Adsorption and thermal degradation of microplastics from aqueous solutions by Mg/Zn modified magnetic biochars.

Microplastics (MPs) derived from plastic wastes have attracted wide attention throughout the world due to the wide distribution, easy transition, and potential threats to organisms. This study proposes efficient Mg/Zn modified magnetic biochar adsorbents for microplastic removal. For polystyrene (PS) microspheres (1 µm, 100 mg/mL) in aqueous solution, the removal efficiencies of magnetic biochar (MBC), Mg modified magnetic biochar (Mg-MBC), and Zn modified magnetic biochar (Zn-MBC) were 94.81%, 98.75%, and 99.46%, respectively. It is supposed that the adsorption process was a result of electrostatic interaction and chemical bonding interaction between microplastics and biochar. The coexisting H2PO4- and organic matters in real water significantly affected the removal efficiency of Zn-MBC due to competitive adsorption effect. Microplastic degradation and adsorbent regeneration were accomplished by thermal treatment simultaneously. The degradation of adsorbed MPs was promoted by the catalytic active sites originated from Mg and Zn, releasing adsorption sites. Thermal regeneration maintained the adsorption capability. Even after five adsorption-pyrolysis cycles, MBC (95.02%), Mg-MBC (94.60%), and Zn-MBC (95.79%) showed high microplastic removal efficiency. Therefore, the low-cost, eco-friendly, and robust Mg/Zn-MBCs have promising potential for application in microplastic removal.

Nanostructure and reactivity of soot particles from open burning of household solid waste.

The main purpose of this work was to quantify and characterize chemically and morphologically the emission of soot particles from the open burning of several common solid waste including paperboard, wood, peel, chemical fiber, polyethylene (PE) and polyvinyl chloride (PVC). The experiment was conducted in a laboratory-scale open-burning combustor with a dilution sampling system to obtain soot particles. The thermogravimetric profiles (TGA) showed an increasing order of oxidation reactivity: PE > PVC > fiber > paper ≈ peel > wood. High resolution transmission electron microscopy (HRTEM) images revealed more detailed information about the morphology and the particle size of soot aggregates. Subsequent quantification of nanostructure by fringe analysis showed that plastics generated soot particles with the looser carbon layers with higher tortuosity compared to the three kind of biomass. Raman spectroscopy further confirms the observed differences. In addition, wood soot exhibited the highest content of C-OH group (17.5%) among the six samples (X-Ray photoelectron spectroscopy, XPS), whereas PE and PVC soot exhibited the highest absorption peaks of aliphatic C-H groups (Fourier transform infrared spectroscopy, FTIR). Comparative analysis revealed that the interlayer distance was more important on the evaluation of reactivity than soot morphologies. The present work concluded that the physiochemical characteristics of soot particles releasing during open burning are strongly depending on waste composition and provided new data for the understanding of soot emissions from open burning.

Co-carbonization of biomass and oily sludge to prepare sulfamethoxazole super-adsorbent materials.

Different biomass materials (walnut shell, coconut shell or cottonwood sawdust) were co-pyrolyzed with carbon-enriched oily sludge to produce aqueous phase sulfamethoxazole (SMZ) adsorption materials. The co-pyrolysis char was activated with K2CO3 to modify its micro-structure and functional groups. Results show that ACs prepared from the mixture contained more mesopores than biomass-based ACs, more porous and higher yield than oily sludge-based ACs. One-step activation method was more attractive than two-step activation in larger specific surface area (up to almost 4 times), wider pore size distribution (2-3 nm), stronger SMZ adsorption ability (higher than 2 times). The maximum BET surface area was 1342 m2/g for the ACs prepared from the mixture of walnut shell and oily sludge by one-step activation and it had the maximum SMZ adsorption capacity up to 361.9 mg/g, which is higher than previous reported values. The capacity of SMZ adsorption of ACs was mainly attributed to pore size distribution, specific surface area and functional groups. Among them, the appropriate content of CO and CO functional groups, larger specific area and more pores range from 2 to 3 nm lead to higher adsorption capacity.

Catalytic decomposition of gaseous 1,2-dichlorobenzene over CuOx/TiO2 and CuOx/TiO2-CNTs catalysts: Mechanism and PCDD/Fs formation.

Gaseous 1,2-dichlorobenzene (1,2-DCBz) was catalytically decomposed in a fixed-bed catalytic reactor using composite copper-based titanium oxide (CuOx/TiO2) catalysts with different copper ratios. Carbon nanotubes (CNTs) were introduced to produce novel CuOx/TiO2-CNTs catalysts by the sol-gel method. The catalytic performances of CuOx/TiO2 and CuOx/TiO2-CNTs on 1,2-DCBz oxidative destruction under different temperatures (150-350 °C) were experimentally examined and the correlation between catalyst structure and catalytic activity was characterized and the role of oxygen in catalytic reaction was discussed. Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) generation during 1,2-DCBz catalytic oxidation by CuOx/TiO2-CNTs composite catalyst was also examined. Results indicate that the 1,2-DCBz destruction/removal efficiencies of CuOx (4 wt%)/TiO2 catalyst at 150 °C and 350 °C with a GHSV of 3400 h(-1) are 59% and 94% respectively and low-temperature (150 °C) catalytic activity of CuOx/TiO2 on 1,2-DCBz oxidation can be improved from 59 to 77% when CNTs are introduced. Furthermore, oxygen either in catalyst or from reaction atmosphere is indispensible in reaction. The former is offered to activate and oxidize the 1,2-DCBz adsorbed on catalyst, thus can be generally consumed during reaction and the oxygen content in catalyst is observed lost from 39.9 to 35.0 wt% after reacting under inert atmosphere; the latter may replenish the vacancy in catalyst created by the consumed oxygen thus extends the catalyst life and raises the destruction/removal efficiency. The introduction of CNTs also increases the Cu(2+)/Cu(+) ratio, chemisorbed oxygen concentration and surface lattice oxygen binding energy which are closely related with catalytic activity. PCDD/Fs is confirmed to be formed when 1,2-DCBz catalytically oxidized by CuOx/TiO2-CNTs composite catalyst with sufficient oxygen (21%), proper temperature (350 °C) and high concentration of 1,2-DCBz feed (120 ppm).

[Study on the optical properties of flame soot in the terahertz spectra domain].

Flame soot is an import product as a result of incomplete combustion of hydrocarbon fuels, and has important effect on the generation of some pollutant. The optical properties of the soot are the base for the optical combustion diagnostics. Terahertz time-domain spectroscopy technique was used to study the optical properties of the soot within 0.2-1.6 THz and the frequency-domain spectra were obtained through Fourier transform. The complex refractive index of the soot was deduced by the fixed-point iteration. The comparison of the complex refractive index between terahertz spectra domain and thermal radiation spectra domain was conducted and two methods of extracting the parameters were also compared. The results indicated that the soot has strong absorption in the studied spectra and the difference in the refractive index between the two spectra domains was not obvious, but the absorptive index variation in the thermal radiation spectra domain was larger. The difference between the two parameter extraction methods was not significant. The deduced results can provide the optical data of soot for the application of terahertz time-domain spectroscopy technique to the optical combustion diagnostics, and extend the optical combustion diagnostics application area.