Herein, polyethylenimine (PEI)-grafted nitrogen (N)-doping magnetic biochar (PEIMW@MNBCBM) was synthesized, and characterization results showed that the microwave-assisted PEI grafting and ball milling-assisted N doping introduced abundant amino, pyridine N and pyrrole N structures onto biochar, which possessed high affinity to Cr(VI) in the anion form. The as-prepared PEIMW@MNBCBM displayed pH-dependence adsorption performance and high tolerance to co-existing ions with maximum uptake capacity of Cr(VI) identified as 183.02 mg/g. Furthermore, PEIMW@MNBCBM could bind Cr(VI) through electrostatic attraction, complexion, precipitation, reduction and pore filling. Especially, effective reduction of Cr(VI) was ascribed to cooperative electron transfer of partial oxygen-containing functional groups, intramolecular pyridine/pyrrole N, protonated amino and Fe²⁺ on the adsorbent, while oxygen-containing and amino functional groups from N-doping biochar and PEI synergistically complexed Cr(III) via providing lone pair electrons to form coordinate bonds. Furthermore, the stable precipitation was formed between Fe³⁺ and Cr(III). Additionally, the Cr(VI) elimination efficiency could maintain 95.83% even after four adsorption-desorption cycles, suggesting PEIMW@MNBCBM as a high-performance adsorbent for Cr(VI) contaminated water remediation.

Plastics are produced and used in large quantities worldwide (e.g. as food packaging). In line with this, plastic particles are found throughout the ecosphere and in various foods. As a result, plastics are also present in energy-rich waste biomass derived from the food industry, supermarkets, restaurants, etc. These waste streams are a valuable source for biogas production but can also be used to feed insects that in turn upcycle it into new high-value biomass. In both applications, the remaining residue can be used as fertilizer. Due to the present plastic particles, these applications could pose a continued threat to the environment, and both human and animal health. Therefore, the need of determining the (micro)plastic content to assess the potential danger is rising. In this research, a closed-vessel microwave-assisted acid digestion method was developed to accurately determine meso- and microplastic contents in food (waste) matrices by solubilising this food matrix. Polyvinyl chloride (PVC) food packaging foil was used to develop the method, using a full factorial design with three parameters (nitric acid concentration (c(HNO₃)), temperature (T), and time (t)). According to this model, the best practical conditions were c(HNO₃) = 0.50 mol/L, T = 170 °C, and t = 5.00 min. Subsequently, the method was tested on five other plastics, namely high- and low-density polyethylene (HDPE and LDPE), polypropylene (PP), polystyrene (PS), and polyethylene terephthalate (PET), mixed with a food matrix, resulting in a mean plastic recovery of 102.2 ± 4.1%. Additionally, the polymers were not oxidised during the microwave digestion. For PVC and PS hardly any degradation was found, while HDPE, LDPE, and PP showed slight chain degradation, although without recovery loss. In conclusion, the method is an accurate approach to quantify the total meso- and microplastic content in food (waste) matrices with minimal change in their intrinsic characteristics.

As persulfate activator, Metal organic frameworks (MOFs) and derivatives are widely concerned in degradation of emerging environmental pollutants by advanced oxygen technology dominated by sulfate radical (▪) (SR-AOPs). However, the poor stability and low catalytic efficiency limit the performance of MOFs, requiring multiple strategies to further enhance their catalytic activity. The aim of this paper is to improve the catalytic activity of MOFs and their derivatives by physical and chemical enhancement strategies. Physical enhancement strategies mainly refer to the activation strategies including thermal activation, microwave activation and photoactivation. However, the physical enhancement strategies need energy consumption and require high stability of MOFs. As a substitute, chemical enhancement strategies are more widely used and represented by optimization, modification, composites and derivatives. In addition, the identification of reactive oxygen species, active site and electron distribution are important for distinguishing radical and non-radical pathways. Finally, as a new wastewater treatment technology exploration of unknown areas in SR-AOPs could better promote the technology development.

Polycyclic aromatic hydrocarbons (PAHs) in soil can be recalcitrant to solvent extraction after aging. We showed in this study that mixing a small amount of water in the extracting solvent during microwave-assisted extraction (MAE) can release recalcitrant PAHs, resulting in significant improvement in the analyzed concentrations. The improvement factor (F) for the total of 16 priority PAHs (∑PAH16) listed by the United States Environmental Protection Agency was 1.44–1.55 for field soils. By comparing the F values for different soil organic components, we demonstrated that the recalcitrant PAHs were primarily associated with biochar, humic acid (HA), and humin (HM), with the F values for ∑PAH16 of 1.94, 6.62, and 4.59, respectively. The results showed that the recalcitrant PAHs comprised a sequestered fraction and a desorption-limited fraction. NMR spectra showed that water worked alone at elevated temperature to promote hydrolysis of biochar and destroy the macromolecular structure, thus causing the release of the otherwise sequestered PAHs during MAE. The substantial reduction in F values for HA and HM after demineralization indicated sequestration of PAHs in organic-mineral complexes, which can be destroyed by hot water treatment. The release of the sequestered fraction was nonselective and independent of compound hydrophobicity. In comparison, the release of the desorption-limited fraction was positively affected by the hydrophobicity of PAHs and was facilitated by the presence of water in the extracting solvent. The results of this study provide important insights into the sequestration and release of recalcitrant PAHs in soil.

Benzothiazoles (BTHs), benzotriazoles (BTRs), and benzenesulfonamides (BSAs) are chemicals used in several industrial and household applications. Despite these compounds are emerging pollutants, there is still a lack of information about their presence in outdoor air samples. In this paper, we developed a new method for the quantification of BTHs, BTRs, and BSAs in airborne particulate matter (PM₁₀). The extraction of fourteen analytes from PM₁₀ was accomplished by microwave-assisted extraction (MAE) using an environmentally friendly mixture of water and ethanol. SPME was used to analyze the target compounds from the MAE extract by gas chromatography-tandem mass spectrometry (SPME-GC-MS/MS), eliminating additional sample clean-up steps. The best working conditions for MAE and SPME were examined multivariately by experimental design techniques. The target compounds were quantified in selected reaction monitoring acquisition mode. The proposed method was carefully validated, and the achieved results were satisfactory in terms of linearity, lower limit of quantification (picograms per cubic meter), intra- and inter-day accuracy (81–118% and 82–114%, respectively), and precision (repeatability and reproducibility in the range 2.3–17% and 7.4–19%, respectively). The application in a real monitoring campaign showed that the developed protocol is a valuable and eco-friendly alternative to the methods proposed so far.

Understanding the migration and conversion of nitrogen in wood-based panels (WBPs) during pyrolysis is fundamentally important for potentially transforming the N-containing species into valuable material-based products. This review firstly summarizes the commonly used methods for examining N evolution during the WBPs pyrolysis before probing into the association between the wood and adhesives.The potential effects of wood-adhesive interaction on the pyrolysis process are subsequently analyzed. Furthermore, the controversial statements from literature on the influence of adhesives on wood pyrolysis behavior are discussed, which is followed by the detailed investigation into the distribution and evolution of N-containing species in gas, liquid and char, respectively, during WBPs pyrolysis in recent studies. The differences in N species due to the heating sources (i.e. electrical heating vs microwave heating) are particularly compared. Finally, based on the characteristics of staged pyrolysis, co-pyrolysis and catalytic pyrolysis, the converting pathways for WBPs are proposed with an emphasis on the production of value-added chemicals and carbon materials, simultaneously mitigating NOₓ emission.

The present work reports microwave-assisted synthesis of SnO₂ nanoparticles via green route using Psidium Guajava extract. For the enhancement of catalytic activity, nanohybrids of SnO₂ were formulated using different ratios of polyaniline (PANI) via ultrasound-assisted chemical polymerization. Formation of nanohybrids was confirmed via IR and XPS studies. The UV–vis DRS spectra of PANI/SnO₂ revealed significant reduction in the optical band gap upon nanohybrid formation. Microwave-assisted catalytic efficiency of pure SnO₂, PANI, PANI/SnO₂ nanohybrids was investigated using DDT as a model persistent organic pollutant. The degradation efficiency of PANI/SnO₂ was found to increase with the increase in the loading of PANI. Around 87% of DDT degradation was achieved within a very short period of 12 min under microwave irradiation using PANI/SnO₂-50/50 as catalyst. The effect of DDT concentration was explored and the degradation efficiency of PANI/SnO₂-50/50 catalyst was noticed to be as high as 82% in presence of 100 mg/L of DDT. The effect of microwave power on the degradation efficiency revealed 79% degradation using the same nanohybrid when exposed to microwave irradiation for 5 min under 1110 W microwave power. Scavenging studies confirmed the generation of OH, O₂⁻ radicals. The fragments with m/z values as low as 86 and 70 were confirmed by LCMS analysis. Recyclability tests showed that PANI/SnO₂-50/50 nanohybrid exhibited 81% degradation of DDT (500 mg/L) even after the third cycle, which reflected high catalytic efficiency as well as remarkable stability of the catalyst. This green nanohybrid could therefore be effectively utilized for the rapid degradation of persistent organic pollutants.

The process improvement, a pilot remediation test and the decontamination mechanism of microwave-induced steam distillation (MISD) for petroleum hydrocarbons (PHs) removal were conducted. Processes of multistage steam distillation and carbon reinforcement were compared to determine the best remediation process. Pilot project was then carried out to explore the applicability of MISD in site-scale remediation. The remediation efficiency, procedures and influencing factors of site-scale MISD project were studied by monitoring variations of soil moisture, temperature and PHs concentrations. Furthermore, the decontamination mechanisms of PHs were clarified based on kinetic analysis. The results showed that the multistage steam distillation could improve 10%∼15% remediation efficiency, and the carbon reinforcement could shorten remediation duration of each steam distillation stage by 50%. Pilot MISD project adopted multistage steam distillation process and went through four (initial, rapid heating-up, gentle heating-up and quasi-equilibrium) remediation stages (overall temperature ≤100 °C). The final PHs removal rate was about 60%, which would get better with greater proportion of low boiling points components and stronger vapor extraction. Kinetic studies showed that PHs was removed by steam stripping and limited by intraparticle diffusion in the “steam distillation zone”, while local high temperature (＞100 °C) greatly improved PHs volatilization and provided activation energy for PHs desorbed and degraded in the “selective heating zone".

Rare earth elements have been increasingly used in modern societies and soils are likely to be the final destination of several REE-containing (by)products. This study reports REE contents for topsoils (0–20 cm) of 175 locations in reference (n = 68) and cultivated (n = 107) areas in Brazil. Benchmark soil samples were selected accomplishing a variety of environmental conditions, aiming to: i) establishing natural background and anthropogenic concentrations for REE in soils; ii) assessing potential contamination of soils - via application of phosphate fertilizers - with REE; and, iii) predicting soil-REE contents using biomes, soil type, parent material, land use, sand content, and biomes-land use interaction as forecaster variables through generalized least squares multiple regression. Our hypotheses were that the variability of soil-REE contents is influenced by parent material, pedogenic processes, land use, and biomes, as well as that cultivated soils may have been potentially contaminated with REE via input of phosphate fertilizers. The semi-total concentrations of REE were assessed by inductively coupled plasma mass spectrometry (ICP-MS) succeeding a microwave-assisted aqua regia digestion. Analytical procedures followed a rigorous QA/QC protocol. Soil physicochemical composition and total oxides were also determined. Natural background and anthropogenic concentrations for REE were established statistically from the dataset by the median plus two median absolute deviations method. Contamination aspects were assessed by REE-normalized patterns, REE fractionation indices, and Ce and Eu anomalies ratios, as well as enrichment factors. The results indicate that differences in the amounts of REE in cultivated soils can be attributed to land use and agricultural sources (e.g., phosphate-fertilizer inputs), while those in reference soils can be attributed to parent materials, biomes, and pedogenic processes. The biomes, land use, and sand content helped to predict concentrations of light REE in Brazilian soils, with parent material being also of special relevance to predict heavy REE contents in particular.

Inductively coupled plasma – mass spectrometry (ICP-MS) analysis of airborne particulate bound mercury was carried out utilizing a high sulfur containing organic compound as a preservation agent to limit the negative bias that affects the determination of low levels of mercury. Between 600% and 1000% more Hg was detected with the use of the additive, lithium tetrathiafulvalene carboxylate (LiCTTF), during the microwave assisted acid digestion sample processing step without influencing the determination of other trace elements. The average Hg concentration was 0.05 ng m⁻³ and 0.4 ng m⁻³ in the absence and presence of LiCTTF, respectively. Stabilization of the mercury ions with the preservation agent resulted in higher precision for ICP-MS measurements with relative standard deviation (RSD) values ranging from 1.07% to 4.36%. The results obtained in this study emphasize the necessity of using a preservation agent in the atomic spectroscopic determination of mercury to prevent losses and is especially critical in low-level analyses such as those routinely performed in environmental mercury pollution trend assessments.