Removal of aqueous toxic Hg(II) by functionalized mesoporous silica materials

BACKGROUND: Hg(II) is one of the most toxic metals and has received particular attention in environmental pollution. Hg(II) pollution is common in water sources, so rapid and efficient methods must be developed for its removal from water samples. Mesoporous silica (MS) is an ideal adsorbent due to its high surface area and biocompatibility. The efficiency and selectivity of MS adsorbents can be improved by surface modification. RESULTS: A new sorbent for trace Hg(II) removal was developed by grafting 1‐(3‐carboxyphenyl)‐2‐thiourea (CPTU) onto SBA‐15 mesoporous silica. The optimum pH range for Hg(II) adsorption was 3‐7 and the maximum static adsorption capacity was 64.5 mg g^?1. An enrichment factor of 150 was obtained with a relative standard deviation < 1.5% (n = 8). Common coexisting ions did not interfere with the adsorption of Hg(II) under optimal conditions. Quantitative recovery was achieved by stripping with a mixed solution of 1 mol L^?1 HCl and 5% CS(NH₂)₂. Efficient adsorption capacity of the recycled material could still be maintained at a level of 95% at the 7th cycle. CONCLUSION: 1‐(3‐carboxyphenyl)‐2‐thiourea functionalized SBA‐15 mesoporous silica was synthesized and applied for Hg(II) removal from water samples with high efficiency and selectivity. Copyright © 2012 Society of Chemical Industry     

Kinetics of CO2 Adsorption/Desorption of Polyethyleneimine‐Mesoporous Silica

The kinetics of adsorption of CO₂ on solid sorbents based on polyethyleneimine/mesoporous silica (PEI/MPS) was studied by following the mass gain during CO₂ flow. Linear (PEI‐423) and branched (PEI‐10k) polymers were studied. The solid sorbents were synthesized by impregnating the PEI into MPS foam. The kinetics of adsorption was fitted with a double‐exponential model. In contrast, the desorption process obeyed first‐order kinetics. The activation energy of desorption of PEI‐423 was lower than that of PEI‐10k, presumably because the branched polymer required more energy to expose its nitrogen to CO₂. To increase the CO₂ sorption capacity, the MPS was treated with nonionic surfactant materials prior to impregnation with PEI. This also lowered the maximum sorption temperature and desorption activation energies.     

Micelles formed by self‐assembly of hyperbranched poly[(amine‐ester)‐co‐(D,L‐lactide)] (HPAE‐co‐PLA) copolymers for protein drug delivery

BACKGROUND: The aim of the work presented was to synthesize a series of amphiphilic hyperbranched poly[(amine‐ester)‐co‐(D ,L ‐lactide)] (HPAE‐co‐PLA) copolymers and study the formation of copolymeric micelles. These copolymeric micelle systems are expected to be potential candidates for applications in protein drug delivery. RESULTS: The chemical structures of the copolymers were confirmed by Fourier transform infrared spectroscopy, ¹³C NMR and thermogravimetric analysis. Fluorescence spectroscopy and dynamic light scattering confirmed the formation of copolymeric micelles of the HPAE‐co‐PLA copolymers. The maintenance of stability of bovine serum albumin (BSA) during release from micelles in vitro was also measured using circular dichroism and fluorescence spectrometry. CONCLUSION: Novel hyperbranched HPAE‐co‐PLA copolymers have been synthesized. Conjugation of PLA to HPAE was proved to be an available method for the preparation of micelles for protein delivery. The BSA‐loaded micelles showed enhanced encapsulation efficiency and the structural stability of BSA was retained during the release process. The hyperbranched polymeric micelles could be useful as drug carriers for protein drug delivery systems. Copyright © 2008 Society of Chemical Industry     

BSA adsorption onto magnetic polyvinylbutyral microbeads

Bovine serum albumin (BSA) adsorption onto novel and feasible magnetic polyvinylbutyral‐based microbeads was investigated. The microbeads were made of Mowital® B30HH, a commercial product, in the range 125–250 μm by a modified solvent evaporation technique. Magnetite particles were embedded in the polymer structure for favorable magnetic properties, 4.80 emu/g microbeads of saturation magnetization at 6000 Gauss magnetic field. Glutaraldehyde (GA) was used as a bonding agent to increase stability and as a ligand for protein adsorption. The amount of adsorbed BSA was optimized by changing the medium pH and the initial concentrations of GA and BSA. Dynamic adsorption data of batch runs fitted best to Langmiur kinetics. The parameters q_max, k^′_f and k^′_r of the model were estimated through nonlinear regression analysis as 138 mg BSA/g adsorbent, 0.058 ml/(mg BSA · min) and 0.002 min⁻¹, respectively, for magnetic microbeads at pH 5.0 and 25°C. The adsorbed BSA was eluted successfully at pH 8.0 and 25°C. Possibly due to surface roughness and magnetic properties, q_max was found higher than the other adsorbents reported in the literature. The results denote that these microbeads can be an alternative protein adsorbent due to high adsorption capacity and rate, as well as remarkable separation characteristics. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 707–715, 2001     

Dynamics of blood proteins adsorption onto poly (2‐hydroxyethyl methacrylate)‐silica nanocomposites: Correlation with biocompatibility

A nanocomposite hybrid of poly(2‐hydroxyethyl methacrylate) (PHEMA) and silica (PHEMA‐Si) was prepared by sol–gel process and characterized by FTIR, environmental scanning electron microscopy (ESEM), and XRD techniques. The prepared hybrid was evaluated for its water sorption capacity and the adsorption of blood proteins such as bovine serum albumin (BSA) and fibrinogen (Fgn) was carried out on the hybrid surfaces. The dynamic nature of the adsorption process was investigated and related kinetic parameters were evaluated. The effect of factors like concentrations of protein solutions, pH, and ionic strength of the adsorption medium and chemical architecture of the hybrid were investigated on the adsorption process. The prepared hybrids were also examined for in vitro blood compatibility. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Cu(II)‐incorporated,histidine‐containing,magnetic‐metal‐complexing beads as specific sorbents for the metal chelate affinity of albumin

N‐Methacryloyl‐(L )‐histidine methyl ester (MAH) was synthesized from metharyloyl chloride and histidine. Spherical beads with an average size of 150–250 μm were obtained by the suspension polymerization of ethylene glycol dimethacrylate and MAH in an aqueous dispersion medium. Magnetic poly(ethylene glycol dimethacrylate‐co‐N‐Methacryloyl‐(L )‐histidine methyl ester) [m‐p(EGDMA‐co‐MAH)] microbeads were characterized with swelling tests, electron spin resonance, elemental analysis, and scanning electron microscopy. The specific surface area of the beads was 80.1 m²/g. m‐p(EGDMA‐co‐MAH) microbeads with a swelling ratio of 40.2% and 43.9 μmol of MAH/g were used for the adsorption of bovine serum albumin (BSA) in a batch system. The Cu(II) concentration was 4.1 μmol/g. The adsorption capacity of BSA on the Cu(II)‐incorporated beads was 19.2 mg of BSA/g. The BSA adsorption first increased with the BSA concentration and then reached a plateau, which was about 19.2 mg of BSA/g. The maximum adsorption was observed at pH 5.0, which was the isoelectric point of BSA. The BSA adsorption increased with decreasing temperature, and the maximum adsorption was achieved at 4°C. High desorption ratios (>90% of the adsorbed BSA) were achieved with 1.0M NaSCN (pH 8.0) in 30 min. The nonspecific adsorption of BSA onto the m‐p(EGDMA‐co‐MAH) beads was negligible. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2669–2677, 2004     

Preparation of pH and temperature dual‐sensitive molecularly imprinted polymers based on chitosan and N‐isopropylacrylamide for recognition of bovine serum albumin

pH and temperature dual‐sensitive protein imprinted microspheres with high absorption capacity have been successfully synthesized on the surface of SiO₂ using chitosan grafted N‐isopropylacrylamide (CS‐g‐NIPAM) as the pH and temperature sensitive monomer, with acrylamide as comonomer, N,N′‐methylenebisacrylamide as the crosslinking agent and bovine serum albumin (BSA) as the template protein. The pH and temperature dual‐sensitivity was also investigated. The results showed that the adsorption capacity and imprinting factor improved slowly with increasing incubation pH from 4.6 to 7.0, and then decreased sharply in alkaline conditions due to the reduction of non‐specific binding from electrostatic and hydrogen bonding interactions. Fourier transform infrared spectroscopy, thermogravimetric analysis and transmission electron microscopy were used to characterize the polymers. The as‐prepared SiO₂@BSA molecularly imprinted polymers were also found to have high adsorption capacity (119.88 mg g^?1) within 2 h, an excellent imprinting factor (α = 2.25), specific selectivity and good reusability. © 2019 Society of Chemical Industry     

Effects of fluoride ion on the formation of earthworm‐like mesoporous silica

In a strong acidic environment, ordered earthworm‐like mesoporous silica has been synthesized with CTAB templating and fluoride ion (F^?) as a counterion. The synthesized products were characterized by small‐angle X‐ray diffraction (SXRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N₂ adsorption‐desorption isotherms, and Fourier‐transform infrared spectroscopy (FTIR). The effects of F/Si mole ratio on the morphology, surface area, and the pore size of the sample were discussed. It was found that a F/Si mole ratio at 0.083 induced the formation of 3D hexagonal mesophase, whereas higher F/Si mole ratios led to the formation of 2D hexagonal mesoporous silica, the optimum molar ratio of F/Si for the formation of delicate earthworm‐like mesoporous silica was observed at 0.250. The effects of the F/Si mole ratio, surfactant chain length, acid concentration, and shear flow on morphology were also studied.     

Textural and Structural Properties of Mesoporous Silica Synthesized Under Refluxing Conditions

Mesoporous silica with pore sizes of 3–6 nm has been synthesized under refluxing and autogenous pressure conditions of hydrothermal synthesis from precursor gels having different alkaline pH. The mesoporous silica prepared is characterized by powder X-ray diffraction, nitrogen adsorption-desorption measurement and scanning electron microscopy. Thermal stability has been tested by XRD analysis of mesoporous silica after thermal treatment at 823 K, 6 h; 1023 K, 1 h and 1223 K, 1 h. The results indicate that the mesoporous silica prepared under refluxing condition from precursor gel of pH 11 has large surface area (ca.1103 m² g^{− 1}) and pore volume (ca. 0.868 cm³ g^{− 1}) and is thermally stable at 1223 K. The surface area, pore volumes and pore wall thickness increase as the pH of the precursor gel is increased for refluxing condition of synthesis. The comparison of textural properties revealed that the refluxing condition is advantageous over autogenous pressure condition for obtaining mesoporous silica with higher surface area (852 m² g^{− 1}), pore volume (0.894 cm³ g^{− 1}) and pore diameter > 4 nm with wall thickness of 1.59 nm, when synthesized from precursor gel of pH 9.2. The ²⁹Si NMR spectra showed that a great part of the Si atoms exists as silanol groups. The mesoporous silica made at the lower pH (9.2) under refluxing conditions have more condensed framework. In calcined mesoporous silica, the proportion of partly condensed silica (Q³) is higher than fully condensed silica (Q⁴).     

Thermosensitive PCL‐PEG‐PCL hydrogels: Synthesis,characterization, and delivery of proteins

In this work, a biodegradable and injectable in situ gel‐forming controlled drug delivery system based on thermosensitive poly(ε‐caprolactone)‐poly(ethylene glycol)‐poly(ε‐caprolactone) (PCL‐PEG‐PCL) hydrogels was studied. A series of PCL‐PEG‐PCL triblock copolymers were synthesized and characterized by ¹H‐NMR and gel permeation chromatography (GPC). Thermosensitivity of the PCL‐PEG‐PCL triblock copolymers was tested using the tube inversion method. The in vitro release behaviors of two model proteins, including bovine serum albumin (BSA) and horseradish peroxidase (HRP), from PCL‐PEG‐PCL hydrogels were studied in detail. The in vivo gel formation and degradation of the PCL‐PEG‐PCL triblock copolymers were also investigated in this study. The results showed that aqueous solutions of the synthesized PCL‐PEG‐PCL copolymers can form in situ gel rapidly after injection under physiological conditions. The PCL‐PEG‐PCL hydrogels showed the ability to control the release of incorporated BSA and HRP. The released HRP was confirmed to conserve its biological activity by specific enzymatic activity assay. The in vivo gel formation and degradation studies indicated that PCL‐PEG‐PCL copolymers hydrogels can sustain at least 45 days by subcutaneous injection. Therefore, owing to great thermosensitivity and biodegradability of these copolymers, PCL‐PEG‐PCL copolymers hydrogels show promise as an in situ gel‐forming controlled drug delivery system for therapeutic proteins. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Synthesis and characterization of an amphiphilic hyperbranched poly(amine‐ester)‐co‐D,L‐lactide (HPAE‐co‐PLA) copolymers and their nanoparticles for protein drug delivery

A series of hyperbranched poly(amine‐ester)‐co‐D ,L ‐lactide (HPAE‐co‐PLA) copolymer were synthesized by ring‐opening polymerization of D ,L ‐lactide with Sn(Oct)₂ as catalyst to a fourth generation branched poly(amine‐ester) (HPAE‐OHs4). The chemical structures of copolymers were determined by FTIR, ¹H‐NMR, ¹³C‐NMR, and TGA. Double emulsion (DE) and nanoprecipitation (NP) method were used to fabricate the nanoparticles of these copolymers encapsulating bovine serum albumin (BSA) as a model. DSC thermo‐grams indicated that the nanoparticles with BSA kept stable below 40°C. Different factors which influence on particular size and encapsulation efficiency (EE) were investigated. Their EE to BSA could reach 97.8% at an available condition. In vitro release behavior of NPs showed a continuous release after a burst release. The stability maintenance of BSA in the nanoparticle release in vitro was also measured via circular dichroism and fluorescence spectrometry. The results showed that the copolymer nanoparticles have a promising potential in protein delivery system. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Synthesis,characterization, and cytotoxicity of star‐shaped polyester‐based elastomers as controlled release systems for proteins

With the growing number of therapeutic proteins on the market, effective delivery systems are receiving particular attention. In this study, biodegradable elastomers, intended for protein drug delivery and based on methacrylic tripoly(ε‐caprolactone‐co‐d ,l ‐lactide) cyclic ester with different ratios of ?‐caprolactone to d ,l ‐lactide and methacrylic bipoly[?‐caprolactone‐b‐poly(ethylene glycol)‐b‐?‐caprolactone], were synthesized and characterized. The degradation behavior, bovine serum albumin (BSA)‐releasing kinetics, and cytotoxicity of the elastomers in vitro were investigated. The elastomers were degraded by the hydrolysis of the ester bond; this resulted in pH changes, which further affected the degradation rate. The BSA‐releasing behavior was strongly dependent on the diffusion mechanism. In the diffusion‐controlled period, nearly sustained and stable BSA release was achieved. Furthermore, the elastomers displayed good biocompatibility, as demonstrated by a 3‐(4,5‐dimethyl thiazol‐2‐yl)?2,5‐diphenyl tetrazolium bromide assay and inflammation–induction experiments, and are considered promising candidates for the controllable delivery of protein drugs. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43393.     

Synthesis of mesoporous silica using a mineral silica source

Mesoporous silica has been applied in catalysis, separations, and drug delivery. It has generally been made using organosilicon precursors such as tetraethyl orthosilicate. For sustainability, it is necessary to find readily accessible mineral sources for making mesoporous silica. In this work, we demonstrate the successful synthesis of mesoporous silica with 10 nm average pore size using the mineral forsterite (Mg₂SiO₄) as a silica source, providing a potentially cheaper and more Earth-friendly route to making technologically important porous silica materials. Pure forsterite was synthesized by a solid-state chemistry route at 1000°C and underwent dissolution–reprecipitation in aqueous hydrochloric acid containing the soft template surfactant, Pluronic P123. Variations of initial reaction pH (−0.2 to 0.6), reaction time (12–24 h), reaction temperature (50 to 90°C), and silica precursor (forsterite and fumed silica) were performed. The mesoporous silica aged at 70°C for 24 h had the highest porosity, with a surface area of 735 m²/g and a pore volume of 1.4 ml/g, comparable to mesoporous silica made using conventional starting materials. This novel geomimetic synthesis route supports the possibility of analogous formation of structured (mesoporous or zeolitic) silica in nature under abiotic or prebiotic conditions.     

Removal of Sr(II) from Aqueous Solutions by Aminosilane Functionalized MCM-48

In this research, NH₂-MCM-48 adsorbent was synthesized by grafting of aminopropyl on the surface of MCM-48 mesoporous silica material. The synthesized adsorbent was characterized by FT-IR, XRD, thermogravimetric, and surface area techniques. The removal of Sr (II) by the synthesized adsorbent was studied and the effect of initial pH, contact time, cation concentration, and temperature on the Sr²⁺ adsorption was studied and optimized. Under optimized conditions, the removal capacity of 5.95 meq/g was obtained. The experimental data were analyzed using the Langmuir and Freundlich equations. Adsorption data was fitted with the Langmuir isotherm, indicating that the process was monolayer and chemical in nature. The calculated thermodynamic parameters, ΔH°, ΔS°, and ΔG° confirmed that the adsorption process was endothermic and spontaneous. The regeneration of the adsorbent was examined and it was found that 92% of the initial capacity was conserved after five successive regeneration cycles.     

CO2 adsorption using amine-functionalized mesoporous silica prepared via anionic surfactant-mediated synthesis

A series of directly amine-functionalized mesoporous silicas was prepared via an anionic surfactant-mediated synthesis method and applied to CO₂ adsorption at room temperature. The structurally robust amine functionality in the material accompanied by preferential positioning of amine groups normal to the surface of a silica support due to the S⁻N⁺  I⁻ mechanism proved to be beneficial for CO₂ adsorption. Rather than surface area or pore volume, amine content of the mesoporous material was found to be the governing factor to achieve high CO₂ adsorption capacity. Covalently bonded amine species in the mesoporous silica were robust enough to maintain steady adsorption performance during 10 repetitions of the adsorption–desorption cycle.     

Dual‐stimuli‐responsive polymer‐coated mesoporous silica nanoparticles used for controlled drug delivery

In this article, a temperature‐ and pH‐responsive delivery system based on block‐copolymer‐capped mesoporous silica nanoparticles (MSNs) is presented. A poly[2‐(diethylamino)ethyl methacrylate)] (PDEAEMA)‐b‐poly(N‐isopropyl acrylamide) (PNIPAM) shell on MSNs was obtained through the surface‐initiated atom transfer radical polymerization. The block copolymer PDEAEMA‐b‐PNIPAM showed both temperature‐ and pH‐responsive properties. The release of the loaded model molecules from PDEAEMA‐b‐PNIPAM‐coated MSNs could be controlled by changes in the temperature or pH value of the medium. The as‐desired drug‐delivery carrier may be applied to biological systems in the future. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42395.     

Adsorption of phosphate and nitrate anions on ammonium-functionnalized mesoporous silicas

Surface modified mesostructured silica materials represent potential adsorbents offering an opportunity to remediate several important water pollutants. In the present work, ammonium-functionnalized MCM-41, MCM-48 and SBA-15 mesoporous silica materials were synthesized via post-synthesis grafting and co-condensation. Their efficiency to remove nitrate and phosphate anions in aqueous solutions was investigated. The adsorbent materials showed high adsorption capacities reaching 46.5 mg NO₃⁻/g and 55.9 mg H₂PO₄⁻/g under the operating conditions explored. The mesoporous silica materials functionalized via post-synthesis grafting method exhibited higher performances in terms of percentage pollutant removal and adsorption capacities if compared to their analogs synthesized according to the co-condensation strategy.     

Synthesis of hollow mesoporous silica (HMS) nanoparticles as a candidate for sulfasalazine drug loading

Hollow mesoporous silica nanoparticles have emerged as attractive drug delivery carriers. In this work, we report successful synthesis of hollow mesoporous silica nanoparticles (HMSNs) using poly tert-butyl acrylate (PtBA) nanospheres as hard templates and CTAB as structure directing agent for loading sulfasalazine into its porous structure. The samples were synthesized using PtBA; sodium dodecyl sulfate (SDS) - in an aqueous solution of CTAB and tetraethylorthosilicate (TEOS) as the inorganic precursor. Two different methods were utilized to remove organic phases including calcination, and acidic/basic ethanolic solvent extraction approach. For the latter, microstructural studies using SEM and N₂ porosimetery revealed the formation of highly uniform mono-dispersed particles of sphere morphology (~ 130 nm) with the high specific surface area (1501 m²/g) and mean pore size of ~ 2.6 nm. However, rather deformed and aggregated sphere-like particles were obtained for the calcined samples. TEM examinations also confirmed the formation of 20–30 nm thick walls for the prepared HMSNs particles. Further, HMSN samples treated by solvent extraction method were functionalized by 3-aminopropyl triethoxysilane (APTS) compound for drug delivery. DTA/TG analysis showed that the total amount of loaded sulfasalazine drug was 5.1 wt%.     

Calcium‐carboxymethyl chitosan hydrogel beads for protein drug delivery system

In this study, carboxymethyl chitosan (CMC) hydrogel beads were prepared by crosslinking with Ca²⁺. The pH‐sensitive characteristics of the beads were investigated by simulating gastrointestinal pH conditions. As a potential protein drug delivery system, the beads were loaded with a model protein (bovine serum albumin, BSA). To improve the entrapment efficiency of BSA, the beads were further coated with a chitosan/CMC polyelectrolyte complex (PEC) membrane by extruding a CMC/BSA solution into a CaCl₂/chitosan gelation medium. Finally, the release studies of BSA‐loaded beads were conducted. We found that, the maximum swelling ratios of the beads at pH 7.4 (17–21) were much higher than those at pH 1.2 (2–2.5). Higher entrapment efficiency (73.2%) was achieved in the chitosan‐coated calcium‐CMC beads, compared with that (44.4%) in the bare calcium‐CMC beads. The PEC membrane limited the BSA release, while the final disintegration of beads at pH 7.4 still leaded to a full BSA release. Therefore, the chitosan‐coated calcium‐CMC hydrogel beads with higher entrapment efficiency and proper protein release properties were a promising protein drug carrier for the site‐specific release in the intestine. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3164–3168, 2007     

Fabrication of ferrogels using different magnetic nanoparticles and their performance on protein adsorption

Magnetic biomaterials were prepared using magnetite and chitosan‐coated magnetite nanoparticles (CSNPs) dispersed in poly(vinyl alcohol) gels. Two different methods were developed to obtain ferrogels: in situ co‐precipitation of magnetite (Ferro‐IS) and by adding previously synthesized CSNPs to the neat matrix (Ferro‐CSNPs). In both cases, the crosslinking was carried out by freezing ? thawing (F‐T). The as‐prepared materials as well as precursor CSNPs were characterized by Fourier transform infrared spectroscopy, electronic microscopy (scanning and transmission), X‐ray diffraction, ζ potential, dynamic light scattering, thermogravimetric analysis, differential scanning calorimetry and magnetic properties. The performance of these gels as protein adsorbents was evaluated. Batch adsorption experiments were carried out using bovine serum albumin (BSA) as a model. Substantially different adsorption behaviour was found using Ferro‐IS and Ferro‐CSNPs. This was assigned to dissimilar bonding mechanisms of BSA to the ferrogel matrix. Hence, biomaterials potentially useful in drug delivery as well as in protein purification fields may be prepared by a relatively simple, non‐toxic and low cost method. © 2013 Society of Chemical Industry