Investigating the selectivity and interference behavior for detoxification of Cr(VI) using lanthanum phosphate polyaniline nanocomposite via adsorption-reduction mechanism

Fe doping enhanced Cr(VI) adsorption efficiency of cerium-based adsorbents: Adsorption behaviors and inner removal mechanisms

Cerium-based adsorbents possessed unique advantages of valence variability and abundant oxygen vacancies in hexavalent chromium (Cr(VI)) adsorption, but high cost and unstable properties restricted their application in Cr(VI) contained wastewater treatment. Herein, a series of bimetallic adsorbents with different cerium/iron ratios (CeFe@C) were prepared by adding inexpensive Fe into Ce-based adsorbents (Ce@C), and the effect of Fe doping on adsorption properties of Ce@C for Cr(VI) was investigated thoroughly. Compared with pristine Ce@C, CeFe@C exhibited excellent removal performance for Cr(VI), and the improved maximum adsorption capacity reached 75.11 mg/g at 25℃. Benefiting from Fe doping, CeFe@C had good regeneration property, with only 25 % decrease after five adsorption-desorption cycles. Contents of trivalent cerium (Ce(III)) and oxygen vacancies (Ov) in bimetallic adsorbents were positively correlated with divalent iron (Fe(II)) doping, indicating that the formation of Ce(III) and surface defects on Ce@C could be effectively regulated by Fe doping. Density functional theory (DFT) calculation results further proved that the doped Fe enhanced the electron transfer effectively and lowered the energy barriers of Cr(VI) adsorption onto Ce@C surface, strengthening the reduction and complexation to Cr(VI). This study provides new insights for improving the Cr(VI) removal performance by modified Ce-based adsorbents, and further promotes the utilization potentiality of low-cost and low-toxicity Ce-based adsorbents in Cr(VI)-containing wastewater treatment.

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.

Amino-modified upcycled biochar achieves selective chromium removal in complex aqueous matrices

Chromium pollution of groundwater sources is a growing global issue, which correlates with various anthropogenic activities. Remediation of both the Cr(VI) and Cr(III), via adsorption technologies, has been championed in recent years due to ease of use, minimal energy requirements, and the potential to serve as a highly sustainable remediation technology. In the present study, a biochar sorbent sourced from pineapple skins, allowed for the upcycling of agricultural waste into water purification technology. The biochar material was chemically modified, through a green amination method, to produce an efficient and selective adsorbent for the removal of both Cr(VI) and Cr(III) from complex aqueous matrices. From FTIR analysis it was evident that the chemical modification introduced new C-N and N-H bonds observed in the modified biochar along with a depletion of N-O and C-H bonds found in the pristine biochar. The amino modified biochar was found to spontaneously adsorb both forms of chromium at room temperature, with binding capacities of 46.5 mg/g of Cr(VI) and 27.1 mg/g of Cr(III). Interference studies, conducted in complex matrices, showed no change in adsorption capacity for Cr(VI) in matrices containing up to 3,000× the concentration of interfering ions. Finally, Cr(III) removal was synergized to 100% adsorption at interfering ions concentrations up to 330× of the analyte, which were suppressed at higher interference concentrations. Considering such performance, the amino modified biochar achieved selective removal for both forms of chromium, showing great potential for utilization in complex chromium pollution sources.

Efficient removal of hexavalent chromium by nano-cerium-based adsorbent: The critical role of valence state and oxygen vacancy

Cerium-based adsorbents have been gradually used for the adsorption removal of highly toxic Cr(VI) from wastewater due to their low toxicity and wide working pH. However, the intrinsic properties of adsorbents contribute significantly to their adsorption performance, and the relationship between them needs to be clarified. Herein, series of nano-cerium based adsorbents (Ce@Cs) with different surface defects and Ce(III) content were prepared to explore their effects on the Cr(VI) adsorption capacity. Results showed that the optimal Ce@C performed well over a wide pH range of 2.0-12.0, and the calculated Cr(VI) adsorption capacity reached 302.43 mg/g at 45 ℃. Ce(III) and surface defects in cerium-based adsorbents exhibited an important influence on the Cr(VI) adsorption performance of Ce@Cs, and their contents showed a good positive correlation with the Cr adsorption capacity (R2 =0.988 and 0.827). A series of evidences confirmed that the generated Ce(III) and oxygen vacancies could provide more sufficient coordination number to promote Cr(VI) complexation with Ce@Cs and lower the impedance of Ce@Cs to improve the reduction of Cr(VI) to low-toxic Cr(III). This work provides new insights into the Cr(VI) adsorption using cerium-based adsorbents, which helps to improve their potential in the purification of Cr(VI)-containing wastewater.

Facile preparation, characterization and application of novel sugarcane bagasse-derived nanoceria-biochar for defluoridation of drinking water: kinetics, thermodynamics, reusability and mechanism

Although expensive, rare-earth oxides are well known for being powerful defluoridation agents. Being costlier, cerium is used as a hybrid adsorbent in conjunction with a prudent and environmentally benign substance like biochar. The novel CeO2/BC (surface area 260.05 m2/g) composite was shaped using the facile chemical precipitation technique without any cross-linkers. Surface properties of synthesised CeO2/BC were investigated using powder XRD, FTIR, BET, pH point of zero charge and SEM. According to XRD analysis, immobilized Ce is primarily in form of CeO2, while pristine biochar is in an amorphous state. Batch mode adsorption tests were carried out with different solution pH, F- initial concentration, adsorbent dosage and contact time and counter anions. CeO2/BC can be used in a varied pH range (2-10) but shows maximum removal at pH 4. The Langmuir adsorption isotherm and a pseudo-second-order kinetic model are best fitted to support the adsorption process with a maximum Langmuir adsorption capacity of 16.14 mg/g (F- concentration 5 to 40 mg/L). The removal phenomenon is non-spontaneous in nature. The plausible mechanism of fluoride uptake was explained using XPS and pHPZC, and it was demonstrated that the fluoride was mainly removed by ion exchange and electrostatic attraction. The adsorbent could be successfully used up to fourth cycle after regenerating.

Synthesis and characterization of PANI-ZrWPO4 nanocomposite: adsorption-reduction efficiency and regeneration potential for Cr(VI) removal

A novel polyaniline zirconium tungstophosphate (PANI-ZrWPO4) nanocomposite was successfully synthesized through an in situ oxidative polymerization reaction followed by a microwave irradiation process. The synthesized nanocomposite was characterized by using FESEM, EDX, TEM, XRD, FTIR, Raman, TGA-DTA, XPS, and N2 adsorption-desorption analysis and chemical analysis to know about the formation of material. The results of the FTIR and Raman spectra confirmed that the conducting PANI polymer interacted with ZrWPO4 to form the PANI-ZrWPO4 nanocomposite. The XRD data showed that the composite had a crystalline nature. The TEM and FESEM images revealed that polyaniline had formed on the exterior of the PANI-ZrWPO4 nanocomposite. Further investigation was done on the efficiency of the PANI-ZrWPO4 nanocomposite as an adsorbent for Cr(VI) removal through batch adsorption experiments. The maximum Langmuir adsorption capacity of PANI-ZrWPO4 was found to be 71.4 mg g-1. The removal of Cr(VI) was optimized with the six variables namely adsorbent dose, initial concentration, Time, pH, Temperature, and stirring rate using the Box-Behnken design (BBD) model. The XPS spectra confirmed simultaneously adsorption reduction occurs Cr(VI) to Cr(III) through in situ chemical reduction. Moreover, the regeneration efficiency of PANI-ZrWPO4 was studied, and it was found to be able to remove around 80% of Cr(VI) even after five cycles, demonstrating its potential as an effective and reusable adsorbent.

Efficient Removal of Heavy Metals from Aqueous Solution Using Licorice Residue-Based Hydrogel Adsorbent

The removal of heavy metals through adsorption represents a highly promising method. This study focuses on the utilization of an abundant cellulose-rich solid waste, licorice residue (LR), as a natural material for hydrogel synthesis. To this end, LR-EPI hydrogels, namely, LR-EPI-5, LR-EPI-6 and LR-EPI-8, were developed by crosslinking LR with epichlorohydrin (EPI), specifically targeting the removal of Pb, Cu, and Cr from aqueous solutions. Thorough characterizations employing Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy confirmed the successful crosslinking of LR-EPIs by EPI, resulting in the formation of porous and loosely structured hydrogels. Batch studies demonstrated the high efficacy of LR-EPI hydrogels in removing the three heavy metal ions from aqueous solutions. Notably, LR-EPI-8 exhibited the highest adsorption capacity, with maximum capacities of 591.8 mg/g, 458.3 mg/g, and 121.4 mg/g for Pb²⁺, Cr³⁺, and Cu²⁺, respectively. The adsorption processes for Pb²⁺ and Cu²⁺ were well described by pseudo-second-order kinetics and the Langmuir model. The adsorption mechanism of LR-EPI-8 onto heavy metal ions was found to involve a combination of ion-exchange and electrostatic interactions, as inferred from the results obtained through X-ray photoelectron spectroscopy and FTIR. This research establishes LR-EPI-8 as a promising adsorbent for the effective removal of heavy metal ions from aqueous solutions, offering an eco-friendly approach for heavy metal removal and providing an environmentally sustainable method for the reutilization of Chinese herb residues. It contributes to the goal of "from waste, treats waste" while also addressing the broader need for heavy metal remediation.

Surface modified Acacia Senegal Gum based spherical hydrogel; fabrication, characterization, and kinetically optimized waste water treatment with remarkable adsorption efficiency

Acacia Senegal Gum hydrogel (HASG) with swollen dimension less than 50 μm were fabricated, and chemically modified with versatile diethylenetriamine (d-amine) to tailor the surface properties for environmental remediation. Negatively charged metal ions, for example, chromate (Cr(III)), dichromate (Cr(VI)), and arsenate (As(V)) were removed from aqueous media by using modified hydrogels (m-HASG). The FT-IR spectra revealed some new peaks due to d-amine treatment. The zeta potential measurements confirm a positively charged surface of HASG upon d-amine modification at ambient conditions. The absorption studies revealed that 0.05 g feed of m-(HASG) possesses 69.8, 99.3, and 40.00% cleaning potential against As(V), Cr(VI), and Cr(III), respectively with 2 h contact time in deionized water. Almost comparable adsorption efficiency was achieved by the prepared hydrogels towards the targeted analytes dissolved in real water samples. Adsorption isotherms, for example, Langmuir, Freundlich and modified Freundlich isotherms were applied to the collected data. Briefly, Modified Freundlich isotherm manifested comparatively agreeable line for the all adsorbents pollutants with highest R² figure. In addition, maximum adsorption capacity (Qm) with 217, 256, and 271 mg g^-1 numerical values were obtained against As(V), Cr(VI), and Cr(III), respectively. In real water samples, 217, 256, and 271 mg g^-1 adsorption capacity was represented by m-(HASG). In brief, m-(HASG) is a brilliant material for environmental application as cleaner candidate towards toxic metal ions.

Synthesis of Ag-Cu-Ni Nanoparticles Stabilized on Functionalized g-C3N4 and Investigation of Its Catalytic Activity in the A3-Coupling Reaction

In the present research, using ethylenediamine and hydrazine hydrate as the capping and reducing agents in this investigation, respectively, Ag-Cu-Ni NPs were immobilized on the functionalized g-C₃N₄ surface. This nanocatalyst was studied in terms of its catalytic activities for the A³-coupling reaction to synthesize propargylamine derivatives. According to the results, in the presence of 1 mL of toluene as the solvent and 20 mg of the g-C₃N₄-TCT-2AEDSEA-Ag-Cu-Ni nanocatalyst, the maximum efficiency of the nanocatalyst occurred at a temperature of 80 °C. Products were purified using thin-layer chromatography plates (silica gel) by employing n-hexane/ethyl acetate with a 90:10 ratio. In addition, the prominent benefits of the synthesized nanocatalyst include its high yields of the product, cost-effectiveness, recyclability, and easy separation. The novelty of the catalyst is due to the presence of Ag-Cu-Ni nanoparticles at the same time in the structure of the functionalized g-C₃N₄ substrate. So, Ag-Cu-Ni can be strongly connected to the substrate. The structure of the synthesized nanocatalyst was characterized using Fourier transformed infrared spectroscopy, X-ray powder diffraction, field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, vibrating-sample magnetometry, and transmission electron microscopy.

Preparation of a novel metal-free polypyrrole-red phosphorus adsorbent for efficient removal of Cr(VI) from aqueous solution

The toxicity and carcinogenicity of Cr(VI) makes it a major threat to the health of animals and people. However, how to efficiently remove Cr(VI) still faces important challenges. In this study, a new metal-free polypyrrole-red phosphorus (PPy-RP) composite is successfully synthesized by in-situ oxidation polymerization for Cr(VI) removal from wastewater. The maximum adsorption capacity (q_m) of Cr(VI) on PPy-RP-1 is 513.2 mg/g when the pH value is 2, which is far superior to RP nanosheets (207.8 mg/g) and PPy (294.9 mg/g). The improved q_m can be ascribe to the good dispersion and increased specific surface area of PPy-RP adsorbent. Encouragingly, PPy-RP adsorbent still exhibits excellent stability after 7 cycles tests without a significant decline in removal efficiency, and remain above 81.4%. Based on the fittings of adsorption isotherms and kinetics, the process conforms to the pseudo-first-order kinetic model and the single-layer adsorption of the Langmuir model with an R² value of 0.98533. The adsorption process is chemical and monolayer. The experimental result demonstrates that the PPy-RP can efficient removal Cr(VI) by electrostatic attraction and complexation reaction (formation of N-Cr(VI) bond) through the PPy on the surface. The results of this study indicate that PPy-RP is a promising adsorbent to remove the Cr(IV).

Anthracite based activated carbon impregnated with HMTA as an effectiveness adsorbent could significantly uptake gasoline vapors

In this study, we synthesized and employed the amine impregnated activated carbon as an efficacious adsorbent for uptaking gasoline vapor. For this regard, anthracite as activated carbon source and hexamethylenetetramine (HMTA) as amine were selected and utilized. Physiochemical characterization of made sorbents were evaluated and investigated using SEM, FESEM, BET, FTIR, XRD, zeta potential, and elemental analysis. The synthesized sorbents provided an excellent textural features as compared with the literature and other activated carbon based sorbents and impregnated with amine. Our findings also suggested that in addition to high surface area (up to 2150 m² / g), the micro- meso pores created (Vmeso / V micro = 0.79 Cm ³ / g) surface chemistry may significantly affect the gasoline sorption capacity, which here the role of mesoporous is further highlighted. V meso for amine impregnated sample and free activated carbon was 0.89 and 0.31 Cm ³ / g, respectively. According to the results, the prepared sorbents have a potential capability in uptaking gasoline vapor and with line this, we report a high sorption capacity of 572.56 mg / g. After, four cycles used the sorbent had a high durability and about 99.11% of the initial uptake was maintained. Taking together the synthesized adsorbents as an activated carbon provided an excellent and unique features and enhanced gasoline uptake, therefore its applicability in uptaking gasoline vapor can be substantially considered.

Thallium removal from wastewater using sulfidized zero-valent manganese: Effects of sulfidation method and liquid nitrogen pretreatment

Zero-valent manganese (ZVMn) possesses high reducibility in theory, while sulfide exhibits strong affinity towards a variety of heavy metals owing to the low solubility of metal sulfides. Yet the performance and mechanisms on using sulfidized zero-valent manganese (SZVMn) to remove thallium (Tl) from wastewater still remain unclear. In this study, the performance of Tl(I) removal using SZVMn synthesized by borohydrides reduction followed by sulfides modification, with and without liquid nitrogen treatment, was compared and the mechanism behind was investigated. The results show that at a S/Mn molar ratio of 1.0, liquid nitrogen modified SZVMn (LSZVMn) possessed more interior channels and pores than SZVMn, with 65.3% higher specific surface area and 73.7% higher porosity, leading to 6.4-8.1% improvement in adsorption of Tl(I) at pH 4-10. LSZVMn showed effectiveness and robustness in Tl(I) removal in the presence of co-existing ions up to 0.1 M. The adsorption of Tl(I) conformed to the pseudo-1st-order kinetic model, and followed the Langmuir isothermal model, with the maximum Tl adsorption capacity of 264.9 mg·g^-1 at 288 K. The mechanism of Tl(I) removal with SZVMn was found to include sulfidation-induced precipitation, manganese reduction, surface complexation, and electrostatic attraction. The liquid nitrogen pretreatment embrittled and cracked the outer shell of S/Mn compounds, resulted in a highly hierarchical structure, enhancing the manganese reduction and improving the Tl(I) removal. Based on the above results, the SZVMn and its liquid nitrogen-modified derivatives are novel and effective environmental materials for Tl(I) removal from wastewater, and the application of SZVMn to the removal of other pollutants merits investigation in future study.

“Gamma Irradiation Synthesis of Carboxymethyl Chitosan-Nanoclay Hydrogel for the Removal of Cr(VI) and Pb(II) from Aqueous Media”

Hydrogel composites comprised of N,O carboxymethyl chitosan crosslinked with different weight ratios of acrylic acid and fabricated with nanoclay particle were prepared via gamma irradiation at 25 kGy irradiation dose. The prepared composites were coded as CsAA1Cl, CsAA2Cl and CsAA3Cl based on the weight ratio of acrylic acid to the chitosan derivative. The claimed hydrogels were characterized by FTIR, TGA and XRD. The TGA data implied that the incorporation of clay nanoparticles enhanced the thermal stability of the composites; the decomposition temperature increased up to 500 °C for CsAA3Cl. Three AFM outcomes were used to compare the surface features of the samples; topography, height and surface roughness. The topography data reveals that the nanoclay particles incorporated in CsAA3Cl are intercalated and exfoliated. Then, the optimized sorbent (CsAA3Cl) was investigated as green sorbents for chromium (VI) and lead (II). The data revealed that CsAA3Cl displayed maximum removal performance towards both lead and chromium with removal efficiencies 125 mg/g and 205 mg/g respectively at the optimum application conditions within 90 min only. Also, it was found that the optimum pH value was 9 for chromium and 8 for lead. The data proved that the adsorption of both cations followed pseudo-first order kinetic model. The prepared composites showed acceptable metal uptake capacity at three successive cycles.

Graphical Abstract

The effect of inorganic salt on the morphology and nucleation of polyaniline nanofibers synthesized via self-assembly

Polyaniline (PANI), due to the various and controllable shapes, the environmental stability, the excellent physical and chemical property, has gained significant attention. PANI with abundant morphologies were successfully prepared through adjusting and controlling the state of the initial micelle-like in the micelle-like system composed by aniline and organic acids with relatively weak intermolecular interaction. Although the influence of the inorganic salts on their morphology, including the surface and the diameter, was investigated, the influence of salt on the nucleation of PANI was still unclear. Therefore, PANI nanofibers were fabricated through the addition of inorganic salt such as NaCl, MgSO₄ and AlCl₃ into the micelle-like composed of aniline and D-camphor-10-sulfonic acid. The influence of types and concentration of inorganic salts, doped acids and temperature on PANI was studied by Transmission Electron Microscope (TEM), UV-vis and Fourier Transform Infrared Spectroscopy (FTIR) spectroscopy. In addition, in situ UV-vis and ¹H Nuclear Magnetic Resonance technology (NMR) were applied to observe the process of aniline polymerization, and it was indicated the polymerization rate of aniline changed after the addition of inorganic salt NaCl into the initial solution.

Performance and mechanism of lanthanum-modified zeolite as a highly efficient adsorbent for fluoride removal from water

Defluoridation of water is still challenging due to the fluoride pollution of both groundwater and surface water worldwide. In this study, lanthanum-modified zeolite (LMZ) was synthesized from coal fly ash and was investigated for fluoride removal from water by conducting batch and column experiments. Our results indicated that the process of fluoride adsorption was endothermic and the adsorption kinetics on LMZ followed the pseudo-second-order model. A higher temperature increased both the capacity and the rate of adsorption. The maximum fluoride adsorption capacity of LMZ reached 141.5 mg/g with a F/La molar ratio of 4.21, as estimated from the Langmuir model which best fitted the isotherm data. Fluoride adsorption greatly depended on pH, with optimal performance being achieved within ∼5.0-∼7.0. The point of zero charge of LMZ was pH 8.8, at which only bicarbonate ions greatly affected fluoride removal. However, no competing effect was observed at pH 6.3 for all tested anions including chloride, sulphate, nitrate, bicarbonate and acetate. The dominant adsorption mechanism was the ligand exchange of fluoride with hydroxyls on LMZ, as illustrated by the rise in pH due to fluoride adsorption and by the molecular scale spectroscopic FTIR, Raman and XPS studies. Fluoride adsorbed on LMZ was successfully desorbed using NaOH solution, and regenerated LMZ could be reused. The results of column studies showed that LMZ granulated with alginate performed well in treating F^--containing water. In conclusion, LMZ is a promising material for efficient defluoridation from water.

Selective reduction of nitrite to nitrogen by polyaniline-carbon nanotubes composite at neutral pH

The selective reduction of nitrite (NO₂^-) to nitrogen by chemical reductant is a desirable strategy to remove NO₂^- from polluted water and wastewater. However, the residue and reuse of chemical reductant are two main issues to be addressed. Herein, a novel polyaniline-carbon nanotubes composite (PANI-CNTs) was developed by in-situ polymerization to selectively reduce NO₂^- to nitrogen gas (N₂). The used PANI-CNTs could be reused after regeneration with NaBH₄. The PANI-CNTs could reduce NO₂^- with 93.9% N₂ selectivity at initial pH of 6.8. The NO₂^- removal efficiency only decreased by 12.08% after five cycles of reduction/regeneration. The interconversion between imine nitrogen (-N) and amine nitrogen (-NH-) groups induced the chemical reduction of NO₂^- and regeneration of PANI-CNTs. PANI-CNTs exhibited an excellent performance for the removal of NO₂^- in the presence of competitive ions and in actual water and wastewater samples. This new PANI-CNTs composite may have great potential for water purification and wastewater denitrification.

Highly efficient removal of Cr(VI) by hexapod-like pyrite nanosheet clusters

Pyrite nanomaterials show an excellent performance in remediating Cr(VI) contaminated wastewater. However, the high surface reactivity makes them easy to agglomerate to reduce their removal efficiency for Cr(VI). In this study, a novel hexapod-like pyrite nanosheet clusters material was successfully synthesized via a facile hydrothermal method with the assistance of fluorides. The products were pyrite microspherulites without fluoride ion. The hexapod-like pyrite nanosheet clusters had dramatically higher Cr(VI) removal efficiencies than microspherulites due to more dissolved Fe(II) and S(-II) into the suspension released for nanosheet clusters should be responsible for the enhanced removal rate of Cr(VI). The XPS analysis revealed that the rapid adsorption on the surface of pyrite nanosheet clusters followed by reduction of Cr(VI) to Cr(III) by FeS₂ and subsequent precipitation of Cr(III) hydroxides/oxyhydroxides are responsible for the high removal capacity of Cr(VI). The hexapod-like pyrite nanosheet clusters material had high stability and longevity, and did not aggregate during the Cr(VI) removal process. The removal efficiency of Cr(VI) was still 100% after 5 cycles. Our study shows that the hexapod-like pyrite nanosheet clusters material could be acted as a recyclable and promising mineral material with high activity, stability, feasibility for remediating Cr(VI) contaminated environment.

Removal of lead from aqueous solutions using three biosorbents of aquatic origin with the emphasis on the affective factors

The biosorptive potentials of three aquatics-based biosorbents, including shells of a bivalve mollusk and scales of two fish species for Pb removal from aqueous solutions were evaluated, for the first time. A Box-Behnken design with the response surface methodology was used to investigate the effects of the seven important variables (contact time, temperature, initial concentration, dosage, size, salinity and pH) on the sorption capacity of the sorbents. Among the seven studied factors, the effects of biosorbent dosage, initial concentration and pH were significant for all the response variables, while biosorbent size was not significant for any of the responses. The initial concentration was the most influential factor. The presence of Pb ions on the surfaces of the biosorbents after the adsorption was clearly confirmed by the SEM-EDX and XRF analyses. The maximum sorption capacities of the biosorbents were comparable to the literature and the descending order was as follows: scales of Rutilus kutum and Oncorhynchus mykiss and the shells of Cerastoderma glaucum. The isotherm studies revealed Langmuir model applicability for the Pb adsorption by R. kutum and O. mykiss scales, while Freundlich model was fitted to the adsorption C. glaucum shells.

Modulation of titania nanoflower arrays transformed from titanate nanowire arrays to boost photocatalytic Cr(vi) detoxification

The integration of the N/S co-doping, anatase/rutile junction construction, and morphology regulation of TiO2 arrays is achieved by a simple method to improve photocatalytic activity.

Fabrication of attapulgite/magnetic aminated chitosan composite as efficient and reusable adsorbent for Cr (VI) ions

An efficient composite was constructed based on aminated chitosan (NH2Cs), attapulgite (ATP) clay and magnetic Fe3O4 for adsorptive removal of Cr(VI) ions. The as-fabricated ATP@Fe3O4-NH2Cs composite was characterized by Fourier Transform Infrared Spectroscopy (FTIR), Thermal Gravimetric Analyzer (TGA), Scanning Electron Microscope (SEM), Zeta potential (ZP), Vibrating Sample Magnetometer (VSM), Brunauer-Emmett-Teller method (BET) and X-ray photoelectron spectroscope (XPS). A significant improve in the adsorption profile was established at pH 2 in the order of ATP@Fe3O4-NH2Cs(1:3) > ATP@Fe3O4-NH2Cs(1:1) > ATP@Fe3O4-NH2Cs(3:1) > Fe3O4-NH2Cs > ATP. The maximum removal (%) of Cr(VI) exceeded 94% within a short equilibrium time of 60 min. The adsorption process obeyed the pseudo 2nd order and followed the Langmuir isotherm model with a maximum monolayer adsorption capacity of 294.12 mg/g. In addition, thermodynamics studies elucidated that the adsorption process was spontaneous, randomness and endothermic process. Interestingly, the developed adsorbent retained respectable adsorption properties with acceptable removal efficiency exceeded 58% after ten sequential cycles of reuse. Besides, the results hypothesize that the adsorption process occurs via electrostatic interactions, reduction of Cr(VI) to Cr(III) and ion-exchanging. These findings substantiate that the ATP@Fe3O4-NH2Cs composite could be effectively applied as a reusable adsorbent for removing of Cr(VI) ions from aqueous solutions.