Amino-functionalized MCM-41 and MCM-48 for the removal of chromate and arsenate

Synthesis and application of SBA-15 adsorbent for the removal of organic and inorganic substances

This study investigates the adsorption of pollutants with different chemical structures; organic Naphtol Green B (NGB) dye and copper on a nanocomposite material with a hexagonal structure of the SBA-15 type. This research is divided into two main parts: the first carries out the synthesis of SBA-15 (Santa Barbra Amourphous) and its derivatives phases functionalized by 3-aminopropyl-triethoxylane (APTES) and calcined at 823 K. The second part presents the influence of the adsorption conditions on the adsorption efficiency of NGB dye and copper. High-resolution X-ray diffractogram (XRD) showed three distinct peaks characteristic of highly ordered mesoporous material. Nitrogen adsorption-desorption isotherm of SBA-15 at 77 K° is type IV typical of mesoporous materials. In addition, Fourier transform infrared spectroscopy (FT-IR) was also used in the characterization before and after the adsorption of the selected pollutants. At optimal conditions of pH 5.2, initial concentration of 50 mg/L, adsorbent dosage of 20 mg, and at adsorption time of 90 min the maximum removal of pollutants reached 76% and the adsorption capacity was 227.25 mg/g for NGB dye and 221.006 mg/g for copper. Furthermore, the adsorption kinetics followed the pseudo-second-order model, indicating that chemisorption was the dominant mechanism and the Sips isotherm model best described the adsorption data. Our research demonstrates that the SBA-15 material after modification is an effective adsorbent for removing effluents regardless of their different chemical structure (organic and inorganic).

Fabrication of a novel porous nanostructure based on NiCuFe2O4@MCM-48, embedded with graphene oxide/poly (p-phenylenediamine) to construct an efficient supercapacitor

In this study, a new nanocomposite was created by combining copper-doped nickel ferrite (NiCuFe2O4) nanoparticles with MCM-48 (Mobil Composition of Matter No. 48) on a graphene oxide (GO) substrate functionalized with poly(ρ-phenylenediamine) abbreviated as (PρPD). This nanocomposite was developed to investigate its potential for enhancing the function of a supercapacitor in energy storage. Following NiCuFe2O4@MCM-48 preparation, Hummer's technique GO was applied. In-situ polymerization of NiCuFe2O4@MCM-48/GO nanoparticles with ρ-phenylenediamine (ρPD) in the presence of ammonium persulfate (APS) produced PρPD, a conductive polymer. Structural characterization of the nanocomposite includes FTIR, XRD, VSM, TGA-DTG, EDX, and FE-SEM. Results from BET indicate a pore size increase of up to 5 nm. Fast ion penetration and higher storage in capacitor material are explained by this. Additionally, the nanocomposite's electrochemical performance was evaluated using GCD and CV tests. The NiCuFe2O4@MCM-48/GO/PρPD nanocomposite has a specific capacitance of 203.57 F g-1 (1 A g-1). Furthermore, cyclical stability is essential for energy storage applications. The nanocomposite retains 92.5% of its original capacitance after 3000 cycles, indicating outstanding electrochemical stability.

Preparation of amino-functionalized fly ash based tobermorite for enhanced removal of Cr(VI)

Amino-functionalized fly ash based tobermorite (NH₂-FAT) was prepared via a two-step process including a hydrothermal preparation of fly ash based tobermorite (FAT) from fly ash (FA) and the impregnation of 3-aminopropyltriethoxysilane (APTES). The characteristics of FA, FAT, and NH₂-FAT were systematically measured. The removal capacity of Cr(VI) by FAT and NH₂-FAT were comparatively studied. The results indicated that the NH₂-FAT presented excellent removal efficiency towards Cr(VI) in the condition of pH of 2. The adsorption capacity of Cr(VI) by NH₂-FAT in this study was up to 498.39 mg/g resulted from Langmuir model, which was more superior to that of FAT, other reported FA based adsorbents and most amino-functionalized adsorbents. Furthermore, the removal mechanisms of Cr(VI) by NH₂-FAT were ascribed to both electrostatic attraction and reduction to Cr(III) by amino groups. Overall, this work indicates the NH₂-FAT is a promising adsorbent for treating wastewater containing Cr(VI), and provides a new utilization method of FA.

As(III, V) Uptake from Nanostructured Iron Oxides and Oxyhydroxides: The Complex Interplay between Sorbent Surface Chemistry and Arsenic Equilibria

Iron oxides/oxyhydroxides, namely maghemite, iron oxide-silica composite, akaganeite, and ferrihydrite, are studied for AsV and AsIII removal from water in the pH range 2-8. All sorbents were characterized for their structural, morphological, textural, and surface charge properties. The same experimental conditions for the batch tests permitted a direct comparison among the sorbents, particularly between the oxyhydroxides, known to be among the most promising As-removers but hardly compared in the literature. The tests revealed akaganeite to perform better in the whole pH range for AsV (max 89 mg g-1 at pH0 3) but to be also efficient toward AsIII (max 91 mg g-1 at pH0 3-8), for which the best sorbent was ferrihydrite (max 144 mg g-1 at pH0 8). Moreover, the study of the sorbents' surface chemistry under contact with arsenic and arsenic-free solutions allowed the understanding of its role in the arsenic uptake through electrophoretic light scattering and pH measurements. Indeed, the sorbent's ability to modify the starting pH was a crucial step in determining the removal of performances. The AsV initial concentration, contact time, ionic strength, and presence of competitors were also studied for akaganeite, the most promising remover, at pH0 3 and 8 to deepen the uptake mechanism.

Meso- and macroporous silica-based arsenic adsorbents: effect of pore size, nature of the active phase, and silicon release

Arsenic pollution in ground and drinking water is a major problem worldwide due to the natural abundance of arsenic by dissolution from ground sediment or mining activities from anthropogenic activities. To overcome this issue, iron oxides as low-cost and non-toxic materials, have been widely studied as efficient adsorbents for arsenic removal, including when dispersed within porous silica supports. In this study, two head-to-head comparisons were developed to highlight the As(v)-adsorptive ability of meso- and macrostructured silica-based adsorbents. First, the role of the textural properties of a meso-(SBA15) and macrostructured (MOSF) silica support in affecting the structural-morphological features and the adsorption capacity of the active phase (Fe2O3) have been studied. Secondly, a comparison of the arsenic removal ability of inorganic (Fe2O3) and organic (amino groups) active phases was carried out on SBA15. Finally, since silica supports are commonly proposed for both environmental and biomedical applications as active phase carriers, we have investigated secondary silicon and iron pollution. The batch tests at different pH revealed better performance from both Fe2O3-composites at pH 3. The values of q m of 7.9 mg g-1 (53 mg gact -1) and 5.5 mg g-1 (37 mg gact -1) were obtained for SBA15 and MOSF, respectively (gact stands for mass of the active phase). The results suggest that mesostructured materials are more suitable for dispersing active phases as adsorbents for water treatment, due to the obtainment of very small Fe2O3 NPs (about 5 nm). Besides studying the influence of the pore size of SBA15 and MOSF on the adsorption process, the impact of the functionalization was analyzed on SBA15 as the most promising sample for As(v)-removal. The amino-functionalized SBA15 adsorbent (3-aminopropyltriethoxysilane, APTES) exhibited a q m of 12.4 mg g-1 and faster kinetics. Furthermore, issues associated with the release of iron and silicon during the sorption process, causing secondary pollution, were evaluated and critically discussed.

Synthesis and application of cationised cellulose for removal of Cr(VI) from acid mine-drainage contaminated water

Background: Acid mine drainage (AMD) leads to contamination of surface and ground water by high levels of toxic metals including chromium. In many cases, these waters are sources of drinking water for communities, and treatment is therefore required before consumption to prevent negative health effects. Methods: Cationised hemp cellulose was prepared by etherification with two quaternary ammonium salts: 3-chloro-2-hydroxypropyl trimethyl ammonium chloride (CHPTAC) and glycidyltrimethylammonium chloride (GTMAC) and examined for (i) the efficiency of Cr(VI) removal under acid mine-drainage (AMD) conditions, and (ii) antibacterial activity. Adsorbents were characterised by electron microscopy, Fourier transform infrared (FTIR), CP-MAS 13C nuclear magnetic resonance (NMR) spectroscopy, elemental composition and surface charge. Results: FTIR and solid state 13C NMR confirmed the introduction of quaternary ammonium moieties on cellulose. 13C NMR also showed that cationisation decreased the degree of crystallisation and lateral dimensions of cellulose fibrils. Nevertheless, 47 %  - 72 % of Cr(VI) ions were removed from solutions at pH 4, by 0.1 g of CHPTAC and GTMAC-cationised cellulose, respectively. Adsorption kinetics followed the pseudo-second order model and isotherms were best described by the Freundlich and Dubinin-Radushkevich models. When GTMAC-modified cellulose was applied to AMD contaminated water (pH 2.7); however, Cr(VI) removal decreased to 22% likely due to competition from Al and Fe ions. Cationised materials displayed considerable antibacterial effects, reducing the viability of Escherichia coli by up to 45 % after just 3 hours of exposure. Conclusions: Together, these results suggest that cationised cellulose can be applied in the treatment of Cr(VI)-contaminated mine water particularly if pre-treatments to reduce Fe and Al concentrations are applied.

The adsorption behavior and mechanism of Cr(VI) on facile synthesized mesoporous NH-SiO2

An efficient Cr(VI) adsorbent, mesoporous amine-functionalized silica (NH-SiO₂), was successfully synthesized within 2 h by a facile one-step route under room temperature and aqueous solution. The structure properties of the obtained materials were characterized by N₂ adsorption-desorption isotherm, XRD, TEM, and FT-IR. The Cr(VI) removal performance was investigated by batch experiment. It was found that Cr(VI) removal performance was dependent on solution pH, and the removal efficiency is above 90% for initial pH in the range of 1.0-4.0. The adsorption process was obeyed by pseudo-second-order model, and the equilibrium adsorption data were fitted well by Langmuir model. The maximum monolayer adsorption capacity was 205.76 mg/g at pH 2.0, which was larger than that of traditional two-step tri-amine-functionalized MCM-41. Additionally, high selectivity was exhibited in NH-SiO₂ for removal Cr(VI) from co-presence anions Cl^-, NO₃^-, PO₄^3-, SO₄^2-, and SiO₃^2-. Furthermore, the spent NH-SiO₂ could be regenerated by 0.005 M NaOH, and Cr(VI) removal is above 92% after NH-SiO₂ recycled four. From the analyzed results of adsorption energy, FT-IR, and XPS, the electrostatic attraction between protonated amine group and HCrO₄^- was the mainly adsorption mechanism. And then some adsorbed Cr(VI) was reduced to low toxicity Cr(III) on the adsorbent surface by electron transfer from nitrogen in -NBr group to Cr(VI).

Synthesis and characterization of lignosulfonate/amino-functionalized SBA-15 nanocomposites for the adsorption of methylene blue from wastewater

The synthesis, characterization, and methylene blue (MB) adsorption study of a new lignosulfonate/amino-functionalized SBA-15 nanocomposite are described.

Selective copper extraction by multi-modified mesoporous silica material, SBA-15

Selective copper (Cu) recovery from wastewater mitigates environmental pollution and is economically valuable. Mesoporous silica adsorbents, SBA-15, with amine-grafting (SBA-15-NH₂) and manganese loading along with amine-grafting (Mn-SBA-15-NH₂) were fabricated using KMnO₄ and 3-aminopropyltriethoxysilane. The characteristics of the synthesized adsorbents were evaluated in detail in terms of its crystal structure peaks, surface area and pore size distribution, transmission electron microscope and X-ray photoelectron spectroscopy. The results established the 2.08mmol/g of Cu adsorption capacity on Mn-SBA-15-NH₂. Furthermore, in a mixed heavy metal solution, high selective Cu adsorption capacity on Mn-SBA-15-NH₂ (2.01mmol/g) was achieved while maintaining 96% adsorption amount as that of a single Cu solution. Comparatively, Cu adsorption on SBA-15-NH₂ decreased by half due to high competition with other heavy metals. Optimal Cu adsorption occurred at pH5. This pH condition enabled grafted amine group in Mn-SBA-15-NH₂ to form strong chelating bonds with Cu, avoiding protonation of amine group (below pH5) as well as precipitation (above pH5). The adsorption equilibrium well fitted to Langmuir and Freundlich isotherm models, while kinetic results were represented by models of linear driving force approximation (LDFA) and pore diffusion model (PDM). High regeneration and reuse capacity of Mn-SBA-15-NH₂ were well established by its capacity to maintain 90% adsorption capacity in a multiple adsorption-desorption cycle. Cu was selectively extracted from Mn-SBA-15-NH₂ with an acid solution.

Nanocomposite functionalized membranes based on silica nanoparticles cross-linked to electrospun nanofibrous support for arsenic(v) adsorption from contaminated underground water

Nanocomposite functionalized membranes were synthesized using surface functionalized mesoporous silica nanoparticles (MCM-NH2 or MCM-PEI) cross-linked to a modified polyacrylonitrile (mPAN) nanofibrous substrate for the removal of 1 mg L-1 of As(v); a concentration much higher than what has been reported for underground water in Argentina. Adsorption studies were carried out in batch mode at pH 8 with nanoparticles in colloidal form, as well as the nanoparticles supported on the modified PAN membranes (mPAN/MCM-NH2 and mPAN/MCM-PEI). Results indicate a twenty-fold improvement in As(v) adsorption with supported nanoparticles (nanocomposite membranes) as opposed to their colloidal form. The adsorption efficiency could be further enhanced by modifying the nanocomposite membrane surface with Fe3+ (mPAN/MCM-NH2-Fe3+ and mPAN/MCM-PEI-Fe3+) which resulted in more than 95% arsenic being removed within the first 15 minutes and a specific arsenic adsorption capacity of 4.61 mg g-1 and 5.89 mg g-1 for mPAN/MCM-NH2-Fe3+ and mPAN/MCM-PEI-Fe3+ nanocomposite membranes, respectively. The adsorption characteristics were observed to follow a pseudo-first order behavior. The results suggest that the synthesized materials are excellent for quick and efficient reduction of As(v) concentrations below the WHO guidelines and show promise for future applications.

Fe3+-bis-ethylenediamine complex bridged periodic mesoporous organosilica for the efficient removal of arsenate and chromate

The direct removal of arsenate (AsO4 3−) and chromate (CrO4 2−) from water were achieved using a Fe3+-bis-ethylenediamine complex-bridged periodic mesoporous organosilica with a 20% organosilane content (Fe-EDPMO-20). The bridged Fe3+-bis-ethylenediamine complex was introduced to the pore wall of the PMO by combining the pre-complexation and co-condensation processes. N,N′-bis[3-(triethoxysilyl)propyl]ethylenediamine (TESEN) and tetramethyl orthosilicate (TMOS) as silica precursors were used with cetyltrimethylammonium bromide (CTABr) as a surfactant under basic conditions for the preparation of highly ordered Fe-EDPMO-20. Transmission electron microscopy, X-ray diffraction, and N2 adsorption-desorption measurements confirmed that the Fe-EDPMO-20 had an ordered hexagonal p6mm mesostructure. The material had a Brunauer-Emmett-Teller surface area of 734 m2 g−1, pore diameter of 2.6 nm, and pore volume of 0.61 cm3 g−1. UV-vis and X-ray photoelectron spectroscopy confirmed that Fe3+ was embedded in the coordination site by the nitrogen atoms from ethylenediamine. The adsorption efficiencies of arsenate and chromate ions by Fe-EDPMO-20 were examined as a function of pH, stirring time, amount of adsorbent, and initial concentration of metal ion solution. The maximum adsorption for arsenate and chromate were 156 and 102 mg g−1 within 6 and 24 h, respectively, at pH 4.

Sol-Gel Synthesis of Ordered β-Cyclodextrin-Containing Silicas

New approaches for β-cyclodextrin-containing silicas synthesis were demonstrated. Materials with hexagonally ordered mesoporous structure were prepared by postsynthesis grafting and by co-condensation methods. β-Cyclodextrin activated by a N,N'-carbonyldiimidazole was employed for postsynthesis treatment of 3-aminopropyl-modified MCM-41 support as well as for sol-gel synthesis with β-cyclodextrin-containing organosilane and tetraethyl orthosilicate participation in the presence of cetyltrimethylammonium bromide. The successful incorporation of cyclic oligosaccharide moieties in silica surface layer was verified by means of FT-IR spectroscopy and chemical analysis. Obtained β-cyclodextrin-containing materials were characterized by X-ray diffraction, transmission electron microscopy, and low-temperature adsorption-desorption of nitrogen. In spite of commensurable loading of β-cyclodextrin groups attained by both proposed approaches (up to 0.028 μmol · m(-2)), it was found that co-condensation procedure provides uniform distribution of β-cyclodextrin functionalities in silica framework, whereas postsynthesis grafting results in modification of external surface of silica surface. Adsorption of benzene from aqueous solutions onto the surface of β-cyclodextrin-containing materials prepared by co-condensation method was studied as the function of time and equilibrium concentration. Langmuir and Freundlich models were used to evaluate adsorption processes and parameters. Adsorption experiments showed that β-cyclodextrin-containing silicas could be promising for the trace amount removal of aromatics from water.

Biocompatible hybrid silica nanobiocomposites for the efficient delivery of anti-staphylococcal drugs

This work reports the non-surfactant templated synthesis and characterization of a new tyrosine-silica/antibiotics (TyR-SiO2/ATBs) nanocomposite, as well as both in vitro and in vivo cytotoxicity and antimicrobial activity against the microbial pathogen Staphylococcus aureus. The in vitro microbiological tests proved that the obtained nanobiostructure significantly enhance the antimicrobial activity of three commonly used antibiotics against S. aureus (i.e. erythromycin (ERI), gentamicin (GEN), and cloxacillin (CLO)) as revealed by the increased diameters of the growth inhibition zones and the decreased minimal inhibitory concentration values, as well as by the inhibitory effect of sub-lethal antibiotic concentrations on the ability of the respective pathogenic strains to adhere and colonize different substrata. These results, correlated with the lack of toxicity against mesenchymal stem cells along with an appropriate in vivo biodistribution highlight the promising therapeutic potential of this carrier that allows a decrease of the required active doses while significantly lessening the harmful side effects of the medication on the host organism.

Electrospun nanofibrous polyethylenimine mat: a potential adsorbent for the removal of chromate and arsenate from drinking water

A nanofibrous adsorbent for sub-ppm level chromate and arsenate removal from drinking water has been fabricated via an electrospinning technique.

Enhanced Adsorption of Trivalent Arsenic from Water by Functionalized Diatom Silica Shells

The potential of porous diatom silica shells as a naturally abundant low-cost sorbent for the removal of arsenic in aqueous solutions was investigated in a batch study. The objective of this work was to chemically modify the silica shells of a diatom Melosira sp. with bifunctional (thiol and amino) groups to effectively remove arsenic in its toxic As(III) form (arsenite) predominant in the aquatic environment. Sorption experiments with this novel sorbent were conducted under varying conditions of pH, time, dosage, and As(III) concentration. A maximum adsorption capacity of 10.99 mg g^-1 was achieved within 26 h for a solution containing 12 mg L^-1 As(III) at pH 4 and sorbent dosage of 2 g L^-1. The functionalized diatom silica shells had a surface morphological change which was accompanied by increased pore size at the expense of reduced specific surface area and total pore volume. As(III) adsorption was best fitted with the Langmuir-Freundlich model, and the adsorption kinetic data using pore surface diffusion model showed that both the external (film) and internal (intraparticle) diffusion can be rate-determining for As(III) adsorption. Fourier transform infrared spectroscopy (FTIR) indicated that the thiol and amino groups potentially responsible for As(III) adsorption were grafted on the surface of diatom silica shells. X-ray photoelectron spectroscopy (XPS) further verified that this unique sorbent proceeded via a chemisorption mechanism through the exchange between oxygen-containing groups of neutral As(III) and thiol groups, and through the surface complexation between As(III) and protonated nitrogen and hydroxyl groups. Results indicate that this functionalized bioadsorbent with a high As(III) adsorption capacity holds promise for the treatment of As(III) containing wastewater.

Mesoporous silica-giant particle with slit pore arrangement as an adsorbent for heavy metal oxyanions from aqueous medium

A newly synthesized giant mesoporous silica particle has been used for arsenate and chromate adsorption studies.

Mesoporous silicas: improving the adsorption efficiency of phenolic compounds by the removal of amino group from functionalized silicas

Removal of the amine template enhances the sorption of phenolic pollutants. The sorption capacity could be dependent of the pore size.

Performance assessment of an analcime-C zeolite–ceramic composite membrane by removal of Cr(vi) from aqueous solution

The aim of this work is to fabricate an analcime-C composite membrane by anin situhydrothermal crystallization method and investigate its separation potential by the ultrafiltration of Cr(vi) from aqueous solution.