Synergistic reduction of Cr(VI) by graphite N and thiophene S of N, S-co-doped hydrochar derived from waste straw

Optimizing visible light absorption, exciton dissociation, and charge transfer through the interaction of donor-acceptor materials to enhance xanthate photodegradation

Bulk heterojunctions, formed by blends of donor and acceptor materials, are attractive for developing efficient photocatalysts due to their tunable optical and electrical properties. However, their potential for enhancing organic wastewater treatment through adjustable light absorption bands and intensities remains largely unexploited. In this work, a novel kaolin (KA) based ternary heterojunction photocatalyst PBT1-C:IDT8CN-M:PDI-V/KA (PIV/KA) with strong absorption capability in the spectral range of 470-800 nm was synthesized through the clever combination of donor and acceptor materials and the construction of Förster resonance energy transfer (FRET) between IDT8CN-M (I) and PDI-V (V). PIV/KA exhibits high photocatalytic performance, degrading 99.8 % of sodium ethyl xanthate (SEX) within 10 min, and achieving high degradation rates for the other four common xanthates. This excellent performance is attributed to the complementary light absorption of PBT1-C (P), I, and V, which broadens the visible light harvesting ability of PIV and promotes exciton generation. Meanwhile, the FRET from V to I alters the exciton jump mode and broadens the pathway of exciton dissociation in the ternary system, facilitating exciton dissociation and charge transport. Finally, thanks to the dispersion stabilization of KA, PIV/KA can efficiently generate a large number of strong oxidizing radicals (∙O2- and ∙OH, etc.) to degrade SEX under visible light irradiation. This study provides theoretical guidance for constructing efficient bulk heterojunction photocatalysts to treat SEX in mineral processing wastewater.

Sustainable Biomass Acts as an Electron Donor for Cr(VI) Reduction during the Subcritical Hydrothermal Process: Molecular Insights into the Role of Hydrochar and Liquid Compounds

Heavy metal pollution is a critical environmental issue that has garnered significant attention from the international community. Subcritical hydrothermal liquefaction (HTL) as an emerging green technology has demonstrated remarkable promise in environmental remediation. However, there is limited research on the remediation of highly toxic Cr(VI) using HTL. This study reveals that the HTL reaction of biomass enables the simultaneous reduction and precipitation of Cr(VI). At 280 °C, the reduction of Cr(VI) was nearly complete, with a high reduction rate of 98.9%. The reduced Cr as Cr(OH)3 and Cr2O3 was primarily enriched in hydrochar, accounting for over 99.9% of the total amount. This effective enrichment resulted in the removal of Cr(VI) from the aqueous phase while simultaneously yielding clean liquid compounds like organic acids and furfural. Furthermore, the elevated temperature facilitated the formation of Cr(III) and enhanced its accumulation within hydrochar. Notably, the resulting hydrochar and small oxygenated compounds, especially aldehyde, served as electron donors for Cr(VI) reduction. Additionally, the dissolved Cr facilitated the depolymerization and deoxygenation processes of macromolecular compounds with lignin-like structures, leading to more small oxygenated compounds and subsequently influencing Cr(VI) reduction. These findings have substantial implications for green and sustainable development.

Fabrication of lignosulfonate-derived porous carbon via pH-tunable self-assembly strategy for efficient atrazine removal

Herein, a straightforward protocol was developed for the one-pot synthesis of N-doped lignosulfonate-derived carbons (NLDCs) with a tunable porous structure using natural amino acids-templated self-assembly strategy. Specifically, histidine was employed as a template reagent, leading to the preparation of 10-NLDC-21 with remarkable characteristics, including the large specific surface area (SBET = 1844.5 m2/g), pore volume (Vmes = 1.22 cm3/g) and efficient adsorption for atrazine (ATZ) removal. The adsorption behavior of ATZ by NLDCs followed the Langmuir and pseudo-second-order models, suggesting a monolayer chemisorption nature of ATZ adsorption with the maximum adsorption capacity reached up to 265.77 mg/g. Furthermore, NLDCs exhibited excellent environmental adaptability and recycling performance. The robust affinity could be attributed to multi-interactions including pore filling, electrostatic attraction, hydrogen bonding and π-π stacking between the adsorbents and ATZ molecules. This approach offers a practical method for exploring innovative bio-carbon materials for sewage treatment.

Amino-Functionalized Lotus Stem Hydrochar for Rapid Adsorption and In Situ Detoxification of Cr(VI) from Water

The development of low-cost, efficient, and environmentally friendly adsorbents is the key to highly toxic hexavalent chromium [Cr(VI)] removal by adsorption. In this paper, amino-functionalized lotus stem hydrochar (ALSHC) was prepared from an agricultural waste lotus stem (LS) for the adsorption removal of Cr(VI) from water. The effects of the initial Cr(VI) concentration, contact time, temperature, coexisting anions, and reusability of ALSHC on Cr(VI) removal were examined in detail. The adsorption mechanism was further discussed by investigating the impact of the solution's initial pH, the relation between the pH change in solution and Cr(VI) removal during the process, the changes of chromium (Cr) species in solution and on ALSHC during adsorption, and the XPS characterization. The results demonstrated that ALSHC effectively removed Cr(VI) from water with rapid adsorption (the removal rate reached 80.90% in only 10 min) and in situ detoxification. Most importantly, ALSHC still had better adsorption performance (adsorption capacity of 30.95 mg g-1) than commercially activated carbon, even at pH = 9.00. The adsorption of Cr(VI) by ALSHC accorded with the pseudo-second-order kinetic model and Langmuir isotherm model, indicating a monolayer chemisorption process. The adsorption process was shown to be spontaneous and endothermic based on the thermodynamic characteristics (ΔG0 < 0, ΔH0 > 0, and ΔS0 > 0). The mechanism of Cr(VI) removal was mainly composed of three parts in sequence: Firstly, Cr(VI) in solution was quickly adsorbed onto ALSHC with protonated -NH2 through electrostatic attraction; subsequently, the adsorbed Cr(VI) on ALSHC was mostly detoxicated by in situ reduction; and finally, the reduced Cr(III) and the remaining Cr(VI) were fixed on the ALSHC surface by complexation. The prepared ALSHC displayed a certain superiority in Cr(VI) adsorption and had the prospect of further development.

One-step synthesis of ferrous disulfide and iron nitride modified hydrochar for enhanced adsorption and reduction of hexavalent chromium in Bacillus LD513 by promoting electron transfer and microbial metabolism

Microbial immobilization technology is effective in improving bioremediation efficiency and heavy metal pollution. Herein, Bacillus LD513 with hexavalent chromium (Cr(VI)) tolerance was isolated and immobilized on a novel ferrous disulfide (FeS2)/iron nitride (FeN) modified hydrochar (Fe3-SNHC) prepared from waste straws. The prepared Fe3-SNHC-based LD513 (FeLD) significantly improves Cr(VI) adsorption and reduction by 31.4 % and 15.7 %, respectively, compared to LD513 alone. Furthermore, the FeLD composite system demonstrates efficient Cr(VI) removal efficiency and good environmental adaptability under different culture conditions. Microbial metabolism and electrochemical analysis indicate that Fe3-SNHC is an ideal carrier for protecting LD513 activity, promoting extracellular polymer secretion, and reducing oxidative stress. Additionally, the carrier serves as an electron shuttle that accelerates electron transfer and promotes Cr(VI) reduction. Overall, FeLD is an environmentally friendly biocomposite that shows good promise for reducing Cr(VI) contamination in wastewater treatment.

Adsorption and reduction of Cr(VI) by N, S co-doped porous carbon from sewage sludge and low-rank coal: Combining experiments and theoretical calculations

Herein, a novel N, S co-doped porous carbon (S5C5-AC) for Cr(VI) removal was prepared by co-hydrothermal carbonization (HTC) of sewage sludge (SS) and low-rank coal (LC) combining with KOH modification. The results showed that S5C5-AC had excellent adsorption performance on Cr(VI), and lower pH value, higher initial concentration and longer contact time were beneficial for Cr(VI) adsorption. The adsorption kinetics and isotherms revealed that Cr(VI) adsorption by S5C5-AC was homogeneous and dominated by chemisorption. The adsorption isotherm showed that the maximum equilibrium adsorption capacity of S5C5-AC for Cr(VI) was 382.04 mg/g at 25 °C. Furthermore, the results showed that the main mechanisms for Cr(VI) removal were the pore filling, electrostatic interaction and reduction. Moreover, the electron transfer mechanism during the adsorption and reduction process was further explored at the molecular and electronic levels by density functional theory (DFT) and front orbital theory (FOT) simulations. The analysis of DFT and FOT indicated that the synergistic effect between S and N functional groups was exhibited during the Cr(VI) removal process. Considering the existence of synergistic effects between N and S functional groups during adsorption, the S and N content and form were modified collaboratively. Increasing the relative content of pyrrolic N may be the most effective pathway for improving removal performance. Besides that, S5C5-AC exhibited excellent adsorption capacity over a high coexisting ion concentration range and various actual water bodies and regeneration performance, which indicated that S5C5-AC had promising potential for the remediation of wastewater in industrial applications.

Ferrous disulfide and iron nitride sites on hydrochar to enhance synergistic adsorption and reduction of hexavalent chromium

In this study, a novel hydrochar containing ferrous disulfide (FeS2) and iron nitride (FeN) was prepared via a one-pot hydrothermal method to enhance the synergistic adsorption and reduction of hexavalent chromium (Cr(VI)). This material (Fe3-SNHC) exhibited a Cr(VI) removal capacity of 431.3 mg·g-1 and high tolerance to coexisting anions at pH 2. Adsorption occurred via monolayer chemisorption. Variation in material structure and density functional theory calculations proved that multiple active sites formed by interactions between heteroatoms improved the chemical inertness of hydrochar. FeN and FeS2 with two electron-donating groups had strong reducing ability to facilitate the conversion of Cr(VI) to trivalent chromium. It was concluded that next to electrostatic adsorption and complexation, synergistic reduction among multiple active sites were the dominant mechanisms involved in the removal Cr(VI). This study shows that Fe3-SNHC is a promising and environment-friendly material for Cr(VI) to remove it from wastewater.