Adsorption Of Cr Research Articles

A kinetic modelling approach to explore mechanism of Cr(VI) detoxification by a novel strain Pseudochrobactrum saccharolyticum NBRI-CRB 13 using response surface methodology.

A novel Pseudochrobactrum saccharolyticum strain NBRI-CRB 13, isolated from tannery sludge, was studied to grow up to 500 mgL-1 of Cr(VI) and showed Cr(VI) detoxification by reducing > 90% of Cr(VI) at different concentrations 25, 50 and 100 mgL-1. Kinetic studies showed that first-order models were fitted (R2 = 0.998) to the time-dependent Cr(VI) reduction with degradation rate constant (k) (1.03-0.429h-1). Cr(VI) detoxification was primarily related to the extracellular fraction of microbial cells, which showed a maximum extracellular reductase enzyme activity led to 94.6% reduction of Cr(VI). Moreover, the strain showed maximum extracellular polymeric substances (EPS) production at 100 mgL-1 Cr(VI), which is presumably the reason for Cr(VI) removal as EPS serves as the metal binding site for Cr(VI) ions. Further, an optimization study using Box-Behnken design was conducted considering parameters viz., pH, temperature, and initial concentration of Cr(VI). The maximum percent reduction of Cr(VI) was obtained at pH 6.5, temperature 30°C with 62.5 mgL-1Cr(VI) concentration. Further, the Cr(VI) reduction and adsorption ability of strain P. saccharolyticum NBRI-CRB13 were confirmed by SEM-EDS, FTIR, and XRD analyses. FTIR analysis confirmed the presence of functional groups (-OH, -COOH, -PO4) on bacterial cell walls, which were more likely to interact with positively charged chromium ions. The study elucidated the reduction of Cr(VI) by the novel bacterium within 24h using the response surface methodology approach and advocated its application in real-time situations.

Synergistic effects of sulfur vacancies and internal electric fields in FeS/MoS2 heterojunctions: A new approach to photocatalytic chromium removal

Molybdenum disulfide (MoS2) is heralded as an exemplary two-dimensional (2D) functional material, largely attributed to its distinctive layered structure. Upon forming heterojunctions with reducing species, MoS2 displays remarkable photocatalytic properties. In this research, we fabricated a novel heterojunction photocatalyst, FeS/MoS2-0.05, through the integration of FeS with hollow MoS2. This composite aims at the efficient photocatalytic reduction of hexavalent chromium (Cr(VI)). A comprehensive array of characterization techniques unveiled that MoS2 flakes, dispersed on FeS, provide numerous active sites for photocatalysis at the heterojunction interface. The inclusion of FeS seemingly promotes the formation of sulfur vacancies on MoS2. Consequently, this heterojunction catalyst exhibits photocatalytic activity surpassing pristine MoS2 by a factor of 3.77. The augmented activity of the FeS/MoS2-0.05 catalyst is attributed chiefly to an internal electric field at the interface. This field enhances the facilitation of charge transfer and separation significantly. Density functional theory (DFT) calculations, coupled with experimental analyses, corroborate this observation. Additionally, DFT calculations indicate that sulfur vacancies act as pivotal sites for Cr(VI) adsorption. Significantly, the adsorption energy of Cr(VI) species shows enhanced favorability under acidic conditions. Our results suggest that the FeS/MoS2-0.05 heterojunction photocatalyst presents substantial potential for the remediation of Cr(VI)-contaminated wastewater.

Ameliorating the detrimental effects of chromium in wheat by silicon nanoparticles and its enriched biochar

Increased anthropogenic activities over the last decades have led to a gradual increase in chromium (Cr) content in the soil, which, due to its high mobility in soil, makes Cr accumulation in plants a serious threat to the health of animals and humans. The present study investigated the ameliorative effect of foliar-applied Si nanoparticles (SiF) and soil-applied SiNPs enriched biochar (SiBc) on the growth of wheat in Cr-polluted soil (CPS). Two levels of CPS were prepared, including 12.5 % and 25 % by adding Cr-polluted wastewater in the soil as soil 1 (S1) and soil 2 (S2), respectively for the pot experiment with a duration of 40 days. Cr stress significantly reduced wheat growth, however, combined application of SiF and SiBc improved root and shoot biomass production under Cr stress by (i) reducing Cr accumulation, (ii) increasing activities of antioxidant enzymes (ascorbate peroxidase and catalase), and (iii) increasing protein and total phenolic contents in both root and shoot respectively. Nonetheless, separate applications of SiF and SiBc effectively reduced Cr toxicity in shoot and root respectively, indicating a tissue-specific regulation of wheat growth under Cr. Later, the Langmuir and Freundlich adsorption isotherm analysis showed a maximum soil Cr adsorption capacity ∼ Q(max) of 40.6 mg g−1 and 59 mg g−1 at S1 and S2 respectively, while the life cycle impact assessment showed scores of −1 mg kg−1 and -211 mg kg−1 for Cr in agricultural soil and − 0.184 and − 38.7 for human health at S1 and S2 respectively in response to combined SiF + SiBC application, thus indicating the environment implication of Si nanoparticles and its biochar in ameliorating Cr toxicity in different environmental perspectives.

Comparison of surface adsorption efficacies of eco-sustainable agro/animal biomass-derived activated carbon for the removal of rhodamine B and hexavalent chromium.

Effective management and remediation strategies are crucial to minimize the impacts of both organic and inorganic contaminants on environmental quality and human health. This study investigates a novel approach utilizing cotton shell activated carbon (CSAC), rice husk activated carbon (RHAC), and wasp hive activated carbon (WHAC), produced through alkali treatment and carbonization under N2 atmosphere at 600°C. The adsorption capacities of biomass-derived mesoporous activated carbons (CSAC, RHAC, WHAC) alongside macroporous commercial activated carbons (CAC) were evaluated for removing rhodamine B (Rh B) and hexavalent chromium (Cr6+). The CSAC exhibits remarkable adsorption efficiency (255.4mg.g-1) for Cr(VI) removal, while RHAC demonstrates superior efficacy (174.2mg.g-1) for Rh B adsorption. Investigating various optimal parameters including initial pH (pH 3 for Cr and pH7 for Rh B), catalyst dosage (200mg.L-1), and initial concentration (20mg.L-1), the Redlich-Peterson isotherm model is applied to reveal a hybrid adsorption mechanism encompassing monolayer (chemisorption) and multilayer (van der Waals adsorption) processes. Kinetic analysis highlights the pseudo-second-order and Elovich models as the most suitable, suggesting physiochemisorption mechanisms. Thermodynamic analysis indicates the endothermic nature of the adsorption process, with increased randomness at the solid-solution interface. Isosteric heat investigations using Clausius-Clapeyron, Arrhenius, and Eyring equations reveal a heterogeneous surface nature across all activated carbons. Further confirmation of Rh B and Cr(VI) adsorption onto activated carbons is provided through FTIR, FESEM, and EDAX analysis. This study highlights the innovation and promise of utilizing biomass-derived activated carbons for effective pollutant removal.

Development of biochar using herbal industry waste for removal of hexavalent chromium from aqueous solution: Column study

Biochar is an rich source of carbon formed through biomas’s thermal decomposition. There is a lot of scope of interest in developing biochar derived from biomass in various disciplines to address the most significant ecological challenges. In the present study herbal waste collected from herbal processing industry (Bangalore, India). So, this biomass will be no use after the extraction process. Hence, present work mainly concentrates the conversion this herbal waste to biochar (BC). Research highlights the BC was prepared from herbal industry waste using pyrolysis method. The obtained BC used as adsorbent for adsorption of Cr (VI) from aqueous solution. A characterization of BC was performed using XRD, SEM-EDS and FT-IR which confirms the material. The adsorption experiments were carried out using batch and fixed bed column. The experimental studies were carried out at room temperature with initial Cr (VI) concentrations (IC) of 10–120 ppm using an adsorbent dosage (AD) of 0.05–0.55 g, agitation speed of 150 rpm for contact time (CT) 15–165 min and temperature (20–40 °C). Then various parameters for column study like bed height, flow rate and IC were also studied. The maximum removal of Cr (VI) was 88 % found at a pH 2, AD 0.55g, CT 90 min, and IC 100 ppm at 30 °C. For column study: higher removal of Cr (VI) achieved by bed height (BH) of 6 cm and at lower flow rate (FR), of 3 mL/min.

Synergy of Adsorption and Solar Photoreduction for Removal Cr(VI) with Spinel CuFe2O4

Synergy of Adsorption and Solar Photoreduction for Removal Cr(VI) with Spinel CuFe2O4

MXene@polydopamine/oxidized sodium alginate modified collagen composite aerogel as sustainable bio-adsorbent for heavy metal ion adsorption and solar driven water evaporation

The design of an environmentally friendly bio-adsorbent for the removal of heavy metal ions from aqueous media is a sustainable strategy to ensure water safety. Herein, a three-dimensional macroscopic aerogel with photothermal conversion and heavy metal wastewater treatment capability was designed using leather collagen, MXene@polydopamine and oxidized sodium alginate as raw materials, named as MPAC composite aerogel. The applicability of the developed MPAC composite aerogel in water evaporation and heavy metal wastewater treatment was studied. MPAC composite aerogel had good Cr(VI) adsorption capacity. This article focused on the study of adsorption kinetics, isotherms and thermodynamics. The adsorption equilibrium time of MPAC composite aerogel was 60 min, and the equilibrium adsorption capacity of MPAC composite aerogel for Cr(VI) reached 80.73, 100.80 and 112.86 mg/g when the initial Cr(VI) concentration was 30, 70 and 100 mg/L, respectively. The adsorption process of Cr(VI) by MPAC composite aerogel conformed to the two-level dynamics model and the Freundlich adsorption isotherm model, and was a spontaneous endothermic reaction. Additionally, the composite aerogel had good solar-driven water evaporation ability and could enhance the water evaporation rate of Cr(VI) solution. Furthermore, the MPAC composite aerogel had high adsorption performance for Cr(VI) under solar illumination conditions. This new aerogel has the advantages of low cost, environmental friendliness, strong adsorption capacity and photothermal conversion performance and is a promising heavy metal ion adsorbent.

Superior comprehensive performance of modified activated carbon as a hexavalent chromium adsorbent

The presence of hexavalent chromium species (CrVI) in wastewater from manufacturing industries such as electroplating and leather production can pose serious health hazards. To address these concerns, this study developed a novel adsorbent based on activated carbon as the primary material to attract CrVI. Activated carbon has been modified with several other components to improve its comprehensive performance, including adsorption capacity, chemical stability, collectability, and reusability. Specifically, decoration with magnetite nanoparticles made it possible to collect the adsorbent magnetically and reuse it several times. On the one hand, the addition of chitosan not only increased the chemical stability of activated carbon, especially under acidic conditions, but also enhanced the Cr adsorption capacity at pH higher than 4, where adsorption of only activated carbon was significantly decreased, probably because the protonated amino groups attracted chromate anions. In addition, the co-existence of tannic acid did not increase the adsorption capacity significantly but appeared to promote the reductive adsorption of CrVI, where the reduction of CrVI means lowering the toxicity of Cr species. It was demonstrated that activated carbon modified with magnetite, chitosan, and tannic acid exhibited superior comprehensive performance that could be repeatedly used over a wide pH range as compared to the parent activated carbon.

From cosmetics to Contamination: Microplastics in personal care products as vectors for chromium in aquatic environments

Microplastics presence in the environment is now a major global issue. Personal care and cosmetic products (PCCPs) contain microbeads and are one of the primary sources of microplastics which contribute to health and ecological risks. The aim of this study was to evaluate the presence of microbeads in a widely used PCCPs (facial scrubs) in the Indian market and the extent to which these microbeads can serve as vectors for toxic compounds like chromium under different environmental conditions. Four of the ten facial scrubs contained microbeads of size ranging from 220 to 600 µm. Based on FTIR analyses, two of the four tested samples (A and B) were made of polypropylene, while the other two samples (C and D) were made of polyethylene. Furthermore, the study revealed that PP microbeads, which are very common, could efficiently adsorb Cr (VI) (3.09 mg Cr/g). Adsorption of Cr (VI) on microbeads was greater in acidic and saline conditions indicating that microbeads can potentially act as vectors for toxic compounds in marine aquatic ecosystems. It was estimated that 4.7 x 1010 microbeads, which amount to 3.8 tonnes of microbeads are released into the environment annually. Based on these results, policy measures for preventing the release of microbeads/microplastics into the environment are suggested.

Batch adsorptive removal of Cr (VI) from aqueous phase using magnetic activated carbon nanocomposite prepared from walnut shells by ZnCl2-FeCl3 activation

ABSTRACT This work aims to assess the physicochemical and adsorptive ability of magnetic activated carbon nanocomposites (MACN) developed from walnut shells (WS) through single-step and dual-step preparation routes utilising ZnCl2-FeCl3 as an activator and magnetising agent for Cr (VI) elimination from the aqueous phase. Synthesis of MACN via a one-step route (MACN1) was achieved through direct activation of WS with ZnCl2-FeCl3. In contrast, the preparation of MACN by dual-steps route (MACN2) was accomplished by carbonising WS at 450°C for 1 h, followed by ZnCl2-FeCl3 activation of the resulting biochar. The N2-adsorption-desorption isotherms, X-ray diffraction (XRD), Field Emission Scanning Electron Microscope (FESEM), Energy Dispersive X-ray (EDX), Transmittance Electron Microscope (TEM), Fourier Transform Infra-Red spectroscopy (FTIR), and Vibrating Sample Magnetization (VSM), were implemented to characterise the MACN samples. BET surface area of MACN1 was 1780.20 m2/g with an average pore diameter of 1.95 nm compared to 283.62 m2/g and 1.91 nm for MACN2. The VSM, FESEM, and TEM measurements ensured the presence of iron oxide nanoparticles on the surface of the composites. Investigating various operating parameters disclosed that the highest adsorptive elimination (AE) of Cr(VI) from its aqueous phase by MACN1 was 99.66% compared to 97.43% for that achieved using MACN2. The adsorption results were best fitted to the Langmuir isotherm using both composites with maximum adsorption capacity of 233.12 mg/g for MACN1 compared to147.55 mg/g for MACN2, suggesting that the adsorption is homogonous and chemical. Moreover, the pseudo-2nd-order kinetics model exhibited the best match for the adsorption of Cr(VI) by both adsorbents, demonstrating that chemisorption was involved in eliminating Cr(VI) from its aqueous phase. After five repetitions, the regeneration experiments confirmed that the MACN adsorbents maintained a high AE. Based on the findings, the as-prepared composites have extensive potential to be applied on the industrial scale.

Efficient Adsorption of Cr(VI) from Aqueous Solutions Using Composites Modified with Ni/Al LDH and Keggin Type Compounds

Efficient Adsorption of Cr(VI) from Aqueous Solutions Using Composites Modified with Ni/Al LDH and Keggin Type Compounds

New insight into multi-functional MOG@COP/SA beads for co-adsorption and mono-detection in CTC-Cr(Ⅵ) co-contamination system and efficient anti-counterfeiting

Co-contamination of antibiotics and heavy metals in water environment has provoked considerable toxicological concerns. Meantime, residue detection of heavy metals as well as national anti-counterfeiting safety also have driven attempts in wastewater treatment. In this paper, a core–shell hybrid MOG@COP is designed with behaviors superior to pristine components by combining a Zr-based metal–organic gel and a guanidine-based covalent organic polymer, for co-adsorption and mono-detection in chlortetracycline hydrochloride (CTC)-Cr(Ⅵ) co-contamination system and efficient anti-counterfeiting. In single/binary system, the adsorption capacities of CTC and Cr(Ⅵ) behave as 133.69 and 63.45 mg·g−1/181.82 and 64.47 mg·g−1, and the high sensitivity and low detection limit of Cr(Ⅵ) render as 1.46*105 M−1 and 0.20 μM/1.49*102 M−1 and 0.63 mM, respectively. In addition, to solve the powder shortcomings of easy agglomeration and difficult recycling, MOG@COP is fixed into sodium alginate (SA) matrix to fabricate MOG@COP/SA beads, yielding reinforced adsorption performance of CTC/Cr(Ⅵ) in both single system (152.91/92.25 mg·g−1) and binary system (174.83/75.30 mg·g−1). More importantly, a self-constructed adsorption-detection-anti-counterfeiting (ADA) platform is ingeniously developed with the MOG@COP/SA beads as the backfills for continuously processing CTC-Cr(Ⅵ) co-contaminated water, realizing real-time visualization of Cr(Ⅵ) adsorption process and optical anti-counterfeiting protection. In conclusion, this work is expected to not only trigger the reasonable design of the core–shell hybrid MOG@COP/SA beads with versatile performances of simultaneous luminescence monitor, capture and anti-counterfeiting, but also allow the original exploration for all-in-one platform.

Effects of aging processes on spent mushroom Substrate-Derived Biochar: Adsorption characteristics of Cd(II) and Cr(VI)

To explore how chemical, physical and biological process impact the adsorption capacity of biochar for cations and anions, five kinds of spent mushroom substrate biochars including PB (carbonized Auricularia auricula substrate at 600 °C for 6 h), NB (Aged PB at 25 °C and 40 % moisture for 12 mon), AB (PB treated with 20 % mixed acid solution at 70 °C for 6 h), FB (PB subjected to 16 freeze–thaw cycles between − 20 °C and 25 °C) and MB (PB incubated with microbes from contaminated soil for 15 cycles) were prepared under simulated conditions, the internal mechanisms were revealed. Results showed that all aging processes caused a variation in crystal quantity and structure on different biochar. AB, NB and MB had higher hydrophilicity and polarity, and more positive charges than PB. Moreover, AB and MB had a higher cation exchange capacity (CEC) (70.7 and 75.3 cmol/kg) and more oxygen-containing functional groups than PB. MB has the maximum adsorption capacity for Cd(II) (24.2 mg/g), followed by PB (23.5 mg/g), FB (22.7 mg/g), NB (22.2 mg/g), and AB (22.0 mg/g). Langmuir model better described the Cd(II) adsorption onto NB, FB, and PB, while Freundlich better described AB and MB. As for Cr(VI), the maximum adsorption capacity followed the order: MB (24.1 mg/g) > AB (23.7 mg/g) > FB (23.5 mg/g) > PB (23.0 mg/g) > NB (22.7 mg/g). Langmuir model was better for Cr(VI) adsorption onto FB and PB, while Freundlich was better for AB, NB and MB. The pseudo-first-order kinetic model fits for Cd adsorption by FB，while the pseudo-second-order kinetic model fit for the adsorption of Cd and Cr by other biochars. The adsorption of Cr by all biochars was significantly related to the content of lactone group. Acidification and organic acids from microorganisms increased the pHPZC values of AB and MB, which was not conducive to the adsorption of Cd. The surface fragmentation of FB caused by the freezing and thawing process promoted its adsorption of Cd.

Intensification of Cr(VI) adsorption using activated carbon adsorbent modified with ammonium persulfate

Granular activated carbon has been modified by ammonium persulfate as a new adsorbent for Cr(VI) adsorption from aqueous solutions. The adsorbent was characterized by nitrogen adsorption–desorption isotherm data and infrared spectroscopy. The impact of different factors, such as the initial pH level of the solution, time, temperature, ionic strength, and initial concentration of the Cr(VI) ion, on the adsorption efficiencies of the adsorbent has been studied by batch experiments. Kinetic studies and the adsorption thermodynamics of Cr(VI) with ammonium persulfate-modified activated carbon adsorbent were carefully studied. The results showed that the Cr(VI) adsorption follows a pseudo-second-order kinetic model and the adsorption reaction is endothermic and spontaneous. The adsorption isotherm was scrutinized, and the fitting results showed that the Langmuir model could well represent the adsorption process. The maximum adsorption capacity of Cr(VI) onto persulfate-modified activated carbon was 108.69 mg g−1. The research results showed that using persulfate-modified activated carbon adsorbent can greatly remove Cr(VI) from aqueous solutions.

Comparison of Hexavalent Chromium Adsorption Behavior on Conventional and Biodegradable Microplastics

Microplastics are omnipresent in aquatic environments and can act as vectors to carry other pollutants, modifying their pathway through the systems. In this study, the differences in the adsorption capacity and mechanism for Cr(VI) sorption with polyethylene (PE, a conventional microplastic) and polylactic acid (PLA, a biodegradable microplastic) were investigated via characterization of the MPs, the determination of kinetic behavior (pseudo-first- and second-order model, the Elovich model), and the degree of fit to Langmuir and Freundlich isothermal models; the adsorption behavior was also studied under different solution conditions. The results indicated that when the dose of MPs was 1 g/L, the adsorption capacity of Cr(VI) on MPs reached the highest value, the adsorption capacities were PLA(0.415 mg/g) > PE(0.345 mg/g). The adsorption of Cr(VI) on PE followed the Langmuir isotherm model, while PLA had a stronger fit with the Freundlich model. Sorption in both cases followed a pseudo-first-order kinetics model. The maximum adsorption capacity of Cr(VI) on PLA (0.54 mg/g) is higher than that on PE (0.38 mg/g). In addition, PLA could reach adsorption equilibrium in about 8 h and can adsorb 72.3% of the total Cr(VI) within 4 h, while PE required 16 h to reach equilibrium, suggesting that PLA adsorbs at a significantly faster rate than PE. Thus, biodegradable MPs like PLA may serve as a superior carrier for Cr(VI) in aquatic environments. When the pH increased from 2 to 6, the adsorption of Cr(VI) by PE and PLA decreased from 0.49 mg/g and 0.52 mg/g to 0.27 mg/g and 0.26 mg/g, respectively. When the concentration of sodium dodecyl sulfate in the Cr(VI) solution was increased from nil to 300 mg/L, the adsorption of Cr(VI) by PE and PLA increased by 3.66 and 3.05 times, respectively. In addition, a higher temperature and the presence of Cu2+ and photoaging promoted the adsorption of Cr(VI) by MPs, while higher salinity inhibited the adsorption. The desorption efficiencies of Cr(VI) on MPs were PLA(57.8%) > PE(46.4%). The characterization results further confirmed that the adsorption mechanism could be attributed to electrostatic attraction, hydrogen bonding, and surface complexation. In sum, PLA could potentially serve as better vectors for Cr(VI) than PE, but the risk associated with PLA might be higher than that with PE.

Efficient removal of Cr (VI) by Bifunction zinc porphyrin COF: Coupling adsorption with Photocatalysis, performance Evaluation, and mechanism analysis

HypothesisHexavalent chromium, recognized as one of the most toxic heavy metals, demands the development of advanced materials capable of both adsorption and photocatalysis for effective Cr (VI) removal. ExperimentsThis study successfully synthesized a two-dimensional zinc porphyrin covalent organic framework (ZnPor-COF) via a solvent-based method. Performance evaluations have demonstrated that the ZnPor-COF possesses outstanding capabilities for the adsorptive and/or photocatalytic elimination of Cr (VI). Particularly noteworthy is the observation that when adsorption and photocatalysis are coupled, the ZnPor-COF attains an exceptional 99.7 % removal rate for a Cr (VI) concentration of 30 mg/L within just 60 min, with minimal susceptibility to coexisting ions. After five consecutive cycles, the material sustains a removal efficiency of 90 %, indicative of its robust cyclability. FindingsTheoretical calculations, as well as experimental validations, have indicated that the integration of Zn ions into the porphyrin COF not only results in an expanded specific surface area and an increased count of adsorption sites but also significantly improves the COF’s photosensitivity and the capability for charge carrier separation. Furthermore, the core of the synergistic effect between adsorption and photocatalysis lies in the ability of photocatalysis to substantially augment the adsorption process.

Efficient removal of chromate from wastewater using a one-pot synthesis of chitosan cross-linked ceria incorporated hydrous copper oxide bio-polymeric composite

Remediating hexavalent chromium [Cr(VI)] from contaminated water systems is a significant concern due to its harmful effects on human health, aquatic life, and plants. To tackle this issue, scientists have created a chitosan cross-linked hydrous ceria incorporated cupric oxide bio-polymeric composite (CHCCO) by combining chitosan biopolymer with corresponding metal ions using glutaraldehyde as a cross-linker. The composite was characterized using advanced analytical instruments such as FTIR, p-XRD, SEM, XPS, etc. The synthesized composite (CHCCO) was then tested for its efficiency in removing Cr(VI) from synthetic Cr(VI) aqueous samples. The parameters examined included pH, material dose, contact time, concentration, temperature, and co-existing ions. The experimental data showed that the kinetics and equilibrium data fit well with the pseudo-second-order and the Freundlich isotherm models, respectively. Thermodynamic analysis demonstrated that the investigated surface adsorption process is spontaneous and endothermic. Except for the SO42− ion, no other species imparts adverse influence significantly on the reaction. The CHCCO bio-composite surfaces were refreshed using a dilute NaOH (1.0 M) solution and effectively recycled five times for Cr(VI) adsorption, indicating no significant surface activity deterioration. This study highlights the high effectiveness of CHCCO bio-polymeric composites in Cr(VI) remediation and the potential for this technology as an easy-to-use technique for environmental restoration.

An effective cascade strategy over a Sn-enriched phosphate material: Upcycling a reductive adsorbent into an environmental catalyst

A calcium phosphate-based material enriched with Sn (8.3 at.%, as revealed by X-ray photoelectron spectroscopy) was successfully used in the reductive adsorption of Cr(VI) to Cr(III) for water remediation and, after use, repurposed into a catalyst for NO oxidation into NO2.The use of multiple characterization techniques (Mӧssbauer spectroscopy, synchrotron X-ray diffraction, TEM, and HAADF-STEM/EDS) provided information on Sn-speciation (Sn(II)/Sn(IV) = 1.2), structural composition, and morphological features. Cassiterite (rutile-type SnO2) and hydroromarchite (tin oxide-hydroxide Sn6O4(OH)4) crystalline phases characterized the material, along with the presence of an amorphous Ca3(PO4)2 phase.Notably, about 15 mgCr(VI)∙g−1 could be effectively reduced over a broad pH range (2–11), even in the simultaneous presence of various anions and cations, with concurrent adsorption of the resulting Cr(III), thanks to the adsorption properties of the phosphate phase. The kinetic constant of Cr(VI) removal was as high as 0.0058 g∙mg−1∙min−1 and increased in the presence of a pool of cations (0.0147 g∙mg−1∙min−1). The catalytic performances of the adsorbent after use in Cr(VI) reductive adsorption were studied in the 150–450 °C interval at 15,000–80,000 h−1 space velocity. About 90 % of NO conversion at 350 °C was observed.This study highlights the adaptability and efficiency of the developed material across different environmental remediation processes.

Smart and responsive nano copper oxide–PDMS composite for “three-in-one” synergistic adsorptive–oxidative / reductive degradation of the persistence of organic pollutants, elimination of nanoparticles and heavy metal ion

Copper-and silica-based materials have been used globally as environmental catalysts and adsorbents for centuries. Despite their differences in their properties and roles in the participation of environmental activity, both have been combined to create various types of functional materials, ranging from copper oxides and polydimethylsiloxane (PDMS) sponge (PS) cores to advanced hybrid composite materials. In this work, CuO was incorporated onto SiO2 (CPC) by calcination of PDMS-Cu2O sponge, and the physicochemical properties and application of CPC were investigated. The CPC was homogeneous in a surface area (326.69 m2g-1), pore size (33.16 Å), pore volume (0.056 cm³g−1), and particle size (183.66 Å). This CPC has been used for the degradation (oxidation/reduction) and adsorption of azithromycin (AZM), 1,4-dichlorobenzene (DCB), rhodamine B (RB), methylene blue (MB), 4-nitrophenol (4-NP), gold nanoparticles (AuNPs), and chromium (VI). Efficiencies of CPC for the above persistence of organic pollutants (POPs) and adsorption of AuNPs and Cr(VI) were ∼72–100% under optimized conditions. CPC followed the pseudo-second-order (PSO) degradation kinetics with a higher r2 (>0.99) with eight cycles of reusability. Moreover, this synthetic strategy can be tailored to produce nanostructured composite materials and/or those associated with other species for diverse environmental and industrial applications.

Grafting of Polyethyleneimines on Porous Silica Beads and Their Use for Adsorptive Removal of Cr(VI) from Aqueous Medium

Porous silica-based adsorbents for hexavalent chromium (Cr(VI)) ion removal were prepared by the combined use of functionalization with (3-glycidyloxypropyl)trimethoxysilane and the grafting of branched and linear polyethyleneimine (BPEI and LPEI). LPEI was prepared from polyethyloxazolin by hydrolysis with HCl. The preparation of LPEI was identified by NMR measurements and the grafting of BPEI and LPEI on the silica beads was confirmed by an XPS analysis. The Cr(VI) ion adsorption of the obtained BPEI-grafted silica beads (BPEI–silica beads) was investigated as a function of the pH value, the content of amino groups, the temperature, the Cr(VI) ion concentration, and the molecular mass of the grafted BPEI chains. The Cr(VI) ion adsorption at pH 3.0 increased with an increase in the content of amino groups, and the maximum adsorption capacity of 1.06 mmol/g was obtained when the content of amino groups was at 2.17 mmol/g. This value corresponds to 589 mg/g−1.8KPEI, and the adsorption ratio of about 0.5 is a noteworthy result. The data fit to the pseudo-second-order kinetic model, and the suitability of this fitting was supported by the results that the adsorption capacity and initial rate of adsorption increased with the temperature. In addition, the equilibrium data followed the Langmuir isotherm model. These results clearly demonstrate that the Cr(VI) adsorption occurred chemically, or through the electrostatic interaction of protonated amino groups on the grafted BPEI chains with hydrochromate (HCrO4−) ions. A higher adsorption capacity was obtained for the silica beads grafted with shorter BPEI chains, and the adsorption capacity of BPEI–silica beads is a little higher than that of linear PEI-grafted silica beads, suggesting that the Cr(VI) ion adsorption is affected by the chain isomerism of PEI (linear and branched) as well as the molecular mass of the grafted PEI chains, in addition to the content of amino groups. The experimental and analytical results derived from this study emphasize that the BPEI–silica beads can be used as an adsorbent for the removal of Cr(VI) ions from an aqueous medium.