Linking groundwater microbiome and functional ecological clusters to geogenic high hexavalent chromium from deep aquifers in a loess plateau.

Geogenic high hexavalent chromium [Cr(Ⅵ)] in groundwater is a global environmental problem. However, the groundwater microbiome and its linkage to geogenic high Cr(Ⅵ) from deep aquifers still need to be elucidated. Here, we evaluated geogenic Cr(Ⅵ), groundwater microbiome with featured functional ecological clusters and their interactive responses in groundwater from a deep aquifer in a loess plateau of Northern Shaanxi, China. We found that the compositions and structures of microbial communities in groundwater from the deep aquifer were significantly different between low Cr(Ⅵ) (LCG, < 50 µg/L) and high Cr(Ⅵ) groundwater (HCG, > 50 µg/L), with higher microbial diversity and richness in HCG (p < 0.05). Functional "specialists" related to Cr biotransformation, including Cr(Ⅵ) reducing bacteria (CRB) Rhodococcus, Nocardioides, Novosphingobium, and Acidovorax and Mn-oxidizing bacteria (MnOB) Sphingobium, and Ralstonia were positively correlated to total Cr and Cr(VI) concentrations in groundwater. Moreover, these CRB and MnOB were dominant in high Cr(VI) groundwater and associated by strong interspecific relation in an ecological cluster (p < 0.05), suggesting their indicator roles for high Cr(Ⅵ) and the contribution of MnOB mediated Cr(III) oxidation to Cr(VI) enrichment. RDA and path analysis further revealed that the geogenic Cr(Ⅵ) directly promoted the key Cr-related functional cluster with the groundwater depth, dissolved oxygen, and total dissolved solids as the cofactors indirectly influencing Cr(Ⅵ) and the functional clusters (p < 0.05). Collectively, our results highlight the significant roles of microbial ecological clusters especially functional "specialists" MnOB and CRB in groundwater Cr(Ⅵ) from deep aquifers in the loess plateau and provide a basis for sustainable management of high Cr(Ⅵ) groundwater.

Hydrogeological controls on chromium enrichment along the groundwater flow path in the Baiyangdian Catchment, North China Plain.

Although the natural occurrence of high chromium (Cr) groundwater has been intensively investigated in bedrock or sedimentary aquifers, the impacts of hydrogeological conditions on dissolved Cr distribution are poorly understood. In this study, groundwater samples from recharge mountain area (Zone I) through runoff area (Zone II) to discharge area (Zone III) were taken from bedrock and sedimentary aquifers approximately along the flow path in Baiyangdian (BYD) catchment, China, to reveal how hydrogeological conditions and hydrochemical evolution contributed to Cr enrichment in groundwater. Results showed that dissolved Cr was dominated by Cr(VI) species (>99 %). Around 20 % of studied samples had Cr(VI) exceeding 10 µg/L. Groundwater Cr(VI) was of natural origin, which generally increased along the flow path, and high concentrations (up to 80.0 µg/L) were observed in deep groundwater of Zone III. At the local scales, geochemical processes including silicate weathering, oxidation, and desorption under weakly alkaline pH, predominately contributed to Cr(VI) enrichment. Principal component analysis showed that oxic conditions were the principal control of Cr(VI) in Zone I, and geochemical processes (especially Cr(III) oxidation and Cr(VI) desorption) predominantly enhanced groundwater Cr(VI) enrichment in Zones II and III. However, at the regional scale, Cr(VI) enrichment was dominantly facilitated by the low flow rate and recharge of paleo-meteoric water due to the long-term water-rock interaction in the BYD catchment.

Transforming Metal-Organic Frameworks into Porous Liquids via a Covalent Linkage Strategy for CO2 Capture.

Porous liquids (PLs), an emerging kind of liquid materials with permanent porosity, have attracted increasing attention in gas capture. However, directly turning metal-organic frameworks (MOFs) into PLs via a covalent linkage surface engineering strategy has not been reported. Additionally, challenges including reducing the cost and simplifying the preparation process are daunting. Herein, we proposed a general method to transform Universitetet i Oslo (UiO)-66-OH MOFs into PLs by surface engineering with organosilane (OS) and oligomer species via covalent bonding linkage. The oligomer species endow UiO-66-OH with superior fluidity at room temperature. Meanwhile, the resulting PLs showed great potential in both CO2 adsorption and CO2/N2 selective separation. The residual porosity of PLs was verified by diverse characterizations and molecular simulations. Besides, CO2 selective capture sites were determined by grand canonical Monte Carlo (GCMC) simulation. Furthermore, the universality of the covalent linkage surface engineering strategy was confirmed using different classes of oligomer species and another MOF (ZIF-8-bearing amino groups). Notably, this strategy can be extended to construct other PLs by taking advantages of the rich library of oligomer species, thus making PLs promising candidates for further applications in energy and environment-related fields, such as gas capture, separation, and catalysis.

Flexible nanoscale thread of MnSn(OH)6 crystallite with liquid-like behavior and its application in nanocomposites.

We reported a solvent-free nanofluid based on MnSn(OH)6 crystallite with thread-like morphology through sulfuric-acid-terminated organosilanes as corona and polyether amine as canopy. The resultant is characterized by various analytical techniques and shows excellent solubility, good dispersity, improved processability and fluidity at room temperature in the absence of any solvents, which offer great potential in applications such as plasticizers with effects of toughening and reinforcement in nanocomposites. In addition, as a kind of plasticizer, it can also improve the Tg of its nanocomposites. These advantages of the flexible nanoscale thread of MnSn(OH)6 crystallite make it can be easily applied on the fabrication of high performance of nanocomposites.