Simultaneous Cr Research Articles

Porous biochar-driven innovative Cr(VI) reduction and resource recovery

Catalyst-mediated Cr(VI) reduction face significant challenges in by-product ion residues and catalyst cost. The development of low-cost catalysts and catalytic technologies with near-zero impurity introduction is therefore of great practical importance. This study developed a pristine biochar-mediated nanoconfinement strategy that facilitated the chemical reaction between oxalic acid (OA) and Cr(VI) with a stoichiometric ratio of 3.3:1. The method achieved the simultaneous Cr(VI) reduction and OA removal, and completed the chromium removal process with near-zero impurity introduction after a precipitation process. While traditional catalyst-mediated reduction relied on mechanisms of functional group or active sites, this study took a novel path by adopting a focus on pore size. The structure–activity relationship, and experimental design demonstrated the predominant role of porous properties in the reaction, thus proposing a nanoconfinement Cr(VI) reduction mechanism. Continuous flow results revealed a treatment capacity of 1750 mL/h for the complete removal of Cr(VI) from Cr electroplating rinse water. The effluent, precipitated with CaO, had 0.06 mg/L of total Cr and 0.56 mg/L of OA, while the precipitate, recovered as CaCr2O4, demonstrated a total Cr recovery efficiency of 90.4%. Compared to industrial Cr(VI) chemical reduction, this study minimizes impurity introduction to the catalytic system. This study explores an effective strategy for Cr(VI) reduction and Cr resource recovery using low-cost pristine biochar, and provides navigation for the removal and resource utilization of other heavy metals or radionuclides.

Comparative role of Ag and Ce doping on WO3 and GO modified nanostructures for bi-functional effective photocatalyst and electro catalyst

The comparative study of Ag and Ce doped WO3 modified with GO ternary composites was conducted. Bi-functional promising catalysts were employed for simultaneous Cr (VI) reduction and phenol oxidation as well as hydrogen evolution reaction (HER) through electro catalysis. Both Ag and Ce indicated their effects on orthorhombic WO3. Morphological studies showed big sheets of WO3 were ruptured by foreign materials. C − Ce − W and C − Ag − W surface linkages were analyzed by FTIR and Raman studies. DRS studies indicated that Ce into WO3 alters electronic configuration of WO3. GO/Ag-WO3 showed long absorption tail in visible region. The remarkable quenching of PL intensities is detected in GO/Ag-WO3. GO/Ag-WO3 comparatively produced small onset potential ∼ −175 mV, high current density of ∼75 mAcm−2, small Tafel slop ∼ 46 mV/dec and low charge-transfer resistance (Rct) ∼ 54 Ω. In HER, electronic interaction is strong driving force between WO3 and Ag while GO controls distribution of Ag on WO3/GO leading to fast conduction of charge transfer to improve HER activity. GO/Ag-WO3 composite exhibited elevated photo reduction of Cr (VI) (∼ 86.0 %) and oxidation of phenol (∼ 80.0 %). Trapping test indicated that O2•― and OH• is significant factor for degradation. It provides opportunities of environmentally friendly materials for multipurpose catalytic applications.

Transcriptome and metabolome analysis reveal key genes and metabolic pathway responses in Leersia hexandra Swartz under Cr and Ni co-stress

Phytoremediation, an eco-friendly approach for mitigating heavy metal contamination, is reliant on hyperaccumulators. This study focused on Leersia hexandra Swart, a known chromium (Cr) hyperaccumulator with demonstrated tolerance to multiple heavy metals. Our objective was to investigate its response to simultaneous Cr and nickel (Ni) stress over 12 days. Results from physiological experiments demonstrated a significant increase in the activities of antioxidant enzymes (APX, SOD, CAT) and glutathione (GSH) content under Cr and Ni stress, indicating enhanced antioxidant mechanisms. Transcriptome analysis revealed that stress resulted in the differential expression of 27 genes associated with antioxidant activity and metal binding, including APX, SOD, CAT, GSH, metallothionein (MT), and nicotinamide (NA). Among them, twenty differentially expressed genes (DEGs) related to GSH metabolic cycle were identified. Notably, GSTU6, GND1, and PGD were the top three related genes, showing upregulation with fold changes of 4.57, 6.07, and 3.76, respectively, indicating their crucial role in metal tolerance. The expression of selected DEGs was validated by quantitative real-time PCR, confirming the reliability of RNA-Seq data. Metabolomic analysis revealed changes in 1121 metabolites, with amino acids, flavonoids, and carbohydrates being the most affected. Furthermore, glucosinolate biosynthesis and amino acid biosynthesis pathways were represented in the KEGG pathway of differentially expressed metabolites (DEMs). This study provides insights into the tolerance mechanisms of L. hexandra under the co-stress of Cr and Ni, offering a new perspective for enhancing its remediation performance.

Achievement of textbook outcome after hepatectomy combined with thermal ablation for colorectal liver metastases.

Hepatic resection combined with intraoperative ablation has been described as a technical solution potentially widening the resectability rate of patients with colorectal liver metastases (CRLM). Nevertheless, the perioperative and oncological benefit provided by this combined approach remains unclear. We hypothesized that textbook outcome (TO), which is a composite measure achieved for patients for whom some desired health indicators are met, may help to refine the indications of this approach. Patients submitted to hepatectomy with curative intent in combination with radiofrequency ablation or microwave ablation for CRLM≤3cm in two tertiary referral centers were included. TO was defined according to a recent definition for liver surgery based on a Delphi process including also the achievement of complete radiological response of the ablated lesion/s at 4weeks. Between 2015 and 2022, 112 patients were enrolled. Among them, 63 (56.2%) achieved a TO. According to multivariate analysis, minimally invasive (MI) approach (OR 2.72, 95% CI 0.99-7.48, p=0.050), simultaneous CR resection (OR 0.28, 95% CI 0.11-0.70, p=0.007), tumor burden score (OR 0.89, 95% CI 0.82-0.96, p=0.004), and major hepatectomy (OR 0.12, 95% CI 0.03-0.52, p=0.004) were significantly associated with the achievement of TO. Median overall survival was longer in those patients who were able to achieve a TO compared to those who did not. The combination of hepatectomy and ablation constitutes a valuable solution in patients affected by multiple CRLM and it may provide, also using a MI approach, adequate perioperative and oncological outcomes, allowing to achieve TO, however, in a selected number of patients and depending on several factors including the burden of disease.

Simultaneous Cr(VI) Reduction and Dexamethasone Phosphate Oxidation with Organo-metallic Sludge Formation Under UV Irradiation: Kinetics, Degradation Pathways, and Mechanism

In this study, we investigated the concurrent elimination of two distinct contaminants: organic matter in the form of dexamethasone phosphate (DexP) and an inorganic substance, chromium (Cr), employing UV irradiation. UV irradiation serves as a potent tool for breaking down organic materials, leading to the production of benign by-products, namely CO2 and H2O. Under optimal conditions characterized by a 30:1 DexP/Cr molar ratio and a pH level of 9, remarkable removal efficiencies were attained. In a mere 20 min, approximately 100% of DexP and 82.73% of Cr were effectively removed. Intriguingly, the removal of Cr exhibited an initially sluggish rate, with deposition commencing only after the breakdown of the DexP structure. This transformation was accompanied by the emergence of various sludge forms, each possessing unique characteristics. Utilizing Fourier-transform infrared (FTIR) analysis, we identified these sludge forms as chromium(III) hydroxide (green sludge), chromium(III) hydroxide (brown sludge), chromium(III) oxide (tiny green crystals), chromium(II) acetate chromium trioxide (red brick), and chromium oxide (black sludge). Further experimentation with varying concentrations of Cr and DexP, ranging from 50 to 150 mg L−1, yielded a range of rate constants (kobs) from 0.33 to 0.15 and removal efficiencies (robs) from 16.8 to 23.4% in the UV/DexP/Cr process. Energy efficiency output (EEO) calculations revealed that Cr precipitation ranged from 24.65 to 5.74 kW h m−3, whereas DexP EEO ranged from 12.54 to 4.73 kW h m−3. Of significant importance is the observation that when these two contaminants are removed simultaneously, the overall energy consumption is substantially lower compared to the scenario where pollutants are addressed individually. This finding underscores the efficiency and potential energy cost savings achievable through the concurrent removal of DexP and Cr using UV irradiation, making it a promising approach for environmental remediation.

Removal of chromium from aqueous solution by CLCh/Fe/MWCNT/TiO2-Ag magnetic composite film: Simultaneous Cr(VI) reduction and Cr(III) adsorption

A catalyst CLCh/Fe/MWCNT/TiO2-Ag film was prepared using multi-walled carbon nanotubes (MWCNT) impregnated with magnetic iron oxide and silver-doped titanium dioxide (TiO2-Ag), being deposited on crosslinked chitosan (CLCh). The physicochemical characterization of the catalyst was performed by various analytical techniques such as ICP-MS, XRD, FTIR, SEM, EDS, Raman spectroscopy, N2 adsorption/desorption and UV–Vis diffuse reflectance spectra (DRS). A solution of Cr(VI) (30 mg/L) was used in the evaluation of the photoreduction of (Cr(VI) to Cr(III)) using UV–visible light (filter cut-off for λ > 300 nm). The composite film allowed, when applied in a solution of 30 mg/L of Cr(VI) at pH 2, the removal and simultaneous photoreduction of 97 % of Cr(VI) to Cr(III) in 120 min. The cationic Cr(III) generated remains retained in the composite film by adsorption on the hydroxyl and carboxyl groups of MWCNTs. The CLCh/Fe/MWCNT/TiO2-Ag film can be mechanically removed from the aqueous solution or by magnetic attraction. In ten consecutive cycles of reuse, the CLCh/Fe/MWCNT/TiO2-Ag film showed an efficiency of 84 % in the photoreduction of Cr(VI).

Simultaneous removal of Cr(Ⅵ) and tetracycline from wastewater by dielectric barrier discharge plasma coupled with TiO2/rGO/Cu2O composites: Performance and mechanism

In this study, dielectric barrier discharge (DBD) plasma combined with titanium dioxide/reduced graphene oxide/copper oxide (TiO2/rGO/Cu2O) composites for simultaneous removal of hexavalent chromium (Cr(Ⅵ)) and tetracycline (TC) from wastewater were explored systematically. The TiO2/rGO/Cu2O composites were successfully prepared to improve the specific surface area and charge carrier separation rate. When Cr(Ⅵ) and TC coexist, the two pollutants have better removal efficiency without changing the initial pH. Moreover, the removal efficiency of Cr(Ⅵ) and TC could be further improved in the DBD-TiO2/rGO/Cu2O system, indicating that the TiO2/rGO/Cu2O composites also exhibited good synergistic effects with the DBD plasma. The mechanism exploration showed that the TiO2/rGO/Cu2O composite catalyst could be activated in DBD system to produce various active species by photocatalytic reaction, among which photo-generated electrons and •O2− could significantly enhance Cr(Ⅵ) reduction, while photo-generated holes and •OH could improve TC degradation. More importantly, the intermediate products obtained from TC degradation can be oxidized to •CO2− by photo-generated holes, which can also facilitate the reduction of Cr(Ⅵ). This study shows that DBD combined with TiO2/rGO/Cu2O composites are capable of simultaneous Cr(Ⅵ) reduction and TC degradation, which would provide novel ideas for practical wastewater remediation.

Simultaneous Cr(VI) reduction and Cr(III) sequestration in a wide pH range by using magnetic chitosan-based biopolymer

The simultaneous reduction of Cr(VI) and sequestration of the resulting Cr(III) in one process is highly desirable as a cost-effective and environmental-friendly approach for the decontamination of Cr(VI)-polluted wastewater. However, most of the existing adsorptive materials are only effective in low pH environments (pH = 1–3), severely restricting the adsorption efficiency and cost effectiveness. Herein, we proposed a chitosan-based magnetic porous microsphere (PPy@PMCS) for simultaneous Cr(VI) reduction and Cr(III) sequestration in a wide pH range. Benefiting from its abundant interaction sites, Cr(VI) was effectively adsorbed on the surface and then immediately reduced to Cr(III) with much lower toxicity. Most importantly, the resulting Cr(III) was in-situ sequestrated by the complexation of chitosan matrix. As a result, PPy@PMCS exhibited a maximum Cr(VI) adsorption capacity of 330.42 mg/g at pH 2.0 and an adsorption capacity of 167.82 mg/g even at near neutral pH (6.0), which is superior to most reported adsorbents. Furthermore, the exhausted PPy@PMCS can be rapidly separated from solutions under an external magnetic field and facilely regenerated. The proposed novel biopolymer-based material shows great application potentials in wastewater treatment.

Exploring Modified Rice Straw Biochar as a Sustainable Solution for Simultaneous Cr(VI) and Pb(II) Removal from Wastewater: Characterization, Mechanism Insights, and Application Feasibility.

This study aimed to investigate the efficacy of a rice straw biosorbent in batch adsorption for the removal of chromium (Cr(VI)) and lead (Pb(II)) heavy-metal ions from wastewater. The biosorbent was chemically synthesized and activated by using concentrated sulfuric acid. The produced biosorbent was then characterized by using Fourier transform infrared (FTIR), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD) analyses, which provided insights into surface morphology and functional groups. The study examined the effects of pH, rice straw dose, ion concentration, and contact time on metal ion adsorption. Optimal conditions for efficient removal (95.57% for Cr(VI) and 85.68% for Pb(II)) were achieved at a pH of 2.0, a biosorbent dose of 2 g/L, an initial concentration of 20 mg/L, and a contact time of 50 min in synthetic solutions. The isotherms and kinetics model fitting results found that both metal ion adsorption processes were multilayer on the hetero surface of rice straw biosorbent via rate diffusion kinetics. Thermodynamic investigations were conducted, and the results strongly indicate that the adsorption process is endothermic and spontaneous. Notably, the results indicated that the highest desorption rate was achieved by adding 0.3 N HCl to the system.

Dually Sulphophilic Chromium Boride Nanocatalyst Boosting Sulfur Conversion Kinetics Toward High-Performance Lithium-Sulfur Batteries.

The sluggish kinetics of sulfur conversions have long been hindering the implementation of fast and efficient sulfur electrochemistry in lithium-sulfur (Li-S) batteries. In this regard, herein the unique chromium boride (CrB) is developed via a well-confined mild-temperature thermal reaction to serve as an advanced sulfur electrocatalyst. Its interstitial-alloy nature features excellent conductivity, while the nano-lamination architecture affords abundant active sites for host-guest interactions. More importantly, the CrB nanocatalyst demonstrates a dual sulphophilicity with simultaneous Cr─S and B─S bondage for establishing strong interactions with the intermediate polysulfides. As a result, significant stabilization and promotion of sulfur redox behavior can be achieved, enabling an excellent Li-S cell cyclability with a minimum capacity fading rate of 0.0176% per cycle over 2000 cycles and a favorable rate capability up to 7C. Additionally, a high areal capacity of 5.2mAhcm-2 , and decent cycling and rate performances are still attainable under high sulfur loading and low electrolyte dosage. This work offers a facile approach and instructive insights into metal boride sulfur electrocatalyst, holding a good promise for pursuing high-efficiency sulfur electrochemistry and high-performance Li-S batteries.

Amorphous/crystalline heterophase W-Zn(Ti)O for the removal of Cr(VI) and tetracycline in single and mixed pollutant systems

A new approach for constructing amorphous/crystalline heterophase W-Zn(Ti)O photocatalyst was develpoed via calcination topological transformation of the self-sacrificial WO42−-pillared ZnTi-LDH (WO4-LDH) precursor together with in-situ W-doping. The amorphous/crystalline heterophase formation could expose enriched active sites, which promoted the transfer and separation of photogenerated e−-h+ pairs. Density functional theory (DFT) calculations further verified that in-situ W-doping regulated the electronic structure and reduced bandgap energy, which made the transport of photogenerated carriers more rapid. Benefiting from the construction of the amorphous/crystalline heterophase, the W-Zn(Ti)O had suitable photo-oxidation/reduction activities, achieving 99.7% removal rate for Cr(VI) reduction, 78.1% for TC oxidation, and simultaneous Cr(VI) reduction (78.0% removal) and TC oxidation (63.2% removal) for 120 min under visible-light. This work provides a new idea for the design of amorphous/crystalline heterophase nanomaterials.

Tuning the hydride stability of the TiVNb-based alloys by equimolar Cr/Al addition

Body-centered multi-principal element alloys (BCC-MPEAs) based only on hydride-forming elements have low equilibrium plateau pressures during reaction with hydrogen and, consequently, high decomposition temperatures due to the high thermodynamic stability of related hydrides. In this work, we present a strategy to decrease the stability of the final hydrides formed in the BCC TiVNb alloy by simultaneous addition of two non-hydride forming elements, Cr and Al. The (TiVNb)100-x(CrAl)x alloys with x = 10, 20, 30, and 40 at.% crystallize as major BCC solid solutions with dendritic microstructures. Pressure-Composition-Temperature diagrams revealed that the combined addition of Cr and Al thermodynamically destabilizes the dihydride formation for x = 10 and 20 at.%. For higher Cr/Al contents the destabilization is too large to form stable hydrides under maximum 100 bar pressure. The absorption/desorption plateau pressure at room temperature for (TiVNb)80(CrAl)20 alloy are 9 and 0.6 bar, respectively, enabling a reversible capacity of about 0.8 H/M (1.4 wt%) at ambient conditions. The present results provide important insights into the effects of simultaneous Cr and Al additions in BCC-MPEAs and shed light on the design of new alloys with hydrogen absorption and desorption ability at ambient conditions.

Functionalized waterworks sludge particles as column packing materials for simultaneous Cr (Ⅵ) removal and oil separation

Highly efficient and low-cost treatment of waterworks sludge and oil-containing Cr (Ⅵ) wastewater in one way is a challenge in the field of water treatment. Herein, a waste-control-waste strategy was proposed to fabricate a functionalized waterworks sludge-based Zn–Al layer double oxides material (Zn–Al LDOs/WS) for simultaneously separating Cr (Ⅵ) and oil. During the column separation process, due to the superhydrophilic/underwater superoleophobicity of Zn–Al LDOs/WS and the memory effect of LDHs, Cr (Ⅵ) will be stabled in the filter layer by electrostatic attraction and surface complexation between the Zn–Al LDHs/WS and Cr (Ⅵ), and the small oil droplets will coalesce into big oil droplets that be blocked in the separation column, thus achieving simultaneous separation. The Zn–Al LDOs/WS with hierarchical porous structure exhibit excellent simultaneous separation efficiency for Cr (Ⅵ) (99.69%) and oil (99.24%), and high separation flux (1063 L m−2 h−1). In addition, the separation efficiency and flux can be flexibly controlled by adjusting the filter layer thickness. The Zn–Al LDOs/WS also display strong acid and alkali resistance (pH 1–11), wide applicability range of initial Cr (Ⅵ) concentration (5–200 mg/L) and outstanding anti-interfering ion ability (Cl−, HCO3−, SO42−, NO3−, H2PO4−, CO32− and F−) in Cr (Ⅵ) and oil separation. Therefore, this work can not only improve treatment efficiency and save costs through simultaneous separation, effectively treat solid waste and complex wastewater, but also provide a theoretical basis for the design and application of functional materials derived from waste sludge.

In-situ CO2[rad]−/[rad]OH redox induced by degradation intermediate organic acids realized simultaneously Cu-EDTA decomplexation and Cr(VI) reduction in a plasma process

It is a great challenge to purify complex wastewater containing high toxic metal ions and heavy metal complexes. In this study, in-situ formation of reductive CO2− and its potential for Cr(VI) reduction were firstly investigated during Cu-EDTA decomposition in a discharge plasma system. Cr(Ⅵ) reduction efficiency and Cu-EDTA decomposition efficiency reached nearly 79% and 100% after 30 min treatment under optimum conditions, respectively, and further enhanced at acidic conditions. OH and 1O2 dominated Cu-EDTA decomposition by attacking chemical bonds in Cu-EDTA, such as Cu-O, C-O, and C-N, leading to the release of carboxylic acids. Reductive CO2− was in-situ generated by reactions between the carboxylic acids (formate and oxalic acid) and OH, and it dominated Cr(Ⅵ) reduction. Compared with single carboxyl byproducts, multiple carboxyl byproducts were more conducive to Cr(Ⅵ) reduction by forming more CO2−. Eaq− also participated in the Cr(Ⅵ) reduction process via electron transfer. Cr(III) and Cu(II) finally existed as Cr2O3, Cr(OH)3, copper based hydroxides and carbonates after CO2−/OH reactions. Possible pathways of simultaneous Cr(Ⅵ) reduction and Cu-EDTA decomposition were proposed finally. This study firstly proved endogenous CO2− formation in the discharge plasma system, which was able to treat complex waterbody, providing an alternative for oxidation-reduction removal of complex pollutants.

Simultaneous Cr (VI) reduction and diazinon oxidation with organometallic sludge formation under photolysis: kinetics, degradation pathways, and mechanism.

In this study, simultaneous removal of an organic matter (diazinon, DIZ) and an inorganic substance (chromium, Cr) was used. Breaking down of organic matter by UV irradiation produces various radicals, including sulfides, carboxyl, hydroxyl, hydrated electrons, and various organic radicals that are highly reactive and help us to precipitation inorganic substance (Cr). The optimal condition was 30:1 DIZ:Cr molar ratio, pH 9, and about 100% and 82.3% of DIZ and Cr were obtained in 30min. Cr deposition was very slow at first. After the destruction of the DIZ structure, Cr deposition began, and various types of sludge with disturbed properties were formed. These sledges were analyzed by FTIR analysis and showed that green sludge could be chromium (III) hydroxide; brown sludge due to chromium (III) hydroxide, tiny green crystals from chromium (III) oxide, red brick from chromium (II) acetate chromium trioxide, as well as black sludge caused by chromium oxide were identified. In UV/DIZ/Cr process, kobs and robs range obtained 0.33-0.15 and 16.8-23.4 $ with both Cr and DIZ concentration increased from 50 to 150mg L-1. Also, EEO for Cr precipitation was 24.65 to 5.74 and for DIZ 12.54 to 4.73 (kwh m-3). Depending on the amount of energy consumption, TCS was 37.19 to 10.47 for Cr precipitation and 4.46 to 1.25 $. It is important to note that when both pollutants are exposed to ultraviolet light, more energy and cost are generally required from UV/DIZ process and less than of UV/Cr process. But it should be noted that in fact 50mg L-1 of chromium and 50mg L-1 of DIZ are being removed at the same time. In UV/DIZ and UV/Cr processes that are exposed to ultraviolet radiation alone, only one of them is removed. Also, when these two pollutants are being removed at the same time, the total amount of energy is much less than the total energy consumption of the pollutants one by one.

Ethane-driven chromate and nitrate bioreductions in a membrane biofilm reactor

Chromium (Cr(VI)) and co-contaminating nitrate (NO3–) pose major threats to human health. Hydrogen- and methane-driven Cr(VI) and NO3– bioreductions have been documented, but unknown is whether or not non-methane short-chain gaseous alkanes (SCGAs), such as ethane (C2H6), also can drive Cr(VI) and NO3– reductions. This study demonstrated simultaneous Cr(VI) and NO3– bioreductions driven by C2H6 oxidation in a membrane biofilm reactor (MBfR) that delivered C2H6 directly to a biofilm by its diffusion through non-porous membranes. Scanning electron microscopy and X-ray photoelectron spectroscopy showed that the biofilm was mainly composed of cocci and bacillus and that a Cr(III) precipitate was the major product of microbial Cr(VI) reduction. Microbial community analysis showed that the C2H6-oxidizing bacterium Mycobacterium oxidized C2H6 and delivered organic intermediates to Cr(VI)-reducing bacteria TM7a, Sediminibacterium, and Deinococcus. Because the first step of ethane catabolism is a monooxygenation, the influent had to have dissolved oxygen, and the dominant respiratory process was O2 reduction. By providing insights into how Cr(VI) and NO3– bioreductions can be driven by C2H6 oxidation, these finding support the application of SCGAs for ex-situ bioremediation of waters contaminated with Cr(VI) and NO3–.

Kraft lignin-based carbon xerogel/zinc oxide composite for 4-chlorophenol solar-light photocatalytic degradation: effect of pH, salinity, and simultaneous Cr(VI) reduction.

Considering the ever-increasing need for efficient wastewater treatment, this study focused on the development of new kraft lignin-based carbon xerogel/zinc oxide (XCL/ZnO w) photocatalysts. The inclusion of the carbon xerogel is expected to cause an improvement in charge transfer throughout the photoactivation process, consequently enhancing its overall photocatalytic efficiency. Characterization shows that the materials developed are composed of both zinc oxide and carbon xerogel. The addition of the lignin-based carbon xerogel caused a significant morphological modification to the composite materials, resulting in a greater specific surface area. Regarding the photocatalytic efficiency, the optimized composite (XCL/ZnO 1.0) displayed superior efficiency to the pure zinc oxide, especially when calcined at 700°C, with an increase of 20% in the overall photodegradation capacity for the 4-chlorophenol (4CP) molecule. The XCL/ZnO 1.0 also displayed better performance than its tannin counterpart, previously reported in the literature, obtaining a 60% increase in the apparent reaction rate constant. The XCL/ZnO 1.0 also displayed better performance for the simultaneous hexavalent chrome (Cr (VI)) reduction/4CP oxidation reaction. Salinity and system pH had a significant influence on the efficiency of the 4CP photodegradation, as higher values of salinity and lower pHs caused a decrease in the overall efficiency of the process. At last, chronoamperometry and open-circuit potential tests confirmed the superiority of the XCL/ZnO 1.0 over the pure ZnO, highlighting the beneficial impact of the carbon xerogel on the charge transport dynamics of the composite.

Effects of pH on simultaneous Cr(VI) and p-chlorophenol removal and electrochemical performance in Leersia hexandra constructed wetland-microbial fuel cell

ABSTRACT Cr(VI) and p-chlorophenol (4-CP) are common pollutants in the aquatic environment but are difficult to degrade and have complex toxic effects. A downflow Leersia hexandra microbial fuel cell (DLCW-MFC) system was constructed to purify Cr(VI) and 4-CP polluted wastewater, as well as to investigate the effects of different pHs on Cr(VI) and 4-CP removal, electrochemical performance, physiological and biochemical responses, and Cr enrichment status of L. hexandra. The results showed that the DLCW-MFC had the highest Cr(VI) and 4-CP removal rates at pH 6.5, which were 99.0% and 78.6%, respectively. At the same time, 543 mV output voltage and 72.25 mW/m2 power density of the system were generated at pH 6.5, which were better than those at pH 7.4 and pH 5.8. The electrochemical performance result showed that pH 6.5 enhanced charge transfer ability and ion diffusion ability of the system. pH 6.5 also promoted growth and photosynthesis, and enhanced the Cr enrichment capacity (4.56 mg/10 plants) of L. hexandra. These results demonstrate that pH 6.5 was the optimum pH for the DLCW-MFC synchronous treatment of Cr(VI) and 4-CP as well as the generation of electricity. The DLCW-MFC designed in this study will provide a reference for purifying polluted wastewater and generating electricity.

Cellulose-based aerogel beads for efficient adsorption- reduction- sequestration of Cr(VI)

The reduction and sequestration of toxic Cr(VI) via a one-step process in an aqueous solution is critical to eliminate its environmental risk. In this study, amine functionalized cellulose-based aerogel beads (CGP) was developed for simultaneous and efficient adsorption- reduction- sequestration of Cr(VI). CGP showed a maximum Cr(VI) adsorption capacity of 386.40 mg/g at 25 °C due to its strong electrostatic attraction towards Cr(VI). The simultaneous Cr(VI) adsorption- reduction- sequestration performance of CGP over a wide Cr(VI) concentration range was examined. The mechanism was investigated in-depth via the analysis of adsorption kinetics, XPS spectra, and FTIR spectra. Moreover, the Cr immobilization stability of CGP after adsorption was evaluated in simulated neutral, acidic, and alkaline conditions. The effect of pH, temperature, ionic strength and the presence of interfering ions on CGP adsorption performance were investigated by batch adsorption experiments. Fixed-bed column adsorption study was performed to explore the application potential of CGP beads in a wastewater treatment process.

An efficient and robust flow-through electrochemical Ti4O7 membrane system for simultaneous Cr(VI) reduction and Cr immobilization with membrane cleaning by a periodic polarity reversal strategy

As for the Cr(VI) reduction and subsequent Cr immobilization from the neutral and basic water, acidification and subsequent alkalization are necessitated, which usually suffers from the cumbersome operation, high chemical cost and increased water salinity. In this study, a porous Ti4O7 reactive electrochemical membrane (REM) was utilized as both the flow-through cathode and microfiltration membrane for the reduction of Cr(VI), and precipitation and interception of Cr(OH)3 particles synchronously, where the electrolysis cell was divided by a polytetrafluoroethylene (PTFE) membrane. As compared with the flow-by mode, the flow-through mode exhibited a 3-fold increase in the mass transfer rate constant and therefore nearly 100% of Cr(VI) was reduced when passing through the Ti4O7 REM cathode. The divided electrolysis cell was operated to generate a high alkaline environment (pH ∼ 11.0) throughout the whole volume of the cathodic chamber regardless of the initial pH changing from 5.0 to 10.0, which favored the formation of Cr(OH)3 particles and its interception by Ti4O7 REM. Thus, increasing initial pH from 5.0 to 10.0 exhibited negligible effects on the Cr(VI) removal efficiency and Cr(total) immobilization efficiency. Under the optimum condition (initial Cr(VI) concentration 500 ppb, current density 1 mA cm−2, flux 287 L m-2 h−1), the Cr(total) removal efficiency could achieve at as high as 95% with residual Cr(total) concentration of 27 μg L-1. As the reaction progressed, Cr(OH)3 passivated the membrane gradually, decreasing the Cr(VI) reduction efficiency to 84% at 30 h. Interestingly, the fouled Ti4O7 REM could be recovered completely after 30 min’s membrane cleaning operation just by periodically reversing the polarity at current density of 5 mA cm−2. Generally, this process can be considered as a promising and suitable treatment method for Cr(VI) detoxification from distributed water with a very low specific energy consumption of 0.109 kWh m−3.