Birnessite is regarded as an efficient oxidizing agent that would significantly influence the environmental fate of elements such as arsenic. This study compared the chemical and photocatalytic oxidation of As(III) over birnessite. During the chemical oxidation, As(III) was oxidized to As(V), while Mn(IV) was reduced to Mn(II), subsequently forming MnOOH. The coverage of the reactive sites by MnOOH inhibited the chemical oxidation of residual As(III). At pH 5.0, after 360 min of reaction, 61% of As(III) was oxidized to As(V), and the oxidation of As(III) decreased with an increase in pH. The photocatalytic oxidation of As(III), where almost all As(III) could be oxidized to As(V) over a pH range of 5.0–8.0 and 360 min, was much more efficient compared to chemical oxidation. In contrast to chemical oxidation, the formation of MnOOH slightly affected the photocatalytic performance of birnessite. It was demonstrated that •O2− radicals and holes (hvb+) played an important role in the photocatalytic oxidation of As(III) over birnessite. Our findings confirmed that light dramatically promoted the oxidation of As(III) by birnessite, broadening the understanding of the environmental behaviors of arsenic.

Aggregation of carbon nanoparticles (CNPs) exerts significant influence on its surrounding environment. To comprehensively evaluate their environmental impacts, it is essential to clarify the relationship between CNP monomers, agglomerates, and their sorption and photocatalysis behaviors. In this work, three agglomerates were prepared by crosslinking one-dimensional oxidized carbon nanotubes (OCNTs), quasi one-dimensional oxidized graphene ribbons (OGRs), and two-dimensional graphene oxide sheets (GOs) with polyacrylamide hydrochloride (PA). Notably, the sorption and photo-reduction behaviors of Cr(VI) are different on the surfaces of CNPs monomers and agglomerates. Overall, all the agglomerates demonstrated higher Cr(VI)-sequestration capacities than the corresponding monomers regardless of dark environment and light irradiation. For CNPs monomers, chromium species were scarcely adsorbed on the particle surface in the dark; the sunlight illumination promoted significantly the transformation of Cr(VI) ions to solid Cr(OH)(3), resulting in sequestration capacities of 16.7, 47.7, and 115.4 mg/g in OCNTs, OGRs and GOs, respectively. After crosslinked by PA, the total sequestration capacity of Cr(VI) pollutants in the agglomerates increased by 3.4 similar to 21.4 times compared to their corresponding monomers. It was noteworthy that the agglomerates almost converted all of Cr(VI) to Cr2O3 under the illumination. This study highlights the discrepancies in Cr(VI)-sequestration behavior between CNPs and their agglomerates, which provides a novel insight into environmental impacts of CNPs and their agglomerates in nature.

To predict the mobility of radiocesium (RCs) in the environment, it is essential to understand the adsorption and desorption processes. In this study, we focused on the effects of certain environmental factors, including typical cations (K + , Na + , and NH 4 + ) and low molecular weight organic acids (LMWOAs) such as acetic acid, malic acid, and citric acid on the behavior of RCs on montmorillonite and vermiculite. The results showed that montmorillonite possesses the strongest adsorption capacity for Cs + than that of vermiculite. Since K + and NH 4 + exhibit similar physicochemical properties to Cs + , there is a significant inhibition of Cs + adsorption on montmorillonite and vermiculite during the competitive interaction with K + and NH 4 + . Compared to NH 4 Cl, the desorption ratios of Cs + on montmorillonite and vermiculite are higher in the presence of KCl as the background solution. Low molecular weight organic acids can cover the surfaces of montmorillonite and vermiculite to different extents, which effectively blocks the adsorption sites for Cs + , and leads to an obvious decrease in the adsorption and desorption of Cs + . Due to the high expandable performance, Cs + is primarily reversibly adsorbed by montmorillonite. Nevertheless, the adsorption of Cs + on vermiculite exhibits typical irreversible characteristics due to the interlayer collapse. After the adsorption of LMWOAs on montmorillonite and vermiculite, the irreversible adsorption of Cs + is increased obviously, mainly due to the blocking effect of organic matters on the adsorption sites with high affinity to Cs + .

The environmental behavior of radioactive cesium (RCs) in contaminated areas is generally governed by soil and sediment components and natural weathering conditions. In this study, desorption tests and spectroscopic approaches were used to explore the interaction between the weathering of micaceous minerals (i.e., biotite and phlogopite) and the adsorption of Cs+ and the critical role of weathering in the environmental behavior of RCs. Results showed that the reaction sequence between weathering and Cs+ adsorption significantly affected the surface species of Cs+ and the structure of biotite and phlogopite. Regardless of whether it occurred before, after, or during Cs+ adsorption, weathering generated more high-affinity adsorption sites, namely, interlayer sites (ITs) and frayed edge sites (FESs), to different extents, and then facilitated the uptake of Cs+ at FESs and ITs on micaceous minerals in a poorly exchangeable state. Cs+ stabilized the micaceous mineral structure once it was absorbed within collapsed interlayers by hindering cation exchange and preventing further destruction during weathering. As important weathering factors, high temperature and Ca2+ content promoted the binding of Cs+ in the interlayers of biotite and phlogopite by enhancing interlayer cation exchange. These findings are beneficial for a better understanding of the environmental behaviors of RCs in the hydrosphere and pedosphere.

Clarifying the reaction process and specific mechanism between variable-valence elements and oxidized carbon nanoparticles is essential to evaluate the environmental impact of carbon nanomaterials. In this study, the photocatalytic reduction of Cr(VI) on oxidized carbon nanotubes (OCNTs), oxidized graphene ribbons (OGRs), and graphene oxide sheets (GOs) was explored by batch experiments and spectroscopic analyses. The reaction efficiencies strongly depended on the number of oxygenated groups in the oxidized carbon nanoparticles. The abundant oxygenated groups enabled the GOs to exhibit the highest photocatalytic activity, followed by the OGRs and OCNTs. As a result, the photoreduction efficiency of Cr(VI) reached 96% for GOs, whereas those of OGRs and OCNTs were only 40% and 13%, respectively. In addition, different types of oxygenated groups exhibited various activities based on molecular model tests, following the sequence carboxylic > hydroxyl > carbonyl > ether > aldehyde > edge. Based on the underlying relationship between the oxygenated groups, topological structures, and mechanical strain in the carbon nanoparticles, we speculate that mechanical strain plays a critical role in the formation of oxygenated groups, thereby regulating their photocatalytic activities. The findings in this work provide novel insights into the roles of oxygenated groups and the mechanical strain of carbon nanoparticles in their environmental behavior.

The environmental behaviors of uranium closely depend on its interaction with natural minerals. Ferrihydrite widely distributed in nature is considered as one main natural media that is able to change the geochemical behaviors of various elements. However, the semiconductor properties of ferrihydrite and its impacts on the environmental fate of elements are sometimes ignored. The present study systematically clarified the photocatalysis of U(VI) on ferrihydrite under anaerobic and aerobic conditions, respectively. Ferrihydrite showed excellent photoelectric response. Under anaerobic conditions, U(VI) was converted to U(IV) by light-irradiated ferrihydrite, in the form of UO2+x (x < 0.25), where •O2− was the dominant reactive reductive species. At pH 5.0, ~50% of U(VI) was removed after light irradiation for 2 h, while 100% U(VI) was eliminated at pH 6.0. The presence of methanol accelerated the reduction of U(VI). Under aerobic conditions, the light illumination on ferrihydrite also led to an obvious but slower removal of U(VI). The removal of U(VI) increased from ~25% to 70% as the pH increased from 5.0 to 6.0. The generation of H2O2 under aerobic conditions led to the formation of UO4•xH2O precipitates on ferrihydrite. Therefore, it is proved that light irradiation on ferrihydrite significantly changed the species of U(VI) and promoted the removal of uranium both under anaerobic and aerobic conditions.

The activity and fate of heavy metals (HMs) from mining and smelting activities in farmland soil is of great significance to effectively prevent the excessive enrichment of HMs in crops. This study focuses on Baiyin area, a typical mining city in northwest China. In this example, the sources, speciation, and fate of HMs in the farmland soil, and the migration and enrichment characteristics of HMs in the different parts of crops planted in different areas were studied in detail combining the chemical sequential extraction and Pb isotope approaches. Results showed that the mean anthropogenic contributions of HMs in farmland soils were approximately 85%, 88%, 76%, and 41% for the ore district (OD), Xidagou sewage irrigation area (XSIA), Dongdagou sewage irrigation area, and the Yellow River irrigation area, respectively, and the risk that HMs were excessively accumulated in crops in OD and XSIA was high. Compared with soil residual fractions, the isotope ratios 206Pb/207Pb in non-residual fractions (1.1304–1.1669) were closer to the values of local ores, suggesting that anthropogenic HMs from mining and smelting activities were mainly enriched in the non-residual fractions. The isotope ratios 206Pb/207Pb in crops (1.1398–1.1686) further confirmed that those anthropogenic HMs were more easily absorbed and concentrated by crops. HMs contents in leaves from OD and XSIA were generally higher than that in roots, suggesting that atmospheric deposition in OD and XSIA had a greater impact on the HMs concentration of crop leaves，while the excess rate of HMs in grain/fruit was the lowest in all parts of crops. The division and classification of crop planting in mining area can effectively help minimize the risk that HMs from anthropogenic source enter the human body through the food chain.

In this study, batch and spectroscopic approaches were used to explore the sorption of Pb(II) on micas (i.e., muscovite, biotite and phlogopite) in the presence of Trichoderma viride (T. viride). Batch sorption showed that ion exchange, outer-sphere complexes (OSCs) and inner-sphere complexes (ISCs) contributed to Pb(II) sorption on biotite and phlogopite in the pH range of 2.0-7.4, whereas the ISCs were predominant for Pb(II) sorption on muscovite. X-ray diffraction and Fourier transform infrared (FT-IR) analyses have confirmed the changes of structure and surface properties of micas after co-culturing with T. viride, which could improve the sorption capacity of micas to Pb(II). Scanning electron microscopy revealed the bio-mineralization of Pb(II) on T. viride and mica-T. viride composites forming lead phosphates. Furthermore, FT-IR analysis showed that the groups of Si-OH, Al-OH from micas, and carboxyl, phosphate and amino groups from T. viride were synergistically contributing to Pb(II) sorption on mica-T. viride composite. X-ray photoelectron spectroscopy further confirmed that both OSCs and ISCs formed for Pb(II) sorption on micas; however, in the case of mica-T. viride composites, the synergistic effects of T. viride and micas were contributing to Pb(II) sorption through forming the ISCs and biomineralization.

A 3D framework based on graphene oxide ribbons promises unique advantages in Cr(vi) remediationviathe synergetic effect of sorption and photocatalysis. The active sites of sorption and photocatalysis are disclosed at a molecular level.

As the important anions in the high-level radioactive waste (HLRW), and the sorption behaviors of Se(VI) and Se(IV) on Beishan granite are important to the safe evaluation and performance assessment of the deep geological repository for HLRW in China. In this study, the sorption behaviors of Se(IV) and Se(VI) on Beishan granite were investigated under different environmental factors combining batch and spectroscopic approaches, such as X-ray photoelectron spectroscopy (XPS) and attenuated total reflection Fourier transformed infrared (ATR-FTIR). The results showed that Se(IV) sorption on Beishan granite was much higher than that of Se(VI) mainly due to their molecule charge densities and speciation in solution. The sorption of Se(IV) was independent of ionic strength, suggesting that the inner-sphere complexes (ISCs) was dominant for Se(IV) sorption on granite. However, Se(VI) sorption on Beishan granite was strongly dependent on ionic strength, which indicated that ion exchange and outer-sphere complexes (OSCs) dominated Se(VI) sorption. ATR-FTIR confirmed that Se(IV) and humic acid (HA) could form a soluble complex of HA-Se(IV) in solution. Therefore, under low pH and HA concentration conditions, the presence of HA could enhance Se(IV) sorption; while inhibited Se(IV) sorption on granite to some extent under high pH and HA concentration conditions. In case of Se(VI), the presence of HA greatly reduced the surface charge density of the Beishan granite, which in turn enhanced the electrostatic repulsion of Se(VI) and granite surfaces, thereby inhibiting Se(VI) sorption on granite surface. When Se(IV) coexisted with Eu (III), the sorption of Se(IV) on granite could be enhanced to a large extent, which might be due to the formation of Eu2(SeO3)3 complex with Se(IV) under alkaline condition (consistent with ATR-FTIR), or surface charge modifications of Beishan granite caused by Eu(III) sorption. Owing to the ISCs of Se(IV) on granite, the presence of anions almost no obvious effect on Se(IV) sorption except for SO32− and HPO42− in terms of the competitive sorption, which inhibited Se(IV) sorption to some extent. It was interesting that CO32− could enhance Se(IV) sorption to a large extent, however the mechanism was still not clear. Furthermore, XPS further confirmed that Se(IV) sorption on granite was dominated by Fe(II) and Fe(III), and the host mineral was biotite.

The transport of radiocesium (RCs) in granite has attracted great concerns for the consideration of a long-term safety assessment and performance evaluation of the nuclear waste disposal repository. In this study, the transport behaviors of Cs+ in granite were addressed and quantified by column experiments, sequential extraction, and a convection-dispersion equation model. The transport of Cs+ in granite experienced at least two stages including a rapid increase and a slow increase stages. The retardation of Cs+ in granite obviously became higher as biotite content increased. However, a consistent breakthrough plateau and almost overlapped breakthrough curves were observed under different feldspar contents, which suggested that the transport behaviors of Cs+ in granite was quite close to feldspar. Compared to Na+, K+ could effectively inhibit Cs+ adsorption and facilitate the mobility of Cs+ in granite column. In the presence of Sr2+, the transport of Cs+ was provoked in the granite column mainly due to the high competition effects. Humic acid (HA) did not obviously change the transport behaviors of Cs+ in granite column; however, HA could weakly change the adsorption species of Cs+ during Cs+ transport in granitic media. Both sequential extraction and two-site non-equilibrium model suggested that feldspar was the main contributor to the weak adsorption sites and biotite was responsible for the strong affinity sites for Cs+ in Beishan granite. The findings could provide important insights into RCs transport and fate in granitic media.