Adsorption of Copper(II) on NH2-MCM-41 and Its Application for Epoxidation of Styrene

Modified Halloysite as an Adsorbent for the Removal of Cu(II) Ions and Reactive Red 120 Dye from Aqueous Solutions

The adsorption of copper ions and Reactive Red 120 azo dye (RR-120) as models of water pollutants on unmodified halloysite (H-NM), as well as halloysites modified with sulfuric acid (H-SA) and (3-aminopropyl)triethoxysilane (H-APTES), was investigated. The results showed that adsorption of both the adsorbates was pH-dependent and increased with the increase in halloysite dosage. The adsorption kinetics were evaluated and the results demonstrated that the adsorption followed the pseudo-second-order model. The adsorption isotherms of Cu(II) ions and RR-120 dye on the halloysites were described satisfactorily by the Langmuir model. The maximum adsorption capacities for the Cu(II) ions were 0.169, 0.236, and 0.507 mmol/g, respectively, for H-NM, H-SA, and H-APTES indicating that the NH2-functionalization rather than the surface area of the adsorbents was responsible for the enhanced adsorption. The adsorption capacities for RR-120 dye were found to be 9.64 μmol/g for H-NM, 75.76 μmol/g for H-SA, and 29.33 μmol/g for H-APTES. The results demonstrated that APTES-functionalization and sulfuric acid activation are promising modifications, and both modified halloysites have good application potential for heavy metals as well as for azo dye removal.

Design and synthesis of drug hydrogels containing carboxymethylcellulose with honeycomb structure and pH-sensitivity as drug delivery systems for adriamycin, metformin, and naproxen

The aim of this research is to prepare and identify functionalized carboxymethylcellulose/mesoporous silica nanohydrogels (CMC/NH2-MCM-41) for obtaining a pH-sensitive system for the controlled release of drugs. The beads of CMC/NH2-MCM-41 nanocomposites were prepared by dispersing NH2-MCM-41 in a CMC polymer matrix and crosslinking with ferric ions (Fe3+). The SEM analysis of samples revealed enhancement in surface porosity of the functionalized nanohydrogel beads compared to the conventional beads. Swelling of the prepared functionalized nanohydrogels was evaluated at various pH values including pH = 7.35-7.45 (simulated body fluid or healthy cells), pH = 6 (simulated intestinal fluid), and pH = 1.5-3.5 (simulated gastric fluid). The swelling of CMC/MCM-41 and CMC/NH2-MCM-41 nanohydrogels at the pH values of simulated body fluid and simulated intestinal fluid is much higher than that of simulated gastric fluid, indicating successful synthesis of pH-sensitive nanohydrogels for drug delivery. The drug loading results showed that drug release in the CMC/NH2-MCM-41 system is much slower than that in the CMC/MCM-41 system. The results of the survival studies for the manufactured systems showed a very good biocompatibility of the designed drug delivery systems for biological applications. By coating the surface of functionalized mesopores with CMC hydrogel, we were able to develop a pH-sensitive intelligent drug delivery system.

Uptake of arsenic(V) using iron and magnesium functionalized highly ordered mesoporous MCM-41 (Fe/Mg-MCM-41) as an effective adsorbent

Mesoporous silica (MCM-41) is widely used as a supporting material due to its large specific surface area and good stability, but it cannot remove heavy metals due to the lack of adsorption active sites. In this study, the MCM-41 (a mesoporous SiO₂ material) decorated with iron and magnesium oxide (Fe/Mg-MCM-41) was found to be an excellent adsorbent to remove arsenic(V) from water. FTIR, BET, TEM-EDS, XRD, XPS, etc. were applied for characterization analysis. Adsorption isotherms were fitted well by the Langmuir model and the experimental maximum adsorption capacity of Fe/Mg₄-MCM-41 (magnesium accounts for 4%) was 71.53 mg/g at pH = 3. Thermodynamics analysis suggested exothermic nature of adsorption behavior. Kinetic process was well described by the pseudo-second-order model and adsorption rate was controlled by intraparticle diffusion and film diffusion. Moreover, the adsorption behavior of As(V) onto Fe/Mg₄-MCM-41 was investigated under different reaction conditions, such as pH, temperature, Mg-doping and competing ions. The results showed that loading a certain amount of magnesium can significantly improve arsenic removal efficiency. Additionally, Fe/Mg₄-MCM-41 exhibits high arsenic(V) removal in the wide pH range of 3-10. The Fe/Mg₄-MCM-41 can be regenerated and used after four consecutive cycles. The high arsenic(V) sorption capacity, wide range of pH applications, ability to regenerate, and reusability of Fe/Mg₄-MCM-41 confirmed that this adsorbent is promising for treating As-contaminated wastewater.

Removal of Copper (II) from Aqueous Solution by a Hierarchical Porous Hydroxylapatite-Biochar Composite Prepared with Sugarcane Top Internode Biotemplate

Porous hydroxyapatite-biochar composites with layered microstructures (SC–HA/C) were prepared by carbonizing sugarcane stem nodes and then soaking them in lime water and (NH4)2HPO4 solutions in rotation. The surface area of SC–HA/C ranges from 8.52 to 28.44 m2/g, and its microstructure inherits various macro-, meso-, and micro-pores in the cell walls of sugarcane and in the pits of the vessel walls. The maximum removal capacities were 11.50, 14.65, and 19.81 mg/g for the Cu (II) immobilization at 25 °C, 35 °C, and 45 °C with the solution Cu (II) concentration of 10~320 mg/L, respectively, which were in accordance with the copper sorption capacities of synthesized nano-hydroxylapatites. The Cu (II)-removal kinetics and isotherm followed the pseudo-second-order equation and the Langmuir equation very well. The formation of the Cu-containing hydroxylapatite solid solutions ((CuxCa1−x)5(PO4)3(OH)) through adsorption, ion exchange (x = 0.01~0.04), and dissolution-coprecipitation (x = 0.13~0.35) was the dominant process for the Cu (II) removal by the SC–HA/C composite.

Facile synthesis of superparamagnetic thiamine/Fe3O4 with enhanced adsorptivity toward divalent copper ions

The development of environmentally friendly adsorbents has been extensively carried out to overcome the detrimental effects of heavy metal accumulation, which has persistently become a global ecological problem. In pursuit of generating eco-friendly adsorbents, a green method for synthesizing thiamine functionalized-Fe₃O₄ (FT) was developed in this study. A one-step chemical oxidation and functionalization technique was used to prepare FT using the ammonia-containing solvent. A molar ratio of ammonia:Fe:thiamine of 15:1:1 was shown to produce FT15 with high yield, adsorptivity, and purity. XRD, XPS, FTIR, SEM, and SQUID characterization of FT15 revealed the formation of superparamagnetic thiamine functionalized Fe₃O₄ in their particles. This superparamagneticity facilitates the easy recovery of FT15 particles from the waste-containing solution by using an external magnetic force. The batch adsorption of Cu(II) onto FT15 showed the best fit with the Sips adsorption isotherm model with a maximum adsorption capacity of 426.076 mg g^-1, which is 5.69-fold higher capacity than the control unmodified Fe₃O₄ (F15). After five adsorption-desorption cycles, the FT15 can maintain up to 1.95-fold higher capacity than the freshly synthesized F15. Observation on the physicochemical properties of the post-adsorption materials showed the contribution of an amine group, pyrimidine ring, and the thiazolium group of thiamine in boosting its adsorption capacity. This study provides important findings to advance the adsorptivity of magnetic adsorbents with promising recoverability from aqueous solution by employing naturally available and environmentally friendly compounds such as thiamine.

Evaluation of Amine Functionalized Thermal Power Plant Solid Waste for Industrial Wastewater Remediation

Micro/nanoparticles generated after the combustion of coal/lignite in the thermal power plants were modified with amino groups of (3-aminopropyl) triethoxysilane (APTES). These silane-based functional particles were applied in textile dye (xylenol orange, XO and methyl orange, MO) removal process to deal with an industrial wastewater problem. The maximum adsorption efficiencies of APTES coated micro/nanoparticles for MO and XO dye molecules were calculated to be around 98% and 75%, respectively. The adsorption behavior of the LCFA against dyes is also assessed by investigating the effect of adsorbent dosage, contact time, pH, and temperature. The optimum dye removal was observed at a pH of 4.0, and the equilibrium was achieved within 5 min. The maximum uptake capacities of LCFA-APTES for MO and XO dye molecules were calculated to be around 17.91 and 14.72 mg g−1, respectively. This value is approximately 3 − 5 times higher than the similar adsorbent in the literature. The uptake mechanism of MO and XO dyes onto LCFA-APTES is governed by electrostatic interaction and hydrogen bonding between dye molecules and APTES. The surface chemical modifications and the nature of functional groups were ascertained by scanning electron microscopy (SEM), thermogravimetric analysis (TGA), X-ray fluorescence (XRF), and X-ray photoelectron spectroscopy (XPS). The application of recovered micro/nanoparticles from solid wastes and their utilization for wastewater treatment is important not only for economy of developing countries but also for protecting the environment.

Efficient removal of chromate ions from aqueous solution using a highly cost-effective ferric coordinated [3-(2-aminoethylamino)propyl]trimethoxysilane-MCM-41 adsorbent

The present investigation involves synthesis and characterization of MCM-41-AEAPTMS-Fe(iii)Cl using coordinated Fe(iii) on MCM-41-AEAPTMS for efficient removal of hazardous Cr(vi) ions from aqueous solution. The adsorbent MCM-41-AEAPTMS-Fe(iii)Cl was characterized using small-angle X-ray diffraction (SAX), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), Fourier-transform infrared (FT-IR) and Brunauer-Emmett-Teller (BET) surface analyzer techniques. The BET surface area was found to be 87.598 m2 g-1. The MCM-41-AEAPTMS-Fe(iii)Cl effectively adsorbs Cr(vi) with an adsorption capacity acquiring the maximum value of 84.9 mg g-1 at pH 3 at 298 K. The data followed pseudo-second-order kinetics and obeyed the Langmuir isotherm model. The thermodynamic data proved the exothermic and spontaneous nature of Cr(vi) ion adsorption on MCM-41-AEAPTMS-Fe(iii). Further, the higher value of ΔH° (-64.339 kJ mol-1) indicated that the adsorption was chemisorption in nature.

Cu-Kojic Acid Complex Anchored to Functionalized Silica-MCM-41: A Promising Regioselective and Reusable Nanocatalyst for Click Reaction

Cu-Kojic acid (KA) complex anchored to functionalized silica-MCM-41 was synthesized via the process of postgrafting and introduced as an effective, new, reusable, and thermally resistant heterogeneous nanocatalyst for the clean synthesis of 1H-1,2,3-triazoles from Click reaction of 2-(azidomethyl)-5-benzyloxy-4-pyrone and azido Kojic acid with a variety of terminal alkynes in excellent yields. The structure of nanocatalyst was analyzed by ICP, BET, XRD, EDS, SEM, TGA, TEM, and FT-IR techniques.

Immobilization of Cr(VI) on engineered silicate nanoparticles: Microscopic mechanisms and site energy distribution

Engineered nanoparticles-mediated contaminant transport has been recognized as a significant process governing the mobility of metals and radionuclides in groundwater. Engineered silicate nanoparticles (ESNPs) are attractive materials for the sequestration or extraction of Cr(VI) and other metals and radionuclides from groundwater. While great efforts have been devoted toward the application of these materials for Cr(VI) sequestration, the underlying interface adsorption mechanism is not thoroughly elucidated. This study investigates the immobilization mechanisms of Cr(VI) on a representative ESNPs, NH₂-MCM-41, over a range of water chemistry conditions. By combining batch adsorption experiments with an array of complementary characterizations, we provided spectroscopic and microscopic evidence that the electrostatic interactions between the positively charged NH₂-MCM-41 surface derived from amino functionality and the negatively charged Cr(VI) species was the dominant mechanism responsible for Cr(VI) immobilization. In addition, the weak hydrogen bonding interactions may also contribute to adsorption to a degree. Furthermore, thermodynamic studies suggested a favorable, spontaneous, and exothermic adsorption process. Site energy analysis illustrated that the distribution of energy binding sites on NH₂-MCM-41 is Cr(VI) loading dependent. The new insights provided here can advance understanding of the transport of Cr(VI) associated NH₂-MCM-41 that benefits the application of ESNPs-based technologies for metals immobilization in groundwater.

Recent advances in the application of silica nanostructures for highly improved water treatment: a review

The demand for high-quality safe and clean water supply has revolutionized water treatment technologies and become a most focused subject of environmental science. Water contamination generally marks the presence of numerous toxic and harmful substances. These contaminants such as heavy metals, organic and inorganic pollutants, oil wastes, and chemical dyes are discharged from various industrial effluents and domestic wastes. Among several water treatment technologies, the utilization of silica nanostructures has received considerable attention due to their stability, sustainability, and cost-effective properties. As such, this review outlines the latest innovative approaches for synthesis and application of silica nanostructures in water treatment, apart from exploring the gaps that limit their large-scale industrial application. In addition, future challenges for improved water remediation and water quality technologies are keenly discussed.

Facile one-pot synthesis of thiol-functionalized mesoporous silica submicrospheres for Tl(I) adsorption: Isotherm, kinetic and thermodynamic studies

For the first time, thiol-modified mesoporous silica submicrospheres (TMS-SMSs) have been applied to remove extremely high toxic Tl(I) ions from aqueous solution by an adsorption approach. TMS-SMSs as a silica-based material is basically environmentally benign, with combined advantages of porosity and functionality. XRD measurement and TEM images clearly exhibited a parallel arrangement of mesopores in TMS-SMSs with a combination of both semi-long-range ordering and wormhole-like motif structures. The batch adsorption of Tl(I) onto TMS-SMSs showed a typical Langmuir adsorption isotherm (among various non-linear isotherm models) with the maximum adsorption capacity of 452.8 mgg^-1. TMS-SMSs show a fast adsorption rate, and pseudo-second-order kinetic model provides the best correlation between experimental data. The thermodynamic constants indicated that the adsorption of Tl(I) ions was an endothermic (ΔH° = 24.80 kJ  mol^-1), entropy driven (ΔS° = 0.161 kJ  mol^-1K^-1), and spontaneous process (ΔG° = 23.15-27.95 kJ mol^-1). This study provides an exciting opportunity to advance our knowledge of functionalized-mesoporous silica submicrospheres as a promising adsorbent for the removal of toxic Tl(I) ions from aqueous solution using adsorption approach.

Effective removal of copper from aqueous solutions by modified magnetic chitosan/graphene oxide nanocomposites

In the present work, a novel magnetic chitosan/graphene oxide nanocomposite (MCGON) was synthesized for the removal of Cu²⁺ from aqueous solutions. The adsorbent was composed of graphene oxide (GO) modified by ethylenediamine (ED), Fe₃O₄ nanoparticles and chitosan-g-poly(acrylic acid-co-2-acrylamido-2-methylpropane sulfonic acid) copolymer. The composition and structure of adsorbents were characterized by FTIR, SEM, EDX, XRD, TGA, VSM and BET analysis. The magnetic MCGON with a high specific surface area of (132.9m²g^-1), large pore volume (4.03cm³g^-1), small particle size (15nm) and strong saturation magnetization (3.82emug^-1) was used as an efficient adsorbent for the removal of Cu²⁺ ions from wastewater. The results showed that the adsorption of Cu²⁺ onto MCGON exhibited a maximum adsorption capacity of 217.4mgg^-1. Kinetics, thermodynamics and equilibrium isotherm of the removal of copper (II) ions were carefully investigated. Adsorption of Cu²⁺ onto nanocomposite followed pseudo-second-order and Langmuir isotherm models. Thermodynamic parameters exhibited that the sorption process was feasible, spontaneous and endothermic in nature. These results provide evidences for the efficient removal of heavy metals from industrial wastewater.

Schiff base-functionalized mesoporous silicas (MCM-41, HMS) as Pb(ii) adsorbents

MCM-41@salen, HMS-C12@salen and HMS-C16@salen sorbents present high sorption capacities for Pb(ii) and are suitable materials for the removal of Pb(ii).

Ethylenediamine grafted to graphene oxide@Fe3O4 for chromium(VI) decontamination: Performance, modelling, and fractional factorial design

A method for grafting ethylenediamine to a magnetic graphene oxide composite (EDA-GO@Fe₃O₄) was developed for Cr(VI) decontamination. The physicochemical properties of EDA-GO@Fe₃O₄ were characterized using HRTEM, EDS, FT-IR, TG-DSC, and XPS. The effects of pH, sorbent dose, foreign anions, time, Cr(VI) concentration, and temperature on decontamination process were studied. The solution pH can largely affect the decontamination process. The pseudo-second-order model is suitable for being applied to fit the adsorption processes of Cr(VI) with GO@Fe₃O₄ and EDA-GO@Fe₃O₄. The intra-particle diffusion is not the rate-controlling step. Isotherm experimental data can be described using the Freundlich model. The effects of multiple factors on the Cr(VI) decontamination was investigated by a 2⁵⁻¹ fractional factorial design (FFD). The adsorption process can significantly be affected by the main effects of A (pH), B (Cr(VI) concentration), and E (Adsorbent dose). The combined factors of AB (pH × Cr(VI) concentration), AE (pH × Adsorbent dose), and BC (Cr(VI) concentration × Temperature) had larger effects than other factors on Cr(VI) removal. These results indicated that EDA-GO@Fe₃O₄ is a potential and suitable candidate for treatment of heavy metal wastewater.

Microwave-assisted one-pot functionalization of metal–organic framework MIL-53(Al)-NH2 with copper(ii) complexes and its application in olefin oxidation

A simple and rapid functionalization of MOF via microwave-assisted one-pot synthesis afforded a Cu(ii)-Schiff-base-MOF as an efficient catalyst for olefin oxidation.

A combined top-down/bottom-up approach to structuring multi-sensing zones on a thin film and the application to SPR sensors

The development of a thin film with well-defined metallic micro/nanostructures, diverse surface functionalities, and superior electronic/optical properties has been a great challenge to researchers seeking an efficient method for the detection of various analytes in chemical and biological sensing applications. Herein, we report a facile and effective approach to the fabrication of an ordered gold island pattern on a glass substrate with contrasted chemical functionalities, which can provide spatially separated sensing zones for multi-detection. In the proposed method, the combination between the micro/nano-imprint lithography and sequential self-assembly approaches exhibited synergistic effects that allowed well-defined structuring and easy surface functionalization in separated sensing zones. Via imprint lithography, the uniform gold islands/glass structure was successfully fabricated from a readily available gold-coated glass film. In addition, a sequential self-assembling strategy and specific chemical-substrate interactions, such as thiol-gold and silane-glass, enabled the surfaces of gold islands and exposed portions of the glass substrate with contrasting chemical functionalities-SH-functionalized gold islands and NH2-functionalized glass substrate. A proof-of-concept experiment for the multi-detection of heavy metal ions (Hg(2+) and Cu(2+)) in an aqueous media was also successfully conducted using the dual-functionalized gold islands/glass structure and surface plasmon resonance measurements. The SH groups on the gold islands and the NH2 groups on the glass substrate functioned as spatially separated and selective receptors for Hg(2+) and Cu(2+) ions, respectively. Therefore, both the detection and quantification of Hg(2+) and Cu(2+) ions could be achieved using a single sensing substrate.

Effects of single- and multi-organic acid ligands on adsorption of copper by Fe3O4/graphene oxide-supported DCTA

The Fe3O4/graphene oxide-supported 1,2-diaminocyclohexanetetraacetic acid composite (Fe3O4/GO/DCTA) was used as an adsorbent for Cu(II) removal. The effects of six organic acid ligands (formate, acetate, benzoate, oxalate, tartrate, and edetate) on the adsorption process were investigated in single- and multi-ligand systems. The results demonstrated that the adsorption processes were affected by solution pH and ionic strength. The experimental data of kinetics and isotherm followed the pseudo-second-order model and the Langmuir model, respectively. In the single-ligand systems, the presence of formate, acetate, and benzoate slightly altered the Cu(II) adsorption property, while the adsorption processes were significantly affected by the oxalate, tartrate, and edetate ligands. In the multi-ligand systems, the Cu(II) adsorption was influenced by the type and concentration of organic acid ligands. The sequence of the main effect was found to be: edetate>oxalate>benzoate>formate>tartrate>acetate, and the sequence of the two-factor interaction effect was found to be: AE (formate×tartrate)>BF (acetate×edetate)>AF (formate×edetate)>BD (acetate×oxalate)>AC (formate×benzoate)>AD (formate×oxalate)>AB (formate×acetate).

Copper-loaded hypercrosslinked polymer decorated with pendant amine groups: a green and retrievable catalytic system for quick [3 + 2] Huisgen cycloaddition in water

A novel heterogeneous copper catalyst based on a 3D-network polymer containing pendant amine groups was synthesized via post-functionalization of the polymeric backbone followed by incorporation of copper(i) ions.

Retracted Article: Olefin epoxidation with chiral salen Mn(iii) immobilized on ZnPS-PVPA upon alkyldiamine

Heterogeneous Jacobsen’s catalysts on ZnPS-PVPA upon alkyldiamines possess superior catalytic performance both for experimental scale and large-scale reactions.

A Facile Synthesis of Ion Imprinted Mesoporous Silica Adsorbents by a Co-Condensation Pathway and Application in a Fixed-Bed Column Study for Lead Removal

Highly selective lead ion imprinted mesoporous silica adsorbents (PbII-IMS) were prepared through a co-condensation pathway with 3-(γ-aminoethylamino)propyltrimethoxysilane (AAPTS) (PbII-IMS-NN) and 3-aminepropyltriethoxysilyl (APTES) (PbII-IMS-N) as monomers. The prepared adsorbents were characterised by FT-IR spectroscopy, X-ray photoelectron spectroscopy, power X-ray diffraction, transmission electron microscopy, scanning electron microscopy, thermogravimetric analysis, and nitrogen adsorption–desorption techniques. The results showed that the synthesised adsorbents presented a highly ordered mesoporous structure. In comparison with PbII-IMS-N, PbII-IMS-NN demonstrated a higher adsorption capacity in a series of static and dynamic adsorption experiments, and was further applied to a continuous fixed-bed column study under different conditions. It was found that the breakthrough time of the fixed-bed increased with an increase in bed depth, but decreased with increased flow rate and initial PbII concentration, and the dynamic adsorption data was more consistent with the Thomas model than the Adams–Bohart model. Furthermore, the PbII-IMS-NN showed a greater recognition and binding affinity towards the target lead ions than PbII-IMS-N.

Design and fabrication of branched polyamine functionalized mesoporous silica: an efficient absorbent for water remediation

A novel branched polyamine (polyethyleneimine, PEI) functionalized mesoporous silica (MS) adsorbent is developed via a facile "grafting-to" approach. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FT-IR) spectroscopy verified the effective surface functionalization of MS with monolayer and polymer. The transmission electron microscopy (TEM) was employed to reveal the morphology of the fabricated materials. The adsorption behavior of the polyamine functionalized mesoporous silica (MS-PEI) is assessed against anionic dyes. The adsorbent characteristics of MS-PEI are compared with a monolayer platform comprising of 3-aminopropyltriethoxy silane (APTES) functionalized mesoporous silica (MS-APTES). The adsorption behavior of the MS-PEI and MS-APTES toward anionic dyes is further evaluated by studying the effect of adsorbent dosage, pH, contact time, and temperature. Langmuir and Freundlich isotherm models are employed to understand the adsorption mechanism. The obtained kinetic data support a pseudo-second-order adsorption behavior for both monolayer and polymer functionalized MS. The associated thermodynamic parameters (ΔG°, ΔH°, and ΔS°) reveal that the process of adsorption with MS-PEI is more spontaneous and energetically favored as compared to the adsorption with MS-APTES. Taken together, the novel adsorbent system derived from a combination of MS and branched polymer (MS-PEI) shows the higher absorption efficiency and capacity toward the anionic dyes than the monolayer based adsorbent (MS-APTES).

Synthesis of a Fe3O4–CuO@meso-SiO2 nanostructure as a magnetically recyclable and efficient catalyst for styrene epoxidation

A novel Fe₃O₄–CuO@meso-SiO₂ composite was fabricated as a magnetically recyclable and efficient catalyst for olefin epoxidation.

Novel layered crystalline organic polymer-inorganic hybrid material comprising calcium phosphate with unique architectures for superior performance catalyst support

Various pores or channels produced by the modification of PS-PVPA chain could contribute to significant impact on the excellent catalytic activity.