Cr Removal Efficiency Research Articles

Eco-friendly Recovery and Utilization of Innovative Industrial Adsorbents for Multi-metal Ion Removal in Aqueous Solutions

This study investigates the ability of recovered industrial bentonite waste RIBW as a nano-, low-cost and new adsorbent to remove the ions of Pb, Cd, Cr, Zn, and Ni that have different electrochemical properties in the form of multi-metal ions from aqueous solutions. The investigated doses of RIBW were (0.1, 0.2, and 0.3) g/100 mL for each system, and the initial concentration of each metal ions in the binary, ternary, quaternary, and quinary system was 50, 33.3, 25, and 20 ppm, respectively, where the total concentration of ions remained constant and equivalent to 100 ppm. The maximum removal efficiency of Pb, Cd, Cr, Zn, and Ni was in the binary system with a dose of 0.3 gm of RIBW and equaled 99.7, 95.7, 99.5, 99.2, and 97.3. The minimum in the quinary system with an adsorbent mass of 0.1 g equaled 80.8, 51.1, 72.7, 71.1, and 36.6, respectively. The correlation coefficient values of R2 for all experiments ranged from 0.91 to 1.00. The adsorption capacity at the level of single- or multi-ion removal decreases with increasing the number of partaken metal ions in an aqueous solution, where the adsorption capacity order of metal ions in binary > ternary > quaternary > quinary system. It was evident that the electrochemical properties, such as atomic weight, ionic radius, hydrated ionic radius, and softness value have essential effects on the adsorption capacity, where the ions metal having high values of these properties was more adsorbed on the surface of RIBW adsorbent. Keywords: Adsorption, Heavy metals, Binary, Recycling, Water treatment

Highly Efficient Removal of Cr(VI) by Biochar Derived from Vietnamese Young Durian Fruit: Comparison of Traditional and Microwave-Assisted Pyrolysis.

This study compares the material characteristics and evaluates the Cr(VI) adsorption capacity of biochar derived from a novel byproduct (young durian fruit, YDF), synthesized using two pyrolysis methods (traditional and microwave-assisted). The optimal pyrolysis conditions for porosity were 800 °C and 800 W for 30 min, respectively. The traditional pyrolysis method yielded a very high surface area and pore volume (668 m2/g; 0.332 cm3/g). XRD patterns and FTIR spectra demonstrated structural and functional group differences, significantly impacting the Cr(VI) removal efficiency in water. pH was a critical factor with optimal adsorption at pH 2.0. The adsorption process reached equilibrium at 180 and 100 min at initial concentrations of 100 and 125 mg/L for biochar synthesized by traditional and microwave-assisted pyrolysis, respectively. The adsorption mechanisms proposed based on modern analytical methods include adsorption-reduction, ion exchange, electrostatic interaction, and surface complexation. Industrial wastewater containing chromium was effectively treated under natural conditions (pH = 5.88; Co = 129.9 mg/L) using biochar synthesized via microwave, achieving a Qe of 21.41 mg/g. The research results pave the way for new directions in the synthesis and application of biochar in environmental treatment, specifically using young fruit materials and microwave methods.

Enhanced adsorption of Cr(VI) from wastewater by utilizing sludge and reed to prepare ceramsite modified with Fe3O4

AbstractA large amount of wastewater containing Cr(VI) is highly toxic and harmful to the environment, which requires effective treatment. In this study, an adsorbed ceramsite was prepared from dredged sludge (DS) and reed powder (RP). Then the prepared ceramsite was introduced Fe3O4 magnetic functional groups by a simple hydrothermal method to enhance the adsorption of Cr(VI) from wastewater. Batch adsorption experiments of Fe3O4‐modified ceramsite (FCS) to remove Cr(VI) were studied systematically. Effects of different contact time, adsorbent mass and initial Cr(VI) concentration on Cr(VI) removal efficiency were investigated and optimized by a response surface methodology. The results show that when the loading content of Fe3O4 is 30% (FCS‐0.3), the highest removal efficiency of Cr(VI) reached 88.48%, and the Cr(VI) adsorbed process can be well described by pseudo‐second‐order kinetics and Langmuir model, indicating that adsorption process is a chemisorption and monolayer adsorption. Moreover, the FTIR, XPS and Zeta potential analysis further revealed the mechanism of efficient removal of Cr(VI) by Fe3O4 loaded onto the ceramsite to increase the specific surface area and functional groups to adsorb Cr(VI). This study provides an effective method to convert solid waste such as DS and RP into a highly efficient magnetic adsorbent to adsorb and remove Cr(VI) from wastewater.

Efficient Removal of Cr (VI) and As (V) from Aqueous Solution Using Magnetically Separable Nickel Ferrite Nanoparticles

A promising nickel ferrite (NiFe2O4) NPs with excellent magnetic characteristics was synthesized using an aqueous-based reflux approach that eliminates the need for calcination temperature. The magnetic nanoparticles obtained were analysed using X-ray diffraction (XRD), Fourier-transform infrared (FTIR), and scanning electron microscopy (SEM). The analysis showed that synthesized nickel ferrite had a spherical shape with an average size ranging from 18 to 29 nm. The synthesized nickel ferrite is utilized for the removal of hexavalent chromium (Cr (VI)) and pentavalent arsenic (As (V)) ions from aqueous solution through adsorption method. The removal of Cr (VI) ions achieved a maximum efficiency of 65% after 120 minutes at a pH of 5, with a ferrite dose of 2 g/L and a concentration of Cr (VI) ions of 25 mg/L. while the removal of As (V) at a pH of 5, with a dose of 1 g/L of ferrite and an initial concentration of 25 mg/L of As (V) ions was 77% after 120 minutes. In addition, the data obtained from the isotherms of Langmuir (R2 = 0.99, 0.98), Freundlich (R2 = 0.86, 0.97) and Temkin (R2 = 0.83, 0.97). The adsorption of Cr (VI) ions is governed by a pseudo first-order kinetics process, whereas the adsorption of As (V) ions is governed by a pseudo second-order kinetics reaction. After five adsorption–desorption cycles at the same optimal operating condition, Cr (VI) and As (V) removal efficiency dropped from 65%, 77% to 25%, 30%, respectively.

Performance Enhancement of Green synthesized ZnO Nanocomposite Ultrafiltration Membrane for Removal of Cr(VI) from Aqueous Solution

Nano-membranes are gaining significant attention for various applications, including water treatment, ion concentration control, desalination, and a range of biomedical uses. However, this advanced technology faces challenges such as toxicity and fouling from contaminants, which raises safety concerns regarding the synthesis of green and sustainable membranes. In this study, green synthesized zinc oxide nanoparticles (ZnO NPs) derived from blue-green algae Arthrospira platensis were combined with cellulose acetate (CA) to fabricate ultrafiltration (UF) nanocomposite membranes designed for the removal of Chromium (VI) from aqueous solutions. This ensures that our material is environmentally friendly and poses no risk of ecotoxicity, unlike conventional synthetic materials that may have harmful environmental impacts. The membranes were synthesized using the phase inversion technique and characterized using Fourier-transform infrared spectroscopy (FTIR), Scanning electron microscope (SEM), X-Ray diffraction (XRD), Energy dispersive X-ray analysis (EDX) and water contact angle (WCA) assess their chemical composition and morphological structure. The performance of the membranes was evaluated by measuring water flux and Cr(VI) removal. The concentration of ZnO NPs influenced the membranes’ morphology, performance, surface hydrophilicity, and Cr(VI) removal efficiency. Various concentrations of ZnO nanoparticles (0.5, 1, 2, and 3 wt%) were added to the CA membrane. The findings revealed that the membrane containing 3 wt% ZnO NPs achieved a Cr(VI) removal efficiency of 94.77 %, an adsorption capacity (qe) of 11.28 µg/cm2, and exhibited excellent hydrophilicity with a contact angle of 34.7°. Additionally, the water flux of the CA/ZnO NPs nanocomposite membrane was 53 % higher than that of the neat CA membrane. The kinetic data suggested that the adsorption of Cr(VI) onto the membrane followed a pseudo-second-order kinetic model. Among the isotherm models applied, the Langmuir adsorption isotherm provided the best fit for the experimental data. In summary, our study not only introduces an environmentally sustainable and economically viable method for producing ZnO NPs, but it also highlights the superior performance of the nanocomposite membranes in treating polluted water. This makes our approach a valuable contribution to the development of green technology for environmental applications, offering promising potential for industrial and ecological implementation.

Capability and Mechanism of Cr(VI) Removal by Phthalic Acid Modified Sulfidated Microscale Zero Valent Iron

Mechanochemically sulfidated microscale zero valent iron (S-mZVIbm) exhibits promising Cr(VI) removal performance but is prone to be passivated by Cr(VI), how to mitigate the passivation is still a challenge. In this study, we successfully synthesized phthalic acid (PA, carboxyl-rich organic acid) modified S-mZVIbm particles (PA-S-mZVIbm (4:1)) through ball milling. The pre-corrosion of the ZVI surface by PA effectively increased the specific surface area of ZVI. Additionally, the carboxyl groups complexed with Cr(VI), thereby enhancing its Cr(VI) removal capacity and alleviating the passivation. The Cr(VI) removal by PA-S-mZVIbm (4:1) was mainly a chemisorption process on the surface and its Cr(VI) removal capacity (55.47mg/g) was 1.26 and 9.94 – 14.83 times that of PA-mZVIbm and S-mZVIbm, respectively. The electron efficiency of Cr(VI) removal by both PA-S-mZVIbm (4:1) and S-mZVIbm was ~100%, however, the Fe(0) utilization efficiency of PA-S-mZVIbm (4:1) was at least 15 times higher than that of S-mZVIbm, explaining the superior performance of PA-S-mZVIbm (4:1). This study confirmed that PA modification could effectively mitigate the passivation and improve the Fe(0) utilization efficiency of S-mZVIbm.

Targeting active sites nickel-porphyrin over BiOBr nanosheets with excellent charge separation for accelerated photoreduction reactions

The energy crisis and environmental pollution severely constrained the sustainable development of society. Herein, nickel-porphyrin active sites have been integrated over BiOBr for enhanced photocatalytic CO2 reduction and Cr(VI) removal. The optimized NiTMCPP/BiOBr-2 photocatalyst exhibits CO generation rate of 14.14 μmol g−1 under irradiation for 5h, which is around 2 times compared with BiOBr. Meanwhile, Cr(VI) removal efficiency over NiTMCPP/BiOBr-2 is 97.72% under visible light irradiation for 40min, which shows enhanced photoreduction ability compared with BiOBr (77.31%). Numerous experimental results indicate that the improved photocatalytic activity for NiTMCPP/BiOBr-2 is mainly owing to the enhanced transport efficiency of photoinduced carriers after the loading of Ni-porphyrin. Especially, the central Ni2+ active site of porphyrin can accept excitation electrons, thus enhancing photoreduction performance. Furthermore, the mechanisms for photocatalytic CO2 and Cr(Ⅵ) reduction were further discussed via in-situ FT-IR and capture experiments. This work gives a promising way to design hybrid photocatalysts for energy conversion and environmental treatment.

Synthesis, Characterization, and Adsorption Performance of (Mg0.4Co0.4Mn0.2)Fe2−2xSmxSnxO4 Nanoparticles for the Removal of Heavy Metal Ions and Water Treatment

AbstractWater contamination by heavy metal ions poses a significant environmental threat. This study investigates (Mg0.4Co0.4Mn0.2)Fe2−2xSmxSnxO4 (0.000 ≤ x ≤ 0.050) ferrite nanoparticles (NPs) as eco‐friendly adsorbents for Cu(II), Cr(III), Fe(III), and Zn(II). X‐ray powder diffraction (XRD) confirmed sample purity, with crystallite size decreasing from 20.28 to 13.31 nm as x increased. Scanning and transmission electron microscopies revealed irregular morphology, whereas energy‐dispersive X‐ray showed successful dopant incorporation into the ferrite lattice. Brunauer–Emmett–Teller analysis indicated a surface area increase from 76.5 to 91.4 m2/g with doping. X‐ray photoelectron spectroscopy identified oxidation states, and Fourier transform infrared spectroscopy confirmed the spinel structure. Doping also increased the direct bandgap energy from 3.224 to 3.245 eV and decreased Urbach energy from 0.374 to 0.352 eV. The NPs achieved high removal efficiencies for Cr(III) at 93.3%, Fe(III) at 98.8%, and Zn(II) at 80.6%, though removal of Cu(II) was minimal. The optimal adsorption performance was observed at x = 0.050. Adsorption followed second‐order kinetics and fit the Langmuir isotherm.

Insights into the removal mechanism of Cr(VI) from groundwater by polypyrrole modified sludge biochar

Taking sludge biochar as the raw material and using iron and magnesium as metal sources respectively, two composite materials, polypyrrole magnesium modified biochar (PPy/MBC) and polypyrrole nano-zero-valent iron modified biochar (PPy/nZVI/BC), were prepared by in-situ oxidation polymerization of pyrrole monomers. The removal effects and mechanisms of these composite materials on hexavalent chromium (Cr(VI)) in groundwater were studied. The research results showed that the removal effect of PPy/MBC was superior to that of PPy/nZVI/BC. The highest removal rates of Cr(VI) and Cr(Total) were 170 and 120 mg·g−1 respectively. The adsorption kinetics followed the quasi-second-order kinetics and the adsorption isotherm conformed to the Langmuir adsorption isothermal model. The Elovich model indicated that the adsorption of Cr(VI) by PPy/MBC was a heterogeneous diffusion adsorption dominated by chemical adsorption. Thermodynamic analysis demonstrated that the adsorption of Cr(VI) by PPy/MBC was a spontaneous endothermic reaction. The specific surface area of the modified PPy/MBC reached 26.0824 m2·g−1, which was 7.9 times higher than that of the unmodified biochar. Positively charged nitrogen (-NH·+-), Mg2+ and Cl− in PPy/MBC removed Cr(VI) from groundwater through electrostatic interaction and ion exchange. Most anions and humic acids in groundwater had no significant effect on the removal of chromium by PPy/MBC. In general, the preparation of PPy/MBC composite material was simple, green and environmentally friendly. It had high adsorption removal efficiency and adsorption stability for Cr(VI) in groundwater, and good anti-interference against the background matrix in groundwater. Therefore, it was a promising adsorbent that could efficiently treat Cr(VI) in groundwater.

Efficient photo-assisted reduction of Cr(VI) via activated carbon mediated Z-scheme FeS2/α-FeOOH/C heterojunction: Focusing on molecular oxygen fate and synergetic reduction mechanism

Herein, pyrite (FeS2), goethite (α-FeOOH) and activated carbon (C) were combined to construct FeS2/α-FeOOH/C composites with C mediated Z-scheme heterojunction for efficient photo-assisted Cr(VI) reduction. Characterization tests indicated the strong interaction via Fe-O-C and C-S-C, the increased amount of crystal defects and surface oxygenic functional groups, and the decreased agglomeration degree during combination strengthened electron transport and visible light conversion efficiency, resulting in synergistic effect for enhanced Cr(VI) removal. Additionally, C mediated Z-scheme heterojunction with lower resistance facilitated the transfer and separation efficiency of photo-generated carriers, further accelerating Cr(VI) reduction. Consequently, almost 100 % of Cr(VI) was reduced via FeS2/α-FeOOH/C in 60 min, 4 times that of pristine FeS2. Quenching, EPR and control experiments confirmed photocatalysis made more contribution than single reductive reagents (FeS2) in Cr(VI) reduction. The specific contribution rate of reductive species like e−, Fe2+, S22− and •O2− in this complicated system was firstly detailedly demonstrated and •O2− played a predominant role under oxic condition. Meanwhile, oxidative species like H2O2, 1O2 and •OH ascribed to DO activation or photo-generated h+ preferred to reacted with Fe2+ and S22− with higher reducibility and-only delayed Cr(VI) reduction rate. Hence, the final total Cr(VI) removal efficiency and generated Cr(III) kept stable in oxic solution.

Magnetic cork as adsorbent to remove hexavalent chromium from aqueous solution

Chromium contamination of water is a severe environmental problem due to the potential carcinogenicity of Cr(VI). In this work, magnetic cork powder was used as a porous material, and its removal efficiency for Cr(VI) was compared to that of natural cork powder through two mechanisms: adsorption and reduction. Adsorption isotherms and adsorption kinetics were utilized to calculate the reaction rate using a pseudo-first-order model, pseudo-second-order model, and intraparticle diffusion. After adsorption, the powder was characterized by scanning electronic microscopy with energy-dispersive X-ray analysis (EDAX), Fourier transform infrared spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy (XPS). EDAX allowed to see a mapping distribution of Fe and Cr, and XPS revealed the presence of Cr2O3 and Cr(OH)3, confirming the reduction of Cr(VI) to Cr(III). All the Cr was efficiently reduced and adsorbed onto the surface of the magnetic cork at 20 °C, 27 °C, and 50 °C within 120 min with stirring. The relative efficiencies to the total milligrams of added adsorbent were 98, 98.6, and 99.7 mg, respectively. This is comparable to the adsorption on the natural cork surface at the same temperatures, which measured 97.8, 98.5, and 99.6 mg, respectively, of 100 mg/L Cr(VI) solution. Furthermore, the magnetic cork offers the advantage of being removable by applying a magnetic field.

Synergistic removal of ammonia nitrogen and hexavalent chromium by the hybrid-system of Acinetobacter baumannii AL-6 and original walnut shell biochar in solution: Mechanism and application

A novel hybrid-system was developed with the Acinetobacter baumannii AL-6 and original walnut shell biochar. Compared with strain AL-6 and biochar, hybrid-system exhibited an excellent synergistic removal ability for ammonia nitrogen (NH4+-N) and hexavalent chromium (Cr(VI)). And the maximum NH4+-N and Cr(VI) removal efficiency of hybrid-system were 93.30 % and 99.63 %, higher than 82.01 % and 56.49 % of strain AL-6, 5.35 % and 14.97 % of biochar, respectively. Strain AL-6 grew well in the presence of biochar and the ammonia oxygenase (AMO) activity of strain AL-6 was improved by adsorption of NH4+-N and Cr(VI) and release of beneficial elements (Ca, K and Mg) on biochar, which enhanced the biodegradation of NH4+-N. Environment persistent free radicals (EPFRs) and oxygen-containing functional groups of biochar could weaken the electron-competition between Cr(VI) and bacteria, biochar, which increased the removal performance of Cr(VI). The hydrophilic functional groups and mesoporous structure of biochar promoted the immobilization capacity of bacteria, which reduced the loose of bacteria from suspended bioreactor. Approximately 84.58 % - 87.97 % of NH4+-N and 1.18 mg·L−1-1.91 mg·L−1 of Cr(VI) were removed by the hybrid-system in sequencing batch reactor (SBR). Particularly, the removal performance of Cr(VI) was significantly improved as the per NH4+-N was degraded with increasing the operational time in SBR.

Removal of Pb(II), Cr(III), Co(II), Cu(II) cations from aqueous solutions using tetraethylenepentamine-functionalized HY cubic zeolite: optimization, characterization, and mechanistic insights.

This research utilized tetraethylenepentamine-functionalized HY cubic zeolite as an adsorbent to effectively remove heavy metals from aqueous solutions. The adsorbent was characterized using FT-IR, XRD, TGA, FE-SEM, and EDS-MAP techniques. The synthesis aimed to optimize and evaluate the removal efficiency of Pb(II), Cr(III), Co(II), and Cu(II) from aqueous solutions by investigating key parameters, including initial pH, concentration, adsorbent dosage, and contact time. The results indicate that the highest adsorption capacities for each metal follow the order: Pb(II) > Cr(III) > Co(II) > Cu(II), with respective percentages of 99.7%, 98.2%, 95.1%, and 92.4%. Analysis of the batch systems reveals that the equilibrium data for Pb(II), Cr(III), Co(II), and Cu(II) align well with the Langmuir and Freundlich isotherms also show a good fit, with correlation coefficients (R2) higher than 0.9335 and 0.9478, respectively. The maximum adsorption capacities (181.82, 175.44, 169.49, and 158.73mg/g) reflect the nature of the adsorption process. Kinetic studies for Pb(II), Cr(III), Cu(II), and Cu(II) yielded correlation coefficients (R2) higher than 0.9971. These high R2 values suggest that the experimental data closely fit a pseudo-second-order model, indicating a two-step adsorption mechanism. Heavy metal removal is attributed to ion exchange and chemisorption within the zeolite pores, involving interactions with nitrogen lone pairs.

Enhanced Cr(vi) removal by Co and PPy co-modified Ca-Al-layered double hydroxides due to adsorption and reduction mechanisms.

Co and polypyrrole co-modified hierarchical CaAl-LDH microspheres (CCALP) were synthesized via hydrothermal and in situ polymerization methods. The synergistic effect of PPy and Co endowed CCALP with higher surface area and more reduction sites than CaAl-LDHs modified by Co or PPy alone, maintaining good recyclability for Cr(vi) removal efficiency over four cycles without any treatment. Compared to Co, PPy doping was the dominant reason for Cr(vi) reduction on CCALP. Under optimized conditions, the theoretical maximum adsorption capacity reached 845.25 mg g-1, and the removal efficiency of Cr(vi) achieved 98.83%. The Langmuir model fitted well with the Cr(vi) adsorption on CCALP, supporting the monolayer adsorption hypothesis. The adsorption process followed the Avrami fractional kinetics (AFO) model, suggesting complex and multiple kinetic stages. Thermodynamic experiments confirmed that the adsorption was a spontaneous exothermic process. The density functional theory (DFT) and electrostatic potential (ESP) calculations confirmed that the oxygen-containing parts of Cr2O7 2- and HCrO4 - were the affinity sites, and the co-doping of Co and PPy significantly improved the Cr(vi) adsorption energy on CCALP. Therefore, the Cr(vi) removal mechanism on CCALP was proposed with electrostatic interaction, ion exchange, complexation and reduction.

Fe-doped MOF(Ti)/Bi2MoO6 heterostructure for boosting oxidation/reduction activities under visible light

Constructing of metal-organic framework (MOF) based heterostructures is a feasible strategy to enhance the photocatalytic activities of MOFs in wastewater treatments. Herein, a novel Fe-doped NH2-MIL-125(Ti)/Bi2MoO6 heterostructure (Fe-MOF(Ti)/BMO) was designed and prepared by modifying Bi2MoO6 nanoparticles on the Fe-MOF(Ti) surface by a simple solvothermal method. As expected, the Fe-MOF(Ti)/BMO composites displayed more conspicuous photocatalytic properties toward the Cr(VI) reduction and methyl orange (MO) degradation compared to the Fe-MOF(Ti) under visible light. Especially, the optimal Fe-MOF(Ti)/BMO0.4 exhibited the highest photocatalytic activities for the Cr(VI) reduction and MO degradation, around 1.2 and 1.4 times as high as those of the Fe-MOF(Ti), while the Cr(VI) removal efficiency was still kept above 96.5 % after 5 cycles, superior to that Fe-MOF(Ti) (95.1 %). The enhanced photocatalytic activity and stability of the Fe-MOF(Ti)/BMO0.4 were owed to the well-dispersed Bi2MoO6 nanoparticles, high interfacial charge transfer and strong interfacial contact between the two components induced by the formation of type II heterostructure. Ultimately, the possible enhanced photocatalytic mechanism over the Fe-MOF(Ti)/BMO heterostructure was also proposed. This work demonstrated the MOF-based heterostructure materials have a great potentiality for semiconductor photocatalysis in environmental remediations.

Bioremediation of Cr (VI) by novel microalgal strain

The present study aims at the isolation of Cr (VI) tolerant microalgae from wastewater collected from local bike garages. The wastewater had a continued spillage of engine oil, petrol, grease, and chain lube waste. The isolated microalgae were first sequenced by using 18S rRNA sequencing method. The nucleotide sequence obtained was analyzed via BLAST, the isolated microalga showed maximum similarity with Scenedesmus species. The sequence was submitted to NCBI, and the microalgae was identified as Scenedesmus species GTAF1 IU accession no. OM903800. The bioremediation potential of the isolated microalgae was evaluated for the removal of Cr (VI) in synthetic wastewater. The Cr (VI) removal efficiency was estimated at 0.2, 0.4, 0.6, and 0.8 g L−1 of inoculum concentration under autotrophic and heterotrophic modes. The highest removal efficiency of 98.9% and 99.9% was obtained at 0.8 g L−1 inoculum concentration under autotrophic and heterotrophic modes of operation respectively. On increasing the metal concentration from 5 to 10 ppm, a decrease in the biomass quality and quantity was observed. This increased metal stress resulted in an enhanced carbohydrate and lipid concentration. However, the protein concentration was found to be decreased. Cr (VI) removal efficiency was highest in heterotrophic conditions. This study provides a novel insight for removing Cr (VI) and concomitantly enhancing the lipid content of isolated strains under heterotrophic conditions. Owing to enhanced lipid content, the reported curation of wastewater may also be used in harnessing the potential of isolated microalga in biofuel production.

Enrichment and catalysis effect of 2D/2D g-C3N4/Ti3C2 for promoting organic matter degradation and heavy metal reduction in plasma systems: Unveiling the promotion and redox mechanism

This work proposes a novel plasma-assisted 2D/2D g-C3N4/Ti3C2 system for treatment of organics-heavy metals composite wastewater. Unlike traditional materials in plasma system, 2D/2D g-C3N4/Ti3C2 not only improved the mass transfer efficiency of plasma by gathering both reactive species and pollutants onto the surface, but also induced photocatalytic reactions. Besides, the higher specific surface area and faster carrier separation rate can enhance the oxidation and reduction activity, and then promoted organic matter degradation and heavy metal reduction. Remarkably, the removal efficiency of sulfamethoxazole (SMX) and Cr(VI) increased by 16.5 % and 73.1 % respectively when introducing 2D/2D g-C3N4/Ti3C2. Roles of·OH,·H,·O2-, 1O2, e-, and h+ in SMX oxidation and Cr(VI) reduction are clarified. The primary aggregated·OH and 1O2 dominate the degradation of SMX. The influencing factors, synergistic mechanism between plasma and catalyst, and redox mechanism were clarified. This work provides a breakthrough idea for treatment of organics-heavy metals composite wastewater.

Chromium(VI) and nitrate removal from groundwater using biochar-assisted zero valent iron autotrophic bioreduction: Enhancing electron transfer efficiency and reducing EPS accumulation

Current strategies primarily utilize heterotrophic or mixotrophic bioreduction for the simultaneous removal of Cr(VI) and NO3− from groundwater. However, given the oligotrophic nature of groundwater, autotrophic bioreduction could be more appropriate, though it remains notably underdeveloped. Here, an autotrophic bioreduction technology utilizing biochar (BC)-assisted zero valent iron (ZVI) is proposed. The pyrolysis temperature of BC was optimized to enhance electron transfer efficiency and reduce extracellular polymeric substances (EPS) accumulation. BC500, with the superior electron transfer capabilities, was the most effective. After an 11-week period, the ZVI + BC500 biotic column still achieved 100% removal efficiency for Cr(VI) and 93.37 ± 0.33% for NO3−, with initial concentrations of 26 mg/L and 50 mg/L, respectively. Its performance significantly surpasses that of ZVI alone, effectively reducing the interference of Cr(VI) on denitrification. The presence of quinone and phenolic compounds in BC500, serving as electron-accepting and electron-donating groups, improves the efficiency of electron transfer between ZVI and microbes. Metagenomic analysis showed an increase in the growth of autotrophic bacteria such as Hydrogenophaga spp. and Rhodanobacter denitrificans, and heterotrophic bacteria including Arenimonas daejeonensis and Chryseobacterium shandongense. The promotion facilitates the expression of genes associated with Cr(VI) reduction (chrR, nemA) and denitrification (narG, nirS). BC500 also enhanced EPS production, which facilitates the adsorption and reduction of Cr(VI), mitigating its inhibitory effects on denitrification. Notably, in the ZVI + BC500 biotic column, the accumulated EPS primarily consists of loosely bound EPS rather than tightly bound EPS, potentially reducing the risk of pore clogging during in-situ groundwater treatment.

Amino-Functionalized Metal-Organic Framework-Mediated Cellulose Aerogels for Efficient Cr(VI) Reduction.

Industrialization activities have increased the discharge of wastewater that is polluted with hexavalent chromium (Cr(VI)), posing risks to ecosystems and humans. The photocatalytic reduction of Cr(VI) is viewed as a promising method for the removal of Cr(VI) species. However, developing photocatalysts with the desired catalytic activity, recyclability, and reusability remains a challenge. Herein, a composite aerogel was designed and fabricated with a Ti-based metal-organic framework (MIL-125-NH2) and carboxylated nanocellulose. MIL-125-NH2 presents a strong visible-light response, and the interactions between the amino groups of MIL-125-NH2 and the carboxyl groups of cellulose produce a strong interface affinity in the composites. The as-prepared aerogels exhibited a micro/macroporous structure. At an optimal MIL-125-NH2 loading of 55 wt%, the MC-5 sample showed a specific surface area of 582 m2·g-1. MC-5 achieved a photocatalytic Cr(VI) removal efficiency of 99.8%. Meanwhile, the aerogel-type photocatalysts demonstrated good stability and recycling ability, as MC-5 maintained a removal rate of 82% after 10 cycles. This work sheds light on the preparation of novel photocatalysts with three-dimensional structures for environmental remediation.

Unraveling the promotive mechanism of nitrogen-doped porous carbon from wasted lignin for Cr (VI) removal

Persistent environmental pollution by heavy metals, particularly Cr (VI), poses significant risks to ecosystems and human health due to its high toxicity and bioaccumulation potential. The development of high-performance, cost-effective adsorbents from sustainable materials remains a critical challenge in the field of Cr (VI) remediation. This study investigates the influence of pyrrolic-N (N-5) within nitrogen-doped hierarchical porous carbon (N-HPC) on its adsorption capacity. Results indicate that N-HPC variants with a higher N-5 content exhibit superior adsorption abilities. The optimal sample demonstrated an exceptional adsorption capacity of 386.2 mg/g for Cr (VI). Even after seven regeneration cycles, this N-HPC variant maintained a remarkable 77.8 % removal efficiency for Cr (VI), highlighting its robust stability and selectivity. The relationship between the physicochemical properties of N-5 and N-HPC was thoroughly examined, revealing that N-5 plays a crucial role in the adsorption process. Due to its high electronegativity, nitrogen-doping into the carbon framework generates a dipole moment, enhancing the electronegativity of N-HPC, altering its local electron density and polarity, increasing specific surface area, carbon defect density, and ion exchange capacity. These factors collectively contribute to significant improvements in pore filling, ion exchange efficiency, and electrostatic adsorption by N-HPC. The reduction complexation mechanism emerges as the dominant factor in the adsorption process. N-5 not only provides reducing electrons as an electron donor, facilitating the continuous conversion of Cr (VI) to Cr (III), but also acts as an adsorption active site, complexing Cr to the surface of N-HPC. This synergistic effect strengthens the reduction complexation, enhances adsorption performance, and improves the regeneration cycle and adsorption selectivity for Cr.