This study focused on the ion release and microstructure of slag during its degradation following erosion by different pH solutions. It focused on controlling factors such as slag particle size range, pH value of the solution, and soaking time. The surface microstructure and particle size distribution of slag with the particle size of 0.075–5.0 mm, the mineral composition of suspended pollutants larger than 0.45 μm, and the phenomenon of nano-scale ion release were examined. When slag was soaked in solutions with different pH values for 30 days, the pH value of leachate tended to be neutral, the release amount of Ca, Mg, Fe, and Cd ions increased and the release rate gradually decreased. The dissolution process of slag in the alkaline solution was slower than that in acid, but suspension and gels formed more easily in an alkaline environment. Nitric acid accelerated the chemical reaction of akermanite, gehlenite, and hawleyite, and released Ca, Mg, and Cd ions. There were clear damage cracks and various irregular pores on the slag surface. Under the attack of alkali solution, the weight of akermanite in slag increased, the Mg ion content in solution decreased, and the suspended solids of calcite and portlandite increased. At pH 12, unlike at pH 3, there were no large surface cracks in the slag and the interface damage was small. Compared with pH 7, there were more irregular substances, such as flakes and spheres. The particle size of slag was mainly 0.1–0.5 mm, the content before and after leaching was 52.80%–55.87% and 55.00%–58.27%, and the slag was in a poor grading state. The findings of this study act as an important reference for understanding the influence of slag leaching on water and soil pollution.

Garden pruning waste is becoming a problem that intensifies the garbage siege. It is of great significance to purify polluted water using biochar prepared from garden pruning waste. Herein, the interaction mechanism between BPS and oriental plane tree biochar (TBC) with different surface functional groups was investigated by adsorption experiments, spectroscopic analysis and theoretical calculations. Adsorption kinetics and isotherm of BPS on TBC can be satisfactorily fitted into pseudo-second-order kinetic and Langmuir models, respectively. A rapid adsorption kinetic toward BPS was achieved by TBC in 15 min. As compared with TBC prepared at low temperature (300 °C) (LTBC), the maximum adsorption capacity of TBC prepared at high temperature (600 °C) (HTBC) can be significantly improved from 46.7 mg g⁻¹ to 72.9 mg g⁻¹. Besides, the microstructure and surface functional groups of HTBC were characterized using SEM, BET-N₂, and XPS analysis. According to density functional theory (DFT) theoretical calculations, the higher adsorption energy of HTBC for BPS was mainly attributed to π-π interaction rather than hydrogen bonding, which was further supported by the analysis of FTIR and Raman spectra as well as the adsorption thermodynamic parameters. These findings suggested that by improving π-π interaction through high pyrolysis temperature, BPS could be removed and adsorbed by biochar with high efficacy, cost-efficiency, easy availability, and carbon-negative in nature, contributing to global carbon neutrality.

In order to study the effect of cadmium ions on the mechanical properties and micro-structure characteristics of the red clay in Guilin, we have conducted triaxial test and the scanning electron microscope tests to analyze the effects of cadmium ion concentration and the number of dry and wet cycles on the mechanical properties and micro-structure changes of the red clay. The results showed the effects of cadmium ions and dry-wet cycles destroy the structure of red clay. The cohesive force of red clay decreases with the increase of cadmium ion concentration, and the internal friction angle first increases and then decreases. With the rise in the number of dry and wet cycles, the cohesive force of cadmium-contaminated red clay first increases and then decreases, and the angle of internal friction rises gradually. Under the action of different cadmium ion concentrations, the stress-strain curve is strain hardening. With the concentration of cadmium ions increases, the strain hardening becomes more apparent; the peak value reached faster. and the axial strain corresponding to the peak value of the line decreases. With the increase in the number of wet and dry cycles, the volume of cadmium-contaminated red clay shrinks and its compactness increases; it gets the peak shear strength faster during the shearing process, and its peak value becomes larger and larger. The main reason for the phenomenon is that cadmium ions destroy the cementation between the particles. The soil particles are mainly in point contact which loosens the structure of the soil; on the other hand, the thickness of the surface diffusion layer of the clay particles increases through chemical action, The exchange of cations increases the porosity of the soil and weakens its strength. The dry-wet cycle shrinks the volume of the red clay, and the soil particles are mainly in surface contact; as the number of dry-wet cycles increases, the soil particles connection is closer, the soil porosity decreases and the strength increases.

The mechanisms of soot’s photochemistry are still unclear, especially, how the microstructure and composition of soot influence its photoactivity. In the current study, we started with the exploration of the microstructure of soot particles and gained new insights. The elemental-carbon fraction of soot (E-soot), considered the core component of soot and can reflect the intrinsic characteristics of soot, was extracted by organic solvents and characterized in terms of structure and chemical reactivity. The intrinsic structure of E-soot was found to be more analogous to reduced graphene oxide than to graphene, in terms of containing similar levels of defective sites such as oxygen-containing functional groups and environmentally persistent free radicals, as well as exhibiting similar optoelectronic performance. The generation of reactive oxygen species via an electron transfer pathway under visible light suggests that reduced graphene oxide-like E-soot can serve as a potential carbo-photocatalyst, which facilitates elucidating the mechanism of E-soot’s role during soot’s photochemical aging. Our study reveals the intrinsic structure of soot and its role in photo-triggered reactive oxygen species production, which is vital for atmospheric and health effects.

Converting biomass waste into biochar by slow pyrolysis with subsequent soil amendment is a prospective approach with multiple environmental benefits including soil contamination remediation, soil amelioration and carbon sequestration. This study selected cow manure as precursor to produce biochar under 300 °C, 400 °C, 500 °C and 600 °C, and a remarkable promotion of carbon (C) retention in biochar by incorporation of exogenous Ca was achieved at all investigated pyrolysis temperatures. The C retention was elevated from 49.2 to 68.3% of pristine biochars to 66.1–79.7% of Ca-composite biochars. It was interesting that extent of this improvement increased gradually with rising of pyrolysis temperature, i.e., doping Ca in biomass promoted pyrolytic C retention in biochar by 16.6%, 23.4%, 29.1% and 31.1% for 300 °C, 400 °C, 500 °C and 600 °C, respectively. Thermogravimetric-mass spectrometer (TG-MS) and X-ray photoelectron spectroscopy (XPS) showed that Ca catalyzed thermal-chemical reactions and simultaneously suppressed the release of small organic molecular substances (C₂–C₇) via physical blocking (CaO, CaCO₃, and CaClOH) and chemical bonding (CO and OC–O). The catalyzation mainly occurred at 200–400 °C, while the suppression was more prominent at higher temperatures. Raman spectra and 2D FTIR analysis on biochar microstructure showed that presence of Ca had negative influence on carbon aromatization and thus weakened biochar's stability, while increasing pyrolysis temperature enhanced the stability of carbon structure. Finally, with integrating “C retention” during pyrolysis and “C stability” in biochar, the maximum C sequestration (56.3%) was achieved at 600 °C with the participation of Ca. The study highlights the importance of both Ca and pyrolysis temperature in enhancing biochar's capacity of sequestrating C.

Biochar has been proven as a soil amendment to improve soil environment. However, mechanistic understanding of biochar on soil physical properties and microbial community remains unclear. In this study, a wood biochar (WB), was incorporated into a highly weathered tropical soil, and after 1 year the in situ changes in soil properties and microbial community were evaluated. A field trial was conducted for application of compost, wood biochar, and polyacrylamide. Microstructure and morphological features of the soils were characterized through 3D X-ray microscopy and polarized microscopy. Soil microbial communities were identified through next-generation sequencing (NGS). After incubation, the number of pores and connection throats between the pores of biochar treated soil increased by 3.8 and 7.2 times, respectively, compared to the control. According to NGS results, most sequences belonged to Anaerolinea thermolimosa, Caldithrix palaeochoryensis, Chthoniobacter flavus, and Cohnella soli. Canonical correlation analysis (CCA) further demonstrated that the microbial community structure was determined by inorganic N (IN), available P (AP), pH, soil organic C (SOC), porosity, bulk density (BD), and aggregate stability. The treatments with co-application of biochar and compost facilitated the dominance of Cal. palaeochoryensis, Cht. flavus, and Coh. soli, all of which promoted organic matter decomposition and ammonia oxidation in the soil. The apparent increases in IN, AP, porosity, and SOC caused by the addition of biochar and compost may be the proponents of changes in soil microbial communities. The co-application of compost and biochar may be a suitable strategy for real world biochar incorporation in highly weathered soil.

China has been faced with severe haze pollution, which is hazardous to human health. Among the air pollutants, PM2.5 (particles with an aerodynamic diameter ≤ 2.5 μm) is the most dangerous because of its toxicity and impact on human health and ecosystems. However, there has been limited research on PM2.5 particle toxicity. In the present study, we collected daily PM2.5 samples from January 1 to March 31, 2018 and selected samples to extract water-soluble species, including SO42−, NO3−, WSOC, and NH4+. These samples represented clean, good, slight, moderate, and heavy pollution days. After extraction using an ultrasonic method, PM2.5 solutions were obtained. We used Chlorella as the test algae and studied the content of chlorophyll a, as well as the variation in fluorescence when they were placed into the PM2.5 extraction solution, and their submicroscopic structure was analyzed using transmission electron microscopy (TEM). The results showed that when the air quality was relatively clean and good (PM2.5 concentration ≤ 75 μg m−3), the PM2.5 extraction solutions had no inhibiting effects on Chlorella, whereas when the air quality was polluted (PM2.5 concentration > 75 μg m−3) and heavily polluted (PM2.5 concentration > 150 μg m−3), with increasing PM2.5 concentrations and exposure time, the chlorophyll a content in Chlorella decreased. Moreover, the maximum photochemical quantum yield (Fv/Fm) of Chlorella obviously decreased, indicating chlorophyll inhibition during polluted days with increasing PM2.5 concentrations. The effects on the chlorophyll fluorescence parameters were also obvious, leading to an increase of energy dissipated per unit reaction center (DIo/RC), suggesting that Chlorella could survive when exposed to PM2.5 solutions, whereas the physiological activities were significantly inhibited. The TEM analysis showed that there were few effects on Chlorella cell microstructure during clean days, whereas plasmolysis occurred during light- and medium-polluted days. With increasing pollution levels, plasmolysis became more and more apparent, until the organelles inside the cells were thoroughly destroyed and most of the parts could not be recognized.

A massive and dense textured layer (ca. 35–50 cm thick) of hardpan was uncovered at the top layer, which capped the unweathered sulfidic Cu-Pb-Zn tailings in depth and physically supported gravelly soil root zones sustaining native vegetation for more than a decade. For the purpose of understanding functional roles of the hardpan layer in the cover profile, the present study has characterized the microstructures of the hardpan profile at different depth compared with the tailings underneath the hardpans. A suit of microspectroscopic technologies was deployed to examine the hardpan samples, including field emission-scanning electron microscopy coupled with energy dispersive spectroscopy (FE-SEM-EDS), X-ray diffraction (XRD) and synchrotron-based X-ray absorption fine structure spectroscopy (XAFS). The XRD and Fe K-edge XAFS analysis revealed that pyrite in the tailings had been largely oxidised, while goethite and ferrihydrite had extensively accumulated in the hardpan. The percentage of Fe-phyllosilicates (e.g., biotite and illite) decreased within the hardpan profile compared to the unweathered tailings beneath the hardpan. The FE-SEM-EDS analysis showed that the fine-grained Ca-sulfate (possibly gypsum) evaporites appeared as platelet-shaped that deposited around pyrite, dolomite, and crystalline gypsum particles, while Fe-Si gels exhibited a needle-like texture that aggregated minerals together and produced contiguous coating on pyrite surfaces. These microstructural findings suggest that the weathering of pyrite and Fe-phyllosilicates coupled with dolomite dissolution may have contributed to the formation of Ca-sulfate/gypsum evaporites and Fe-Si gels. These findings have among the first to uncover the microstructure of hardpan formed at the top layer of sulfidic Cu-Pb-Zn tailings, which physically capped the unweathered tailings in depth and supported root zones and native vegetation under semi-arid climatic conditions.

Graphene oxide (GO) may strongly interact with toxic metal ions and mineral particles upon release into the soil environment. We evaluated the mutual effects between GO and Ni (Ni(II)) with regard to their adsorption and co-adsorption on two minerals (goethite and hematite) in aqueous phase. Results indicated that GO and Ni could mutually facilitate the adsorption of each other on both goethite and hematite over a wide pH range. Addition of Ni promoted GO co-adsorption mainly due to the increased positive charge of minerals and cation–π interactions, while the presence of GO enhanced Ni co-adsorption predominantly due to neutralization of positive charge and strong interaction with oxygen-containing functional groups on adsorbed GO. Increasing adsorption of GO and Ni on minerals as they coexist may thus reduce their mobility in soil. Extended X-ray absorption fine structure (EXAFS) spectroscopy data revealed that GO altered the microstructure of Ni on minerals, i.e., Ni formed edge-sharing surface species (at RNᵢ₋Fₑ∼3.2 Å) without GO, while a GO-bridging ternary surface complexes (at RNᵢ₋C∼2.49 Å and RNᵢ₋Fₑ∼4.23 Å) was formed with GO. These findings improved the understanding of potential fate and toxicity of GO as well as the partitioning processes of Ni ions in aquatic and soil environments.

This paper investigated the impacts of various real microplastics (MPs), i.e., polyethylene (PE) and polyethylene terephthalate (PET) with different sizes (1000–2000 and 100–200 μm) and different dosages (0.5 and 5% on a dry weight basis), on the toluene removal during the thermally enhanced air injection treatment. First, microscopic tests were carried out to determine the MPs' microstructure and behavior. The PE was mainly a small block, and PET appeared filamentous and sheeted with a larger slenderness ratio. Second, the interactions between MPs and toluene-contaminated soils were revealed by batch adsorption equilibrium experiments and low-field magnetic resonance. The morphological differences and dosage of the MPs impacted soils’ total porosity (variation range: 39.2–42.7%) and proportion of the main pores (2–200 μm). Third, the toluene removal during the air injection consisted of compaction, rapid growth, rapid reduction, and tailing stages, and the MPs were regarded as an emerging solid state to affect these removal stages. The final cumulative toluene concentrations of soil-PET mixtures were influenced by total porosity, and those of soil-PE mixtures were controlled by total porosity (influence weight: 0.67) and adsorption capacity (influence weight: 0.33); meanwhile, a self-built comprehensive coefficient of MPs can reflect the relationship between them and cumulative concentrations (correlation coefficient: 0.783).