Adsorption behavior of engineered carbons and carbon nanomaterials for metal endocrine disruptors: Experiments and theoretical calculation

An experimental study about the effects of phosphorus loading in river sediment on the transport of lead and cadmium at sediment-water interface

Phosphorus (P) in the river sediment plays an important role in the fate and transport of heavy metals at sediment-water interface of the aquatic eutrophication environment. To explicate the effect of P loading, the sediments with different P contents were employed in this study to experimentally investigate the adsorption/desorption of Pb²⁺ and Cd²⁺ and the releasing behavior of P during the adsorption/desorption processes. Results illustrated a strong affinity between Pb²⁺ ions and the P-containing sediments in both single Pb and binary Pb + Cd systems. In single-metal systems, the Pb²⁺ adsorption capacities of all types of sediments (15.04-19.44 mg g^-1) were higher than those for Cd²⁺ (4.68-5.56 mg g^-1). While in binary-metal systems, the Pb²⁺ adsorption was slightly influenced by the coexisting Cd²⁺, but the Cd²⁺ adsorption capacities were decreased by over 5 times. Moreover, the adsorption amount and retention ability of Pb²⁺ on sediment were enhanced by increasing content of P in the sediment. Meanwhile, the releasing of P was also closely depended and significantly inhibited by the Pb²⁺ attached on the sediment. The P release amounts during the desorption processes of Pb- and Pb + Cd-loaded sediments were over 50 times lower than those from the raw sediments (sediments without heavy metals adsorbed), but the values decreased by a factor of two for the single Cd-loaded sediments. Furthermore, the results of X-ray photoelectron spectroscopy indicated the crucial role of P loading in Pb transport in the sediment and overlaying water. The findings in this study showed important implications for the transport of heavy metals and P at the sediment-water interface and offered new insights for further explicating the mechanisms of secondary pollution caused by heavy metals and P in aquatic eutrophication environment.

Sustainable hydrogen production by molybdenum carbide-based efficient photocatalysts: From properties to mechanism

Hydrogen is considered to be a promising energy carrier to solve the issue of energy crisis. Molybdenum carbide (Mo_xC) is the typical material, which has similar properties of Pt and thought to be an attractive alternative to noble metals for H₂ evolution. The study of Mo_xC as alternative catalyst for H₂ production is almost focused on electrocatalytic field, while the application of Mo_xC as a co-catalyst in photocatalytic H₂ evolution has received in-depth research in recent years. Particularly, Mo_xC exhibits significant enhancement in the H₂ production performance of semiconductors under visible light irradiation. However, a review discussing Mo_xC serving as a co-catalysts in the photocatalytic H₂ evolution is still absent. Herein, the recent progress of Mo_xC on photocatalytic H₂ evolution is reviewed. Firstly, the preparation methods including chemical vapor deposition, temperature programming, and organic-inorganic hybridization are detailly summarized. Then, the fundamental structure, electronic properties, and specific conductance of Mo_xC are illustrated to illuminate the advantages of Mo_xC as a co-catalyst for H₂ evolution. Furthermore, the different heterojunctions formed between Mo_xC and other semiconductors for enhancing the photocatalytic performance are emphasized. Finally, perspectives regarding the current challenges and the future research directions on the improvement of catalytic performance of Mo_xC-based photocatalysts are also presented.

Phytostabilization of Cd and Pb in Highly Polluted Farmland Soils Using Ramie and Amendments

In-situ remediation of heavy-metal-contaminated soil in farmland using phytostabilization combined with soil amendments is a low-cost and effective technology for soil pollution remediation. In this study, coconut shell biochar (CB, 0.1% and 0.5%), organic fertilizer (OF, 3.0%), and Fe-Si-Ca material (IS, 3.0%) were used to enhance the phytostabilization effect of ramie (Boehmeria nivea L.) on Cd and Pb in highly polluted soils collected at Dabaoshan (DB) and Yangshuo (YS) mine sites. Results showed that simultaneous application of CB, OF, and IS amendments (0.1% CB + 3.0% OF + 3.0% IS and 0.5% CB + 3.0% OF + 3.0% IS, DB-T5 and DB-T6) could significantly increase soil pH, reduce the concentrations of CaCl₂-extractable Cd and Pb, and increase the contents of Ca, P, S, and Si in DB soil. Under these two treatments, the growth of ramie was significantly improved, its photosynthesis was enhanced, and its levels of Cd and Pb were reduced, in comparison with the control (DB-CK). After applying DB-T5 and DB-T6, the concentrations of Cd and Pb in roots were decreased by 97.7–100% and 64.6–77.9%, while in shoots they were decreased by up to 100% and 92.9–100%, respectively. In YS-T4 (0.5% CB + 3.0% OF), the concentrations of Cd and Pb in roots were decreased by 39.5% and 46.0%, and in shoots they were decreased by 44.7% and 88.3%. We posit that phytostabilization using ramie and amendments could reduce the Cd and Pb bioavailability in the soil mainly through rhizosphere immobilization and plant absorption. In summary, this study suggests that the use of tolerant plant ramie and simultaneous application of coconut shell biochar, organic fertilizer, and Fe-Si-Ca materials is an effective stabilization strategy that can reduce Cd and Pb availabilities in soil. Ultimately, this strategy may reduce the exposure risk of crops to heavy metal pollution in farmland.

Antimicrobial efficacy and mechanisms of silver nanoparticles against Phanerochaete chrysosporium in the presence of common electrolytes and humic acid

In this study, influences of cations (Na⁺, K⁺, Ca²⁺, and Mg²⁺), anions (NO₃^-, Cl^-, and SO₄^2-), and humic acid (HA) on the antimicrobial efficacy of silver nanoparticles (AgNPs)/Ag⁺ against Phanerochaete chrysosporium were investigated by observing cell viability and total Ag uptake. K⁺ enhanced the antimicrobial toxicity of AgNPs on P. chrysosporium, while divalent cations decreased the toxicity considerably, with preference of Ca²⁺ over Mg²⁺. Impact caused by a combination of monovalent and divalent electrolytes was mainly controlled by divalent cations. Compared to AgNPs, however, Ag⁺ with the same total Ag content exhibited stronger antimicrobial efficacy towards P. chrysosporium, regardless of the type of electrolytes. Furthermore, HA addition induced greater microbial activity under AgNP stress, possibly originating from stronger affinity of AgNPs over Ag⁺ to organic matters. The obtained results suggested that antimicrobial efficacy of AgNPs was closely related to water chemistry: addition of divalent electrolytes and HA reduced the opportunities directly for AgNP contact and interaction with cells through formation of aggregates, complexes, and surface coatings, leading to significant toxicity reduction; however, in monovalent electrolytes, the dominating mode of action of AgNPs could be toxic effects of the released Ag⁺ on microorganisms due to nanoparticle dissolution.

Activity and stability of biochar in hydrogen peroxide based oxidation system for degradation of naphthenic acid

This study investigated the stability and catalytic activity of wheat straw biochar (WS), hardwood biochar (HW) and commercial activated carbon (AC) in hydrogen peroxide (H₂O₂) based oxidation system for degradation of model naphthenic acids compound, 1-methyl-1- cyclohexane carboxylic acid (MCCA). WS showed excellent catalytic activity for decomposition of H₂O₂ and MCCA degradation as demonstrated by high H₂O₂ decomposition rate (2.0*10^-4 M^-1s^-1), amount of hydroxyl (OH) radicals generated (182 mg/L) and degradation efficiency of MCCA (100% at C_o - 100 mg/L). 2-Methyl pentatonic acid was identified as reaction intermediate and 99% mineralization of MCCA was obtained within 4 h. The real wastewater conditions were simulated by addition of chloride (Cl^-) and bicarbonate ions (HCO₃^-) and found that lower concentrations of Cl^- and HCO₃^- have minimal influence on MCCA removal. Overall, biochar catalyzed H₂O₂ based oxidation process has great potential and can be applied for degradation of NAs in oil-sand processed water.

Hierarchical porous carbon material restricted Au catalyst for highly catalytic reduction of nitroaromatics

In this study, four kinds of porous carbon materials were used as supports to anchor gold nanoparticles (AuNPs) for catalytic reduction of nitroaromatics and 4-nitrophenol (4-NP) was employed as a model material. Results identified that carbon black (CB) restricted-Au catalyst (Au/CB) provided large specific surface area, small AuNPs size, and low cost, which showed highly catalytic activity for 4-NP reduction. Besides, with the increase of Au loadings, the catalytic activity of Au/CB was enhanced and the 1.2 wt% of Au loading exhibited the best catalytic activity with the high rate of 0.8302 min^-1 and the turnover frequency of 492.50 h^-1. Universality and real water application demonstrated that the as-prepared Au/CB catalyst was promising candidate for other phenols and azo dyes reduction and had great potential for practical application. Furthermore, after ten cycles, Au/CB still retained satisfying stability and activity. These results suggested that the larger specific surface area and smaller particle size attributing to the porosity of CB were conducive to improving the catalytic activity of Au catalysts. This design shows high potential of hierarchical porous carbon materials for highly catalytic reaction in many fields, especially the water purification.

Visible-light-driven photocatalytic degradation of sulfamethazine by surface engineering of carbon nitride：Properties, degradation pathway and mechanisms

Polymeric carbon nitride semiconductor has been explored as emerging metal-free photocatalyst for solving the energy shortage and environmental issues. However, the efficiency of carbon nitride is still not satisfying. Herein, a facile copolymerization between L-cysteine and dicyandiamide has been applied to forming the modified carbon nitride photocatalysts. The photocatalytic performance was evaluated through degrading sulfamethazine under visible light illumination. The ameliorative structure and tuned energy band result in visible-light adsorption enhancement. In addition, nitrogen vacancies offer more sites to adsorbing molecular oxygen, thereby facilitating the transfer of electrons from carbon nitride to the surface adsorbed oxygen. As a result, the degradation rate of optimized modified carbon nitride sample for sulfamethazine was 0.1062 min^-1, which was almost 12 times than that of carbon nitride (0.0086 min^-1). Superoxide radicals and holes were mainly responsible for the sulfamethazine photodegradation by modified carbon nitride. Two reaction intermediates/products were observed and identified by high performance liquid chromatography-mass spectrometer, and a possible reaction pathway was proposed. This study provides new insights into the design of highly efficient photocatalyst for other organic pollutants degradation.

A sustainable ferromanganese biochar adsorbent for effective levofloxacin removal from aqueous medium

This present study reported the synthesis and characterization of a low-cost, environment friendly and high efficient biochar, ferromanganese modified biochar (Fe/Mn-BC) for the removal of levofloxacin (LEV) from aqueous medium. Fe/Mn-BC was synthesized through the facile co-precipitation of Fe, Mn with vinasse wastes and then pyrolysis under controlled conditions. The characterization of Fe/MnBC was analyzed by scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffraction patterns (XPS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and Raman. Some influencing factors (e.g., pH, Fe/Mn-BC dosage, initial LEV concentration, ionic strength, contact time and temperature) were comprehensively investigated. The results manifested that the adsorption process of LEV onto Fe/Mn-BC was high pH dependence and the maximum adsorption capacity was achieved at pH 5. Moreover, the adsorption capacity of LEV was increased with increasing ionic strength. To gain a clearer perspective on the adsorption behavior of LEV onto Fe/Mn-BC, the adsorption kinetics and isotherms were also performed, revealing pseudo-second-order and Freundlich model had a better fitting effect. Reusability experiments indicated that Fe/Mn-BC could maintain a certain adsorption capacity for LEV after 5 recycles. Overall, this work showed that Fe/Mn-BC was an effective and promising adsorbent for eliminating LEV from aqueous medium.

A competent green methodology for the synthesis of aryl thioethers and 1H-tetrazole over magnetically retrievable novel CoFe2O4@l-asparagine anchored Cu, Ni nanocatalyst

The current work describes the successful synthesis of a magnetic CoFe₂O₄ centered asparagine functionalized noble metal (M = Cu, Ni) anchored nanocomposite. The novel materials, synthesized by post-functionalization approach, have been characterized by XRD, SEM, EDX, X-ray elemental mapping, FT-IR and VSM studies. The materials are proved to be efficient heterogeneous catalyst in the synthesis of diarylthioethers by C-S cross coupling reaction and 5-substituted 1H-tetrazoles by azide-alkyne cycloaddition reaction under green conditions. The current methodology is advantageous in terms of simplicity of procedure, facile synthesis, high yield in short reaction time, easy magnetic isolation and reusability of catalysts in consecutive runs with insignificant change in catalytic activity.

Molecularly Imprinted Phase-Change Microcapsule System for Bifunctional Applications in Waste Heat Recovery and Targeted Pollutant Removal

An innovative design of a molecularly imprinted phase-change microcapsule (MIM) system for bifunctional applications in waste heat recovery and targeted pollutant removal was reported in this work. This molecularly imprinted system was successfully constructed by encapsulating n-eicosane with a SiO₂ base shell through emulsion-templated interfacial polycondensation and then coating a molecularly imprinted polymeric layer with bisphenol A (BPA) as a template molecule through surface free-radical polymerization. The morphology, microstructure, and chemical structure of the resultant molecularly imprinted phase-change microcapsules (MIMs) were characterized, and their phase-change behavior, thermal energy-storage performance, and selective adsorption capability were investigated intensively. The MIMs developed in this study achieved an outstanding latent heat-storage capability with a high capacity more than 165 J/g and also showed an excellent phase-change reliability with a very small fluctuation in phase-change temperatures and enthalpies after 500 thermal cycles. Moreover, the MIMs also presented a high thermal stability over 200 °C and good shape stability up to 120 °C. Most of all, an effective specific recognition capability and high recognition efficiency were achieved for the MIMs due to the formation of BPA-molecular imprinting sites on their surface. As a result, the MIMs exhibited good adsorption selectivity toward the BPA molecules and satisfactory reusability for targeted removal of BPA with a removal efficiency of 61.7% after 10 cycles of the rebinding-elution procedure. In view of a smart combination of thermal energy-storage and selective adsorption functions, the MIMs developed in this study demonstrate a great potential in applications for waste heat recovery and targeted pollutant removal of industrial and domestic wastewaters.

Degradation of naphthalene with magnetic bio-char activate hydrogen peroxide: Synergism of bio-char and Fe-Mn binary oxides

This study investigated the hydrogen peroxide (H₂O₂) activation potential of Fe-Mn binary oxides modified bio-char (FeMn/bio-char) for the degradation of naphthalene, the dominant PAHs in drinking water. Results showed that FeMn/bio-char exhibited 80.7- and 2.18-times decomposition rates towards H₂O₂ than that of pure bio-char and Fe-Mn binary oxides, respectively, and consequently the FeMn/bio-char/H₂O₂ photo-Fenton system presented highest naphthalene removal efficiency. The enhanced catalytic activity could be ascribed to the synergistic effect of the combination of bio-char and Fe-Mn binary oxides, such as promoting the adsorption capacity towards contaminant, increasing concentration of persistent free radicals (PFRs) and introducing Fe-Mn binary oxides as new activator. According to the batch-scale experiments, FeMn/bio-char/H₂O₂ photo-Fenton system could degrade naphthalene effectively at a wide pH ranges, and 82.2% of naphthalene was degraded under natural pH of 5.6 within 148 min. Free radicals quenching studies and electron spin resonance (ESR) analyses verified that the dominant free radical within FeMn/bio-char/H₂O₂ photo-Fenton system was hydroxyl radical (•OH). According to the preliminary analysis, the generation of •OH were ascribed to the activation of H₂O₂ by Fe (II), Mn (II) and PFRs on the catalyst surface. The mainly degradation intermediates of naphthalene were identified by GC-MS analysis. Consequently, the possible degradation pathways were proposed. Moreover, naphthalene degradation experiments were also conducted in river, tap water, industrial wastewater as well as medical wastewater, and the results indicated that the FeMn/bio-char/H₂O₂ photo-Fenton system was effective in the treatment of naphthalene in natural waters. This study brings a valuable insight for the potential environmental applications of modified bio-char.

Alleviation of heavy metal and silver nanoparticle toxicity and enhancement of their removal by hydrogen sulfide in Phanerochaete chrysosporium

Hydrogen sulfide (H₂S), an important cellular signaling molecule, plays vital roles in mediating responses to biotic/abiotic stresses. Influences of H₂S on metal removal, cell viability, and antioxidant response of Phanerochaete chrysosporium upon exposure to heavy metals and silver nanoparticles (AgNPs) in the present study were investigated. An enhancement in Pb(ΙΙ) removal with an increase in concentration of the H₂S donor sodium hydrosulfide (NaHS) was observed, and the maximum removal efficiencies increased by 31% and 17% under 100 and 200 mg/L Pb(ΙΙ) exposure, respectively, in the presence of 500 μM NaHS. Application of 500 μM NaHS increased the cell viability by 15%-39% under Pb(II) stress (10-200 mg/L) with relative to the untreated control. Increase in total Ag uptake and cell survival was also elicited by NaHS in a concentration-dependent manner under AgNP stress. Meanwhile, activities of superoxide dismutase and catalase were significantly enhanced with the introduction of NaHS under stresses of Pb(II), Cd(II), Cu(II), Zn(II), Ni(II), and AgNPs. The inhibition in lipid peroxidation and oxidative stress was observed in P. chrysosporium cells exposed to these toxicants following NaHS pretreatment, which could be attributed to the upregulation in antioxidant enzymes. The results obtained suggest that H₂S can alleviate heavy metals and AgNP-induced toxicity to P. chrysosporium and improve the removal efficiency of these toxicants from wastewater.

Biochar facilitated the phytoremediation of cadmium contaminated sediments: Metal behavior, plant toxicity, and microbial activity

Cadmium (Cd) contamination in river sediments becomes increasingly serious, and phytoremediation has been used to remediate Cd contaminated sediments, but the remediation efficiency needs to be improved. In this study, tea waste derived biochar (TB) was used to facilitate the phytoremediation of Cd contaminated sediments. Results showed that TB at 100, 500 and 1000 mg kg^-1 increased Cd accumulation and translocation in ramie seedlings by changing Cd speciation in sediments and altering the subcellular distribution of Cd in plant cells. TB at low contents alleviated Cd induced toxicity in ramie seedlings by promoting plant growth and mitigating the oxidative stress. In addition, the activities of urease-, phosphatase-, and catalase-producing microbes in the Cd contaminated sediments were promoted by the application of TB. These findings demonstrated that biochar at low concentrations could improve the phytoremediation efficiency and mitigating Cd-induced toxicity to plants and microbes in Cd contaminated sediments. This study herein provides a novel technological application of waste biomass in controlling and mitigating risks of heavy metals.