One-Step “Green” Synthetic Approach for Mesoporous C-Doped Titanium Dioxide with Efficient Visible Light Photocatalytic Activity

Mesoporous C-doped TiO2 nanomaterials with anatase phase are synthesized by a one-step “green” synthetic approach with low-cost inorganic Ti(SO4)2 and glucose as precursors for the first time. This facile method avoids treatment at high temperature, use of expensive or unstable precursors, and production of undesirable byproducts in the synthesis process. The physicochemical properties of as-prepared samples are characterized in detail by X-ray diffraction (XRD), Raman spectroscopy (Raman), N2 adsorption−desorption isotherms, transmission electron microscopy (TEM), Fourier transform-infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TG), UV−vis diffuse reflectance spectroscopy (UV−vis DRS), and photoluminescence (PL). The results indicate that oxygen sites in the TiO2 lattice are substituted by carbon atoms and an O−Ti−C bond is formed. The observed new electronic states above the valence band edge are directly responsible for the electronic origin of the band gap narrowing and visible light photoactivity of the C-doped TiO2. Furthermore, the possible formation mechanism of mesoporous C-doped TiO2 is also discussed. The as-prepared C-doped TiO2 exhibits excellent visible light photocatalytic activity in degradation of toluene in the gas phase compared with that of commercial TiO2 photocatalyst (P25) and C-doped TiO2 prepared by the solid state method. The efficient activity can be attributed to the large surface area and pore volume. Our novel synthesis approach is energy-efficient and environmentally friendly, which can provide an effective approach for industrial applications owing to its low cost and easy scaling up

Photocatalytic Oxidative Coupling of Methane to Ethane Using Water and Oxygen on Ag₃PO₄‑ZnO

Photocatalytic oxidative coupling is an effective way of converting CH4 to high-value-added multi-carbon chemicals under mild conditions, where the breaking of the C–H bond is the main rate-limiting step. In this paper, the Ag3PO4-ZnO heterostructure photocatalyst was synthesized for photocatalytic oxidative coupling of methane (OCM) to C2H6. In addition, an excellent C2H6 yield (16.62 mmol g–1 h–1) and a remarkable apparent quantum yield (15.8% at 350 nm) at 49:1 CH4/Air and 20% RH are obtained, which is more than three times that of the state-of-the-art photocatalytic systems. Ag3PO4 improves the adsorption and dissociation ability of O2 and H2O, benefiting the formation of surface hydroxyl species. As a result, the C–H bond activation energy of CH4 on ZnO was obviously reduced. Meanwhile, the improved separation of photogenerated carriers on the Ag3PO4-ZnO heterostructure also accelerates the OCM process. Moreover, Ag nanoparticles (NPs) derived from Ag3PO4 reduction by photoelectrons promote the coupling of *CH3, which can inhibit the overoxidation of CH4 and increase C2H6 selectivity. This research provides a guide for the design of catalyst and reaction systems in the photocatalytic OCM process

Solubility and Phase Transitions of Calcium Sulfate in KCl Solutions between 85 and 100 °C

The solubility(s) of the three phases of CaSO4, namely, CaSO4·2H2O (DH), CaSO4·0.5H2O (α-HH), and CaSO4 (AH II), in 0.0−18.0 wt % KCl solutions were systemically investigated at temperatures ranging from 85 to 100 °C. At fixed temperature, the solubility(s) of the three phases all change with KCl concentration and possess a maximum value. The relative magnitudes of the variance of solubility for AH and α-HH are larger than that for DH. This was considered to be correlated to the combined effects of the temperature and concentration of KCl solution on the activity coefficients and water activity. The phase transition behaviors of α-HH and DH are presented with possible intermediate phases, which can be well-explained by the solubility difference of the three forms of CaSO4 and the tendency of forming görgeyite (K2Ca5(SO4)6·H2O)

Simultaneous Absorption of NO_<i>x</i> and SO₂ Using Magnesia Slurry Combined with Ozone Oxidation

To achieve simultaneous removal of NO_<i>x</i> and SO₂ in flue gas, an effective technology combined with ozone oxidation was explored in this paper. The simulated flue gas was initially oxidized by ozone (O₃), turning NO into NO₂ or N₂O₅, and then absorbed by alkaline slurries to achieve simultaneous removal of NO_<i>x</i> and SO₂. It was found that the MgO slurry was a suitable absorbent for the simultaneous removal of NO_<i>x</i> and SO₂. The operating parameters, such as the pH of the liquid phase, initial SO₂ concentration, and MgO concentration, were investigated for the NO₂ removal efficiency of the MgO slurry, where the optimal NO₂ removal efficiency (at ca. 75%) was obtained with the pH value at 6.5 and the MgO concentration at 0.02 mol/L. In the case of N₂O₅, the absorption efficiency of the MgO slurry was maintained at a high level because of the rapid reaction between N₂O₅ and H₂O. Furthermore, it was noted that the absorption efficiency of SO₂ could be at a high level (i.e., approaching 100%) when the pH of the MgO slurry was above 4. Finally, the simultaneous removal mechanism and the reaction pathways were discussed on the basis of the experimental results

High-Efficiency Electrocatalytic Reduction of N₂O with Single-Atom Cu Supported on Nitrogen-Doped Carbon

Nitrous oxide (N2O) is a potent greenhouse gas with a high global warming potential, emphasizing the critical need to develop efficient elimination methods. Electrocatalytic N2O reduction reaction (N2ORR) stands out as a promising approach, offering room temperature conversion of N2O to N2 without the production of NOx byproducts. In this study, we present the synthesis of a copper-based single-atom catalyst featuring atomic Cu on nitrogen-doped carbon black (Cu1–NCB). Attributed to the highly dispersed single-atom Cu sites and the effective suppression of the hydrogen evolution reaction, Cu1–NCB demonstrated an optimal N2 faradaic efficiency (82.1%) and yield rate (3.53 mmol h–1 mgmetal–1) at −0.2 and −0.5 V vs RHE, respectively, outperforming previously reported N2ORR electrocatalysts. Further, a gas diffusion electrode cell was employed to improve mass transfer and achieved a 28.6% conversion rate of 30% N2O with only a 14 s residence time, demonstrating the potential for practical application. Density functional theory calculations identified Cu–N4 as the crucial active site for N2ORR, highlighting the significance of the unsaturated coordination and metal–support electronic structure. O-terminal adsorption of N2O was favored, and the dissociative adsorption (*ON2 → *O + N2) was the rate-determining step. These findings reveal the broad prospects of N2O decomposition via electrocatalysis

Catalytic Combustion of Dichloromethane over HZSM-5-Supported Typical Transition Metal (Cr, Fe, and Cu) Oxide Catalysts: A Stability Study

In this paper, three kinds of HZSM-5-supported transition metal (Cr, Fe, and Cu) oxide catalysts were prepared by the wet impregnation method, and their stability performances for catalytic combustion of dichloromethane (DCM) were investigated. Different behaviors were observed for these three catalysts during a 300 min catalytic reaction running at 320 °C. It was found that the Cr–O/HZSM-5 catalyst showed good catalytic stability, while both Fe–O/HZSM-5 and Cu–O/HZSM-5 suffered obvious deactivation. Characterizations using XRD, BET, XPS, O2-TG, O2-TP-MS, NH3–IR, and temperature-programmed surface reaction (TPSR) techniques were then carried out to disclose the deactivation mechanisms. The results revealed that the main cause of the deactivation over the Fe–O/HZSM-5 catalyst was coke formation, which could be mainly attributed to its lower deep oxidation capacity of the intermediate products, i.e., the methoxy groups, and it could also be obtained that the Cu–O/HZSM-5 catalyst was severely poisoned by chlorine species owing to the formation of stable Cu­(OH)Cl species. Based on the results above, it could be concluded that the close proximity and synergy between acidic sites and active oxygen species were crucial to avoid coke deposition during the chlorinated volatile organic compound catalytic oxidation process

DRIFT Study of Manganese/Titania-Based Catalysts for Low-Temperature Selective Catalytic Reduction of NO with NH₃

Manganese oxides and iron-manganese oxides supported on TiO2 were prepared by the sol−gel method and used for low-temperature selective catalytic reduction (SCR) of NO with NH3. Base on the previous study, Mn(0.4)/TiO2 and Fe(0.1)−Mn(0.4)/TiO2 were then selected to carry out the in situ diffuse reflectance infrared transform spectroscopy (DRIFT) investigation for revealing the reaction mechanism. The DRIFT spectroscopy for the adsorption of NH3 indicated the presence of coordinated NH3 and NH4+ on both of the two catalysts. When NO was introduced, the coordinated NH3 on the catalyst surface was consumed rapidly, indicating these species could react with NO effectively. When NH3 was introduced into the sample preadsorbed with NO + O2, SCR reaction would not proceed on Mn(0.4)/TiO2. However, for Fe(0.1)−Mn(0.4)/TiO2 the bands due to coordinated NH3 on Fe2O3 were formed. Simultaneously, the bidentate nitrates were transformed to monodentate nitrates and NH4+ was detected. And NO2 from the oxidation of NO on catalyst could react with NH4+ leading to the reduction of NO. Therefore, it was suggested that the SCR reaction on Fe(0.1)−Mn(0.4)/TiO2 could also take place in a different way from the reactions on Mn(0.4)/TiO2 proposed by other researchers. Furthermore, the SCR reaction steps for these two kinds of catalysts were proposed

Enhancement of the Visible Light Photocatalytic Activity of C-Doped TiO₂ Nanomaterials Prepared by a Green Synthetic Approach

Mesoporous C-doped TiO2 nanomaterials with an anatase phase are prepared by a one-pot green synthetic approach using sucrose as a carbon-doping source for the first time. A facile post-thermal treatment is employed to enhance visible light photocatalytic activity of the as-prepared photocatalyst. The enhancement effect of post-thermal treatment between 100 and 300 °C is proved by the photodegradation of gas-phase toluene, and the optimum temperature is 200 °C. Physicochemical properties of the samples are characterized in detail by X-ray diffraction, Raman spectroscopy, N2 adsorption–desorption isotherms, transmission electron microscopy, Fourier transform-infrared spectroscopy, X-ray photoelectron spectroscopy, UV–vis diffuse reflectance spectroscopy, and photoluminescence. The results indicate that the promotive effect of the post-thermal treatment can be attributed to the changes of the catalysts’ surface and optical properties. The results also show that the recombination of electron–hole pairs is effectively inhibited after thermal treatment due to the reduction of surface defects. The facile post-thermal treatment provides a new route for potential industrial applications of C-doped TiO2 nanomaterials prepared by a green approach owing to its low cost and easy scale-up

Adsorptive Removal of Carbon Dioxide Using Polyethyleneimine Supported on Propanesulfonic-Acid-Functionalized Mesoporous SBA-15

One-step synthesized sulfonic-acid-functionalized SBA-15 (denoted as αSSBA-15) impregnated with polyethyleneimine (PEI) was used for CO₂ capture in this study. The resulted sorbents were characterized via a range of analytical techniques, including transmission electron microscopy (TEM), ²⁹Si magic angle spinning (MAS) nuclear magnetic resonance (NMR), infrared (IR), thermogravimetry–differential scanning calorimetry (TG–DSC), etc. Experimental results showed that the incorporation of propanesulfonic acid groups into the inner structure of the silica support had brought dramatic improvement in CO₂ adsorption capacity, of which PEI/5SSBA-15 showed the highest CO₂ adsorption amount. The main reason of this increased capacity could be attributed to the enhanced CO₂ diffusion into bulk networks of PEI polymers because of its better dispersion in the pores of support, where the extended propanesulfonic acid groups on the inner surface could spatially disperse the subsequent loaded PEI molecules. Furthermore, the PEI/5SSBA-15 also exhibited superior stable cyclic adsorption/desorption performance compared to PEI/SBA-15, especially after 5 cycles. This was assumed because the enhanced surface acidity of PEI/5SSBA-15 anchored the NH₂/NH groups through acid–base interaction, reducing the loss of active sites

Effect of Water Layer in a Microreactor on the Low-Temperature Synthesis of High-Activity Cu/ZnO Catalysts

The effect of a water layer on the precipitation process in a three-channel microreactor at low temperatures was investigated. Fourier-transform infrared spectroscopy, X-ray powder diffraction, thermal gravimetric analysis, X-ray photoelectron spectroscopy, temperature-programmed reduction, and Brunauer–Emmett–Teller analysis were employed for studying the structural evolution of the intermediate products during the preparation of both zincian georgeite-derived and zincian malachite-derived catalysts, and catalytic activities were measured for methanol synthesis from syngas. It is manifested that the effect of uniform precipitates acts consecutively on the subsequent aging process, Zn incorporation in precursors, thermal decomposition, reduction, and catalytic performance of the catalysts. Numerical simulation revealed the change of species properties, and reaction rates at varying temperatures can lead to different regulations of the water layer, denoting that disparate ratios of the water layer were required for obtaining uniform precipitates under different conditions, which further suggests the key role of uniformity of the precipitates in preparing high-activity Cu/ZnO catalysts