Effect of copper loadings on product selectivities in microwave-enhanced degradation of phenol on alumina-supported copper oxides

Experimental study of microwave-catalytic oxidative degradation of COD in livestock farming effluent by copper-loaded activated carbon

The problem of massive discharge of livestock wastewater is becoming more and more severe, causing irreversible damage to the ecological environment, and how to treat livestock wastewater efficiently and rapidly deserves to be studied in depth. In this work, CuO/granular activated carbon (GAC) loaded catalysts were prepared and characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), nitrogen adsorption/desorption techniques, and X-ray energy spectroscopy (EDS). The results showed that CuO was successfully attached to the GAC surface with good adsorption performance. The effects of catalyst dosage, H2O2 dosage, initial pH, microwave power and microwave irradiation time in different reaction systems on the degradation efficiency of chemical oxygen demand (COD) in wastewater were investigated, and the orthogonal experiments were used to explore the importance ranking of these factors. The highest degradation rate of COD was found to be enhanced by 12.1% in the reaction system of CuO/GAC, and the initial pH had the greatest effect on the COD removal rate. The combined MW/catalyst/H2O2 method used in this work provided a rapid and effective degradation of COD in wastewater, which can be helpful for reference in other microwave catalytic oxidation studies.

Photocatalytic activity of synthetic ZnO/WO3 nanocomposites immobilized on a Y-zeolite in removal of gas-phase styrene

PURPOSE

The widespread use of styrene along with its harmful effects on human health has led to many studies on how to control and reduce its vapors in the workplace. In this study, efficient removal of styrene molecules in the gas phase was attempted by using Y-ZnO/WO₃ hybrid photocatalysts.

METHODS

ZnO/WO₃ nanocomposites with different WO₃ Wt% were prepared and immobilized on Y-zeolite. The samples' characteristics were evaluated using X-ray diffraction (XRD), energy dispersive X-ray spectrum (EDS), Brunauer-Emmet-Teller (BET) and field emission scanning electron microscopy (FESEM).

RESULTS

The Y- ZnO/WO₃ catalyst exhibits an improved photocatalytic activity as compared to Y-ZnO and Y-zeolite alone. This higher photocatalytic activity of the ZnO/WO₃ supported on Y-zeolite can be attributed to a more efficient interaction of the ZnO/WO₃ with the zeolite leading to higher adsorption capacities. Results reveal that the photocatalyst was highly photoactive in mineralizing styrene. The high activity can be attributed to the synergetic effects of strong UV, ZnO/WO₃ nanocomposite and surface hydroxyl groups. The photocatalytic degradation reaction of styrene with the Y-ZnO/WO₃ follows Langmuir-Hinshelwood kinetics.

CONCLUSIONS

The results of this study indicate that this photocatalyst is suitable for the removal of styrene under UV light. The highest removal efficiency achieved was with Y-ZnO/WO₃ at 2%.

Enhancing the catalytic behaviour of HKUST-1 by graphene oxide for phenol oxidation

The composites of graphite oxide (GrO) and the HKUST-1 framework were synthesized by the typical solvothermal method and applied as heterogeneous catalysts for catalytic wet peroxide oxidation (CWPO) of phenol. XRD, FT-IR, Raman and SEM were conducted to characterize the samples. For catalytic oxidation of 150 mL 100 mg L^-1 phenol, the dose of 30 mg (0.2 g L^-1) catalysts and 0.46 mL H₂O₂ were kept constant. The GrO-3/HKUST-1 (3% content of GrO) showed higher catalytic activity than the HKUST-1 framework and other GrO/HKUST-1 composites with 99% phenol conversion and 86% COD removal efficiency were obtained at 50°C after 30 min and 8 h. The effect of temperature (40-80°C) and pH (4-9) on catalytic oxidation of phenol by GrO-3/HKUST-1 was investigated. The results showed that the degradation of phenol was obtained with optimum efficiency at 60°C with complete phenol conversion and 93% COD reduction. Furthermore, the acid and alkali resistance abilities were enhanced to a certain degree by the integration of GrO compared with the parent framework HKUST-1. Three successive runs were conducted in the natural pH (6.8) of 150 mL 100 mg L^-1 phenol solution which indicated that the synthesized GrO-3/HKUST-1 composite had satisfactory reusability due to the prevention of carbon deposit and negligible Cu²⁺ leaching (8 ppm). The GrO/HKUST-1 composite could be a kind of promising heterogeneous catalysts for catalytic degradation of organic compounds. Similar to other catalysts, the catalytic oxidation of phenol also relies on the formation of hydroxyl radicals.

A novel CWPO/H2O2/VUV synergistic treatment for the degradation of unsymmetrical dimethylhydrazine in wastewater

In this paper, the catalytic wet peroxide oxidation (CWPO) combined with vacuum ultraviolet (VUV) irradiation was developed to mineralize the wastewater with high concentration of unsymmetrical dimethylhydrazine (UDMH), especially to decompose the main byproduct of UDMH decomposition, N-nitrosodimethylamine (NDMA). CuO-NiO-MgO/γ-Al₂O₃ was used as the catalyst and H₂O₂ as the resources of ⋅ O H . Fourier Transform Infrared spectroscopy (FT-IR), X-ray Powder Diffraction (XRD), Scanning Electron Microscopy (SEM) and Energy-Dispersive X-ray spectroscopy (EDX) were employed to evaluate the structure of the catalyst. The treatment performances such as the UDMH degradation efficiency, chemical oxygen demand (COD) removal efficiency, and the concentration of N-nitrosodimethylamine (NDMA) were investigated in the treating process. The optimal conditions were obtained based on the results of single-factor experiments including parameters such as the initial UDMH concentration, catalyst dosage, initial pH, H₂O₂ dosage and temperature. The comprehensive results indicated that CWPO/H₂O₂/VUV process presented remarkable treatment performance to the reaction conditions with about 100% UDMH conversion efficiency, 95.02% COD removal efficiency and approximately 100% UDMH removal within 30 min.

Microwave irradiation directly excites semiconductor catalyst to produce electric current or electron-holes pairs

Generally, photon of Microwave (MW) electromagnetic waves have long been thought to be lower energy, which could not excite metals or semiconductor materials to generate electric current and electron-holes pairs (e⁻_cb + h⁺_vb). In this paper, we report an unexpected, Microwave “photoelectric effect”, when MW irradiates on the semiconductor materials, leading to generate electric current and electron-holes pairs (e⁻_cb + h⁺_vb), on the semiconductor materials and on the MW catalyst. Further, we show that the action mechanism of Microwave “photoelectric effect” made water adsorbing on the surface of Microwave catalyst transform into hydroxyl radical (∙OH). Thus, this study has revealed the principle of generation Microwave “photoelectric effect” under MW irradiation, and the mechanism of MW catalytic oxidation degradation of organic in the wastewater and the mechanism of MW reduction method for preparation of nano-particle metal supported catalysts. Our findings challenge the classic view of MW irradiation only as heating method, which cannot excite to produce electric current and electron-holes pairs (e⁻_cb + h⁺_vb). Our findings will open new field to use MW technology for MW catalytic oxidation degradation of organics in the wastewater, and for MW reduction method of metal supported catalysts preparation.

Microwaves in the Catalytic Valorisation of Biomass Derivatives

The application of microwave irradiation in the transformation of biomass has been receiving particular interest in recent years due to the use of polar media in such processes and it is now well-known that for biomass conversion, and particularly for lignocellulose hydrolysis, microwave irradiation can dramatically increase reaction rates with no negative consequences on product selectivity. However, it is only in the last ten years that the utilisation of microwaves has been coupled with catalysis aiming towards valorising biomass components or their derivatives via a range of reactions where high selectivity is required in addition to enhanced conversions. The reduced reaction times and superior yields are particularly attractive as they might facilitate the transition towards flow reactors and intensified production. As a consequence, several reports now describe the catalytic transformation of biomass derivatives via hydrogenation, oxidation, dehydration, esterification and transesterification using microwaves. Clearly, this technology has a huge potential for biomass conversion towards chemicals and fuels and will be an important tool within the biorefinery toolkit. The aim of this chapter is to give the reader an overview of the exciting scientific work carried out to date where microwave reactors and catalysis are combined in the transformation of biomass and its derivatives to higher value molecules and products.

Highly efficient degradation of 4-nitrophenol over the catalyst of Mn2O3/AC by microwave catalytic oxidation degradation method

A new microwave catalytic oxidation process based on two kinds of catalysts, the commercially available activated carbon (AC) and Mn2O3 nanoparticle modified AC (Mn2O3/AC), was reported for the degradation of 4-nitrophenol (4-NP) without adding any oxidant. Effects of microwave power, catalyst dosage, irradiation time, and initial concentration for the degradation efficiency were studied. Results indicated that catalyst of Mn2O3/AC showed much higher catalytic activity than pure AC and Mn2O3 particles. Significantly, 4-NP degradation efficiency reached 99.6%, corresponding to 93.5% TOC removal under optimal conditions with microwave power of 400W, Mn2O3/AC dosage of 2g, reaction time of 5min, and initial concentration of 100mg/L. Hydroxyl radicals (OH) generated during catalytic reaction is the main oxidant, and O2 can not effectively improve removal rate. We proposed the microwave 'photoelectric effect' to interpret the generation of OH in view that microwave irradiation can directly excite the catalyst to produce electron-hole pairs and then transform H2O into OH on the surface of catalyst in solution. The obtained kinetic equation for microwave catalytic oxidation degradation of 4-NP was in line with pseudo-first-order kinetic model, that is, apparent rate constant increased as microwave power density increase.

Polymer-templated mesoporous hybrid oxides of Al and Cu: highly porous sorbents for ammonia

Hybrid mesostructures consisting of copper and aluminum oxides were synthesized via co-condensation of suitable precursors in the presence of a triblock copolymer, Pluronic F127.

Catalyst for the degradation of 1,1-dimethylhydrazine and its by-product N-nitrosodimethylamine in propellant wastewater

A three-component metal catalyst was prepared and used in the process of catalytic wet peroxide oxidation (CWPO) for the degradation of unsymmetrical dimethylhydrazine (UDMH) in propellant wastewater with H₂O₂.

Degradation of phenol by air and polyoxometalate nanofibers using a continuous mode

K₅PMo₁₀V₂O₄₀/PAN nanofibers, synthesized by an electrospinning technique, were used as catalysts in phenol degradation by air under room temperature in a continuous mode. 100% degradation efficiency of phenol and 94.5% TOC removal have been achieved.