Mechanism for the elimination of pollutants from aqueous solutions adopting NiR2O4 (R = Fe, Cr and Al) with microwave energy

Current status of applying microwave-associated catalysis for the degradation of organics in aqueous phase - A review

Interactions between microwaves and certain catalysts can lead to efficient, energy-directed convergence of a relatively dispersed microwave field onto the reactive sites of the catalyst, which produces thermal or discharge effects around the catalyst. These interactions form "high-energy sites" (HeS) that promote energy efficient utilization and enhanced in situ degradation of organic pollutants. This article focuses on the processes occurring between microwaves and absorbing catalysts, and presents a critical review of microwave-absorbing mechanisms. This article also discusses aqueous phase applications of relevant catalysts (iron-based, carbon-based, soft magnetic, rare earth, and other types) and microwaves, special effects caused by the dimensions and structures of catalytic materials, and the optimization and design of relevant reactors for microwave-assisted catalysis of wastewater. The results of this study demonstrate that microwave-assisted catalysis can effectively enhance the degradation rate of organic compounds in an aqueous phase and has potential applications to a variety of engineering fields such as microwave-assisted pyrolysis, pollutant removal, material synthesis, and water treatment.

Detoxification of municipal solid waste incinerator (MSWI) fly ash by single-mode microwave (MW) irradiation: Addition of urea on the degradation of Dioxin and mechanism

The detoxification of municipal solid waste incinerator (MSWI) fly ash dioxins urgently requires an effective treatment technology. In this study, we adopted a single-mode microwave (MW)-based pyrolysis to treat MSWI fly ash under N₂ atmosphere and further elucidated the main influencing factors, including the chemical inhibitor, for dioxin control. The results show that (1) the detoxification process was optimized with a mass ratio of fly ash to SiC of 1:9, 23.1% (wt%) urea addition and pyrolysis temperature of ˜ 480 °C; (2) the total polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) destruction efficiency and the bioassay-derived 2,3,7,8-TCDD toxic equivalent (Bio-TEQ) removal efficiency reached 98.5% and 97.9%, respectively, accompanied with ˜ 1.3% of the total amount of dioxin being submitted to exhaust gas; (3) the MW-based pyrolysis of urea (133˜300 °C) was favourable for the generation of hot spots as well as the PCDD/F rapid destruction in fly ash. In addition, the leaching toxicity of heavy metals was also partially reduced after MW pyrolysis reactions. To the best of our knowledge, this is the first report adopting a MW-based pyrolysis to eliminate dioxin in MSWI fly ash with the addition of urea, which is a promising alternative to current methods.

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.