Well-dispersed Pd nanoparticles on porous ZnO nanoplates via surface ion exchange for chlorobenzene-selective sensor

Enhancing the Photoelectrochemical Activity of CuO/ZnO Junction Photocathodes for Water Splitting

To facilitate fast transfer of photogenerated electrons and surface stability, the CuO photocathode needs to be coupled with another heterojunction material. Here, we propose CuO/ZnO heterojunctions as photocathodes for photoelectrochemical (PEC) water splitting. First, CuO was grown on a Cu substrate, either in the form of a foil or mesh gauge, via anodization followed by postheating treatment. Subsequently, ZnO was electrodeposited on the grown CuO. The grown CuO film was composed of two-dimensional nanoplates aligned vertically against the substrate. The film morphology changed to flower-like or nearly spherical when ZnO was deposited by electrodeposition. Based on its open-circuit potential (OCP), overpotential and current density, CuO/ZnO grown on the Cu mesh exhibited better PEC performance than its counterpart grown on the Cu foil. When the mesh substrate was used, the surface area of the grown nanostructures was high and reached approximately 102.42 m2 g-1. The OCP of the CuO/ZnO mesh reached a low value of approximately -137 mV; this value quantitatively indicated that its PEC activity was more favorable for the hydrogen evolution reaction (HER). Moreover, the overpotential at the benchmark current density of 10 mA cm-2 for the Cu mesh was 379 mV, and this value was lower than those of the other photocathode materials.

Catalytic removal of harmful volatile organic compounds by reutilizing zinc rods waste from spent batteries as a palladium catalyst support

The emission of volatile organic compounds (VOCs) has led to significant deterioration in air quality, making it imperative to ensure that these compounds are removed from emission sources before they are released into the atmosphere. In this context, the present study recycled spent primary batteries to use their zinc rods waste (ZRW) as a palladium catalyst support for the removal of harmful VOCs. To this end, palladium supported on ZRW (Pd/ZRW) catalysts were prepared and tested for the catalytic oxidation of benzene, methylbenzene and 1,2-dimethylbenzene. The physicochemical properties of the Pd/ZRW catalysts were carefully characterized by ICP-OES, BET, SEM, XRD, FE-TEM, XPS, and H2-TPR analyses. The main component of ZRW was identified as ZnO. Consistent with expectations, increases in the loading of Pd from 0.1 to 1.0 wt% in the Pd/ZRW catalysts resulted in enhanced VOCs removal efficiency. The reaction temperature required for the complete oxidation (100% removal efficiency) of methylbenzene and 1,2-dimethylbenzene on the 1.0 wt% Pd/ZRW catalyst was below 340 °C at a gas hourly space velocity of 50,000 h-1. TEM, XPS, and H2-TPR results implied that the enhancement of catalytic activity with the addition of Pd could be attributed to the readily movable surface lattice oxygen as well as the active component (Pd species). Ultimately, ZRW of spent primary batteries appear to show promise as a catalyst support for VOCs removal. This study has introduced a novel strategy for reducing air pollutants by utilizing waste, which promotes the disposal of hazardous solid waste and ensures clean air quality.

A UiO-66 3D photonic crystal optical sensor for highly efficient chlorobenzene vapor detection

Chlorobenzene (C6H5Cl) is a flammable liquid with high vapor activity, which is a severe threat to the environment and human health. Therefore, it is essential to develop a highly efficient sensor to detect C6H5Cl vapor. Herein, we developed a UiO-66 three-dimensional photonic crystal (3D PC) optical sensor and investigated its sensing properties toward the C6H5Cl vapor. The UiO-66 3D PCs optical sensor shows a high sensitivity of C6H5Cl vapor, in the concentrations range of 0-500 ppm, the reflectance intensity response to be 0.06% ppm with a good linear relationship, detection limit can reach 1.64 ppm and the quality factor is 10.8. Additionally, the UiO-66 3D PC optical sensor demonstrated great selectivity with the values of selectivity (S) varying from 2.24 to 10.65 for the C6H5Cl vapor as compared with carbon tetrachloride (CCl4), dichloromethane (CH2Cl2), 1,1,2-trichloroethane (C2H3Cl3), benzene (C6H6), deionized water (H2O), ethanol (C2H5OH) and methyl alcohol (CH3OH) vapors. Moreover, the UiO-66 3D PC optical sensor shows an ultrafast optical response time and recovery times of 0.5 s and 0.45 s with exceptional stability and repeatability to 500 ppm C6H5Cl vapor. These excellent sensing properties are attributed to the efficacy of signal transduction, increased porosity and gas adsorption sites, which are intrinsically endowed by the design of the 3D optical structure. The design and fabrication of this UiO-66 3D PC optical sensor might open up potential applications for the detection of the C6H5Cl vapor.

Preparation of highly dispersed Pd/SBA-15 catalysts for dodecahydro-N-ethylcarbazole dehydrogenation reaction by ion exchange-glow discharge

Dehydrogenation reactions are critical in hydrogen storage based on a liquid organic hydrogen carrier (LOHC) system. Speeding up the dehydrogenation rate and lowering the reaction temperature are the main focuses of LOHC dehydrogenation catalysts. In this paper, Pd/SBA-15 catalysts (Pd-IP/S15) were prepared by NaOH treatment of surface hydroxyl groups on SBA-15, the ion exchange of Na⁺ with Pd(NH₃)₄²⁺, and then reduction of Pd ions via glow discharge plasma. The dehydrogenation performance of dodecahydro-N-ethylcarbazole on the prepared catalysts is studied. The turnover frequency of Pd-IP/S15 is 13.94 min^-1 at 170°C, which is 10.25 times that of commercial Pd/C. It is ensured via the ion exchange method that Pd(NH₃)₄²⁺ could be precisely targeted at the Si-OH of SBA-15 to form Si-O-Pd(NH₃)₄²⁺, which effectively prevents the aggregation and uncontrollable growth of Pd nanoparticles (NPs) during the in situ reduction by plasma. Pd NPs with high dispersion are obtained on SBA-15, which enhances the catalytic activity of Pd-IP/S15. The coordination of Pd NPs with O of Si-OH on SBA-15 enabled Pd-IP/S15 to exhibit excellent catalytic stability. After 7 dehydrogenation cycles at 180°C, the dehydrogenation efficiency remained above 97%.

Understanding Hydrodechlorination of Chloromethanes. Past and Future of the Technology

Chloromethanes are a group of volatile organic compounds that are harmful to the environment and human health. Abundant studies have verified that hydrodechlorination might be an effective treatment to remove these chlorinated pollutants. The most outstanding advantages of this technique are the moderate operating conditions used and the possibility of obtaining less hazardous valuable products. This review presents a global analysis of experimental and theoretical studies regarding the hydrodechlorination of chloromethanes. The catalysts used and their synthesis methods are summarized. Their physicochemical properties are analyzed in order to deeply understand their influence on the catalytic performance. Moreover, the main causes of the catalyst deactivation are explained, and prevention and regeneration methods are suggested. The reaction systems used and the effect of the operating conditions on the catalytic activity are also analyzed. Besides, the mechanisms and kinetics of the process at the atomic level are reviewed. Finally, a new perspective for the upgrading of chloromethanes, via hydrodechlorination, to valuable hydrocarbons for industry, such as light olefins, is discussed.

A novel highly selective electrochemical chlorobenzene sensor based on ternary oxide RuO2/ZnO/TiO2 nanocomposites

A novel electrochemical (EC) chlorobenzene (CBZ) sensor was fabricated using a ternary oxide RuO₂/ZnO/TiO₂ nanocomposite (NC)-decorated glassy carbon electrode (GCE). The nanoparticles (NPs) were synthesized by a wet-chemical method and characterized by X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDS), and ultraviolet-visible (UV-vis) spectroscopy. The synthesized RuO₂/ZnO/TiO₂ NC was layered as thin film on a GCE with Nafion (5% suspension in ethanol) adhesive, and the as-prepared sensor was subjected to CBZ analysis using an electrochemical approach. The calibration of the proposed CBZ sensor was executed with a linear relation of current versus concentration of CBZs known as the calibration curve. The sensitivity (32.02 μA μM⁻¹ cm⁻²) of the CBZ sensor was calculated from the slope of the calibration curve by considering the active surface area of the GCE (0.0316 cm²). The lower detection limit (LD; 98.70 ± 4.90 pM) was also calculated at a signal-to-noise ratio of 3. Besides these, the response current followed a linear relationship with the concentration of chlorobenzene and the linear dynamic range (LDR) was denoted in the range of 0.1 nM to 1.0 μM. Moreover, the CBZ sensor was found to exhibit good reproducibility, reliability, stability, and fast response time. Finally, the sensing mechanism was also discussed with the energy-band theory of ternary doped semiconductor materials. The sensing activity of the proposed sensor was significantly enhanced due to the combined result of depletion layer formation at the heterojunction of RuO₂/ZnO/TiO₂ NCs as well as the activity of RuO₂ NPs as oxidation catalysts. The proposed CBZ sensor probe based on ternary oxide RuO₂/ZnO/TiO₂ NCs was developed with significant analytical parameters for practical application in monitoring the environmental pollutants of CBZs for the safety of environmental fields on a large scale.

A novel electrochemical (EC) chlorobenzene (CBZ) sensor was fabricated using a ternary oxide RuO₂/ZnO/TiO₂ nanocomposite (NC)-decorated glassy carbon electrode (GCE).