H2O Vapor Research Articles

Experimental Determination of the Temperature‐Dependent Broadening Effect of Water Vapour on the S‐Branch Raman Linewidths of Nitrogen

ABSTRACTThis work reports the S‐branch Raman linewidths of N2 broadened by H2O vapour at temperatures 870–1900 K determined using the picosecond time‐resolved pure rotational coherent anti‐Stokes Raman scattering (RCARS) approach. The coherent dephasing time constant of nitrogen in a binary mixture was determined from the time trace fitting of the RCARS signal. Raman linewidths of N2 for four different binary mixture compositions up to 20% H2O were obtained for each temperature and the N2‐H2O broadening coefficient was determined. The decay of nitrogen broadened by water vapour is faster than that of self‐broadened nitrogen for all temperatures leading to a higher Raman linewidth. Respectively, the S‐branch Raman linewidths of N2‐H2O deviate significantly in magnitude and slope from the Q‐branch Raman linewidth calculated by the modified energy gap (MEG) law. Therefore, taking into account the broadening effect of water molecules in nitrogen has the potential to significantly improve thermometry and species concentration determination. The determined S‐branch Raman linewidths and broadening coefficient will therefore find application in combustion and reactive flow diagnostics.

Dynamically Confined Active Silver Nanoclusters with Ultrawide Operating Temperature Window in CO oxidation.

Supported metal nanoclusters are often highly active in many catalytic reactions but less stable particularly under harsh reaction conditions. Here, we demonstrate that this activity-stability trade-off can be efficiently broken through rational design of surrounding microenvironment of the supported nanocatalyst including gas adsorbate overlayer and underneath support surface chemistry. Our studies reveal that chemisorbed oxygen species on Ag surface and surface hydroxyl groups on oxide support, which are dynamically consumed during reaction but sustained by reaction environment (O2 and H2O vapor), drive spontaneous redispersion of Ag particles and stabilization of highly active Ag nanoclusters. Such a dynamic confinement effect from gas-catalyst-support interaction enables the Ag nanoclusters to exhibit complete catalytic oxidation of CO over a wide temperature window of 25 - 500 °C under dry conditions and 200 - 800 °C under wet conditions as well as remarkable stability at 300 °C over 1000 h.

Dynamically Confined Active Silver Nanoclusters with Ultrawide Operating Temperature Window in CO oxidation

Supported metal nanoclusters are often highly active in many catalytic reactions but less stable particularly under harsh reaction conditions. Here, we demonstrate that this activity‐stability trade‐off can be efficiently broken through rational design of surrounding microenvironment of the supported nanocatalyst including gas adsorbate overlayer and underneath support surface chemistry. Our studies reveal that chemisorbed oxygen species on Ag surface and surface hydroxyl groups on oxide support, which are dynamically consumed during reaction but sustained by reaction environment (O2 and H2O vapor), drive spontaneous redispersion of Ag particles and stabilization of highly active Ag nanoclusters. Such a dynamic confinement effect from gas‐catalyst‐support interaction enables the Ag nanoclusters to exhibit complete catalytic oxidation of CO over a wide temperature window of 25 ‐ 500 °C under dry conditions and 200 ‐ 800 °C under wet conditions as well as remarkable stability at 300 °C over 1000 h.

Tight coupling of oxygen vacancies and acidity on α-MnO2 through cerium doping engineering for efficient removal of multi-component VOCs

An α-MnO2-based MnCe catalyst was synthesised by incorporating Ce, which demonstrated outstanding catalytic performance in the oxidation of multicomponent VOCs. Notably, the MnCe-7% catalyst achieved over 90% conversion and CO2 selectivity at temperatures below 300 °C in the presence of both toluene and chlorobenzene (CB). Furthermore, the catalytic activity remained above 80% at 256 °C in the presence of 5.0 vol.% H2O vapor. Structural analyses and DFT calculations indicated that the highly dispersed Ce could replace K in the interlayer and Mn in the intralayer of α-MnO2, resulting in a substantial increase in the number of oxygen vacancies and acidic sites. The close interaction between oxygen vacancies and acidic sites facilitated the oxidation and adsorption of VOCs, which was crucial for the high activity demonstrated by the MnCe-7% catalyst. Furthermore, the VOC-TPD and in situ DRIFTS results suggested that the mixed catalysis of toluene and CB on MnCe-7% concurrently engaged the MvK and E-R mechanisms. Toluene was found to supply additional H atoms, promoting the cleavage of C–Cl bonds in CB and enhancing the reaction kinetics.

Interfacial Bi-O-C bonds and rich oxygen vacancies synergistically endow carbon quantum dot/Bi2MoO6 with prominent photocatalytic CO2 reduction into CO

Developing the photocatalysts with the low charge-transfer resistance and fast charge kinetics is crucial to photocatalytic CO2 reduction into hydrocarbon fuels. Herein, we depict the interfacial Bi-O-C bond-bridged carbon quantum dot (CD)/oxygen vacancy-rich Bi2MoO6 (VOR-BMO) Ohmic junction photocatalysts. They were constructed by in-situ anchoring carbon quantum dots (CDs) onto the VOR-BMO hierarchical petal-like structures (HPs), which are self-assembled from numerous nanosheet subunits. Experimental analysis together with density functional theory (DFT) calculations indicate that the Bi-O-C bonds can provide the atomic-level interfacial channels, and introducing rich oxygen vacancies (VOs) into the BMO HPs can induce the enhanced built-in electric field (IEF) of the Ohmic heterojunction formed between VOR-BMO HPs and CDs, synergistically contributing the eminent charge transfer kinetics, so as to sharply boost the separation and transfer of the photoinduced electrons of VOR-BMO HPs into CDs with a near-zero resistance; Besides, the CD/VOR-BMO heterostructures can not only change the endoergic rate-determining step of VO-poor (VOP)-BMO HPs (i.e., CO* desorption to form CO) to an exoergic reaction process, thus promoting the CO* desorption from the photocatalyst surface, but also decrease the overall activation energy barrier. Consequently, in the presence of H2O vapor with no sacrificial agent, the optimum photocatalyst (CD/VOR-BMO-1.2) exhibits the fantabulous performances of CO2 photoreduction into CO with the production rate and selectivity of 60.00 μmol·g−1·h−1 and near 100 %, respectively. Such performances are comparable with the most recently reported photocatalysts for CO2 conversion. The study offers a valid strategy that harnesses the synergistic effect of the interfacial chemical bonds and Vo-induced enhanced IEF to design the high-efficiency photocatalysts for both energy and environmental applications.

Hydroxylation of an ultrathin Co3O4(111) film on Ir(100) studied by in situ ambient pressure XPS and DFT

In the present work, we have studied the interaction of water with spinel cobalt oxide (Co3O4), an effect which has been considered a major cause of its catalytic deactivation. Employing a Co3O4(111) model thin film grown on Ir(100) in (ultra)high vacuum, and ambient pressure X-ray photoelectron spectroscopy (APXPS), hydroxylation in 0.5 mbar H2O vapor at room temperature was monitored in real time. The surface hydroxyl (OH) coverage was determined via two different models based (i) on the termination of a pristine and OH-covered Co3O4(111) surface as derived from density functional theory (DFT) calculations, and (ii) on a homogeneous cobalt oxyhydroxide (CoO(OH)) overlayer. Langmuir pseudo-second-order kinetics were applied to characterize the OH evolution with time, suggesting two regimes of chemisorption at the mosaic-like Co3O4(111) film: (i) plateaus, which were quickly saturated by OH, followed by (ii) slow hydroxylation in the “cracks” of the thin film. H2O dissociation and OH formation, blocking exposed Co2+ ions and additionally consuming surface lattice oxygen, respectively, may thus account for catalyst deactivation by H2O traces in reactive feeds.

Macadamia nut residue-derived biochar: An eco-friendly solution for β-naphthol and Reactive Black-5 removal

The generation of liquid waste containing dyes and complex organic compounds is a problem in the textile industries. In this work, we evaluated the use of macadamia nut residue as a precursor of a biochar for the treatment of these effluents through the adsorption process. The macadamia nut endocarp undergoes a sequential treatment involving pyrolysis at 600 °C followed by physical activation with CO2 and H2O vapor at 700 °C. Characterization of the resulting macadamia nut residue-derived biochar (MB) is accomplished through various techniques, including X-ray diffractometry (XRD), thermogravimetric analysis (TGA), scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDS), nitrogen physisorption analysis and the pH at the zero charge point (pHZCP). Performance studies reveal that pH exerts minimal influence on the adsorption phenomenon. The Elovich kinetic model effectively describes the adsorption kinetics for both β-naphthol and Reactive Black 5 (RB5), with adjusted coefficients of determination (R2adj) of 0.99 and 0.94, respectively. Further analysis using the intraparticle diffusion model demonstrates that β-naphthol adsorption kinetics involve multiple mechanisms, while RB5 adsorption is predominantly governed by intraparticle diffusion. Equilibrium adsorption data for both adsorbates fit well with the Sips isothermal model, yielding maximum adsorption capacities of qmax β-naphthol = 15.16 mg∙g−1 and qmax RB5 = 3.08 mg∙g−1 at 55 °C. The adsorption process for both compounds is spontaneous and endothermic, based on the enthalpy values, it can be inferred that the β-naphthol adsorption is governed by weak van der Waals forces, indicating physisorption. As for RB5, the enthalpy value suggests that the phenomenon occurs due to electrostatic interactions between the molecule and the surface groups with higher energy involved. This study highlights the potential of macadamia nut residue biomass as a precursor for biochar, demonstrating its favorable attributes for application as an effective adsorbent material in the removal of organic compounds such as β-naphthol and RB5 from wastewater streams within the textile industry.

Synergistic effect between sulfur vacancies and S-scheme heterojunctions in WO3/VS-Zn3In2S6 for enhanced photocatalytic CO2 reduction in H2O vapor

Converting CO2 into CO, CH4, and other hydrocarbons using solar energy presents a viable approach for addressing energy shortages. In this study, photocatalysts with S-deficient WO3/Zn3In2S6 (WO3/VS-ZIS) S-scheme heterojunctions have been successfully synthesized. Under UV–vis light irradiation, 20 %WO3/VS-ZIS demonstrated significantly improved CO2 reduction activity and CH4 selectivity. Detailed characterization and density functional theory (DFT) calculations reveal that the enhanced performance is due to the synergistic optimization of the S-scheme heterojunction and sulfur vacancies (VS) for CO2 reduction. The presence of VS aids in the adsorption and activation of CO2 and enhances the separation of charge carriers. The 2D/2D S-scheme heterostructure assembled with WO3 nanosheets not only accelerates the migration and separation of photoexcited charge carriers but also improves the adsorption of H2O and the formation of VS, thereby increasing the adsorption and activation of CO2 and facilitating the protonation of CO* to produce CH4. This study clarifies the synergistic effect of VS and S-scheme heterostructures in improving photocatalytic performance, offering valuable insights into the photoactivation process of CO2 at VS in S-scheme heterojunctions.

Proton-conductive properties of a stable three-dimensional aluminum(III)-organic framework constructed by porphyrinlcarboxylate

The proton conductivity (σ) of the highly stable metal-organic frameworks (MOFs) built by carboxylic acid ligand and aluminum metal has not been fully investigated. Herein, a three-dimensional aluminum-based MOF, [(AlOH)2TCPP]n (namely Al-TCPP) with exceptional structural stability was solvothermally synthesized using an organic multifunctional bridging ligand, meso-tetra(4-carboxyphenyl)porphine (H4TCPP) with a large stiff ring structure and Al(NO3)3⋅9H2O as raw materials. The dependency of σ on temperature and relative humidity (RH) was surveyed using the AC impedance test after the MOF's thermal, water, and chemical stabilities, as well as nitrogen and H2O vapor adsorptions, were all characterized. Experimental results demonstrated that this highly stable MOF with a high specific surface area exhibited impressive proton conductivity, with an optimal σ of 3.2 × 10-4 S/cm under 100 °C/98% RH. Furthermore, the proton-conducting mechanism inside the framework was highlighted using computed activation energy and structural analysis. This study provides new inspiration for designing and searching for high-performance proton-conductive materials.

Advanced visualisation of biomass charcoal combustion dynamics using MWIR hyperspectral and LWIR thermal imaging under varied airflow conditions

Biomass charcoal combustion is a complex process, significantly influenced by various operating parameters. Among these parameters, air supply emerges as a critical factor affecting combustion efficiency, gas emissions, and thermal dynamics. In this study, we explored these complex interdependencies using a novel combination of mid-wavelength infrared (MWIR) hyperspectral imaging and long-wavelength infrared (LWIR) thermal imaging, under different airflow rates. Our findings demonstrated that while increased airflow accelerated the overall combustion rate, it simultaneously decreased combustion efficiency. Specifically, the thermal profiles showed an increased surface temperature at a low flowrate (0.5 L/min) while decreasing in temperature with higher flowrates. The decreased system temperature led to a lower combustion efficiency because of the reduced conversion rate from combustible gases (CH4 and CO) into CO2 and H2O. Additionally, the results also demonstrated that cooling effects of the high flowrates primarily impeded the solid-phase combustion stage. This is further corroborated by the temporal and spatial variation in the emissions of key gas species (H2O vapor, CH4, CO, and CO2) observed through hyperspectral imaging. The emission evolution of these gases displayed the different stages of the gas-phase and solid-phase combustion. The spatial distribution of the trace gases showed a decreased distribution radius due to the enhanced diffusion to the fuel surface when the airflow increases, aligning well with the two-film model established in the literature. Furthermore, we utilised spectral radiance ratios (CO/CO2, CH4/CO2, H2O/CO2) to gain additional insights into the combustion dynamics. These ratios evidenced the decrease in combustion efficiency at high airflow rates. Finally, the increased H2O/CO2 ratio further demonstrated the impeded char combustion and a shift towards pyrolysis at higher airflow rates because of the decreased thermal equilibrium of the system. The findings from this study provide critical insights into the dynamics of biomass charcoal combustion and illuminates the path for optimising energy efficiency and assessing the environmental implications from burning biomass fuels.

Influence of the Structure of Hydrothermal-Synthesized TiO2 Nanowires Formed by Annealing on the Photocatalytic Reduction of CO2 in H2O Vapor.

The present study investigates the photocatalytic properties of hydrothermally synthesized TiO2 nanowires (NWs) for CO2 reduction in H2O vapor. It has been demonstrated that TiO2 NWs, thermally treated at 500-700 °C, demonstrate an almost tenfold higher yield of products compared to the known commercial powder TiO2 P25. It has been found that the best material is a combination of anatase, TiO2-B and rutile. The product yield increases with increasing heat treatment temperature of TiO2 NWs. This is associated with an increase in the degree of crystallinity of the material. It is shown that the best product yield of the CO2 reduction in H2O vapor is achieved when the TiO2 NW photocatalyst is heated to 100 °C.

Variable valence I3−/I− ionic bridge assisting CuI nanoparticle/BiOI nanosheet S-scheme photocatalyst with hydrophobic surface for boosting CO2 conversion with 100 % CO selectivity

The photocatalyst film, composed of tetragonal BiOI nanosheets and cubic phase CuI nanoparticles, was synthesized on the FTO substrate by a simple electro-deposition method. The orderly crisscrossed nanosheet structure caused exterior hydrophobic property, resisting the excess H2O molecules and further inhibiting the competitive H2O reduction process. The novel BiOI/CuI catalyst exhibited excellent photocatalytic ability of CO2 reduction into CO with 100 % selectivity in H2O vapor. Typically, the optimal 150BiOI/CuI photocatalyst exhibited CO yield of 7237.65 μmol/cm2 after 11 h of simulated sunlight illumination, achieving quantum efficiency of 2.5 % at 380 nm. The excellent performance of the BiOI/CuI composite film in photocatalytic CO2 reduction can be attributed to the construction of hydrophobic surface and S-scheme heterojunction with I3−/I− redox mediator, as confirmed by the in-situ XPS, hole injection test and cyclic voltammetry results. This study lays the groundwork for employing highly efficient iodide-based photocatalysts in gas-liquid-solid triphase catalytic systems.

2.7 μm backward wave optical parametric oscillator source for CO2 spectroscopy.

In this work, a novel 2.7 µm source used for CO2 and H2O vapor spectroscopy using the backward propagating wave of a backward wave optical parametric oscillator (BWOPO) is demonstrated for the first time to our knowledge. The unique properties of BWOPOs eliminate the need for additional spectral narrowing or wavelength stabilization, enabling the use of a multi-longitudinal mode Q-switched pump laser centered around 1030 nm. A full characterization of the source is presented, revealing a central output at 2712 nm, showcasing a temperature tuning of -1.77 GHz/K, and achieving an output pulse energy of 2.3 µJ. Novel methods are introduced for measuring the linewidth and wavelength stability using the ambient laboratory air. These approaches demonstrate a narrow output of 43 pm and establish an upper limit of stability at 65 MHz, with no active means of stabilization. These findings underscore the potential of BWOPOs as a robust platform for future differential absorption lidar (DIAL) systems.

Synthesis and bio-medical applications of multifunctional phosphorester cyclic amide anchored sterculia network

The main focus of the present research is to design network hydrogels derived from natural polymers to promote a sustainable future. Multifunctional hydrogels were prepared by combining sterculia gum (SG), phosphorester -cyclic amide polymers for bio-medical applications including drug delivery (DD). The antibiotic drug ceftriaxone was incorporated into hydrogels to enhance wound healing potential. The surface morphology of copolymers was investigated by using FESEM and AFM techniques. FTIR and 13C NMR spectroscopic techniques provided insight into the formation of network structures. In FTIR analysis, distinctive bands were identified: at 1649 cm−1 attributed to CO stretching of the cyclic amide of PVP, at 1147 cm−1 and 974 cm−1 representing PO stretching and P-O-C of poly(BMEP), respectively. In the 13C NMR spectrum, a prominent peak at 63.272 ppm revealed the presence of (O-CH2) linkage of poly(BMEP). XRD demonstrated amorphous characteristics of hydrogels. The interactions of copolymer with blood, bio-membrane and encapsulated drug illustrated their biocompatibility, bio-adhesion and controlled DD properties. The dressings expressed a hemolytic index value of 2.58 ± 0.03 %. The hydrogels exhibited mucoadhesive character, revealed from the adhesion force of 50.0 ± 5 mN needed to separate polymer dressing from the mucosa. Dressings exhibited antioxidant properties and displayed 33.73 ± 0.3 % radical scavenging in the DPPH assay. Protein adsorption test of copolymer illustrated 9.48 ± 0.970 % of albumin adsorption. The tensile strength of the dressing was found 0.54 ± 0.03 N mm−2 while the burst strength 9.92 ± 0.27 N was observed. The sustained release of the drug was provided by supra-molecular interactions. Drug release followed a non-Fickian diffusion mechanism and the release profile was best described by the Higuchi kinetic model. Additionally, hydrogel dressings revealed permeability to H2O vapors and O2 and antimicrobial activity. These findings suggest the suitability of sterculia gum-based hydrogels for DD uses.

Reactive adsorption and catalytic oxidation of gaseous hydrogen sulfide using a prototype air purifier built with bismuth-doped titanium dioxide

A prototype air purifier (AP) module has been constructed using bismuth-doped titanium dioxide (Bix-P25: x(%) as Bi/Ti molar ratios of 1.1, 2.1, 3.3, 5.3, and 8.7). The reactive adsorption property of Bix-P25 materials is evaluated against H2S gas at a recirculation rate of 160 L min−1 in a 17 L closed chamber. The AP (Bi5.3-P25) exhibits superior performance against 10 ppm H2S in dry air under dark conditions (i.e., without light irradiation), with a removal efficiency (XH2S)= 99% in 5 mins, reaction kinetic rate (r (at X = 10%))= 7.3 mmol h−1g−1, and partition coefficient= 0.18 mol kg−1 Pa−1. As such, its superiority is evident over the reference AP (P25) filter with XH2S < 10%. The clean air delivery rate (CADR) of AP (Bi5.3-P25) increases noticeably from 9.9 to 17.8 L min−1 with increasing relative humidity (RH) from 0 to 80%, respectively. In contrast, the CADR decreases from 9.9 to 5.8 L min−1 as the H2S increases from 10 to 20 ppm. According to density functional theory (DFT), the presence of H2O vapor enhances the hydroxylation of Bix-P25 surface to promote H2S mineralization through the formation of TiS3 (i.e., thermodynamic reaction of S atom with the catalytic surface). Complete removal of H2S on the Bi5.3-P25 surface is also confirmed consistently through gas chromatography-mass spectrometry (GC-MS), in-situ diffuse reflection infrared spectroscopy (in-situ DRIFTS), and elemental analysis (EA). This work represents the first utilization of Bix-P25 materials fabricated on an AP platform toward the desulfurization of H2S at room temperature (RT). The practical utility of Bix-P25 is overall validated by its eminent role in reactive adsorption and catalytic oxidation (RACO) of H2S from the air.

Sustainable nitrogen fixation by bubble discharge plasma: Performance optimization and mechanism

Sustainable nitrogen fixation driven by renewable energy sources under mild conditions has been widely sought to replace the industrial Haber-Bosch process. The fixation of nitrogen in the form of NOx− and NH4+ into aqueous solutions using electricity-driven gas–liquid discharge plasma is considered a promising prescription. In this paper, a scalable bubble discharge excited by nanosecond pulse power is employed for nitrogen fixation in the liquid phase. The nitrogen fixation performance and the mechanisms are analyzed by varying the power supply parameters, working gas flow rate and composition. The results show that an increase in voltage and frequency can result in an enhanced NO3− yield. Increases in the gas flow rate can result in inadequate activation of the working gas, which together with more inefficient mass transfer efficiencies can reduce the yield. The addition of O2 effectively elevates NO3− production while simultaneously inhibiting NH4+ production. The addition of H2O vapor increases the production of OH and H, thereby promoting the generation of reactive nitrogen and enhancing the yield of nitrogen fixation. However, the excessive addition of O2 and H2O vapor results in negative effect on the yield of nitrogen fixation, due to the significant weakening of the discharge intensity. The optimal nitrogen fixation yield was up to 16.5 μmol/min, while the optimal energy consumption was approximately 21.3 MJ/mol in this study. Finally, the mechanism related to nitrogen fixation is discussed through the optical emission spectral (OES) information in conjunction with the simulation of energy loss paths in the plasma by BOLSIG + . The work advances knowledge of the effect of parameter variations on nitrogen fixation by gas–liquid discharge for higher yield and energy production.

Real-time monitoring of CH4 and N2O emissions from livestock using mid-infrared external cavity quantum cascade laser absorption spectroscopy

The largest share of greenhouse gas (GHG) emissions related to livestock originates from methane (CH4) and nitrous oxide (N2O) which have a far higher influence on global warming, it is therefore necessary to accurately monitor CH4 and N2O emissions to provide theoretical and practical basis for further estimating and regulating GHG emissions from livestock and improving livestock production performance. For the purpose of sensing CH4 and N2O emissions during livestock living process in real time, an optical sensor based on continuous-wave (CW) external cavity quantum cascade laser (EC-QCL) operating at room temperature was developed. CH4 and N2O absorption lines, located around 8 μm, of the ν4 and ν1 fundamental vibrational bands, respectively, were chosen for direct absorption spectroscopy, which allows for sensitive, selective and simultaneous measurement of CH4 and N2O concentrations. Use of a Herriot multi-pass cell with an effective path-length of 100 m, 1σ (SNR = 1) limits of detection of 26.8 ppbv, 20.3 ppbv and 0.01 % for CH4, N2O and H2O vapor were achieved, respectively. Field measurement of CH4 and N2O emissions from horses has been carried out in a stable over two weeks at the Vernaelde farm in Couderkerque Branche city, France. Concentrations of CH4 and N2O up to 10 times and 1.5 times higher than their levels in the local ambient air (∼ 2.12 ppmv and ∼ 427 ppbv) were observed, respectively.

Oxidizing Role of Cu Cocatalysts in Unassisted Photocatalytic CO2 Reduction Using p-GaN/Al2O3/Au/Cu Heterostructures.

Photocatalytic CO2 reduction to CO under unassisted (unbiased) conditions was recently demonstrated using heterostructure catalysts that combine p-type GaN with plasmonic Au nanoparticles and Cu nanoparticles as cocatalysts (p-GaN/Al2O3/Au/Cu). Here, we investigate the mechanistic role of Cu in p-GaN/Al2O3/Au/Cu under unassisted photocatalytic operating conditions using Cu K-edge X-ray absorption spectroscopy and first-principles calculations. Upon exposure to gas-phase CO2 and H2O vapor reaction conditions, the composition of the Cu nanoparticles is identified as a mixture of CuI and CuII oxide, hydroxide, and carbonate compounds without metallic Cu. These composition changes, indicating oxidative conditions, are rationalized by bulk Pourbaix thermodynamics. Under photocatalytic operating conditions with visible light excitation of the plasmonic Au nanoparticles, further oxidation of CuI to CuII is observed, indicating light-driven hole transfer from Au-to-Cu. This observation is supported by the calculated band alignments of the oxidized Cu compositions with plasmonic Au particles, where light-driven hole transfer from Au-to-Cu is found to be thermodynamically favored. These findings demonstrate that under unassisted (unbiased) gas-phase reaction conditions, Cu is found in carbonate-rich oxidized compositions rather than metallic Cu. These species then act as the active cocatalyst and play an oxidative rather than a reductive role in catalysis when coupled with plasmonic Au particles for light absorption, possibly opening an additional channel for water oxidation in this system.

The practical utility of nitrogen doped TiO2 as a photocatalyst for the oxidative removal of gaseous formaldehyde

This study reports the development of nitrogen-doped TiO2 (N–TiO2: N/Ti molar ratio = 1) photocatalyst with the enhanced photoelectronic properties for the phtocatalytic oxidation (PCO) of formaldehyde (FA). The N–TiO2 photocatalyst is coated with ceramic beads and placed in a packed-bed tube reactor to examine the PCO-based mineralization of FA vapor (100 - 500 ppm) under ultraviolet (UV)-A illumination (32 W light source) with the control of flow rate (100–500 mL min−1), O2 (0–21%), and relative humidity (RH: 0–100%). Accordingly, the N-TiO2 in dry conditions showcases 100% degradation of 100 ppm FA with high stability over 5 reuse cycles (compared to the P25 (75.9%) and bare TiO2 (69.2%)) at a flow rate of 100 mL min−1 and a 21 % O2 level (quantum yield = 1.72.E−02 molecules photon−1 and space-time yield = 3.44.E−03 molecules photon−1 mg−1). The superior performance of N–TiO2 may reflect the combination of N/O atoms in the crystal structure to enhance the photo-redox reactivities with the heightened valence band enegry and prolonged lifespan of charge carrier (1.34 ns) relative to 1.04 ns of P25 and 1 ns of pure (anatase) TiO2. The PCO efficiency of N–TiO2 increases by around 1.6 times in slightly humid conditions (74.6%: RH 20%) compared to dry conditions (47%: RH 0%) while the absence of oxygen (at 0% O2) reduces it significantly down to 13.6%. In situ diffuse reflectance infrared Fourier transform spectroscopy and electron paramagnetic resonance studies confirm the critical role of O2 and H2O vapor on the enhanced FA mineralization rate (CO2 yield = 91 %) through the generation of •O2-/•OH oxidative radicals. This study offers deep insights into the practical utility of N–TiO2 for the photocatalytic mineralization of aldehyde VOCs.

Removal of tritiated water molecules by isotope exchange reaction between H2O vapor and tritium water

Developing a cost-effective method for separating and concentrating tritium water (HTO) from light water (H2O) without consuming additional energy is crucial for achieving reliable and safe nuclear fission and fusion energy technologies. However, this presents a significant challenge because of the difficulties in obtaining basic information, such as the chemical and physical properties of HTO molecules. Here, we investigate the isotope exchange reaction (IER) between HTO molecules in H2O solution and H2O vapor in the atmosphere. The reduction and purification rates of HTO-containing water were measured by varying the system conditions, such as temperature (20−50 °C) and humidity (50 %–90 %), under an equilibrium state between the liquid phase (water) and vapor phase (air). Our findings indicate that the concentration of HTO in the solution can be significantly reduced by increasing H2O vapor in the atmosphere. This result can be quantitatively explained by considering the entropy of mixing between the solution and vapor phases. The results obtained here provide both basic understanding on the exchange process between liquid- and vapor-water molecules and a passive technology for treating HTO-containing water.