Cadmium tolerance and accumulation in fifteen wetland plant species from cadmium-polluted water in constructed wetlands

Variations in cadmium (Cd) tolerances and accumulations among fifteen wetland plant species in moderately (0.5 mg·L⁻¹) and heavily (1.0 mg·L⁻¹) Cd-polluted wastewaters were investigated in constructed wetlands. Cd removal efficiencies from the wastewaters were more than 90%, and 23.5% and 16.8% of the Cd in the water accumulated in wetland plants for 0.5 and 1.0 mg·L⁻¹ Cd treatments, respectively. The variations among the plant species were 29.4-fold to 48.7-fold in plant biomasses, 5.4-fold to 21.9-fold in Cd concentrations, and 13.8-fold to 29.6-fold in Cd accumulations. The plant species were also largely diversified in terms of Cd tolerance. Some species were tolerant of heavy Cd stress, and some others were sensitive to moderate Cd level. Four wetland plant species were selected for the treatment of Cd-polluted wastewater for their high Cd accumulating abilities and relative Cd tolerances. Plant Cd quantity accumulations are correlated positively and significantly (P <0.05) with plant biomasses and correlated positively but insignificantly (P >0.05) with plant Cd concentrations. The results indicate that the Cd accumulation abilities of wetland plant species are determined mainly by their biomasses and Cd tolerances in growth, which should be the first criteria in selecting wetland plant species for the treating Cd-polluted wastewaters. Cd concentration in the plants may be the second consideration.     

Removing phosphorus from aqueous solutions by using iron-modified corn straw biochar

Iron-modified corn straw biochar was used as an adsorbent to remove phosphorus from agricultural runoff. When agricultural runoffs with a total phosphorus (TP) concentration of 1.86 mg·L⁻¹ to 2.47 mg·L⁻¹ were filtered at a hydraulic retention time of 2 h through a filtration column packed with the modified biochar, a TP removal efficiency of over 99% and an effluent TP concentration of less than 0.02 mg·L⁻¹ were achieved. The isotherms of the phosphorus adsorption by the modified biochar fitted the Freundlich equation better than the Langmuir equation. The mechanism of the phosphorus adsorbed by the modified biochar was analyzed by using various technologies, i.e. scanning electron microscopy (SEM), X-ray diffraction (XRD) analysis, X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR). The results indicated that the surface of the modified biochar was covered by small iron granules, which were identified as Fe₃O₄. The results also showed that new iron oxides were formed on the surface of the modified biochar after the adsorption of phosphorus. Moreover, new bonds of Fe-O-P and P-C were found, which suggested that the new iron oxides tend to be Fe₅(PO₄)₄(OH)₃. Aside from removing phosphorus, adding the modified biochar into soil also improved soil productivity. When the modified biochar-to-soil rate was 5%, the stem, root, and bean of broad bean plants demonstrated increased growth rates of 91%, 64%, and 165%, respectively.     

Combined process of biofiltration and ozone oxidation as an advanced treatment process for wastewater reuse

The effluent of a wastewater treatment plant was treated in a pilot plant for reclaimed water production through the denitrification biofilter (DNBF) process, ozonation (O₃), and biologic aerated filtration (BAF). The combined process demonstrated good removal performance of conventional pollutants, including concentrations of chemical oxygen demand (27.8 mg·L⁻¹) and total nitrogen (9.9 mg·L⁻¹) in the final effluent, which met the local discharge standards and water reuse purposes. Micropollutants (e.g., antibiotics and endocrine-disrupting chemicals) were also significantly removed during the proposed process. Ozonation exhibited high antibiotic removal efficiencies, especially for tetracycline (94%). However, micropollutant removal efficiency was negatively affected by the nitrite produced by DNBF. Acute toxicity variations of the combined process were estimated by utilizing luminescent bacteria. Inhibition rate increased from 9% to 15% during ozonation. Carbonyl compound concentrations (e.g., aldehydes and ketones) also increased by 58% as by-products, which consequently increased toxicity. However, toxicity eventually became as low as that of the influent because the by-products were effectively removed by BAF. The combined DNBF/O₃/BAF process is suitable for the advanced treatment of reclaimed water because it can thoroughly remove pollutants and toxicity.     

Microprofiles of activated sludge aggregates using microelectrodes in completely autotrophic nitrogen removal over nitrite (CANON) reactor

Microsensor measurements and fluorescence in situ hybridization (FISH) analysis were combined to investigate the microbial populations and activities in a laboratory-scale sequencing batch reactor (SBR) for completely autotrophic nitrogen removal over nitrite (CANON). Fed with synthetic wastewater rich in ammonia, the SBR removed 82.5±5.4% of influent nitrogen and a maximum nitrogen-removal rate of 0.52 kgN·m⁻³·d⁻¹ was achieved. The FISH analysis revealed that aerobic ammonium-oxidizing bacteria (AerAOB) Nitrosomonas and anaerobic ammonium-oxidizing bacteria (AnAOB) dominated the community. To quantify the microbial activities inside the sludge aggregates, microprofiles were measured using pH, dissolved oxygen (DO), NH4+, NO2− and NO3− microelectrodes. In the outer layer of sludge aggregates (0–700 μm), nitrite-oxidizing bacteria (NOB) showed high activity with 4.1 μmol·cm⁻³·h⁻¹ of maximum nitrate production rate under the condition of DO concentration higher than 3.3 mg·L⁻¹. Maximum AerAOB activity was detected in the middle layer (depths around 1700 μm) where DO concentration was 1.1 mg·L⁻¹. In the inner layer (2200–3500 μm), where DO concentration was below 0.9 mg·L⁻¹, AnAOB activity was detected. We thus showed that information obtained from microscopic views can be helpful in optimizing the SBR performance.     

Treatment of swine wastewater in aerobic granular reactors: comparison of different seed granules as factors

The granulation process, physic-chemical properties, pollution removal ability and bacterial communities of aerobic granules with different feed-wastewater (synthetic wastewater, R1; swine wastewater, R2), and the change trend of some parameters of two types of granules in long-term operated reactors treating swine wastewater were investigated in this experiment. The result indicated that aerobic granulation with the synthetic wastewater had a faster rate compared with swine wastewater and that full granulation in R1 and R2 was reached on the 30th day and 39th day, respectively. However, although the feed wastewater also had an obvious effect on the biomass fraction and extracellular polymeric substances of the aerobic granules during the granulation process, these properties remained at a similar level after long-term operation. Moreover, a similar increasing trend could also be observed in terms of the nitrogen removal efficiencies of the aerobic granules in both reactors, and the average specific removal rates of the organics and ammonia nitrogen at the steady-state stage were 35.33 mg·g⁻¹ VSS and 51.46 mg·g⁻¹ VSS for R1, and 35.47 mg·g⁻¹ VSS and 51.72 mg·g⁻¹ VSS for R2, respectively. In addition, a shift in the bacterial diversity occurred in the granulation process, whereas bacterial communities in the aerobic granular reactor were not affected by the seed granules after long-term operation.     

Microbial electrolysis cells with biocathodes and driven by microbial fuel cells for simultaneous enhanced Co(II) and Cu(II) removal

Cobalt and copper recovery from aqueous Co(II) and Cu(II) is one critical step for cobalt and copper wastewaters treatment. Previous tests have primarily examined Cu(II) and Co(II) removal in microbial electrolysis cells (MECs) with abiotic cathodes and driven by microbial fuel cell (MFCs). However, Cu(II) and Co(II) removal rates were still slow. Here we report MECs with biocathodes and driven by MFCs where enhanced removal rates of 6.0±0.2 mg?L⁻¹?h⁻¹ for Cu(II) at an initial concentration of 50 mg?L⁻¹ and 5.3±0.4 mg?L⁻¹ h⁻¹ for Co(II) at an initial 40 mg?L⁻¹ were achieved, 1.7 times and 3.3 times as high as those in MECs with abiotic cathodes and driven by MFCs. Species of Cu(II) was reduced to pure copper on the cathodes of MFCs whereas Co(II) was removed associated with microorganisms on the cathodes of the connected MECs. Higher Cu(II) concentrations and smaller working volumes in the cathode chambers of MFCs further improved removal rates of Cu(II) (115.7 mg?L⁻¹?h⁻¹) and Co(II) (6.4 mg?L⁻¹?h⁻¹) with concomitantly achieving hydrogen generation (0.05±0.00 mol?mol⁻¹ COD). Phylogenetic analysis on the biocathodes indicates Proteobacteria dominantly accounted for 67.9% of the total reads, followed by Firmicutes (14.0%), Bacteroidetes (6.1%), Tenericutes (2.5%), Lentisphaerae (1.4%), and Synergistetes (1.0%). This study provides a beneficial attempt to achieve simultaneous enhanced Cu(II) and Co(II) removal, and efficient Cu(II) and Co(II) wastewaters treatment without any external energy consumption.     

One-pot preparation of graphene oxide magnetic nanocomposites for the removal of tetrabromobisphenol A

A simple solvothermal method was used to prepare monodisperse magnetite (Fe₃O₄) nanoparticles attached onto graphene oxide (GO) sheets as adsorbents to remove tetrabromobisphenol A (TBBPA) from an aqueous solution. These Fe₃O₄/GO (MGO) nanocomposites were characterized by transmission electron microscopy. The adsorption capacity at different initial pH, contact duration, and temperature were evaluated. The kinetics of adsorption was found to fit the pseudo-second-order model perfectly. The adsorption isotherm well fitted the Langmuir model, and the theoretical maximum of adsorption capacity calculated by the Langmuir model was 27.26 mg?g^-1. The adsorption thermodynamics of TBBPA on the MGO nanocomposites was determined at 303 K, 313 K, and 323 K, respectively. The results indicated that the adsorption was spontaneous and endothermic. The MGO nanocomposites were conveniently separated from the media by an external magnetic field within several seconds, and then regenerated in 0.2 M NaOH solution. Thus, the MGO nanocomposites are a promising candidate for TBBPA removal from wastewater.     

Fe-Mn-sepiolite as an effective heterogeneous Fenton-like catalyst for the decolorization of reactive brilliant blue

A study of the decolorization of reactive brilliant blue in an aqueous solution using Fe-Mn-sepiolite as a heterogeneous Fenton-like catalyst has been performed. The Fourier transform infrared (FTIR) spectra of the catalyst showed bending vibrations of the Fe-O. The X-ray diffraction (XRD) patterns of the catalyst showed characteristic diffraction peaks of α-Fe₂O₃, γ-Fe₂O₃ and MnO. A four factor central composite design (CCD) coupled with response surface methodology (RSM) was applied to evaluate and optimize the important variables (catalyst addition, hydrogen peroxide dosage, initial pH value and initial dye concentration). When the reaction conditions were catalyst dosage= 0.4 g, [H₂O₂]= 0.3 mL, pH= 2.5, [reactive brilliant blue]_o = 50 mg·L⁻¹, and volume of solution= 500 mL at room temperature, the decolorization efficiency of reactive brilliant blue was 91.98% within 60 min. Moreover, the Fe-Mn-sepiolite catalyst had good stability for the degradation of reactive brilliant blue even after six cycles. Leaching of iron ions (<0.4 mg·L⁻¹) was observed. The decoloring process was reactive brilliant blue specific via a redox reaction. The benzene ring and naphthalene ring were first oxidized to open ring; these were then oxidized to the alcohol and carboxylic acid. The reactive brilliant blue was decomposed mainly by the attack of ·OH radicals including surface-bound ·OH radicals generated on the catalyst surface.     

氨基化氧化石墨烯(AGO)的制备及其对六价铬的吸附机制

以乙二胺盐酸盐(EDH)为改性剂改性氧化石墨烯(GO),水热法制备氨基化氧化石墨烯(Amino-functionalized;graphene;oxide,AGO).SEM、XRD、FTIR和Zeta电位表征分析发现,AGO表面含有羟基、羧基及氨基基团,Zeta电位为pH=10.14.以水中低浓度六价铬Cr(Ⅵ)为污染物,探讨了乙二胺盐酸盐(EDH)用量、pH、AGO用量、Cr(Ⅵ)初始浓度以及常见干扰离子对AGO吸附Cr(Ⅵ)影响.结果表明,在pH=6.0、7-AGO用量为0.8;mg·L^-1和Cr(Ⅵ)初始浓度为2.0;mg·L^-1,7-AGO对Cr(Ⅵ)去除率可达95.1%;SO₄^2-会明显抑制AGO对Cr(Ⅵ)的吸附.AGO对Cr(Ⅵ)的吸附过程符合二级动力学模型,吸附机制主要为静电作用.     

One-step ball milling-prepared nano Fe2O3 and nitrogen-doped graphene with high oxygen reduction activity and its application in microbial fuel cells

• Nano Fe₂O₃ and N-doped graphene was prepared via a one-step ball milling method. • The maximum power density of Fe-N-G in MFC was 390% of that of pristine graphite. • Active sites like nano Fe₂O₃, pyridinic N and Fe-N groups were formed in Fe-N-G. • The improvement of Fe-N-G was due to full exposure of active sites on graphene. Developing high activity, low-cost and long durability catalysts for oxygen reduction reaction is of great significance for the practical application of microbial fuel cells. The full exposure of active sites in catalysts can enhance catalytic activity dramatically. Here, novel Fe-N-doped graphene is successfully synthesized via a one-step in situ ball milling method. Pristine graphite, ball milling graphene, N-doped graphene and Fe-N-doped graphene are applied in air cathodes, and enhanced performance is observed in microbial fuel cells with graphene-based catalysts. Particularly, Fe-N-doped graphene achieves the highest oxygen reduction reaction activity, with a maximum power density of 1380±20 mW/m² in microbial fuel cells and a current density of 23.8 A/m² at –0.16 V in electrochemical tests, which are comparable to commercial Pt and 390% and 640% of those of pristine graphite. An investigation of the material characteristics reveals that the superior performance of Fe-N-doped graphene results from the full exposure of Fe₂O₃ nanoparticles, pyrrolic N, pyridinic N and excellent Fe-N-G active sites on the graphene matrix. This work not only suggests the strategy of maximally exposing active sites to optimize the potential of catalysts but also provides promising catalysts for the use of microbial fuel cells in sustainable energy generation.     

Selective recovery of Cu2+ and Ni2+ from wastewater using bioelectrochemical system

As the bioelectrochemical system, the microbial fuel cell (MFC) and the microbial electrolysis cell (MEC) were developed to selectively recover Cu²⁺ and Ni²⁺ ions from wastewater. The wastewater was treated in the cathode chambers of the system, in which Cu²⁺ and Ni²⁺ ions were removed by using the MFC and the MEC, respectively. At an initial Cu²⁺ concentration of 500 mg·L^-1, removal efficiencies of Cu²⁺ increased from 97.0%±1.8% to 99.0%±0.3% with the initial Ni²⁺ concentrations from 250 to 1000 mg·L^-1, and maximum power densities increased from 3.1±0.5 to 5.4±0.6 W·m^-3. The Ni²⁺ removal mass in the MEC increased from 6.8±0.2 to 20.5±1.5 mg with the increase of Ni²⁺ concentrations. At an initial Ni²⁺ concentration of 500 mg·L^-1, Cu²⁺ removal efficiencies decreased from 99.1%±0.3% to 74.2%±3.8% with the initial Cu²⁺ concentrations from 250 to 1000 mg·L^-1, and maximum power densities increased from 3.0±0.1 to 6.3±1.2 W·m^-3. Subsequently, the Ni²⁺ removal efficiencies decreased from 96.9%±3.1% to 73.3%±5.4%. The results clearly demonstrated the feasibility of selective recovery of Cu²⁺ and Ni²⁺ from the wastewater using the bioelectrochemical system.     

Catalytic wet air oxidation of phenol,nitrobenzene and aniline over the multi-walled carbon nanotubes (MWCNTs) as catalysts

Wet air oxidation (WAO) is one of effective technologies to eliminate hazardous, toxic and highly concentrated organic compounds in the wastewater. In the paper, multi-walled carbon nanotubes (MWCNTs), functionalized by O₃, were used as catalysts in the absence of any metals to investigate the catalytic activity in the catalytic wet air oxidation (CWAO) of phenol, nitrobenzene (NB) and aniline at the mild operating conditions (reaction temperature of 155°C and total pressure of 2.5 MPa) in a batch reactor. The MWCNTs were characterized with scanning electron microscopy (SEM), transmission electron microscopy (TEM), gas adsorption measurements (BET), fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS). The functionalized MWCNTs showed good catalytic performance. In the CWAO of phenol over the functionalized MWCNTs, total phenol removal was obtained after 90 min run, and the reaction apparent activation energy was ca. 40 kJ·mol^-1. The NB was not removed in the CWAO of single NB, while ca. 97% NB removal was obtained and 40% NB removal was attributed to the catalytic activity after 180 min run in the presence of phenol. Ca. 49% aniline conversion was achieved after 120 min run in the CWAO of aniline.     

Removal of lead from aqueous solution by hydroxyapatite/manganese dioxide composite

A novel composite adsorbent, hydroxyapatite/manganese dioxide (HAp/MnO₂), has been developed for the purpose of removing lead ions from aqueous solutions. The combination of HAp with MnO₂ is meant to increase its adsorption capacity. Various factors that may affect the adsorption efficiency, including solution pH, coexistent substances such as humic acid and competing cations (Ca²⁺, Mg²⁺), initial solute concentration, and the duration of the reaction, have been investigated. Using this composite adsorbent, solution pH and coexistent calcium or magnesium cations were found to have no significant influence on the removal of lead ions under the experimental conditions. The adsorption equilibrium was described well by the Langmuir isotherm model, and the calculated maximum adsorption capacity was 769 mg·g⁻¹. The sorption processes obeyed the pseudo-second-order kinetics model. The experimental results indicate that HAp/MnO₂ composite may be an effective adsorbent for the removal of lead ions from aqueous solutions.     

Influencing mechanism of high solid concentration on anaerobic mono-digestion of sewage sludge without agitation

High-solids anaerobic digestion of sewage sludge was a promising process, but high solid concentration negatively influenced methane production. The influencing mechanism was systematically analyzed in this study through a series of static anaerobic digestion experiments at total solids (TS) contents of 3%–15%. The results showed that TS 6% was the boundary between low-solids and high-solids anaerobic digestion, and the accumulative methane yield decreased exponentially when TS increased from 6% to 15%. The performance of anaerobic digestion was directly determined by the efficiency of mass transfer, and the relation between methane yield and sludge diffusive coefficients was well described by a power function. Thus, the increasing TS resulted in an exponential increase in sludge viscosity but an exponential decrease in diffusive coefficient. The blocked mass transfer led to the accumulation of volatile fatty acids (VFAs) and free ammonia. Acetic metabolism was the main process, whereas butyric and propionic metabolisms occurred at the initial stage of high-solids anaerobic digestion. The concentration of VFAs reached the maximum at the initial stage, which were still lower than the threshold influencing methanogens. The concentration of free ammonia increased gradually, and the methanogenesis was inhibited when free ammonia nitrogen exceeded 50 mg·L⁻¹. Consequently, the deterioration of high-solids anaerobic digestion was related to the blocked mass transfer and the resulting ammonia accumulation.     

Inhibition of bromate formation by reduced graphene oxide supported cerium dioxide during ozonation of bromide-containing water

GO or RGO promotes bromate formation during ozonation of bromide-containing water. CeO₂/RGO significantly inhibits bromate formation compared to RGO during ozonation. CeO₂/RGO shows an enhancement on DEET degradation efficiency during ozonation. Ozone (O₃) is widely used in drinking water disinfection and wastewater treatment. However, when applied to bromide-containing water, ozone induces the formation of bromate, which is carcinogenic. Our previous study found that graphene oxide (GO) can enhance the degradation efficiency of micropollutants during ozonation. However, in this study, GO was found to promote bromate formation during ozonation of bromide-containing waters, with bromate yields from the O₃/GO process more than twice those obtained using ozone alone. The promoted bromate formation was attributed to increased hydroxyl radical production, as confirmed by the significant reduction (almost 75%) in bromate yield after adding t-butanol (TBA). Cerium oxide (less than 5 mg/L) supported on reduced GO (xCeO₂/RGO) significantly inhibited bromate formation during ozonation compared with reduced GO alone, and the optimal Ce atomic percentage (x) was determined to be 0.36%, achieving an inhibition rate of approximately 73%. Fourier transform infrared (FT-IR) spectra indicated the transformation of GO into RGO after hydrothermal treatment, and transmission electron microscope (TEM) results showed that CeO₂ nanoparticles were well dispersed on the RGO surface. The X-ray photoelectron spectroscopy (XPS) spectra results demonstrated that the Ce³⁺/Ce⁴⁺ ratio in xCeO₂/RGO was almost 3‒4 times higher than that in pure CeO₂, which might be attributed to the charge transfer effect from GO to CeO₂. Furthermore, Ce³⁺ on the xCeO₂/RGO surface could quench Br⋅ and BrO⋅ to further inhibit bromate formation. Meanwhile, 0.36CeO₂/RGO could also enhance the degradation efficiency of N,N-diethyl-m-toluamide (DEET) in synthetic and reclaimed water during ozonation.     

Effects of Al3+ on pollutant removal and extracellular polymeric substances (EPS) under anaerobic,anoxic and oxic conditions

The highest removal efficiencies of COD and TN were achieved under 10 mg/L of Al³⁺. The highest TP removal efficiency occurred under 30 mg/L of Al³⁺. EPS, PS and PN concentrations increased with the addition of Al³⁺. Sludge properties significantly changed with the addition of Al³⁺. Aluminum ions produced by aluminum mining, electrolytic industry and aluminum-based coagulants can enter wastewater treatment plants and interact with activated sludge. They can subsequently contribute to the removal of suspended solids and affect activated sludge flocculation, as well as nitrogen and phosphorus removal. In this study, the effects of Al³⁺ on pollutant removal, sludge flocculation and the composition and structure of extracellular polymeric substances (EPS) were investigated under anaerobic, anoxic and oxic conditions. Results demonstrated that the highest chemical oxygen demand (COD) and total nitrogen (TN) removal efficiencies were detected for an Al³⁺ concentration of 10 mg/L. In addition, the maximal dehydrogenase activity and sludge flocculation were also observed at this level of Al³⁺. The highest removal efficiency of total phosphorus (TP) was achieved at an Al³⁺ concentration of 30 mg/L. The flocculability of sludge in the anoxic zone was consistently higher than that in the anaerobic and oxic zones. The addition of Al³⁺ promoted the secretion of EPS. Tryptophan-like fluorescence peaks were detected in each EPS layer in the absence of Al³⁺. At the Al³⁺ concentration of 10 mg/L, fulvic acid and tryptophan fluorescence peaks began to appear, while the majority of protein species and the highest microbial activity were also detected. Low Al³⁺ concentrations (<10 mg/L) could promote the removal efficiencies of COD and TN, yet excessive Al³⁺ levels (>10 mg/L) weakened microbial activity. Higher Al³⁺ concentrations (>30 mg/L) also inhibited the release of phosphorus in the anaerobic zone by reacting with PO₄^3-.     

Achieving biodegradability enhancement and acute biotoxicity removal through the treatment of pharmaceutical wastewater using a combined internal electrolysis and ultrasonic irradiation technology

Actual pharmaceutical wastewater was treated using a combined ultrasonic irradiation (US) and iron/coke internal electrolysis (Fe/C) technology. A significant synergetic effect was observed, showing that ultrasonic irradiation dramatically enhanced the chemical oxygen demand (COD) removal efficiencies by internal electrolysis. The effects of primary operating factors on COD removal were evaluated systematically. Higher ultrasonic frequency and lower pH values as well as longer reaction time were favorable to COD removal. The ratio of biochemical oxygen demand (BOD) and COD (B/C) of the wastewater increased from 0.21 to 0.32 after US-Fe/C treatment. An acute biotoxicity assay measuring the inhibition of bioluminescence indicated that the wastewater with overall toxicity of 4.3 mg-Zn²⁺·L^-1 was reduced to 0.5 mg-Zn²⁺·L^-1 after treatment. Both the raw and the treated wastewater samples were separated and identified. The types of compounds suggested that the increased biodegradability and reduced biotoxicity resulted mainly from the destruction of N,N-2 dimethyl formamide and aromatic compounds in the pharmaceutical wastewater.     

G-CNTs/PVDF mixed matrix membranes with improved antifouling properties and filtration performance

A novel nanocomposite OMWCNT-A-GO was synthesized by conjugating OMWCNT and GO. The P-OMWCNT-A-GO membrane was fabricated by non-solvent induced phase inversion. The P-OMWCNT-A-GO exhibits the best water flux, BSA rejection and flux recovery. It should be due to the enhanced membrane pore size, porosity and hydrophilicity. Although carbon nanomaterials have been widely used as effective nanofillers for fabrication of mixed matrix membranes (MMMs) with outstanding performances, the reproducibility of the fabricated MMMs is still hindered by the non-homogenous dispersion of these carbon nanofillers in membrane substrate. Herein, we report an effective way to improve the compatibility of carbon-based nanomaterials with membrane matrixes. By chemically conjugating the oxidized CNTs (o-CNTs) and GO using hexanediamine as cross-linker, a novel carbon nanohybrid material (G-CNTs) was synthesized, which inherited both the advanced properties of multi-walled carbon nanotubes (CNTs) and graphene oxide (GO). The G-CNTs incorporated polyvinylidene fluoride (PVDF) MMMs (G-CNTs/PVDF) were fabricated via a non-solvent induced phase separation (NIPS) method. The filtration and antifouling performances of G-CNTs/PVDF were evaluated using distillate water and a 1 g/L bovine serum albumin (BSA) aqueous solution under 0.10 MPa. Compared to the MMMs prepared with o-CNTs, GO, the physical mixture of o-CNTs and GO and pure PVDF membrane, the G-CNTs/PVDF membrane exhibited the highest water flux up to 220 L/m²/h and a flux recovery ratio as high as 90%, as well as the best BSA rejection rate. The excellent performances should be attributed to the increased membrane pore size, porosity and hydrophilicity of the resulted membrane. The successful synthesis of the novel nanohybrid G-CNTs provides a new type of nanofillers for MMMs fabrication.     

Electroconductive RGO-MXene membranes with wettability-regulated channels: improved water permeability and electro-enhanced rejection performance

● Electroconductive RGO-MXene membranes were fabricated. ● Wettable membrane channels were established between RGO and MXene nanosheets. ● Hydrophilic MXene reduces the resistance of water entering the membrane channels. ● Water permeance of RGO-MXene membrane is 16.8 times higher than that of RGO membrane. ● Electro-assistance can enhance the dye rejection performance of RGO-MXene membrane. Reduced graphene oxide (RGO) membranes are theoretically more conducive to the rapid transport of water molecules in their channels compared with graphene oxide (GO) membranes, as they have fewer oxygen-containing functional groups and more non-oxidized regions. However, the weak hydrophilicity of RGO membranes inhibits water entry into their channels, resulting in their low water permeability. In this work, we constructed wettable RGO-MXene channels by intercalating hydrophilic MXene nanosheets into the RGO membrane for improving the water permeance. The RGO-MXene composite membrane exhibits high pure water permeance of 62.1 L/(m²·h·bar), approximately 16.8 times that of the RGO membrane (3.7 L/(m²·h·bar)). Wettability test results and molecular dynamics simulations suggest that the improved water permeance results from the enhanced wettability of RGO-MXene membrane and increased rate of water molecules entering the RGO-MXene channels. Benefiting from good conductivity, the RGO-MXene membrane with electro-assistance exhibits significantly increased rejection rates for negatively charged dyes (from 56.0% at 0 V to 91.4% at 2.0 V for Orange G) without decreasing the permeate flux, which could be attributed to enhanced electrostatic repulsion under electro-assistance.     

Hydrophilic/underwater superoleophobic graphene oxide membrane intercalated by TiO2 nanotubes for oil/water separation

GO/TiO₂ membrane was prepared by assembling GO nanosheets and TiO₂ nanotubes. The intercalation of TiO₂ nanotubes enlarged the space of GO interlayers and modified the surface morphology. Hydrophilic/underwater superoleophobic property of GO/TiO₂ membrane was obtained. Water permeability, hydrophilicity, oleophobicity and antifouling ability of GO-based membrane were all enhanced by intercalating TiO₂ nontubes. Membrane technology for oil/water separation has received increasing attention in recent years. In this study, the hydrophilic/underwater superoleophobic membrane with enhanced water permeability and antifouling ability were fabricated by synergistically assembling graphene oxide(GO) nanosheets and titanium dioxide (TiO₂) nanotubes for oil/water separation. GO/TiO₂ membrane exhibits hydrophilic and underwater superoleophobic properties with water contact angle of 62° and under water oil contact angle of 162.8°. GO/TiO₂ membrane shows greater water permeability with the water flux up to 531 L/(m²·h·bar), which was more than 5 times that of the pristine GO membrane. Moreover, GO/TiO₂membrane had excellent oil/water separation efficiency and anti-oil-fouling capability, as oil residual in filtrate after separation was below 5 mg/L and flux recovery ratios were over 80%.The results indicate that the intercalation of TiO₂ nanotubes into adjacent GO nanosheets enlarged the channel structure and modified surface topography of the obtained GO/TiO₂ membranes, which improved the hydrophilicity, permeability and anti-oil-fouling ability of the membranes, enlightening the great prospects of GO/TiO₂ membrane in oil-water treatment.