Preparation of N-doped cellulose-based hydrothermal carbon using a two-step hydrothermal induction assembly method for the efficient removal of Cr(VI) from wastewater.

Cr(VI) pollution is a growing problem that causes the deterioration of the environment and human health. We report the development of an effective adsorbent for the removal of Cr(VI) from wastewater. N-doped cellulose-based hydrothermal carbon (N-CHC) was prepared via a two-step hydrothermal method. The morphology and structural properties of N-CHC were investigated by various techniques. N-CHC has many O and N groups, which are suitable for Cr(VI) adsorption and reduction. Intermittent adsorption experiments showed that N-CHC had an adsorption capacity of 151.05 mg/g for Cr(VI) at pH 2, indicating excellent adsorption performance. Kinetic and thermodynamic analyses indicates that the adsorption of Cr(VI) on N-CHC follows a monolayer uniform adsorption process, which is a spontaneous endothermic process dominated by chemical interaction and limited by diffusion within particles. In a multi-ion system (Pb2+, Cd2+, Mn7+, Cl-, and SO42-), the selectivity of N-CHC toward Cr(VI) was 82.62%. In addition, N-CHC demonstrated excellent reuse performance over seven adsorption-desorption cycles; the Cr(VI) removal rate of N-CHC in 5-20 mg/L wastewater was >99.87%, confirming the potential of N-CHC for large-scale applications. CN/C-OR, pyridinic-N, and pyrrolic-N were found to play a critical role in the adsorption process. This study provides a new technology for Cr(VI) pollution control that could be utilized in large-scale production and other environmental applications.

Photoinduced Dual Shape Programmability of Covalent Adaptable Networks with Remarkable Mechanical Properties.

As classic shape memory polymers featuring shape reconfiguration of temporary state, covalent adaptable networks containing reversible bonds can enable permanent-state reconfigurability through topological rearrangement via dynamic bond exchange. Yet, such an attractive dual shape programmability is limited by the actuation mode of direct heat transfer and poor mechanical properties, restricting its control precision and functionality. Herein, we presented a method to create nanocomposites with photomodulated dual shape programmability and remarkable mechanical properties leading the fields of covalent adaptable networks. MXene, whose photothermal efficiency was revealed to be regulated by the etching method and delamination, was introduced into polyurethane networks. Upon adjusting the light intensity, the dual shape programmability of both permanent and temporary states could be accomplished, which exhibited potential in information recognition, photowriting paper, etc. Furthermore, owing to the dynamic transcarbamoylation at elevated temperatures, such a phototriggered dual shape programmability could be maintained after the self-healing and reprocessing.

Two-stage hydrothermal oxygenation for efficient removal of Cr(VI) by starch-based polyporous carbon: Wastewater application and removal mechanism.

Cr(VI) is of concern because of its high mobility and toxicity. In this work, a two-stage hydrothermal strategy was used to activate the O sites of starch, and by inserting K-ion into the pores, starch-based polyporous carbon (S-PC) adsorption sites was synthesized for removal of Cr(VI). Physicochemical characterization revealed that the O content of the S-PC reached 20.66 % after activation, indicating that S-PC has excellent potential for adsorption of Cr(VI). The S-PC removal rate for 100 mg/L Cr(VI) was 96.29 %, and the adsorption capacity was 883.86 mg/g. Moreover, S-PC showed excellent resistance to interference, and an equal concentration of hetero-ions reduced the activity by less than 5 %. After 8 cycles of factory wastewater treatment, the S-PC maintained 81.15 % of its original activity, which indicated the possibility of practical application. Characterization and model analyses showed that the removal of Cr(VI) from wastewater by the S-PC was due to CC, δ-OH, ν-OH, and C-O-C groups, and the synergistic effect of adsorption and reduction was the key to the performance. This study provides a good solution for treatment of Cr(VI) plant wastewater and provides a technical reference for the use of biological macromolecules such as starch in the treatment of heavy metals.

Enhancement of Cr(VI) adsorption on lignin-based carbon materials by a two-step hydrothermal strategy: Performance and mechanism.

Cr(VI) is a carcinogenic heavy metal that forms an oxygen-containing anion, which is difficult to remove from water by adsorbents. Here, industrial alkali lignin was transformed into a Cr(VI) adsorbent (N-LC) by using a two-step hydrothermal strategy. The characterization results of the adsorbent showed that O and N were uniformly distributed on the surface of the adsorbent, resulting in a favorable morphology and structure. The Cr(VI) adsorption of N-LC was 13.50 times that of alkali lignin, and the maximum was 326.10 mg g-1, which confirmed the superiority of the two-step hydrothermal strategy. After 7 cycles, the adsorption of N-LC stabilized at approximately 62.18 %. In addition, in the presence of coexisting ions, N-LC showed a selective adsorption efficiency of 85.47 % for Cr(VI), which is sufficient to support its application to actual wastewaters. Model calculations and characterization showed that N and O groups were the main active factors in N-LC, and CO, -OH and pyridinic-N were the main active sites. This study provides a simple and efficient method for the treatment of heavy metals and the utilization of waste lignin, which is expected to be widely applied in the environmental, energy and chemical industries.

Three-dimensional lignin-based polyporous carbon@polypyrrole for efficient removal of reactive blue 19: A synergistic effect of the N and O groups.

Reactive blue 19 is one of the abundant carcinogens commonly used in industrial applications. This study transformed industrial lignin into a lignin-based polyporous carbon@polypyrrole (LPC@PPy) by a hydrothermal-activation-in situ polymerization strategy for removal of reactive blue 19. The hydrothermal reaction and polypyrrole polymerization provide abundant O and N groups, and the pore-making process promotes the even distribution of O and N groups in the 3D pore of LPC@PPy, which is favorable for the adsorption of reactive blue 19. The adsorption capacity of LPC@PPy for reactive blue 19 is 537.52 mg g-1, which is 2.04 times the performance of LPC (only hydrothermal and activation process, only have O groups) and 3.36 times that of LC (direct lignin activation, lack of O and N groups). After 8 cycles, LPC@PPy still maintained a high adsorption capacity of 92.14 % for reactive blue 19. In addition, this study found that N and O groups in the material played an important role in adsorption, mainly pyridinic-N, C-OH, -COOR, -C-O- and CC. This work provides a new strategy for the removal of reactive blue 19 and determines the groups that mainly interact with reactive blue 19, which provides a new reference for adsorption, catalysis and related fields.

Coupling of soil methane emissions at different depths under typical coastal wetland vegetation types.

As an important source of atmospheric methane, methane emissions from coastal wetlands are affected by many factors. However, the methane emission process and interrelated coupling mechanisms in coastal wetland soils of a variety of environments remain unclear owing to complex interactions between intensified anthropogenic activities and climate change in recent years. In this study, we investigated methane cycling processes and the response mechanisms of environmental and microbial factors in soils at different depths under four typical coastal wetland vegetation types of the Yellow River Delta, China, using laboratory culture and molecular biology techniques. Our results show that methane generation pathways differed among the different soil layers, and that the methane emission process has a special response to soil N compounds (NO3-, NH4+). We found that nitrogen can indirectly affect methane emission by impacting key physicochemical properties (pH, oxidation reduction potential, etc.) and some functional communities (mcrA, ANME-2d, sulfate-reducing bacteria (SRB), narG, nosZII). Methane production processes in shallow soils compete closely with sulfate reduction processes, while methane emissions facilitated in deeper soils due to denitrification processes. We believe that our results provide a reference for future research and wetland management practices that seek to mitigate the global greenhouse effect and climate change.

Soil nitrogen content and key functional microorganisms influence the response of wetland anaerobic oxidation of methane to trivalent iron input.

Trivalent iron (Fe3+)-dependent anaerobic oxidation of methane (Fe-AOM), which is mediated by metal-reducing bacteria, is widely recognized as a major sink for the greenhouse gas methane (CH4), and is a key driver of the carbon (C) biogeochemical cycle. However, the effect of Fe3+ addition on AOM in the present investigation is still ambiguous, and the mechanism is vague. In this study, we investigated the mechanism of changes in AOM response to Fe3+ input at different wetlands by using laboratory incubation methods combined with molecular biology techniques. Results indicated that Fe3+ input did not always lead to promoted AOM rates, which may be mediated by complex environmental factors, while lower soil total nitrogen (TN) had a positive effect on the response of AOM subjected to Fe3+ input. Notably, the promoted response of AOM was regulated by higher soil microbial diversity, of which the Shannon index was a key indicator leading to variation in the AOM response. Additionally, several biomarkers, including Planctomycetota and Burkholderiaceae, were key microorganisms responsible for alterations in AOM response. Our results suggest that the capacity of Fe3+ cycling-mediated AOM may gradually decrease in light of increasing anthropogenic N and Fe inputs to global estuarine wetlands, while its reaction processes will become more complex and more strongly coupled with multiple environmental factors. This finding contributes to the enhanced understanding and prediction of the wetland CH4-related C with Fe cycles, as well as provides theoretical support for the underlying mechanisms.

Soil nitrogen substances and denitrifying communities regulate the anaerobic oxidation of methane in wetlands of Yellow River Delta, China.

Anaerobic oxidation of methane (AOM) in wetland soils is widely recognized as a key sink for the greenhouse gas methane (CH4). The occurrence of this reaction is influenced by several factors, but the exact process and related mechanism of this reaction remain unclear, due to the complex interactions between multiple influencing factors in nature. Therefore, we investigated how environmental and microbial factors affect AOM in wetlands using laboratory incubation methods combined with molecular biology techniques. The results showed that wetland AOM was associated with a variety of environmental factors and microbial factors. The environmental factors include such as vegetation, depth, hydrogen ion concentration (pH), oxidation-reduction potential (ORP), electrical conductivity (EC), total nitrogen (TN), nitrate (NO3-), sulfate (SO42-), and nitrous oxide (N2O) flux, among them, soil N substances (TN, NO3-, N2O) have essential regulatory roles in the AOM process, while NO3- and N2O may be the key electron acceptors driving the AOM process under the coexistence of multiple electron acceptors. Moreover, denitrification communities (narG, nirS, nirK, nosZI, nosZII) and anaerobic methanotrophic (ANME-2d) were identified as important functional microorganisms affecting the AOM process, which is largely regulated by the former. In the environmental context of growing global anthropogenic N inputs to wetlands, these findings imply that N cycle-mediated AOM processes are a more important CH4 sink for controlling global climate change. This studying contributes to the knowledge and prediction of wetland CH4 biogeochemical cycling and provides a microbial ecology viewpoint on the AOM response to global environmental change.

Efficient Cr(VI) removal from wastewater by D-(+)-xylose based adsorbent: Key roles of three-dimensional porous structures and oxygen groups.

Reducing the harm of heavy metals to the environment has been a major scientific challenge. In this study, D-(+)-xylose was used to prepare an adsorbent with rich O groups and three-dimensional porous structures for Cr(VI) adsorption. What's more, the adsorption sites of many oxygen groups in the material were combined with the three-dimensionally connected porous structures, which made the adsorption sites fully in contact with Cr(VI). At the concentration of 300 mg/L, the removal rate of Cr(VI) was 94.50%, 6.4 times that of the non-porous treatment and 9.6 times that of the non-porous and O group treatment. The adsorbent showed a high adsorption capacity (910.10 mg/g) for Cr(VI), and the adsorption model proved that the adsorbent was a multi-molecular layer adsorbent. In addition, the adsorption was controlled by chemical reaction and diffusion, which was also attributed to the three-dimensional porous structure and abundant oxygen groups of the material. XPS and FTIR indicated that four O groups participated in the adsorption reaction (-OH, C-O-C, CO, and C-O), and C-O-C and C-O were the main reaction sites. After treating wastewater from electroplating plants with X-PC, the discharged water met international and domestic discharge standards (Cr(VI) removal rate> 99.90%). This work provides a new idea for the application of sugars in the environment and the design of porous adsorbents.

Biotemplated g-C3N4/Au Periodic Hierarchical Structures for the Enhancement of Photocatalytic CO2 Reduction with Localized Surface Plasmon Resonance.

Graphitic carbon nitride (g-C3N4) is a promising photocatalyst for CO2 reduction to alleviate the greenhouse effect. However, the low light absorption, small specific surface area, and rapid charge recombination limit the photocatalytic efficiency of g-C3N4. Herein, we demonstrate a bioinspired nanoarchitecturing strategy to significantly improve the light harvesting and charge separation of the g-C3N4/Au composite, as proven by the remarkable photocatalytic CO2 reduction. Specifically, a biotemplating approach is employed to transfer the sophisticated hierarchical structures and the related light-harvesting functionality of Troides helena butterfly wings to the g-C3N4/Au composite. The resulting g-C3N4/Au composite shows high photocatalytic efficiency under UV-visible excitation with triethanolamine as the sacrificial agent. The yields of CO and CH4 are 331.57 and 39.71 µmol/g/h, respectively, which are ∼36 times and ∼88 times that of pure g-C3N4 under the same conditions. Detailed experiments and the finite-difference time-domain method suggest that the superb photocatalytic activity should be ascribed to the unique periodic hierarchical structure which assists the light absorption and the localized surface plasmon resonance for promoted charge separation in addition to the more effective CO2 diffusion and larger specific surface area. Our work provides a new path for the design and optimization of photocatalysts based on biological structures that are usually unattainable artificially.

Preparation and characterization of nanocrystalline cellulose/Eucommia ulmoides gum nanocomposite film.

The nanocomposite films were prepared using Eucommia ulmoides gum (EUG) matrix reinforced with nanocrystalline cellulose (NCC) at different concentrations. Subsequently, the obtained films were characterized by Raman spectra, AFM, XRD, TGA, and DSC. Meanwhile, the wettability, mechanical, and water vapor barrier properties of these films were analyzed. AFM noticed that the average sizes of NCC were 81.95×50.17×13.06nm, while the size of molecular chain for EUG was 2530×57.33×1.28nm. In comparison with control film, a certain amount of NCC obviously improved elongation at break and enhanced their crystallinity and ΔHm. More importantly, NCC/EUG nanocomposite films presented lower thermal stability, glass transition temperature (Tg), melting temperature (Tm), and water vapor permeability (WVP) values, especially the WVP values of 4% NCC film were the lowest as 0.28×10-9, 0.30×10-9, and 0.58×10-9g/m/h/Pa at RH 34%, 55%, and 76%, respectively.

Removal of Cr6+ ions from water by electrosorption on modified activated carbon fibre felt.

Electrosorption is a novel desalination technique that has many advantages in the treatment of sewage. However, commercially available activated carbon electrodes for electrosorption commonly have low microporosity, poor moulding performance, and low adsorption and regeneration efficiency. Here, we evaluated a novel adsorbent material, activated carbon fibre felt (ACFF), for electrosorption of chromium ions (Cr6+) in sewage treatment. The ACFF was modified with 20% nitric acid and its modified structure was characterized. The modified ACFF was used as an adsorbing electrode to investigate its desalination effect by electrosorption. Results showed that compared with those of unmodified ACFF, the modified ACFF had more carbonyl and carboxyl groups and the specific surface area, average pore size and micropore volume of the modified ACFF also improved by 32.2%, 2.5% and 23.1%, respectively. The kinetics of Cr6+ adsorption conformed to the pseudo-second-order kinetic equation, and the adsorption isotherm conformed to the Langmuir model. In addition, the regeneration rate of the modified ACFF electrode was more than 94%. In conclusion, the modified ACFF exhibits excellent electrosorption and regeneration performance for Cr6+ removal from water and thus is of great value for promotion in sewage treatment.