet highly challenging, which is known as the “Holy Grail” reaction. In this work, we prepare the PdxCuy NCs supported on mesoporous sulfur-carbon materials and investigate their catalytic DOMM performance. The Pd14Cu1 NCs exhibits the excellent DOMM performance with the productivity of 34.3 mmol g−1 h−1 and the selectivity of 92.3 % at 150 °C when H2/O2 as active oxygen species, which was obviously superior to other PdCu catalysts. The enhanced performance of Pd14Cu1 NCs in DOMM is attributed to the non-crystalline atomic arrangement of tiny cluster structures and the synergistic electronic effect between Pd and Cu atoms, which can reduce the desorption temperature for methane, improve the in-situ generation of H2O2, and provide more active oxygen. The time-resolved in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) demonstrated that a radical-involved reaction pathway on Pd14Cu1 NC. This work provides the understanding for synergistic effect dual metallic and helps to design highly efficient and selective catalysts for the direct oxidation of CH4.

Synthesis of Co/Ni-Doped mesoporous spinel ferrite microspheres for enhanced Low-Temperature SCR performance

The iron-based catalysts commonly used in the selective catalytic reduction (SCR) process cannot meet the increasingly stringent low-temperature NOx emission targets. In this study, mesoporous microspherical MFe2O4 (M=Co, Ni) spinel ferrite catalysts were synthesized by hydrothermal method and applied to the SCR of ammonia (NH3-SCR) reaction. Compared to Fe3O4, both NiFe2O4 and CoFe2O4 catalysts showed higher SCR catalytic activity at low temperature. The NiFe2O4 catalyst achieved a NO conversion of 95.5 % at 240 °C, while CoFe2O4 exhibited a high NO conversion of 97.6 % at 180 °C and a N2 selectivity of 99.6 %. Various characterization experiments revealed that the introduction of Co and Ni resulted in the formation of a specific mesoporous microsphere morphology in CoFe2O4 and NiFe2O4 catalysts, along with the generation of a large number of oxygen vacancies and acidic sites on the surface. These features facilitate the sequential adsorption and activation of NH3 and NOx species, resulting in excellent catalytic activity at low temperatures. Detailed in situ diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) measurements showed that on NiFe2O4 the reaction follows the Eley–Rideal (E–R) mechanism, whereas it proceeds through the Langmuir–Hinshelwood (L–H) and Eley–Rideal (E–R) mechanisms on the CoFe2O4 catalyst. This work provides a feasible strategy for enhancing the low-temperature SCR reaction over iron-based catalysts; moreover, the elucidation of the complete reaction mechanism offers a solid foundation for future improvements in denitrification catalysts.

0D/2D Schottky heterojunction of CsPbBr3 nanocrystals on MoN nanosheets for enhancing charge transfer and CO2 photoreduction

Solar-driven conversion of CO2 to value-added chemical fuels has been regarded as a promising strategy for solving the climate problem and energy crisis. To realize this goal, it is vital to design photocatalysts with abundant catalytic active sites and excellent charge separation efficiency. Here, perovskite nanocrystals (CsPbBr3) were anchored on two-dimensional molybdenum nitride (MoN) using an in-situ growth method, forming a new and effective 0D/2D CsPbBr3@MoN (CPB@MoN) nanoheterosturcture with close contact interface for CO2 photoreduction. The introduction of MoN, acting as a charge transfer channel, could quickly trap the photoinduced charge from CsPbBr3 and provide abundant catalytic sites for CO2 photocatalytic reactions. For optimized CsPbBr3@MoN composites, the CO yield was 13.86μmol/gh−1 without any sacrificial reagent, which was a 4.5-fold enhancement of the pure CsPbBr3. Further, in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) revealed the catalytic mechanism for the CO2 photoreduction process. This work provides a new platform for constructing superior perovskite/MoN-based photocatalysts for photocatalytic CO2 reduction.

Influence of Thermal Treatment on the Chemical and Structural Properties of Geopolymer Gels Doped with Nd2O3 and Sm2O3.

In this research, the influence of the thermal treatment of geopolymer gels at 300 °C, 600 °C and 900 °C when incorporated with 5% rare earth elements (REEs) in the form of (GP-Sm) Sm2O3 and (GP-Nd) Nd2O3 was investigated. Changes in the chemical and structural properties of the geopolymer gels during thermal treatment for 1 h were monitored. Physico-chemical characterization was performed using the following methods: diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), scanning electron microscopy with energy dispersive spectrometry (SEM-EDS), and X-ray photoelectron spectroscopy (XPS). Besides the characterization of the fundamental properties, some practical macroscopic properties were analyzed as well: sorptivity, open porosity, and Archimedean density. The stretching vibrations of Nd-O-Si and Sm-O-Si were confirmed at a value of around 680 cm-1and an Nd-O-Si absorption band at a higher value, together with the most dominant band of Si-O stretching vibration similar for all the samples. No significant chemical changes occurred. Structural analysis showed that for GP-Nd, the largest pore diameter was obtained at 900 °C, while for GP-Sm, the largest pore diameter was obtained at 600 °C. EDS confirmed the amount of dopant to be about 5%. X-ray photoelectron spectroscopy showed that for GP-Nd, the ratio of Si and Al changed the most, while for GP-Sm, the ratio of Si and Al decreased with increasing temperature. The contributions of both dopants in the GP-gel structure remained almost unchanged and stable at high temperatures. The atomic percentages obtained by XPS analysis were in accordance with the expected trend; the amount of Si increased with the temperature, while the amount of Al decreased with increasing temperature. The sorptivity and open porosity showed the highest values at 600 °C, while the density of both geopolymers decreased linearly with increasing temperature.

Dehydration of Tetrahydrofurfuryl Alcohol Into Dihydropyran on γ-Al2O3 Catalyst: Reaction Monitoring by In Situ DRIFT Spectroscopy

AbstractIn this study, in situ diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy was used to analyze the surface reactivity during the dehydration of tetrahydrofurfuryl alcohol (THFA) to 3,4-dihydro-2H-pyran (DHP). The dehydration reaction of THFA is carried out in the gas phase at 648 K using activated γ-Al2O3 as catalyst. Under these conditions, a yield of 84% DHP is obtained in a fixed-bed reactor and the catalyst shows no signs of deactivation after 70 h. The information obtained with DRIFT in situ spectroscopy depends on the reaction conditions, with the concentration of THFA in the gas phase being a critical variable. The temperature and time on stream have also been studied. This technique has allowed to identify DHP, the product of interest, two products with carbonyl group (C = O) formed in the surface of the catalyst during the reaction, and also the formation of carboxylates from the reaction of surface species with the oxygens of the oxide catalyst. This is of considerable significance, as an understanding of the molecular processes occurring at the surface during the reaction would permit the rational design of catalysts to enhance their catalytic properties. Therefore, in situ DRIFT spectroscopy is a valuable tool for studying active catalysts in the THFA dehydration reaction.

Bi4O5Br2 co-modified with oxygen vacancy and Bi metal for efficient photothermal conversion of CO2 to C2 hydrocarbons

Photothermal catalytic reduction of CO2 into high value-added C2 hydrocarbon products is a promising method for efficient CO2 conversion. However, current photocatalysts still encounter obstacles including limited photoabsorption range, rapid recombination of photogenerated carriers, and inadequate surface active sites. Herein, Bi4O5Br2 co-modified with oxygen vacancy (OV) and metal bismuth (Bi) (Bi4O5Br2-OV@Bi) has been prepared to optimize these crucial issues. Bi4O5Br2-OV@Bi delivers a remarkably improvement in CO2 photothermal conversion, reflecting by the notable increase in C1 (CO and CH4) and newly generated C2 (C2H4 and C2H6) products compared to pristine Bi4O5Br2. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) spectrometry reveals that OC−COH* intermediate promotes the C–C coupling for produce C2 hydrocarbons. This study strengthens the understanding of metal modification and defect engineering for forming C2 hydrocarbons on bismuth-based photocatalysts.

Photocatalytic activity of Ho3+-Yb3+ activated BiVO4 upconverting phosphors

The BiVO4:Ho3+-Yb3+ upconverting phosphors have been synthesized by using the chemical co-precipitation method and optimized with 0.7 % Ho3+ + 6 % Yb3+ combination through frequency upconversion emission study. The synthesized phosphors have been characterized through XRD (X-Ray diffraction), FESEM (Field emission scanning electron microscopy), HR-TEM (High resolution- Transmission electron microscopy), UV–vis diffuse reflectance spectroscopy (DRS), Raman, and FT-IR (Fourier transform infrared spectroscopy). The XPS (X-ray photoelectron spectroscopy) analysis has been performed to study the elemental composition, chemical, and electronic states of the atoms present in the optimized sample. The specific surface area of the pure and optimized phosphors has been determined through BET (Brunauer-Emmett-Teller) analysis. From the XRD analysis, it is clear that on doping, the crystal structure of BiVO4 changes from monoclinic to tetragonal structure. The values of rate constants for the photocatalytic performance of the upconverting codoped and pure BiVO4 phosphors under the illumination with an artificial solar lamp for degradation of MB dye are found to be 0.00498 min−1 and 0.00269 min−1, respectively. To verify these results, the same experiment has also been performed under the visible LED (Light-emitting diode) light illumination. This enhancement of ∼ 85 % in the rate constant of the photocatalytic performance ensured the utilization of the NIR portion of the light by the codoped BiVO4 phosphors through the frequency upconversion process. The material’s recycling photocatalysis experiment for three cycles has been performed to check its reusability. The upconversion emission and XRD analysis of the materials after photocatalysis have been performed. From this study, it is confirmed that the stability of the sample is better even after three cycles of photocatalytic dye degradation experiment.

Electroadsorption of La3+ and Ce3+ from aqueous media with a carbon paste electrode modified with HMS-CMPO

This work deals with the electroadsorption of rare earths cerium and lanthanum in aqueous solution by using a carbon paste electrode modified with a silica mesoporous material functionalized with carbamoyl methyl phosphine oxide (CMPO). This functionalization was carried out in a two-step synthesis, the intermediate product was synthesized by attaching N-(2-aminoethyl)-3-aminopropyltrimethoxysilane (APTMS) to the surface of the HMS by a grafting method synthesis, then this intermediate was modified by CMPO, in a further condensation reaction. The final product CMPO obtained was characterized by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), thermal gravimetric analysis (TGA) and N2 adsorption/desorption isotherms using BJH and BET models. Showing thermal stability, a surface area higher than 450m2g-1 and mesoporous properties. The CMPO material was used to modify the mixture of the carbon paste electrode producing an enhancement in the interaction between the electrode surface and the lanthanides studied, at the same time it produces and improvement in the electroactive area by over two orders of magnitude. The modified carbon paste electrode (CMPO-CPE) developed in this work shows an increase in the conductivity, observed with the electrochemical impedance spectroscopy studies, and an increase in the electroactive area of 47 % was calculated from cyclic voltammetry experiments. CMPO-CPE was used to extract La3+ and Ce3+ from aqueous solution using NaNO3 as support electrolyte, by using a fixed potential program over time, measuring the obtained current by Chronoamperometric method. The adsorption and desorption results were corroborated with Inductively coupled plasma atomic emission spectroscopy (ICP-OES) demonstrated the capacity of extraction of the electrode were 74 μg after ten cycles for La3+ at pH 5.0 and 15 μg after ten cycles for Ce3+ at pH 6.0, using a CMPO modified electrode of small surface (3 mm radius). This electrode was tested for over 50 cycles without losing their electroactive properties under tested electrochemical conditions.

Analysis of silicon surfaces etched in aqueous HF-(HBr)–Br2-mixtures

Solutions containing hydrofluoric acid (HF), hydrobromic acid (HBr) and bromine (Br2) were investigated as novel acidic, NOx-free mixtures for wet-chemical etching of silicon wafers. HF–Br2-mixtures exhibit isotropic etching behaviour towards silicon, etch rates up to 4.0 ​μm ​min−1 were observed at room temperature, which are higher than the etch rates of commercially used alkaline solutions. HF–HBr–Br2-mixtures show anisotropic etching behaviour, texturing the surface of monocrystalline silicon wafers with random upright or random inverted pyramidal structures. Etch rates up to 2.4 ​μm ​min−1 were observed, the etch rate increases linearly with the concentration of Br2 in the etching solution. Silicon surfaces were investigated by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The light trapping efficiency of wafers etched by HF–HBr–Br2 solutions was compared to commercially available textured wafers by UV/Vis-reflectivity measurements indicating lower reflectivities for the HF–HBr–Br2-treated samples. A reaction scheme for the anisotropic dissolution of silicon in bromine-containing aqueous HF-solutions is proposed, which involves bromine as oxidizing agent.